Cost-effective adsorbent from arabinogalactan and pectin of cactus pear peels: Kinetics and thermodynamics studies.

Cactus pear peel as agricultural waste containing arabinogalactan and pectin was thermally treated at 300 °C for 4 h and the resultant carbonized material was applied as adsorbent for the removal of methylene blue dye as a model cationic dye. The prepared adsorbent was characterized by means FTIR for structural characterization, N2 physisoprtion measurements for texture properties, SEM and EDAX for morphological and elemental analysis. The characterization results clearly show that the prepared material is porous with several -OH and CO terminals. The point of zero charge was found to be 7 as detected by batch equilibrium method. The adsorption process was optimized in terms of pH values, contact time, initial dye concentration and temperature. The kinetic study indicated that the pseudo-second-order model can perfectly describe the investigated adsorption process; moreover, the equilibrium results were best fitted by Freundlich model. Furthermore, at pH 8.0, the adsorption capacity was achieved to the maximum value of methylene blue as 102 mg/g. Thermodynamic investigation showed that the adsorption process is spontaneous, endothermic in nature with higher entropy, while the activation energy calculations indicated a physisorption process. The obtained results showed the high potential of the bio-based adsorbent for removal of methylene blue from wastewater.