Selective adsorption of anionic dye from wastewater using polyethyleneimine based macroporous sponge: Batch and continuous studies

Dyes are well known for their hazardous impacts on public health and the environment. Dye removal using monolithic adsorbents is an attractive approach for industrial applications and process design owing to their utilization in both static and dynamic adsorption experiments. In the present work, polyethyleneimine (PEI) based macroporous monolithic sponge (S100) was engineered by ice-templating method and used as an adsorbent. Both batch and continuous operations for dye removal were studied. The effect of various parameters such as pH, adsorbent amount, flow rate, influent dye concentration, and adsorbent bed height on adsorption performance of S100 was studied and modelled using Langmuir/Freundlich isotherms for static operations and Adam-Bohart/Thomas model in packed-bed column experiments. Under optimum conditions, the adsorbent showed a remarkably higher adsorption capacity towards CR (1666.67 mg/g), which is considerably higher than most PEI-based adsorbents. Amine groups in S100 offered exceptional selectivity for anionic Congo red (CR) against cationic Methylene blue (MB) dye (separation factor of 208 and 87 in absence and presence of sodium chloride, respectively). It can be easily regenerated in alkaline medium without a significant loss in percent adsorption capacity and shows good thermal and mechanical stability. Notably, in column studies, a relatively smaller percentage of unused bed height (32.3%) was observed with higher dye uptake for 16 mg S100 at flow rate 10 mL/h and inlet concentration 300 mg/L. Thus, the adsorbent displays an outstanding physiochemical characteristic, excellent selectivity for anionic dye, ease of regeneration and high adsorption performance in both batch and continuous studies.