Arsenic(III) sorption on nanostructured cerium incorporated manganese oxide (NCMO): A physical insight into the mechanistic pathway

Arsenic(III) sorption was investigated with nanostructured cerium incorporated manganese oxide (NCMO). The pH between 6.0 and 8.0 was optimized for the arsenic(III) sorption. Kinetics and equilibrium data (pH = 7.0 ± 0.2, T = 303 ± 1.6 K, and I = 0.01 M) of arsenic(III) sorption by NCMO described, respectively, the pseudo-second order and the Freundlich isotherm equations well. The sorption process was somewhat complicated in nature and divided into two different segments, initially very fast sorption followed by slow intraparticle diffusion process. Sorption reaction of arsenic(III) on NCMO was endothermic (ΔH° = +13.46 kJ mol−1) and spontaneous (ΔG° = −24.75 to −30.15 kJ mol−1 at T = 283–323 K), which took place with increasing entropy (ΔS° = +0.14 kJ mol−1 K−1) at solid–liquid interface. Energy of arsenic(III) sorption estimated by analyzing the equilibrium data using the D–R isotherm model was 15.4 kJ mol−1, indicating the ion-exchange type mechanism. Raman, FT-IR, pH effect, desorption, etc. studies indicated that arsenic(III) was oxidized to arsenic(V) during the sorption process.

Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (43 K)Download as PowerPoint slideHighlights► Nanostructured cerium incorporated manganese oxide (NCMO) has high affinity for arsenic(III) binding at acid and neutral pH. ► Pseudo-second order equation describes the arsenic(III) sorption kinetics at pH 7.0 and 303 K. ► Freundlich isotherm describes the arsenic(III) sorption equilibriums at pH 7.0 and 303 K. ► Arsenic sorption process is endothermic but spontaneous. ► Arsenic(III) to arsenic(V) oxidation occurs on NCMO surface presumably via electron transfer process.