氧化石墨烯表面吸附态Pb(Ⅱ)在弱碱性环境中的解吸附特征

Desorption of adsorbed Pb(Ⅱ) on graphene oxide under alkaline groundwater conditions

基于氧化石墨烯(graphene oxide,GO)的材料构成特征及其环境应用,通过人工配制弱碱性(碳酸氢钠)地下水,研究GO表面含氧基团在碱度胁迫下的变化及吸附态Pb(Ⅱ)的解吸附特征.结合在弱碱性条件下释放Pb(Ⅱ)的存赋形态,讨论被附Pb(Ⅱ)的GO吸附剂的环境稳定性.结果表明,NaHCO3条件能诱发GO表面氧化碎片(oxidative debris,OD)的剥落,剥落过程在20 h后达到平衡;吸附Pb(Ⅱ)的GO-Pb进入人工配制弱碱性地下水环境后,表面吸附态Pb(Ⅱ)随OD的剥落,以OD-Pb(Ⅱ)络合物的形式进入水相,并保持稳定的分散状态.OD-Pb(Ⅱ)的粒径在10 nm左右,因此强化了Pb(Ⅱ)在地层中的迁移能力,进而加剧GO-Pb(Ⅱ)进入水环境后的二次污染风险.

Heavy metal pollution is a major environmental concern worldwide and graphene oxide has generally been used as an adsorbent in aquatic environment.Based on the environmental application and characteristics of the materials,the change of oxygen-containing groups on the surface of GO and the release of adsorbed Pb(Ⅱ)on spent GO under alkaline conditions were studied by preparing simulated groundwater(sodium bicarbonate).Combined with the morphological forms of the released Pb(Ⅱ)under alkaline conditions,the environmental stability of GO adsorbent with Pb(Ⅱ)attached was discussed.The results demonstrated that oxide debris(OD)on the surface of GO was stripped off gradually under mildly alkaline conditions and the stripping kinetic process was very slow,almost 20 h until reaching equilibrium.After GO-Pb(Ⅱ)entered the simulated groundwater system,the adsorbed Pb(Ⅱ)on spent GO desorbed together with OD stripping from GO and released to water as an OD-Pb(Ⅱ)complexes,which dispersed steadily in water.OD-Pb(Ⅱ)with 10 nm size enhanced the mobility of Pb(Ⅱ)in the groundwater and further exacerbated the risk of secondary pollution in the aqueous environment.