Finding affordable and environment-friendly options to decontaminate wastewater generated with heavy metals and dyes to prevent the depletion of accessible freshwater resources is one of the indispensable challenges of the 21st century. Adsorption is yet to be the most effective and low-cost wastewater treatment method used for the removal of pollutants from wastewater, while naturally derived adsorbent materials have garnered tremendous attention. One promising example of such adsorbents is hydrogels (HGs), which constitute a three-dimensional polymeric network of hydrophilic groups that is highly capable of adsorbing a large quantity of metal ions and dyes from wastewater. Although HGs can also be prepared from synthetic polymers, natural polymers have improved environmental benignity. Recently, cellulose-based hydrogels (CBHs) have been extensively studied owing to their high abundance, biodegradability, non-toxicity, and excellent adsorption capacity. This review emphasizes different CBH adsorbents in the context of dyes and heavy metals removal from wastewater following diverse synthesis techniques and adsorption mechanisms. This study also summarizes various process parameters necessary to optimize adsorption capacity followed by future research directions.

Disposal of reactive dye contaminants in surface waters causes serious health risks to the aquatic living bodies and populations adjacent to the polluted water sources. This study investigated the applicability of banana peels to remediate water contamination with reactive dyes used in the textile industry. A set of batch experiments was conducted using a standard dye solution to determine optimum adsorption parameters, and these parameters were used for the removal of dyes from actual wastewater. Fitting experimental data into the isotherm and kinetic models suggested monolayer dye adsorption with chemisorption rate-limiting step. The maximum adsorption found from modeling results was 28.8 mg/g. Fourier transformed infrared (FTIR) spectra revealed the existence of hydroxyl, amine and carboxylic groups, contributing to high adsorption of dye molecules onto the adsorbent surface. About 93% of the dyes from the standard solution were removed at optimum conditions (pH—7.0, initial dye concentration—100 mg/L, contact time—60 min, and adsorbent dose—0.5 g) while this value was 84.2% for industrial textile wastewater. This difference was mainly attributed to the composition difference between the solutions. However, the removal efficiency for actual wastewater is still significant, indicating the high potentiality of banana peel removing dyes from textile effluent. Furthermore, desorption studies showed about 95% of banana peel can be recovered with simple acid-base treatment.