Biochar derived from giant reed and water lettuce for adsorptive and oxidative remediation of crystal violet dye in water

This study explores a low-cost biochar derived from invasive plants, Giant Reed (GR) and Water Lettuce (WL), for the remediation of triphenylmethane dye Crystal Violet (CRV). GR and WL biochar produced via slow pyrolysis at 500 °C were tested at varying experimental conditions of adsorbent dose, pH, and initial dye concentration. To further enhance CRV degradation, hydrogen peroxide was introduced to induce a Fenton-like reaction, leveraging the inherent transition metals in the biochar. FTIR characterization of biochar confirmed the presence of carboxyl and hydroxyl functional groups, and SEM analysis revealed a porous biochar structure. The zero-point charge indicated that both GR and WL biochar were alkaline. Kinetic and isotherm models showed that WL (qmax = 610 mg/g) adsorbed the dye better than GR (qmax = 435 mg/g); however, GR showed satisfactory performance for the oxidation of dye owing to its trace metal composition, with both biochar samples yielding dye discoloration after 30 min. ToxTrax assays confirmed reduced toxicity in treated solutions, while UV–Vis spectra of degradation byproducts showed peaks between 300 and 400 nm. These findings highlight GR and WL biochar as an effective, sustainable alternative for dye remediation and invasive weed biomass management.