The extensive rise in industrial activities has led to the presence of heavy metals, many dyes, and various pollutants in industrial wastewater effluents. From all the technologies available for treating the wastewater, adsorption is found to be the most economically feasible and easily operated technology. Different adsorbents such as activated carbon, different types of zeolites, bio-polymers, clays and various nano composites have been used in removing impurities from water. However, there are several bottlenecks yet to be addressed when using these adsorbents on an industrial scale. Toxicity, recyclability, scaling up and selectivity are some key challenges to be addressed. Therefore, development of sustainable and green adsorbents with minimized cross-contamination of the feed water, which have high selectivity towards certain contaminants is crucial. Recently, novel mussel-inspired material as polydopamine (PDA) has emerged as an efficient adsorbent for water treatment by adsorption technology. PDA is derived from dopamine (DA) and consists of catechol, amine and imine functional moieties. Its similar structure with mussel adhesive proteins is responsible for high binding ability with different substances even on wet surfaces. However, the adsorption capacity of PDA alone is low compared to other adsorbents which meet indusial demands. Therefore, it is crucial to increase the adsorptive capacity of PDA to be useful on industrial scale and help to utilize all of its functional groups without deterioration in adsorption.
Increasing the surface-active sites for adsorption can be achieved by modification of its surface area and charge. One possible route for developing PDA with high adsorption capacity is to modify the adsorbent via Schiff-based addition reaction with sustainable green solvent such as ionic liquids (ILs). ILs are widely used in different applications, including separation and extraction processes, as they are capable of multiple types of interactions (ÏâÏ, nâÏ, and hydrogen bonding). The usage of sustainable ILs is gaining more emphasis because of their high thermal and chemical stability, low volatility, environmental-friendly behavior and very high ability to dissolve a wide range of compounds. Due to positively or negatively charged groups, ILs can be explored in the modification of different adsorbents, such as graphene oxide (GO), and its surface in order to enhance adsorption capacity via electrostatic, hydrogen bonding and Ï-Ï interactions. This work will be focused on developing novel and highly selective mussel-inspired Green and Sustainable Adsorbents (MIGSA) using PDA mediated IL. The selectivity of the polydopamine-ionic liquid (PDA-IL) adsorbent will depend not only on the charge of the IL used, but also on the components of the IL counterparts.
The selectivity for a certain type of heavy metal/dye/anionic species would be studied by considering types of surface functional groups of the respective adsorbents. This research work focuses on studying dependence of adsorption capacity and selectivity for specific pollutants, which is controlled by both surface area and surface functional groups of new adsorbents.
In this work, a task specific IL was used in the production of novel MIGSA adsorbent from DA via mussel-inspired enabled Schiff-base addition approach. Synthesis methodology has been optimized based on reaction time, temperature, weight % of DA and TSIL, and degree of functionalization. The fabricated bio-inspired green adsorbent, PDA-IL, has been characterized using different techniques such as FTIR, TGA, XRD, SEM and TEM to collect information about the weight percentage of IL mediated on PDA, confirmation of having imine groups, particle size and morphology of the fabricated adsorbent. Thus far, synthesized bio-inspired green adsorbent of PDA-IL showed good adsorption capacity for anionic pollutants such as phosphates as well as positively charged dyes such as Alizarin Red S. Furthermore, we believe that the fabricated adsorbent has a promising potential for selective removal of heavy metals, specifically, chromium. Bio-inspired PDA-IL would be a novel type of adsorbents, which have not been reported previously. The developed novel and green adsorbents will have a tremendous potential for removing heavy metals, nitrates, phosphates, sulphates, and toxic dyes from aqueous solutions and wastewater. Moreover, in addition to the strong adhesive abilities of PDA, by altering the cation and anion of ILs different contaminates can be selectively removed from wastewater. Ultimately, using a bio-inspired green adsorbent can make the wastewater treatment process more efficient and extremely sustainable.
