Synthesis and characterization of modified bio-chars from biomass waste using microwave-assisted pyrolysis for methylene blue removal

Abstract

Bio-char (BC) is a unique renewable resource which is porous and carbonrich. In the past years, microwave-assisted pyrolysis has arisen to be a promising alternative to conventional pyrolysis due to its low cost, short processing time and energy efficiency. Banana pseudo-stem based bio-char (BP-BC) and palm kernel shell based bio-char (PK-BC) were produced by microwave-assisted pyrolysis and used to remove methylene blue (MB) in this study. The banana pseudo-stem and palm kernel shell were collected and grinded to desired particle size (200µm). The pre-treated materials then underwent microwave-assisted pyrolysis at 800W for 20min. The physicochemical properties of the BP-BC and PK-BC were characterized using Fourier tranform infrared spectroscopy, thermo-gravimetric analysis, Brunauer-Emmett-Teller and scanning electron microscope. The BET surface area of BP-BC and PK-BC were 46.58 and 12.54 m2/g, where the BP-BC was higher. Batch adsorption experiment of MB was studied with BP-BC and PK-BC and the effect of initial concentration of MB and contact time were investigated. The BP-BC exhibited the highest maximum adsorption capacity of 165.2 mg/g. From the kinetic data, the MB adsorption onto BP-BC reached equilibrium within 100 min of contact time whereas the MB adsorption onto PK-BC reached equilibrium within 270 min. The kinetic data have also shown that the MB adsorption onto BP-BC followed pseudo second order kinetic model whereas MB adsorption onto PK-BC followed pseudo first order. This indicated that the adsorption of MB onto BP-BC was chemical whereas the adsorption of MB onto PK-BC was physical. According to the isotherm data, adsorption of MB onto BP-BC and PK-BC was monolayer. Last but not least, the thermodynamic studies showed that the adsorption of MB onto BP-BC was endothermic and spontaneous whereas the adsorption of MB onto PK-BC was exothermic and non-spontaneous. This study revealed that the BP-BC had high yield and high performance in the MB adsorption.