Preparation Of G-C₃N₄/TiO₂ Photocatalyst And Its Degradation Of Tch In Water Under Visible Light

The water pollution caused by tetracycline antibiotics has already been imminent and tetracycline pollution is more significant therein.Tetracycline hydrochloride?TCH?,the combination of tetracycline and hydrochloric acid,has a higher solubility and chemical stability,which will seriously threaten human health and water environment security.As one type of advanced oxidized water treatment method,photocatalysis has been studied for a long time due to its obvious advantages,which can remove refractory organic compounds in water effectively.However,the conventional ultraviolet photocatalysis is limited in many aspects.In view of the above problems,based on graphene carbon nitride?g-C₃N₄?,whosed visible light activity is enhanced by means of semiconductor combination,a series of studies on removal of TCH in water has been conducted.Firstly,g-C₃N₄/TiO₂ composite visible-light photocatalyst was successfully prepared by a simple high-temperature thermal condensation-planetary grinding method.During the visible-light photocatalysis,the removal efficieny of TCH was marked as an evaluation index to optimize the catalyst preparation.X-ray diffraction?XRD?,scanning electron microscope?SEM?,transmission electron microscope?TEM?,UV-visible diffuse reflection spectroscopy?UV-vis DRS?were used to analyze the catalyst.The results showed that when using urea as the precursor,the heating rate was 2?/min and the combination mass ratio of g-C₃N₄ and TiO₂ was 1:2,the achieved g-C₃N₄?1:2?exhibited the highest activity in visible light,that TCH removal efficieny for 3h can as high as 92.1%.SEM,TEM and other results confirmed the successful combination of g-C₃N₄ and TiO₂.Uv-vis DRS showed that the visible light catalytic activity of g-C₃N₄?1:2?was significantly improved compared with that of g-C₃N₄.Subsequently,in consideration of efficiency factors of visible-light photocatalysis during the actual water treatment process,g-C₃N₄?1:2?was used to explore the effect on TCH removal efficieny of several factors,including pH value,the initial concentration of TCH,the catalyst dosage and some ions which often exist in wastewater.It was found that neutral partial alkaline?pH=9?was more conducive to TCH elimination.When the initial concentration of TCH was 10mg/L,the photocatalytic activity of g-C₃N₄?1:2?would be higher and keep the concentration of the catalyst as 1.0g/L in system was more reasonable.In the ion-influence experiment,NO₃^-showed no obvious influence.However,SO₄^2-and ammonia nitrogen would effectively retain the photocatalytic efficiency,leading to a lower TCH removal efficieny.Meanwhile,with the concentration of Cl^-increased,the TCH removal rate exhibited a trend of rise first and then decline.The removal rate of TCH for 150min can reach up to 96.1%with a Cl^-concentration of 15 mmol/L.In addition,considering the complexity of actual wastewater,the photocatalytic removal of TCH in actual wastewater under visible light were also carried out.When set domestic sewage as the water quality background,the TCH removal rate for 3h could reach 86.9%.At the same time,the TCH removal rate would reach 82.8%when the water quality background was antibiotic wastewater.Therefore,it was believed that the removal effect of TCH was still perfect even for complex actual wastewater.Compared with the simulated wastewater,the main reason for the decrease of TCH removal rate was the existence of ammonia nitrogen and COD in actual wastewater.During the cyclic degradation experiment,g-C₃N₄?1:2?showed high chemical stability and can keep a high photocatalytic for TCH degradation for a long time.Finally,aiming to complete mechanism analysis,both the degradation pathway of TCH and the photocatalytic mechanism of g-C₃N₄?1:2?were analyzed by means of UPLC-MS/MS and UV-visible full-wavelength scanning.According to the experimental results of free radical capture,superoxide free radical?·O₂^-?was the most important free radical for degradating of TCH,followed by photogenerated hole?h⁺?and hydroxyl free radical?·OH?played an auxiliary role.During the photocatalytic process,the TOC removal rate for 3h can reach 44.2%.·O₂^-can oxidize-NH₂ in TCH,attack the benzene ring structure in TCH and then complete the decomposition and mineralization of intermediate products to achieve the removal of TCH.