Abstract
Currently, macroporous hydrogels have been receiving attention in wastewater treatment due to their unique structures. As a natural polymer, alginate is used to remove cationic dyes due to its sustainable features such as abundance, low cost, processability, and being environmentally friendly. Herein, alginate/montmorillonite composite macroporous hydrogels (cryogels) with high porosity, mechanical elasticity, and high adsorption yield for methylene blue (MB) were generated by the one-step cryogelation technique. These cryogels were synthesized by adding montmorillonite into gel precursor, followed by chemical cross-linking employing carbodiimide chemistry in a frozen state. The as-prepared adsorbents were analyzed by FT-IR, SEM, gel fraction, swelling, uniaxial compression, and MB adsorption tests. The results indicated that alginate/montmorillonite cryogels exhibited high gelation yield (up to 80%), colossal water uptake capacity, elasticity, and effective dye adsorption capacity (93.7%). Maximum adsorption capacity against MB was 559.94 mg g−1 by linear regression of Langmuir model onto experimental data. The Pseudo-Second-Order model was fitted better onto kinetic data compared to the Pseudo-First-Order model. Improved porosity and mechanical elasticity yielding enhanced dye removal capacity make them highly potential alternative adsorbents compared to available alginate/montmorillonite materials for MB removal.
Highlights
In recent years, dye contamination in-ground and freshwaters have been a challenging problem due to their non-biodegradability and toxicity to ecosystems
MMT was incorporated into alginate cryogels to improve mechanical strength and dye removal performance
We benefitted from carbodiimide chemistry to cross-link carboxylic groups on the alginate with di-amine terminated cystamine
Summary
Dye contamination in-ground and freshwaters have been a challenging problem due to their non-biodegradability and toxicity to ecosystems. Various synthetic dyes accumulated in nature are toxic, cationic dyes such as methylene blue (MB) (Figure 1) pose more damage to the environment and humans due to their charge [2,3] These unfavorable features of dyes have prompted the development of strategies like photodecomposition, coagulation, flocculation, ion exchange, applying chemical oxidizing agents, and adsorption to remove them from contaminated waters [4,5,6]. Adsorption has been found to be superior in economical and effective ways for the recovery of synthetic dyes owing to the selectivity of adsorbent types, sorbent reusability, and ease of operation [2,4,7,8] Various materials such as activated carbon, solid agricultural by-products, carbonbased compounds, metallic compounds, polymers, industrial wastes, and clays are applied for dye adsorption in the forms of porous matrices, nanoparticles, membranes, and bulk materials hydrogels [1,5,10]. Hydrogels have been used to remove dyes in polluted water due
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