Hexagonal WO_3 nanorods were synthesized through a facile hydrothermal method. The nanorods properties were investigated by scanning electron microscope（SEM）, transmission electron microscope（TEM）, energy dispersi...Hexagonal WO_3 nanorods were synthesized through a facile hydrothermal method. The nanorods properties were investigated by scanning electron microscope（SEM）, transmission electron microscope（TEM）, energy dispersive spectroscopy（EDS）, and x-ray diffraction（XRD）. The NO_2-sensing performances in terms of sensor response, response/recovery times and repeatability at room temperature were optimized by varying the heat treatment temperature of WO_3 nanorods. The optimized NO_2sensor（400-℃-annealed WO_3 nanorods） showed an ultra-high sensor response of 3.2 and short response time of 1 s to 5-ppm NO_2. In addition, the 400-℃-annealed sample exhibited more stable repeatability.Furthermore, dynamic responses measurements of annealed samples showed that all the annealed WO_3 nanorods sensors presented p-type behaviors. We suppose the p-type behavior of the WO_3 nanorods sensor to be that an inversion layer is formed in the space charge layer when the sensor is exposed to NO_2 at room temperature.Therefore, the 400-℃-annealed WO_3 nanorods sensor is one of the most energy conservation candidates to detect NO_2 at room temperature.展开更多
Density functional theory （DFT） calculations are employed to explore the NO2-sensing mechanisms of pure and Ti-doped WO3 （002） surfaces. When Ti is doped into the WO3 surface, two substitution models are considere...Density functional theory （DFT） calculations are employed to explore the NO2-sensing mechanisms of pure and Ti-doped WO3 （002） surfaces. When Ti is doped into the WO3 surface, two substitution models are considered： substitution of Ti for W6c and substitution of Ti for Wsc. The results reveal that substitution of Ti for 5-fold W forms a stable doping structure, and doping induces some new electronic states in the band gap, which may lead to changes in the surface properties. Four top adsorption models of NO2 on pure and Ti-doped WO3 （002） surfaces are investigated： adsorptions on 5-fold W （Ti）, on 6-fold W, on bridging oxygen, and on plane oxygen. The most stable and likely NO2 adsorption structures are both N-end oriented to the surface bridge oxygen Olc site. By comparing the adsorption energy and the electronic population, it is found that Ti doping can enhance the adsorption of NO2, which theoretically proves the experimental observation that Ti doping can greatly increase the WO3 gas sensor sensitivity to NO2 gas.展开更多
SnO2 nano particles with various Pd-doping concentrations were prepared using a template-free hydrothermal method.The effects of Pd doping on the crystal structure,morphology,microstructure,thermal stability and surfa...SnO2 nano particles with various Pd-doping concentrations were prepared using a template-free hydrothermal method.The effects of Pd doping on the crystal structure,morphology,microstructure,thermal stability and surface chemistry of these nano particles were characterized by transmission electron microscope,X-ray diffractometer and X-ray photoelectron spectroscope respectively.It was observed that Pd-doping had little effect on the grain sizes of the obtained SnO2 nano particles during the hydrothermal route.During thermal annealing,Pd-doping could restrain the growth of grain sizes below 500℃ while the grain growth was promoted when the temperature increased to above 700℃.XPS results revealed that Pd existed in three chemical states in the as-synthesized sample as Pd^0,Pd^2＋ and Pd^4＋,respectively.Pd^4＋ was the main state which was responsible for improving the gas-sensing property.The optimal Pd-doping concentration for better gas-sensing property and thermal stability was 2.0%-2.5% （mole fraction）.展开更多
Nanocomposites composed of SnO2 and CuO were prepared by hydrothermal method. The microstructures of obtained SnO2-CuO powders were characterized by X-ray diffraction, scanning electron microscopy, transmission electr...Nanocomposites composed of SnO2 and CuO were prepared by hydrothermal method. The microstructures of obtained SnO2-CuO powders were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and nitrogen adsorption-desorption test. The results show that the nanocomposites exhibited coral-like nanostructure, and the average crystalline size of SnO2 was 12 nm. The specific surface area of the four samples, SnO2- 0.2CuO, SnO2-0.5CuO, SnO2-1.0CuO and SnO2-2.0CuO are 72.97, 58.77, 49.72 and 54.95 m2/g, respectively. The gas sensing performance of the four samples to ethanol, formaldehyde and H2S was studied. The sensor of SnOa-0.5CuO exhibited high response to hydrogen sulfide （4173 to 10 ppm H2S, where ppm represent 10-6）, and low response to ethanol and formaldehyde. The good selectivity exhibited that the SnO2-0.5CuO nanocomposite can be a promising candidate for highly sensitive and selective gas-sensing material to H2S.展开更多
SnO2-reduced graphene oxide （SnO2-rGO） composites were prepared via a hydro-thermal reaction of graphene oxide （GO） and SnCI2·2H2O in the mixed solvent of ethylene glycol and water. During the redox reaction,...SnO2-reduced graphene oxide （SnO2-rGO） composites were prepared via a hydro-thermal reaction of graphene oxide （GO） and SnCI2·2H2O in the mixed solvent of ethylene glycol and water. During the redox reaction, GO was reduced to rGO while Sn2＋ was oxidized to Sn02, uniformly depositing on the surface of rGO sheets. The composites were characterized by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, thermogravimetric analysis （TGA）, infrared spectra analysis （IR） and transmission electron microscopy （TEM）, respectively, and their gas sensing properties were further investigated. Compared with pure SnO2 nanoparticles, the as-prepared SnO2-rGO gas sensor and response-recovery time to ethanol and H2S at responding and low cost SnO2-rGO gas sensor could showed much better gas sensing behavior in sensitivity ow concentrations. Overall, the highly sensitive, quick- be potentially applied in environmental monitoring area.展开更多
Low-concentration acetone detection is of great importance for acetone sensor in the fields of environmental protection and noninvasive diagnosis.In this work,mesoporous Fe_(2)O_(3)/Cr_(2)O_(3)n-p heterojunctions were...Low-concentration acetone detection is of great importance for acetone sensor in the fields of environmental protection and noninvasive diagnosis.In this work,mesoporous Fe_(2)O_(3)/Cr_(2)O_(3)n-p heterojunctions were constructed for efficient improvement of low-concentration acetone gas sensing.The gas-sensing results indicated that the mesoporous Fe_(2)O_(3)/Cr_(2)O_(3)composites with a significantly large specific surface area exhibited significantlyenhanced acetone gas-sensitive performance compared to pure Fe_(2)O_(3).The Fe_(2)O_(3)/Cr_(2)O_(3)composites demonstrated a high response,good selectivity and excellent stability over200 days to 10 ppm acetone at 220℃.And the theoretical detection limit was calculated to reach 0.285 ppm acetone.A feasible acetone sensing mechanism was proposed through electronic band structure and density functional theory.The improved low-concentration acetone sensing performance was due to the formed mesoporous Fe_(2)O_(3)/Cr_(2)O_(3)n-p heterojunctions with a large specific surface area.The Fe_(2)O_(3)/Cr_(2)O_(3)composites showed excellent acetone gas-sensitive performance,which could be a promising candidate for developing low-concentration acetone sensing devices at low working temperatures.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.60771019,61271070,and 61274074)the Tianjin Key Research Program of Application Foundation and Advanced Technology,China(Grant No.11JCZDJC15300)
文摘Hexagonal WO_3 nanorods were synthesized through a facile hydrothermal method. The nanorods properties were investigated by scanning electron microscope（SEM）, transmission electron microscope（TEM）, energy dispersive spectroscopy（EDS）, and x-ray diffraction（XRD）. The NO_2-sensing performances in terms of sensor response, response/recovery times and repeatability at room temperature were optimized by varying the heat treatment temperature of WO_3 nanorods. The optimized NO_2sensor（400-℃-annealed WO_3 nanorods） showed an ultra-high sensor response of 3.2 and short response time of 1 s to 5-ppm NO_2. In addition, the 400-℃-annealed sample exhibited more stable repeatability.Furthermore, dynamic responses measurements of annealed samples showed that all the annealed WO_3 nanorods sensors presented p-type behaviors. We suppose the p-type behavior of the WO_3 nanorods sensor to be that an inversion layer is formed in the space charge layer when the sensor is exposed to NO_2 at room temperature.Therefore, the 400-℃-annealed WO_3 nanorods sensor is one of the most energy conservation candidates to detect NO_2 at room temperature.
基金supported by the National Natural Science Foundation of China (Grant Nos. 60771019 and 60801018)Tianjin Key Research Program of Application Foundation and Advanced Technology, China (Grant No. 11JCZDJC15300)+1 种基金Tianjin Natural Science Foundation, China (Grant No. 09JCYBJC01100)the New Teacher Foundation of the Ministry of Education, China(Grant No. 200800561109)
文摘Density functional theory （DFT） calculations are employed to explore the NO2-sensing mechanisms of pure and Ti-doped WO3 （002） surfaces. When Ti is doped into the WO3 surface, two substitution models are considered： substitution of Ti for W6c and substitution of Ti for Wsc. The results reveal that substitution of Ti for 5-fold W forms a stable doping structure, and doping induces some new electronic states in the band gap, which may lead to changes in the surface properties. Four top adsorption models of NO2 on pure and Ti-doped WO3 （002） surfaces are investigated： adsorptions on 5-fold W （Ti）, on 6-fold W, on bridging oxygen, and on plane oxygen. The most stable and likely NO2 adsorption structures are both N-end oriented to the surface bridge oxygen Olc site. By comparing the adsorption energy and the electronic population, it is found that Ti doping can enhance the adsorption of NO2, which theoretically proves the experimental observation that Ti doping can greatly increase the WO3 gas sensor sensitivity to NO2 gas.
基金Projects(60806032,20975107) supported by the National Natural Science Foundation of ChinaProject(2009R10064) supported by the Scientific Research Foundation for the Returned Overseas Chinese Scholars of Education Ministry,China+2 种基金 Project(2009R10064) supported by "Qianjiang Talent Program"Projects(2009A610058,2009A610030) supported by the Ningbo Natural Science Foundation,ChinaProject supported by K.C.WONG Magna Fund in Ningbo University,China
文摘SnO2 nano particles with various Pd-doping concentrations were prepared using a template-free hydrothermal method.The effects of Pd doping on the crystal structure,morphology,microstructure,thermal stability and surface chemistry of these nano particles were characterized by transmission electron microscope,X-ray diffractometer and X-ray photoelectron spectroscope respectively.It was observed that Pd-doping had little effect on the grain sizes of the obtained SnO2 nano particles during the hydrothermal route.During thermal annealing,Pd-doping could restrain the growth of grain sizes below 500℃ while the grain growth was promoted when the temperature increased to above 700℃.XPS results revealed that Pd existed in three chemical states in the as-synthesized sample as Pd^0,Pd^2＋ and Pd^4＋,respectively.Pd^4＋ was the main state which was responsible for improving the gas-sensing property.The optimal Pd-doping concentration for better gas-sensing property and thermal stability was 2.0%-2.5% （mole fraction）.
基金financially supported by the National Natural Science Foundation of China (No. 51072141)the scientific research projects of Education Department of Hubei province (D20141503)the President Foundation of Wuhan Institute of Technology (No. 2014029)
文摘Nanocomposites composed of SnO2 and CuO were prepared by hydrothermal method. The microstructures of obtained SnO2-CuO powders were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and nitrogen adsorption-desorption test. The results show that the nanocomposites exhibited coral-like nanostructure, and the average crystalline size of SnO2 was 12 nm. The specific surface area of the four samples, SnO2- 0.2CuO, SnO2-0.5CuO, SnO2-1.0CuO and SnO2-2.0CuO are 72.97, 58.77, 49.72 and 54.95 m2/g, respectively. The gas sensing performance of the four samples to ethanol, formaldehyde and H2S was studied. The sensor of SnOa-0.5CuO exhibited high response to hydrogen sulfide （4173 to 10 ppm H2S, where ppm represent 10-6）, and low response to ethanol and formaldehyde. The good selectivity exhibited that the SnO2-0.5CuO nanocomposite can be a promising candidate for highly sensitive and selective gas-sensing material to H2S.
基金supported by the University of Science and Technology BeijingNational Center for Nanoscience and Technology Beijingthe National Basic Research Program of China (No.2007CB714304)
文摘SnO2-reduced graphene oxide （SnO2-rGO） composites were prepared via a hydro-thermal reaction of graphene oxide （GO） and SnCI2·2H2O in the mixed solvent of ethylene glycol and water. During the redox reaction, GO was reduced to rGO while Sn2＋ was oxidized to Sn02, uniformly depositing on the surface of rGO sheets. The composites were characterized by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, thermogravimetric analysis （TGA）, infrared spectra analysis （IR） and transmission electron microscopy （TEM）, respectively, and their gas sensing properties were further investigated. Compared with pure SnO2 nanoparticles, the as-prepared SnO2-rGO gas sensor and response-recovery time to ethanol and H2S at responding and low cost SnO2-rGO gas sensor could showed much better gas sensing behavior in sensitivity ow concentrations. Overall, the highly sensitive, quick- be potentially applied in environmental monitoring area.
基金financially supported by the National Natural Science Foundation of China(Nos.62374154 and12374128)the National Key R&D Program of China(Nos.2022YFB3903200 and 2022YFB3903203)
文摘Low-concentration acetone detection is of great importance for acetone sensor in the fields of environmental protection and noninvasive diagnosis.In this work,mesoporous Fe_(2)O_(3)/Cr_(2)O_(3)n-p heterojunctions were constructed for efficient improvement of low-concentration acetone gas sensing.The gas-sensing results indicated that the mesoporous Fe_(2)O_(3)/Cr_(2)O_(3)composites with a significantly large specific surface area exhibited significantlyenhanced acetone gas-sensitive performance compared to pure Fe_(2)O_(3).The Fe_(2)O_(3)/Cr_(2)O_(3)composites demonstrated a high response,good selectivity and excellent stability over200 days to 10 ppm acetone at 220℃.And the theoretical detection limit was calculated to reach 0.285 ppm acetone.A feasible acetone sensing mechanism was proposed through electronic band structure and density functional theory.The improved low-concentration acetone sensing performance was due to the formed mesoporous Fe_(2)O_(3)/Cr_(2)O_(3)n-p heterojunctions with a large specific surface area.The Fe_(2)O_(3)/Cr_(2)O_(3)composites showed excellent acetone gas-sensitive performance,which could be a promising candidate for developing low-concentration acetone sensing devices at low working temperatures.
