Effective strategy for simultaneous removal of Congo red and Cr(VI) by ferroan brucite

Mg 0.6 Fe 0.4 (OH) 2 enables simultaneous removal of CR and Cr(VI) from wastewater. • Maximum removal capacities reach 2861.56 mg/g for CR and 295.68 mg/g for Cr(VI). • Removal mechanisms mainly include interlayer immobilization, degradation and precipitation. • Mg 0.6 Fe 0.4 (OH) 2 maintains high efficiency across pH 3–13 and in presence of competing anions. Organic dyes and the heavy metal frequently coexist in industrial wastewater, such as from textile dyeing processes, posing a serious threat to the environment and human health. In this study, an efficient and environmentally friendly Fe 2+ -doped brucite, Mg 0.6 Fe 0.4 (OH) 2 , was successfully synthesized for the simultaneous removal of the anionic dye Congo red (CR) and heavy metal Cr(VI) from wastewater. Mg 0.6 Fe 0.4 (OH) 2 achieved maximum removal capacities of 2861.56 mg/g for CR and 295.68 mg/g for Cr(VI) in single pollutant systems. In the coexisting system of CR and Cr(VI), due to the higher binding energy between CR and Mg 0.6 Fe 0.4 (OH) 2 as revealed by molecular simulation calculations, Mg 0.6 Fe 0.4 (OH) 2 exhibited preferential removal of CR. The presence of CR significantly inhibited the removal of Cr(VI), while Cr(VI) had a minimal effect on CR removal. Mechanism studies revealed that CR removal was achieved through interlayer immobilization, hydrogen bonding, and degradation (with 1 O 2 and ·O 2 − as the main active species). Cr(VI) removal occurred primarily via interlayer immobilization and reductive precipitation (forming (Fe,Mg)(Cr,Fe) 2 O 4 ). Moreover, Mg 0.6 Fe 0.4 (OH) 2 maintained excellent removal performance across a wide pH range (3−13) and in the presence of common coexisting anions. The reusability was tested and illustrated that Mg 0.6 Fe 0.4 (OH) 2 can be reused for several times. This work provides an efficient and feasible material for the simultaneous treatment of wastewater co-contaminated dyes and heavy metals, demonstrating significant potential for practical application.