Microporous Development in Cashew Branch Activated Carbon: Comparative Effects of Sodium and Potassium Hydroxides

Abstract

Chemical activation of lignocellulosic biomass is a cost‑effective route to tailor microporosity in activated carbons (ACs) for adsorption and gas purification. This study evaluates the comparative effects of sodium hydroxide (NaOH) and potassium hydroxide (KOH) on the development of microporosity in activated carbon derived from cashew (Anacardium occidentale) branch biomass. The precursor was size‑reduced, sieved (pass at 8 mm; retain at 4 mm), impregnated for 24 h in alkaline solutions (typically 500 ppm), oven‑dried (24 h), carbonized in lidded porcelain containers at 500 °C for 3h10 (NaOH) or 3 h 00 (KOH), and subsequently washed to near‑neutral pH and re‑dried. Yield was quantified by mass balance. Microporosity was assessed using the iodine number test (0.1 N I₂, titration with 0.1 N Na₂S₂O₃, starch indicator), a well‑established proxy for the presence of small pores in ACs. Under the stated conditions, average production yields were ~35%. The iodine numbers obtained were ~533 mg·g⁻¹ for NaOH‑activated samples and ~571 mg·g⁻¹ for KOH‑activated samples at 500 °C, indicating a modest advantage of KOH in creating/expanding micropores in this feedstock. Overall, activation agent, impregnation ratio, and thermal schedule critically determine micropore development; KOH shows slightly higher efficacy than NaOH in the present cashew branch system. The results support the viability of cashew branch biomass as a local, sustainable precursor for microporous AC production.