Preparation And Functionalization Of Graphene Hydrogels And Their Removal Properties With PPCPs

More and more pharmaceuticals and personal care products?PPCPs?were detected in the aqueous environment due to the growing consumption.Consequently,they pose considerable potential threats to microbial communities,plants,animals as well as humans.Adsorption is an effective and economical technique to remove PPCPs from water without producing any toxic by-products.However,adsorbents with high specific surface area,adsorption capability and recyclability are still in urgent need.Among them,graphene hydrogel is considered to be an ideal adsorbent because of its high porosity and surface area,what's more,it could be modified by kinds of facile methods.In this work,an efficient graphene hydrogel adsorbent was prepared to remove typical PPCPs from water,the adsorption process was investigated systematically and adsorption mechanism was illustrated.Less layered graphene oxide was prepared using modified Hummers method,it was then reduced by using environment-friendly biological material-caffeic acid to produce graphene hydrogels through self-assembly process under mild reaction conditions.The equilibrium adsorption capacity of graphene hydrogel to pnitrophenol was 47 mg/g,and the adsorption reached equilibrium until 10 h.The adsorption capacity decreased with increasing pH due to the inhibited electrostatic interaction between pnitrophenol and graphene hydrogel.The equilibrium adsorption capacities of enrofloxacin and phenacetin were 90 mg/g and 46 mg/g,respectively,adsorption all reached equilibrium 10 h later.The adsorption kinetics fits pseudo-second order kinetic model,and the adsorption isotherm conforms to the Freundlich adsorption model.The?-?interaction,hydrophobic effect,hydrogen bonding and electrostatic all contributes to adsorption of phenacetin and enrofloxacin on graphene.For electrostatic interaction dominated the adsorption of enrofloxacin,the removal efficiency was influenced by pH and ionic strength dramatically.Graphene was also prepared by reducing graphene oxides by using NaHSO₃,and then was modified by polyethyleneimine to introduce amino group on surface.The characterization results of XPS and XRD confirmed existence of abundant amino group on modified graphene.Finally,the resultant graphene hydrogel was freeze dried before application.The high strength showed that pore channel was conserved during drying.The results showed that adsorption capacity of graphene increased from 95 mg/g to 133 mg/g by grafting amino onto the surface.The adsorption kinetics fits pseudo-second order kinetic model,and the adsorption isotherm conforms to the Freundlich adsorption model.The pH determined adsorption capacity by changing the surface charge of adsorbent and dissociation extent of diclofenac.