g-C3N4 Monolayer Research Articles

First Principle Study of Na and P Co-Doped Heptazine Based Monolayer g-C<sub>3</sub>N<sub>4</sub>

Elements doping is a powerful way to alter the electronic structure and enhancing the photo catalytic activity of materials by relaxing the surrounding chemical bonds and forming new chemical bond. In this work, we have performed, the first principle density functional theory calculations to investigate the geometric, electronic and optical properties of pristine, Na-doped and P-doped as well as Na and P (Na/P) co-doped heptazine based monolayer graphitic carbon nitride (g-C3N4). The co-doping process results in significantly narrow band gap of g-C3N4. The optical absorption shows better visible-light response compare to pristine g-C3N4. After doping the highest occupied molecular orbitals (HOMO) and lowest unoccupied molecular orbitals (LUMO) show strong delocalization and indicates photo generated electron/hole (e-/h+) pair disunion abilities of doped systems are superior than pristine heptazine based monolayer g-C3N4. Thus the co-doping with Na and P elements is an effective technique to boost the photocatalytic performance of heptazine based monolayer g-C3N4.

Insight into the effect of boron doping on electronic structure, photocatalytic and adsorption performance of g-C3N4 by first-principles study

Non-metal doping is an effective technique to adjust the electronic structure and modify the photocatalytic activity of graphitic carbon nitride (g-C3N4). On the basis of first-principles density functional theory, the formation energies, electronic, optical, and adsorption characteristics of boron doped monolayer g-C3N4 were determined. The results show that boron atom preferentially substitutes for the edge N2 atom. The energy band gap was reduced from 3.06 eV to 1.33–1.80 eV because of the introduction of boron impurity through three sites (N2, C1, interstitial). The strengthen delocalization of the HOMO and LUMO distribution caused by B-N2 and B-interstitial doping could facilitate the enhancement of the carrier mobility. The interstitial doped B atom acted as a bridge between two adjacent units, which is partly helpful to improve the carrier mobility and to separate photo-generated e−/h+ pairs. The absorption of visible light was also enhanced by the doping of B impurities. Furthermore, the interstitial doping of B atom significantly promoted the adsorption of pollutants by g-C3N4. The computational results could provide useful insights and effective strategies for design of non-metal photocatalysts.

Strain-tunable electronic and optical properties in two dimensional GaSe/g-C3N4 van der Waals heterojunction as photocatalyst for water splitting

Abstract Restacking diverse two dimensional (2D) nanosheets into a bilayer van der Waals (vdW) heterojunction opens up a promising platform for designing high performance photocatalyst. In this work, by employing HSE06 hybrid functional, we have systematically studied the electronic and optical properties of GaSe/g-C3N4 bilayer heterojunction, whose different layers with a interlayer spacing of 3.49 A at equilibrium are bound together through the vdW interaction. Our computations indicate that the GaSe/g-C3N4 heterostructure, whose bandedge positions can stride over the redox levels of water and bandgap is much smaller than that of GaSe monolayer, is suitable for photocatalytic water splitting. By applying strains in the range from 6% pressure to 6% tension, these bandgaps of GaSe/g-C3N4 heterojunction can be narrowed to the range of 1.70–2.84 eV. Particularly, GaSe/g-C3N4 heterojunction with 6% tension, whose conduction band minimum (CBM) and valence band maximum (VBM) are situated at different slabs, can realize the efficient separation of electron–hole pairs. Meanwhile, GaSe/g-C3N4 heterojunction with 6% tension, whose bandgap decreases to 2.31 eV, can make the utmost of the sunlight. In contrast with GaSe and g-C3N4 monolayers, the distinct red shifts of optical absorption appear in GaSe/g-C3N4 heterojunctions with 6% tension, which results in the narrowing of the bandgaps. Even in the VIS region about 460 nm, there is an absorption peak in the optical absorption spectrum of GaSe/g-C3N4 heterojunctions with 6% tension. Therefore, GaSe/g-C3N4 heterojunctions should have promising applications as photocatalysts for water decomposition to generate hydrogen.

Fabrication of exfoliated graphitic carbon nitride, (g-C3N4) thin film by methanolic dispersion

This paper reports the successful exfoliation of nanosheets from bulk g-C3N4 by using urea as a precursor. The alteration from bulk g-C3N4 powder, changed its semiconductor arrangements such as the optical absorption, chemical bonding, and topography images. A slow direct low thermal treatment (∼40 °C, 24 h) was proposed as a formation of a thinner layer by layer, complete and effective polymerization for an exfoliated g-C3N4. The photocurrent responses were more than two times higher for exfoliated g-C3N4 compared with bulk g-C3N4, reaching ∼4.37 μA cm−2 up to 10.21 μA cm−2 at 1.23 vs. (Ag/AgCl). This fabrication method involved dispersing of the highly stable g-C3N4 suspension onto FTO surface via spin coating, followed by a moderate post-annealing temperature at 350 °C. The monolayer g-C3N4 act as a photoelectrode, responding to light and dark current, and maintained its own intrinsic n-types properties. The interaction of the C and N atom with molecules of methanol (CH3OH) followed with vibration force (ultrasonication) produces the ultrafast drying and can transmit to disrupt the van der Waals forces within the g-C3N4 structure. Therefore, due to the ability the good performance, the exfoliated g-C3N4 can be envisioned as a potential application such as water splitting, solar cell, and environmental remediation.

Monolayer SiP2S6: metal-free photocatalyst with spontaneous hydrogen and oxygen evolution half reactions

Two-dimensional photocatalysts for water splitting with spontaneous hydrogen and oxygen evolution half reactions are long-desired materials for solving the environmental pollution and energy crisis. To date, several such photocatalysts have been reported, all based on metal-containing materials. Here, we propose a novel metal-free candidate, SiP2S6 monolayer, on the basis of first principles calculations. SiP2S6 monolayer holds a moderate band gap of 2.78 eV and suitable band edge positions for overall water splitting. Also, it harbors excellent optical absorption, even comparable to that of g-C3N4 monolayer. More remarkably, the photocatalytic hydrogen and oxygen evolution half reactions on the surface of SiP2S6 monolayer can occur spontaneously with only solar light irradiation, without needing sacrificial reagents or co-catalysts. This discovery not only reveals the great potential of SiP2S6 monolayer in photocatalytic applications but also broadens the scientific impact of two-dimensional photocatalysts.

Adsorption behaviors of HCN, SO2, H2S and NO molecules on graphitic carbon nitride with Mo atom decoration

In this paper, we explored the adsorption structure, electronic states, and charge transfer of toxic gas molecules, including HCN, SO2, H2S and NO, on pristine and Mo atom embedded graphitic carbon nitride (g-C3N4) by first-principles calculations. Our results show that single Mo atom prefers to be embedded at the six-fold cavity with high stability. The adsorption of those gas molecules on pristine g-C3N4 monolayer exhibits weak interaction, while Mo atom doping can significantly enhance their adsorption energy. Partial density of states analysis illustrate strong hybridization among Mo-4d, gas molecule and g-C3N4. Charge transfer analysis indicates that HCN, SO2, and NO act as acceptors, while H2S acts as donor. The magnetism of g-C3N4/Mo also undergoes great change after the gas molecules adsorption. The adsorption of HCN, SO2, H2S makes the system exhibit semimetal properties, while the adsorption of NO produces much smaller magnetic moment. Therefore, the magnetism of the Mo/g-C3N4 can be modified by the gas molecule adsorption. Our calculations demonstrate that Mo decorated g-C3N4 monolayer can be a promising adsorbent for gas molecule and the variation of magnetic moment through gas adsorption can also be utilized.

Electric field and strain effects on the electronic and optical properties of g-C3N4/WSe2 van der Waals heterostructure

Efficient carrier separation and regulable visible light absorption are important characteristics for eligible nanoscale photoelectric devices. In this work, tunable electronic structure and optical properties of novel g-C3N4/WSe2 van der Waals heterostructure under various electric fields and biaxial strains are systematically investigated by first principle calculations. The results show that the g-C3N4/WSe2 heterostructure is a direct band gap semiconductor (1.395 eV) with intrinsic type-I band alignment and exhibits good UV and visible light absorption compared to the isolated g-C3N4 and WSe2 monolayers. Applied external electric-field can effectively adjust the interlayer coupling and charge transfer, which can further alter the band structure and achieve the transition of type I to type II band alignment for the g-C3N4/WSe2 heterostructure. The biaxial strain causes charge redistribution in the interfacial regions and triggers an indirect-direct band gap transition in the g-C3N4/WSe2 heterostructure, which is strongly associated with the modification of band structure contributed by W dz2 and dxy orbitals near the Fermi level. Besides, the systematical red shift and blue shift of absorption peaks is also observed under the tensile and compressive strains, respectively. The tunable electronic structure and optical properties make g-C3N4/WSe2 vdW heterostructure potential candidates for application in the photoelectronic device.

Mechanism of Photocatalytic Reduction of CO2 by Ag3PO4(111)/g-C3N4 Nanocomposite: A First-Principles Study

Density functional theory (DFT) calculations have been performed to investigate the electronic structure and photocatalytic activity of a hybrid Ag3PO4(111)/g-C3N4 structure. Due to Ag(d) and O(p) states forming the upper part of the valence band and C(p), N(p) and Ag(s) the lower part of the conduction band, the band gap of the hybrid material is reduced from 2.75 eV for Ag3PO4(111) and 3.13 eV for monolayer of g-C3N4 to about 2.52 eV, enhancing the photocatalytic activity of the Ag3PO4(111) surface and g-C3N4 sheet in the visible region. We have also investigated possible reaction pathways for photocatalytic CO2 reduction on the Ag3PO4(111)/g-C3N4 nanocomposite to determine the most favored adsorption geometries of reaction intermediates and the related reaction energies. For CO2 reduction, our findings demonstrate that the Ag3PO4(111)/g-C3N4 heterostructure thermodynamically exhibits a higher selectivity towards CH4 production than that of CH3OH. The CO2 reduction process takes place through either HCOOH* or HOCOH* as an intermediate species, where the highest exothermic reaction energy of -2.826 eV belongs to the hydrogenation of t-COOH* to HCOOH* and the lowest reaction energy of -0.182 eV for hydrogenations of CH2O* to CH2OH* and HCO* to c-HCOH*. Our results from charge density difference calculations of the Ag3PO4(111)/Ag/g-C3N4 revealed that the charge transfer between the Ag3PO4(111) slab and g-C3N4 monolayer occurs through mediation of atomic Ag, thus proposing a Z-scheme mechanism. Moreover, a smaller band gap energy of 0.73 eV is calculated for this ternary nanocomposite due to the mid-gap states of the atomic Ag at the interface. These results provide in depth understanding of the reaction mechanism in the reduction and conversion of CO2 to useful chemicals via an Ag3PO4 and g-C3N4-based nanocomposite photocatalyst under visible light.

First-principles investigation on hydrogen evolution reaction in KNbO3 (100)/g-C3N4 heterojunction

Constructing the two-dimensional (2D) heterojunction photocatalysts is a highly efficient strategy for utilizing solar energy and speeding up the separation rate of photogenerated charge carriers. In this contribution, we systematically investigate the electronic and photocatalytic performances of the 2D KNbO3/g-C3N4 heterojunction using first-principles calculations, along with the origin of the photocatalytic performance. Our results indicate that the KNbO3/g-C3N4 heterojunction is a very promising photocatalytic material for water splitting, particularly for the hydrogen evolution reaction, well consistent with the reported experimental results. The KNbO3/g-C3N4 heterojunction owns a type-Ⅱ band alignment. Moreover, the density charge difference (DCD) and Mulliken population analysis show that the g-C3N4 monolayer can absorb visible light and effectively improve the optical properties of KNbO3. After g-C3N4 combined with KNbO3 (100) surface, the band gap has been significantly reduced and a red shift occurs in the visible light region. Additionally, the application of an external electric field and biaxial strain have been evident as efficient methods to obtain modulated band gaps for the heterojunctions. Interestingly, a linear evolution trend of the band gap is presented for the heterojunctions under the compression and tensile strain. Heterojunctions have a tendency to convert from semiconductors to conductors. Overall, these findings provide theoretical support for the research about KNbO3/g-C3N4 heterojunctions and pave a way of enhancing the photocatalytic performance under visible light irradiation.

The novel two-dimensional photocatalyst SnN3 with enhanced visible-light absorption for overall water splitting.

Herein, we proposed a novel excellent two-dimensional photocatalyst, the SnN3 monolayer, using first-principles calculations. The stability of the SnN3 monolayer was examined via formation energy, phonon spectroscopy and ab initio molecular dynamics simulations. The SnN3 monolayer has an ultra-high optical absorption capacity of the order of 105 cm-1 in the visible region, which is 3, 4 and 10 times those of SnP3, MoS2 and g-C3N4 monolayers, respectively. Moreover, it has a higher carrier mobility, 769.19 cm2 V-1 s-1, than the other monolayers; the available electrostatic potential of -5.02 eV and the appropriate band gap of 1.965 eV indicate its applicability as a catalyst for overall water splitting over a wide strain range. The electronic properties of the SnN3 monolayer could also be engineered effectively by altering the external strain and electric field.

2D/2D heterojunction of Ti3C2/g-C3N4 nanosheets for enhanced photocatalytic hydrogen evolution.

Photocatalytic hydrogen evolution from water has received enormous attention due to its ability to address a number of global environmental and energy-related issues. Here, we synthesize 2D/2D Ti3C2/g-C3N4 composites by electrostatic self-assembly technique and demonstrate their use as photocatalysts for hydrogen evolution under visible light irradiation. The optimized Ti3C2/g-C3N4 composite exhibited a 10 times higher photocatalytic hydrogen evolution performance (72.3 μmol h-1 gcat-1) than that of pristine g-C3N4 (7.1 μmol h-1 gcat-1). Such enhanced photocatalytic performance was due to the formation of 2D/2D heterojunctions in the Ti3C2/g-C3N4 composites. The intimate contact between the monolayer Ti3C2 and g-C3N4 nanosheets promotes the separation of photogenerated charge carriers at the Ti3C2/g-C3N4 interface. Furthermore, the ultrahigh conductivity of Ti3C2 and the Schottky junction formed between g-C3N4/MXene interfaces facilitate the photoinduced electron transfer and suppress the recombination with photogenerated holes. This work demonstrates that the 2D/2D Ti3C2/g-C3N4 composites are promising photocatalysts thanks to the ultrathin MXenes as efficient co-catalysts for photocatalytic hydrogen production.

Recyclable Visible Light-Driven O-g-C3N4/Graphene Oxide/N-Carbon Nanotube Membrane for Efficient Removal of Organic Pollutants.

Organic pollutants are harmful to human health, which creates a global need for the development of novel and effective materials for efficiently removing contaminants. Accordingly, an efficient visible light-driven heterostructured membrane combined with oxygen-modified monolayer g-C3N4, graphene oxide, and nitrogen-doped carbon nanotubes (CNTs) (O-g-C3N4/GO/N-CNT) was successfully fabricated through electrostatic interactions and subsequent vacuum filtration. The results suggested that the O-g-C3N4/GO/N-CNT membrane exhibited higher degradation rate than those of O-g-C3N4/GO and pure O-g-C3N4 under visible light exposure. This enhanced photocatalytic performance was attributed to the introduction of GO and N-CNT, which acted as electronic acceptors for monolayer O-g-C3N4 that effectively inhibited recombination of photogenerated electron-hole pairs, thus enhancing visible light photocatalytic activity. Furthermore, the enrichment and degradation rates of O-g-C3N4/GO/N-CNT membranes were demonstrated for tetracycline hydrochloride, which were found to be 96.64 and 94.30%, respectively, and no distinct enrichment or catalytic activity reduction was observed when their reusability was measured. These results suggested that these recyclable O-g-C3N4/GO/N-CNT membranes provide a new strategy for the highly efficient removal of environmental pollutants.

Two-dimensional g-C3N4/InSe heterostructure as a novel visible-light photocatalyst for overall water splitting: a first-principles study

The enhanced visible-light harvesting, low recombination of electron–hole pairs and high carrier mobility are found in a novel g-C3N4/InSe hybrid two-dimensional (2D) heterostructure photocatalyst by using first-principles calculations for the first time. The photocatalytic mechanism of g-C3N4/InSe is comprehensively investigated. Our calculations show that 2D g-C3N4/InSe heterostructure has a direct band gap of 1.93 eV and a typical type-II band alignment with holes and electrons located in metal-free g-C3N4 monolayer and non-noble metal InSe nanosheet, respectively. A remarkable visible-light absorption can thus be expected. The electrons and holes located in InSe and g-C3N4 monolayers have a high mobility (104 and 102 cm2 V−1 s−1), which is beneficial for improving the catalytic efficiency. The charge density difference and type-II band structure indicate that the photo-generated electrons easily transfer from g-C3N4 monolayer to InSe nanosheet, and the holes are transferred from InSe to g-C3N4, reducing the electron–hole recombination. Compared with the well-known 2D g-C3N4/MoS2 hybrid photocatalyst composed of g-C3N4 nanosheet and MoS2 monolayer with a low electron mobility (<200 cm2 V−1 s−1) and fast electron–hole recombination due to its direct bandgap, g-C3N4/InSe heterostructure photocatalyst has a distinctive advantage in improving the photocatalytic hydrogen evolution performance due to the high carrier mobility and suppressing the recombination of photo-generated electrons and holes by the indirect band gap of InSe monolayer. These clearly prove that g-C3N4/InSe is an energetic photocatalyst for overall water splitting under visible-light irradiation.

Synergistic Effect of Doping and Compositing on Photocatalytic Efficiency: A Case Study of La2Ti2O7.

Charge generation and separation are two key issues in developing a high-efficiency semiconductor for the visible-light-driven photocatalysis. Here, we use the layered perovskite-type wide-gap semiconductor La2Ti2O7 (LTO) as a model to systematically explore the synergistic effect of doping (with sulfur or nitrogen) and heterojunction (with graphitic C3N4) on improving visible light absorption and photoexcited charge separation by means of density functional theory calculations. It is found that the anion (N or S) doping into the LTO(010) surface can not only shift the optical absorption edge to the visible region, but also creates some partially occupied or unoccupied states in the band gap that would facilitate the formation of recombination centers. For the purpose of promoting electron-hole separation, the (N or S-doped) LTO(010) surfaces were hybridized with the monolayer g-C3N4. Interestingly, we found that the (S-doped) LTO/g-C3N4 heterostructure forms a type-II heterojunction, with the valence band maximum residing in the (S-doped) LTO and the conduction band minimum in g-C3N4, respectively. This band alignment feature facilitates efficient electron-hole separation. Moreover, we found that the S-doped LTO/g-C3N4 composite has a short interfacial distance (about 2.1 Å), implying that the interfacial interaction of this composite might be a chemical bond rather than a weak van der Walls interaction. The chemical bonding can enhance charge separation. Our theoretical findings provide design principles for optimizing the photocatalytic performance of the wide-gap photocatalysts and demonstrate that the S-doped LTO/g-C3N4 composite would be a potential candidate for the photocatalysis of water splitting.

Interfacial coupling induced direct Z-scheme water splitting in metal-free photocatalyst: C3N/g-C3N4 heterojunctions

Mimicking the natural photosynthesis in green plants, artificial Z-scheme photocatalysis enables more efficient utilization of solar energy for photocatalytic water splitting. Most currently designed g-C3N4-based Z-scheme heterojunctions are usually based on metal-containing semiconductor photocatalysts, thus exploiting metal-free photocatalysts for Z-scheme water splitting is of huge interest. Herein, we propose two metal-free C3N/g-C3N4 heterojunctions with the C3N monolayer covering g-C3N4 sheet (monolayer or bilayer) and systematically explore their electronic structures, charge distributions and photocatalytic properties by performing extensive hybrid density functional calculations. We clearly reveal that the relative strong built-in electric fields around their respective interface regions, caused by the charge transfer from C3N monolayer to g-C3N4 monolayer or bilayer, result in the bands bending, renders the transfer of photogenerated carriers in these two heterojunctions following the Z-scheme instead of the type-II pathway. Moreover, the photogenerated electrons and holes in these two C3N/g-C3N4 heterojunctions can not only be efficiently separated, but also have strong redox abilities for water oxidation and reduction. Compared with the isolated g-C3N4 sheets, the light absorption in visible to near-infrared region are significantly enhanced in these proposed heterojunctions. These theoretical findings suggest that these proposed metal-free C3N/g-C3N4 heterojunctions are promising direct Z-scheme photocatalysts for solar water splitting.

Adjustable photocatalytic ability of monolayer g-C3N4 utilizing single–metal atom: Density functional theory

Single–atom catalysis is an effective method to improve the catalytic efficiency. With the aid of density functional theory calculations, we investigated the thermodynamic performances during water splitting besides the structural and electronic performances of monolayer g–C3N4 embedded with single Ni, Pd, Pt, Cu, Ag or Au atom. Based on the detailed analysis of the electronic redistributions and chemical bond relaxations, the ratio of ionic and covalent bonding parts of chemical bonds were adjusted by the single atoms, it changed the adsorption energy of intermediates, the free energy changes during reaction and then the overpotentials of oxidation evolution reaction (OER) and hydrogen evolution reaction (HER). Interestingly, the overpotentials of OER and HER reduce as the percentage of covalent bonding parts is close to a certain value, which are conductive to improve the OER and HER efficiency. In addition, the differences of redox potentials between catalysts and water oxidation/H+ reduction are larger than the corresponding overpotentials of OER and HER on Pd1/ and Pt1/g–C3N4, thus the OER and HER can happen on them.

The electronic structure and photoactivity of TiO2 modified by hybridization with monolayer g-C3N4

In this work, first-principles calculation based on density functional theory (DFT) was used to study the enhanced photocatalytic mechanism of TiO2 hybridized with pristine and defective g-C3N4 systematically. The theoretical investigations on both geometry structure and electronic properties, involving band structure, density of states, electron population and charge density difference, were carried out to characterize the improved property of TiO2. It was found that the combination TiO2 with g-C3N4 could be verified for high thermodynamic stability. The interaction between TiO2 and g-C3N4 led to form a built-in electric field at the interface, which facilitated the separation of electron-hole pairs and restrained photo-generated carrier recombination. Furthermore, electrons transiting from the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO) promoted the separation of electrons and holes. The effective separation of electron-hole pairs prolonged the lifetime of carries and enhanced the photocatalytic activity of TiO2/g-C3N4. The theoretical investigations could verify the experimental observation results [Chem. Sci., 5(2014), 3946–3951, Phys. Chem. Chem. Phys., 17(2015), 17406–17412] and illustrate the mechanisms of photocatalytic enhancement of TiO2/g-C3N4 composite photocatalysts. Furthermore, the calculated optical absorption curves demonstrated that the absorption edge of TiO2/g-C3N4 composites shifted to visible-light region and its photocatalytic activity increased under visible-light irradiation. The theoretical investigation might provide referable and valuable information for understanding the observed enhanced photocatalytic mechanism in experiments.

Electronic properties of g-C3N4/CdS heterojunction from the first-principles

In this work, electronic structures of two-dimensional (2D) g-C3N4/CdS heterojunction are systematically investigated by means of the first-principles calculations. Our results indicate that g-C3N4 monolayer and CdS monolayer form a standard type-Ⅱ heterojunction, with both the valence band maximum (VBM) and the conduction band minimum (CBM) of CdS monolayer higher than those of g-C3N4 monolayer, and the water reduction and oxidation potentials lie in-between the VBM and CBM of g-C3N4/CdS heterojunction. Moreover, the charge density difference of g-C3N4/CdS heterojunction indicates that an internal electric field forms between g-C3N4 monolayer and CdS monolayer, which will further restrain the recombination of photogenerated carriers. These results suggest that g-C3N4/CdS heterojunction is beneficial to enhance the efficiency of photocatalytic water splitting under visible-light irradiation.

Gold/monolayer graphitic carbon nitride plasmonic photocatalyst for ultrafast electron transfer in solar-to-hydrogen energy conversion

Gold (Au) plasmonic nanoparticles were grown evenly on monolayer graphitic carbon nitride (g-C3N4) nanosheets via a facile oil-bath method. The photocatalytic activity of the Au/monolayer g-C3N4 composites under visible light was evaluated by photocatalytic hydrogen evolution and environmental treatment. All of the Au/monolayer g-C3N4 composites showed better photocatalytic performance than that of monolayer g-C3N4 and the 1% Au/monolayer g-C3N4 composite displayed the highest photocatalytic hydrogen evolution rate of the samples. The remarkable photocatalytic activity was attributed largely to the successful introduction of Au plasmonic nanoparticles, which led to the surface plasmon resonance (SPR) effect. The SPR effect enhanced the efficiency of light harvesting and induced an efficient hot electron transfer process. The hot electrons were injected from the Au plasmonic nanoparticles into the conduction band of monolayer g-C3N4. Thus, the Au/monolayer g-C3N4 composites possessed higher migration and separation efficiencies and lower recombination probability of photogenerated electron-hole pairs than those of monolayer g-C3N4. A photocatalytic mechanism for the composites was also proposed.

Electronic and optical performances of (Cu, N) codoped TiO2/g-C3N4 heterostructure photocatalyst: A spin-polarized DFT + U study

The geometrical, electronic and optical properties of Cu or/and N (co)doped TiO2/g-C3N4 heterostructure systems have been investigated systematically on the basis of spin-polarized density functional theory calculations. Our calculated results indicate that the band gap of TiO2/g-C3N4 heterostructure has an obvious narrowing compared with pure TiO2 (1 0 1) surface, and (Cu, N) codoping can induce some impurity states of N 2p and hybridized states of Cu 3d and N 2p appearing in the forbidden gap of TiO2/g-C3N4 heterostructure, which lead to a decrease of the photon excitation energy and an obvious redshift of the optical absorption edge. Moreover, the charge density difference calculations of Cu or/and N (co)doped TiO2/g-C3N4 heterostructure systems show that the excited electrons and holes will eventually accumulate in (co)doping TiO2 (1 0 1) surface and g-C3N4 monolayer, respectively, which can effectively reduce the recombination of the photogenerated electron-hole pairs by the interfacial coupling of between TiO2 (1 0 1) surface and g-C3N4 monolayer. This work not only investigates systematically the electronic and optical properties of Cu or/and N (co)doped TiO2/g-C3N4 heterostructure, but also suggests that (Cu, N) codoped TiO2/g-C3N4 heterostructure is a preferable visible-light photocatalyst.