Engineered nano-zerovalent zinc functionalized biochar for selenite and selenate removal from water: Experimental evaluation, removal mechanism, and molecular simulation

Nano-zerovalent zinc functionalized biochar (nZn0-BC) was synthesized and used for the removal of selenite and selenate from water. In batch experiments, selenite and selenate were removed by 93 % and 94 %, respectively, after 24 h of contact time. This was achieved by employing 2 g/L of nZn0-BC in individual solutions of selenite and selenate (10 mL) in water with an initial concentration of 10 mg/L. The adsorption process was best described by the pseudo-second-order kinetic model and Langmuir isotherm. The effects of minerals and heavy metals in groundwater (K+, Mg2+, Na+, Ca2+, NO3–, As3+, and Pb2+) on selenite and selenate removal were not significant. However, SO42−, and PO43− reduced the removal of both selenite and selenate. Higher removal of both selenite and selenate was achieved over a wide pH range (4–10). Field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy were used for characterizing virgin and spent nZn0-BC. It was found that both adsorption and reduction were involved in the removal of Se oxyanions. Furthermore, the density functional theory reveals that stable complexes formed between nZn0-BC and selenite and selenate with the calculated adsorption energies of −2,205 kcal/mol and −2,209 kcal/mol, respectively. The density of states revealed that the presence of nZn0 in nZn0-BC increased the electronic states near the Fermi level. The increase in electronic states improved the adsorption of Se oxyanions, rendering the nZn0-BC a highly promising adsorbent for treating Se-contaminated water. According to the molecular dynamic simulations, the highest adsorption efficiency of nZn0-BC was attributed to the bidentate complexes of Se oxyanions with Zn atoms of nZn0-BC. © 2025