In this study, zinc oxide hollow microspheres were successfully prepared by a facile one-pot hydrothermal route with the assistance of glucose only using cheap Zn(NO3)3·6H2O as starting materials, followed by a simple calcination treatment. The zinc oxide hollow microspheres were characterized via scanning electron microscopy, transmission electron microscopy and X-ray diffraction. The prepared zinc oxide hollow microspheres were further employed to fabricate a gas sensor to detect volatile organic pollutants. The gas sensing measurement results revealed that the zinc oxide hollow microsphere sensor showed excellent sensing performances to ppm levels of probe gas ethanol vapor including high response, short response–recovery times and good reversibility. The sensor also showed high response to other ppm levels of volatile organic pollutants such as n-butanol, acetone, methanol, toluene and benzene, implying its promising gas sensor application in detecting volatile organic pollutants. Zinc oxide hollow microspheres, prepared by a facile one-pot hydrothermal route, based gas sensor showed excellent sensing performances to ppm levels of volatile organic pollutants including high response, short response–recovery times and good reversibility.Open image in new window

Pure and Fe-doped In2O3 hollow microspheres (HMSs) constructed from numerous nanoparticles have been successfully synthesized via a simple and efficient one-pot method combined with a subsequent thermal treatment. Various techniques were employed to acquire the crystalline and morphological information of the as-obtained samples. Structural characterization indicated that the as-prepared Fe-doped In2O3 HMSs displayed a porous structure with a coarse surface and a diameter of approximately 1 μm. The lattice constants for In2O3 in the Fe-doped product were slightly smaller than those in the pure one, which could be apparently revealed by XRD results. Furthermore, gas sensing performance of the pure In2O3, Fe-doped In2O3 and pure Fe2O3-based gas sensors to the ppm level of formaldehyde (HCHO) vapor was also systematically investigated at a low operating temperature of 260 °C. It has been demonstrated that the Fe-doped In2O3 sensor showed enhanced sensing properties compared with the pure ones with a response of about 12.9 to 100 ppm of HCHO vapor, as well as good selectivity for indoor carcinogenic gases and long-term stability. The enhanced sensing properties could result from the unique hollow structure with a porous shell and the synergic electronic interaction between the guest α-Fe2O3 dopant and the host In2O3 material.

•SnO2 hollow microspheres (HMSs) were prepared by a templates/surfactants-free method.•The HMSs consist of small SnO2 nanoparticles, with rough and loose surface shells.•High response, short response/recovery rate, good stability and selectivity to HCHO.•Unique hollow and rough/loose features contribute to excellent sensing performances.SnO2 hollow microspheres (HMSs) were successfully synthesized by a one-pot hydrothermal method only using cheap Na2SnO3·3H2O as starting material, without using any templates or surfactants. The characterization results revealed that the SnO2 HMSs, with a diameter range of 450–800 nm, composed of numerous small SnO2 nanoparticles, possess a rough and loose surface shell structure. The SnO2 HMSs were employed to fabricate a gas sensor for detecting formaldehyde. The SnO2 HMS sensor exhibited a high response, quick response/recovery characteristic, good reproducibility, and preferable selectivity to ppm level of formaldehyde, suggesting its promising application as a formaldehyde gas sensor. The SnO2 HMSs can be further applied in other fields such as photocatalysts, dye-sensitized solar cells and lithium-ion batteries.

Spinel ZnFe2O4 nanoparticle-decorated rod-like ZnO nanoheterostructures have been successfully synthesized via a facile, one-pot and environmentally friendly low-temperature hydrothermal strategy. The structural and composition information about the obtained ZnFe2O4/ZnO nanoheterostructures has been examined by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray powder diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Considering the promising gas sensor applications, we have investigated the gas sensing performances of the ZnFe2O4/ZnO nanoheterostructures for detecting several common reducing volatile organic pollutants including n-butanol, ethanol, acetone, methanol and formaldehyde. The gas sensing measurement results demonstrated that the fabricated ZnFe2O4/ZnO nanoheterostructure sensor displayed high response, quick response/recovery characteristics, and good reproducibility for these tested gases, and good selectivity for n-butanol, revealing its promising application as a gas sensor for detecting these polluting gases and selectively detecting n-butanol. It is interesting to find that the ZnFe2O4/ZnO nanoheterostructure sensor exhibited much enhanced gas sensing performances compared with the pristine ZnO sensor. The excellent gas sensing performances can be attributed to the unique 1D rod-like nanostructures and the formation of the heterojunctions at the ZnFe2O4/ZnO interfaces. It is expected that the current synthesis methodology can be extended to fabricate other rod-like ZnO based nanoheterostructures, such as CuO/ZnO and SnO2/ZnO, for a wide application range including chemical sensors, photocatalysis and optical devices.

One-dimensional ZnO@ZnS core/shell microrods (MRs) were successfully synthesized by a facile two-step hydrothermal route, employing the low-cost inorganic salt Na2S as a sulfurizing agent. The sulfurizing time plays an important role in the growth of ZnS shells. The thickness of the ZnS shell could be adjusted by controlling the sulfurizing time. This facile surface sulfidation strategy might provide an opportunity for preparing other semiconductor metal oxide-sulfide core/shell nanostructures for a wide range of applications. For investigating the gas sensor application of the prepared ZnO@ZnS core/shell MRs, several common reductive volatile organic pollutants (VOPs) (n-butanol, ethanol, acetone, methanol and ether) were used as the probe gases for the gas sensing measurements. Due to the distinctively core/shell MR heterostructure and the heterojunction action between the ZnO core and the ZnS shell, the ZnO@ZnS core/shell MR sensor exhibited excellent gas sensing performance including high response, short response and recovery times, and good reproducibility to these VOPs, as well as much enhanced gas sensing performance compared with the bare ZnO MR sensor, demonstrating the potential application as gas sensors. It is believed that the current ZnO@ZnS core/shell MRs will also offer potential applications in other fields such as photocatalysis, electrical devices and optical devices.

In this paper, brookite-TiO2/α-Fe2O3 heterostructured nanorods were synthesized by a facile two-step solution approach without using any templates or surfactants. α-Fe2O3 nanorods were first successfully obtained via a simple solution method at room temperature. The α-Fe2O3 nanorods were further employed as supports to construct nanoheterostructures for gas sensor application. The gas sensor based on the as-fabricated TiO2/α-Fe2O3 nanoheterostructures exhibited an excellent gas-sensing performance, with markedly enhanced responses in comparison with the pristine α-Fe2O3 nanorod sensor, and fast response–recovery speeds as well as good reproducibility to Volatile Organic Pollutants (VOPs), such as methanol, ethanol, n-butanol, acetone, ether, xylene, toluene and benzene, demonstrating its potential application in detecting these VOPs. The enhanced gas-sensing behavior should be attributed to the unique porous α-Fe2O3 nanorod morphology, the strong interfacial interaction between TiO2 and α-Fe2O3, the presence of TiO2/α-Fe2O3 heterojunctions and the catalytic effect of brookite TiO2 nanoparticles. The as-prepared TiO2/α-Fe2O3 nanoheterostructures may also lead to novel applications in other fields, such as lithium-ion batteries, catalysis, and waste water treatment.

In this work, TiO2(B) nanoparticle (NP)-functionalized WO3 nanorods (NRs) were synthesized by a two-step solution strategy, with a hydrothermal process for WO3 NRs and hydrolyzation of Ti(OBu)4 for the functionalization of TiO2(B) NPs. Various techniques, including scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS), were employed to investigate the morphology, microstructure, crystalline nature and chemical composition of the prepared TiO2(B) NP-functionalized WO3 NRs. SEM and TEM results revealed that the TiO2(B)–WO3 composite showed a rod-like nanostructure with a diameter in the range from 93 to 154 nm and a rough surface, which could increase the accessible surface area and the amount of surface active sites, thus improving the properties or performance of the as-prepared composite NRs. XRD and XPS analysis clearly verified that monoclinic TiO2(B) NPs, a metastable polymorph of TiO2, were successfully supported on the WO3 NRs. Gas sensing measurement results for several common reductive organic gases such as acetone, ethanol, ether, methanol and formaldehyde demonstrated that the sensor based on the as-obtained TiO2(B) NP-functionalized WO3 NRs exhibited obviously enhanced responses compared with a pure WO3 NR based sensor, as well as fast response–recovery speeds, good reproducibility and good stability, indicating their promising application in gas sensors. The excellent gas sensing performance could be attributed to the unique 1D rod-like nanostructure with a rough surface, the existence of TiO2–WO3 heterojunctions and the catalytic effect of the TiO2(B) NPs. The as-prepared TiO2(B) NP-functionalized WO3 NRs will also have very good prospects in electrochromic devices and catalysis applications.

In this contribution, ZnFe2O4–ZnO composite hollow microspheres were successfully synthesized by a glucose-assisted hydrothermal method only using Fe(NO3)3·9H2O, Zn(NO3)2·6H2O and glucose as starting materials, followed by a calcination treatment. The characterization results from scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray powder diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) revealed that the as-synthesized ZnFe2O4–ZnO composite hollow microspheres, with a diameter range of 1 to 2.5 μm and a shell thickness of about 60 nm, consist of numerous small cubic spinel ZnFe2O4 nanoparticles and hexagonal wurtzite ZnO nanoparticles. In order to investigate the potential applications, the resulting ZnFe2O4–ZnO composite hollow microspheres were employed to fabricate a gas sensor using four common volatile organic pollutants (VOPs) namely n-butanol, acetone, ethanol and methanol as probe gases. The gas sensing measurement results demonstrated that the sensor based on the as-obtained ZnFe2O4–ZnO composite hollow microspheres exhibited a high response, good reversibility and reproducibility, and quick response and recovery characteristics. The composite sensor also showed enhanced responses compared with the pure ZnO sensor, which could be contributed to the unique rough, porous and hollow structure of the ZnFe2O4–ZnO composite hollow microspheres, and the heterojunction action at the interfaces of ZnFe2O4–ZnO. It is expected that the current ZnFe2O4–ZnO composite hollow microspheres have promising applications in gas sensors and can be further applied in other fields such as photocatalysis and magnetic resonance imaging.

1D unique porous α-Fe2O3 nanoshuttles (NSs) were synthesized by a template-/surfactant-free low temperature hydrothermal approach (60 °C, 48 h), followed by a simple annealing process (300 °C, 1 h). The prepared α-Fe2O3 NSs (ca. 40 nm in diameter and 250 nm in length) have a rugged surface and a porous structure with numerous nanopore inlets (about 1–10 nm in diameter). The hydrothermal time dependent experiment demonstrated that the formation of the NSs is a gradual process, which underwent growth, strong, spilt, and re-spilt processes as reaction times were prolonged from 6 to 48 h. The reaction temperature also has a significant influence on the morphology of the α-Fe2O3 products. Increasing reaction temperature to 100 and 120 °C led to the formation of rod-like nanostructures instead of NSs, and a higher reaction temperature of 140 °C produced a large solid sphere-like morphology (700 nm–1 μm in diameter). Gas sensing properties of the porous α-Fe2O3 NSs were investigated for toluene detection. The sensor showed excellent gas sensing performance for toluene with good reproducibility, short response and recovery time (3–8 and 2–4 s, respectively), and high response. Notably, the α-Fe2O3 NS sensor showed a nearly linear response in the range of 10–100 ppm of toluene, indicating the potential for application in ppm-level toluene gas sensors. The present work is expected to provide new insights into the easy and effective development of 1D porous α-Fe2O3 nanostructures.

Porous Au/α-Fe2O3 NRs are one-pot synthesized, and used as gas sensors for in situ VOCs detection. The sensor shows four times higher response to C6H6 than a pure α-Fe2O3 sensor and short response/recovery time (<30 s), which may be useful to establish an effective C6H6 real-time monitoring system in environmental protection and oil reservoirs' prediction.

A novel and facile strategy was applied to synthesize Au nanoparticles (Au NPs)-functionalized ZnO microsheet (MS) hybrid-materials. First, the layered 2D porous ZnO MSs were fabricated by a simple hydrothermal method followed by a calcination process, only using zinc acetate dihydrate and urea as the sources. Then the as-prepared ZnO MSs were further functionalized by small Au NPs, assembled by using green, non-toxic lysine as a capping agent. The obtained samples were characterized by means of XRD, TGA, SEM, TEM and EDS. In order to prove the enhanced combining properties of the hybrid materials, gas sensors were fabricated based on them. And the obtained results showed that, after functionalization with Au NPs, the porous ZnO MS hybrid sensor exhibited enhanced sensing performances towards several volatile organic compounds (VOCs) including n-butanol, ethanol, methanol, acetone and benzene, indicating its potential application as a gas sensor in detecting VOCs. The enhanced sensing properties are related to the unique structure of porous ZnO MSs and the strong spillover effect of small Au NPs for catalyzing sensing reactions, as well as the increased Schottky barriers caused by the electronic interaction between Au NPs and the ZnO support.

A novel sensing hybrid-material of Au nanoparticles (Au NPs)-functionalized ZnO nanowires (Au–ZnO NWs) was successfully synthesized by a two-stage solution process. First, ZnO NWs were fabricated via a low-temperature one-pot hydrothermal method with SDSN introduced as a structure-directing agent. Afterward, the as-prepared ZnO NWs were used as supports to load Au NPs with small sizes via precipitating HAuCl4 aqueous solution with ammonia. The obtained samples were characterized by means of XRD, SEM, TEM and EDX. Both pristine and Au–ZnO NWs were practically applied as gas sensors to compare the effect of Au NPs on the sensing performances and the obtained results demonstrated that after functionalization by catalytic Au NPs, the hybrid sensor exhibited not only faster response and recovery speeds but also a higher response to benzene and toluene than the pristine ZnO sensor at 340 °C, especially showing high selectivity and long-term stability for low concentration toluene, which is rarely reported with this method, indicating its original sensor application in detecting benzene and toluene. To interpret the enhanced gas sensing mechanism, the strong spillover effect of the Au NPs and the increased Schottky barriers caused by the electronic interaction between Au NPs and ZnO NW support are believed to contribute to the improved sensor performance.

Well-defined three-dimensional (3D) hierarchical tin dioxide (SnO2) nanoflowers (NFs) constructed by two-dimensional (2D) nanosheets (NSs) are successfully fabricated by a simple one-pot low-temperature (90 °C) hydrothermal strategy. The influence of the experiment parameters on the morphology of the products is investigated in detail. Field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD) demonstrate that the size and shape of the 3D hierarchical SnO2 NFs can be tailored by modulating the molar ratio of OH− to Sn2+, reaction time and reaction temperature in the process of hydrothermal synthesis. A possible formation process and growth mechanism for such fabricated 3D hierarchical SnO2 nanostructures has been proposed based on the experimental results. The gas sensing tests of the SnO2 NF sensor for several reducing volatile organic compounds (VOCs) including ethanol, n-butanol, acetone, methanol, chloroform and benzene have been performed at the relatively low operating temperature of 240 °C. The excellent gas sensing performances of the unique 3D hierarchical SnO2 NFs at low operating temperature of 240 °C indicate their potential application as gas sensors. The unique 3D hierarchical SnO2 NFs with high accessible surface area and commodious inter space can also be expected to use as catalyst, dye-sensitive solar cell and Li ion battery materials.

Due to the synergetic or complementary effects between organic and inorganic components, which could result in improved properties or performances, the organic/inorganic hybrid materials have recently gained extensive interest in many fields. Up to date, many reports have been published based on the organic/inorganic hybrid materials for the sensor applications. The paper provided a comprehensive review about recent progress of the organic/inorganic hybrid sensors. The organic/inorganic hybrid sensing materials could be fabricated in several configuration types such as intercalating type, core–shell type, coating type and mixed type. The sensing form of the hybrid sensors could be presented in thin-film, thick-film or pellet form, and the sensing performances could by measured in the flowing or static-state system. The hybrid sensing materials have been applied in gas sensors, humidity sensors, ultraviolet sensors, strain sensors, electrochemical immunosensors and fluorescent chemosensors. Finally, several suggestions related to future development of organic/inorganic hybrid sensing materials were also made.

A series of gold-supported tin dioxide (Au/SnO2) nanocatalysts were prepared by a deposition–precipitation method using SnO2 powders prepared by the sol–gel dialytic processes as supports, and were characterized by means of XRD and XPS techniques. The catalytic properties of the prepared Au/SnO2 nanocatalysts were evaluated by low-temperature carbon monoxide oxidation using a microreactor-GC system. The results showed that the catalytic behavior of the Au/SnO2 system was remarkably influenced by the deposition pH, the reaction solution concentration and the thermal pretreatment temperature of the catalyst. The DRIFTS study results indicated that CO adsorbed on the Au/SnO2 catalyst reacted with support surface lattice oxygens and hydroxyl groups to form oxidation products, i.e., CO2–, HCOO–, CO32–, HCO3– and CO2, and the gas phase oxygen acted as an activator for the reaction of CO with support surface lattice oxygens and hydroxyl groups.

Mesoporous copper–cerium–oxygen hybrid nanostructures were prepared by one-pot cetyltrimethylammonium bromide surfactant-assisted method, and were characterized by thermogravimetry, X-ray diffraction, transmission electron microscopy, nitrogen adsorption–desorption, X-ray photoelectron spectroscopy and temperature-programmed reduction techniques. Low temperature carbon monoxide oxidation was used as probe reaction to investigate the application of the prepared mesoporous copper–cerium–oxygen hybrid nanostructures in catalysis. The product calcined at 400 °C, with disordered wormlike mesoporous structure, high specific surface area (SSA) of 117.4 m2/g and small catalyst particle size of 8.3 nm, shows high catalytic activity with the 100 % CO conversion at 110 °C, indicating its potential application in catalysis. Catalytic activity results from the samples calcinied at different temperature suggested that high SSA, small catalyst particle size, finely dispersed CuO species and synergistic effect between CuO and CeO2 were responsible for the high catalytic activity of the catalysts.

CuO nanoparticle decorated porous ZnO nanorods were synthesized via a two-stage solution process. First, porous ZnO nanorods were fabricated by a low-temperature hydrothermal method. Afterward, the porous ZnO nanorods were used as supports to load CuO nanoparticles by a non-aqueous solution method. The morphology and structure of the prepared samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). To demonstrate the practical application of the synthesized heterostructured porous CuO/ZnO nanorod hybrid, the sensing properties for H2S at low operating temperatures were investigated. The high sensitivity, reversible response and good selectivity indicated its potential application as a chemical sensor.Highlights► Porous ZnO NRs were synthesized by a simple low-temperature hydrothermal method. ► CuO NP decorated porous ZnO NRs were synthesized via the non-aqueous solution method. ► High sensitivity, reversible response and good selectivity for detecting H2S. ► The improved sensor performances are attributed to the unique porous structure and p–n heterojunctions.

ZnO nanorods were fabricated by a simple low-temperature hydrothermal process in high yield (about 85%), starting with Zn(OH)42− aqueous solution in the presence of CTAB, the CTAB serving as a structure director, and no calcination process was needed. The morphology and crystal structure of the prepared ZnO nanorods were characterized by X-ray diffraction (XRD), Scanning electron microscope (SEM) and Transmission electron microscope (TEM). The ZnO nanorods were then used to construct a gas sensor for ethanol detection at different operating temperature. The as-prepared ZnO nanorod gas sensor exhibited a high, reversible and fast response to ethanol, indicating its potential application as a gas sensor to detect ethanol.

Ternary nanostructured CuO/Ti0.8Ce0.2O2 catalysts were prepared by a one-step surfactant-assisted method of nanoparticle assembly. The textural and structural properties of the CuO/Ti0.8Ce0.2O2 catalysts were characterized by XRD, TGA, BET, XPS and H2-TPR. Their catalytic performance for low-temperature CO oxidation was studied by using a catlab system. CuO supported on binary Ti0.8Ce0.2O2 support showed higher catalytic activity than CuO supported on single CeO2 or TiO2 support. The calcination temperature had a remarkable influence on the catalytic activity of the CuO/Ti0.8Ce0.2O2 catalysts. The CuO/Ti0.8Ce0.2O2 catalyst calcined at 500 °C exhibited the highest catalytic activity with T50% and T100% at 82 and 123 °C, respectively. According to the XRD, BET and H2-TPR analyses, the higher surface areas and more highly dispersed small particle size CuO should be responsible for the high catalytic activity of catalysts.

In the paper, mesoporous SnO2 nanopowders were synthesized via a simple and mild SnCl4 hydrolysis process using cationic surfactant (cetyltrime thylammonium bromide, CTAB: CH3(CH2)15N+(CH3)3Br−) as structure directing agent and ammonia as an alkali source at room temperature, combined with a subsequent calcination process. The products were characterized by X-ray diffraction analysis (XRD), thermogravimetric analysis (TGA), transmission electron microscopy (TEM) and nitrogen adsorption–desorption experiment. A gas sensor was fabricated from the as-prepared mesoporous SnO2 nanopowders and used to test the response to different concentrations of ethanol, methanol, hexane, NH3, H2 and CO at different operating temperatures. The results showed that the mesoporous SnO2 sensor exhibited high sensitivity, good selectivity and quick response–recovery characteristics to ethanol, implying the potential application of the sensor for detecting ethanol.Highlights► Mesoporous SnO2 nanopowders were synthesized via a simple and mild surfactant-assisted. ► The SnO2 sample cacined at 300 °C had a high BET surface area and an ordered mesoporous structure. ► The SnO2 sensor exhibited high sensitivity and quick response-recovery characteristics to ethanol. ► The SnO2 sensor also showed good selectivity to ethanol.

Nanostructure tin dioxide (SnO2) powders prepared by sol-gel dialytic processes using tin (IV) chloride and anhydrous alcohol as start materials, ammonia gas as catalyst of the formation of colloid solution and agent of removing Cl−, and by introducing dialytic processes to improve and accelerate the formation of gels. From the result of TG–DTA analyses, the dried samples were calcined at 673 K in air for 3 h. Tin dioxide nanoparticles were characterized by thermogravimetry and differential thermal analyses (TG–DTA), X-ray diffraction (XRD), nitrogen adsorption–desorption, X-ray photoelectron spectroscopy (XPS). The average particle size of the as-prepared tin dioxide was about 5 nm. The as-prepared SnO2 possessed mesoporous structure and large surface area. The Au/SnO2 catalysts for low-temperature CO oxidation were prepared by the deposition–precipitation method using as-prepared SnO2 powders as the support. The Au/SnO2 catalysts exhibited high catalytic activity for low-temperature CO oxidation. The nanostructure SnO2 has promising applications in sensor, catalyst, catalytic support, mesoporous membranes, etc.

A study on the low-temperature CO gas sensors based on Au/SnO2 thick film was reported. Au/SnO2 powders, with different Au loading from 0.36 to 3.57 wt%, were prepared by a deposition–precipitation method. Thick films were fabricated from Au/SnO2 powders. The Au/SnO2 thick-film sensors exhibited high sensitivity to CO gas at relatively low operating temperature (83–210 °C). We also reported the effect of the Au loading in Au/SnO2 on the CO gas sensing behavior. The optimal Au loading in as-prepared Au/SnO2 was 2.86 wt%.

Polyaniline (PANI) was prepared by the chemical oxidative polymerization of aniline, and ZnO, with the mean particle size of 28 nm, was synthesized by a non-aqueous solvent method. The organic-inorganic PANI/ZnO hybrids with different mass fractions of PANI were obtained by mechanically mixing the prepared PANI and ZnO. The gas sensing properties of PANI/ZnO hybrids to different volatile organic compounds (VOCs) including methanol, ethanol and acetone were investigated at a low operating temperature of 90 °C. Compared with the pure PANI and ZnO, the PANI/ZnO hybrids presented much higher response to VOCs. Meanwhile, the PANI/ZnO hybrid exhibited a good reversibility and a short response-recovery time, implying its potential application for gas sensors. The sensing mechanism was suggested to be related to the existence of p-n heterojunctions in the PANI/ZnO hybrids.

•Novel Au nanoparticles decorated wurtzite ZnS hollow spheres (Au NPs-ZnS HSs) were successfully synthesized by simple solution methods.•The Au NPs-ZnS HSs have been demonstrated to be one of the extremely promising candidate materials in gas sensor applications.•The gas sensing mechanism is also discussed.Novel Au nanoparticles decorated wurtzite ZnS hollow spheres (Au NPs-ZnS HSs) were successfully synthesized by simple hydrothermal and deposition-precipitation methods without using any surfactants or toxic organic solvents. The fabribated Au NPs-ZnS HSs based gas sensor showed high responses, quick response/recovery characteristics, excellent reproducibility and simultaneously highly improved responses compared with the pristine ZnS HSs based sensor to several volatile organic pollutants (VOPs) such as ethanol, n-propanol and n-butanol at a low operating temperature of 260 °C. In terms of other VOPs, the sensor also displayed a high response to acetone (84.4%) and formaldehyde (75.8%), and a certain response to toluene (46.9%) and benzene (37.8%), indicating its multifunctional gas sensor application. The superior gas sensor performances could be attributed to the catalytic and spillover effect of Au NPs and the unique rough, porous and hollow structure which can improve the accessible surface area of the gas sensing materials, form conjugated electron depletion layers on both the outer and inner surfaces and facilitate the diffusion and transport of the tested gases. The as-synthesized Au NPs-ZnS HSs are considered to be one of the extremely promising candidate materials in gas sensor applications, and are also expected to provide other potential applications in the future.

Polythiophene/WO3 (PTP/WO3) organic-inorganic hybrids were synthesized by an in situ chemical oxidative polymerization method, and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and thermo-gravimetric analysis (TGA). The Polythiophene/WO3 hybrids have higher thermal stability than pure polythiophene, which is beneficial to potential application as chemical sensors. Gas sensing measurements demonstrate that the gas sensor based on the Polythiophene/WO3 hybrids has high response and good selectivity for detecting NO2 of ppm level at low temperature. Both the operating temperature and PTP contents have an influence on the response of PTP/WO3 hybrids to NO2. The 10 wt% PTP/WO3 hybrid showed the highest response at low operating temperature of 70 °C. It is expected that the PTP/WO3 hybrids can be potentially used as gas sensor material for detecting the low concentration of NO2 at low temperature.

Porous α-Fe2O3 was synthesized by a simple hydrothermal treatment of FeCl3 aqueous solution followed by a calcination process. In the synthesis of porous α-Fe2O3, no templates or pore-directing agents were used. The as-prepared porous α-Fe2O3 was further employed as a support for loading Pt nanoparticles. The gas sensing performance of the obtained porous α-Fe2O3-supported Pt to VOCs was investigated. The sensor presented a high response and fast response-recovery characteristic to several VOCs including acetone, ether, methanol, ethanol, butanol and hexanol. Meanwhile, it exhibited a much higher response than the pure α-Fe2O3 at the operating temperature of 260°C. The enhanced sensing properties may be related to the unique porous structure of the α-Fe2O3 support and the promoting effect of active Pt nanoparticles for the sensing reactions.

Nanometer SnO2 particles were synthesized by sol-gel dialytic processes and used as a support to prepare CuO supported catalysts via a deposition-precipitation method. The samples were characterized by means of TG-DTA, XRD, H2-TPR and XPS. The catalytic activity of the CuO/TiO2-SnO2 catalysts was markedly depended on the loading of CuO, and the optimum CuO loading was 8 wt.% (T100 = 80 °C). The CuO/TiO2-SnO2 catalysts exhibited much higher catalytic activity than the CuO/TiO2 and CuO/SnO2 catalysts. H2-TPR result indicated that a large amount of CuO formed the active site for CO oxidation in 8 wt.% CuO/TiO2-SnO2 catalyst.

ZnO nanorods were fabricated by a simple low-temperature hydrothermal process in high yield (about 85%), starting with Zn(OH)42− aqueous solution in the presence of CTAB, the CTAB serving as a structure director, and no calcination process was needed. The morphology and crystal structure of the prepared ZnO nanorods were characterized by X-ray diffraction (XRD), Scanning electron microscope (SEM) and Transmission electron microscope (TEM). The ZnO nanorods were then used to construct a gas sensor for ethanol detection at different operating temperature. The as-prepared ZnO nanorod gas sensor exhibited a high, reversible and fast response to ethanol, indicating its potential application as a gas sensor to detect ethanol.

Mesoporous CuO/TixZr1 − xO2 catalysts were prepared by a surfactant-assisted method, and characterized by N2 adsorption/desorption, TEM, XPS, in-situ FTIR and H2-TPR. The catalysts exhibited high specific surface area (SBET = 241 m2/g) and uniform pore size distribution. XPS and in-situ FTIR displayed that Cu+ and Cu2+ species coexisted in the catalysts. The CuO/TixZr1 − xO2 catalysts presented obviously higher activity in CO oxidation reaction than the CuO/TiO2 and CuO/ZrO2 catalysts. Effect of molar ratios of Ti to Zr and calcination temperature on catalytic activity was investigated. The CuO/Ti0.6Zr0.4O2 catalyst calcined at 400 °C exhibited excellent activity with 100% CO conversion at 140 °C.Mesoporous CuO/TixZr1 − xO2 catalysts with high specific surface area were prepared by a surfactant-assisted method. The CuO/TixZr1 − xO2 catalysts presented obviously higher activity on CO oxidation than the CuO/TiO2 and CuO/ZrO2 catalysts. The CuO/Ti0.6Zr0.4O2 catalyst calcined at 400 °C exhibited excellent activity with 100% CO conversion at 140 °C.Download full-size imageHighlights► Mesoporous CuO/TixZr1 − xO2 catalysts were prepared by a surfactant-assisted method. ► The catalysts exhibited high specific surface area (SBET = 241 m2/g). ► XPS and in-situ FTIR displayed that Cu+ and Cu2+ species coexisted on the catalysts. ► CuO/Ti0.6Zr0.4O2 catalyst calcined at 400 °C showed excellent activity with T100% at 140 °C.

A novel sensing hybrid-material of Au nanoparticles (Au NPs)-functionalized ZnO nanowires (Au–ZnO NWs) was successfully synthesized by a two-stage solution process. First, ZnO NWs were fabricated via a low-temperature one-pot hydrothermal method with SDSN introduced as a structure-directing agent. Afterward, the as-prepared ZnO NWs were used as supports to load Au NPs with small sizes via precipitating HAuCl4 aqueous solution with ammonia. The obtained samples were characterized by means of XRD, SEM, TEM and EDX. Both pristine and Au–ZnO NWs were practically applied as gas sensors to compare the effect of Au NPs on the sensing performances and the obtained results demonstrated that after functionalization by catalytic Au NPs, the hybrid sensor exhibited not only faster response and recovery speeds but also a higher response to benzene and toluene than the pristine ZnO sensor at 340 °C, especially showing high selectivity and long-term stability for low concentration toluene, which is rarely reported with this method, indicating its original sensor application in detecting benzene and toluene. To interpret the enhanced gas sensing mechanism, the strong spillover effect of the Au NPs and the increased Schottky barriers caused by the electronic interaction between Au NPs and ZnO NW support are believed to contribute to the improved sensor performance.

In this work, TiO2(B) nanoparticle (NP)-functionalized WO3 nanorods (NRs) were synthesized by a two-step solution strategy, with a hydrothermal process for WO3 NRs and hydrolyzation of Ti(OBu)4 for the functionalization of TiO2(B) NPs. Various techniques, including scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS), were employed to investigate the morphology, microstructure, crystalline nature and chemical composition of the prepared TiO2(B) NP-functionalized WO3 NRs. SEM and TEM results revealed that the TiO2(B)–WO3 composite showed a rod-like nanostructure with a diameter in the range from 93 to 154 nm and a rough surface, which could increase the accessible surface area and the amount of surface active sites, thus improving the properties or performance of the as-prepared composite NRs. XRD and XPS analysis clearly verified that monoclinic TiO2(B) NPs, a metastable polymorph of TiO2, were successfully supported on the WO3 NRs. Gas sensing measurement results for several common reductive organic gases such as acetone, ethanol, ether, methanol and formaldehyde demonstrated that the sensor based on the as-obtained TiO2(B) NP-functionalized WO3 NRs exhibited obviously enhanced responses compared with a pure WO3 NR based sensor, as well as fast response–recovery speeds, good reproducibility and good stability, indicating their promising application in gas sensors. The excellent gas sensing performance could be attributed to the unique 1D rod-like nanostructure with a rough surface, the existence of TiO2–WO3 heterojunctions and the catalytic effect of the TiO2(B) NPs. The as-prepared TiO2(B) NP-functionalized WO3 NRs will also have very good prospects in electrochromic devices and catalysis applications.

In this paper, brookite-TiO2/α-Fe2O3 heterostructured nanorods were synthesized by a facile two-step solution approach without using any templates or surfactants. α-Fe2O3 nanorods were first successfully obtained via a simple solution method at room temperature. The α-Fe2O3 nanorods were further employed as supports to construct nanoheterostructures for gas sensor application. The gas sensor based on the as-fabricated TiO2/α-Fe2O3 nanoheterostructures exhibited an excellent gas-sensing performance, with markedly enhanced responses in comparison with the pristine α-Fe2O3 nanorod sensor, and fast response–recovery speeds as well as good reproducibility to Volatile Organic Pollutants (VOPs), such as methanol, ethanol, n-butanol, acetone, ether, xylene, toluene and benzene, demonstrating its potential application in detecting these VOPs. The enhanced gas-sensing behavior should be attributed to the unique porous α-Fe2O3 nanorod morphology, the strong interfacial interaction between TiO2 and α-Fe2O3, the presence of TiO2/α-Fe2O3 heterojunctions and the catalytic effect of brookite TiO2 nanoparticles. The as-prepared TiO2/α-Fe2O3 nanoheterostructures may also lead to novel applications in other fields, such as lithium-ion batteries, catalysis, and waste water treatment.