Upcycling Plastic Waste and Coconut Shell into Highly Efficient Adsorbents for Groundwater Decontamination of As(III) and Plant Growth Studies

Abstract

Arsenic contamination of water resources poses a global threat to environmental and public health, affecting millions of people. To overcome this, novel and effective graphene oxidemodified plastic waste (GO-PW) was synthesized by combining non-recyclable grade-7 plastic CDs with coconut shell-derived GO, creating a dual waste-valorization pathway. GO-PW exhibited a maximum As(III) adsorption capacity of 274.7 mg/g, 40% higher than pristine GO (195.3 mg/g), with >99% removal efficiency at an optimal dose of 0.5 g/L. Kinetic studies indicated pseudo-second-order adsorption (R2 = 0.998), while isotherm analysis showed an excellent Langmuir fit, indicating monolayer adsorption. Thermodynamic evaluation revealed a spontaneous, exothermic process (ΔH° = -0.0029 kJ/mol; ΔG° < 0), confirming a strong affinity for As(III). In real contaminated water samples (2.2 ppm As(III)), GO-PW reduced arsenic levels to 0.03 ppm within 2.5 h, also decreasing Cd 2+ , Pb 2+ , Hg 2+ , and Cu 2+ concentrations below WHO limits. The adsorbent maintained an efficiency of over 90% across five cycles, demonstrating its stability. Unlike most lab-scale studies, practical validation was achieved through plant assays, in which barley (H. vulgare) irrigated with treated water exhibited healthy germination and shoots ~3 times longer than those of arsenic-contaminated controls. This study provides the first demonstration of integrating plastic waste and coconut shell residues into a high-performance As(III) adsorbent with real-world applicability, offering a low-cost, eco-friendly solution for groundwater remediation and agricultural safety.