Synthesis of Sago Bark-Derived Magnetic-Activated Carbon for Methylene Blue Removal

Nur Amalina Naimah, Hamidon (2024) Synthesis of Sago Bark-Derived Magnetic-Activated Carbon for Methylene Blue Removal. Masters thesis, Universiti Malaysia Sarawak.

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Abstract

While adsorption is recognized as an effective water treatment method, the high cost associated with conventional adsorbents hinders its feasibility for widespread applications. Therefore, this study aims to synthesis and characterise magnetic-activated carbon derived from sago bark (SBMAC), an abundant agriculture waste, as a low-cost adsorbent for the removal of methylene blue dye from an aqueous solution. Beforehand, the optimal SBMAC preparation parameters were determined using the response surface methodology Box-Behnken Design (BBD) via the Stat-Ease Design Expert software. The response surface methodology BBD revealed that the optimal preparation parameters for SBMAC were an impregnation ratio of 1.5, a pyrolysis temperature of 700°C, and a heating time of 60 minutes. By employing the optimal preparation parameters, SBMAC was prepared through single-stage pyrolysis and impregnated with FeCl3.6H2O and FeSO4.7H2O as magnetic media and KOH as an activating agent. The sago bark powder (SBP), SBMAC, and SBMAC after dye adsorption (SBMAC2) were characterised using BET, SEM-EDX, and FTIR analyses. Furthermore, The BET analysis of SBMAC reveals a specific surface area of 849.906 m²/g and a total pore volume of 2.47 cm³/g, 30 times higher than SBP and decreasing after adsorption. The FTIR analysis of SBMAC and SBMAC2 indicates the presence of the stretching vibration of Fe-O, which is absent in SBP. Additionally, stronger O-H peak intensities and the presence of C-Cl band following methylene blue adsorption indicate the occurrence of methylene blue adsorption. The SEM analysis displays a granular texture for SBP and SBMAC, although SBMAC exhibits fewer visible pores than SBP. Additionally, EDX analysis of SBP reveals a high percentage of carbon and oxygen, whereas SBMAC and SBMAC2 have high percentages of carbon, oxygen, and iron elements. The SBMAC was employed in batch adsorption experiments to evaluate iv adsorption kinetics, isotherms, the effect of temperature and adsorption thermodynamics, the effect of adsorbent dosage, and the pHPZC and the effects of pH. The batch kinetics experiments were conducted at four distinct dye concentrations (100 mg/L, 200 mg/L, 300 mg/L, and 500 mg/L). The results indicate that the highest initial dye concentration required the longest duration to reach equilibrium, in contrast to the lower concentrations. Furthermore, the adsorption of all four initial concentrations exhibited the best fit with the pseudo-second-order (PSO) kinetic model, displaying R2 values exceeding 0.998, in contrast to the pseudo-first-order (PFO) model. Notably, the kinetic adsorption data did not align with the intraparticle diffusion model (ID), indicating that multiple processes influence the dye adsorption onto SBMAC. In the context of adsorption isotherms, the model that fits best is the Freundlich isotherm model, exhibiting an R2 value of 0.9662 along with a maximum adsorption capacity (qmax) of 1655.05 mg/g. Meanwhile, for the effect of temperature and adsorption thermodynamics, the highest adsorption capacity was attained at the lowest temperature of 30°C, and the adsorption process was found to be exothermic. For the effect of adsorbent dosage, the most optimal adsorbent dosage was observed at 1.0 g/L for the removal of dye. For pHPZC and the effect of pH, the pHPZC of the adsorption was calculated at pH 6.74 and the highest adsorption capacity was obtained at the initial pH 11. In conclusion, SBMAC was successfully prepared from sago bark having a high-adsorption capacity adsorbent for the removal of methylene blue dye applications.

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