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[Display omitted] • Three-dimensional porous MIL-88A-Fe/gelatin aerogel (PMGA) was prepared. • The PMGA/H 2 O 2 system has dual functions of oxidation and adsorption. • Surface •OH and surface •OOH are the main oxide species of As(III). • The Fenton-like catalytic activity of PMGA originates from the exposed (1 0 0) facet. • PMGA can effectively repair the arsenic pollution in different real water samples. Metal-organic frameworks (MOFs) are considered a reliable adsorbent for controlling arsenic contamination. However, developing rapid and efficient MOF adsorbents with the capability of easy recovery is still challenging. Herein, we prepared a three-dimensional porous MIL-88A-Fe/gelatin aerogel (PMGA) with macroscopic size and coupled it with H 2 O 2 to fabricate a heterogeneous catalytic oxidation adsorption system to remove As(III) in water. The green synthesis strategy of this catalyst by foaming and low-temperature carbonization not only avoided the use of toxic chemical crosslinkers but also endowed PMGA with a rich hierarchical porous structure and exposed more active sites. Thus, the PMGA/H 2 O 2 system was able to reduce the concentration of As(III) from 1106 to below 10 µg/L and simultaneously realize the complete oxidation of As(III) to As(V) in only 120 min. Meanwhile, the system exhibited an excellent saturation adsorption capacity (24.863 mg/g) for As(III), superior to most similar bio-based or iron-based materials. Quenching experiments, EPR and DFT calculations showed that the active species (surface •OOH and surface •OH) generated by the Fenton-like interaction between the exposed (1 0 0) facet of MIL-88A-Fe in PMGA and H 2 O 2 played an essential role in promoting the oxidative removal of As(III). Moreover, the reaction system could work efficiently for As(III) in a wide pH range and was hardly affected by other substances such as chlorides, sulfates, carbonates, silicates, and humic acids. Simultaneously, the fixed bed column filled with PMGA could stably and continuously treat As(III) in groundwater. Therefore, this study not only broadens the horizon for the development and design of 3D functional materials but also provides a new strategy in water purification to eliminate arsenic pollutants using Fe-MOF aerogels. [ABSTRACT FROM AUTHOR]

[Display omitted] • Coupling of FeMnO with S(IV) improves the removal speed of As(III). • The FeMnO/S(IV) system integrates adsorption and oxidation functions. • Active Mn(III) is mainly responsible for the oxidation of As(III). • The possible activation pathway of S(IV) in the FeMnO/S(IV) system is proposed. • FeMnO has excellent stability and regeneration/recovery ability. The activation of sulfite [S(IV)] by transition metals, a new generation of advanced oxidation processes, has been widely studied for water purification. However, the application of this process to oxidize and remove arsenite [As(III)] from water through Fe-based S(IV) activation and the associated mechanisms are not fully understood. In particular, rapid removal of As(III) and secondary metal contamination have presented challenges. Herein, we develop a novel sea urchin-like magnetic Fe-Mn bimetallic oxides (FeMnO)-activated S(IV) process to address these issues. Under neutral pH, the FeMnO/S(IV) system achieved a 99.2 % removal of As(III) within only 10 min with residual arsenic concentration below 10 µg/L, and the removed As(III) was fully oxidized to arsenate [As(V)]. Additionally, FeMnO was recyclable and capable of treating actual arsenic-contaminated water. Furthermore, the oxidation mechanism of non-radical active trivalent manganese [Mn(III)] was discovered during the reaction between the FeMnO/S(IV) system and As(III). The FeMnO catalyst activated S(IV) to generate oxysulfur radicals (i.e., SO 5 •–, SO 4 •– and SO 3 •–), but they were not the primary oxidizing species for As(III). Instead, As(III) oxidation was mainly attributed to the active Mn(III) generated by the electron transfer between the FeMnO catalyst and SO 5 •– radicals. The discovery of active Mn(III) species in this work may provide a new avenue for developing novel Fe-Mn-type adsorbents to purify arsenic-contaminated water. [ABSTRACT FROM AUTHOR]

• The FeMnO x /S(IV) system has faster removal speed and higher adsorption capacity for As(III) compared to FeMnO x alone. • The As(III) (1079 µg/L) could be decreased to less than 10 µg/L within 10 min. • The SO 5 •− radicals generated by S(IV) acting as the driving force for the redox cycle between As(III) and Mn(II/III/IV). • The possible mechanism of As(III) oxidation and removal for the FeMnO x /S(IV) system was proposed. • The FeMnO x nanocellulose aerogel broadened the scope of FeMnO x /S(IV) system in engineering applications. Manganese (Mn)-containing composite metal adsorbents are very effective at removing arsenite (As(III)) from contaminated water, however, the low removal speed and oxidation efficiency have limited their further application. In this study, a nonhomogeneous catalytic oxidation–adsorption system was constructed by coupling iron–manganese composite oxide (FeMnO x) with sulfite (S(IV)) to enhance the recovery of oxidative capacity and accelerate the removal of As(III). Experimental results showed that the FeMnO x /S(IV) system decreased the As(III) concentration from 1079 to <10 µg/L within 10 min and almost completely oxidized As(III) to As(V). In contrast, FeMnO x alone removed only 82.4% of As(III) within 30 min, and 60.0% of the adsorbed As(III) was not oxidized. Meanwhile, the adsorption capacity of FeMnO x /S(IV) system for As(III) was considerably higher than that of the only-FeMnO x system (76.5 > 46.3 mg/g). The efficient and fast As(III) removal was attributed to the SO 5 •− radical generated by S(IV) acting as the driving force for the redox cycle between As(III) and Mn(II/III/IV). Several environmental factors (e.g., solution pH and inorganic anions) and the reusability and practicality of FeMnO x were systematically investigated, and the results further confirmed the superiority of the FeMnO x /S(IV) system in As(III) removal. In particular, the proposed FeMnO x nanocellulose aerogel effectively purified arsenic-contaminated groundwater using a fixed-bed column. Thus, FeMnO x –S(IV) coupling is very promising for the purification of arsenic-contaminated water bodies. [Display omitted] [ABSTRACT FROM AUTHOR]

Here, we prepared a novel nanostructured Fe–Cu–Mn composite oxide (FCMO x) adsorbent using an ultrasonic coprecipitation method. The maximum adsorption capacity of As(III) and As(V) reached 158.5 and 115.2 mg/g under neutral conditions, respectively. The effects of several environmental factors (coexisting ions, solution pH, etc.) on the removal of inorganic arsenic using FCMO x were studied through batch experiments. The results showed that except for PO 4 3– and high initial pH, it was not significantly affected by ionic strength and other existing anions, implying a higher selectivity and adaptability. Combined with EPR, FTIR, and XPS analysis, we concluded that the Cu component and the reactive oxygen species (ROS) it generates played a decisive role in maintaining the stability of the redox cycle between Mn(IV)/Mn(III)/Mn(II) and enhancing the oxidation efficiency of As(III). Meanwhile, the adsorption mechanism of As(V) was mainly through the replacement of the FCMO x surface –OH to form stable inner-sphere arsenic complexes, while the removal mechanism of As(III) may involve the process of synergistic oxidation and chemisorption coupling. Additionally, the effective removal of As from the simulated As-contaminated water and its satisfactory reuse performance make FCMO x adsorbents favorable candidates for the removal of As-contaminated water in the future. [Display omitted] ● A novel FCMO x adsorbent was employed to remove As(III) and As(V) from aqueous solutions. ● The FCMO x exhibited excellent photocatalytic activity under visible-light irradiation. ● The redox cycle between Mn(II)/Mn(III)/Mn(IV) was mainly driven by the Cu component in FCMO x. ● The coupling effect of photocatalytic oxidation, chemical oxidation and adsorption enhanced the removal of As(III). [ABSTRACT FROM AUTHOR]