Study On Syntherize And Gas-sensing Properties Of WO₃、In₂O₃with Structure Of Eggshell Membrane

In this paper, the general classifications, the development progresses and the applications of gassensor are generally introduced, then the biological synthesis process of materials are simply summarized,the preparation of WO₃and In₂O₃nano-materials and their applications in gas sensor are reviewed. Themain points of this paper are as follows:1. The treatment process of eggshell membrane （ESM） are firstly exploratory, two differenttreatment process are researched to choose a scientific, economical and environmental protection way. TheWO₃material with hierarchical structure of eggshell membrane （ESM） was successfully prepared usingeggshell membrane as template by an aqueous soakage technique followed by calcination treatment, thecontrast sample are prepared by thermal decomposition of ammonium tungstate. The gas sensor wasprepared by using these as-prepared materials and gas sensitive properties were measured with stationarystate gas distribution method. The research shows that materials prepared with two different methods showthe same diffraction peaks which can be indexed to monoclinic WO₃, sample treated with the aqueoussoakage technique can successfully replicated the interwoven meshwork conformation exactly, while thecontrast sample prepared by thermal decomposition have no special structure. The average crystallite sizesare about17nm of template samples and29nm of non-ESM template one according Scherrer’s equation. Itshows that the introduction of EMS can reduce the crystallite size effectively. The gas sensing researchshows that the sensitivity of gas sensor prepared with material with hierarchical structure of ESM to H₂S(volume ratio of30×10^-6) reaches89at200°C with a short response time of less than2s.2. A series of WO₃materials were synthesized with different treatment processes by using the ESM as template, the phase composition and microstructure of the prepared nano-material werecharacterized by XRD, SEM, and TEM, the gas sensing properties were then measured. The results showthat calcination temperature is crucial for the synthesis, replication of ESM networks can be obtained byWO₃only when the calcination temperature is below700°C, the hierarchical structure cannot be replicatedas the calcination temperature increasing to800°C. The gas sensing properties show that the sensitivity ofmaterial calcinated at700°C to30ppm H₂S reaches687with a short response time less than1s whichresult from the special surface texture. On contrast, all samples under different precursors replicate thenetworks of ESM successfully and exhibit hierarchical porous structure. The differences are that fibers ofsample prepared with lower concentration precursor look like thin and smooth and the whole structureexhibits porous conformation obviously which may be benefit to the gas diffusion and be good at thesensing properties. The gas sensing test indicated that the response decreased with the increase ofconcentration. Besides, the impact of operating temperature to recover time was also studied and someplausible mechanisms are proposed.3. A series of In₂O₃with hierarchical structures of ESM were fabricated by controlling thesynthesis condition of pH, immersing time and calcined temperature. The phase composition andmicrostructure of the prepared nano-material were characterized by XRD, SEM, and TEM. The resultsshow that all samples show the same diffraction peaks which can be indexed to cubic In₂O₃the hierarchicalstructure cannot be replicated as the calcination temperature increasing to800°C, the fibers are thinnerunder the condition of precursor with lower pH value and the fibers are no longer smooth with the increaseof immersing time. At last, the plausible mechanism was discussed according to some literatures.