•Nanoporous TiO2 was synthesized by a hydrothermal method without using of surfactant.•Nanoporous TiO2 shows good gas response, selectivity and response/recovery for acetone.•The good sensing properties attribute to the high specific surface area of nanoporous TiO2.•Nanoporous TiO2 could be expected for development of an excellent acetone gas sensor.Nanoporous titanium dioxide was synthesized by a hydrothermal method without using of surfactant or template. The structure, morphology, surface chemical states and specific surface area were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and N2 adsorption-desorption isotherms, respectively. The as-synthesized products are anatase-TiO2 with small grain size (about 12.27 nm) and high surface area (147.17 m2 g−1). The as-synthesized porous TiO2 powder was used to fabricate indirect-heating gas sensor whose gas-sensing characteristics toward acetone were investigated. At its optimal operation temperature, the sensor possesses a good sensitivity, selectivity, linear dependence, low detection limitation, and response/recovery, repeatability as well as long-term stability. Especially for the high sensitivity and fast response/recovery, its response reaches 25.97 for 500 ppm acetone, which is several times higher that of the reported TiO2-based sensors. The response and recovery times are only 13 and 8 s, respectively. Those values demonstrate the potential of using as-synthesized TiO2 for acetone gas detection, particularly in the dynamic monitoring. Apart from these, the mechanism related to the advanced properties was also investigated and presented.Nanoporous titanium dioxide synthesized by a hydrothermal method without using of surfactant or template exhibits good gas response, selectivity, linear dependence, low detection limitation, and response/recovery, repeatability as well as long-term stability toward acetone gas, which attributed the high specific surface area of nanoporous TiO2.

•CeO2/MWCNTs composites were synthesized by a hydrothermal method.•CeO2/MWCNTs composites possess the excellent capacitive behaviors.•CeO2/MWCNTs composites improve the specific capacitance and the cycle stability.•The ratios of CeO2 and MWCNTs play major role on capacitive character.Cerium oxide nanoparticles/multi-wall carbon nanotubes (MWCNTs) composites are synthesized by a facile hydrothermal method without any surfactant or template. The morphology and microstructure of samples are examined by scanning electron microscopy (SEM), transition electron microscopy (TEM), X-ray diffraction (XRD), Raman spectrum and X-ray photoelectron spectroscopy (XPS). Electrochemical properties of the MWCNTs, the pure CeO2, and the CeO2/MWCNTs nanocomposites electrodes are investigated by cyclic voltammetry (CV), galvanostatic charge/discharge (GDC) and electrochemical impedance spectroscopy (EIS) measurements. The CeO2/MWCNTs nanocomposite (at the mole ratio of 1:1) electrode exhibits much larger specific capacitance compared with both the MWCNTs electrode and the pure CeO2 electrode and significantly improves cycling stability compared to the pure CeO2 electrode. The CeO2/MWCNTs nanocomposite (at the mole ratio of 1:1) achieves a specific capacitance of 455.6 F g−1 at the current density of 1 A g−1. Therefore, the as prepared CeO2/MWCNTs nanocomposite is a promising electrode material for high-performance supercapacitors.Cerium oxide nanoparticles/multi-wall carbon nanotubes (MWCNTs) composites synthesized by hydrothermal method exhibit the excellent capacitive behaviors.

•β-Co(OH)2 nanoplatelets were successfully synthesized by a template-free chemical method.•β-Co(OH)2 nanoplatelets exhibit irregular hexagonal disk with angles of adjacent edges of 120°.•β-Co(OH)2 nanoplatelets prepared at 100 °C for 8 h show 100% conversion efficiency of CO at 120 °C.•There are correlations of Co3+/Co2+, absorbed Ox− and surface OH group with catalytic activity.A facile, cost-effective, template-free chemical method was developed for the synthesis of β-Co(OH)2 nanoplatelets under the different preparation conditions. The morphology and microstructure of as-synthesized samples were examined by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectrum (XPS), respectively. The observations revealed the formation of a single phase of the hexagonal brucite-like β-Co(OH)2, which had an irregular hexagonal disk with angles of adjacent edges of 120°, edge lengths ranging from 200 to 300 nm, and thicknesses of 20–40 nm. When investigated as catalyst for CO oxidation, the β-Co(OH)2 nanoplatelets exhibited good catalytic activity for CO. Among β-Co(OH)2 nanoplatelets, the sample prepared at 100 °C for 8 h performed the best, giving the T100% (the temperature required for achieving a CO of 100%) of 120 °C for the oxidation of CO. There are good correlations of Co3+/Co2+, the absorbed Ox− ions and surface OH group with catalytic activity of the samples for CO oxidation.β-Co(OH)2 nanoplatelets synthesized by a facile, cost-effective, template-free chemical method exhibit a activity in CO oxidation probably related to the facile redox nature of the cycle transition of Co3+/Co2+, the absorbed Ox− ions and surface OH group of β-Co(OH)2 nanoplatelets.Download full-size image

Beta-manganese dioxide (β-MnO2) microrods were hydrothermally synthesized from ammonium persulfate [(NH)4S2O8] solution using manganese sulfate (MnSO4) as reductant at 180 °C for 3 h. The characterizations, including X-ray diffraction, scanning electron microscopy, and transmission electron microscopy, showed that the crystallinity and morphology of the as-synthesized samples were well-defined β-MnO2 microrods with the diameters of about 100 nm and lengths of about 2–4 μm. To explore the optimal degradation conditions, the as-synthesized β-MnO2 microrods were employed into the degradation of methyl orange dye solution with the concentration of 20 mg/L in the presence of H+ with pH values equalling 1.0, 1.5, 2.0, 3.0, 5.0, and 7.0, respectively. The results indicate that the degradation efficiency could reach 98% after 9 min at the pH value of 1.0 or 2.0. Also, the lower the pH value, the higher the degradation efficiency. Based on these experimental results, a proper mechanism of the degradation process of methyl orange is proposed and the rationality of the mechanism is further investigated through the scientific control tests.

In this paper, the NiCo2O4 nanoparticles were synthesized via a facile one-step solvothermal method without annealing treatment. XRD, TEM, XPS, and N2 adsorption/desorption were used to characterize the composition, morphology, and BET surface area of as-prepared sample, respectively. The analysis results indicated that the NiCo2O4 nanoparticles with spinel structure were successfully obtained. The NiCo2O4 sample was prepared into supercapacitors electrode materials. At room temperature, the electrode materials were investigated with cyclic voltammetry (CV) and galvanostatic charging-discharging in a 6 mol L−1 KOH aqueous electrolyte. Three-electrode systems, in which Hg/HgCl was employed as reference electrode, were used. The NiCo2O4 exhibited a specific capacitance of 717.9 F g−1 at the current density of 0.5 A g−1. Moreover, the specific capacitance remained 84% after 1000 continuous charge-discharge cycles under the current density of 10 A g−1.

•Porous Ag-loaded ZnO heterojunction nanocomposite was prepared by solution combustion.•Ag-loaded ZnO heterojunction nanocomposite has the excellent sensing properties for HCHO gas.•Ag-loaded ZnO heterojunction nanocomposite is a promising candidate for detector to HCHO gas.In this paper, a convenient solution combustion method to synthesis hierarchically porous Ag-loaded ZnO heterojunction nanocomposites with various Ag contents was reported. The analysis of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and Brunauer-Emmett-Teller (BET) nitrogen adsorption-desorption were conducted to characterize the ingredients, microstructure and surface morphology. Ag and ZnO show separate phases due to the reduction of Ag+ and the faster crystallization rate of ZnO. The as-synthesized powders were used as gas sensing materials to fabricate gas sensors. The gas-sensing performance was tested towards 100 ppm formaldehyde at an optimum operating temperature of 240 °C and Ag-loaded ZnO (with the different Ag atomic ratio) based gas sensors showed a superior gas-sensing performance comparing with pure ZnO. Especially 1 at% Ag-loaded ZnO has the highest gas response as 170.42. The possible gas-sensing mechanism was discussed in this paper. For example, the influence of surface area, the formation of heterostructure, Ag elements, adsorbed oxygen and so on.Hierarchically porous Ag-loaded ZnO heterojunction nanocomposites with 1 at% Ag shows an excellent gas response, linear dependence, repeatability, and selectivity, making it to be promising candidate for practical detectors for HCHO.Download high-res image (177KB)Download full-size image

•Pd-SnO2 composites were successfully obtained via a solvothermal method.•The sensing response of 10 mol% Pd-SnO2 composite is up to 315.34 for 3000 ppm hydrogen.•Sensor based on 10 mol% Pd-SnO2 composite displays a low operating temperature of 200 °C.•Composite exhibits good dynamic properties, selectivity, repeatability and stability.•Composite could be expected for development of an excellent hydrogen gas sensor.SnO2-composite Pd nanoparticles (0, 2.5, 7.5, 10 mol% Pd loading) were synthesized via solvothermal method, followed by calcination. The structure, morphology, chemical state and specific surface area of the Pd-SnO2 composite were analyzed with X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), N2 physisorption, respectively. It is found that the composites consist of large amount of SnO2 microspheres with average diameters up to hundreds of nanometers, and the microspheres are assembled by numerous nanoparticles with average sizes of about 8 nm. To demonstrate their potential application, gas sensors based on the as-synthesized Pd-SnO2 composites were fabricated to test their sensing performances. The 10 mol% Pd-SnO2 composite shows an excellent sensing response towards different concentrations of hydrogen at 200 °C. The highest sensing response is up to 315.34 for 3000 ppm hydrogen with a fast response-recovery time (4 s/10 s), which is over 8 times higher than that of pristine SnO2, and the lowest detection limit is down to 10 ppm. More significantly, it presents excellent selectivity and stability for hydrogen. The improved sensing response characteristics of the composite could be attributed to the chemical sensitization and electronic sensitization of Pd catalyst.Download high-res image (265KB)Download full-size image

•SnO2 microspheres were successfully synthesized by a facile hydrothermal method.•SnO2 microspheres are composed of large small spheres with average diameters of about 250 nm.•Small spheres consist of numerous primary nanocrystallites with average sizes of about 8 nm.•SnO2 microspheres have excellent gas sensing properties for formaldehyde gas.•SnO2 microspheres are promising candidate for practical detectors for formaldehyde gas.Tin oxide microspheres were successfully obtained through a facile hydrothermal method without any polymer templates or surfactant. The as-synthesized SnO2 microspheres are composed of large amount of small spheres with average diameters of about 250 nm, and every small sphere consists of numerous primary nanocrystallites with average sizes of about 8 nm. The resultant product was used as sensing material for gas sensor to detect the formaldehyde (HCHO) gas. The gas response, response and recovery time, selectivity and stability were carefully studied. It was found that the response value of the sensor to 100 ppm HCHO was 38.3 at the operating temperature of 200 °C. The gas sensor based on SnO2 microspheres has excellent gas response, good response-recovery properties, linear dependence, repeatability and selectivity, making it to be a promising candidate for practical detectors for HCHO.SnO2 microspheres not only have excellent gas response but also has good response-recovery properties, linear dependence, repeatability, and selectivity, making it to be promising candidate for practical detectors for HCHO.

Cerium oxide nanoparticles and cerium oxide nanoparticle-decorated graphene oxide (GO) are synthesized via a facile chemical coprecipitation method in the presence of hexadecyltrimethylammonium bromide (CTAB). Nanostructure studies and electrochemical performances of the as-prepared samples were systematically investigated. The crystalline structure and morphology of the nanocomposites were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM), transition electron microscopy (TEM), Raman spectrum, and X-ray photoelectron spectroscopy (XPS). Electrochemical properties of the CeO2 electrode, the GO electrode, and the nanocomposites electrodes were investigated by cyclic voltammetry (CV), galvanostatic charge/discharge (GCD), and electrochemical impedance spectroscopy (EIS) measurements. The CeO2 nanoparticle-decorated GO (at the mole ratio of CeO2/GO = 1:4) electrode exhibited excellent supercapacitive behavior with a high specific capacitance of 382.94 F/g at the current density of 3.0 A/g. These superior electrochemical features demonstrate that the CeO2 nanoparticle-decorated GO is a promising material for next-generation supercapacitor systems.

Here, CuO micro-sheets were successfully synthesized from Cu foil using the annealing procedure. Cupric oxalate (CuC2O4·xH2O) micro-sheets were firstly peeled off by immersing Cu foil in oxalic acid solution at room temperature, and then they were converted into CuO with preserved configuration after thermal treatment at 350 °C. Various techniques were employed for the characterization of the structure and morphology of as-prepared products. Results revealed that the samples were composed of a large amount of porous CuO micro-sheets, which were constructed by plenty of nano-sized primary particles. A gas sensor was fabricated using as-prepared CuO micro-sheets and was systematically investigated for its ability to detect n-butanol. Due to the porous structure of CuO micro-sheets, the sensor based on CuO micro-sheets manifests a remarkably improved sensing performance, including high response, good selectivity, excellent reproducibility and stability, and limit of detection as low as 10 ppm at 160 °C, suggesting its greatly promising applications in gas sensing.

Binder-free NiO@MnO2 core-shell structure was deposited on Ni foam used as electrode of supercapacitor. The rod-like NiO core was prepared by thermal decomposition of NiC2O4 synthesized by corrosion of Ni foam with oxalic acid under hydrothermal conditions. Sphere-like MnO2 shell was deposited on the surface of NiO core through hydrothermal treatment with KMnO4 solution. The structure, composition, morphology evolution and surface chemical state of the NiO@MnO2 electrode were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The obtained NiO and NiO@MnO2 electrodes were directly used as electrodes of supercapacitor, and their electrochemical performances were tested with cyclic voltammograms, galvanostatic charge/discharge and electrochemical impedance spectroscopy. The results show that the sphere-like MnO2 shell leads to an impressive enhancement of the performance including the areal capacitance (AC) and cycling stability, particular in the AC. To be more specific, the NiO@MnO2 exhibits a high AC of 3.584 F/cm2 at a current density of 5 mA/cm2, which is much higher than that of NiO electrode whose AC is 1.483 F/cm2 at the same current density, demonstrating the potential to use NiO@MnO2 electrode for supercapacitor. At the same time, the related mechanisms for the superior performance were also discussed.Binder-free NiO@MnO2 core-shell structure applied as electrodes of supercapacitor shows an impressive enhancement of the performance including the areal capacitance and cycling stability.

Cd doped porous Co3O4 nanosheets were successfully synthesized via a facile chemical coprecipitation method without using of surfactant or template. The samples were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), N2 adsorption/desorption isotherms (BET) and X-ray photoelectron spectrum (XPS) for their composition, structure/morphology, and BET surface area, respectively. The nanosheets consisting of nanoparticles prepared here are porous in nature, with average pore sizes of approximately 50 nm or smaller. The electrochemical properties of the Cd doped porous Co3O4 nanosheets were investigated by cyclic voltammetry (CV), galvanostatic charge–discharge, electrochemical impedance spectroscopy (EIS) in 6 mol/L KOH solution. The 5% Cd doped porous Co3O4 nanosheets electrode shows the maximum specific capacitance as high as 737 F/g at the current density of 1 A/g, which is 69% higher than that of the undoped porous Co3O4 nanosheets electrode. Furthermore, it has good specific capacitance retention of ca. 96% after 1000 continuous charge–discharge cycles. It shows a better cyclic stability than undoped porous Co3O4 nanosheets electrode, indicating that the Cd doped porous Co3O4 nanosheets is a promising electroactive material for supercapacitor.Cd doped porous Co3O4 nanosheets applied as electrode of supercapacitor shows an impressive enhancement of the performance including the areal capacitance and cycling stability.

Anatase–rutile mixed-phase TiO2 is proved to have better photocatalytic activity than pure anatase TiO2, but the preparation of the mixed-phase TiO2 usually needs thermal treatments at more than 500 °C. In this study, we present a one-step nonaqueous sol–gel route to form mixed-phase TiO2 at relatively low temperatures from 160 to 220 °C. The structure, morphology and surface chemical state were examined with X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS), respectively. The influence of the preparation temperature on the structural characteristics including grain size and phase content were investigated using the Rietveld refinement. Through TEM, the evolution from sphere-like anatase nanoparticle to hexagonal rutile single-crystal was investigated. The photocatalytic activities of the obtained anatase and anatase-rutile TiO2 were evaluated by degradation of Rhodamine B under visible light, and a distinct enhanced activity was observed. Through the UV-vis spectrum and mass spectrum, the pathway of RhB degradation caused by the mixed-phase TiO2 with visible light was studied. At the same time, the mechanism of the enhanced photocatalytic properties was presented. The mechanisms were verified with UV-vis measurements. It is believed that the obtained mixed-phase TiO2 is one promising candidate for wastewater treatment.

Here, pristine and WO3 decorated TiO2 nanoparticles were synthesized by a one-step hydrothermal method without the use of a surfactant or template and used to fabricate gas sensors. Various techniques were employed for the characterization of the structure and morphology of the as-prepared products. The gas-sensing characteristics of the fabricated sensors were investigated for various concentrations of xylene at different temperatures. At a low operation temperature of 160 °C, the sensors possess an excellent gas response, selectivity, linear dependence, low detection limitation, and repeatability as well as long-term stability. In particular, for the high gas response of the 10.0 mol% WO3 decorated TiO2 nanoparticles based sensor, its response reaches 92.53 for 10 ppm xylene, which is much higher than that of the pristine TiO2 based sensor. And the detection limit is 1 ppm. Those values demonstrate the potential of using WO3 decorated TiO2 nanoparticles for xylene gas detection, particularly with low concentration xylene. Apart from this, the mechanism related to the advanced properties was also investigated and presented.

•MnO2 hollow microspheres consisted of MnO2 nanoribbons were successfully prepared.•MnO2 hollow microspheres possess good microwave absorption performances.•The excellent microwave absorption properties are in X and Ku microwave band.•Electromagnetic impedance matching is great contribution to absorption properties.MnO2 hollow microspheres consisted of nanoribbons were successfully fabricated via a facile hydrothermal method with SiO2 sphere templates. The crystal structure, morphology and microwave absorption properties in X and Ku band of the as-synthesized samples were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM) and a vector network analyzer. The results show that the three-dimensional (3D) hollow microspheres are assembled by ultra thin and narrow one-dimensional (1D) nanoribbons. A rational process for the formation of hollow microspheres is proposed. The 3D MnO2 hollow microspheres possess improved dielectric and magnetic properties than the 1D nanoribbons prepared by the same procedures with the absence of SiO2 hard templates, which are closely related to their special nanostructures. The MnO2 microspheres also show much better microwave absorption properties in X (8–12 GHz) and Ku (12–18 GHz) microwave band compared with 1D MnO2 nanoribbons. The minimum reflection loss of −40 dB for hollow microsphere can be observed at 14.2 GHz and reflection loss below −10 dB is 3.5 GHz with a thickness of only 4 mm. The possible mechanism for the enhanced microwave absorption properties is also discussed.MnO2 hollow microspheres composed of nanoribbons show the excellent microwave absorption properties in X and Ku band.

Reduced graphene oxide/cryptomelane (RGO/KMn8O16) composites are successfully synthesized from α-MnO2 nanorods and GO using a water-bathing precipitation method. The unique structure of KMn8O16 nanorods, with a length of 2–4 μm, dispersed on the surface of RGO leads to a much enhanced electrical conductivity and ionic transport, finally achieving composites with an improved electrochemical performance. Electrochemical measurement results show a specific capacitance of 222.3 F/g at a current density of 0.2 A/g, much higher than that of the original α-MnO2. After 500 cycles at 2.0 A/g, the RGO/KMn8O16 composite electrode still retains 92.6% of its initial specific capacitance. The excellent electrochemical performance and durability observed for this composite electrode suggest its potential application for electrochemical capacitors.

•NiO/RGO composites were synthesized under the different calcination temperatures.•Calcination temperature impacts capacitive properties as electrode.•NiO/RGO composites calcined at low temperature possess the excellent capacitive behaviors.•Crystallinity, component and surface defects play major role on capacitive character.A series of NiO/RGO composites based on NiO nanoparticles anchored on layered RGO surfaces were proposed by the same hydrothermal method combined with different calcination temperatures (250, 300, 400 and 500 °C). The effects of calcination temperatures on the capacitive behaviors have been discussed by investigating the components, morphologies, surface conditions of the NiO/RGO composites. The specific capacitance values of NiO/RGO composites calcined at 250, 300, 400 and 500 °C are 950, 553, 375 and 205 F/g at the current density of 1 A/g and the corresponding capacitance retention are 91.3%, 83.9%, 71.9% and 67.3% after 1000 cycles at the current density of 10 A/g. The results suggest the calcination temperature plays an important role in the electrochemical performances of NiO/RGO composites and the electrochemical performances were deteriorated with the increasing calcination temperatures.NiO/RGO composites synthesized by hydrothermal method combined with the different calcination temperatures exhibit the excellent capacitive behaviors.

•Hierarchically porous WO3 synthesized by combustion process.•Hierarchically porous WO3 exhibits high gas response and excellent selectivity for acetone.•The excellent sensing property was plausibly attributed to the porous morphology.An easy, inexpensive combustion route was designed to synthesize hierarchically porous WO3. The tungsten source was fresh peroxiotungstic acid by dissolving tungsten powder into hydrogen peroxide. To promote the combustion reaction, a combined fuel of both glycine and hydrazine hydrate was used. The microstructure was well-connected pores comprised of subunit nanoparticles. Upon exposing towards acetone gas, the porous WO3 based sensor exhibits high gas response, rapid response and recovery, and good selectivity in the range of 5–1000 ppm under working temperature of 300 °C. This excellent sensing performance was plausibly attributed to the porous morphology, which hence provides more active sites for the gas molecules' reaction.Hierarchically porous WO3 synthesized by combustion process exhibits high gas response, rapid response and recovery, and excellent selectivity for acetone, making it to be promising candidates for practical detectors for acetone.

•ZnO hollow spheres were synthesized via a PSS template.•ZnO hollow spheres based gas sensor shows a high response towards n-butanol.•Sensor has good repeatability, stability, fast response and recovery towards n-butanol.•Hollow structure increases surface area and oxygen specie to promote oxidation of n-butanol.ZnO hollow spheres with high crystallinity were prepared successfully via a simple template process using ZnCl2, carbamide and polystyrene spheres (PSS) as raw materials. The structural and morphological characterizations of the samples were carried out by X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS), respectively. Indirect-heating sensor using ZnO hollow spheres as sensing materials was fabricated on an alumina tube with Au electrodes and Pt wires. The gas sensing properties of the as-synthesized ZnO hollow spheres for n-butanol were investigated. It is shown that the sensor exhibited good sensing performances, characterized by high response, very short response time, and stability to n-butanol gas at operating temperature of 385 °C. These results indicate that the ZnO hollow spheres are highly promising candidates for practical detectors for n-butanol.ZnO hollow spheres based sensor exhibits high response, very short response and recovery time, and stability to n-butanol gas at operating temperature of 385 °C.

•Ag-functionalized In2O3/ZnO (IZO) nanocomposites were fabricated by a nonaqueous route.•High nanocrystalline Ag-functionalized IZO shows highly sensitive for formaldehyde.•The high sensing properties attribute to the unique structure of IZO nanocomposites.•The approach could be expected to be extended for development of an excellent gas sensor.In this work, Ag-functionalized In2O3/ZnO (IZO) nanocomposites with various contents were successfully fabricated by a nonaqueous route. The ZnO and In2O3 showed separated phases and different sizes deriving from the faster growth of ZnO than In2O3 using benzyl alcohol as the oxygen supplying agent. To demonstrate the usage of such Ag-functionalized IZO, the gas sensors have been fabricated and investigated for formaldehyde (HCHO) detection. The results reveal that the as-synthesized 3 wt% Ag-functionalized IZO samples exhibit high response of about 842.9 towards 2000 ppm HCHO at operating temperature of 300 °C. All sensors show rapid response and recovery. The highly sensing properties are attributed to the synergistic effects arising from the presence of these multiple functional materials, i.e. the special structure of IZO nanocomposites, the formation of the heterojunctions, the influence of Ag nanoparticles, and the mutual doping effect.3 wt% Ag-functionalized In2O3/ZnO (IZO) nanocomposites synthesized by a nonaqueous route exhibits ultra-high sensitivity and a rapid response/recovery time towards formaldehyde gas, which attributed the unique structure of IZO nanocomposites, the formation of heterostructure between In2O3 and ZnO, the influence of Ag nanoparticles, and the mutual doping effect during In2O3 and ZnO growth.

•Mesoporous Co3O4 nanosheets were synthesized without using of surfactant or template.•Mesoporous Co3O4 nanosheets based gas sensor shows a high response towards VOCs.•Sensor has good repeatability, stability, fast response and recovery towards VOCs.•Mesoporous structure increases surface area and oxygen specie to promote oxidation of VOCs.Mesoporous Co3O4 nanosheets were synthesized via a facile chemical coprecipitation method without using of surfactant or template. Mesoporous Co3O4 material was characterized using X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) to examine the morphology and microstructure to find out the cause for the highly sensitive sensing behavior. SEM and TEM analyses reveal that the Co3O4 nanosheets consisting of nanoparticles prepared here are porous in nature, with average pore sizes of approximately 50 nm or smaller. The sensor based on porous Co3O4 nanaosheets was used for detecting the volatile organic compounds (VOCs) including ethanol, methanol, acetone, isopropanol, formaldehyde and n-butanol. The results demonstrate that the sensor shows potential for detecting VOCs. The significant improvement of sensitivity is attributed to the porous structure, good contact and relatively small crystal size. The gas sensor shows high response values, fast response and recovery times towards VOCs. So, porous Co3O4 nanosheets are considered as promising sensor material for detecting VOCs.Gas sensor based on mesoporous Co3O4 nanosheets synthesized via a facile chemical coprecipitation method without using of surfactant or template show a high response to volatile organic compounds.

•SnO2-Pd-Pt-In2O3 composite was successfully obtained via a solid-phase reaction method.•Composite displays ultra-high response to methanol at an operating temperature of 160 °C.•Composite exhibits good dynamic properties, selectivity, repeatability and stability.•Composite could be expected for development of an excellent methanol gas sensor.As a new methanol sensing material, the composite of palladium-platinum-In2O3 composited nanocrystalline SnO2 was successfully obtained by a solid-phase reaction method. The phase composition and the unique structure of as-prepared SnO2-Pd-Pt-In2O3 composite were comprehensively characterized using the techniques such as X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), respectively. The results of gas sensing properties indicate that the sensor based on the as-prepared SnO2-Pd-Pt-In2O3 composite shows the ultra-high response to methanol at an optimal operating temperature of 160 °C when the mass ratio of SnO2, Pd, Pt and In2O3 is 100:0.8:2:30. The gas response toward 100 ppm of methanol reaches as high as 320.73. The detection limit of the sensor is estimated to be 0.1 ppm. The sensor also exhibited good response-recovery properties, selectivity, remarkable repeatability and stability, suggesting its greatly promising application in gas sensing. This work could stimulate an effective means to fabricate methanol sensor with superior performance. At the same time, a possible sensing mechanism of the SnO2-Pd-Pt-In2O3 composite is discussed.The gas sensor fabricated by palladium-platinum-In2O3 composited nanocrystalline SnO2 exhibits high response, good response-recovery properties, selectivity, remarkable repeatability and stability towards methanol, making it to be promising candidates for practical detectors for methanol.

•Al-doping macro-/nanoporous ZnO was synthesized by a self-sustained decomposition route.•Al-doping macro-/nanoporous ZnO based gas sensor shows a high response towards n-butanol.•Sensor has good repeatability, selectivity, fast response and recovery towards n-butanol.•Al doping porous ZnO could be expected for development of an excellent n-butanol gas sensor.Macro-/nanoporous Al-doping ZnO powders with enhanced gas sensing properties are prepared by a solution combustion method using Zn(CH3COO)2·2H2O, Zn(NO3)2·6H2O, Al(NO3)3·9H2O, N2H4·H2O and C2H5NO2 as precursors. Characterization by TEM, SEM and BET techniques demonstrates that the Al-doping ZnO powders have a coral-like morphology with a hierarchically porous structure from macro pores, with the wall containing smaller mesopores. The gas-sensing characteristics of the ZnO samples with different Al-doping concentrations are investigated and the results indicate that the gas sensor prepared from 2.5 at% Al doping ZnO powders shows the highest gas sensitivity and selectivity towards n-butanol. A maximum gas response of 751.95 towards 100 ppm n-butanol is achieved at the operating temperature of 300 °C. The mechanisms of responses are also proposed considering the unique material structure.2.5 at.% Al-doping macro-/nanoporous ZnO synthesized by self-sustained decomposition of Zn-based complex exhibits ultra-high gas response, selectivity, and a rapid response/recovery time toward n-butanol gas, which attributed the unique structure of macro-/nanoporous ZnO and the Al doping effect.

Pt activated SnO2 nanoparticle clusters were synthesized by a simple solvothermal method. The structure, morphology, chemical state and specific surface area were analyzed by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and N2-sorption studies, respectively. The SnO2 nanoparticle cluster matrix consists of tens of thousands of SnO2 nanoparticles with an ultra-small grain size estimated to be 3.0 nm. And there are abundant random-packed wormhole-like pores, caused by the inter-connection of the SnO2 nanoparticles, throughout each cluster. The platinum element is present in two forms including metal (Pt) and tetravalent metal oxide (PtO2) in the Pt activated SnO2 nanoparticle clusters. The as-synthesized pure and Pt activated SnO2 nanoparticle clusters were used to fabricate gas sensor devices. It was found that the gas response toward 500 ppm of ammonia was improved from 6.48 to 203.44 through the activation by Pt. And the results indicate that the sensor based on Pt activated SnO2 not only has ultrahigh sensitivity but also possesses good response–recovery properties, linear dependence, repeatability, selectivity and long-term stability, demonstrating the potential to use Pt activated SnO2 nanoparticle clusters as ammonia gas sensors. At the same time, the formation mechanisms of the unique nanoparticle clusters and highly enhanced sensitivity are also discussed.

Pure MnO2 nanorods and MnO2 nanorod/reduced graphene oxide (RGO) nanocomposites are prepared for microwave absorption by using a simple one-step hydrothermal method without using any toxic solvents. The results demonstrate that the MnO2 phases possess a high crystallization degree in both the pure nanorods and the nanocomposites but the nanocomposites exhibit two hybrid Mn phases, distinct from MnO2 in the pure nanorods. The electromagnetic characteristics and electromagnetic wave (EMW) absorption properties of the materials are investigated. The thickness dependent reflection loss shows that the peak frequency and effective absorption bandwidth all decrease with the increasing material thickness. Compared with the pure MnO2 nanorods, the introduction of RGO enhances the microwave absorbing intensity and effective absorption bandwidth. The maximum reflection loss value of the nanocomposites reaches −37 dB at 16.8 GHz with a thickness of 2.0 mm and the wide bandwidth corresponding to the reflection loss below −10 dB starts from 13 GHz until a value of −22 dB at 18 GHz. The enhanced microwave absorbing properties can be ascribed to the improved permittivity, dielectric loss and especially the synergistic effects between MnO2 nanorods and RGO nanosheets at their interfaces in the unique nanostructures of the MnO2/RGO nanocomposites.

Ternary oxide Zn2SnO4 was introduced to a rod-like nanostructured SnO2 gas sensor for formaldehyde detection by a facile one-step hydrothermal synthesis. The effects of the Zn2SnO4 additive on the structure, morphology and gas-sensing property of SnO2 were investigated in this study. It was confirmed that control of the Zn amounts in the precursor solution was effective in realizing well-developed one- and two-dimensional coexisting structured SnO2–Zn2SnO4 (SnZn) nanocomposites. The gas sensing properties of the resulting SnZn composites to HCHO vapor were tested. The results showed that the presence of Zn2SnO4 species in SnO2 powders could effectively enhance electrical conductivity, reduce optimal operating temperature and improve the gas response of the sensors. The composite exhibited the highest response towards HCHO in the case of 35 at% Zn2SnO4 nanoplates coupling with hierarchical branched structures of SnO2 nanorods (SnZn35) at a relatively lower operating temperature of 162 °C. The good gas-sensing performance of the SnZn35 composite can be ascribed to the smaller particle size, the larger surface area and the more absorbed Ox− species, which all are favorable for gas diffusion and sensing reactions. This work renders great potential in the fabrication of gas sensors using a binary–ternary oxide composite, which can be further applied in indoor pollution detection.

ZnO quantum dots (QDs), a few nanometers in size, were synthesized by a sol–gel method using different solvents (methanol, ethanol and hexanol). The structural, morphological and photoluminescent properties were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), photoluminescence spectrometry, and UV-vis spectroscopy. The results indicated that ZnO QDs with good dispersion, ranging in size from 3.3 nm to 7.7 nm, could be controlled easily by the solvents. The ZnO QDs exhibited strong visible emission from green to orange. The reasons for the change in emission color are believed to be the quantum size effect and the change in defect concentration due to the different solvents used in their preparation. A possible mechanism for the photoluminescence of ZnO QDs is also presented.

Ag–ZnO heterostructure nanoparticles were synthesized by a one-step solvothermal route from zinc acetate dihydrate (Zn(CH3COO)2·2H2O), silver nitrate (AgNO3), potassium hydroxide (KOH) and methanol (CH3OH). The structure, morphology, component and optical properties were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, UV-vis spectroscopy and photoluminescence spectroscopy, respectively. The results show that highly crystalline wurtzite-type ZnO nanoparticles matrices with an average grain size of 7.4 nm are obtained. Highly crystalline metallic Ag nanoparticles are observed on the ZnO matrix with a good combination. The absorption spectra of the Ag–ZnO heterostructure nanoparticles show the existence of a special two-absorption-region (strong UV-light and weak visible-light at 421 nm). The intensities of photoluminescence in the visible light region have a regular decrease with the increase in the load amount of Ag. The photoactivity of the as-synthesized samples was tested by measuring the degradation of azo dye Congo red (CR) under visible light irradiation. And it is found that both ZnO nanoparticles and Ag–ZnO heterostructured nanoparticles have better photocatalytic efficiency than commercial TiO2 (P-25), and an appropriate loading amount of Ag nanoparticles can significantly enhance the photocatalytic efficiency. The photodegradation mechanism as well as enhancement of the photoactivity in the presence of silver nanoparticles is further investigated. The experimental results indicate the potential of using Ag–ZnO heterostructured nanoparticles for degradation of Congo red dye.

Cryptomelane type manganese oxide α-MnO2 and Ni doped KMn8O16 nanostructures were synthesized by water-bathing methods at 80 °C for 24 h using NiSO4·H2O as the dopant sources. The structures, morphologies and physical properties were investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The results show that the products are Ni doped KMn8O16 nanorods after the introduction of NiSO4·H2O during the reaction process. The electromagnetic characteristics and microwave absorption properties of the materials were carried out with a vector network analyzer (VNA) and the transmission line (TML) theory. The dielectric loss and microwave absorption properties of the cryptomelane materials are improved after Ni doping. The thickness dependent reflection loss shows that the peak frequency and effective absorption bandwidth all decrease with the increasing material thickness. With the increase of Ni doping concentration, the peak frequency shifts to higher frequency bands and the effective absorption bandwidth increases. The electromagnetic performance of cryptomelane can be attributed to its unique tunnel structures and the improvement of Ni doping can be due to the enhanced electromagnetic polarization.

This article describes a new option for butane detection: W-doped TiO2 nanoparticles with high sensitivity and fast response/recovery toward butane, which were obtained from a simple, non-aqueous sol–gel route. The structure, morphology, surface chemical state and specific surface area were analyzed by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectrum (XPS) and N2-sorption isotherm, respectively. The obtained products are anatase-type TiO2 with a small grain size (7.5 ± 1.4 nm) and a high specific surface area (181.15 m2 g−1). Tungsten element presents in the +6 oxidation state. The resistance–temperature measurements indicate that tungsten dopant leads to the decrease in resistance. The as-prepared pure and W-doped TiO2 nanoparticles were used to fabricate gas sensor devices. Gas response toward 3000 ppm butane is increased from 6 to 17.8 through the doping of 5% tungsten. Meanwhile, the response and recovery time toward 3000 ppm butane are as fast as 2 and 12 s, respectively. Moreover, the sensor also possesses low detection limit, good linear dependence, good repeatability and long-term stability, indicating the potential of using W-doped TiO2 nanoparticles for butane gas detection. In addition, a possible mechanism for the enhanced sensitivity of W-doped TiO2 nanoparticles toward butane is also offered.

Meso- and macroporous coral-like Co3O4 was synthesized via a facile self-sustained decomposition using the complexes of metallic salts and organics (metal-organic complexes). Porous Co3O4 material was characterized using X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, and X-ray photoelectron spectrum (XPS) to examine the morphology and microstructure to find out the cause. Co3O4 with the meso- and macroporous structure consisting of nanoparticles has a coral-like shape with a size of tens of micrometers and exhibits the hierarchically porous morphology, in which the walls of the macropores contain smaller mesopores. The gas-sensing characteristics of the porous Co3O4 for volatile organic compounds (VOCs) were investigated. The gas response to 1000 ppm n-butanol reaches a maximum of 27.7 at an operating temperature of 120 °C, and about five times of the Co3O4 particles. The porous Co3O4 also exhibits certain selectivity and response/recovery time.

A series of ordered mesoporous silica loaded with samarium oxide (Sm-MCM-41) were synthesized by a facile one-step sol–gel route using hexadecyltrimethylammonium bromide (CTAB) as the template, tetraethylorthosilicate (TEOS) as the silica source, and hexahydrated samarium chloride as the precursor. The as-synthesized materials with the Sm/Si molar ratio ranging from 0.2 to 0.8 were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and N2 adsorption–desorption measurements. All obtained compounds possess an ordered hexagonal mesoporous structure with a high surface area, a large pore volume, and uniform pore size. The mesoporous composites were used as the novel adsorbents for phosphate ion (H2PO4−) removal from synthetic aqueous solutions. The phosphate removal capacity of Sm-MCM-41 with a Sm/Si molar ratio of 0.6 was up to 20 mg P/g. The Sm functionalized mesoporous silica materials show a higher phosphate removal capacity compared to MCM-41 and Sm2O3 particles, making them promising candidates for water quality control and protection.

•1D Co3O4/ZnO core/shell NRs were synthesized on nickel foil by a two-step synthetic strategy.•The thickness of ZnO coating is determined to be about 20 nm.•Co3O4/ZnO NRs exhibited better photocatalytic performance for MB degradation under UV irradiation.•The formation of p-n junctions confirmed by PL is a critical factor for photocatalytic enhancement.•The working mechanism for Co3O4/ZnO NRs as photocatalyst was proposed.One-dimension (1D) Co3O4/ZnO core/shell nanorods (NRs) were synthesized on nickel foil substrate by means of a two-step synthetic strategy. Co3O4 NRs were initially fabricated by a facile hydrothermal reaction and then ZnO was coated via a simple thermal decomposition. The results verified that the surface of the p-type Co3O4 core was uniformly assembled by the n-type ZnO nanoparticles with approximate 20 nm thickness. Compared with pristine Co3O4 NRs, Co3O4/ZnO core/shell NRs was exhibited to have a much higher photocatalytic properties in the decomposition of a model dye compound, methylene blue (MB), under ultraviolet irradiation. As confirmed by Photoluminescence (PL) spectra, the formation of p-n junction heterostructures gives rise to the enhanced photocatalystic performance of Co3O4/ZnO core/shell NRs. This study provides a general and effective method in the fabrication of 1D composition NRs with sound heterojunctions that show remarkable enhancement of photocatalytic performance.

A facile hydrothermal method has been developed for the synthesis of nanosized Cu–CeO2 composites with various Cu contents. The obtained catalysts, with a Cu/CeO2 atomic ratio in the range of 0–40%, were characterized as to their structure, morphology, and redox features by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, N2 physisorption, and temperature programmed reduction with hydrogen. The experimental results show that the particles are highly crystalline CeO2 nanopowders of 5–8 nm primary particle size and the Cu nanoparticles indeed coexist with the CeO2 nanoparticles (cubic fluorite CeO2). The influence of Cu contents on their catalytic performance for CO oxidation was also studied. As for the catalytic reactivity, nanosized Cu–CeO2 composites have a higher catalytic activity than CeO2 in CO oxidation. It is ascribed to the effect between the cycle transition of Ce4+/Ce3+, oxygen vacancies and surface area, which are induced by copper. The catalytic activity of the Cu–CeO2 composites exhibits Cu content dependence where the best catalytic activity occurs at a Cu/CeO2 atomic ratio of 30%. In addition, nanosized Cu–CeO2 composites also show high catalytic activity for selective oxidation of CO in excess H2 at relatively low temperature.

•Ordered mesoporous NiO/MCM-41 composite is prepared by chemical precipitation method.•Ordered mesoporous NiO/MCM-41 composite have a specific surface area of 435.9 m2 g−1.•Ordered mesoporous NiO/MCM-41 composite exhibit promising adsorption for methylene blue.Highly ordered mesoporous material MCM-41 was synthesized from tetraethylorthosilicate (TEOS) as Si source and cetyltrimethylammonium bromide (CTAB) as template. Well-dispersed NiO nanoparticles were introduced into the highly ordered mesoporous MCM-41 by chemical precipitation method to prepare the highly ordered mesoporous NiO/MCM-41 composite. X-ray diffraction (XRD) analysis, transmission electron microscopy (TEM) and high-resolution TEM (HRTEM), and nitrogen adsorption–desorption measurement were used to examine the morphology and the microstructure of the obtained composite. The morphological study clearly revealed that the synthesized NiO/MCM-41 composite has a highly ordered mesoporous structure with a specific surface area of 435.9 m2 g−1. A possible formation mechanism is preliminary proposed for the formation of the nanostructure. The adsorption performance of NiO/MCM-41 composite as an adsorbent was further demonstrated in the removal azo dyes of methyl orange (MO), Congo red (CR), methylene blue (MB) and rhodaming B (RB) under visible light irradiation and dark, respectively. The kinetics and mechanism of removal methylene blue were studied. The results show that NiO/MCM-41 composite has a good removal capacity for organic pollutant MB from the wastewater under the room temperature. Compared with MCM-41 and NiO nanoparticles, 54.2% and 100% higher removal rate were obtained by the NiO/MCM-41 composite.Ordered mesoporous NiO/MCM-41 composite powders exhibit a high adsorption for methylene blue in aqueous solution.

Three-dimensional macro/mesoporous Co3O4–CeO2 was prepared via a facile self-sustained decomposition of metal–organic complexes. Porous Co3O4–CeO2 was characterized using X-ray diffraction, scanning electron microscopy/transmission electron microscopy imaging, N2 adsorption/desorption and X-ray photoelectron spectroscopy to examine the morphology and microstructure to find out the cause. Co3O4–CeO2 with the 3D hierarchical porous structure consisting of nanoparticles is a coral-like shape with a size of tens of micrometers and exhibits the hierarchically porous morphology, in which the walls of the macropores contain smaller mesopores. The catalytic performance of the porous Co3O4–CeO2 for CO oxidation has been studied. Among the obtained catalysts, the porous Co3O4–CeO2 with 20 wt% Co exhibits the best catalytic activity and the 50 % CO conversion can be reached at 74 °C. The presence of transition metal element Co can promote the production of oxygen vacancies and improve oxygen mobility, which result in enhancing the oxygen-storage capacity of porous Co3O4–CeO2 and its catalytic performance for CO conversion.

The synthesis as well as the electrochemical properties study of highly crystalline ZnCo2O4 powders is presented. ZnCo2O4 powders with a particle diameter of 15–35 nm have been successfully prepared with the surfactant-mediated method. The thorough structural characterization including X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were employed to examine the morphology and the microstructure of the final product. The as-synthesized powders were used as anode materials for lithium-ion battery, whose charge–discharge properties, cyclic voltammetry, and cycle performance were examined and revealed very good properties. Galvanostatic cycling of ZnCo2O4 powders in the voltage range 0.005–3.0 V versus Li at 60 mA g−1 maintained charge and discharge capacities of 1,308 and 1,336 mAh g−1 after 40 cycles when cycled at 25 °C, respectively.

•3D macro/mesoporous Co3O4 was successfully synthesized by a flash synthesis.•Porous Co3O4 exhibits the hierarchically porous morphology.•Porous Co3O4 shows 100% conversion efficiency of CO to CO2 at 140 °C.•Porous Co3O4 is more efficient for CO oxidation than Co3O4 nanoparticles.Three-dimensional macro/mesoporous tricobalt tetraoxide Co3O4 was prepared via a facile self-sustained decomposition using the complexes of metallic salts and organics (metal–organic complexes). Porous Co3O4 material was characterized using X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, and X-ray photoelectron spectrum (XPS) to examine the morphology and microstructure to find out the cause. Co3O4 with the 3D hierarchical porous structure consisting of nanoparticles has a coral-like shape with a size of tens of micrometers and exhibits the hierarchically porous morphology, in which the walls of the macropores contain smaller mesopores. The catalytic performance of the porous Co3O4 for CO oxidation has been studied with a continuous flow fixed-bed quartz microreactor. The porous Co3O4 exhibits excellent catalytic activity for CO oxidation, the CO conversion rate reaches 100% at 140 °C.

Pt-functionalized SnO2 sheets with Pt contents of 0, 0.5, 1, and 2 wt% were synthesized by a facile solution combustion synthesis, and their crystal structure, morphology, and chemistry have been thoroughly characterized. In the combustion process, the urea (CO(NH2)2) has been employed as a fuel. The obtained products appear as porous sheets formed by the interconnected and loosely packed SnO2 nanoparticles. Pt nanoparticles are assembled together with SnO2 nanoparticles in several up to tens of nanometer clusters. The as-synthesized products were used as sensing materials in the sensors to detect the isopropanol (IPA) gas. Gas sensing tests exhibited that the Pt-functionalized SnO2 are highly promising for gas sensor applications, as the operating temperature was lower than current IPA sensors and the response to IPA was significantly enhanced. The 2 wt% Pt–SnO2 sheet based gas sensor displayed a response value of 190.50 for 100 ppm IPA at an optimized operating temperature of 220 °C, whereas the pristine SnO2 based gas sensor only showed a response of 21.53 under the same conditions. The roles of Pt nanoparticles on electronic sensitization of SnO2, catalytic oxidation (spillover effect), and the increased quantities of oxygen species on the surface of SnO2 are plausible reasons to explain the significant enhancement in response to a Pt-functionalized SnO2 sheet based gas sensor.

Lanthanum dioxide carbonate La2O2CO3 nanorods with high crystallinity were successfully prepared from La(OH)3 nanorods. The structural and morphological characterizations of the products were performed by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectrum (XPS). La(OH)3 nanorods were shape-preserved transformed to La2O2CO3 nanorods at 400 oC for 2 h. TEM images indicate that the as-obtained La2O2CO3 entirely consists of uniform nanorods in high yield with diameter of 13-15 nm and length of 100-150 nm. The indirect-heating sensor using La2O2CO3 nanorods as sensitive material was fabricated on an alumina tube with Au electrodes and platinum wires. The sensing properties of the sensor based on La2O2CO3 nanorods were investigated. It is shown that the sensor exhibits high gas response for CO2 gas at operating temperature of 325oC, making it to be potential candidate for practical detectors for CO2 gas.

The authors report a facile chemical precipitation method for the fabrication of a highly ordered mesoporous Mn2O3/MCM-41 composite. Examination of the acquired samples using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and nitrogen adsorption–desorption measurement has provided fundamental insight into the structure and properties of the Mn2O3/MCM-41 composite. It is found that the as-prepared Mn2O3/MCM-41 composite has a highly ordered mesoporous structure with a specific surface area of 793 m2 g−1. The performance of Mn2O3/MCM-41 composite as a remover was further demonstrated in the removal of azo dyes of methyl orange (MO), Congo red (CR), methylene blue (MB), and rhodamine B (RB) with/without visible light irradiation at room temperature. The results show that the Mn2O3/MCM-41 composite has an excellent removal performance for MB and RB, making it a promising candidate for wastewater treatment.

Well-crystalline tin oxide nanorods assembled with SnO2 nanocrystals were prepared by calcination of SnC2O4 nanorods synthesized by a chemical precipitation method using SnCl2·2H2O and PEG 400 as precursors. The phase and morphology of the resulting material were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectrum (XPS). Indirect-heating sensors using SnO2 nanorods as sensitive materials were fabricated on an alumina tube with Au electrodes and platinum wires. The as-fabricated sensor based on SnO2 nanorods showed high response, fast response and recovery toward isopropanol gas, making them promising candidates for practical detectors of isopropanol gas.

•Rod-like ZnO with the different morphologies were grown on polycrystalline Zn substrate.•Nanostructured ZnO on substrate was used directly to remove azo dye Congo red from wastewater.•Remove Congo red from wastewater requiring no external energy or reagents input.•Remove Congo red from wastewater can be carried out under various ambient conditions.Rod-like ZnO with the different morphologies were grown on polycrystalline Zn substrate by a simple hydrothermal process in a NaOH or NH4OH solution at the hydrothermal temperature range from 80 to 150 °C for different reaction time. Variations preparation in the different alkali solution concentration, hydrothermal temperature, and reaction times were explored to shed light on the morphology of the rod-like nanostructures. The thorough structural characterization including X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), electron diffraction, and X-ray photoelectron spectrum (XPS) were employed to examine the morphology and the microstructure of the final products. It was found that alkali solution concentration, hydrothermal temperature and time have important influence on the morphology of the rod-like nanostructures. The dye removal efficiency of ZnO nanorods was explored by the decoloration of azo dye Congo red (CR). In order to obtain the optimum removal conditions of Congo red, the performance of removing CR with various initial concentrations by ZnO nanorods on Zn substrates with different morphologies was tested under various ambient conditions (visible light illumination and darkness). All prepared samples showed an excellent dye removal efficiency for organic pollutants CR from wastewater, making them promising candidates for the wastewater treatment.

•The facile hydrothermal method for the synthesis of Co3O4 nanorods (NRs) has been reported.•The Co3O4 NRs initially grouped into bundle structure and then formed spark.•The length of Co3O4 NRs is several micrometers up to tens of micrometers with diameter of 1 μm.•The NRs are stacked layer-by-layer from single grains in 50–200 nm.Co3O4 nanorods (NRs) were successfully synthesized on nickel foil by a facile hydrothermal reaction. The X-ray diffraction (XRD) investigation confirms the formation of spinel Co3O4 phase. Owing to the mismatch between Co3O4 and substrate, the Co3O4 NRs initially grouped into bundle structure and then formed dispersed NRs. The length of Co3O4 NRs varies from several micrometers up to tens of micrometers with uniform diameter of about 1 μm. Transmission electron microscopy (TEM) characterization demonstrated that the NRs are stacked layer-by-layer from single grains in 50–200 nm. This facile hydrothermal method for preparation of Co3O4 NRs is significant in the synthesis and future applications of one-dimensional (1D) nanostructures.

•A 3D macro-/nanoporous ZnCo2O4 was fabricated by a novel and feasible template-free route.•ZnCo2O4 possesses a coral-like shape with a size of tens of micrometers•ZnCo2O4 exhibits the hierarchically porous morphology.•The effective method can fabricate a 3D macro-/nanoporous ternary oxide.This letter describes the synthesis as well as characterization of the 3D macro-/nanoporous ZnCo2O4 using flash synthesis via self-sustained decomposition of metal–organic complexes. The sample was characterized by X-ray diffraction, SEM/TEM imaging, Raman spectrum and X-ray photoelectron spectroscopy. ZnCo2O4 with the 3D hierarchical porous structure consisted of nanoparticles has a coral-like shape with a size of tens of micrometers and exhibits the hierarchically porous morphology, in which the walls of the macropores contain smaller nanopores. The results show that the flash synthesis directly decomposing a metal–organic complex is a rapid and feasible route to fabricate macro-/nanoporous ZnCo2O4 with high porosity.A 3D macro-/nanoporous ZnCo2O4 possessed a coral-like shape with a size of tens of micrometers and the hierarchically porous morphology has been prepared by a novel, rapid and feasible flash synthesis via self-sustained decomposition of metal–organic complexes.

•The transparent nanocrystalline ZnO thin films with different Mn doping contents were prepared by a sol–gel technique.•The surface roughness and average crystallite size of thin films are sensitive to Mn doping contents.•A board UV peak ascribed to the free exciton emission is observed in the undoped or doped ZnO thin film.The transparent nanocrystalline thin films of undoped zinc oxide and Mn-doped (Zn1−xMnxO) have been deposited on glass substrates via the sol–gel technique using zinc acetate dehydrate and manganese chloride as precursor. The as-deposited films with the different manganese compositions in the range of 2.5–20 at% were pre-heated at 100 °C for 1 h and 200 °C for 2 h, respectively, and then crystallized in air at 560 °C for 2 h. The structural properties and morphologies of the undoped and doped ZnO thin films have been investigated. X-ray diffraction (XRD) spectra, scanning electron microscopy (SEM), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS) were used to examine the morphology and microstructure of the thin films. Optical properties of the thin films were determined by photoluminescence (PL) and UV/Vis spectroscopy. The analyzed results indicates that the obtained films are of good crystal quality and have smooth surfaces, which have a pure hexagonal wurtzite ZnO structure without any Mn related phases. Room temperature photoluminescence is observed for the ZnO and Mn-doped ZnO thin films.Graphical AbstractThe transparent nanocrystalline thin films of undoped zinc oxide and Mn-doped (Zn1-xMnxO) and their optical properties are reported.

The synthesis and the gas sensing properties of novel mixed phase (i.e., tetragonal and orthorhombic phase) coexistence SnO2 nanorods are presented. The mixed phases SnO2 nanorods were obtained by calcinations of SnC2O4 synthesized with a chemical precipitation method using SnCl2·2H2O and PEG 400 as precursors. The resulting nanorods appear as polycrystalline composed of spherical mixed phases SnO2 nanocrystals and have a high surface area. It was observed that the calcination temperature was the key parameter determining the content of the orthorhombic phase. The as-synthesized compounds were used as sensing materials of the sensors of indirect heating structure and tested for their ability to detect volatile organic compounds (VOCs), such as isopropanol, acetone, alcohol, and formaldehyde. Gas sensing tests showed that these mixed phases SnO2 nanorods are highly promising for gas sensor applications, as the gas response for isopropanol was significantly enhanced by the presence of orthorhombic phase (S = 61.5 at 1000 ppm isopropanol and response time and recovery time of 4 and 10 s). The as-prepared two phases SnO2 nanorods with the highest content of the orthorhombic phase exhibit excellent gas response, selectivity, and stability toward isopropanol gas at the optimized operating temperature of 255 °C. The enhancement in sensitivity is attributed to the presence of small orthorhombic SnO2 crystals with average radius shorther than the Debye screening length of 7 nm for SnO2.

A new and facial (low temperature and low cost) method for a direct synthesis of the stable and crystalline phase pure Ni(OH)2 nanosheets was developed using cationic surfactant cetyltrimethylammonium bromide (CTAB). X-ray diffraction (XRD) analysis, Fourier transformed infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) were used to examine the morphology and the microstructure of the obtained compound. The morphological study clearly revealed that obtained compounds appear in a flake-like nanosheet form with a typical length in the range of several hundreds of nanometers and a width in the range of several tens of nanometers. A possible formation mechanism is preliminary proposed for the formation of the nanostructure. The adsorption properties of Ni(OH)2 nanosheets were tested by the adsorption of azo dye Congo red (CR). The results show an excellent removal capacity for organic pollutant CR from the wastewater, making them a promising candidate for wastewater treatment.Ni(OH)2 nanosheets fabricated by a facile and green method exhibit an outstanding adsorption performance for Congo red in aqueous solution.Highlights► Ni(OH)2 nanosheets are fabricated by a facile and green method. ► The Ni(OH)2 nanosheets are crystalline with a hexagonal crystal structure. ► The Ni(OH)2 nanosheets exhibit outstanding adsorption performance for Congo red.

•One-dimensional Ni-doped ZnO nanorods with variable dopant contents are fabricated.•Ni-doped ZnO nanorods are crystalline hexagonal wurtzite ZnO crystal structure.•Ni is in situ doped into the lattice of wurtzite ZnO nanorods.•The Ni-doped ZnO nanorods exhibit promising UV-light activity for rhodamine B degradation.The one-dimensional (1D) Ni-doped ZnO powders with variable dopant contents were synthesized at a low temperature (90 °C) using ZnCl2, NiCl2 and NaOH solution as reaction precursors by a simple water bath method. The morphology and the microstructure of the as-prepared undoped and Ni-doped ZnO samples have been characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectra, X-ray Photoelectron Spectroscopy (XPS), and UV–vis spectroscopy. The results revealed that the samples were one-dimensional nanorods. Ni-doped ZnO nanorods were crystalline hexagonal wurtzite ZnO crystal structure, and the Ni ion was in a 2+ charge state in the crystal lattice of ZnO. The absorption spectra presented the existence of special two-absorption-region (strong UV-light and weak visible-light at 550–800 nm). The performance of Ni-doped ZnO powders as efficient photocatalyst was further demonstrated in the degradation of Rhodamine B (RB) under UV-light irradiation. The Ni-doped ZnO powders show high photocatalytic activity during the degradation of RB under UV-light. It was found that an appropriate amount of Ni dopant can greatly increase photocatalytic activity and the sample with 10% Ni doping exhibits the highest photocatalytic efficiency.Graphical abstractNi-doped ZnO powders with variable dopant contents fabricated at a low temperature exhibit high photocatalytic efficiency for rhodamine B in aqueous solution.

Single crystalline tungsten oxide plates were prepared by hydrothermal method using cetyltrimethyl ammonium bromide (CTAB) supermolecular template. The phase and the morphology of the resulting material were characterized by X-ray diffraction (XRD), Fourier transformed infrared (FTIR) spectrum, scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), and Raman spectroscopy, respectively. Indirect-heating sensors using single crystalline WO3 plates as sensitive materials were fabricated on an alumina tube with Au electrodes and platinum wires. The as-fabricated sensor based on WO3 plates showed high response, fast response and recovery toward acetone gas. Compared with the sensor fabricated with WO3 particles prepared by a surfactant-mediated method, the results show that WO3 plates sensor has about 4 times increase in response and good dynamic response.

Zinc oxide nanorods with different Al doping contents were prepared by the hydrothermal method from zinc chloride solution and aluminum chloride solution assisted by cetyltrimethylammonium bromide (CTAB) in this paper. The effects of Al doping on the structural characteristics and optical properties of the nanorods were studied. The morphology and microstructure of as-synthesized samples were characterized by X-ray diffraction (XRD) spectra, Fourier transformed infrared (FTIR) spectra, scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM) and UV–vis spectroscopy. The results reveal that all the products are one-dimensional rod-like nanostructures and have the high crystalline hexagonal wurtzite ZnO crystal structure. Two blue emissions located at 451 and 468 nm, and two weak green emissions located at about 484 and 493 nm are observed, and the room temperature photoluminescence (PL) mechanisms are discussed.Graphical abstractThe effects of Al doping on the microstructures and the optical properties of ZnO nanorods with the high crystalline hexagonal wurtzite structure are reported. Highlights► Zinc oxide nanorods with different Al doping contents were prepared by the hydrothermal method. ► The aspect ratio of ZnO nanorods is sensitive to the concentration of Al:Zn. ► The emission intensity increase with increases in the aluminum doping level of the ZnO nanorods.

This paper describes a method to prepare tungsten doped anatase TiO2 (WTO) nanoparticles with high surface area based on a polymer-assisted sol–gel process and using simple chemical reagents. The samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (including high-resolution imaging-HRTEM), X-ray photoelectron spectroscopy (XPS), and Brunauer–Emmett–Teller (BET). WTO nanoparticles are obtained with small particle size (ca. 9 nm in mean grain size) and good crystallinity. The as-prepared samples are used as an electrode material for a lithium-ion battery, whose charge–discharge properties, cyclic voltammetry, and cycle performance are examined and revealed to have very good properties. A highly stable capacity of 170 mA h g−1 is found after 100 cycles.

The synthesis as well as the electrochemical properties study of niobium-doped TiO2 (NTO) with mesoporosity and high surface area is presented. The mesoporous NTO was prepared using a novel poly(ethylene-co-butylene)-b-poly(ethylene oxide) amphiphilic diblock copolymer as a template and simple titanium reagents (TiCl4 and Nb(OC2H5)5) by a polymer-assisted sol−gel process. The samples were characterized by differential scanning calorimetry and thermogravimetric analysis (DSC-TGA), X-ray diffraction (XRD), Fourier transformed infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (including high-resolution imaging-HRTEM), and the Brunauer−Emmett−Teller (BET). All samples are highly crystalline and have pore-solid architectures after removal of the polymer template by calcination. The resulting mesoporous NTO shows a high porosity of 46% and a high surface area of 128 m2/g, respectively. The as-prepared samples were used as positive electrode materials for lithium-ion battery, whose charge−discharge properties, cyclic voltammetry, and cycle performance were examined and revealed very good properties. A highly stable capacity of 160 mA h g−1 was found after 100 cycles.

Briers-like ZnO nanoarchitectures, which consisted of sword-like ZnO nanosheets, have been prepared by a facile organic CTAB (cetyltrimethylammonium bromide, CH3(CH2)15N+(CH3)3Br−) inducing deposition process on the titanium substrate. The nanostructured composite has been characterized by X-ray powder diffraction (XRD), field emission scanning electron microscopy (FE-SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray photoemission spectra (XPS). The XRD pattern indicates that the sward-like ZnO nanosheets are the high ordered nanolayered inorganic–organic composites. The ordered layered nanocomposite exhibits the room temperature photoluminescence (RTPL) characteristics. It is inferred that the RTPL of ZnO/CTAB ordered nanolayered composite might be induced by the interfacial effect between the ZnO and the surfactant CTAB.

Antimony-doped tin dioxide (ATO) nanoparticles with high crystallinity during solvothermal synthesis in alcohol were generated from the inorganic precursors (SnCl4 and Sb(OC2H5)3) and the cationic surfactant (cetyltrimethylammonium bromide, CTAB). The structural and morphological characterizations of the products were performed by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), N2-sorption isotherm and X-ray photoelectron spectrum (XPS). The resulting particles were highly crystalline oxide particles in the nanometer range (10–14 nm). The indirect-heating sensors using ATO nanoparticles as sensitive materials were fabricated on an alumina tube with Au electrodes and platinum wires. The sensing properties of these sensors based on ATO nanoparticles were investigated. Compared to the original undoped sensor, the results show that the ATO nanoparticles have about 2.5 times increase in response and good dynamic response to NH3 at low operating temperature (79 °C).

Antimony-doped SnO2 (ATO) nanopowders with high crystallinity were obtained by a polymer-assisted sol−gel process based on a novel amphiphilic block-copolymer (“KLE” type, poly(ethylene-co-butylene)-block-poly(ethylene oxide) and simple tin reagents (SnCl4 and Sb(OC2H5)3). As-synthesized samples were analyzed by Thermogravimetric analysis (TGA), powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron micrographs (TEM), N2 adsorption−desorption isotherms, and X-ray photoelectron spectroscopy (XPS). The results showed that the particles were the high crystalline ATO nanopowders of 5−8 nm primary particle size and the Sb was indeed incorporated into the SnO2 crystal structure (cassiterite SnO2). The as-prepared samples were used as negative electrode materials for lithium-ion batteries, whose charge−discharge properties, cyclic voltammetry, and cycle performance were examined. A high initial discharge capacity about 2400 mA h g−1 was observed at a constant discharge current density of approximately C/5 in a potential range of 0.005−3.0 V. A highly stable capacity of 637 mA h g−1 after 100 cycles is substantially higher than that of most previously reported SnO2 nanostructures. The high reversible capacity for ATO nanopowders may be due to the presence of Sb for Sn, leading to an improved formation of metals with respect to structure and formation dynamics from ATO.

Antimony doped SnO2 (ATO) microspheres composed of ATO nanoparticles were prepared by using a hydrothermal process in a nonaqueous and template-free solution from the inorganic precursors (SnCl4 and Sb(OC2H5)3). The physical properties of the as-synthesized samples were investigated by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2 adsorption–desorption isotherms, and X-ray photoelectron spectrum (XPS). The resulting particles were highly crystalline ATO microspheres in the diameter range of 3–10 μm and with many pores. The as-prepared samples were used as negative materials for lithium-ion battery, whose charge–discharge properties, cyclic voltammetry, and cycle performance were examined. The results showed that a high initial discharge capacity of 1981 mAh g−1 and a charge capacity of 957 mAh g−1 in a potential range of 0.005–3.0 V was achieved, which suggests that tin oxide-based materials work as high capacity anodes for lithium-ion rechargeable batteries. The cycle performance is improved because the conducting ATO nanoparticles can also perform as a better matrix for lithium-ion battery anode.

Perovskite structure of LnFeO3 (Ln = La, Sm, and Eu) oxides with uniform particle size was prepared by the cationic surfactant CTAB (cetyltrimethylammonium bromide) assisting method from the inorganic precursor and alkali source (Ln—chlorate, FeCl3 and NH4OH). The final products were characterized and the results showed that the pure and high crystalline perovskite structure of LnFeO3 materials were obtained after calcining at 850 °C. Gas sensors of the indirect-heating structure using LnFeO3 as sensitive materials were fabricated on alumina tube with Au electrodes and platinum wires. The gas-sensing characteristics of LnFeO3 to acetone, gasoline, and formaldehyde were investigated and exhibited good response properties to acetone (LaFeO3), gasoline (SmFeO3), and formaldehyde (EuFeO3) gases, respectively. The LnFeO3 oxides-based on gas sensors enable them to be promising candidates for the detection of the gases in monitoring environment.

The porous sphere-like ZnO inorganic–organic nanocomposites have been prepared by self-assembly at the present of CTAB (cetyltrimethylammonium bromide, CH3(CH2)15N+(CH3)3Br−) surfactant on the titanium substrate. After high temperature oxidation, all the organic were removed and the porous sphere-like ZnO dendrite nanocrystals were obtained. The resultant products have been characterized by X-ray powder diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM). The XRD pattern shows that the as-synthesized porous sphere-like is multilayered inorganic–organic nanocomposite, and the sample calcined at 500 °C for 2 h has a hexagonal wurtzite crystal structure. FE-SEM and TEM images demonstrate that porous sphere-like ZnO dendrite nanocrystals are formed. A possible formation mechanism is preliminary proposed for the formation of the novel nanostructure.

The SnO2 nanoparticles coated on SiO2 microspheres were prepared with the hydrous tin chloride, NH3·H2O and the slurry of amorphous silica microspheres in an aqueous medium. X-ray powder diffraction (XRD), Fourier transformed infrared (FTIR) spectra, field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray photoelectron spectrum (XPS), and UV–vis spectrophotometer were used to characterize the SiO2–SnO2 core–shell structured particles. The XRD of the SnO2 nanoparticles coated on SiO2 microspheres yields diffraction peaks corresponding to the cassiterite SnO2 phase. The FE-SEM and TEM images show that the SnO2 nanoparticles (diameter 3.9 nm) coated SiO2 surface as thin layers or nanoclusters, depending on the reactant concentration. UV–vis spectrum shows an absorption edge at around 315 nm, which is markedly blue-shifted compared to that of bulk SnO2 (350 nm).

The CdO-mixed In2O3 materials with a molar ratio of 1:1 calcined at different temperatures were prepared using the solid-state synthesis technologies. The effect of the different calcining temperatures on the phase structures of CdO-mixed In2O3 was investigated by powder X-ray diffraction. Indirect-heating sensors using CdO-mixed In2O3 calcined at different temperatures as sensitive materials were fabricated on an alumina tube with Au electrodes and Platinum wires. Gas-sensing characteristics of CdO-mixed In2O3 to formaldehyde were investigated. It is found that CdIn2O4 came into be formed from CdO-mixed In2O3 more than 700 °C. The results show that the phase structure, the electronic and the gas sensing properties to formaldehyde were changed with the different calcining temperatures. The CdO-mixed In2O3 based gas sensors exhibit highest response to formaldehyde after calcining at 650 °C, making them to be promising candidates for practical detectors for formaldehyde.

Gas-sensing characteristics of CdO-mixed In2O3 to formaldehyde were investigated. Gas sensors of indirect heating type were fabricated by the sensitive materials. The phases in the resulting materials and the morphologies of the sensing layers were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively, before and after calcination. The effects of operating temperature on the sensor response and the response versus gas concentration properties of the CdO–In2O3 sensors were investigated. It was shown that the sensors exhibited good response properties to formaldehyde gas at low operating temperature, making them to be promising candidates for practical detectors to formaldehyde gas.

Flake-like ZnO/surfactant ordered layered nanocomposite has been synthesized by self-assembly at room temperature with the presence of cetyltrimethylammonium bromide (CTAB, CH3(CH2)15N+(CH3)3Br−) surfactant. The procedure described in this study is attractive since it gives high yields of ordered layered nanocomposite with flake-like architecture. XRD results showed the formation of a layered structure with two layered spacings ca. 18.56 Å. SEM and FT-IR spectroscopy were used to further characterize ZnO/CTAB nanolayered composite. The ZnO/CTAB-ordered layered nanocomposite exhibits the room temperature photoluminescence (RTPL) characteristics. It is inferred that the RTPL of ZnO/CTAB-layered nanocomposite might be induced by the interfacial effect between the ZnO and the surfactant.

The gas-sensing materials, NiFe2O4, were prepared by inverse titrating chemical co-precipitation. After calcinations at 350–700 °C for 1 h, respectively, p-type semiconductor gas-sensing materials with inverse spinel structure were obtained. Effects of the calcining temperature on the phase constituents and microstructure were studied and characterized by simultaneous differential scanning calorimetry and thermogravimetry analysis (DSC–TGA), X-ray diffraction (XRD) and transmission electron microscopy (TEM). NiFe2O4 used as sensitive materials of indirect heating structure sensors were fabricated on an alumna tube with Au electrodes and platinum wires. The gas-sensing properties were determined for using reducing gases. The results demonstrated that the sensors based on NiFe2O4 had good sensitivity and good selectivity to toluene. The difference in response for various tested gases might be attributed to absorption of reducing gases and reaction between these gases and the absorbed oxygen.

•Mn3O4/AC composites were prepared by a hydrothermal process and subsequent heat treatment.•Mn3O4/AC composites possess the excellent capacitive behaviors.•Mn3O4/AC composites improve the specific capacitance and the cycle stability.The natural coconut shell activated carbon (AC) was firstly treated with KOH in advance, and the Mn3O4/AC composites in various AC rations were prepared by the hydrothermal process and subsequent heat treatment. The resulting Mn3O4/AC composites were characterized by means of different techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and so on. Morphological studies reveal the hierarchical porous structure of Mn3O4/AC composites. Mn3O4/AC nanocomposite with the activated carbon quality percentage of 10% exhibits the highest specific capacitance of 491.2 F g−1 at the current density of 2 A g−1 in 6 M KOH aqueous electrolyte measured from the charge–discharge process. The value is nearly 6 times higher than that of the pure Mn3O4 nanoparticles as an electrode for supercapacitor. The good performance of the as-prepared Mn3O4/AC composites as electrode materials may be attributed to the synergistic effects of the activated carbon and the Mn3O4.

Perovskite structure of LnFeO3 (Ln = La, Sm, and Eu) oxides with uniform particle size was prepared by the cationic surfactant CTAB (cetyltrimethylammonium bromide) assisting method from the inorganic precursor and alkali source (Ln—chlorate, FeCl3 and NH4OH). The final products were characterized and the results showed that the pure and high crystalline perovskite structure of LnFeO3 materials were obtained after calcining at 850 °C. Gas sensors of the indirect-heating structure using LnFeO3 as sensitive materials were fabricated on alumina tube with Au electrodes and platinum wires. The gas-sensing characteristics of LnFeO3 to acetone, gasoline, and formaldehyde were investigated and exhibited good response properties to acetone (LaFeO3), gasoline (SmFeO3), and formaldehyde (EuFeO3) gases, respectively. The LnFeO3 oxides-based on gas sensors enable them to be promising candidates for the detection of the gases in monitoring environment.

Antimony-doped tin dioxide (ATO) nanoparticles with high crystallinity during solvothermal synthesis in alcohol were generated from the inorganic precursors (SnCl4 and Sb(OC2H5)3) and the cationic surfactant (cetyltrimethylammonium bromide, CTAB). The structural and morphological characterizations of the products were performed by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), N2-sorption isotherm and X-ray photoelectron spectrum (XPS). The resulting particles were highly crystalline oxide particles in the nanometer range (10–14 nm). The indirect-heating sensors using ATO nanoparticles as sensitive materials were fabricated on an alumina tube with Au electrodes and platinum wires. The sensing properties of these sensors based on ATO nanoparticles were investigated. Compared to the original undoped sensor, the results show that the ATO nanoparticles have about 2.5 times increase in response and good dynamic response to NH3 at low operating temperature (79 °C).

•3D macro-/nanoporous MCo2O4 were fabricated by a novel and feasible template-free route.•MCo2O4 exhibits the hierarchically porous morphology.•Combustion to oxidizer ratio is important to obtain the pure spinel cobaltites MCo2O4.•The effective method can fabricate a 3D macro-/nanoporous ternary oxide.3D macro-/nanoporous spinel MCo2O4 (M = Zn, Ni, Cu and Fe) have been successfully fabricated by means of an untemplate and flash synthesis via self-sustained decomposition of metal-organic complexes The effects of the combustion agent to metal nitrate ratio on the combustion behavior, phase and morphology of the products were studied. Pure cobaltites with the hierarchically porous morphology were obtained directly through the combustion of the precursors under fuel-lean conditions in one-step without further heat treatment. The samples were characterized by X-ray diffraction, SEM/TEM imaging, mercury intrusion porosimetry, which indicate that the products possess hierarchical porous structure. A possible forming mechanism was given based on the series of experimental data.A 3D macro-/nanoporous MnCo2O4 has been prepared by a novel, rapid and feasible flash synthesis through the combustion of the precursors under fuel-lean conditions in one-step without further heat treatment.

Gas-sensing characteristics of CdO-mixed In2O3 to formaldehyde were investigated. Gas sensors of indirect heating type were fabricated by the sensitive materials. The phases in the resulting materials and the morphologies of the sensing layers were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively, before and after calcination. The effects of operating temperature on the sensor response and the response versus gas concentration properties of the CdO–In2O3 sensors were investigated. It was shown that the sensors exhibited good response properties to formaldehyde gas at low operating temperature, making them to be promising candidates for practical detectors to formaldehyde gas.

Pt-functionalized SnO2 sheets with Pt contents of 0, 0.5, 1, and 2 wt% were synthesized by a facile solution combustion synthesis, and their crystal structure, morphology, and chemistry have been thoroughly characterized. In the combustion process, the urea (CO(NH2)2) has been employed as a fuel. The obtained products appear as porous sheets formed by the interconnected and loosely packed SnO2 nanoparticles. Pt nanoparticles are assembled together with SnO2 nanoparticles in several up to tens of nanometer clusters. The as-synthesized products were used as sensing materials in the sensors to detect the isopropanol (IPA) gas. Gas sensing tests exhibited that the Pt-functionalized SnO2 are highly promising for gas sensor applications, as the operating temperature was lower than current IPA sensors and the response to IPA was significantly enhanced. The 2 wt% Pt–SnO2 sheet based gas sensor displayed a response value of 190.50 for 100 ppm IPA at an optimized operating temperature of 220 °C, whereas the pristine SnO2 based gas sensor only showed a response of 21.53 under the same conditions. The roles of Pt nanoparticles on electronic sensitization of SnO2, catalytic oxidation (spillover effect), and the increased quantities of oxygen species on the surface of SnO2 are plausible reasons to explain the significant enhancement in response to a Pt-functionalized SnO2 sheet based gas sensor.

Here, CuO micro-sheets were successfully synthesized from Cu foil using the annealing procedure. Cupric oxalate (CuC2O4·xH2O) micro-sheets were firstly peeled off by immersing Cu foil in oxalic acid solution at room temperature, and then they were converted into CuO with preserved configuration after thermal treatment at 350 °C. Various techniques were employed for the characterization of the structure and morphology of as-prepared products. Results revealed that the samples were composed of a large amount of porous CuO micro-sheets, which were constructed by plenty of nano-sized primary particles. A gas sensor was fabricated using as-prepared CuO micro-sheets and was systematically investigated for its ability to detect n-butanol. Due to the porous structure of CuO micro-sheets, the sensor based on CuO micro-sheets manifests a remarkably improved sensing performance, including high response, good selectivity, excellent reproducibility and stability, and limit of detection as low as 10 ppm at 160 °C, suggesting its greatly promising applications in gas sensing.

This paper describes a method to prepare tungsten doped anatase TiO2 (WTO) nanoparticles with high surface area based on a polymer-assisted sol–gel process and using simple chemical reagents. The samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (including high-resolution imaging-HRTEM), X-ray photoelectron spectroscopy (XPS), and Brunauer–Emmett–Teller (BET). WTO nanoparticles are obtained with small particle size (ca. 9 nm in mean grain size) and good crystallinity. The as-prepared samples are used as an electrode material for a lithium-ion battery, whose charge–discharge properties, cyclic voltammetry, and cycle performance are examined and revealed to have very good properties. A highly stable capacity of 170 mA h g−1 is found after 100 cycles.

A series of ordered mesoporous silica loaded with samarium oxide (Sm-MCM-41) were synthesized by a facile one-step sol–gel route using hexadecyltrimethylammonium bromide (CTAB) as the template, tetraethylorthosilicate (TEOS) as the silica source, and hexahydrated samarium chloride as the precursor. The as-synthesized materials with the Sm/Si molar ratio ranging from 0.2 to 0.8 were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and N2 adsorption–desorption measurements. All obtained compounds possess an ordered hexagonal mesoporous structure with a high surface area, a large pore volume, and uniform pore size. The mesoporous composites were used as the novel adsorbents for phosphate ion (H2PO4−) removal from synthetic aqueous solutions. The phosphate removal capacity of Sm-MCM-41 with a Sm/Si molar ratio of 0.6 was up to 20 mg P/g. The Sm functionalized mesoporous silica materials show a higher phosphate removal capacity compared to MCM-41 and Sm2O3 particles, making them promising candidates for water quality control and protection.