Study On The Preparation Of G-C₃N₄/Tianying Rock Composite Photocatalyst And Its Photocatalytic Degradation Performance For Organic Pollutant

The discharge of organic matter such as organic dyes and antibiotics into water has posed a serious threat to the ecological environment and people’s health.Photocatalytic degradation technology is a kind of efficient treatment method which directly degrades organic pollutants under mild conditions by using light irradiation to stimulate catalyst to produce strong oxidizing active species.The key to the treatment of organic pollutants lies in the performance of photocatalyst.The photocatalysts developed at present generally have some problems,such as low utilization rate of light,high recombination rate of electron hole pair,low quantum efficiency,lack of selectivity to pollutants and incomplete degradation,and poor separation,recovery and recycling performance.To solve these problems,in this study,several novel g-C₃N₄/Tianying Rock composite photocatalyst materials were constructed by using graphite phase C₃N₄（g-C₃N₄）and natural mineral TYR as main materials,combined with molecular imprinting and magnetic separation technology.The photocatalytic degradation of rhodamine B（Rh B）and ciprofloxacin（CIP）was investigated systematically,and the mechanism of adsorption and photocatalytic degradation of organic pollutants was discussed.g-C₃N₄/Tianying Rock composite photocatalyst（g-C₃N₄/TYR）was prepared by calcination method.The effects of the ratio of g-C₃N₄and celestite,calcination time and temperature on the photocatalytic degradation performance of g-C₃N₄/TYR were investigated.The catalytic degradation performance of g-C₃N₄/TYR under visible light irradiation was studied.The photocatalytic degradation mechanism was also discussed.The results show that the best preparation conditions are as follows:When the dosage of g-C₃N₄/TYR was 50 mg and exposed to visible light for 90 min,the photocatalytic degradation rate of Rh B could reach 99.1%.When TYR reaches 3 g,Eg decreases from 2.6 e V to 2.5 e V,which widens the absorption spectrum,reduces the recombination rate of photogenic e^-/H⁺pairs,and effectively improves the visible light catalytic degradation performance of organic pollutants.The active species produced by the catalytic process include·O₂^-,·OH and H⁺,among which·O₂^-is the main active species.In addition,g-C₃N₄/TYR also has excellent stability and recycling performance.A molecular imprinted composite photocatalyst（g-C₃N₄/TYR-MIP）based on g-C₃N₄/TYR was prepared by thermal polymerization using g-C₃N₄/TYR as matrix,CIP as template molecule,methacrylic acid as functional monomer,ethylene glycol dimethacrylate as crosslinking agent and azo diisobutyronitrile as initiator.The adsorption and photocatalytic degradation of CIP were investigated,and the mechanism of adsorption and photocatalytic degradation was discussed.The results show that g-C₃N₄/TYR-MIP has excellent selective adsorption capacity for CIP,with a maximum adsorption capacity of 57.2 mg/g and a selective adsorption coefficient of 160.5.The adsorption process follows the Langmuir model.When the dosage of g-C₃N₄/TYR-MIP was 50 mg and the irradiation time was 105 min,the degradation rate of CIP reached 85.1%.Compared with g-C₃N₄/TYR,the pore volume and aperture of g-C₃N₄/TYR-MIP are larger,Eg is reduced to 2.4 e V,and the absorption range of light is widened.The active substances produced in the catalytic process also include·O₂^-,·OH and H⁺,and·O₂^-is the main one.Therefore,the addition of molecularly imprinted membrane（MIP）not only provides an active site for CIP selective adsorption,but also effectively promotes the catalytic degradation of adsorptive CIP by photoliving species,thus improving the performance of CIP selective catalytic degradation.In addition,the prepared g-C₃N₄/TYR-MIP maintained good thermal stability below 300℃and had good recycling performance.In order to further improve the separation performance of g-C₃N₄/TYR-MIP after use,magnetic Fe₃O₄microspheres were added in the preparation process of g-C₃N₄/TYR-MIP,and magnetic molecularly imprinted composite photocatalytic material Fe₃O₄/g-C₃N₄/TYR-MIP was prepared by thermal polymerization.The adsorption and photocatalytic degradation of CIP were investigated,and the mechanisms of CIP adsorption and photocatalytic degradation were discussed.The results show that the saturation magnetization（Ms）of Fe₃O₄/g-C₃N₄/TYR-MIP is 62.5 emu/g.It also has excellent selective adsorption performance for CIP,with a maximum adsorption capacity of 50.7 mg/g and a selective adsorption coefficient of160.1.When Fe₃O₄/g-C₃N₄/TYR-MIP dosage is 50 mg and visible light irradiation is 105 min,the degradation rate of CIP can reach 79.5%and total organic carbon（TOC）can reach 73.2%.After four cycles,the degradation rate of CIP was only reduced by 3.6%,showing good degradation and mineralization of CIP and recycling performance.In addition,Fe₃O₄/g-C₃N₄/TYR-MIP also has excellent magnetic separation performance.In conclusion,the combination of g-C₃N₄and TYR can effectively reduce the band gap of the composite photocatalyst,improve the absorption efficiency of visible light and the photocatalytic degradation of pollutants.g-C₃N₄/TYR-MIP was prepared by constructing molecularly imprinted film on g-C₃N₄/TYR,which significantly improved the selectivity of CIP adsorption and selective photocatalytic degradation.Fe₃O₄/g-C₃N₄/TYR-MIP was further synthesized with magnetic Fe₃O₄microspheres,which also endowed the photocatalytic material with excellent magnetic separation performance.Therefore,this kind of photocatalytic materials has a broad application prospect in the treatment of organic pollutants such as organic dyes and antibiotics.