Highly Efficient Photocatalytic Water Splitting over Edge-Modified Phosphorene Nanoribbons

Enhanced electron transport and optical properties of experimentally synthesized monolayer Si9C15: a comprehensive DFT study for nanoelectronics and photocatalytic applications

Two-dimensional silicon-carbide (SixCy) materials stand out for their compatibility with current silicon-based technologies, offering unique advantages in nanoelectronics and photocatalysis. In this study, we employ density functional theory and nonequilibrium Green's function methods to investigate the electronic properties, electron transport characteristics, and optoelectronic qualities of experimentally synthesized monolayer Si9C15. Utilizing the modified deformation potential theory formula, we unveil Si9C15's significant directional anisotropy in electron mobility (706.42 cm2 V-1 s-1) compared to holes (432.84 cm2 V-1 s-1) in the a direction. The electrical transport calculations reveal that configurations with a 3 nm channel length demonstrate an ON state when biased, reaching a peak current of 150 nA. Moreover, this maximum current value escalates to 200 nA under tensile strain, marking an increase of approximately 100 times compared to the 5 nm channel, which remains in an OFF state. Si9C15 exhibits high light absorption coefficients (∼105 cm-1) and suitable band edge positions for water splitting at pH 0-7. Applying 1-5% tensile strain can tune the conduction band minimum and valence band maximum closer to the standard redox potentials, enhancing photocatalytic water splitting efficiency. Remarkably, under illumination at pH 0 and 7, Si9C15 can spontaneously catalyze water splitting, demonstrating its potential as a highly efficient photocatalyst. Our findings emphasize the importance of strain control and device length optimization for performance enhancement in nanoelectronics and renewable energy applications, positioning Si9C15 as a promising material for high-performance field-effect transistors and photocatalytic water splitting.

Asymmetric Potential Model of Two-Dimensional Imine Covalent Organic Frameworks with Enhanced Quantum Efficiency for Photocatalytic Water Splitting

Two-dimensional (2D) covalent organic frameworks (COFs) assembled using building blocks have been widely employed in photocatalysis due to their customizable optoelectronic characteristics and porous structure, which facilitate charge carrier and mass movement. Nevertheless, the development of COF photocatalysts encounters a continuous obstacle in enhancing the efficiency of photocatalysis, impeded by a limited comprehension of the orbital interaction between molecular fragments and linkers. In this study, we present a model that examines the interaction between molecular fragments in an imine-based COF at the frontier molecular orbital level, enabling us to comprehend the impact of manipulating linkers on light adsorption, exciton efficiency, and catalytic activity. Our findings demonstrate that altering the connecting orientation of 14 R-C=N-R imine linkers in 2D COFs can enhance solar-to-hydrogen (STH) efficiency under visible light from 2.76% to 4.24%. This research has the potential to provide a valuable model for refining photocatalysts with enhanced photocatalytic performance.

Seeded growth of single-crystal black phosphorus nanoribbons

Two-dimensional materials have emerged as an important research frontier for overcoming the challenges in nanoelectronics and for exploring new physics. Among them, black phosphorus, with a combination of a tunable bandgap and high mobility, is one of the most promising systems. In particular, black phosphorus nanoribbons show excellent electrostatic gate control, which can mitigate short-channel effects in nanoscale transistors. Controlled synthesis of black phosphorus nanoribbons, however, has remained an outstanding problem. Here we report large-area growth of black phosphorus nanoribbons directly on insulating substrates. We seed the chemical vapour transport growth with black phosphorus nanoparticles and obtain uniform, single-crystal nanoribbons oriented exclusively along the [100] crystal direction. With comprehensive structural calculations, we discover that self-passivation at the zigzag edges holds the key to the preferential one-dimensional growth. Field-effect transistors based on individual nanoribbons exhibit on/off ratios up to ~104, confirming the good semiconducting behaviour of the nanoribbons. These results demonstrate the potential of black phosphorus nanoribbons for nanoelectronic devices and also provide a platform for investigating the exotic physics in black phosphorus.

Efficient photoreduction of carbon dioxide to ethanol using diatomic nitrogen-doped black phosphorus

Successful conversion of CO2 into C2 products requires the development of new catalysts that overcome the difficulties in efficient light harvesting and CO-CO coupling. Herein, density functional theory (DFT) is used to assess the photoreduction properties of nitrogen-doped black phosphorus. The geometric structure, redox potential, first step of hydrogenation activation, CO desorption, and CO-CO coupling are systematically calculated, based on which the diatomic nitrogen-doped black phosphorus (N2@BPV) stands out. The calculated results of the CO2RR pathway demonstrate that N2@BPV has excellent selectivity and high activity for CH3CH2OH production. The results of the time-dependent ab initio nonadiabatic molecular dynamics simulation show that the diatomic N active sites of N2@BPV facilitate charge separation and inhibit electron-hole recombination. In addition, the activation mechanism of CO2 is studied. The main reason for CO2 activation is attributed to the imbalance in electron transfer that destroys the symmetry of CO2. We expect that our study will offer some theoretical guidance in CO2 conversion.

Investigating the mechanism of phosphorene nanoribbon synthesis by discharging black phosphorus intercalation compounds

Phosphorene nanoribbons (PNRs) can be synthesised in intrinsically scalable methods from intercalation of black phosphorus (BP), however, the mechanism of ribbonisation remains unclear. Herein, to investigate the point at which nanoribbons form, we decouple the two key synthesis steps: first, the formation of the BP intercalation compound, and second, the dissolution into a polar aprotic solvent. We find that both the lithium intercalant and the negative charge on the phosphorus host framework can be effectively removed by addition of phenyl cyanide to return BP and investigate whether fracturing to ribbons occurred after the first step. Further efforts to exfoliate mechanically with or without solvent reveal that the intercalation step does not form ribbons, indicating that an interaction between the amidic solvent and the intercalated phosphorus compound plays an important role in the formation of nanoribbons.

Ultrasound-Driven Non-Metallic Fenton-Active Center Construction for Extensive Chemodynamic Therapy

Chemodynamic therapy (CDT) is an emerging tumor microenvironment-responsive cancer therapeutic strategy based on Fenton/Fenton-like reactions. However, the effectiveness of CDT is subject to the slow kinetic rate and non-homogeneous distribution of H2 O2 . In this study, a conceptual non-metallic "Fenton-active" center construction strategy is proposed to enhance CDT efficiency using Bi0.44 Ba0.06 Na0.5 TiO2.97 (BNBT-6) nanocrystals. The separated charge carriers under a piezoelectric-induced electric field synchronize the oxidation of H2 O and reduction of H2 O2 , which consequently increases hydroxyl radical (·OH) yield even under low H2 O2 levels. Moreover, acceptor doping induces electron-rich oxygen vacancies to facilitate the dissociation of H2 O2 and H2 O and further promote ·OH generation. In vitro and in vivo experiments demonstrate that BNBT-6 induces extensive intracellular oxidative stress and enhances cell-killing efficiency by activating necroptosis in addition to the conventional apoptotic pathway. This study proposes a novel design approach for nanomaterials used in CDT and presents a new treatment strategy for apoptosis-resistant tumors.

Recent Advances in Phosphorene: Structure, Synthesis, and Properties

Phosphorene is a 2D phosphorus atomic layer arranged in a honeycomb lattice like graphene but with a buckled structure. Since its exfoliation from black phosphorus in 2014, phosphorene has attracted tremendous research interest both in terms of synthesis and fundamental research, as well as in potential applications. Recently, significant attention in phosphorene is motivated not only by research on its fundamental physical properties as a novel 2D semiconductor material, such as tunable bandgap, strong in-plane anisotropy, and high carrier mobility, but also by the study of its wide range of potential applications, such as electronic, optoelectronic, and spintronic devices, energy conversion and storage devices. However, a lot of avenues remain to be explored including the fundamental properties of phosphorene and its device applications. This review recalls the current state of the art of phosphorene and its derivatives, touching upon topics on structure, synthesis, characterization, properties, stability, and applications. The current needs and future opportunities for phosphorene are also discussed.

Enhance Hydrogen Evolution Reaction Performance via Double-Stacked Edges of Black Phosphorene

Based on the density functional theory (DFT) calculations, we explored the structures and HER catalytic properties of reconstructed and double-stacked black phosphorene (BP) edges. Ten bilayer BP edges were constructed by the double stacking of three typical monolayer edges, i.e., zigzag (ZZ) edge, armchair (AC) edge, skewed diagonal (SD) edge, and their reconstructed derivatives with their layer's configurations, edge deformations and thermodynamic stabilities were discussed. Based on these edges, five chemical sites on four bilayer BP edges were selected to be promising candidates for a HER catalyst, which present higher HER activities than that of Pt(111). Besides, among these four edges, two edges have even lower energetic barriers for the Tafel reaction. Compared with the monolayer edges, these selected bilayer BP edges confirm the remarkable enhancement of the HER catalytic properties, which can be attributed to their unique edge structures and the enhanced electronic densities after the hydrogen adsorptions. Finally, the thermostability of these edges at room temperature has also been proved by the DFT-MD simulations. This theoretic study deepens our fundamental understanding of the double-stacked edge structures of the BP and provides a new way for the rational design of highly efficient and noble-metal-free HER catalysts.

Kagome-like BiP3 Monolayer: An Emerging Quasi-Direct Auxetic Semiconductor Coupled with High Anisotropic Mobility toward Visible-Light-Driven Photoelectrocatalytic pH-Robust Overall Water-Splitting

Two-dimensional (2D) Janus materials exhibit an outstanding potential that can meet the rigorous requirements of photocatalytic water splitting resulting from their unique atomic arrangement. However, these materials are quite scarce. Through ab initio density functional theory calculations, we introduce a kagome topology into the honeycomb lattice of blue phosphorene using phosphorus and bismuth atoms to build a hybrid honeycomb-like kagome lattice, realized by a hitherto unknown kagome-like Janus-like BiP3 monolayer with robust stability. Excitingly, the out-of-plane asymmetry benefiting from kagome and honeycomb topologies gives rise to a significantly negative out-of-plane Poisson's ratio and an obvious built-in electric field pointing from the sublayer of the P atom to the sublayer of the Bi atom. In conjunction with the investigations that encompass semiconducting properties, such as a quasi-direct gap, suitable band-edge positions, effective visible-light absorption, and high carrier mobility, the BiP3 monolayer achieves overall water splitting at pH 0-14 regardless of strain. Moreover, this intrinsic electric field provides a sufficient photogenerated carrier driving force for water splitting. The bare BiP3 comprises P and Bi atoms that function as catalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) active sites, respectively. Upon exposure to light, the reaction of water into H2 and O2 can be observed across a pH range of 0-14. Meanwhile, by designing a transition-metal single-atom catalyst (TM@BiP3), our investigations have shown that embedding a single TM on BiP3 is a feasible route to improving the HER/OER activity by reducing the overpotentials to -0.039 and 0.58 eV for Mo and Os atoms, respectively. In this case, the positive value of the external potential acts as a sufficient OER driving force, i.e., in the light environment, the Os@BiP3 system can promote water molecules spontaneously oxidized into O2 at pH 0-14.

D-π-A array structure of Bi4Ti3O12-triazine-aldehyde group benzene skeleton for enhanced photocatalytic uranium (VI) reduction

Photocatalytic reduction of U^VI to U^IV can help remove U from the environment and thus reduce the harmful impacts of radiation emitted by uranium isotopes. Herein, we first synthesized Bi₄Ti₃O₁₂ (B1) particles, then B1 was crosslinked with 6-chloro-1,3,5-triazine-diamine (DCT) to afford B2. Finally, B3 was formed using B2 and 4-formylbenzaldehyde (BA-CHO) to investigate the utility of the D-π-A array structure for photocatalytic U^VI removal from rare earth tailings wastewater. B1 lacked adsorption sites and displayed a wide band gap. The grafted triazine moiety in B2 introduced active sites and narrowed the band gap. Notably, B3, a Bi₄Ti₃O₁₂ (donor)-triazine unit (π-electron bridge)-aldehyde benzene (acceptor) molecule, effectively formed the D-π-A array structure, which formed multiple polarization fields and further narrowed the band gap. Therefore, U^VI was more likely to capture electrons at the adsorption site of B3 and be reduced to U^IV due to energy level matching effects. U^VI removal capacity of B3 under simulated sunlight was 684.9 mg g^-1, 2.5 times greater than B1 and 1.8 times greater than B2. B3 was still active after multiple reaction cycles, and U^VI removal from tailings wastewater reached 90.8%. Overall, B3 provides an alternative design scheme for enhancing photocatalytic performance.

Prediction of 2D IV-V semiconductors: flexible monolayers with tunable band gaps and strong optical absorption as water-splitting photocatalysts

Seeking novel photocatalysts for water splitting is one of the tasks in developing 2D materials. In the framework of density functional theory, we predict a family of 2D pentagonal sheets called penta-XY₂ (X = Si, Ge, and Sn; Y = P, As, and Sb), and modulate their properties via strain engineering. Penta-XY₂ monolayers exhibit flexible and anisotropic mechanical properties, due to their low in-plane Young's modulus in the range of 19-42 N m^-1. All six XY₂ sheets are semiconductors with a band gap ranging from 2.07 eV to 2.51 eV, and the positions of their conduction and valence band edges match well with the reaction potentials of H⁺/H₂ and O₂/H₂O, so they are suitable for photocatalytic water splitting. Under tensile/compression strains, the band gaps, band edge positions and light absorption of GeAs, SnP₂ and SnAs₂ could be tuned to improve their photocatalytic performance.

Facile construction of a robust CuS@NaNbO3 nanorod composite: A unique p-n heterojunction structure with superior performance in photocatalytic hydrogen evolution

The construction of heterojunctions is commonly regarded as an efficient way to promote the production of hydrogen via photocatalytic water splitting through the enhancement of interfacial interactions. The p-n heterojunction is an important kind of heterojunction with an inner electric field based on the different properties of semiconductors. In this work, we reported the synthesis of a novel CuS/NaNbO₃ p-n heterojunction by depositing CuS nanoparticles on the external surface of NaNbO₃ nanorods, using a facile calcination and hydrothermal method. Through the screening of different ratios, the optimum hydrogen production activity reached 1603 μmol·g^-1·h^-1, which is much higher than that of NaNbO₃ (3.6 times) and CuS (2.7 times). Subsequent characterizations proved semiconductor properties and the existence of p-n heterojunction interactions between the two materials, which inhibited the recombination of photogenerated carriers and improved the efficiency of electron transfer. This work provides a meaningful strategy to utilize the p-n heterojunction structure for the promotion of photocatalytic hydrogen production.

Materials design of edge-modified polymeric carbon nitride nanoribbons for the photocatalytic CO2 reduction reaction

Nanoribbon construction and modification with functional groups are important methods to improve the performance of photocatalysts. In this paper, density functional theory (DFT) calculations are applied to assess the electron absorption capacity of different model structures in the photocatalytic CO₂ reduction reaction (CO₂RR), i.e., melon-based carbon nitride nanoribbons (MNRs) and edge-modified melon-based carbon nitride nanoribbons (X-MNRs, X = NO₂, CF₃, CN, CHO, F, Cl, CCH, OH, SH, CH₃, and H). It is found that X-MNRs (X = NO₂, CN, CHO, CCH, OH, and H) have a significantly reduced band gap. Meanwhile, the VBM and CBM are effectively separated with the same optical absorption wavelength range, agreeing with the experimental observations. More importantly, the Gibbs free energy difference of the CO₂RR rate-determining step is greatly reduced in MNRs, CHO-MNRs, CN-MNRs etc. with the formation of CO or HCOOH. The mechanism investigation indicates that the materials design via edge-group modification can optimize the CO₂RR process.

Fully Dispersed IrOx Atomic Clusters Enable Record Photoelectrochemical Water Oxidation of Hematite in Acidic Media

Ir-based materials are still the benchmark catalysts for various reactions in acidic environment, but the high loading and low atom utilization limit their large-scale deployment. Herein, we report an effective strategy for implanting fully dispersed iridium-oxide atomic clusters onto hematite for boosting photoelectrochemical water oxidation in acidic solution. The resulting photoanode achieves a record-high photocurrent of 1.35 mA cm^-2 at 1.23 V, corresponding to a mass activity of 172.70 A g^-1 (3 times higher than electrodeposited control sample) and demonstrating the merits from the high atomic utilization of Ir. The systematically experimental and theoretical results reveal that the performance improvement correlates with the modulated electronic structure including the adjusted Fermi level and d-band center, which significantly enhances charge separation efficiency and promotes the conversion from intermediate *O into *OOH.

InN/XS2 (X = Zr, Hf) vdW heterojunctions: promising Z-scheme systems with high hydrogen evolution activity for photocatalytic water splitting

Z-scheme van der Waals heterojunctions are very attractive photocatalysts attributed to their excellent reduction and oxidation abilities. In this paper, we designed InN/XS₂ (X = Zr, Hf) heterojunctions and explored their electronic structure properties, photocatalytic performance, and light absorption systematically using first-principles calculations. We found that the valence-band maximum (VBM) and conduction-band minimum (CBM) of the InN/XS₂ (X = Zr, Hf) heterojunctions are contributed by InN and XS₂, respectively. Photo-generated carriers transferring along the Z-path can accelerate the recombination of interlayer electron-hole pairs. Therefore, the photogenerated electrons in the CBM of the InN layer can be maintained making the hydrogen evolution reaction occur continuously, while photogenerated holes in the VBM of the Ti₂CO₂ layer make the oxygen evolution reaction occur continuously. The band edge positions of heterojunctions can straddle the required water redox potentials, while pristine InN and XS₂ (X = Zr, Hf) can only be used for photocatalytic hydrogen evolution or oxygen evolution, respectively. Furthermore, the HER barriers can be tuned by transition metal doping. With Cr doping, the hydrogen evolution reaction (HER) barriers decrease to -0.12 for InN/ZrS₂ and -0.05 eV for InN/HfS₂, very close to the optimal value (0 eV). In addition, the optical absorption coefficient is as high as 10⁵ cm^-1 in the visible and ultraviolet regions. Therefore, the InN/XS₂ (X = Zr, Hf) heterojunctions are expected to be excellent photocatalysts for water splitting.

Quasi-one-dimensional phosphorene nanoribbons grown on silicon by space-confined chemical vapor transport

Phosphorene nanoribbons (PNRs) combine the flexibility of one-dimensional (1D) nanomaterials with the large specific surface area and the edge and electron confinement effects of two-dimensional (2D) nanomaterials. In spite of the substantial advances in bulk black phosphorus (BP) manufacturing, achieving PNRs without degradation is still a big challenge. In this work, we present a strategy for the space-confined chemical vapor transport synthesis of quasi-one-dimensional surface-passivated monocrystalline PNRs on a silicon substrate. The growth mechanism of the PNRs is proposed by combining experimental results and DFT calculations, indicating that the P₄ molecules can break, restructure, and epitaxially nucleate on the surface of the Au₃SnP₇ catalyst, and finally prefer to grow along the zigzag (ZZ) direction to form PNRs. The low gas flow rate and an appropriate phosphorus molecule concentration allow the growth of PNRs with structural integrity, which can be regulated by the amount of red phosphorus and the confined space.

Interface Engineering in 2D/2D Heterogeneous Photocatalysts

Assembling different 2D nanomaterials into heterostructures with strong interfacial interactions presents a promising approach for novel artificial photocatalytic materials. Chemically implementing the 2D nanomaterials' construction/stacking modes to regulate different interfaces can extend their functionalities and achieve good performance. Herein, based on different fundamental principles and photochemical processes, multiple construction modes (e.g., face-to-face, edge-to-face, interface-to-face, edge-to-edge) are overviewed systematically with emphasis on the relationships between their interfacial characteristics (e.g., point, linear, planar), synthetic strategies (e.g., in situ growth, ex situ assembly), and enhanced applications to achieve precise regulation. Meanwhile, recent efforts for enhancing photocatalytic performances of 2D/2D heterostructures are summarized from the critical factors of enhancing visible light absorption, accelerating charge transfer/separation, and introducing novel active sites. Notably, the crucial roles of surface defects, cocatalysts, and surface modification for photocatalytic performance optimization of 2D/2D heterostructures are also discussed based on the synergistic effect of optimization engineering and heterogeneous interfaces. Finally, perspectives and challenges are proposed to emphasize future opportunities for expanding 2D/2D heterostructures for photocatalysis.

Engineering the Near-Surface Structure of WO3 by an Amorphous Layer with Trivalent Ni and Self-Adapting Oxygen Vacancies for Efficient Photocatalytic and Photoelectrochemical Acidic Oxygen Evolution Reaction

Exploiting an effective strategy to tailor the construction, composition, and local electronic structure of the photocatalyst surface is pivotal to photocatalytic activity, but remains challenging. Transition metal elements can boost the oxygen evolution reaction activity especially one like Ni in high oxidation states, whereas it is uneasy to prepare Ni³⁺ under mild conditions or play to their strengths in acidic conditions. In this article, we report a facile "etch and dope" synthesis of Ni³⁺-doped WO₃ nanosheets with oxygen vacancies. Through detailed experimental and theoretical studies, it is established that the abundant oxygen vacancies and the doped Ni³⁺ ions in the near-surface amorphous layer can synergistically optimize the surface electronic structure of WO₃ and the adsorption and desorption of intermediates. Impressively, the etched WO₃ nanosheets coupled with Ni³⁺ offer a greatly promoted photocatalytic performance of 1.78 mmol g^-1 h^-1, and the photoanode achieves a photocurrent density of 2.11 mA cm^-2 at 1.23 V versus reversible hydrogen electrode (V_RHE). This work provides a new inspiration for rational manufacture of defects and high-valence metal ions in catalysts for photocatalytic and photoelectrochemical reactions.

Rational Design of Black Phosphorus-Based Direct Z-Scheme Photocatalysts for Overall Water Splitting: The Role of Defects

Black phosphorus (BP) has received increasing interest as a promising photocatalyst for water splitting. Nevertheless, exploring the underlying hydrogen evolution reaction (HER) mechanism and improving the water oxidizing ability remains an urgent task. Here, using first-principles calculations, we uncover the role of point defects in improving the HER activity of BP photocatalysts. We demonstrate that the defective phosphorene can be effectively activated by the photoinduced electrons under solar light, exhibiting high HER catalytic activity in a broad pH range (0-10). Besides, we propose that the direct Z-scheme in the defective BP/SnSe₂ heterobilayer is quite feasible for photocatalytic overall water splitting. This mechanism could be further verified based on the excited state dynamics method. The role of point defects in the photocatalytic mechanism provides useful insights for the development of BP photocatalysts.

Electronic Modulation of Ru Nanosheet by d-d Orbital Coupling for Enhanced Hydrogen Oxidation Reaction in Alkaline Electrolytes

The alkaline polymer electrolyte fuel cells (APEFCs) hold great promise for using nonnoble metal-based electrocatalysts toward the cathodic oxygen reduction reaction (ORR), but are hindered by the sluggish anodic hydrogen oxidation reaction (HOR) in alkaline electrolytes. Here, a strategy is reported to promote the alkaline HOR performance of Ru by incorporating 3d-transition metals (V, Fe, Co, and Ni), where the conduction band minimum (CBM) level of Ru can be rationally tailored through strong d-d orbital coupling. As expected, the obtained RuFe nanosheet exhibits outstanding HOR performance with the mass activity of 233.46 A g_PGM ^-1 and 23-fold higher than the Ru catalyst, even threefold higher than the commercial Pt/C. APEFC employing this RuFe as anodic catalyst gives a peak power density of 1.2 W cm^-2 , outperforming the documented Pt-free anodic catalyst-based APEFCs. Experimental results and density functional theory calculations suggest the enhanced OH-binding energy and reduced formation energy of water derived from the downshifted CBM level of Ru contribute to the enhanced HOR activity.

Enhanced Photocatalytic Hydrogen Production Activity by Constructing a Robust Organic-Inorganic Hybrid Material Based Fulvalene and TiO2

A novel redox-active organic-inorganic hybrid material (denoted as H₄TTFTB-TiO₂) based on tetrathiafulvalene derivatives and titanium dioxide with a micro/mesoporous nanomaterial structure has been synthesized via a facile sol-gel method. In this study, tetrathiafulvalene-3,4,5,6-tetrakis(4-benzoic acid) (H₄TTFTB) is an ideal electron-rich organic material and has been introduced into TiO₂ for promoting photocatalytic H₂ production under visible light irradiation. Notably, the optimized composites demonstrate remarkably enhanced photocatalytic H₂ evolution performance with a maximum H₂ evolution rate of 1452 μmol g⁻¹ h⁻¹, which is much higher than the prototypical counterparts, the common dye-sensitized sample (denoted as H₄TTFTB-5.0/TiO₂) (390.8 μmol g⁻¹ h⁻¹) and pure TiO₂ (18.87 μmol g⁻¹ h⁻¹). Moreover, the composites perform with excellent stability even after being used for seven time cycles. A series of characterizations of the morphological structure, the photoelectric physics performance and the photocatalytic activity of the hybrid reveal that the donor-acceptor structural H₄TTFTB and TiO₂ have been combined robustly by covalent titanium ester during the synthesis process, which improves the stability of the hybrid nanomaterials, extends visible-light adsorption range and stimulates the separation of photogenerated charges. This work provides new insight for regulating precisely the structure of the fulvalene-based composite at the molecule level and enhances our in-depth fundamental understanding of the photocatalytic mechanism.

Versatile Gold Telluride Iodide Monolayer as a Potential Photocatalyst for Water Splitting

Two-dimensional materials promise great potential for photochemical water splitting due to the abundant active sites and large surface area, but few of the known materials meet the rigorous requirements. In this work, we systematically investigate structural, electronic, and optical properties of an experimentally unexplored 2D material, i.e., gold telluride iodide (AuTeI) monolayer using density functional theory and Bethe–Salpeter equation approaches. Bulk AuTeI is a layered material and was realized in experiments a few decades ago. However, its bandgap is relatively small for water splitting. We find the exfoliation of monolayer AuTeI from the bulk phase is highly favorable, and 2D AuTeI is dynamically stable. The bandgap of 2D AuTeI becomes larger due to the quantum confinement effect. Importantly, the edge positions of the conduction band minimum and valence band maximum of 2D AuTeI perfectly fit the water oxidation and reduction potentials, enabling it a promising photocatalyst for water splitting. Additionally, the exciton binding energy of 2D AuTeI is calculated to be 0.35 eV, suggesting efficient electron-hole separation. Our results highlight a new and experimentally accessible 2D material for potential application in photocatalytic water splitting.

Modified, Solvothermally Derived Cr-doped SnO2 Nanostructures for Enhanced Photocatalytic and Electrochemical Water-Splitting Applications

Cr-doped SnO₂ nanostructures with a dopant concentration ranging from 1 to 5% have been successfully prepared using low-temperature modified solvothermal synthesis. The as-prepared nanoparticles showed a rutile tetragonal structure with a rough undefined morphology having no other elemental impurities. The particle shape and size, band gap, and specific surface area of the samples were investigated by scanning electron microscopy, transmission electron microscopy (TEM), high-resolution TEM, UV-visible diffused reflectance spectroscopy, and Brunauer-Emmett-Teller surface area studies. The optical band gap was found in the range of 3.23-3.67 eV and the specific surface area was in the range of 108-225 m²/g, which contributes to the significantly enhanced photocatalytic and electrochemical performance. Photocatalytic H₂ generation of as-prepared Cr-doped SnO₂ nanostructures showed improved effect of the increasing dopant concentration with narrowing of the band gap. Electrochemical water-splitting studies also stressed upon the superiority of Cr-doped SnO₂ nanostructures over pristine SnO₂ toward hydrogen evolution reaction and oxygen evolution reaction responses.

Perylenetetracarboxylic acid nanosheets with internal electric fields and anisotropic charge migration for photocatalytic hydrogen evolution

Highly efficient hydrogen evolution reactions carried out via photocatalysis using solar light remain a formidable challenge. Herein, perylenetetracarboxylic acid nanosheets with a monolayer thickness of ~1.5 nm were synthesized and shown to be active hydrogen evolution photocatalysts with production rates of 118.9 mmol g⁻¹ h⁻¹_. The carboxyl groups increased the intensity of the internal electric fields of perylenetetracarboxylic acid from the perylene center to the carboxyl border by 10.3 times to promote charge-carrier separation. The photogenerated electrons and holes migrated to the edge and plane, respectively, to weaken charge-carrier recombination. Moreover, the perylenetetracarboxylic acid reduction potential increases from −0.47 V to −1.13 V due to the decreased molecular conjugation and enhances the reduction ability. In addition, the carboxyl groups created hydrophilic sites. This work provides a strategy to engineer the molecular structures of future efficient photocatalysts.

While organic semiconductors provide a highly tailorable set of systems for solar-to-fuel conversion, such materials often show worse activities than inorganic materials. Here, authors prepare perylene-based nanosheets that demonstrate excellent performances for photocatalytic H₂ evolution.

Engineering 2D Materials for Photocatalytic Water-Splitting from a Theoretical Perspective

Splitting of water with the help of photocatalysts has gained a strong interest in the scientific community for producing clean energy, thus requiring novel semiconductor materials to achieve high-yield hydrogen production. The emergence of 2D nanoscale materials with remarkable electronic and optical properties has received much attention in this field. Owing to the recent developments in high-end computation and advanced electronic structure theories, first principles studies offer powerful tools to screen photocatalytic systems reliably and efficiently. This review is organized to highlight the essential properties of 2D photocatalysts and the recent advances in the theoretical engineering of 2D materials for the improvement in photocatalytic overall water-splitting. The advancement in the strategies including (i) single-atom catalysts, (ii) defect engineering, (iii) strain engineering, (iv) Janus structures, (v) type-II heterostructures (vi) Z-scheme heterostructures (vii) multilayer configurations (viii) edge-modification in nanoribbons and (ix) the effect of pH in overall water-splitting are summarized to improve the existing problems for a photocatalytic catalytic reaction such as overcoming large overpotential to trigger the water-splitting reactions without using cocatalysts. This review could serve as a bridge between theoretical and experimental research on next-generation 2D photocatalysts.

Two-dimensional InSb/GaAs- and InSb/InP-based tandem photovoltaic device with matched bandgap

The past several years have witnessed remarkable research efforts to develop high-performance photovoltaics (PVs), to curtail the energy crisis by avoiding dependence on traditional fossil fuels. In this regard, there is an urgent need to accelerate research progress on new low-dimensional semiconductors with superior electronic and optical properties. Herein, combining abundant related PV experimental data in the literature and our systematic theoretical calculations, we propose two-dimensional (2D) InSb/GaAs and InSb/InP-based tandem PVs with high solar-to-electric efficiency up to near 30.0%. Firstly, according to first-principles calculations, the stability, electronic and optical properties of single-layer group-III-V materials (XY, X = Ga and In, Y = N, P, As, Sb, and Bi) are systematically introduced. Next, due to the high bandgap (E_g) of GaAs and InP being a perfect match with the low E_g of InSb, InSb/GaAs- and InSb/InP-based tandem PVs are constructed. In addition, the complementary absorption spectra of these two subcells can facilitate the achievement of high tandem power conversion efficiency. Furthermore, we have analyzed in detail the influencing factors for PCE and the physical mechanism of the optimized match between the top and bottom subcells in the tandem configurations. Our designed 2D-semiconductor-based PVs can be expected to bring a new perspective for future commercialized high-efficiency energy devices.

Efficient Photoinduced Electron Transfer from Pyrene-o-Carborane Heterojunction to Selenoviologen for Enhanced Photocatalytic Hydrogen Evolution and Reduction of Alkynes

A series of pyrene or pyrene-o-carborane-appendant selenoviologens (Py-SeV²⁺ , Py-Cb-SeV²⁺ ) for enhanced photocatalytic hydrogen evolution reaction (HER) and reduction of alkynes is reported. The efficient photoinduced electron transfer (PET) from electron-rich pyrene-o-carborane heterojunction (Py-Cb) with intramolecular charge transfer (ICT) characteristic to electron-deficient selenoviologen (SeV²⁺ ) (k_ET = 1.2 × 10¹⁰ s^-1 ) endows the accelerating the generation of selenoviologen radical cation (SeV^+• ) compared with Py-SeV²⁺ and other derivatives. The electrochromic/electrofluorochromic devices' (ECD and EFCD) measurements and supramolecular assembly/disassembly processes of SeV²⁺ and cucurbit[8]uril (CB[8]) results show that the PET process can be finely tuned by electrochemical and host-guest chemistry methods. By combination with Pt-NPs catalyst, the Py-Cb-SeV²⁺ -based system shows high-efficiency visible-light-driven HER and highly selective phenylacetylene reduction due to the efficient PET process.

Designing Direct Z-Scheme Heterojunctions Enabled by Edge-Modified Phosphorene Nanoribbons for Photocatalytic Overall Water Splitting

Direct Z-scheme photocatalyst possess promising potential to utilize solar radiation for photocatalytic overall water splitting; however, the design and characterization remain challenging. Here, we construct and verify a direct Z-scheme heterojunction using edge-modified phosphorene-nanoribbons (X-PNRs, where X = OH and OCN) with first-principles ground-state and excited-state density functional theory (DFT) calculations. The ground-state calculations provide fundamental properties such as geometric structure and band alignment. The linear-response time-dependent DFT (LR-TDDFT) calculations exhibit the photogenerated charge distribution and demonstrate the generation of interlayer excitons in heterojunctions, which are advantageous to the electron-hole recombination in Z-scheme heterojunctions. The ultrafast charge transfer at the interface studied by time-dependent ab initio nonadiabatic molecular dynamics (NAMD) simulations indicates that interlayer electron-hole recombination is prior to intralayer recombination for the OH/OCN-PNRs heterojunction, showing the characteristics of a Z-scheme heterojunction. Therefore, our computational work provides a universal strategy to design direct Z-scheme heterojunction photocatalysts for overall water splitting.

Layered post-transition-metal dichalcogenide SnGe2N4 as a promising photoelectric material: a DFT study

First-principles calculations were performed to study a novel layered SnGe₂N₄ compound, which was found to be dynamically and thermally stable in the 2H phase, with the space group P6̄m2 and lattice constant a = 3.143 Å. Due to its hexagonal structure, SnGe₂N₄ exhibits isotropic mechanical properties on the x–y plane, where the Young’s modulus is 335.49 N m⁻¹ and the Poisson’s ratio is 0.862. The layered 2H SnGe₂N₄ is a semiconductor with a direct band gap of 1.832 eV, allowing the absorption of infrared and visible light at a rate of about 10⁴ cm⁻¹. The DOS is characterized by multiple high peaks in the valence and conduction bands, making it possible for this semiconductor to absorb light in the ultraviolet region with an even higher rate of 10⁵ cm⁻¹. The band structure, with a strongly concave downward conduction band and rather flat valence band, leads to a high electron mobility of 1061.66 cm² V⁻¹ s⁻¹, which is substantially greater than the hole mobility of 28.35 cm² V⁻¹ s⁻¹. This difference in mobility is favorable for electron–hole separation. These advantages make layered 2H SnGe₂N₄ a very promising photoelectric material. Furthermore, the electronic structure of 2H SnGe₂N₄ responds well to strain and an external electric field due to the specificity of the p–d hybridization, which predominantly constructs the valence bands. As a result, strain and external electric fields can efficiently tune the band gap value of 2H SnGe₂N₄, where compressive strain widens the band gap, meanwhile tensile strain and external electric fields cause band gap reduction. In particular, the band gap is decreased by about 0.25 eV when the electric field strength increases by 0.1 V Å⁻¹, making a semiconductor–metal transition possible for the layered SnGe₂N₄.

The promising photoelectric semiconductor 2H SnGe₂N₄ has a tunable electronic structure which is favorable for the absorption of light in the infrared and visible regions.

Janus monolayer HfSO with improved optical properties as a novel material for photovoltaic and photocatalyst applications

First principles calculations were performed to investigate the photocatalytic behavior of 2D Janus monolayer HfSO at equilibrium and under the influence of strains and external electric fields.

An efficient strategy to enhance the photocatalytic activity of Ir-doped SrTiO3: a hybrid DFT approach

Present study revealed that the codoping of Al, Cr, and La not only stabilize Ir in preferred oxidation state, but also form charge compensated system, thereby ensuring improved photoconversion efficiency under visible light.

Efficient Combination of G-C3 N4 and CDs for Enhanced Photocatalytic Performance: A Review of Synthesis, Strategies, and Applications

Recently, heterogeneous photocatalysts have achieved much interest on account of their great potential applications in resolving many tough energy and environmental troubles around the world through an ecologically sustainable way. Heterogeneous nanocomposites composed of graphitic carbon nitride (g-C₃ N₄ ) and carbon dots (CDs) possess broad spectrum absorption, appropriate electronic band structures, rapid carrier mobility, abundant reserves, excellent chemical stability, and facile synthesis methods, which make them promising composite photocatalysts for suitable applications such as photocatalytic solar fuels production and contaminant decomposition. With the rapid development in photocatalysis by hybridization of g-C₃ N₄ and CDs, a systematic summary and prospection of performance improvement are urgent and meaningful. This review first focuses on various kinds of effectively synthetic methods of composites. Following, the strategies available for enhanced performance, including morphology optimization, spectral absorption improvement, ternary or quaternary composition hybrid, lateral or vertical heterostructures construction, heteroatom doping, and so forth, are fully discussed. Then, the applications mainly in efficient photocatalytic hydrogen generation, photocatalytic carbon dioxide reduction, and organic pollutants degradation are systematically demonstrated. Finally, the remaining issues and prospect of further development are proposed as some kind of guidance for powerful combination of g-C₃ N₄ and CDs with high efficiency to photocatalysis.

How size, edge shape, functional groups and embeddedness influence the electronic structure and partial optical properties of graphene nanoribbons

The armchair and zigzag edge shape makes graphene nanoribbons (GNRs) exhibit interest in different applications. However, the relationship between influencing factors and properties is not clear. Herein, the many-body Green's function theory and the TDDFT method are used to investigate the effect of size, edge shape and functional groups on the electronic and optical properties of GNRs and h-BN-embedded GNRs. We find that ZGNRs have a smaller band gap and absorption edge than AGNRs having the same size and functional groups. The relationship between S₁ and T₁ is mainly determined by the size and edge shape of GNRs, while the redox ability of water splitting mainly relies on the kind of the functional group. When h-BN is embedded in GNRs, the edge shape of GNRs and the contact part between two substances control the direction of electron transfer in both the ground state and the excited state. These results can provide theoretical support for further improvements and applications of GNRs.

Toward Quantum Confinement in Graphitic Carbon Nitride-Based Polymeric Monolayers

Graphitic carbon nitride (g-C₃N₄) has garnered much attention due to its potential as an efficient metal-free photocatalyst. This study examines the evolution of properties in zero-dimensional quantum dots up to sizable clusters that mimic extended g-C₃N₄ monolayers. We employ density functional theory to investigate systematically the structural, electronic, and optical properties of the g-C₃N₄-based melamine and heptazine building blocks using a "bottom-up" construction of polymeric monolayers. The results from our computations indicate that the melamine- and heptazine-based polymeric g-C₃N₄ systems must be reduced to at least 2.74 and 4.00 nm, respectively, to observe an increase of its optical gap with a size reduction. The present study also examines the nature of the electronic transitions exhibited by g-C₃N₄-based monolayers through full natural transition orbital and density of state analyses. The most promising sites for water splitting and subsequent chemical doping studies are identified, which generally correspond to the nitrogen and carbon atoms, respectively.

Facile construction of 2D g-C3N4 supported nanoflower-like NaBiO3 with direct Z-scheme heterojunctions and insight into its photocatalytic degradation of tetracycline

Photocatalytic oxidation using solar energy is a promising green technology to degrade antibiotic contaminants. Herein, a 2D g-C₃N₄ supported nanoflower-like NaBiO₃ with direct Z-scheme heterojunction was synthesized via a facile hydrothermal approach, and the photocatalytic performance of g-C₃N₄/NaBiO₃ was remarkable better than that of g-C₃N₄ and NaBiO₃ for tetracycline degradation under visible light. Photoinduced electrons accumulated on the conduction band of g-C₃N₄ and holes gathered on the valence band of NaBiO₃, which was more suitable for generating superoxide and hydroxyl radicals. Meanwhile, the built-in electric field between g-C₃N₄ and NaBiO₃ was proved by their different work functions based on DFT calculations, which enhanced the charges separation. The formed radicals were determined by ESR, and their role in the degradation of tetracycline was examined by the active species trapping test. Moreover, the sites attacked by free radicals and degradation pathways for tetracycline were inferred by the results of Gaussian 09 program and HPLC-MS. The effects of water matrix and three other organic contaminants was further studied for actual use evaluation. Importantly, the prepared g-C₃N₄/NaBiO₃ showed stable photodegradation activity for eight cycles. This work not only provides a promising photocatalyst, but also gets insight into the photocatalytic removal of tetracycline.

Imidazolatic-Framework Bimetal Electrocatalysts with a Mixed-Valence Surface Anchored on an rGO Matrix for Oxygen Reduction, Water Splitting, and Dye Degradation

This paper presents a simple strategy for manufacturing bifunctional electrocatalysts-graphene nanosheets (GNS) coated with an ultrafine NiCo-MOF as nanocomposites (denoted NiCo-MOF@GNS) having a N-doped defect-rich and abundant cavity structure through one-pool treatment of metal-organic frameworks (MOFs). The precursors included N-doped dodecahedron-like graphene nanosheets (GNS), in which the NiCo-MOF was encompassed within the inner cavities of the GNS (NiCo-MOF@GNS) at the end or middle portion of the tubular furnace with several graphene layers. Volatile imidazolate N _x species were trapped by the NiCo-MOF nanosheets during the pyrolysis process, simultaneously inserting N atoms into the carbon matrix to achieve the defect-rich porous nanosheets and the abundantly porous cavity structure. With high durability, the as-prepared nanomaterials displayed simultaneously improved performance in the oxygen reduction reaction (ORR), the oxygen evolution reaction (OER), and photocatalysis. In particular, our material NiCo-MOF@GNS-700 exhibited excellent electrocatalytic activity, including a half-wave potential of 0.83 V (E _ORR, 1/2), a low operating voltage of 1.53 V (E _OER, 10) at 10 mA cm^-2, a potential difference (ΔE) of 1.02 V between E _OER, 10 and E _ORR, 1/2 in 0.1 M KOH, and a low band gap of 2.61 eV. This remarkable behavior was due to the structure of the defect-rich porous carbon nanosheets and the synergistic impact of the NPs in the NiCo-MOF, the N-doped carbon, and NiCo-N _x . Furthermore, the hollow structure enhanced the conductivity and stability. This useful archetypal template allows the construction of effective and stable bifunctional electrocatalysts, with potential for practical viability for energy conversion and storage.

2D phosphorene nanosheets, quantum dots, nanoribbons: synthesis and biomedical applications

Phosphorene, also known as black phosphorus (BP), is a two-dimensional (2D) material that has gained significant attention in several areas of current research. Its unique properties such as outstanding surface activity, an adjustable bandgap width, favorable on/off current ratios, infrared-light responsiveness, good biocompatibility, and fast biodegradation differentiate this material from other two-dimensional materials. The application of BP in the biomedical field has been rapidly emerging over the past few years. This article aimed to provide a comprehensive review of the recent progress on the unique properties and extensive medical applications for BP in bone, nerve, skin, kidney, cancer, and biosensing related treatment. The details of applications of BP in these fields were summarized and discussed.

Anisotropic Janus SiP2 Monolayer as a Photocatalyst for Water Splitting

The design of materials meeting the rigorous requirements of photocatalytic water splitting is still a challenge. Anisotropic Janus 2D materials exhibit great potential due to outstandingly high photocatalytic efficiency. Unfortunately, these materials are scarce. By means of ab initio swarm-intelligence search calculations, we identify a SiP₂ monolayer with Janus structure (i.e., out-of-plane asymmetry). The material turns out to be semiconducting with an indirect band gap of 2.39 eV enclosing the redox potentials of water. Notably, the oxygen and hydrogen evolution half reactions can happen simultaneously at the Si and P atoms, respectively, driven merely by the radiation-induced electrons and holes. The carrier mobility is found to be anisotropic and high, up to 10^-4 cm² V^-1 s^-1, facilitating fast transport of the photogenerated carriers. The SiP₂ monolayer shows remarkably strong optical absorption in the visible-to-ultraviolet range of the solar spectrum, ensuring efficient utilization of the solar energy.

Recent advances of monoelemental 2D materials for photocatalytic applications

As a sustainable environmental governance strategy and energy conversion method, photocatalysis has considered to have great potential in this field due to its excellent optical properties and has become one of the most attractive technologies today. Among 2D materials, the emerging two-dimensional (2D) monoelemental materials mainly distributed in the -IIIA, -IVA, -VA and -VIA groups and show excellent performance in solar energy conversion due to their graphene-like 2D atomic structure and unique properties, thereby drawing increasing attention. This review briefly summarizes the preparation processes and fundamental properties of 2D single-element nanomaterials, as well as various modification strategies and adjustment mechanisms to enhance their photocatalytic properties. In particular, this article comprehensively discusses the related practical applications of 2D single-element materials in the field of photocatalysis, including photocatalytic degradation for contaminants removal, photocatalytic pathogen inactivation, photocatalytic fouling control and photocatalytic energy conversion. This review will provide some new opportunities for the rational design of other excellent photocatalysts based on 2D monoelemental materials, as well as present tremendous novel ideas for 2D monoelemental materials in other environmental conservation and energy-related applications, such as supercapacitors, electrocatalysis, solar cells, and so on.