| Cubic silicon carbide?3C-Si C?is a semiconducting compound that has shown exceptional properties,such as suitable band gap and good chemical inertness.In addition,the redox potential of the 3C-Si C conduction band is relatively negative,which makes it an ideal new catalyst material for hydrogen?H2?evolution from water reduction.However,the low specific surface area of industrially prepared 3C-Si C and rapid recombination of photogenerated electrons and holes of Si C have limited its application.The design and synthesis of 3C-Si C with high specific surface and modifying 3C-Si C to promote the separation of photogenerated electrons and holes are necessary.In this thesis,the 3C-Si C and modified 3C-Si C with high specific surface were synthesized by one-step carbothermal reduction method using widely sourced raw materials.Based on the analysis of the morphology,properties and reaction process of raw materials and products,the mechanism of 3C-Si C formation was proposed.In addition,the effects of specific surface area and modification on the photocatalytic properties of Si C materials were investigated.The mechanism of photocatalytic H2evolution over the Si/3C-Si C composite was also discussed.The main results are as follows:?1?The 3C-Si C with high Brunauer–Emmett–Teller?BET?specific surface area of 84 m2/g and106 m2/g were synthesized through one-step process using precipitated silica and corn cob activated carbon as template,respectively.A new Si C formation mechanism was proposed,by which precipitated silica served as a template and silicon source.The reaction of molten Si O2 with C or CO to generate Si C was conducted in situ in Si O2.The photocatalytic H2 production from 3C-Si C were investigated under simulated sunlight irradiation in pure water without any sacrificial agent.The results showed that the H2 production of the products was positively correlated with its specific surface area.?2?A series of doped 3C-Si C were synthesized by carbothermal reduction using precipitated silica and corn cob activated carbon as template,respectively.The characterization results indicated that the recombination of electron-hole pairs was suppressed and the photon absorption ability of 3C-Si C was improved.The rate of photocatalytic H2 production was enhanced observed in doped 3C-Si C synthesized by activated carbon as template.The average H2 production rate of 3C-Si C doped with B,P,and La increased from 7.18?L/?g·h?of pure Si C to 32?L/?g·h?,13.8?L/?g·h?,and 15.3?L/?g·h?,respectively.?3?The Si/3C-Si C composite photocatalyst and B,La,P doped Si/3C-Si C composite photocatalysts were synthesized by using corn cob activated carbon as template.The rate of photocatalytic H2 production was enhanced to 340?L/?g·h?observed in Si/3C-Si C composite photocatalyst,which was approximately 50 times higher than that of pure 3C-Si C.The H2 production of B doped Si/3C-Si C was further enhanced to 2694?L/?g·h?.The photocatalytic water splitting mechanism for the Si/3C-Si C composite was that the Si and 3C-Si C formed heterojunction,the recombination rate of the photogenerated charges was efficiently reduced,and the photocatalytic activity was remarkably enhanced.Compared to the photocatalytic performance of 3C-Si C improved by loading noble metal and graphene,the novel Si/3C-Si C is a suitable solar–H2 production photocatalyst due to its low cost,scalability,and environmentally friendly characteristics. |
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