Preparation Of Carbon Nitride/fe-based Photo-fenton Catalysts And Their Application In The Degradation Of Pollutants

The photo-Fenton synergy technology has been considered the environment-friendly and effective method for degradation of pollutants.Graphitic carbon nitride（g-C₃N₄）emerge as a feasible alternative material for metal-based photocatalyst after Ti O₂ has received considerable recent interests because of its unique advantages of stable electronic band structure and visible light responsiveness.However,the utilization of visible light for g-C₃N₄ is considerably low,and the photocatalytic activity is severely limited by the the rapid electron-hole recombination rate.To address these challenges,two modifications for g-C₃N₄ including morphology engineering and heterojunction construction were applied in this work,and the main contents are as follows:（1）A hybrid photo-Fenton catalyst（FeS₂@g-C₃N₄）was prepared by coupling FeS₂with g-C₃N₄ via a simple hydrothermal method.After systematical optimization of the preparation procedure,the obtained FeS₂@g-C₃N₄ exhibited a substantially enhanced degradation activity as the model molecule（Rh B,50 mg/L）can be completely degraded in 60 min in the presence of 5 m M H₂O₂under visible light irradiation.According to characterizations of UV-Vis diffuse reflectance spectroscopy（UV-Vis DRS）,photoluminescence（PL）spectroscopy,time-solved PL decay spectra and electrochemical impedance spectroscopy（EIS）,the results demonstrated that the heterostructure between FeS₂ and g-C₃N₄ can regulate the band structure and accelerate the separation and transportation of photoexcited charge carriers.Based on the quenching experiments and electron spin resonance spectrum（ESR）analyses,it can be found that the formation of the heterostructure can not only boost Fe²⁺catalyzed·OH production via H₂O₂,but also increases the formation of·O₂^-from O₂.Moreover,the generated·OH and·O₂^-as well as the photoinduced holes have all contributed to the improvement of degradation efficiency.Compared with other photo-Fenton catalysts,the FeS₂@g-C₃N₄ composite exhibits promising practical usability in water purification.（2）Morphological engineering strategies were used to further improve the photocatalytic performance of FeS₂@g-C₃N₄.Carbon nitride with various morphology were fabricated through self-assembly and molten salt-assisted calcination,and among them,hollow tubular g-C₃N₄（HTCN）has the best photocatalytic performance.Then,thioglycolic acid as stabilizer,FeS₂ nanoparticles were immobilized on the wall of HTCN by a heating reflux method.Compared with FeS₂@g-C₃N₄,FeS₂@HTCN has larger specific surface area,and the degradation rate of Rh B for FeS₂@HTCN was increased by 1.6 times.Notably,the analyses of PL,time-solved PL decay spectra,EIS and ESR demonstrated that the heterostructure and hollow porous structure can provide abundant channels for enhancing electron transfer and charge separation,leading to improving the Fe³⁺/Fe²⁺recycling and reinforcing the·OH generation.（3）Simulated wastewaters are significantly different from real industrial ones,and the concentration decrease of model pollutants cannot reflect the degradation efficiency unless the pollutants were degraded rather than transformed to other compounds.Therefore,the adaptability of FeS₂@HTCN was explored in the degradation of real painting wastewater,which was taken from painting unit of Anhui Jianghuai Automobile Group Co.,Ltd.Firstly,the chemical oxygen demand（COD）values were taken as index of removal rate,and potassium biphthalate as a standard compound for evaluating the COD was selected in the optimized experiments.Then,an aliquot of 2 L wastewater sample（COD 8040 mg/L,p H 6.5-7.0）can be completely treated in 90 min along with FeS₂@HTCN and H₂O₂ under a LED lamp irradiation（λ,450-770 nm）.Comparisons in operating costs,sludge production,process stability,and cycle numbers among the traditional Fenton treatment options were examined.This work is expected to provide a strategy for the treatability of paint wastewater.