Geopolymer composite spheres derived from graphene-modified fly ash/slag: Facile synthesis and removal of lead ions in wastewater

Geopolymer composite spheres derived from potassium-activated graphene-modified slag/fly ash powder were produced in a polyethylene glycol (PEG 400) solvent. The effect of graphene type (graphene oxide (GO) and few layered graphene (GNP)) on the pore structure and lead ions (Pb2+) removal performance of the spheres were evaluated. The results showed that the composite spheres modified with GOs (0.1-0.4 wt%) and GNPs (1-4 wt%) could be spheroidized with an improved performance to adsorb Pb2+ in solution. The graphene-containing spheres reached a maximum BET surface area of 68.85 m2/g. Pseudo-second-order and Langmuir isotherm models could express the adsorption process, which was controlled by both monolayer adsorption and chemisorption. The obtained spheres also showed high adsorption capacities for Ni2+, Cu2+, Zn2+ and Cd2+ ions. Chemical, physical, electrostatic, ion exchange and cation-pi interaction were attributed to the adsorption mechanism of the spheres. The spheres showed good cycling ability compared to those without graphene, which had potential application in heavy metal wastewater treatment.

Automated summary

The effect of graphene oxide (GO) and few layered graphene (GNP) on the pore structure and lead ions (Pb2+) removal performance of the composite spheres was evaluated, and the results showed that the modified GO (0.1-0.4 wt%) and GNP (1-4 wt%) composite spheres had improved performance in adsorbing Pb2+.