Modified rice husk polymeric hydrogel as biodegradable adsorbent for the effective removal of organic pollutant methylene blue dye

Rice husk, sourced from a local processing mill, has been utilized in crafting biodegradable adsorbents: plain rice husk (PRH) and modified rice husk (MRH) polymeric hydrogels. To delve into their structure and morphology, FT-IR and SEM analyses have been conducted. These analyses shed light on the functional groups and structural arrangements, crucial for understanding the adsorption process, particularly for cationic methylene blue (MB) dye removal from water. Batch experiments explored varying parameters such as pH (ranging from 2 to 9), time (up to 300 min), adsorbent dose (0.12 to 0.5 g), and dye concentration (60-120 mg/L). Both PRH and MRH hydrogels demonstrated efficacy in removing methylene blue dye, especially within a time frame of 300 min at 100 mg/L concentration. The efficiency of PRH and MRH hydrogels for MB adsorption was notably high, reaching 85% (315 mg/g) and 90% (333 mg/g), respectively, at 0.37 g of polymeric hydrogel. Results indicated that MB adsorption increased with rising initial concentrations and extended time durations, plateauing at 300 min. Additionally, higher doses of adsorbent enhanced MB removal. The Freundlich isotherm model fitting the equilibrium adsorption data suggested a pseudo-second-order model, indicating monolayer adsorption without an upper coverage limit. This model elucidated surface heterogeneity and the exponential distribution of active site energy. Overall, the study demonstrates the potential of utilizing rice husk-derived hydrogels as effective adsorbents for water purification, with insights into their structural characteristics and adsorption mechanisms, critical for further applications in environmental remediation.