Adsorption of methylene blue and phenol by wood waste derived activated carbon

The phosphoric acid activated carbon (PAC) was derived from waste wooden pallets by a two-step chemical activation technique, carbonization and phosphoric acid activation in sequence. A widely used commercial activated carbon, Calgon Filtrasorb 400 (F400), was studied in parallel for comparison. The physical properties and surface chemistry of the activated carbons were characterized using BET- N2 adsorption, elemental analysis, Boehm's titration, Fourier transform infrared spectroscopy, and x-ray photoelectron spectroscopy. PAC possessed physical properties (surface area and pore volume) that were comparable to those of F400, but displayed distinct surface chemistry in terms of pHPZC, surface acidity and basicity, and surface functional groups. Batch studies were conducted to evaluate the methylene blue (MB) and phenol adsorption capacity of PAC and F400 and their dependence on pH, contact time, and initial adsorbate concentration. Experimental results showed that the solution pH slightly influenced the adsorption of MB and phenol on F400, whereas it had no effect on their adsorption on PAC. Equilibrium adsorption data were fitted with an Langmuir isotherm equation. In comparison with F400, PAC showed a higher adsorption capacity for MB but lower for phenol. Given the comparable physical properties of PAC and F400 and the polar nature of MB and phenol, surface chemistry of the two carbons appeared to determine the adsorption mechanism and capacity. The strongly negative surface of PAC, due to phosphoric acid activation, facilitated the adsorption of positively charged MB, whereas the presence of oxygen-containing functional groups on PAC inhibited phenol adsorption.