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 oxide-modified 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⁻¹, 40% higher than pristine GO (195.3 mg g⁻¹), with >99% removal efficiency at an optimal dose of 0.5 mg L⁻¹. 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⁻¹; 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 Cd²⁺, Pb²⁺, Hg²⁺, and Cu²⁺ 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.