Bimetallic reduced graphene oxide/zeolitic imidazolate framework hybrid aerogels for efficient heavy metals removal

Graphene oxide is a promising adsorption material. However, it has been difficult to recycle and separate graphene oxide in the solution. To alleviate this problem, graphene oxide was thermally reduced to produce porous hydrogel which was then functionalized with polydopamine. The functional groups act as not only adsorption sites but also nucleation sites for in situ crystallization of cobalt-doped zeolitic-imidazolate-framework-8 nano-adsorbents. The effects of cobalt-doping contents on the physicochemical and adsorption properties of the resulting aerogel were also evaluated by varying the cobalt concentration. For instance, the reduced graphene oxide-polydopamine/50cobalt-zeolitic-imidazolate-framework-8 aerogel exhibited a high surface area of 900 m²·g⁻¹ and maintained the structure in water after ten days. The assynthesized aerogels showed an ultrahigh adsorption capacity of 1217 ± 24.35 mg·g⁻¹ with a removal efficiency of > 99% of lead, as well as excellent adsorption performance toward other heavy metals, such as copper and cadmium with adsorption capacity of 1163 ± 34.91 and 1059 ± 31.77 mg·g⁻¹, respectively. More importantly, the lead adsorption stabilized at 1023 ± 20.5 mg·g⁻¹ with a removal efficiency of > 80% after seven cycles, indicating their potential in heavy metal removal from industrial wastewater.