Biogenic synthetic schwertmannite photocatalytic degradation of acid orange 7 (AO7) assisted by citric acid

Nitrogen-doped titanium dioxide/schwertmannite nanocomposites as heterogeneous photo-Fenton catalysts with enhanced efficiency for the degradation of bisphenol A

Potential health risks related to environmental endocrine disruptors (EEDs) have aroused research hotspots at the forefront of water treatment technologies. Herein, nitrogen-doped titanium dioxide/schwertmannite nanocomposites (N-TiO2/SCH) have been successfully developed as heterogeneous catalysts for the degradation of typical EEDs via photo-Fenton processes. Due to the sustainable Fe(III)/Fe(II) conversion induced by photoelectrons, as-prepared N-TiO2/SCH nanocomposites exhibit much enhanced efficiency for the degradation of bisphenol A (BPA; ca. 100% within 60 min under visible irradiation) in a wide pH range of 3.0-7.8, which is significantly higher than that of the pristine schwertmannite (ca. 74.5%) or N-TiO2 (ca. 10.8%). In this photo-Fenton system, the efficient degradation of BPA is mainly attributed to the oxidation by hydroxyl radical (•OH) and singlet oxygen (1O2). Moreover, the possible catalytic mechanisms and reaction pathway of BPA degradation are systematically investigated based on analytical and photoelectrochemical analyses. This work not only provides a feasible means for the development of novel heterogeneous photo-Fenton catalysts, but also lays a theoretical foundation for the potential application of mineral-based materials in wastewater treatment.

Enhancement of norfloxacin degradation by citrate in S-nZVI@Ps system: Chelation and FeS layer

The degradation of organic pollution by sulfur-modified nano zero-valent iron(S-nZVI) combined with advanced oxidation systems has been extensively studied. However, the low utilization of nZVI and low reactive oxygen species (ROS) yield in the system have limited its wide application. Herein, a natural organic acid commonly found in citrus fruits, citric acid (CA), was combined with the conventional S-nZVI@Ps system to enhance the degradation of norfloxacin (NOR). The addition of CA increased the NOR removal by about 31% compared with the conventional S-nZVI@Ps system under the same experimental conditions. Among them, the enhanced effect of CA is mainly reflected in its ability to promote the release of Fe2+ and accelerate the cycling of Fe2+ and Fe3+ to further improve the utilization of nZVI and the generation of ROS; it also promotes the dissolution of the active substance (FeS) on the surface of S-nZVI to further improve the degradation rate of NOR. More importantly, the chelate of CA and Fe2+ (CA-Fe2+) had higher reactivity than alone Fe2+. Free radical quenching and electron spin resonance (ESR) experiments indicated that the main ROS for the degradation of NOR in the CA/S-nZVI@Ps system were SO4•- and OH•. CA-bound sulfur-modifying effects on NOR degradation was systematically investigated, and the degradation mechanism of NOR in CA/S-nZVI@Ps system was explored by various techniques. Additionally, the effect of common anions in water matrix on the degradation of NOR in CA/S-nZVI@Ps system and its degradation of various pollutants were also studied. This study provides a new perspective to enhance the degradation of pollutants by S-nZVI combined with advanced oxidation system, which can help to solve the application boundary problem of S-nZVI.

Sulfate-accelerated photochemical oxidation of arsenopyrite in acidic systems under oxic conditions: Formation and function of schwertmannite

The weathering of arsenopyrite is closely related to the generation of acid mine drainage (AMD) and arsenic (As) pollution. Solar radiation can accelerate arsenopyrite oxidation, but little is known about the further effect of SO₄^2- on the photochemical process. Here, the photooxidation of arsenopyrite was investigated in the presence of SO₄^2- in simulated AMD environments, and the effects of SO₄^2- concentration, pH and dissolved oxygen on arsenopyrite oxidation were studied as well. SO₄^2- could accelerate the photooxidation of arsenopyrite and As(III) through complexation between nascent schwertmannite and As(III). Fe(II) released from arsenopyrite was oxidized to form schwertmannite in the presence of SO₄^2-, and the photooxidation of arsenopyrite occurred through the ligand-to-metal charge-transfer process in schwertmannite-As(III) complex along with the formation of reactive oxygen species in the presence of O₂. The photooxidation rate of arsenopyrite first rose and then fell with increasing SO₄^2- concentration. In the pH range of 2.0-4.0, the photooxidation rate of arsenopyrite progressively increased in the presence of SO₄^2-. This study reveals how SO₄^2- promotes the photooxidation of arsenopyrite and As release in the AMD environment, and improves the understanding of the transformation and migration of As in mining areas.

Porous urchin-like 3D Co(ii)Co(iii) layered double hydroxides for high performance heterogeneous Fenton degradation

Heterogeneous Fenton processes can overcome the generation of iron sludge and the production of more solid wastes.

Fabricating Fe3O4-schwertmannite as a Z-scheme photocatalyst with excellent photocatalysis-Fenton reaction and recyclability

Here we reported an effective method to solve the rate-limiting steps, such as the reduction of Fe³⁺ to Fe²⁺ and an invalid decomposition of H₂O₂ in a conventional Fenton-like reaction. A magnetic heterogeneous photocatalyst, Fe₃O₄-schwertmannite (Fe₃O₄-sch) was successfully developed by adding Fe₃O₄ in the formation process of schwertmannite. Fe₃O₄-sch shows excellent electrons transfer ability and high utilization efficiency of H₂O₂ (98.5%). The catalytic activity of Fe₃O₄-sch was studied through the degradation of phenol in the heterogeneous photo-Fenton process. Phenol degradation at a wide pH (3 - 9) was up to 98% within 6 min under visible light illumination with the Fe₃O₄-sch as heterogeneous Fenton catalyst, which was higher than that using pure schwertmannite or Fe₃O₄. The excellent photocatalytic performance of Fe₃O₄-sch is ascribed to the effective recycling between Fe³⁺ and Fe²⁺ by the photo-generated electron, and also profit from the formation of the "Z-Scheme" system. According to the relevant data, photocatalytic mechanism of Fe₃O₄-sch for degrading phenol was proposed. This study not only provides an efficient way of enhancing heterogeneous Fenton reaction, but also gives potential application for iron oxyhydroxysulfate mineral.

Feasibility and mechanism of enhanced 17β-estradiol degradation by the nano Zero Valent Iron-citrate system

17β-Estradiol (17β-E2) as a non-conventional pollutant with high damage, the effective removal of 17β-E2 had been studied wildly. In recent years, nano materials application enabled the rapid removal of 17β-E2. Nano zero valent iron (nZVI) as one of the most widely used nano materials could also be used to degrade 17β-E2. But, the degradation performance of nZVI was limited by oxidation and aggregation. Therefore, this study explored the degradation mechanisms of 17β-E2 by nZVI and the enhancement mechanisms of nZVI by citrate. Firstly, 17β-E2 could be effectively degraded under acidic conditions without the addition of citrate. Citrate had protective effect on nZVI, so the degradation efficiency in neutral condition and degradation rate at all pH values of 17β-E2 were enhanced greatly in nZVI-citrate system. 17β-E2 degradation was mainly about group change and cleavage of ring A, as well as dominated by O₂^-▪ and OH∙ in the absence and presence of citrate. The formation of dimers and trimers proved the existence of laccase-like reaction during the 17β-E2 degradation process by nZVI. In nZVI-citrate system, the laccase-like reaction was replaced by specific cross-coupling of 17β-E2, E1, and citrate. Overall, the study proved that citrate could enhance the degradation of 17β-E2 by nZVI.

Anion-Dominated Copper Salicyaldimine Complexes-Structures, Coordination Mode of Nitrate and Decolorization Properties toward Acid Orange 7 Dye

A salicyaldimine ligand, 3-tert-butyl-4-hydroxy-5-(((pyridin-2-ylmethyl)imino)methyl)benzoic acid (H₂L_salpyca) and two Cu(II)−salicylaldimine complexes, [Cu(HL_salpyca)Cl] (1) and [Cu(HL_salpyca)(NO₃)]_n (2), have been synthesized. Complex 1 has a discrete mononuclear structure, in which the Cu(II) center is in a distorted square-planar geometry made up of one HL_salpyca⁻ monoanion in an NNO tris-chelating mode and one Cl⁻ anion. Complex 2 adopts a neutral one-dimensional zigzag chain structure propagating along the crystallographic [010] direction, where the Cu(II) center suits a distorted square pyramidal geometry with a τ value of 0.134, consisted of one HL_salpyca⁻ monoanion as an NNO tris-chelator and two NO₃⁻ anions. When the Cu∙∙∙O semi coordination is taken into consideration, the nitrato ligand bridges two Cu(II) centers in an unsymmetrical bridging-tridentate with a μ, κ⁴O,O′:O′,O″ coordination. Clearly, anion herein plays a critical role in dominating the formation of discrete and polymeric structures of copper salicyaldimine complexes. Noteworthy, complex 2 is insoluble but highly stable in H₂O and various organic solvents (CH₃OH, CH₃CN, acetone, CH₂Cl₂ and THF). Moreover, complex 2 shows good photocatalytic degradation activity and recyclability to accelerate the decolorization rate and enhance the decolorization performance of acid orange 7 (AO7) dye by hydrogen peroxide (H₂O₂) under daylight.

A novel approach coupling ferrous iron bio-oxidation and ferric iron chemo-reduction to promote biomineralization in simulated acidic mine drainage

A novel Acidithiobacillus ferrooxidans-mediated approach coupling biological oxidation and chemical reduction for treating acid mine drainage (AMD) was investigated. The results showed that controlled addition of zero valent iron (ZVI) into the coupling system did not exhibit a significant adverse influence on the bacterial activity of Acidithiobacillus ferrooxidans but markedly increased the formation of secondary Fe-minerals. Nutrition did not affect the efficiency of coupling process, except for the bacteria density of A. ferrooxidans. 2 days cyclic treatment performed better than that of 4 and 8 days. After 14 cycles of the coupling process, 89.4% of total iron (2.23 g L-1) was transferred into Fe-minerals finally. In addition, the combined system was highly effective in removing sulfate (63%) from a simulated AMD that contained soluble Cu, Zn, Al, and Mn. Valuable iron-sulfate material e.g. schwertmannite was formed with little co-precipitation of other metals. Therefore, the integration of A. ferrooxidans into the reduction by ZVI may have considerable potential in the enhancement of biomineralization efficiency, which may further decrease soluble TFe and sulfate loads in AMD before lime neutralization.

Combination of microbial oxidation and biogenic schwertmannite immobilization: A potential remediation for highly arsenic-contaminated soil

Here, a novel strategy that combines microbial oxidation by As(III)-oxidizing bacterium and biogenic schwertmannite (Bio-SCH) immobilization was first proposed and applied for treating the highly arsenic-contaminated soil. Brevibacterium sp. YZ-1 isolated from a highly As-contaminated soil was used to oxidize As(III) in contaminated soils. Under optimum culture condition for microbial oxidation, 92.3% of water-soluble As(III) and 84.4% of NaHCO₃-extractable As(III) in soils were removed. Bio-SCH synthesized through the oxidation of ferrous sulfate by Acidithiobacillus ferrooxidans immobilize As(V) in the contaminated soil effectively. Consequently, the combination of microbial oxidation and Bio-SCH immobilization performed better in treating the highly As-contaminated soil with immobilization efficiencies of 99.3% and 82.6% for water-soluble and NaHCO₃-extractable total As, respectively. Thus, the combination can be considered as a green remediation strategy for developing a novel and valuable solution for As-contaminated soils.

Magnetic Activated-ATP@Fe3O4 Nanocomposite as an Efficient Fenton-Like Heterogeneous Catalyst for Degradation of Ethidium Bromide

Magnetic attapulgite-Fe₃O₄ nanocomposites (ATP-Fe₃O₄) were prepared by coprecipitation of Fe₃O₄ on ATP. The composites were characterized by scanning electron microscopey, X-ray diffractometry, Brunauer-Emmett-Teller analysis, X-ray photoelectron spectroscopy, energy dispersive spectrometer and transmission electron microscopy. Surface characterization showed that Fe₃O₄ particles with an average size of approximately 15 nm were successfully embedded in matrix of ATP. The capacity of the Fe₃O₄-activated ATP (A-ATP@Fe₃O₄) composites for catalytic degradation of ethidium bromide (EtBr, 80 mg/L) at different pH values, hydrogen peroxide (H₂O₂) concentrations, temperatures, and catalyst dosages was investigated. EtBr degradation kinetics studies indicated that the pseudo-first-order kinetic constant was 2.445 min⁻¹ at T = 323 K and pH 2.0 with 30 mM H₂O₂, and 1.5 g/L of A-ATP@Fe₃O₄. Moreover, a regeneration study suggested that A-ATP@Fe₃O₄ maintained over 80% of its maximal EtBr degradation ability after five successive cycles. The effects of the iron concentrations and free radical scavengers on EtBr degradation were studied to reveal possible catalytic mechanisms of the A-ATP@Fe₃O₄ nanocomposites. Electron Paramagnetic Resonance revealed both hydroxyl (∙OH) and superoxide anion (∙O₂⁻) radicals were involved in EtBr degradation. Radical scavenging experiment suggested EtBr degradation was mainly ascribed to ∙OH radicals, which was generated by reaction between Fe²⁺ and H₂O₂ on the surface of A-ATP@Fe₃O₄.

The influence of fractal nature on schwertmannite adsorption properties

Schwertmannite (SCH), a ferric oxyhydroxy sulfate mineral, had attracted extensive interests due to its excellent adsorption performance in decontamination processes.

Enhancing the reactivity of bimetallic Bi/Fe(0) by citric acid for remediation of polluted water

In this study, the environmentally benign citric acid (CA) was utilized to improve the aerobic degradation of 4-chlorophenol (4-CP) over bismuth modified nanoscale zero-valent iron (Bi/Fe(0)). The characterization results revealed the existence of bismuth covering on the Fe(0) surface under zero-valent state. And, the Bi/Fe(0)-CA+O2 system performed excellent reactivity in degradation of 4-CP due to the generation of reactive oxygen species (ROS), which was confirmed by electron spin resonance (ESR) spectroscopy. After 30min of reaction, 80% of 4-CP was removed using Bi/Fe(0)-CA+O2 accompanying with high dechlorination rate. The oxidative degradation intermediates were analyzed by HPLC and LC-MS. We found that CA could promote the bismuth-iron system to produce much reactive oxygen species ROS under both aerobic and anaerobic conditions due to its ligand function, which could react with Fe(3+) to form a ligand complex (Fe(III)Cit), accompanying with a considerable production of Fe(2+) and H2O2. This study provides a new strategy for generating ROS on nZVI and suggests its application for the mineralization of many recalcitrant pollutants.