Removal Of Antibiotics And Heavy Metals From Aqueous Solutions By Modified Activated Carbon Prepared From Phragmites Australis

Antibiotics and heavy metals in water have become two major sources of water pollution.Their pollution is widespread,harmful and time-consuming,so the removal of antibiotics and heavy metal residues in water has become an urgent problem to be solved.Among the various treatment methods,activated carbon(AC)adsorption is considered to be an effective method to remove antibiotics and heavy metals in water due to its advantages of economy,practicality,simple operation and remarkable effect.Wetland plant-Phragmites australis(PA),it has upright steam,high fiber content and developed aeration tissue,so it is a good raw material for the preparation of activated carbon.In this study,PA-based activated carbon(PAC)was prepared from PA by activation of H3PO4.On the basis of this preparation process,Powdery puffed waterfowl feather(PPWF)and manganese formate hydrate(MFH)were used to modify the PAC.ACs were characterized by various methods and the effects of different conditions on adsorption capacity were studied by batch adsorption experiments.By comparing PAC with modified PAC,the adsorption behavior and mechanism of antibiotics and heavy metal Ni(Ⅱ)adsorbed by modified carbons were studied through the differences of physical and chemical properties and adsorption capacity of ACs.The main conclusions of this study are as follows:(1)In the experiments of adsorption of antibiotics by PAC and PPWF modified activated carbon(FPAC),the physical characterization results showed that the ACs were amorphous carbon.The total specific surface area of ACs was not significantly different,but the microporous surface area(557.7 m2/g)and pore volume(0.70 cm3/g)of the FPAC were much larger than that of PAC(208.1 m2/g and 0.26 cm3/g),indicating that the modification increased the microporous structure of activated carbon.The chemical characterization results showed that the acid functional groups of the FPAC were more than that of the PAC,and the N-containing functional groups appeared on the surface of FPAC.The results of adsorption experiments showed that the removal rate of FPAC was at least 15%higher than that of PAC.The adsorption kinetics data of amoxicillin(AMX)and cephalexin(CEX)from ACs were in line with the pseudo-second order model,the adsorption isotherm of AMX was well fitted to the Langmuir adsorption isotherm model,and the adsorption isotherm of CEX was in line with the Freundich adsorption isotherm model.Under different pH values,the adsorbents of the two samples showed different removal rates,but the change trend was consistent.With the increase of the pH of the initial solution,the removal rate rises to a peak,then slowly decreases and then rapidly decreases.At pH = 6,the removal rate of AMX was the highest,and at pH = 7,the removal rate of CEX was the highest.The adsorption of AMX and CEX by ACs is mainly chemical adsorption,and the main adsorption mechanism includes electrostatic attraction and covalent binding.(2)In the experiment of adsorption of heavy metal Ni(Ⅱ)by PAC and manganese formate hydrate(PAC-MFH),the physical characterization results showed that the ACs were amorphous.The specific surface area(927.6 m2/g)of PAC-MFH was smaller than that of PAC(990.2 m2/g).However,the surface area(473.6 m2/g)and pore volume(0.46 cm3/g)of PAC-MFH were larger than that of PAC,which proved that the microporous structure of PAC-MFH was more than that of PAC.The chemical characterization results showed that the surface of PAC-MFH contained more O-containing functional groups than PAC.The adsorption experiments showed that the Ni(Ⅱ)adsorption capacity of PAC-MFH was 20%higher than that of PAC.The adsorption kinetics conforms to the pseudo-second order model,and the adsorption isotherm conforms to the Langmuir adsorption isotherm model.In the pH range of the study(2-8),the removal rate increased with the increase of pH value,and the increasing trend became fast firstly and then slow.The adsorption of the Ni(Ⅱ)by ACs mainly depends on the chemical combination of Ni(Ⅱ)and the surface O-containing functional groups of ACs,and the adsorption mechanism mainly includes electrostatic attraction,ion exchange and surface complexation.