Synthesis and photocatalytic H2-production activity of plasma-treated Ti3C2Tx MXene modified graphitic carbon nitride

Plasma processing technology, as a promising method to enhance photocatalytic activity of catalyst, is gradually attracting extensive interest from researchers. However, the main mechanism of plasma-treated photocatalyst on hydrogen production is not clear. In this work, 2D Ti₃C₂T_x MXene is selected as a co-catalyst of graphitic carbon nitride (g-C₃N₄), which carries out a plasma treatment (500°C) under N₂/H₂ atmosphere. Due to plasma treatment, there is a higher proportion Ti–O functional groups on surface of layered Ti₃C₂T_x MXene, especially for Ti⁴⁺. The obtained g-C₃N₄/p-Ti₃C₂T_x photocatalyst with sandwich-like structure shows an enhanced photocatalytic activity. The rate of hydrogen generation of CN/pTC3.0 sample without Pt co-catalyst is 25.4 and 2.4 times that of pure g-C₃N₄ and CN/TC3.0 samples, respectively. The improved photocatalytic activity is attributed to presence of Ti⁴⁺ due to plasma treatment, which can capture photo-induced electron from g-C₃N₄ and improve the separation of electrons and holes after visible light irradiation. The cyclic hydrogen production of the photocatalyst demonstrates good photocatalytic stability. In addition, this method of plasma treatment under N₂/H₂ atmosphere is feasible to develop a high-performance co-catalyst, which can be extended to other photocatalysts with two-dimensional structure for photocatalytic water-splitting applications.     

Visible-light-driven Ni3FeN/g-C3N4 Z-scheme heterostructure for remarkable photocatalytic water splitting

It is very essential to grow efficient and abundant photocatalysts for overall water cracking to produce hydrogen. Ni₃FeN nanosheets were synthesized by combining simple sol–gel and calcining methods using urea as nitrogen source. A heterostructure was constructed between Ni₃FeN and g-C₃N₄ to enhance the absorption capacity of visible light. The reformed Z-scheme Ni₃FeN/g-C₃N₄ heterojunction exhibited an excellent visible-light photocatalytic activity. The average hydrogen evolution rate of 5 wt% Ni₃FeN/g-C₃N₄ composite is 528.7 μmol h⁻¹ g⁻¹ due to the Z-scheme Ni₃FeN/g-C₃N₄ junction, which promotes the separation of photogenerated e⁻/h⁺. Interestingly, the average H₂ production of Ni₃FeN/g-C₃N₄ is nearly 8.3 and 3.6 times higher than that of Fe₄N/g-C₃N₄ and Ni₄N/g-C₃N₄, respectively, indicating that bimetallic nitrides as cocatalysts are more conducive to enhancing the performance of photocatalysts. Importantly, the Ni₃FeN/g-C₃N₄ composite exhibited good cycle stability, and the hydrogen production performance hardly changed after four cycle experiments. Furthermore, photoluminescence, electrochemical impedance spectroscopy, and transient photocurrent response show that Ni₃FeN/g-C₃N₄ heterojunction improves the separation efficiency of photoinduced e⁻/h⁺. This work provides a feasibility of the cocatalyst Ni₃FeN for use in photocatalytic hydrogen production.     

A facile and novel construction of attapulgite/Cu2O/Cu/g-C3N4 with enhanced photocatalytic activity for antibiotic degradation

A high-performance photocatalyst, attapulgite/Cu₂O/Cu/g-C₃N₄ (ATP/Cu₂O/Cu/g-C₃N₄), was constructed via a one-pot redox strategy under anoxic calcination. The as-prepared composites were characterized by Fourier transform infrared spectra (FT-IR), X-ray diffraction (XRD), transmission electron microscopy (TEM), N₂ adsorption-desorption isotherms (BET), photoluminescence emission (PL), and electrochemical impedance spectra (EIS). Results indicate that ultra-fine CuO nanoparticles on the surface of rod-like attapulgite are in-situ reduced by NH₃ gas to generate Cu and minority Cu₂O during the pyrocondensation of melamine. Meanwhile, the generated g-C₃N₄ membrane is uniformly encapsulated on the surface of attapulgite/Cu₂O/Cu to assemble Z-scheme Cu₂O/Cu/g-C₃N₄ heterostructure. ATP/Cu₂O/Cu/g-C₃N₄ shows improved visible light response ability and hole-electron suppression compared with ATP/g-C₃N₄. The photocatalytic performance and mechanism of the obtained photocatalyst for antibiotic degradation were evaluated by UV–Vis spectrometer and liquid chromatograph. ATP/Cu₂O/Cu/g-C₃N₄ can exhibit favorable photocatalytic activity and reusability for chloramphenicol. In addition, h⁺ and·OH radicals are the main active sites in the photocatalytic process, and Cu species play a vital role in separation and retarding recombination of electron-hole pairs.     

0D CoP cocatalyst/ 2D g-C3N4 nanosheets: An efficient photocatalyst for promoting photocatalytic hydrogen evolution

In this work, cobalt phosphide (CoP) nanoparticles were successfully decorated on an ultrathin g-C₃N₄ nanosheet photocatalysts by in situ chemical deposition. The built-in electric field formed by heterojunction interface of the CoP/g-C₃N₄ composite semiconductor can accelerate the transmission and separation of photogenerated charge-hole pairs and effectively improve the photocatalytic performance. TEM, HRTEM, XPS, and SPV analysis showed that CoP/g-C₃N₄ formed a stable heterogeneous interface and effectively enhanced photogenerated electron-hole separation. UV-vis DRS analysis showed that the composite had enhanced visible light absorption than pure g-C₃N₄ and was a visible light driven photocatalyst. In this process, NaH₂PO₂ and CoCl₂ are used as the source of P and Co, and typical preparation of CoP can be completed within 3 hours. Under visible light irradiation, the optimal H₂ evolution rate of 3.0 mol% CoP/g-C₃N₄ is about 15.1 μmol h⁻¹. The photocatalytic activity and stability of the CoP/g-C₃N₄ materials were evaluated by photocatalytic decomposition of water. The intrinsic relationship between the microstructure of the composite catalyst and the photocatalytic performance was analyzed to reveal the photocatalytic reaction mechanism.     

Environmentally friendly supermolecule self-assembly preparation of S-doped hollow porous tubular g-C3N4 for boosted photocatalytic H2 production

Utilization of graphitic carbon nitride (g–C₃N₄)–based materials for photocatalytic hydrogen production to alleviate energy problems is a hot topic of research nowadays, thus the design and synthesis of highly efficient g-C₃N₄ materials remains a significant challenge. Herein, the sulphur-doped hollow porous tubular g-C₃N₄ (S-HPTCN) was successfully synthesized by a facile environmentally friendly supramolecule self-assembly strategy. Photocatalytic H₂ evolution tests show that the as-prepared optimal S-HPTCN achieved a high H₂ production of up to 22.04 mmol g⁻¹ h⁻¹ with the turnover frequency (TOF) of 429.7 h⁻¹ and the apparent quantum efficiency (AQE) of as high as 7.8% at wavelength of 420 nm. The enhancement of remarkable photocatalytic H₂ performance is mainly attributed to the synergetic effect of morphology and elemental doping. This research provides an effective design idea of developing high-efficient g–C₃N₄–based material for solar to hydrogen.     

Construction of sandwich structured photocatalyst using monolayer WS2 embedded g-C3N4 for highly efficient H2 production

The construction of sandwich structured binary composite can enlarge its specific surface and strengthen the contact of binary interface. This can enhance H₂ generation efficiency of the photocatalyst. In this study, two-step strategy for the preparation of novel sandwich-structured g-C₃N₄/WS₂ is proposed. Step one is hydrothermal process producing the layered WO₃, which is used as the precursor for monolayer WS₂. While step two involves one-pot calcination process that generates sandwich structured g-C₃N₄/WS₂. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), inductively coupled plasma optical emission spectrometry (ICP-OES), Brunauer Emmett Teller method (BET), and transmission electron microscopy (TEM) are employed to characterize the composition, structure and morphology of g-C₃N₄/WS₂. Photocatalytic H₂ generation tests show that the optimal H₂ generation rate of g-C₃N₄/WS₂ is 599.7 μmol h^-1 g^-1 (20 mg of photocatalyst), which is about 25 times higher than that of bare g-C₃N₄. Moreover, UV–vis diffuse reflectance spectroscopy (UV–vis DRS), photoluminescence (PL) and electrochemical tests are employ to establish possible mechanism of photocatalytic H₂ evolution in sandwich-structured g-C₃N₄/WS₂.     

Synthesis of MoS2/g-C3N4 as a solar light-responsive photocatalyst for organic degradation

A novel molybdenum disulfide (MoS₂) and graphitic carbon nitride (g-C₃N₄) composite photocatalyst was synthesized using a low temperature hydrothermal method. MoS₂ nanoparticles formed on g-C₃N₄ nanosheets greatly enhanced the photocatalytic activity of g-C₃N₄. The photocatalyst was tested for the degradation of methyl orange (MO) under simulated solar light. Composite 3.0 wt.% MoS₂/g-C₃N₄ showed the highest photocatalytic activity for MO decomposition. MoS₂ nanoparticles can increase the interfacial charge transfer and thus prevent the recombination of photo-generated electron–hole pairs. The novel MoS₂/g-C₃N₄ composite is therefore shown as a promising catalyst for photocatalytic degradation of organic pollutants using solar energy.     

Controlled preparation of P-doped g-C3N4 nanosheets for efficient photocatalytic hydrogen production

Hydrogen production by photolysis of water by sunlight is an environmentally-friendly preparation technology for renewable energy. Graphitic carbon nitride (g-C₃N₄), despite with obvious catalytic effect, is still unsatisfactory for hydrogen production. In this work, phosphorus element is incorporated to tune g-C₃N₄'s property through calcinating the mixture of g-C₃N₄ and NaH₂PO_2, sacrificial agent and co-catalyst also been supplied to help efficient photocatalytic hydrogen production. Phosphorus (P) doped g-C₃N₄ samples (PCN-S) were prepared, and their catalytic properties were studied. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and ultraviolet diffuse reflection (UV-DRS) were used to study their structures and morphologies. The results show that the reaction rate of PCN-S is 318 μmol h⁻¹ g⁻¹, which is 2.98 times as high as pure carbon nitride nanosheets (CN) can do. Our study paves a new avenue, which is simple, environment-friendly and sustainable, to synthesize highly efficient P doping g-C₃N₄ nanosheets for solar energy conversion.     

H2+CO2 Synergistic Plasma Positioning Carboxyl Defects in g-C3N4 with Engineered Electronic Structure and Active Sites for Efficient Photocatalytic H2 Evolution

Defective functional-group-endowed polymer semiconductors, which have unique photoelectric properties and rapid carrier separation properties, are an emerging type of high-performance photocatalyst for various energy and environmental applications. However, traditional oxidation etching chemical methods struggle to introduce defects or produce special functional group structures gently and controllably, which limits the implementation and application of the defective functional group modification strategy. Here, with the surface carboxyl modification of graphitic carbon nitride (g-C₃N₄) photocatalyst as an example, we show for the first time the feasibility and precise modification potential of the non-thermal plasma method. In this method, the microwave plasma technique is employed to generate highly active plasma in a combined H₂+CO₂ gas environment. The plasma treatment allows for scalable production of high-quality defective carboxyl group-endowed g-C₃N₄ nanosheets with mesopores. The rapid H₂+CO₂ plasma immersion treatment can precisely tune the electronic and band structures of g-C₃N₄ nanosheets within 10 min. This conjoint approach also promotes charge-carrier separation and accelerates the photocatalyst-catalyzed H₂ evolution rate from 1.68 mmol h⁻¹g⁻¹ (raw g-C₃N₄) to 8.53 mmol h⁻¹g⁻¹ (H₂+CO₂-pCN) under Xenon lamp irradiation. The apparent quantum yield (AQY) of the H₂+CO₂-pCN with the presence of 5 wt.% Pt cocatalyst is 4.14% at 450 nm. Combined with density functional theory calculations, we illustrate that the synergistic N vacancy generation and carboxyl species grafting modifies raw g-C₃N₄ materials by introducing ideal defective carboxyl groups into the framework of heptazine ring g-C₃N₄, leading to significantly optimized electronic structure and active sites for efficient photocatalytic H₂ evolution. The 5.08-times enhancement in the photocatalytic H₂ evolution over the as-developed catalysts reveal the potential and maneuverability of the non-thermal plasma method in positioning carboxyl defects and mesoporous morphology. This work presents new understanding about the defect engineering mechanism in g-C₃N₄ semiconductors, and thus paves the way for rational design of effective polymeric photocatalysts through advanced defective functional group engineering techniques evolving CO₂ as the industrial carrier gas.     

Preparation and photocatalytic activity of g-C3N4/TiO2 heterojunctions under solar light illumination

The solar light sensitive g-C₃N₄/TiO₂ heterojunction photocatalysts containing 20, 50, 80, and 90 wt% graphitic carbon nitride (g-C₃N₄) were prepared by growing Titania (TiO₂) nanoparticles on the surfaces of g-C₃N₄ particles via one step hydrothermal process. The hydrothermal reactions were allowed to take place at 110 °C at autogenous pressure for 1 h. Raman spectroscopy analyses confirmed that an interface developed between the surfaces of TiO₂ and g-C₃N₄ nanoparticles. The photocatalyst containing 80 wt% g-C₃N₄ was subsequently heat treated 1 h at temperatures between 350 and 500 °C to improve the photocatalytic efficiency. Structural and optical properties of the prepared g-C₃N₄/TiO₂ heterojunction nanocomposites were compared with those of the pristine TiO₂ and pristine g-C₃N₄ powders. Photocatalytic activity of all the nanocomposites and the pristine TiO₂ and g-C₃N₄ powders were assessed by the Methylene Blue (MB) degradation test under solar light illumination. g-C₃N₄/TiO₂ heterojunction photocatalysts exhibited better photocatalytic activity for the degradation of MB than both pristine TiO₂ and g-C₃N₄. The photocatalytic efficiency of the g-C₃N₄/TiO₂ heterojunction photocatalyst heat treated at 400 °C for 1 h is 1.45 times better than that of the pristine TiO₂ powder, 2.20 times better than that of the pristine g-C₃N₄ powder, and 1.24 times better than that of the commercially available TiO₂ powder (Degussa P25). The improvement in photocatalytic efficiency was related to i) the generation of reactive oxidation species induced by photogenerated electrons, ii) the reduced recombination rate for electron-hole pairs, and iii) large specific surface area.     

Constructing 0D/2D Z-Scheme Heterojunction of CdS/g-C3N4 with Enhanced Photocatalytic Activity for H2 Evolution

0D/2D Pt-C₃N₄/CdS heterojunction photocatalyst were fabricated with CdS quantum dots interspersed on g-C₃N₄ nanosheets via successive ionic layer absorption process. The obtained Pt-C₃N₄/CdS Z-scheme heterojunction with Pt cocatalyst deposited on g-C₃N₄ nanosheets exhibited H₂ production rate of 35.3 mmol g^?1 h^?1, which is 3.1 times higher than that of Pt-CdS/C₃N₄. The enhanced photocatalytic activity are attributed to the Z-scheme charge carrier transfer mechanism with stronger redox ability. The photocatalytic mechanism of the CdS/g-C₃N₄ composite is investigated and demonstrated in this work. It may provide unique insights to design 0D/2D Z-scheme heterojunction photocatalyst systems using a facile method for highly efficient H₂ production.

Graphic Abstract

Schematic illustration of charge transfer modulated by the metal cocatalyst selective deposition on heterojunction-type II (a) and direct Z-Scheme mechanisms (b) over the C₃N₄/CdS heterostructure composites under visible light irradiation.

     

Ti3C2@TiO2/g-C3N4 heterojunction photocatalyst with improved charge transfer for enhancing visible-light NO selective removal

Control of Nitrogen dioxide (NO₂) byproducts is of great importance for the photocatalytic NO removal and environmental remedy. However, individual semiconductor photocatalysts generally show limited capabilities for selective NO removal due to severe charge recombination and inadequate redox potentials. Herein, the cotton-like g-C₃N₄ was modified with Ti₃C₂@TiO₂ to construct a heterojunction photocatalyst Ti₃C₂@TiO₂/g-C₃N₄, which showed outperformed photocatalytic NO removal and MB degradation abilities compared to the individual photocatalysts under visible light irradiation. The UV–vis absorption spectra and photoluminescence (PL) spectra confirmed that Ti₃C₂@TiO₂/g-C₃N₄ photocatalyst was endowed with superior light utilization and separation/transfer ability of charge carriers due to the presence of n-n heterojunction and Schottky barrier. Furthermore, the g-C₃N₄, Ti₃C₂, and TiO₂ were closely contacted showing a high specific surface area, which promoted the charge transfer and the exposure of more active sites, further inducing the formation of more active species. Therefore, the designed photocatalyst delivered a high removal rate of NO and a suppressed discharge of NO₂. Notably, the photocatalyst Ti₃C₂@TiO₂/g-C₃N₄ also presented superior NO removal ability during the cycling experiment, indicating their outstanding stability and recyclability. Besides, the effects of active species were monitored using a trapping experiment to propose probable photocatalytic mechanism. This study could shed a new light to the design of photocatalyst for air purification in the future.     

Facile construction Z-scheme anatase/rutile TiO2/g-C3N4 hybrid for efficient photocatalytic H2 evolution under visible-light irradiation

Z-scheme anatase/rutile TiO₂/g-C₃N₄ hybrids (denoted as LTARCN-x, x represents calcination temperature) were designed and synthesized by growing TiO₂ nanorods on the surface of g-C₃N₄ utilizing impregnation-calcination method. Furthermore, through the etched effect of hydrochloric acid and calcination treatment, the as-prepared LTARCN-x possessed abundant pore structure and larger surface area, and the surface area of LTARCN-425 was 8.5 times than that of bulk g-C₃N₄. Meanwhile, the g-C₃N₄ would play a role of carrier to prevent from the aggregation of TiO₂ nanorods. In addition, under visible light irradiation, the Z-scheme heterostructure would be constructed between the rutile TiO₂ nanorod and g-C₃N₄ nanosheet, respectively. The optimized photocatalyst LTARCN-425 exhibited a preferable activity, the photocatalytic hydrogen production rate of LTARCN-425 was about 1031 μmol g^?1 h^?1, and it was about 6.3 and 13.6 times than that of g-C₃N₄ and TiO₂, respectively. Moreover, the photocatalytic mechanism of the hydrogen production was studied intensively via designing fluorescent probe, Pt and PbO₂ deposition experiment, and the characterizations of EPR, TEM, HRTEM and XPS.     

Au nanoparticles-doped g-C3N4 nanocomposites for enhanced photocatalytic performance under visible light illumination

Surface and bandgap engineering of graphitic carbon nitride (g-C₃N₄) could be vital in enhancing photocatalytic performance by suppressing the recombination rate of photogenerated electron-hole pairs. The present report investigated the doping effects of various wt.% (0.2–5.0%) of gold nanoparticles (Au NPs) to g-C₃N₄ (Au/g-C₃N₄) for the enhancement of the photocatalytic efficiency of g-C₃N₄ nanocomposites. A straightforward and cost-effective synthesis methodology has been applied for the desired nanocomposites. Relevant characterization tools such as XRD, XPS, TEM, FTIR, and UV–Vis were utilized to analyze various physicochemical properties. The TEM images clearly show that spherical Au NPs were homogeneously distributed into the thin carbon nitride graphitic layers, confirming the successful doping of Au. The higher-magnification TEM image confirms that the sizes of the Au NPs varied from 15 to 25 nm. The photoactivity of the newly designed Au/g-C₃N₄ nanocomposites has been evaluated for the degradation of both methylene blue dye and the drug gemifloxacin mesylate, and their efficiencies were compared with that of bare g-C₃N₄. Our findings revealed that Au/g-C₃N₄ nanocomposites with various Au contents had superior photocatalytic activity compared to bare g-C₃N₄. However, the 1%Au/g-C₃N₄ nanocomposite could be considered the optimum photocatalyst, producing 95.13% destruction of the target dye molecule in 90 min, in contrast to the 69% achieved with bare g-C3N4, under the clean energy of visible light illumination. Additionally, the photodegradation rate of the 1%Au/g-C₃N₄ nanocomposite is 2.69 times higher than the rate of bare g-C₃N₄. This report might open a new gateway towards a straightforward and cost-effective synthesis approach for Au/g-C₃N₄ nanocomposites and provides a smooth and robust platform for the utilization of this new nanocomposite for environmental remediation processes.     

Facile one-step synthesis of pellet-press-assisted saddle-curl-edge-like g-C3N4 nanosheets for improved visible-light photocatalytic activity

Graphitic carbon nitride (g-C₃N₄) has attracted increasing interest as a visible-light-active photocatalyst. In this study, saddle-curl-edge-like g-C₃N₄ nanosheets were prepared using a pellet presser (referred to as g-CN P nanosheets). Urea was used as the precursor for the preparation of g-C₃N₄. Thermal polymerization of urea in a pellet form significantly affected the properties of g-C₃N₄. Systematic investigations were performed, and the results for the modified g-C₃N₄ nanosheets are presented herein. These results were compared with those for pristine g-C₃N₄ to identify the factors that affected the fundamental properties. X-ray diffraction analysis and high-resolution transmission electron microscopy revealed a crystallinity improvement in the g-CN P nanosheets. Fourier-transform infrared spectroscopy provided clear information regarding the fundamental modes of g-C₃N₄, and X-ray photoelectron spectroscopy (XPS) peak-fitting investigations revealed the variations of C and N in detail. The light-harvesting property and separation efficiency of the photogenerated charge carriers were examined via optical absorption and photoluminescence studies. The valence band edge and conduction band edge potentials were calculated using XPS, and the results indicated a significant reduction in the bandgap for the g-CN P nanosheets. The Brunauer–Emmett–Teller surface area increased for the g-CN P nanosheets. The photocatalytic degradation performance of the g-CN P nanosheets was tested by applying a potential and using the classical dye Rhodamine B (RhB). The RhB dye solution was almost completely degraded within 28 min. The rate constant of the g-CN P nanosheets was increased by a factor of 3.8 compared with the pristine g-C₃N₄ nanosheets. The high crystallinity, enhanced light absorption, reduced bandgap, and increased surface area of the saddle-curl-edge-like morphology boosted the photocatalytic performance of the g-CN P nanosheets.     

Tungsten-doped foam g-C3N4 with improved photocatalytic properties for degradation of pollutant and hydrogen evolution

As a potential material applied in the photocatalytic field, graphitic carbon nitride (g-C₃N₄) has attracted extensive attention for its advantages of visible-light response, excellent thermodynamic, and chemical stability. However, the photocatalytic performance of g-C₃N₄ is still limited in practical applications. Here, using a facile thermal polymerization method, unique W-doped foam g-C₃N₄ was synthesized to realize enhanced photocatalytic performance for the degradation of Rhodamine B and the evolution of hydrogen. Compared with pure foam g-C₃N₄, tungsten doping modified the foam g-C₃N₄ and efficiently improved its specific surface area, leading to enhanced photocatalytic performance. The average rate of hydrogen evolution was as high as 8818 μmol·h⁻¹·g⁻¹, which was better than most photocatalysts. This work proposes a new effective method and idea to modify g-C₃N₄ for improving its photocatalytic performance.     

One-Step Synthesis of g-C3N4 Nanosheets with Enhanced Photocatalytic Performance for Organic Pollutants Degradation Under Visible Light Irradiation

Graphitic carbon nitride (g-C₃N₄) has received much interest as a visible-light-driven photocatalyst for degrading pollutants such as organic dyes and antibiotics. However, g-C₃N₄ bulk activity could not meet expectations due to its rapid recombination of photogenerated electron–hole pairs and low specific surface area. In our study, melamine was thermally treated one-step in the presence of NH₄Cl to produce g-C₃N₄ nanosheets. The characterizations of surface morphology and optical properties of all g-C₃N₄ samples were investigated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectrum (XPS), transmission electron microscopy (TEM), and UV–visible diffuse reflectance spectroscopy. Compared to bulk g-C₃N₄, g-C₃N₄ nanosheets demonstrated excellent photocatalytic activities, with approximately 98% RhB removal after 210 min of visible light irradiation. Furthermore, the effect of catalyst dosage, pH, and RhB concentration on the removal percentage dye of g-C₃N₄ nanosheets was also investigated. h⁺ and ^?O₂^? species were demonstrated as the key reactive species for the RhB. Besides, ECN exposed a tetracycline degradation efficiency of 80.5% under visible-light irradiation for 210 min, which is higher than BCN (60.8%). The improved photocatalytic activity of g-C₃N₄ nanosheets is due to the restriction of the recombination of photogenerated electrons/hole pairs, as provided by photoluminescence spectra and Nyquist plot. As a result, our research may offer an effective approach to fabricating g-C₃N₄ nanosheets with high photocatalytic activity and high stability for environmental decontamination.

     

Visible light-activated degradation of microcystin-LR by ultrathin g-C3N4 nanosheets-based heterojunction photocatalyst

Microcystins (MCs) is a harmful toxin generated by blue-green algae in water, which has seriously threatened the ecological safety of water and human body. It is urgent to develop new catalysts and techniques for the degradation of MCs. A feasible electrostatic self-assembly method was carried out to synthesize BiVO₄/g-C₃N₄ heterojunction photocatalyst with highly efficient photocatalytic ability, where BiVO₄ nanoplates with exposed {010} facets anchored to the g-C₃N₄ ultrathin nanosheets. The morphology and microstructure of the heterojunction photocatalysts were identified by XRD, SEM, TEM, XPS, and BET. The g-C₃N₄ nanosheets have huge surface area over 200 m²/g and abundant mesoporous ranging from 2-20 nm, which provides tremendous contact area for BiVO₄ nanoplates. Meanwhile, the introduction of BiVO₄ led to red-shift of the absorption spectrum of photocatalyst, which was characterized by UV-vis diffuse reflection spectroscopy (DRS). Compared with pure BiVO₄ and g-C₃N₄, the BiVO₄/g-C₃N₄ heterojunction shows a drastically enhanced photocatalytic activity in degradation of microcystin-LR (MC-LR) in water. The MC-LR could be removed within 15 minutes under the optimal ratio of BiVO₄/g-C₃N₄. The outstanding performance of the photocatalyst is attributed to synergetic effect of interface Z-scheme heterojunction and high active facets {010} of BiVO₄ nanoplates, which provides an efficient transfer pathway to separate photoinduced carriers meanwhile endows the photocatalysts with strong redox ability.     

Silver/Platinum Supported on TiO<Subscript>2</Subscript> P25 Nanocatalysts for Non-photocatalytic and Photocatalytic Denitration of Water

Denitration of water was investigated by non-photocatalytic and/or photocatalytic processes (UV-A irradiation at 365 nm) using a mixture of Ag/P25?+?Pt/P25 monometallic catalysts and Ag–Pt(Pt–Ag)/P25 bimetallic catalysts (2 wt% Ag; 4 wt% Pt) prepared by drop-wise wetness impregnation of TiO₂ P25 support. In the bimetallic samples, the influences of the Pt precursor (H₂PtCl₆·6H₂O; K₂PtCl₆) and of the impregnation order of the metallic salts were examined. The highest N₂ yield (42.3%) in the non-photocatalytic process was achieved with the Ag/P25?+?Pt/P25 mixture but with ca. 12.6% NO₂ ^? yield. Photocatalytic activity was enhanced in presence of H₂ in comparison to H₂-free condition. Ag/P25 is the most active photocatalyst, however high NO₂ ^? yield is obtained (32.5%). The bimetallic samples exhibit high versatility, being active both in the non-photocatalytic and the photocatalytic processes. Low NO₃ ^? conversion and high NO₂ ^? selectivity results were obtained from impregnation of Ag first. In contrast, impregnation of Pt precursor from K₂PtCl₆ first effectively promoted NO₃ ^? reduction towards N₂ yield of 36% and particularly low NO₂ ^? yield of 2.7%, due the presence of metallic nanoparticles of different sizes and interaction with TiO₂ with a peculiar strong Pt and Ag interaction. Best results obtained in non-photocatalytic and photocatalytic processes are almost similar.     

Fabrication of g-C3N4/TiO2 heterojunction composite for enhanced photocatalytic hydrogen production

In this study, graphitic carbon nitride (g-C₃N₄) was successfully coupled with TiO₂ using hydrothermal method, to develop an advanced heterojunction photocatalyst. The interaction between g-C₃N₄ and TiO₂ was confirmed through analysis of X-Ray spectroscopy (XPS) C 1s, N 1s, O 1s high resolution core level spectra of g-C₃N₄, TiO₂ and g–C₃N₄–TiO₂ heterojucntion. Further, through valence band spectra analysis, conduction band offset (0.12 eV) and valence band offset (0.28 eV) of g–C₃N₄–TiO₂ heterojunction were estimated. Also, composite material was identified as type II heterojunction between g-C₃N₄ and TiO₂. XRD, UV–vis, BET and HRTEM were employed to understand the changes in physicochemical properties. Photocatalytic hydrogen production rates were evaluated through water splitting experiments. Under visible light irradiation highest hydrogen production rate was achieved for g–C₃N₄–TiO₂ heterojunction sample with high content of TiO₂, and was about 1041 μmol/g.h. The improved photocatalytic activity of the heterojunction material was explained in detail.