Density functional theory-based modeling of the half-metallic g-C3N4/CoN4 heterojunction for photocatalytic water splitting reaction

Using density functional theory (DFT), we have investigated the structural, optical, electronic and magnetic properties of a graphitic carbon nitride (g-C3N4) and CoN4 composite to explore the effect of the heterojunction on the photocatalytic performance of g-C3N4. The structure of g-C3N4 is modified while complexing with CoN4 and the corresponding stabilization is confirmed through adhesion energy calculation. The phonon spectra analysis furthermore guaranteed the lattice-dynamic stability of the CoN4 bulk and the CoN4 slab. Pristine g-C3N4 is a wide band gap semiconductor, which becomes half metallic upon CoN4 inclusion. The metallicity in the g-C3N4/CoN4 composite originates from the spin down channel, keeping the spin up channel in a semiconducting state. The charge density analysis and work function calculation suggest a substantial amount of charge transfer from g-C3N4 to the CoN4 unit in the g-C3N4/CoN4 heterojunction. The model heterojunction of the g-C3N4/CoN4 composite can enhance the utilization ratio of visible light for the g-C3N4 photocatalyst. In g-C3N4/CoN4, the valence band maximum (VBM) has a more positive potential compared to O2/H2O (+1.23 V) on the normal hydrogen electrode (NHE) scale. However, the conduction band minimum (CBM) displays a more negative potential compared to H+/H2 (0 V) on the NHE scale. The details of the band structure, density of states and band edge position determining calculations confirm that the g-C3N4/CoN4 composite forms a type 1 heterojunction, making it a suitable photocatalyst for water splitting reaction. The practical application of the g-C3N4/CoN4 heterostructure as a photocatalyst was substantiated in the presence of polar solvent (water) by calculating the band gap, charge transfer interaction and charge density difference. There is a significant decrease of charge transfer and thereby charge density difference in the g-C3N4/CoN4 heterojunction in the presence of water; however, it still holds potential for use as a photocatalyst for water splitting reaction. The state-of-the-art theoretical modeling of the g-C3N4/CoN4 heterojunction is the first theoretical study incorporating the CoN4 crystal.

Photocatalytic Efficiency for CO2 Reduction of Co and Cluster Co2O2 Supported on g-C3N4: A Density Functional Theory and Machine Learning Study

It is well known from experimental results that a single atom of cobalt supported on g-C3N4 is an efficient photocatalyst for the reduction of CO2 to CO, with a better photocatalytic activity than g-C3N4. In this work, we investigate the performance as catalysts for the CO2 reduction of single atoms of cobalt and Co2O2 clusters supported on graphitic carbon nitride (g-C3N4). Employing density functional theory plus Hubbard (DFT + U) calculations, we investigate in detail the reduction mechanisms to CO and HCOOH for the first time. We find that deposition of cobalt on g-C3N4 decreases the work function of g-C3N4 to 6.6 eV and provides a better candidate for the reduction reaction. In addition, we find that the preferred product of CO2 reduction on Co@g-C3N4 is CO, with a rate-determining barrier of 0.97 eV, while on Co2O2@g-C3N4, CO2 reduces to formate with a rate-determining barrier of 0.44 eV. We determine the creation of CO2 from COOH to only take place on Co2O2@g-C3N4, with a (relatively high) barrier of 2.27 eV. In order to obtain more easily the transition state energies of the reactions mentioned above, we applied machine learning methods to search for high-importance descriptors for these quantities, in the case of single transition metal atoms supported on C3N4. Interestingly, our results show that our quantities of interest are closely related to the adsorption energies of products and normalized valence electrons of the products of the elementary reactions as well as those of the metal atoms. The former of these two sets of features can be straightforwardly obtained via DFT, while the latter energies are extensively tabulated. Our results offer guidance for the design of catalysts and photocatalysts for CO2 reduction on single-metal atoms supported on C3N4.

Controlled Ni doping on a g-C3N4/CuWO4 photocatalyst for improved hydrogen evolution

The development of a low-cost, environment-friendly and suitable semiconductor-based heterogeneous photocatalyst poses a great challenge towards extremely competent and substantial hydrogen evolution. A series of environment-friendly and proficient S-scheme Ni-doped CuWO4 nanocrystals supported on g-C3N4 nanocomposites (Ni-CuWO4/g-C3N4) were constructed to ameliorate the photocatalytic efficacy of pure g-C3N4 and Ni-CuWO4 and their activity in H2 generation through photocatalytic water splitting was evaluated. The Ni-CuWO4 nanoparticles were synthesized through doping of Ni2+ on wolframite CuWO4 crystals via the chemical precipitation method. An elevated hydrogen generation rate of 1980 μmol h-1 g-1 was accomplished over the 0.2Ni-CuWO4/g-C3N4 (0.2NCWCN) nanocomposite with an apparent quantum yield (AQY) of 6.49% upon visible light illumination (λ ≥ 420 nm), which is evidently 7.1 and 17.2 fold higher than those produced from pristine g-C3N4 and Ni-CuWO4. The substantial enhancement in the photocatalytic behaviour is primarily because of the large surface area, limited band gap energy of the semiconductor composite and magnified light harvesting capability towards visible light through the inclusion of g-C3N4, thus diminishing the reassembly rate of photoinduced excitons. Further, density functional theory (DFT) calculations were performed to investigate the structural, electronic and optical properties of the composite. Theoretical results confirmed that the Ni-CuWO4/g-C3N4 composite is a potential candidate for visible-light-driven photocatalysts and corroborated with the experimental findings. This research provides a meaningful and appealing perspective on developing cost-effective and very proficient two-dimensional (2D) g-C3N4-based materials for photocatalytic H2 production to accelerate the separation and transmission process of radiative charge carriers.

Graphitic carbon nitride-based photocatalysts in the applications of environmental catalysis

Semiconductor photocatalytic technology has shown great prospects in converting solar energy into chemical energy to mitigate energy crisis and solve environmental pollution problems. The key issue is the development of high-efficiency photocatalysts. Various strategies in the state-of-the-art advancements, such as heterostructure construction, heteroatom doping, metal/single atom loading, and defect engineering, have been presented for the graphitic carbon nitride (g-C₃N₄)-based nanocomposite catalysts to design their surface chemical environments and internal electronic structures to make them more suitable for different photocatalytic applications. In this review, nanoarchitecture design, synthesis methods, photochemical properties, potential photocatalytic applications, and related reaction mechanisms of the modified high-efficiency carbon nitride-based photocatalysts were briefly summarized. The superior photocatalytic performance was identified to be associated with the enhanced visible-light response, fast photoinduced electron-hole separation, efficient charge migration, and increased unsaturated active sites. Moreover, the further advance of the visible-light harvesting and solar-to-energy conversions are proposed.

Tunable Photocatalytic Water Splitting Performance of Armchair MoSSe Nanotubes Realized by Polarization Engineering

The photocatalytic properties of Janus transition metal dichalcogenide (TMD) nanotubes are closely correlated with the electrostatic potential difference between their inner and outer surfaces (ΔΦ). However, due to some distraction from the tubular structures, it remains a great challenge to calculate their ΔΦ directly. Here, we creatively work out the ΔΦ of Janus MoSSe armchair single-walled nanotubes (A-SWNTs) with their corresponding building block models by first-principles calculations. The ΔΦ increases as the diameter reduces. After considering ΔΦ, we find that all of these MoSSe A-SWNTs possess suitable band-edge positions required for water redox reactions and high solar-to-hydrogen (STH) conversion efficiencies. The built-in field induced by the ΔΦ promotes the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) to proceed separately on the inner and outer surfaces. Especially, the photoexcited carriers exhibit adequate driving forces for OER and HER. Besides, constructing a double-walled nanotube can dramatically increase ΔΦ, which also further improves the separation and redox capacity of photoexcited carriers as well as the STH conversion efficiency. Moreover, all of these MoSSe armchair nanotubes have outstanding optical absorption in the visible light range. Our studies provide an effective strategy to improve the photocatalytic water-splitting performance of Janus TMD nanotubes.

Density Functional Theory Study on the Enhancement Mechanism of the Photocatalytic Properties of the g-C3N4/BiOBr(001) Heterostructure

The van der Waals heterostructures fabricated in two semiconductors are currently attracting considerable attention in various research fields. Our study uses density functional theory calculations within the Heyd-Scuseria-Ernzerhof hybrid functional to analyze the geometric structure and electronic structure of the g-C₃N₄/BiOBr(001) heterojunction in order to gain a better understanding of its photocatalytic properties. The calculated band alignments show that g-C₃N₄/BiOBr can function as a type-II heterojunction. In this heterojunction, the electrons and holes can effectively be separated at the interface. Moreover, we find that the electronic structure and band alignment of g-C₃N₄/BiOBr(001) can be tuned using external electric fields. It is also noteworthy that the optical absorption peak in the visible region is enhanced under the action of the electric field. The electric field may even improve the optical properties of the g-C₃N₄/BiOBr(001) heterostructure. Given the results of our calculations, it seems that g-C₃N₄/BiOBr(001) may be significantly superior to visible light photocatalysis.

Effects of Fluorination and Molybdenum Codoping on Monoclinic BiVO4 Photocatalyst by HSE Calculations

Monoclinic phase bismuth vanadate (BiVO₄) is one of the most promising photoelectrochemical materials used in water-splitting photoelectrochemical cells. It could be even better if its band gap and charge transport characteristics were optimized. Although codoping of BiVO₄ has proven to be an effective strategy, its effects are remarkably poorly understood. Using the Heyd-Scuseria-Ernzerhof (HSE) hybrid functional, we estimate the formation energy, electronic properties, and photocatalytic activities of F and Mo codoped BiVO₄. We find that Mo atoms prefer to replace V atoms, whereas F atoms prefer to replace O atoms (F_OMo_V-doped BiVO₄) under oxygen-poor conditions according to calculated formation energies. BiVO₄ doped with F_OMo_V is found to be shallow-level doped, occurring with some continuum states above the conduction band edge, which is advantageous for photochemical catalysis. Moreover, F_OMo_V-doped BiVO₄ shows absorption stronger than that of pure BiVO₄ in the visible spectrum. Based on the band-edge calculation, BiVO₄ doped with F_OMo_V still retains a high oxidizing capacity. It has been shown that F_OMo_V-doped BiVO₄ exhibits a very high photocatalytic activity under visible light.

C7N6/Sc2CCl2 Weak van der Waals Heterostructure: A Promising Visible-Light-Driven Z-Scheme Water Splitting Photocatalyst with Interface Ultrafast Carrier Recombination

Designing and characterizing high-efficiency direct Z-scheme photocatalysts both from theoretical and experimental aspects still remain a big challenge. Here, based on extensive first-principles calculations combined with excited state dynamics simulations, we report that a weak van der Waals (vdW) C₇N₆/Sc₂CCl₂ heterostructure is a mediator-free direct Z-scheme photocatalyst for solar water splitting. Theoretical results clearly reveal that this heterostructure displays a nice light-harvesting performance extending to the near-infrared region. The relatively strong interfacial non-adiabatic coupling accelerates the interlayer carrier recombination in the time scale of sub-picoseconds. The well separated electrons and holes with a strong redox capacity make the hydrogen evolution reaction spontaneously occur on the C₇N₆ surface and the oxygen evolution reaction on the Se-doped Sc₂CCl₂ surface, respectively, when the proposed heterostructure is radiated with solar light.

Crystal-reconstructed BiVO4 semiconductor photoelectrochemical sensor for ultra-sensitive tumor biomarker detection

In this study, we developed a crystal-reconstructed-BiVO₄ aptamer photoelectrochemical (PEC) biosensor by a high-energy laser treatment technique. This biosensor achieves a limit of detection (LOD) (0.82 ag mL^-1), linear detection range (1 ag mL^-1 to 2 ng mL^-1), and resolution ratio (∼18 molecules per mL) for prostate-specific antigen (PSA) tumor biomarker detection. Furthermore, reconstructed surface microstructure and oxygen vacancy doping energy formation after crystal reconstruction induce the stereo-hindrance effect and photogenerated hole energy is reduced during PSA target detection. In this case, a photocurrent inhibition phenomenon for PSA detection is noticed. Based on this photocurrent inversion phenomenon, some dysoxidizable nucleonic acid tumor (miRNA-21) and virus biomarkers (RdRp-COVID) can be detected with a LOD level of ∼10^-16 M by linking the corresponding base paring probe on the surface of the crystal-reconstructed photoanode. In addition to high sensitivity, this PEC biosensor presents high detection specificity, stability, and accuracy in clinical verification. Thus, this crystal-reconstructed PEC biosensor shows application potential in the fields of multi-tumor or viral biomarker detection.

Structural, electronic, optical and photocatalytic properties of KTaO3 with NiO cocatalyst modification

Density functional theory calculations reveal that NiO serves as an oxidation cocatalyst to form type-II band alignment with KTaO3, which suppresses the recombination of photoinduced carriers and enhances the photocatalytic activity of KTaO3.

A promising catalytic solution of NO reduction by CO using g-C3N4/TiO2: A DFT study

The direct catalytic reduction of nitric oxide (NO) by carbon monoxide (CO) to form harmless N₂ and CO₂ is an ideal strategy to simultaneously remove both these hazardous gases. To investigate the feasibility of using graphitic carbon nitride/titanium dioxide (g-C₃N₄/TiO₂) to catalyze the NO reduction by CO, we systematically explore the effect of the interfacial coupling between g-C₃N₄ and TiO₂ on the photo-induced carrier separation, the light absorption, and the surface reaction for the NO reduction by using density functional theory. The g-C₃N₄/TiO₂ is predicted to have a better photocatalytic activity for NO reduction than g-C₃N₄, due to the enhanced light absorption intensity and the accelerated separation of the photo-excited electron-hole pairs. By comparing the reaction routes on g-C₃N₄/TiO₂ and g-C₃N₄, the results indicate that the introduction of TiO₂ can keep the surface reaction process intact with the NO dissociation (N₂O formation) being the rate-determining (crucial) step. Moreover, TiO₂ can facilitate the desorption of NO reduction products, avoiding the deactivation of g-C₃N₄. This work shows that the composition of TiO₂ into g-C₃N₄ provides a promising catalyst in NO reduction by CO.

Sunlight driven photocatalytic degradation of organic pollutants using a MnV2O6/BiVO4 heterojunction: mechanistic perception and degradation pathways

In the field of photocatalysis, fabrication of a heterojunction structure with effective charge separation at the interface and charge shift to enhance the photocatalytic activity has acquired extensive consideration. In the present investigation, MnV₂O₆/BiVO₄ heterojunction samples with excellent photocatalytic performance under sunlight irradiation were conveniently synthesized by a hydrothermal technique, and characterized by UV-Vis, FTIR, XRD, FESEM, HRTEM, PL, BET and XPS techniques. The prepared samples were investigated as photocatalysts for degrading MB and RhB dyes under sunlight. Among various samples of MnV₂O₆/BiVO₄, the S-V hetero-junction sample exhibited maximum photocatalytic activity with 98% and 96% degradation of MB and RhB dyes, respectively, in 6 and 35 min. The high photocatalytic activity of MnV₂O₆/BiVO₄ may be due to the successful generation and shift of charges in the presence of visible light. The average reduction of chemical oxygen demand (COD) was found to be 75% after irradiation with direct sunlight. In the degradation process of dyes, superoxide anion radicals were the main responsive species, as revealed by trapping experiments. The degradation efficiency of MnV₂O₆/BiVO₄ heterojunction did not diminish even after four cycles. In addition, the catalytic performance of the fabricated heterojunction was also explored for reducing 4-nitrophenols (4-NP) by using NaBH₄. Absolute conversion of 4-NP to 4-aminophenol (4-AP) occurred without the production of intermediate byproducts.

Construction of Ag/NaBiO3 with dual active sites for photocatalytic NO deep oxidation and long-lasting organic pollutants degradation in the dark

Ag/NaBiO₃ with dual active sites and high capacitance was prepared by the photo-deposition method. Upon light illumination, the reduction of Ag⁺ to Ag, the introduction of oxygen vacancies, and the electron storage in Ag nanoparticles simultaneously happened. NO, and O₂ adsorbed and activated at Ag site and oxygen vacancy site, respectively, to produce active ON* and •O₂^- radical species. The increased concentrations of the active oxygen species and the pre-oxidation of NO resulted in the enhanced NO removal with inhibited production of NO₂. Moreover, the high capacitance of Ag and the continuous charge transfer from defective NaBiO₃ to Ag offered the enhanced and long-lasting dark catalytic activity of the Ag/NaBiO₃. The stored electrons in Ag were directly released in dark to decompose methyl orange and/or tetracycline. This work provides a novel idea of designing and preparing a multifunctional catalytic material for environmental cleaning.

The stability and electronic and photocatalytic properties of the ZnWO4 (010) surface determined from first-principles and thermodynamic calculations

We present the results of the generalized-gradient approximation of Perdew, Burke and Ernzerhof (GGA-PBE) and the Heyd-Scuseria-Ernzerhof (HSE06) hybrid functional calculations of the atomic and the electronic structures of ZnWO₄ (010) surfaces. The total energies obtained from these calculations are used to analyze the thermodynamic stability of the surfaces. The surface phase diagrams are constructed by surface Gibbs free energies obtained as a function of temperature and oxygen partial pressure. Our results suggested that the stable area of the surface terminations of ZnWO₄ (010) has little correlation with the functional selected. The stability phase diagram shows that O-Zn, DL-W, and DL-Zn terminations of ZnWO₄ (010) can be stabilized under certain thermodynamic equilibrium conditions. Based on the HSE06 hybrid functional, we calculate the electronic structures for three possible stability surface terminations. It is found that there is a fat band of the surface states in DL-W termination, which shows a delocalized feature. This fat band acts as an electron transition bridge between the valence band (VB) and conduction band (CB). It contributes to visible-light absorption by two-step optical transition with the first transition from the VB to the fat band and the second from the fat band to the CB. Significantly, the conduction band minimum (CBM) band edge position of DL-W termination is favourable for H₂ evolution as the CBM edge is located above the water reduction level (H⁺/H₂). Simultaneously, DL-W termination's valence band maximum (VBM) potential shows a strong potential for O₂ generation from water oxidation because of the higher VBM edge with respect to the water oxidation level (H₂O/O₂). These results may help explore ZnWO₄ (010) surfaces' intrinsic properties, providing a helpful strategy for experimental studies of ZnWO₄-based photocatalysts in the future.

The Thermodynamic Stability, Electronic and Photocatalytic Properties of the ZnWO4(100) Surface as Predicted by Screened Hybrid Density Functional Theory

Zinc tungstate (ZnWO₄) is an outstanding photocatalyst for water splitting and organic contaminant degradation under visible light irradiation. Surface termination stabilities are significant for understanding the photochemical oxidation and reactions on the ZnWO₄ surface. Based on density functional theory, we calculated the thermodynamic stability of possible surface terminations for ZnWO₄(100). The surface stability phase diagrams show that the Zn₂O₄-Zn₈W₆O₂₈, W₂O₄-Zn₈W₁₀O₃₆, and Zn₂-Zn₈W₆O₂₄ terminations of ZnWO₄(100) can be stabilized under certain thermodynamic equilibrium conditions. The electronic structures for these three possible stability surface terminations are calculated based on the Heyd-Scuseria-Ernzerhof (HSE06) hybrid functional to give dependable theoretical band gap values. It is found that the surface states of W₂O₄-Zn₈W₁₀O₃₆ termination are in the band gap, which shows a delocalized performance. The calculated absorption coefficients of W₂O₄-Zn₈W₁₀O₃₆ termination show stronger absorption than bulk ZnWO₄ in the visible-light region. The band edge calculation shows that the valence band maximum and conduction band minimum of the W₂O₄-Zn₈W₁₀O₃₆ termination can fulfill the hydrogen evolution reaction and oxygen evolution reaction requirements at the same time. Furthermore, work functions are extraordinarily distinct for various surface terminations. This result suggests that the ZnWO₄-based direct Z-scheme heterostructure can be controlled by obtaining the thermodynamically preferred surface termination under suitable conditions. Our results can predict ZnWO₄(100) surface structures and properties under the entire range of accessible environmental conditions.

Band alignment of Zr2CO2/MoS2 heterostructures under an electric field

Tunable energy bands of Zr2CO2/MoS2 heterostructures by an external electric field.

Hybrid Density Functional Theory Study of Native Defects and Nonmetal (C, N, S, and P) Doping in a Bi2WO6 Photocatalyst

Native defects and nonmetal doping have been shown to be an effective way to optimize the photocatalytic properties of Bi2WO6. However, a detailed understanding of defect physics in Bi2WO6 has been lacking. Here, using the Heyd-Scuseria-Ernzerhof hybrid functional defect calculations, we study the formation energies, electronic structures, and optical properties of native defects and nonmetal element (C, N, S, and P) doping into Bi2WO6. We find that the Bi vacancy (Bivac), O vacancy (Ovac), S doping on the O site (SO), and N doping on the O site (NO) defects in the Bi2WO6 can be stable depending on the Fermi level and chemical potentials. By contrast, the substitution of an O atom by a C or P atom (CO, PO) has high formation energy and is unlikely to form. The calculated electronic structures of the Bivac, Ovac, SO, and NO defects indicate that the band-gap reduction of Ovac 2+, Bivac 3-, and SO defects is mainly due to forming shallow impurity levels within the band gap. The calculated absorption coefficients of Ovac 2+, Bivac 3-, and SO show strong absorption in the visible light region, which is in good agreement with the experimental results. Hence, Ovac 2+, Bivac 3-, and SO defects can improve the adsorption capacity of Bi2WO6, which helps enhance its photocatalytic performance. Our results provide insights into how to enhance the photocatalytic activity of Bi2WO6 for energy and environmental applications through the rational design of defect-controlled synthesis conditions.

Tunable Electronic Properties of Type-II SiS2/WSe2 Hetero-Bilayers

First-principle calculations based on the density functional theory (DFT) are implemented to study the structural and electronic properties of the SiS₂/WSe₂ hetero-bilayers. It is found that the AB-2 stacking model is most stable among all the six SiS₂/WSe₂ heterostructures considered in this work. The AB-2 stacking SiS₂/WSe₂ hetero-bilayer possesses a type-II band alignment with a narrow indirect band gap (0.154 eV and 0.738 eV obtained by GGA-PBE and HSE06, respectively), which can effectively separate the photogenerated electron–hole pairs and prevent the recombination of the electron–hole pairs. Our results revealed that the band gap can be tuned effectively within the range of elastic deformation (biaxial strain range from −7% to 7%) while maintaining the type-II band alignment. Furthermore, due to the effective regulation of interlayer charge transfer, the band gap along with the band offset of the SiS₂/WSe₂ heterostructure can also be modulated effectively by applying a vertical external electric field. Our results offer interesting alternatives for the engineering of two-dimensional material-based optoelectronic nanodevices.

Transforming Photocatalytic g-C3 N4 /MoSe2 into a Direct Z-Scheme System via Boron-Doping: A Hybrid DFT Study

Z-scheme photocatalytic systems are an ideal band alignment structure for photocatalysis because of the high separation efficiency of photo-induced carriers while simultaneously preserving the strong reduction activity of electrons and oxidation activity of holes. However, the design and construction of Z-scheme photocatalysts is challenging because of the need for appropriate energy band alignment and built-in electric field. Here, we propose a novel approach to a Z-scheme photocatalytic system using density functional theory calculations with the HSE06 hybrid functional. The undesirable type-I g-C₃ N₄ /MoSe₂ heterojunction is transformed into a direct Z-scheme system through boron doping of g-C₃ N₄ (B-doped C₃ N₄ /MoSe₂ ). Detailed analysis of the total and partial density of states, work functions and differential charge density distribution of the B-doped C₃ N₄ /MoSe₂ heterojunction shows the proper band alignment and existence of a built-in electric field at the interface, with the direction from g-C₃ N₄ to MoSe₂ , demonstrating a direct Z-scheme heterojunction. Further investigation on the absorption spectra reveals a large enhancement of the light absorption efficiency after boron doping. The results consistently confirm that electronic structures and photocatalytic performance can be effectively manipulated by a facile boron doping. Modulating the band alignment of heterojunctions in this way provides valuable insights for the rational design of highly efficient heterojunction-based photocatalytic systems.

Efficient BiVO4 photoanode decorated with Ti3C2TX MXene for enhanced photoelectrochemical sensing of Hg(II) ion

A highly sensitive photoelectrochemical (PEC) sensing platform was constructed for Hg²⁺ determination based on the Schottky heterojunction between an emerging 2D material Ti₃C₂T_X MXene and a promising semiconductor material BiVO₄. Through simply spin-coating the single-layer Ti₃C₂T_X onto the surface of BiVO₄ film, the modified electrode exhibited significantly enhanced PEC activity. However, the boost in photocurrent could be noticeably suppressed due to the consumption of hole-scavenging agents (reduced glutathione) by the added Hg²⁺. Owing to the selective decrease in the photocurrent with the addition of Hg²⁺, the PEC sensor based on BiVO₄/Ti₃C₂T_X displayed a wide linear range from 1 pM to 2 nM with the limit of detection down to 1 pM. Moreover, the PEC sensor also exhibited satisfactory accuracy and repeatability in practical sample water, the Yangtze River water, demonstrating the great potential for monitoring heavy metal ions in natural water resources.

Enhanced Power Conversion Efficiency of Dye-Sensitized Solar Cells by Band Edge Shift of TiO2 Photoanode

By simple soaking titanium dioxide (TiO₂) films in an aqueous Na₂S solution, we could prepare surface-modified photoanodes for application to dye-sensitized solar cells (DSSCs). An improvement in both the open-circuit voltage (V_oc) and the fill factor (FF) was observed in the DSSC with the 5 min-soaked photoanode, compared with those of the control cell without any modification. The UV–visible absorbance spectra, UPS valence band spectra, and dark current measurements revealed that the Na₂S modification led to the formation of anions on the TiO₂ surface, and thereby shifted the conduction band edge of TiO₂ in the negative (upward) direction, inducing an increase of 29 mV in the V_oc. It was also found that the increased FF value in the surface-treated device was attributed to an elevation in the shunt resistance.

g-C3N4/Pt/BiVO4 nanocomposites for highly efficient visible-light photocatalytic removal of contaminants and hydrogen generation

Inspired by natural photosynthesis, artificial heterojunction photocatalysts have been extensively studied. Herein, a novel ternary graphitic carbon nitride/platinum/bismuth vanadate (g-C₃N₄/Pt/BiVO₄) photocatalytic system was successfully synthesized, where Pt/BiVO₄ nanosheet is anchored on the surface of layered g-C₃N₄, as evidenced by structural observations. Ultraviolet photoelectron spectroscopy and ultraviolet-visible diffuse reflectance spectroscopy are carried out to identify the position of the conduction band and valence band. A Z-scheme is used to interpret the superior photocatalytic performance of g-C₃N₄/Pt/BiVO₄ and further verified by the capture of free radicals and terephthalic acid photoluminescence experiments. Compared with the g-C₃N₄/BiVO₄ binary system, the Z-scheme g-C₃N₄/Pt/BiVO₄ photocatalyst not only possesses enhanced carrier separation efficiency but also maintains sufficient redox properties, thus inducing superior photocatalytic activity. More importantly, the novel Z-scheme photocatalyst exhibits excellent recycle stability, which could provide inspiration for the rational design of efficient and practical photocatalysts for environmental pollution treatment. The ternary photocatalyst also exhibits significantly enhanced visible-light photocatalytic hydrogen production performance.

Photocatalytic properties and energy band offset of a tungsten disulfide/graphitic carbon nitride van der Waals heterojunction

Semiconductor heterojunctions have higher photocatalytic performance than a single photocatalytic material. However, the energy band offset and the photocatalytic reaction mechanism of these heterojunctions remain controversial. Here, tungsten disulfide (WS₂)/graphitic carbon nitride (GCN) heterojunction photocatalytic water splitting is investigated with the hybrid density functional method. The band structures and the density of states (DOS) indicate that the WS₂/GCN heterojunction is a type-II heterojunction, and its valence band offset and conduction band offset are 0.27 and 0.04 eV, respectively. The differential charge density distribution and the work function calculation indicate that a built-in electric field is formed in the WS₂/GCN heterojunction. The potential of the built-in electric field is 0.16 V, and its direction is from the GCN surface to the WS₂ surface. The built-in electric field separates the photogenerated electrons and the holes in space, effectively improving the photocatalytic efficiency of the WS₂/GCN heterojunction. Our work provides insights into the electronic properties and the photocatalytic hydrogen evolution mechanism of the WS₂/GCN heterojunction.

WS₂/GCN heterojunction is a type-II heterostructure and its electric field separates the electrons and the holes in space.

Fabrication of ultra-sensitive photoelectrochemical aptamer biosensor: Based on semiconductor/DNA interfacial multifunctional reconciliation via 2D-C3N4

In this work, we fabricate a novel bismuth vanadate/two dimensional-carbon nitride/deoxyribonucleic acid (BiVO₄/2D-C₃N₄/DNA) aptamer photoelectrochemical (PEC) sensor, and this sensor provides a record detection sensitivity area (5 × 10^-7 μg/L - 10 μg/L) for Microcystin-LR (MC-LR). Meanwhile, except for MC-LR detection, this sensor presents highly sensitivity for tumor marker, heavy metal ion, antibiotic also by changing the DNA aptamer. Photo charge dynamic and theory calculation results reveal that 2D-C₃N₄ is a key material for multifunctional interface reconciliation of this PEC aptamer sensor. Firstly, it can serve as photogenerated hole oriented-transfer medium from the BiVO₄ photoanode to the detective target; In addition, 2D-C₃N₄ with large area of π electron cloud can fix the DNA aptamer parallelly by π-π bonding with the nucleic acid in the DNA aptamer to shorten the hole transfer distance from the semiconductor to target. So that, a record MC-LR detection sensitivity has been achieved by the 2D-C₃N₄ modified BiVO₄/DNA aptamer sensor.

Visible light-driven enhanced CO2 reduction by water over Cu modified S-doped g-C3N4

We synthesized Cu modified S-doped g-C₃N₄ thin sheets using calcination followed by a wet-impregnation method. The photocatalytic activity was studied for reduction of CO₂ to CO and CH₄ in the presence of water and a plausible mechanism is explained.

Construction of plasmonic Ag modified phosphorous-doped ultrathin g-C3N4 nanosheets/BiVO4 photocatalyst with enhanced visible-near-infrared response ability for ciprofloxacin degradation

To realize the full utilization of solar energy, the design of highly efficient photocatalyst with improved visible-near-infrared photocatalysis performance has attracted great attentions for environment pollutant removal. In this work, we rationally employed the surface plasmon resonance effect of metallic Ag in the phosphorus doped ultrathin g-C₃N₄ nanosheets (PCNS) and BiVO₄ composites to construct a ternary Ag@PCNS/BiVO₄ photocatalyst. It was applied for the photodegradation of ciprofloxacin (CIP), exhibiting 92.6% removal efficiency under visible light irradiation (λ>420nm) for 10mg/L CIP, and presenting enhanced photocatalytic ability than that of single component or binary nanocomposites under near-infrared light irradiation (λ>760nm). The improved photocatalytic activity of the prepared Ag@PCNS/BiVO₄ nanocomposite can be attributed to the synergistic effect among the PCNS, BiVO₄ and Ag, which not only improves the visible light response ability and hinders the recombination efficiency of the photogenerated electrons and holes, but also retains the strong the redox ability of the photogenerated charges. According to the trapping experiment and ESR measurements results, OH, h⁺ and O₂^- all participated in the photocatalytic degradation process. Considering the SPR effect of metallic Ag and the established local electric field around the interfaces, a dual Z-scheme electrons transfer mechanism was proposed.

Fabrication of g-C3N4 and a promising charcoal property towards enhanced chromium(VI) reduction and wastewater treatment under visible light

The visible light driven photoactivity of g-C₃N₄ can be enhanced using charcoal as a supporter. Charcoal/g-C₃N₄ composite materials were prepared by the simultaneous thermal condensation of melamine and charcoal. The effect of different atmospheres (O₂, air, and argon) on the reaction was investigated. The effect of different weight ratios of charcoal to melamine (1:1 and 1:4 wt%) was also investigated. The physical properties of the charcoal/g-C₃N₄ materials were analyzed using XRD, SEM, TEM, XPS, BET and FTIR techniques. It was found that an oxidation reaction of charcoal and g-C₃N₄ during preparation greatly affected the photoactivity. A composite of charcoal:melamine (1:4 wt%) prepared under an air atmosphere provided good photooxidation of methylene blue; whereas a composite of charcoal:melamine (1:4 wt%) prepared under an oxygen atmosphere exhibited good photoreduction of chromium (VI).

Noble-metal-free Ni3N/g-C3N4 photocatalysts with enhanced hydrogen production under visible light irradiation

Noble-metal-free Ni₃N/g-C₃N₄ heterojunctions that show high photocatalytic hydrogen evolution activity comparable to platinized g-C₃N₄ were successfully synthesized.

Synergistic Effects of Ag Nanoparticles/BiV1-xMoxO4 with Enhanced Photocatalytic Activity

In recent years, BiVO₄ has drawn much attention as a novel photocatalyst given its excellent ability to absorb visible light. This work reports the development of Ag-modified BiV_1-xMo_xO₄ composites through a facile hydrothermal synthesis with the subsequent photoinduced reduction of Ag⁺ at almost neutral pH conditions. Metallic Ag nanoparticles were deposited on the (040) facet of Mo-doped BiVO₄ powders. The crystal structure and morphology of the as-prepared samples were studied by XRD and SEM analyses. Moreover, the photocatalytic performance of BiVO₄, Ag/BiVO₄, and Ag-modified BiV_1-xMo_xO₄ were evaluated by the degradation of rhodamine B (RhB). The Ag/BiV_0.9925Mo_0.0075O₄ composite exhibited the most efficient photocatalytic performance. The present work provides greater insight into the application of BiVO₄ in the field of photocatalysis.

Electrospinning Preparation of Nanostructured g-C3N4/BiVO4 Composite Films with an Enhanced Photoelectrochemical Performance

Nanostructured g-C₃N₄/BiVO₄ composite films with an enhanced photoelectrochemical (PEC) performance have been fabricated via the facile electrospinning technique. The g-C₃N₄ nanosheets can not only form heterojunctions with BiVO₄ but also prevent the agglomeration of BiVO₄, helping the formation of nanostructures. The as-prepared g-C₃N₄/BiVO₄ films exhibit good coverage and stability. The PEC performance of the g-C₃N₄/BiVO₄ films is much more enhanced compared with that for individual BiVO₄ films because of the enhanced electron-hole separation. The photocurrent density is 0.44 mA/cm² for g-C₃N₄/BiVO₄ films at 0.56 V in the linear sweep current-voltage test, over 10 times higher than that of individual BiVO₄ films (0.18 mA/cm²). The effects of the preparation conditions including the g-C₃N₄ content, collector temperature, calcination temperature, and electrospinning time on the PEC performance were investigated, and the reasons for the effects were proposed. The optimal preparation condition was with 3.9 wt % g-C₃N₄ content in the electrospinning precursor, 185 °C collector temperature, 450 °C calcination temperature, and 40 min electrospinning time. The excellent PEC performance and the facile preparation method suggest that the g-C₃N₄/BiVO₄ films are good candidates in energy and environmental remediation area.

Electronic and optical properties of MoS2/α-Fe2O3(0001) heterostructures: a first-principles investigation

This study investigates the effect of interfacial structure of MoS₂/α-Fe₂O₃(0001) heterostructure on its photocatalytic activity.

Hollow Sr/Rh-codoped TiO2 photocatalyst for efficient sunlight-driven organic compound degradation

Sunlight-driven photocatalysis has emerged as a potential technology to address organic pollutant issues.