990533 - A Novel Biochar/ZnO Composite for Enhancement of Hexavalent Chromium Removal from Aqueous Solution (Student Poster 21)

Biochar, a low-cost material, can be used to remove heavy metals from aqueous solution However, the drawbacks of biochar are low adsorption capacity and poor selectivity toward heavy metals. To improve the adsorption performance, a new strategy about large surface area with the porous network with high chemical affinity and functional groups of a new composite of zinc oxide (ZnO) to supported biochar property is discovered. This study, biochar derived from pineapple leaves (PLB) and rice husk (RHB) with ZnO (biochar-ZnO) were prepared by the low-temperature hydrothermal method for the removal of Cr(VI) from wastewater. The specific surface area (SSA) of PLB and RHB were 4.48, 132.4 m2g-1, while the SSA of PLB-ZnO, and RHB-ZnO increased to 39.70 and 146.4 m2g-1 respectively, indicating the SSA of original biochar increased after combined with ZnO. The FTIR results of the composite showed the basic element composition include C, O, and Zn with a large number of oxygen-containing functional groups (-OH, COOH, and O-C=O) observed on the composite surface. The maximum Cr(VI) adsorption capacities of PLB-ZnO and RHB-ZnO were 54.21and 51.80 mg g-1 at the initial pH 2.0, higher than the PLB and RHB (27.63 and 24.18 mg g-1, respectively). As compare to adsorption capacities, the specific surface area of PLB-ZnO was significantly less than that of its corresponding RHB-ZnO, but PLB-ZnO still had a higher absorption capacity than the RHB-ZnO, indicating that the Cr(VI) adsorption by PLB-ZnO did not mainly depend on its pore structure. As can be observed from the FTIR spectra, the characteristic peaks of -OH stretching vibration of the carboxylic acid was enhanced for PLB-ZnO after modification indicating that some -OH, which may come from ZnO, was introduced after the modification. The -OH functional groups were protonated to form positively charged -OH2+ functional groups, then the Cr-containing anions could be adsorbed and migrated to the ZnO surface via electrostatic interaction. Therefore, electrostatic interaction might be the dominant mechanism adsorption for Cr (VI) by the modified biochar. These results presented that some -OH formed on modified biochar surfaces. The adsorption kinetics and isotherm data were fitted well by pseudo-second-order kinetic model and the Freundlich isothermal adsorption model, which indicated Cr(VI) adsorption mechanism was a chemisorption based multi-layer adsorption. The possible adsorption mechanisms of Cr (VI) adsorption on to biochar/ZnO composite were proposed based on the analysis of FTIR, SEM, EDX, and XPS techniques. The possible adsorption mechanisms occurring between Cr(VI) anions and the composite due to the contribution of ZnO present in the biochar structure after combined by Zn. The reduction of Cr(VI) to Cr(III) through electron-donor groups (-OH) on the composite surface. Then, Cr(VI) interacted with the electron-donor groups, and Cr(VI) is reduced to Cr(III). Overall, this study demonstrates that generation of modified biochar with ZnO from heavy metals polluted biomass could be an attractive approach to improve the efficiency of biochar on Cr(VI)adsorption.