Ce and Mn/bio-waste-based activated carbon composite: Characterization, phenol adsorption and regeneration

The present work deals with the use of activated carbon (AC)-metal composites for phenol adsorption from wastewater and decomposition of the adsorbed-phenol by thermal oxidation of the saturated AC-metal composites. The rice straw-based AC was modified by manganese oxide and ceria individually and jointly, in different metal/AC weight ratios (0.25–1.5) and calcination at different temperatures (300–700 ℃). The lowest temperature and metal/AC weight ratio resulted in the optimized AC-metal composites. CeO2 crystallite phase as clogs was detected on the adsorbent surface, and magnesia was uniformly dispersed as fine amorphous particles. Metal oxide species at low weight ratios led to an increase in the percentage of micropore volume (from ~46% to ~68%) by partially blocking the opening of some mesopores and converting them into finer pores; this is one of the strengths of the modification technique. The oxidation of carbon-hydrogen bonds by introducing metal oxides was demonstrated by FTIR analyses. According to the thermogravimetric study, the minimum temperature for dry oxidation of adsorbed phenol on AC-metal composites was 300 ℃. Oxidation at such a low temperature made the AC-manganese oxide composite a suitable choice for use in cyclic phenol adsorption-oxidation. The overall performance of manganese oxide was better than ceria and the mixed composite when the oxidation of adsorbed phenol was carried out under air atmosphere. In contrast, the phenol-loaded AC requires a higher temperature (>400 ℃) for phenol oxidation, which will result in a higher mass loss of the adsorbent.