Functionalization of cellulose cryogels cross-linked by tetraethylenepentamine for heavy metal removal and oil adsorption.

Water contamination by oils, hazardous organic solvents, and heavy metal ions is a severe environmental problem. Adsorption is considered an efficient method due to its simplicity, cost-effectiveness, and reusability. Cellulose-based cryogels are green and effective adsorbents that are used to eliminate such harmful chemicals. The cellulose cryogels are also a kind of flexible material that is easily functionalized to enhance their adsorption capacity because of the many hydroxyl groups in the cellulose chains. In this study, a novel fabrication has been developed for the first time to obtain cellulose cryogels functionalized by tetraethylenepentamine (TEPA). First of all, a cellulose sol was prepared by dissolving microcrystalline cellulose in an alkaline-urea solvent system at a low temperature. Then, the sol was cured at 70 °C and gelated by ethanol exchange to form a stable cellulose gel rapidly. Finally, the gel was functionalized by soaking in TEPA solution before freeze-drying to create amine-modified cellulose cryogel, followed by surface modification with methyltrimethoxysilane (MTMS) to get the hydrophobic cryogel. The physicochemical properties of the synthesized cryogels were characterized by advanced methods such as infrared spectroscopy, thermogravimetry, scanning electron microscopy, and Brunauer, Emmett, and Teller surface area analyses. The adsorption capacities of the prepared cryogels towards heavy metal ions, oils, and organic solvents are also studied. The results showed that the as-fabricated cryogels have low density (0.07-0.12 g/cm3) and high porosity (87.90-94.75%). The presence of TEPA helps to improve the Chromium ions (Cr3+) adsorption of the cryogels with the adsorption capacity of up to 167.63 mg/g. Compared with the previous works, the TEPA-modified cellulose cryogels have better Cr3+ adsorption capacity than chitosan-based composite cryogels (0.85 mg/g) and silica aerogels (86.84 mg/g). Moreover, TEPA significantly strengthens the texture and reduces the shrinkage of the functionalized cryogels after drying compared with the un-functionalized samples. The hydrophobic MTMS-modified cryogels can adsorb various types of organic solvents, such as kerosene (6.85 g/g), engine oil (3.98 g/g), ethanol (5.85 g/g), and hexane (4.87 g/g). Consequently, the analytical results have demonstrated the effectiveness of in situ coating of TEPA with the gels to generate the TEPA-functionalized cryogels, followed by modification with MTMS, indicating that it is an advanced fabrication of a novel adsorbent for the removal of metal ions and organic pollutants in wastewater treatment. [ABSTRACT FROM AUTHOR]