Facile synthesis of poly o-toluidine modified lanthanum phosphate nanocomposite as a superior adsorbent for selective fluoride removal: A mechanistic and kinetic study

This work reports the synthesis of a new adsorbent material (LaP-POT), synthesised by sol-gel polymerisation method from lanthanum phosphate (LaP) and poly o-toluidine (POT). The sustainability and selectivity of the material as a potential adsorbent is evaluated for the removal of fluoride from aqueous as well as real water samples using batch experimental techniques. FESEM and TEM images showed the successful incorporation of rod-shaped lanthanum phosphate into the poly o-toluidine polymer matrix. The increased degradation temperature of LaP-POT from TGA curve inferred a definite interaction between two. XPS study revealed the successful binding of fluoride onto LaP-POT. The selectivity of fluoride ion onto LaP-POT material was ascertained by the distribution coefficient value. The co-anions showed little effect on fluoride removal. Kinetic study suggested that intraparticle diffusion is not the only rate controlling step; the external mass transfer or chemical interaction also impacts the fluoride adsorption. The maximum adsorption was observed at room temperature with a maximum Langmuir uptake capacity of 10.94 mg g⁻¹. The reusability of the material is tested up to 5 successive cycles for a workable commercial application purpose. The results showed that LaP-POT provides more active sites, thus making it a promising adsorbent for the removal of fluoride.