Search

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., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

[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]

[Display omitted] • A functionalized carboxymethyl chitosan aerogel is explored for Cu(Ⅱ) adsorption. • The maximum capacity of PCCSA-1.0 for absorbing Cu(Ⅱ) is 175.56 mg/g. • Continuous filtration of industrial wastewater with fixed bed columns is achieved. • PCCSA-1.0 is conducive to inhibit the enrichment of Cu(Ⅱ) ions in rice. • The generated waste after adsorption is converted into a material for secondary use. Copper ions (Cu(II)) in water pose a huge threat to human health and ecosystem security. Therefore, developing eco-friendly and sustainable strategies to eliminate the toxicity risk of Cu(II) in the aqueous environment remains a great challenge. In this work, an elastic polyethyleneimine-modified carboxymethyl chitosan aerogel was developed via a freeze-drying process for the adsorption of Cu(II). The adsorption kinetic and isotherm experiments demonstrated that the adsorption process was monolayer chemisorption and the maximum adsorption capacity calculated from Langmuir model was 175.56 mg g−1. The obtained aerogels exhibited preferential selectivity for Cu(II) even when the competing cations and organics existed. Besides, about 0.93 g of aerogel realized continuous fixed-bed column filtration of industrial wastewater with an effective purification volume of 4.14 L. Mechanistic analysis via FTIR and XPS revealed that the excellent adsorption performance for Cu(II) might be attributed to the strong electrostatic force, Vander Waals' force and coordination of N/O -containing functional groups. It is worth mentioning that the adsorbed Cu(II) ions in the aerogel were converted into a reusable photocatalyst, avoiding the secondary leakage of heavy metals. This work opened a door to synthesize carboxymethyl chitosan aerogel, promising for heavy metal wastewater treatment and realizing the concept of waste utilization. [ABSTRACT FROM AUTHOR]