Engineered adsorbents comprising nanopowders embedded in various substrates have the potential to display higher sorption capacities and faster kinetics compared to conventional sorbents due to their high specific surface area, short intraparticle diffusion distances, tunable pore size and surface chemistry, while also maintaining compatibility with existing treatment processes (e.g., slurry reactors, fixed bed). In designing these “nano-enabled sorbents”, care must be taken to embed the nanomaterials into the scaffold without losing their functionality, while minimizing their release and facilitating reuse of the sorbent.
In this work, we report the synthesis and evaluation of nanocomposite beads comprising a chitosan matrix embedded with layered double hydroxide (LDH). As an abundant and low cost biosorbent, chitosan is an attractive substrate that is also effective for removing a number of toxic metals including chromium, cadmium, mercury, and copper. LDH is known for its high anion exchange capacities and ability to remove anions over a large pH range, including selenium oxoanions, the focus contaminant in this study. Selenium is found in trace levels in groundwater and from agricultural and industrial wastewater contamination and can cause severe toxicity at very low levels of occurrence.
This talk will present the results of our investigation on nanocomposite formation using two different preparation methods, one that embeds the LDH into the beads using direct mixing of nanopowder into the chitosan gel, and one that synthesizes the LDH “in-situ” within the chitosan matrix. The effect of the preparation route on the nanocomposite structure, maximum loading of LDH in the composite, and selenium removal kinetics and maximum sorption capabilities are studied and compared to LDH nanopowders and granular media. From these studies, we aim to understand how the sorption properties of the LDH are affected when it is utilized in different form factors (i.e., as a nanopowder sorbent, granular media, or nanocomposite bead) to shed light on how best to design and fabricate high performance nano- enabled sorbents for water treatment applications.