Pristine Graphitic Carbon Nitride Research Articles

Efficient Rhodamine B dye uptake onto MgZrO3@g-C3N4 nanostructures: Fabrication and adsorption mechanism

Pristine graphitic carbon nitride (g-C3N4) was synthesized by calcination of urea under elevated temperature. A blend of g-C3N4 nanosheets and nanosized ZrO2 and MgO precursors were used to prepare MgZrO3@g-C3N4 hybrid nanocomposite (MZCN) then it was assessed for the adsorption of Rhodamine B (RhB) dye from aqueous solution. The X-ray diffraction analysis revealed the development of the monoclinic ZrO2, cubic MgO, and hexagonal graphitic carbon nitride phases. The energy diffraction X-rays (EDX), photoelectron electron, and Fourier transformed infrared (FT-IR) spectroscopy analyses collectively validated the formation of the presumed composite. An improved porosity with a surface area 35.86 m2.g−1 and pore volume 0.087 cm3.g−1 were determined by N2 adsorption setup. The adsorption kinetics fitted well with the pseudo-first-order model (R2 > 0.99), which designated an adsorption process influenced by physisorption. The kinetics models investigations revealed a film diffusion control of the adsorption process. The adsorption equilibrium matched perfectly with the Langmuir isotherm model (R2 > 0.99) marking a maximum adsorption capacity of 370.8 mg g−1, demonstrating outstanding monolayer adsorption process. In addition, the Freundlich constant (n = 1.76) value is falling in the range 1–10 suggested a favorable adsorption of RhB onto the composite surface. The mechanistic enquiry suggested van der Waal, hydrogen bonds and π–π electron–donor interactions between the electron-rich RhB and the functional groups in the adsorbent’s molecule. This work stipulates that MgZrO3@g-C3N4 holds promise as efficient adsorbent for organic dyes from contaminated wastewater.

Sulfur and chloride co-doped g-C3N4 in photocatalytic peroxymonosulfate activation for enhanced acetaminophen removal: Combination of experiments and DFT calculations

As a green photocatalyst with simple synthesis method, excellent electronic structure, and metal-free properties, the deficiencies of pristine graphitic carbon nitride, such as high electron transfer resistance and narrow energy band gap, inhibit its photocatalytic activity to some extent. In this paper, we synthesized a sulfur and chlorine co-doped g-C3N4 (SCl-CN) capable of efficient photocatalytic activation of peroxymonosulfate (PMS) by calcining a mixture of ammonium chloride and thiourea. By means of DFT calculation, the contribution of sulfur and chlorine to photogenic electron hole separation was discussed. The electrostatic potential of SCl-CN and the adsorption model between SCl-CN and PMS were deduced, and the activation mechanism of PMS was further analyzed. According to the calculated results, the incorporation of sulfur and chlorine tuned the electronic configuration of the material and intensified the interactions between SCl-CN and PMS. It is shown that free and non-free radicals act simultaneously in the SCl-CN/PMS/Vis system. This study provides a new idea for the study of photocatalytic activation of PMS by non-metallic co-doped carbon nitride.

Constructing B─N─P Bonds in Ultrathin Holey g-C3N4 for Regulating the Local Chemical Environment in Photocatalytic CO2 Reduction to CO.

The lack of intrinsic active sites for photocatalytic CO2 reduction reaction (CO2RR) and fast recombination rate of charge carriers are the main obstacles to achieving high photocatalytic activity. In this work, a novel phosphorus and boron binary-doped graphitic carbon nitride, highly porous material that exhibits powerful photocatalytic CO2 reduction activity, specifically toward selective CO generation, is disclosed. The coexistence of Lewis-acidic and Lewis-basic sites plays a key role in tuning the electronic structure, promoting charge distribution, extending light-harvesting ability, and promoting dissociation of excitons into active carriers. Porosity and dual dopants create local chemical environments that activate the pyridinic nitrogen atom between the phosphorus and boron atoms on the exposed surface, enabling it to function as an active site for CO2RR. The P-N-B triad is found to lower the activation barrier for reduction of CO2 by stabilizing the COOH reaction intermediate and altering the rate-determining step. As a result, CO yield increased to 22.45µmolg-1h-1 under visible light irradiation, which is ≈12 times larger than that of pristine graphitic carbon nitride. This study provides insights into the mechanism of charge carrier dynamics and active site determination, contributing to the understanding of the photocatalytic CO2RR mechanism.

Ultratrace Aromatic Anhydride Dopant as Intermediate Island to Promote Charge Transfer of Graphitic Carbon Nitride for Enhancing the Photocatalytic Degradation of Rhodamine B.

In this work, 0.75 wt ‰ 2,3-pyridinedicarboxylic anhydride (PDA) as a novel dopant was utilized to obtain modified graphitic carbon nitride with ultratrace doping (3MCN-PDA3) by facile thermal polymerization. Characterization of the microstructure, surface state, and porosity properties of the samples indicated that 3MCN-PDA3 has a thinner sheet-like, larger-scale, and tighter lamellar stacking structure than that of pristine graphitic carbon nitride (3MCN). Based on photo/electrochemical analysis, the PDA dopant formed an extended coplanar conjugated system by anhydride-amine thermal condensation with heptazine rings, and the channels of amide covalent bonds and superconjugation of the solitary pair of electrons of the nitrogen atoms of PDA synergistically promoted the charge transport performance of 3MCN-PDA3. Under visible light, the photodegradation efficiency of Rhodamine B (RhB) over 3MCN-PDA3 reached 92.4% in 60 min and realized almost entire removal in 200 min (99.2%), 1.43 times that of 3MCN. Furthermore, the experimental results and generalized density theory calculations confirmed that PDA acts as an intermediate molecular island and constructs an efficient carrier transfer pathway between different heptazine units. The results indicate that PDA is a promising candidate to enhance the charge transfer performance through ultratrace doping in the large-scale preparation and application of the graphitic carbon nitride photocatalyst.

Photocatalytic activity of dual defect modified graphitic carbon nitride is robust to tautomerism: machine learning assisted ab initio quantum dynamics.

Two-dimensional graphitic carbon nitride (GCN) is a popular metal-free polymer for sustainable energy applications due to its unique structure and semiconductor properties. Dopants and defects are used to tune GCN, and dual defect modified GCN exhibits superior properties and enhanced photocatalytic efficiency in comparison to pristine or single defect GCN. We employ a multistep approach combining time-dependent density functional theory and nonadiabatic molecular dynamics (NAMD) with machine learning (ML) to investigate coupled structural and electronic dynamics in GCN over a nanosecond timescale, comparable to and exceeding the lifetimes of photo-generated charge carriers and photocatalytic events. Although frequent hydrogen hopping transitions occur among four tautomeric structures, the electron-hole separation and recombination processes are only weakly sensitive to the tautomerism. The charge separated state survives for about 10 ps, sufficiently long to enable photocatalysis. The employed ML-NAMD methodology provides insights into rare events that can influence excited state dynamics in the condensed phase and nanoscale materials and extends NAMD simulations from pico- to nanoseconds. The ab initio quantum dynamics simulation provides a detailed atomistic mechanism of photoinduced evolution of charge carriers in GCN and rationalizes how GCN remains photo-catalytically active despite its multiple isomeric and tautomeric forms.

A DFT study the role of pristine and metal doped of g-CN nanosheet for drug delivery system

This research focuses on investigating how a targeted drug delivery system (DDS) can improve distribution and bioavailability of a drug on tumor cells. Specifically, study examines the use of pristine and Al-doped graphitic carbon nitride (C3N) sheets as the delivery system. By employing density functional theory (DFT), researchers analyze interaction between anticancer drug cisplatin (Cis) and sheets. Results demonstrate that doping process modifies characteristics of pristine sheets, leading to improved adsorption of anticancer drugs. Al-doped sheet exhibits a cohesive energy within range of 4.96 eV, indicating its high stability. Present work has uncovered that adsorption of Cis drug over pristine C3N sheet is weak, with low adsorption energy (Eads) values of approximately −3.26 eV and −2.19 eV in a gaseous (aqueous) phase, respectively. However, Eads is significantly enhanced by approximately 85.92 % through introduction of Al doping in pristine C3N sheet. Primary interactions within the complexes are examined employing non-covalent interaction (NCI) analysis, utilizing a reduced density gradient (RDG) map. Cis@Al-C3N complex reveals that non-covalent interactions have a significant role in drug adsorption. Moreover, NCI indicates van der Waals interactions exert a substantial impact on interaction between carrier sheets and anticancer drug. Present investigation sets foundation for future research focusing on utilization of doped C3N sheets as effective drug carriers in targeted DDSs, potentially benefiting a wide range of drugs.

A facile tert-butyl nitrite-assisted preparation of deamino graphitic carbon nitride (DA-gCN) as a photocatalyst for the C-H arylation of heteroarenes using anilines as radical source.

In pristine graphitic carbon nitride (g-CN), amino groups often function as structural defects that trap photogenerated charges, resulting in low photocatalytic activity as well as reaction with nitrite, aldehyde, etc., ensuing in poor product yield. Without significantly altering the optical characteristics, the removal of amino groups is necessary to increase the photocatalytic activity and structural stability of pristine g-CN. The deamino graphitic carbon nitride (DA-gCN-5) was prepared by tert-butyl nitrite (TBN)-treatment, characterized and used as a photocatalyst for the radical C-H arylation of heteroarenes using anilines as radical source. Indeed, the photophysical characteristics of DA-gCN-5 and those of pristine g-CN are very comparable, except that DA-gCN-5 has a fewer residual amino groups, higher crystallinity, and compressed structure with a different morphology. Moreover, DA-gCN-5-catalyzed C-H arylation reaction offers greater product yield in a shorter reaction time compared to that of pristine g-CN in the coupling between heteroarenes and the in situ generated aryl diazonium salts from anilines under visible light irradiation. The amino groups in pristine g-CN absorbed the TBN that was added to convert aniline into the appropriate diazonium ions during the reaction. As a result, deamino graphitic carbon nitride produced by chemical treatment has better photophysical properties and catalytic activity than pristine g-CN. Additionally, this is the first method that uses diazotization reaction for the preparation of deamino graphitic carbon nitride, as far as we are aware.

Highly crystalline carbon nitrogen polymer with a strong built-in electric fields for ultra-high photocatalytic H2O2 production

Efficient photogenerated charge separation and rapid migration provide more charges for surface redox reactions. Herein, the carbon nitride polymer with highly crystalline is prepared for efficient photocatalytic H2O2 generation. The strong built-in electric field induced by its high crystallinity is beneficial for promoting exciton dissociation, resulting in a surface photovoltage of 19.24 mV. Meanwhile, the formed nanocrystals shorten the charge migration distance to facilitate photogenerated charge rapid migration. The abundant surface −CN/−OH groups provide more active sites for the adsorption of O2. As a result, the photocatalytic H2O2 production rate (16.01 mmol∙L−1∙h−1∙g−1) under visible light (λ > 400 nm) was increased 77-fold relative to pristine graphitic carbon nitride, with a quantum efficiency of 25.1% at 405 nm. The photocatalytic H2O2 production reached 80.36 mM after 8 h. The highly crystalline carbon nitride polymer throws prospect on photocatalytic H2O2 production, showing a new perspective for the design of photocatalysts.

Silica wastes derived multifunctional coatings for formaldehyde photodegradation and autonomous indoor humidity buffering

To maintain a comfortable and healthy indoor environment without large amounts of energy consumption is of great importance. The progress of multifunctional indoor coatings with formaldehyde photodegradation and humidity buffering capability is necessary. From the viewpoints of circular economy, the preparation of effective photocatalysts (denoted as sFCC/GCN-x and ESF/GCN-y) via the decoration of recycling industrial wastes (i.e., spent fluid catalytic cracking catalysts (sFCC) and enhancement silica fume (ESF)) onto graphitic carbon nitride (GCN) by using a simple route is reported. The obtained results show that the prepared sFCC/GCN-0.15 and ESF/GCN-0.15 photocatalysts have the rate constants of formaldehyde degradation of 0.0075 and 0.0082 min−1, respectively, which are superior to that of pristine GCN (0.0044 min−1) under visible-light irradiation. The enhanced transfer kinetics of photogenerated electrons and declined recombination of electron-hole pairs may account for the surpassing photocatalytic performance. Results obtained from electron paramagnetic resonance spectra and Mott-Schottky plots indicate that the formation of ･O2− via the reaction of O2 with electrons generated on the conduction band is the major reaction pathway to photodegrade formaldehyde under visible light. To further assess the real applications of prepared photocatalysts, the sFCC/GCN-0.15 and ESF/GCN-0.15 are used to fabricate the multifunctional coatings (denoted as s- and E-coatings) with sFCC and ESF as the main compositions. Experimentally, the E-coatings could reach the formaldehyde degradation efficiency of ca. 84.5% after 3 h of visible light irradiation and excellent humidity buffering ability (293.8 g m−2) which is at least 10-folds higher than commercial coatings (28.9 g m−2). This notable progress of humidity buffering capacity on E-coatings can be attributed to their surface textural properties. Most importantly, this study exemplifies the valorization of inorganic silica wastes to produce sustainable and multifunctional coatings which may offer the practical and cost-effective applications in the indoor living space.

Efficient Photocatalytic Degradation of Aqueous Atrazine over Graphene-Promoted g-C3N4 Nanosheets

Atrazine is a systemic herbicide widely used in weed control. In recent years, it has been largely detected in surface and groundwater in several locations all over the world. Photocatalysis is a green and sustainable technology with huge application prospects in pollution control and the degradation of organic water pollutants. In this work, photodegradation of aqueous atrazine was investigated over pristine graphitic carbon nitride (g-C3N4) synthesized via urea pyrolysis and graphene/g-C3N4 composite synthesized via the in situ growth method involving direct deposition of g-C3N4 nanosheets on the graphene surface. The obtained photocatalysts were characterized using transmission and scanning electron microscopy, Fourier-transformed infrared spectroscopy, UV-visible spectroscopy, photoluminescence spectroscopy, X-ray diffraction, and surface area measurements. It was demonstrated that the composite material exhibited remarkable photocatalytic properties for the efficient degradation of aqueous atrazine under visible light at ambient temperature. After 5 h of reaction, atrazine conversion reached 100% in the presence of graphene/g-C3N4 composite, while the pristine g-C3N4 allowed 40% conversion under the same conditions, thus demonstrating the positive effect of graphene on the photocatalytic activity of g-C3N4. Moreover, graphene/g-C3N4 was shown to keep its activity even when it was recycled five times, thus proving its stability and its potential to be used at the industrial scale.

Boosting piezocatalytic activity of graphitic carbon nitride for degrading antibiotics through morphologic regulation and chlorine doping

Graphitic carbon nitride (GCN) has been demonstrated to be a potential piezocatalyst in environmental remediation. The common piezoelectric materials synthesized by GCN are often designed to have a larger specific surface area to increase the adsorption and degradation performance of environmental pollutants. However, these process will also decrease the particle size of two-dimensional GCN, which thus affect the in-plane polarization intensity and inhibit the piezoelectric catalytic performance. Herein, we proposed an NH4Cl assistant synthesis to obtain ultrathin Cl-doped GCN (Cl-GCN) with large surface area and developed porosity. The introduced Cl with strong electronegativity can better change the electron cloud density distribution in GCN. From the experiment measurements and the theoretical calculation, Cl dopant in GCN skeleton resulted in partially destroyed crystal symmetry, and increased the structural polarity. As a result, the Cl-GCN simultaneously possessing large surface area and high piezoelectric polarization contributed enhanced piezocatalytic activity for degradation of antibiotics compared to the pristine GCN. Within 30 min, the degradation efficiency of tetracycline hydrochloride (TC-HCl) reached to ca. 94%. Besides, the effects of antibiotic concentration as well as the piezocatalytic durability for eliminating different antibiotics were investigated. Finally, based on determinations of mainly active species and the intermediate products during the piezocatalytic process, a plausible piezocatalytic degradation mechanism was proposed. This study implies that enhancing the piezoelectric polarization of piezocatalyst by heteroatomic doping and meanwhile improving its surface area are promising strategies to promoting piezocatalytic performance both for environmental application and for clean energy production.

Development and characterization of silver modified novel graphitic-carbon nitride (Ag-ZnO/C3N4) coupled with metal oxide photocatalysts for accelerated degradation of dye-based emerging pollutants

Industrial wastewater undesirably affects aquatic life and the environment. One of the main sources of aquatic pollution is organic dyes, which are discharged into the mainstream water without any treatment. Therefore, organic dyes and their derivatives must be degraded by heterogeneous photocatalysts before discharge into wastewater. In this study, we synthesized three different photocatalysts using a low-cost material, i.e., melamine (as a ground material). The photocatalysts, pristine graphitic-carbon nitride (g-C3N4), coupled with zinc oxide (ZnO/C3N4), and modified with a silver (Ag-ZnO/C3N4), were synthesized by the calcination of melamine, following a hydrothermal process. The novel synthesized photocatalysts were characterized by different electro-analytical techniques such as X-ray diffraction (XRD), Transmission Electron Microscopy (TEM), Fourier Transform Infra-red (FT-IR), and Thermogravimetric analysis (TGA). The XRD results reveal the crystalline nature of the synthesized photocatalysts, which increases further with silver modification. TEM analysis discloses that the average particle sizes of ZnO and Ag NPs were 3–5 nm and 20–22 nm, respectively. Where the g-C3N4 displays a 2-D sheet-like structure. The photocatalysts were deeply investigated to study the degradation of organic dyes under UV light for Bromophenol Blue (BBP) and Methylene Blue (MB). Effects of different parameters such as contact time, Dye dose, photocatalyst dose, and pH were also investigated. In all three photocatalysts, Ag-ZnO/C3N4 was the most effective, showing high degradation for both dyes; BPB showed 99.2 percent degradation, whereas in MB the maximum degradation was 97.3 percent. The maximum degradation observed in the pH study was different for both dyes, BPB shows high degradation at pH-1 with 96.8 percent degradation, whereas in MB the maximum degradation is observed at pH-14 with 99.3 percent. The kinetics of the dyes BPB and MB, which follow pseudo-first-order kinetics, were also calculated. In short, the results revealed that the novel g-C3N4 photocatalysts were extremely active in the degradation of target organic dyes, which encourages more work on the degradation of these pollutants from wastewater.

Computational investigation of Zn doped graphitic carbon nitride (gCN) monolayer for CO2 sensing

In the present work, we have investigated the sensing behavior of pristine graphitic carbon nitride (gCN) and Zn doped gCN monolayer (Zn-gCN) for CO2 gas sensing using DFT calculations. Structural and electronic properties such as adsorption energy, band structure, and density of states (DOS) have been investigated. The calculated adsorption energy of pristine gCN is −1.33 eV. To improve this value, doping is patterned at three sites (i.e., terminal N site, edge N site, and ring N site). The adsorption is maximum at the terminal N site followed by ring N site and edge N site with a value of −8,29 eV, −2.48 eV, and −2.16 eV, respectively. Band gap structure also reflects that the doping at terminal N site is most favorable with a 52.7% shrinking of band gap subsequent to adsorption of CO2 gas compared to pristine gCN. Further, the DOS values also exhibit noticeable change after doping Zn atom at different sites in gCN towards adsorption of CO2 with a maximum increase at the terminal N site. The present study reveals that the sensing performance of the Zn-gCN is significantly enhanced compared to pristine gCN and can be a promising material for CO2 gas sensing.

Synergistic effect of n-π* electronic transitions in porous ultrathin graphitic carbon nitride nanosheets for efficient photocatalytic hydrogen production

The visible light absorption capacity and active sites of graphitic carbon nitride (GCN) are crucial roles for photocatalytic hydrogen (H2) production. However, the fabrication of ultrathin GCN nanosheets with enhanced light absorption via n-π* electronic transitions remain challenging. Here, we report on the successful preparation of porous ultrathin GCN nanosheets with activating n-π* electronic transitions simultaneously by microwave heating the mixture of urea and ammonium chloride (NH4Cl) compression strategy. Such the unique structure of GCN is composed of a curved porous thin layer and has numerous wrinkles that not only largely expand visible light absorption range to ∼ 650 nm but also significantly enhance the unmber of active sites and the mobility of photoexcited charges. The highest photocatalytic H2 production rate reached 99.1 μmol h−1 under visible light irradiation (λ > 420 nm), which is 8.8 folds higher than that of pristine GCN (11.2 μmol h−1). This work presents a promising and effective strategy for the engineering of GCN, which fully utilizes n-π* electronic transitions to largely expand the visible light absorption while enhancing the active sites.

Stable and fast oil recovery by environmentally friendly and easy to synthesize pristine graphitic carbon nitride

Stable and fast oil recovery by environmentally friendly and easy to synthesize pristine graphitic carbon nitride

Improved performance of visible-light photocatalytic H2-production and Cr(VI) reduction by waste pigeon guano doped g-C3N4 nanosheets

In this study, waste pigeon guano (PG) was re-utilized as an ideal biomass adulterant to improve the photocatalytic activity of the pristine graphitic carbon nitride (g-C3N4). Waste PG and melamine were employed as precursors to fabricate a novel porous multielement-doped g-C3N4 (CN-PG-S) nanosheets photocatalyst via in situ thermal polycondensation coupled with thermal exfoliation strategy. The CN-PG-S owned abundant uniformly porous structures, superior conductivity, and excellent photocatalytic abilities, resulting in highly-efficient H2-production (1950 μmol g–1 h–1) and Cr(VI) reduction (99.1%) under visible light, which increased by 22.9-folds and 5.3-folds more than that of pristine g-C3N4. The non-metallic (P, S, and O) and metallic elements in CN-PG-S played a crucial role in expanding the visible-light absorption range and promoting the separation-migration of photogenerated electron-hole pairs. And the uniformly porous nanosheet structure of CN-PG-S shortens the diffusion paths of photogenerated carriers and exposes more active sites for photocatalytic reactions. This study proposed an eco-friendly resources integration strategy of waste PG to prepare excellent CN-PG-S photocatalysts for highly-efficient H2-production and Cr(VI) reduction.

Exploration of optimal reaction conditions on lactic acid production from glucose photoreforming over carbon nitride

Biomass valorization by photoreforming approach provides a promising and alternative strategy to generate value-added chemicals and fuels. In this work, we demonstrate the selective production of lactic acid from glucose photoreforming over pristine graphitic carbon nitride (g-C3N4) photocatalyst. Control experiments screen the best condition for the highest yield of lactic acid, including modulating pH, catalyst loading, and reaction time. 100% glucose conversion is achieved along with almost 100% lactic acid yield under the optimized condition. Density functional theory (DFT) calculations reveal that the rate-determining step (RDS) of the overall reaction on g-C3N4 is the conversion of pyruvaldehyde, where an electron transfer takes place. This present work provides experimental insights and theoretical understanding for selective lactic acid production from biomass photoreforming.

Aminobenzaldehyde convelently modified graphitic carbon nitride photocatalyst through Schiff base reaction: Regulating electronic structure and improving visible-light-driven photocatalytic activity for moxifloxacin degradation.

Graphitic carbon nitride (GCN) has been demonstrated to be a potential visible-light-driven photocatalyst for eliminating organic pollutants. However, its practical application is limited by low photocatalytic efficiency originating from high recombination of photogenerated charges. In this work, the electronic structure of GCN was regulated by doping aminobenzaldehyde (ABA) into the skeleton through a solid-state Schiff base reaction. Photoelectrochemical characterizations illustrated that the obtained catalyst (CNABA) exhibited narrower band gap, lower recombination rate of photoinduced electron-hole pair and higher charge transfer ability than the pristine GCN, further indicating its excellent photocatalytic activity. Using moxifloxacin (MOX) as a model pollutant, the ABA doping content was firstly optimized and the optimal activity of the CNABA photocatalyst was 3.1 times higher than that of the GCN. Subsequently, the effects of pH value, photocatalyst dosage and MOX concentration on the photocatalytic behavior were also studied. Superior stability and photocatalytic reusability were confirmed by five repeated tests. By substituting tap water/natural lake water for deionized water and sunlight for xenon light, the CNABA also exhibited high elimination efficiency, implying its good practicability. Superoxide radical, hydroxyl radical and photogenerated hole were identified as the main active species to degrade MOX. Finally, possible degradation pathways for MOX to mineralize small molecules were proposed by determining intermediate products during photocatalysis. This work provides a solid-state method to rationally design aromatic system-modified GCN photocatalysts, and the obtained CNABA is a promising visible-light-driven photocatalyst for eliminating antibiotics.

Phosphorus doped and defect modified graphitic carbon nitride for boosting photocatalytic hydrogen production.

The enhancement of photogenerated carrier separation efficiency is a significant factor in the improvement of photocatalyst performance in photocatalytic hydrogen evolution. Heteroatom doping and defect construction have been considered valid methods to boost the photocatalytic activity of graphitic carbon nitride. Herein, we report graphitic carbon nitride modified with P doping and N defects (PCNx), and the effects of doping and defects were investigated in photocatalytic H2 evolution. Its hydrogen evolution rate can reach up to about 59.1 μmol h-1, which is more than 123.1 times higher than pristine graphitic carbon nitride under visible light irradiation. Importantly, the apparent quantum efficiency reaches 8.73% at 420 nm. The excellent performance of the PCNx photocatalyst was attributed to the following aspects: (I) the large BET surface area of PCNx affords more active sites for H2 production and (II) the introduction of P and N defects can accelerate the charge carrier separation and transfer efficiency, leading to more efficient photocatalytic hydrogen production. The photocatalyst showed obviously enhanced activities.

Improved charge transport through 2D framework in fully condensed carbon nitride for efficient photocatalytic hydrogen production

The 1D molecular structure of traditional graphitic carbon nitride (GCN) leads to the space-confined transport of charge carriers along the chains and prohibits transport across the chains. Therefore, the formation of 2D network which can provide more convenient transfer paths is of great desirable. In this work, a fully condensed carbon nitride with the real 2D framework was successfully developed by post-calcining 1D GCN in a LiCl/KCl molten salt. The newly formed 2D molecular structure significantly promoted the charge transfer and separation, resulting in remarkably enhanced photocatalytic hydrogen production activity. Moreover, N-doped graphene quantum dots (NGQDs) incorporation can be simultaneously realized via the simple one step “co-dissolution and recrystallization” method. Especially, the as-prepared 2D-CN/NGQDs sample presents a further increased photocatalytic hydrogen evolution rate up to about 30 times that of pristine GCN. The apparent quantum efficiency (AQE) for H2 evolution of 2D-CN/NGQDs reaches 36 % at 420 nm.