Synthesis Of Layered Silicon Derived From Natural Layered Minerals And Its Photocatalytic Hydrogen Evolution Performance

Faced with the problems of resource depletion and environmental degradation,people continue to develop and research green renewable energy,among them,hydrogen energy has the characteristics of abundant resources,low price,high combustion heat,clean and pollution-free,and high theoretical hydrogen capacity.Many researchers here are conducting continuous research and exploration.The photocatalytic hydrogen production experiment based on semiconductor materials is an important way for hydrogen energy development.Silicon materials with excellent light absorption capacity are ideal catalyst materials for semiconductor photocatalytic hydrogen production.Bulk silicon has low photocatalytic hydrogen production efficiency due to its relatively small forbidden band width and small specific surface area.Due to its unique morphology and structure,layered silicon can effectively adjust the energy band structure of the material and greatly increase the specific surface area of the sample,thereby promoting the efficiency of photocatalytic hydrogen production.In nature,there are many natural minerals with high silicon content and layered structure,such as montmorillonite,vermiculite,talc,etc.,which are ideal precursors for preparing synthetic layered silicon materials.In view of this,this dissertation selects vermiculite(（Mg,Fe,Al）₃[（Si,Al）₄O₁₀（OH）₂].4H₂O),talc(Mg₃[Si₄O₁₀]（OH）₂)and mica（KAl₂）(Al Si₃O₁₀)（OH）₂)Three natural layered minerals,synthetic layered silicon materials（SiNS）were prepared based on the magnesium thermal reduction process,and the photocatalytic hydrogen production properties of the synthetic materials were compared.The specific research content is as follows:1.Synthesis of layered silicon from natural layered minerals.The layered silicon materials were prepared by magnesium thermal reduction process using vermiculite,talc and mica as precursors.The doping ratio of raw materials and magnesium powder in magnesium thermal reduction was studied in detail,and the effects of the reduction temperature on the phase structure,chemical composition,microstructure,specific surface area,optical properties and energy band structure of three natural layered minerals was also studied.The results show that three kinds of natural layered minerals can all be reduced by magnesium,and the three kinds of silicon materials have retained the original layered structure of natural minerals.Moreover,in the process of magnesium thermal reduction,magnesium vapor traps O atoms in natural minerals to form abundant mesoporous structures.Compared with vermiculite and talc,the specific surface area of SiNS made of mica Stone is 33.365 m² g^-1,which is lower than that of SiNS made of vermiculite and talc,the reason for this difference is the high content of Al₂O₃ in muscovite,the reduction of Al₂O₃ by magnesium is more difficult than that of other oxides,and the mesoporous structure is relatively less.From the analysis of optical properties,the band gap width of the three minerals is 2.7-3.0 e V,and the ultraviolet spectrum shows that the three samples can not only use ultraviolet light,it can also make good use of the visible light part of the solar energy,and solve the problem of low solar energy efficiency of the simple silicon.The emission spectrum also shows that SiNS is a good photocatalyst,and the PL intensity is lower,the stronger the catalytic hydrogen production efficiency.2.Study on Photocatalytic Hydrogen Production Performance of SiNS Materials.The photocatalytic hydrogen production performance of the prepared layered silicon materials as photocatalyst were researched.Under the irradiation of visible light,the rate of hydrogen production from SiNS prepared by vermiculite is 899.7423μmol h^-1g^-1,and the rate of hydrogen production from SiNS prepared by talc is 1071.9794μmol h^-1 g^-1,and the rate of hydrogen production from SiNS prepared by mica stone was1006.9087μmol h^-1 g^-1.The specific surface area is proportional to the hydrogen production efficiency,but the hydrogen production rate of muscovite increases rather than decreases,which is due to the Al element contained in muscovite.In the process of hydrogen production,Al³⁺ion is more beneficial to the separation of photoelectron-hole pair,which promotes hydrogen production efficiency.The lowest hydrogen production efficiency of the SiNS made from vermiculite is mainly due to the variety of elements in vermiculite,which leads to the decrease of sample purity and the decrease of hydrogen production efficiency.This experiment also tested the hydrogen production cycle stability of the three samples in detail.The hydrogen production stability of the three samples was relatively poor,especially in the third cycle test,the hydrogen production rate of the samples dropped by nearly 50%.The main reason for the poor stability of hydrogen production is that in the process of catalytic hydrogen production,SiNS material consumes elemental silicon in water and forms a silicon dioxide passivation film,thereby reducing the hydrogen production efficiency of the sample.