The critical role of the surface iron-oxalate complexing species in determining photochemical degradation of norfloxacin using different iron oxides

Insights into sunlight-driven transformation of tetracycline by iron (hydr)oxides: The dominating role of self-generated hydrogen peroxide

Iron (hydr)oxides are abundant in surface environment, and actively participate in the transformation of organic pollutants due to their large specific surface areas and redox activity. This work investigated the transformation of tetracycline (TC) in the presence of three common iron (hydr)oxides, hematite (Hem), goethite (Goe), and ferrihydrite (Fh), under simulated sunlight irradiation. These iron (hydr)oxides exhibited photoactivity and facilitated the transformation of TC with the initial phototransformation rates decreasing in the order of: Hem > Fh > Goe. The linear correlation between TC removal efficiency and the yield of HO• suggests that HO• dominated TC transformation. The HO• was produced by UV-induced decomposition of self-generated H2O2 and surface Fe2+-triggered photo-Fenton reaction. The experimental results indicate that the generation of HO• was controlled by H2O2, while surface Fe2+ was in excess. Sunlight-driven H2O2 production in the presence of the highly crystalline Hem and Goe occurred through a one-step two-electron reduction pathway, while the process was contributed by both O2-induced Fe2+ oxidation and direct reduction of O2 by electrons on the conduction band in the presence of the poorly crystalline Fh. These findings demonstrate that sunlight may significantly accelerate the degradation of organic pollutants in the presence of iron (hydr)oxides.

Distinct photochemistry of adsorbed and coprecipitated dicarboxylates with ferrihydrite: Implications for iron reductive dissolution and carbon stabilization

Although ligand-promoted photodissolution of ferrihydrite (FH) has long been known for low molecular weight organic acids (LMWOAs), such as oxalate (Oxa) and malonate (Mal), photochemistry of coprecipitated FH with Oxa and Mal remains unknown, despite the importance of these mineral-organic associations in carbon retention has been acknowledged recently. In this study, ferrihydrite-LMWOAs associations (FLAs) were synthesized under circumneutral conditions. Photo-dissolution kinetics of FLAs were compared with those of adsorbed LMWOAs on FH surface and dissolved Fe-LMWOAs complexes through monitoring Fe(II) formation and organic carbon decay. For aqueous Fe(III)-LMWOAs complexes, Fe(II) yield was controlled by the initial concentration of LMWOAs and nature of photochemically generated carbon-centered radicals. Inner-sphere mononuclear bidentate (MB) configuration dominated while LMWOAs were adsorbed on the FH surface. MB complex of FH-Oxa was more photoreactive, leading to the rapid depletion of Oxa. Oxa can be readsorbed but in the form of binuclear bidentate and outer-sphere complexation, with much lower photoreactivity. While LMWOAs was coprecipitated with FH, the combination mode of LMWOAs with FH includes surface adsorption with a mononuclear bidentate structure and internal physical inclusion. Higher content of LMWOAs in the FLAs promoted the photo-production of Fe(II) as compared to pure FH, while it was not the case for FLAs containing moderate amounts of LMWOAs. The distinct photochemistry of adsorbed and coprecipitated Fe-LMWOAs complexes is attributed to ligand availability and configuration patterns of LMWOAs on the surface or entrapped in the interior structure. The present findings have significant implications for understanding the photochemical redox cycling of iron across the interface of Fe-organic mineral associates.

Oxalate enhanced aniline degradation by goethite: Structural dependent activity, hydroxyl radicals generation and toxicity evaluation

A photochemical system combining iron (hydr)oxides and oxalate (Ox) shows application prospects in wastewater treatment due to the abundance of reactive oxygen species (ROS) generation. Nevertheless, it is a challenge to the investigate photochemical activity of iron (hydr)oxides/Ox systems with varying structural properties. Herein, the photochemical behaviors of Ox on goethite (Gt) surface from the view of structural dependent activity, containment degradation, and ROS generation were explored in detail. Results confirmed that bidentate mononuclear was formed on Gt surface after complexing Ox. Combined with density functional theory calculation and pH time evolution during aniline degradation, the photochemical activity of the Gt/Ox system fell in between that of ferrihydrite/Ox and hematite/Ox systems. After irradiating 120 min visible light, 96.5% aniline was degraded by 1.0 mM Ox and 0.2 g/L Gt. The amount of •OH in vis/Gt/Ox system could be up to 309.3 μM and its generation was closely associated with Fe(II) while slightly affected by the generated H2O2. Moreover, as revealed by high-performance liquid chromatography with mass spectrometric and Ecological Structure Activity Relationships software, the toxicity of the intermediates of aniline degradation in the vis/Gt/Ox system towards fish and green algae increased first but then declined accompanied by the generation of non-toxic ring-opening products at the end of reaction. According to the findings in the presented study, it could be concluded that vis/Gt/Ox is a promising approach to wiping out aniline wastewater.

Closing the knowledge gap on the composition of the asbestos bodies

Asbestos bodies (AB) form in the lungs as a result of a biomineralization process initiated by the alveolar macrophages in the attempt to remove asbestos. During this process, organic and inorganic material deposit on the foreign fibers forming a Fe-rich coating. The AB start to form in months, thus quickly becoming the actual interface between asbestos and the lung tissue. Therefore, revealing their composition, and, in particular, the chemical form of Fe, which is the major component of the AB, is essential to assess their possible role in the pathogenesis of asbestos-related diseases. In this work we report the result of the first x-ray diffraction measurements performed on single AB embedded in the lung tissue samples of former asbestos plant workers. The combination with x-ray absorption spectroscopy data allowed to unambiguously reveal that Fe is present in the AB in the form of two Fe-oxy(hydroxides): ferrihydrite and goethite. The presence of goethite, which can be explained in terms of the transformation of ferrihydrite (a metastable phase) due to the acidic conditions induced by the alveolar macrophages in their attempt to phagocytose the fibers, has toxicological implications that are discussed in the paper.

Ferruginous bodies exert a strong proinflammatory effect

One of the main problems related to ferruginous-asbestos bodies (ABs) exposure is their potential pathogenetic role in asbestos-related diseases. The aim of this study was to examine whether purified ABs, might stimulate inflammatory cells. ABs were isolated by exploiting their magnetic properties, therefore avoiding the strong chemical treatment usually employed for this purpose. This latter treatment, which is based upon the digestion of organic matter with concentrated hypochlorite, may markedly modify the AB structure and consequently also their "in vivo" manifestations. ABs were found to induce secretion of human neutrophil granular component myeloperoxidase, as well as stimulate rat mast cell degranulation. Data demonstrated that by triggering secretory processes in inflammatory cells, purified ABs may play a role in the pathogenesis of asbestos-related diseases by continuing and enhancing the pro-inflammatory activity of the asbestos fibers.

Development of iron-based biochar for enhancing nitrate adsorption: Effects of specific surface area, electrostatic force, and functional groups

The problem of nitrate contamination in water has attracted widespread attention. Original biochar has a poor adsorption capacity for nitrate adsorption. Iron impregnation and acid protonation (base deprotonation) are common modification methods for biochar. In order to develop iron-mediated biochar containing multi-functional groups for enhancing nitrate adsorption, Fe-BC@H and Fe-BC@OH were prepared using a two-stage development process, including an iron-based carbon pyrolysis followed by acid protonation (or base deprotonation). The pseudo-second-order kinetic and Langmuir models can well describe the adsorption process which is a physicochemical complex monolayer adsorption. The data proved that Fe-BC@H (9.35 mg/g NO₃^--N) had a stronger adsorption capacity than Fe-BC@OH (2.95 mg/g NO₃^--N). Surface morphologies, functional groups, and mineral compositions of Fe-BC@H and Fe-BC@OH were analyzed through Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Characterization results showed that acid protonation can further improve the specific surface area (SSA), pore volume, and Zeta potential of Fe-based biochar, providing more adsorption sites for nitrate and enhancing the electrostatic force between nitrate and biochar. However, these effects were suppressed through base deprotonation. In addition, acid protonation can significantly increase the type and number of functional groups of biochar to enhance the chemisorption of nitrate. Such results suggested that the acid protonation can further improve the adsorption capacity of Fe-based biochar for nitrate, while base deprotonation had an inhibitory effect on that of Fe-based biochar. Overall, this study reveals that specific surface area, electrostatic force, and functional groups are crucial effects of the nitrate adsorption on acid/base modified biochar.

Facet-Dependent Activation of Oxalic Acid over Magnetic Recyclable Fe3S4 for Efficient Pollutant Removal under Visible Light Irradiation: Enhanced Catalytic Activity, DFT Calculations, and Mechanism Insight

Photo-Fenton-like reaction based on oxalic acid (OA) activation is a promising method for the fast degradation of pollutants due to the low cost and safety. Hence, the magnetic recyclable greigite (Fe₃S₄) with the exposed {011} facet (FS-011) was prepared using a facile one-pot hydrothermal method and activated OA under visible light irradiation for pollutant removal, in which the removal efficiency values of FS-011 for metronidazole (MNZ) and hexavalent chromium were 2.02 and 1.88 times higher than that of Fe₃S₄ with the exposed {112} facet, respectively. Density functional theory calculations revealed that OA was more easily adsorbed by the {011} facet of Fe₃S₄ than by the {112} facet, and the in situ-generated H₂O₂ preferred to diffuse away from the active sites of the {011} facet of Fe₃S₄ than from that of the {112} facet, which was conducive to the continuous adsorption and efficient activation of OA. Moreover, the analyses of Fukui index and dual descriptor confirmed the degradation mechanism that the imidazole ring of MNZ was easy to be attacked by electrophilic species, while the amino group of MNZ was easy to be attacked by nucleophilic species. These findings deeply analyzed the mechanism of enhanced OA activation by facet engineering and consolidated the theoretical basis for practical application of Fenton-like reactions.

Fast peroxydisulfate oxidation of the antibiotic norfloxacin catalyzed by cyanobacterial biochar

Peroxydisulfate (PDS) is a common oxidant for organic contaminant remediation. PDS is typically activated by metal catalysts to generate reactive radicals. Unfortunately, as radicals are non-selective and metal catalysts may cause secondary contamination, alternative selective non-radical pathways and non-metal catalysts need attention. Here we investigated PDS oxidation of commonly detected antibiotic Norfloxacin (NOR) using cyanobacterial nitrogen rich biochars (CBs) as catalysts. NOR was fully degraded by CB pyrolysed at 950 °C (CB950) within 120 min. CB950 caused threefold faster degradation than low pyrolysis temperature (PT) CBs and achieved a maximum surface area normalized rate constant of 4.38 × 10^-2 min^-1 m^-2 L compared to widely used metal catalysts. CB950 maintained full reactivity after four repeated uses. High defluorination (82%) and mineralization (>82%) were observed for CB950/PDS. CBs were active over a broad pH range (3-10), but with twice as high rates under alkaline compared with neutral conditions. NOR is degraded by organic, ^•OH and SO₄^•- radicals in low PT CBs/PDS systems, where the presence of Mn^II promotes radical generation. Electron transfer reactions with radicals supplemented dominate high PT CBs/PDS systems. This study demonstrates high PT biochars from algal bloom biomass may find use as catalysts for organic contaminant oxidation.

Catalytic Oxygen Activation over the Defective CuO Nanoparticles for Ultrafast Dehalogenation

The nucleophilic superoxide radical (O₂^•-)-based dehalogenation reaction shows great potential to degrade the toxic halogenated organic compounds (HOCs). But such an O₂^•--mediated reductive reaction often suffers from the competition of the secondary oxidative species (e.g., •OH), leading to inferior electron efficiency and possible disinfection byproduct formation. Here, an O₂^•--dominant ultrafast dehalogenation system is developed via molecular O₂ activation by the oxygen vacancy (OV)-rich CuO nanoparticles (nCuO). The nCuO delivers a remarkable dechlorination rate constant of 3.92 × 10^-2 L min^-1 m^-2 for 2,4-dichlorophenol, much higher than that of the conventional zerovalent (bi)metals. The absorbed O₂ on the nCuO surface is exclusively responsible for O₂^•- generation, and its reactivity increases with the elevated OV content because of the enhanced orbital hybridization between the O p- and Cu d-orbitals. More importantly, the ubiquitous carbonate species firmly bound to the surface OVs block the formation of the secondary oxidative species via H₂O₂ activation, assuring the dominant role of the in situ generated O₂^•- for the selective HOC dehalogenation. The carbonate-deactivated OVs of the nCuO can be feasibly recovered via air annealing for sustainable dehalogenation. This work provides a new opportunity for selective O₂^•- generation via interfacial defect engineering for dehalogenation and other environmental applications.

Fate of metal-EDTA complexes during ferrihydrite aging: Interaction of metal-EDTA and iron oxides

The widespread presence of ferrihydrite in the environment makes many contaminants including metal-EDTA complexes being adsorbed on it. However, the fate of metal-EDTA complexes during the transformation of ferrihydrite was poorly understood. Understanding the migration and speciation changes of metal-EDTA adsorbed on ferrihydrite during the transformation was helpful to predict its fate in some natural and engineering environments. In this work, the interaction of the two metal-EDTA complexes (Ni(II)-EDTA and Ca(II)-EDTA) and ferrihydrite during the 9-day transformation of ferrihydrite at different pH values was studied. The results showed that part of EDTA complexing metals changed to non-complexed metals during the ferrihydrite transformation, which was due to the fact that metal in the metal-EDTA exchanged with Fe(III) on ferrihydrite. Besides, different speciation of metal ions migrated during the transformation of ferrihydrite. Meanwhile, Fe(III)-EDTA formed in this process, and the exchange of metal in Ca(II)-EDTA with Fe(III) in ferrihydrite was faster than that of Ni(II)-EDTA. Besides, the presence of metal-EDTA affected the transformation rate of ferrihydrite under neutral and alkaline condition, and metal-EDTA accelerated the dissolution of ferrihydrite to form goethite. Therefore, ferrihydrite and metal-EDTA influenced each other during the transformation of ferrihydrite. The results of this work revealed that the process of metal-EDTA dissolving ferrihydrite not only included the dissociation of metal-EDTA, but also involved the migration of metal ions and affected the transformation of ferrihydrite.

Predicting the trend and utility of different photocatalysts for degradation of pharmaceutically active compounds: A special emphasis on photocatalytic materials, modifications, and performance comparison

The rapid rise in the healthcare sector has led to an increase in pharmaceutically active compounds (PhACs) in different aqueous bodies. The toxicity of the PhACs and their ability to persist after conventional treatment processes have escalated research in the field of photocatalytic treatment. Although different photocatalysts have been successful in degrading PhACs, their inherent drawbacks have severely limited their application on a large scale. A substantial amount of research has been aimed at overcoming the high cost of the photocatalytic material, low quantum yield, the formation of toxic end products, etc. Hence, to further research in this field, researchers must have a fair idea of the current trends in the application of different photocatalysts. In this article, the trends in the use of various photocatalysts for the removal of different PhACs have been circumscribed. The performance of different groups of photocatalysts to degrade PhACs from synthetic and real wastewater has been addressed. The drawbacks and advantages of these materials have been compared, and their future in the field of PhACs removal has been predicted using S-curve analysis. Zinc and titanium-based photocatalysts were efficient under UV irradiation, while bismuth and graphene-based materials exhibited exemplary performance in visible light. However, iron-based compounds were found to have the most promising future, which may be because of their magnetic properties, easy availability, low bandgap, etc. Different modification techniques, such as morphology modification, doping, heterojunction formation, etc., have also been discussed. This study may help researchers to clarify the current research status in the field of photocatalytic treatment of PhACs and provide valuable information for future research.

Migration behavior of Cr(VI) during the transformation of ferrihydrite-Cr(VI) co-precipitates: The interaction between surfactants and co-precipitates

Redistribution of Cr(VI) in ferrihydrite-Cr(VI) co-precipitates (Fh-Cr) was affected by co-precipitates transformation and coexisting substances. These effects were crucial for predicting the migration path of Cr(VI) in ferrihydrite-Cr(VI) co-precipitates. This work investigated the effects of the extensively used surfactants of anionic surfactant sodium dodecylbenzene sulfonate (SDBS) and cationic surfactant cetyltrimethylammonium bromide (CTAB) on the Fh-Cr transformation and redistribution of Cr(VI) for 10 days at different pH values (5.0, 7.5 and 9.0) and concentration of surfactants (0.5, 2.0 and 5.0 mM). The results showed that SDBS hindered the transformation of Fh-Cr to hematite and tended to transform into goethite. SDBS inhibited hematite formation by inhibiting the aggregation of Fh-Cr particles, and it enhanced the dissolution of Fh-Cr to facilitate the formation of goethite. Affected by the inhibition of Fh-Cr transformation, the process of Cr(VI) redistribution was delayed. CTAB did not affect the transformation of Fh-Cr, but allowed more Cr(VI) to enter the interior of iron minerals. When the surfactants were adsorbed on the Fh-Cr, SDBS decreased the adsorption of Cr(VI) by Fh-Cr, while CTAB increased the Cr(VI) adsorption. The findings of this study contribute to understand the effects of surfactants on the transformation of Fh-Cr and the behaviors of Cr(VI) during this process.

Selective Adsorption of Aqueous Diclofenac Sodium, Naproxen Sodium, and Ibuprofen Using a Stable Fe3O4-FeBTC Metal-Organic Frameworka

The FeBTC metal–organic framework (MOF) incorporated with magnetite is proposed as a novel material to solve water contamination with last generation pollutants. The material was synthesized by in situ solvothermal methods, and Fe₃O₄ nanoparticles were added during FeBTC MOF synthesis and used in drug adsorption. X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and Raman spectroscopy characterized the materials, with N₂-physisorption at 77 K. Pseudo-second-order kinetic and Freundlich models were used to describe the adsorption process. The thermodynamic study revealed that the adsorption of three drugs was a feasible, spontaneous exothermic process. The incorporation of magnetite nanoparticles in the FeBTC increased the adsorption capacity of pristine FeBTC. The Fe₃O₄–FeBTC material showed a maximum adsorption capacity for diclofenac sodium (DCF), then by ibuprofen (IB), and to a lesser extent by naproxen sodium (NS). Additionally, hybridization of the FeBTC with magnetite nanoparticles reinforced the most vulnerable part of the MOF, increasing the stability of its thermal and aqueous media. The electrostatic interaction, H-bonding, and interactions in the open-metal sites played vital roles in the drug adsorption. The sites’ competition in the multicomponent mixture’s adsorption showed selective adsorption (DCF) and (NS). This work shows how superficial modification with a low-surface-area MOF can achieve significant adsorption results in water pollutants.