Preparation Of Carbon Nitride Materials And Study Of Their Photocatalytic Properties

As industrialization and urbanization continue,the demand for fossil energy sources such as oil,coal and natural gas is increasing and the energy crisis is causing more and more concern.As a result,the need for clean energy is becoming increasingly urgent.Photocatalysis,a green and non-polluting technology that uses sunlight to drive semiconductors to degrade pollutants,has received a lot of attention in solving the energy crisis as well as environmental pollution.Graphitic phase carbon nitride（g-C3N4）is a photocatalytic material that can produce hydrogen,carbon dioxide reduction and degradation of organic pollutants.He has the advantages of visible light response,good stability,green,non-toxic,environmentally friendly and recyclable,but low visible light absorption efficiency and easy compounding of photogenerated electrons and holes.In this work,carbon nitride was prepared by different methods for improving the photocatalytic performance of graphite-phase carbon nitride.（1）Herein,simultaneously adjustable N-defect and C-doped of g-CN-X（graphite phase carbon nitride）with accordion 3D structure assembled by nanosheets have been prepared through a one-step steam approach in the ratio of water to ethanol.This approach can greatly increase light absorption of g-CN-X by extending the absorption edge up to the whole visible light region.Interestingly,the energy gap of the g-CN-X（1,82-2.48 eV）could be precisely tuned on demand via defect engineering.Moreover,the N vacancy and C doped g-CN-X provided a driving force for the dissociation of excitons into free charges,it achieving an effective spatial separation during photocatalytic process.The accordion 3D hierarchical structure of g-CN-X materials coupled to defected surface properties endow more active sites,and increase charge separation efficiency with a prolonged charge lifetime,synergistically drastically promoting their photooxidation-reduction performance.The optimized catalyst（gCN-10）presents an impressive hydrogen evolution rate of 27.6 m mol h-1 g-1 is 16.2 times as much as bulk-g-CN,with an apparent quantum yield of 9.13%at 420 nm.It also showed the enhanced activity for CO2 photoreduction,giving the CO evolution rate of 226.1 μ mol h-1 g1far exceeding that of bulk g-CN（7.9 μ mol h-1 g-1）and increased by 28.6 times.The modified photocatalyst（g-CN-10）degraded RhB at a rate 3.75 times higher than that of bulk-g-CN,and the degradation effect did not decay after five cycles of the experiment.Comprehensive characterization and theoretical calculation show that the enhanced photocatalysis is caused by the increase of specific surface area,the reduction of band gap caused by dual functions of N-defect and C-doped and the accordion 3D structure,and the material yield is high,conducive to industrial applications,and the material yield is high,conducive to industrial applications.（2）This study exhibits a Na-doped g-C3N4 with willow-leaf-shaped structure and high degree of crystallinity,which was synthesized with a convenient thermal polymerization using sodium carbonate（Na2CO3）as the sodium source.The π-conjugated systems of g-C3N4 were improved by doping sodium,which could accelerate the electron transport efficiency resulting in outstanding photocatalytic properties.Furthermore,optimum Na-doped g-C3N4（CN-0.05）attributed its enhanced irradiation efficiency of light energy to its narrower band gap and significant improvement in charge separation.Consequently,the H2 evolution rate catalyzed with CN-0.05 can achieve 3559.8 μ molg-h-1,which is about 1.9 times higher than that with pristine g-C3N4.The rate of CN-0.05 for reduction of CO2 to CO（3.66 μ molg-1 h-1）is 6.6 times higher than that of pristine g-C3N4.In experiments of pollutants degradation,the reaction constants of degradation of rhodamine B（RhB）and methyl orange（MO）with CN-0.05 were 0.0271 and 0.0101 min-1,respectively,which are 4.7 and 7.2 times more efficient than pristine g-C3N4,respectively.This work provides a simple preparation method for tailoring effective photocatalyst for the sustainable solution of environmental issues.（3）A novel 2D/2D g-C3N4/BiOCl heterojunction photocatalyst was synthesized by a onestep grinding method at room temperature.The prepared photocatalyst was characterized by X-ray diffraction,scanning electron microscopy and UV-visible spectroscopy.The photocatalytic activity of the catalyst was investigated for the decomposition of rhodamine B and tetracycline in visible light and for the reduction of the greenhouse gas CO2.The results showed that the visible light absorption performance of the 2D/2D g-C3N4/BiOCl heterojunction photocatalyst was significantly improved compared with that of pure g-C3N4 and pure BiOCl.The synergistic interaction between the heterostructure and oxygen vacancies can effectively promote the generation and separation of electron-vacancies,resulting in more oxidation·O2-and h+with energy input.Thus,the degradation rate of 2D/2D g-C3N4/BiOCl heterojunction for rhodamine B（RhB）was 87.5%in 1 h under visible light,which was 19.0 and 2.3 times faster than that of pure g-C3N4 and pure BiOCl,respectively.The degradation rate of tetracycline（TC）was 89.8%within 2 h,which was 1.9 and 1.2 times faster than pure g-C3N4 and pure BiOCl,respectively.In the photocatalytic CO2 reduction reaction,the 2D/2D g-C3N4/BiOCl heterojunction photocatalyst reduced CO2 to CO at a rate of 2.00 μ mol h-1 g-1,which was 1.1 and 3.2 times faster than that of pure g-C3N4 and pure BiOCl,respectively.