High Energy Ball Milling Assisted Synthesis And Properties Of Potassium-doped Carbon Nitride/Cadmium-Zinc Sulfide Photocatalysts

Energy crisis and environmental pollution are significant problems faced by the world.One of the“green technology”-photocatalysis technique,opens a vast and applicable gate to solve the predicament.Graphitic carbon nitride?g-C₃N₄?is widely watched due to its advantages of chemical stability and low cost,but there are some problems require further modifications.In this paper,cation doping and heterojunction construction were synergistically used to synthesize g-C₃N₄ matrix composite with a narrow band gap and low recombination rate of photogenerated electronhole pairs.High energy ball milling was also introduced to increase the synthetic efficiency and enlarge the specific surface area of the composite.Two kinds of K+ doped g-C₃N₄ was obtained by thermal polymerization with urea as the raw material,potassium chloride?KCl?and potassium hydroxide?KOH?as different source of potassium?K?.The effects of the amount of doping and source of potassium on K+ doped g-C₃N₄'s crystallization,chemical composition,band structure,and microstructure have been studied by XRD,FT-IR,XPS,SEM,and BET.The results show that K+ doped g-C₃N₄ has folded 2D layer structures and when the doping amount reaches 3mmol,The photocatalytic hydrogen production rate?HPR?of the sample KCN-3 prepared with KCl as the potassium source is 1267.75 ?mol/g h under visible light irradiation??>420 nm?,which is 3.92 times of g-C₃N₄.The HPR of the sample KOHCN-3 prepared with KOH as the potassium source was 803.2?mol/g·h,which was 1.48 times higher than g-C₃N₄.In the experiment of degrading rhodamine B?RhB?,KCN-3 also showed good catalytic activity,the degradation rate is 4.9 times of g-C₃N₄ and KOHCN-3's degradation rate is 1.39 times over the non-doped sample.The reasons for the improvement of catalytic performance was that the K+ doping changed the band structure of g-C₃N₄,improved the harvest of visible light,and reduce the recombination of photogenerated electron-hole pairs.On the basis of doping potassium,KCN-3 was used as the matrix to construction semiconductor heterojunction with Cd0.5Zno.5S?CZS?by hydrothermal method.The influence of reaction time,reaction temperature and loading amount were investigated.After 12h hydrothermal reaction at 140 ?,the HPR of the sample loaded 24 wt.%CZS?KCN/CZS 24wt.%?reaches 1.83 mmol/g·h which is 5.6 times of g-C₃N₄,and the degradation rate on RhB is 7.9 times higher than g-C₃N₄.The results of XPS valence band spectrum and UV-vis DRS indicate KCN-3 and CZS can form type II heterojunction and force the photo-generated electron-hole pairs separate spatially which improve the catalytic activity.High energy ball milling was introduced to obtain KCN/CZS,the influence of ball milling time and loading amount of CZS on KCN/CZS's catalytic activity was studied.The results show that after 15 min milling,the HPR of the sample loaded 24 wt.%CZS is 2.05 mrmol/g·h,which is 6.8 time of g-C₃N₄ and it can completely degrade RhB solution in 45 min.The high-speed vibration and milling made KCN-3 and CZS thoroughly mixed and at the same time,enlarging the specific surface area of the composite to 88.24 m²/g,increases the reactive sites,and further enhances the catalytic activity of g-C₃N₄,this paper provide a new approach to obtain g-C₃N₄ matrix composite with high photocatalytic activity.