Enhanced Cr(VI) reduction using highly conductive material synthesized by modified chitosan coated with natural iron-manganese minerals

• Chitosan based biochar coated magnetite/rhodochrosite composites were prepared and evaluated. • Cr(VI) removal by MaRh@Ch composite were highly pH-dependent. • MaRh@Ch-500 showed the best Cr(VI) removal performance (104.5mg/g) at pH 2. • 99.33% of Cr(VI) species was reduced to Cr x Fe 1-x (OH) 3 /Cr 2 O 3 and immobilized on the MaRh@Ch-500. • The remarkable electrical conductivity of MaRh@Ch-500 enhanced the Cr(VI) removal efficiency. This work presents a novel chitosan coated magnetite/rhodochrosite composites prepared by thermal reduction method were used to efficient remove Cr(VI) from aqueous solution. A series characterization including XPS, XRD, FTIR, SEM, TEM and electrochemical measurement were used to investigate the characterization of prepared materials. SEM and TEM results show that the chitosan carbon (Ch-BC) firmly coated the thermally modified rhodochrosite and magnetite, and composites prepared at 900℃ can further improve its specific surface area. The removal of Cr(VI) by MaRh@Ch-500, MaRh@Ch-700 and MaRh@Ch-900 are all highly pH dependent. At pH 5, MaRh@Ch-500 showed the best Cr(VI) removal capacity than others, which is 13.4, 18.1 and 9.9 times of natural magnetite, rhodochrosite and Ch-BC, respectively. Additionally, maximum adsorption capacity for MaRh@Ch-500 fitted by Langmuir model was 104.5 mg/g at pH 2, 30℃. Electrochemical analysis confirmed that based on coated of Ch-BC, the MaRh@Ch-500 presented stronger redox activity, lower resistance and stronger electrical conductivity than others, which is more favorable to electron transfer. XPS results show that nearly 92.33% Cr(VI) was converted to Cr x Fe 1-x (OH) 3 /Cr 2 O 3 and loaden on the surface of MaRh@Ch-500. Our results provide theoretical support for the development of efficient treatment of Cr(VI) polluted water.