Multifunctional carbonaceous materials derived from tea waste: Towards sustainable solutions for wastewater treatment and hydrogen evolution

The depletion of conventional energy sources and the alarming rise in water contamination underscore the urgent need for advanced materials that can simultaneously address wastewater treatment and hydrogen evolution reactions (HER). While existing materials offer solutions to either wastewater treatment or HER, multifunctional materials have been developed to address both challenges concurrently. Biomass-derived carbonaceous materials, particularly from abundant and sustainable sources like tea waste, present an environmentally friendly, cost-effective solution. This study presents novel, multifunctional nanomaterials derived from tea waste via facile synthesis method including KOH activation of tea waste ashes (GCW), microwave-assisted carbonization (GCOM), and hydrothermal modification (GCOH) of GCW to create materials capable of efficient dye adsorption and excellent HER activity. The FESEM, TEM, XRD, FTIR, Raman spectroscopy, TGA, BET, the XPS techniques were employed to thoroughly examine the morphological and structural properties of the materials. Among the synthesized materials, hydrothermally treated one (GCOH) after KOH activation of tea waste ashes demonstrated the highest adsorption capacity. Specifically, it showed values of 48 mg/g for the cationic dye Methylene Blue (MB) and 43 mg/g for the anionic dye Methyl Orange (MO). Additionally, GCOH exhibited excellent HER activity in an acidic medium, with an onset overpotential of 349 mV (466 mV at 50 mA cm⁻²) and a lower Tafel slope of 128 mV dec⁻¹. These findings suggest that biomass-derived carbonaceous materials, particularly from tea waste, can serve as dual-functional agents, offering a sustainable approach to addressing critical environmental and energy challenges.