The use of dyes at an industrial level has become problematic, since the discharge of dye effluents into water disturbs the photosynthetic activity of numerous aquatic organisms by reducing the penetration of light and oxygen, in addition to causing carcinogenic diseases and mutagenic effects in humans, as well as alterations in different ecosystems. Chitosan (CS) is suitable for removing anionic dyes since it has favorable properties, such as acquiring a positive charge and a typical macromolecular structure of polysaccharides. In this study, the optimization of CS beads crosslinked with glutaraldehyde (GA) for the adsorption of reactive blue dye 4 (RB4) in an aqueous solution was carried out. In this sense, the response surface methodology (RSM) was applied to evaluate the concentration of CS, GA, and sodium hydroxide on the swelling degree in the GA-crosslinked CS beads. In the same way, RSM was applied to optimize the adsorption process of the RB4 dye as a function of the initial pH of the solution, initial concentration of the dye, and adsorbent dose. The crosslinking reaction was investigated by scanning electron microscopy (SEM), Fourier transformed infrared spectroscopy (FTIR), and X-ray diffractometry (XRD). The design described for the swelling degree showed an R2 (coefficient of determination) adjusted of 0.8634 and optimized concentrations (CS 3.3% w/v, GA 1.7% v/v, and NaOH 1.3 M) that were conveniently applied with a concentration of CS at 3.0% w/v to decrease the viscosity and facilitate the formation of the beads. In the RB4 dye adsorption design, an adjusted R2 (0.8280) with good correlation was observed, where the optimized conditions were: pH = 2, adsorbent dose 0.6 g, and initial concentration of RB4 dye 5 mg/L. The kinetic behavior and the adsorption isotherm allowed us to conclude that the GA-crosslinked CS beads’ adsorption mechanism was controlled mainly by chemisorption interactions, demonstrating its applicability in systems that require the removal of contaminants with similar structures to the model presented.

Dyes present in industrial effluents have been treated by many methods, among which adsorption stands out for its high efficiency, low costs, simple operation processes, and the absence of hazardous byproducts. In this research, two adsorbents were obtained from chitosan beads (CS) cross-linked with glutaraldehyde (GLA), graphene oxide (GO), and titanium dioxide nanoparticles (TiO2) for the adsorption of the anionic dye FD&C Red 40 used as a model pollutant. The optimum removal conditions of FD&C Red 40 dye using CS-TiO2-GLA beads were determined (pH = 1.73, TiO2 amount =279.77 mg, and initial dye concentration = 55.23 mg L−1) with a central composite design with surface response methodology (RSM). The effect of the graphene oxide (GO) in the adsorption properties of CS-TiO2-GLA beads was evaluated, showing a considerable improvement in the removal efficiency of the model dye. The intraparticle diffusion mechanism best described the adsorption kinetics for the two adsorbents. This research demonstrates the potential of chitosan beads incorporated with graphene oxide and titanium dioxide nanoparticles to remove anionic contaminants from wastewater.