AUTHOR=Xu Shuiping , Liang Meina , Ding Yanmei , Wang Dunqiu , Zhu Yinian , Han Linbo 

TITLE=Synthesis, Optical Characterization, and Adsorption of Novel Hexavalent Chromium and Total Chromium Sorbent: A Fabrication of Mulberry Stem Biochar/Mn-Fe Binary Oxide Composite via Response Surface Methodology

JOURNAL=Frontiers in Environmental Chemistry

VOLUME=2

YEAR=2021

URL=https://www.frontiersin.org/journals/environmental-chemistry/articles/10.3389/fenvc.2021.692810

DOI=10.3389/fenvc.2021.692810

ISSN=2673-4486

ABSTRACT=<p>In this study, a new generation chromium sorbent, mulberry stem biochar/Mn-Fe binary oxide composite (MBC-MFC), was fabricated by chemical precipitation on carbonized mulberry stem according to response surface methodology (RSM) results. RSM was more convenient to figure out the optimized preparation condition of MBC-MFC theoretically for achieving a maximum removal efficiency of Cr(VI) and total chromium (T<sub>Cr</sub>), compared to labor-intensive orthogonal experiments. The RSM results showed that Fe/Mn concentration (C<sub>Fe</sub>; C<sub>Mn</sub>), MBC activation temperature after soaking in KOH solution (<italic>T</italic>), and pH during precipitation of Fe-Mn oxide were three main factors to significantly affect the efficiency of MBC-MFC (<italic>p</italic> &lt; 0.05) in Cr(VI) and T<sub>Cr</sub> removal. With the selected condition (<italic>C</italic><sub>Fe</sub> = 0.28 mol/L; <italic>C</italic><sub>Mn</sub> = 0.14 mol/L; <italic>T</italic> = 790°C; pH = 9.0), MBC-MFC was synthesized with a large surface area (318.53 m<sup>2</sup>/g), and the point of zero charge values of MBC-MFC was 5.64. The fabricated MBC-MFC showed excellent adsorption performance of Cr(VI) and T<sub>Cr</sub> in an aqueous solution. The maximum Cr(VI) and T<sub>Cr</sub> removal capacity of MBC-MFC was 56.18 and 54.97 mg/g (<italic>T</italic> = 25°C, pH = 3.0, <italic>t</italic> = 48 h, and dosage = 0.10 g/50 ml), respectively, and the maximum Cr(VI) adsorption of MBC-MFC was 4.16 times that of bare MBC, suggesting the synergistic effects of Fe/Mn oxides and MB on the performance of MBC-MFC in Cr(VI) and T<sub>Cr</sub> removal. The adsorption mechanism of MBC-MFC on chromium was mainly contributed by surface complexation and electrostatic attraction. Our study offers valuable outlooks to develop high-performance biochar-based sorbents for heavy metal removal and sustainable environmental remediation.</p>