Modeling and Optimization of the Adsorption of Cr (VI) in a Chitosan-Resole Aerogel Using Response Surface Methodology

Abstract

In this paper, a model for Cr (VI) removal and optimization was made using a novel aerogel material, chitosan-resole CS/R aerogel, where a freeze-drying and final thermal treatment was employed to fabricate the aerogel. This processing ensures a network structure and stability for the CS, despite the non-uniform ice growth promoted by this process. Morphological analysis indicated a successful aerogel elaboration process., FTIR spectroscopy corroborated the aerogel precursor’s identity and ascertained chemical bonding after adsorption. Owing to the variability of formulations, the adsorption capacity was modeled and optimized using computational techniques. The response surface methodology (RSM), based on the Box–Behnken design using three levels, was used to calculate the best control parameters for the CS/R aerogel: the concentration at %vol (50–90%), the initial concentration of Cr (VI) (25–100 mg/L), and adsorption time (0.3–4 h). Analysis of variance (ANOVA) and 3D graphs reveal that the CS/R aerogel concentration and adsorption time are the main parameters that influence the initial concentration of CS/R aerogel metal-ion uptake. The developed model successfully describes the process with a correlation coefficient of R2 = 0.96 for the RSM. The model obtained was optimized to find the best material design proposal for Cr (VI) removal. Numerical optimization was used and showed superior Cr (VI) removal (94.4%) under conditions of a CS/R aerogel concentration of 87/13 %vol, with an initial concentration of Cr (VI) of 31 mg/L, and an adsorption time of 3.02 h. These results suggest that the proposed computational model can obtain an effective and viable model for CS material processing and for optimization of the uptake of this metal.

Chitosan–Resole–Pectin Aerogel in Methylene Blue Removal: Modeling and Optimization Using an Artificial Neuron Network

“…From Figure 4c,d, we concluded that increasing the volume of polysaccharide slightly decreased the diameter of the pores, as the precursor polysaccharide base presented a dense porous surface. The comparison of the open pores after the cross section in Figure 4c,d is recognizable in accordance with previous reports; when the amount of R limits the substrate for the structure of the three-dimensional network aerogel, although it strengthens the structure, the pores tend to increase in size [16,19]. From Figure 4d, it can also be seen that the aerogel had a flexible and porous structure with nonuniform axial growths, adjusted and controlled by the volume concentration and the crosslinking interaction between them, which determines the structure.…”

“…The resole (R) solution was made by dissolving phenol-formaldehyde resin (1:3.5) on NaOH at 0.1 M and stirring at 70 • C for 1 h. After that, the pH was adjusted, and the solution was placed in a rotary evaporator for 1.15 h in a water bath at 50 • C. The remaining liquid resole was removed and refrigerated. The synthesis of resole was detailed in our previous work [19].…”

“…Unfortunately, nanomaterials as enhancers are complicated to use due to their low bulk and high costs, and physical and chemical crosslinking would change the chemical disposition of the free species to ionic exchange. Therefore, we envision a cost-conscious approach using a thermosetting enforcer with a phenol/formaldehyde liquid resole reinforcement, as in a previously reported work [19], with the integration of pectin (P) as another polysaccharide chain for a 3D substrate for the sol-gel reaction with physical crosslinking in conjunction with the resole and chemical crosslinking for mechanical stability. We understand the variability of the experimental data required to find the optimal processing parameters, and to overcome this issue, we aim to propose a model.…”