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Graphical abstract Highlights • The first derivative of XANES for As(III) adsorbed systems of all adsorbents are observed to have with mixed oxidation. • As(V) adsorbed samples of Ni, and Cu systems agree with that of As(V) standards. • Both reduction and oxidation behavior of arsenic is observed on to these metal oxide adsorbents. • EXAFS analysis was observed with As O bond distances in the range of 1.7–1.8 Å. • The As-M bond distances are around 2.7, 3.2 and 3.6 Å confirmed the formation of surface complexes. Abstract The present study is about surface complexation behavior of arsenic species adsorbed onto ternary metal oxide adsorbents (Ni-Al-Fe, Co-Al-Fe, Mn-Al-Fe, and Cu-Al-Fe). The analysis is carried out by X-ray absorption spectroscopy (XAS) tool. XANES (μ(E) vs. E) spectra close to the absorption edge (i.e., As K -edge) of all samples are observed along with the As(III) and As(V) standards. The first derivative of XANES for Ni-As(V), and Cu-As(V) samples agree with that of As(V) standards, respectively. Whereas, As(III) adsorbed adsorbent systems (i.e., Ni, Co, Mn, and Cu) are observed with mixed oxidation state of arsenic. A total of 65–85 % is observed with initial oxidation state (As(III) or As(V)), and remaining 15–35 % is observed with modified oxidation state (As(V) or As(III)) that explains the occurrence of possible charge transfer. EXAFS analysis shows the As-O bond distances in the range of 1.7–1.8 Å. The corresponding As-M bond distances are around 2.7, 3.2, and 3.6 Å which confirms the formation various edge sharing (2E), and corner sharing (2C, 1V) surface complexes. Surface coverage is understood as an important parameter as bidentate attachments (2E, 2C) are evident in As(III), and As(V), but monodentate attachments (1V) are only observed in As(V). [ABSTRACT FROM AUTHOR]

The understanding of mechanistic insights in environmental remediation and mitigation systems is attracting larger attention, in recent days. Here in, aluminium substituted copper ferrite impregnated rGO hybrid (CAF-rGO) is verified to understand the adsorption/electrosorption mechanism of arsenic in aqueous systems. Near-surface study (XPS: As 3d, Cu 2p, Fe 2p, Al 2p, O 1s, C 1s) proposes redox, and ligand exchange reactions between contaminant, and CAF-rGO. Adsorption capacities are observed around 128.8 mg g−1 [As(III)], 153.5 mg g−1 [As(V)] with Freundlich model isotherms. Kinetics study follows the PSO model with influence of solar light (> 420 nm). Cyclic voltammetry (CV) analysis in different molarity conditions observed with signals around +0.1 and −0.6 V confirm the redox abilities, and N 2 /O 2 purged environments understood that electrosorption occurred through both reduction and sorption. Electrosorption study with pH variation shows the effect of protonation on the redox activity of individual arsenic species. Consistent signal around −0.6 ± 0.05 V in all the CV plots (i.e., Molarity, Environment, pH) recommends the usage of CAF-rGO for arsenic mitigation. Possible influence of photo-current (∼40 μA/cm2 at ∼ 0 V) towards As(III/V) decontamination is understood though photoelectrochemical analysis. Impedance plot shows low-resistance and better diffusion of arsenic oxy-anions during light irradiation. Synergistic nature of CAF-rGO generates reactive oxygen species (i.e., ●OH/●O 2 −/ 1 O2) in mitigating highly toxic As(III) species is also detailed in the present work. Image 1 • Mechanistic insights of arsenic (As) adsorption and electrosorption in aqueous systems. • In-situ CV analysis in various molarities, gas purging environment and pH conditions. • A constructive correlation is drawn between individual redox signals and CV plot areas. • Photo-catalytic aspects on As loading and photo-electrochemical behavior (I vs. t, EIS). • ROS signals onto the hybrid surface in influencing As remediation and mitigation. [ABSTRACT FROM AUTHOR]