Sustainable preparation of Fe(OH)3 and α-Fe2O3 nanoparticles employing Acacia catechu extract for efficient removal of chromium (VI) from aqueous solution

Abstract

Indiscriminate disposal of industrial effluents containing undesired polyvalent metal ions such as Cr(III) and Cr(VI) into water bodies causes serious threat to public health and ecosystem. Therefore, it is necessary to develop new and sustainable methods for the efficient removal of such ions from water. Herein, iron hydroxide, Fe(OH)3, nanoparticles (NPs), have been prepared employing an aqueous extract of Acacia catechu leaves as green reducing as well as stabilizing agent. The annealing of Fe(OH)3 NPs results in the formation of highly crystalline α-Fe2O3 NPs. Thus prepared Fe(OH)3 and α-Fe2O3 NPs have been characterized for crystallinity, shape, size and porosity and tested for adsorptive removal of Cr(VI) from aqueous solution at varying pH, dose of NPs and initial concentration of Cr(VI). Removal efficacy of both forms of NPs (Fe(OH)3 and α-Fe2O3) towards Cr(VI) has been correlated with their structural aspects. Under optimal conditions, Fe(OH)3 NPs and α-Fe2O3 NPs have been found to remove 84.9 % and 22 % of Cr(VI) from aqueous solutions. The presence of surface –OH groups of polyols and that of NPs are assigned to be responsible for adsorption of Cr(VI) ions from aqueous solution. The maximum monolayer adsorption capacity of Fe(OH)3 NPs for Cr(VI), calculated from Langmuir isotherm is 29.5 mg g−1 at pH = 2 and 25 °C. It is expected that the present study would highlight the importance of the presence of bio-based templates on the surface of NPs for efficient removal of metal ions from aqueous solution.