Modulation of Z-Scheme Heterojunction Interface between Ultrathin C3N5 Nanosheets and Metal-Organic Framework for Boosting Photocatalysis

Cocatalyst Embedded Ce-BDC-CeO2 S-Scheme Heterojunction Hollowed-Out Octahedrons With Rich Defects for Efficient CO2 Photoreduction

Constructing heterojunction photocatalysts with optimized architecture and components is an effective strategy for enhancing CO2 photoreduction by promoting photogenerated carrier separation, visible light absorption, and CO2 adsorption. Herein, defect-rich photocatalysts (Ni2P@Ce-BDC-CeO2 HOOs) with S-scheme heterojunction and hollowed-out octahedral architecture are prepared by decomposing Ce-BDC octahedrons embedded with Ni2P nanoparticles and subsequent lactic acid etching for CO2 photoreduction. The hollowed-out octahedral architecture with multistage pores (micropores, mesopores, and macropores) and oxygen vacancy defects are simultaneously produced during the preparation process. The S-scheme heterojunction boosts the quick transfer and separation of photoinduced charges. The formed hollowed-out multi-stage pore structure is favorable for the adsorption and diffusion of CO2 molecules and gaseous products. As expected, the optimized photocatalyst exhibits excellent performance, producing CO with a yield of 61.6 µmol h-1 g-1, which is four times higher than that of the original Ce-BDC octahedrons. The X-ray photoelectron spectroscopy, scanning Kelvin probe, and electron spin resonance spectroscopy characterizations confirm the S-schematic charge-transfer route. The key intermediate species during the CO2 photoreduction process are detected by in situ Fourier transform infrared spectroscopy to support the proposed mechanism for CO2 photoreduction. This work presents a synthetic strategy for excellent catalysts with potential prospects in photocatalytic applications.

MOCHAs: An Emerging Class of Materials for Photocatalytic H2 Production

Production of green hydrogen (H2) is a sustainable process able to address the current energy crisis without contributing to long-term greenhouse gas emissions. Many Ag-based catalysts have shown promise for light-driven H2 generation, however, pure Ag-in its bulk or nanostructured forms-suffers from slow electron transfer kinetics and unfavorable Ag─H bond strength. It is demonstrated that the complexation of Ag with various chalcogenides can be used as a tool to optimize these parameters and reach improved photocatalytic performance. In this work, metal-organic-chalcogenolate assemblies (MOCHAs) are introduced as effective catalysts for light-driven hydrogen evolution reaction (HER) and investigate their performance and structural stability by examining a series of AgXPh (X = S, Se, and Te) compounds. Two catalyst-support sensitization strategies are explored: by designing MOCHA/TiO2 composites and by employing a common Ru-based photosensitizer. It is demonstrated that the heterogeneous approach yields stable HER performance but involves a catalyst transformation at the initial stage of the photocatalytic process. In contrast to this, the visible-light-driven MOCHA-dye dyad shows similar HER activity while also ensuring the structural integrity of the MOCHAs. The work shows the potential of MOCHAs in constructing photosystems for catalytic H2 production and provides a direct comparison between known AgXPh compounds.

Simultaneous Efficient Photocatalytic Hydrogen Evolution and Degradation of Dye Wastewater without Cocatalysts and Sacrificial Agents Based on g-C3N5 and Hybridized Ni-MOF Derivative-CdS-DETA

Inspired by energy conversion and waste reuse, hybridized Ni-MOF derivative-CdS-DETA/g-C3N5, a type-II heterojunction photocatalyst, is synthesized by a hydrothermal method for simultaneous and highly efficient photocatalytic degradation and hydrogen evolution in dye wastewater. Without the addition of cocatalysts and sacrificial agents, the optimal MOF-CD(2)/CN5 (i.e. Ni-MOF derivative-CdS-DETA (20 wt.%)/g-C3N5) exhibit good bifunctional catalytic activity, with a H2 evolution rate of 2974.4 µmol g-1 h-1 during the degradation of rhodamine B (RhB), and a removal rate of 99.97% for RhB. In the process of H2-evolution-only, triethanolamine is used as a sacrificial agent, exhibiting a high H2 evolution rate (19663.1 µmol g-1 h-1) in the absence of a cocatalyst, and outperforming most similar related materials (such as MOF/g-C3N5, MOF-CdS, CdS/g-C3N5). With the help of type-II heterojunction, holes are scavenged for the oxidative degradation of RhB, and electrons are used in the decomposition of water for H2 evolution during illumination. This work opens a new path for photocatalysts with dual functions of simultaneous efficient degradation and hydrogen evolution.

S-scheme NiO/C3N5 heterojunctions with enhanced interfacial electric field for boosting photothermal-assisted photocatalytic H2 and H2O2 production

Heterostructured visible-light-responsive photocatalysts represent a prospective approach to achieve efficient solar-to-chemical energy conversion. Herein, we propose a facile self-assembly technique to synthesize NiO nanoparticles/C3N5 nanosheets (NOCN) heterojunctions for hydrogen (H2) evolution catalysis and hydrogen peroxide (H2O2) production under visible light. In this regard, the black NiO nanoparticles (NPs) were tightly anchored on the surface of C3N5 nanosheets (CNNS) to construct S-scheme NOCN heterojunction, enabling efficient charge separation and high redox capability. Obtained results elucidated that the incorporated NiO NPs significantly promote light-harvesting efficiency and photo-to-thermal capacity over the NOCN composites. The enhanced photothermal effect facilitates the charge carrier transfer rate across the heterojunction and boosts the surface reaction kinetics. Accordingly, the photocatalytic performances of CNNS for H2 release and H2O2 production can be manipulated by introducing NiO NPs. The modified photocatalytic properties of NOCN composites are ascribed to the synergistic effects of all integrated components and the S-scheme heterojunction formation. Impressively, the high H2 evolution photocatalysis efficiency of NOCN nano-catalysts in seawater certifies their potential environmental applicability. Among all, the 12-NOCN nano-catalyst exhibits a higher photocatalytic efficiency for H2 release (112.2 μmol∙g-1∙h-1) and H2O2 production (91.2 μmol∙L-1∙h-1). Besides, the 12-NOCN nano-catalyst reveals excellent recyclability and structural stability. Additionally, the possible mechanism for photothermal-assisted photocatalysis is proposed. This work affords a feasible pathway to design photothermal-assisted S-scheme heterojunctions for diverse photocatalytic applications.

C3N5-based nanomaterials and their applications in heterogeneous catalysts, energy harvesting, and environmental remediation

Over the past few decades, the global reliance on fossil fuels and the exponential growth of human population have escalated global energy consumption and environmental issues. To tackle these dual challenges, metal catalysts, in particular precious metal ones, have emerged as pivotal players in the fields of environment and energy. Among the numerous metal-free and organic catalyst materials, C3N5-based materials have a major advantage over their carbon nitride (CxNy) counterparts owing to the abundant availability of raw materials, non-toxicity, non-hazardous nature, and exceptional performance. Although significant efforts have been dedicated to synthesising and optimising the applicable properties of C3N5-based materials in recent years, a comprehensive summary of the immediate parameters of this promising material is still lacking. Given the rapid development of C3N5-based materials, a timely review is essential for staying updated on their strengths and weaknesses across various applications, as well as providing guidance for designing efficient catalysts. In this study, we present an extensive overview of recent advancements in C3N5-based materials, encompassing their physicochemical properties, major synthetic methods, and applications in photocatalysis, electrocatalysis, and adsorption, among others. This systematic review effectively summarises both the advantages and shortcomings associated with C3N5-based materials for energy and environmental applications, thus offering researchers focussed on CxNy-materials an in-depth understanding of those based on C3N5. Finally, considering the limitations and deficiencies of C3N5-based materials, we have proposed enhancement schemes and strategies, while presenting personal perspectives on the challenges and future directions for C3N5. Our ultimate aim is to provide valuable insights for the research community in this field.

II-Scheme Heterojunction Frameworks Based on Covalent Organic Frameworks and HKUST-1 for Boosting Photocatalytic Hydrogen Evolution

Covalent organic frameworks (COFs) are one type of promising polymer semiconductors in solar-driven hydrogen production, but majority of COFs-based photocatalytic systems show low photocatalytic efficiency owing to lack of metal active sites. Herein, we reported II-Scheme heterojunction frameworks based on COF (TpPa-1) and metal-organic framework (HKUST-1) for highly efficient hydrogen production. The coordination bonding directed self-assembly of HKUST-1 on the surface of TpPa-1 endows the heterojunction frameworks (HKUST-1/TpPa-1) with strong interface interaction, optimized electronic structures and abundant redox active sites, thus remarkably boosting photocatalytic hydrogen evolution. The hydrogen evolution rate for optimal HKUST-1/TpPa-1 is as high as 10.50 mmol g-1 h-1, which is significantly enhanced when compared with that of their physical mixture (4.13 mmol g-1 h-1), TpPa-1 (0.013 mmol g-1 h-1) and Pt-based counterpart (6.70 mmol g-1 h-1). This work offers a facile approach to the construction of noble-metal-free II-Scheme heterojunctions based on framework materials for efficient solar energy conversion.

A novel visible-light-driven Z-scheme C3N5/BiVO4 heterostructure with enhanced photocatalytic degradation performance

As a visible-light response semiconductor materials, bismuth vanadate (BiVO4) is extensively applied in photodegradation organic dye field. In this study, we synthesized C3N5 nanosheets and coupled with decahedral BiVO4 to construct a Z-scheme C3N5/BiVO4 heterostructure with close interface contact. By introducing C3N5 into BiVO4, the built Z-scheme transfer pathway provides silky channel for charge carrier migration between different moieties and enables photoexcited electrons and holes accumulated on the surface of BiVO4 and C3N5. The accelerated separation of charge carriers ensures C3N5/BiVO4 heterostructures with a powerful oxidation capacity compared with pure BiVO4. Due to the synergistic effect in Z-scheme heterostructure, the C3N5/BiVO4 demonstrated an improved photodegradation ability of rhodamine B (RhB) and methylene blue (MB) that of bare BiVO4.

Enhanced Charge Transfer via S-Scheme Heterojunction Interface Engineering of Supramolecular SubPc-Br/UiO-66 Arrays for Efficient Photocatalytic Oxidation

Constructing heterojunction of supramolecular arrays self-assembled on metal-organic frameworks (MOFs) with elaborate charge transfer mechanisms is a promising strategy for the photocatalytic oxidation of organic pollutants. Herein, H12 SubPcB-Br (SubPc-Br) and UiO-66 are used to obtain the step-scheme (S-scheme) heterojunction SubPc-Br/UiO-66 for the first time, which is then applied in the photocatalytic oxidation of minocycline. Atomic-level B-O-Zr charge-transfer channels and van der Waals force connections synergistically accelerated the charge transfer at the interface of the SubPc-Br/UiO-66 heterojunction, while the establishment of the B-O-Zr bonds also led to the directional transfer of charge from SubPc-Br to UiO-66. The synergy is the key to improving the photocatalytic activity and stability of SubPc-Br/UiO-66, which is also verified by various characterization methods and theoretical calculations. The minocycline degradation efficiency of supramolecular SubPc-Br/UiO-66 arrays reach 90.9% within 30 min under visible light irradiation. The molecular dynamics simulations indicate that B-O-Zr bonds and van der Waals force contribute significantly to the stability of the SubPc-Br/UiO-66 heterojunction. This work reveals an approach for the rational design of semiconducting MOF-based heterojunctions with improved properties.

Isotype heterojunction: tuning the heptazine/triazine phase of crystalline nitrogen-rich C3N5 towards multifunctional photocatalytic applications

Photocatalytic technology has been well studied as a means to achieve sustainable energy generation through water splitting or chemical synthesis. Recently, a low C/N atomic ratio carbon nitride allotrope, C3N5, has been found to be highly prospective due to its excellent electronic properties and ample N-active sites compared to g-C3N4. Tangentially, crystalline g-C3N4 has also been a prospective candidate due to its improved electron transport and extended π-conjugated system. For the first time, our group successfully employed a one-step molten salt calcination method to prepare novel N-rich crystalline C3N5 and elucidate the effect of calcination temperature on the heptazine/triazine phase. Calcination temperatures of 500 °C (CC3N5-500) and 550 °C (CC3N5-550) lead to crystalline carbon nitride with both heptazine and triazine phases, forming an intimate isotype heterojunction for robust interfacial charge separation. An excellent photocatalytic hydrogen evolution rate (359.97 μmol h-1; apparent quantum efficiency (AQE): 12.86% at 420 nm) was achieved using CC3N5-500, which was 15-fold higher than that of pristine C3N5. Furthermore, CC3N5-500 exhibited improved activity for simultaneous benzyl alcohol oxidation and hydrogen production, as well as H2O2 production (AQE: 9.49% at 420 nm), signifying its multitudinous photoredox capabilities. Moreover, the recyclability tests of the optimal CC3N5-500 on a 3D-printed substrate also showed a 92% performance retention after 4 cycles (16 h). This highlights that crystalline C3N5 significantly augmented the reaction performance for diverse multifunctional solar-driven applications. As such, these results serve as a guide toward the structural tuning of 2D metal-free carbon nanomaterials with tunable crystallinity toward achieving boosted photocatalysis.

Introducing a Pyrazinoquinoxaline Derivative into a Metal-Organic Framework: Achieving Fluorescence-Enhanced Detection for Cs+ and Enhancing Photocatalytic Activity

Conventional photoresponsive materials have low photon utilization due to irregular distribution of photoactive groups, which severely limits the related real applications. Metal-organic frameworks (MOFs) can modulate the regular arrangement of functional groups to improve the electron transport paths and enhance the photon utilization, which provides strong support for the development of photoactive materials with excellent performance. In this work, one effective strategy for constructing a photoactive MOF had been developed via the utilization of Cd2+ and pyrazinoquinoxaline tetracarboxylic acid. The structural advantages of the Cd-MOF, such as a porous structure, abundant subject-object interaction sites, and a stable framework, ensure the prerequisite for various applications, while the better synergistic effect of Cd3 clusters and the pyrazinoquinoxaline derivative ensures efficient electron transfer efficiency. Therefore, by virtue of these structural advantages, the Cd-MOF can achieve fluorescence quenching detection for a variety of substrates, such as Fe3+, Cr2O72-, MnO4-, nitrofuran antibiotics, and TNP explosives, while fluorescence enhancement detection can be achieved for halogen ions, Cs+, Pb2+, and NO2-. In addition, the Cd-MOF can be used as a photocatalyst to successfully achieve the photocatalytic conversion of benzylamine to N-benzylbenzimidate under mild conditions. Thus, the Cd-MOF as a whole shows the possibility of application as a diverse fluorescence detection and photocatalyst and also illustrates the feasibility of preparing high-performance photoactive materials using the pyrazinoquinoxaline derivative.

Metal-Organic Framework Based on Pyrazinoquinoxaline Tetracarboxylic Acid for Fluorescence Sensing for Nitro Explosives

The rapid and selective detection of nitro explosives has become one of the current urgent environmental and safety issues. Fluorescent metal-organic frameworks (MOFs) provide strong support for the development of photoactive materials with excellent sensing performances. In this work, Zn2+ and pyrazinoquinoxaline tetracarboxylic acid with high nitrogen content were selected to construct a MOF structure termed Zn-MOF, which had excellent optical properties. The fluorescence sensing performance of Zn-MOF for nitro explosives was also investigated. The structural advantages of Zn-MOF, such as its porous structure, abundant host-guest interaction sites, and stable framework, ensure the prerequisites for various applications. Zn-MOF is not only capable of responding to a wide range of substrates, such as Fe3+, Cr2O72-, and MnO4-, to achieve fluorescence quenching detection but also able to achieve sensitive fluorescence sensing behavior for nitro explosives. In particular, for trinitrotoluene, the Ksv value can reach 8.72 × 103 M-1. The results show that the introduction of pyrazinoquinoxaline groups into MOFs can be an effective strategy for the preparation of highly efficient fluorescent sensing materials for nitro explosives.

Nitrogen-rich carbon nitride (C3N5) coupled with oxygen vacancy TiO2 arrays for efficient photocatalytic H2O2 production

Developing efficient and facilitated recycling photocatalysts for H2O2 formation is an ideal strategy for solar-to-chemical energy conversion. In this work, we synthesized ultrathin C3N5 nanosheets through the process of thermal polymerization and polyvinylpyrrolidone (PVP)-assisted solvent exfoliation. Subsequently, the obtained ultrathin C3N5 nanosheets were tightly attached to the surface of TiO2-x arrays, resulting in an enhanced photocatalytic H2O2 production rate. The density functional theory (DFT) calculations demonstrate that an internal electric field (IEF) is generated between the TiO2-x array and the ultrathin C3N5 due to the different work functions. The presence of IEF provides an additional driving force for carrier separation and transfer in the heterointerface. Benefitting from this unique strategy, the optimal heterojunction obtains the highest H2O2 formation rate (2.93 μmol/L/min), which is about 4.1 times than that of TiO2-x arrays. The rotating disk electrode (RDE) analysis manifests H2O2 formation through 2e--dominated oxygen reduction reaction (ORR). This research provides an innovative strategy for assembling a type-II heterojunction with a useful IEF for efficient photocatalytic H2O2 production.

Promoted Photocatalytic Hydrogen Evolution by Tuning the Electronic State of Copper Sites in Metal-Organic Supramolecular Assemblies

The electronic state in terms of charge and spin of metal sites is fundamental to govern the catalytic activity of a photocatalyst. Herein, we show that modulation of the electronic states of Cu sites, without changing the coordination environments, of two metal-organic supramolecular assemblies based on π⋅⋅⋅π stacking can significantly improve photocatalytic activity. The use of these heterogeneous photocatalysts, without using noble metal cocatalysts, resulted in an increase of the hydrogen production rate from 522 to 3620 μmol h-1  g-1 . A systematical analysis revealed that the charge density and spin density of the metal centers are efficiently modulated via the modulation of the coordination fields around active copper (II) centers by the variation of the non-coordination groups of terminal ligands, leading to the significant enhancement of photocatalytic activity. This work provides an insight into the electronic state of active metal centers for designing high-performance photocatalysts.

Metal-organic frameworks (MOFs) for energy production and gaseous fuel and electrochemical energy storage applications

The increasing energy demands in society and industrial sectors have inspired the search for alternative energy sources that are renewable and sustainable, also driving the development of clean energy storage and delivery systems. Various solid-state materials (e.g., oxides, sulphides, polymer and conductive nanomaterials, activated carbon and their composites) have been developed for energy production (water splitting-H2 production), gaseous fuel (H2 and CH4) storage and electrochemical energy storage (batteries and supercapacitors) applications. Nevertheless, the low surface area, pore volume and conductivity, and poor physical and chemical stability of the reported materials have resulted in higher requirements and challenges in the development of energy production and energy storage technologies. Thus, to overcome these issues, the development of metal-organic frameworks (MOFs) has attracted significant attention. MOFs are a class of porous materials with extremely high porosity and surface area, structural diversity, multifunctionality, and chemical and structural stability, and thus they can be used in a wide range of applications. In the present review, we precisely discuss the interesting properties of MOFs and the various methodologies for their synthesis, and also the future dependence on the valorization of solid waste for the recovery of metals and organic ligands for the synthesis of new classes of MOFs. Subsequently, the utilization of these interesting characteristics for energy production (water splitting), storage of gaseous fuels (H2 and CH4), and electrochemical storage (batteries and supercapacitors) applications are described. However, although MOFs are efficient materials with versatile uses, they still have many challenges, limiting their practical applications. Therefore, finally, we highlight the challenges associated with MOFs and show the way forward in overcoming them for the development of these highly porous materials with large-scale practical utility.

Plasma synthesis of oxygen vacancy-rich CuO/Cu2(OH)3NO3 heterostructure nanosheets for boosting degradation performance

Defect regulation and the construction of a heterojunction structure are effective strategies to improve the catalytic activity of catalysts. In this work, the rapid conversion of CuO to Cu2(OH)3NO3 was achieved by fixing nitrogen in air as NO3- using dielectric barrier discharge (DBD) plasma. This innovative approach resulted in the successful synthesis of a CuO/Cu2(OH)3NO3 nanosheet heterostructure. Notably, the samples prepared using plasma exhibit thinner thickness and larger specific surface area. Importantly, oxygen vacancies are introduced, simultaneously forming heterojunction interfaces within the CuO/Cu2(OH)3NO3 structure. CuO/Cu2(OH)3NO3 using plasma effectively degraded 96% of methyl orange within 8 min in the dark. The degradation rate is 81 and 23 times that of CuO and Cu2(OH)3NO3 using hydrothermal methods, respectively. The high catalytic activity is attributed to the large specific surface area, the abundance of active sites, and the synergy between oxygen vacancies and the strong heterojunction interfacial interactions, which accelerate the transfer of electrons and the production of reactive oxygen species (˙O2- and ˙OH). The mechanism of plasma preparation was proposed on account of microstructure characterization and online mass spectroscopy, which indicated that gas etching, gas expansion, and the repulsive force of electrons play key roles in plasma exfoliation.

Plasmonic Au Nanoparticle of a Au/TiO2-C3N4 Heterojunction Boosts up Photooxidation of Benzyl Alcohol Using LED Light

Plasmonic Au nanoparticles (NPs) employing localized surface plasmon resonance excitation have exhibited superior visible light absorption for many organic transformations. In this work, we prepared a ternary composite catalyst comprising plasmonic Au NPs and a 2D/2D TiO₂-C₃N₄ heterojunction via a photoreduction method of chloroauric acid in the presence of TiO₂-C₃N₄. The introduction of plasmonic nanogold particles embedded onto the TiO₂ surface of the TiO₂-C₃N₄ heterojunction can significantly improve the photocatalytic performance during photooxidation of benzyl alcohol to benzaldehyde under mild conditions (1 bar air, white LED irradiation at ambient temperature). The productivity over Au/TiO₂-C₃N₄ (0.25 mmol_reacted BA g_cat.^-1 h^-1) is found to be ∼5.6, 8.3, and 8.2-fold of these over the Au/TiO₂, TiO₂-C₃N₄, and C₃N₄-Au-TiO₂ heterojunctions, respectively. Trapping experiments and electron spin resonance (ESR) spectroscopy confirm that the superoxide (^·O₂^-) and hydroxyl radicals (^·OH) act as the reactive oxygen species during photooxidation. Furthermore, the experimental results combined with density functional theory calculations reveal that the chemisorbed benzyl alcohol population, surface oxygen vacancies, and lifetime of photoexcited electrons and holes are largely improved by plasmonic Au NPs. This study on nanogold composites provides some hints for developing new efficient and practical photocatalysts.

3D Lanthanide Neodymium Porphyrin Metal-Organic Framework for Photocatalytic Oxidation of Styrene

A novel three-dimensional lanthanide porphyrin-based MOF (Nd-PMOFs) was synthesized by using tetracarboxyphenyl porphyrin as the ligand and the lanthanide Nd as the coordination metal. Its specific crystal structure information was obtained by single-crystal diffraction with the space group C2/c and the empirical formula C₇₂H₄₅N₆Nd₂O_15.25. This new Nd porphyrin-based MOF with an organic framework formed by a unique coordination method enables the effective separation of photogenerated electrons and holes under photoluminescence, giving it excellent photocatalytic property which could be verified by the characterization data. The photocatalytic performance was examined by taking tert-butyl hydroperoxide as the oxidant and Nd-PMOFs as the catalyst for photocatalytic oxidation of styrene to benzaldehyde with 91.4% conversion and 81.2% benzaldehyde selectivity under optimal reactions, which surpasses most of the results reported in the literature. Several styrenes with other substituents were screened to explore the general applicability of Nd-PMOF for photocatalysis of styrene, among which Nd-PMOFs also exhibited excellent photocatalytic performance. This work offers the possibility to apply lanthanide organometallic frameworks, which are widely used in fluorescent materials, to photocatalysis. In addition, it also provides a new method for the catalytic generation of benzaldehyde from styrene that is consistent with the needs of modern green development.

Methylthio-functionalized UiO-66 to promote the electron-hole separation of ZnIn2S4 for boosting hydrogen evolution under visible light illumination

Solar-driven water splitting offers a leading-edge approach to storing abundant and intermittent solar energy and producing hydrogen as a clean and sustainable energy carrier. More importantly, constructing well-designed photocatalysts is a promising approach to develop clean hydrogen energy. In this paper, flower spherical UiO-66-(SCH₃)₂/ZnIn₂S₄ (UiOSC/ZIS) photocatalysts are successfully synthesized by a simple two-step hydrothermal method, and they exhibit high hydrogen production activity in light-driven water splitting. The optimized 30-UiOSC/ZIS (the content of UiOSC was 30 mg) composite exhibits optimal hydrogen production activity with a hydrogen production of 3433 μmol g^-1 h^-1, which is 5 and 235 times higher than that of pure ZIS and UiOSC, respectively. In addition, a long-cycling stability test has shown that the UiOSC/ZIS composite has good stability and recyclability. Experimental and characterization results show the formation of a type-II heterojunction between UiOSC and ZIS. This effectively suppresses the recombination of electrons-holes and promotes the carrier transfer, thus significantly improving the hydrogen production performance. This research further promotes the application of UiO-66-(SCH₃)₂ in the field of photocatalytic hydrogen production and provides a reference for the rational design of UiO-66-based composite photocatalysts.

Metal-organic frameworks in photocatalytic Z-scheme heterojunctions: an emerging technology

There is an urgent need for cleaner production processes for chemicals. An efficient and promising alternative for such reactions is heterogeneous photocatalysis, which works on the principle of converting (visible) light, including solar energy, into chemical energy. To that end, properly designed semiconductor based photocatalysts are necessary to trigger the photocatalytic reactions. Many commonly used photocatalysts have too large bandgaps (3-3.4 eV) to use visible light and a too low surface area for efficient production. Metal-organic frameworks (MOFs) have emerged as an encouraging class of materials for photocatalytic applications due to their (i) large surface area and porosity that facilitate adsorption towards chemicals, (ii) tunable crystallinity and optical and electronic properties for efficient light absorption in the visible region, (iii) tunable composition and functionality that make them versatile photocatalysts for a wide range of reactions, and (iv) facile development of composites with other semiconductors to produce Z-scheme heterojunctions that can effectively suppress the recombination of photogenerated charges. Ongoing research has started focusing on the judicious construction of Z-scheme heterojunctions in MOFs, to mimic natural photosynthesis, such that the MOF photocatalysts have higher light harvesting capacity, spatially separated reductive and oxidative active sites, and well-preserved redox ability. This review provides a concise compilation of the recent progress in the development and applications of MOF-based Z-scheme photocatalysts, their advanced characterization, and future perspectives for further advancements.

Engineered g-C3N5-Based Nanomaterials for Photocatalytic Energy Conversion and Environmental Remediation

Photocatalysis plays a vital role in sustainable energy conversion and environmental remediation because of its economic, eco-friendly, and effective characteristics. Nitrogen-rich graphitic carbon nitride (g-C₃N₅) has received worldwide interest owing to its facile accessibility, metal-free nature, and appealing electronic band structure. This review summarizes the latest progress for g-C₃N₅-based photocatalysts in energy and environmental applications. It begins with the synthesis of pristine g-C₃N₅ materials with various topologies, followed by several engineering strategies for g-C₃N₅, such as elemental doping, defect engineering, and heterojunction creation. In addition, the applications in energy conversion (H₂ evolution, CO₂ reduction, and N₂ fixation) and environmental remediation (NO purification and aqueous pollutant degradation) are discussed. Finally, a summary and some inspiring perspectives on the challenges and possibilities of g-C₃N₅-based materials are presented. It is believed that this review will promote the development of emerging g-C₃N₅-based photocatalysts for more efficiency in energy conversion and environmental remediation.

Dual-Ligand Ti-MOFs with Push-Pull Effect for Photocatalytic H2 Production

Enhancing the photogenerated electrons transfer efficiency is crucial for photocatalytic reactions. Herein, a dual-ligand-induced push-pull effect was manipulated to intensify the transfer of photogenerated electrons between organic ligands and metal clusters using NH₂-MIL-125(Ti), a kind of Ti-based metal-organic framework (MOF), as the model system. The dual-ligand MOF, NH₂/Cl-MIL-125, was designed and synthesized based on the Hammett constant (σ_m), in which -NH₂ (σ_m = -0.16) and -Cl (σ_m = 0.37) were selected as the electron-pushing group and the electron-pulling group, respectively. Meanwhile, -CH₃ (σ_m = -0.07, electron-pushing) and -H (σ_m = 0, neither electron-pushing nor electron-pulling) were selected as the reference groups to prepare NH₂/CH₃-MIL-125 and NH₂/H-MIL-125, respectively, to validate the electron push-pull effect. NH₂/Cl-MIL-125 (5.32 mmol g^-1 h^-1) exhibits a higher photocatalytic H₂ evolution activity than single-ligand NH₂-MIL-125 (1.93 mmol g^-1 h^-1), NH₂/CH₃-MIL-125 (4.45 mmol g^-1 h^-1), and NH₂/H-MIL-125 (4.73 mmol g^-1 h^-1) under full-spectrum irradiation. The result can be attributed to the electron push-pull effect between -NH₂ and -Cl, which boosts the electron transfer along the ligand-metal-ligand direction. Our dual-ligand-induced push-pull strategy for enhancing the electron transfer may offer some novel insights into the rational design and synthesis of photocatalysts for many other reactions.