Removal Of Cd(?) And Cu(?) With Phosphated NZVI

The emerging environmental issues,arisen from the improper discharge of industrial water,the excessive exploitation of mines,and the abuse of pesticides,become more and more serious along with the rapid development of modern society and economy.Particularly,the pollution induced by heavy metals,such as cadmium,copper,lead or mercury in the water environmental has received increasing attention.Therefore,it is urgent to explore the green and cheap strategies for the heavy metal pollution control to realize the sustainable development.Recent years,nanoscale zero-valent iron(nZVI),with large specific surface area and high reactivity,was widely used to remove organic pollutants and heavy metal ions.However,because of the nonselective electron transfer ability,nZVI could also transfer electron to the other species,such as hydrogen proton or dissolved oxygen co-existed with target heavy metal pollutants in water environment,and thus result in the low utilization rate of electrons.Surface modification of nZVI is regarded as an efficient approach to overcome this drawback.Therefore,we designed and synthesized a novel surface phosphorylated nanoscale zero-valent iron(P-nZVI)via inducing phosphate during the nZVI preparation process with using sodium borohydride reduction method,and investigated its performance and mechanism on removing two kinds of typical heavy metal ions in water environment.The main research contents of this master's thesis are summarized as follows:First,we characterized the structure of the nZVI,and investigated its performance on Cd(?)removal before and after the phosphorylated treatment.SEM and BET characterization results indicated that phosphorylated treatment could decrease and enlarge the particle size and surface areas of nZVI,respectively.IR characterization result suggested that phosphate could chelated on the iron oxide surface with the formation of a new oxide shell.In comparison with pristine nZVI,phosphorylated treatment could promote its Cd(?)removal performance from 15.0%to 99.0%within 3 hours.Both of the Cd(?)removal processes by nZVI and P-nZVI were obeyed second-order model kinetic equation,implying that the chemisorption played a dominate role in the adsorption process.Isotherm adsorption curve fitting results suggested that Cd(?)removal process by nZVI was obeyed Freundlich isotherm adsorption model,while Cd(?)removal process by nZVI was fitted well with the langumir isotherm adsorption of monolayer adsorption model.Moreover,phosphorylated treatment could increase the theoretical Cd(?)adsorption capacity of nZVI from 27.49 mg/g to 79.90 mg/g.XPS characterization results indicated that the surface adsorbed Cd(?)mainly bonded with iron hydroxide oxide of nZVI and P-nZVI,and diffused into the inner of nZVI through the pores.This study elucidated the performance difference between nZVI and P-nZVI on Cd(?)removal,and also shed lights on the preliminary Cd(?)removal mechanism by these two kinds of nZVI.Then,we checked the performance of nZVI on Cu(?)removal before and after the phosphorylated treatment.In comparison with pristine nZVI,phosphorylated treatment could promote its Cu(?)removal performance from 50.0%to 99.5%within 45 min.Both of the Cu(?)removal processes by nZVI and P-nZVI were obeyed pseudo first-order model kinetic equation,while the apparent Cu(?)removal rate constantsby P-nZVI(0.12013 min-1)was almost 9 times that by n-ZVI(0.01342 min-1).More importantly,P-nZVI could also efficiently work at different initial pH values.XPS characterization results indicated reduction played a dominate role during the Cu(?)removal process by P-nZVI with the formation of Cu and Cu2O.Electrochemical impedance characterization results and Tafel curve suggested that phosphorylated treatment could slow the electrons release from iron core of the nZVI for inhibiting the occurrence of side reactions between nZVI and hydrogen proton or dissolved oxygen,thus enhancing the efficiency and electron selectivity of nZVI toward Cu(?)removal.This result elucidated the performance and mechanism differences between nZVI and P-nZVI on Cu(?)removal,and also provided an efficient and environmentally friendly Cu(?)treatment strategy.This study reveals the reason why phosphorylation significantly increases the removal of two heavy metals from nZVI,which provides a theoretical basis for the actual environmental application of P-nZVI.