Role of polymer network and gelation kinetics on the mechanical properties and adsorption capacity of chitosan hydrogels for dye removal

Abstract

Chitosan (CS) hydrogels are receiving growing attention as adsorbents for water purification purposes. The conditions of preparation of this class of materials play a crucial in the determination of their performances; however, this aspect is often neglected in the literature. In this study, we deal with this issue, focusing on the structure-property relationships of CS hydrogels obtained by phase inversion method. We show that the concentration of the starting solution determines the density and strength of intermolecular interactions, and that the gelation kinetics dictates the hydrogel structure at the microscale. Consequently, even subtle changes in the preparation protocol can cause significant differences in the performances of CS hydrogels in terms of mechanical properties and dye adsorption capacity. The observed trends are often neither trivial nor monotonic. Nonetheless, we demonstrate that they can be interpreted looking at the CS network structure, which can be inferred by rheological measurements

Behavior of In Situ Cross‐Linked Hydrogels with Rapid Gelation Kinetics on Contact with Physiological Fluids

“…It was anticipated that the microstructure of these gels would be different as microstructure development is dependent on polymer concentration and gelation kinetics . In particular, gels that form rapidly tend to have a microstructure with larger pore sizes and regions of densely packed polymer when compared with gels that develop over a longer period of time . Furthermore, less densely packed structures are prone to molecular rearrangements resulting in microstructural collapse and subsequent changes to functionality.…”

Dye removal by biosorption using cross-linked chitosan-based hydrogels

“…So, the chemical step may cause a significant decrease in dye uptake efficiency and biosorption capacities, especially in the case of chemical reactions involving amine groups, since the amino groups of the polymers are much more active than the hydroxyl groups that can be much more easily attacked by cross-linkers. Consequently, it is important to control and characterize the conditions of the cross-linking reaction since they determine and allow the modulation of the cross-linking density, which is the main parameter influencing properties of gels (Ahmed 2015;Ullah et al 2015;Akhtar et al 2016;de Luna et al 2017a). Indeed, the conditions of preparation of hydrogels used as biosorbents for dye removal play a crucial role in the determination of their performances and in the better comprehension of the biosorption mechanisms (Crini 2005(Crini , 2015.…”

“…Indeed, the conditions of preparation of hydrogels used as biosorbents for dye removal play a crucial role in the determination of their performances and in the better comprehension of the biosorption mechanisms (Crini 2005(Crini , 2015. However, this aspect is often neglected in the literature (Ahmed 2015;Crini 2015;Mohamed et al 2015;Ullah et al 2015;Akhtar et al 2016;de Luna et al 2017a;Pakdel and Peighambardoust 2018;Van Tran et al 2018).…”

“…The hydrogels were obtained by phase inversion method in order to efficiently combine the dye biosorption ability of chitosan and the capacity of the porous particles of trapping pollutant molecules. The particles exhibited improved mechanical properties with possible use in batch or column procedures (de Luna et al 2017a). Batch biosorption experiments revealed a synergistic effect between chitosan and hydrogels, and the samples are able to remove both anionic and cationic dyes such as Indigo Carmine (q max = 118 mg/g), Rhodamine 6G (q max = 78 mg/g) and Sunset Yellow (q max = 72 mg/g) from water (de Luna et al 2017b).…”

“…Yet, the performance can vary depending on the conditions and the mode of preparation of hydrogels. However, this aspect is often neglected in the literature (Ahmed 2015;Ullah et al 2015;Akhtar et al 2016;de Luna et al 2017a;Pakdel and Peighambardoust 2018;Van Tran et al 2018). A more detailed study appears to be necessary to show how the chemical structure of the hydrogels affects the biosorption performance.…”