چكيده به لاتين
Abstract:
In this research, ammonium phosphomolybdate nanostructures substituted by silver, nickel and silver/nickel, Ax(NH4)3-xPMo12O40.4H2O (x=Ag, Ni) with Keggin structure as a class of mixed metal oxides were prepared using facile and rapid microwave-assisted method in solid phase and also, mechanochemical reaction. In addition, mixed metal oxides nanostructures of Ag6Mo10O33, Bi2MoO6 and Bi2Mo3O12 were synthesized by mechanochemical procedure. Urea and acetamide were applied as promoter agent to direct reactions towards formation of nanostructures. The synthesized products were characterized by FT-IR, XRD, SEM, TEM, ICP, CHN, EDX, UV-Vis DRS and XPS techniques. To study gasochromic effect, films of the prepared polyoxometalates was prepared by their ultrasound dispersion in water, coating on the glass substrate and then, annealing at 70 °C. the gasochromic properties of these films were studied for sensing of H2S gas. A simple optical home-made set-up was designed and used to test gasochromic effect via monitoring light intensity variations passing through the samples as voltage variations based on their color change in exposure to H2S gas. Response factor and time were calculated for samples in coloration step in different gas concentrations from 5 to 100 mg.L-1 and the results compared. The results indicated the increase of response factor up to about 83-93% with reduction of response time up to about 38-12 s in coloration step. Bleaching step was performed using oxygen flow passed on H2O2 and the colored samples were turned to initial color. The repeatability of the gasochromic performance of the samples was also evaluated in several coloration-bleaching steps. A probable mechanism was proposed for gasochromic behavior of the synthesized smaples. Likewise, the effect of relative humidity (RH) was studied on the sensing response of samples in coloration step in constat gas concentration of 70 mg.L-1 at room temperature. The results showed that the coloration response factor of mixed salts of ammonium phosphomolybdate is approximately constant in RH levels up to 50% while in higher levels of RH, the coloration response decreases. The Bi2MoO6 compound with a layered structure tends to adsob high levels of humidity so that in hgiher RH level of 33% indicates greater reduction in coloration response.
Keywords: Mixed metal oxides, Nanostructure, Gasochromic, Mechanochemical reaction, Microwave, Polyoxometalate.
