A smart recycling solution: WS2-halloysite nanocomposite for heavy metals remediation from wastewater and postliminar application in electrochemical supercapacitor for energy storage

In this research study we have showcased a conversion strategy called "waste-to-wealth" that employs Ni-adsorbed Hal-WS2 NCs for supercapacitor application. A nanocomposite (Hal-WS2 NCs) consisting of tungstate sulfide (WS2) decorated halloysite nanotubes (Hal) was synthesized successfully for the removal of Hg2+, Pb2+, and Ni2+ metal ions. The Hal-WS2 NCs exhibited high adsorption efficacy of 96.42%, 93.2%, and 87.09% for Hg2+, Pb2+, and Ni2+, respectively. The adsorption data complied with the pseudo-second-order (P-so) kinetic and Langmuir isotherm model and supported the monolayer chemisorption nature. To prevent any potential environmental impact during waste-adsorbent disposal, we opted to repurpose the spent Ni(II)-adsorbed Hal-WS2 NCs as a high-performance electrochemical supercapacitor. This approach ensures the responsible and sustainable utilization of the material while minimizing the risk of secondary pollution. The nanocomposite based on Ni(II)-Adsorbed Hal-WS2 NCs displayed a specific capacitance of approximately 175 Faraday/g (F/g) at 4 Ampere/g (A/g). Additionally, the Ni(II)-Adsorbed HAL-WS2 NCs maintained capacitance stability of 92% even after 10,000 cycles in an electrolytic solution of 1 M Na2SO4. This study provided a comprehensive method for effectively recycling spent adsorbents, which could be expanded to advance energy application-oriented reprocessing of other hazardous solid wastes in a cost-effective and environmentally-friendly manner.