Mixed-Mode Remediation of Cadmium and Arsenate Ions Using Graphene-Based Materials

Cadmium (Cd) and arsenate (As) are notorious environmental contaminants, and co-contamination usually requires opposing treatment strategies due to their differing physico-chemical properties. Developing adsorbents that can bind both contrasting contaminants simultaneously is desirable. Two prepared graphene materials, graphene oxide (GO) and iron-oxide-modified reduced-GO (FeG), are evaluated for Cd- and As-sorption, and performance is compared to a mixed-mode commercial adsorbent. Negatively charged GO shows affinity toward cationic Cd, and positively charged FeG shows affinity toward anionic As. Sorption is pH dependent: Increase in pH-promotes Cd-sorption and retards As-sorption. GO displays excellent Cd-sorption even in acidic conditions. The maximum amounts adsorbed by GO and FeG are 782mol Cdg(-1) and 408mol Asg(-1), respectively. Competition by calcium strongly suppresses Cd-sorption, whereas competition by phosphate does not hinder As-sorption. A mixture of GO and FeG demonstrates successful simultaneous sorption of Cd and As from co-contaminated solutions, including a natural water sample, displaying greater sorption than the commercial adsorbent. Data highlight the potential application of graphene materials in effective mixed-mode remediation of multiple contaminants (cations and anions).