Photoadsorptive Removal of Anionic Dye Using Ammonia-Doped Magnetic Carbon Nanotubes: Efficiency, Mechanism, Characterization, and Antibacterial resistance

Magnetic ammonia-doped multi-walled carbon nanotubes (MWCNTs/NH₃) were synthesized and evaluated for the sunlight-enhanced removal of Acid Red 73 (AR73) dye. Characterization of FTIR, SEM, and EDX confirmed a porous structure (70–110 nm diameters) with functional groups (O-H, N-H, C≡C) critical for adsorption. FTIR confirmed functional groups (O-H, N-H, C≡C, C=C) critical for dye adsorption. SEM revealed a porous, entangled MWCNT structure with high surface area (70–110 nm tube diameters). EDX showed 88.10% carbon and 10.59% oxygen, with trace Si, Ca, and Fe. TGA indicated ammonia decomposition (100–250°C) and CNT oxidation (300–900°C). Batch experiments demonstrated rapid removal (97% within 30 minutes) and equilibrium at 180 minutes. Optimal conditions included pH 5 (99.16% efficiency) and 0.02 g/L dosage (100% removal), though adsorption capacity decreased at higher doses. The Langmuir isotherm (R²=0.939) revealed monolayer adsorption with a high capacity (312.5 mg/g), while pseudo-second-order kinetics (R²=0.999) indicated chemisorption dominance. Electrostatic interactions between protonated NH₃⁺ and anionic dye, hydrogen bonding, and π-π stacking were key mechanisms. Sunlight further enhanced removal via photocatalytic degradation. Despite limited antibacterial activity (low sensitivity for Staphylococcus aureus and Vibrio fluvialis), the composite showed no broad-spectrum efficacy. This study highlights ammonia-doped MWCNTs as a sustainable, energy-efficient adsorbent for high-capacity dye removal, leveraging solar energy to mitigate industrial wastewater pollution.