Mesoporous phosphorus-doped activated carbon from Acacia falcata: Mechanistic insights into Cr (VI) removal, regeneration, and spiking studies

Document Type

Article

Publication Title

Diamond and Related Materials

Abstract

The escalating threat of hexavalent chromium (Cr(VI)) contamination in wastewater has rendered the development of high-performance carbonaceous materials from biomass a critical research imperative. The need for sustainable, efficient, and cost-effective solutions to mitigate Cr(VI) pollution has spurred interest in exploring biomass-derived carbonaceous materials as potential adsorbents. This study presents the preparation of phosphorus-doped activated carbon from Acacia falcata leaves via low-temperature activation with orthophosphoric acid. The resulting activated carbon exhibits a mesoporous structure, with a specific surface area of 406.65 m2/g. Characterization via FESEM, EDS, BET and XPS analyses revealed a mesoporous structure with an irregular surface, micropores, micro-cracks, and micro-pits, with an average pore size of 4.03 nm. Post-Cr(VI) adsorption analysis indicated a smoother surface, likely due to pore filling and chromium oxide formation, with EDS confirming chromium presence (peaks at 0.57 keV and 5.41 keV). XPS deconvolution identified Cr(III) (63.18 %) and Cr(VI) (36.82 %) species, highlighting the material's dual function in Cr(VI) adsorption and reduction. Batch experiments followed pseudo-second-order kinetics and the Freundlich model, achieving a maximum adsorption capacity of 60.14 mg/g at optimum conditions of pH 2, 150 rpm, 0.2 g/L adsorbent dose and 303 K. Thermodynamic analysis indicated a positive ΔH° (33.69 kJ/mol) and ΔS° (132.61 J/mol K), alongside a negative ΔG°, confirming the adsorption's spontaneous, endothermic nature with increased randomness. The presence of cations had a negligible effect on removing Cr(VI), but anions, especially nitrate and phosphate, slightly reduced adsorption efficiency. However, the adsorbent proved highly resilient, maintaining over 77.05 % Cr(VI) removal efficiency after four regeneration cycles. Moreover, it demonstrated exceptional performance in treating water from diverse sources, including river, lake, and well, highlighting its promise as a cost-effective and eco-friendly wastewater treatment solution.

DOI

10.1016/j.diamond.2025.112015

Publication Date

3-1-2025

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