Anionic Group Self-Doping as a Promising Strategy: Band-Gap Engineering and Multi-Functional Applications of High-Performance CO32–-Doped Bi2O2CO3

Boosting the photocatalytic decontamination efficiency using a supramolecular photoenzyme ensemble

Continuous industrialization has raised daunting environmental concerns, and there is an urgent need to develop a sustainable strategy to tackle the contamination issues. Here, we report a supramolecular photoenzyme ensemble enabling the harvest of solar energy to remove contaminations in water. The well-sourced oxidoreductase, laccase, is confined into a photoactive hydrogen-bonded organic framework (PHOF) through an in situ encapsulation method. The direct electron migration between the oxidation center in a PHOF and the reduction center in laccase facilitates synergistic photoenzyme-coupled catalysis, showing two orders of magnitude higher activity than free laccase for pollutant degradation under visible light, without the need for sacrificial agents or costly co-mediators. Such high decontamination efficiency also surpasses the reported catalysts. The structure and decontamination function of this supramolecular photoenzyme ensemble remain highly stable in complex environment matrices, presenting desirable reusability and almost 100% conversion efficiency of pollutants for real sewage samples. Our conceptual photoenzyme hybrid catalyst offers important insights into green and sustainable water decontamination.

Shaping and Doping Metal-Organic Framework-Derived TiO2 to Steer the Selectivity of Photocatalytic CO2 Reduction toward CH4

Steering selectivity in photocatalytic conversion of CO2, especially toward deep reduction products, is vital to energy and environmental goals yet remains a great challenge. In this work, we demonstrate a facet-dependent photocatalytic selective reduction of CO2 to CH4 in Cu-doped TiO2 catalysts exposed with different facets synthesized by a topological transformation from MIL-125 (Ti) precursors. The optimized round cake-like Cu/TiO2 photocatalyst mainly exposed with the (001) facet exhibited a high photocatalytic CO2 reduction performance with a CH4 yield of 40.36 μmol g-1 h-1 with a selectivity of 94.1%, which are significantly higher than those of TiO2 (001) (4.70 μmol g-1 h-1 and 52.6%, respectively), Cu/TiO2 (001 + 101) (18.95 μmol g-1 h-1 and 69.6%, respectively), and Cu/TiO2 (101) (14.73 μmol g-1 h-1 and 78.9%, respectively). The results of experimental and theoretical calculations demonstrate that the Cu doping dominating the promoted separation and migration efficiencies of photogenerated charges and the preferential adsorption on (001) facets synergistically contribute to the selective reduction of CO2 to CH4. This work highlights the significance of synergy between facet engineering and ion doping in the design of high-performance photocatalysts with respect to selective reduction of CO2 to multielectron products.

Fabrication of Ag-doped BiOF-reduced graphene oxide composites for photocatalytic elimination of organic dyes

Bismuth oxyfluoride (BiOF) is an emerging class of material with notable chemical stability, unique layered structure and striking energy band structure. Bi-based semiconductor materials and reduced graphene oxides (rGOs) have attracted considerable attention due to their broad spectrum of potential applications. Herein, we successfully synthesised an efficient photocatalyst comprising BiOF-rGO nanocomposites with embedded Ag nanoparticles using a simple hydrothermal method. The synthesised nanocomposites were characterised through Fourier-transform infrared spectroscopy, X-ray diffraction (XRD), field emission scanning electron microscopy and ultraviolet (UV)-visible spectroscopy. The XRD results indicated the crystalline structures of the BiOF, Ag-doped BiOF and Ag-doped BiOF-rGO composites. Photocatalytic activity assessments focused on the degradation of methylene blue (MB) and methyl orange (MO) dyes under UV-light and sunlight irradiation. The Ag-doped BiOF-rGO composite exhibited significantly enhanced degradation efficiency, achieving 61.81 % and 74.25 % degradation of MB and MO, respectively, after 300 min under UV-light irradiation. On the contrary, pure BiOF demonstrated only 17.63 % and 48.29 % degradation for MB and MO, respectively, under similar conditions. Furthermore, under sunlight irradiation, the Ag-doped BiOF-rGO composite exhibited an MB removal efficiency of 43.87 % after 300 min, whereas pure BiOF showed only 27.47 % under identical conditions. These results underscore the potential of Ag-doped BiOF-rGO composites as highly efficient and adaptable photocatalysts for the photodegradation of organic dyes in industrial wastewater.

Cyano-deficient g-C3N4 for round-the-clock photocatalytic degradation of tetracycline: Mechanism and application prospect evaluation

Without light at night, the system for photocatalytic degradation of refractory organic pollutants in aquatic environments based on free radicals will fall into a dormant state. Hence, a round-the-clock photocatalyst (CCN@SMSED) was prepared by in situ growth of cyanide-deficient g-C3N4 on the surface of Sr2MgSi2O7:Eu2+,Dy3+ through a simple calcination method. The CCN@SMSED exhibits an outstanding oxidative degradation ability for refractory tetracycline (TC) in water under both light and dark conditions, which is attributed to the synergistic effect of free radical (•O2- and •OH) and non-radical (h+ and 1O2). Electrochemical analyses further indicate that direct electron transfer (DET) is also one of the reasons for the efficient degradation of TC. Remarkably, the continuous working time of the round-the-clock photocatalyst in a dark environment was estimated for the first time (about 2.5 h in this system). The degradation pathways of TC mainly include demethylation, ring opening, deamination and dehydration, and the growth of Staphylococcus aureus shows that the process is biosafe. More importantly, CCN@SMSED holds significant promise for practical application due to its low energy consumption and suitability for removing TC from a variety of complex water bodies. This work provides an energy consumption reference for the practical application of round-the-clock photocatalytic degradation of organic pollutants.

Regulating band structure, charge transfer and separation, oxygen adsorption and activation by surface ion modification

As a most promising environmental technology, the substantial enhancement of photocatalytic efficiency is still a big challenge for practical applications. In this work, the surface of Bi2O2CO3 (BOC) nanotubes are modified by Cl and I. The as-obtained samples at different hydrothermal temperatures (T) are designated as T-X-BOC (X = Cl, I). X-ray diffraction (XRD), energy dispersive X-ray (EDX) spectroscopy and X-ray photoelectron spectroscopy (XPS) prove that Cl and I merely chemically adsorb on the BOC surface, rather than dope into the crystal lattice. The surface modification of Cl and I slightly increases light absorption range, while significantly promotes the photoelectron migration from bulk to the surface that greatly enhances the carrier separation efficiency. Density functional theory (DFT) calculations further prove that surface Cl and I have adjusted band structure and surface charge distribution. Besides, the surface Cl and I favor the O2 adsorption and trap the surface photoelectrons, thus promoting the formation of •O2-; while the surface Cl and I impede the surface adsorption of H2O, thus refraining the generation of •OH. In the degradation of rhodamine B (RhB), holes and •O2- radicals play the crucial role. Under ultraviolet light irradiation (λ < 420 nm) for 45 min, the RhB degradation ratios over 150-Cl-BOC (94%) and 150-I-BOC (85%) are 4.2 and 3.7 times higher than that of original BOC (18%), respectively. This work demonstrates that the simple surface halogenation modification greatly improves the photocatalytic activity.

Dynamic ion exchange engineering bismuth ferrite-derived Bi2O2CO3 for rapid piezo-photocatalytic degradation of tetracycline

Piezoelectric materials can generate the built-in electric field under ultrasound assistance, which is beneficial to the separation of the photogenerated electron-hole pairs in photocatalysis. Meanwhile, the ultrasound stress usually leads to accelerate electron transfer and enhance catalytic activity. Thus, piezo-photocatalysis technique is believed to be one of the effective techniques for organic pollutant degradation. In this work, a binary piezoelectric integrated piezo-photocatalytic Z-Scheme heterojunction with bismuth ferrite (BFO) and bismuth oxycarbonate (Bi2O2CO3, BOC) based on the in situ production of Bi2O2CO3 on Bi25FeO40 surface in dichloromethane, where Bi25FeO40 was employed as piezoelectric materials and Bi source, CO2 dissolved in dichloromethane was used as carbon source. Under 60 min ultrasound and visible light irradiation, the optimal BFO/BOC presented a higher piezo-photocatalytic tetracycline (TC) degradation rate (95 %) than Bi25FeO40 (30 %) and Bi2O2CO3 (17 %). Moreover, the optimal BFO/BOC illustrated higher piezo-photocatalytic TC degradation rate under ultrasound and visible light irradiation than that under visible light condition and ultrasound condition, respectively. These results strongly demonstrated the synergistically piezo-photocatalytic degradation of TC by BFO and BOC. This work not only provides a novel piezo-photocatalyst for pollutant degradation, but also provides a novel method to prepare Bi2O2CO3-based piezo-photocatalytic composite catalyst.

Preparation of Novel Layered High Entropy Bismuth-Based Materials and their Photocatalytic Degradation Mechanism

We prepared BiOCl, BiO(ClBr), BiO(ClBrI), and BiO[ClBrI(CO3)0.5] materials using a simple coprecipitation method. It was found that adjusting the number of anions in the anion layer was conducive to adjusting the band structure of BiOX and could effectively promote the migration and separation of photogenerated carriers, thus improving the photocatalytic activity. We first selected methyl orange (MO) as the study pollutant and compared it with BiOCl, BiO(ClBr), and BiO(ClBrI). The first-order kinetic constants of MO degradation by BiO[ClBrI(CO3)0.5] increased by 90.3, 33.9, and 3.1 times, respectively. The photocatalytic degradation rate of methylene blue by BiO[ClBrI(CO3)0.5] was 89.5%, indicating the excellent photocatalytic performance of BiO[ClBrI(CO3)0.5]. The stability of BiO[ClBrI(CO3)0.5] was demonstrated through cyclic experiments and XRD analysis before and after the reaction. The photocatalytic degradation of MO by BiO[ClBrI(CO3)0.5] showed that h+ and 1O2 were the main active oxidizing species and •O2- was the secondary active substance. Overall, our work provides new ideas for the synthesis and degradation of organic pollutants by using two-dimensional anionic high-entropy materials.

Zn-Doped MnCO3/CS Composite Photocatalyst for Visible-Light-Driven Decomposition of Organic Pollutants

Zn-doped MnCO3/carbon sphere (Zn-doped MnCO3/CS) composites were synthesized using a simple hydrothermal procedure. Among various samples (ZM-50, ZM-05, and ZMC-0), the ternary Zn-doped MnCO3/CS (ZMC-2) catalyst demonstrated excellent visible light-induced photocatalytic activity. This improvement comes from the Zn addition and the conductive CS, which facilitate electron movement and charge transport. The catalyst exhibited efficient degradation of methylene blue (MB) over a wide pH range, achieving a removal efficiency of 99.6% under visible light. Radical trapping experiments suggested that •OH and •O2- played essential roles in the mechanism of organic pollutant degradation. Moreover, the catalyst maintained good degradation performance after five cycles. This study offers valuable perspectives into the fabrication of carbon-based composites with promising photocatalytic activity.

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.

Reactive Capture and Conversion of CO2 into Hydrogen over Bifunctional Structured Ce1-xCoxNiO3/Ca Perovskite-Type Oxide Monoliths

Carbon capture, utilization, and storage (CCUS) technologies are pivotal for transitioning to a net-zero economy by 2050. In particular, conversion of captured CO2 to marketable chemicals and fuels appears to be a sustainable approach to not only curb greenhouse emissions but also transform wastes like CO2 into useful products through storage of renewable energy in chemical bonds. Bifunctional materials (BFMs) composed of adsorbents and catalysts have shown promise in reactive capture and conversion of CO2 at high temperatures. In this study, we extend the application of 3D printing technology to formulate a novel set of BFMs composed of CaO and Ce1-xCoxNiO3 perovskite-type oxide catalysts for the dual-purpose use of capturing CO2 and reforming CH4 for H2 production. Three honeycomb monoliths composed of equal amounts of adsorbent and catalyst constituents with varied Ce1-xCox ratios were 3D printed to assess the role of cobalt on catalytic properties and overall performance. The samples were vigorously characterized using X-ray diffraction (XRD), energy-dispersive spectroscopy (EDS), N2 physisorption, X-ray photoelectron spectroscopy (XPS), H2-TPR, in situ CO2 adsorption/desorption XRD, and NH3-TPD. Results showed that the Ce1-xCox ratios-x = 0.25, 0.50, and 0.75-did not affect crystallinity, texture, or metal dispersion. However, a higher cobalt content reduced reducibility, CO2 adsorption/desorption reversibility, and oxygen species availability. Assessing the structured BFM monoliths via combined CO2 capture and CH4 reforming in the temperature range 500-700 °C revealed that such differences in physiochemical properties lowered H2 and CO yields at higher cobalt loading, leading to best catalytic performance in Ce0.75Co0.25NiO3/Ca sample that achieved 77% CO2 conversion, 94% CH4 conversion, 61% H2 yield, and 2.30 H2/CO ratio at 700 °C. The stability of this BFM was assessed across five adsorption/reaction cycles, showing only marginal losses in the H2/CO yield. Thus, these findings successfully expand the use of 3D printing to unexplored perovskite-based BFMs and demonstrate an important proof-of-concept for their use in combined CO2 capture and utilization in H2 production processes.

Research progress on photocatalytic reduction of CO2 based on ferroelectric materials

Transforming CO2 into renewable fuels or valuable carbon compounds could be a practical means to tackle the issues of global warming and energy crisis. Photocatalytic CO2 reduction is more energy-efficient and environmentally friendly, and offers a broader range of potential applications than other CO2 conversion techniques. Ferroelectric materials, which belong to a class of materials with switchable polarization, are attractive candidates as catalysts due to their distinctive and substantial impact on surface physical and chemical characteristics. This review provides a concise overview of the fundamental principles underlying photocatalysis and the mechanism involved in CO2 reduction. Additionally, the composition and properties of ferroelectric materials are introduced. This review expands on the research progress in using ferroelectric materials for photocatalytic reduction of CO2 from three perspectives: directly as a catalyst, by modification, and construction of heterojunctions. Finally, the future potential of ferroelectric materials for photocatalytic CO2 reduction is presented. This review may be a valuable guide for creating reasonable and more effective photocatalysts based on ferroelectric materials.

Upgrading Pyrolytic Residue from End-of-Life Tires to Efficient Heterogeneous Catalysts for the Conversion of Glycerol to Acetins

Recovered carbon blacks (rCBs) produced from end-of-life tires using pyrolysis were transformed into solid acid catalysts for the synthesis of acetins, i.e., products with a wide spectrum of practical applications. Tuning the chemical properties of the surface of samples and introducing specific functional groups on the rCBs were achieved through carbon functionalization with concentrated H2SO4. The initial and modified rCBs were thoroughly characterized using techniques such as elemental analysis, potentiometric back titration, thermogravimetric technique, scanning and transmission microscopy, X-ray photoelectron spectroscopy, etc. The catalytic activities of the samples were measured via batch mode glycerol acetylation performed at 110 °C and compared to the catalytic performance of the functionalized commercial carbon black. The modified rCBs were found to show a significant catalytic effect in the tested reaction, giving high glycerol conversions (above 95%) and satisfactory combined yields of diacetins and triacetin (~72%) within 4 h; this behavior was attributed to the presence of -SO3H moieties on the surface of functionalized rCBs. The reusability tests indicated that the modified samples were catalytically stable in subsequent acetylation runs. The obtained results evidenced the feasibility of using end-of-life tires for the production of effective acid catalysts for glycerol valorization processes.

Carbonized Polymer Dots/Bi/β-Bi2O3 for Efficient Photosynthesis of H2O2 via Redox Dual Pathways

A novel heterojunction photocatalyst of carbonized polymer dots (CPDs)/Bi/β-Bi2O3 is successfully synthesized via a one-pot solvothermal method by adjusting the reaction temperature and time. As a solvent and carbon source, ethylene glycol not only supports the conversion of Bi3+ to β-Bi2O3 but also undergoes its polymerization, cross-linking, and carbonization to produce CPDs. In addition, partial Bi3+ is reduced to Bi by ethylene glycol. As a result, the CPDs and Bi are deposited in situ on the surface of β-Bi2O3 microspheres. There are four built-in electric fields in the CPDs/Bi/β-Bi2O3 system, namely, the n-type semiconductor β-Bi2O3/H2O interface, the p-type CPDs/H2O interface, the ohmic contact between Bi and β-Bi2O3, and the Schottky junction between Bi and CPDs. Under the action of four built-in electric fields, the Z-type charge separation mechanism is formed. It promotes the effective separation of the photogenerated electron-hole and greatly improves the yield of H2O2. Under irradiation for 2 h, the H2O2 production is 1590 μmol g-1 h-1. The solar energy to H2O2 conversion efficiency is 0.11%.

Suppressed charge recombination via defect engineering of confined semiconducting quantum dots for photoelectrocatalysis

Confined semiconducting CuSe quantum dots with abundant Se vacancies are synthesized by pulsed laser deposition with in situ vacuum annealing. With the presence of Se vacancies, the photogenerated charge recombination is suppressed by the self-introduced in-gap trapping states, thus enhancing the photoelectrocatalytic activity under solar illumination.

Internal electric fields drive dual S-scheme heterojunctions: Insights into the role of the triple interlaced lattice

The internal electric field induced by the lattice interfaces in a heterojunction can facilitate charge transfer, thereby improving the photocatalytic performance. However, the details of the relationship between the lattice interfaces and the charge transfer mechanism in heterojunctions remain unclear. In this study, a Bi2WO6/Bi2O2CO3/C3N4 heterojunction (BBC) with an interlaced lattice was prepared, and the role of the interlaced lattice in charge transfer was revealed. Compared to pristine Bi2O2CO3, Bi2WO6, and C3N4, BBC exhibited an increased ciprofloxacin degradation rate constant (0.0573 min-1). A series of experiments were performed to reveal the role of the interlaced lattice interface in the enhanced photocatalytic performance. The results show that the driving force provided by the interlaced lattice interface changes the charge transfer mechanism from a dual Ⅱ-scheme to a dual S-scheme. This work provides profound insights into the effects of lattice interfaces in heterojunctions and the design of efficient photocatalysts.

Face-Dependent Reconstruction of Bi-Oxyiodides toward Selective Growth of (BiO)2 CO3 Edge Side to Maximize CO2 Conversion Efficiency

Chemical reconstruction of bismuth oxyiodides using bicarbonates is tried to selectively grow (BiO)2 CO3 edge side. Orthorhombic o-Bi5 O7 I undergoes a total reconstruction process by its phase transformation into tetragonal (BiO)2 CO3 (BOC-o) to form a well-aligned nanosheet array with maximally exposing CO3 2- moiety at the edge side. The post-reconstruction BOC-o catalyst achieved 100 % Faradaic efficiency at -0.86 V vs. RHE for CO2 -to-formate conversion. However, another conservative reconstruction of tetragonal t-BiOI into tetragonal (BiO)2 CO3 (BOC-t) exposed majorly a less reactive [BiO]+ layer. At low overpotential regions, the catalytic cycle of BOC-o begins with the initial conversion of the CO3 2- moiety into formate at the [-OBi-(CO3 )-BiO-] site, but at high overpotential regions, the [BiO]+ layer undergoes reduction to metallic Bi and multi-catalytic species proceed with CO2 reduction. Otherwise, the deactivation of Bi+ site by an organic molecule switched on another catalysis of proton reduction, preventing CO2 reduction.

Insight into the improved photocatalytic removal of tetracycline hydrochloride by constructing cobalt doping in 2D/2D (BiO)2CO3/BiOCl type-II heterojunctions

Element doping coupled with heterojunction construction and morphology control is an efficient way to improve the properties of photocatalytic materials. Here, a thiourea-modified 2D/2D cobalt-doped (BiO)₂CO₃/BiOCl heterojunction photocatalyst (denoted as Co-(BC/BL)_Tu) was constructed by a simple one-pot hydrothermal method. The photocatalytic property of Co-(BC/BL)_Tu product was evaluated by the photocatalytic degradation of tetracycline hydrochloride (TC-HCl). Compared with the pure (BiO)₂CO₃ sample, the as-prepared Co-(BC/BL)_Tu product displayed outstanding visible-light-driven photodegradation property. The photodegradation rate constant k value of the Co-(BC/BL)_Tu product was 5.2 times higher than that of pure (BiO)₂CO₃, which was the result of the synergistic effect of the 2D/2D structure, cobalt doping and type-Ⅱ heterostructures. It could simultaneously boost the visible light harvesting of the photocatalytic system as well as charge separation. This study provides a facile and promising strategy for constructing a high-effective photocatalytic system by combining morphology control engineering, doping engineering, and heterostructure engineering.

Development of biohybrid Ag2CrO4/rGO based nanocomposites with stable flotation properties as enhanced Photocatalyst for sewage treatment and antibiotic-conjugated for antibacterial evaluation

The proposed research outlines a facile method to synthesize Silver Chromate/reduced graphene oxide nanocomposites (Ag₂CrO₄/rGO NCs) with a narrow dissemination size for the ecological treatment of hazardous organic dyes. The photodegradation performance toward the decontamination of model artificial methylene blue dye was assessed under solar light irradiation. The crystallinity, particle size, recombination of photogenerated charge carriers, energy gap and surface morphologies of synthesized nanocomposites were determined. The experiment objective is to use rGO nanocomposites to increase Ag₂CrO₄ photocatalytic efficiency in the solar spectrum. Tauc plots of ultraviolet-visible (UV-vis) spectrum were used to calculate the optical bandgap energy of the produced nanocomposites ~1.52 eV, which resulted in a good photodegradation percentage of ~92 % after 60 min irradiation of Solar light. At the same time, pure Ag₂CrO₄ and rGO nanomaterials showed ~46 % and ~ 30 %, respectively. The ideal circumstances were discovered by investigating the effects of several parameters, including catalyst loading and different pH levels, on the degradation of dyes. However, the final composites maintain their ability to degrade for up to five cycles. According to the investigations, Ag₂CrO₄/rGO NCs are an effective photocatalyst and can be used as the ideal material to prevent water pollution. Furthermore, antibacterial efficacy for the hydrothermally synthesized nanocomposite was tested against gram-positive (+ve) bacteria viz. Staphylococcus aureus and gram-negative (-ve) bacteria viz. Escherichia coli. The maximum zone of inhibition for S. aureus and E. coli were 18.5 and 17 mm, respectively.

Light Control-Induced Oxygen Vacancy Generation and In Situ Surface Heterojunction Reconstruction for Boosting CO2 Reduction

The weak adsorption of CO₂ and the fast recombination of photogenerated charges harshly restrain the photocatalytic CO₂ reduction efficiency. The simultaneous catalyst design with strong CO₂ capture ability and fast charge separation efficiency is challenging. Herein, taking advantage of the metastable characteristic of oxygen vacancy, amorphous defect Bi₂O₂CO₃ (named BO_vC) was built on the surface of defect-rich BiOBr (named BO_vB) through an in situ surface reconstruction progress, in which the CO₃^2- in solution reacted with the generated Bi^(3-x)+ around the oxygen vacancies. The in situ formed BO_vC is tightly in contact with the BO_vB and can prevent the further destruction of the oxygen vacancy sites essential for CO₂ adsorption and visible light utilization. Additionally, the superficial BO_vC associated with the internal BO_vB forms a typical heterojunction promoting the interface carriers' separation. Finally, the in situ formation of BO_vC boosted the BOvB and showed better activity in the photocatalytic reduction of CO₂ into CO (three times compared to that of pristine BiOBr). This work provides a comprehensive solution for governing defects chemistry and heterojunction design, as well as gives an in-depth understanding of the function of vacancies in CO₂ reduction.

Recent Progress in Interface Engineering of Nanostructures for Photoelectrochemical Energy Harvesting Applications

With rapid and continuous consumption of nonrenewable energy, solar energy can be utilized to meet the energy requirement and mitigate environmental issues in the future. To attain a sustainable society with an energy mix predominately dependent on solar energy, photoelectrochemical (PEC) device, in which semiconductor nanostructure-based photocatalysts play important roles, is considered to be one of the most promising candidates to realize the sufficient utilization of solar energy in a low-cost, green, and environmentally friendly manner. Interface engineering of semiconductor nanostructures has been qualified in the efficient improvement of PEC performances including three basic steps, i.e., light absorption, charge transfer/separation, and surface catalytic reaction. In this review, recently developed interface engineering of semiconductor nanostructures for direct and high-efficiency conversion of sunlight into available forms (e.g., chemical fuels and electric power) are summarized in terms of their atomic constitution and morphology, electronic structure and promising potential for PEC applications. Extensive efforts toward the development of high-performance PEC applications (e.g., PEC water splitting, PEC photodetection, PEC catalysis, PEC degradation and PEC biosensors) are also presented and appraised. Last but not least, a brief summary and personal insights on the challenges and future directions in the community of next-generation PEC devices are also provided.

Study of the oxidation process of bismuth nanoparticles using NaClO

Bismuth nanoparticles (NPs) colloids synthesized in deionized water by laser ablation of solids in liquids technique (LASL) were oxidized using NaClO solutions at different concentrations. Oxidized nanomaterials were characterized using several techniques. The crystalline phases of the bismuth compound were determined using Raman microspectroscopy, and the crystallographic structure was identified by x-ray diffraction (XRD). The size and morphology of the obtained nanomaterials were studied by transmission electron microscopy (TEM). The chemical states were determined using x-ray photoelectron spectroscopy (XPS), and the optical properties of the colloids were characterized by UV-vis spectroscopy. The absorption spectra were analyzed using the Tauc method to determine the band gaps of the obtained nanomaterials. Our results showed morphological changes, starting from small nanoparticles to nanosheets and a mixture of nanosheets with hollow nanoparticles. Two kinds of nanomaterials were found depending on the NaClO solution concentration: Bi₂O₂CO₃single phase and a mixture ofδ-Bi₂O₃and Bi₂O₂CO₃. Some samples were tested as photocatalysts and showed good performance in the degradation of methylene blue in solution. To the best of our knowledge, this is the first study on the oxidation process of bismuth colloidal nanoparticles at room temperature.

Composite of α-FeOOH and Mesoporous Carbon Derived from Indian Blackberry Seeds as Low-Cost and Recyclable Photocatalyst for Degradation of Ciprofloxacin

This study aims to analyse the use of biowaste-derived carbon in enhancing the photocatalytic effect of Earth-abundant visible light active goethite (α−FeOOH). The biowaste material used in this case is seeds of the Indian blackberry fruit. The FeOOH/C composite has been synthesized using an assisted sonochemical technique. The photocatalysts have been characterized using powder x-ray diffraction, nitrogen adsorption isotherms and scanning electron microscopy technique. FTIR and Raman studies have been carried out to understand the structure bonding correlation. The band gap has been ascertained using Tauc plots. The adsorption and consequent photodegradation of CIP have been studied via UV-visible spectroscopy and the mechanism has been ascertained by using radical quenching techniques. The charge separation efficiency has been ascertained through photoluminescence (PL) studies and electrochemical impedance studies (EIS). The pivotal role played by photogenerated holes (h+) in the photocatalytic degradation of CIP has been highlighted. The low cost biowaste-derived carbon as a constituent of the FeOOH/C composite shows great promise as a supporting material for enhancing the photocatalytic properties of such semiconductor materials.

Typical layered structure bismuth-based photocatalysts for photocatalytic nitrogen oxides oxidation

Traditional NO_x treatment methods require external reducing reagents and harsh reaction conditions, which is not conducive to effectively eliminate NO_x at low concentration, especially at ppb levels. Fortunately, low concentration NO_x can be removed by photocatalytic oxidation under mild reaction conditions. Bismuth (Bi)-based photocatalysts with the layered structure have obtained considerable concerns of photocatalytic NO_x oxidation. This review focused on typical layered Bi-based photocatalysts (Bi₂WO₆, Bi₂O₂CO₃, BiOY (YCl, Br, and I), BiOIO₃, and BiOCOOH) with the structure of [Bi₂O₂]²⁺ layer for photocatalytic NO_x oxidation. The strategies (morphological control, defect engineering, heterostructure construction, etc.) to improve photocatalytic oxidation activity were summarized. Furthermore, the mechanism involving various free radicals (hydroxyl radical, superoxide radical, etc.) of photocatalytic oxidation of NO_x was proposed. In addition, the non-NO₂ selectivity was also illuminated. Lastly, the current drawbacks and further research directions for photocatalytic NO_x oxidation were elaborated. The development of photocatalysts with high photocatalytic activity, wide light absorption range, and non-NO₂ selectivity is the focus of future research. This review aims to provide a pandect and theoretical guidance for the practical application of photocatalytic oxidation of NO_x.

Ceftriaxone sodium degradation by carbon quantum dots (CQDs)-decorated C-doped α-Bi2O3 nanorods

A novel carbon quantum dots decorated C-doped α-Bi₂O₃ photocatalyst (CBO/CQDs) was synthesized by solvothermal method. The synergistic effect of adsorption and photocatalysis highly improved contaminants removal efficiencies. The ceftriaxone sodium degradation rate constant (k) of CBO/CQDs was 11.4 and 3.2 times that of pure α-Bi₂O₃ and C-doped α-Bi₂O₃, respectively. The interstitial carbon doping generated localized states above the valence band, which enhanced the utilization of visible light and facilitated the separation of photogenerated electrons and holes; the loading of CQDs improved the charge carrier separation and extended the visible light response; the reduced particle size of CBO/CQDs accelerated the migration of photogenerated carriers. The •O₂ ^- and h⁺ were identified as the dominant reactive species in ceftriaxone sodium degradation, and the key role of •O₂ ^- was further investigated by NBT transformation experiments. The Fukui index was applied to ascertain the molecular bonds of ceftriaxone sodium susceptible to radical attack, and intermediates analysis was conducted to explore the possible degradation pathways. The toxicity evaluation revealed that some degradation intermediates possessed high toxicity, thus the contaminants require sufficient mineralization to ensure safe discharge. The present study makes new insights into synchronous carbon dopping and CQDs decoration on modification of α-Bi₂O₃, which provides references for future studies.

Recent trends in Bi-based nanomaterials: challenges, fabrication, enhancement techniques, and environmental applications

One of the most enticing approaches to environmental restoration and energy conversion is photocatalysis powered by solar light. Traditional photocatalysts have limited practical uses due to inadequate light absorption, charge separation, and unknown reaction mechanisms. Discovering new visible-light photocatalysts and investigating their modification is crucial in photocatalysis. Bi-based photocatalytic nanomaterials have gotten much interest as they exhibit distinctive geometric shapes, flexible electronic structures, and good photocatalytic performance under visible light. They can be employed as stand-alone photocatalysts for pollution control and energy production, but they do not have optimum efficacy. As a result, their photocatalytic effectiveness has been significantly improved in the recent decades. Numerous newly created concepts and methodologies have brought significant progress in defining the fundamental features of photocatalysts, upgrading the photocatalytic ability, and understanding essential reactions of the photocatalytic process. This paper provides insights into the characteristics of Bi-based photocatalysts, making them a promising future nanomaterial for environmental remediation. The current review discusses the fabrication techniques and enhancement in Bi-based semiconductor photocatalysts. Various environmental applications, such as H2 generation and elimination of water pollutants, are also discussed in terms of semiconductor photocatalysis. Future developments will be guided by the uses, issues, and possibilities of Bi-based photocatalysts.

Preparation and characterization of novel Niln2S4/UiO-66 photocatalysts for the efficient degradation of antibiotics in water

Photocatalysis is considered an economical, environmentally friendly, and effective technology for removing pollutants. The construction of Z-Scheme heterojunctions has been identified as one of the feasible solutions capable of enhancing the photocatalytic activity. Herein, a series of visible light responsive photocatalysts (NiIn₂S₄/UiO-66 composites) with excellent activity and stability were prepared by using a solvothermal process. It is found that 20 mg L^-1 of tetracycline (TC) could be almost completely degraded under visible light irradiation within 1 h, when the mass ratio of NiIn₂S₄ to UiO-66 is 0.5:1 (NISU-0.5) and the solution pH = 11. In addition, after six cycles, the degradation rate of tetracycline photocatalyzed by NISU-0.5 still reach up to 90%. Ultraviolet photoelectron spectra (UPS), X-ray photoelectron spectra (XPS) and electron spin resonance measurements (ESR) confirm the formation of the Z-Scheme heterostructure between NiIn₂S₄ and UiO-66. The synergistic effect between built-in electric field, energy band bending and coulomb interactions in interface of Z-Scheme heterojunction is conducive to restrain the recombination of photogenerated electrons and holes, which greatly improve the photocatalytic activity. In conclusion, this study offers a new thought for design and synthesis of Z-Scheme heterojunctions and provides a cost-effective strategy for solving environmental pollution and energy problems in the future.

Molybdenum Carbide-Based Photocatalysts: Synthesis, Functionalization, and Applications

As an effective non-noble, molybdenum carbide (Mo_xC: MoC or Mo₂C) has attracted extensive attention and is regarded as a promising research area in the near future owing to its good biocompatibility, high stability, band gap adjustability, rich valence states, and excellent catalytic activity. This Perspective summarizes the recent progress and achievements for the molybdenum carbide-based catalysts. First, the crystal and band structures of molybdenum carbides are generally presented. Second, various modifying strategies for molybdenum carbides are outlined to enhance the photocatalytic performance, including doping engineering, vacancy engineering, morphology and structure engineering, and the establishment of molybdenum carbide-based composite catalysts. Finally, potential applications in the photocatalysis area of molybdenum carbide-based photocatalyst are generalized. Future development trends and perspective for this promising material are also discussed.

Ni3B as p-Block Element-Modulated Cocatalyst for Efficient Photocatalytic CO2 Reduction

Due to the multiple electron and proton transfer processes involved, the photogenerated charges are easily recombined during the photocatalytic reduction of CO₂, making the generation of the eight-electron product CH₄ kinetically more difficult. Herein, Ni₃B nanoparticles modulated by p-block element were combined with TiO₂ nanosheets to construct a novel Schottky junction photocatalyst (Ni₃B/TiO₂) for the selective photocatalytic conversion of CO₂ to CH₄. The formed Ni₃B/TiO₂ photocatalyst with Schottky junction ensures a transfer pathway of photogenerated electrons from TiO₂ to Ni₃B, which facilitates the accumulation of electrons on the surface of Ni₃B and subsequently improves the activity of photocatalytic CO₂ reduction to CH₄. The optimized Ni₃B/TiO₂ Schottky junction shows an improved CH₄ yield of 30.03 μmol g^-1 h^-1, which was much higher than those of TiO₂ (1.62 μmol g^-1 h^-1), NiO/TiO₂ (2.44 μmol g^-1 h^-1), and Ni/TiO₂ (4.3 μmol g^-1 h^-1). This work demonstrated that the introduction of p-block elements can alleviate the scaling relationship effect of pure metal cocatalysts to a certain extent, and the modified Ni₃B can be used as a promising new cocatalyst to effectively improve the selective photocatalytic of CO₂ to CH₄.

High-efficient mineralization of formaldehyde by three-dimensional "PIZZA"-like bismuth molybdate-titania/diatomite composite

The application of TiO₂-based photocatalysts in air pollution control has attracted much attention thanks to their advantageous green and sustainable performance. However, how to improve the degradation efficiency under visible light is still challenging. Herein, we report a ternary three-dimensional "PIZZA"-like Bi₂MoO₆-TiO₂/diatomite (BTD) composite with high-efficient mineralization and recycling performance towards gaseous formaldehyde (HCHO) under visible light. The high-efficient adsorption-photocatalysis collaborative system with intimate interface combination is successfully established among Bi₂MoO₆ (BMO), TiO₂ and diatomite. The HCHO mineralization rate constant of BTD-1:2 composite is up to around 4.03 times and 2.18 times higher than those of bare BMO and binary Bi₂MoO₆-TiO₂ composite, respectively. It is indicated that the introduction of diatomite increases active sites and plays the vital role in the improvement of photocatalysis. In addition, the photogenerated holes (h⁺) and hydroxyl radical (OH) are proved to be the main active species for HCHO mineralization. Furthermore, there is a competitive adsorption relationship between water (H₂O) molecules and HCHO molecules, and both H₂O molecules and oxygen (O₂) molecules participated in the reaction of HCHO mineralization based on in-situ DRIFTs spectra analysis. Our work would give a new perspective on gaseous HCHO purification.

Dual-quantum-dots heterostructure with confined active interface for promoted photocatalytic NO abatement

Constructing heterostructure is an effective way to fabricate advanced photocatalysts. However, the catalytic performance of typical common multi-dimensional bulk heterostructure still suffers from the limited active interface and inefficient carrier migration. Herein, we successfully synthesize the SnO₂/Cs₃Bi₂I₉ dual-quantum-dots nanoheterostructure (labeled as SCX, X = 1, 2, 3) for efficiently and stably photocatalytic NO removal under visible light irradiation. The NO removal rate of SC2 is almost 8 and 17 times higher than that of the single SnO₂ and Cs₃Bi₂I₉, respectively. Moreover, the SC2 photocatalyst shows only 3 % attenuation after five consecutive cycles, demonstrating good photocatalytic stability. Systematic experimental characterization and theoretical density functional theory calculations revealed that the high activity and stability of SCX originated from the efficient charge transfer at the confined interface between SnO₂ and Cs₃Bi₂I₉ quantum dots. This work provides a new perspective for constructing innovative dual-quantum-dots nanoheterostructure and assesses their potential in photocatalytic environmental applications.

The spatially separated active sites for holes and electrons boost the radicals generation for toluene degradation

Hydroxyl (⸱OH) and superoxide (⸱O₂^-) radicals are the main drivers for photocatalysis in toluene degradation, but their generation mechanisms are still ambiguous due to the lack of direct evidence. The spatially separated active sites for holes and electrons can help to clarify the dynamic process of radicals generation. By performing theoretical calculations, it is demonstrated that the spatially separated active sites for holes and electrons on the Bi₂O₂CO₃ surface can be constructed by introducing oxygen vacancies in the [Bi₂O₂]²⁺ layer. H₂O and O₂ molecules can be better adsorbed and activated at hole and electron active sites, separately. Accordingly, the pristine and defective Bi₂O₂CO₃ are prepared. The dynamic behavior of H₂O and O₂ molecules at the matching active sites is revealed, which indicates the efficient adsorption of reactants and the substantial production of radicals. Significantly, the specificity of the spatially separated holes and electrons active sites for ⸱OH and ⸱O₂^- radicals generation, respectively, is demonstrated by in situ EPR with the H₂O vapor atmosphere. This work provides a design concept for unraveling reaction mechanisms to realize controllable radicals generation.

Bridging 1D Inorganic and Organic Synthesis to Fabricate Ultrathin Bismuth-Based Nanotubes with Controllable Size as Anode Materials for Secondary Li Batteries

The growth of ultrathin 1D inorganic nanomaterials with controlled diameters remains challenging by current synthetic approaches. A polymer chain templated method is developed to synthesize ultrathin Bi₂ O₂ CO₃ nanotubes. This formation of nanotubes is a consequence of registry between the electrostatic absorption of functional groups on polymer template and the growth habit of Bi₂ O₂ CO₃ . The bulk bismuth precursor is broken into nanoparticles and anchored onto the polymer chain periodically. These nanoparticles react with the functional groups and gradually evolve into Bi₂ O₂ CO₃ nanotubes along the chain. 5.0 and 3.0 nm tubes with narrow diameter deviation are synthesized by using branched polyethyleneimine and polyvinylpyrrolidone as the templates, respectively. Such Bi₂ O₂ CO₃ nanotubes show a decent lithium-ion storage capacity of around 600 mA h g^-1 at 0.1 A g^-1 after 500 cycles, higher than other reported bismuth oxide anode materials. More interestingly, the Bi materials developed herein still show decent capacity at very low temperatures, that is, around 330 mA h g^-1 (-22 °C) and 170 mA h g^-1 (-35 °C) after 75 cycles at 0.1 A g^-1 , demonstrating their promising potential for practical application in extreme conditions.

Oxygen Limitation Accelerates Regeneration of Active Sites on a MnO2 Surface: Promoting Transformation of Organic Matter and Carbon Preservation

Birnessite (δ-MnO₂) is a layered manganese oxide widely present in the environment and actively participates in the transformation of natural organic matter (NOM) in biogeochemical processes. However, the effect of oxygen on the dynamic interface processes of NOM and δ-MnO₂ remains unclear. This study systematically investigated the interactions between δ-MnO₂ and fulvic acid (FA) under both aerobic and anaerobic conditions. FA was transformed by δ-MnO₂ via direct electron transfer and the generated reactive oxygen species (ROS). During the 32-day reaction, 79.8% of total organic carbon (TOC) in solution was removed under anaerobic conditions, unexpectedly higher than that under aerobic conditions (69.8%), suggesting that oxygen limitation was more conducive to the oxidative transformation of FA by δ-MnO₂. The oxygen vacancies (O_V) on the surface of δ-MnO₂ were more exposed under anaerobic conditions, thus promoting the adsorption and transformation of FA as well as regeneration of the active sites. Additionally, the reaction of FA with δ-MnO₂ weakened the strongly bonded lattice oxygen (O_latt), and the released O_latt was an important source of ROS. Interestingly, a part of organic carbon (OC) was preserved by forming MnCO₃, which might be a novel mechanism for carbon preservation. These findings contribute to an improved understanding of the dynamic interface processes between MnO₂ and NOM and provide new insights into the effects of oxygen limitation on the cycling and preservation of OC.

Carbon vacancy-mediated exciton dissociation in Ti3C2Tx/g-C3N4 Schottky junctions for efficient photoreduction of CO2

Earth-abundant g-C₃N₄ is a promising photocatalyst for CO₂ reduction, but its practical application is severely limited by the excitonic effect of g-C₃N₄ derived from strong binding energy and lack of electron-enriched active sites. Herein, we design a novel 2D/2D Schottky junction photocatalysts comprising of Ti₃C₂T_x-modified defective g-C₃N₄ nanosheets with carbon vacancy (denoted as Ti₃C₂T_x/V_c-CN) by a self-assembly method. The carbon vacancies in g-C₃N₄ promote exciton dissociation into free charge, while the formed Schottky junctions between Ti₃C₂T_x and V_c-CN further enables a directional charge transfer, thus providing an electron-rich catalytic surface for the CO₂ reduction. Thanks to the synergy of promoted exciton dissociation and directional electron transfer, the optimal 20% Ti₃C₂T_x/V_c-CN display a high CO evolution rate of 20.54 µmol·g^-1·h^-1 under visible light irradiation, which is 7.4 times higher than that of bare CN. This work highlights the synergy of the promoted exciton dissociation and directional electron transfer in the activity enhancement of photocatalytic CO₂ reduction.

Efficient and Selective CO2 Reduction to Formate on Pd-Doped Pb3 (CO3 )2 (OH)2 : Dynamic Catalyst Reconstruction and Accelerated CO2 Protonation

Exploring catalyst reconstruction under the electrochemical condition is critical to understanding the catalyst structure-activity relationship as well as to design effective electrocatalysts. Herein, a PbF₂ nanocluster is synthesized and its self-reconstruction under the CO₂ reduction condition is investigated. F^- leaching, CO₂ -saturated environment, and application of a cathodic potential induce self-reconstruction of PbF₂ to Pb₃ (CO₃ )₂ (OH)₂ , which effectively catalyze the CO₂ reduction to formate. The in situ formed Pb₃ (CO₃ )₂ (OH)₂ discloses >80% formate Faradaic efficiencies (FEs) across a broad range of potentials and achieves a maximum formate FE of ≈90.1% at -1.2 V versus reversible hydrogen electrode (RHE). Kinetic studies show that the CO₂ reduction reaction (CO₂ RR) on the Pb₃ (CO₃ )₂ (OH)₂ is rate-limited at the CO₂ protonation step, in which proton is supplied by bicarbonate (HCO₃ ^- ) in the electrolyte. To improve the CO₂ RR kinetics, the Pb₃ (CO₃ )₂ (OH)₂ is further doped with Pd (4 wt%) to enhance its HCO₃ ^- adsorption, which leads to accelerated protonation of CO₂ . Therefore, the Pd-Pb₃ (CO₃ )₂ (OH)₂ (4 wt%) reveals higher formate FEs of >90% from -0.8 to -1.2 V versus RHE and reaches a maximum formate FE of 96.5% at -1.2 V versus RHE with a current density of ≈13 mA cm^-2 .

Construction of plasmonic Bi/Bismuth oxycarbonate/Zinc bismuth oxide ternary heterojunction for enhanced charge carrier separation and photocatalytic performances

In this work, a novel plasmonic ternary Bi/Bismuth oxycarbonate/Zinc bismuth oxide (Bi-Bi₂O₂CO₃-ZnBi₂O₄) is synthesized synergistically by a one-step hydrothermal method. The results show that the metallic Bi spheres and ZnBi₂O₄ nanoparticles are uniformly distributed on the surface of flower-like Bi₂O₂CO₃ layer. Compared with the bare ZnBi₂O₄ and Bi-Bi₂O₂CO₃, the ternary Bi-Bi₂O₂CO₃-ZnBi₂O₄ heterojunction displays a significantly improved solar energy harvesting efficiency and enhanced photocatalytic degradation activity for environmental organic pollutants. The degradation efficiency of organics reaches to 98.4% under simulated solar light illumination. The degradation kinetics indicates that the photocatalytic reaction rate constant of ternary system is about 4.4 and 29.5 times higher than that of pure ZnBi₂O₄ and Bi-Bi₂O₂CO₃, respectively. Moreover, O₂^- and h⁺ are the main active species in the photodegradation reaction. The improvement of the photocatalytic activity of the composites is attributed to the synergistic effect of ternary heterostructure and surface plasmon resonance (SPR), which promotes charge transfer and effectively inhibits the recombination of photogenerated carriers.

Recent advancement in Bi5O7I-based nanocomposites for high performance photocatalysts

Bi₅O₇I belongs to the family of bismuth oxyhalides (BiOX, X = Cl, Br, I), having a unique layered structure with an internal electrostatic field that promotes the separation and transfer of photo-generated charge carriers. Interestingly, Bi₅O₇I exhibits higher thermal stability compared to its other BiOX member compounds and absorption spectrum extended to the visible region. Bi₅O₇I has demonstrated applications in diverse fields such as photocatalytic degradation of various organic pollutants, marine antifouling, etc. Unfortunately, owing to its wide band gap of ∼2.9 eV, its absorption lies mainly in the ultraviolet region, and a tiny portion of absorption lies in the visible region. Due to limited absorption, the photocatalytic performance of pure Bi₅O₇I is still facing challenges. In order to reduce the band gap and increase the light absorption capability of Bi₅O₇I, doping and formation of heterostructure strategies have been employed, which showed promising results in the photocatalytic performance. In addition, the plasmonic heterostructures of Bi₅O₇I were also developed to further boost the efficiency of Bi₅O₇I as a photocatalyst. Here, in this review article, we present such recent efforts made for the advanced development of Bi₅O₇I regarding its synthesis, properties and applications. The strategies for photocatalytic performance enhancement have been discussed in detail. Moreover, in the conclusion section, we have presented the current challenges and discussed possible prospective developments in this field.