Eco-friendly chromium(VI) cleanup: Guava seed biosorbent performance in equilibrium, kinetic, and thermodynamic studies

The contamination of water resources by toxic hexavalent chromium (Cr(VI)) poses significant environmental and health risks. This study explores the potential of guava seed powder (GSP), an agricultural byproduct, as a sustainable biosorbent for Cr(VI) removal. Comprehensive characterization using FTIR, SEM-EDX, XRD, and BET analysis revealed GSP's mesoporous structure (98.7 m 2 /g surface area) and abundant oxygen-containing functional groups (─OH, ─COOH), which facilitate effective Cr(VI) binding. Batch adsorption experiments demonstrated optimal removal (>85%) at pH 2 and 30°C, with equilibrium data best described by the Sips isotherm (R 2 = 0.990), indicating a maximum adsorption capacity of 3.0 mg/g. Kinetic analysis confirmed chemisorption as the dominant mechanism (pseudo-second-order model, R 2 = 0.985), while thermodynamic studies revealed the process to be exothermic (ΔH° = −8.72 kJ/mol) and spontaneous (ΔG° = −21.62 to −23.32 kJ/mol). The adsorption mechanism involved electrostatic attraction, surface complexation, and pore diffusion. Comparative analysis highlighted GSP's superior performance over other low-cost biosorbents, underscoring its potential as an eco-friendly and cost-effective solution for Cr(VI) remediation. This work not only advances sustainable water treatment but also aligns with circular economy principles by valorizing agricultural waste. A preliminary cost analysis confirmed the exceptional economic viability of GSP, with production costs estimated at $1.5–3.0 per kg, underscoring its potential as a low-cost and sustainable alternative to commercial adsorbents for large-scale wastewater treatment • Guava seed powder effectively removes toxic chromium (CrVI) from water as a natural, low-cost solution. • Works best in acidic conditions (pH 2) at room temperature (30°C), removing over 85% of chromium. • Can absorb up to 3.0 mg of chromium per gram of powder, which is better than many other natural materials. • Works through strong chemical bonding between chromium and the powder's natural components. • The powder has a rough, porous surface with many active sites that attract chromium. • Requires no special preparation - just drying and grinding the seeds is enough. • The removal process happens naturally and gives off slight heat. • Performs better than similar materials like pineapple peel or rice husk. • Could be used to clean industrial wastewater or contaminated water sources.