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Copper-based ternary metal oxide (i.e., Cu0.52Al0.01Fe0.47O4) impregnated reduced graphene oxide nanohybrid is verified for microbial and arsenic treatment. Growth inhibition of colonies are observed around 99.99% (E. coli), and 99.83% (S. aureus) at 10–20 μg/mL of hybrid dosage, respectively. The inhibition rates for both the colonies are increased to 99.9998% at 80 μg/mL. TEM images have shown insight of cell-content/lipid leakage behavior after inoculating with the hybrid. The efficient hindrance towards microbial colony growth is attributed to better charge transfer, reactive oxygen species generation, and metal-ion release. Maximum arsenic sorption capacities are observed around 248 and 314 mg/g for As(III), and As(V), respectively (Ci ~ 500 ppm). Surface morphology studies onto arsenic adsorption are reported with atomic force microscope, and FT-IR/Raman analysis. A detailed discussion onto individual spectra of As 3d spectra confirmed the occurrence of redox transformation in arsenic species [As(III)]. The variation in the quantity (at. %) of oxygen functional groups in O1s spectra (i.e., M–O, M-OH, and -OH2) onto the hybrid supported the ligand-exchange behavior. Cyclic voltammetry study in arsenic electrolytes (10 µM – 1 mM) provides the occurrence of various in-situ electrochemical reactions supporting the redox activity. A significant electromagnetic wave absorption characteristics of the present hybrid is proposed with plausible airborne antimicrobial-agent abilities. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Mn, and Cu based ternary metal oxide nano adsorbents are studied for arsenic remediation. • XPS of As(3d), Fe(2p), Cu(2p), Mn(2p), and O(1s) is performed to understand remediation mechanism. • As(0) (∼25–78 at.%) onto the adsorbent shows environmentally responsible behavior to address arsenic leaching issue. • Trace metal voltammetry inferred a better As(III) mitigation (∼75–90 % at C i ∼ 1 ppm). • Cyclic voltammetry (CV) confirmed arsenic mitigation, and immobilization by reduction, and sorption. Abstract Arsenic mitigation behavior in aqueous systems is being evaluated for Mn-Al-Fe, Cu-Al-Fe nano adsorbents. Morphological, and vibrational spectroscopy analysis are observed with As-OH, and As-O surface complexes. XPS study of individual As(3d) spectra at different parameters is observed with multiplet peak behavior attributed to redox behavior of Mn-Al-Fe, Cu-Al-Fe. Significant proportions of As(0) signal (∼25 at.% in pH 7, ∼78 at.% in pH 2, ∼58 at.% in pH 12) implicate an environmentally stable behavior of these adsorbents to address the arsenic leaching issue. Adsorption kinetics are observed with Pseudo Second Order (PSO) model, and Freundlich model supported multilayer adsorption behavior is observed for adsorption isotherms. Trace metal voltammetry studies are observed with 75–90 % of As(III) mitigation in aliquot samples. Detailed study of Mn(2p), Cu(2p), Fe(2p), and O(1 s) spectra explains redox active, and surface ligand exchange synergism in arsenic adsorption. Low equilibrium concentrations (C e < 10 ppb) in As(V) systems (C i ∼ 100 and 500 ppb) indicate the drinking water application of these systems. Cyclic-voltammetry (CV) studies implicate the mitigation and immobilization of arsenic species onto adsorbent by both reduction, and sorption phenomenon. [ABSTRACT FROM AUTHOR]

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]

Aluminum (Al3+) doped manganese (Mn)/copper (Cu) ferrite impregnated rGO hybrids are verified for photo-electrocatalytic water-splitting and super-capacitor electrode applications. Energy band gaps of 2.17 eV (Mn) and 2.25 eV (Cu) confirm photocatalytic activity in the visible-band. High anodic photo-currents around 18–40 and 2–9 mA/cm2 (1 V vs. Ag/AgCl) are observed for Mn and Cu systems. Formation of oxygen vacancies due to aluminum doping assisted in efficient charge transfer behavior both at surface and lattice orders due to the structural adjustments. 2-D rGO surface disorders (I D /I 2D) emphasized the retardation of the charge recombination at the metal-oxide and rGO junction. During visible-light irradiation current densities are increased by 0.7–9.2 mA/cm2 with a better redox behavior. The difference in transient currents are observed around 0.01–0.02 mA/cm2 at 0 V vs. Ag/AgCl [0.7 mA/cm2 at 0.5 V]. Intrinsic photo-current at zero voltage infers built-in potentials at the hybrid and electrolyte interface (Schottky- junction). Impedance study implicates better electron-transfer/ion diffusion characteristics during photon irradiation with a semi-infinite diffusion rate-limiting step. Specific-capacities (Three-electrode) are observed around 216 F g−1 (Mn), 142 F g−1 (Cu) with combined pseudo-capacitance and EDLC characteristics. Li+-intercalation results in ultrahigh stability up to 100,000 cycles (t ~ 69.4 h) at 0.8 V s−1 with a capacity retention of 127%. Two-Electrode performance shows 99.1% capacity retention after 5000 cycles with decrease in the impedance (1.38 Ω to 1.06 Ω), and a maximum areal energy density of 0.54 μWh cm−2 at power density of 50 μW cm−2. Image 1 [ABSTRACT FROM AUTHOR]