| Energy shortage and environmental pollution have become common problems in the world which need to solve urgently.Semiconductor photocatalysis technology is expected to become an effective way to solve the future energy crisis and environmental pollution owing to its efficient energy conversion and pollutants removal capabilities.Therefore,exploring photocatalysts with high efficiency and good stability has been a research hotspot.Graphitic carbon nitride（g-C3N4）has the advantages of non-toxic,economical and good stability.In view of the low separation rate of photoinduced carriers and limited visible light absorption of g-C3N4,some approaches have been proposed to improve photocatalytic performance of g-C3N4.In this study,oxygen-doped g-C3N4（O-g-C3N4）was obtained using urea as raw material by an acid-assisted method,and then Cu2（OH）2CO3/O-g-C3N4（CuCN）composite was synthesized in situ via a coprecipitation method using O-g-C3N4 as a precursor.CuCN heterojunction composite which is used for visible-light driven photocatalytic hydrogen evolution and photocatalytic degradation of malachite green（MG）to explore its photocatalytic performance.The as-prepared composites were characterized to investigate the mechanism of photocatalytic hydrogen evolution and photocatalytic degradation MG by XRD,FT-IR,SEM,TEM,BET,UV-vis,PL,EIS and XPS.In addition,the optimal experimental conditions for photocatalytic hydrogen evolution and photocatalytic degradation MG were also analyzed and predicted by the response surface methodology.This study mainly draws the following conclusions:（1）O-g-C3N4 is a mesoporous material with a lamellar structure,ordered pores and evenly dispersed particles.O-g-C3N4 has a larger specific surface area and pore size than g-C3N4,and O-g-C3N4 has a narrower band gap than g-C3N4.O-g-C3N4 can promote more effectively the separation of photogenerated electrons and holes than g-C3N4.O-g-C3N4 exhibited a relatively higher photocatalytic performance of H2generation at a rate of 322μmolg-1h-1,which was around 3 times of g-C3N4.And the MG degradation rate of O-g-C3N4 is 51%,which was about 1.2 times of g-C3N4.In addition,g-C3N4 and O-g-C3N4 possess the good stability during the photocatalytic hydrogen evolution and photocatalytic degradation MG.（2）CuCN composite material can be successfully prepared by a coprecipitation method,and Cu2（OH）2CO3 particles were evenly filled into the porous structure of O-g-C3N4.The specific surface area and pore size of the composite are 89.06 m2.g-1 and16.34 nm,respectively.The addition of Cu2（OH）2CO3 in the composite can effectively enhance the response ability of O-g-C3N4 to visible light,as well as increase the separation rate and transfer rate of photogenerated electrons and holes in O-g-C3N4.In the experiment of exploring the effect of different raw material ratios,different nitric acid treatment concentrations and different nitric acid treatment times on the photocatalytic hydrogen production performance of the composite during the preparation process,it was found that 60CuCN composite presented an extremely excellent photocatalytic activity of H2 generation at a rate of up to 2499μmolg-1h-1,which was around 23.36,7.76 and 44.63 times higher than that of g-C3N4,O-g-C3N4and Cu2（OH）2CO3,respectively.In that,60CuCN composite was synthesized by using O-g-C3N4 as a precursor obtained by acidifying g-C3N4 for 4 h with 10 M HNO3solution.The study also found that the CuCN composite prepared by in situ co-precipitation method showed more outstanding photocatalytic hydrogen evolution performance than the composite prepared by physical hybrid method.Moreover,CuCN composite exhibited better photocatalytic hydrogen evolution performance than Cu2（OH）2CO3/g-C3N4（the raw material ratio of the two composites is the same）.In addition,60CuCN showed good photocatalytic stability in the cycle stability and long-term stability tests of photocatalytic hydrogen evolution.（3）The excellent photocatalytic hydrogen evolution performance of CuCN composite under visible light is mainly attributed to two reasons.On the one hand,the heterojunction effect between Cu2（OH）2CO3 and O-g-C3N4 can effectively promote the separation of photogenerated electrons and holes.On the other hand,the photocatalyst,sacrificial agent and photosensitizer have synergistic effects accounted for enhanced photocatalytic hydrogen evolution performance in reaction system.In addition,the optimal experimental conditions for the photocatalytic hydrogen evolution system are as follows:the concentration of the photosensitizer（Eosin Y）is 1.30 g/L,the concentration of the photocatalyst（60CuCN composite）is 1.01 g/L and the volume fraction of sacrificial agent（TEOA）is 3.13%.（4）Through the control experiment of CuCN composite photocatalytic degradation MG,it can be concluded that organic pollutants MG can be effectively removed only under the condition that both light and CuCN composite photocatalyst coexist.Among the composites with different raw material ratios,60CuCN showed better photocatalytic degradation MG performance than other composites,and the MG degradation rate of 60CuCN was as high as 91%within 3 h under visible light irradiation,which was around 2.2,1.8 and 4.8 times as much as that of g-C3N4,O-g-C3N4 and Cu2（OH）2CO3,respectively.In addition,60CuCN composite showed good cycling stability during photocatalytic degradation MG under visible light.（5）CuCN composite presented an extremely outstanding photocatalytic degradation MG activity under visible light,mainly because the heterojunction effect between Cu2（OH）2CO3 and O-g-C3N4 promoted the effective separation of photogenerated electrons and holes,making h+and·O2-played a leading role in destroying the conjugated structure of MG to degrade it.In addition,the optimal experimental conditions for the photocatalytic degradation MG system are as follows:the p H of MG solution is 8.11,the initial concentration of MG solution is 46.30 mg/L,and the dosage of the photocatalyst is 0.14 g/L. |
