Recent Advances in Semiconductor Heterojunctions and Z-Schemes for Photocatalytic Hydrogen Generation

A novel ZnO/Fe3+-doped Bi2WO6 photocatalyst with triple synergistic effect for solar-driven tetracycline degradation

To address the limited visible-light absorption and rapid charge recombination of Bi2WO6 photocatalysts, this work constructs a Z-scheme ZnO/Fe3+-doped Bi2WO6 heterojunction via a hydrothermal-calcination method. The Fe3+ doping induces the formation of oxygen vacancies and optimizes the band structure, which cooperates with the interface reconstruction of ZnO to expand the light absorption to 480 nm. The hierarchical pore structure simultaneously enhances the mass transfer efficiency, and finally realizes the efficient degradation of tetracycline under visible light (the removal rate is 95.5% in 60 minutes, and the rate is 2.28 times higher than that of the pure phase) and the stable cycle performance is good. Mechanistic studies demonstrate that Z-scheme charge transfer driven by an interfacial built-in electric field ensures effective carrier separation, with photogenerated holes (h+) as key reactive species. The proposed "defect-heterojunction-interface trinity" strategy establishes a new design scheme for bismuth-based Z-scheme photocatalysts.

Rational Design of Core-Shell MoS2@ZIF-67 Nanocomposites for Enhanced Photocatalytic Degradation of Tetracycline

Zeolitic imidazolate frameworks (ZIFs) and their composites are attractive materials for photocatalytic applications due to their distinct characteristics. Core-shell ZIFs have lately emerged as a particularly appealing type of metal-organic frameworks, with improved light-absorption and charge-separation capabilities. In this study, hybrid nanocomposite materials comprising a zeolitic imidazolate framework-67 and molybdenum disulfide (MoS2) were fabricated with a core-shell structure. The prepared core-shell MoS2@ZIF-67 nanocomposites were studied using XRD, FTIR, XPS, and HR-TEM techniques. The crystalline nature and the presence of characteristic functional groups of the composites were analyzed using XRD and FTIR, respectively. The photocatalytic degradation of antibiotic tetracycline (TC) was measured using visible light irradiation. Compared to pristine MoS2 (12%) and ZIF-67 (34%), the most active MoS2@ZIF-67 nanocomposite (72%) exhibited a greater tetracycline degradation efficacy.

Z-Scheme Enabled 1D/2D Nanocomposite of ZnO Nanorods and Functionalized g-C3 N4 Nanosheets for Sustainable Degradation of Terephthalic Acid

The urgent need to mitigate water pollution and achieve Sustainable Development Goal 14 (SDG 14)-Life below water, necessitates developing efficient and eco-friendly wastewater treatment technologies. This research addresses this challenge by photocatalytic degradation of terephthalic acid, a precursor for PET bottles using environment-friendly and biocompatible photocatalysts. The 1D/2D nanocomposite comprising zinc oxide (ZnO) nanorods and functionalized graphitic carbon nitride (Zn-TG) nanosheets were synthesized and thoroughly characterized. The nanocomposite effectively mitigated the individual drawbacks of Zn-TG agglomeration and the wide band gap of ZnO as confirmed through zeta potential and Tauc's plot studies, respectively. The synthesized nanocomposite achieved ~100 % degradation within 60 minutes, exhibiting superior kinetics (~2.5 times) compared to pristine samples. The enhanced degradation efficiency was elucidated by efficient charge carrier transfer (~5 times faster) and separation (~2 times improved) as confirmed through electrochemical impedance spectroscopy and time-resolved photoluminescence studies. The proposed Z-scheme pathway provides mechanistic insights. This proposed mechanism is supported by extensive electron paramagnetic resonance (EPR) and scavenger studies. The liquid chromatography-mass spectrometry (LC-MS) analysis confirms the formation of less toxic byproducts for ensuring that the wastewater treatment process is efficient and environmentally friendly. This research helps in developing a highly effective and sustainable wastewater treatment technology.

UV and Visible Light-Induced Photocatalytic Efficiency of Polyaniline/Titanium Dioxide Heterostructures

The concept of using polyaniline/titanium dioxide heterostructures as efficient photocatalysts is based on the synergistic effect of conducting polymer and metal oxide semiconductors. Due to inconclusive literature reports, the effect of different polyaniline/TiO2 ratios on photocatalytic activity under UV and visible light was investigated. In most papers, non-recommended dyes are used as model compounds to evaluate visible light activity. Therefore, colorless phenol was used instead of dyes in this study to clarify the real visible light-induced photocatalytic activity of polyaniline/TiO2 composites. This publication also includes a discussion of whether materials derived from bulk (non-nanostructured) polyaniline and TiO2 by the standard in situ oxidative polymerization method are suitable candidates for promising photocatalytic materials. The evaluation of photocatalytic activity was performed in both UV and visible light systems. X-ray diffraction and UV-Vis diffuse reflectance spectroscopy methods were applied to characterize the obtained samples. Obtained polyaniline (pure and in composites) was identified as emeraldine salt. In the UV system, none of the prepared samples with different polyaniline-titania ratios had activity better than reference P25 titania. It has been observed that the presence of polyaniline adversely affects the photocatalytic properties, as the polyaniline layer covering the titania surface can shield the UV light transmission by blocking the contact between the TiO2 surface and organic molecules. In the case of using visible light, no synergies have been observed between polyaniline and titania either. The photodegradation efficiencies of the most active samples were similar to those of pure polyaniline. In conclusion, in order to obtain efficient polyaniline/titania photocatalysts active in UV and/or visible light, it is necessary to take into account the morphological and surface properties of both components.

Unveiling the potential of step-scheme and Type II photocatalysts in dinitrogen reduction to ammonia

Innovative photocatalytic systems designed to enhance efficiency of nitrogen fixation processes, specifically focusing on sustainable ammonia (NH3) production strategies via dinitrogen (N2) reduction into ammonia (NH3). This process is critical for sustainable agriculture and energy production. To improve photocatalyst activity, catalyst stability and reusability, reduction efficiency due to electron/hole recombination, and light-absorption efficiency has drawn extensive attention. Herein, a broad range of research progress and comprehensive overview of step-scheme/type-II heterojunctions focusing on dinitrogen (N2) reduction are reviewed with focus on general synthesis, characterization by their unique charge separation mechanisms that improve light absorption and electron-hole pair utilization. The review highlights recent advancements in material design, which have shown promising results in enhancing photocatalytic activity under visible light irradiation. A significant portion of the review delves into the underlying mechanisms which these heterojunctions operate. Despite the promising literature results, several challenges facing this field, such as scalability, stability of photocatalysts, and environmental impact under operational conditions were also discussed. In summary, this review provides valuable insights into the potential of step-scheme/type-II photocatalysts for dinitrogen reduction to ammonia. The need for interdisciplinary approaches to overcome existing challenges such as incorporation of piezoelectric biomaterials and unlocking the full potential of these materials in addressing global nitrogen demands sustainably are highlighted, outlining future directions for further research and innovations.

Fast and Facile Synthesis of Cobalt-Doped ZIF-8 and Fe3O4/MCC/Cobalt-Doped ZIF-8 for the Photodegradation of Organic Dyes under Visible Light

Co-doped ZIF-8 as a water-stable visible light photocatalyst was prepared by using a one-pot, fast, cost-effective, and environmentally friendly method. The band structure of ZIF-8 was tuned through the incorporation of different percentages of cobalt to attain an optimal band gap (E g) that enables the activation of ZIF-8 under visible light and minimizes the recombination of photogenerated charge carriers. A magnetic composite of Co-doped ZIF-8 was also synthesized to facilitate catalyst recycling and reusability through the application of an external magnetic field. Surface modification of magnetic Fe3O4 nanoparticles with microcrystalline cellulose (MCC) was used to reduce the level of agglomeration. The photocatalytic activities of Co-doped ZIF-8 (Co-ZIF-8) and Fe3O4/MCC/Co-ZIF-8 were evaluated for the photodegradation of methylene blue (MB) under visible light irradiation from a 20 W LED source. Co-ZIF-8 showed considerably higher photocatalytic activity than pure ZIF-8, confirming the success of the doping strategy. Both Co20%-ZIF-8 and Fe3O4/MCC/Co20%-ZIF-8 exhibited similar and remarkable photocatalytic activity under visible light (achieving 97% MB removal). The mechanism of photodegradation of MB by Fe3O4/MCC/Co20%-ZIF-8 was studied, revealing a first-order degradation kinetics (k = 13.78 × 10-3 min-1), with peroxide and hole species as the predominant active reagents. The magnetic composite successfully displayed recyclability and reusability over multiple cycles with negligible reduction in MB photodegradation efficiency.

Emerging Trends in CdS-Based Nanoheterostructures: From Type-II and Z-Scheme toward S-Scheme Photocatalytic H2 Production

Cadmium sulfide (CdS) based heterojunctions, including type-II, Z-scheme, and S-scheme systems emerged as promising materials for augmenting photocatalytic hydrogen (H2) generation from water splitting. This review offers an exclusive highlight of their fundamental principles, synthesis routes, charge transfer mechanisms, and performance properties in improving H2 production. We overview the crucial roles of Type-II heterojunctions in enhancing charge separation, Z-scheme heterojunctions in promoting redox potentials to reduce electron-hole (e-/h+) pairs recombination, and S-scheme heterojunctions in combining the merits of both type-II and Z-scheme frameworks to obtain highly efficient H2 production. The importance of this review is demonstrated by its thorough comparison of these three configurations, presenting valuable insights into their special contributions and capability for augmenting photocatalytic H2 activity. Additionally, key challenges and prospects in the practical applications of CdS-based heterojunctions are addressed, which provides a comprehensive route for emerging research in achieving sustainable energy goals.

Heterojunction semiconductor nanocatalysts as cancer theranostics

Cancer nanotechnology is a promising area of cross-disciplinary research aiming to develop facile, effective, and noninvasive strategies to improve cancer diagnosis and treatment. Catalytic therapy based on exogenous stimulus-responsive semiconductor nanomaterials has shown its potential to address the challenges under the most global medical needs. Semiconductor nanocatalytic therapy is usually triggered by the catalytic action of hot electrons and holes during local redox reactions within the tumor, which represent the response of nontoxic semiconductor nanocatalysts to pertinent internal or external stimuli. However, careful architecture design of semiconductor nanocatalysts has been the major focus since the catalytic efficiency is often limited by facile hot electron/hole recombination. Addressing these challenges is vital for the progress of cancer catalytic therapy. In recent years, diverse strategies have been developed, with heterojunctions emerging as a prominent and extensively explored method. The efficiency of charge separation under exogenous stimulation can be heightened by manipulating the semiconducting performance of materials through heterojunction structures, thereby enhancing catalytic capabilities. This review summarizes the recent applications of exogenous stimulus-responsive semiconducting nanoheterojunctions for cancer theranostics. The first part of the review outlines the construction of different heterojunction types. The next section summarizes recent designs, properties, and catalytic mechanisms of various semiconductor heterojunctions in tumor therapy. The review concludes by discussing the challenges and providing insights into their prospects within this dynamic and continuously evolving field of research.

Gas-Phase Photocatalytic Coprocessing of CO2 - H2O(v) to Energy Products Promoted by the n,n-Junction In2O3@g-C3N4 under VIS-Light

Carbon dioxide capture and utilization is a strategic technology for moving away from fossil-C. The conversion of CO2 into fuels demands energy and hydrogen that cannot be sourced from fossil-C. Co-processing of CO2 and water under solar irradiation will have a key role in the long-term for carbon-recycling and energy products production. This article discusses the synthesis, characterization and application of the two-phase composite photocatalyst, In2O3@g-C3N4, formed by thermal condensation of melamine in the presence of indium(III)nitrate. The composite exhibits a n,n-heterojunction between two n-type semiconductors, g-C3N4 and In2O3, leading to a more efficient charge separation. The composite has a flat band potential enabling it to effectively catalyze the reduction of CO2 in the gas phase to produce CO, CH4 and CH3OH. While the composite's overall photocatalytic efficiency is comparable to that of neat g-C3N4, its ability to promote multielectron-transfer and Proton Coupled to Electron Transfer (PCET) suggests that there is a potential for further optimization of its properties. The use of labelled 13CO2 has allowed us to clearly exclude that the reduced species are derived from the photocatalyst decomposition or the degradation of contaminants.

Development of a MOF-5/g-C3N4 nanocomposite: an effective type 2 heterojunction photocatalyst for rhodamine B dye degradation

The field of environmental and water remediation faces a significant challenge in removing organic dyes from wastewater, particularly Rhodamine B (RhB), a stubborn dye used in various industries. Traditional treatment methods struggle with its resistance to decomposition, posing risks to water quality, human health, and aquatic life. This study demonstrates a novel approach to enhance photocatalytic efficiency for RhB degradation by constructing a MOF-5/g-C3N4 composite through a facile mechanical grinding method, which is unprecedented. The composite addresses the limitations of g-C3N4, such as rapid recombination of electron-hole pairs, low electron transfer rates, and small surface area, by forming a heterojunction with MOF-5. The composite exhibits enhanced photocatalytic efficiency for the degradation of RhB under sunlight, with a degradation of 91.5% achieved within 90 min. Optimization studies highlight the importance of pH and catalyst dosage in the degradation process. The reusability test shows consistent performance over five successive cycles, maintaining a degradation efficiency of over 90%. Total organic carbon (TOC) analyses confirm the mineralization of the dye solution to 82.05% after 90 min of irradiation, demonstrating the environmental benignity of the composite. Trapping experiments suggest the involvement of superoxide radicals, electrons, and holes in the photocatalytic mechanism. This study introduces a promising strategy for addressing challenges in dye degradation through innovative composite materials.

Recent progress and new insights on semiconductor heterojunctions powered photocatalytic desulphurization: A review

Desulphurization of fossil fuels is a critical process in reducing the sulphur content from environment, which is a major contributor to atmospheric pollution. Traditional desulphurization techniques, while effective, often involve high energy consumption and the use of harsh chemicals. Recently, photocatalytic desulphurization has emerged as a promising, eco-friendly alternative, leveraging the potential of photocatalysts especially semiconductor heterojunctions to enhance photocatalytic efficiency. This review comprehensively discusses the significance and mechanism of photocatalytic desulphurization reactions, designing of various heterojunctions such as conventional, p-n, Z-scheme and S-scheme, their charge transfer mechanism and properties and their contribution to the photocatalytic desulphurization activity. Heterojunctions, formed by combining different semiconductor materials, facilitate efficient charge separation and broaden the light absorption range, thereby improving the photocatalytic performance under visible light. Furthermore, the recent advancements in the heterojunction systems in the field of photocatalytic desulphurization activity have been discussed in detail and summarized. The current limitations and challenges in this particular field are also explored. The paper concludes with an outlook on future research directions and the potential industrial applications of heterojunction-powered photocatalytic desulphurization, emphasizing its role in achieving cleaner energy production and environmental sustainability.

Updates on Hydrogen Value Chain: A Strategic Roadmap

A strategic roadmap for noncarbonized fuels is a global priority, and the reduction of carbon dioxide emissions is a key focus of the Paris Agreement to mitigate the effects of rising temperatures. In this context, hydrogen is a promising noncarbonized fuel, but the pace of its implementation will depend on the engineering advancements made at each step of its value chain. To accelerate its adoption, various applications of hydrogen across industries, transport, power, and building sectors have been identified, where it can be used as a feedstock, fuel, or energy carrier and storage. However, widespread usage of hydrogen will depend on its political, industrial, and social acceptance. It is essential to carefully assess the hydrogen value chain and compare it with existing solar technologies. The major challenge to widespread adoption of hydrogen is its cost as outlined in the roadmap for hydrogen. It needs to be produced at the levelized cost of hydrogen of less than $2 kg-1 to be competitive with the established process of steam methane reforming. Therefore, this review provides a comprehensive analysis of each step of the hydrogen value chain, outlining both the current challenges and recent advances.

Imogolite Nanotubes and Their Permanently Polarized Bifunctional Surfaces for Photocatalytic Hydrogen Production

To date, imogolite nanotubes (INTs) have been primarily used for environmental applications such as dye and pollutant degradation. However, imogolite's well-defined porous structure and distinctive electro-optical properties have prompted interest in the system's potential for energy-relevant chemical reactions. The imogolite structure leads to a permanent intrawall polarization arising from the presence of bifunctional surfaces at the inner and outer tube walls. Density functional theory simulations suggest such bifunctionality to encompass also spatially separated band edges. Altogether, these elements make INTs appealing candidates for facilitating chemical conversion reactions. Despite their potential, the exploitation of imogolite's features for photocatalysis is at its infancy, thence relatively unexplored. This perspective overviews the basic physical-chemical and optoelectronical properties of imogolite nanotubes, emphasizing their role as wide bandgap insulator. Imogolite nanotubes have multifaceted properties that could lead to beneficial outcomes in energy-related applications. This work illustrates two case studies demonstrating a step-forward on photocatalytic hydrogen production achieved through atomic doping or metal co-catalyst. INTs exhibit potential in energy conversion and storage, due to their ability to accommodate functions such as enhancing charge separation and influencing the chemical potentials of interacting species. Yet, tapping into potential for energy-relevant application needs further experimental research, computational, and theoretical analysis.

Bismuth-Based Z-Scheme Heterojunction Photocatalysts for Remediation of Contaminated Water

Agricultural runoff, fuel spillages, urbanization, hospitalization, and industrialization are some of the serious problems currently facing the world. In particular, byproducts that are hazardous to the ecosystem have the potential to mix with water used for drinking. Over the last three decades, various techniques, including biodegradation, advanced oxidation processes (AOPs), (e.g., photocatalysis, photo-Fenton oxidation, Fenton-like oxidation, and electrochemical oxidation process adsorption), filtration, and adsorption techniques, have been developed to remove hazardous byproducts. Among those, AOPs, photocatalysis has received special attention from the scientific community because of its unusual properties at the nanoscale and its layered structure. Recently, bismuth based semiconductor (BBSc) photocatalysts have played an important role in solving global energy demand and environmental pollution problems. In particular, bismuth-based Z-scheme heterojunction (BBZSH) is considered the best alternative route to overhaul the limitations of single-component BBSc photocatalysts. This work aims to review recent studies on a new type of BBZSH photocatalysts for the treatment of contaminated water. The general overview of the synthesis methods, efficiency-enhancing strategies, classifications of BBSc and Z-scheme heterojunctions, the degradation mechanisms of Z- and S-schemes, and the application of BBZSH photocatalysts for the degradation of organic dyes, antibiotics, aromatics compounds, endocrine-disrupting compounds, and volatile organic compounds are reviewed. Finally, challenges and the future perspective of BBZSH photocatalysts are discussed.

Cs3Bi2Br9/g-C3N4 Direct Z-Scheme Heterojunction for Enhanced Photocatalytic Reduction of CO2 to CO

Lead-free halide perovskite derivative Cs3Bi2Br9 has recently been found to possess optoelectronic properties suitable for photocatalytic CO2 reduction reactions to CO. However, further work needs to be performed to boost charge separation for improving the overall efficiency of the photocatalyst. This report demonstrates the synthesis of a hybrid inorganic/organic heterojunction between Cs3Bi2Br9 and g-C3N4 at different ratios, achieved by growing Cs3Bi2Br9 crystals on the surface of g-C3N4 using a straightforward antisolvent crystallization method. The synthesized powders showed enhanced gas-phase photocatalytic CO2 reduction in the absence of hole scavengers of 14.22 (±1.24) μmol CO g-1 h-1 with 40 wt % Cs3Bi2Br9 compared with 1.89 (±0.72) and 5.58 (±0.14) μmol CO g-1 h-1 for pure g-C3N4 and Cs3Bi2Br9, respectively. Photoelectrochemical measurements also showed enhanced photocurrent in the 40 wt % Cs3Bi2Br9 composite, demonstrating enhanced charge separation. In addition, stability tests demonstrated structural stability upon the formation of a heterojunction, even after 15 h of illumination. Band structure alignment and selective metal deposition studies indicated the formation of a direct Z-scheme heterojunction between the two semiconductors, which boosted charge separation. These findings support the potential of hybrid organic/inorganic g-C3N4/Cs3Bi2Br9 Z-scheme photocatalyst for enhanced CO2 photocatalytic activity and improved stability.

Heterojunction Photocatalyst Loaded on Electrospun Nanofibers for Synergistic Enhanced Photocatalysis and Real-Time Temperature Monitoring

Bi2WO6:Ho3+, Yb3+/g-C3N4 (BHY/CN) photocatalysts are successfully loaded on polyacrylonitrile (PAN) nanofibers by electrospinning technology, which combines an upconversion effect and heterojunctions to achieve dual-functional characteristics. Polymer-modified photocatalytic materials offer a large specific surface area of 24.1 m2/g and a pore volume of 0.1 cm3/g, promoting the utility of solar energy. The introduction of rare earth ions and g-C3N4 optimizes the structural band gap, which broadens the light absorption range and promotes electron transfer. Moreover, the heterojunction between Bi2WO6 and g-C3N4 has suppressed the complexation of photoinduced carriers, further improving catalytic performance. The optimized photocatalysts have higher photocatalytic activity with degrading 92.6% tetracycline-hydrochloride (120 min) under simulated sunlight irradiation. The optical thermometry has also been achieved based on the fluorescence intensity ratio technique, where the maximum absolute and relative sensitivity values of BHY/CN-1:6@PAN are 3.322% K-1 and 0.842% K-1, respectively. This dual-functional nanofibers with excellent mechanical properties provide noncontact temperature feedback and efficient catalytic performance for better wastewater treatment and ecological restoration in extreme harsh environments.

Environmental remediation of hazardous pollutants using MXene-perovskite-based photocatalysts: A review

Photocatalysis utilizing semiconductors offer a cost-effective and promising solution for the removal of pollutants. MXene and perovskites, which possess desirable properties such as a suitable bandgap, stability, and affordability, have emerged as a highly promising material for photocatalytic activity. However, the efficiency of MXene and perovskites is limited by their fast recombination rates and inadequate light harvesting abilities. Nonetheless, several additional modifications have been shown to enhance their performance, thereby warranting further exploration. This study delves into the fundamental principles of reactive species for MXene-perovskites. Various methods of modification of MXene-perovskite-based photocatalysts, including Schottky junction, Z-scheme and S-scheme are analyzed with regard to their operation, differences, identification techniques and reusability. The assemblance of heterojunctions is demonstrated to enhance photocatalytic activity while also suppressing charge carrier recombination. Furthermore, the separation of photocatalysts through magnetic-based methods is also investigated. Consequently, MXene-perovskite-based photocatalysts are seen as an exciting emerging technology that necessitates further research and development.

Colloidal semiconductor nanocrystals: from bottom-up nanoarchitectonics to energy harvesting applications

Colloidal semiconductor nanocrystals (NCs) have been extensively investigated owing to their unique properties induced by the quantum confinement effect. The advent of colloidal synthesis routes led to the design of stable colloidal NCs with uniform size, shape, and composition. Metal oxides, phosphides, and chalcogenides (ZnE, CdE, PbE, where E = S, Se, or Te) are few of the most important monocomponent semiconductor NCs, which show excellent optoelectronic properties. The ability to build quantum confined heterostructures comprising two or more semiconductor NCs offer greater customization and tunability of properties compared to their monocomponent counterparts. More recently, the halide perovskite NCs showed exceptional optoelectronic properties for energy generation and harvesting applications. Numerous applications including photovoltaic, photodetectors, light emitting devices, catalysis, photochemical devices, and solar driven fuel cells have demonstrated using these NCs in the recent past. Overall, semiconductor NCs prepared via the colloidal synthesis route offer immense potential to become an alternative to the presently available device applications. This feature article will explore the progress of NCs syntheses with outstanding potential to control the shape and spatial dimensionality required for photovoltaic, light emitting diode, and photocatalytic applications. We also attempt to address the challenges associated with achieving high efficiency devices with the NCs and possible solutions including interface engineering, packing control, encapsulation chemistry, and device architecture engineering.

Solar-based photocatalytic ozonation employing novel S-scheme ZnO/Cu2O/CuO/carbon xerogel photocatalyst: effect of pH, salinity, turbidity, and temperature on salicylic acid degradation

This paper proposes the study of a solar-based photocatalytic ozonation process for the degradation of salicylic acid (SA) using a novel S-scheme ZnO/Cu2O/CuO/carbon xerogel photocatalyst. The incorporation of CuO and Cu2O aims to enhance charge mobility through the formation of p-n heterojunctions with ZnO, whereas the carbon xerogel (XC) was selected due to its eco-friendly nature, capacity to stabilize S-scheme heterojunctions as a solid-state electron mediator, and ability to function as a reducing agent under high temperatures. The characterization of the composites demonstrates that the presence of the XC during the calcination step led to the reduction of a fraction of the CuO into Cu2O, forming a ternary semiconductor heterojunction system. In terms of photocatalysis, the XC/ZnO-CuxO 5% composite achieved the best efficiency for salicylic acid degradation, mainly due to the stabilization of the S-scheme charge transfer pathway between the ZnO/CuO/Cu2O semiconductors by the XC. The total organic carbon (TOC) removal during heterogeneous photocatalysis was 80% for the solar-based process and 68% for the visible light process, after 300 min. The solar-based photocatalytic ozonation process was highly successful regarding the degradation of SA, achieving a 75% increase in the apparent reaction rate constant when compared to heterogeneous photocatalysis. Furthermore, a 78% TOC removal was achieved after 150 min, which is half the time required by the heterogeneous photocatalysis to obtain the same result. Temperature, salinity, and turbidity had major effects on the efficiency of the photocatalytic ozonation process; the system's pH did not cause any major performance variation, which holds relevance for industrial applications.

Single-Particle Measurements Reveal the Origin of Low Solar-to-Hydrogen Efficiency of Rh-Doped SrTiO3 Photocatalysts

Solar-powered photochemical water splitting using suspensions of photocatalyst nanoparticles is an attractive route for economical production of green hydrogen. SrTiO₃-based photocatalysts have been intensely investigated due to their stability and recently demonstrated near-100% external quantum yield (EQY) for water splitting using wavelengths below 360 nm. To extend the optical absorption into the visible, SrTiO₃ nanoparticles have been doped with various transition metals. Here we demonstrate that doping SrTiO₃ nanoparticles with 1% Rh introduces midgap acceptor states which reduce the free electron concentration by 5 orders of magnitude, dramatically reducing built-in potentials which could otherwise separate electron-hole (e-h) pairs. Rhodium states also function as recombination centers, reducing the photocarrier lifetime by nearly 2 orders of magnitude and the maximum achievable EQY to 10%. Furthermore, the absence of built-in electric fields within Rh-doped SrTiO₃ nanoparticles suggests that modest e-h separation can be achieved by exploiting a difference in mobility between electrons and holes.

Understanding the Principles and Applications of Dual Z-Scheme Heterojunctions: How Far Can We Go?

In the past seven years, dual Z-scheme heterojunctions evolved as favorable approaches for enhanced charge carrier separation through direct or indirect charge transfer transportation mechanisms. The dynamics of the charge transfer is the major strategy for understanding their photoactivity and stability through the formation of distinctive redox centers. The understanding of currently recognized principles for successful fabrication and classification in different energy and pollution remediation strategies is discussed, and a universal charge transfer-type-based classification of dual Z-schemes that can be adopted for Z-scheme and S-scheme heterojunctions is proposed. Methods used for determining the charge transfer as proof of dual Z-scheme existence are outlined. Most importantly, a new macroscopic N-scheme and a triple Z-scheme that can also be adopted as triple S-scheme heterostructures composed of four semiconductors are proposed for generating both oxidatively and reductively empowered systems. The proposed systems are expected to possess properties that enable them to harvest solar light to drive important chemical reactions for different applications.