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To develop a high sensitive and low temperature NO2 gas sensor, the novel BiVO4/Cu2O heterojunctions were synthesized by a modified metal organic decomposition method to decorate BiVO4 nanoplates using Cu2O nanoparticles for enhancement of BiVO4 sensing performance to NO2. The structure and morphology of BiVO4, Cu2O and BiVO4/Cu2O composites were characterized by XRD, SEM and TEM spectra. The results indicate that the BiVO4/Cu2O heterojunctions are composed of monoclinic BiVO4 nanoplates with the thickness about 1.0–1.2 μm and 30–40 nm diameters of cubic Cu2O nanoparticles. The gas-sensing tests display that the composite exhibits rapid and linear responses to low concentration NO2 (from 100 ppb to 8.0 ppm), the highest response reaches 4.2 towards 4 ppm NO2 at 60 °C and relative humidity of 28.3%, which is more than 2 times of pure BiVO4 at the same condition. The enhanced sensing properties benefit from the novel p-n heterojunction between BiVO4 and Cu2O, which forms a depletion layer at the interface, leading to resistance increase of composites in NO2. The work demonstrates the as-synthesized BiVO4/Cu2O is a promising sensing material to detect NO2 gas.

Efficient charge separation and rapid surface reaction kinetics play a significant part in the efficiency of solar water splitting. A novel triadic MoO3/BiVO4/CoMnZn photoanode was prepared success...

BiVO4 is an ideal photoanode material for solar-driven photoelectrochemical (PEC) water splitting but it easily suffers from the recombination of photogenerated electrons and holes due to its low carrier mobility thus cause low efficiency of PEC water splitting. Herein, the BiVO4/CdS/NiCo-LDH photoanode was prepared by combining methods of metal organic decomposition, chemical and electrodeposition. The photoanode photocurrent density reaches 2.72 mA cm−2 at 1.23 V (vs. RHE), which is 3.6 folds of pure BiVO4 photoanode and onset potential shifts 450 mV toward cathodic. The incident photon-to-electron conversion efficiency (IPCE) value is 2.86 folds of BiVO4, the calculated photon–to–current efficiency (ABPE) is 1.24% at 0.62 V (vs. RHE). The obtained results are higher than that of most BiVO4 based photoanodes published so far. The enhancement benefits from increase of visible light absorption capacity, enhancement of separation efficiency of photoexcited electron-hole and fast transfer of holes accumulated on electrode/electrolyte surface for water oxidation, which has been confirmed by calculating carrier density and carrier transport rate.

Ordered mesoporous WO3 nanocrystals have been successfully synthesized by a hydrothermal method using mesoporous silica of KIT-6 as a template and phosphotungstic acid as a precursor of WO3. The structure, morphology, and specific surface of WO3 nanocrystals were systematically characterized by XRD, SAXS, HR-TEM, and BET. To improve the sensing properties of WO3 to NO2, a series of different ZnO amounts were loaded on the mesoporous WO3 to construct nanocomposites with n–n heterojunction for the fabrication of NO2 sensors. The gas-sensing behaviors show that the sensor based on WO3/5 wt% ZnO composite to 1 ppm of NO2 not only exhibits the high response, but also has good selectivity and stability at operating temperature of 150 °C, which can be contributed to the large specific surface and porous channels provided by mesoporous structures, and the formation of n–n heterojunctions at interface between both oxides.

he Co3O4/ZnO composites with porous and high specific surface were prepared by calcination of Co and Zn-based bimetallic organic framework (MOFs). The influence of the calcination temperature on structure and morphology of composite has been discussed by means of the analysis of XRD, FESEM, HRTEM and XPS spectra. Gas-sensing experiment reveals that the response of composite (Co/ Zn =4:1 At.) is 5 times higher than that of pristine Co3O4 to 10 ppm HCHO at 120 °C and exhibits a rapid response, good selectivity, and stability. Such excellent performance is attributed to the large specific surface area and porous structure resulting from pyrolyzing of MOFs framework, which is beneficial to gas adsorption, diffusion and surface reaction. This MOF-driven strategy is expected to be a promising method for preparation of other metal oxide composites and application in detecting toxic gas.

The NiFe-layered double hydroxide (LDH) nanosheets were decorated on the surface of doped BiVO4 to structure an integrating photoanode for improving solar photoelectrochemical (PEC) water splitting efficiency, which is a dynamic research topic to solve the energy crisis and remit environmental pollution caused by fossil fuel combustion. The fabricated photoanode exhibits rapid response to visible light, enhances photocurrent density and shows significant cathodic shift compared to BiVO4. Moreover, the measured incident photon-to-current efficiency (IPCE) of the photoanode is comparable to that reported in the literature. The amount of evolution oxygen was measured and the faradaic efficiency produced oxygen was also obtained by comparing the theoretical calculation value. The enhancement is attributed to the increase of the carrier density, the effective separation of photogenerated electron-hole and consuming of the photogenerated holes accumulated at the electrode surface, which has been confirmed by electrochemical impedance spectra (EIS) and the intensity modulated photocurrent spectra (IMPS). The work may offer a promising method for designing a high efficiency and low-cost photoanode.

Silver, as a cheaper and good conductivity noble metal, has successfully been decorated on SnO2 nanoparticles to structure the Ag-SnO2 composites by a facile hydrothermal and in situ reduction method. The difference of structure and properties between SnO2 and composite was characterized by XRD, FESEM, elemental mapping, UV–vis spectroscopy, BET and XPS surface analysis. The sensing performance of SnO2 and composite to formaldehyde were also examined. The composite of 3.7 wt% Ag decorated SnO2 not only exhibits the high response to 10 ppm of formaldehyde but also has better stability and selectivity at an operating temperature of 125 °C. Moreover, the detection limit of the composite was determined to be 0.53 ppm, which is lower than that of pure SnO2 nanoparticles. The response mechanism of the composite to formaldehyde was also discussed in detail, which is attributed to the catalytic effect and the spillover effect of Ag nanoparticles.

The precursors (ZnSn(OH)6) of ZnSnO3 hierarchical microspheres have been synthesized by an facile chemical precipitation method at room temperature followed by self-assembly, and then, the precursors were converted into hierarchical ZnSnO3 microspheres composed of nanoparticles by annealing. The structure and morphologies of the products were characterized by a series of analysis methods. The sensing performance of the ZnSnO3 microspheres to formaldehyde was studied, and the sensing mechanism was also discussed in detail. The sensing tests indicate that doping Pd can significantly improve the sensing properties of ZnSnO3 to formaldehyde, especially when the doping proportion of Pd is 4 wt%. In addition, the material has low detection limit of 100 ppb and shows linear response to formaldehyde in the concentration range from 0.1 to 10 ppm at operating temperature of 103 °C. All the above properties indicate that the 4 wt% Pd-doped composite is an attractive sensing material for detection of formaldehyde.

It is essential to develop a high activity and stability photoanode for enhancing PEC water splitting performance. According to energy band matching principle the Fe2O3/BiVO4 heterojunction based photoanode is constructed by electrodeposition and metal organic decomposition, following by electrodeposited NiFe-LDH on heterojunction to structure a trinary integrating photoanode. The structure of material and PEC properties of the photoanode are systemically studied, the results show that the photoanode achieves the highest photocurrent density that is about 4.25 times and 2 times higher than that of pristine α-Fe2O3 and BiVO4 photoanodes. The IPCE value is 3.7 times higher than α-Fe2O3 and the onset potential has a significant cathodic shift of 400 mV compared to the pristine α-Fe2O3 for the ternary integrating photoanode. These results are higher than or are comparable to other α-Fe2O3 composites reported in literatures, which is attributed to the efficient separation of the photoexcited electron-hole pairs and alleviates holes accumulation at the surface of electrode due to the double action of semiconductor junction and co-catalyst of NiFe-LDH.

The volatile gas of Triethylamine (TEA) can cause environment pollution and lead to the serious hurt of the human respiratory system. Therefore, it is necessary to detect low concentrations of TEA in our daily lives rapidly. The hybrid of pine dendritic BiVO4/reduced graphene oxide (rGO) has been synthesized firstly by one step hydrothermal process. The gas sensing tests show that the 13.0 wt% rGO hybrid not only exhibits high response of 5.9 and rapid response of 11.4 s, but also exclusive selectivity and long-term stability to 10 ppm of TEA at the operating temperature of 180 °C. The formation of heterojunction and the incoporation of rGO are responsible for the improving sensing properties of the hybrid to TEA, the former results in reduction of the electron depletion layer at interface in hybrid, while the latter enhances the specific surface of the hybrid and accelerates the transfer of electrons. The research is expected to have wide application in the development of composite based gas sensors made of rGO/metal oxide semiconductors.

We report a novel composite of α-Fe2O3/BiVO4 with n-n heterojunctions for the first time and application in detecting low concentration NO2 gas. The flower-like α-Fe2O3 hierarchical nanostructures were prepared by the solvothermal method followed by BiVO4 nanoparticles decorated on α-Fe2O3 surface by metal-organic decomposition to structure the heterojunctions of α-Fe2O3/BiVO4. The structure and morphology of material were characterized and the sensing properties to NO2 were examined. The results show that the α-Fe2O3/BiVO4 composite (atomic ratio of 8:1:1 for Fe: Bi: V) to 2 ppm NO2 exhibits a four times higher response than pristine α-Fe2O3 at 110 °C, excellent selectivity, and long-term stability. The enhanced sensing properties can be attributed to the porous hierarchical structure of composite and the formation of inner electronic field (IEF) caused by n-n heterojunction at interface between α-Fe2O3 and BiVO4.

Combining semiconductor heterojunction and cocatalyst is an important strategy to improve photoelectrochemical (PEC) water splitting efficiency. Here, a photoanode of WO3/Fe2O3 heterojunction decorated by NiFe-layered double hydroxide (LDH) was fabricated by two-step hydrothermal methods. As expected, the photocurrent density of the ternary photoanode reaches up to 3.0 mA·cm–2, which respectively are 5 times and 7 times of WO3 and α-Fe2O3. The improvement benefits from the extending absorption of visible light, the effective separation of photogenerated charge carriers, and acceleration of water oxidizing reaction, which is caused by narrowing band gap and electron directionally flowing of heterojunction as well as catalyst timely consuming of holes accumulated at the electrode surface. The electron lifetime and the steady-state carrier density for four photoanodes were estimated from electrochemical impedance spectra (EIS) and were further confirmed by the intensity modulated photocurrent spectra (IMPS)....

One dimensional ZnO-SnO2 hollow nanofibers were synthesized via a one-step electrospinning method and annealing treatment. The morphology and structure of the nanofibers have been characterized by various analysis methods, and the sensing properties to 0.5–5 ppm NO2 have also been examined. The results reveal that the 20 atm%Zn composite not only exhibits the highest response that is 9 and 5.2 times higher than that of pristine ZnO and SnO2 respectively, but also exhibits rapid response, excellent selectivity and stability at low operating temperature of 90 °C. So, herein synthesized composite is a promising sensing material for detection of NO2. The enhancing sensing mechanism is discussed in detail, which is attributed to the unique one-dimensional hollow nanostructures and the formation of heterojunctions at interface between both metal oxides.

The spherelike Cu2O and the hybrids with reduced graphene oxide (rGO) have been synthesized successfully by a facile solution-based self-assembly method. The structure, morphology, composition, and specific surface area of composite were characterized by XRD, SEM, FTIR, XPS, and BET analysis, respectively. The gas-sensing properties to 1 ppm of NO2 at room temperature were also examined. The results indicated that the 1 wt % rGO/Cu2O composite not only exhibits 2.8 times higher response than that of pristine Cu2O and excellent selectivity but also owns rapid response and recovery at room temperature, indicating the composite is a promising sensing material for room temperature detection of low-concentration NO2. The enhanced sensing properties were discussed in detail, which can mainly be attributed to increased gas adsorption active sites and the fast carriers transport due to the incorporating of rGO.

The composite of ZnSnO3 hierarchical microspheres decorated with NiO nanosheets have been synthesized by a facile solution-based chemical precipitation at 85 °C followed by self-assembly and annealing, which is low-cost and high-yield. The structure, morphology, composition and specific surface of composite were characterized by XRD, SEM, TG, XPS and BET analysis, respectively. The gas sensing experiments show that the sensor based on composite of NiO/ZnSnO3 mole ratio of 1:10 not only exhibits high response of 2.2 and 10.4 to 0.1 and 1 ppm formaldehyde, respectively and good selectivity to some of reducing gases, but also has low detection limit and rapid response and recovery at operating temperature of 85 °C. The mechanism of composite enhancing gas sensing was also discussed in detail, which can be ascribed to the large specific surface area of composite and the formation of p-n heterojunctions at the interface between NiO and ZnSnO3.

The SnO2/NiO composites were synthesized by hydrothermal followed by calcination using metal-organic framework (MOF) consisting of the ligand of p-benzene-dicarboxylic acid (PTA) and the Sn and Ni center ions as sacrificial templates. The structure and morphology of Sn/Ni-based MOF and SnO2/NiO composites were characterized by XRD, SEM, TEM, FT-IR, TG, XPS and Brunauer-Emmett-Teller analysis. Sensing experiments reveal that the SnO2/NiO composite with the molar ratio of 9:1 not only exhibits the highest response of 14.03 that is 3 times higher than pristine SnO2 to triethylamine at 70 °C, but also shows good selectivity. Such excellent performance is attributed to the MOF-driven strategy and the formation of p-n heterojunctions, because the metal ions can be highly dispersed and separated in the MOFs and can prevent the metal ions aggregation during the MOF decomposition process. The work is a novel route for synthesis of gas sensing material.

The rGO/ZnSnO 3 composites have been elaborately synthesized by a facile solution-based self-assembly synthesis method at low temperature. The structure, morphology, thermal stability, composition and specific surface area of composite were characterized by XRD, SEM, TG, XPS and BET analysis, respectively. The sensing experiments show that the sensor based on 3 wt% rGO composite not only exhibits high sensitivity (low limit of detection), excellent selectivity and linearity relationship between responses and formaldehyde concentration from 1 to 10 ppm, but also exhibits fast response and recovery at operating temperature of 103 °C. The enhanced sensing mechanism of the hybrid to formaldehyde was discussed in detail, which can mainly be ascribed to the large specific surface area for gas adsorption, porous channels for gas diffusion, the fast carrier transport benefited from rGO and the formation of heterojunction at the interface between the rGO and ZnSnO 3 .

A Cu2O/BiVO4 p-n heterojunction based photoanode in photoelectrochemical (PEC) water splitting is fabricated by a two-step electrodeposition method on an FTO substrate followed by annealing treatment. The structures and properties of the samples are characterized by XRD, FESEM, HRTEM, XPS and UV-visible spectra. The photoelectrochemical activity of the photoanode in water oxidation has been investigated and measured in a three electrode quartz cell system; the obtained maximum photocurrent density of 1.72 mA cm-2 at 1.23 V vs. RHE is 4.5 times higher than that of pristine BiVO4 thin films (∼0.38 mA cm-2). The heterojunction based photoanode also exhibits a tremendous cathodic shift of the onset potential (∼420 mV) and enhancement in the IPCE value by more than 4-fold. The enhanced photoelectrochemical properties of the Cu2O/BiVO4 photoelectrode are attributed to the efficient separation of the photoexcited electron-hole pairs caused by the inner electronic field (IEF) of the p-n heterojunction.

The NiO nanosheets assembled hollow spheres have been synthesized by a facile precipitation method using SiO2 spheres as hard template, and the Fe was doped into NiO to improve the sensing properties of triethylamine (TEA). The structure, morphology and gas sensing properties of undoped and doped NiO were characterized by various analysis methods. The results show that the NiO microspheres have large specific surface, and excellent sensing response to 10 ppm triethylamine, so, it is a promising sensing material for detection of TEA.

The carbon-coated chevrel phase of Mo6S8 as electrode material was fabricated for the first time. Compared with the bare Mo6S8 and 10%C-Mo6S8 anodes, the 5%C-Mo6S8 anode possesses excellent rate capability and cyclic performance at the cutoff voltage of 1.5 V using LiMn2O4 as the cathode, which delivers a reversible capacity of ∼ 85 mAh·g−1 and an average discharge voltage of as high as ∼ 2 V maintains 93% of initial discharge capacity even after 400 cycles at 1C and in 21 M aqueous electrolyte. This study provides a promising anode material for aqueous lithium-ion batteries because of its high capacity, stability and environmental inertness. Furthermore, the results demonstrate that this method could expand the synthesis and application of these unique compounds.

The SnO 2 /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 SnO 2 /NiO nanocomposite with molar ratio of 4:1 not only exhibits the highest response to 500 ppb NO 2 , which is 8 times and 13 times higher than that of SnO 2 and NiO, respectively, but also has excellent selectivity, outstanding stability and trend of linear response to low concentrations of NO 2 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 SnO 2 and NiO, leading to the significant increase of depletion layer thickness at interface.

The rGO-NiO/ZnO composites were successfully synthesized by hydrothermal and hydrazine hydrate reduction methods and were used to detect NO2. The structure and morphology of the composites were characterized using spectrum techniques. The sensing tests showed that the triadic composite of rGO (0.5 wt%)-NiO/32ZnO exhibits a liner response toward NO2 in the concentration range of 0.5–3 ppm and the highest response reaches 75.3 to 2 ppm NO2 at 140 °C, which is 4.55 times and 1.38 times higher than that of pure ZnO and binary composite of NiO/32ZnO, respectively. The composite also exhibits a fast response of 39 s and a low detection limit of 46 ppb. The improvement mechanism is ascribed to the formation of p-n heterojunction that benefits from the formation of an additional depletion layer at the junction interface and the decoration of rGO increases surface active sites and accelerates electron transfer.

The Co3O4 hollow spheres with 3D hierarchical structure have been synthesized successfully by a facile precipitation method using SiO2 spheres as hard template. The hierarchical structure of Co3O4 as a good substrate material can be further functioned because of its stable and porous structure as well as large specific surface. To improve the gas sensing properties of Co3O4, ZnO nanoparticles were introduced to modify Co3O4 into the Co3O4/ZnO composites. The structure and properties of composite were characterized by XRD, FESEM, HRTEM and XPS analysis. Gas-sensing experiments reveal that the hollow Co3O4/ZnO composite not only exhibits high sensitivity that is 4 times higher than that of pristine Co3O4, rapid response and recovery but also has excellent selectivity and relatively low operating temperature to 10 ppm HCHO. Such excellent performance may be attributed to the hollow hierarchical structure and the formation of p-n heterojunctions at interface between both oxides.

A network structure of PANI / SnO 2 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 SnO 2 . 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.

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.

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.

A smart sensor based on α-MoO 3 /PANI hybrids was fabricated by loading α-MoO 3 nanorods on polyethylene terephthalate (PET) thin film as a building framework and then the PANI was covered on the framework via in-situ chemical oxidation polymerization. The morphology and structure of the hybrids have been characterized by XRD, SEM, TEM and XPS etc. The sensor shows high sensitivity and good selectivity to triethylamine (TEA), and exhibits linear response to TEA concentration from 10 to 100 ppm at room temperature. The sensing mechanism of α-MoO 3 enhancing PANI response to TEA has also been discussed in detail, which is attributed to the well-defined morphology and formation of p-n heterojunctions at interface of hybrid. The study will open a new window for development of a high sensitive and portable sensor to online detect VOCs at room temperature.

We fabricated the PPy/WO 3 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 WO 3 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.

Sb-doped tungsten oxides have been synthesized successfully by a hydrothermal method without any surfactant at 120 °C for 24 h. The structure and morphology of product were examined by XRD and SEM. The sensing tests reveal that the enhancement to NO2 response by Sb doping is very significant compared to that reported in literatures. Especially, the highest response of 3.5 wt%-Sb doped WO3 exhibits 9 times higher than that of undoped sample. The transient responses of the sample to different concentrations of NO2 were also measured and modeled using L–H heterogeneous reaction mechanism. The mechanism of enhancing sensing performance is also discussed in detail, which attributed to the changes of material intrinsic defects and binding energies and has been confirmed by the room temperature PL and XPS spectra. The first-principle calculations indicate that the dopant as acceptor enter into tungsten oxide resulting in reduce in free electron concentration of system, which is in good agreement with the increase in resistance obtained from experiment measurements.

We report on the interfacial passivation mechanism in CdSe quantum dot-sensitized ZnO nanocrystalline thin film, where different sulfide semiconductors (such as ZnS and CdS) and sulfide ions are used to modify ZnO nanocrystalline thin film before deposition of CdSe quantum dots (QDs). It is noticed that the highest light-to-electric conversion efficiency of CdSe quantum dot-sensitized ZnO nanocrystalline thin film solar cell is attained up to 4.18 % after CdS interfacial modification. Meanwhile, a simple treatment of ZnO nanocrystalline thin film in Na2S solution can also increase the conversion efficiency of CdSe quantum dot-sensitized solar cell up to 3.45 %. The electron transfer and recombination processes occurred in the interface of QD-sensitized nanocrystalline thin films with and without the different interfacial modifications are detected by measuring intensity modulated photovoltage spectroscopy and electrochemical impedance spectroscopy of solar cells. These results indicate that adsorption of S2− ions on the surface active sites of ZnO nanoparticles is the main reason for the conversion efficiency improvement due to the interfacial passivation of sulfide semiconductors.

Photoelectrochemical (PEC) water splitting technology offers a sound strategy for the production of chemical energy using abundant solar energy. Herein, a ternary photoanode of SnO2/BiVO4/rGO was fabricated by plain chemical vapor deposition (CVD) and metal-organic decomposition followed by spin-coated rGO on the SnO2/BiVO4 junction. The ternary photoanode yields the highest photocurrent density of 2.05 mA cm−2 at 1.23 V vs. RHE, which is 3.73 times of the BiVO4 photoanode (0.55 mA cm−2). The incident photon-to-electron conversion efficiency (IPCE) of the ternary photoanode is 2.47 times that of the BiVO4 photoanode at 400 nm, and the onset potential exhibits a cathodic shift of ∼300 mV. This enhancement can be attributed to the formation of n-n heterojunctions between the SnO2 and BiVO4, and decoration of rGO on said heterojunctions because they synergistically improve the absorption of visible light, enhance the efficiency of charge separation , and accelerate electron transfer at the electrode/electrolyte interface.

The combination of semiconductor heterojunction with rGO is recognized to be a promising method to improve the sensing performance of gas sensor. The 3.7 wt% rGO-NiO-BiVO4 composite was synthesized successfully by a simple hydrothermal and metal organic decomposition method. The gas-sensing tests reveal that the highest response of the ternary composite is 4 times and 8 times higher than the rGO-NiO junction and the pure NiO, respectively, towards 2 ppm NO2 at 60 °C, and the ternary composite exhibits rapid response. Moreover, the composite exhibits the highest response to NO2 among all tested gases, such as CO, toluene, ethanol, NH3 and formaldehyde, that is, the composite towards NO2 has excellent selectivity. The improvement is attributed to the effective electron transfer at interface of heterojunction and the increase of surface area and surface defect due to rGO loading. The work has reference value for improving gas sensing performance of p-type semiconductor.

NO2 is a toxic gas that can cause photochemical smog, acid rain and ozone layer depletion. The reduced graphene oxide (rGO) decorated nanocomposites of semiconductor metal oxides (MOS) as sensing materials of NO2 sensors have received much attention. Here, BiVO4/Cu2O/rGO nanocomposite was successfully prepared by a facile solvothermal method and thermal reduction method. The gas-sensing test indicates that the response of optimum nanocomposite to 1 ppm NO2 is 8 times higher than the pure BiVO4 and 5 times higher than the p-n heterojunction of BiVO4/Cu2O, respectively at 60 °C operating temperature. The response time and recovery time also shortened compared to pure BiVO4 and BiVO4/Cu2O composite, and this composite has better stability for detection of NO2, which benefits from the superimposed effect of p-n heterojunction formation and rGO decoration. This work can provide reference for improving the sensing properties of metal oxide semiconductor composites for detection of NO2.

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.

We prepared a heterostructure hybrid of PANI and SnO 2 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 NH 3 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 NH 3 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 SnO 2 and PANI, and formation of p−n heterojunction at the interface in hybrid.

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 fo...

A facile and controllable one-step hydrothermal method to synthesize nanodisks and nanorods of zinc oxide with exposed different crystal facets of (0001), ( ${1}\bar {1}{00) ,}$ ( ${01}\bar {1}{0)}$ , and ${ (10}\bar {1}{0)}$ has been realized. It was found that the average percentage of exposed (0001) crystal facets follows the order of nanodisks > nanorods-1 > nanorods-2 > nanorods-3, while the average percentage of exposed ( ${1}\bar {1}{00)}$ , ${(01}\bar {1}{0)}$ , and ( ${10}\bar {1}{0)}$ crystal facets decreases monotonically. The sensing tests to NO2 indicate that the nanodisks exhibit higher sensitivity. It has also been validated that the (0001) crystal facet has the highest surface energy and the lowest binding energy, which is considered to be the key factor of high gas-sensing by the calculations of density functional theory. This finding will open a new window to explore the relationship between gas-sensing and exposed facets and will be useful for designing gas-sensing materials with specifically exposed surfaces.

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.

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.

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.

Although the gas sensing properties of p-type semiconductors (such as Co3O4) generally are lower than those of n-type oxide semiconductors, high quality gas sensors can still be designed by various modified methods due to their distinctive surface reactivity. In the work, the rGO/Co3O4 composites with different formulations have been successfully synthesized by a facile hydrothermal reaction. The morphology, structure and composition of as-prepared composites were characterized by XRD, FESEM, Raman, TG, XPS spectrum and BET analysis, respectively. The sensing tests indicate that the 5 wt% rGO composite to toluene not only exhibits the highest response and excellent selectivity, but also has linear response in concentration lower 5 ppm, indicating the composite is a promising sensing material for detection of toluene. Furthermore, the mechanism of rGO enhanced composite gas sensing is also discussed in detail, which is attributed to rGO action in composite and the formation of p–p isotype heterojunction at the interface between rGO and Co3O4.

A novel ternary photoanode consists of semiconductor heterojunction (WO3/CdS) and co-catalyst (Co-Pi) was successfully designed and fabricated by hydrothermal, impregnation and photo-assisted deposition methods. The morphology and structure of material were characterized and the PEC properties of photoanode were systematically investigated. The results indicate that the heterojunction significantly extends the absorption range of visible-light and enhances the photocurrent density, and the onset potential shows a significant cathodic shift compared with pristine WO3 and CdS photoanodes. Moreover, the measured incident photon-to-current efficiency (IPCE) value exhibits a large enhancement as well. The mechanism of heterojunction and co-catalyst enhancing PEC performance also was discussed in detail in the work, which is attributed to effective separation of photogenerated electron and hole and timely transfer of the photogenerated holes accumulated at the electrode surface for water oxidation and has been confirmed by increase of carrier density and accelerating of carrier transfer from M − S plots, EIS and IMPS spectra.

The novel sensing materials of rGO decorated CdS/CdO heterojunction have been synthesized successfully for the first time by a facile one-step hydrothermal method combining with calcination treatment. The structure, morphology, composition, and specific surface of the composite were characterized by XRD, SEM, XPS spectra and BET analysis, respectively. The gas sensing properties to 2 ppm of NO2 were examined. The results show that the 4.0 wt % rGO/CdS/CdO composite not only exhibits 9 times higher response and 4.75 times lower detection limit than that of pristine CdS, but also owns rapid response and recovery, indicating the composite is a promising novel sensing material for detecting of low-concentration NO2. The enhancement mechanism was also discussed in detail, which benefits from the formation of the heterojunctions between CdS and CdO and the decoration of rGO. rGO also as an efficient electron mediator increases gas adsorption and accelerates electron transfer of the composite.

The development of new materials forever is research front for various application fields, otherwise becomes making bricks without straw. A novel sensing material of rGO decorated W-doped BiVO4 was synthesized for the first time by metal organic decomposition combined with hydrothermal methods for detection of trimethylamine (TEA) vapor. The structure and morphology of material were characterized by spectroscopy techniques. The sensing properties of sensor to TEA were measured. The results showed that the 6WBiVO4/rGO5 composite exhibits response of 12.8 and response time of 16 s, which is 5.12 times higher and 2.75 times lower than that of BiVO4, respectively. Moreover, the sensor shows excellent selectivity and stability to 20 ppm TEA at 135 °C. The enhancement is ascribed to the increase of electron density, enhancement of specific surface and accelerating of electron transfer for BiVO4 due to W doping, rGO decoration and formation of heterojunctions.