Sustainable Adsorption of Heavy Metals and Dyes Using Polyurethane Filters Doped with Banana-Derived Activated Carbon

The enhanced discharge of heavy metals and synthetic dyes into water bodies is a notable environmental concern as they are toxic, bioaccumulative, and refractive to routine treatment methods. In this work, we report a new and sustainable approach for the removal of pollutants with the support of bio-enhanced polyurethane foam filters. The filters were doped with raw banana stem powder or banana stem biomass-based activated carbon—a readily available form of agricultural waste.

Both adsorbent materials were thoroughly characterized by means of Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), iodine and phenol indices, granulometry, and zeta potential measurements. The modified filters were fabricated by changing the additive concentrations (1%, 5%, and 10%) and tested for their efficiency to remove lead (Pb²⁺), copper (Cu²⁺), crystal violet, and methyl orange from aqueous solutions. Our results indicated that carbon-doped filters exhibited significantly higher adsorption capacity compared to raw banana powder because of enhanced microporosity and negatively charged functional groups. Performance was further influenced by pH conditions, the number of filtration cycles, and additive concentration. Notably, the filters could be regenerated using hydrochloric acid, indicating that they were susceptible to reuse and cost reduction. This study not only advances low-cost and environmentally sustainable adsorbents but also recycles agricultural waste, with a circular route for green cleaning of the environment. The composite filters present an inspiring alternative to decentralized water treatment for industry and rural communities and are in line with sustainable development principles. Our findings enable the possibility of scale-up applications in environmental separations that combine green chemistry, waste valorization, and material innovation to counter one of the world's greatest water quality challenges today.