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SnO 2 quantum wire/reduced graphene oxide nanocomposites (SnO 2 QW/rGO) were synthesized by a facile one-step hydrothermal method with rGO and SnCl 4 . 5H 2 O as the precursors. The SnO 2 QW/rGO nanocomposites well-dispersed in ethanol were spin-coated onto ceramics substrates to construct chemiresistive gas sensors. The H 2 S-sensing isotherm curves were obtained based on the real-time response curves of the SnO 2 QW/rGO gas sensors when operated at different temperatures ranging from 30 °C to 70 °C, from which the adsorbing/sensing performance of the specific materials were extracted and the kinetic parameters (such as response rate constant k and activation energy E a ) of the sensing-materials were quantitatively modeled. The H 2 S-sensing mechanism was found to follow Langmuir isotherm and pseudo-first-order model. Compared to pure SnO 2 QW sensors, the SnO 2 QW/rGO gas sensors exhibited higher sensitivity and faster response rate toward H 2 S, which was attributed to its lower activation energy. The SnO 2 QW/rGO gas sensors can even detect H 2 S at room temperature, highly attractive for the detection of H 2 S detection with lower power consumption. [ABSTRACT FROM AUTHOR]

Abstract: Pure and Cu-doped SnO2 thin films are prepared by aerosol-assisted chemical vapor deposition for H2S detection. Three doping routes are used to prepare thin films with different structures. The response and recovery characteristics are analyzed. The thin film is able to completely recover between testing cycles at room temperature and has the response and recovery times of 60 and 90sec, respectively. The selectivity test illustrates that the film is only sensitive to H2S and acts no response to CO and CH4 at all. The relationships between response and gas concentration as well as operating temperature are also discussed. [Copyright &y& Elsevier]

Abstract: SnO2 thin films are prepared by sol–gel spin-coating technique and different cooling rates are employed in annealing process. The influences of cooling rate and re-annealing on gas sensing characteristics of thin films are investigated, concluding slow cooling rate benefits gas sensing characteristics. The variation of oxygen vacancies density is found to be responsible for the conclusions. Thus, a model of oxygen vacancy distribution is proposed based on the formation and dynamics of vacancies. The diffusion equation is established on the basis of diffusion and exclusion of vacancies in cooling process and the steady state solution reveals a gradient distribution of oxygen vacancies, which exhibits a trend that vacancies accumulate near the surface. Combining the solution of distribution equation and Schottky model, the quantitative expressions of film resistance (R/R 0) and response (S) are formulated. The validity and limitation of the model are also discussed. [Copyright &y& Elsevier]

Abstract: SnO2 thin films on alumina and silicon substrates are prepared by sol–gel technique using dip-coating method. The films are sensitive to H2S gas and the one on alumina exhibits response of 81 at low concentration of 3.4ppm. The sensor response and film conductance are measured in the atmosphere with different reducing gas concentration and furthermore the relationship between film conductance variation and gas concentration is summarized as a linear curve in a logarithmic coordinate with the slope of 1/2, coinciding with the power law. Based on this relationship, the modification of the gas diffusion theory is performed by substituting the former linear assumption with a new one. The modified expression is validated by correlations of experimental sensor response versus film thickness and gas concentration. The probable application of the modified expression on explaining response of thin films to various reducing and oxidizing gases is proposed. [Copyright &y& Elsevier]