The interaction of perrhenate and acidic/basic oxygen-containing groups on biochar surface: A DFT study

Biochar has a good adsorption ability for perrhenate (ReO4-), which can be attributed to its abundant oxygen-containing groups, yet the effects of oxygen-containing groups on ReO4- adsorption are still unclear. Here, the interaction of ReO4- and acidic/basic oxygen-containing groups (hydroxyl, carboxyl, pyrone and chromene) on biochar were investigated by density functional theory (DFT) calculation with conductor-like screening model (COSMO). According to the calculated results, it was evidenced that the adsorption of oxygen-containing group functionalized BC towards ReO4- was gradually strengthened as decreased pH, and the protonated positively charged oxygen-containing groups presented stronger chemisorption to ReO4- mainly through electrostatic interaction, complexation and atomic orbital hybridization. The protonated hydroxyl and carboxyl and the protonated etheric oxygen of pyrone and chromene can offer favorable binding sites to ReO4-. Compared with the acidic oxygen-containing groups, the higher adsorption energy values, and the larger Mayer bond order indexes of interacting atoms identified that the basic oxygen-containing groups have stronger affinity with ReO4-. Pyrone had the strongest adsorption stability toward ReO4-. Our results can provide new ideas into the design and preparation of separation materials for ReO4- or the other anions capture from the aqueous solution.