Photocatalytic Properties Of Self-doped TiO₂/g-C₃N₄ Supported By Co Nanoparticles

In recent years,the rapid development of science and technology has led to the continuous improvement of human industrial level,which has an irreversible impact on the earth.On the one hand,industrial production requires a large amount of non-renewable fossil fuels,which will eventually run out of resources day after day of exploitation.On the other hand,large-scale burning of fossil fuels produces a large amount of carbon dioxide discharged into the atmosphere,which cannot be consumed in a timely manner,which accumulates to cause global warming.Therefore,it has become a top priority to find a clean and efficient alternative energy for the sustainable development of the society.As a clean,efficient,nonhazardous,inexhaustibly abundant,and high-energy fuel,hydrogen is considered as emerging green energy source for the growing energy demand,which has received widespread attention.Among the various methods of producing hydrogen sustainably and economically,solar-driven hydrogen evolution,the most natural and reliable method for producing hydrogen,using semiconductor materials remains the focus of scientific research.Hence,it is important for a sustainable future to explore efficient and stable photocatalysts for solar-driven hydrogen evolution without any auxiliary catalysts or sacrificial agents.As a representative n-type semiconductor,titanium dioxide was first applied to hydrogen evolution by Fujishima A.and Honda K.Since then,because of its thermodynamic stability,non-toxicity,environmental protection,cheap and easy to obtain,titanium dioxide has been studied as an ideal photocatalyst and favored by many researchers.However,the defects of titanium dioxide in photocatalysis are also obvious.With a large band gap～3.2e V,it can only be excited by ultraviolet light,which limits the utilization of sunlight.The photocatalytic efficiency of titanium dioxide is determined by the separation rate of photoexcited electron-hole pairs,but it recombine rapidly,result in low photocatalytic efficiency.Graphite phase carbon nitride（g-C₃N₄）has similar advantages and disadvantages,adjustable photoelectric properties,non-toxic materials,abundant C and N elements,and low separation rate and specific surface area of photoexcited electron-hole pairs.Whether is TiO₂ or g-C₃N₄,to further expand the application in the field of photocatalysis,it is necessary to obtain more photogenerated electrons and holes,and to accelerate the separation and transfer of these electrons and holes.In this paper,nitrogen-doped carbon/cobalt material（N-d-C/Co）was used to modify TiO₂ and g-C₃N₄ to improve photocatalytic hydrogen production performance,and a series of physical and chemical experiments were used to systematically study the morphology,chemical composition,specific surface area and photoelectric properties of the samples prepared.This paper expounds from the following two aspects:（1）.TiO₂ nanotubes were synthesized with titanium oxysulfate（TiOSO₄）as precursor and further treated with N-d-C/Co at 800℃.Ti³⁺self-doped mesoporous titanium dioxide nanotubes/nitrogen doped carbon/cobalt nanoparticles(Ti³⁺-d-TiO₂-MNTs/N-D-C/Co NPs)composites with excellent photocatalytic activity were synthesized.The characterization results show that the composite material has a narrower band gap,a larger specific surface area,and a faster photoelectron-hole separation rate.Compared with the original TiO₂,the composite material shows a significantly improved performance of photocatalytic hydrogen production and photodegradation of pollutants.Under visible light irradiation,the hydrogen production rate of TiO₂ and the composite was～0.92 mmol h^-1g^-1 and～3.98 mmol h^-1g^-1,respectively,and the photodegradation efficiency of tetracycline was79.11%and 83.14%,respectively.In addition,the cyclic experiment proves the excellent stability of the composite.（2）.g-C₃N₄ was synthesized with melamine as precursor,then g-C₃N₄/N-d-C/Co-NPs with excellent photocatalytic activity was synthesized at 550℃,modified by N-d-C/Co.The characterization results show that it has a narrower band gap,increased specific surface area,faster photocarrier separation efficiency,and better photocatalytic activity than the original g-C₃N₄.In the visible light range,the hydrogen production rates of g-C₃N₄ and the composite are 14.64μmolg^-1h^-1 and 270.05μmolg^-1h^-1,respectively.The cyclic experiment also proved the stability of the composite.