Plant-derived biosorbents for the removal of textile dyes and Cr(VI) using Hippophae rhamnoides raw biomass

Environmental contamination by synthetic dyes and toxic heavy metals from textile effluents has emerged as a serious global concern. This study evaluates untreated Hippophae rhamnoides sea buckthorn leaf biomass (SBLB) as a low-cost biosorbent for the simultaneous removal of Methylene Blue (MB), Congo Red dye (CRD), and hexavalent chromium [Cr(VI)] from aqueous solutions. Batch adsorption experiments were conducted by varying pH (2–10), adsorbent dosage (0–6 g L−1), contact time (5–240 min), and initial concentration. Optimal adsorption was achieved at pH 5–6 with a dosage of 2 g L−1, reaching equilibrium at 180 min for MB and CRD and 120 min for Cr(VI). Maximum adsorption capacities (qₘ) were 78.74 mg g−1 (MB), 45.45 mg g−1 (CRD), and 106.38 mg g−1 (Cr(VI)), while experimental equilibrium capacities (qₑ) were ∼35.7, 39.8, and 32.8 mg g−1, respectively. Kinetic data followed the pseudo-second-order model (R2 > 0.99), and equilibrium behavior was best described by Freundlich isotherm, indicating heterogeneous multilayer adsorption. Thermodynamic analysis confirmed a spontaneous and mildly endothermic process. Fourier Transform Infrared (FTIR) spectroscopy and Scanning Electron Microscopy (SEM) analyses confirmed the role of surface functional groups and morphology in adsorption, highlighting SBLB as an efficient, low-cost biosorbent for contaminants removal.