Synthesis and characterization of renewable carbon cryogel beads from empty fruit bunch for adsorption of ethyl orange

Abstract

Liquefaction of empty palm fruit bunch (EFB) to lignin was carried out by using ionic liquid [BMIM]Cl. Response surface methodology (RSM) was employed to identify the optimum condition for lignin yield. The liquefied product (i.e. lignin EFB) was reacted with furfural to synthesize resin. The resin was washed, freeze-dried and carbonized to obtain carbon cryogel beads (CCBs). The CCBs were then chemically activated with potassium hydroxide (KOH) to produce activated CCBs (A-CCBs). Both CCBs and A-CCBs were characterized for their morphology and physical properties using Fourier Transform Infrared Spectroscopy, Scan Electron Microscope, X-Ray Diffraction, Breuner, Emmer and Teller (BET) and Thermogravimetric Analysis. The performance of A-CCBs towards the removal of ethyl orange dye via adsorption process was performed. The adsorption mechanism was revealed through adsorption kinetic, isotherm and thermodynamic properties. The results indicate that the optimum lignin yield of 26.6% was produced at temperature of 150.5oC, time of 151 minutes, ionic liquid to EFB weight ratio of 3:1, and sulfuric acid concentration of 4.73 %. The results obtained reveal that chemical activation with KOH increased the BET surface area to 58 m2g-1 and 1068 m2g-1 for CCBs and A-CCBs, respectively. The experimental data were appropriately described by the Langmuir model with correlation coefficient of 0.997. The adsorption kinetics followed the pseudo-second order. The negative values of the free energy change indicated the adsorption is spontaneous. The positive value of enthalpy change (414.36 J/mol) and entropy change (191.97 J/K.mol) confirmed the endothermic nature and showed the increment of structural changes at solid-solution interface during adsorption process, respectively. It can be concluded that the prepared A-CCBs derived from lignin EFB provide reasonable ethyl orange dye removal capability by up to 83% removal capacity.