Dewaxed Honeycomb as an Economic and Sustainable Scavenger for Malachite Green from Water

Abstract

Dewaxed honeycomb powder (HCP) was used as a promising adsorbent for removal of malachite green (MG) from aqueous solution. Raw honeycomb was strategically dewaxed by petroleum ether, and the purified product was characterized by Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), pH_zpc, and proximate analysis. A high uptake capacity (123 mg/g) was found at neutral pH. Experimental data follow pseudo-second-order kinetics (<i>k</i> ₂ as 0.45 × 10^-2 g/min/mg, <i>R</i> ² = 0.986) and Langmuir isotherm with <i>R</i> ² 0.999. Thermodynamic parameters suggested a spontaneous (Δ<i>G</i> = -26.28 kJ/mol) and exothermic (Δ<i>H</i> = -11.61 kJ/mol) process, which suggests increased randomness (Δ<i>S</i> = 0.0486 kJ/mol) at the solid-liquid interface during the adsorption process. The material can be regenerated by ordinary salt solution (1 M NaCl) and efficiently reused for three cycles with a minimal loss in efficiency. Adsorption mechanism is proposed to be a combination of electrostatic interaction and π-π stacking between aromatic units of HCP and MG. Abundant availability, possibility of wax commercialization, economic sustainability, and comprehensive waste management make HCP an ideal choice for dye decolorization.