Preparation Of S-scheme G-g-C₃N₄ Composites And Their Photocatalytic Activity For Decomposition Of Tetracycline

The issue of environmental pollution and energy scarcity has been highly concerned by people,photocatalytic technology is an effective means to improve the current situation.Graphitic carbon nitride（g-C₃N₄）is an excellent visible light-responsive photocatalyst,which has been widely studied in improving water pollution and producing hydrogen gas.Due to the rapid recombination of photogenerated charges,limited photo response range and active sites,g-C₃N₄（CN）still has limitations in practical photocatalytic applications.Reasonable modification research is the key to enhancing the photocatalytic activity of CN,and using cocatalysts to construct heterojunctions is an effective modification strategy.Among them,the S-scheme heterostructure has a high reduction potential and excellent charge transfer ability,and their photocatalytic activity is significantly enhanced.Therefore,based on the assumption of constructing S-scheme g-C₃N₄-based composite materials,this paper studied the photocatalytic degradation of tetracycline（TC）and hydrogen production activity of modified CN composite materials by loading Zn In₂S₄ QDs（ZIS QDs）,Cu In S₂ QDs（CIS QDs）,and Co Fe₂O₄（CFO）on lamellar carbon nitride.The main contents and results are as follows:（1）In this chapter,CN-nanosheets and ZIS QDs were synthesized by high-temperature calcination and hydrothermal methods,respectively.Then,we prepare Zn In₂S₄ QDs/g-C₃N₄（ZIS/CN）composites with a certain mass ratio by solvothermal evaporation.In the test of photocatalytic degradation of TC,the degradation rate of 20%ZIS/CN to tetracycline（40 mg/L 100 m L）in 120 min was 54.82%,3.1 times that of pure CN（17.68%）;In the meanwhile,the hydrogen generation rate of 20%ZIS/CN by photocatalytic water-splitting is 75.2μmol·g^–1·h^–1,which is 32 times of CN(2.35μmol·g^–1·h^–1).Based on material characterization and active species capture experiments,we proposed an S-scheme heterojunction carrier transfer mechanism between 0D ZIS QDs and 2D CN within the system and elaborated the mechanism of photocatalytic degradation TC by composite materials and the main reasons for enhanced photocatalytic activity.（2）In this chapter,CuInS₂QDs/g-C₃N₄（CIS/CN）composite was applied to degradation of TC and hydrogen production from photocatalytic water splitting.The preparation of CN is the same as the first part.CIS QDs are prepared by the one-pot solvothermal method,and CIS/CN composites are prepared by the in-situ growth method.The photocatalytic activity of the sample was tested by photocatalytic degradation of TC and water splitting for hydrogen production.The results showed that 10%CIS/CN had the best photocatalytic activity,52.16%TC（40 mg/L 100 m L）could be degraded after120 min exposure to visible light,and 102.4μmol H₂could be generated after 1 h exposure,3.5 times and 49 times of CN respectively.Based on the experimental datas,we believe that the enhancement of the photocatalytic activity of CIS/CN is based on the formation of S-scheme heterojunction.Under the synergetic effect of coulomb force,built-in electric field and band bending,the carrier separation rate of CIS/CN composite increases,and holes（h⁺）with strong oxidation ability and strong reducing electrons（e^-）participate in the reaction,thus effectively enhancing the photocatalytic activity of the system.（3）In this chapter,CFO-coupled CN nanocomposites were synthesized by hydrothermal and polymerization methods.The results show that CFO nanoparticles grow orderly on the surface of the CN nano-sheet,and a good contact interface is formed between them.In the sonocatalytic degradation of TC,compared with single CN,25%Co Fe₂O₄/g-C₃N₄（CFO/CN）showed enhanced sonocatalytic activity.Based on PL,flat-band potential and photocurrent characterization analysis,we proposed a mechanism for the sonocatalytic degradation of TC by CFO/CN based on S-scheme heterojunction.This work provides a new idea for the use of semiconductor nanomaterials to eliminate the antibiotics in the environment.