Comparative Adsorption Behavior of Orange Peel Powder and Its Chars for Dye Removal

This study evaluates the efficacy of orange peel powder (OP), a readily available agri-food waste, and its muffle furnace char (MF) and nitrogen-assisted char (NA), for crystal violet (CV) adsorption. Char samples analyzed using thermogravimetric analysis, Fourier-transform infrared spectrometry, scanning electron microscopy, and proximate analysis showed substantial structural changes. The impacts on absorption of pH, adsorbent, contact time, dye concentration, and temperature were evaluated. Orange peel powder showed maximum adsorption capacity (49.35 mg g^-1, Langmuir isotherm), compared to those of MF (19.05 mg g^-1) and NA (12.87 mg g^-1), due to its abundant surface sites and functional groups. Enhanced pH tolerance and process stability and other parameters were exhibited by MF and NA but with reduced adsorption capacity for CV. All adsorbents conformed to the Langmuir isotherm and exhibited pseudo-second order kinetics, indicative of monolayer chemisorption. Crystal violet adsorption on OP was exothermic and spontaneous at ambient temperature, while MF and NA exhibited endothermic and temperature-dependent behavior. Although orange peel exhibited superior adsorption capacity, chars have practical benefits for effective dye removal, facilitating waste valorization and sustainable water management.