Enhanced photo-Fenton activity over a sunlight-driven ignition synthesized α-Fe2O3-Fe3O4/CeO2 heterojunction catalyst enriched with oxygen vacancies

Synthesis of 3D Sb2O3-based heterojunction reinforced by SPR effect and photo-Fenton mechanism for upgraded oxidation of metronidazole in water environments

The traditional homogenous and heterogenous Fenton reactions have frequently been restrained by the lower production of Fe2+ ions, which significantly obstructs the generation of hydroxyl radicals from the decomposition of H2O2. Thus, we introduce novel photo-Fenton-assisted plasmonic heterojunctions by immobilizing Fe3O4 and Bi nanoparticles onto 3D Sb2O3 via co-precipitation and solvothermal approaches. The ternary Sb2O3/Fe3O4/Bi composites offered boosted photo-Fenton behavior with a metronidazole (MNZ) oxidation efficiency of 92% within 60 min. Among all composites, the Sb2O3/Fe3O4/Bi-5% hybrid exhibited an optimum photo-Fenton MNZ reaction constant of 0.03682 min- 1, which is 5.03 and 2.39 times higher than pure Sb2O3 and Sb2O3/Fe3O4, respectively. The upgraded oxidation activity was connected to the complementary outcomes between the photo-Fenton behavior of Sb2O3/Fe3O4 and the plasmonic effect of Bi NPs. The regular assembly of Fe3O4 and Bi NPs enhances the surface area and stability of Sb2O3/Fe3O4/Bi. Moreover, the limited absorption spectra of Sb2O3 were extended into solar radiation by the Fe3+ defect of Fe3O4 NPs and the surface plasmon resonance (SPR) effect of Bi NPs. The photo-Fenton mechanism suggests that the co-existence of Fe3O4/Bi NPs acts as electron acceptor/donor, respectively, which reduces recombination losses, prolongs the lifetime of photocarriers, and produces more reactive species, stimulating the overall photo-Fenton reactions. On the other hand, the photo-Fenton activity of MNZ antibiotics was optimized under different experimental conditions, including catalyst loading, solution pH, initial MNZ concentrations, anions, and real water environments. Besides, the trapping outcomes verified the vital participation of •OH, h+, and •O2- in the MNZ destruction over Sb2O3/Fe3O4/Bi-5%. In summary, this work excites novel perspectives in developing boosted photosystems through integrating the photocatalysis power with both Fenton reactions and the SPR effects of plasmonic materials.

Red mud accommodated mesoporous black TiO2 framework with enhanced organic pollutant photodegradation

In this work, black TiO2 (BTiO2) loaded on black red mud (BRM) was successfully prepared with the conversion of Fe2O3 into magnetic Fe3O4 in red mud and the reduction of partial Ti4+ to Ti3+ in TiO2 via the facile sol-gel method and H2 reduction treatment. The obtained low-cost BRM/BTiO2 composites exhibit remarkable photocatalytic degradation toward rhodamine B (91.2%) and tetracycline (83.6%) under visible light irradiation, much better than pristine TiO2. This enhancement is attributed to the narrow bandgap with the desired solar-light excitation, the black color with good solar-light absorption, and the heterojunctions with the efficient separation of photogenerated electron-hole pairs. Moreover, the desired magnetic separation of BRM/BTiO2 composites realizes the recycle and recovery of photocatalysts, favoring practical applications in environment. This work provides a cost-efficiency way to prepare RM-supported TiO2 composites for treating organic pollutants in the wastewater, which is of great significance to the comprehensive utilization of RM waste, the cost saving of the photocatalyst, and the visible-light active enhancement of TiO2.

Constructing α-Fe2O3/g-C3N4/SiO2 S-scheme-based heterostructure for photo-Fenton like degradation of rhodamine B dye in aqueous solution

This work successfully fabricated graphitic carbon nitride and magnetically recoverable α-Fe2O3/g-C3N4/SiO2 photo-Fenton catalysts using thermal polycondensation and in situ-simple precursor drying-calcination process, respectively, was examined for model synthetic rhodamine B (RhB) dye in the presence of H2O2 and acidic pH under simulated visible light irradiation. An aqueous suspension of the reaction mixture of dye-containing wastewater was fully degraded and reached 97% of photo-Fenton degradation efficiency within 120 min followed by the production of hydroxyl radical (•OH). The dominant hydroxyl radical position generated surface charge, electrostatic potential distribution, and average local ionization potential, which contributed to the complete mineralization of RhB dye, according to the density functional theory (DFT) calculations. HPLC and GCMS experiments were performed to examine the degradation fragments of RhB and draw a plausible mechanistic pathway which showed that RhB degradation generated a series of N-deethylated products, followed by a one-time ring-opening, which indicated that photosensitization induced a photocatalysis reaction mechanism.

Defect-enriched (H2PO4-, Cr3+)-α-Fe2O3/β-In2S3 composites for visible light degradation of 4-nitrophenol

In this work, the high-activity (H₂PO₄^-, Cr³⁺)-α-Fe₂O₃ (PCF) with abundant oxygen vacancies (OVs) and the high specific area was obtained by co-adding H₂PO₄^- and Cr³⁺. Defect-enriched PCF/β-In₂S₃ composites were prepared by low-temperature hydrothermal processes. The prepared composites exhibited improved photocatalytic degradation of 4-nitrophenol under visible light irradiation.The SO bond between PCF and β-In₂S₃ promoted the formation of tight heterojunction composites and increased the OVs concentration. Under the synergistic effect of photo-Fenton, defects, and heterojunction, the PCF/β-In₂S₃ composites effectively promoted the separation of photogenerated carriers and accelerated the production of active substances (•OH, •O₂^-, ¹O₂, and h⁺), leading to the improvement of photocatalytic-Fenton degradation performance. This work provided a new strategy for the preparation of highly efficient photocatalysts.

Creating Highly Active Iron Sites in Electrochemical N2 Reduction by Fabricating Strongly-Coupled Interfaces

Electrochemical N_c reduction has been regarded as one of the most promising approaches to producing ammonia under mild conditions, but there are remaining pressing challenges in improving the reaction rate and efficiency. Herein, an unconventional galvanic replacement reaction is reported to fabricate a unique hierarchical structure composed of Fe₃ O₄ -CeO₂ bimetallic nanotubes covered by Fe₂ O₃ ultrathin nanosheets. Control experiments reveal that CeO₂ species play the essential role of stabilizer for Fe²⁺ cations. Compared with bare CeO₂ and Fe₂ O₃ nanotubes, the as-obtained Fe₂ O₃ /Fe₃ O₄ -CeO₂ possesses a remarkably enhanced NH₃ yield rate (30.9 µg h^-1 mg_cat ^-1 ) and Faradaic efficiency (26.3%). The enhancement can be attributed to the hierarchical feature that makes electrodes more easily to contact with electrolytes. More importantly, as verified by density functional theory calculations, the generation of Fe₂ O₃ -Fe₃ O₄ heterogeneous junctions can efficiently optimize the reaction pathways, and the energy barrier of the potential determining step (the *N₂ hydrogenates into *N*NH) is significantly decreased.

2D/1D MoS2 /TiO2 Heterostructure Photocatalyst with a Switchable CO2 Reduction Product

Regulating the transfer pathway of charge carriers in heterostructure photocatalysts is of great importance for selective CO₂ photoreduction. Herein, the charge transfer pathway and in turn the redox potential succeeded to regulate in 2D MoS₂ /1D TiO₂ heterostructure by varying the light wavelength range. Several in situ measurements and experiments confirm that charge transfer follows either an S-scheme mechanism under simulated solar irradiation or a heterojunction approach under visible light illumination, elucidating the switchable property of the MoS₂ /TiO₂ heterostructure. Replacing the simulated sunlight irradiation with the visible light illumination switches the photocatalytic CO₂ reduction product from CO to CH_4. ¹³ CO₂ isotope labeling confirms that CO₂ is the source of carbon for CH₄ and CO products. The photoelectrochemical H₂ generation further supports the switching property of MoS₂ /TiO₂ . Unlike previous studies, density functional theory calculations are used to investigate the band structure of Van der Waals MoS₂ /TiO₂ S scheme after contact, allowing to propose accurate charge transfer pathways, in which the theoretical results are well matched with the experimental results. This work opens the opportunity to develop photocatalysts with switchable charge transport and tunable redox potential for selective artificial photosynthesis.

Enriched Surface Oxygen Vacancies of Fe2(MoO4)3 Catalysts for a PDS-Activated photoFenton System

The environmentally benign Fe₂(MoO₄)₃ plays a crucial role in the transformation of organic contaminants, either through catalytically decomposing oxidants or through directly oxidizing the target pollutants. Because of their dual roles and the complex surface chemical reactions, the mechanism involved in Fe₂(MoO₄)₃-catalyzed PDS activation processes remains obscure. In this study, Fe₂(MoO₄)₃ was prepared via the hydrothermal and calcine method, and photoFenton degradation of methyl orange (MO) was used to evaluate the catalytic performance of Fe₂(MoO₄)₃. Fe₂(MoO₄)₃ catalysts with abundant surface oxygen vacancies were used to construct a synergistic system involving a photocatalyst and PDS activation. The oxygen vacancies and Fe²⁺/Fe³⁺ shuttle played key roles in the novel pathways for generation of •O₂^-, h⁺, and ¹O₂ in the UV-Vis + PDS + FMO-6 photoFenton system. This study advances the fundamental understanding of the underlying mechanism involved in the transition metal oxide-catalyzed PDS activation processes.

Dual Z-scheme core-shell PANI-CeO2-Fe2O3-NiO heterostructured nanocomposite for dyes remediation under sunlight and bacterial disinfection

Nowadays, environmental pollution due to discharge of organic pollutants from food, textile, and pharmaceutical industries into clean water and development of contagious diseases due to pathogenic organisms provide impetus to material researcher to fabricate novel design for efficient photocatalyst and antimicrobial agents. In this regard, designing a core-shell heterojunction catalyst based on metal oxides is considered an auspicious approach. In present study, combating the problems of singular oxides, core-shell PANI-CeO₂-Fe₂O₃-NiO nanocomposite (PCFN) and CeO₂-Fe₂O₃-NiO nanocomposite (CFN) was synthesized through sol-gel and oxidative polymerization route with cetyletrimethylammonium bromide (CTAB) as surfactant. The XRD, FTIR, and Raman confirmed the formation of nanocomposites with core-shell morphology composed of PANI (shell) and oxides (Core) in PCFN with a particle size of 52 nm (TEM). Surprisingly, PCFN has lower band gap, e^-/h⁺ recombination, and larger charge transfer character than CFN. The decomposition test using MB and MO dyes showed that PCFN degraded 99%, 98%, while CFN degraded only 73% and 54%, respectively, under 50 min sunlight illumination. The reusability was assessed up to 7th cycle for PCFN. The influence of operational parameters (catalyst dose, dye concentration, pH) was tested for PCFN. Further, the antimicrobial action against S. aureus (gram + ve), E. coli (gram -ve) were also tested. The supreme performance of PCFN has been credited to heterostructure dual Z-scheme formation and core-shell morphology supported with PANI, which suppresses the e^-/h⁺ recombination process by promoting their separation. The present finding indicated that the PCFN is a promising modifier for bacterial disinfection and acts as a superb photocatalyst through core-shell formation with PANI support.

One-Step Hydrothermal Synthesis of Anatase TiO2 Nanotubes for Efficient Photocatalytic CO2 Reduction

The hydrothermal dissolution-recrystallization process is a key step in the crystal structure of titania-based nanotubes and their composition. This work systematically studies the hydrothermal conditions for directly synthesizing anatase TiO₂ nanotubes (ATNTs), which have not been deeply discussed elsewhere. It has been well-known that ATNTs can be synthesized by the calcination of titanate nanotubes. Herein, we found the ATNTs can be directly synthesized by optimizing the reaction temperature and time rather than calcination of titanate nanotubes, where at each temperature, there is a range of reaction times in which ATNTs can be prepared. The effect of NaOH/TiO₂ ratio and starting materials was explored, and it was found that ATNTs can be prepared only if the precursor is anatase TiO₂, using rutile TiO₂ leads to forming titanate nanotubes. As a result, ATNTs produced directly without calcination have excellent photocatalytic CO₂ reduction than titanate nanotubes and ATNTs prepared by titanate calcination.

Solid Fe Resources Separated from Rolling Oil Sludge for CO Oxidation

The efficient recycling of valuable resources from rolling oil sludge (ROS) to gain new uses remains a formidable challenge. In this study, we reported the recycling of solid Fe resources from ROS by a catalytic hydrogenation technique and its catalytic performance for CO oxidation. The solid Fe resources, after calcination in air (Fe2O3-H), exhibited comparable activity to those prepared by the calcinations of ferric nitrate (Fe2O3-C), suggesting that the solid resources have excellent recycling value when used as raw materials for CO oxidation catalyst preparation. Further studies to improve the catalytic performance by supporting the materials on high surface area 13X zeolite and by pretreating the materials with CO atmosphere, showed that the CO pretreatment greatly improved the CO oxidation activity and the best activity was achieved on the 20 wt.%Fe2O3-H/13X sample with complete CO conversion at 250 °C. CO pretreatment could produce more oxygen vacancies, facilitating O2 activation, and thus accelerate the CO oxidation reaction rate. The excellent reducibility and sufficient O2 adsorption amount were also favorable for its performance. The recycling of solid Fe resources from ROS is quite promising for CO oxidation applications.

Novel and Green Synthesis of Nitrogen-Doped Carbon Cohered Fe3O4 Nanoparticles with Rich Oxygen Vacancies and Its Application

A one-pot and green synthesis methodology was successfully designed to prepare nitrogen-doped carbon (NC) cohered Fe3O4 nanoparticles with rich oxygen vacancies (Fe3O4-OVs/NC). The preparation was achieved via cold-atmospheric-pressure air plasma using Fe2O3 nanoparticles as the only precursor, and pyridine as the carbon and nitrogen source. Systematic characterization results of the as-prepared Fe3O4-OVs/NC confirmed the transition from Fe2O3 to Fe3O4, along with the generation of oxygen vacancies, while preserving the original needle-like morphology of Fe2O3. Moreover, the results indicated the formation of the NC attaching to the surface of the formed Fe3O4 nanoparticles with a weight percent of ~13.6%. The synthesized nanocomposite was further employed as a heterogeneous Fenton catalyst to remove phenol from an aqueous solution. The material has shown excellent catalytic activity and stability, demonstrating a promising application for wastewater treatment.

Contribution of photocatalytic and Fenton-based processes in nanotwin structured anodic TiO2 nanotube layers modified by Ce and V

In the present work, nanotwin structured TiO₂ nanotube (TNT) layers are prepared by the electrochemical anodization technique to form the anatase phase and by surface modification via spin-coating of Ce and V precursors to form Ce-TNT and V-TNT, respectively. The surface and cross-sectional images by SEM revealed that the nanotubes have an average diameter of ∼130 nm and a length of ∼14 μm. In addition, the TEM images revealed the nanotwin structures of the nanotubes, especially the anatase (001) and (112) twin surfaces, that increase the transport of photogenerated charges. The photoinduced degradation of caffeine (CAF) by TNT, Ce-TNT, and V-TNT led to a degradation extent of 16%, 26% and 33%, respectively, whereas it increased to 26%, 38%, and 46% in the presence of H₂O₂, owing to the involvement of Fenton-based processes (in addition to photocatalysis). The effect of the Fenton-based processes accounts for about 10% of the total degradation extent of CAF. Finally, the mechanism of the photoinduced degradation of CAF was investigated. The main oxidative species were the hydroxyl radicals, and the better efficiency of V-TNT over Ce-TNT and TNT was ascribed to its negative surface, thus improving the interactions with CAF.

Facile synthesis of Mn, Ce co-doped g-C3N4 composite for peroxymonosulfate activation towards organic contaminant degradation

Peroxymonosulfate (PMS)-based advanced oxidation processes for wastewater treatment have received extensive attention in the past years. Here, a novel Mn, Ce co-modified g-C₃N₄ (MnCe-CN) composite was successfully synthesized by one-step pyrolysis for activating PMS. The physical and chemical characterization of MnCe-CN/PMS was conducted, indicating that Mn and Ce were evenly distributed on g-C₃N₄ and existed in the form of Mn-N structure and CeO₂, respectively. The MnCe-CN/PMS system could effectively degrade pollutants such as acetaminophen (ACT), methylparaben (MeP), p-nitrophenol (PNP), and 2,4-dichlorophenol (2,4-DCP). Among them, 2,4-DCP could be rapidly degraded, reaching 100% within 30 min. The masking experiments and electrochemical testing results revealed that 2,4-DCP was degraded via superoxide radicals (O₂˙-), singlet oxygen (¹O₂), and electron transfer path. The cyclic experiments and real water treatment experiments testified that the oxidative system had excellent stability and applicability. This study provides a facile synthetic method to fabricate bimetallic co-modified g-C₃N₄ for the enhancement of PMS activation.

T, Dhileepan MD, Neppolian B, K. LN. Surface defect-engineered CeO2−x by ultrasound treatment for superior photocatalytic H2 production and water treatment

We designed a CeO2−x photocatalyst under the influence of low-frequency ultrasonic waves to generate surface oxygen vacancies for efficient photocatalytic performance.