Hybrids of ethylenediamine-modified reduced graphene oxide (RGO) and polythiophene (PTh) were synthesized successfully by in situ chemical polymerization at room temperature for 2 h and loaded on a flexible PET film to construct a smart sensor. The structure and properties of the hybrids have been characterized by XRD, SEM, TG, UV–vis, and FTIR analysis. The NO2-sensing performance of pure PTh- and hybrids-based sensors was examined at room temperature, the results indicate that the hybrid film sensor with 5 wt % RGO not only exhibits high sensitivity to 10 ppm of NO2 gas which is nearly 4 times higher than that of pure PTh and excellent selectivity but also is flexible, low cost, portable, and wearable. The mechanism of sensing performance enhanced by incorporating graphene into PTh also was discussed, which is attributed to large specific surface of the hybrid and synergetic effects between the components in a hybrid.

WO3 nanoparticles doped with Sb, Cd, and Ce were synthesized by a chemical method to enhance the sensing performance of WO3 for NO2 at room temperature. The doping with Sb element can significantly enhance the NO2-sensing properties of WO3. Upon exposure to 10 ppm of NO2, particularly the 2 wt % Sb-doped WO3 sample exhibits a 6.8-times higher response and an improved selectivity at room temperature compared with those of undoped WO3. The enhanced NO2-sensing mechanism of WO3 by doping is discussed in detail, which is mainly ascribed to the increase of oxygen vacancies in the doped WO3 samples as confirmed by Raman, photoluminescence, and X-ray photoelectron spectroscopy spectra. In addition, the narrower band gap may also be responsible for the enhancement of response as observed from the corresponding ultraviolet–visible spectra.

It is of great interest to develop gas-sensing materials with excellent performance in a facile and mild route. In this work, dandelion-like hollow ZnO hierarchitectures assembled with ZnO nanoparticles have been synthesized by annealing a zinc complex precursor, which was produced from zinc acetate and ammonium bicarbonate at room temperature. The nanoparticle size in the hierarchitectures enlarges from 10 to 23 nm with the annealing temperature increasing from 350 to 550 °C. The ZnO hierarchitectures have shown high sensing response (34.5), fast response (6 s) and recovery (7 s), and low optimal operating temperature (250 °C) toward 50 ppm ethanol because of large surface area and rich pore. Also, the obtained ZnO dandelion-like hierarchitectures exhibits good selectivity toward alcohols. The obtained results suggest that the dandelion-like ZnO hierarchitectures synthesized herein are a promising gas sensing material.

•Sn/Ni composite oxides were synthesized by a facile co-calcination method.•The response of composite is 13 times higher than that of SnO2 to 0.5 ppm NO2.•The operating temperature of composite based sensor is reduced to 80 °C.•Improving sensing properties is ascribed to formation of heterojunction at interface.The SnO2/NiO nanocomposites were successfully prepared by a facile co-calcination method. The structure and the property of the composites were characterized by XRD, FESEM, HRTEM and XPS. The sensing test results indicate that the SnO2/NiO nanocomposite with molar ratio of 4:1 not only exhibits the highest response to 500 ppb NO2, which is 8 times and 13 times higher than that of SnO2 and NiO, respectively, but also has excellent selectivity, outstanding stability and trend of linear response to low concentrations of NO2 at relatively low operating temperature of 80 °C. The mechanism of enhancing sensing properties was also discussed in detail, which is attributed to the formation of p-n heterojunction at the interface between SnO2 and NiO, leading to the significant increase of depletion layer thickness at interface.Download high-res image (190KB)Download full-size imageThe smart sensor based on SnO2/NiO composite not only exhibits high response and excellent selectivity to NO2 at relatively low temperature, but also has outstanding stability and linear response to low concentration of NO2 (below a concentration of 1 ppm). The sensing mechanism was also discussed in detail, which is attributed to the significant increase in resistance in NO2 due to the formation of p-n heterojunction.

•Rapid synthesis of PANI has novelty, which is different with that reported before.•Enhancement of gas sensing is attributed to synergistic effect and heterojunction.•PET film is used as substrate to obtain a flexible, wearable and smart sensor.•Room temperature operating of sensor leads to save energy, safety and long life.A network structure of PANI/SnO2 hybrid was synthesized by an in situ chemical oxidative polymerization using cheaper ZnO nanorods as sacrificial template and the hybrid was loaded on a flexible polyethylene terephthalate (PET) thin film to construct a flexible smart sensor. The sensor not only exhibits high sensitivity which is 20 times higher than that of pure PANI to 10 ppm triethylamine, good selectivity and linear response at room temperature but also has flexible, structure simple, economical and portable characters compared with recently existing sensors. Room temperature operating of the sensor is also particularly interesting, which leads to low power consumption, environmental safety and long life times. The improvement of sensing properties is attributed to the network structure of hybrid and formation of p-n heterojunction at the interface between the PANI and SnO2. The research is expected to open a new window for development of a kind of wearable electronic devices based on the hybrid of conducting polymer and metal oxides.Download high-res image (179KB)Download full-size image

•WO3 nanoparticles enhanced the response of PPy to TEA at room temperature.•PET film is used as a substrate to obtain a flexible, wearable and smart sensor.•Room temperature operating of sensor leads to save energy, safety and long life.We fabricated the PPy/WO3 hybrids with p-n heterojunction by in situ chemical oxidation polymerization and loaded on a substrate of flexible PET thin film to structure a smart triethylamine sensor. The structure, morphology and thermal stability of the hybrid were characterized by various analysis methods. The sensing properties of the sensor to trace amounts of TEA were examined at room temperature. Compared to those reported in literature, the smart sensor not only exhibits high sensitivity, good selectivity and wide linear response to triethylamine at room temperature but also has been flexible, structure simple and portable performance. The mechanism of enhancing gas sensing properties was discussed in detail, which is attributed to the complementary effect and the formation of p-n heterojunction at an interface between WO3 and PPy. The research is expected to open a new window for development of a kind of flexible and wearable electronic devices based on various heterostructure hybrids.

•rGO act an important role to extend PPy in application of sensor.•PET film is used as substrate to obtain a flexible, wearable and smart sensor.•Room temperature operating of sensor leads to save energy, safety and long life.Polypyrrole (PPy)-reduced graphene oxide (rGO) hybrid was successfully synthesized by a facile in situ polymerization. The as-synthesized PPy nanoparticles with diameter of ca. 80 nm were uniformly distributed on the surface of the rGO sheets to prepare the hybrid of PPy/rGO. Then the pure PPy and their hybrids were loaded on the substrate of flexible polyethylene terephthalate (PET) film to construct a thin film NH3 sensor, which has the advantages of being flexible, economical, portable and able to operable at room temperature (RT). The gas-sensing results reveal that the 5 wt% rGO-PPy hybrid based sensor not only exhibits the highest response to 10 ppm NH3, which is 2.5 times higher than that of pure PPy, but also excellent selectivity to some of VOCs. The enhancement of gas-sensing properties may be attributed to the π-π stacking and H-bonding formation between PPy and rGO, larger surface accessibility and fast transport of carriers.Figure optionsDownload full-size imageDownload high-quality image (164 K)Download as PowerPoint slide

The development of highly active, sensitive and durable gas sensing materials for the detection of volatile organic compounds (VOCs) is extremely desirable for gas sensors. Herein, a series of mesoporous hierarchical Co3O4–TiO2 p–n heterojunctions have been prepared for the first time via the facile thermal conversion of hierarchical CoTi layered double hydroxides (CoTi-LDHs) precursors at 300–400 °C. The resulting Co3O4–TiO2 nanocomposites showed superior sensing performance towards toluene and xylene in comparison with Co3O4 and TiO2 at low temperature, and the sample with a Co/Ti molar ratio of 4 shows an optimal response (Rg/Ra = 113, Rg and Ra denote the sensor resistance in a target gas and in air, respectively) to 50 ppm xylene at 115 °C. The ultrahigh sensing activity of these Co3O4–TiO2 p–n heterojunctions originates from their hierarchical structure, high specific surface area (>120 m2 g−1), and the formation of numerous p–n heterojunctions, which results in full exposure of active sites, easy adsorption of oxygen and target gases, and large modulation of resistance. Importantly, hierarchical Co3O4–TiO2 heterojunctions possess advantages of simple preparation, structural stability, good selectivity and long-term durability. Therefore, this work provides a facile approach for the preparation of hierarchical Co3O4–TiO2 p–n heterojunctions with excellent activity, sensitivity and durability, which can be used as a promising material for the development of high-performance gas sensors.

Pd–Ir mesocrystals with rough surface and highly branched structure were synthesized through a facile co-reduction method. The morphology evolution shows the mesocrystals were formed by oriented attachment of nanoparticles, and abundant defects sites as well as synergetic effect between building units were formed during mesocrystals oriented attachment process. Therefore, the supported Pd–Ir mesocrystals show a significant enhancement in catalytic performance in hydrogenation of 2-ethylanthraquinone compared with conventional Pd–Ir nanoparticles. The high activity can be ascribed to high densities of defect sites in Pd–Ir MCs catalyst, which facilitated H2 activation. In addition, the geometric effect of Pd–Ir MCs catalyst was responsible for inhibiting further hydrogenation of eAQH2 to undesired consecutive byproducts.

A facile method to prepare SnO2 hollow microspheres has been developed by using SiO2 microspheres as template and Na2SnO3 as tin resource. The obtained SnO2 hollow microspheres were characterized by X-ray diffraction, scanning electron microscopy, high resolution and transmission electron microscopy, and Brunauer–Emmett–Teller analysis, and their sensing performance was also investigated. It was found that the diameter of SnO2 hollow microspheres can be easily controlled in the range of 200–700 nm, and the shell thickness can be tuned from 7.65 to 30.33 nm. The sensing tests showed that SnO2 hollow microspheres not only have high sensing response and excellent selectivity to acetone, but also exhibit low operating temperature and rapid response and recovery due to the small crystal size and thin shell structure of the hollow microspheres, which facilitate the adsorption, diffusion, and reaction of gases on the surface of SnO2 nanoparticles. Therefore, the SnO2 hollow microsphere is a promising material for the preparation of high-performance gas sensors.

A p–n heterostructure hybrid based on polyaniline–SnO2 was synthesized by a rapid and facile in situ chemical oxidation polymerization at very low monomer concentration, and the hybrid was loaded on a flexible polyethylene terephthalate (PET) film substrate to structure a smart triethylamine (TEA) sensor. The structure, morphology and composition of the hybrid have been characterized by various analysis methods. The sensor not only exhibits high sensitivity, good selectivity to some other volatile organic compounds and wide linear response to 10–100 ppm triethylamine (TEA) at room temperature but is also flexible, has a simple structure and wearable performance. The mechanism of enhanced gas sensing is discussed in detail, which is attributed to the thickening of the depletion layer due to the formation of a p–n heterojunction at an interface in the hybrid. The research is expected to open a new window for the development of a kind of portable and wearable electronic device based on various p–n heterostructure hybrids.

Hierarchical polyaniline microspheres were prepared on polyethylene terephthalate (PET) film by facile and rapid in situ chemical oxidative polymerization of aniline, in the presence of ZnO microspheres, to construct a smart sensor for the detection of NH3. The sensor not only exhibits high sensitivity, good selectivity and a low detection limit at room temperature but also possesses the features of flexibility, portability and optical transparency compared with traditional sensors based on substrates of glass, quartz slide or ceramic tube. Particularly, the low operating temperature of 21 °C is favorable for saving energy, for safety and for the long life of the sensor. The mechanism of the ZnO microspheres enhanced sensing properties towards polyaniline is attributed to the morphology design, enhancement of crystallinity and protonation degree, which has been confirmed by XRD, SEM and XPS analysis. The study will also open a new window to develop a type of portable electronic device.

The sodium manganese oxide, Na0.44MnO2, was synthesized by a solid-state reaction routine combined with a sol–gel process using Mn(CH3CO2)2·4H2O as the manganese source. Results show that the capacity and cycling stability of Na0.44MnO2 cathodes are enhanced significantly by using a hybrid aqueous electrolyte (Na2SO4, ZnSO4 and MnSO4). The energy storage mechanism of as-prepared Na0.44MnO2 in the hybrid aqueous electrolyte is associated with the insertion/extraction of zinc and sodium multi-ions with the help of synergistic effects between zinc and manganese ions and the quasi-reversible deposition–dissolution process of Mn2+ ions. The Na0.44MnO2 electrode displays both excellent storage properties with zinc, sodium and manganese ions (∼340 mA h g−1 at 100 mA g−1 after 150 cycles) and reversibility (∼100% coulombic efficiency during cycling). The excellent reversibility and good cycling properties indicate that the Na0.44MnO2 can be a promising material for energy storage devices by using a hybrid aqueous electrolyte.

Polyaniline (PANI)–tungsten oxide (WO3) nanocomposites have been successfully synthesized using different weight percentages of tungsten oxide (10–50%) dispersed in a polyaniline matrix by a facile in situ chemical oxidation polymerization. The sensors based on PANI–WO3 nanocomposites were fabricated on a substrate of polyethylene terephthalate (PET) films for detection of triethylamine (TEA) gas at room temperature. It was observed that the sensors of PANI–WO3 nanocomposites show better sensitivity, selectivity, and reproducibility compared to pure PANI, particularly the sensor based on PANI–30% WO3 operating at room temperature exhibits maximum response of 81 to 100 ppm TEA gas, that is 13 times higher than that of pure PANI. The sensing mechanism of the nanocomposites in the presence of TEA atmosphere was discussed in detail, and is attributed to the increase of percentage of doping protonic acid and the formation of p–n heterojunctions between p-type PANI and n-type WO3.

•CuO–SnO2 p–n heterojunction nanofibers were successfully prepared by a relatively facile and versatile electrospun technique.•The obtained 30 wt% CuO–SnO2 composite detects low ppm-level CO, which not only exhibits high sensitivity, excellent selectivity but also reduces the sensing temperature. The sensing performance of composite is much better than those reported before.•The mechanism enhanced gas sensing properties is discussed in detail, which is ascribed to the formation of p–n heterojunction in the interface between CuO and SnO2 except for the gas adsorption and oxidizing reaction on surface of material.SnO2–CuO heterostructures have been synthesized via electrospinning method, which overcomes the defect of SnO2 generally prepared at high temperature. The structure, morphology, size, specific surface, thermal stability and surface composition of nanocomposite were characterized by XRD, SEM, TEM, BET, TG and XPS. The results testify that the change in property and structure of composite depends on the CuO content in composite. The SnO2 composite with 30 wt% CuO not only exhibits excellent selectivity and high response that is 16 and 2.5 times higher than that of pure CuO and SnO2, respectively, but also reduces the operating temperature from 295 °C to 235 °C. The mechanism enhanced sensing properties was discussed in detail, except for enhancing adsorption of gas on the material surface; the enhancement can be attributed to the formation of p–n heterojunction at the interface between the SnO2 and the CuO.CuO–SnO2 nanocomposites were obtained via electrospinning and subsequent annealing. The p–n heterojunctions formed at interface between two oxides are responsible for enhancement of gas sensing properties, which makes the composite a novel and promising sensing material for detection of toxic gases.

•Rapid synthesis of PANI has novelty, which is different to that reported before.•SnO2 enhances the response of PANI by their complementary and synergistic effect.•PET film is used as substrate to obtain a flexible, wearable and smart sensor.•Room temperature operating of sensor leads to save energy, safety and long life.We prepared a heterostructure hybrid of PANI and SnO2 by a rapid and facile in situ chemical oxidation polymerization under very low monomer concentration, and the hybrid was loaded on a flexible PET thin film to structure a smart NH3 sensor. The structure, morphology and thermal stability of the hybrid were characterized by various analysis methods. Compared with those reported in literatures, the hybrid-based sensor not only has high sensitivity, good selectivity and wide linear response to NH3 at room temperature of 21 °C but also has flexible, structure simple and wearable performance. The room temperature operating of the sensor is particularly interesting, which leads to low-power consumption, environmental safety and long life times of the sensing materials. The improvement of sensing properties is attributed to the complementary and synergistic effect between SnO2 and PANI, and formation of p−n heterojunction at the interface in hybrid.

Oxidation and hydrogenation catalysis plays a crucial role in the current chemical industry for the production of key chemicals and intermediates. Because of their easy separation and recyclability, supported catalysts are widely used in these two processes. Layered double hydroxides (LDHs) with the advantages of unique structure, composition diversity, high stability, ease of preparation and low cost have shown great potential in the design and synthesis of novel supported catalysts. This review summarizes the recent progress in supported catalysts by using LDHs as supports/precursors for catalytic oxidation and hydrogenation. Particularly, partial hydrogenation of acetylene, hydrogenation of dimethyl terephthalate, methanation, epoxidation of olefins, elimination of NOx and SOx emissions, and selective oxidation of biomass have been chosen as representative reactions in the petrochemical, fine chemicals, environmental protection and clean energy fields to highlight the potential application and the general functionality of LDH-based catalysts in catalytic oxidation and hydrogenation. Finally, we concisely discuss some of the scientific challenges and opportunities of supported catalysts based on LDH materials.

This research was motivated by the need to develop a smart ammonia (NH3) sensor based on a flexible polyethylene terephthalate (PET) thin film loaded with a reduced graphene oxide–polyaniline (rGO–PANI hybrid) using in situ chemical oxidative polymerization. The sensor not only exhibited high sensitivity, good selectivity and a fast response at room temperature but was also flexible, cheap and had wearable characteristics.

Flower-like hierarchical Au/NiAl-LDH catalysts were synthesized for selective oxidation of alcohols. The abundant hydrogen vacancies at the edge of the flowers as nucleation centers contributed to the uniform dispersion of Au NPs. The confinement effect of the hierarchical pores promoted 60% higher activity than the common Au/NiAl-LDH nanoparticle catalyst in the oxidation of benzyl alcohol by heightening the effective collisions between substrates and active sites. The evolution process of the hierarchical pores in the support was further proposed. Moreover, the reaction mechanism of the cooperation among Brønsted base sites, NiIII coordinatively unsaturated metal sites and isolated gold cations was concretely proved. In the oxidation of other typical alcoholic substrates, the flower-like catalyst showed higher activity than the common nanoparticle one except for linear alcohols, which could be attributed to the shape selectivity of straight macropores.

NiTi-layered double hydroxide (NiTi-LDH) with rich defective sites was synthesized and used as the support for the preparation of a novel supported PdAg nanoalloy catalyst for the partial hydrogenation of acetylene. The obtained PdAg/NiTi-LDH catalyst exhibited a remarkable catalytic performance. When the conversion of acetylene reached 90%, the selectivity towards ethene maintained 82%. Superior hydrogenation activity was ascribed to two key factors. Small particle size and high dispersion of PdAg nanoparticles were responsible for boosting the catalytic activity. In addition, Ti3+ defective sites in the support also played an important role in the enhancement of activity. The interface at the Ti3+ species and active metals acting as new active sites enhanced the activation and dissociation of hydrogen and therefore further improved the catalytic activity. Preferable selectivity was assigned to the electronic effect between the NiTi-LDH support and the PdAg nanoalloys. The electron transfer from the Ti3+ species to the Pd resulted in the increase of electron density and the linearly coordinated sites of Pd and therefore facilitated the desorption of ethene. Moreover, due to the reducibility of NiTi-LDH, the selectivity and stability over the reduced PdAg/NiTi-LDH catalyst were further enhanced on account of the strong metal–support interaction.

Hollow Co3O4 hierarchical microspheres assembled from many compact nanowires have been successfully synthesized via a facile hydrothermal method from the precursor Co(CO3)0.5(OH)·0.11H2O followed by annealing treatment. The product has a well-defined morphology, is porous, and has a larger surface area as seen through various analytical characterizations; thus, it can act as a good basis for further modification to improve its gas-sensing properties. The sensing tests indicate that the Ag@Co3O4 composite formed via Ag modification can not only improve the sensing response to formaldehyde by several times that of pure Co3O4, but also reduce the optimum operating temperature of the sensor. Furthermore, the gas-sensing mechanism is also discussed in detail, including the effect of Ag addition on the electronic transfer of the Ag@Co3O4 composite. There are still many challenges in making a formaldehyde sensor with high sensitivity using the cheaper noble metal Ag as modified reagent via a facile synthesis and doping method.

In this work, a Ni–Al layered double hydroxide/graphene (NiAl-LDH/RGO) nanocomposite which was synthesized by introducing NiAl-LDH on the surface of graphene oxide (GO) and simultaneously reducing graphene oxide without any additional reducing agents was utilized as the support for Au nanoparticles. Raman spectroscopy and XPS analysis revealed that the NiAl-LDH/RGO composite had both defect sites and oxygenic functional groups in RGO to control the directional growth of Au nanoparticles and lead to a small particle size. Compared to an Au catalyst supported on single GO and RGO or NiAl-LDH, this composite-supported Au catalyst (Au/NiAl-LDH/RGO) exhibited superior catalytic activity and stability in the selective oxidation of benzyl alcohol using molecular oxygen under low pressure. Improved activity was mainly ascribed to the small Au particle size effect caused by RGO and the contribution of basic sites in NiAl-LDH. Moreover, the preferable catalytic stability of the Au/NiAl-LDH/RGO catalyst was attributed to the defect sites and oxygenic functional groups in RGO which anchored the Au NPs and prevented the agglomeration, meanwhile, the agglomeration of RGO was inhibited by the introduction of NiAl-LDH.

Hybrids of reduced graphene oxide (rGO)–MoO3 nanorods were synthesized successfully by a facile in situ solution growth method under a relatively low temperature of 150 °C for 1 h. The structure and properties of the hybrids have been characterized by XRD, SEM, TEM, Raman, PL and XPS analysis. The sensing performance of pure MoO3 and rGO–MoO3 hybrids to H2S were examined, the results indicate that the hybrids exhibit higher response and lower operating temperature compared with the pure MoO3 nanorods, especially, the 2.5 wt% rGO–MoO3 hybrid exhibits the highest sensitivity and the fastest response to H2S, which makes them promising candidates in the field of gas sensors for detection of H2S gas. The sensing mechanism for MoO3 to H2S which is enhanced is also discussed in detail from rGO action in the hybrid and formation of a hetero-junction at the interface of the hybrid.

•Porous ZnO spherical aggregates have been prepared by a simple method.•The ZnO was composed of nanoparticles and has a specific surface area of 51 m2 g−1.•The ZnO spherical aggregates show excellent photocatalytic performance.Mesoporous ZnO spherical aggregates self-assembled with nanoparticles were prepared in a surfactant-free and template-free route under mild conditions. This ZnO spherical aggregates exhibit excellent photocatalytic degradation performance due to the small nanoparticles, high specific surface area, and porous structures, and also have easy separation and good recycling performance because of the large secondary particle size.ZnO spherical aggregates composed of nanoparticles have been prepared by a simple method. The obtained ZnO spherical aggregates exhibit excellent photocatalytic degradation performance due to the small nanoparticles, high specific surface area, and porous structures, and also have easy separation and good recycling performance because of their large secondary particle size.

•Multicolor hybrid pigments were prepared by co-precipitation method.•The intercalation significantly improves the thermostability of the acid dyes.•The color of the pigments can be easily tuned by altering the molar ratio of dyes.•Guest–guest interactions have significant influence on the color of the pigments.C.I. Acid Yellow 25 and C.I. Acid Blue 25 have been co-intercalated into the interlayer galleries of ZnAl layered double hydroxides by co-precipitation method to produce multicolor organic–inorganic hybrid pigments. The obtained pigments are characterized by X-ray diffraction, scanning electron microscopy, fourier transform infrared spectroscopy, thermogravimetric-differential thermogravimetric-differential thermal analysis, ultraviolet–visible spectroscopy, chemical composition and CIE 1976 L*a*b* color scales. The results suggest that there exist host–guest interactions between host sheets and guest dye anions and guest–guest interactions between the dye anions. The intercalation into the interlayer region of layered double hydroxides significantly improves the thermostability of the two dyes. The color of the organic–inorganic hybrid pigments can be easily tuned from orange yellow to yellow green, yellowish green, green, bluish green and blue by adjusting the molar ratio of dye anions in the interlayer room of layered double hydroxides.

Zero-dimensional Fe2O3 nanoparticles were successfully decorated on three-dimensional WO3 architectures to constitute a photocatalyst of Fe2O3@WO3 heterojunction. The obtained samples were characterized in detail by X-ray diffraction, scanning electron microscopy, elemental mapping, X-ray photoelectron spectroscopy and UV-Vis absorption spectra. The results indicate that rhombohedral α-Fe2O3 nanoparticles are homogeneously decorated on the surface of monoclinic WO3 architectures, and the constituted n+–n heterojunction results in “redshift” of the optical absorption. The photocatalyst of 1%Fe2O3@WO3 annealed at 400 °C exhibits the highest photocatalytic activity for degradation of Rhodamine B under visible light irradiation. The degradation obeys first-order reaction kinetics with an apparent rate constant of 0.057 min−1. It is suggested that the potential-energy difference between Fe2O3 and WO3 accelerates the separation of photogenerated electron–hole pairs, dominating the enhanced photocatalytic activity. The results presented herein provide new insight for development of a novel visible-light-driven photocatalyst and its potential application in harmful pollutant degradation.

It is of increasing interest to develop high-performance antioxidants for polypropylene (PP). Here, we have developed an organic–inorganic hybrid antioxidant by direct intercalation of low-molecular-weight hindered phenolic antioxidant (AO) into the interlayer region of layered double hydroxides (LDH), prepared the AO-LDH/PP composites following a simple solvent washing method, and investigated the thermal stability of the AO-LDH/PP composites by an accelerated aging method at 150 °C under air atmosphere. The results show that the one-step synthesis method is available to produce the AO-LDH with a basal spacing of 2.8 nm and that the addition of AO-LDH does not influence the crystallization behavior of PP. Furthermore, the radical-scavenging ability of AO-LDH is similar to that of the AO species. The AO-LDH significantly improves the long-term thermal stability of PP related to the CO3-LDH. The AO-LDH exhibits excellent antioxidative performance with promising applications in the field of polymers.

Al-doped flower-like ZnO nanostructures have been synthesized by a facile hydrothermal method at 95 °C for 7 h. The structure and morphology of the product were characterized by XRD, FTIR and SEM analysis. The sensing tests reveal that the response is significantly enhanced by Al doping, and the 0.3 wt% Al-doped sample exhibits the highest response of 464 to 10 ppm CO at an operating temperature of 155 °C. A change of the structural defects in Al-doped ZnO is responsible for the enhancement of the sensing properties, which has been confirmed by the room temperature photoluminescence (PL) spectra and X-ray photoelectron spectroscopy (XPS). The response time is reduced disproportionately with the increase in CO concentration by modeling the transient responses of the sensor using the Langmuir–Hinshelwood reaction mechanism. The band structures and density of states for pure ZnO and Al-doped supercells have been calculated using first principles based on density functional theory (DFT). The calculated results show that the band gap is narrowed and the conductance is increased by Al doping, which coincides with the experimental results of gas sensing.

•Hierarchically assembled WO3·H2O are synthesized by a facile sonochemical approach.•After annealing, orthorhombic WO3·H2O transforms into monoclinic WO3.•Such WO3 architecture exhibits structure-induced enhancement of NO2 response.•Gas diffusion and mass transfer in the WO3 architecture are significantly enhanced.Hierarchically assembled WO3·H2O spheres have been synthesized successfully by a facile sonochemical approach using oxalic acid as capping agent. The resultant WO3·H2O spheres with diameter of 1–3 μm are actually assembled by many interlaced nanosheets with thickness of 10–20 nm. The as-obtained orthorhombic WO3·H2O transforms into monoclinic WO3 without obvious change in morphology through annealing and dehydration. Furthermore, such 3D hierarchical spheres exhibit a strong structure-induced improvement in gas-sensing properties to ppm-level NO2, since the specific surface of sensing material and the gas diffusion are significantly enhanced due to its porous nano/microstructure. This work presents new insight towards the design of novel gas-sensing materials and improvement of sensor performance.

In this work, we prepared ZnO nanoparticles with sizes ranging from 5 to 270 nm by annealing the precursor of zinc carbonate hydroxide at four different temperatures (200, 400, 600 and 800 °C) and investigated their morphology, structure and optical properties as well as sensing performances to NO2. The precursor with small particle size and narrow size distribution was synthesized by a simple method involving separate nucleation and aging steps (SNAS). Among four obtained ZnO samples, the ZnO-400 (annealed at 400 °C) exhibits the best optical properties and the highest sensing response to NO2. The ZnO-400 shows fast response (≤30 s) and recovery (≤120 s) to NO2 and high selectivity to NO2. Besides, we further discussed a correlation between the gas sensing response and the defects of ZnO nanoparticles.

Supported Pd nanowire and cuboctahedron catalysts have been synthesized in an ethylene glycol–poly(vinylpyrrolidone)–KBr system using a precipitation–reduction method. KBr plays a critical role in controlling the morphology of Pd: with a variety of relatively low KBr concentrations, Pd nanowires with different lengths were obtained, but after adding sufficient KBr, shape evolution from nanowires to cuboctahedrons was observed. HRTEM images showed that the twisted Pd nanowires were actually composed of primary cuboctahedrons. Furthermore, lattice distortion was observed at interfacial regions, and the number of crystal boundaries increased with increasing length of the nanowires. The catalytic performance of the Pd materials was investigated in the selective hydrogenation of acetylene. The activities of the Pd nanowire catalysts were significantly higher than those of the cuboctahedron catalyst and gradually increased with the increasing number of crystal boundaries, indicating that the defect sites at crystal boundaries are more active owing to the exposure of larger numbers of Pd atoms. However, higher activity resulted in excessive hydrogenation and a decrease in ethylene selectivity. Therefore, the Pd cuboctahedron catalyst possessed higher selectivity. The relationship between crystal boundaries and catalytic performance was quantified, and the catalytic activity was found to increase linearly with an increasing number of crystal boundaries, whereas the trend in the selectivity was the reverse.Keywords: acetylene-selective hydrogenation; crystal boundary; cuboctahedron; defect sites; nanowire; supported Pd catalyst;

A new route was introduced to synthesize novel mesoporous spherical alumina supports by in situ growth of alumina whiskers on the surface, and in the pores, of conventional spherical alumina using urea as an OH– donor and a surfactant as a structure-directing agent. BET results indicate that the modified spherical alumina exhibited much higher surface area and more regular mesoporous structure than the unmodified alumina. The whisker-modified spherical aluminas with a flowerlike arrangement of whiskers and higher surface area were then used as support to prepare highly dispersed Pd catalysts. Catalytic performances of the catalysts were studied in the catalytic hydrogenation/oxidation of 2-ethylanthraquinone (EAQ). Compared with a conventional Pd/alumina catalyst, novel Pd/whisker-modified alumina catalysts exhibited much higher Pd dispersion which resulted in more catalytically active sites and therefore significantly higher hydrogenation efficiency. Moreover, shorter diffusion distance reduced the deep hydrogenation of EAQ and consequently achieved higher selectivity and structural stability.

The Acid Blue 25 (1-amino-9,10-dihydro-9,10-dioxo-4-(phenylamino)-2-anthracenesulphonate) anion intercalated layered double hydroxides (LDH) film was fabricated through an ion-exchange method using a ZnAl–NO3–LDH/porous anodic alumina/aluminum (PAO/Al) film as the precursor. The prepared film was investigated by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Scanning electron microscopy (SEM), Thermogravimetric–differential thermal analysis (TG–DTA) and the CIE 1976 L⁎a⁎b⁎ color difference method. XRD patterns and FT-IR spectra confirm the successful incorporation of ADPA anions into the interlayer spacings of ZnAl–LDH with an expansion of d-spacing from 0.87 nm to 2.49 nm and the disappearance of characteristic IR absorption band of NO3− anions at 1384 cm−1. The SEM morphologies show that the LDH films are mainly oriented with the ab face of the platelet crystallites perpendicular to the substrate surface. Additionally, the obtained results suggest that the intercalation of ADPA into ZnAl–LDH host markedly improves the thermal stability and light fastness of ADPA.Highlights► An Acid Blue 25 anion–pillared LDH film has been fabricated by anion-exchange method. ► Intercalation into the film of ZnAl–LDH enhances the thermal stability of the dye. ► The obtained film shows better light fastness than the dye.

Incorporation of anions of Acid Red 114 dye (1,3-naphthalenedisulfonic acid, 8-[2-[3,3′-dimethyl-4′-[2-[4-[[(4-methylphenyl)sulfonyl]oxy] phenyl]diazenyl] [1,1′-biphenyl]-4-yl]diazenyl]-7-hydroxy-, disodium salt) (denoted as NPDA) into ZnAl-layered double hydroxides (LDHs) has been carried out by an anion-exchange method in an effort to improve their thermal stability and light fastness. After intercalation of NPDA anions, the interlayer distance of the LDHs increases from 0.87 to 2.18 nm, confirming their incorporation into the interlayer galleries of the LDHs host. Infrared spectroscopy and thermogravimetric analysis revealed the presence of host–guest interactions between LDHs layers and NPDA anions. The thermal stability of NPDA and ZnAl–NPDA–LDHs was compared by thermogravimetric-differential thermal analysis, UV–visible spectroscopy and infrared spectroscopy. It was found that the thermal stability of NPDA anions was markedly improved by incorporation into the ZnAl–LDHs matrix, while the light fastness was also enhanced.Graphical abstractTG–DTG–DTA curves of ZnAl–NPDA–LDHs.Highlights► Acid Red 114 (NPDA)-incorporated ZnAl-LDHs were prepared by anion-exchange method. ► Intercalation of NPDA into LDHs significantly enhances its thermal stability. ► NPDA-incorporated ZnAl-LDHs has better light fastness than NPDA.

Quantum-sized ZnO nanoparticles have been synthesized at room temperature by a mild sol–gel process using tetraethylorthosilicate (TEOS) as the capping agent to control the particle growth of ZnO. The crystal structure, particle size and optical properties have been investigated by X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), photoluminescence (PL) spectra and Raman spectra, respectively. The results show that the ZnO nanoparticles exhibit hexagonal wurtzite structure and the average crystallite size is 5.7 nm which is a little less than TEM results. It has been testified by room-temperature PL spectra that the TEOS capped the surface of ZnO nanoparticles and obviously reduced grain size, as an emission at 520 nm almost disappeared and a new peak with an anomalous blue shift as great as 9 nm, appeared for the TEOS capped ZnO. The sensing tests indicate that the ZnO based sensors not only show a high response to NO2 but also exhibit high selectivity over CO and CH4 at a low operating temperature of 290 °C. The response increases with NO2 concentration and decreases with calcination temperature, and is in agreement with Raman and XRD results.

The Acid Yellow 49(4-[2-(5-amino-3-methyl-1-phenyl-1H-pyrazol-4-yl)diazenyl]-2,5-dichloro benzenesulfonic acid) (denoted as PPDB) anion intercalated layered double hydroxides (LDH) film was fabricated through an ion-exchange method using a ZnAl–NO3–LDH/alumina/aluminum film as precursor. The prepared film was investigated by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Scanning electron microscopy (SEM), Thermogravimetric–differential thermal analysis (TG–DTA), UV–visible spectroscopy and the CIE 1976 L*a*b* color difference method. XRD patterns and FT-IR spectra confirm the successful incorporation of PPDB anions into the interlayer galleries of ZnAl–LDH with an expansion of d-spacing from 0.88 nm to 2.51 nm and the disappearance of characteristic absorption band of NO3− anions at 1384 cm−1. The SEM morphologies show that the LDH films are mainly oriented with c axis of the platelet crystallites parallel to the substrate surface. Additionally, the obtained results suggest that the intercalation of PPDB into ZnAl–LDH host markedly improve the thermal stability and light fastness of PPDB.Highlights► A PPDB anion–pillared LDH film has been fabricated by anion-exchange method. ► Intercalation into the film of ZnAl–LDH enhances the thermal stability of PPDB. ► The obtained yellow film has better light fastness than PPDB.

Aurintricarboxylic acid (ATA), a UV absorbent, has successfully been intercalated into the interlayer spacing of Zn–Al–NO3-LDHs precursor through an anion-exchange reaction. The structure and the thermal- and photostability of the intercalated product were investigated by various techniques such as powder X-ray diffraction (XRD), infrared spectroscopy (FT-IR), thermogravimetry and differential thermal analysis (TG–DTA), and UV–vis spectroscopy. The increase of the basal spacing from 0.90 to 1.52 nm as observed by XRD suggests that the ATA anions have replaced the NO3– anions in the interlayer region of the precursor LDHs. The results of infrared spectroscopy and thermogravimetry and differential thermal analysis (TG–DTA) also reveal the presence of supramolecular host–guest interactions between the brucite-like sheet and the intercalated ATA anions. The intercalation of the ATA anions into the LDHs markedly enhances the thermal stability of this UV absorbent. After incorporation of 1 wt % ZnAl-ATA-LDHs to polypropylene (PP), also, the resulted ZnAl-ATA-LDHs/PP composite has much higher resistance to UV degradation related to PP.

Pd(NH3)2Cl2/MgAl-CO32−-layered double hydroxide (LDH) precursor has been synthesized in situ on the surface of spherical Al2O3 using urea as a precipitant. Pd(NH3)2Cl2 particles were observed highly dispersed on the surface of MgAl-LDH/Al2O3 by Scanning electron microscopy. After calcinations, a PdO/MgO-Al2O3 catalyst precursor was obtained. In the process of calcination, the MgAl-LDH crystallites grown on the surface of Al2O3 prevented the migration and aggregation of Pd2+, therefore the PdO particles with uniform size still highly dispersed on the surface of MgO-Al2O3. As a comparison, a PdO/Al2O3 catalyst precursor was prepared by a conventional impregnation method. Low temperature N2 adsorption−desorption, temperature programmed desorption of hydrogen and ammonia showed that PdO/MgO-Al2O3 possessed larger surface area, higher metal dispersion, and lower surface acidity compared with PdO/Al2O3. After reduction, the selective hydrogenation of acetylene was studied over Pd/MgO-Al2O3 and Pd/Al2O3 catalysts. The Pd/MgO-Al2O3 exhibited higher activity, selectivity and better stability.

Spherical mesoporous ZrO2-Al2O3 composites containing different zirconia content have been synthesized by an oil-column sol-gel method. A mixed alumina-zirconia hydrosol and hexamethylenetetramine solution were mixed together and added dropwise into a hot oil column. Due to the surface tension, spherical gel particles were formed in the oil column. The spherical gel particles were then aged and washed by deionized water and dried at 120 °C for 12 h and then calcined at 600 °C for 8 h, 960 °C for 8 h or 1200 °C for 12 h. X-ray diffraction and nitrogen adsorption-desorption measurements indicated that the presence of zirconia prevents the sintering of alumina and the obtained ZrO2-Al2O3 composites have much larger surface areas than pure alumina. Temperature-programmed desorption of ammonia results illustrated that the addition of zirconia leads to an increase in the number of strong acid sites and the total number of acid sites compared with pure alumina. Thus, the spherical mesoporous ZrO2-Al2O3 composites prepared in this way were shown to be suitable for high temperature catalytic processes as a catalyst support.

One-dimensional (1D) ZnO nanorods with pencil-like shape and high aspect ratio were successfully synthesized using a cetyltrimethylammonium bromide (CTAB)-assisted hydrothermal process at 90 °C. The surface morphology and structure of nanocrystals were characterized by FE-SEM, XRD and XPS analysis. Experimental results show that the surfactant and base concentration play important roles in the formation and growth orientation of ZnO nanorods. The ZnO nanorods synthesized exhibits high response and selectivity to NO2, the highest response to 40 ppm NO2 reached 206 and the selectivity with respect to CO and CH4 at same concentration reached 10.3 and 30 times, respectively. The effects of synthesis method, surfactant and calcination condition on sensing properties were systematically investigated. The results indicate that the CTAB-assisted low temperature hydrothermal process is a potentially facile method for synthesis of 1D ZnO nanorods and excellent potential candidates as gas sensing materials.

Reaction under alkaline conditions of N,N-bis(phosphonomethyl)glycine (glyphosine, GLYP) with an MgAl-NO3-layered double hydroxide (LDH) precursor, prepared by a method involving separate nucleation and aging steps (SNAS) led to the replacement of the interlayer nitrate anions by GLYP3− anions. The resulting MgAl-GLYP-LDH was characterized by X-ray diffraction (XRD), Fourier transfrom infrared (FT-IR), thermogravimetry and differential therm analysis (TG-DTA), elemental analysis, and scanning electron microscopy (SEM). MgAl-GLYP-LDH was mixed with low density polyethylene (LDPE) using a masterbatch method. LDPE films filled with MgAl-GLYP-LDH showed a higher mid- to far-infrared absorption than films filled with MgAl-CO3-LDH in the 7−25 μm range, particularly in the key 9−11 μm range required for application in agricultural plastic films.

5, 5′-Thiodisalicylic acid (TDSA) has been intercalated into a ZnAl–NO3 layered double hydroxide (LDH) by an ion-exchange reaction. After intercalation of TDSA, the basal spacing in the LDH increased from 0.89 to 1.53 nm, suggesting that the TDSA anions were arranged in the interlayer galleries of ZnAl–TDSA–LDH as a tilted monolayer arrangement of dianions. The samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetry and differential thermal analysis (TGA–DTA), and UV–Visible spectroscopy (UV–Vis). The results show that the NO3− anions in the precursor have been completely replaced by TDSA anions to give ZnAl–TDSA–LDH having crystalline-layered structure. Detailed studies reveal the presence of a complex system of supramolecular interactions between LDH layers and TDSA anions. TGA–DTA curves suggest that the thermostability of TDSA was markedly enhanced by intercalation in the LDH host. Photostability tests show that the film of ZnAl–TDSA–LDH/PP possessed higher stability to UV radiation than either the film of TDSA/PP or pristine PP.

A UV absorber, 5,5′-methylenedisalicylic acid (MDSA), has been intercalated into a ZnAl−NO3 layered double hydroxide (LDH) by an ion-exchange method. After intercalation of MDSA, the basal spacing in the LDH increased from 0.90 to 1.53 nm, suggesting that the MDSA anions were arranged in the interlayer galleries of ZnAl−MDSA LDH as a tilted monolayer arrangement of dianions. Infrared spectroscopy and thermogravimetry and differential thermal analysis (TGA−DTA) curves revealed the presence of a complex system of supramolecular host−guest interactions. The thermal stability of the intercalated UV absorbent was investigated by TGA−DTA, which showed that the thermostability was markedly enhanced after intercalation into the LDH host. After addition of 1 wt % ZnAl−MDSA LDH to polypropylene (PP), the resistance of the polymer to UV degradation was significantly improved.

An MgAl-NO3-layered double hydroxide (LDH) precursor has been prepared by a method involving separate nucleation and aging steps (SNAS). Reaction with iminodiacetic acid (IDA) under weakly acidic conditions led to the replacement of the interlayer nitrate anions by iminodiacetic acid anions. The product was characterized by XRD, FT-IR, TG-DTA, ICP, elemental analysis and SEM. The results show that the original interlayer nitrate anions of LDHs precursor were replaced by iminodiacetic acid anions and that the resulting intercalation product MgAl-IDA-LDH has an ordered crystalline structure. MgAl-IDA-LDH was mixed with low density polyethylene (LDPE) using a masterbatch method. LDPE films filled with MgAl-IDA-LDH showed a higher mid to far infrared absorption than films filled with MgAl-CO3-LDH in the 7–25 μm range, particularly in the key 9–11 μm range required for application in agricultural plastic films.Intercalation of iminodiacetic acid (IDA) anions in a MgAl-NO3-layered double hydroxide host leads to an enhancement of its infrared absorbing ability for application in agricultural plastic films.

One-dimensional (1D) needle-like ZnO nanorods with aspect ratio about 50 were successfully synthesized by a sodium dodecylsulphate (SDS)-assisted hydrothermal process at lower temperature (85 °C). The morphology and structure of crystals were characterized by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD) analysis. Experimental results show that SDS, ratio of OH−/Zn2+ and hydrothermal reaction time play important roles in the formation and oriented growth of ZnO nanorods. Gas sensors have been fabricated using 1D ZnO powders to examine the response towards 40 ppm CO over a range of operating temperature from 150 °C to 450 °C. The highest response is 49.58 at the operating temperature of 400 °C. The response was greatly enhanced by doping Nd element as surface modifier or ZrO2 as secondary oxide. The effect of doping on the ZnO structure and gas sensing has been discussed by X-ray photoelectron spectroscopy (XPS) analysis.

An organic UV absorbent has been intercalated into a layered double hydroxide (LDH) host by ion exchange of a Zn–Al–LDH-nitrate precursor with a solution of 2,3-dihydroxynaphthalene-6-sulfonic acid (DNSA) sodium salt in water. After intercalation of the UV absorbent, the powder X-ray diffraction (XRD) pattern shows that the interlayer distance in the LDHs increases from 0.90 to 1.59 nm. The possible structure is that the interlayer DNSA anions arrange in a monolayer and in a perpendicular orientation toward the hydroxide layers. Infrared spectra and TG–DTA curves reveal the presence of a complex system of supramolecular host–guest interactions between layers. The thermal stability of the intercalated UV absorbent was investigated by TG–DTA and it was found that this material is more stable than the original organic UV absorbent at high temperature, showing that the thermostability is markedly enhanced after intercalation into the LDH host. The UV absorbent-intercalated LDHs exhibit excellent UV photostability in polypropylene composites.

Spherical mesoporous CeO2−Al2O3 composites containing 2, 5, and 8 wt % ceria have been prepared by an oil-drop sol−gel method. A mixed alumina−ceria hydrosol and hexamethylenetetramine solution were mixed together and added dropwise into a hot oil column where spherical gel particles were formed due to surface tension. The spherical gel particles were then aged, washed, dried, and calcined at 600, 960, or 1200 °C. The resulting materials were characterized by X-ray diffraction, nitrogen adsorption−desorption, and temperature-programmed desorption of ammonia. At 1200 °C sintering of pure alumina is severe, whereas the presence of ceria prevents the alumina from sintering, so that the CeO2−Al2O3 composites have much larger BET surface areas than pure alumina. Addition of ceria also leads to an increase in the number of strong acid sites and the total number of acid sites compared with pure alumina. These results show that the spherical mesoporous CeO2−Al2O3 composites prepared in this way are suitable supports for high temperature catalytic processes.

A series of Ni2+−Co2+−Fe2+−Fe3+−SO42− layered double hydroxide precursors with different Ni/Co ratios have been synthesized by a method involving separate nucleation and aging steps. After calcination at 900 °C, the corresponding Ni1-xCoxFe oxides were obtained. Vibrating sample magnetometry indicated that the Ni1-xCoxFe oxide samples not only had high specific saturation magnetization, but also low coercivity and remanence. Ni1-xCoxFe oxides showed the optimum combination of magnetic properties for x = 0.2. Silica was coated onto the surface of Ni0.8Co0.2Fe oxide particles, and the coated particles were used as magnetic cores to prepare magnetic Ni0.8Co0.2Fe oxide/SiO2/γ-Al2O3 particles by hydrolysis of aluminum isopropoxide. After repeating the hydrolysis twice more, Ni0.8Co0.2Fe oxide/SiO2/γ-Al2O3 particles with about 20 wt % Ni0.8Co0.2Fe oxide were obtained and shown to be suitable for practical applications as a magnetic catalyst or catalyst support by virtue of their efficacious magnetic properties and pore structure.

A purified alumina hydrosol has been prepared by removing metal impurities using a new reduction-magnetic separation process. The amount of iron in the alumina hydrosol was reduced by over 78% from 0.0094% to 0.0020%. As a result of co-crystallization, the copper content was simultaneously reduced from 0.0003% to 0.0001%. Spherical γ-alumina granules were prepared by the oil-drop method using the purified alumina hydrosol as starting material. The γ-alumina granules had a bulk density of about 0.50 g cm−3, crush strength of around 90N per granule, specific surface area of about 200 m2 g−1 and pore volume of about 0.75 cm3 g−1. The purification process employed during the preparation of the alumina hydrosol had no effect on the physical properties, pore structure and crystal structure of the final spherical alumina granules.

5-sulfosalicylic acid (SSA) anions have been intercalated into layered double hydroxides (LDHs) by an anion-exchange reaction using ZnAl–NO3–LDHs as a precursor. The samples were characterized by XRD, FT-IR, TG-DTA/MS and UV–visible spectroscopy. The results show that the NO3− anions in the precursor have been completely replaced by SSA anions to give ZnAl–SSA–LDHs having a high degree of crystallinity. Detailed studies reveal the existence of a supramolecular structure in ZnAl–SSA–LDHs involving electrostatic attraction between opposite charges, hydrogen bonding and other weak chemical bonding interactions between host layers and SSA anions. The thermal stability of ZnAl–SSA–LDHs is considerably enhanced compared with that of a mixture of ZnAl–NO3–LDHs and SSA. After addition of 2.0 wt% ZnAl–SSA–LDHs to polypropylene (PP), the resistance of the polymer to UV degradation is significantly improved.UV–visible absorbance curves of SSA (a), ZnAl–NO3–LDHs precursor (b) and ZnAl–SSA–LDHs (c).

Nanoscale NiAl-NO3-LDHs with good crystallinity have been synthesized by a method, Separate Nucleation and Aging Steps (SNAS). An NiAl-NO3-LDHs/LDPE composite was prepared by blending NiAl-NO3-LDHs and LDPE in a heated double-roller mixer. The color of this composite changed from olive green to steel gray under UV irradiation. After heating at 80°C for 2 h, the color returned to olive green. The effect of varying the amount of added NiAl-NO3-LDHs and UV exposure time on the photochromic properties of the composite has been investigated. The results showed that the photochromic phenomenon becomes more apparent with increasing amount of NiAl-NO3-LDHs. When the amount reaches 5%, the composite exhibits good photochromic properties and reproducibility. The color change rate of the composite reaches a maximum when the irradiation time exceeds 20 min. The addition of LDPE improves the photochromic cyclability of NiAl-NO3-LDHs significantly. The addition of nanoscale NiAl-NO3-LDHs also improves the mechanical properties of LDPE to some extent.

Intercalation of 2-naphthalenecarboxylic acid, 4-((4-chloro-5-methyl-2-sulfophenyl) azo)-3-hydroxy-, calcium salt (1:1) (C.I. Pigment Red 52:1, also known as New Rubine S6B) into a layered double hydroxide (LDHs) host was carried out using MgAl–NO3–LDHs as a precursor in an effort to improve the thermal and photo stability of the pigment. After intercalation, the powder X-ray diffraction (XRD) pattern shows that the basal spacing of the LDHs increased from 0.86 to 1.92 nm. Infrared spectra and TG–DTA curves demonstrate that there are supramolecular host–guest interactions. It was found that the intercalated material is more stable than the pristine pigment at high temperatures. The pigment anion-pillared LDHs also exhibit much higher photostablity to UV-light than the pristine pigment.

•Pd–Ga/MgO–Al2O3 catalysts were synthesized by an in situ LDH precursor method.•Bimetallic Pd–Ga nanoalloys were highly and stably dispersed.•Ethene selectivity was improved owing to bimetallic synergistic effect.•Due to net trap confinement effect, Pd–Ga catalysts exhibit preferable stability.An effective and versatile synthetic approach is presented to produce highly dispersed bimetallic Pd–Ga catalysts that can be used as hydrogenation catalysts. Mg–Ga–Al-layered double hydroxide (LDH) was synthesized in situ on the surface of spherical alumina to obtain MgGaAl-LDH@Al2O3 precursor, followed by the introduction of PdCl42-. The positive charge of MgGaAl-LDH layer offers an opportunity to realize uniform dispersion of PdCl42-, which facilitates the formation of bimetallic Pd–Ga nanoalloys. Upon thermal reduction of PdCl42-/MgGaAl-LDH@Al2O3 precursor, highly stable dispersed bimetallic Pd–Ga/MgO–Al2O3 catalysts were obtained. Owing to high dispersion and synergistic effect of bimetallic nanoalloys, Pd–Ga/MgO–Al2O3 catalysts exhibited comparable activity and much higher selectivity compared with the monometallic Pd/MgO–Al2O3 in partial hydrogenation of acetylene. More significantly, this good catalytic performance can be totally retained after three times recycling due to the net trap confinement effect, which suppressed the migration and aggregation of bimetallic Pd–Ga nanoalloys.Bimetallic Pd–Ga/MgO–Al2O3 catalysts prepared by in situ LDH precursor route exhibited much preferable selectivity and durability in comparison with the monometallic Pd/MgO–Al2O3 catalyst in partial hydrogenation of acetylene.Download high-res image (174KB)Download full-size image

•Trimetallic PdAuAg catalysts with two different morphologies are prepared by a co-reduction method.•Both of the trimetallic catalysts exhibit higher selectivity than mono- and bimetallic catalysts.•Compared with the cuboctahedral catalyst, the mesocrystal catalyst exhibits higher activity and selectivity.•Enhanced activity could be ascribed to the high concentration of defect sites.•Increase of facet (1 1 1)/(1 0 0) ratio and Pd–C phase contribute to the improved selectivity.To simultaneously achieve thorough purification of acetylene and maximum ethene increment, a sea urchinlike trimetallic PdAuAg mesocrystal catalyst as targeting sample and cuboctahedral trimetallic PdAuAgx and bimetallic catalyst as control samples were prepared by a co-reduction method, immobilized on MgAl hydrotalcite. Compared with bimetallic PdAu and PdAg catalysts, trimetallic PdAuAgx catalyst gave prior selectivity due to the positive synergetic effect. Significantly, PdAuAg2 mesocrystal catalyst exhibited a turnover frequency of 0.063 s−1, 46.5% higher than that of cuboctahedral PdAuAg2 catalyst. A 76.2% ethene selectivity was achieved for the thorough purification of acetylene over PdAuAg mesocrystal catalyst with H2:C2H2 of 2:1. Further improving H2:C2H2 to 3, 76.5% yield can be maintained at 140 °C. Enhanced activity of the mesocrystal catalyst could be attributed to a high concentration of defect sites and a low activation barrier. Improved ethene selectivity could be ascribed to the increase in the (1 1 1)/(1 0 0) facets ratio and the formation of a Pd-C phase.Download high-res image (122KB)Download full-size image

•MgxTi1−xOy with tunable acidity/basicity is prepared as new supports for acetylene hydrogenation.•PdAg/Mg0.5Ti0.5Oy shows excellent performance with 83.8% selectivity at >99% conversion.•Moderate acidity promotes hydrogen-spillover effect, which favors hydrogen dissociation.•Negatively-charged Pd caused by basic sites and Ti3+ favors desorption of ethene.•High alloying degree of PdAg/Mg0.5Ti0.5Oy also contributes to the improved selectivity.A series of reducible Mg-Ti mixed oxides supported PdAg catalysts with tunable acidity/basicity were synthesized for selective acetylene hydrogenation, to investigate the implications of acid-base property on the nature of active component. Catalytic performance of PdAg/MgxTi1−xOy varied with Mg/Ti ratio increasing as volcano curve, which corresponded well with amount of medium acid and weak basic sites. PdAg/Mg0.5Ti0.5Oy exhibited >99% conversion and 83.8% selectivity at 70 °C. Enhanced activity was attributed to the promoted hydrogen-spillover effect by moderate acidic sites of Mg0.5Ti0.5Oy support, which facilitated hydrogen activation/dissociation. Preferred selectivity was reasonably owing to the significant geometric effect resulting from high alloying degree of Pd-Ag, which increased the number of Pd linearly coordinated sites, and therefore facilitated the desorption of ethene. Additionally, the increased Pd electronic density caused by the electron transfer from the basic sites and Ti3+ species of Mg0.5Ti0.5Oy support also contributed to the improvement of selectivity.Download high-res image (134KB)Download full-size image

MgAl–CO3-layered double hydroxides (MgAl-LDHs) have been synthesized on the surface of spherical γ-Al2O3 by an in situ synthesis technique using urea as a precipitant. After calcination, LDH crystallites are transformed into complex metal oxides (LDO) with high homogeneity and MgAl-LDO/γ-Al2O3 solid base catalysts containing different LDO content were obtained. X-ray diffraction, scanning electron microscopy, and surface area measurements using the Brunauer–Emmett–Teller method indicated that the MgAl-LDO/γ-Al2O3 catalysts possess high specific surface area and rich mesoporous structure. The MgAl-LDO/γ-Al2O3 catalysts were used to regenerate anthraquinone degradation products formed in the anthraquinone process for the manufacture of hydrogen peroxide. The efficiency of regeneration of the anthraquinone degradation products was found to increase with increasing LDO loading in the catalysts. Compared with commercial catalysts of NaOH/γ-Al2O3 and MgO/γ-Al2O3 prepared by the impregnation method, MgAl-LDO/γ-Al2O3 catalysts exhibited not only higher activity but also longer life.Graphical abstractDownload high-res image (98KB)Download full-size imageHighlights► MgAl-LDHs was synthesized on the surface of γ-Al2O3 as a catalyst precursor. ► Calcination of MgAl-LDHs/γ-Al2O3 precursor, LDO/γ-Al2O3 catalyst was obtained. ► The surface basicity of the catalysts increased with increasing LDO loading. ► LDO/γ-Al2O3 exhibits high efficiency of anthraquinone degradation regeneration.

An Ni2+–Al3+–CO32--layered double hydroxides (NiAl–LDHs) precursor has been synthesized in the pores of spherical γ-Al2O3 particles. After calcination at 500 °C, a NiO/γ-Al2O3 catalyst precursor was obtained. X-ray photoelectron spectroscopy, temperature programmed reduction, and temperature programmed desorption of hydrogen showed that in the material prepared by calcination of NiAl–LDHs supported on Al2O3, the NiO was characterized by higher reduction temperature, stronger interactions with Al2O3, and higher nickel dispersion compared with the NiO in a material prepared by conventional impregnation of γ-Al2O3 with an aqueous solution of Ni2+ ions followed by calcination at 500 °C. The vapor phase hydrodechlorination of chlorobenzene using molecular hydrogen was studied using Ni/γ-Al2O3 catalysts prepared by reduction of the NiO/γ-Al2O3 catalyst precursors synthesized by the two different methods. Under identical reaction conditions, the Ni/γ-Al2O3 catalyst obtained from the LDHs precursor exhibited not only higher activity but also better stability.A Ni2+–Al3+–CO32--layered double hydroxide precursor has been synthesized in the pores of spherical γ-Al2O3 particles. After calcination and reduction, a highly dispersed Ni/γ-Al2O3 catalyst was obtained.Download high-res image (109KB)Download full-size image

NiTi-layered double hydroxide (NiTi-LDH) with rich defective sites was synthesized and used as the support for the preparation of a novel supported PdAg nanoalloy catalyst for the partial hydrogenation of acetylene. The obtained PdAg/NiTi-LDH catalyst exhibited a remarkable catalytic performance. When the conversion of acetylene reached 90%, the selectivity towards ethene maintained 82%. Superior hydrogenation activity was ascribed to two key factors. Small particle size and high dispersion of PdAg nanoparticles were responsible for boosting the catalytic activity. In addition, Ti3+ defective sites in the support also played an important role in the enhancement of activity. The interface at the Ti3+ species and active metals acting as new active sites enhanced the activation and dissociation of hydrogen and therefore further improved the catalytic activity. Preferable selectivity was assigned to the electronic effect between the NiTi-LDH support and the PdAg nanoalloys. The electron transfer from the Ti3+ species to the Pd resulted in the increase of electron density and the linearly coordinated sites of Pd and therefore facilitated the desorption of ethene. Moreover, due to the reducibility of NiTi-LDH, the selectivity and stability over the reduced PdAg/NiTi-LDH catalyst were further enhanced on account of the strong metal–support interaction.

Flower-like hierarchical Au/NiAl-LDH catalysts were synthesized for selective oxidation of alcohols. The abundant hydrogen vacancies at the edge of the flowers as nucleation centers contributed to the uniform dispersion of Au NPs. The confinement effect of the hierarchical pores promoted 60% higher activity than the common Au/NiAl-LDH nanoparticle catalyst in the oxidation of benzyl alcohol by heightening the effective collisions between substrates and active sites. The evolution process of the hierarchical pores in the support was further proposed. Moreover, the reaction mechanism of the cooperation among Brønsted base sites, NiIII coordinatively unsaturated metal sites and isolated gold cations was concretely proved. In the oxidation of other typical alcoholic substrates, the flower-like catalyst showed higher activity than the common nanoparticle one except for linear alcohols, which could be attributed to the shape selectivity of straight macropores.

This research was motivated by the need to develop a smart ammonia (NH3) sensor based on a flexible polyethylene terephthalate (PET) thin film loaded with a reduced graphene oxide–polyaniline (rGO–PANI hybrid) using in situ chemical oxidative polymerization. The sensor not only exhibited high sensitivity, good selectivity and a fast response at room temperature but was also flexible, cheap and had wearable characteristics.

Oxidation and hydrogenation catalysis plays a crucial role in the current chemical industry for the production of key chemicals and intermediates. Because of their easy separation and recyclability, supported catalysts are widely used in these two processes. Layered double hydroxides (LDHs) with the advantages of unique structure, composition diversity, high stability, ease of preparation and low cost have shown great potential in the design and synthesis of novel supported catalysts. This review summarizes the recent progress in supported catalysts by using LDHs as supports/precursors for catalytic oxidation and hydrogenation. Particularly, partial hydrogenation of acetylene, hydrogenation of dimethyl terephthalate, methanation, epoxidation of olefins, elimination of NOx and SOx emissions, and selective oxidation of biomass have been chosen as representative reactions in the petrochemical, fine chemicals, environmental protection and clean energy fields to highlight the potential application and the general functionality of LDH-based catalysts in catalytic oxidation and hydrogenation. Finally, we concisely discuss some of the scientific challenges and opportunities of supported catalysts based on LDH materials.

Al-doped flower-like ZnO nanostructures have been synthesized by a facile hydrothermal method at 95 °C for 7 h. The structure and morphology of the product were characterized by XRD, FTIR and SEM analysis. The sensing tests reveal that the response is significantly enhanced by Al doping, and the 0.3 wt% Al-doped sample exhibits the highest response of 464 to 10 ppm CO at an operating temperature of 155 °C. A change of the structural defects in Al-doped ZnO is responsible for the enhancement of the sensing properties, which has been confirmed by the room temperature photoluminescence (PL) spectra and X-ray photoelectron spectroscopy (XPS). The response time is reduced disproportionately with the increase in CO concentration by modeling the transient responses of the sensor using the Langmuir–Hinshelwood reaction mechanism. The band structures and density of states for pure ZnO and Al-doped supercells have been calculated using first principles based on density functional theory (DFT). The calculated results show that the band gap is narrowed and the conductance is increased by Al doping, which coincides with the experimental results of gas sensing.

Quantum-sized ZnO nanoparticles have been synthesized at room temperature by a mild sol–gel process using tetraethylorthosilicate (TEOS) as the capping agent to control the particle growth of ZnO. The crystal structure, particle size and optical properties have been investigated by X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), photoluminescence (PL) spectra and Raman spectra, respectively. The results show that the ZnO nanoparticles exhibit hexagonal wurtzite structure and the average crystallite size is 5.7 nm which is a little less than TEM results. It has been testified by room-temperature PL spectra that the TEOS capped the surface of ZnO nanoparticles and obviously reduced grain size, as an emission at 520 nm almost disappeared and a new peak with an anomalous blue shift as great as 9 nm, appeared for the TEOS capped ZnO. The sensing tests indicate that the ZnO based sensors not only show a high response to NO2 but also exhibit high selectivity over CO and CH4 at a low operating temperature of 290 °C. The response increases with NO2 concentration and decreases with calcination temperature, and is in agreement with Raman and XRD results.

The development of highly active, sensitive and durable gas sensing materials for the detection of volatile organic compounds (VOCs) is extremely desirable for gas sensors. Herein, a series of mesoporous hierarchical Co3O4–TiO2 p–n heterojunctions have been prepared for the first time via the facile thermal conversion of hierarchical CoTi layered double hydroxides (CoTi-LDHs) precursors at 300–400 °C. The resulting Co3O4–TiO2 nanocomposites showed superior sensing performance towards toluene and xylene in comparison with Co3O4 and TiO2 at low temperature, and the sample with a Co/Ti molar ratio of 4 shows an optimal response (Rg/Ra = 113, Rg and Ra denote the sensor resistance in a target gas and in air, respectively) to 50 ppm xylene at 115 °C. The ultrahigh sensing activity of these Co3O4–TiO2 p–n heterojunctions originates from their hierarchical structure, high specific surface area (>120 m2 g−1), and the formation of numerous p–n heterojunctions, which results in full exposure of active sites, easy adsorption of oxygen and target gases, and large modulation of resistance. Importantly, hierarchical Co3O4–TiO2 heterojunctions possess advantages of simple preparation, structural stability, good selectivity and long-term durability. Therefore, this work provides a facile approach for the preparation of hierarchical Co3O4–TiO2 p–n heterojunctions with excellent activity, sensitivity and durability, which can be used as a promising material for the development of high-performance gas sensors.