Effect of the degree of carboxylation of carboxylated graphene oxide on the adsorption of Bi³+

The contamination of water sources by heavy metals poses significant risks to human health and the environment, driving the need for effective remediation strategies. Adsorption is considered one of the most efficient methods for removing metal ions from wastewater. While graphene oxide (GO) has shown promise as an adsorbent, its ability to adsorb metal cations is still limited. In this study, we enhanced the adsorption performance of GO through carboxylation, leveraging the ability of ionized carboxyl groups (-COO−) to form electrostatic and coordination complexes with Bi³+ ions. The influence of carboxylation degree on Bi³+ adsorption was systematically investigated, along with the role of reaction temperature in modulating the extent of carboxyl functionalization. Successful grafting of chloroacetic acid onto GO via nucleophilic substitution was confirmed through material characterization. XPS and ICP analyses demonstrated that higher carboxylation degrees, achieved at elevated temperatures, correlate strongly with improved Bi³+ adsorption. The carboxylated GO synthesized at 80 °C exhibited a maximum adsorption capacity of 12.18 mg/L. These results underscore that increasing the carboxyl group content significantly enhances Bi³+ uptake. This work offers a feasible strategy for designing functionalized GO-based adsorbents for the efficient removal of heavy metals.