Cr(VI) detoxification and organic matter (OM) stabilization are usually influenced by the biological transformation of iron (Fe) minerals; however, the underlying mechanisms of metal-reducing bacteria on the coupled kinetics of Fe minerals, Cr, and OM remain unclear. Here, the reductive sequestration of Cr(VI) and immobilization of fulvic acid (FA) during the microbially mediated phase transformation of ferrihydrite with varying Cr/Fe ratios were investigated. No phase transformation occurred until Cr(VI) was completely reduced, and the ferrihydrite transformation rate decreased as the Cr/Fe ratio increased. Microscopic analysis was uncovered, which revealed that the resulting Cr(III) was incorporated into the lattice structure of magnetite and goethite, whereas OM was mainly adsorbed on goethite and magnetite surfaces and located within pore spaces. Fine line scan profiles showed that OM adsorbed on the Fe mineral surface had a lower oxidation state than that within nanopores, and C adsorbed on the magnetite surface had the highest oxidation state. During reductive transformation, the immobilization of FA by Fe minerals was predominantly via surface complexation, and OM with highly aromatic and unsaturated structures and low H/C ratios was easily adsorbed by Fe minerals or decomposed by bacteria, whereas Cr/Fe ratios had little effect on the binding of Fe minerals and OM and the variations in OM components. Owing to the inhibition of crystalline Fe minerals and nanopore formation in the presence of Cr, Cr sequestration and C immobilization can be synchronously favored at low Cr/Fe ratios. These findings provide a profound theoretical basis for Cr detoxification and synchronous sequestration of Cr and C in anoxic soils and sediments.

Reductive Sequestration of Cr(VI) and Immobilization of C during the Microbially Mediated Transformation of Ferrihydrite-Cr(VI)-Fulvic Acid Coprecipitates.

Boosting Persulfate Activation via Paper Mill Sludge-based Biochar for Efficient Degradation of Bisphenol A: Inherent multiple active sites

Novel Fe/N co-doping biochar based electro-Fenton catalytic membrane enabling enhanced tetracycline removal and self-cleaning performance

Quantitative analysis on the redox conversion mechanism of Cr(VI) and As(III) by iron carbide based biochar composites

Recent advances toward structural incorporation for stabilizing heavy metal contaminants: A critical review

The coprecipitation of heavy metals (HMs) with Fe(III) in the presence of dissolved organic matter (DOM) is a crucial process to control the mobility of HMs in the environment, but its underlying immobilization mechanisms are unclear. In this study, Cr(III) immobilization by coprecipitation with Fe(III) in the presence of straw-derived DOMs under different Fe/C molar ratios, pHs, and ionic strengths was investigated using scanning transmission X-ray microscopy (STXM) and ptychography and X-ray absorption near-edge structure (XANES) spectroscopy. The results showed that Cr(III) retention was enhanced in the presence of DOM, a maximum of which was achieved at an Fe/C molar ratio of 0.5. The increase of pH and ionic strength could also promote Cr(III) immobilization. Cr K-edge XANES results indicated that Fe (oxy)hydroxide fractions, instead of organics, provided the predominant binding sites for Cr(III), which was directly confirmed by high spatial resolution STXM-ptychography analysis at the sub-micron- and nanoscales. Moreover, organics could indirectly facilitate Cr immobilization by improving the aggregation and deposition of coprecipitate particles through DOM bridging or electrostatic interactions. Additionally, C K-edge XANES analysis further indicated that the carboxylic groups of DOM were complexed with Fe (oxy)hydroxides, which probably contributed to DOM bridging. This study provides a new insight into Cr(III) immobilization mechanisms in its coprecipitation with Fe(III) and DOM, which could have important implications on the management of Cr(III)-enriched soils, particularly with crop straw returning.

Molecular Insights into Roles of Dissolved Organic Matter in Cr(III) Immobilization by Coprecipitation with Fe(III) Probed by STXM-Ptychography and XANES Spectroscopy.

Gradient-distributed NiCo2O4 nanorod electrode for redox flow batteries: Establishing the ordered reaction interface to meet the anisotropic mass transport

Effect of metal doping (Me = Zn, Cu, Co, Mn) on the performance of bismuth ferrite as peroxymonosulfate activator for ciprofloxacin removal.

In order to efficiently degrade ibuprofen (IBU) by peroxymonosulfate (PMS) activation, manganese cobalt oxide nanoparticles-decorated functionalized multi-walled carbon nanotubes (MnCo 2 O 4 /FCNTs) were prepared using a facile hydrothermal method. Comprehensive characterization of this PMS activator in multi-scale suggested that MnCo 2 O 4 nanoparticles were uniformly decorated on FCNTs. The catalytic performance was systematical evaluated under various environmental conditions, including temperature, pH, and the presence of different common water matrix species (e.g., Cl - , HCO 3 - , and natural organic matter). The as-synthesized MnCo 2 O 4 /FCNTs demonstrated excellent catalytic activity with k app ranging 0.285–0.327 min −1 under a wide pH range of 3–9 within 10 min, which achieved a complete removal of IBU and a mineralization rate higher than 90%. During oxidation process for stability and reusability test, recycled MnCo 2 O 4 /FCNTs was found durable with negligible leaching of metal ions from spent catalyst, exhibiting its high stability for PMS activation with merely slight decrease of k app from 0.285 to 0.201 min −1 in the fourth cycle. Electron paramagnetic resonance analysis further confirmed that • OH, SO 4 •- and 1 O 2 were generated in the robust MnCo 2 O 4 /FCNTs-PMS system. Both radical and nonradical reactions were found to be responsible for the enhanced IBU degradation. Overall, this study sheds light on practical knowledge of IBU removal using MnCo 2 O 4 /FCNTs for PMS activation. • MnCo 2 O 4 /FCNTs-PMS system exhibits excellent removal and mineralization of IBU. • MnCo 2 O 4 /FCNTs presents good and stable reactivity within a wide pH range of 3–9. • Recycled MnCo 2 O 4 /FCNTs is robust with negligible leaching of metal ions. • Both radical and nonradical reactions are responsible for enhanced IBU degradation. 

Reinforced degradation of ibuprofen with MnCo2O4/FCNTs nanocatalyst as peroxymonosulfate activator: Performance and mechanism

Molecular mechanisms of Chromium(III) sorption by organo-ferrihydrite coprecipitates induced by crop straws.

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