Construction And Performance Study Of Graphite Phase Nitrided Carbon Based （g-C₃N₄） Composite Materials

In recent years,the rapid development of the industrial economy has generated a large amount of industrial wastewater,posing a serious threat to animals,plants,and human health.Among them,organic pollutants and antibiotic pollutants are highly toxic and difficult to degrade,so it is particularly important to find an effective method for their treatment.Among various water treatment methods,semiconductor photocatalytic technology has the advantages of high removal rate and green economy,and has become a highly promising method for wastewater treatment.Graphite phase carbon nitride（g-C₃N₄）is widely used in adsorption and photocatalysis due to its simple preparation,low cost,suitable band gap and stable physical and chemical properties.However,the g-C₃N₄sample prepared by conventional thermal polymerization has a small specific surface area,easy recombination of photo generated electrons and holes,and low quantum efficiency,which limits its application.It has been found that doping modification can effectively improve the performance of g-C₃N₄,and doping with alkali metal chlorides can significantly increase the specific surface area of g-C₃N₄materials,thereby improving the performance of g-C₃N₄.This article first used lithium chloride（LiCl）as an embedding agent to expand the specific surface area of the material and prepared Li-C₃N₄material.However,the experiment found that the photocatalytic performance of a single material was still limited.Therefore,a low-cost and easily available zinc oxide semiconductor（ZnO）was subsequently introduced onto Li-C₃N₄to construct a Li-C₃N₄/ZnO binary system to improve photocatalytic performance;In addition,to further improve the defect of easy recombination of g-C₃N₄photo induced carriers,bismuth iodide oxide（BiOI）semiconductors with suitable bandgap were introduced into Li-C₃N₄/ZnO to construct a Li-C₃N₄/ZnO/BiOI ternary system.Detailed analysis was conducted on the crystal structure,surface structure,and optical properties of the synthesized materials using methods such as field emission scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,X-ray diffraction（XRD）,and photoluminescence spectroscopy（PL）.Meanwhile,based on semiconductor photocatalysis technology and adsorption method,using methylene blue（MB）and tetracycline（TC）as pollutant models,the adsorption performance and photocatalytic activity of the materials were explored,and the corresponding adsorption and photocatalytic mechanisms were explored.The main research content and results of this paper are as follows:（1）Through high-temperature annealing method,a series of Li-C₃N₄-x materials with different ratios were successfully prepared by intercalating g-C₃N₄with LiCl and adjusting the ratio of LiCl to precursor melamine.Compared with g-C₃N₄,the specific surface area of Li-C₃N₄prepared by this method is about 119.3 m²/g,which is 14 times that of g-C₃N₄（8.3 m²/g）.The pore volume of Li-C₃N₄is three times that of g-C₃N₄.Using MB as the target pollutant,the adsorption performance of Li-C₃N₄was tested.The results showed that the adsorption capacity of Li-C₃N₄for MB dye was as high as704 mg/g within 5 minutes.Li-C₃N₄can easily and quickly adsorb MB,overcoming the disadvantage of slow kinetics in traditional adsorbents.（2）In order to improve the photodegradation performance of g-C₃N₄,a series of Li-C₃N₄/ZnO-x composites were synthesized by introducing ZnO semiconductor into Li-C₃N₄through a simple hydrothermal method and adjusting the ratio of Li-C₃N₄to ZnO.The photodegradation experiment was carried out with TC as the target pollutant.The results showed that the photocatalytic degradation ability of Li-C₃N₄/ZnO-5 was the best,which was 2.0 times and 4.1 times higher than that of single Li-C₃N₄and ZnO,respectively.Through PL testing of the optical properties of Li-C₃N₄/ZnO-5,it was found that Li-C₃N₄/ZnO-5 has a lower PL emission peak,indicating that Li-C₃N₄/ZnO-5has good photo generated carrier separation ability.In addition,the conduction and valence band positions of semiconductors were tested using UV-vis DRS,and it was determined that the improvement in the photocatalytic performance of Li-C₃N₄/ZnO-5was due to the formation of Z-Scheme heterostructures with band matching between Li-C₃N₄and ZnO.（3）In order to further improve the photocatalytic performance of the material,a one-step hydrothermal method was used to introduce BiOI semiconductors into the Li-C₃N₄/ZnO binary composite system.By changing the ratio of Li-C₃N₄/ZnO to BiOI,a series of Li-C₃N₄/ZnO/BiOI-x ternary composite materials were synthesized.The photodegradation experiment was carried out with TC as a model pollutant.The results showed that the degradation rate of Li-C₃N₄/ZnO/BiOI-5 for 10 mg/L TC solution reached 92.60%in 20 minutes,which could quickly realize the degradation of TC.Compared with Li-C₃N₄,ZnO,BIOI and Li-C₃N₄/ZnO-5,the photodegradation capacity of Li-C₃N₄/ZnO/BiOI-5 was increased by 3.4,6.5,2.0 and 1.56 times,respectively.The heterojunction structure between Li-C₃N₄and ZnO and BiOI exhibits high photocatalytic activity.The charge transfer path improves the separation of photo generated electron hole pairs in Li-C₃N₄/ZnO/BiOI-5.