Abstract:
Textile effluents have become a major concern to environmentalists due to the bio-persistent nature of the dyes. The azo dyes are toxic to human and aquatic life. In recent years, treatment of contaminated effluents by natural resources has been proposed as the most sustainable solution for this problem. In this work, Moringa oleifera seeds derived biochar in combination with chitosan and ZnO were used to produce three binary composites such as Biochar-Chitosan (BC), Biochar-ZnO (BZ), and Chitosan-ZnO(CZ) along with a ternary composite Chitosan-ZnO/Biochar (CZB). The prepared composites were characterized by Fourier Transform-Infrared Spectroscopy (FTIR), Field Emission Scanning Electron Microscope (SEM), and X-ray diffraction (XRD). The surface area of the prepared materials was measured by the Brunauer-Emmett-Teller (BET) analyzer. The adsorption efficiency of these composites was evaluated against a cationic azo dye, methylene blue (MB). Spectroscopic analysis of the biochar-based composites established that the modification of biochar by chitosan and ZnO enhanced different functional groups e.g., -OH, -COOH, R-CH, R-OH, -NH2, etc., and active groups on the biochar surface. The presence of micro and mesopores in the structure of biochar is revealed by FESEM images. Pore development of biochar by ZnO particles was also visible. The XRD results showed the highly amorphous structure and increased crystallinity of biochar by the modification. The surface area ranged from 0.90± 0.00 to 14.48 ± 1.13 m2g-1 for prepared samples, where the highest surface area was found for BZ and the lowest for BC. Basic pH was found to be favorable for adsorption. Rapid dye adsorption was observed in the time range of 0-20 min, reaching its saturation at 90 min. The impact of dye concentration dependence was evaluated in the range of 10-70 mgL-1. The kinetics data were linearized by two different kinetics models e.g., pseudo 1st order and pseudo 2nd order model. Isotherm reveals the favorability of Langmuir isotherm over the Freundlich and Tempkin models. The highest adsorption capacity was found for BC followed by the second-highest for CZB. For the binary composite BC and ternary composite CZB, the RSM optimizations were also conducted, which gave similar results that were observed in the experiments. The characterization and experimental results prefigure the chemical functionalities were the critical parameters over the surface area for the adsorption process.
