Peroxymonosulfate activation by black TiO2 nanotube arrays under solar light: Switching the activation mechanism and enhancing catalytic activity and stability

Switching reactive oxygen species reactions derived from Mn-Pt anchored zeolite for selective catalytic ozonation

Rationally switching reactive oxygen species (ROS) reactions in advanced oxidation processes (AOPs) is urgently needed to improve the adaptability and efficiency for the engineering application. Herein we synthesized bimetallic Mn-Pt catalysts based on zeolite to realize the switching of ROS reactions in catalytic ozonation for sustainable degradation of organic pollutants from water. The ROS reactions switched from singlet oxygen (1O2, 71.01%) to radical-dominated (93.79%) pathway by simply introducing defects and changing Pt/Mn ratios. The oxygen vacancy induced by anchoring Mn-Pt species from zeolite external surface (MnPt/H-Beta) to internal framework (MnPt@Si-Beta) exposes more electron-rich Pt2+/Pt4+ redox sites, accelerating the decomposition of O3 to generate •OH via electron transfer and switching ROS reactions. The Mn site acted as a bridge plays a critical role in conducting electrons from organic pollutants to Pt sites, which solidly solves the electron loss of catalysts, facilitating the efficient degradation of pollutants. A 34.7-fold increase in phenol degradation compared with the non-catalytic ozonation and an excellent catalytic stability are achieved by MnPt@Si-Beta/O3. The 1O2-dominated ROS reaction originated from MnPt/H-Beta/O3 exhibits superior performances in anti-interference for Cl-, HCO3-, NO3-, and SO4-. This work establishes a novel strategy for switching ROS reactions to expand the targeted applications of O3 based AOPs for environmental remediation.

The effects of water, substrate, and intermediate adsorption on the photocatalytic decomposition of air pollutants over nano-TiO2 photocatalysts

The photocatalytic performance of nano-TiO2 photocatalysts in air pollutant degradation greatly depends on the adsorption of water, substrates, and intermediates. Especially under excessive humidity, substrate concentration, and intermediate concentration, the competitive adsorption of water, substrates, and intermediates can seriously inhibit the photocatalytic performance. In the past few years, extensive studies have been performed to investigate the influence of humidity, substrate concentration, and intermediates on the photocatalytic performance of TiO2, and significant advances have been made in the area. However, to the best of our knowledge, there is no review focusing on the effects of water, substrate, and intermediate adsorption to date. A comprehensive understanding of their mechanisms is key to overcoming the limited application of nano-TiO2 photocatalysts in the photocatalytic decomposition of air pollutants. In this review, the progress in experimental and theoretical fields, including a recent combination of photocatalytic experiments and adsorption and photocatalytic simulations by density functional theory (DFT), to explore the impact of adsorption of various reaction components on nano-TiO2 photocatalysts is comprehensively summarized. Additionally, the mechanism and broad perspective of the impact of their adsorption on the photocatalytic activity of TiO2 in air treatment are also critically discussed. Finally, several solutions are proposed to resolve the current problems related to environmental factors. In general, this review contributes a comprehensive perspective of water, substrate, and intermediate adsorption toward boosting the photocatalytic application of TiO2 nanomaterials.

Visible-light-driven AgI/Bi4O5I2 S-scheme heterojunction for efficient tetracycline hydrochloride removal: Mechanism and degradation pathway

The existence of excessive tetracycline hydrochloride (TCH) in the ecological environment has seriously threatened human health, so there is an urgent need to develop a high-performance photocatalyst that can efficiently and greenly remove TCH. Currently, most photocatalysts have the problems of fast recombination of photogenerated charge carriers and low degradation efficiency. Herein, S-scheme AgI/Bi₄O₅I₂ (AB) heterojunctions was constructed for TCH removal. Compared with the single component, the apparent kinetic constant of the 0.7AB is 5.6 and 10.2 time as high as the AgI and Bi₄O₅I₂, and the photocatalytic activity only decreases by 3.0% after four recycle runs. In addition, to verify the potential practical application of the fabricated AgI/Bi₄O₅I₂ nanocomposite, the photocatalytic degradation of TCH was performed under different conditions by regulating the dosage of photocatalyst, the TCH concentration, pH, and the existence of various anions. Systematical characterizations are conducted to investigate the intrinsic physical and chemical properties of the constructed AgI/Bi₄O₅I₂ composites. Based on the synergetic characterizations by in situ X-ray photoelectron spectroscopy, band edge measurements, as well as reactive oxygen species (ROS) detections, the S-scheme photocatalytic mechanism is proved. This work provides a valuable reference for developing efficient and stable S-scheme AgI/Bi₄O₅I₂ photocatalyst for TCH removal.

Ice-templated synthesis of tungsten oxide nanosheets and their application in arsenite oxidation

Tungsten oxide (WO₃) nanosheets were prepared as catalysts to activate hydrogen peroxide (H₂O₂) in arsenite (As(III)) oxidation. Ice particles were employed as templates to synthesize the WO₃ nanosheets, enabling easy template removal via melting. Transmission electron microscopy and atomic force microscopy revealed that the obtained WO₃ nanosheets were plate-like, with lateral sizes ranging from dozens of nanometers to hundreds of nanometers and thicknesses of <10 nm. Compared to that of the WO₃ nanoparticle/H₂O₂ system, a higher efficiency of As(III) oxidation was observed in the WO₃ nanosheet/H₂O₂ system. Electron spin resonance spectroscopy, radical quenching studies, and As(III) oxidation experiments under anoxic conditions suggested that the hydroperoxyl radical (HO₂^●) acted as the primary oxidant. The WO₃ nanosheets possessed numerous surface hydroxyl groups and electrophilic metal centers, enhancing the production of HO₂^● via H₂O₂ activation. Various anions commonly present in As(III)-contaminated water exhibited little effect on As(III) oxidation in the WO₃ nanosheet/H₂O₂ system. The high oxidation efficiency was maintained by adding H₂O₂ when it was depleted, suggesting that the catalytic activity of the WO₃ nanosheets did not deteriorate after multiple catalytic cycles.

Co/N co-doped porous carbon as a catalyst for the degradation of RhB by efficient activation of peroxymonosulfate

We report on the preparation of Co/N-NPC_x/y with porous structure and excellent activation properties. The synthesis involves the preparation of Zn/Co-ZIF_x and the carbonization of Zn/Co-ZIF_x at a high temperature in an inert atmosphere. The volatilization of zinc during carbonization results in a porous structure, which is beneficial to the migration of pollutants. The sizes, specific surface areas, and pore size distribution of Co/N-NPC_x/y can be achieved by tuning Zn/Co ratio. The calcination temperatures mainly affect the crystalline phase, crystallinity, and magnetic properties of the as-prepared materials. The effects of the as-prepared materials properties and activation conditions on the Rhodamine B (RhB) degradation by PMS activation were investigated. Overall, it exhibited superior catalytic activity in PMS activation, as evidenced by almost complete removal of RhB (0.020 mM, 100 mL) by using 5 mg/L Co/N-NPC_0.5/900 and 1.250 mM PMS within 30 min. Furthermore, it confirmed the participation of SO₄^•-, •OH, and ¹O₂ in the catalytic reaction, and both SO₄^•- and ¹O₂ were the main reactive oxygen species that play a major role.

Spontaneous FeIII/FeII redox cycling in single-atom catalysts: Conjugation effect and electron delocalization

The mechanism of spontaneous Fe^III/Fe^II redox cycling in iron-centered single-atom catalysts (I-SACs) is often overlooked. Consequently, pathways for continuous SO₄ ^·-/HO⋅ generation during peroxymonosulfate (PMS) activation by I-SACs remain unclear. Herein, the evolution of the iron center and ligand in I-SACs was comprehensively investigated. I-SACs could be considered as a coordination complex created by iron and a heteroatom N-doped carbonaceous ligand. The ligand-field theory could well explain the electronic behavior of the complex, whereby electrons delocalized by the conjugation effect of the ligand were confirmed to be responsible for the Fe^III/Fe^II redox cycle. The possible pyridinic ligand in I-SACs was demonstrably weaker than the pyrrolic ligand in Fe^III reduction due to its shielding effect on delocalized π orbitals by local lone-pair electrons. The results of this study significantly advance our understanding of the mechanism of spontaneous Fe^III/Fe^II redox cycling and radical generation pathways in the I-SACs/PMS process.