Cellulosic Ternary Nanocomposite for Affordable and Sustainable Fluoride Removal

Adsorption is shown to be an extremely affordable and sustainable way of producing clean water, particularly in resource-limited settings. In this paper, we sought to synthesize an effective cellulose-based composite adsorbent from eco-friendly, earth-abundant, and consequently affordable ingredients at room temperature for fluoride removal from drinking water. We utilized the synergistic effect of various renewable materials and active sites of metal oxyhydroxides in developing an effective adsorbent, which is physically stable under the conditions of use. Nanoscale oxyhydroxides of aluminum and iron were scaffolded into a matrix of carboxymethyl cellulose (CMC) to form a nanocomposite adsorbent, which was prepared in water, eventually making a water-stable porous solid. This was used in batch and cartridge adsorption experiments for fluoride removal. The adsorbent surface before (in situ) and after fluoride uptake was characterized using various analytical techniques. The in situ composite exhibited a surface area of 134.3 m2/g with an amorphous solid structure with Al and Fe uniformly distributed in the cellulose matrix. From the batch adsorption experiments, we observed 80% fluoride removal within the first 3 min of contact, with a maximum uptake capacity of 75.2 mg/g as modeled by the Langmuir adsorption isotherm, better than most reported materials. The adsorbent effectively reduced F– levels in field water from 10 to 0.3 mg/L, less than 1.5 mg/L the World Health Organization upper limit for drinking water. Optimum F– removal was achieved between the pH of 4–9; however, the effectiveness of the adsorbent was reduced in the presence of competing ions in the order PO4 3– > SiO3 2– > CO3 2– > HCO3 – > SO4 2–. A cartridge experiment demonstrated the applicability of the adsorbent in a domestic point-of-use water purifier for defluoridation. Sustainability metrics of the material were evaluated. Defluoridation using the material is estimated to cost $3.3 per 1000 L of treated water at the scale of community implementation projects.