Eco-friendly cellulose–bentonite porous composite hydrogels for adsorptive removal of azo dye and soilless culture

Cellulose hydrogels are a three-dimensional (3D) network of cross-linked cellulosic fibers that have the potential to be used as an environmentally friendly adsorbent. Bentonite clay is also a low cost inorganic adsorbent and has been frequently used to remove toxic organic compounds from water. However, in most cases, bentonite is often ground to a fine powder to increase the available surface area for adsorption, which makes its separation from an aqueous mixture difficult. In this study, we demonstrate straightforward fabrication of cellulose–bentonite (CB) porous composite hydrogels and its potential as an adsorbent for dye removal. The preparation, formation mechanism, and the adsorption performance of CB hydrogels with homogeneously dispersed clay particles were investigated. The adsorption isotherms, kinetics, and thermodynamics of CB hydrogels were examined toward an anionic dye pollutant (Congo red). The results showed that physisorption is the predominant adsorption mechanism of Congo red onto CB hydrogels. The equilibrium adsorption and kinetic data were well fitted by Langmuir isotherm and pseudo-second-order models, respectively. The theoretical maximum adsorption capacity of the CB30 hydrogel with 30 wt% clay loading was found to be 45.77 mg g⁻¹, which was the highest value among other fabricated hydrogels. We also demonstrate the potential application of these CB hydrogels as soilless growing media for legume (Vigna radiata L.) and small flowering plants (Arabidopsis thaliana).