Adsorption Of Emerging Contaminant Metformin Using Graphene Oxide

The occurrence of emerging contaminants in our water resources poses potential threats to the livings.Pharmaceutical and Personal Care Products(PPCPs)were a series of compounds including analgesics,antibiotics,contraceptives,lipid regulators,in addition to the active ingredients in soaps,detergents,perfumes,and skin,hair,and dental care products.In recent years,their increasing consumption and adverse effects on ecological or human body have been attained extensive attention.The emission of these emerging contaminants has emerged as an environmental problem and rather poor wastewater management could not effectively eliminate these compounds.Therefore,there is a widespread demand that this kind of contamination requires effective elimination.Metformin was reported that it would be one of the nontraditional endocrine disrupting chemicals(EDCs)in the environment.Despite a large conversion inwastewater treatment plants(WWTPs)before discharge,metformin was still one of the most abundant pharmaceuticals found in WWTP effluent and surface-waters,and it could usually reach 6 tons per year in individual WWTPs of urban areas.In this study,Graphene oxide(GO)was tested for the first time for its capacity to remove a kind of emerging wastewater contaminants,metformin.GO was studied for the first time to remove metformin from aqueous solution and characterized by scanning electron microscope(SEM),transmissionelectron microscope(TEM),X-ray diffraction(XRD),Fourier transform infrared spectroscopy(FTIR),X-ray photoelectron spectroscopy(XPS),Brunauer-Emmett-Teller(BET)and zeta potential to investigate its adsorption behaviors.The results indicated that GO could rapidly and efficiently reduce the concentration of metformin,which can provide a solution in handling this problem.The uptake of metformin on the graphene oxide was strongly dependent on temperature,pH,ionic strength,andbackground electrolyte.The adsorption kinetic experiments revealed that almost 80%removal of metformin was achieved within 20 min for all the doses studied,correspondingto the relatively high k\(0.232/min)and k2(0.007 g/mg min)values in the kinetic models.It indicated that the highest adsorption capacity in the investigated range(qm)of GO for metformin was at pH 6.0 and 288 K.Thermodynamic study indicated that the adsorption was a spontaneous(?G0<0)and exothermic(?H0<0)process.The adsorptionof metforminincreased when the pH values changed from 4.0 to 6.0,and decreased adsorption were observed at pH 6.0-11.0.GO still exhibited excellent adsorption capacity after several desorption/adsorption cycles.Besides,both so-called ?-? interactions and hydrogen bonds might be mainly responsible for the adsorption of metformin onto GO.