PERFORMANCE OF DIFFERENT BIOCHARS IN THE DEGRADATION AND ADSORPTION OF CATIONIC AND ANIONIC DYES

Abstract

In this work, sawdust (SD) and manure pellet (MP) feedstocks were utilized to synthesize biochars. Three pyrolysis temperatures (300, 500 and 700 °C) and non-activation and steam activation were selected to prepare twelve biochar samples labeled as SD-300 NA, SD-500 NA, SD-700 NA, SD-300 SA, SD-500 SA, SD-700 SA, MP-300 NA, MP-500 NA, MP-700 NA, MP-300 SA, MP-500 SA, and MP-700 SA. The synthesized biochars were utilized to evaluate their sorption efficiency towards methylene blue (MB) and methyl orange (MO). Batch sorption experiments were conducted by varying the process parameters, e.g., contact time, and initial concentration. The biochars were characterized by Brunauer-Emmett-Teller (BET) surface area, X-ray Diffraction (XRD), Scanning Electronic Microscope (SEM), and Fourier Transform Infrared Spectroscopy (FTIR). Increasing pyrolysis temperature from 300 to 700 °C significantly enhanced the surface area of SD biochars (0.8 to 302 m2/g for non-activated, and 3.8 to 356 m2/g for steam-activated SD biochars), however, the effect of pyrolysis temperature had no effect on the surface area of MP biochars. SEM indicated that increasing pyrolysis temperature and steam activation introduced several pores and cracks on the surface of the SD and MP biochars. XRD spectra of SD biochars exhibited a highly amorphous structure, however, the presence of high inorganic contents of MP biochars portrayed several crystalline peaks. FTIR validates the presence of several oxygenated functional groups in the SD and MP biochars. Increasing pyrolysis temperature decreases several groups due to the destructions of functional groups, and steam activation increased functional groups of C-H2, C=O, C-H, and aromatic C-H stretching on SD and MP biochars produced at 500 °C. The Qm and Qe values for SD and MP biochar prepared at 500 °C pyrolysis temperature (both non-activated and steam-activated) provided better performance compared to biochar prepared at pyrolysis temperatures of 300 and 700 °C. The MP-500 SA and MP-700 SA biochars showed a significant increase in adsorption capacities towards MB, which are 135.38 and 126.40 mg/g, respectively. The isotherm analysis confirms the good alignment of experimental data with the Langmuir isotherm model, which infers the monolayer adsorption of MB and MO molecules on the biochar surface. In addition, the equilibrium time for MB and MO adsorption onto SD and MP biochar was found to be 125 min. The kinetic data aligns with the pseudo-2nd order model infers that the adsorption of MB and MO on the non-activated and steam-activated SD and MP can be interpreted as chemisorption.