Ultrathin Bi 2 MoO 6 Nanosheets for Photocatalysis: Performance Enhancement by Atomic Interfacial Engineering

Defect Engineering in Bi-based Photo/electrocatalysts for Nitrogen Reduction to Ammonia

Main group Bi-based materials have gained popularity as N2 reduction reaction (NRR) photo/electrocatalysts due to their ability to inhibit competitive H2 evolution reactions (HER) and the unique N2 adsorption activities. The introduction of defects in Bi-based catalysts represents a highly effective strategy for enhancing light absorption, promoting efficient separation of photogenerated carriers, optimizing the activity of free radicals, regulating electronic structure, and improving catalytic performance. In this review, we outline the various applications of state of the defect engineering in Bi-based catalysts and elucidate the impact of vacancies on NRR performance. In particular, the types of defects, methods of defects tailoring, advanced characterization techniques, as well as the Bi-based catalysts with abundant defects and their corresponding catalytic behavior in NRR were elucidated in detail. Finally, the main challenges and opportunities for future development of defective Bi-based NRR catalysts are discussed, which provides a comprehensive theoretical guidance for this field.

A Comprehensive Review on the Boosted Effects of Anion Vacancy in the Heterogeneous Photocatalytic Degradation, Part II: Focus on Oxygen Vacancy

Environmental problems, including the increasingly polluted water and the energy crisis, have led to a need to propose novel strategies/methodologies to contribute to sustainable progress and enhance human well-being. For these goals, heterogeneous semiconducting-based photocatalysis is introduced as a green, eco-friendly, cost-effective, and effective strategy. The introduction of anion vacancies in semiconductors has been well-known as an effective strategy for considerably enhancing the photocatalytic activity of such photocatalytic systems, giving them the advantages of promoting light harvesting, facilitating photogenerated electron-hole pair separation, optimizing the electronic structure, and enhancing the yield of reactive radicals. This Review will introduce the effects of anion vacancy-dominated photodegradation systems. Then, their mechanism will illustrate how an anion vacancy changes the photodegradation pathway to enhance the degradation efficiency toward pollutants and the overall photocatalytic performance. Specifically, the vacancy defect types and the methods of tailoring vacancies will be briefly illustrated, and this part of the Review will focus on the oxygen vacancy (OV) and its recent advances. The challenges and development issues for engineered vacancy defects in photocatalysts will also be discussed for practical applications and to provide a promising research direction. Finally, some prospects for this emerging field will be proposed and suggested. All permission numbers for adopted figures from the literature are summarized in a separate file for the Editor.

Anion-Mediated In Situ Reconstruction of the Bi2MoO6 Precatalyst for Enhanced Electrochemical CO2 Reduction over a Wide Potential Window

Electrochemical CO2 reduction reaction (eCO2RR) is a viable approach to achieve carbon neutrality. Bismuth-based electrocatalysts demonstrate exceptional selectivity in CO2-to-formate conversion, but their reconstruction mechanisms during the eCO2RR remain elusive. Herein, the reconstruction processes of bismuth molybdate (Bi2MoO6) nanoplates are elucidated during the eCO2RR. Operando and ex situ measurements reveal the in situ partial reduction of Bi2MoO6 to Bi metal, forming Bi@Bi2MoO6 at negative potentials. Meanwhile, CO32- ions in the electrolyte spontaneously exchange with MoO42- in Bi2MoO6. The obtained Bi@Bi2MoO6/Bi2O2CO3 delivers a formate Faradaic efficiency (FE) of 95.2% at -1.0 V. Notably, high formate FEs (>90%) are maintained within a wide 500 mV window. Although computational calculations indicate a higher energy barrier for *OCHO formation on Bi2O2CO3, the prevention of excessive reduction to metal Bi significantly enhances long-term stability. Furthermore, the CO32- ion exchange process occurs in various 2D Bi-containing precatalysts, which should be emphasized in further studies.

Oxygen-deficient WO3-x spheres for electrochemical N2 oxidation to nitrate

Nitrate synthesis via the electrochemical nitrogen oxidation reaction (e-NOR) is widely recognized as a potential alternative to the energy-intensive Ostwald process. However, electrocatalysts with strong N2 adsorption and activation abilities remain largely undeveloped due to kinetic hindrances caused by the high bond energy of NN. Here we designed a hollow WO3 sphere with an optimal concentration of oxygen vacancies and studied its e-NOR performance. The optimally synthesized oxygen-deficient WO3 (WO3-x) achieved a high nitrate yield of 311.15 µmol h-1gcat.-1 and a Faraday efficiency of 2.00 %, which is probably due to the presence of a moderate amount of oxygen vacancies on the WO3-x surface and the hollow spherical structure, which further improves the accessibility of the inner active surface. Our work could potentially stimulate research into transition metal oxide-based materials for e-NOR applications.

Degradation of dimethyl phthalate by morphology controlled β-MnO2 activated peroxymonosulfate: The overlooked roles of high-valent manganese species

Activated peroxymonosulfate (PMS) processes have emerged as an efficient advanced oxidation process to eliminate refractory organic pollutants in water. This study synthesized a novel spherical manganese oxide catalyst (0.4KBr-β-MnO2) via a simple KBr-guided approach to activate PMS for degrading dimethyl phthalate (DMP). The 0.4KBr-β-MnO2/PMS system enhanced DMP degradation under different water quality conditions, exhibiting an ultrahigh and stable catalytic activity, outperforming equivalent quantities of pristine β-MnO2 by 8.5 times. Mn(V) was the dominant reactive species that was revealed by the generation of methyl phenyl sulfone from methyl phenyl sulfoxide oxidation. The selectivity of Mn(V) was demonstrated by the negligible inhibitory effects of Inorganic anions. Theoretical calculations confirmed that Mn (V) was more prone to attack the CO bond of the side chain of DMP. This study revealed the indispensable roles of high-valent manganese species in DMP degradation by the 0.4KBr-β-MnO2/PMS system. The findings could provide insight into effective PMS activation by Mn-based catalysts to efficiently degrade pollutants in water via the high-valent manganese species.

In Situ Formation of Ba3CoNb2O9/Ba5Nb4O15 Heterostructure in Electrolytes for Enhancing Proton Conductivity and SOFC Performance

The in situ formation of a heterostructure delivers superior electrochemical properties as compared to the mechanical mixing, which shows great promise for developing new electrolytes for solid oxide fuel cells (SOFCs). Herein, in an SOFC constructed by the Ba5Nb4O15 electrolyte and Ni0.8Co0.15Al0.05LiO2-δ anode, an in situ formation of Ba3CoNb2O9/Ba5Nb4O15 heterostructure is designed by Co-ion diffusion from the anode to the electrolyte during cell operation, resulting in improved ion conductivity and fuel cell performance. An abnormal phenomenon is observed that the SOFC based on the Ba3CoNb2O9/Ba5Nb4O15 electrolyte delivered a peak power density of 703 mW/cm2 at 510 °C, which is higher than that at 550 °C. Characterization in terms of X-ray photoelectron spectroscopy and X-ray diffraction verifies that the operating temperature affected the Co doping concentrations, leading to different conducting behaviors of the heterostructure. Furthermore, it is found that the heterojunction of Ba3CoNb2O9 and Ba5Nb4O15 can restrict the electron migration to avoid current leakage of the cell and simultaneously enhance the proton conductivity. These findings manifest the developed in situ Ba3CoNb2O9/Ba5Nb4O15 heterostructure as a promising electrolyte for SOFCs.

Quantitative Contribution of Oxygen Vacancy Defects to Arsenate Immobilization on Hematite

Hematite is a common iron oxide in natural environments, which has been observed to influence the transport and fate of arsenate by its association with hematite. Although oxygen vacancies were demonstrated to exist in hematite, their contributions to the arsenate immobilization have not been quantified. In this study, hematite samples with tunable oxygen vacancy defect (OVD) concentrations were synthesized by treating defect-free hematite using different NaBH4 solutions. The vacancy defects were characterized by positron annihilation lifetime spectroscopy, Doppler broadening of annihilation radiation, extended X-ray absorption fine structure (EXAFS), thermogravimetric mass spectrometry (TG-MS), electron paramagnetic resonance (EPR), and X-ray photoelectron spectroscopy (XPS). The results revealed that oxygen vacancy was the primary defect type existing on the hematite surface. TG-MS combined with EPR analysis allowed quantification of OVD concentrations in hematite. Batch experiments revealed that OVDs had a positive effect on arsenate adsorption, which could be quantitatively described by a linear relationship between the OVD concentration (Cdef, mmol m-2) and the enhanced arsenate adsorption amount caused by defects (ΔQm, μmol m-2) (ΔQm = 20.94 Cdef, R2 = 0.9813). NH3-diffuse reflectance infrared Fourier transform (NH3-DRIFT) analysis and density functional theory (DFT) calculations demonstrated that OVDs in hematite were beneficial to the improvement in adsorption strength of surface-active sites, thus considerably promoting the immobilization of arsenate.

Cerium-terephthalic acid metal-organic frameworks for ratiometric fluorescence detecting and scavenging·OH from fuel combustion gas

Hydroxyl radical (•OH) in fuel combustion gas seriously damages human health. The techniques for simultaneously detecting and scavenging •OH in these gases are limited by poor thermal resistance. To meet this challenge, herein, metal organic frameworks (MOFs) with high thermal stability (80-400 °C) and dual function (•OH detection and elimination) are developed by coordinating Ce ions with terephthalic acid (TA) (Ce-BDC). Due to the reversible conversion between Ce³⁺ and Ce⁴⁺, and the high concentration of Ce³⁺ on the surface of Ce-BDC MOFs (89.6%), an •OH scavenging efficiency over 90% is realized. Ratiometric fluorescence (I_440 nm/I_355 nm) detection of •OH with a low detection limit of ∼4 μM is established by adopting Ce ions as an internal standard and TA as an •OH-responsive fluorophore. For real applications, the Ce-BDC MOFs demonstrate excellent •OH detection sensitivity and high •OH scavenging efficiency in gas produced from cigarettes, wood fiber and machine oil. Mouse model results show that the damage caused by •OH in cigarette smoke can be greatly reduced by Ce-BDC MOFs. This work provides a promising strategy for sensitively detecting and efficiently eliminating •OH in fuel combustion gas.

Surface mechanism and optimization of catalytic ozonation with CoxFe oxides as catalyst for degradation of sodium p-toluenesulfonate in water

In this study, the removals of sodium p-toluenesulfonate (NaTSA) by catalytic ozonation with two different cobalt-iron compounds, Co_xFe oxides prepared by co-precipitation/calcination (CPO) and Co_xFe oxides prepared by direct calcination (DCO), as the catalysts, had a difference of about 12%. It was found that the CPO surface contained active type c water, which was generally adsorbed on the oxygen vacancy. The test of oxygen temperature-programmed desorption (O₂-TPD) showed that the surface of CPO was rich in oxygen vacancy. Through the electrochemical oxygen evolution reaction (OER) detection, a pair of Co valence redox peaks were detected from the CV curves, and the results of XPS test showed the replacement of octahedral Co³⁺ with Fe^{3 +} in the Co₃O₄ during preparation of CPO. The enriched oxygen vacancy could be used as active sites for ozone adsorption and improve the charge transfer capacity. The number of hydroxyl radicals was detected by electron spin resonance (EPR) and it indicated that CPO contained more hydroxyl radicals, so it had higher effect in catalytic ozonation for organic pollutant degradation. In this paper, the relationship between oxygen vacancy and reactive center in the microstructure of the catalysts was established to discuss their working mechanism. The influence of the initial pH value, catalyst dosage, and ozone concentration on the removal of NaTSA was investigated by response surface design, and the optimal experimental conditions were predicted and verified.

Oxygen-Deficient BiOCl Combined with L-Buthionine-Sulfoximine Synergistically Suppresses Tumor Growth through Enhanced Singlet Oxygen Generation under Ultrasound Irradiation

Excess generation of reactive oxygen species (ROS) based on sensitizers under ultrasound (US) excitation can cause the death of tumor cells via oxidative damage, but sonosensitizers are largely unexplored. Herein, oxygen-deficient black BiOCl (B-BiOCl) nanoplates (NPs) are reported, with post-treatment on conventional BiOCl by simple UV excitation, showing stronger singlet oxygen (¹ O₂ ) generation than commercial TiO₂ nanoparticles and their derivatives under US irradiation. Moreover, L-buthionine-sulfoximine (BSO), a GSH biosynthesis inhibitor, is incorporated into B-BiOCl NPs. The authors find that BSO can be released owing to the degradation of B-BiOCl NPs in the presence of acid and GSH, which are overexpressed in tumors. The results show that BSO/B-BiOCl-PEG NPs have a multifunctional synergistic effect on improving ROS production. In particular, BiOCl has remarkable near-infrared light absorption after UV treatment and is good for photoacoustic imaging that can guide subsequent sonodynamic therapy. This work shows that just with a simple oxygen deficiency treatment, strong ¹ O₂ generation can be provided to a conventional material under US irradiation and, interestingly, this effect can be amplified by using a small inhibitor BSO, and this is clearly demonstrated in cell and mice experiments.

Gold Catalyst Anchored to Pre-Reduced Co3O4 Nanorods for the Hydrodeoxygenation of Vanillin Using Alcohols as Hydrogen Donors

The preparation of highly dispersed metal catalysts with strong electronic metal-support interactions (EMSIs) is of great significance. In this study, oxygen vacancies (OVs) were generated on the surfaces of Co₃O₄ nanorods (NRs) through NaBH₄ treatment, and then the generated surface OVs were used to anchor gold clusters. The resulting catalyst was used for the hydrodeoxygenation (HDO) of vanillin based on transfer hydrogenation with alcohol donors. The conversion of vanillin and the selectivity to 2-methoxy-4-methylphenol (MMP) both reached 99% under the optimized reaction conditions, and these values were significantly higher than those obtained for the gold catalyst supported on the untreated Co₃O₄ NRs. The obtained results were verified by theoretical calculations and experimental data and confirmed the existence of strong EMSIs between the OV-enriched Co₃O₄ NRs (Co₃O₄ NRs-OVs) and the gold clusters, which allows electron transfer from the Co₃O₄ NRs to gold. Increasing the number of electrons on the gold surface can promote the catalytic hydrogen transfer of alcohol, in addition to selectively adsorbing the C═O group in vanillin to improve the selectivity toward MMP. This strategy based on the OV-anchoring of metals onto the surface of a support can be extended to other metals, thereby providing a promising method for the design of advanced and highly efficient metal catalysts.

2D Piezoelectric Bi2 MoO6 Nanoribbons for GSH-Enhanced Sonodynamic Therapy

Reducing the scavenging capacity of reactive oxygen species (ROS) and elevating ROS production are two primary goals of developing novel sonosensitizers for sonodynamic therapy (SDT). Hence, ultrathin 2D Bi₂ MoO₆ -poly(ethylene glycol) nanoribbons (BMO NRs) are designed as piezoelectric sonosensitizers for glutathione (GSH)-enhanced SDT. In cancer cells, BMO NRs can consume endogenous GSH to disrupt redox homeostasis, and the GSH-activated BMO NRs (GBMO) exhibit an oxygen-deficient structure, which can promote the separation of electron-hole pairs, thereby enhancing the efficiency of ROS production in SDT. The ultrathin GBMO NRs are piezoelectric, in which ultrasonic waves introduce mechanical strain to the nanoribbons, resulting in piezoelectric polarization and band tilting, thus accelerating toxic ROS production. The as-synthesized BMO NRs enable excellent computed tomography imaging of tumors and significant tumor suppression in vitro and in vivo. A piezoelectric Bi₂ MoO₆ sonosensitizer-mediated two-step enhancement SDT process, which is activated by endogenous GSH and amplified by exogenous ultrasound, is proposed. This process not only provides new options for improving SDT but also broadens the application of 2D piezoelectric materials as sonosensitizers in SDT.

Enhanced degradation of tetracycline in water over Cu-doped hematite nanoplates by peroxymonosulfate activation under visible light irradiation

Herein, Cu-doped hematite nanoplates (named as CuHNPs) with abundant oxygen-vacancies were prepared through a facile one-pot solvothermal method and used for efficient peroxymonosulfate (PMS) activation to degrade tetracycline (TC) in water. The catalytic activity of optimal CuHNPs-7.5 catalyst to activate PMS for the degradation of TC in water under visible light irradiation is 7.74 and 2.93 times higher than that of pure one without and with visible light irradiation. CuHNPs-7.5 exhibited excellent degradation for TC in the broad pH range from 2.14 to 10.75, and the removal of TC was barely inhibited by co-anions. The combination of free radicals and non-radical pathway, including sulfate radicals (SO₄^·-), hydroxide radicals (·OH), superoxide radical (·O₂^-) and single oxygen (¹O₂), contributed to TC oxidation. The introduction of Cu²⁺ not only accelerated the transformation of Fe(III)/Fe(II) redox cycle but also induced rich oxygen defects in the structure of hematite, boosting more generation of reactive oxygen species (ROSs) for TC degradation. Density functional theory (DFT) calculation and electrochemical impedance spectroscopy (EIS) tests confirmed the accelerated electrons transfer of CuHNPs-7.5 in PMS activation. This study provides a strategy to construct effective catalysts of PMS activation combining radicals and non-radical pathways for environmental remediation.

Atomic-Level Charge Separation Strategies in Semiconductor-Based Photocatalysts

Semiconductor-based photocatalysis as a productive technology furnishes a prospective solution to environmental and renewable energy issues, but its efficiency greatly relies on the effective bulk and surface separation of photoexcited charge carriers. Exploitation of atomic-level strategies allows in-depth understanding on the related mechanisms and enables bottom-up precise design of photocatalysts, significantly enhancing photocatalytic activity. Herein, the advances on atomic-level charge separation strategies toward developing robust photocatalysts are highlighted, elucidating the fundamentals of charge separation and transfer processes and advanced probing techniques. The atomic-level bulk charge separation strategies, embodied by regulation of charge movement pathway and migration dynamic, boil down to shortening the charge diffusion distance to the atomic-scale, establishing atomic-level charge transfer channels, and enhancing the charge separation driving force. Meanwhile, regulating the in-plane surface structure and spatial surface structure are summarized as atomic-level surface charge separation strategies. Moreover, collaborative strategies for simultaneous manipulation of bulk and surface photocharges are also introduced. Finally, the existing challenges and future prospects for fabrication of state-of-the-art photocatalysts are discussed on the basis of a thorough comprehension of atomic-level charge separation strategies.

Oxygen exchange in Bi2MoO6 nanosheets with different thicknesses during oxidative dehydrogenation of 1-butene

A series of Bi₂MoO₆ nanosheet catalysts with different thicknesses were synthesized for oxidative dehydrogenation (ODH) of 1-butene and the oxygen exchange process during ODH was clarified.

Modulation of Bi2 MoO6 -Based Materials for Photocatalytic Water Splitting and Environmental Application: a Critical Review

Highly active photocatalysts driving chemical reactions are of paramount importance toward renewable energy substitutes and environmental protection. As a fascinating Aurivillius phase material, Bi₂ MoO₆ has been the hotspot in photocatalytic applications due to its visible light absorption, nontoxicity, low cost, and high chemical durability. However, pure Bi₂ MoO₆ suffers from low efficiency in separating photogenerated carriers, small surface area, and poor quantum yield, resulting in low photocatalytic activity. Various strategies, such as morphology control, doping/defect-introduction, metal deposition, semiconductor combination, and surface modification with conjugative π structures, have been systematically explored to improve the photocatalytic activity of Bi₂ MoO₆ . To accelerate further developments of Bi₂ MoO₆ in the field of photocatalysis, this comprehensive Review endeavors to summarize recent research progress for the construction of highly efficient Bi₂ MoO₆ -based photocatalysts. Furthermore, benefiting from the enhanced photocatalytic activity of Bi₂ MoO₆ -based materials, various photocatalytic applications including water splitting, pollutant removal, and disinfection of bacteria, were introduced and critically reviewed. Finally, the current challenges and prospects of Bi₂ MoO₆ are pointed out. This comprehensive Review is expected to consolidate the existing fundamental theories of photocatalysis and pave a novel avenue to rationally design highly efficient Bi₂ MoO₆ -based photocatalysts for environmental pollution control and green energy development.

Integrated adsorption and photocatalytic degradation of volatile organic compounds (VOCs) using carbon-based nanocomposites: A critical review

Volatile organic compounds (VOCs) are harmful for human and surrounding ecosystem, and a great number of VOC abatement technologies have been developed during the past few decades. However, the single method has some problems such as high energy consumption, unfriendly environment, and low removal efficiency. Recently, the integration of adsorption and photocatalytic degradation of VOCs is considered as a promising one. Carbon material, with large surface area, high adsorption capacity, and fast electron transfer ability, is widely used in integrated adsorptive-photocatalytic removal of VOCs. It is thus crucial to digest and summarize recent research advances in carbon-based nanocomposites as the adsorbent-photocatalyst for VOC removal. To satisfy this need, this work provides a critical review of the related literature with focuses on: (1) the advantages and disadvantages of various carbon-based nanocomposites for the applications of VOC adsorption and photocatalytic degradation; (2) models and mechanisms of adsorptive-photocatalytic removal of VOCs according to the material properties; and (3) major factors controlling adsorption-photocatalysis processes of VOCs. The review is aimed to establish the "structure-property-application" relationships for the development of innovative carbon-supported nanocomposites and to promote future research on the integrated adsorptive and photocatalytic removal of VOCs.

Morphological evolution of Co phosphate and its electrochemical and photocatalytic performance

Cobalt phosphates with different compositions and morphologies were prepared via a one-step hydrothermal method.