Chitosan Deposited onto Fumed Silica Surface as Sustainable Hybrid Biosorbent for Acid Orange 8 Dye Capture: Effect of Temperature in Adsorption Equilibrium and Kinetics

Abstract

Chitosan was deposited on fumed silica without the addition of cross-linkers or activating agents. The chitosan surface layer has a high affinity toward organic molecules, e.g., Acid Orange 8 (AO8) dye, robust to a broad range of simulated conditions (variance with respect to temperature, time, and concentration of solute). Experimental equilibrium data were analyzed by the generalized Langmuir equation taking into consideration the energetic heterogeneity of the adsorption system. The effect of temperature on dye uptake and adsorption rate was studied. According to the calculated thermodynamic functions Δ G °, Δ H °, and Δ S ° from the equilibrium data at different temperatures, the adsorption of AO8 onto chitosan–fumed silica composite is exothermic and spontaneous. The studies of temperature effect on adsorption equilibrium show that the maximum adsorption capacity (determined from the Langmuir–Freundlich equation) of synthesized composite toward AO8 is about one-third higher in the case of an isotherm measured at 5 °C than this value obtained for the isotherm measured at 45 °C. The quantitative binding of dye molecules to chitosan coating on the surface of silica was proved by 1 H MAS NMR. The deep kinetics study through the application of various theoretical models—the first-order equation, pseudo-first-order equation, second-order equation, pseudo-second-order equation, mixed first, second-order equation, and multiexponential equation—was applied for getting inside the mechanism of AO8 binding to the chitosan coating. Structural characteristics of chitosan-coated silica were obtained from the low-temperature adsorption/desorption isotherms of nitrogen and imaging by scanning electron microscopy. The effects of a synthetic route for polymer coating on thermal stability and the ability to degrade were studied by differential scanning calorimetry.

Nucleotide Interaction with Chitosan Layer Deposited on Fumed Silica Surface: Practice and Theory towards Establishing the Mechanism at the Molecular Level

“…This approach of composites processing is in agreement with the principles of Green Chemistry [29,30]. The synthesized composite belongs to a hybrid material of Class I, where the organic (chitosan) and inorganic (silica) parts are combined through weak interactions, such as hydrogen bonds between the amine, acetamid or hydroxyl groups of the biopolymer and silanol groups of silica or electrostatic forces between protonated amino groups and dissociated hydroxyl groups [14,[31][32][33].…”

“…Chitosan combined with an inorganic oxide such as silica could has the potential for concentrating molecules of different nature: extended specific surface, accessibility of functional groups and thermal stability [13,14,21]. The impregnation of fumed silica with slightly acidic chitosan solution is a rapid, effective and sustainable way of composite preparation.…”

Insights into thep-nitrophenol adsorption by amidoxime-modified poly(acrylonitrile-co-acrylic acid): characterization, kinetics, isotherm, thermodynamic, regeneration and mechanism study

“…This would result in less physical adsorption and worse removal efficiency. 18,60 These ndings were, once again, in line with the work of Yang et al, which described the adsorptive removal of PNP through a designed, hierarchical porous carbon from semi-coke via a facile preparation method for p-nitrophenol adsorption. Due to the nding in the present work, further adsorption analysis in this study was carried out at 298 K.…”

Nucleotide Interaction with a Chitosan Layer on a Silica Surface: Establishing the Mechanism at the Molecular Level

“…Chitosan combined with an inorganic oxide such as silica could have the potential for concentrating molecules of different nature: extended specific surface, accessibility of functional groups, and thermal stability. 13 , 14 , 20 The impregnation of fumed silica with a slightly acidic chitosan solution is a rapid, effective, and sustainable way of composite preparation. This approach of composite processing is in agreement with the principles of Green Chemistry .…”

“… 29 , 30 The synthesized composite belongs to a hybrid material of class I, where the organic (chitosan) and inorganic (silica) parts are combined through weak interactions, such as hydrogen bonds between the amine, acetamid, or hydroxyl groups of the biopolymer and silanol groups of silica or electrostatic forces between protonated amino groups and dissociated hydroxyl groups. 14 , 31 − 33 …”