Triazine-based Carbon Nitride Research Articles

Intramolecular Quaternary Carbon Nitride Homojunction for Enhanced Visible Light Hydrogen Production.

In this work, an intramolecular carbon nitride (CN)-based quaternary homojunction functionalized with pyridine rings is prepared via an in situ alkali-assisted copolymerization strategy of bulk CN and 2-aminopyridine for efficient visible light hydrogen generation. In the obtained structure, triazine-based CN (TCN), heptazine-based CN (HCN), pyridine unit incorporated TCN, and pyridine ring inserted HCN constitute a special multicomponent system and form a built-in electric field between the crystalline semiconductors by the arrangement of energy band levels. The electron-withdrawing function of the conjugated heterocycle can trigger the skeleton delocalization and edge induction effect. Highly accelerated photoelectron-hole transfer rates via multi-stepwise charge migration pathways are achieved by the synergistic effect of the functional group modification and molecular quaternary homojunction. Under the addition of 5mg 2-aminopyridine, the resulting homojunction framework exhibits a significantly improved hydrogen evolution rate of 6.64mmol g-1 h-1 with an apparent quantum efficiency of 12.27% at 420nm. Further, the catalyst verifies its potential commercial value since it can produce hydrogen from various real water environments. This study provides a reliable way for the rational design and fabrication of intramolecular multi-homojunction to obtain high-efficient photocatalytic reactions.

Matched Redox Kinetics on Triazine-Based Carbon Nitride/Ni(OH)2 for Stoichiometric Overall Photocatalytic CO2 Conversion.

Mismatched reaction kinetics of CO2 reduction and H2 O oxidation is the main obstacle limiting the overall photocatalytic CO2 conversion. Here, a molten salt strategy is used to construct tubular triazine-based carbon nitride (TCN) with more adsorption sites and stronger activation capability. Ni(OH)2 nanosheets are then grown over the TCN to trigger a proton-coupled electron transfer for a stoichiometric overall photocatalytic CO2 conversion via "3CO2 + 2H2 O = CH4 + 2CO + 3O2 ." TCN reduces the energy barrier of H2 O dissociation to promote H2 O oxidation to O2 and supply sufficient protons to Ni(OH)2 , whereby the CO2 conversion is accelerated due to the enhanced proton-coupled electron transfer process enabled by the sufficient proton supply from TCN. This work highlights the importance of matching the reaction kinetics of CO2 reduction and H2 O oxidation by proton-coupled electron transfer on stoichiometric overall photocatalytic CO2 conversion.

Dual Heterojunction of Etched MIL-68(In)-NH2 Supported Heptazine-/Triazine-Based Carbon Nitride for Improved Visible-Light Nitrogen Reduction.

This work reports a dual heterojunction of etched MIL-68(In)-NH2 (MN) supported heptazine-/triazine-based carbon nitride (HTCN) via a facile hydrothermal process for photocatalytic ammonia (NH3 ) synthesis. By applying the hydrothermal treatment, MN microrods are chemically etched into hollow microtubes, and HTCN with nanorod array structures are simultaneously tightly anchored on the outside surface of the microtubes. With the addition of 9 wt% HTCN, the resulting dual heterojunction presents an enhanced photocatalytic ammonia yield rate of 5.57mm gcat -1 h-1 with an apparent quantum efficiency of 10.89% at 420nm. Moreover, stable ammonia generation using seawater, tap water, lake water, and turbid water in the absence of sacrificial reagents verifies the potential of the dual-heterojunction composites as a commercially viable photosystem. The obtained one-dimensional (1D) microtubes and coating of HTCN confers this unique composite with extended visible-light harvesting and accelerated charge carrier migration via a multi-stepwise charge transfer pathway. This work provides a new strategy for optimizing nitrogen (N2 )-into-ammonia conversion efficiency by designing novel dual-heterojunction catalysts.

Molten-Salt Synthesis of Triazine-Based Carbon Nitride and Its Photocatalytic Degradation Mechanism Investigation by In Situ NMR

Carbon nitride-based catalysts are nonmetallic materials with efficient photocatalysis for water splitting, degradation of organic dyes, and CO2 reduction. In this paper, a one-step molten salt method was employed for the synthesis of ionic doped carbon nitride materials named CNs (carbon nitride catalysts), which exhibited excellent adsorption performance and photocatalytic activity. The adulteration of Zn2+ ions created a unique nanosheet stack morphology, leading to more effective active sites and better electron transfer efficiency. Additionally, the degradation mechanism was investigated by the quasi-in situ NMR method. The reaction products and photocatalytic process were fully discussed, providing a new degradative pathway of methylene blue (MB) by such CN-based catalysts.

Photochemical Synthesis of Porous Triazine-/Heptazine-Based Carbon Nitride Homojunction for Efficient Overall Water Splitting.

Porous triazine-/heptazine-based carbon nitride (THCN) homojunction with chloride (Cl) doping was synthesized by a simple, one-step photochemical synthesis route for efficient visible-light-driven overall water splitting. The phase ratio of triazine-based carbon nitride (TCN) and heptazine-based carbon nitride (HCN), texture and morphology of the THCN isotype junction were finely tuned by varying ultraviolet irradiation time and washing solvents. After washing with acetonitrile, the resulting porous THCN nanosheets with 48 h irradiation contain 21 wt % TCN and 79 wt % HCN units and reveal a significantly improved photocatalytic performance with H2 and O2 production rates up to 7.9 and 4.2 μmol h-1 , respectively, about 3.8 times higher than that of THCN prepared by 36 h illumination. The dual-phase interaction, holey structure, and Cl dopants favor the exposure of active sites, extended visible-light harvesting, accelerated charge transfer, and enhanced photoreduction ability, thereby improving photocatalytic activity.

Selective Photocatalytic CO2 Reduction to CH4 on Tri-s-triazine-Based Carbon Nitride via Defects and Crystal Regulation: Synergistic Effect of Thermodynamics and Kinetics.

Realizing the high selectivity of CH4 from the photocatalytic CO2 reduction reaction (CO2 RR) remains a great challenge owing to the lower efficiency of multi-electron transfer and the similar thermodynamic properties of CH4 and CO. Herein, nitrogen-deficient carbon nitride two-dimensional (2D) nanosheets were prepared via the high-temperature crystalline phase transformation process. Optimizing crystallinity enhances the in-plane polarization along the a-axis. Owing to the increased electron density of the N defect, the kinetic possibilities of CH4 production have increased. Furthermore, the potential energy of the mid-gap states introduced by the N defect favors the thermodynamics of CH4 production. The selectivity values of CH4 based on yield and electrons are 87.1 and 96.4%. This work unravels the mechanism to selectively produce CH4 from CO2 photoreduction through the crystalline phase and defect regulation and provides significant guidance for the rational design of CO2 reduction photocatalysts for selective CH4 production.

NiS as a Cocatalyst Decorated Heptazine-/Triazine-Based Carbon Nitride Coupled with Cd0.5Zn0.5S Solid Solution Heterojunction Photocatalysts: Efficient Interfacial Charge Transfer and Enhanced Photocatalytic Hydrogen Production Activity

NiS as a Cocatalyst Decorated Heptazine-/Triazine-Based Carbon Nitride Coupled with Cd_0.5Zn_0.5S Solid Solution Heterojunction Photocatalysts: Efficient Interfacial Charge Transfer and Enhanced Photocatalytic Hydrogen Production Activity

Modified triazine-based carbon nitride as a high efficiency fluorescence sensor for the label-free detection of Ag+

Abstract

Sunlight-induced uranium extraction with triazine-based carbon nitride as both photocatalyst and adsorbent

Extracting uranium from high salinity seawater at ultralow concentrations would beneficially contribute to the sustainable utilization of nuclear energy, but it poses a significant challenge. Here we report a sunlight-driven photocatalysis-assisted extraction (SUPER) method by utilizing a bifunctional carbon nitride material, CN550, which has shown about a tenfold improvement in both adsorption capacity and photocatalytic activity compared to g-C3N4. Uranyl ions could be captured on the surface of CN550, and then deposited as metastudtite nanoparticles with light illumination. Compared with the pure physicochemical adsorption (PA) method, a tenfold higher uranium extraction capacity, up to 1556 mg g−1, has been attained. Additionally, a 25 times improvement of the partition coefficient (PC), from 0.312 to 7.778 L g−1, has also been achieved. In spiked real seawater, the extraction capacity can still achieve more than 1000 mg g−1, and the SUPER method has been found to work under natural sunlight illumination as well.

Band structure engineering of PTI in C-PTI/ZnO heterostructures for enhanced visible-light-driven H2 evolution

Polytriazine imide (PTI), a triazine-based carbon nitride has a wider band gap and more positive conduction band (CB) potential compared to those of graphitic carbon nitride (g-C3N4). Therefore, it is highly desired to develop an effective strategy to optimize the band structure of PTI for the enhancement of the photocatalytic performance, especially upshift the conductive band potential. Here, a ternary C-PTI/ZnO (CPZ) photocatalyst was developed via a simple one-step molten salt method. In the obtained CPZ sample, the carbon ring in-plane connects to the triazine ring, leading to the formation of C-PTI nanosheets. The carbon ring incorporation not only efficiently narrows the band gap of PTI, but also shifts its conduction band potential negatively and accelerates the photogenerated electron transport. In addition, ZnO nanoparticles are well dispersed on the C-PTI nanosheets, further promoting the charge carriers transfer and separation. As a result, the CPZ sample presents a photocatalytic H2 evolution rate up to 52 μmol h−1 under visible light, which is 60 and 179 times higher than that of C-PTI and PTI, respectively.

One-Pot Ionothermal Synthesized Carbon Nitride Heterojunction Nanorods for Simultaneous Photocatalytic Reduction and Oxidation Reactions: Synergistic Effect and Mechanism Insight

Band structure and crystallinity engineering of polymeric semiconductors provides effective strategies for photocatalytic activity enhancement. Here, a facile one-step ionothermal method was developed to achieve the in situ growth of carbon nitride (CN) isotype heterojunctions (ms-CN-x) using KCl/LiCl eutectic salts as the high-temperature solvent and urea as the starting material, which are demonstrated to be efficient photocatalysts for removal of toxic heavy metal and organic pollutant in a single or coexisting system. The as-obtained ms-CN-x composite material appears as well-ordered nanorod structure with high crystallinity and consists of phases of both heptazine-based CN and triazine-based CN. With structural and morphological merits, the ms-CN-0.5 photocatalyst exhibits remarkable adsorption–photodegradation performance for high-level methylene blue (MB). Moreover, simultaneously enhanced photocatalytic reaction rate of Cr(VI) reduction and MB oxidation over ms-CN-0.5 are achieved and systematical...

Molecular Doping of Electrochemically Prepared Triazine-Based Carbon Nitride by 2,4,6-Triaminopyrimidine for Improved Photocatalytic Properties.

Copolymerization of melamine with 2,4,6-triaminopyrimidine (TAP) in an electrochemically induced polymerization process leads to the formation of molecular doped poly(triazine imide) (PTI). The polymerization is based on the electrolysis of water and evolving radicals during this process. The incorporation of TAP is shown by techniques such as elemental analysis, Fourier transform infrared and NMR spectroscopies, and powder X-ray diffraction, and it is shown that the carbon content can be tuned by the variation of the molar ratio of the two precursors. This incorporation of TAP directly influences the electronic structure of PTI and as a result, a red shift can be observed in UV–vis spectroscopy. The smaller band gap and the increased absorption in the visible range lead to improved photocatalytic properties. In dye degradation experiments, it was possible to observe an increase of the rate of the degradation of methylene blue by a factor of 4 in comparison to undoped PTI or 7 if compared to melon.

Pd nanoparticles confined within triazine-based carbon nitride NTs: An efficient catalyst for Knoevenagel condensation-reduction cascade reactions

Pd nanoparticles (NPs) were immobilized within triazine-based g-C3N4 nanotubes (NTs) to obtain a novel bifunctional catalyst, which was used as an efficient catalyst in the Knoevenagel condensation-reduction tandem reaction. The results of Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), UV–vis diffuse reflectance spectra (DRS), X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA) demonstrated that Pd NPs were successfully immobilized within triazine-based g-C3N4 NTs. The base amounts of the catalysts were determined by CO2 temperature programmed desorption (CO2-TPD). The textural and morphology of Pd/triazine-based g-C3N4 NTs were characterized by N2 adsorption-desorption, scanning electronic micrograph (SEM), transmission electron microscope (TEM) and CO adsorption. The characterization results indicated that Pd NPs were mainly immobilized on the inner surface of triazine-based g-C3N4 NTs. Pd/triazine-based g-C3N4 NTs showed excellent catalytic performance in the tandem reaction, in which the conversion of benzaldehyde and selectivity to benzylmalononitrile were 100% and 99.2%, respectively. The result was attributed to the high base amounts (especially -NH2 and -NH groups) and the high catalytic activities of Pd NPs within Pd/triazine-based g-C3N4 NTs. Furthermore, the high catalytic activity of Pd/triazine-based g-C3N4 NTs is also attributed to the confinement effect of the nanotube structure. The structure of nanotube not only tune the Pd particle size of the catalysts, but also provide spatial restriction on metal catalyst encapsulated in their channels, which hampered particles aggregation during the reaction, thus maintaining good catalytic activity and stability. Moreover, the anchor and stabilization effects of pyridine N atoms of triazine-based g-C3N4 NTs inhibited the aggregation and the leak of active sites, thereby achieving a good catalytic recyclability with almost unchanged catalytic activity for more than eight times in the tandem reaction.

A New Synthesis Approach for Carbon Nitrides: Poly(triazine imide) and Its Photocatalytic Properties.

Poly(triazine imide) (PTI) is a material belonging to the group of carbon nitrides and has shown to have competitive properties compared to melon or g-C3N4, especially in photocatalysis. As most of the carbon nitrides, PTI is usually synthesized by thermal or hydrothermal approaches. We present and discuss an alternative synthesis for PTI which exhibits a pH-dependent solubility in aqueous solutions. This synthesis is based on the formation of radicals during electrolysis of an aqueous melamine solution, coupling of resulting melamine radicals and the final formation of PTI. We applied different characterization techniques to identify PTI as the product of this reaction and report the first liquid state NMR experiments on a triazine-based carbon nitride. We show that PTI has a relatively high specific surface area and a pH-dependent adsorption of charged molecules. This tunable adsorption has a significant influence on the photocatalytic properties of PTI, which we investigated in dye degradation experiments.

Challenges in calculating the bandgap of triazine-based carbon nitride structures

Graphitic carbon nitrides form a popular family of materials, particularly as photoharvesters in photocatalytic water splitting cells.

Dendritic Tip-on Polytriazine-Based Carbon Nitride Photocatalyst with High Hydrogen Evolution Activity

Developing stable, ubiquitous, and efficient water-splitting photocatalyst material that has extensive absorption in the visible-light range is desired for a sustainable solar energy-conversion device. We herein report a triazine-based carbon nitride (CN) material with different C/N ratios achieved by varying the monomer composition ratio between melamine (Mel) and 2,4,6-triaminopyrimidine (TAP). The CN material with a different C/N ratio was obtained through a two-step synthesis protocol: starting with the solution state dispersion of the monomers via hydrogen-bonding supramolecular aggregate, followed by a salt-melt high temperature polycondensation. This protocol ensures the production of a highly crystalline polytriazine imide (PTI) structure consisting of a copolymerized Mel-TAP network. The observed bandgap narrowing with an increasing TAP/Mel ratio is well simulated by density functional theory (DFT) calculations, revealing a negative shift in the valence band upon substitution of N with CH in the ...

Stability and electronic structures of triazine-based carbon nitride nanotubes

In contrast to the case of carbon nanotubes, the negative strain energy indicates that single-walled and double-walled triazine-based carbon nitride nanotubes (TACNNTs) are appreciably more stable than the single layer and the bilayer of gt-C3N4, respectively. Boron-doping turns the material into a magnetic semiconductor.

Harvesting solar light with crystalline carbon nitrides for efficient photocatalytic hydrogen evolution.

Described herein is the photocatalytic hydrogen evolution using crystalline carbon nitrides (CNs) obtained by supramolecular aggregation followed by ionic melt polycondensation (IMP) using melamine and 2,4,6-triaminopyrimidine as a dopant. The solid state NMR spectrum of (15)N-enriched CN confirms the triazine as a building unit. Controlling the amount and arrangements of dopants in the CN structure can dramatically enhance the photocatalytic performance for H2 evolution. The polytriazine imide (PTI) exhibits the apparent quantum efficiency (AQE) of 15% at 400 nm. This method successfully enables a substantial amount of visible light to be harvested for H2 evolution, and provides a promising route for the rational design of a variety of highly active crystalline CN photocatalysts.