Facile and large-scale fabrication of (Mg,Ni)(Fe,Al)2O4 heterogeneous photo-Fenton-like catalyst from saprolite laterite ore for effective removal of organic contaminants

Construction of an S-scheme electron transfer channel in Cu0/CuFe2O4 magnetic plate column reactor for the LEV degradation: New strategy of visible Photo-Fenton system application

The complicated loading process and easy falling off of powder catalysts still restrict the wide application of Photo-Fenton technology in practical water treatment. In this study, a magnetic fixed film plate column water treatment equipment is designed as a visible Photo-Fenton reactor to remove levofloxacin (LEV). The effect of magnetic force can ensure that the catalyst is firmly fixed, and the multi-level shallow column plate structure achieves full contact and efficient reaction between the catalyst and wastewater. Simultaneously, the Cu0/CuFe2O4 (STCCF) utilizes Cu0 to construct an S-scheme electron transfer channel, which improves the separation efficiency of photo-generated carriers and provides sufficient photo-generated electrons for the reduction of Fe (Ⅲ) and Cu (Ⅱ). The pseudo-first-order reaction kinetic constant k for the degradation of LEV in the visible Photo-Fenton system is 0.0349 min-1, which is 15.9 times that of the photocatalytic system and 4.8 times that of the Fenton system. After continuous operation for 72 h, the magnetic fixed film plate column reactor can still remove more than 90 % of LEV and 82 % of COD in the secondary effluent of simulated antibiotic pharmaceutical wastewater treatment process, and the effluent is stable and meets the standard. The magnetic fixed film plate column reactor can be used for advanced treatment of antibiotic pharmaceutical wastewater. This study provides a new insight into the application of the Photo-Fenton process.

From Fenton and ORR 2e−-Type Catalysts to Bifunctional Electrodes for Environmental Remediation Using the Electro-Fenton Process

Currently, the presence of emerging contaminants in water sources has raised concerns worldwide due to low rates of mineralization, and in some cases, zero levels of degradation through conventional treatment methods. For these reasons, researchers in the field are focused on the use of advanced oxidation processes (AOPs) as a powerful tool for the degradation of persistent pollutants. These AOPs are based mainly on the in-situ production of hydroxyl radicals (OH•) generated from an oxidizing agent (H2O2 or O2) in the presence of a catalyst. Among the most studied AOPs, the Fenton reaction stands out due to its operational simplicity and good levels of degradation for a wide range of emerging contaminants. However, it has some limitations such as the storage and handling of H2O2. Therefore, the use of the electro-Fenton (EF) process has been proposed in which H2O2 is generated in situ by the action of the oxygen reduction reaction (ORR). However, it is important to mention that the ORR is given by two routes, by two or four electrons, which results in the products of H2O2 and H2O, respectively. For this reason, current efforts seek to increase the selectivity of ORR catalysts toward the 2e− route and thus improve the performance of the EF process. This work reviews catalysts for the Fenton reaction, ORR 2e− catalysts, and presents a short review of some proposed catalysts with bifunctional activity for ORR 2e− and Fenton processes. Finally, the most important factors for electro-Fenton dual catalysts to obtain high catalytic activity in both Fenton and ORR 2e− processes are summarized.

Novel heterostructured metal doped MgFe2O4@g-C3N4 nanocomposites with superior photo-Fenton preformance for antibiotics removal: One-step synthesis and synergistic mechanism

A novel metal doped MgFe₂O₄@g-C₃N₄ (m-MF@CN) nanocomposite was synthesized by one-pot method using saprolite laterite nickel ore and urea as raw materials. The heterostructure was verified as an effective heterogeneous Fenton-like catalyst for degrading antibiotics including tetracycline, oxytetracycline and chlortetracycline hydrochloride, and the related catalytic mechanism was elaborated in detail. Under the optimum conditions, the m-MF@CN/H₂O₂/vis system exhibited superior photo-Fenton property (degradation efficiency of 93.15% within 30 min, TOC removal efficiency was as high as 60.54% within 120 min) and cycle stability for tetracycline removal. The combination of MgFe₂O₄ and g-C₃N₄ enhanced the absorption of visible light, and the energy level matched heterojunction promoted the separation of photogenerated electron-holes to accelerate the redox cycle of ≡Fe³⁺/≡Fe²⁺. Free radical quenching and electron spin resonance (ESR) analysis confirmed that O₂^- was the main active species, h⁺ and OH also played a synergistic role in the degrading reactions. Notably, a possible degradation pathway of tetracycline was proposed according to the intermediates produced in the reaction process. The one-step synthesized m-MF@CN nanocomposite catalysts possessed high catalytic performance, good stability and recoverability, which not only realized the high-value utilization of ore raw materials, but also provided a potential practical way for efficient treatment of antibiotic wastewater.

Application of visible light active photocatalysis for water contaminants: A review

Organic water pollutants are ubiquitous in the natural environment arising from domestic products as well as current and legacy industrial processes. Many of these organic water pollutants are recalcitrant and only partially degraded using conventional water and wastewater treatment processes. In recent decades, visible light active photocatalyst has gained attention as a non-conventional alternative for the removal of organic pollutants during water treatment, including industrial wastewater and drinking water treatment. This paper reviews the current state of research on the use of visible light active photocatalysts, their modified methods, efficacy, and pilot-scale applications for the degradation of organic pollutants in water supplies and waste streams. Initially, the general mechanism of the visible light active photocatalyst is evaluated, followed by an overview of the major synthesis techniques. Because few of these photocatalysts are commercialized, particular attention was given to summarizing the different types of visible light active photocatalysts developed to the pilot-scale stage for practical application and commercialization. The organic pollutant degradation ability of these visible light active photocatalysts was found to be considerable and in many cases comparable with existing and commercially available advanced oxidation processes. Finally, this review concludes with a summary of current achievements and challenges as well as possible directions for further research. PRACTITIONER POINTS: Visible light active photocatalysis is a promising advanced oxidation process (AOP) for the reduction of organic water pollutants. Various mechanisms of photocatalysis using visible light active materials are identified and discussed. Many recent photocatalysts are synthesized from renewable materials that are more sustainable for applications in the 21st century. Only a small number of pilot-scale applications exist and these are outlined in this review.

In-situ constructing nanostructured magnesium ferrite on steel slag for Cr(VI) photoreduction

An innovative method is created for transforming iron-rich RO phase (MgO_0.239FeO_0.761) on steel slag surface into nanostructured Mg_0.04Fe_2.96O₄ layer. The phase change process is investigated, and it is found that salicylic acid modification and alkaline roasting procedures remarkably increase the specific surface area from 0.46 m²/g (raw steel slag) to 69.5 m²/g (Mg_0.04Fe_2.96O₄), and the generation of Mg_0.04Fe_2.96O₄ enhances the absorption of visible light and Cr(VI) conversion with 2-times increasement than raw steel slag. Surface complexation between H₂C₂O₄ ligands and Fe metal moiety on Mg_0.04Fe_2.96O₄ induces the intramolecular electron transfer under visible light irradiation based on a ligand-to-metal charge transfer mechanism, thus resulting in Cr(VI) photoreduction, and the catalytic efficiency is above 90% for Cr(VI) (40 mg/L) under inherent pH= 5.5 conditions. Moreover, recyclability tests based on magnetic separation show that the photoreactivity is closely related to Mg content of Mg_0.04Fe_2.96O₄ layer where Mg leaching occurs and finally generates cubic spinel configuration Fe₃O₄. This work highlights the importance of surface functionalization in post-use phases of steel slag in which surface reactivity and application potential can be greatly altered by chemical exposure history and surface transformations. It also provides valuable references for studying the metastable state mechanism of magnesium ferrite photocatalysts.

An efficient and low-cost magnetic heterogenous Fenton-like catalyst for degrading antibiotics in wastewater: Mechanism, pathway and stability

Metal-doped MgFe₂O₄ spinel ferrite synthesized from saprolite laterite nickel ore was verified as an efficient heterogeneous Fenton-like catalyst for degrading antibiotics including tetracycline (TC) and metronidazole (MNZ) in a "catalyst/oxalic acid (H₂C₂O₄)/visible light (vis)" system. The degradation efficiencies reached over 95% and total organic carbon (TOC) removal efficiencies were nearly 50% of the two antibiotics within 210 min, under the optimal conditions, especially 90% catalytic activity of the fresh catalyst was maintained after five cycles, suggesting the ferrite possessed excellent degrading performance, cycling stability and applicability. Moreover, the degradation mechanism and pathway of TC were elucidated in detail. Results revealed that the [≡Fe(C₂O₄)₃]^3- complex ions formed by octahedral Fe³⁺ in spinel ferrite with oxalate ions on the surface of MgFe₂O₄, played the key role in production of ·OH radicals which decomposed antibiotic TC into small molecules even mineralized in three pathways. Cost-effective preparation, high catalytic performance and long cycle life may accelerate the practical application of the heterogeneous Fenton-like catalyst.

Development of reactive iron-coated natural filter media for treating antibiotic residual in swine wastewater: Mechanisms, intermediates and toxicity

Degradation mechanisms, surface phenomena, and the influence of co-existing organic matter on heterogeneous Fenton-like reactions were investigated using low-cost natural materials, to remove three veterinary antibiotics. Zeolite rock, laterite rock, and pumice rock were modified by adding ferric chloride. Fenton-like reactions yielded more than 50 % of antibiotic removal at a neutral pH. The modified zeolite exhibited the highest antibiotic removal efficiency. The heterogeneous Fenton-like reaction could be indicated by the simultaneous detection of Fe(II) and Fe(III) on the surface of the modified zeolite. Leaching iron was also observed to reduce the antibiotics with homogeneous Fenton-like reaction. The co-existing organic matter expressed by the COD below 400 mg/L did not have a considerable adverse impact on antibiotic removal. An H₂O₂ concentration as low as 20 μM was sufficient to react with the modified zeolite and degraded more than 70 % of the antibiotics at a neutral pH. The modified zeolite could be reused at least three times, with a removal efficiency of at least 80 %. The antibiotic degradation efficiencies in real treated swine wastewater were above 75 %. Moreover, the degradation intermediates and bacterial inhibition after treatment were investigated.

Long cyclic stability of acidic aqueous zinc-ion batteries achieved by atomic layer deposition: the effect of the induced orientation growth of the Zn anode

Aqueous Zn-ion batteries with economical ZnSO₄ solution as the electrolyte suffer from a tremendous tendency of dendrite formation under mildly acidic conditions; moreover, utilization of Zn(CF₃SO₃)₂ delivers superior performance, but is expensive. Herein, we optimize the ZnSO₄ electrolyte by inducing 50 μL of 10 M sulfuric acid in 10 mL electrolyte, which can achieve long cycle life (1000 h at 0.1 mA cm^-2, 300 h at 1 mA cm^-2 and 250 h at 10 mA cm^-2) when the Zn foil is protected by three metallic oxides deposited by atomic layer deposition (ALD). The nucleation behaviour of the (002) facet has proved to play a critical role in the reversible lifespan. The Al₂O₃ layer would restrict the stripping procedure, leading to the highest overpotential, while the TiO₂ layer and Fe₂O₃ layer tended to strip all orientations but the (002) facet. Al₂O₃@Zn demonstrated a preference for a compact hillock-like (101) orientation texture in the deposition procedure, while TiO₂@Zn and Fe₂O₃@Zn were favourable to obtain a smooth terrace texture. Additionally, symmetric cells with Fe₂O₃@Zn expressed the lowest overpotential (31.64 mV) and minimal voltage hysteresis (23.6 mV) at 1 mA cm^-2. A Zn-MnO₂ battery with Fe₂O₃@Zn also displayed superior capacity, which could reach 280 mA h g^-1 at a current density of 1 A g^-1. The diffusion coefficient of Zn²⁺ discloses that among the three ALD layers, full cells with Fe₂O₃@Zn are the most favourable for diffusion of Zn²⁺ in acidic electrolyte.

Catalytic activity comparison of natural ferrous minerals in photo-Fenton oxidation for tertiary treatment of dyeing wastewater

Natural ferrous minerals are readily available and recyclable catalysts in photo-Fenton-like oxidation for wastewater treatment. In this work, typical ferrous oxide and sulfide minerals including magnetite, chalcopyrite, and pyrrhotite were exploited as catalysts in heterogeneous photo-Fenton oxidation for purification of biological effluent of dyeing wastewater. In a wide initial pH range (3.0~7.5), ferrous mineral-based heterogeneous photo-Fenton-like reactions were proven to be effective on the oxidation of recalcitrant pollutants. COD removals achieved 60.57%, 58.83%, and 57.41% using pyrrhotite, chalcopyrite, and magnetite, respectively, as catalyst under ultraviolet irradiation of 220~275 nm at H₂O₂ concentration of 9.8 mM. The corresponding COD removals were 51.75% and 34.09% with or without ferrous sulfate additions in UV/H₂O₂ systems. Minerals exhibited excellent stability and reusability with photo-catalytic activity reduction of less than 10% in the reuse of 5 cycles. Dissolved iron concentrations were determined to be 1.86 mg L^-1, 4.62 mg L^-1, and 7.53 mg L^-1 for magnetite, chalcopyrite, and pyrrhotite, respectively, at pH 3 and decreased to zero in neutral pH environment, which were much lower than those required for homogenous Fenton reaction. It was deduced that oxidation of recalcitrant pollutants was mainly catalyzed by Fe(II) on the mineral surface. The more reactive oxygen species such as hydroxyl radicals were resulted from the reaction of surface Fe (II) with H₂O₂, H₂O₂ photolysis, and charge separation of minerals under UV irradiation.

In-situ synthesis of CuS@carbon nanocomposites and application in enhanced photo-fenton degradation of 2,4-DCP

Novel CuS nanoparticles embedded into carbon nanosheets (CuS@CNs) were prepared in situ by applying wheat straw cellulose/feather protein hydrogel beads as templates and were used to photocatalytically activate H₂O₂ to degrade 2,4-dichlorphenol (2,4-DCP). The photo-Fenton catalytic properties of the nanocomposite catalysts obtained under different synthetic conditions, including different Cu²⁺ concentrations, S^2- concentrations and calcination temperatures, were evaluated. The results showed that CuS@CNs with 0.1 M Cu²⁺, 0.1 M S^2- at 800 °C presented excellent photo-Fenton degradation performance for 2,4-DCP (25 mg/L) in the presence of H₂O₂ and could remove 90% of 2,4-DCP in 2.5 h. The water quality parameters (pH, Cl^-, HCO₃^-, H₂PO₄^- and SO₄^2-) exhibited different effects on the photocatalytic degradation process. The catalytic activity of the CuS@CNs used in the cycle could be recovered after thermal regeneration. Radical quenching and electron paramagnetic resonance (EPR) experiments confirmed that ·OH species were main active radicals contributing to the degradation of 2,4-DCP. The photocatalytic mechanism of CuS@CNs was also explored by photoelectrochemical (PEC) measurements and UV-vis diffuse reflectance spectroscopy (DRS). Incorporation of carbon nanosheets could significantly improve the separation of photogenerated charge carriers to stimulate pollutant degradation by CuS. Based on the detected intermediates, the degradation pathway of 2,4-DCP in the CuS@CNs/H₂O₂ reaction system was also proposed.

Direct Synthesis of Magnetic CoFe2O4 Nanoparticles as Recyclable Photo-Fenton Catalysts for Removing Organic Dyes

Herein, CoFe₂O₄ nanoparticles were directly synthesized through a solution combustion method using ferric nitrate, cobalt nitrate, and glycine as raw materials. The effects of glycine on the phase composition and magnetic properties of the CoFe₂O₄ products were investigated. When the fuel/ferric nitrate ratio was 0.8, the obtained product was pure CoFe₂O₄ with an average particle size of 25 nm. Furthermore, the saturation magnetization is 77.3 emu/g, which is about 95.7% that of CoFe₂O₄ bulk materials at room temperature and good for recycling. The photo-Fenton catalytic properties of CoFe₂O₄ were investigated for assessing its efficacy in removing dyes. It could degrade the 20 ppm MB in 75 min. To improve the photo-Fenton catalytic performance, NH₄HCO₃ and glucose were employed as additives. Due to the pores formed by NH₄HCO₃ and glucose, the G-CoFe₂O₄ and N-CoFe₂O₄ could degrade the 20 ppm MB in 40 and 25 min, respectively. The results indicated that these additives can effectively improve the catalytic activity of CoFe₂O₄. The modified CoFe₂O₄ is a promising alternative recyclable photo-Fenton catalyst for removing organic dyes.