The search for new single-atom photocatalysts (SAPs) has garnered significant focus for CO2 reduction reaction (CO2RR) due to their maximum atom utilization efficiency. However, the rational design of SAPs remains elusive due to the lack of fundamental understanding behind the dynamic electron transfer between the anchored atoms and the semiconductor support. Herein, density functional theory calculations were performed to study the SAPs constituting transition metal (TM) in graphitic carbon nitride with a stoichiometry of C6N6 (gC6N6). A total of 26 single-atom elements from the TM group were investigated in this work. The in-depth analysis demonstrates that the selectivity for CO2RR over hydrogen evolution reaction (HER) is highly correlated with the degree of electrons transfer between the single TM atom and gC6N6. The coexistence of partially occupied states and empty states is essential for active CO2 adsorption for these SAPs. Overall, the findings from this work will steer experimental progress towards the designof efficient SAPs for CO2RR.

Tapping into the use of near-infrared (NIR) light is important in order to improve the utilization of the solar spectrum. Chlorine-functionalized titanium carbide MXene (Ti3C2Cl2 MX) quantum dots with up-conversion luminescence offer augmented absorption in the UV-vis-NIR spectral range and possess the capability to produce high-energy radiation via the conversion of low-energy incident light. Here, we demonstrate that the integration of Ti3C2Cl2 MXQDs onto a homo-heterostructure comprising oxygen-defective BiVO4 nanosheets (BiVO4-Ov) and red/black phosphorus (RP/BP), namely MX@BiVO4-Ov@RP/BP, exhibited vis-NIR-driven CO2 photoreduction. Under visible (>400 nm) and NIR (>700 nm) light irradiation, the 1MX@BiVO4-Ov@RP/BP system achieved high CH4 yields of 43.71 and 6.71 mu mol g(-1), respectively, after 6 h of reactions. The synergistic effect between Ti3C2Cl2 MXQDs and BiVO4-Ov@RP/BP promote photogeneration and migration of charge carriers. This study presents an effective strategy for enhancing the application of photocatalysts in the NIR region, thereby maximizing the utilization of solar energy.

AbstractElemental phosphorus in its various allotropes has received tremendous research attention recently due to its intriguing electronic and structural properties. Notably, the application of nanostructured materials to overcome the inherent flaws in bulk materials is promising. However, many challenges need to be addressed before its widespread implementation. Thus, a specific tenet to design novel and robust nanomaterials is a decisive factor in the desired outcome, and the most daunting task before realizing this is solving the Schrödinger equation. First principle density functional theory (DFT) calculations have emerged as an insightful and accurate design tool to investigate the structural, electronic, and possible synthesis scenarios of yet undiscovered materials at atomic levels. In this review, the basic principles and the importance of DFT are discussed, followed by a summary of recent advances in the first principle study of elemental phosphorus‐based nanomaterials. Elemental phosphorus‐based nanomaterials and their allotropes have attracted growing interest in the renewable energy community due to their modulable product selectivity. However, the understanding of the physical phenomena of allotropic modification is still lacking. Therefore, the aim is to motivate experimental researchers to conduct DFT studies and experiments to comprehend relevant engineered nanomaterials better. Finally, the challenges and potential future research directions for further theoretical and computational development of phosphorus‐based nanomaterials are outlined.

We revise the Fowler–Dubridge model for multiphoton over-barrier photoemission from two-dimensional (2D) materials to include the effects of reduced dimensionality, non-parabolic, and anisotropic energy dispersion of 2D materials. Two different directions of electron emission are studied, namely, vertical emission from the surface and lateral emission from the edge. Our analytical model reveals a universal temperature scaling of Tβ with β = 1 for the surface emission over a wide class of 2D materials and β = 3/2 for the edge emission from the 2D material with anisotropic parabolic energy dispersion, which are distinct from the traditional scaling of β = 2 originally derived for the traditional bulk materials. Our comparison shows good agreement with two experiments of photoelectron emitted from graphene for both surface and edge emission. Our calculations also show that the photoelectron emission is more pronounced than the coexisting thermionic emission for materials with low temperature and Fermi energy. This model provides helpful guidance in choosing proper combinations of light intensity, temperature range, and type of 2D materials for the design of photoemitters, photodetectors and other optoelectronics.

The existence of native point defects in crystalline solids are inevitable during synthesis. Such native defects will usually strongly impact the device performance of materials in catalysis applications. In recent years, the ability of first-principles approaches to accurately predict defect behavior has seen major progress. The underlying issue, as one would have guessed, is that these predictions of defect behavior and catalytic efficiency are extremely sensitive to the atomic structure of defect. Therefore, the proper identification of possible defect sites, their ground-state and metastable structures, and the correction scheme is crucial to resolving our understanding and control of defects’ role on catalytic performance. In this Comment, we aim to highlight recent advances of first-principles prediction for defect behavior while proposing a protocol for rigorous computational modelling.

The creation of an isotype phase junction has been recognized as an effective means of improving the spatial charge separation and migration in g-C3N4 materials. Nevertheless, due to a lack of electrostatic control in the internal electric field, isotype heterojunction alone is incapable of providing a sufficient driving force to maximize charge carrier transfer. Herein, we present an interface engineering strategy for co-integrating isotype and p-n heterojunctions to fabricate g-C3N4/g-C3N4 nanohybrids using a facile ultrasonic-assisted self-assembly method. The coherent boundary between the two distinct phases of g-C3N4 demonstrates that an intimate 2D interfacial contact can be easily established by pi-pi stacking interactions because of their high structural similarities and low lattice strain. Furthermore, their compatible and well-matched electronic band structures led to a staggered type II alignment in the lateral heterojunction, which confers the resulting composite with strong redox ability, efficient exciton dissociation, and desirable optoelectronic characteristics beyond those of the two constituents. Essentially, the isotype and p-n heterojunctions work in tandem to create a robust built-in electric field, allowing for effective interfacial charge steering for directional electron migration from BCN to CNx. Benefiting from these merits, the BCN/CNx nanohybrid manifested remarkable CH4 generation from photocatalytic CO2 reduction, outperforming its CNx and BCN counterparts by 1.91 and 6.88-fold, respectively. The midgap states induced by nitrogen defects in CNx also pose a positive effect on the improved photoactivity of the binary composite by acting as an electron reservoir to mediate electron transfer and further impede charge carrier recombination. This proof-of-concept study highlights the significance of interface engineering in charge flow manipulation and utilization for photocatalytic enhancement.

CO 2 photoreduction into hydrocarbon fuels is a promising strategy in closing the carbon cycle to realize a sustainable energy economy. Among the many photocatalysts that have been developed thus far, porous graphitic carbon nitride (gC 6 N 6 ) has emerged as a potential photocatalyst candidate in view of its unique optoelectronic properties, metal-free nature and two-dimensional versatile structure that can be easily modified. In this work, the enhancement of equivalent stoichiometry carbon nitride (gC 6 N 6 ) through single transition metal atom modification was systematically studied from first principles density functional theory calculations. The formation energy calculations revealed that incorporating single Co, Cu, Ni or Pd atom into gC 6 N 6 is energetically favorable, with the exception of Pt. The computed density of states plot indicates that a greater degree of hybridization of the transition metal atom d-orbitals with the p-orbitals of O atom from CO 2 will lead to stronger adsorption interaction. The optical absorption spectra show that Cu, Pd, and Pt promotes greater light absorption by extending the optical absorption to the NIR region. The presence of additional dopant states near the Fermi surface was found to have affected the optical absorption. The band structures of the Co,Cu,Pd,Pt@gC 6 N 6 show bandgap narrowing due to the shifting of conduction band edge closer to the Fermi level. Contrastingly, Ni@gC 6 N 6 exhibits bandgap narrowing through the shifting of the valence band edge to the Fermi level. The band edge positions suggest that anchoring gC 6 N 6 with single Co, Cu, Ni, Pd and Pt atom dopants possesses the capability to reduce CO 2 into C1 products. Among all the transition metals studied, Pd@gC 6 N 6 and Cu@gC 6 N 6 are identified as the most promising single-atom photocatalysts for CO 2 reduction due to their energetically favorable formation energy, stable CO 2 adsorption configuration, narrow bandgap, low charge carrier recombination, extended light absorption range and suitable band edge positions.

Sunlight‐driven CO2 conversion into value‐added fuels emerges as an avant‐garde strategy to mitigate the imminent energy scarcity and global warming. Nevertheless, sluggish charge kinetics and rapid carrier recombination are deemed as the foremost bottlenecks of efficient CO2 photoreduction. In this contribution, the aforementioned shortcomings are addressed by assembling a homo–hetero architecture comprising oxygen‐defective ultrathin BiVO4 (BiVO4–Ov) and red/black phosphorus (RP/BP) homojunction with a built‐in nanoscale dual Z‐scheme electronic configuration. The development of BiVO4–Ov@RP/BP confers two electron relaying channels, that is, one from the RP/BP homojunction and another from the BiVO4–Ov/RP heterojunction, which warrant the efficient separation of electron–hole pairs. Besides, the ultrathin 2D and oxygen vacant nature of BiVO4–Ov exposes more active sites and renders electron trapping for efficient utilization of photogenerated charges. Amalgamating the desirable properties, the meticulously developed dual Z‐scheme homo–heterojunction system on the basis of surface defect‐engineered ultrathin BiVO4–Ov nanosheets integrated with RP/BP offers a new avenue for the exploration, design, and fabrication of new generation photocatalysts with exceptional photocatalytic activities. In particular, the BiVO4–Ov@RP/BP system demonstrates a remarkably high CH4 yield of 14.52 μmol g−1 after 6 h of visible light illumination, which resembles a leading‐edge photocatalytic performance among the existing BiVO4‐ and P‐based semiconductors.

Establishing an effective metal-free photocatalyst for sustainable applications remains a huge challenge. Herein, we developed ultrathin oxygen-doped g-C3N4 nanosheets with carbon defects (OCvN) photocatalyst via a facile gas bubble template-assisted thermal copolymerization method. A series of OCvN with different dopant amounts ranging from 0 to 10% were synthesized and used as photocatalysts under illumination of low-power (2 × 18 W, 0.18 mW/cm2) and commercially available energy-saving light bulbs. Upon testing for photocatalytic Escherichia coli inactivation, the best-performing sample, OCvN-3, demonstrated an astonishing disinfection activity of over 7-log reduction after 3 h of illumination, boasting an 18-fold improvement in its antibacterial activity compared to that of pristine g-C3N4. The enhanced performance was attributed to the synergistic effects of increased surface area, extended visible light harvesting, improved electronic conductivity, and ultralow resistance to charge transfer. This study successfully introduced a green photocatalyst that demonstrates the most effective disinfection performance ever recorded among metal-free g-C3N4 materials. Its disinfection capabilities are comparable to those of metal-based photocatalysts when they are exposed to low-power light.

MgPc photosensitizers facilitate electron excitation in the NIR region to further enhance the photocatalytic activity of Bi 2 WO 6 .

ZnIn 2 S 4 (ZIS) is an efficient photocatalyst for solar hydrogen (H 2 ) generation from water splitting owing to its suitable band gap, excellent photocatalytic behaviour and high stability. Nevertheless, modifications are still necessary to further enhance the photocatalytic performance of ZIS for practical applications. This has led to our interest in exploring phosphorus doping on ZIS for photocatalytic water splitting, which has not been studied till date. Herein, phosphorus-doped ZnIn 2 S 4 (P-ZIS) was modelled via Density Functional Theory to investigate the effects of doping phosphorus on the structural and electronics properties of ZIS as well as its performance toward photocatalytic water splitting. This work revealed that the replacement of S3 atom by substitutional phosphorus gave rise to the most stable P-ZIS structure. In addition, P-ZIS was observed to experience a reduction in band gap energy, an upshift of valence band maximum (VBM), an increase in electron density near VBM and a reduction of H* adsorption–desorption barrier, all of which are essential for the enhancement of the hydrogen evolution reaction. In overall, detailed theoretical analysis carried out in this work could provide critical insights towards the development of P-ZIS-based photocatalysts for efficient H 2 generation via solar water splitting.

Surface defect engineering on the nanoscale has attracted extensive research attention lately; however, its role in modulating the properties and catalytic performance of a semiconducting material has not been comprehensively covered. Here, we systematically unraveled the effect of defect engineering towards textural, electronic and optical properties of graphitic carbon nitride (g-C3N4), as well as its photocatalytic mechanism of CO2 reduction using first-principle calculations by density functional theory through the introduction of various defect sites. Among the five unique atoms in g-C3N4, the vacancy site was found to be the most feasible at the two-coordinated nitrogen, N2. By initiating N2 point defects, an asymmetric electron density distribution was engendered around the vacancy region, which resulted in an evolution of semiconducting properties. We also discovered an improved charge separation efficiency and CO2 adsorption affinity in g-C3N4, which rendered a more thermodynamically feasible pathway for CO2 reduction to CO, CH3OH and CH4 fuels. This theoretical finding is hoped to shed light on the importance of the defect engineering strategy towards photocatalytic enhancement in g-C3N4.

Resembling a distinctive stratum of chemical transformations, photocatalysis employs the energy from the Sun to drive thermodynamically uphill reactions by simply emulating what nature does best -photosynthesis; photocatalysis therefore promises a sustainable solution to circumvent the increasingly tense environmental threats and energy crisis. In this contribution, we shed light on the opportune design and development of a dual Z-scheme photocatalytic system with homo-hetero junctions using mixed-phase red/black phosphorus (RP/BP) and tungsten oxide (WO3) in regulating charge steering for directional electron-hole transfer to drive efficient CO2 reduction. Fascinatingly, the ternary composite material (RP/BP@WO3) displayed a striking enhancement in optical absorption capacity, which extended from the ultraviolet up to the near-infrared region, rendering its capability of maximizing photon absorption to power efficacious photocatalytic reactions. With the endowment of two effective charge transport pathways that feature a cascade electron flow profile, the RP/BP@WO3 dual Z-scheme photocatalyst achieved a CH4 yield of 6.21 mu mol g-1 over 6 h under visible light illumination, whereas the pristine counterparts, namely, RP, WO3, and RP/BP, did not produce any CH4 yield. The amalgamation of RP/BP homojunction as the reduction catalyst and WO3 as the oxidation catalyst intriguingly serve as a complement to provoke CO2 reduction to CH4. The phenomenon is explicated by the formation of an arrow-up dual Z-scheme system that is governed by an internal electric field from the homo- hetero junctions which bestows strong redox potentials and favors the separation and transfer of photoinduced charge carriers, leading to increased participation of electron-hole pairs in redox reactions for improved photoconversion performance.

Photocatalytic reduction of CO2 has attracted enormous interest as a sustainable and renewable source of energy. In the past decade, numerous bulk-type semiconductors have been developed, but the existing designs suffer many limitations, namely rapid recombination of charge carriers and weak light absorption ability. Herein, a bottom-up approach was developed to design atomically thin sulfur-doped Bi2 WO6 perovskite nanosheets (S-BWO) with improved reduction ability, extended visible light absorption, prolonged lifetime of charge carriers, enhanced adsorption of CO2 , and reduced work function. Compared with pristine Bi2 WO6 (P-BWO), S-BWO nanosheets exhibited a 3-fold improvement in photocatalytic reduction of CO2 under simulated sunlight irradiation. Experimental studies and density functional theory calculations revealed the synergistic roles of atomically thin nanosheets and S atoms in promoting photocatalytic efficiency.

Materials engineering of allotropism provides a possible strategy for controling CO2 photoreduction into various C1 products. However, the understanding of the mechanism for tuning products selectivity through allotropism is still lacking. Herein, three structures of known phosphorus allotrope, i.e. black phosphorus (BP), fibrous red phosphorus (RP), and helical coil phosphorus (CP), were modelled as a CO2 reduction photocatalyst and studied by first principles density functional theory calculations. Three adsorption sites (P6C, P2B, and PT) of CO2 on the phosphorus allotropes were investigated. The most stable adsorption configuration for each allotrope was then selected for further study. The quantum topological analysis revealed that CO2 adsorption interaction on BP and RP exhibits physical binding of van der Waals interaction while CP shows physical binding of Keesom interaction. The CO2 adsorption interaction is shown to be crucial in determining the activation barrier for the initial proton-coupled electron transfer of CO2 → COOH. The pathways for different C1 products, including CO, HCOOH, C, CH2O, CH3OH, and CH4, were examined by comparing the rate determining step (RDS) obtained via Gibbs free energy analysis. RP and CP show higher selectivity towards the two- and four-electron C1 products. CP evidences a lower activation barrier for the two- and four-electron products RDS while BP exhibits higher selectivity towards the six- and eight-electron reduction products. The difference in selectivity of each of the allotropes was attributed to its distinct p-band center. This study divulges an important understanding on the possible product selectivity modulation for CO2 photoreduction based on allotropism.

Universal access to clean water has been a global ambition over the years. Photocatalytic water disinfection through advanced oxidation processes has been regarded as one of the promising methods for breaking down microbials. The forefront of this research focuses on the application of metal-free photocatalysts for disinfection to prevent secondary pollution. Graphitic carbon nitride (g-C3N4) has achieved instant attention as a metal-free and visible-light-responsive photocatalyst for various energy and environmental applications. However, the photocatalytic efficiency of g-C3N4 is still affected by its rapid charge recombination and sluggish electron-transfer kinetics. In this contribution, two-dimensionally protonated g-C3N4 was employed as metal-free photocatalyst for water treatment and demonstrated 100 % of Escherichia coli within 4 h under irradiation with a 23 W light bulb. The introduction of protonation can modulate the surface charge of g-C3N4; this enhances its conductivity and provides a "highway" for the delocalization of electrons. This work highlights the potential of conjugated polymers in antibacterial application.

Photocatalysis is a perennial solution that promises to resolve deep-rooted challenges related to environmental pollution and energy deficit through harvesting the inexhaustible and renewable solar energy. To date, a cornucopia of photocatalytic materials has been investigated with the research wave presently steered by the development of novel, affordable, and effective metal-free semiconductors with fascinating physicochemical and semiconducting characteristics. Coincidentally, the recently emerged red phosphorus (RP) semiconductor finds itself fitting perfectly into this category ascribed to its earth abundant, low-cost, and metal-free nature. More notably, the renowned red allotrope of the phosphorus family is spectacularly bestowed with strengthened optical absorption features, propitious electronic band configuration, and ease of functionalization and modification as well as high stability. Comprehensively detailing RP's roles and implications in photocatalysis, this review article will first include information on different RP allotropes and their chemical structures, followed by the meticulous scrutiny of their physicochemical and semiconducting properties such as electronic band structure, optical absorption features, and charge carrier dynamics. Besides that, state-of-the-art synthesis strategies for developing various RP allotropes and RP-based photocatalytic systems will also be outlined. In addition, modification or functionalization of RP with other semiconductors for promoting effective photocatalytic applications will be discussed to assess its versatility and feasibility as a high-performing photocatalytic system. Lastly, the challenges facing RP photocatalysts and future research directions will be included to propel the feasible development of RP-based systems with considerably augmented photocatalytic efficiency. This review article aspires to facilitate the rational development of multifunctional RP-based photocatalytic systems by widening the cognizance of rational engineering as well as to fine-tune the electronic, optical, and charge carrier properties of RP.

Photocatalytic dry reformation of methane (DRM) is an appealing alternative to transform CO2 into precious syngas for the Fischer-Tropsch synthesis while simultaneously reducing greenhouse gas emissions. However, the reaction mechanisms of DRM over photocatalysts have not been fully explored to date. In this work, two-dimensional graphitic carbon nitride (gC(3)N(4)) nanosheets are taken as a case study to shed light on their behaviors under the multistep reaction of DRM through first-principles calculations. The results show that gC(3)N(4) is a promising candidate for DRM due to its suitable electronic band structure to drive the redox reaction and its ability to facilitate the adsorption of reactants (CO2 + CH4) and the desorption of products (CO + H-2). The systematic Gibbs free energy calculations identified the possible reaction pathways for the reforming of CH4 to syngas using CO2. We observed that the H atoms from CH4 dissociation are more likely to form H-2 since the Gibbs free pathway indicates that the main contributor of CO formation is the direct reduction of CO2 to CO rather than the oxidation of CH4 to CO due to the large activation barrier required for the formation of the CH2O intermediate. Overall, our work sheds light on the mechanism underlying the photocatalytic dry reforming of CH4 over gC(3)N(4) nanosheets.

In this work, the intramolecular structure of a pristine graphitic carbon nitride (GCN) was modified to investigate how it would affect the photocatalytic activity towards hydrogen evolution reaction (HER) under simulated solar irradiation. The intramolecular bonding of GCN was broken by subjecting it to a simple thermal treatment under a controlled environment. Both experimental and computational studies revealed that removal of inter-heptazine CN(H)C groups from the pristine structure induced an amorphous phase and additional energy bands to GCN. It was also observed that a mid-gap state was formed between the conduction band (CB) of the amorphous carbon nitride (ACN) and the H+/H-2 reduction potential. The presence of the mid-gap state not only served as an additional reduction site for HER, but also acted as a buffer to reduce the recombination rate of photogenerated charge carriers. The optimum ACN sample displayed an enhanced photocatalytic performance achieving a HER rate of 789 mu mol/gcat, which was about 2-fold higher than that of pristine GCN. This could be ascribed to the synergistic effect of improved light absorption, increased surface area, suppressed charge recombination and increased charge carrier densities for the ACN samples to drive the overall reduction-oxidation process.