Preparation Of Graphitic Carbon Nitride Based Photocatalyst And The Study Of Their Photocatalytic Performance

Environment pollution and energy crisis are two major problems that human are facing,especially the greenhouse effect has become a global problem,which caused by carbon dioxide（CO₂）that produced by burning fossil fuels and released into the air.Although the CO₂ is an environmental pollutant,it is also an important source of carbon,finding a suitable way to convert CO₂ into value products can solve the environment problem as well as energy crisis.Photocatalysis technology is an environmental friendly technology with mild reaction conditions,it’s powered by solar energy and will not produce toxic and harmful by-products,it’s well applied in photocatalytic reduction CO₂.The technology of photocatalytic reduction CO₂ is a simulation of plant photosynthesis immobilized CO₂,the CO₂ which causes the greenhouse effect is converted into hydrocarbon fuels such as CH₄ and CH₃OH.There were many photocatalytic materials have been reported,but their applications were limited because of the narrow range of light response,low photocatalytic performance and the instability of the photocatalyst,therefore,the focus of the present research is to develop efficient and stable new photocatalyst.Graphitic carbon nitride（g-C₃N₄）has attracted much attention because of its visible light responsiveness and good development prospect,however,the specific surface area of g-C₃N₄ is small and the separation rate of photo-generated carriers is low,which leads to the low photocatalytic performance.In this paper,we aim to modify g-C₃N₄ and improve its photocatalytic performance,the specific works are as follows:（1）Prepared the hollow titanium dioxide（TiO₂）by hard template,then by simple stirring method,the titanium dioxide and g-C₃N₄ nanosheet were closely interrelate by electrostatic incorporation,and a composite photocatalyst was formed.A series of characterization methods were used to analyze its phase,optical properties and morphology,and its specific surface area was analyzed by BET.The catalytic performance of the samples was evaluated by photocatalytic reduction of CO₂ in visible light,and the cycling stability was measured by multiple cyclic experiments.The characterization results shown that the composites have larger specific surface area,higher photo-generated carrier separation rate and light absorbing ability.The result of reduction CO₂ displayed that the composite photocatalyst not only possess better photocatalytic performance,but also have good stability and can be used for many times.（2）Hollow cerium oxide（CeO₂）nanospheres were prepared by using carbon spheres as template,the g-C₃N₄/CeO₂ composite was synthesized by hydrothermal method.The phase,morphology,composition and optical properties of the samples were tested and analyzed by XRD,TEM,FT-IR,PL and BET,and the ability of photocatalytic reduction CO₂ was tested under visible light.The heterostructure which was formed between CeO₂ and g-C₃N₄effectively accelerated the transmission of photo-induced electrons and restrain photo-generated carriers recombined,and thus enhancing the photocatalytic activity.The characterization results showed that the optical properties and absorption of the composite photocatalysts were enhanced,and the specific surface area increased,which was beneficial to providing more adsorbent sites.The photocatalytic results showed that the composites photocatalyst have higher photocatalytic performance.（3）The MnO₂/Ag/g-C₃N₄ nanocomposites were successfully synthesized by a simple hydrothermal method,the raw materials were easy to be obtained and the method was simple.The catalyst was characterized by means of XRD,FT-IR,TEM,Uv-vis DRS,PL and BET.The results showed that the band gap of the composites was significantly reduced,The light absorption edge has obvious red shift phenomenon,and the light response range of g-C₃N₄has enlarged;The specific surface area of composites is greatly increased,which helps to provide more reactive sites.The results of photocatalytic reduction of carbon dioxide under visible light by composites showed that the yield of methanol by CO₂ conversion was higher than pure g-C₃N₄.