Preparation And Photocatalytic Performance Study Of Carbon Nitride-based Heterojuction

Semiconductor photocatalysis can absorb sunlight and then be excited to produce photon-generated carriers that can effectively degrade various organic pollutants.The prerequisite for developing photocatalysis technology is to explore efficient and recyclable semiconductor photocatalysts.C₃N₄?band gap: ².7 e V?has attracted a lot of attention because of its low cost,nontoxicity,and high photocatalytic activity/stability.However,the photocatalytic efficiency of g-C₃N₄ is still unsatisfactory for the practical application,due to the limited visible-light photoresponce range?⁴60 nm?from its relatively wide band-gap?².7 e V?and photoactivity from the high recombination rate of photogenerated charge carriers.The formation of semiconductor heterojunctions of two or more material has been demonstrated to be an effective method for improving photoresponce range and photoactivity,includinge semiconductor-semiconductor heterojunction,semiconductor-carbon heterojunction,multicomponent semiconductor heterojunction and metal-semiconductor heterojunction.Therefore,in order to improve the photocatalytic activity of g-C₃N₄,we prepared g-C₃N₄-Cu2 O p-n heterojunction and g-C₃N₄-Cd S heterojunction photocatalyst,and photocatalytic degradation efficiencies of organic pollutants were studied.The main research contents are as follows:1.Firstly,g-C₃N₄ nanosheets were synthetized by calcination-exfoliation method,and then in-situ growth of Cu2 O on g-C₃N₄ nanosheets was realized by hydrothermal method.Compared with g-C₃N₄?⁴60 nm?,g-C₃N₄-Cu2 O heterojunctions exhibit a broad photoabsorption at ⁵25 nm with an obvious red-shift.g-C₃N₄-Cu2 O heterojunctions have stronger photocurrent?⁷.2 ?A/cm2?than pure g-C₃N₄?³.0 ?A/cm2?or Cu2O?⁵.1 ?A/cm2?.Furthermore,g-C₃N₄-Cu2 O heterojunctions can degrade rhodamine B?Rh B,92%?,tetracycline?TC,90%?and 4-chlorophenol?4-CP,82%?after 120 min,which is higher than those by pure Cu2O?32% Rh B,29% TC,28% 4-CP?and g-C₃N₄?46% Rh B,50% TC,49% 4-CP?.2.g-C₃N₄-Cd S heterojuctions were successfully synthesized by calcination-exfoliation-hydrothermal method.Firstly,urea as the precursor to prepare bulk g-C₃N₄ at 550 °C for 5 h.The g-C₃N₄ nanosheets were prepared by exfoliation of g-C₃N₄ bulk via a sonication.Then in-situ grow Cd S on g-C₃N₄ nanosheets was realized by hydrothermal method.g-C₃N₄-Cd S heterojunctions can degrade rhodamine B?Rh B,99%?,tetracycline?TC,89%?and 4-chlorophenol?4-CP,87%?after 120 min.g-C₃N₄-Cd S heterojunctions show the highest photocatalytic performance.Compared with pure g-C₃N₄?³.0 ?A/cm2?and Cd S?³.6 ?A/cm2?,the photocurrent intensity of g-C₃N₄-Cd S heterojunction can reach to ⁴.4 ?A/cm2.The degradation of Rh B by g-C₃N₄-Cd S heterojunctions maintains at 83% after four cycles,which shows that g-C₃N₄-Cd S heterojunctions have good stability.