A sustainable innovative water remediation approach for methylene blue removal: activated carbon from biomass and synthetic fiber waste.

The present work focuses on the development of activated carbon materials from two waste sources: natural biomass waste (NBW) and synthetic fiber waste (SFW). This study introduces a novel composite carbon material (CCM) derived from a 75 : 25 mixture of natural waste activated carbon (NWC) and synthetic waste activated carbon (SWC), the first report of such a composite from mixed waste streams. Unlike previous single-precursor studies limited to synthetic solutions, this work systematically optimizes the precursor ratio and validates the CCM on real textile wastewater, achieving 91% removal in synthetic solutions and 75% in real effluent. NBW was activated by sodium hydroxide, and SFW was activated by hydrochloric acid. The prepared materials were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, Brunauer-Emmett-Teller (BET), and scanning electron microscopy. Fourier Transform Infrared Spectroscopy analysis showed the presence of oxygen functional groups (O-H, C[double bond, length as m-dash]O, and C-O), which are responsible for hydrogen bonding and electrostatic interactions with dye molecules. X-ray diffraction confirmed the amorphous nature of the prepared carbons, which provides a large number of adsorption-active sites. BET analysis showed specific surface areas of 465, 280, and 510 m2 g-1 for NWC, SWC, and CCM, respectively. Batch adsorption experiments were performed to explore the effect of initial dye concentration, contact time, pH, adsorbent dosage, and temperature on the adsorption performance. Under optimized conditions, NWC exhibited 89% removal efficiency with the equilibrium adsorption capacity of 4.45 mg g-1 at pH 6, contact time of 10 min, and adsorbent dosage of 0.1 g. SWC showed a removal efficiency of 75% and an equilibrium adsorption capacity of 3.50 mg g-1 at pH 7.2, contact time of 50 min, and adsorbent dosage of 0.2 g. CCM (75% NWC + 25% SWC) exhibited the highest removal efficiency of 91% with the equilibrium adsorption capacity of 2.28 mg g-1 at pH 7 after 25 min using 0.2 g of adsorbent dosage. As per the Langmuir model, the maximum adsorption capacities for NWC, SWC, and CCM were 13.11, 2.34, and 25.45 mg g-1, respectively. The adsorption kinetics of all prepared materials were best described by the pseudo-second-order model (R 2 = 0.998-0.9999), which indicated favorable adsorption kinetics. The equilibrium data of CCM were in good agreement with both Langmuir and Freundlich models, reflecting its mixed microporous and mesoporous structure, which supports both monolayer and multilayer adsorption. Comparing with previously reported adsorbents, CCM showed higher adsorption capacity than date-pit-based adsorbents (18 mg g-1) and comparable performance to chitosan/activated carbon composites (22.5 mg g-1). Moreover, the optimized CCM was evaluated using real textile wastewater containing high organic loads characterized by chemical oxygen demand (3300 mg L-1), biochemical oxygen demand (2000 mg L-1), total suspended solids (520 mg L-1), and trace inorganic contaminants such as zinc, copper, iron, and chromium. The CCM was found to be effective in dye removal under the complex wastewater conditions with an efficiency of 75%, confirming its practical applicability for sustainable textile wastewater treatment. The dual-waste valorization approach provides an efficient way of transforming problematic waste streams into sustainable adsorbents for wastewater treatment.