Photocatalytic Degradation Of Typical Pharmaceutical Pollutants Carbamazepine,rifampicin And Tetracycline Hydrochloride In Aqueous Solution

With large usage and limited absorption by human beings,more and more pharmaceuticals are discharged and existed in the environment,especially in aquatic environment with the concentration of ng/L～μg/L.Currently,many pharmaceuticals were detected in the effluent from sewage treatment plants,surface water,groundwater,drinking water and even in the soil or sewage sludge.They may cause chronic toxicity to aquatic organism through biological accumulation and even give rise to a potential threat for human health.Photocatalytic technology has an excellent effect on removing these pharmaceuticals when compared with conventional wastewater treatment technology and biological technology.Howerer,it is little reported about the application of phptocatalytic technology in the treatment of pharmaceutical pollutants.Therefore,study on photocatalytic degradation of three typical pharmaceuticals（carbamazepine,rifampicin and tetracycline）by Zn In₂S₄ in aqueous solution was investigated in this paper and so as to provide theoretical basis for the removal of these pharmaceuticals in actual aqutic enviroment.In this paper,ZnIn₂S₄ photocatalyst was synthesized via a hydrothermal method and its properties were characterized by UV-vis DRS,SEM,XRD and BET.Photocatalytic activity of Zn In₂S₄ for these pharmaceuticals in aqueous solution was investigated through a batch reactor.The researches showed that the removal efficacy of CBZ was up to 100%while exposed to the irradiation for 30min by an iodine-gallium lamp with the wavelength of350-450 nm,and other reaction parameter 100μg/L of CBZ concentration,pH of solution 5-9 and dosage of the catalyst 50mg/L.More than 3 hours of reaction time were required for carbamazepine to achieve the same removal efficiency when the reaction solution contained traces of methanol.As for rifampicin and tetracycline hydrochloride,they can be completely degraded in 90min of illumination reaction.Reaction kinetics analysis indicated that photocatalytic degradations of carbamazepine and tetracycline hydrochloride were in accord with first-order kinetics and their degradation rate was affected by the intial concentration of reactants.Reaction rate constant of carbamazepine with catalyst were 2.85 times and 10.44 times than those without catalysts in water solution with trace methanol and ultrapure water solution,respectively.Therefore,Zn In₂S₄improved reaction rate significantly in reaction.Stablity of the catalyst was checked and the results showed the removal rate of CBZ reduced from 90%to 70%and from 91%to 84%after 5 times of recycle usage in water solution with traces of methanol and ultrapure water solution,respectively,which declared catalyst owned high catalytic activity and a stable structure.Trapping experiments showed that hydroxy radical（·OH）was the main active specie and super oxygen(O₂^·-)and holes（h⁺）were the secondary active species in the decomposition of the pharmaceuticals.Intermediates of target contaminants were determined by LCMS-IT-TOF and tentative reaction degradation pathways were proposed.With reacting with·OH,they were transformed into small molecular products with simple structures trough a series of redox reactions the including hydroxylation,cleavage,broken bond,ring-opening reaction etc.Experiments demonstrated that ZnIn₂S₄ can effectively degrade carbamazepine,rifampicin and tetracycline in aqueous solution,but the mineralization degree was very low and biological toxicity of some intermediates was still unknown.Thus,it is necessary to strengthen related research in the future.