Waste-to-graphene: Sustainable upcycling of fouled membranes into laser-induced graphene electrodes and filters for water treatment and sensing

Polymer membranes are widely used in desalination and water treatment due to their ability to produce high-quality water through simple, cost-effective processes. However, more than 840,000 end-of-life (EoL) membrane modules are disposed of in landfills annually, underscoring the need for sustainable, environmentally friendly solutions. Here, we repurpose fouled ultrafiltration (UF) and reverse osmosis (RO) membranes into functional porous laser-induced graphene (LIG) via CO₂ laser engraving, effectively upcycling spent polymer material into high-value carbon for multiple applications, including electrodes, pollutant removal, interfacial evaporation, microbial inactivation, and sensing. The resultant LIG is systematically compared with LIG derived from pristine UF and RO membranes. Electrochemical analysis revealed comparable responses across all LIG materials, indicating similar charge-transfer characteristics. Also, pollutant-removal studies showed similar methylene blue removal from pristine and fouled UF-based LIGs. Moreover, when LIG from fouled/pristine RO membranes was heated using Joule heating, average evaporation rates of ∼0.8 and 0.7 kg m⁻² h⁻¹ were achieved at 5 V for deionized (DI) water and 3.5 wt% NaCl solution, respectively, whereas solar-driven evaporation reached ∼1.0 and 0.9 kg m⁻² h⁻¹. Also, the upcycled LIG filters achieved greater than 90% disinfection of MS2 bacteriophage and Escherichia coli . In addition, the LIG prepared from both fouled and pristine RO membranes could detect diclofenac when used as a sensor, with sensitivities of 0.1128 and 0.1217 μA μM⁻¹, respectively. Overall, this study demonstrates a scalable approach to upcycle the end-of-life (EoL) membranes into multifunctional LIG surfaces, thereby reducing waste and costs associated with LIG substrate materials.