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Abstract In this work, hollow MoO 3 microcages were triumphantly synthesized using a facile hydrothermal method without any template, and a possible growth mechanism of this microstructure arising from the co-effect of inside-out Ostward-ripening mechanism and the acidic etching was speculated. Subsequently, gas sensor based on such MoO 3 with hollow characteristic was fabricated to investigate the gas-sensing properties for ethanol as compared to solid MoO 3 polyhedrons. It was found that the hollow cages exhibited lager ethanol gas response than that of solid polyhedrons. The enhanced sensing behavior may originate from its unique hollow structures, leading to sufficient sensing reaction on the surface as well as abundant gas diffusion. Graphical abstract The hollow MoO 3 microcages were successfully synthesized via a simple hydrothermal method without any template. Such hollow structure based sensor presented enhanced gas response to ethanol than that of solid MoO 3 polyhedrons based sensor. The hollow nature led to sufficient sensing reaction on the surface as well as abundant gas diffusion. Image 1 Highlights • Hollow MoO 3 microcages were successfully synthesized. • The gas sensor based on the MoO 3 presented enhanced gas response to ethanol. • The hollow structure of the MoO 3 cages enhanced surface sensing reaction. [ABSTRACT FROM AUTHOR]

Recently, spinel cobalt oxide (Co 3 O 4 ) structure has been widely investigated due to its excellent sensitivity towards various noxious gases and good response/recovery speed at low concentration. In this work, we designed and synthesized two kinds of different Co 3 O 4 micro-structure (cube and octahedron) with a similar size. After fabricating them into gas sensors, we found that the crystal plane structure of Co 3 O 4 has an important effect on its gas sensing performance. Furthermore, the {111} planes of Co 3 O 4 may be more sensitive than {100} planes to various testing gases. Co 3 O 4 octahedrons micro-structure exhibits an excellent sensitivity (about 12.6), good response/recovery speed and cycling stability (no decline even after 2 days) under 50 ppm ethanol gases at working temperature of 200 °C. As such, thisCo 3 O 4 octahedrons micro-structure is a promising candidate for a high-performance gas sensing material. [ABSTRACT FROM AUTHOR]

Composed of the heart, cardiac valves and blood vessels, the blood circulation system can manage the aggregation and the movement of the blood regularly and efficiently. Due to the analogical fluidity of the charge carrier and the blood, such system may act as the inspiration to design the advanced gas-sensing material. As a proof-of-concept, firstly, the porous WO 3 monomer was synthesized and recombined with the one-dimensional NiO monomer through the P-N junction to construct a similar structure. Subsequently, a series of gas-sensing tests towards the ethanol were measured. The obtained result indicates this nature-inspired nanocomposite indeed shows an enhanced gas-sensing property towards the ethanol, testifying the rationality of our design. [ABSTRACT FROM AUTHOR]

The NiO nanoflowers were prepared by a facile surfactant assisted hydrothermal method using Ni(NO 3 ) 2 –6H 2 O or NiCl 2 –6H 2 O as precursor compound. The microstructure of the samples was characterized by SEM and XRD. The gas sensing properties of the NiO nanoflowers toward ethanol was also investigated. The results show that surfactant plays a key role in the synthesis of flower-like NiO. The NiO nanoflowers show excellent sensing performances to ethanol gas. This morphology holds substantial promise for applying NiO as a potential gas sensing material for future sensor application. [ABSTRACT FROM AUTHOR]

In this paper, WO 3 ·H 2 O with different nanostructures from 0D to 3D were successfully synthesized via a simple yet cost-effective hydrothermal method with the assistance of surfactants. The structures and morphologies of products were investigated by XRD and SEM. Besides, we systematically explained the evolution process and formation mechanisms of different WO 3 ·H 2 O morphologies. It is noted that both the kinds and amounts of surfactants strongly affect the formation of WO 3 ·H 2 O crystals, as reflected in the tailoring of WO 3 ·H 2 O morphologies. Furthermore, the gas sensing performance of the as-prepared samples towards methanol was also investigated. 3D flower-like hierarchical architecture displayed outstanding response to target gas among the four samples. We hoped our results could be of great benefit to further investigations of synthesizing different dimensional WO 3 ·H 2 O nanostructures and their gas sensing applications. [ABSTRACT FROM AUTHOR]

Hollow spheres are usually fabricated by hard template methods or soft template methods with soft surfactants, which is quiet tedious and time-consuming. In this paper, NiO hollow spheres with fluffy surface were successfully synthesized by a facile hydrothermal method and subsequent calcination, where bubbles acted as the template. NiO hollow spheres exhibited excellent gas sensing performances, which results from its hollow structure and high specific surface area. In addition, a possible evolution mechanism of NiO hollow spheres was proposed based on experimental results. [ABSTRACT FROM AUTHOR]

Abstract: WO3 H2O with different morphologies were synthesized through hydrothermal method by adding different surfactants. The effect of surfactants on tailing morphology was investigated through XRD and SEM analyses in detail and the possible formation mechanism was discussed. Furthermore, the gas-sensing performances of obtained samples to ethanol were investigated. The results revealed that the WO3 H2O with the hierarchical architectures assembled by nanosheets shows the highest response to ethanol among four kinds of the nanostructures WO3. These results on the preparation, mechanism and gas sensing properties of WO3 H2O nanostructures hold great potential for the syntheses of oxide materials with novel nanostructures and their applications. [Copyright &y& Elsevier]

Abstract: We successfully synthesized variant hierarchical assembled flower-like SnO2 via a simple hydrothermal technique and subsequent calcination. The structures and morphologies of the 3D nanostructures were investigated by means of powder X-ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM). The formation mechanism of these materials were proposed in detail. The gas-sensing performances of the as-prepared SnO2 were investigated towards ethanol. It is noted that the flower-sheet SnO2 sensor displayed particular response to the target gas, rendering SnO2 as a potential gas-sensing material for a broad range of future sensor applications. [Copyright &y& Elsevier]

Abstract: NiO nanowires with high aspect ratio and dispersive distribution have been synthesized by a hydrothermal reaction of NiCl2 with Na2C2O4 and H2O in the simultaneous presence of ethylene glycol (EG) and polyethylene glycol (PEG). Then the products were obtained by the subsequent annealing at 400°C in air. The effect of –OH from EG and –O– from PEG in the formation of nanowires was discussed. And the gas sensing properties of the as-prepared NiO nanowires toward ethanol were investigated. A novel formation mechanism of nanowires was presented and the NiO nanowires were proved to have an excellent gas sensing performance. [Copyright &y& Elsevier]

Based on the first-principles method of density functional theory (DFT), the adsorption properties, bond strength and electronic structure of two sulfur-containing compounds (H 2 S and CH 3 SH) in oil and natural gas were analyzed by means of adsorption energy, partial density of states (PDOS) and charge difference density. The adsorption energy of H 2 S and CH 3 SH molecules on the LB site of Fe (110) surface is the lowest. Their adsorption energies are −2.88 eV and −3.13 eV, respectively. When the H 2 S symmetry axis is perpendicular to the surface, the S–H bond is easy to break. The generated S atom is firmly adsorbed on the hollow site. The results of partial density of states show that the hybrid conjugation peaks of the three adsorbed species appear on the substrate surface, and new bonds are formed between the surface molecules and the iron substrate. The charge around the three adsorbates is redistributed, and the order of interaction size between these molecules and the Fe (110) surface is S > CH 3 SH > H 2 S. This also shows that in oil and gas, H 2 S, CH 3 SH and S atoms generated after dissociation are very easy to adsorb on the surface of iron pipes, which directly affects the accuracy of the determination of sulfide gas in oil and natural gas. • The adsorption of H 2 S and CH 3 SH on four highly symmetric sites of Fe (110) surface is calculated. • The adsorption configurations of hydrogen sulfide and methyl mercaptan on Fe (110) surface were constructed. • The adsorption structure, adsorption energy, bonding and the change of electronic structure were discussed in detail. • The H 2 S molecules adsorbed horizontally are easy to dissociate. [ABSTRACT FROM AUTHOR]

Abstract: The structural, adsorptive and electronic properties of H2 adsorption on SnO2–F (110) surface are investigated by first-principles calculation. The results show that the F-doped (110) surface is more reducible than that of undoped SnO2 surfaces, which is mainly attributed to formation of the surface states and larger charges transfer between H2 molecule and the F-doped (110) surface. This simulation mechanism may provide the instruction to further explore the SnO2-based sensing materials. [Copyright &y& Elsevier]

Abstract: New morphologies often play an important role in deciding the properties of nanomaterials. In current study, we synthesize various types of low dimensional SnO2 nanostructure materials using a simple hydrothermal process. We find that the SnO2 nanorods, nanowires and nanosheets show higher gas response as well as lower operating temperature as compared to that of nanospheres. In addition, the obtained nanosheets SnO2 are found to show best sensing performances owing to the largest surface area and porous structure providing many quick passages to absorb and desorb gas, suggesting that the gas sensing properties of nanocrystals can be significantly improved by tailoring the shape and morphology of nanocrystals. Such an unexpected morphology holds substantial promise for rendering low dimensional nano-SnO2 as a potential gas sensing material for future sensor application. [Copyright &y& Elsevier]

Abstract: In this work we report microstructure and gas sensing property of the pristine SnO2 and (Ti,Sn)O2 solid solutions prepared via the hydrothermal method. Of all the examined volatile organic compound gases, the (Ti,Sn)O2 solid solution exhibits somewhat lower gas response as compared to that of pristine SnO2. Further, we perform a first principles calculation to establish a surface model for solid solution and estimate its atomic configuration. The tightness of Ti6C(Sn6C)O2C bond and high oxygen vacancy formation energy for solid solution suggest that less amount of pre-adsorbed oxygen was formed on the surface, ultimately resulting in sensing performance weakening. [Copyright &y& Elsevier]

Abstract: The structural, adsorptive and electronic properties of CO adsorption on TiO2 are investigated by the first principles calculations with special focus on three experimentally confirmed facets, namely (001), (100) and (101) surfaces, respectively. Calculation results predict that CO adsorbed on Ti site is the most energetically favorable mode among three low index TiO2 surfaces. It is found that the (100) surface hold more benefit for CO adsorption than that of other surfaces, which is mainly attributed to significant change of the electronic property of adsorbed surface and large electrons transfer between CO molecule and the surface. Calculation results theoretically verify the experimental fact that highly oriented TiO2 enable exhibit distinct sensing performance. These findings render a careful synthesis of TiO2 films so as to form a high orientation of (100) facet, which will be primarily important for further enhance CO sensing performance of TiO2-based sensor. [Copyright &y& Elsevier]

Abstract: We report the microstructure and gas-sensing properties of La–TiO2 nanobelts prepared by the hydrothermal method. In particular, we make a comparison of the volatile organic compounds (VOCs) sensing properties between La–TiO2 nanobelts and La–TiO2 nanospheres. The results show that La–TiO2 nanobelts exhibit higher gas response as well as lower working temperature as compared to that of La–TiO2 nanospheres, suggesting that the gas sensing properties of nanocrystals can be significantly improved by tailoring the shape and the surface structure of nanocrystals. [Copyright &y& Elsevier]

Abstract: Most of volatile organic compounds (VOCs) are often harmful or even toxic for environment, which require in situ detection. Here, we demonstrate that the TiO2 additive can enhance significantly gas-sensing properties of the SnO2-based sensor to VOCs, independent of its content and the concentration of tested gases. The improved gas-sensing quantities of matter, i.e., maximum sensitivity, minimum gas concentration, optimal operating temperature, and response and recovery times, are found to satisfy the basic needs for a practical application, which renders the TiO2–SnO2 composite material promising for the development of sensor devices to VOCs. [ABSTRACT FROM AUTHOR]

We successfully synthesized MoO 3 hierarchical structures assembled with nanofibers and nanosheets via a hydrothermal method assisted with hexadecyl trimethyl ammonium bromide (CTAB) and polyvinyl pyrrolidone (PVP), respectively. Then, we characterized the structure and morphology of the as-synthesized samples by X-ray diffraction and scanning electron microscopy. We analyzed the formation process of the two structures and verified the effects of different dimensionality assembly units on their gas-sensing properties through gas sensing experiments. Remarkably, nanosheet-assembled hierarchical MoO 3 structures, which possess abundant semi-closed microreaction spaces, exhibited an enhanced gas response. The gas response (the ratio of test voltage in the air to test voltage in the target gas) of a nanosheet-assembled MoO 3 based-sensor to 400 ppm ethanol reached 32 at an operating temperature of 300 °C. While nanofiber-assembled hierarchical structures showed a shorter response (3.2s) and recovery time (2.4s), which was due to the faster gas and electronic diffusion rate of the nanofibers. MoO 3 hierarchical structures assembled by nanofibers and nanosheets have been synthesized under hydrothermal conditions assisted with CTAB and PVP, respectively. Nanofiber-assembled hierarchical MoO 3 structures demonstrate less response and recovery time than the other. However, sensors based on nanosheet-assembled structures exhibit a higher gas response. The differences in the above properties can be attributed to their different dimensionality assembly units. Image 1 [ABSTRACT FROM AUTHOR]

Nanorod-assembled flower-like ZnO was successfully synthesized using a simple hydrothermal method. The measurement results demonstrated that the ethanol sensing properties of the as-prepared ZnO nanostructure were improved once under UV illumination, with higher response and faster response-recovery speed as compared to that in dark condition. The sensing enhancement could be ascribed to the co-effect of the 3D ZnO nanostructure and UV irradiation. Specifically, the 3D framework constructed from 1D nanorods provided plenty of reaction sites and effective gas diffusion pathways. In addition, owing to photo-induced electron-hole pairs under UV irradiation, more energetically free carriers interacted with gas molecules, which accounted for the improvement in ethanol sensing behaviours. [ABSTRACT FROM AUTHOR]

The influence of transition metal (TM) atoms (Au, Ag) doping on the structure parameters and electronic properties of MoS 2 monolayer was studied based on DFT calculations. In order to realize the adsorption mechanism, the adsorption structures, adsorption energy, charge transfer, density of states (DOS), and electron density difference of water (H 2 O) molecule absorbed on two kinds of doped-MoS 2 monolayer were analyzed. The results show that the electronic properties of TM (Au, Ag) doped-MoS 2 monolayer have significantly changes and the chemical activity is obviously enhanced compared with the MoS 2 monolayer. Moreover, Au or Ag doped-MoS 2 monolayer both exhibits excellent adsorption capacity to H 2 O molecule and the processes of absorption both are chemical. The influence of transition metal (TM) atoms (Au, Ag) doping on the structure parameters and electronic properties of MoS 2 monolayer was studied based on DFT calculations. We found Au or Ag doped-MoS 2 monolayer exhibits excellent adsorption capacity to H 2 O molecule and the processes are chemical absorption. Image 1 • The effect of TM (Au, Ag) dopant on structural and electronic properties of MoS 2 monolayer were discussed in detail. • The adsorption performances of TM (Au, Ag) doped-MoS 2 monolayer to H 2 O were discussed in detail. • Theoretical studies have applied to analyze the gas sensing mechanism of TM (Au, Ag) doped-MoS 2 monolayer to H 2 O. [ABSTRACT FROM AUTHOR]

Cu 2 O microspheres with hollow and solid features were successfully prepared via a convenient liquid phase reducing method. Interestingly, we found that the discrepancy in morphology arose from a simply changing on the adding sequence of aqueous sodium dodecyl sulfate (SDS) and CuCl 2 with other conditions unchanged. Based on experimental results, the feasible formation mechanisms of both morphologies were deduced, where the relative concentration of SDS and CuCl 2 was a crucial factor that effect the resultant morphologies. In comparison with the solid microspheres, the hollow Cu 2 O exhibited superior gas sensing performance. The significant performance might ascribe to its unique hollow structure, contributing to plenty of active sites existed on both the inner and outer surface and unrestricted gas diffusion in the hollow microspheres. In this work, hollow and solid cuprous oxide microspheres were successfully synthesized by liquid phase reducing method and the gas sensing performance of the samples was investigated. In addition, we also explore the effect of the adding sequence of aqueous sodium dodecyl sulfate (SDS) and CuCl 2 on the resultant morphologies of Cu 2 O and propose the growth formation mechanism. Image 1 • Cu 2 O microspheres with hollow and solid features were successfully prepared. • The hollow structure exhibited superior gas sensing performance than the solid microspheres. • The adding sequence played a vital role on the morphology of materials. [ABSTRACT FROM AUTHOR]

Abstract To investigate the morphology and crystalline structure effect on the oxygen reduction reaction (ORR) electrocatalytic, in this work, α-MnO 2 nanowires, α-MnO 2 nanorods, β-MnO 2 nanowires and β-MnO 2 nanorods have been successfully synthesized via a hydrothermal process, and their microstructures and electrocatalytic activities were investigated for the ORR. Among the four different types of one-dimension (1D) MnO 2 , the α-MnO 2 nanowires exhibited significantly larger electrocatalytic property than the others, which may contribute to the special crystalline structure and larger specific surface area. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

Monoclinic scheelite BiVO 4 nanoplates have been prepared via a facile hydrothermal method with monoethanolamine as a surfactant. The obtained BiVO 4 nanoplates were characterized by XRD, SEM, Raman microscope and N 2 adsorption-desorption analysis. The BiVO 4 prepared with MEA is monoclinic scheelite plates which is composed of nanocrystallite with the average size of 100 nm. The sensors based on BiVO 4 nanoplates show good sensitivity to alcohols gases, especially to n-butanol. The sensitivity to 100 ppm n-butanol gas is 61.6 at 260 °C, and the sensors exhibit low sensitivity to xylene, formaldehyde and toluene. The BiVO 4 nanoplates could be a promising candidate for high selectivity and high sensitivity n-butanol gas-sening materials. [ABSTRACT FROM AUTHOR]

Nanosized tungsten disulfide (WS 2 ) sensitized titanium dioxide (TiO 2 ) was successfully prepared via a simple yet facile hydrothermal process. The nanocomposite exhibited a wide and intensive absorption in the visible light region of 400–700 nm, and may have a potential application as a visible photocatalyst. In addition, the sensitization mechanism of the nano-WS 2 was proposed to elaborate the wide visible light absorption of the WS 2 /TiO 2 nanocomposites. [ABSTRACT FROM AUTHOR]

Abstract: Unique assembled sphere-like WO3 architectures were successfully synthesized through a facile hydrothermal method in the presence of malic acid followed by subsequent heat treatment. We found that malic acid played a significant role in governing morphologies of WO3·xH2O precursors during hydrothermal process. A possible formation mechanism was also proposed in detail. Experimental results showed that the optimized hydrothermal precursor could be dehydrated to mixed composition of hexagonal and monoclinic WO3 with the unique sphere-like porous architecture after being annealed at 400°C for 2.5h. Besides, gas-sensing measurement indicated that the well-defined 3D assembled sphere-like architectures exhibited the highest sensor response to ethanol at the optimal temperature of 250°C among the samples. [Copyright &y& Elsevier]

Abstract: ZnO nanocrystals with various morphologies are synthesized via a simple and facile HMT assisted hydrothermal process. Here, HMT is introduced as a structure directing and assembling agent to controllable synthesis of ZnO architectures and the concentration of HMT play a critical role in producing such different ZnO morphologies. We find that the sandglass-like ZnO exhibit excellent sensing performances to the target ethanol gas owing to its largest amount of Zn-terminated ZnO (0001) polar surfaces, which can easily adsorb more oxygen species on the surface and therefore improve the gas-sensing performances of ZnO. Such an unexpected morphology holds substantial promise for rendering ZnO as a potential gas-sensing material for future sensor applications. [Copyright &y& Elsevier]

The detection of SF 6 decomposed gases is essential link for the fault diagnosis of gas-insulated switchgear (GIS). In this paper, the gas sensing properties of a new planar 2D material indium triphosphide (InP 3) had been proposed and studied towards four types of SF 6 decomposed gases (H 2 S, SO 2 , SOF 2 and SO 2 F 2) by DFT methods. The structural parameters, density of states and frontier molecular orbitals were calculated and analyzed via building the models of four adsorption systems. The simulation results of MoS 2 , graphene and InP 3 systems adsorbing four gas molecules were compared, and it was found that the InP 3 monolayer is a promising sensing material for detecting SF 6 characteristic gases. Desorption time of all InP 3 adsorption systems was investigated in various working temperature to evaluate its potential application in four main SF 6 decomposed gases detection. • First time InP 3 monolayer used for the adsorption performances of H 2 S, SO 2 , SOF 2 and SO 2 F 2 gases investigation. • The adsorption characteristics of MoS 2 , graphene and InP 3 systems to the four gas molecules were compared. • Desorption time of all adsorption systems in various working temperature was calculated. [ABSTRACT FROM AUTHOR]

Through Density functional theory and Boltzmann transport theory, the ideal strength, electronic structure, elastic constants and thermoelectric performance of cubic phase PbTe are investigated. When the compressive strain is applied, both band gap and Seebeck coefficient decrease, while the electrical conductivity, power factor, thermal conductivity and ZT increase. According to the ZT of PbTe, the thermoelectric performance of p type is superior to that of n type. The optimal ZT value of p type could reach 3.88 at 0.5% strain, while the optimal ZT value of n type could reach 3.05 at 2.0% strain. Compared to the thermoelectric performance without strain, the thermoelectric performance under strain could be significantly improved, indicating that the strain engineering could be an effective strategy to improve the thermoelectric performance of PbTe. [Display omitted] • The electronic structure of PbTe is calculated, including density of states (DOS), relaxation time, mobility of carrier and effective mass. • The thermoelectric property of p type is found to be significantly better than that of n type. • For n type, the largest ZT value of 3.05 could be obtained at 2.0% strain and 850 K. • For p type, the largest ZT value of 3.88 could be obtained at 0.5% strain and 850 K. • The strain engineering could be an effective strategy to improve the thermoelectric performance of PbTe. [ABSTRACT FROM AUTHOR]

It is essential to detect the characteristic gas products of SF 6 decomposition for fault diagnosis of gas-insulated switchgear (GIS). The model of Rh doped MoS 2 was built by Materials Studio software. The micro process of three SF 6 partial dissociation products (SO 2 , SOF 2 , SO 2 F 2) approaching the Rh–MoS 2 surface and reaching a stable state was simulated. The modification effect of Rh doped MoS 2 was studied by the key adsorption parameters such as the adsorption structure, bandgap, absorption energy, charge transfer, the total and partial density of states and electron density difference. As a result, the electrical property and chemical activity are significantly improved in comparison with the pristine MoS 2 monolayers by selecting the most stable Rh doping site. Simultaneously, it was found that Rh–MoS 2 monolayer had good selectivity and gas sensitivity to SO 2 and SOF 2 with chemical adsorption. It can also be proved by the desorption time. From the adsorption energy, the adsorption reaction of SO 2 F 2 is not strong, but the transferred charge is large. • Theoretical studies have applied to analyze the gas sensing mechanism of Rh-doped MoS 2 to SF 6. • The excellent adsorption performances of Rh–MoS 2 monolayer to SO 2 , SOF 2 and SO 2 F 2 were discussed in detail. • Rh–MoS 2 surface has a strong chemical adsorption effect on SO 2 and SOF 2 , weaker physical adsorption effect on SO 2 F 2. • Rh dopant can significantly improve the sensitivity and selectivity of MoS 2 materials. [ABSTRACT FROM AUTHOR]

In this work, gas-sensing materials based on Co 3 O 4 /Fe 2 O 3 nanocubes were prepared via a MOF hybrid-assisted approach with the aid of ion-exchange. Structural characterizations proved the as-prepared Co 3 O 4 /Fe 2 O 3 nanocubes possessed hollow porous structures. The formation mechanisms were also investigated. Gas-sensing measurements revealed that the Co 3 O 4 /Fe 2 O 3 nanocubes showed high response (R g /R a = 3.27) towards acetone, which was 3.06 times higher than that of Co 3 O 4 nanocubes (R g /R a = 1.07). The enhanced sensing mechanism of Co 3 O 4 /Fe 2 O 3 nanocubes were also discussed, which could be explained by synergistic effects aroused by the as-formed p-n heterojunctions and hollow porous structures that offered numerous diffusion channels and an additional modulation in resistance. Our studies shed a new light to design p-n naoncomposites by a facile MOF hybrid-assisted method. Moreover, the as-designed Co 3 O 4 /Fe 2 O 3 nanocubes have potential application for fabricating high performance acetone sensors. • A novel Co 3 O 4 /Fe 2 O 3 nanocubes were successfully prepared via a MOF hybrid-assisted approach. • Co 3 O 4 /Fe 2 O 3 nanocubes have potential application for fabricating high performance acetone sensors. • Our studies shed a new light to design arrays in-situ on sensor devices by a facile method. [ABSTRACT FROM AUTHOR]

Well-oriented Co 3 O 4 nanowire arrays were synthesized in-situ on Al 2 O 3 substrates via a simple hydrothermal method without seed layers. The phase structure and array morphology of Co 3 O 4 nanowire arrays were investigated by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It was revealed that the array density of Co 3 O 4 nanowire arrays could be controlled by the concentration of ammonium fluoride. The gas-sensing measurement revealed that the array structure on the surface of gas sensors exerted great impact on their performances. It was found the response value enhanced and then decayed with the increased array density of Co 3 O 4 nanowires. We concluded that the Co 3 O 4 nanowire arrays with moderate array density can possess highly exposed effective surface area to provide more pathways for gas diffusion than other samples. Our studies can provide a significant guidance on array design to fabricate high performance gas sensors. Moreover, the as-designed Co 3 O 4 nanowire arrays have potential application in trimethylamine (TEA) detection. • Co 3 O 4 nanowire arrays with different array density were fabricated without seed layers. • The response of Co 3 O 4 nanowires improved and then decayed with the increased array density. • Our studies can provide a significant guidance on array design to fabricate high performance gas sensors. [ABSTRACT FROM AUTHOR]

In this work, novel n-type heterostructures of ZnSnO 3 modified p-type Co 3 O 4 (Co 3 O 4 –ZnSnO 3) nanowire arrays were fabricated in-situ on flat alumina substrates via a simple hydrothermal method without seed layers. SEM and TEM characterizations revealed that the Co 3 O 4 nanowire arrays were fully covered by ZnSnO 3 nanosheets. The gas-sensing measurement revealed that the Co 3 O 4 –ZnSnO 3 composite arrays showed the highest response 5.57 (R g /R a) towards ethanol, which was 2.04 times higher than that of Co 3 O 4 nanowire arrays (R g /R a = 2.73). Meanwhile, the enhanced sensing mechanism of Co 3 O 4 –ZnSnO 3 composite arrays was also discussed, which could be explained by the special heterojunction structure arrays that offered an additional modulation in resistance. Our studies shed a new light to design p-n heterostructure arrays in-situ sensing device by a facile method. Moreover, the as-designed Co 3 O 4 –ZnSnO 3 composite arrays have potential application for fabricating high performance ethanol sensors. • Co 3 O 4 –ZnSnO 3 arrays were fabricated in-situ on alumina substrates without seed layers. • The Co 3 O 4 –ZnSnO 3 arrays showed the highest response towards ethanol than pristine Co 3 O 4. • The enhanced gas-sensing mechanism was ascribed to the p-n heterojunction structures. [ABSTRACT FROM AUTHOR]