Polythiophene-Decorated Graphene Oxide Binary and Iron-Modified Ternary Composites for Efficient Arsenic Removal and a Novel Approach toward Sludge Management

This study reports the development of two novel composites─polythiophene-decorated graphene oxide (GO/PTh) binary composite and iron-modified ternary composite (GO/PTh/Fe)─for the efficient removal of As(III) and As(V) from contaminated water. The ternary composite (GO/PTh/Fe) has been prepared using a green agent, viz., Kalanchoe pinnata leaf extract. Different characterization techniques, such as FTIR, XRD, SEM–EDX, and X-ray photoelectron spectrometer, confirm the successful formation of the GO/PTh and GO/PTh/Fe composites. VSM analysis of the GO/PTh/Fe composite was also performed, revealing that the composite possesses a slight magnetism. GO/PTh composite demonstrated 90.4% and 91.6% removal efficiency for As(III) and As(V), respectively, while GO/PTh/Fe composite demonstrated superior removal efficiency with 99.03% and 99.27% As(III) and As(V) removal, respectively, at the same adsorbent dose of 0.3 g/L. Both the composites showed good removal efficiency at neutral pH, signifying their practical applicability in arsenic removal. To determine the practical applicability of both composites for arsenic removal, the effects of the arsenic concentration, contact time, and temperature were extensively examined. Adsorption data are well fitted with pseudo-second-order kinetic model and the Langmuir adsorption isotherm model for both GO/PTh and GO/PTh/Fe composites. The maximum adsorption capacity (qmax) for the GO/PTh/Fe composite was obtained as 42.84 and 45.39 mg/g for As(III) and As(V), respectively. Both composites displayed substantial reusability, and competing anions such as phosphate affect arsenic removal efficiency. Density-functional theory analysis was also performed to acquire a better understanding of the arsenic adsorption process. Both composites demonstrated semiconducting properties, as evidenced by the derived I–V curve. However, arsenic adsorption altered the semiconducting properties. Notwithstanding this change, the alterations were not substantial enough to exclude their possible applicability in electronic applications.