Particulate Photocatalysts for Light-Driven Water Splitting: Mechanisms, Challenges, and Design Strategies

General self-fission strategy via supramolecular self-assembly for high-yield and cost-effective synthesis of g-C3N4 nanostructures for photocatalytic hydrogen evolution

Graphitic carbon nitride (g-C3N4) is one of the most promising candidates as a photocatalyst. However, the practical application of g-C3N4 has been hindered by its high-cost, low-yield synthesis methods. Herein, we develop a high-yield, cost-effective synthesis strategy for fabricating g-C3N4 nanostructures by low-temperature (430 °C) air pre-etching, which can induce the self-fission of supramolecular precursors (SMPs). This new synthesis strategy can achieve a production yield of ∼35 wt% and ∼41 wt% for g-C3N4 nanosheets (CNs) and sulfur-doped g-C3N4 nanotubes (SCNt), notably higher than the yields of conventional methods (<10 wt%). The underlying mechanism for the higher production yield is that this low-temperature etching method can effectively slow down the decomposition rate of SMPs and in this way promote their polymerization into g-C3N4. The pre-etching method can significantly increase the specific surface areas of the obtained sample, resulting in higher BET values of CNs (132.7 m2 g-1) and SCNt (112.9 m2 g-1), which are 2.5 and 3.2 times those for the samples without pre-etching treatment. Moreover, the as-prepared nanostructures exhibit remarkable photocatalytic performance, with hydrogen production rates of 1464.2 and 2883.4 μmol h-1 g-1 for CNs and SCNt, respectively, achieving 10.2- and 20.1-fold enhancements over bulk g-C3N4. In addition, the successful synthesis of nanosheets from 2,4,6-triaminopyrimidine-cyanuric acid and commercially available melamine-cyanurate precursors further demonstrates the broad applicability of this strategy. Notably, the successful synthesis of 70 g of CNs confirms that the proposed strategy is capable of large-scale production of novel photocatalysts. This scalable and economical strategy lays a solid foundation for future industrial applications of g-C3N4-based photocatalysts.

Vacancy engineering of single-layer lateral heterojunction for efficient Z-scheme photocatalytic water reduction

Optimizing the Z-scheme charge transmission of lateral heterojunction constructed by single-layer (SL) nanosheets is an appealing yet challenging tactics to boost photocatalytic efficiency for solar fuel production and environmental remediation. Herein, we reported the edge/corner-specific growth of SL ZnIn2S4-MoSe2 lateral heterojunction with intensified Z-scheme charge transmission through intimate Mo-S connection and S vacancies (VS) engineering. The Mo-S chemical bonds inside ZnIn2S4-MoSe2 heterojunction offer a speedy channel for Z-scheme charge transmission as confirmed via surface photovoltage spectroscopy, radical production, and in situ photo-irradiated X-ray photoelectron spectroscopy tests as well as density functional theory calculation, while VS engineering enlarges Fermi level difference between ZnIn2S4 and MoSe2 to strengthen internal electric field and driving force for photo-carriers transmission, resulting in an excellent photocatalytic H2 evolution (PHE) capability. Isotopic labeling experiment verified the photocatalytic water reduction by ZnIn2S4-MoSe2 heterojunction, which exhibited a visible-light-driven PHE rate up to 55.70 mmol g-1h-1 (or 550.70 μmol/10 mg/h) with an apparent quantum yield reaching 38.9 % at 400 nm. Moreover, the ZnIn2S4-MoSe2 heterojunction also possessed a robust stability during long-term photocatalytic reaction. The research findings could inspire new idea to enhance the photocatalytic capability of two-dimensional (2D) heterojunction by strengthening Z-scheme charge transmission at atomic level.

Efficient visible-light-driven photocatalytic overall water-splitting on CuZnGaS/BiVO4 S-scheme heterojunctions

The technique of photocatalytic overall water splitting has emerged as a highly promising and feasible approach for achieving renewable energy conversion. This method effectively transforms solar energy into hydrogen and oxygen, contributing to sustainable energy development. In this study, a CuZnGaS/BiVO4 S-scheme heterojunction system was synthesized using a simple hydrothermal method to enhance photocatalytic water splitting efficiency. The system, incorporating 17 wt% CuZnGaS, exhibited outstanding performance, achieving hydrogen and oxygen evolution rates of 163.3 μmol g-1 h-1 and 69.4 μmol g-1 h-1, respectively, while maintaining stability over a 20-h period. Notably, a quantum efficiency of 0.0222 % at a 365 nm wavelength was accurately measured and documented. The formation of an S-scheme heterojunction within the system significantly accelerates the separation of photogenerated carriers and effectively extends the lifetime of charge carriers. These findings provide valuable insights for designing advanced systems for long-term solar energy conversion.

Cu doping induced asymmetric Cu-Vs-In active sites in In2S3 for efficient photocatalytic C2H4 conversion from CO2

Selective reduction of CO2 to value-added C2-chemical fuels, (such as C2H4) holds great promise for directly converting solar energy into chemical energy. However, the weak adsorption of CO2 on photocatalysts directly affects its conversion efficiency. Here we use Cu doping to create asymmetric Cu-S-vacancies-In (Cu-VS-In) sites in the two-dimensional In2S3, which greatly improves CO2 adsorption, achieving efficient photocatalytic reduction of CO2 to C2H4. Experiments and DFT (Density functional theory) calculations show that Cu doping, due to the influence of charge balance, will induce S vacancies and change the coordination environment around In atoms. This changes the mode of CO2 adsorption and decreases the adsorption energy of CO2. The asymmetric Cu-VS-In sites promote charge transfer to the CO bond, increasing catalytic activity. The concept of using asymmetric sulfur vacancies to simultaneously regulate both adsorption and charge transfer between catalysts and reactants provides a design guide for the development of advanced catalytic materials aimed at photocatalytic CO2 reduction.

The hierarchical assembly of ultra-thin polymeric carbon nitride nanosheet on LaOBr for enhanced photocatalytic overall water splitting

Photocatalytic water splitting represents a promising approach for solar energy conversion and hydrogen production. Polymeric carbon nitride (PCN) exhibits potential but suffers from charge recombination and low specific surface area. This study introduces a novel LaOBr@PCN one-photon excited heterojunction designed to mitigate these challenges. By anchoring Melon, a PCN precursor, onto LaOBr through acid-base coordination followed by in-situ thermal polymerization, three-dimensional hierarchical PCN nanosheets are fabricated on LaOBr microplates. This structure increases the specific surface area, exposes more active sites, enhances light-harvesting ability, and improves charge carrier separation. Consequently, the optimized LaOBr@PCN achieves hydrogen and oxygen production rates of 69.9 μmol/h and 34.7 μmol/h, respectively. This work provides a viable strategy for developing advanced PCN-based composite photocatalysts.

D1-D2-A ternary conjugated microporous polymers synthesized via direct CH arylation for enhancing photocatalytic hydrogen evolution

Conjugated microporous polymers (CMPs), featured by broad tunability in molecule design, structure and properties, have been widely used as photocatalysts for water splitting to produce hydrogen. However, the conventional donor-acceptor (D-A) binary CMPs have not achieved satisfactory performance so far. In this contribution, a series of D1-D2-A ternary CMPs are synthesized by the atom-economical direct CH arylation polymerization (DArP), wherein the dibenzo[b,d]thiophene-S,S-dioxide (BTDO), tetraphenylethylene (TPE) and 3,4-ethylenedioxythiophene (EDOT) units serve as the acceptor (A), donor D1 and donor D2, respectively. The structure-property correlations of the CMPs are systematically investigated by optical, electrochemical, water contact angle, and hydrogen production performance tests, revealing that the ternary D1-D2-A CMPs can maximize hydrophilicity and charge separation through the synergistic effect of BTDO, EDOT, and TPE building blocks. As a result, the ternary CMP-3 with an optimal D/A ratio achieves the highest photocatalytic hydrogen evolution rate up to 81.4 mmol g-1 h-1 without the aid of Pt co-catalyst, which has a 26-fold and 101-fold improvement compared to the pristine D1-A and D1-D2 binary CMPs, respectively. Meanwhile, a high apparent quantum yield of 11.1 % at 500 nm is successfully achieved. Density functional theory calculation discloses that D1-D2-A ternary CMPs possess the desirable molecular geometry and superior charge separation. This work provides a new design and synthetic strategy for the high-performance CMP-based photocatalysts.

Cobalt-modified crystalline carbon nitride homojunction with enhanced interfacial charge separation for photocatalytic pure water splitting

Photocatalytic hydrogen production in pure water without oxygen precipitation is highly effective owing to the minimal efficiency of water oxidation for oxygen generation and the complexity of the reaction, yet it presents a significant hurdle. Here, we report the preparation of crystalline carbon nitride (CCN) homojunction-anchored Co atoms using the molten salt and reflux method. Our findings indicate that elevated temperature during ionothermal synthesis promotes the phase transition of poly(heptazine) imides (PHI) to poly(triazine) imides (PTI), and the homogeneous junction formed in this process promotes exciton dissociation as well as carrier migration through the built-in electric field formed by the semi-coherent interface. During water splitting, the Co atom on CCN can modulate the generation of H2O2 and insitu decomposition to produce •OH. Consequently, the refined Co-modified crystalline carbon nitride homojunction exhibited an impressive hydrogen production rate of 425.81 μmol g-1 h-1 under visible light (λ > 400 nm), which provides new ideas for a green and clean process of coupled photocatalytic hydrogen production.

Preparation and Photocatalytic Performance Study of TiO2-TMP Composites Under Effect of Crystal Structure Modulation

Nano-titanium dioxide (TiO2) is currently the most widely studied photocatalyst. However, its rapid recombination of photogenerated carriers and narrow range of light absorption have limited its development. Crystal form regulation and polymer modification are important means for improving the photocatalytic activity of single-phase materials. In this paper, TiO2 materials of different crystal forms were prepared by changing the synthesis conditions, and they were compounded with trimesoyl chloride-melamine polymers (TMPs) by the hydrothermal synthesis method. Then, their photocatalytic performance was evaluated by degrading methylene blue (MB) under visible light. The mechanisms of influence of TiO2 crystal form on the photocatalytic activity of TiO2-TMP were explored by combining characterization and theoretical calculation. The results showed that the TiO2 crystal form, through interface interaction, the built-in electric field intensity of the heterojunction, and active sites, affected the interface charge separation and transfer, thereby influencing the photocatalytic activity of TiO2-TMP. In the 4T-TMP photocatalytic system, the degradation rate of MB was the highest. These studies provide theoretical support for understanding the structure-property relationship of the interfacial electronic coupling between TiO2 crystal forms and TMP, as well as for developing more efficient catalysts for pollutant degradation.

Engineering bidirectional charge transport channels boosts solar driven sulfion oxidation upgrading coupled with hydrogen production

The inefficient charge separation and transport remains a bottleneck in photocatalysis. While various strategies have been explored to improve this process, most focus on single-sided modulation either the conduction-band electrons or valence-band holes, limiting overall improvement. Herein, an innovative coupling modification approach is adopted where Ru and α-Fe2O3 (FO) nanoparticles are integrated onto ZnIn2S4 (ZIS) to prepare Ru/ZnIn2S4/α-Fe2O3, and constructs dual charge transfer pathways for electrons and holes. This bidirectional channel configuration significantly enhances carrier separation and accumulation, enabling Ru as an electron (e-) mediator and FO as a hole (h+) extraction facilitator, driving simultaneous redox reactions, and enabling substantial improvement in the photocatalytic sulfur oxidation process coupled with hydrogen generation. This approach enhances interface charge separation/spatial accumulation and provides valuable guidance for designing and developing advanced high-efficiency photocatalytic systems.

Improved photocatalytic performance of double-walled TeSi nanotubes: a hybrid density functional calculation

The geometric and electronic structures of TeSi nanotubes were examined using the HSE06 method with Gaussian basis sets. Single-walled (SW) and double-walled (DW) TeSi NTs with (n,n) and (n,n)@(2n,2n) chiralities were investigated for photocatalytic performance. SWNTs exhibit an indirect band gap (∼2.55 eV) and an improved solar-to-hydrogen (STH) conversion efficiency (3.68-4.87%) compared to single-layered TeSi (2.41%). Moreover, strain engineering and heterostructures were used to boost the efficiency of photocatalytic H2O splitting. For strain engineering, our findings indicate that uniaxial strain modifies the band gap, with the band gap of the (30,30) SWNT reaching a 1.72 eV minimum under -5% strain, while the STH conversion efficiency is enhanced through compressive strain. For heterostructure NTs, the STH conversion efficiency was 10.29-15.13%, and the DWNTs showed type II band structure features with smaller band gaps compared to SW ones. Additionally, the larger-diameter DWNTs displayed promising band edge locations for photocatalytic hydrolysis redox potential with pH ranging from 0 to 7. These findings explain the mechanism of the enhanced photocatalytic performance of DWNTs over SWNTs.

Chemistry of Materials Underpinning Photoelectrochemical Solar Fuel Production

Since its inception, photoelectrochemistry has sought to power the generation of fuels, particularly hydrogen, using energy from sunlight. Efficient and durable photoelectrodes, however, remain elusive. Here we review the current state of the art, focusing our discussion on advances in photoelectrodes made in the past decade. We open by briefly discussing fundamental photoelectrochemical concepts and implications for photoelectrode function. We next review a broad range of semiconductor photoelectrodes broken down by material class (oxides, nitrides, chalcogenides, and mature photovoltaic semiconductors), identifying intrinsic properties and discussing their influence on performance. We then identify innovative in situ and operando techniques to directly probe the photoelectrode|electrolyte interface, enabling direct assessment of structure-property relationships for catalytic surfaces in active reaction environments. We close by considering more complex photoelectrochemical fuel-forming reactions (carbon dioxide and nitrogen reduction, as well as alternative oxidation reactions), where product selectivity imposes additional criteria on electrochemical driving force and photoelectrode architecture. By contextualizing recent literature within a fundamental framework, we seek to provide direction for continued progress toward achieving efficient and stable fuel-forming photoelectrodes.

Photocatalytic oxidation of glycerol with red light employing quinacridone sensitized TiO2 nanoparticles

Photocatalytic nanomaterials combining organic dyes and inorganic semiconductor nanoparticles (NPs) are extensively investigated for light-driven production of solar fuels and for conversion of organic feedstocks. However, their applications for the valorization of abundant raw materials by exploiting low-energy visible light remain limited. In this study, we report a facile preparation of TiO2 nanoparticles sensitized with a quinacridone (QA) industrial pigment for the aqueous oxidation of glycerol to glyceraldehyde with red light (λ = 620 nm), reaching 47.5 ± 5.0 μmol gNP -1 h-1 of productivity and 80% selectivity in the presence of TEMPO co-catalyst. The hybrid material outperforms the single components and shows recyclability up to at least 5 additional times under red light while maintaining intact productivity; furthermore, it demonstrates versatility by operating also under green, yellow or white light irradiation. We believe that this work will provide a new avenue for using industrial pigment-sensitized materials in photocatalysis exploiting low energy light, providing novel strategies for the future development of this field.

Boosting Dual Photocatalytic Activity of Hydrogen Production and Selective Coupling of Benzyl Alcohol Using Assembled Poly(ionic liquid)s and CdS Quantum Dots

Dual photocatalysis converts renewable solar energy into clean fuel and concomitantly value-added chemical synthesis through hydrogen generation and selective organic transformation, using semiconductor catalysts. The catalytic activity of solitary component semiconductor photocatalysts is impeded by their inefficient charge separation and transfer. We, herein, present a facile method, electrostatic assembly, to create hybrid photocatalysts that consist of CdS quantum dots and non-conjugated poly(ionic liquid)s including poly(diallyl dimethyl ammonium bromide) (P(DADMA)) and poly(1-ethyl-3-vinylimidazolium bromide) (P(VEIM)). Poly(ionic liquid)s acted as electron donors to CdS, resulting in an increase in charge separation and transportation in CdS/P(DADMA) and CdS/P(VEIM) hybrids, as demonstrated by experimental and computational results. The optimal photocatalysis of benzyl alcohol (BA) in water was achieved by CdS/P(DADMA) under 12 h LED370 illumination in a nitrogen-atmosphere. This process produced 12.8 mmol gcat -1 h-1 of H2 and 12.5 mmol gcat -1 h-1 of racemic hydrobenzoin (HB) with 99 % selectivity. In photocatalysis, CdS/P(DADMA) outperformed CdS/P(VEIM) and CdS by a significant margin. Our photocatalytic system enabled the BA-to-HB conversion in water, of which the reaction is commonly sluggish due to a mass transfer constraint. The insightful DFT calculation confirmed that poly(ionic liquid)s may stabilize active intermediate species in the process, significantly enhancing photogenerated charge expedition and photocatalytic performance.

Self-Trapped Excitons Activate Pseudo-Inert Basal Planes of 2D Organic Semiconductors for Improved Photocatalysis

2D organic semiconductors are widely considered superior photocatalysts due to their large basal planes, which host abundant and tunable reaction sites. However, here, it is discovered that these basal planes can be pseudo-inert, fundamentally challenging conventional design strategies that assume uniform activity on the surface of 2D organic semiconductors. Using 2D potassium-poly (heptazine imide) (KPHI) for hydrogen peroxide photocatalysis as a model, it is demonstrated that the pseudo-inertness of basal planes stems from preferential exciton transport to edges, instead of interlayer transport in highly ordered structures. Thus, their dimension reduction enables controlled localization of exciton due to the self-trapping mechanism, whereby the basal planes can transform from pseudo-inert state into active catalytic sites. With this knowledge, a modified 2D KPHI capable of generating 35 mmol g-1 h-1 of H2O2, which is over 350% increase compared to pristine KPHI, is reported. More interestingly, the activated basal planes promote H2O2 production through a reaction pathway distinct from that of pseudo-inert basal planes. These findings establish fundamental principles connecting crystal structure, exciton dynamics, and reactive site distribution, providing new insights into the design of high-performance photocatalysts.

Unveiling the reaction mechanism of photocatalytic H2 evolution coupled with selective bio-mass monosaccharide upgrading over single palladium atom-engineered carbon-rich graphitic carbon nitride

The simultaneous utilization of photogenerated electrons and holes in the coupled redox reactions of H2 production and selective biomass upgrading is a promising strategy to offer both economic and environmental benefits. Nevertheless, the method faces challenges of low H2 evolution efficiency and poor selectivity to biomass-derived chemicals. Herein, a supramolecular preorganisation-thermal polymerization-photo-assisted reduction strategy was designed to fabricate single palladium atom-engineered carbon-rich g-C3N4 (Pd1/BCNx) catalysts, and the interlayer Pd-N4 coordination configuration was confirmed for stabilizing the isolated Pd atoms. Under simulated sunlight irradiation, the optimized 0.39 %Pd1/BCN2 catalyst demonstrated superior performance in the co-generation of H2 and lactic acid by the substitution of monosaccharide (fructose or xylose) for traditional hole scavenger. In a dilute NaOH system (1 or 1.5 mol/L) and after 4 h light irradiation, the conversion of monosaccharide reached 100 %, the H2 evolution rate and selectivity to lactic acid approached 5.7 mmol gcat-1 h-1 and 71.8 % (fructose system) and 7.0 mmol gcat-1 h-1 and 64.1 % (xylose system). The reaction mechanism studies unveiled that the Pd1/BCNx catalysts with the accelerated photogenerated charge transfer dynamics and the maximum Pd atoms utilisation efficiency greatly facilitated the coupled redox reaction; moreover, the synergy of the as-generated reactive oxygen species (ROSs) and ROSs-induced xylose (or fructose)-based radical intermediates played a pivotal role on the production of LA with high activity and selectivity via a C-C bond cleavage pathway.

Molten salt synthesis of 1T phase dominated O-MoS2 for enhancing photocatalytic hydrogen production performance of CdS via Ohmic junction

In photocatalysis, establishing an Ohmic junction could create an internal electric field between semiconductors and cocatalysts [1,2], effectively enhancing the transfer of photogenerated electrons. In this study, the 1T phase dominated oxygen atom doped MoS2 cocatalyst (O-MoS2), synthesized from KSCN molten salt with in-situ oxidation for the first time, is combined with CdS for boosting photocatalytic hydrogen production. In the hybrid photocatalyst, electrons could be efficiently extracted from CdS to O-MoS2 due to the presence of Ohmic contact, thereby significantly enhancing the utilization of photogenerated electrons and the photocatalytic hydrogen evolution performance. The results demonstrate that an initial hydrogen evolution rate of 532.8 μmol-1 could be achieved for CdS with the optimum loading amount of O-MoS2 (CdS-5), 26.6 times higher than that of CdS alone. Additionally, CdS-5 exhibits an apparent quantum yield (AQY) of 80.4 % at 420 nm. The increased photocatalytic performance of CdS-5 is primarily attributed to the efficient electron transfer (ET) process between the CdS and O-MoS2 in the presence of Ohmic junction, which accelerates the separation of the photogenerated carriers from CdS. It is strongly confirmed by the (photo)electrochemical experiments, steady-state/time-resolved photoluminescence (PL) spectra, Kelvin probe force microscope (KPFM), femtosecond transient absorption spectra (fs-TAS) and Density functional theory (DFT) calculation.

Internal energy recycling in FAPbI3/MXene for enhanced photocatalytic H2 evolution

Carrier recombination is a significant impediment to efficient charge separation, thereby severely limiting the performance of photocatalytic systems. In this study, we feature an innovative internal energy cycling mechanism through the non-radiative fluorescence resonance energy transfer (FRET) between perovskite and MXene, to exploit the energy released by carrier recombination for enhancing H2 evolution rate. Consequently, a rapid H2 evolution rate of 2394 µmol g-1 h-1 under 1.5 AM simulated sunlight, from the composite of FAPbI3/MXene/Pt, was acquired, which is more than one order of magnitude higher than that of FAPbI3/Pt (64 µmol g-1 h-1). The innovative approach of FRET induced internal energy cycling will open up opportunities to design other novel heterogeneous catalytic materials and promote their application potential in various catalytic fields.

Luminescence quenching of pyrene-labelled fluorescent dendrons by surface anchoring of ruthenium nanoparticles

Hybrid nanostructures, comprising ruthenium nanoparticles (Ru NPs) and Fréchet-type dendrons of first (G1) and second (G2) generations bearing two and four pyrene units, respectively, and a carboxylic acid group as an anchoring function, have been prepared by taking advantage of the organometallic approach and ligand exchange. Their optical properties have been studied by absorption and fluorescence spectroscopy and compared with those of their counterparts prepared under the same conditions but with pyrene acetic acid and pyrene butyric acid as fluorophores. Pyrene-labelled Fréchet-type dendrons display more pyrene units at a longer distance from the Ru surface than pyrene acetic acid and pyrene butyric acid fluorophores. Interestingly, and unlike pyrene acetic acid- and pyrene butyric acid-derived nanohybrids, the dendron-functionalized Ru NPs exhibit significant to efficient quenching of the pyrene fluorescence (67% for G2 and 94% for G1 with respect to the free dendrons). The quenching effect of the Ru metallic cores on the fluorophore units opens up new prospects for the use of such nanohybrids as antennas for photocatalytic applications.

Enhanced Photocatalytic O2 Evolution over Layered Perovskite Oxyiodide Ba2Bi3Nb2O11I through Flux Synthesis and Surface Modifications

Sillén-Aurivillius oxyiodides, particularly Ba2Bi3Nb2O11I with double-perovskite layers, are promising photocatalysts for visible-light-driven water splitting due to their excellent light absorption and carrier transport properties. However, efforts to enhance their photocatalytic performance through advancements in synthesis methods or surface modifications remain limited. Here, we report the flux synthesis of Ba2Bi3Nb2O11I and the optimization of cocatalyst loading. Single-phase Ba2Bi3Nb2O11I was successfully synthesized using molten alkali iodide salts under appropriate reaction conditions. The heating rate during the synthesis significantly influenced crystallinity and carrier lifetime, as shown by time-resolved microwave conductivity measurements. By optimizing the reaction conditions to enhance crystallinity (prolong carrier lifetime), the flux-synthesized sample exhibited a higher sacrificial O2 evolution rate than that prepared via the conventional solid-state reaction. Furthermore, precise control over the loading conditions of the iron-ruthenium oxide cocatalyst ((Fe,Ru)Ox) significantly enhanced nonsacrificial O2 evolution from an aqueous Fe3+ solution. Electrochemical analysis revealed that the tuned loading conditions enhanced the catalytic activity of the (Fe,Ru)Ox cocatalyst for both water oxidation and Fe3+ reduction. Finally, Z-scheme water splitting using the optimized (Fe,Ru)Ox-loaded Ba2Bi3Nb2O11I photocatalyst showed superior efficiency than that using the previously reported unoptimized sample. This study provides valuable insights into enhancing the O2 evolution activity of oxyiodide photocatalysts for water-splitting applications.

Phase effect of TiO2 on surface hydrogen adsorption/desorption in controlling photocatalytic methane conversion

Identifying the rate-determining step is crucial for designing an effective photocatalytic system. The surface adsorption/desorption behaviour of reactants has received much less attention in photocatalyst design because the charge separation and transfer in the bulk is commonly regarded as a more sluggish process. In this work, we investigate photocatalytic methane (CH4) conversion (PMC) on various titanium oxide (TiO2) surfaces, including rutile and anatase, and reveal that the influence of surface CH4 adsorption can outweigh the photogenerated charge separation and transfer. Specifically, the rutile TiO2 surface is totally inert for CH4 activation. Further theoretical calculations reveal the significance of the hydrogen-adsorption/desorption process during the initial C-H bond cleavage on the TiO2 surface. A reversible hydrogen adsorption/desorption process with a small Gibbs free energy not only enables the activation of the first C-H bond in CH4 but also ensures a timely clearance of surface-adsorbed species, leading to a continuous PMC process. The findings of the phase effect study on the interaction between the photocatalyst surface and hydrogen atoms provide new insights into the rational design of efficient photocatalysts towards PMC. It also highlights the gap in transferring the knowledge of photocatalytic water splitting into PMC.

Phase-Migrating Z-Scheme Charge Transportation Enables Photoredox Catalysis Harnessing Water as an Electron Source

Z-schematic photocatalytic reactions are of considerable interest because of their potential for application to reductive molecular conversions to value-added chemicals using water as an electron source. However, most demonstrations of Z-scheme photocatalysis have been limited to overall water splitting. In particular, it has been basically impossible to couple the reduction of "water-insoluble compounds" with water oxidation by conventional Z-scheme systems in aqueous solution. In this work, an unconventional Z-scheme electron transportation system with a "phase-migrating" redox mediator is constructed that enables photocatalytic conversion of water-insoluble compounds by using water as an electron/proton source. In a dichloroethane (DCE)/water biphasic solution, a molecular Ir(III) complex acts as a photoredox catalyst for the reductive coupling of benzyl bromide by using ferrocene (Fc) as an electron donor in the DCE phase. On the other side, an aqueous dispersion of a Bi4TaO8Cl semiconductor loaded with a (Fe,Ru)Ox cocatalyst photocatalyzed water oxidation using ferrocenium (Fc+) as an electron acceptor. Because the partition coefficients of Fc+/Fc are significantly different, the Fc+ and Fc generated by photoinduced electron transfer in each reaction could be selectively extracted to the opposite liquid phase. Spontaneous phase migration enables direction-selective electron transport across the organic/water interface that connects the reduction and oxidation reactions in the separated reaction phase. Eventually, photocatalytic reductive conversion of "water-insoluble" organic compounds using "water as the electron/proton source" was demonstrated through the step-by-step Z-scheme photocatalysis with the phase-migrating Fc+/Fc electron transportation.

Deep photocatalytic NO oxidation on ZnTi-LDH: Pivotal role of surface hydroxyls dynamic evolution

Surface defect engineering has been regarded as an appealing strategy to improve photocatalytic performance, but defects are susceptible to inactivation and thus lose their function as active sites. In this study, we successfully tailored and identified the dynamic evolution of surface hydroxyl defects over ZnTi-layered double hydroxide (ZnTi-LDH) photocatalyst. The enrichment of surface hydroxyl electrons and the dynamic circulation of hydroxyl defects result in enhanced separation and transport capabilities of photogenerated carriers, thereby ensuring the perpetual activation of small molecules into •O2- and •OH. The optimized structure has demonstrated NO removal efficiency values as high as 70.0 %, while concurrently suppressing the emission of NO2 - a dangerous byproduct. Furthermore, ZnTi-LDH exhibits remarkable adaptability to varying environmental conditions and satisfactory durability over extended periods of reaction. This research offers valuable insights into the key role of surface hydroxyl in sustainable NOx removal technologies, and the findings contribute significantly to the advancement of environmental remediations.

Singlet-Oxygen-Driven Cooperative Photocatalytic Coupling of Biomass Valorization and Hydrogen Peroxide Production Using Covalent Organic Frameworks

Traditional H2O2 photocatalysis primarily depends on photoexcited electrons and holes to drive oxygen reduction and water oxidation, respectively. However, singlet oxygen (1O2), often underappreciated, plays a pivotal role in H2O2 production. Meanwhile, photocatalytic biomass conversion has attracted attention, yet studies combining H2O2 synthesis with biomass valorization remain rare and typically yield low-value products. Herein, a strategy of photocatalytic valorization of furfuryl alcohol (FFA) coupled with the efficient co-production of H2O2 is reported, enabled by covalent organic frameworks (COFs) induced, 1O2-participated Achmatowicz rearrangement. This study introduces polyimide-based COF-N0-3 with tailored nitrogen content, representing an unprecedently efficient platform for 1O2 production. Remarkably, reducing the nitrogen content of the COF enhances 1O2 production, significantly boosting the H2O2 generation rate. In FFA, the primary pathway for H2O2 production is Achmatowicz rearrangement, achieving a rate ten times higher than that reliant on oxygen reduction reaction in pure water, reaching 4549 µmol g⁻¹ h⁻¹. Mechanism studies revealed 1O2 selectively engaged FFA, bypassing hole oxidation to trigger the Achmatowicz rearrangement, producing valuable 6-hydroxy-(2H)-pyranone with 99% conversion and 92% selectivity. This work establishes a coupling strategy for simultaneous synthesis of H2O2 and biochemicals, offering a transformative approach to sustainable photocatalysis.

Photodriven PtPdCo-TiO2 heterostructure modified with hyaluronic acid and folic acid enhances antioxidative stress through efficient hydrogen/oxygen delivery and thermal effects in rheumatoid arthritis therapy

Rheumatoid arthritis (RA) is an autoimmune disease characterized by chronic synovitis and progressive joint damage, primarily caused by oxidative injury from reactive oxygen species (ROS) and hypoxia in immune cells. Hydrogen (H2) has demonstrated potential in scavenging excess ROS and correcting redox imbalances, while oxygen supplementation can alleviate hypoxia, promoting inflammatory remission. This study introduces a novel FA-HA-PtPdCo-TiO2 (F-HPPCT) nano-system for targeted RA therapy. Comprising TiO2 quantum dots on PtPdCo polyhedra, decorated with folate-hyaluronic acid (FA-HA), F-HPPCT selectively targets inflammatory cells. Its metal-semiconductor heterostructure forms Schottky junctions that enhance electron transfer, enabling efficient hydrogen evolution and a photothermal effect under near-infrared light. Additionally, F-HPPCT mimics catalase activity, decomposing overexpressed H2O2 to relieve hypoxia and oxidative stress. The system synergistically scavenges ROS and replenishes oxygen, effectively reducing inflammation and oxidative damage. Both in vitro and in vivo experiments in arthritis models confirmed its efficacy, highlighting F-HPPCT's potential as a groundbreaking nanocatalyst for gas therapy in RA treatment.

Boosting Photocatalytic Hydrogen Evolution of 2D Multinary Copper Chalcogenide Nanocrystals Enabled by Tuning Metal Precursors

It is challenging to clarify modulation mechanisms and structure-activity relationships in the ion-regulation engineering of multinary copper chalcogenide nanocrystals (NCs) for solar-to-hydrogen conversion. Herein, quaternary 2D Cu-In-Zn-S NCs are fabricated using various indium precursors to expose a high proportion of (0002) crystal facets that are positively correlated with their photocatalytic activities. Theoretical calculations demonstrate that the specific adsorption of anions on the crystal facets significantly influences their anisotropic growth and, in turn, photocatalytic performance. Furthermore, 2D Cu-In-Ga-Zn-S (CIGZS) NCs are prepared by partially or completely substituting In3+ with Ga3+ cations. As the Ga3⁺ content gradually increases, the resulting photocatalytic activities follow a bell-shaped trend. The initial increase is attributed to a synergistic effect of optimized catalytic ability and a stronger electron driving force introduced by Ga3⁺ incorporation. However, excessive Ga3⁺ substitution widens the bandgap, reducing light absorption and conversion, ultimately leading to a decline in photocatalytic activities. Notably, the photocatalytic activity of Cu-Ga-Zn-S NCs with the highest hydrogen evolution rate of 1566.8 µmol g-1 h-1 under visible light surpassed those of all In-based NCs due to enhanced electron-hole separation efficiency and highly effective active sites. This study provides valuable insights into the rational design of multinary copper-based photocatalysts for solar-driven hydrogen production.

Ammonia-Treated Graphene Oxide/ZnIn2S4 Composite for Enhanced Photocatalytic Hydrogen Production under Visible Light Irradiation

In the pursuit of solar-driven photocatalytic energy generation, environmental remediation, and carbon neutrality, the development of semiconductor-based heterojunction photocatalysts presents a promising strategy. However, the photocatalytic efficiency of pristine ZnIn2S4 (ZIS) is hindered by rapid electron-hole recombination and a relatively small surface area. Meanwhile, pure graphene oxide (GO) is not an ideal photocatalyst due to its inappropriate bandgap and the presence of oxygenated functional groups. To overcome these limitations, a surfactant-assisted ZIS synthesis was combined with ammonia-treated GO (NGO) to form an NGO/ZIS composite that enhances light absorption, charge carrier separation and transport, and overall hydrogen production efficiency under visible light illumination. Among the evaluated materials, 0.1NGO/ZIS exhibited the highest hydrogen evolution rate (18.8 mmol·g-1 h-1), demonstrating enhancements of 3-fold and 940-fold increased compared to pristine ZIS (5.8 mmol·g-1 h-1) and NGO (0.02 mmol·g-1 h-1), respectively. This superior photocatalytic performance is attributed to improved interfacial charge transfer between NGO and ZIS, facilitated by the incorporation of amine and amide groups into GO. Furthermore, density functional theory (DFT) calculations were conducted to validate the impact of ammonia treatment on GO and support the experimental findings. The synthesized photocatalysts were characterized by using X-ray diffraction (XRD), Fourier-transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET), diffuse reflectance sorption spectroscopy (DRS), photoluminescence (PL), electrochemical impedance spectroscopy (EIS), electron spin resonance (ESR), and time-resolved photoluminescence (TRPL) analyses. This study presents a simple yet effective approach to fabricating NGO/ZIS composites, contributing to the advancement of high-performance photocatalysts for sustainable energy applications.

Ultrahigh photocatalytic hydrogen evolution of linear conjugated terpolymers enabled by an ultra-low ratio of the benzothiadiazole monomer

Conjugated terpolymers bearing three kinds of π-monomers have been regarded as a promising platform for photocatalytic hydrogen production (PHP). However, the high-performance terpolymers reported so far typically involve large portions (≥20 mol%) of the third monomer. Efficiently modulating the terpolymer by utilizing minimum content of the third component remains a critical challenge. Herein, we report a donor-acceptor linear terpolymer prepared by atom-economical C-H/C-Br coupling with an ultra-low ratio (0.5 mol%) of benzothiadiazole (BT) as the third monomer, which can efficiently modulate properties and afford a hydrogen evolution rate of up to 222.28 mmol h-1 g-1 with an apparent quantum yield of 24.35% at 475 nm wavelength in the absence of a Pt co-catalyst. Systematic spectroscopic studies reveal that even a minimal amount of the BT monomer can effectively tune the light absorption and frontier molecular orbitals of the resulting terpolymers. Compared to the BT-free BSO2-EDOT bi-polymer, the terpolymer BSED-BT0.5% involving 0.5 mol% of BT has a much faster electron transfer (5.76 vs. 1.13 ns) and much lower exciton binding energy (61.35 vs. 32.03 meV), showcasing an important discovery that the BT building block even with an ultra-low ratio enables the effective modulations of terpolymers with ultra-high PHP performance.

Structural Analysis of Selenium Coordination Compounds and Mesoporous TiO2-Based Photocatalysts for Hydrogen Generation

This study reports the synthesis of ten coordination compounds (1-10) derived from the ligand bis((3-aminopyridin-2-yl)selanyl)methane (L) and different metal centers (CoII, CuI, CuII, ZnII, and AgI). Single crystals of the complexes were obtained via slow diffusion from overlaid solutions of ligand L and the corresponding metal. Their crystalline structures were determined by single-crystal X-ray diffraction (SCXRD) and further characterized using spectroscopic, spectrometric, and voltammetric techniques. Complexes 1-5, 7, and 10 were evaluated as cocatalysts of mesoporous titanium dioxide (m-TiO2) for photocatalytic hydrogen production via water photolysis under solar light simulation, using triethanolamine (TEOA) as the sacrificial agent. The results showed that complexes 4, 5, 7, and 10 enhanced m-TiO2 photocatalytic activity, achieving hydrogen evolution rates at least four times higher than standard m-TiO2 and P25. Among these, the photocatalyst m-TiO2-7 (7 = [Cu2(μ-SO4)2L2]) exhibited the highest hydrogen production, reaching approximately 7800 μmol/g over a 6-h experiment-nearly 26 times greater than pure m-TiO2 (300 μmol/g). These findings highlight the potential of organoselenium metal complexes for the development of novel photocatalytic materials based on nonprecious metals.

Data-Driven Approach Considering Imbalance in Data Sets and Experimental Conditions for Exploration of Photocatalysts

In the field of data-driven material development, an imbalance in data sets where data points are concentrated in certain regions often causes difficulties in building regression models when machine learning methods are applied. One example of inorganic functional materials facing such difficulties is photocatalysts. Therefore, advanced data-driven approaches are expected to help efficiently develop novel photocatalytic materials even if an imbalance exists in data sets. We propose a two-stage machine learning model aimed at handling imbalanced data sets without data thinning. In this study, we used two types of data sets that exhibit the imbalance: the Materials Project data set (openly shared due to its public domain data) and the in-house metal-sulfide photocatalyst data set (not openly shared due to the confidentiality of experimental data). This two-stage machine learning model consists of the following two parts: the first regression model, which predicts the target quantitatively, and the second classification model, which determines the reliability of the values predicted by the first regression model. We also propose a search scheme for variables related to the experimental conditions based on the proposed two-stage machine learning model. This scheme is designed for photocatalyst exploration, taking experimental conditions into account as the optimal set of variables for these conditions is unknown. The proposed two-stage machine learning model improves the prediction accuracy of the target compared with that of the one-stage model.

Revisiting Photocatalytic CO2 Reduction to Methanol: A Perspective Focusing on Metal-Organic Frameworks

Photocatalytic CO2 reduction to CH3OH, particularly with metal-organic frameworks (MOFs) as photocatalysts, has garnered significant attention due to its long-term potential to harness sunlight for converting CO2 into a valuable fuel and chemical feedstock. Numerous studies in the literature report the successful formation of CH3OH from photocatalytic CO2 reduction, sometimes supplemented with sacrificial agents, with claims substantiated by isotopic labelling measurements. However, in this Scientific Perspective, we note that much of the existing evidence has not been obtained under sufficiently rigorous experimental conditions to conclusively confirm the formation of a highly reactive product like CH3OH from the chemically stable CO2 molecule. This Scientific Perspective outlines best practices designed to provide robust evidence for CH3OH formation in photocatalytic processes, which could be instrumental in clarifying the state-of-the-art and accelerating the development of this technology toward practical applications.

Double heterojunction photocatalysts: strategic fabrication and mechanistic insights towards sustainable fuel production

Excessive energy crisis has triggered the transformation of solar energy into chemical energy via photocatalysis to establish a sustainable and carbon-neutral society. In this regard, the fabrication of visible-light-active photocatalysts with favourable band edge positions is preferred for achieving maximum solar energy conversion efficiency. However, a single semiconductor suffers from several disadvantages, such as rapid electron-hole recombination, inefficient electron-hole separation and sluggish charge migration dynamics. To improve photocatalytic performance, constructing heterostructures using two semiconductors has been considered an effective strategy. Nonetheless, these binary heterostructures also present several challenges, which can be addressed by combining three semiconductors to form double heterojunctions. The formation of double heterojunctions enhances visible light absorption, increases charge carrier concentration and facilitates superior charge separation owing to the presence of in-built electric fields, thereby ameliorating the photocatalytic efficacy of these heterostructures compared to binary ones. This review article provides a deep insight into the charge transfer mechanisms that occur in different types of double heterojunctions. Moreover, it highlights the applications of these heterostructures in various fields of photocatalysis, such as water splitting, CO2 reduction, N2 fixation and pollutant degradation.

Recyclable Molecular Ferroelectrics to Harvest Mechanical Energy for Sustained Hydrogen Generation

Production of hydrogen fuel from water and renewable energy offers one of the most promising pathways for carbon neutrality and sustainable development. However, existing hydrogen generation technologies struggle with durability issues, such as poisoning, coking, and fouling, so it is a crucial economic concern to find a long-term hydrogen generation catalyst or approach. Herein, we report a recyclable cyclic supersaturation strategy harnessing molecular ferroelectric (TMFM)0.26(TMCM)0.74CdCl3 (MF-1) for hydrogen generation, which enables cycles of recrystallization and dissolution of molecular ferroelectric nanocrystals in supersaturated aqueous solution systems. The molecular ferroelectric nanocrystals generate hydrogen through the piezoelectric effect and dissolve in aqueous solution, enabling complete hydrogen desorption. Additionally, their low acoustic impedance, closely matching that of water, facilitates efficient mechanical energy transmission, thereby enhancing hydrogen generation efficiency. We achieve a robust hydrogen generation rate of record-high 11.56 mmol g-1 h-1 (mechanical-to-hydrogen energy conversion efficiency of 35.6%), with outstanding durability surpassing 1500 h. This work not only provides a new strategy for efficient and sustainable hydrogen generation but also boosts the outlook for the application of water-soluble molecular ferroelectric materials.

Ultrasmall Organic Nanocrystal Photocatalyst Realizing Highly Efficient Symmetry Breaking Charge Separation and Transport

The high exciton binding energy and short exciton diffusion length (typical 5-10 nm) of organic photocatalysts (OPCs) hinder efficient charge separation and subsequent charge transfer, limiting their potential for solar energy conversion. Inspired by the symmetry breaking charge separation (SBCS) in natural photosystem II, we employed a freeze assembly (FA) strategy to assemble symmetric perylene diimide (PDI) dimers into ultrasmall (sub-5 nm) nanocrystals (NCs) with ordered molecular stacking, exhibiting SBCS characteristics. The SBCS NCs (p-5 nm) showed 12.3-fold enhancement in charge separation efficiency compared to non-SBCS NCs (PDI-5 nm). Furthermore, the charge transfer efficiency in p-5 nm (94.7%) was 1.6 times greater than that of weak SBCS NCs (m-5 nm, 60.4%). Consequently, we achieved a comparable photocatalytic hydrogen evolution rate (1824 μmol h-1 g-1) among the PDI-based photocatalysts in p-5 nm. This study highlights the importance of ultrasmall NCs in fulfilling bioinspired SBCS and the potential of the FA strategy for developing high-performance OPCs.

Donor-Acceptor-π-Acceptor-Donor-Type Photosensitive Covalent Organic Framework for Effective Photocatalytic Aerobic Oxidation

Developing effective photocatalysts for the oxidation reaction is of great significance in chemical synthesis but is still challenging. Herein, linking photochromic triphenylamine with pyrene units by the in situ formed robust imidazole moieties, a covalent organic framework (COF), PyNTB-COF, containing a rare donor-acceptor-π-acceptor-donor (D-A-π-A-D) fragment, was successfully synthesized for photocatalytic aerobic oxidation. Structure characterizations confirm its crystalline framework, high porosity, and good stability. Property studies reveal its photoelectric semiconductor feature with high photoresponsive charge separation and migration activity derived from the D-A-π-A-D fragments, proven by the experimental results and theoretical calculations. Photocatalytic experiments not only display its highly effective photoresponsive activity in triggering the generation of ·O2- under visible light irradiation but also exhibit its high photocatalytic efficiency in the aerobic oxidations of toluene and the amidation of aldehydes. This work demonstrates that the integration of photochromic units into framework materials to construct π-conjugated D-A moieties could enhance photocatalytic charge separation and migration efficiency, achieving promising photocatalysts for photocatalytic aerobic oxidation.

Spontaneous Exciton Dissociation in Sc-Doped Rutile TiO2 for Photocatalytic Overall Water Splitting with an Apparent Quantum Yield of 30

Achieving high-efficiency photocatalytic overall water splitting with earth-abundant materials like TiO2 under ambient conditions is a compelling renewable energy solution. However, this remains challenging due to both the presence of rich deep-level defects and lack of strong driving force in particulate photocatalysts, limiting the separation of photogenerated charges. Here, we developed a scandium (Sc)-doped rutile TiO2 with fully passivated detrimental Ti3+ defects and very strong built-in electric field arising from engineered (101)/(110) facet junctions. The Sc3+ doping enables a much lower exciton binding energy of 8.2 meV (28.6 meV for undoping) than room-temperature thermal fluctuation energy, indicating spontaneous exciton dissociation. These features enable the photogenerated electrons and holes to selectively transfer to the (110) and (101) facets, respectively. The resulting Sc-doped TiO2 with cocatalyst delivers photocatalytic overall water splitting with an apparent quantum yield of 30.3% at 360 nm and a solar-to-hydrogen conversion efficiency of 0.34%, representing the highest values reported for TiO2-based photocatalysts under ambient conditions.

Critical impacts of metal cocatalysts on oxidation kinetics and optimal reaction conditions of photocatalytic methane reforming

Metal cocatalysts in photocatalysis are typically regarded as promoting only the reduction reactions. Here, we demonstrate that photocatalytic oxidation kinetics and optimal pressure of methane vary significantly with the loading amount of metal cocatalysts. These variations are well described by kinetic analyses treating molecular-level congestion of oxidation intermediates.

High-Performance Overall Water Splitting Dominated by Direct Ligand-to-Cluster Photoexcitation in Metal-Organic Frameworks

Expanding the spectral response of photocatalysts to facilitate overall water splitting (OWS) represents an effective approach for improving solar spectrum utilization efficiency. However, the majority of single-phase photocatalysts designed for OWS primarily respond to the ultraviolet region, which accounts for a small proportion of sunlight. Herein, we present a versatile strategy to achieve broad visible-light-responsive OWS photocatalysis dominated by direct ligand-to-cluster charge transfer (LCCT) within metal-organic frameworks (MOFs). Three synthesized OWS MOFs, namely Fe2MCbz (M2+ = Mn2+, Co2+, Ni2+), exhibited intrinsic OWS capability without the requirement for extra photosensitizer or sacrificial agent or cocatalyst. Among these, Fe2NiCbz was identified as the superior performer, and when dispersed with polyacrylonitrile nanofibers using electrospinning technology, it achieved the highest OWS rates of 170.2 and 85.1 μmol g-1 h-1 for H2 and O2 evolution, surpassing all previously documented MOF-based photocatalysts. Experimental and theoretical analyses revealed that direct LCCT played a crucial role in enhancing the photocatalytic efficiency, with exceptional performance of Fe2NiCbz attributed to its well-optimized energy level structures and highly efficient charge transfer mechanism. This work not only sets a benchmark in OWS MOF photocatalysts but also paves the way for maximizing solar spectrum utilization, thereby advancing renewable hydrogen production strategy.

Overcoming tumor hypoxic bismuth-based ternary heterojunctions enable defect modulation-augmented tumor sonocatalytic immunotherapy

Inducing reactive oxygen species (ROS) via sonocatalysis to initiate inflammatory programmed cell death (PANoptosis) and immunogenic cell death (ICD) presents a promising strategy for activatable cancer immunotherapy. However, the limited ROS generation by sonosensitizers under ultrasound and the immunosuppressive tumor microenvironment hinder the efficiency of sono-immunotherapy. To overcome these challenges, a bismuth-based ternary heterojunction, Bi@Bi2O3-Pt-PEG (BBOP), was developed for sonocatalytic therapy aimed at activating immune responses. This system enhances ROS production during sonocatalysis and leverages dual therapeutic mechanisms by inducing PANoptosis and ICD to achieve improved anti-tumor efficacy. BBOP forms a Z-scheme heterojunction and Schottky contact through the formation of an intermediate Bi2O3 layer and the introduction of Pt. These structures significantly enhance sonocatalytic activity, while the Pt nanozyme exhibits catalase-like behavior, supplying oxygen for sonocatalysis, boosting ROS generation, and effectively relieving tumor hypoxia to reduce immune suppression. Further in vitro and in vivo experiments confirmed BBOP's ability to activate immune responses under ultrasound, inhibiting tumor growth and metastasis. RNA sequencing revealed the therapeutic biological mechanisms. The construction of this catalytic system not only provides insights for optimizing sonosensitizers but also offers a safer and more effective sono-immunotherapy activation strategy and theoretical basis for clinical cancer treatment.

Tailoring Ultrashort Inter‐Fullerene Spacing in a Continuous Fullerene Stacking Array to Enhance Electron Transport for Boosting Solar‐Driven Hydrogen Production

The efficiency of organic semiconductor photocatalysts is typically limited by their capability of photogenerated electron transport. Herein, a photocatalyst is proposed initially through the specific axial coordination interaction between imidazole‐C60 (ImC60) and zinc tetraphenyl porphyrin (ZnTPP) named ImC60‐ZnTPP. Subsequently, detailed structural characterizations along with theoretical calculation reveal that the unique ImC60‐ZnTPP possesses head‐to‐tail stacking supra‐structures, leading to the formation of a continuous array of C60–C60 with ultrashort spacing and ensuring strong π–π interactions and homogeneous electronic coupling, which could tremendously promote electron transport along the (−111) crystal facet of ImC60‐ZnTPP. Consequently, compared to other fullerene‐based photocatalysts, ImC60‐ZnTPP shows exceptional photocatalytic hydrogen production activity, with an efficiency of up to 80.95 mmol g−1 h−1. This study provides a novel strategy to design highly efficient fullerene‐based photocatalytic systems for solar‐driven energy conversion and extend their artificial photosynthetic use.

Rational Design of Methylated Triazine-Based Linear Conjugated Polymers for Efficient CO2 Photoreduction with Water

The development of semiconducting conjugated polymers for photoredox catalysis holds great promise for sustainable utilization of solar energy. Herein a new family of porous methylated triazine-based linear conjugated polymers is reported that enable efficient photoreduction of carbon dioxide (CO2) with water (H2O) vapor, in the absence of any additional photosensitizer, sacrificial agents or cocatalysts. It is demonstrated that the key lies in the generation of methylated triazine linkages through a facile condensation reaction between benzamidine and acetic anhydride, which impedes the formation of conventional triazine-based frameworks. It is also shown that regulating conjugated linear backbones with different lengths of electron-donated benzyl units provides a facile means to modulate their optical properties and the exciton dissociation, thereby affording more long-lived photogenerated charge carriers and boosting charge separation and transfer. A high-performance carbon monoxide (CO) production rate of 218.9 µmol g-1 h-1 is achieved with ≈ 100% CO selectivity, which is accompanied by exceptional H2O oxidation to oxygen (O2). It anticipates this new study will advance synthetic approaches toward polymeric semiconductors and facilitate new possibilities for triazine-based conjugated polymers with promising potential in artificial photocatalysis.

Fluorination-mediated polarization engineering in block copolymers for enhanced photocatalytic hydrogen evolution

Porous polymers have emerged as promising candidates for photocatalytic hydrogen evolution, but their structural rigidity and crosslinking pose significant challenges, often leading to charge recombination and inadequate water/polymer interfaces. This study introduces novel block copolymers (BCPs) comprising a rigid pyrene core and various fluorinated benzene structures coupled with flexible diethyl ether-based hydrophilic units. By computationally predicting monomer structures and dipoles, the relationship between structure and function in these BCPs is examined, particularly focusing on local charge delocalization. Four fluorinated block copolymers (F-BCPs), sharing identical π-conjugated skeletons but differing in the positions and quantities of fluorine atoms on the benzene rings, are explored. Experimental and theoretical analyses reveal that fine-tuning fluorination induces local charge polarization and delocalization. Notably, Py-DE-2F, with fluorination at two ortho positions on benzene, exhibits a remarkable hydrogen evolution rate of 77.68 μmol/h under visible light (λ > 420 nm) without any co-catalyst, surpassing other F-BCPs by an order of magnitude. These results underscore the potential of utilizing fluorination-mediated polarization engineering for developing advanced metal-free polymer photocatalysts.

An Overview of Dynamic Descriptions for Nanoscale Materials in Particulate Photocatalytic Systems from Spatiotemporal Perspectives

Particulate photocatalytic systems using nanoscale photocatalysts have been developed as an attractive promising route for solar energy utilization to achieve resource sustainability and environmental harmony. Dynamic obstacles are considered as the dominant inhibition for attaining satisfactory energy-conversion efficiency. The complexity in light absorption and carrier transfer behaviors has remained to be further clearly illuminated. It is challenging to trace the fast evolution of charge carriers involved in transfer migration and interfacial reactions within a micro-nano-single-particle photocatalyst, which requires spatiotemporal high resolution. In this review, comprehensive dynamic descriptions including irradiation field, carrier separation and transfer, and interfacial reaction processes have been elucidated and discussed. The corresponding mechanisms for revealing dynamic behaviors have been explained. In addition, numerical simulation and modeling methods have been illustrated for the description of the irradiation field. Experimental measurements and spatiotemporal characterizations have been clarified for the reflection of carrier behavior and probing detection of interfacial reactions. The representative applications have been introduced according to the reported advanced research works, and the relationships between mechanistic conclusions from variable spatiotemporal measurements and photocatalytic performance results in the specific photocatalytic reactions have been concluded. This review provides a collective perspective for the full understanding and thorough evaluation of the primary dynamic processes, which would be inspired for the improvement in designing solar-driven energy-conversion systems based on nanoscale particulate photocatalysts.

Divalent Cation Doping into SrTiO3 for Enhancing the Photocatalytic Performance of Water Splitting

Perovskite SrTiO3 (STO) is a widely used semiconductor photocatalyst whose photocatalytic activity is significantly influenced by cation doping. In this work, we explore effective divalent dopants to improve the photocatalytic performance of water splitting through both theoretical and experimental approaches. First-principles calculations suggest that divalent Mg2+ and Zn2+ are promising dopants replacing Ti4+ sites of STO to help mitigate charge recombination processes associated with defect levels caused by oxygen vacancies. Experimental analysis of synthesized STO confirms the photocatalytic performance, consistent with the theoretical predictions.

Impact of Reaction Environment on Photogenerated Charge Transfer Demonstrated by Sequential Imaging

Most photocatalysis research focuses on understanding the photogenerated charge transfer processes within the solid catalysts themselves. However, these studies often overlook the impact of the reaction environment on photogenerated charge separation and reactions. To address this gap, our study employed a sequential imaging methodology that integrates surface photovoltage microscopy (SPVM), in situ atomic force microscopy (AFM), and scanning electrochemical microscopy (SECM) to track the transfer of photogenerated charges from the space charge region to the reactants at the nanoscale on individual BiVO4 particles. It identifies the key role that surface charges at the photocatalyst-electrolyte interface play in photogenerated charge transfer. Specifically, we demonstrated that the surface charge generates an additional driving force, which adjusts the interface electric field and reverses the photovoltage of {010} facet from 90 to -25 mV in a neutral electrolyte. This competitive or even larger driving force compels the photogenerated electrons, which are confined within the bulk, to migrate to the surface, ultimately leading to the redistribution of photogenerated charges. Furthermore, our findings uncovered that the difference between the solution pH and the isoelectric point of the facet serves as the origin of the interfacial electric field. Overall, our sequential imaging research fills an important gap in understanding the driving and influencing factors of charge transfer across the solid-liquid interface for photocatalytic reactions in solution. It provides significant insights into clarifying the bottleneck issue of charge separation in photocatalytic reactions.

Olefin-Linked Covalent Organic Frameworks as Prospective Artificial Platforms for Efficient Photocatalysis

The development of semiconducting materials for photoredox catalysis holds great promise for sustainable utilization of solar energy. Olefin-linked covalent organic frameworks (COFs), which are built by linking organic structs into crystalline frameworks through C=C bonds, have attracted tremendous attention in photocatalysis due to their saliant advantages such as extended π-conjugation, permanent porosity, exceptional chemical stability, light-harvesting and charge separation abilities. This review offers a comprehensive overview of recent new advances toward the development of olefin-linked COFs and their uses as artificial platforms for photocatalytic applications, like hydrogen evolution, carbon dioxide reduction and organic transformations. Structural design strategies, preparation methods and structure-function relationships in various photoredox reactions are summarized, which is accompanied by various approaches to boost their catalytic performance. The challenges and future prospectives are further discussed.

Heterophase Junction Effect on Photogenerated Charge Separation in Photocatalysis and Photoelectrocatalysis

ConspectusThe conversion of solar energy into chemical energy is promising to address energy and environmental crises. For solar conversion processes, such as photocatalysis and photoelectrocatalysis, a deep understanding of the separation of photogenerated charges is pivotal for advancing material design and efficiency enhancement in solar energy conversion. Formation of a heterophase junction is an efficient strategy to improve photogenerated charge separation of photo(electro)catalysts for solar energy conversion processes. A heterophase junction is formed at the interface between the semiconductors possessing the same chemical composition with similar crystalline phase structures but slightly different energy bands. Despite the small offset of Fermi levels between the different phases, a built-in electric field is established at the interface of the heterophase junction, which can be the driving force for the photogenerated charge separation at the nanometer scale. Notably, slight variations in the energy band of the two crystalline phases result in small energy barriers for the photogenerated carrier transfer. Moreover, the structural similarity of the two different crystalline phases of a semiconductor could minimize the lattice mismatch at the heterophase junction, distinguishing it from a p/n junction or heterojunction formed between two very different semiconductors.This Account provides an overview of the understanding, design, and application of heterophase junctions in photocatalysis and photoelectrocatalysis. It begins with a conceptualization of the heterophase junction and reviews recent advances in the synthesis of semiconductors with a heterophase junction. The phase transformation method with the advantage of forming a heterophase junction with an atomically matched interface and the secondary seed growth method for unique structures with excellent electronic and optoelectronic properties are described. Furthermore, the mechanism of the heterophase junction for improving the photogenerated charge separation is discussed, followed by a comprehensive discussion of the structure-activity relationship for the heterophase junction. The home-built spatially resolved and time-resolved spectroscopies offer direct imaging of the built-in electric field across the heterophase junction and then the direct detection of the photogenerated charge transfer between the two crystalline phases driven by the built-in electric field. Such an efficient interfacial charge transfer results in the improvement of the photogenerated charge separation, a higher yield of long-lived charges, and thus the inhibition of the charge recombination. Benefiting from these insights, structural design strategies for the heterophase junction, such as precise tuning of band alignment, exposed heterophase amounts, phase alignment, and interface structure, have been developed. Finally, the challenges, opportunities, and perspectives of heterophase junctions in the design of advanced photo(electro)catalyst systems for solar energy to chemical energy conversion will be discussed.

In situ formation of an active oxygen evolution catalyst via photodegradation of [Ru(bpy)3]2

[Ru(bpy)3]2+ is a widely used molecular photosensitizer (PS) for light-driven reactions in combination with separate catalysts, although the PS alone is known to promote water oxidation under aqueous conditions as well. In contrast, this behavior has not been reported for organic and aqueous solvent mixtures before. Here, we provide mechanistic insights into the role of [Ru(bpy)3]2+ as PS and oxygen evolution catalyst precursor in organic media.

Recent Progress in External-Field Enhanced Photo-Electrochemistry

The ever-growing demands for energy supply have put great stress on environment protections. Photo-electrochemistry (PEC) is a repaid developing technique which can directly transform solar energy into chemical compounds and have been regarded as a promising strategy to solve the energy and environmental problems. However, the biggest restriction is the fast recombination of photo-generated charge carriers which greatly limits the PEC efficiency. In recent years, introducing external-field into PEC system have been proved to be a powerful method to enhance the PEC performance and attracted more and more attentions. In this review, we summarized the remarkable progresses in external-field enhanced PEC reactions including mechanical stress field, thermal field, electrical field, magnetic field and muti-field coupling. The enhancing principles of different external-fields have also been systemically discussed. Furthermore, the challenges and outlook of the external-field enhanced PEC reactions are presented.

Mechanistic elucidation of Ta3N5/LaTiO2N heterojunction formation for improving photocatalytic activity

A Ta3N5/LaTiO2N junction is applied in photocatalytic reactions since the favorable band alignment of the two components promotes the separation of photogenerated carriers. This inference is mainly based on the properties of the two isolated, non-interacting materials. However, experiments reveal negligible information on the real nature of the interface, stoichiometry and composition of oxide layers and atomic arrangements in the heterojunction photocatalyst. In this work, we investigated the characteristics of Ta3N5/LaTiO2N using density functional theory calculations. Heterojunction models include the Ta3N5(110) surface interfaced with the LaTiO2N(010) surface and the Ta3N5(020) surface matched with the LaTiO2N(002) surface. Results show that owing to strong interfacial covalent bonds, the formation of a Ta3N5/LaTiO2N junction is an energetically favorable process. Ab initio molecular dynamics simulations also prove the stability of the studied interfacial structures. Light absorption becomes stronger and is extended after the formation of the heterojunction structure, which is favorable for enhancing the utilization efficiency of solar energy. Ta3N5/LaTiO2N is expected to behave as a type II heterojunction, irrespective of the surfaces of the two semiconductors involved in the junction, in which the band edges of Ta3N5 are lower in energy than those of LaTiO2N. This type of band alignment is favorable for the separation of photogenerated carriers upon photoexcitation, where electrons move toward Ta3N5 and holes toward LaTiO2N. On account of the larger driving force for separating charge carriers, the Ta3N5(110)/LaTiO2N(010) interface is predicted to outperform the Ta3N5(020)/LaTiO2N(002) one. The formation of an interfacial structure between Ta3N5 and LaTiO2N induces a more significant separation of photogenerated charge carriers, which may be the origin of an enhanced photocatalytic efficiency compared with isolated components.

Advanced TiO2-Based Photocatalytic Systems for Water Splitting: Comprehensive Review from Fundamentals to Manufacturing

The global imperative for clean energy solutions has positioned photocatalytic water splitting as a promising pathway for sustainable hydrogen production. This review comprehensively analyzes recent advances in TiO2-based photocatalytic systems, focusing on materials engineering, water source effects, and scale-up strategies. We recognize the advancements in nanoscale architectural design, the engineered heterojunction of catalysts, and cocatalyst integration, which have significantly enhanced photocatalytic efficiency. Particular emphasis is placed on the crucial role of water chemistry in photocatalytic system performance, analyzing how different water sources-from wastewater to seawater-impact hydrogen evolution rates and system stability. Additionally, the review addresses key challenges in scaling up these systems, including the optimization of reactor design, light distribution, and mass transfer. Recent developments in artificial intelligence-driven materials discovery and process optimization are discussed, along with emerging opportunities in bio-hybrid systems and CO2 reduction coupling. Through critical analysis, we identify the fundamental challenges and propose strategic research directions for advancing TiO2-based photocatalytic technology toward practical implementation. This work will provide a comprehensive framework for exploring advanced TiO2-based composite materials and developing efficient and scalable photocatalytic systems for multifunctional simultaneous hydrogen production.