Complexation mechanism of Pb2+ on Al-substituted nanohematite. A modeling study and theoretical calculation

LIANG, YU; XIANG, YONGJIN; WEI, ZHIYUAN; WANG, MINGXIA; XIONG, JUAN; HOU, JINTAO; AVENA, MARCELO; TAN, WENFENG

Bahía Blanca

Congreso; XXII Encuentro de superficies y materiales nanoestructurados; 2023

Nano2023

Hematite nanoparticles commonly undergo isomorphic substitution of Fe3+ by Al3+ in nature. The effects of this substitution on the adsorption behavior of environmentally relevant contaminants remain poorly understood. Herein, the interfacial reactions between Al-substituted hematite and Pb2+ were investigated via CD-MUSIC modeling and DFT calculations. As the Al content increased from 0% to 9.4%, Al-substitution promoted the increase of (001) facets and the increase of the total active site density from 5.60 to 17.60 sites/nm2. The surface positive charge of hematite significantly increased from 0.096 to 0.418 C/m2 at pH 5.0 due to the increase in site density and proton affinity. The extent of Pb2+ adsorption increased from 3.92 to 9.74 mmol/kg with increasing Al content at pH 5.0 and 20 μmol/L initial Pb2+ concentration. The adsorption affinity of bidentate Pb complexes slightly increased while that of tridentate Pb complexes decreased with increasing Al content due to the increasing presence of ≡AlOH-0.5 and ≡Fe2AlO-0.5 surface sites. Tridentate Pb complexes were dominant species on the surface of pure hematite, but bidentate complexes became more dominant with increasing Al content. The changes on morphology and adsorption performance produced by the substitution are schematically resumed in Figure 1. The obtained model parameters and molecular scale information are of great importance for better describing and predicting the environmental fate of toxic heavy metals in terrestrial and aquatic environments.