Functional carboxylated graphene oxide aerogel spheres for high-efficiency cationic dye adsorption: Synergistic design, mechanism, and regeneration

Cationic dyeing wastewater poses severe environmental threats by releasing persistent aromatic dyes that suppress aquatic photosynthesis, accumulate in soil to inhibit plant growth, and generate carcinogenic byproducts through photodegradation or chlorination, thereby disrupting ecosystem stability. Carboxylated graphene oxide/sodium alginate-activated carbon aerogel spheres (CGO-AC/SA) were engineered to address cationic dye pollution through a synergistic integration of tailored carboxylation, hierarchical porosity, and DFT-guided mechanistic insights. The composite achieved unprecedented adsorption capacities of 650.695, 546.471, and 385.634 mg/g for methyl violet (MV), methylene blue (MB), and basic fuchsin (BF), respectively. Multi-scale analyses revealed that carboxylation amplified surface charge density ( COO − ) and enabled selective electrostatic interactions with cationic dyes, while hierarchical porosity (24.67 nm avg. pore diameter, 5.583 m 2 /g surface area) facilitated rapid diffusion kinetics (equilibrium within 16 h). DFT calculations correlated dye selectivity with electronic properties, identifying MV's low energy gap (ΔE GAP  = 2.686 eV) and high dipole moment (μ = 2.004 D) as key drivers for enhanced π-π and electrostatic binding. Adsorption followed pseudo-second-order kinetics (R 2  > 0.993) and Sips isotherm models (R 2  > 0.997), confirming chemisorption-driven multilayer mechanisms. Despite robust regeneration (>78 % efficiency over five cycles via 0.10 M HCl), gradual capacity decline highlighted challenges in Ca 2+ -H + exchange stability. The aerogel's dual-function design, combining tunable surface chemistry with structural resilience, positions it as a scalable, high-performance solution for sustainable wastewater remediation.