Removal Efficiency And Mechanism Of Novel Stabilized N-FeS Colloids For Cr(VI) And Tetrabromobisphenol A In Water

As a promising iron-based environmental material for soil and water environmental remediation,nano-ferrous sulfide(n-FeS)not only has excellent reducibility,but also has the characteristics of large specific surface area,many adsorption sites,and high interfacial reactivity.Therefore,in recent years,many scholars have studied the removal effect of n-FeS on heavy metals and halogenated hydrocarbons.However,because n-FeS has the technical problems of easy agglomeration and inactivation,it has not been applied to the practical environment on a large scale.Therefore,it has important practical significance for the research and application of n-FeS stabilized functional materials.In this study,two novel stabilized n-FeS colloids with high-efficiency adsorption-reduction characteristics were synthesized by reference to colloidal chemistry theory.On the one hand,the composition,structure,stability and destabilization mechanism of these stabilized n-FeS colloids have been studied.On the other hand,the removal efficiency and mechanism of stabilized n-FeS colloid on the removal of pollutants(Cr(?)and tetrabromobisphenol A)in water were explored.In addition,this study revealed the efficiency and mechanism of the HA-FeS colloid on the removal of TBBPA under anoxic/aerobic and natural light conditions by increasing dissolved oxygen and light intensity in the external environment.The results of this study can provide theoretical and technical support for the treatment and environmental remediation of water polluted by heavy metals and halogenated organic compounds.The main research results and conclusions of this study are as follows,a.Based on the characteristics of high dispersion,reactivity and fluidity of colloid,a novel composite colloid was synthesized using polyacrylic acid salt(PAA)and n-FeS.PAA can enhance the electrostatic repulsion on the surface of n-FeS particles and improve the stability and dispersion of n-FeS.The composite colloid enhanced the reduction removal efficiency of Cr(?)in water.The results showed that The surface-coated PAA-n-FeS colloid was prepared,which was combined with n-FeS through the carboxyl group on the surface of PAA.The hydrodynamic diameter of PAA-n-FeS ranged from 65.04 to 90.09 nm and the zeta potential was from-27 to-54 m V at p H varying from 4.5 to 9.0.PAA was coated on the surface of n-FeS,which improved the dispersibility and stability of n-FeS by increasing the steric hindrance and electrostatic repulsion between n-FeS particles.Moreover,the Cr(?)maximum removal amount PAA-n-FeS was 432.79 mg/g,which was significantly higher than that of n-FeS(218.29 mg/g)and PAA(12.32 mg/g).The mechanism of PAA-n-FeS removal of Cr(?)was mainly derived from its own reducibility.The reaction products were mainly Cr(OH)₃,Cr(III)-Fe(III),Cr₂O₃,and Cr₂S₃.In addition,the p H,anions and HA of the reaction system had no significant effect on the removal efficiency of Cr(?)by PAA-n-FeS,while high concentrations of Ca²⁺and Mg²⁺(?8g/L)reduce the removal efficiency of Cr(?).This research not only finds a new stabilizer for preventing n-FeS agglomeration,but also provides a novel n-FeS composited colloid for promoting the practical application to Cr(?)removal from water.b.HA modified FeS colloid(HA-n-FeS)was prepared by modifying the surface of n-FeS particles with natural organic matter(HA).This colloid further enhanced the reduction removal efficiency of Cr(?)by n-FeS.Because HA enhances the reducibility and dispersibility of n-FeS particles.Results showed that the HA modified FeS(HA-n-FeS)had good stability and reduced FeS agglomeration.The hydrodynamic diameter of HA-n-FeS was between 235 and 241 nm,which was much smaller than that of the unmodified FeS.The maximum removal quantity of Cr(?)by HA-n-FeS was 7.74 and 2.35 times higher that of HA and the unmodified FeS,respectively,and the maximum removal quantity of HA-n-FeS was 675.03 mg/g.Further,HA-n-FeS performed better efficiency in removing the dissolved Cr(?)with high or low concentration.With an increasing concentration of Ca²⁺and Mg²⁺,the efficiency of HA-n-FeS to remove Cr(?)showed a decreasing trend.The removal mechanism of Cr(?)mainly relies on the reducibility of Fe²⁺and S^2-.XPS and XRD measurements further revealed that 95.03%of Cr(?)was converted to Cr(III)(Fe Cr₂O₄,Cr(OH)₃ and Cr₂O₃),and another 4.58%of Cr(?)was adsorbed by HA-n-FeS.Therefore,this study demonstrated an efficient method to improve the nano-FeS stability and reactivity for the rapid repair of Cr(?)contamination in natural water.c.The removal process and mechanism of TBBPA by HA-n-FeS colloid were investigated under aerobic and anoxic conditions.The results showed that the removal rates of different concentrations of TBBPA(5,10 and 20?m)by HA-n-FeS colloid were 33.16%,20.48%and 22.37%under anoxic condition,respectively.During the removal process,the concentration of Fe(II)and S(-II)remained stable,the adsorption of HA-n-FeS is the main mechanism of removing TBBPA under anoxic condition.Under aerobic condition,the removal rates of TBBPA by HA-n-FeS colloid are82.37%,56.80%and 43.78%respectively,the concentration of Fe(II)and S(-II)decreased rapidly with the increase of time.Among them,adsorption is the main mechanism of removing TBBPA by HA-n-FeS colloid,among which pore adsorption and functional group binding(C=C group,O-H group and C-O group)of HA-n-FeS colloid play a major role in removing TBBPA.However,under aerobic conditions,HA-n-FeS colloid can reduce a small amount of TBBPA to BPA.Among them,Fe(II)is the main contributor to the reduction degradation of TBBPA,because when HA-n-FeS colloid reacts with TBBPA,a large amount of Fe(II)is oxidized directly to Fe(III).In addition,active species(¹O₂ and·O₂^-)also play a minor role in the removal of TBBPA by HA-n-FeS colloids under aerobic conditions.d.The stability of HA-n-FeS was analyzed by measuring the hydrodynamic diameter and zeta potential of HA-n-FeS,and then the removal mechanism and possible degradation pathway of tetrabromobisphenol A(TBBPA)by HA-n-FeS under continuous illumination were discussed.The results showed that the hydrodynamic diameter of FeS was reduced and the stability of FeS was improved,and it was easily suspended after FeS combined with the HA in the water.The combination of HA and FeS promoted the removal of TBBPA in water,no matter it was in the presence or absence of light.Besides,compared with the absence of light,the removal efficiency of TBBPA was improved by HA-n-FeS with continuous light.There were two reasons for the increase in the removal efficiency of TBBPA by HA-n-FeS.On the one hand,Fe(II)and S(-II)of HA-n-FeS had more stable chemical valence and obtained better reducibility under continuous light than that in the dark.On the other hand,light induced the release of active species(^·O₂^-,¹O₂,and·OH)in the HA-n-FeS composite colloid and further promoted the degradation of organic pollutants.Therefore,photoinduction plays a beneficial role in the removal of organic pollutants by HA-n-FeS colloid.