Photocatalysts For Generation Research Articles

Fluoro-polymer/TiO2 based photocatalysts for high efficiency hydrogen generation

In view of limited number of studies on photoreforming of synthetic polymers, herein, a series of new glycopolymers are synthesized via RAFT polymerization to obtain diblock copolymers containing fluorinated and non-fluorinated segments in the glucopyranoside. These glycopolymers are used as probes to investigate photocatalytic reactions at different pH values of the modulated TiO2 photocatalyst. Through structural and surface characterizations, photocatalytic activities are investigated. Fluoro-polymers with deacetylated glucose, hydrophilic segment, PGD such as PPFPM-b-PGD and PPFBM-b-PGD could synergistically increase hydrogen generation rate up to 1368 μmol g-1h−1 and 1549 μmol g-1h−1 with quantum yields of 3.34 % and 3.79 % compared to non-fluoro glycopolymers. The presence of both fluorinated and non-fluorinated groups in diblock copolymers enhanced the rate of photocatalytic hydrogen generation compared to the homopolymer. The accelerated photo-reforming is attributed to in-situ fluorine-doped TiO2 along with high affinity and activation of water molecules. These polymers can generate hydrogen via photo-reforming process.

Thiocoumarin-based Au(I) Complexes and Au(0) Systems over TiO2 as Hybrid Photocatalysts for Hydrogen Generation under UV-Vis Light.

This work focuses on the photocatalytic production of hydrogen from the photodehydrogenation of ethanol using several gold(I) complexes and gold(0) systems over titanium dioxide (P90 TiO2) as hybrid photocatalysts. The photocatalytic systems are composed of at least one coumarin-based ligand, which can enhance the photocatalytic activity by its photon-absorbing capacity due to its chromophore properties. The photocatalytic behavior for hydrogen generation of the studied samples is compared under UV-vis light setting the total gold-based co-catalyst loading at 1 wt% onto the TiO2 photocatalysts and when the gold content is maintained at 0.25 wt%. The incorporation of gold co-catalysts results in an enhancement of hydrogen production up to 2.7 times compared to a conventional Au/TiO2 reference sample. The results show an increase in the total hydrogen production under UV-vis light due to the combined presence of coumarin chromophore, gold-based co-catalysts, and gold plasmonic nanoparticles. A deep characterization of the samples from each group is performed by UV-vis spectroscopy, XPS, HRTEM, and HAADF-STEM, observing the presence of plasmonic gold nanoparticles for sample "AuL1NPs" and the reduction of the gold present in sample "AuL1a," which explains the highest observed hydrogen production rates of this study.

Engineering of visible light-activated ZnIn2S4/N-rGO S-scheme heterojunction photocatalyst for H2 generation

The design of S-scheme heterojunction photocatalysts emerges as high-profile candidates for hydrogen (H2) generation. Herein, by integrating heterojunction creation and heteroatom-doping approaches, ZnIn2S4/N-rGO photocatalyst is synthesized using a hydrothermal process. Crystallinity, morphology, surface area, light absorption, interfacial interaction, and charge separation and migration properties of ZnI2S4/Nitrogen-doped reduced graphene oxide (ZnIn2S4/N-rGO) are analytically explored to authenticate its successful construction. Consequently, the H2 generation performance of ZnIn2S4/N-rGO reached 2847 µmolh-1g-1 under visible light illumination, which is about 9.7 and 1.6 times as high as that of ZnIn2S4 and ZnIn2S4/rGO, respectively, with efficient stability. ZnIn2S4/N-rGO exhibits enhancement in the optical response, promotes the surface area, and improves separation and transport of photoexcited electron/hole pairs, attributing to higher H2 generation activity. The S-scheme charge migration mechanism is authenticated through EPR spectra. The current study not only signifies that ZnIn2S4/N-rGO is an excellent photocatalyst for H2 generation but also offers a route to develop outstanding and stable photocatalysts by combining heterojunction creation and heteroatom-doping approaches.

Hedgehog Zinc Oxide-Graphene Quantum Dot Heterostructures as Photocatalysts for Visible-Light-Driven Water Splitting.

The development of efficient photocatalysts for sustainable hydrogen production via water splitting is vital for advancing renewable energy technologies. In this study, we present the synthesis and characterization of a novel visible-light-active photocatalyst comprising hedgehog-shaped zinc oxide (ZnO) nanostructures coupled with graphene quantum dots (GQDs). Optical properties assessed by UV-visible and photoluminescence (PL) spectroscopy revealed that the ZnO/GQDs heterostructure possessed a reduced band gap (2.86 eV) compared with pristine ZnO (3.10 eV), resulting in improved light absorption and charge separation. Electrochemical analyses indicated a significantly higher photocurrent response and lower charge transfer resistance for the ZnO/GQDs heterostructure compared with the pristine ZnO nanostructure. Photocatalytic tests demonstrated that the ZnO/GQDs heterostructure achieved over 3-fold higher hydrogen (H2) production rates, with an apparent quantum yield (AQY) of 1.51% at 440 nm, and maintained stable activity over prolonged reaction periods. These results highlight the enhanced photocatalytic efficiency and stability of the ZnO/GQDs heterostructure, underscoring its potential as a high-performance photocatalyst for sustainable hydrogen generation. The synergistic effects between ZnO nanostructures and GQDs offer valuable insights into the design of advanced photocatalytic materials for renewable energy applications.

Engineering of g-C3N4 for Photocatalytic Hydrogen Production: A Review.

Graphitic carbon nitride (g-C3N4)-based photocatalysts have garnered significant interest as a promising photocatalyst for hydrogen generation under visible light, to address energy and environmental challenges owing to their favorable electronic structure, affordability, and stability. In spite of that, issues such as high charge carrier recombination rates and low quantum efficiency impede its broader application. To overcome these limitations, structural and morphological modification of the g-C3N4-based photocatalysts is a novel frontline to improve the photocatalytic performance. Therefore, we briefly summarize the current preparation methods of g-C3N4. Importantly, this review highlights recent advancements in crafting high-performance g-C3N4-based photocatalysts, focusing on strategies like elemental doping, nanostructure design, bandgap engineering, and heterostructure construction. Notably, sophisticated doping techniques have propelled hydrogen production rates to a 104-fold increase. Ingenious nanostructure designs have expanded the surface area by a factor of 26, concurrently extending the fluorescence lifetime of charge carriers by 50%. Moreover, the strategic assembly of heterojunctions has not only elevated charge carrier separation efficiency but also preserved formidable redox properties, culminating in a dramatic hundredfold surge in hydrogen generation performance. This work provides a reliable and brief overview of the controlled modification engineering of g-C3N4-based photocatalyst systems, paving the way for more efficient hydrogen production.

Lignin-derived carbon as rapid charge-transfer bridge for efficient solar-driven H2O2 production over CN/Mxene heterojunction

Graphitic carbon nitride (g-C3N4, CN) has been recognized as an environmentally friendly, and promising photocatalyst, particularly for solar-driven synthesis of hydrogen peroxide (H2O2). Heterostructure engineering to decorated CN is an effective approach for boosting photocatalytic H2O2 production. However, the current challenge lies in the efficient transmission of interfacial charge carriers. Herein, we propose a breakthrough approach to synthesize g-C3N4/Mxene (CNM) composites with lignin-derived carbon (L) as a bridge for electron transfer. The optimal ternary heterojunction (CNM,L) demonstrated its impressive performance (0.75 mmol/L) for photocatalytic H2O2 production, which was three times higher than that of pristine CN. The significance of lignin-derived carbon in g-C3N4/Mxene composites not only improves light adsorption, but also promotes electron transfer between the interfacial g-C3N4 and Mxene during the oxygen reduction reaction (ORR) process for H2O2 evolution. This work provides an eco-friendly design of lignin-derived carbon, which efficiently tunes the photo-generated charge transfer of CN-based photocatalysts for H2O2 generation.

Bifunctional g-C3N4 nanospheres/CdZnS QDs S-scheme photocatalyst with boosted H2 evolution and furfural synthesis mechanism

Photocatalytic H2 evolution coupled with organic oxidation could replace the slow four-electron water oxidation and utilize charge carriers to obtain high-valued chemicals. Herein, inorganic CdZnS quantum dots (QDs) are skillfully deposited on g-C3N4 nanospheres to construct an inorganic-polymeric S-scheme heterostructure. The C3N4-CdZnS photocatalyst presents enhanced light absorption, abundant active sites, and intimate interface contact. The optimized composite exhibits an enhanced H2 evolution rate of 582.3 μmol/g/h and a furfuryl alcohol (FAL) conversion of 84.2 %. Femtosecond transient absorption (fs-TA) spectroscopy, in-situ irradiation X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR), and theoretical calculation (DFT) verify the S-scheme mechanism, which promotes charge separation and strengthens carrier redox ability. In-situ infrared spectra reveal that FAL is first activated to ·C5H5O2 radical by holes in CdZnS and further oxidized to furfural (FF) with dehydrogenation of its hydroxyl group. This work supplies new insight into designing efficient photocatalysts for H2 generation and organic synthesis.

Morphology induced defects and crystal facet engineering in CQD@CdS photocatalyst for efficient hydrogen generation

Morphology induced defects and crystal facet engineering in CQD@CdS photocatalyst for efficient hydrogen generation

InP/PtS2 heterojunctions: Z-scheme photocatalysts with enhanced light absorption for high solar-to-hydrogen conversion efficiency

In this paper, the structure and electronic properties of InP/PtS2 heterojunction as well as the photocatalytic and solar hydrogen production efficiency are studied by first principles. Studies have shown that InP/PtS2 heterojunction is type II band alignment, typical Z heterostructure, has strong light absorption coefficient in the absorption spectrumand, InP/PtS2 heterojunction with an indirect bandgap of 1.97 eV，the band edge positions that meet the energy band prerequisites for water splitting across different pH levels，The band edge positions and light absorption capabilities have been modified through biaxial strain, with tensile strain enhancing the absorption capacity within the visible light spectrum ranging from 450 to 800 nm(nm). The InP/PtS2 heterojunction achieves a solar-to-hydrogen conversion efficiency (ηSTH) of 32.5%, which is higher than that of most heterojunctions. The InP/PtS2 heterojunction is anticipated to emerge as a promising contender for the next generation of photocatalysts.

Metal single atom photocatalysts for sunlight-driven hydrogen production: Recent and future development

Photocatalytic hydrogen evolution has been considered the most compelling approach for green hydrogen technology. Heretofore, restricted light adsorption, fast charge recombination, and limited surface-active sites have been considered as bottle-neck issues, causing poor catalytic performance. In this context, metal single atom-incorporated photocatalysts have attracted tremendous attention for their ability to overcome these obstacles while maximizing atomic metal utilization efficiency. The presented perspective aims at highlighting the cutting-edge development of metal single-atom photocatalysts. Indeed, the formation manner and features of metal single atom- anchored photocatalysts are presented. Also, various preparation methods employed to deploy metal atoms onto parent materials are unveiled. Furthermore, recent outstanding metal single atom- anchored semiconductors, which are precious, transition, dual metal single atom- decorated are discussed in detail. In addition, it is also expected to pave the way for the next generation of photocatalysts for sunlight-driven hydrogen generation and contribute to fill the missing puzzles in the picture of green hydrogen production.

Machine learning accelerates the screening of efficient metal-oxide catalysts for photocatalytic water splitting

Photocatalytic water splitting represents a sustainable avenue for hydrogen production, yet the traditional trial-and-error approach for identifying efficient photocatalysts among numerous candidates is cumbersome. In this paper, we introduce a machine learning (ML)-driven approach for rapid screening of promising metal oxide photocatalysts for hydrogen generation. This methodology comprises three key steps: the construction of a comprehensive material library, ML-accelerated material screening, and Density Functional Theory (DFT) calculations for verification. Through this process, we successfully identify ten metal oxides with good energy levels and charge carrier transport properties from an initial library of 860 candidates. Notably, CsYO2 emerges as a standout candidate, exhibiting excellent photocatalytic water-splitting performance on its (001) crystal face, with Y atoms identified as active sites through DFT calculations. This study demonstrates the efficacy of applying machine learning to the precise and rapid screening of vast material databases, paving the way for discovering novel and efficient photocatalysts.

Heterogeneous organophotocatalytic HBr oxidation coupled with oxygen reduction for boosting bromination of arenes

Developing mild photocatalytic bromination strategies using sustainable bromo source has been attracting intense interests, but there is still much room for improvement. Full utilization of redox centers of photocatalysts for efficient generation of Br+ species is the key. Herein we report heterogenous organophotocatalytic HBr oxidation coupled with oxygen reduction to furnish Br2 and H2O2 for effective bromination of arenes over Al2O3 supported perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA). Mechanism studies suggest that O-vacancy in Al2O3 can provide Lewis-acid-type anchoring sites for O2, enabling unexpected dual-electron transfer from anchored photoexcited PTCDA to chemically bound O2 to produce H2O2. The in-situ generated H2O2 and Br2 over redox centers work together to generate HBrO for bromination of arenes. This work provides new insights that heterogenization of organophotocatalysts can not only help to improve their stability and recyclability, but also endow them with the ability to trigger unusual reaction mode via cooperative catalysis with supports.

Single-Atom based Metal-Organic Framework Photocatalysts for Solar-Fuel Generation.

The growing demand for fossil fuels and subsequent CO2 emissions prompted a search for alternate sources of energy and a reduction in CO2. Photocatalysis driven by solar light has been found as a potential research area to tackle both these problems. In this direction, SAC@MOF (Single-atom loaded MOFs) photocatalysis is an emerging field and a promising technology. The unique properties of single-atom catalysts (SACs), such as high catalytic activity and selectivity, are leveraged in these systems. Photocatalysis, focusing on the utilization of Metal-Organic Frameworks (MOFs) as platforms for creating single-atom catalysts (SACs) characterized by metal single-atoms (SAs) as their active sites, are noted for their unparalleled atomic efficiency, precisely defined active sites, and superior photocatalytic performance. The synergy between MOFs and SAs in photocatalytic systems is meticulously examined, highlighting how they collectively enhance photocatalytic efficiency. This review examines SAC@MOF development and applications in environmental and energy sectors, focusing on synthesis and stabilization methods for SACs on MOFs and also characterization techniques vital for understanding these catalysts. The potential of SAC@MOF in CO2 Photoreduction and Photocatalytic H2 evolution is highlighted, emphasizing its role in green energy technologies and advances in materials science and Photocatalysis.

Regulating the Topology of Covalent Organic Frameworks for Boosting Overall H2O2 Photogeneration

AbstractPhotocatalytic oxygen reduction reactions and water oxidation reactions are extremely promising green approaches for massive H2O2 production. Nonetheless, constructing effective photocatalysts for H2O2 generation is critical and still challenging. Since the network topology has significant impacts on the electronic properties of two dimensional (2D) polymers, herein, for the first time, we regulated the H2O2 photosynthetic activity of 2D covalent organic frameworks (COFs) by topology. Through designing the linking sites of the monomers, we synthesized a pair of novel COFs with similar chemical components on the backbones but distinct topologies. Without sacrificial agents, TBD‐COF with cpt topology exhibited superior H2O2 photoproduction performance (6085 and 5448 μmol g−1 h−1 in O2 and air) than TBC‐COF with hcb topology through the O2‐O2⋅−‐H2O2, O2‐O2⋅−‐O21‐H2O2, and H2O‐H2O2 three paths. Further experimental and theoretical investigations confirmed that during the H2O2 photosynthetic process, the charge carrier separation efficiency, O2⋅− generation and conversion, and the energy barrier of the rate determination steps in the three channels, related to the formation of *OOH, *O21, and *OH, can be well tuned by the topology of COFs. The current study enlightens the fabrication of high‐performance photocatalysts for H2O2 production by topological structure modulation.

Regulating the Topology of Covalent Organic Frameworks for Boosting Overall H2O2 Photogeneration.

Photocatalytic oxygen reduction reactions and water oxidation reactions are extremely promising green approaches for massive H2O2 production. Nonetheless, constructing effective photocatalysts for H2O2 generation is critical and still challenging. Since the network topology has significant impacts on the electronic properties of two dimensional (2D) polymers, herein, for the first time, we regulated the H2O2 photosynthetic activity of 2D covalent organic frameworks (COFs) by topology. Through designing the linking sites of the monomers, we synthesized a pair of novel COFs with similar chemical components on the backbones but distinct topologies. Without sacrificial agents, TBD-COF with cpt topology exhibited superior H2O2 photoproduction performance (6085 and 5448 μmol g-1 h-1 in O2 and air) than TBC-COF with hcb topology through the O2-O2⋅--H2O2, O2-O2⋅--O2 1-H2O2, and H2O-H2O2 three paths. Further experimental and theoretical investigations confirmed that during the H2O2 photosynthetic process, the charge carrier separation efficiency, O2⋅- generation and conversion, and the energy barrier of the rate determination steps in the three channels, related to the formation of *OOH, *O2 1, and *OH, can be well tuned by the topology of COFs. The current study enlightens the fabrication of high-performance photocatalysts for H2O2 production by topological structure modulation.

NiS modified SrTiO3:Al bifunctional photocatalyst for H2 generation and cathodic protection

Developing low-cost and high-efficiency non-precious metal cocatalysts is the key to the practical application of photocatalysis technology. Here, nickel sulfide (NiS) nanoparticles were synthesized on the surface of strontium titanate (SrTiO3) via a hydrothermal method, identifying the optimal loading molar concentration of NiS as 10 %. The solar-to-hydrogen efficiency (STH) of 10%NiS/SrTiO3:Al was enhanced by 97 times compared to SrTiO3:Al and by 1.62 times compared to RhCrCoOx/SrTiO3:Al. This improvement is primarily attributed to the metallic-like properties of NiS, which enhance the photocatalyst's light absorption capacity and charge transfer capability. Additionally, the STH value of samples loaded with both NiS and RhCrCoOx reached 0.436 %, indicating a positive synergistic effect in photocatalysis between NiS and RhCrCoOx. Their photocathodic protection capability was also studied in simulated seawater conditions, showing a reduced self-corrosion potential (−0.31V) and a low interface charge impedance (5962 KΩ). This work reveals the potential of NiS as an alternative to precious metal cocatalysts, offering new possibilities for developing cost-effective and high-performance materials for photocatalytic water splitting and photocathodic protection.

Efficient hierarchical ZIF-based electro/photocatalyst toward hydrogen generation and evolution

In this study, a well-designed hierarchical BiFeO3/ZIF-67 (BFO-ZIF) composite was successfully synthesized to improve the performance of photocatalytic hydrogen generation in comparison to bare BiFeO3 and ZIF-67. Moreover, the behavior of the resultant electrocatalysts was also investigated in the hydrogen evolution reaction (HER). The synthesized electro-photocatalysts were characterized by various physical and photo/electrochemical analyses. The remarkable outcomes of the composite with 50 wt% of ZIF-67 in hydrogen generation correspond to the high specific surface area of the photocatalyst concurrently with the formation of active sites and new charge channels, leading to a modified charge transfer pathway and lower electron-hole recombination. The maximum H2 generation rate over the optimal BFO-ZIF composite (BFO-ZIF(50)) attained 1617 μmol g−1 h−1 during visible light exposure, surpassing the rates observed for pure BFO and ZIF-67. Furthermore, the BFO-ZIF(50) electrocatalyst, with the onset potential of −0.089 V, resulted in an overpotential of −0.19 V at a current density of 10 mA cm−2, while a Tafel slope of 81.6 mV dec−1 in 1.0 M KOH showed the highest activity. The elevated photocatalytic hydrogen generation and improved HER performance of the developed catalysts signify a synergistic effect resulting from the junction and the Z-scheme charge transfer mechanism between the ZIF-67 and BFO nanomaterials. This introduces the BFO-ZIF composite as an efficient photocatalyst and electrocatalyst for hydrogen generation and evolution reaction.

Geometrical Stabilities and Electronic Structures of Ru3 Clusters on Rutile TiO2 for Green Hydrogen Production.

In response to the vital requirement for renewable energy alternatives, this research delves into the complex interactions between ruthenium (Ru3) clusters and rutile titanium dioxide (TiO2) (110) interfaces, with the aim of enhancing photocatalytic water splitting processes to produce environmentally friendly hydrogen. As the world shifts away from traditional fossil fuels, this study utilizes the density functional theory (DFT) and the HSE06 hybrid functional to thoroughly assess the geometric and electronic properties of Ru3 clusters on rutile TiO2 (110) surfaces. Given TiO2's renown role as a photocatalyst and its limitations in visible light absorption, this research investigates the potential of metals like Ru to serve as additional catalysts. The results indicate that the triangular Ru3 cluster exhibits exceptional stability and charge transfer effectiveness when loaded on rutile TiO2 (110). Under ideal adsorption scenarios, the cluster undergoes oxidation, leading to subsequent changes in the electronic configuration of TiO2. Further exploration into TiO2 surfaces with defects shows that Ru3 clusters influence the creation of oxygen vacancies, resulting in a greater stabilization of TiO2 and an increase in the energy required for creating oxygen vacancies. Moreover, the attachment of the Ru3 cluster and the creation of oxygen vacancies lead to the emergence of polaronic and hybrid states centered on specific titanium atoms. These states are vital for enhancing the photocatalytic performance of the material within the visible light spectrum. This DFT study provides essential insights into the role of Ru3 clusters as potential supplementary catalysts in TiO2-based photocatalytic systems, setting the stage for practical experiments and the development of highly efficient photocatalysts for sustainable hydrogen generation. The observed effects on electronic structures and oxygen vacancy generation underscore the intricate relationship between Ru3 clusters and TiO2 interfaces, offering a valuable direction for future research in the pursuit of clean and sustainable energy solutions.

Ternary Oxides of s - and p -Block Metals for Photocatalytic Solar-to-Hydrogen Conversion

Oxides containing metals or metalloids from the p block of the periodic table (e.g., In, Sn, Sb, Pb, and Bi) are of technological interest as transparent conductors and light absorbers for solar-energy conversion due to the tunability of their electronic conductivity and optical absorption. Comparatively, these oxides have found limited applications in hydrogen photoelectrolysis, primarily due to their high electronegativity, which impedes electron transfer for reducing protons into hydrogen. We have shown recently that inserting s-block cations into p-block metal oxides is effective at lowering electronegativities while affording further control of band gaps. Here, we explain the origins of this dual tunability by demonstrating the mediator role of s-block cations in modulating orbital hybridization while not contributing to frontier electronic states. From this result, we carry out a comprehensive computational study of 109 ternary oxides of s- and p-block metal elements as candidate photocatalysts for solar hydrogen generation. We down-select the most desirable materials using band gaps and band edges obtained from Hubbard-corrected density-functional theory, with Hubbard parameters computed entirely from first principles, evaluate the stability of these oxides in aqueous conditions, and characterize experimentally four of the remaining materials, synthesized with high phase uniformity, to validate and further develop the computational models. We thus propose nine oxide semiconductors, including CsIn3O5, Sr2In2O5, and KSbO2, which, to the extent of our literature review, have not been previously considered as water-splitting photocatalysts. Published by the American Physical Society 2024

Naphthalenediimide‐Based Polymer Dots with Dual Acceptors as a New Class of Photocatalysts for Photocatalytic Hydrogen Generation under Visible Light Irradiation

Organic‐conjugated polymer dots (Pdots) are emerging as promising photocatalysts for solar‐driven hydrogen production. However, organic solvents are commonly used as cosolvents in photocatalytic systems to promote the dispersion of organic materials and improve the overall efficiency of the photocatalytic process. Herein, two naphthalenediimide (NDI)‐based Pdots, with and without surfactant, are fabricated and presented as highly efficient and stable photocatalysts for visible‐light‐driven hydrogen generation in a solvent‐free organic system for the first time. The prepared Pdots exhibit high photocatalytic activity and remarkable photostability. Achieving high efficiency and long‐term photostability is essential for the future commercialization of large‐scale hydrogen production. Furthermore, the NDI‐BTF‐PS‐PEG‐COOH Pdots of the dual acceptor (A1‐D‐A2‐D system) consisting of a strong acceptor (NDI, A1) and a weak acceptor (BTF, A2) exhibit high photocatalytic efficiencies and stabilities with Pt‐cocatalyst over 72 h. Thus, constructing A1‐D‐A2‐D NDI‐based Pdots is a promising approach to developing efficient and stable photocatalysts for solar‐driven hydrogen production.