Synergistic effects of tungstate trioxide hemihydrate decorated reduced graphene oxide for the adsorption of heavy metals and dyes and postliminary application in supercapacitor device

Simultaneously managing water pollution, energy crises, and adherence to green chemistry standards poses a significant challenge. The objective of this investigation is to synthesize a novel material suitable for adsorbing contaminants that are typically found in wastewater, and to suggest an alternative approach for managing the spent adsorbent. A tungstate trioxide hemihydrate (WO30.5H2O) decorated reduced graphene oxide (RGO) nanocomposite (RGO-WO30.5H2O NCs) was synthesized and their batch and continuous operation for the removal of heavy metal ions and dyes from synthetic wastewater was investigated. The RGO-WO30.5H2O NCs presented batch adsorption capacity (removal percentage) of 28.005 mg/g (93.35%), 26.985 mg/g (89.95%), 25.935 mg/g (86.45%), 242.69 mg/g (97.07%), 186.97 mg/g (93.48%) for Pb2+, Cd2+, Ni2+, MB and CV, respectively. The fixed-bed column adsorption experiments presented the adsorption amount in between 123 and 79 mg/g for MB and 93 to 71 mg/g for CV as the concentration varied from 100 to 50 mg/L and 52 to 30 mg/g for Pb2+, 45 to 28 mg/g for Cd2+, and 36 to 25 mg/g for Ni2+, as the concentration varied from 50 to 20 mg/L and the breakthrough curves were fitted by the Yoon-Nelson and Thomas models. After then, the spent adsorbent was repurposed for energy storage based on the "waste-to-wealth" principle to prevent secondary pollution. The nanomaterial based on WO30.5H2O NPs, RGO-WO30.5H2O NCs, Ni(II)-Adsorbed RGO-WO30.5H2O exhibited specific capacitance of 306.42, 276.96, and 241.06 F/g, respectively, at 1.25 A/g. The Ni(II)-Adsorbed RGO-WO30.5H2O showed almost comparable capacitance stability of 75% with RGO-WO30.5H2O NCs (82%) after 12000 cycles in 1 M Na2SO4. The fabricated Ni(II)-Adsorbed RGO-WO30.5H2O-based symmetric supercapacitor device displayed energy density of 47.77 Wh/kg at power density of 45 kW/kg while exhibiting specific capacitance of 90% after 10,000 cycles. This research presents a novel methodology for the utilization of spent-adsorbent in energy storage applications, showcasing a significant environmental impact towards reducing the waste generated by conventional adsorption method.