Adsorption of methylene blue onto carboxymethyl sago pulp-immobilized sago waste hydrogel beads

In this study, sago waste (SW) exhibited great potential in developing an efficient adsorbent in removing methylene blue (MB) from aqueous solution. Three types of adsorbents, namely, powdered SW, carboxymethyl sago pulp (CMSP) hydrogel beads and CMSP-immobilized SW hydrogel beads (CMSP-SW), were produced using SW as the precursor. The MB adsorption was investigated in a batch system to study the effects of experimental parameters of contact time, shaking speed (100–250 rpm), pH (4–10), dosage of SW (0.05–0.30 g) and initial MB concentration (50–250 mg/L). Among the adsorbents, CMSP hydrogel beads showed the lowest adsorption capacity; however, it showed capability in immobilizing SW to prevent the fungal infection and to ease the separation process. The combination of SW and CMSP has resulted in high adsorption capacity of CMSP-SW hydrogel beads for methylene blue, with Langmuir maximum adsorption capacity of 158 mg/g. Equilibrium adsorption data of CMSP-SW were observed to be fitted well into Langmuir isotherm model demonstrating adsorption process was limited to monolayer. On the other hand, the adsorption kinetics of MB onto CMSP-SW was found to be fitted well into pseudo-second order model, suggesting adsorption process was chemisorption. Based on the results obtained from the intraparticle diffusion model, CMSP-SW exhibited two-stage intraparticle diffusion. The reusability test using 50 mg/L of MB showed that the CMSP-SW could be reused up to three cycles with a total of 171 mg/g of MB being removed.