Adsorptive Removal of Methylene Blue from Aqueous Solution Using Dalbergia Sissoo Leaf Powder as a Low-Cost Biosorbent

Abstract

In this study, Dalbergia sissoo leaf powder (DSLP) was evaluated as a plant-waste adsorbent for methylene blue
(MB) removal from water. SEM, EDS, and FTIR characterization revealed a rough, irregular surface and functional groups (
OH, –NH, C=O, and C=C). Small FTIR shifts (approximately 4 cm⁻¹) provided tentative evidence of their involvement in dye
binding. Batch experiments examined initial dye concentrations (27–68 mg/L), adsorbent doses, and contact times (15–60 min).
Adsorption capacity increased with dye concentration, ranging from 2.82 to 7.50 mg/g. The highest removal in the contact
time experiment (73.98%) occurred at 45 min; however, equilibrium time could not be precisely established. In the dose
experiment, removal peaked at 61.74% with 0.3 g adsorbent before decreasing at 0.4 g, potentially due to particle aggregation.
Adsorption capacity decreased with increasing dose. Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich (D–R)
models were evaluated. Langmuir fitted poorly and yielded non-physical parameters, preventing reliable determination of
maximum monolayer capacity. Freundlich (R² = 0.978) and Temkin (R² = 0.968) showed comparatively better fits than D–R
(R² = 0.913). However, only four concentrations were tested, limiting model discrimination. The low D–R mean adsorption
energy (E = 0.516 kJ/mol) tentatively suggests physical interactions. The pseudo-second-order model (R² = 0.93) fitted better
than the pseudo-first-order model (R² = 0.84), although this does not establish the adsorption mechanism. Overall, DSLP
demonstrates potential as a low-cost adsorbent for dye-contaminated wastewater.

Keywords: Plant-based adsorbent, characterization heterogeneous surface, functional groups, dyes.