Chemical Transformation Of Graphene Oxide In Aqueous Environment And Its Effect On The Adsorption Behavior Of Antibiotics

Upon exposure in aquqtic environment,Graphene Oxide(GO)could be suspended and transported in water columns for some time,where transformation and degradation processes mediated by oxidation or reducing agents would be transformed and degrade.And the surface properties and dispersion or composition of GO are altered during transformation and degradation,and will directly affect the fates and adsorption behavior with organic pollutants of GO.This work will establish a fundamental and useful database for environmental behavior prediction and risk assessment of GO and organic pollutants.By far,the relevant research has not been reported.Therefore,this study examines the surface properties change and colloid stability of GO under the low concentration of sodium sulfite,and quinolones ofloxacin(OFL)and norfloxacin(NOR),tetracycline class antibiotics tetracycline(TC)and oxytetracycline(OTC)as a model pollutant,studies the four kinds of antibiotics in the GO and law of adsorption on the GO under sodium sulfite coexistence.The structural changes of GO and CGO before and after transformation were analyzed by SEM,XRD,FTIR,XPS and Zeta potentials,and the changes in the colloidal stability of GO in the presence of sodium sulfite were studied.The results showed that under the low concentration of sodium sulfite,GO has occurred obvious reduction,but the degree of reduction is not high.The overall oxygen content of GO changed to some extent after transformation,mainly because carboxyl groups were broken and converted to hydroxyl groups.In the presence of low concentration sodium sulfite,the stability of GO colloid is significantly reduced,which may be due to the decreased content of oxygen-containing functional groups,increased surface hydrophobicity,and decreased surface electronegativity,which accelerates GO agglomeration.The adsorption mechanism of antibiotics was further analyzed by kinetic experiment and adsorption desorption experiment.Dynamic experimental data analysis results show that the presence of sodium sulfite inhibits adsorption quinolones adsorption rate,and promoted the adsorbent adsorption rate of tetracycline class of antibiotics,which is due to the different types of antibiotics has different physical and chemical properties,and after join the sodium sulfite,its mechanism is different because of the sudden increase of Na⁺concentration and reducibility of SO₃^2-.The results of adsorption isotherm experiments show that quinolones conform to LM model and tetracycline antibiotics conform to FM model.Among the three adsorption systems,the main adsorption mechanisms of tetracycline antibiotics are?-?EDA action and hydrophobic action,because of the reduction of GO,its hydrophobic surface increases and the content of electron donor(-OH group)increases,so the adsorption of tetracycline antibiotics increases.The main adsorption mechanism of quinolones is hydrogen bonding,and the reduction of oxygen-containing functional groups in the reduction process leads to the reduction of adsorption.By comparing the desorption performance of antibiotics,it was found that the desorption hysteresis of OFL and NOR was not obvious in the three adsorption systems,and their desorption curves were basically identical.TC and OTC have more obvious desorption resistance on adsorbents.Desorption behaviour was also analysed by comparing the desorption release rate(RR)and the quinolones showed a higher RR than tetracycline for a given sorbent,with the exception of OTC,the sorbent RR decreased with increasing solid concentration.