Preparation Of Noble Metals/TiO₂Photocatalyst By Atmospheric-pressure Cold Plasma

TiO2, as the medium of solar energy conversion, is regarded as the most promisingphotocatalytic materials. However, the Optical generated electron-hole recombination rateresults in low photocatalytic efficiency, which limiting its practical application. To overcomethe problem, noble metals(Ag, Au, Pt, Pd) were widely adopted to modify TiO2surface todecrease electronic-hole recombination rate, consequently improving the photocatalyticefficiency of TiO2. At the same time, the preparation of TiO2and its modification methods arealso affect the TiO2photocatalytic efficiency. As a result, people began to look for effectivepreparation methods to improve the performance of TiO2, the plasma technology has openedup a new field at material preparation process.In the paper, The metal ion/TiO2presomas were prepared by a conventionalimpregnation method, and atmospheric-pressure dielectric barrier discharge (DBD) coldplasma was employed to reduce metal ions, to fabricate noble metal/TiO2photocatalyst. Thesupported metal TiO2(M/TiO2) exhibited high photocatalytic activity due to small size andhigh dispersion of metal particles, and the enhanced metal-support interaction. XRD, TEM,BET and XPS were used to characterize the M/TiO2photocatalyst. Its photocatalytic activitywas investigated by simulated pollutants methylene blue solution(MB), Results showed that:1. the supported Ag ions had been completely reduced to their metallic states after treatmentby atmospheric pressure cold plasma. The Ag surface plasmon peak became narrower andshifted to shorter wavelengths when the discharge voltage was increased, which indicated adecrease in size and size distribution of the Ag nanoparticles. The average particle size of Agwas determined to be7.4nm at36kV, and the Ag/TiO2catalyst exhibited a high activity forMB degradation under visible light (λ≥420nm).2. Compared with thermal reduction, themean particle size of Pt (1.7nm) reduced by DBD plasma was much smaller and that Ptparticles were better dispersed. In addition, The highest apparent rate constant was obtainedwhen the Pt content was0.5wt%. This was much lower than that prepared by conventionalmethods (around1-1.5wt%)3. Pd nanoparticles prepared by atmospheric-pressure coldplasma was partially crystallized decorated on TiO2. As a result of the partially crystallized Pdnanoparticles, the transfer of photogenerated electrons from TiO2to Pd was facilitated,thereby enhancing the photocatalytic performance of Pd/TiO2.Based On the above research work, XPS, XRD and OES spectra were used to analyzethe mechanism for reduction of noble metal ions by atmospheric-pressure DBD cold plasma. Results show that: neither the commonly believed atomic hydrogen (H) radicals nor energeticelectrons were the reducing agent in this study, and excited-state H2molecules were thoughtto be the reducing agent in the work. Furthermore, non-noble metal copper ions were reducedsuccessfully by atmospheric-pressure DBD cold plasma.