Synthesis Of SiC/SiO₂ Nanocomposites And Basic Research On Its Application In Photocatalysis

With the rapid growth of the global economy,human beings are increasingly demanding energy.Hydrogen is regarded as the most ideal clean energy in the 21st century due to its high heat release efficiency,cleanliness and regenerability.So research on the hydrogen production performance of silicon carbide photolysis water has attracted the attention of many researchers.However,since photogenerated electrons and holes are easy to recombine during the procedure of Photolysis water,the quantum efficiency is low.Therefore,it is necessary to modify or compound silicon carbide to improve its photolysis performance.In this paper,SiC/SiO₂nanocomposites with core-shell structure were prepared by compounding silicon carbide with silicon dioxide to improve the photolysis water performance of silicon carbide.And the mechanism of the reaction process and the charge transport process in SiC/SiO₂nanocomposites were explored.In this paper,SiC/SiO₂nanocomposites with different carbon-to-silicon ratio and different particle size were prepared.The composition,structure and morphology of SiC/SiO₂nanocomposites were analyzed by XRD,SEM,TEM and optical microscopy.The reaction mechanism was explored and the photocatalytic hydrogen production performance was characterized by gas chromatography.The fluorescence lifetime was characterized by transient fluorescence spectrometer.Main conclusions are as follows:The reaction mechanism of SiC/SiO₂nanocomposites was studied.The study found that because of the softening of amorphous silica at high temperatures during the reaction,the amorphous carbon formed by carbonization of PVP can fully contact with silica and undergo liquid-solid reaction in situ to form a core-shell structure material of silicon carbide-coated silica.The effects of different carbon-to-silicon ratios,different silicon sources and silicon removal on the photocatalytic properties of the materials were investigated.The study found that in the samples prepared by using 50-100nm,200nm and 500nm silicon dioxide as silicon sources,the photolysis performance first increases and then decreases with the increase of carbon-to-silicon ratio.When the ratio of carbon to silicon is 4:1,the photolysis performance is the best.The sample prepared by using 2?m silica as the silicon source has the best photohydrolysis performance of carbon to silicon ratio of 3:1.When the ratio of carbon to silicon is 4:1 and 5:1,the photocatalytic performance of the sample decreases with the increase of the particle size of the silicon source.Samples prepared with 2?m silica at a carbon to silicon ratio of 3:1 shows the best photocatalytic performance.The possible reason is that the silicon carbide layer is the thinnest at this time,and the light energy is irradiated to all the silicon carbide particles,and the generated photogenerated electrons are close to the core silica,and the driving force for driving the outward migration is strong,so that the photolysis property is optimal.Four groups of 50-100nm?4:1?,200nm?4:1?,500nm?4:1?,and 2?m?3:1?which have the best photocatalytic performance in their own group were selected to do the comparative test of photocatalytic performance before and after silicon removal.It is found that the presence of silica can improve the photolysis performance of the material.The charge transport process in SiC/SiO₂nanocomposites was studied.Studies have shown that core silica promotes the diffusion of photogenerated electrons away from the silica.