Performance Of Graphitic Carbon Nitride Research Articles

Graphitic Carbon Nitride Q-Switched Tm:CNNGG Laser at 2 Micrometer Wavelength Region

The Q-switching performance of graphitic carbon nitride (g-C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> ) based on saturated absorption is demonstrated in 2 micrometer wavelength region for the first time. The g-C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> saturable absorbers, processed by thermal oxidation etching, are employed for passive Q-switching in a Tm:CNNGG laser. With a 5 hours long thermal oxidation etched g-C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> saturable absorber, the Q-switched Tm:CNNGG laser generates a shortest pulse duration of 132 ns with a repetition frequency of 16 kHz and a peak power of 98.5 W. The experimental results indicate that g-C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> is an excellent saturable absorber for passive Q-switching in 2 micrometer wavelength region.

Nitrogen deficient carbon nitride for efficient visible light driven tetracycline degradation: a combination of experimental and DFT studies

The narrow visible-light absorption range and a high recombination rate of photo-excited electrons and holes are the main reasons for the confined photocatalytic performance of graphitic carbon nitride (g-C3N4).

Construction of ZnO Hollow Spheres Coupled with g-C3N4 as Enhanced Photocatalysts under Simulated Solar Light

Rapid photon-induced e−-h+ pairs recombination rate is a fatal factor restricting the photocatalytic performance of graphitic carbon nitride (g-C3N4). In this work, ZnO hollow spheres (ZnO HS) coupled with g-C3N4 photocatalysts were prepared by a simple mechanical agitation of the mixture of g-C3N4 and ZnO HS in ethanol solution. The as-prepared samples were systematically measured via were characterized by XRD, SEM, DRS, FT-IR and PL. As analysis from the PL test results, the g-C3N4/ZnO HS has much lower photo-generated e−-h+ pairs recombination rate than that of pure g-C3N4. Under the illumination of simulated solar light, the effect of ZnO HS concentration on the photocatalytic properties of as-prepared gC3N4/ZnO HS photocatalysts with different ZnO amount was discussed by the degradation of methyl orange (MO) in detail. The optimum photodegradation performance of g-C3N4/ZnO HS with 5% ZnO HS is almost 47.43% higher than that of pristine g-C3N4. Our research results present a simple and convenient synthetic protocol for processing g-C3N4-based photocatalysts for the degradation of environmental pollutants.

Enhanced photoelectrochemical sensing performance of graphitic carbon nitride by nitrogen vacancies engineering

Ciprofloxacin (CIP) as a typical antibiotic is widely used to produce antimicrobial drugs. Determination of CIP has raised extensive concern due to its possible toxic effects on human health. Here, a simple photoelectrochemical (PEC) sensor for detecting CIP has been developed by using the nitrogen-deficient graphitic carbon nitride (ND-g-CN) as a PEC active material. The ND-g-CN material exhibits two-dimension (2D) thin sheet structure with abundant nitrogen vacancies. The 2D thin sheet structure can enable the effective charge separation and transfer, thus dramatically improving the PEC performance. Simultaneously, nitrogen vacancies can serve as charge trap to efficiently inhibit the charge recombination. Furthermore, the synergistic effect of the two can widen the absorption edge and decrease the band gap of ND-g-CN material, resulting in increasing light harvesting and enhancing PEC performance. CIP can be oxidized by the holes of ND-g-CN, thus realizing effective charge separation, which can result in the amplification of the photocurrent. The designed PEC sensor demonstrated a wide detection range from 60 to 19090 ng L−1 and a low detection limit of 20 ng L−1 for CIP assay. This strategy broadens the application of graphitic carbon nitride (g-CN) material in PEC field and presents a promising potential for the practical application in the environmental monitoring.

Facile Fabrication of Fe2O3/Nitrogen Deficient g-C3N4-x Composite Catalysts with Enhanced Photocatalytic Performances

The modification of graphitic carbon nitride can significantly improve the photocatalytic performance of graphitic carbon nitride (g-C3N4). Fe2O3/nitrogen-deficient g-C3N4-x composite catalysts were prepared with dicyandiamide as the precursor and Fe3+ doped in this study. The composite catalysts were characterized by XRD, SEM, FT-IR, XPS and photocurrent measurements. Close interaction occurred between Fe2O3 and nitrogen deficient g-C3N4-x, more photogenerated electrons were created and effectively separated from the holes, resulting in a decrease of photocarrier recombination, and thus enhancing the photocurrent. Photocatalytic performance experiments showed that Fe2O3 / nitrogen deficient g-C3N4-x could utilize lowenergy visible light more efficiently than pure g-C3N4, and the removal rate was 92% in 60 minutes.

Functional groups to modify g-C3N4 for improved photocatalytic activity of hydrogen evolution from water splitting

Rational modification by functional groups was regarded as one of efficient methods to improve the photocatalytic performance of graphitic carbon nitride (g-C3N4). Herein, g-C3N4 with yellow (Y-GCN) and brown (C-GCN) were prepared by using the fresh urea and the urea kept for five years, respectively, for the first time. Experimental results show that the H2 production rate of the C-GCN is 39.06 μmol/h, which is about 5 times of the Y-GCN. Meantime, in terms of apparent quantum efficiency (AQE) at 420 nm, C-GCN has a value of 6.3% and nearly 7.3 times higher than that of Y-GCN (0.86%). The results of XRD, IR, DRS, and NMR show, different from Y-GCN, a new kind of functional group of NCH was firstly in-situ introduced into the C-GCN, resulting in good visible light absorption, and then markedly improving the photocatalytic performance. DFT calculation also confirms the effect of the NCH group band structure of g-C3N4. Furthermore, XPS results demonstrate that the existence of NCH groups in C-GCN results in tight interaction between C-GCN and Pt nanoparticles, and then improves the charge separation and photocatalytic performance. The present work demonstrates a good example of “defect engineering” to modify the intrinsic molecular structure of g-C3N4 and provides a new avenue to enhance the photocatalytic activity of g-C3N4via facile and environmental-friendly method.

Amorphous Bimetallic Cobalt Nickel Sulfide Cocatalysts for Significantly Boosting Photocatalytic Hydrogen Evolution Performance of Graphitic Carbon Nitride: Efficient Interfacial Charge Transfer.

Noble metals usually work as the cocatalyst for photocatalytic water splitting, but their rare and expensive properties narrowed their wide development. Transition-metal sulfides have appeared to be promising non-noble metal cocatalysts in the hydrogen evolution reaction (HER) to meet future energy demands. Meanwhile, many studies focus on the fabrication of bimetallic catalysts because of their remarkably superior catalytic activity compared with monometallic substances. Herein, amorphous bimetallic cobalt nickel sulfide (CoNiSx) was fabricated to work as a cocatalyst in the photocatalytic H2 evolution reaction, which can couple with pristine graphitic carbon nitride (g-C3N4). CoNiSx-CN exhibits a larger specific surface area compared with g-C3N4, making it possess more reaction active sites. Moreover, the contacted interface in the CoNiSx-CN composite photocatalyst contributes to higher separation efficiency of photogenerated carriers, which was proved by experimental and theoretical calculations. More importantly, the theoretical calculation also verified that CoNiSx-CN has relatively closer Gibbs free energy to zero than pure g-C3N4 and corresponding monometallic cocatalyzed g-C3N4. Therefore, the prepared CoNiSx-CN composite exhibited a dramatic photocatalytic HER performance of 2.366 μmol mg-1 h-1, which is about 76-fold higher in comparison with pristine g-C3N4 and comparable to g-C3N4 with Pt as a cocatalyst under 420 nm light irradiation. This study reveals a promising and efficient bimetallic cocatalyst for the photocatalytic H2 evolution reaction.

A Laboratory-based Experiment on the Efficacy of Graphitic Carbon Nitride Doped with Tungsten Chloride in the Purification of Industrial Wastewater through Degradation of Organic Dye Pollutant

Water is an essential commodity whose quantity and quality needs to be secured for easier accessibility at both the industrial, public and household levels. However, its availability in adequate quality and quantity has continued to decline worldwide. Indeed, rise in human population coupled with the climate change phenomena have greatly impacted on the quality of water resources through increased organic and inorganic pollution. Rhodamine B (RhB) dye is a common organic pollutant majorly in industrial wastewater and with numerous environmental and human health effects. The application of graphitic carbon nitride (G-C3N4) in the purification of industrial wastewater to enhance the removal of RhB is a technology of interest to most environmental quality regulators and agencies. The study was therefore aimed at investigating the performance of graphitic carbon nitride doped with tungsten chloride in the degradation of organic dye pollutant rhodamine B dye from industrial wastewater. The study showed that the as-prepared hybrid photo catalyst exhibits an improved photo degradation performance because of its synergetic effect. Indeed, the photo excited electrons from g-C3N4 were able to efficiently separate and are injected to the conductive band of WO3. The optimum photo activity occurred at the optimum ratio of 0.25WO3/g- C3N4. There was also stability and efficiency within the hybrid catalyst within the photo degradation process. Indeed, the composite indicates a high activity for degradation of RhB under visible light irradiation. The presence of g-C3N4 proved to be beneficial for enhancement in photo catalytic activity of the g-C3N4-WO3 composite and proved to be one of the best alternative modes of n the degrading organic dye pollutant Rhodamine B dye from wastewater.

Noble-metal-free Fe2P–Co2P co-catalyst boosting visible-light-driven photocatalytic hydrogen production over graphitic carbon nitride: The synergistic effects between the metal phosphides

Photocatalytic hydrogen evolution from water splitting driven by visible light is a promising approach to solve energy crisis and environmental problems, and noble-metal-free co-catalysts for boosting the hydrogen evolution reaction are highly desired. Herein, we explore a novel noble-metal-free Fe2P–Co2P co-catalyst for the first time to boost the photocatalytic performance of graphitic carbon nitride (g-C3N4). The resultant Fe2P–Co2P/g-C3N4 with optimum ratio exhibits a hydrogen production rate of 347 μmol h−1 g−1 in the absence of noble-metal co-catalyst, which is 87 times higher than that of pristine g-C3N4 under the same conditions. The significant enhancement in the photocatalytic performance of Fe2P–Co2P/g-C3N4 can be ascribed to the Schottky junction formed between Fe2P–Co2P and g-C3N4, which produces a strong driving force for the transfer of electrons from g-C3N4 to Fe2P–Co2P, promoting the separation and transfer of photogenerated electrons and holes. Furthermore, due to the synergistic effects between the two metal phosphides (Fe2P and Co2P), the Schottky junction in Fe2P–Co2P/g-C3N4 can produce stronger driving force than that in Fe2P/g-C3N4 and Co2P/g-C3N4, resulting in the fact that the hydrogen production rate over Fe2P–Co2P/g-C3N4 is much higher than that over Fe2P/g-C3N4 and Co2P/g-C3N4. This work may shed light on the careful design of co-catalyst by utilizing the synergistic effect of different components.

Steering charge kinetics boost the photocatalytic activity of graphitic carbon nitride: heteroatom-mediated spatial charge separation and transfer

Charge kinetics plays a vital role in determining the quantum efficiency of solar-to-chemical conversion in photocatalysis. For most layered compounds, the photocatalytic performance is largely hindered by its sluggish charge transfer kinetics. Herein, we propose a novel strategy—heteroatom-mediated spatial charge separation and transfer—to accelerate photogenerated charge kinetics for boosting the photocatalytic performance of graphitic carbon nitride (CN). Both the experimental results and first-principle calculations show that out-of-plane charge transport and in-plane charge separation within CN nanosheets can be accelerated via F intercalation and B intralayer modification. The B implantation could realize in-plane charge-separation by spatial separation of HOMO and LUMO to promote efficient exciton dissociation, and the F heteroatom, as interlayer electron channel, accelerates the out-of-plane oriented charge transport. The visible-light photocatalytic activity of codoped CN nanosheets is greatly boosted via modulating the charge kinetics, which can be demonstrated by degrading methyl orange and colorless phenol as models. Moreover, the samples exhibit excellent photo-electrocatalysis OER activity, outperforming the metal CoSe2 catalyst. The enhanced catalytic activities are attributed to synergistically utilizing 2D ultrathin structural advantage and accelerating charge kinetics. This work proposes a novel strategy to tune charge carrier separations and migrations in functionalized 2D layered materials for environmental catalysis and advanced energy.HighlightsA novel heteroatom-mediated spatial charge separation and transfer strategy is proposed in B/F codoped CN nanosheets.Both the experimental results and first-principle calculations show that photogenerated charge kinetics can be accelerated within B/F codoped CN nanosheets.The B implantation could realize in-plane charge-separation by spatial separation of HOMO and LUMO to promote efficient exciton dissociation.The F heteroatom, as interlayer electron channel, accelerates the out-of-plane oriented charge transport.The optimized B/F codoped CN nanosheets have highly efficient catalytic activity for degrading organic pollutant and OER activity.

Enhancement of Hydrogen Evolution Reaction Performance of Graphitic Carbon Nitride with Incorporated Nickel Boride

Graphitic carbon nitride (g-C3N4) functioning as a semiconductor catalyst and sustainable and clean energy carrier to substitute fossil energy is gaining the attention of researchers. Hydrogen is regarded as the right energy carrier to meet future conditions, and hence, developing hydrogen economy is intensively investigated for its great electrocatalytic property. However, it is blocked as an electrocatalyst due to its poor conductivity and electrochemical activity. Therefore, to conquer such shortcomings, changing the nanostructure and increasing active sites are studied. Here, we report a facile method by incorporation of nickel boride (Ni2B) nanoparticles into bulk g-C3N4 to enlarge the specific surface area, exfoliate the layers, and improve the electronic conductivity. The obtained catalysts exhibit better hydrogen evolution reaction (HER) performance with a low onset overpotential of 300 mV, a Tafel slope of 221 mV dec–1, and an overpotential of 707 mV at the current density of 10 mA cm–2, superior...

Peroxymonosulfate improved photocatalytic degradation of atrazine by activated carbon/graphitic carbon nitride composite under visible light irradiation

The photocatalytic degradation of atrazine by activated carbon/graphitic carbon nitride composites with peroxymonosulfate (PMS) was investigated under visible light irradiation. The photocatalysts were prepared at different activated carbon (AC) loaded percentages and characterized by XRD, FT-IR, BET surface area, SEM, UV–Vis absorbance, photocurrent response and EIS. Several parameters which might influence the degradation efficiency were studied including PMS concentration, solution pH, catalyst dosage, initial atrazine concentration as well as water matrix effect. The results indicated that incorporation of AC contributes effectively in suppressing the recombination of electron-holes pairs and enhancing the photocatalytic performance of graphitic carbon nitride. More significantly, the degradation efficiency of atrazine showed remarkable improvement with PMS addition under visible light irradiation. The reaction rate constant of the 10% AC/g-C3N4/Vis/PMS system (0.0376 min−1) was approximately 2.9 times higher than that of g-C3N4/Vis/PMS system (0.0128 min−1). Results from quenching tests revealed that both sulfate and hydroxyl radicals were involved in the degradation of atrazine, while the latter is the main contributor. This paper constitutes an insight for the metal-free catalyst activation of PMS by photocatalysis for environmental remediation.

Graphitic Carbon Nitride and Titanium Dioxide Modified with 1 D and 2 D Carbon Structures for Photocatalysis.

Enhancing the photocatalytic performance of graphitic carbon nitride (g-C3 N4 , GCN) and titanium dioxide (TiO2 ) has played a key role in the energy and environmental protection research community. Therefore, it is necessary to explore the synergy of both materials with carbon nanostructures for photocatalysis. Among the variety of carbon materials, graphene flakes and nanotubes, as nanoadditives to improve electron charge transfer and the optical absorption behavior in the visible-light region, have been widely explored. Thus, flake-like (2 D) and tubular (1 D) carbon structures in composition with GCN and/or TiO2 are reviewed, as are their photocatalytic response. Current trends clearly indicate that this type of molecular hybrids can be efficiently exploited in this field. This Minireview covers state-of-the-art research over the period of 2015 to 2018.

The effects of bismuth (III) doping and ultrathin nanosheets construction on the photocatalytic performance of graphitic carbon nitride for antibiotic degradation

To further enhance the photocatalytic performance of graphitic carbon nitride (g-C3N4), we rationally combined two strategies (foreign metal doping and ultrathin nanosheet construction) to synthesize bismuth (III) (Bi3+) doped ultrathin g-C3N4 nanosheets (Bi-CNNS) via one-step thermal polymerization method using melamine as the raw material, bismuth nitrate pentahydrate (Bi(NO3)3·5H2O) as the dopant source, and nitric acid (HNO3) and acetic acid (AC) as soft templates for the ultrathin nanosheets construction. The Bi-CNNS catalysts exhibited an excellent photocatalytic performance in tetracycline (TC) degradation. The TC removal efficiency reached to be 94.1% in 30 min under visible-light irradiation over 0.03Bi-CNNS, which is 6.03 times higher than that of pure g-C3N4 (CN). The higher specific surface area, narrower bandgap, the improved photoexcited electron-hole pair transfer and separation efficiency, and prolonged carrier lifetimes in the Bi3+-doped ultrathin g-C3N4 nanosheets led to a significantly enhanced photocatalytic performance. The main radical species responsible for the degradation of tetracycline over 0.03Bi-CNNS were O2− and OH. Moreover, the possible photodegradation intermediate products of TC were detected by gas chromatography–mass spectroscopy (GC–MS), and a possible pathway was proposed.

Enhanced charge separation ability and visible light photocatalytic performance of graphitic carbon nitride by binary S, B co-doping

As a metal-free visible light photocatalyst, the photocatalytic performance of graphitic carbon nitride (g-C3N4) is limited. To improve the activity of g-C3N4, we herein report a binary S, B co-doped g-C3N4 (SBCN) by thermally treating the precursor mixture of thiourea, melamine and boron oxide. Characterization results show the obtained SBCN has ultrathin sheet-like morphology and these doped heteroatoms are uniform distributed in the sample. Compared to the pristine g-C3N4, the SBCN has a small band gap with additional absorption in visible light region, decreased photoluminescence emission and electric resistance and enhanced photocurrent response. These advantages endue SBCN with excellent photocatalytic activity for degradation of organic dyes, and its reaction rate is 6.5 times higher than that of the g-C3N4. Moreover, the successive cycles demonstrate that this SBCN possesses a superior stability and reusability. Finally, we propose a possible photocatalytic mechanism based on the band structure and mainly active species.

Synthesis of halogen doped graphite carbon nitride nanorods with outstanding photocatalytic H2O2 production ability via saturated NH4X (X = Cl, Br) solution-hydrothermal post-treatment

Doping is a very effective method to promote the photocatalytic performance of graphitic carbon nitride (g-C3N4) based catalyst. However, the traditional co-condensation method causes the large particle size, small surface area and low separation rate of electrons-holes. In this work, halogen doped g-C3N4 nanorods with outstanding photocatalytic H2O2 production ability were prepared via saturated NH4X (X = Cl, Br) solution-hydrothermal post-treatment. XRD, N2 adsorption, UV–Vis, SEM, XPS, EPR, EIS and PL were used to characterize the obtained catalysts. Saturated salt solution-hydrothermal post-treatment changed the morphology and surface area of as-prepared g-C3N4 catalyst, as well as doped the halogen atoms into g-C3N4 lattice simultaneously. Br doped g-C3N4 catalyst displayed higher photocatalytic H2O2 production ability than that of Cl doped g-C3N4 catalyst. Compared with traditional co-condensation method, the catalyst prepared via saturated salt solution-hydrothermal post-treatment exhibited larger surface area, more effective separation rate and higher photocatalytic H2O2 production ability. This work can provide a new strategy for doping heteroatoms into g-C3N4 based catalyst.

Formation of BiOI/g-C3N4 nanosheet composites with high visible-light-driven photocatalytic activity

Constructing binary heterojunctions is an important strategy to improve the photocatalytic performance of graphitic carbon nitride (g-C3N4). In this paper, a novel g-C3N4 nanosheet-based composite was constructed via in situ growth of bismuth oxyiodide (BiOI) nanoplates on the surface of g-C3N4 nanosheets. The crystal phase, microstructure, optical absorption and textural properties of the synthesized photocatalysts were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), ultraviolet-visible (UV-vis) diffuse reflectance spectroscopy (DRS), and nitrogen adsorption-desorption isotherm measurements. The BiOI/g-C3N4 nanosheet composite showed high activity and recyclability for the photodegradation of the target pollutant rhodamine B (RhB). The conversion of RhB (20 mg L−1) by the photocatalyst was nearly 100% after 50 min under visible-light irradiation. The high photoactivity of the BiOI/g-C3N4 nanosheet composite can be attributed to the enhanced visible-light absorption of the g-C3N4 nanosheets sensitized by BiOI nanoplates as well as the high charge separation efficiency obtained by the establishment of an internal electric field between the n-type g-C3N4 and p-type BiOI. Based on the characterization and experimental results, a double-transfer mechanism of the photoinduced electrons in the BiOI/g-C3N4 nanosheet composite was proposed to explain its activity. This work represents a new strategy to understand and realize the design and synthesis of g-C3N4 nanosheet-based heterojunctions that display highly efficient charge separation and transfer.

Ultrasound-Assisted Fabrication of Hierarchical Rodlike Graphitic Carbon Nitride with Fewer Defects and Enhanced Visible-Light Photocatalytic Activity

The catalytic performance of graphitic carbon nitride (g-C3N4) is significantly affected by its microstructure and intrinsic defects. Here, rodlike g-C3N4 (RCN) with hierarchical structure and fewe...

The effect of metallic Fe(ii) and nonmetallic S codoping on the photocatalytic performance of graphitic carbon nitride.

The metallic Fe(ii) ion and nonmetallic S codoped g-C3N4 photocatalyst was synthesized through the polymerization of melamine, ferrous chloride and trithiocyanuric acid (TCA) at elevated temperature. The performance of Fe(ii)–S codoped g-C3N4 compounds in RhB photocatalytic degradation was found to increase 5 times. This significant enhancement in catalytic activity is probably related to the enhanced visible light adsorption and the mobility of photoinduced electron/hole pairs, attributable to bandgap narrowing and also lowering in the surface electrostatic potential compared to that of the pure g-C3N4 nanosheets. XRD and XPS results indicate that the Fe species binds with N-atoms to form Fe–N bonds in the state of Fe(ii) ions. Fe(ii) doping increases the specific surface area, and enhances the photoinduced electron/hole pairs illustrated by PL, EIS spectra and transient photocurrent response measurements. The theoretical results show that divalent Fe(ii) ions coordinating in the pore centre among three triazine units form discrete dopant bands and S dopants substituting the N in triazine skeletons excite much stronger delocalized HOMO and LUMO states, facilitating the migration of photogenerated charge carriers, thus enhancing the visible-light driven photocatalytic performance.

Graphitic Carbon Nitride with S and Fe(III) Codoping for Improved Photodegradation Performance

The visible light photocatalytic performance of graphitic carbon nitride (g-C3N4) can be enhanced by tuning its electronic structure and bandgap via metal and nonmetal elements doping. The Fe and S codoped g-C3N4 is synthesized by the polymerization of melamine, iron chloride and trithiocyanuric acid at elevated temperature and characterized as crimped nanosheets with mesoporous structures. The photocatalytic performance of Fe–S codoped g-C3N4 for RhB degradation increases seven times by enhancing visible light adsorption and increasing the mobility of photoinduced electron/hole pair by narrowing its bandgap compared to the pure g-C3N4 nanosheets. The synergetic effect of Fe(III) ion coordinated in the pore centre among three triazine units and S dopant substituted the N in triazine skeleton causes much stronger delocalized HOMO and LUMO and increases the reactive sites, facilitating the migration of photogenerated charge carriers, thus enhances the visible-light driven photocatalytic performance.