Comparative Analytical Evaluation of Reduced Graphene Oxide and Coded Graphene-Derivative Adsorbents for Trace-Level Heavy-Metal Removal

Abstract

Graphene oxide (GO), reduced graphene oxide (rGO) and chemically modified graphene-based materials have been widely studied as efficient sorbents used in analytical and environmental chemistry. They primarily obtain their strengthening effects from possessing significant specific surface area along with the high frequency of oxygenated functional groups, modifiable surface charge and capacity for host-guest hybridization which all promote the capture of low levels of heavy metals from flow water sources. Herein, an experimental dataset was implemented to establish a publishing-oriented comparative characterization of rGO and four coded graphene-derivative adsorbents (D242, D202, D232, and D229) for the removal of Pb (II), Cd(II), Ni(II), Co(II), Cr(III), and Cr(VI) from 1.00 ppm aqueous standards at pH=5; 6; & 7. Metal standard solutions were prepared from high-purity salts dissolved in deionized water, when necessary stabilized with dilute mineral acid and further adjusted to the initial pH required then sequentially treated with each adsorbent using a set of common batch-screening conditions. The residual metal concentrations were measured after filtration for drying the loaded adsorbents, and their regeneration was also carried out using concentrated HNO₃ (for cationic metals) or NaOH (for Cr (VI)).

       The results demonstrated a well-describable pH-dependent adsorption behavior. Cationic metal removals were generally higher but with the exception of Cr6+, which was almost completely removed at pH 5, most likely due to its presence as anionic chromate or dichromate species under near-neutral conditions. Among the assayed adsorbents, D242 exhibited the highest total efficacy for cationic metals (99.5% Pb(II), 97% Cd(II), 93% Ni(II), 90% Co(II) and 94% Cr (III)) at pH7. Compared to that, rGO was the most efficient material toward Cr (VI) with 82% removal at pH 5. Compared to peer-reviewed studies on graphene-based adsorbents, the materials investigated here are measured to have competitive removal of trace heavy-metals, but many published works measure maximum uptake at higher initial concentrations rather than % removal at 1.00 ppm [28,29]. In summary, the results reveal that D242 is the most effective adsorbent for polishing low concentration cationic heavy metals and rGO (including various functionalized rGO-based hybrids) are a more desirable development.