From wild thornbush to high-performance activated carbon using a novel integrated furnace-microwave activation

Activated carbon with high adsorption capacity for 4-nitrophenol (4NP) is synthesized from profusely proliferating Prosopis juliflora thornbush by implementing a novel sequential arrangement of carbonization in the furnace followed by microwave activation. The adsorption capacity of the integrated furnace-microwave activated carbon (FMAC) was 179 mg/g which was 25% and 14% higher than those of conventional furnace activated carbon (FAC) and microwave activated carbon (MAC). SEM analysis revealed the presence of well-developed pores on these activated carbons. EDX analysis showed maximum carbon content (87.5%) and lowest phosphate content (3%) in FMAC when compared to FAC (81.5% and 7.1%) and MAC (73.3% and 11.9%). The BET surface area (1086 m(2)/g) and micropore volume (0.846 cc/g) of FMAC based on CO2 adsorption isotherm were higher than FAC (936 m(2)/g and 0. 642 cc/g) and MAC (646 m(2)/g and 0.415 cc/g). FTIR analysis revealed the presence of hydroxyl, carboxylic acids, quinones, phosphates, and polyphosphate ester groups on AC surfaces. The thermal stability of FMAC given by TGA analysis was also significantly enhanced. Adsorption mechanism of 4NP on FMAC was explained using Weber-Morris intraparticle diffusion and Boyd models. These models revealed two distinct regimes corresponding to diffusion in mesopores and micropores. The adsorption of 4NP was explained in terms of electrostatic forces, H-bonding, pi-pi interaction, and pore filling. Regeneration studies of FMAC revealed an efficiency of 85% after 4 cycles. Through the novel sequential furnace-microwave treatment, wild thornbush precursor could be transformed into a high-capacity reusable adsorbent with excellent thermal stability.