Adsorption Characteristics And Mechanisms Of Sulfamethazine In Water By Various Solid Waste Carbon Materials

Antibiotics are widely used due to their good effect and broad-spectrum antibacterial characteristics,which leads to a large number of antibiotics entering the environment through various ways.In recent years,the detection rate of sulfanilamide antibiotics in soil,surface water and groundwater in china is high.Because of its difficult degradation and limited treatment technology,it has a lot of adverse effects on the ecological environment and human health.How to effectively remove or reduce the harm of antibiotic pollutants to the environment has aroused widespread concern.Biochar technology based on waste utilization can not only avoid environmental pollution,but also achieve the goal of waste recycling.At present,the research on the prevention and control of sulfonamide migration to groundwater environment,especially the use of solid waste to prevent and control sulfanilamide antibiotics is very limited,and it is difficult to support the prevention and control of pollution risk in reclaimed water supplement groundwater source.Therefore,in this paper,whether the new products after carbonization of solid waste can effectively enhance the adsorption of sulfonamides and related mechanisms were studied.Three kinds of common solid wastes?cow dung,eggplant stem and coal gangue?were selected as raw materials to make adsorbent to adsorb sulfamethazine?SMZ?in water.The optimal adsorption conditions were determined by the single factor experiment of the amount of adsorbent,p H value of solution and ionic strength.The composite solid waste carbon materials?A/C-300,A/C-400 and A/C-500?were carbonized from attapulgite waste decolorizing soil?SDE?at 300,400 and 500?at high temperature.The SMZ was adsorbed by the above six solid waste carbon materials under the optimal adsorption conditions.The adsorption properties and adsorption properties of six carbon materials for SMZ were studied by kinetics,isothermal adsorption and thermodynamics.The adsorption materials were characterized by elemental analysis,scanning electron microscopy?SEM?,transmission electron microscopy?TEM?,zeta potential analyzer,specific surface area and pore volume analyzer,FT-IR and Boehm titration.The adsorption results of single solid waste carbon showed that the adsorption of SMZ by cow dung carbon,straw carbon and coal gangue carbon reached equilibrium at 24 h.The adsorption kinetics of SMZ on three kinds of carbon materials can be well simulated by quasi second order kinetic model.R²is between 0.996 and 0.999,and the adsorption rate decreases with the decrease of effective adsorption sites on carbon materials.The reaction process can be divided into three stages:membrane diffusion,intra particle diffusion and equilibrium.Freundlich model can better fit the reaction data.R²is between 0.993 and 0.999,which is mainly physical adsorption and spontaneous exothermic reaction.Under the condition of p H value of 4,carbon material dosage of 0.05 g and no inorganic salt,the adsorption effect is the best.The order of the maximum adsorption capacity of the three carbon materials was cow dung carbon(19.64 mg·g^-1)>coal gangue carbon(12.06 mg·g^-1)>straw carbon(9.16 mg·g^-1).The adsorption mechanisms of SMZ on the three kinds of carbon materials mainly include hydrogen bonding,electrostatic adsorption of multi molecular layer and pore filling.Electrostatic adsorption is the main adsorption mechanism.The best adsorption performance of cow dung carbon is mainly due to its rich oxygen-containing functional groups,more negative charges,larger specific surface area and pore volume.The results show that the adsorption process of composite solid waste carbon?A/C?is similar to that of single solid waste carbon.The quasi second order kinetic equation and Freundlich equation can also well simulate the adsorption of SMZ on the composite solid waste carbon material.However,the adsorption of SMZ on the composites belongs to endothermic reaction,which is beneficial to the reaction with increasing temperature.The adsorption capacity of A/C-300 was the best,and the maximum adsorption capacity was 53.19 mg·g^-1.The adsorption mechanism is as follows:1)electrostatic adsorption:the SMZ presented as cationic state can be adsorbed by A/C with negative surface charges by electrostatic interaction at p H=4;2)H-Bonding:hydroxyl groups on A/C can react with phenyl rings of SMZ to form hydrogen bonds;3)?-?EDA interactions:sulfonamide and amino groups on SMZ acted as electron acceptors and carbon atoms on A/C surface acted as electron donors to form?-?EDA interactions;4)Hydrophobic interaction:A/C surface distributes a certain number of hydrophobic sites,which can produce hydrophobic effect and adsorb hydrophobic SMZ.Among them,the H-Bonding and?-?EDA interactions may be the main mechanisms in the adsorption process.The work provides a new adsorption material for the inhibition of sulfonamide antibiotics,and provides a new idea of"treating pollution by waste".