การดูดซับสีย้อมเมทิลออเรนจ์ด้วยถ่านกัมมันต์จากเศษกะลาแมคคาเดเมียที่ผ่านการกระตุ้นด้วยสารละลายโซเดียมไฮดรอกไซด์ร่วมกับคลื่นไมโครเวฟ

Piyarut  Moonsri; Jinnapada  Inthong

Authors

Piyarut Moonsri Phetchabun Rajabhat University
Jinnapada Inthong Phetchabun Rajabhat University

Keywords:

Activated carbon, Macadamia nut shell, methyl orange, ; microwave activation

Abstract

Methyl orange (MO) is a persistent azo dye that is difficult to degrade and poses significant adverse impacts on water quality and the environment. Meanwhile, macadamia shell is an abundant agricultural waste that remains largely underutilized. This study aimed to investigate the adsorption of methyl orange using activated carbon prepared from macadamia shell waste via sodium hydroxide–assisted microwave activation (MAC-MC) and to compare its performance with activated carbon produced by conventional pyrolysis (MAC-PC). The results demonstrated that NaOH activation combined with microwave heating at a power of 800 W for 15 min produced activated carbon with a highly porous surface, characterized by micron-sized pores uniformly distributed throughout the surface structure. SEM–EDS analysis revealed that MAC-MC contained 73.56% carbon and 23.60% oxygen, which were comparable to those of MAC-PC prepared by pyrolysis at 800 °C for 3 h, exhibiting carbon and oxygen contents of 81.09% and 16.60%, respectively. These findings highlight the effectiveness of microwave activation in enhancing carbon content within a significantly shorter processing time. FTIR analysis further indicated that the functional groups present in the raw macadamia shell markedly decreased after both microwave and thermal activation, confirming the increased carbon purity of the prepared activated carbons. Batch adsorption experiments conducted at pH 3 and 30 °C using 0.1 g of adsorbent in 100 mL of 300 mg L^-1 MO solution for 120 min showed that MAC-MC exhibited superior adsorption performance compared to MAC-PC, achieving a higher removal efficiency (≈81.97% versus 77.41%) and a greater equilibrium adsorption capacity (q_e ≈ 245.91 versus 232.24 mg g^-1). Adsorption isotherm analysis revealed that the Freundlich model provided the best fit, indicating a heterogeneous surface and multilayer adsorption behavior. The Dubinin–Radushkevich model yielded a mean adsorption energy of approximately 18.26 kJ mol^-1, suggesting that the adsorption mechanism involved ion exchange and chemisorption. Thermodynamic analysis showed a negative enthalpy change (DH = -17.58 kJ mol^-1), confirming that the adsorption process was exothermic, while negative Gibbs free energy values (DG < 0) at all studied temperatures indicated spontaneous adsorption, with improved favorability at lower temperatures. Overall, activated carbon prepared from macadamia shell waste via sodium hydroxide–assisted microwave activation represents an efficient and promising approach for upgrading agricultural waste into a high-performance adsorbent for dye removal from wastewater.

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