Challenges of modeling nanostructured materials for photocatalytic water splitting

Direct Z-scheme system of UiO-66 cubes wrapped with Zn0.5Cd0.5S nanoparticles for photocatalytic hydrogen generation synchronized with organic pollutant degradation

Optimized fabrication of Z-scheme photocatalyst based on MOF materials offers sustainable energy generation and environmental improvement due to their attractive properties. The Z-scheme heterojunctions consisting of UiO-66 cubes covered with Zn0.5Cd0.5S nanoparticles were fabricated by a facile solvothermal method. Thanks to the Z-scheme carrier transport under simulated sunlight irradiation, UiO-66@Zn0.5Cd0.5S exhibited enhanced photocatalytic performance of H2 generation synchronized with organic pollutant degradation in fluoroquinolone antibiotic wastewater. Synergistically, the highest comprehensive performance was obtained in ciprofloxacin solution. The H2 yield reached 224 μmol∙ g-1∙ h-1 and simultaneously the removal efficiency was up to 83.6 %. The degradation pathways revealed that the process of piperazine ring cleavage and decarboxylation also generates H protons, further promoting the production of H2. Therefore, the effective spatial separation and transfer of the photoinduced carriers are attributed to the good band structure, large specific surface area, and cooperative reduction and oxidation reactions of UiO-66@Zn0.5Cd0.5S, resulting in significant photocatalytic activity. The toxicity assessment of antibiotics and intermediate products during the photocatalytic reaction also verifies the reduction of environmental risk. This study highlights a promising way to expand the application of the MOFs-based photocatalyst in clean energy conversion coupling with water remediation.

Identification, Characterization, and Electronic Structures of Interconvertible Cobalt-Oxygen TAML Intermediates

The reaction of Li[(TAML)CoIII]·3H2O (TAML = tetraamido macrocyclic tetraanionic ligand) with iodosylbenzene at 253 K in acetone in the presence of redox-innocent metal ions (Sc(OTf)3 and Y(OTf)3) or triflic acid affords a blue species 1, which is converted reversibly to a green species 2 upon cooling to 193 K. The electronic structures of 1 and 2 have been determined by combining advanced spectroscopic techniques (X-band electron paramagnetic resonance (EPR), electron nuclear double resonance (ENDOR), X-ray absorption spectroscopy/extended X-ray absorption fine structure (XAS/EXAFS), and magnetic circular dichroism (MCD)) with ab initio theoretical studies. Complex 1 is best represented as an S = 1/2 [(Sol)(TAML•+)CoIII---OH(LA)]- species (LA = Lewis/Brønsted acid and Sol = solvent), where an S = 1 Co(III) center is antiferromagnetically coupled to S = 1/2 TAML•+, which represents a one-electron oxidized TAML ligand. In contrast, complex 2, also with an S = 1/2 ground state, is found to be multiconfigurational with contributions of both the resonance forms [(H-TAML)CoIV═O(LA)]- and [(H-TAML•+)CoIII═O(LA)]-; H-TAML and H-TAML•+ represent the protonated forms of TAML and TAML•+ ligands, respectively. Thus, the interconversion of 1 and 2 is associated with a LA-associated tautomerization event, whereby H+ shifts from the terminal -OH group to TAML•+ with the concomitant formation of a terminal cobalt-oxo species possessing both singlet (SCo = 0) Co(III) and doublet (SCo = 1/2) Co(IV) characters. The reactivities of 1 and 2 at different temperatures have been investigated in oxygen atom transfer (OAT) and hydrogen atom transfer (HAT) reactions to compare the activation enthalpies and entropies of 1 and 2.

Advances in Computational Methods for Modeling Photocatalytic Reactions: A Review of Recent Developments

Photocatalysis is a fascinating process in which a photocatalyst plays a pivotal role in driving a chemical reaction when exposed to light. Its capacity to harness light energy triggers a cascade of reactions that lead to the formation of intermediate compounds, culminating in the desired final product(s). The essence of this process is the interaction between the photocatalyst's excited state and its specific interactions with reactants, resulting in the creation of intermediates. The process's appeal is further enhanced by its cyclic nature-the photocatalyst is rejuvenated after each cycle, ensuring ongoing and sustainable catalytic action. Nevertheless, comprehending the photocatalytic process through the modeling of photoactive materials and molecular devices demands advanced computational techniques founded on effective quantum chemistry methods, multiscale modeling, and machine learning. This review analyzes contemporary theoretical methods, spanning a range of lengths and accuracy scales, and assesses the strengths and limitations of these methods. It also explores the future challenges in modeling complex nano-photocatalysts, underscoring the necessity of integrating various methods hierarchically to optimize resource distribution across different scales. Additionally, the discussion includes the role of excited state chemistry, a crucial element in understanding photocatalysis.

Modulating the Primary and Secondary Coordination Spheres of Single Ni(II) Sites in Metal-Organic Frameworks for Boosting Photocatalysis

Though the coordination environment of single metal sites has been recognized to be of great importance in promoting catalysis, the influence of simultaneous precise modulation of primary and secondary coordination spheres on catalysis remains largely unknown. Herein, a series of single Ni(II) sites with altered primary and secondary coordination spheres have been installed onto metal-organic frameworks (MOFs) with UiO-67 skeleton, affording UiO-Ni-X-Y (X = S, O; Y = H, Cl, CF3) with X and Y on the primary and secondary coordination spheres, respectively. Upon deposition with CdS nanoparticles, the resulting composites present high photocatalytic H2 production rates, in which the optimized CdS/UiO-Ni-S-CF3 exhibits an excellent activity of 13.44 mmol g-1, ∼500 folds of the pristine catalyst (29.6 μmol g-1 for CdS/UiO), in 8 h, highlighting the key role of microenvironment modulation around Ni sites. Charge kinetic analysis and theoretical calculation results demonstrate that the charge transfer dynamics and reaction energy barrier are closely correlated with their coordination spheres. This work manifests the advantages of MOFs in the fabrication of structurally precise catalysts and the elucidation of particular influences of microenvironment modulation around single metal sites on the catalytic performance.

Two-Dimensional Layered Heterojunctions for Photoelectrocatalysis

Two-dimensional (2D) layered nanomaterial heterostructures, arising from the combination of 2D materials with other low-dimensional species, feature a large surface area to volume ratio, which provides a high density of active sites for catalytic applications and for (photo)electrocatalysis (PEC). Meanwhile, their electronic band structure and high electrical conductivity enable efficient charge transfer (CT) between the active material and the substrate, which is essential for catalytic activity. In recent years, researchers have demonstrated the potential of a range of 2D material interfaces, such as graphene, graphitic carbon nitride (g-C3N4), metal chalcogenides (MCs), and MXenes, for (photo)electrocatalytic applications. For instance, MCs such as MoS2 and WS2 have shown excellent catalytic activity for hydrogen evolution, while graphene and MXenes have been used for the reduction of carbon dioxide to higher value chemicals. However, despite their great potential, there are still major challenges that need to be addressed to fully realize the potential of 2D materials for PEC. For example, their stability under harsh reaction conditions, as well as their scalability for large-scale production are important factors to be considered. Generating heterojunctions (HJs) by combining 2D layered structures with other nanomaterials is a promising method to improve the photoelectrocatalytic properties of the former. In this review, we inspect thoroughly the recent literature, to demonstrate the significant potential that arises from utilizing 2D layered heterostructures in PEC processes across a broad spectrum of applications, from energy conversion and storage to environmental remediation. With the ongoing research and development, it is likely that the potential of these materials will be fully expressed in the near future.

Estimating Nonradiative Excited-State Lifetimes in Photoactive Semiconducting Nanostructures

The time evolution of the exciton generated by light adsorption in a photocatalyst is an important feature that can be approached from full nonadiabatic molecular dynamics simulations. Here, a crucial parameter is the nonradiative recombination rate between the hole and the electron that form the exciton. In the present work, we explore the performance of a Fermi's golden rule-based approach on predicting the recombination rate in a set of photoactive titania nanostructures, relying solely on the coupling of the ground and first excited state. In this scheme the analysis of the first excited state is carried out by invoking Kasha's rule thus avoiding computationally expensive nonadiabatic molecular dynamics simulations and resulting in an affordable estimate of the recombination rate. Our results show that, compared to previous ones from nonadiabatic molecular dynamics simulations, semiquantitative recombination rates can be predicted for the smaller titania nanostructures, and qualitative values are obtained from the larger ones. The present scheme is expected to be useful in the field of computational heterogeneous photocatalysis whenever a complex and computationally expensive full nonadiabatic molecular dynamics cannot be carried out.

Modeling photo-generated charge extraction in bulk heterojunction nanoparticles

We present a drift-diffusion model for predicting currents generated through the absorption of solar energy inside bulk heterojunction organic nanoparticles, which are, for example, promising nanomaterials for photo-catalytic water splitting. By coupling a model of the internal microstructure of the nanoparticle with the electronic properties, we show how different characteristics of the microstructure influence the efficiency of the conversion of solar energy into electrical energy. Our model provides a foundation for using computational modeling to optimize the design of photocatalytic nanoparticles.

Selectively Adsorbed p-Aminothiophenol Molecules Improve the Electrocatalytic and Photo-Electrocatalytic Hydrogen Evolution on Au/TiO2

Electrocatalytic hydrogen evolution reaction (HER) is receiving increasing attention as an effective process to produce clean energy. The commonly used precious metal catalysts can be hybridized with semiconductors to form heterostructures for the improvement of catalytic efficiency and reduction of cost. It will be promising to further improve the efficiency of heterostructure-based nanocatalysts in electrocatalytic and photocatalytic HER using a simple and effective method. Herein, we improve the efficiency of Au/TiO2 in electrocatalytic and photo-electrocatalytic HER by selectively adsorbing p-aminothiophenol (PATP) molecules. The PATP molecules are adsorbed on the gold surface by using a simple solution-based method and favor the charge separation at the Au-TiO2 interface. We also compare the PATP molecules with other thiophenol molecules in the enhancement of electrocatalytic HER. The PATP-induced enhancement in electrocatalysis is then further investigated by density functional theory (DFT) calculations, and this enhancement is attributed to a reduction in Gibbs energy of adsorbed hydrogen after surface adsorption of PATP molecules. This work provides a simple, cost-effective, and highly efficient approach to improve the electrocatalytic and photo-electrocatalytic efficiency of Au/TiO2, and this approach could be easily extended to other heterostructure-based nanocatalysts for performance enhancement and may be used in many other catalytic reactions.

Intermetallic Nanocrystals for Fuel-Cells-Based Electrocatalysis

Electrocatalysis underpins the renewable electrochemical conversions for sustainability, which further replies on metallic nanocrystals as vital electrocatalysts. Intermetallic nanocrystals have been known to show distinct properties compared to their disordered counterparts, and been long explored for functional improvements. Tremendous progresses have been made in the past few years, with notable trend of more precise engineering down to an atomic level and the investigation transferring into more practical membrane electrode assembly (MEA), which motivates this timely review. After addressing the basic thermodynamic and kinetic fundamentals, we discuss classic and latest synthetic strategies that enable not only the formation of intermetallic phase but also the rational control of other catalysis-determinant structural parameters, such as size and morphology. We also demonstrate the emerging intermetallic nanomaterials for potentially further advancement in energy electrocatalysis. Then, we discuss the state-of-the-art characterizations and representative intermetallic electrocatalysts with emphasis on oxygen reduction reaction evaluated in a MEA setup. We summarize this review by laying out existing challenges and offering perspective on future research directions toward practicing intermetallic electrocatalysts for energy conversions.

Boosting CO2 Photoreduction via Regulating Charge Transfer Ability in a One-Dimensional Covalent Organic Framework

Two-dimensional (2D) imine-based covalent organic frameworks (COFs) hold potential for photocatalytic CO2 reduction. However, high energy barrier of imine linkage impede the in-plane photoelectron transfer process, resulting in inadequate efficiency of CO2 photoreduction. Herein, we present a dimensionality induced local electronic modulation strategy through the construction of one-dimensional (1D) pyrene-based covalent organic frameworks (PyTTA-COF). The dual-chain-like edge architectures of 1D PyTTA-COF enable the stabilization of aromatic backbones, thus reducing energy loss during exciton dissociation and thermal relaxation, which provides energetic photoelectron to traverse the energy barrier of imine linkages. As a result, the 1D PyTTA-COF exhibits significantly enhanced CO2 photoreduction activity under visible-light irradiation when coordinated with metal cobalt ion, yielding a remarkable CO evolution of 1003 μmol g-1 over an 8-hour period, which surpasses that of the corresponding 2D counterpart by a factor of 59. These findings present a valuable approach to address in-plane charge transfer limitations in imine-based COFs.

Data-Driven Discovery of a Covalent Organic Framework Heterojunction as Efficient Photocatalysts for Overall Solar Water Splitting

Searching for highly efficient visible-light photocatalysts is a high-cost and time-consuming process in the water splitting field. The integration of data-driven screening based on the database and density functional theory calculations represents a promising approach. In this study, we first present a topologically assembled single-layer covalent organic framework (COF) that is used to build a COF heterojunction database via AA stacking. Then we propose a systematic search procedure for COF heterojunctions as overall solar water splitting photocatalysts, including suitable band gap (screen 1), appropriate band edge position (screen 2), spontaneous catalytic reactions for water splitting (screen 3), and efficient separation of photogenerated electrons and holes (proof). Finally, we successfully identify 1 heterojunction from the pool of 222 items as an efficient photocatalyst for overall solar water splitting. Clearly, this kind of data-driven screening procedure, based on a COF heterojunction database, opens up new avenues and inspires the development of high-performance photocatalysts.

Three-Dimensional Fully Conjugated Covalent Organic Frameworks for Efficient Photocatalytic Water Splitting

Covalent organic frameworks (COFs) are promising photocatalysts for water splitting, but their efficiency lags behind that of inorganic counterparts partly due to the limited charge transport and optical absorption properties. To overcome this limitation, we proposed to employ three-dimensional (3D) fully conjugated (FC) COFs with a topological assembly of cyclooctatetraene derivatives for photocatalytic water splitting. On the basis of first-principles calculations, we demonstrated that these 3D FC-COFs are semiconductors with exceptional charge transport and optical absorption properties. The carrier mobilities are comparable to those of inorganic semiconductors and superior to the record mobility observed in two-dimensional COFs. Additionally, the 3D FC-COFs exhibit broad visible light absorption with direct band gaps and high optical absorption coefficients. Among them, two 3D FC-COFs are identified for overall water splitting, while three others can facilitate the hydrogen evolution half-reaction. This study pioneers the design of 3D FC-COF photocatalysts, potentially advancing their applications in photocatalysis and optoelectronics.

Tandem cells for unbiased photoelectrochemical water splitting

Hydrogen is an essential energy carrier which will address the challenges posed by the energy crisis and climate change. Photoelectrochemical water splitting (PEC) is an important method for producing solar-powered hydrogen. The PEC tandem configuration harnesses sunlight as the exclusive energy source to drive both the hydrogen (HER) and oxygen evolution reactions (OER), simultaneously. Therefore, PEC tandem cells have been developed and gained tremendous interest in recent decades. This review describes the current status of the development of tandem cells for unbiased photoelectrochemical water splitting. The basic principles and prerequisites for constructing PEC tandem cells are introduced first. We then review various single photoelectrodes for use in water reduction or oxidation, and highlight the current state-of-the-art discoveries. Second, a close look into recent developments of PEC tandem cells in water splitting is provided. Finally, a perspective on the key challenges and prospects for the development of tandem cells for unbiased PEC water splitting are given.

The landscape of computational approaches for artificial photosynthesis

Artificial photosynthesis is an attractive strategy for converting solar energy into fuels, largely because the Earth receives enough solar energy in one hour to meet humanity's energy needs for an entire year. However, developing devices for artificial photosynthesis remains difficult and requires computational approaches to guide and assist the interpretation of experiments. In this Perspective, we discuss current and future computational approaches, as well as the challenges of designing and characterizing molecular assemblies that absorb solar light, transfer electrons between interfaces, and catalyze water-splitting and fuel-forming reactions.

Electrochemistry of Thin Films and Nanostructured Materials

In the last few decades, the development and use of thin films and nanostructured materials to enhance physical and chemical properties of materials has been common practice in the field of materials science and engineering. The progress which has recently been made in tailoring the unique properties of thin films and nanostructured materials, such as a high surface area to volume ratio, surface charge, structure, anisotropic nature, and tunable functionalities, allow expanding the range of their possible applications from mechanical, structural, and protective coatings to electronics, energy storage systems, sensing, optoelectronics, catalysis, and biomedicine. Recent advances have also focused on the importance of electrochemistry in the fabrication and characterization of functional thin films and nanostructured materials, as well as various systems and devices based on these materials. Both cathodic and anodic processes are being extensively developed in order to elaborate new procedures and possibilities for the synthesis and characterization of thin films and nanostructured materials.

Electronic and energy level structural engineering of graphitic carbon nitride nanotubes with B and S co-doping for photocatalytic hydrogen evolution

The ideal photocatalyst used for photocatalytic water splitting requires strong light absorption, fast charge separation/transfer ability and abundant active sites. Heteroatom doping offers a promising and rational approach to optimize the photocatalytic activity. However, achieving high photocatalytic performance remains challenging if just relying on single-element doping. Herein, Boron (B) and sulfur (S) dopants are simultaneously introduced into graphitic carbon nitride (g-C₃N₄) nanotubes by supramolecular self-assembly strategy. The developed B and S co-doped g-C₃N₄ nanotubes (B,S-TCN) exhibited an outstanding photocatalytic performance in the conversion of H₂O into H₂ (9.321 mmol g^-1h^-1), and the corresponding external quantum efficiency (EQE) reached 5.3% under the irradiation of λ = 420 nm. It is well evidenced by the closely combined experimental and (density functional theory) DFT calculations: (1) the introduction of B dopants can facilitate H₂O adsorption and drive interatomic electron transfer, leading to efficient water splitting reaction. (2) S dopants can stretch the VB position to promote the oxidation ability of g-C₃N₄, which can accelerate the consumption of holes and thus inhibit the recombination with electrons. (3) the simultaneous introduction of B and S can engineer the electronic and energy level structural of g-C₃N₄ for optimizing interior charge transfer. Finally, the purpose of maximizing photocatalytic performance is achieved.

Toward a Rigorous Theoretical Description of Photocatalysis Using Realistic Models

This Perspective aims at providing a road map to computational heterogeneous photocatalysis highlighting the knowledge needed to boost the design of efficient photocatalysts. A plausible computational framework is suggested focusing on static and dynamic properties of the relevant excited states as well of the involved chemistry for the reactions of interest. This road map calls for explicitly exploring the nature of the charge carriers, the excited-state potential energy surface, and its time evolution. Excited-state descriptors are introduced to locate and characterize the electrons and holes generated upon excitation. Nonadiabatic molecular dynamics simulations are proposed as a convenient tool to describe the time evolution of the photogenerated species and their propagation through the crystalline structure of photoactive material, ultimately providing information about the charge carrier lifetime. Finally, it is claimed that a detailed understanding of the mechanisms of heterogeneously photocatalyzed reactions demands the analysis of the excited-state potential energy surface.

Crystal properties without crystallinity? Influence of surface hydroxylation on the structure and properties of small TiO2 nanoparticles

Titania (TiO₂) nanoparticles (NPs) are widely employed in applications that take advantage of their photochemical properties (e.g. pollutant degradation, photocatalysis). Here, we study the interrelation between crystallinity, surface hydroxylation and electronic structure in titania NPs with 1.4-2.3 nm diameters using all electron density functional theory-based calculations. We show how the distribution of local coordination environments of the atoms in thermally annealed quasi-spherical non-crystalline NPs converge to those in correspondingly sized faceted crystalline anatase NPs upon increasing hydroxylation. When highly hydroxylated, annealed NPs also possess electronic energy gaps with very similar energies and band edge orbital characters to those of the crystalline anatase NPs. We refer to the crystallite-mimicking non-crystalline annealed NPs as "crystalikes". Small stable crystalike NPs could allow for photochemical applications of titania in the size range where crystalline anatase NPs tend to become thermodynamically unfavoured (<3-5 nm). Our work implies the anatase crystal structure may not be as essential as previously assumed for TiO₂ NP applications and generally suggests that crystalikes could be possible in other nanomaterials.

Carbon Dioxide Conversion on Supported Metal Nanoparticles: A Brief Review

The increasing concentration of anthropogenic CO2 in the air is one of the main causes of global warming. The Paris Agreement at COP 21 aims to reach the global peak of greenhouse gas emissions in the second half of this century, with CO2 conversion towards valuable added compounds being one of the main strategies, especially in the field of heterogeneous catalysis. In the current search for new catalysts, the deposition of metallic nanoparticles (NPs) supported on metal oxides and metal carbide surfaces paves the way to new catalytic solutions. This review provides a comprehensive description and analysis of the relevant literature on the utilization of metal-supported NPs as catalysts for CO2 conversion to useful chemicals and propose that the next catalysts generation can be led by single-metal-atom deposition, since in general, small metal particles enhance the catalytic activity. Among the range of potential indicators of catalytic activity and selectivity, the relevance of NPs’ size, the strong metal–support interactions, and the formation of vacancies on the support are exhaustively discussed from experimental and computational perspective.

Metal-Organic Frameworks as Photocatalysts for Solar-Driven Overall Water Splitting

Metal-organic frameworks (MOFs) have been frequently used as photocatalysts for the hydrogen evolution reaction (HER) using sacrificial agents with UV-vis or visible light irradiation. The aim of the present review is to summarize the use of MOFs as solar-driven photocatalysts targeting to overcome the current efficiency limitations in overall water splitting (OWS). Initially, the fundamentals of the photocatalytic OWS under solar irradiation are presented. Then, the different strategies that can be implemented on MOFs to adapt them for solar photocatalysis for OWS are discussed in detail. Later, the most active MOFs reported until now for the solar-driven HER and/or oxygen evolution reaction (OER) are critically commented. These studies are taken as precedents for the discussion of the existing studies on the use of MOFs as photocatalysts for the OWS under visible or sunlight irradiation. The requirements to be met to use MOFs at large scale for the solar-driven OWS are also discussed. The last section of this review provides a summary of the current state of the field and comments on future prospects that could bring MOFs closer to commercial application.

Mesokinetics as a Tool Bridging the Microscopic-to-Macroscopic Transition to Rationalize Catalyst Design

Heterogeneous catalysis is the workhorse of the chemical industry, and a heterogeneous catalyst possesses numerous active sites working together to drive the conversion of reactants to desirable products. Over the decades, much focus has been placed on identifying the factors affecting the active sites to gain deep insights into the structure-performance relationship, which in turn guides the design and preparation of more active, selective, and stable catalysts. However, the molecular-level interplay between active sites and catalytic function still remains qualitative or semiquantitative, ascribed to the difficulty and uncertainty in elucidating the nature of active sites for its controllable manipulation. Hence, bridging the microscopic properties of active sites and the macroscopic catalytic performance, that is, microscopic-to-macroscopic transition, to afford a quantitative description is intriguing yet challenging, and progress toward this promises to revolutionize catalyst design and preparation.In this Account, we propose mesokinetics modeling, for the first time enabling a quantitative description of active site characteristics and the related mechanistic information, as a versatile tool to guide rational catalyst design. Exemplified by a pseudo-zero-order reaction, the kinetics derivation from the Pt particle size-sensitive catalytic activity and size-insensitive activation energy suggests only one type of surface site as the dominant active site, in which the Pt(111) with almost unchanged turnover frequency (TOF₁₁₁) is further identified as the dominating active site. Such a method has been extended to identify and quantify the number (N_i) of active sites for various thermo-, electro-, and photocatalysts in chemical synthesis, hydrogen generation, environment application, etc. Then, the kinetics derivation from the kinetic compensation effects suggests a thermodynamic balance between the activation entropy and enthalpy, which exhibit linear dependences on Pt charge. Accordingly, the Pt charge can serve as a catalytic descriptor for its quantitative determination of TOF_i. This strategy has been further applied to Pt-catalyzed CO oxidation with nonzero-order reaction characteristic by taking the site coverages of surface species into consideration.Hence, substituting the above statistical correlations of N_i and TOF_i into the rate equation R = ∑N_i × TOF_i offers the mesokinetics model, which can precisely predict catalytic function and screen catalysts. Finally, based on the disentanglement of the factors underlying Pt electronic structures, a de novo strategy, from the interfacial charge distribution to reaction mechanism, kinetics, and thermodynamics parameters of the rate-determining step, and ultimately catalytic performance, is developed to map the unified mechanistic and kinetics picture of reaction. Overall, the mesokinetics not only demonstrates much potential to elucidate the quantitative interplay between active sites and catalytic activity but also provides a new research direction in kinetics analysis to rationalize catalyst design.

Carbon-doped anatase titania nanoparticles: similarities and differences with respect to bulk and extended surface models

C-Doping of titania nanoparticles is analyzed by using all-electron density functional theory-based calculations considering the (TiO₂)₈₄ nanoparticle as a realistic representative of nanoparticles in the scalable regime. Several sites are evaluated including substituting oxygen (C_O) and titanium (C_Ti) sites as well as interstitial (C_i) situations. The formation energy of such a doped structure is studied as a function of the oxygen chemical potential (or oxygen partial pressure). Our calculations predict that low partial oxygen pressure favors the formation of C-doped (TiO₂)₈₄ NPs at oxygen and interstitial sites. For the former, the most stable situation is for O sites at the inner part of the nanoparticle. Interestingly, the substitution of O by C at facet sites requires formation energies as those reported in previous studies where the bulk anatase and surfaces models were considered. However, C-doping - at other low coordinated sites not presented in extended models - is even more favorable which shows the need to employ more realistic models for nanostructures involved in photocatalytic processes.

Highly Dispersion Cu2O QDs Decorated Bi2WO6 S-Scheme Heterojunction for Enhanced Photocatalytic Water Oxidation

Developing suitable photocatalysts for the oxygen evolution reaction (OER) is still a challenging issue for efficient water splitting due to the high requirements to create a significant impact on water splitting reaction kinetics. Herein, n-type Bi₂WO₆ with flower-like hierarchical structure and p-type Cu₂O quantum dots (QDs) are coupled together to construct an efficient S-scheme heterojunction, which could enhance the migration efficiency of photogenerated charge carriers. The electrochemical properties are investigated to explore the transportation features and donor density of charge carriers in the S-scheme heterojunction system. Meanwhile, the as-prepared S-scheme heterojunction presents improved photocatalytic activity towards water oxidation in comparison with the sole Bi₂WO₆ and Cu₂O QDs systems under simulated solar light irradiation. Moreover, the initial O₂ evolution rate of the Cu₂O QDs/Bi₂WO₆ heterojunction system is 2.3 and 9.7 fold that of sole Bi₂WO₆ and Cu₂O QDs systems, respectively.