Dialysis Membrane-assisted Removal Of Trace Pb(II) From Water By Adsorption Of Graphene Oxide-based Hydrosols

In recent years, removal of heay metal ions from wastewater by adsorption of 2-D graphene oxide rich in oxygenated functional groups on the surface has been a focus in environment remidation research, which mainly covers two directions, i.e. how to further enchance the GO adsorption properties and how to avoid the repollution resulting from difficult separation of GO from water. Based on our technique to remove metal ions by adsorption of GO hydrogels sealed in dialysis membrane, two approaches to improve the adsorption performance of GO-based hydrosols were developed as followed:(1) Preparation of GO with higher oxdidation degree via Hummers method using small-sheet-size natrural flake graphite as raw mateirials;(2) Self-assembly fabrication of carbon nanotube @ graphene oxide hybrid hydrosol to inhibt GO restacking during adsorption and achieve the adsorption synergistic reinforcing effects. The disertation systematically studied the effects of p H, time,and temperature, etc. and CNT@GO on the Pb(II) adsorption, conducted a kinetic and thermodynamic analysis on adsorption model and micromechanism,dealt with the relation of sheet size, oxidaiton degree and adsorption performance of GO, observed the adsorption synergistic reinforcing effects of CNT@GO hybrid hydrosol, and finally investigated reusability and influencing factors of GO and CNT@GO.The results showed that the maximum adsorption capacities of Pb(II) at p H=5.9±0.1,T=303K were, respectively, 924.45 mg g-1?1162.6 mg g-1and 1609.54 mg g-1 for micrometer graphene oxide(MGO) submicrometer graphene oxide(SMGO), and CNT@GO(MCNT:MGO=1:4) hydeosol, which was higher than any other adsorbents reported so far. Under the same synthetic conditions, the smaller sheet size of GO resulted in the enhanced adsorption capacity due the higher oxidation degree of GO. Significantly, the maximum adsorption capacity of CNT@GO(MCNT:MGO=1:4) hydeosol was discovered to be increased by 77.11% than that of SMGO, indicating remarkable synergistic enhancement effects. The studies on adsorption thermodynamics and kinetics showed that the adsorption of Pb(II) on MGO, SMGO and CNT@GO hydeosol were endothermic, spontaneous and monolayer adsorption processes, which well fitted the Langmuir sorption model and pseudo-second-order model. The p H value was proved to be the critical factor influencing Pb(II) adsorption/ desorption on the GO-based adsorbents. The maximum desorption rates of Pb(II) on MGO, SMGO and CNT@GO hydeosol at p H=5.9±0.1,T=303K were 94.3%, 95.77% and 94.31%, respectively. Significantly, after fifth consecutive adsorption–desorption cycle, the adsorption capacities of Pb(II) on MGO, SMGO and CNT@GO hydeosol were 514.26 mg g-1, 700.35 mg g-1 and 774.58 mg g-1, respectively, higher than maximum adsorption capacties of most other adsorbents available. In summary, two novel facile routes to effectively enhance Pb(II) removal performance of GO-based hydrosol originally has been proposed in the dissertation, which is promising of broad applications in eliminating other pollutants from wasterwater.