Nitrogen-deficient Carbon Nitride Research Articles

(Invited) Polymeric Carbon Nitride for Photocatalytic Overall Water Splitting

Photocatalytic overall water splitting can be achieved using Z-scheme systems that mimic natural photosynthesis by combining dissimilar semiconductors in series. However, coupling well-suited H2- and O2-evolving components remains challenging. Here, we fabricate a Z-scheme system for photocatalytic overall water splitting based on boron-doped, nitrogen-deficient carbon nitride two-dimensional (2D) nanosheets. We prepare ultrathin carbon nitride nanosheets with varying levels of boron dopants and nitrogen defects, which leads to nanosheets that can act as either H2- or O2-evolving photocatalysts. Using an electrostatic self-assembly strategy, the nanosheets are coupled to obtain a 2D/2D polymeric heterostructure. Owing to their ultrathin nanostructures, strong interfacial interaction and staggered band alignment, a Z-scheme route for efficient charge-carrier separation and transfer is realized. The obtained heterostructure achieves stoichiometric H2 and O2 evolution in the presence of Pt and Co(OH)2 co-catalysts, and the solar-to-hydrogen efficiency reaches 1.16% under one-sun illumination.

Fabricating metal-free Z-scheme heterostructures with nitrogen-deficient carbon nitride for fast photocatalytic removal of acetaminophen

Photocatalytic technology has been increasing explored for the elimination of pollutants from aquatic environments. However, constructing powerful photocatalyst to drive rapid decontamination remains challenging. Here, we assemble boron-doped nitrogen-deficient carbon nitride (BNCN) into metal-free Z-scheme heterojunction via a facile approach to boost photocatalytic degradation of acetaminophen. Incorporating boron dopants and nitrogen defects to C3N4 significantly increase the photoabsorption. Furthermore, the constructed heterojunction exhibited decreased band gap and remarkably enhanced separation efficiency of photogenerated carriers compared with individual BNCN. Owing to the modulation of band structures and the better separation of photogenerated carriers, acetaminophen conversion approaching 100 % was achieved in just 30 mins under simulated sunlight, outperforming equivalent quantities of bulk carbon nitride and commercial TiO2 by 3.1 and 2.7 times, respectively. Two possible photodegradation pathways were proposed with hydroxylation and ring-opening reactions as dominant degradation reactions. Our findings provide an instructive catalyst design strategy to boost photocatalytic degradation efficiency.

Supramolecular Polymer Intertwined Free-Standing Bifunctional Membrane Catalysts for All-Temperature Flexible Zn–Air Batteries

HighlightsRational design of 3D flexible free-standing membrane catalysts with protonation between supramolecular polymers and nitrogen-deficient carbon nitride nanotubes frameworks via facile bottom-up self-conversion approach.PEMAC@NDCN demonstrates the lowest reversible oxygen bifunctional activity of 0.61 V with exceptional long-lasting durability, surpassing the commercial and reported champion oxygen catalysts.Engineering catalytically active cathode materials enabled all-temperature flexible Zn–air batteries with high electrochemical and mechanical performances (temperature of − 40 to 70 °C) under harsh operations.

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.

Tin nanoparticle in-situ decorated on nitrogen-deficient carbon nitride with excellent sodium storage performance

Tin (Sn)-based electrodes, featuring high electrochemical activity and suitable voltage plateau, gain tremendous attention as promising anode materials for sodium-ion batteries. However, the application of Sn-based electrodes has been largely restricted by the serious pulverization upon repeated cycling due to their large volume expansion, especially at high current densities. Herein, a unique three-dimensional decorated structure was designed, containing ultrafine Sn nanoparticles and nitrogen-deficient carbon nitride (Sn/D-C3N4), to efficiently alleviate the expansion stress and prevent the aggregation of Sn nanoparticles. Furthermore, the density functional theory calculations have proved the high sodium adsorption ability and improved diffusion kinetics through the hybridization of D-C3N4 with Sn nanoparticles. Further combining the high electronic/ionic conductivity provided by the porous C3N4 matrix, high charge contribution from capacitive behavior, and high sodium storage activity of ultrafine Sn nanoparticles, the resultant Sn/D-C3N4 can achieve an ultrahigh reversible capacity of 518.3 mA g−1 after 300 cycles at 1.0 A g−1, and even maintaining a reversible capacity of 436.1 mAh g−1 up to 500 cycles (5.0 A g−1). What’s more, the optimized Sn/D-C3N4∥Na3V2(PO4)3/C full cell can keep a high capacity retention of 87.1% at 1.0 A g−1 even after 5000 cycles, manifesting excellent sodium storage performance.

Selective oxidation of glucose to gluconic acid and glucaric acid with chlorin e6 modified carbon nitride as metal-free photocatalyst

Photocatalysis has exhibited huge potential in many reactions, but the design of metal-free photocatalytic material for selective upgrading of biomass is rarely achieved. Here, we report that the metal-free photocatalyst consisted of nitrogen-deficient carbon nitride (BNCN) and chlorin e6 (Ce6) can efficiently and selectively oxidize glucose into gluconic acid and glucaric acid. Introducing nitrogen defects could significantly enhance the optical absorption and modulate the band structure. In addition, the combination of Ce6 with BNCN further improve the optical absorption property and promote effective separation of photon-generated carriers. As expected, the resultant Ce6@BNCN catalyst gave a total selectivity of gluconic acid, glucaric acid and arabinose as high as 70.9% at glucose conversion up to 62.3%, as is superior to previously reported photocatalytic systems. The mechanism for the enhancement of catalytic performance and the reaction pathway were revealed by experimental studies combined with DFT calculations.

Constructing three-dimensional network C, O Co-doped nitrogen-deficient carbon nitride regulated by acrylic fluoroboron overall marine antifouling

To deal with unwanted biofouling adsorption, which impacts the economy and the environment, significant research has been devoted to composite systems involving a photocatalyst combined with self-renewal resin to provide synergistic antifouling. Here, photocatalyst based on three-dimensional (3D) network of carbon–oxygen-doped nitrogen-deficient carbon nitride and acrylic fluoroboron polymer as a system was successfully synthesized. 3D networks carbon nitride with carbon–oxygen dopants and nitrogen defects were prepared as skeletons, which effectively support and regulate the hydrolysis rate of the polymer. These composite systems exhibits excellent diatom anti-adhesion performance and high antibacterial rates for Escherichia coli and Staphylococcus aureus of up to 91.87% and 88.52%, respectively. In addition, self-cleaning function of the composite system are proved by and higher efficiency of chemical oxygen demand (COD) removal owing to efficient charge-carrier separation and transfer within the 3D network carbon nitride network. The great potential applications of this strategy demonstrated in marine engineering in the future.

One-step fabrication of nitrogen-deficient carbon nitride through pyrolysis of melamine and 1,2,4-triazole for its enhanced photocatalytic degradation

The construction of defects in semiconductor photocatalysts, as a kind of modification methods, plays an indispensable role in the enhancement of the photocatalytic performance. Herein, nitrogen defects were successfully introduced into the framework of graphite carbon nitride (CN-Tx) through thermal polymerization with melamine and 1,2,4-triazole as precursors. The existence of nitrogen defects in CN-Tx were confirmed to be located at the two-coordinated (N2c) CN–C lattice sites, which resulted in the destruction of its planar structure and the initiation of n-π∗ electron transition that greatly expanded the response range to visible light and improved the separation efficiency of photogenerated charge carrier. More significantly, CN-Tx could enhance photocatalytic water purification activity towards different kinds of pollutants. The photocatalytic rates of CN-T3 were estimated to be 2.54 (tetracycline) and 2.31 (2-hydroxynaphthalene) times higher than those of pristine g-C3N4. Furthermore, the possible photocatalytic degradation mechanism over CN-Tx photocatalyst was proposed by free radical trapping experiments combined with ERS characterization. This work provides an in-depth understanding of the important role of nitrogen defects in the electronic structure and chemical properties of g-C3N4 and its photocatalytic water purification performance.

Boron-doped nitrogen-deficient carbon nitride-based Z-scheme heterostructures for photocatalytic overall water splitting

Photocatalytic overall water splitting can be achieved using Z-scheme systems that mimic natural photosynthesis by combining dissimilar semiconductors in series. However, coupling well-suited H2- and O2-evolving components remains challenging. Here, we fabricate a Z-scheme system for photocatalytic overall water splitting based on boron-doped, nitrogen-deficient carbon nitride two-dimensional (2D) nanosheets. We prepare ultrathin carbon nitride nanosheets with varying levels of boron dopants and nitrogen defects, which leads to nanosheets that can act as either H2- or O2-evolving photocatalysts. Using an electrostatic self-assembly strategy, the nanosheets are coupled to obtain a 2D/2D polymeric heterostructure. Owing to their ultrathin nanostructures, strong interfacial interaction and staggered band alignment, a Z-scheme route for efficient charge-carrier separation and transfer is realized. The obtained heterostructure achieves stoichiometric H2 and O2 evolution in the presence of Pt and Co(OH)2 co-catalysts, and the solar-to-hydrogen efficiency reaches 1.16% under one-sun illumination. Splitting water using suspensions of particulate carbon nitride-based photocatalysts may be a cheap way to produce hydrogen, but efficiencies have remained low. Now, Shen and colleagues use doped carbon nitride-based Z-scheme heterostructures to split water with a solar-to-hydrogen efficiency of 1.1% in the presence of metal-based co-catalysts.

The pivotal role of defects in fabrication of polymeric carbon nitride homojunctions with enhanced photocatalytic hydrogen evolution

Fabrication of homojunctions is a cost-effective efficient way to enhance the photocatalytic performance of polymeric carbon nitride (CN), but the generation of defects upon synthesizing CN homojunctions and their roles in the homojunction fabrication were hardly reported. Herein, nitrogen-deficient CN homojunctions were simply synthesized by calcining dicyandiamide-loaded CN (prepared from urea and denoted as UCN) with dicyandiamide polymerizing into CN (denoted as DCN) and simultaneous formation of nitrogen vacancies in the surface of UCN. Fabrication of the nitrogen-deficient UCN (dUCN)/DCN homojunction depends on the nitrogen vacancy content in dUCN which can tune the energy band structure of dUCN from not matching to matching with that of DCN. The dUCN/DCN homojunction exhibits extended optical absorption and remarkably enhanced charge separation and photocatalytic H2 evolution, compared with UCN and DCN. This work illustrates the pivotal role of defects in fabricating CN homojunctions and supplies a new facile way to synthesize nitrogen-deficient CN.

Defect-enhanced activation of carbon nitride/horseradish peroxidase nanohybrids for visible-light-driven photobiocatalytic water purification

Enzymatic biodegradation offers a powerful tool to remediate the contaminated environments under mild conditions. Unfortunately, its large-scale implementation is restricted by the limited stability of extracellular enzymes. Semi-biological catalysis provides an attractive approach to address the current challenges. In this paper, we report the construction of defect-mediated enzyme-photo nanoarchitectures by coupling ultrathin carbon nitride nanosheets with horseradish peroxidase. We observed the significantly enhanced generation of reactive species over nitrogen-deficient carbon nitride. This abiotic/biotic hybrids not only provided on-demand stimuli for activating horseradish peroxidase into oxidation state, but also exhibited great potential for restraining the undesirable denaturation of extracellular enzymes. The synergistic effect between defect-engineered polymers and biological molecules contributed to the 13.2-fold increased oxidation degradation (0.0327 min−1) of methyl orange (MO) in wastewater compared to pristine carbon nitride (0.0024 min−1). This work opens a new avenue of modulating the enzymatic functionality through defect engineering for high-efficiency photobiocatalytic applications.

Incorporating nitrogen defects into novel few-layer carbon nitride nanosheets for enhanced photocatalytic H2 production

Carbon nitride nanosheets have shown a great promise for photocatalytic water splitting among numerous photocatalysts due to the versatile advantages. The crucial issues of the weak visible-light absorption and the separation of photo-generated carrier remain a matter of serious concern. Herein, we report a facile calcination-solvothermal-calcination method to prepare nitrogen-deficient carbon nitride nanosheets (DCNS) for the first time, which leads to the simultaneous introduction of nitrogen defects and formation of a fragmented few-layer nanosheet structure. The fragmented few-layer nanosheet structure is known to possess a high specific surface area and abundant interfacial reaction sites, contributing to the rapid consumption of photo-generated carrier. The nitrogen defects are responsible for further boosting the photocatalytic performance by regulating the band structure and optical properties as well as improving the separation efficiency of photo-generated carrier. The optimized DCNS-120 delivers a superior H2 production rate of 5375 μmol·g−1·h−1, considerably higher than that of bulk carbon nitride (164 μmol·g−1·h−1). We anticipate that this work may pave a new pathway to engineering carbon nitride with a matched structure to achieve the desired efficient photocatalytic H2 production under visible-light irradiation.

Unique nitrogen-deficient carbon nitride homojunction prepared by a facile inserting-removing strategy as an efficient photocatalyst for visible light-driven hydrogen evolution

Efficiently improving photocatalytic efficiency of carbon nitride (g-C3N4), a promising candidate, for H2 production is of great significance but remains a challenge. Herein, a unique N-deficient g-C3N4 homojunction (I/R-CN) prepared by an inserting-removing strategy via thermal polymerization of a freeze-dried mixture containing dicyandiamide, NH4Cl, and a prepolymer from 3-amino-1,2,4-triazol (3-AT) is reported, in which the prepolymerization process of 3-AT under optimized conditions is indispensible. I/R-CN features the N-deficient g-C3N4 microdomains (NDMD) from prepolymer inserting into a porous N-defects modified g-C3N4 with two kinds of N defects (N vacancies and cyano groups) formed by removing N atoms from the skeleton of g-C3N4, unambiguously confirmed by various characterizations. I/R-CN exhibits notably promoted photocatalysis with a high H2 evolution rate of 3882.5 μmol h−1 g−1 and a large apparent quantum yield of 8.6 % at 420 nm, originating from the efficient recombination inhibition of electron-hole pairs by the markedly promoted charge mobility as well as the improved light absorption capacity and enlarged reduction potential. This work paves a new avenue for designing other highly-efficient carbon nitride photocatalysts for solar applications.

Densely colonized isolated Cu-N single sites for efficient bifunctional electrocatalysts and rechargeable advanced Zn-air batteries

The rational design of earth-abundant, highly efficient, and robust bifunctional oxygen electrocatalysts remains a contemporary challenge toward the widespread implementation of reversible metal-air batteries and fuel cells. Here, we report a universal strategy for the fabrication of single-atom (Cu, Co, and Fe) incorporated hollow nano-spheroids of nitrogen-deficient carbon nitride frameworks (CuSA@HNCNx. The interconnected three-dimensional 3D porous and hollow robust single-atom spheroid frameworks display a high surface area of 1286 m2 g−1, favorable electronic structure, local chemical coordination, effective density of active sites (Cu-Nx, pyridinic, graphitic CN etc.), and mass transport pathways. The obtained CuSA@HNCNx exhibited outstanding bifunctional reversible electrocatalytic activity and robustness for oxygen reduction and evolution reactions (ORR half-wave potential of 0.91 V, OER overpotential of 1.55 V at 10 mA cm-2, ΔE = 0.64 V, 5000 cycles), outperforming benchmarked Pt/C and RuO2. Electrocatalytic activity towards ORR/OER was analyzed by d-band center correlation using density functional theory (DFT) calculations. Moreover, reversible alkaline Zn-air batteries with the designed CuSA@HNCNx cathode illustrated a high power 212 mW cm-2, high energy density 1031 Wh kgZn−1, and excellent discharge-charge cycle life of 1800 cycles for 300 h @10 mA cm-2 with voltaic efficiency of 64.51 %. Notably, all-solid-state flexible ZABs showed long cycle life of 250 h with 1500 cycles at 25 mA cm-2 with efficiency of 66.31 %. This unique strategy offers controlled design of entangled single-atom frameworks as advanced cathodes for next-generation energy storage technology.

Double defective group modified nitrogen-deficient carbon nitride with bimetallic PtSn as a cocatalyst for efficient photocatalytic hydrogen evolution up to 765 nm.

Cyano- and urea-defective group co-modified nitrogen-deficient carbon nitride with PtSn as a cocatalyst was constructed to optimize the optical and electronic structure as well as the photocatalytic activity. Defective engineering over carbon nitride gave rise to a stronger light absorption in the visible and near-infrared regions, more negative conduction band edge potential and more efficient separation behavior of photogenerated charge carriers. The optimal photocatalyst exhibited a high hydrogen yield of 2.96 mmol g-1 h-1 with an apparent quantum yield of 8.42% at 435 nm. Moreover, the photocatalytic hydrogen generation capability was maintained under illumination up to 765 nm with an apparent quantum yield of 0.076%.

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).

Boosting photocatalytic hydrogen evolution rate over carbon nitride through tuning its crystallinity and its nitrogen composition

The photocatalytic activity of graphitic carbon nitride (CN) is mainly restricted by its high recombination rate of charge carriers and narrow visible light absorption. In the present work, nitrogen-deficient CN (NDCCN) nanosheets with high crystallinity were synthesized using molten salt (NaLiCO3) as an etching agent and high-temperature solvent. The electronic structure and energy band levels of the obtained NDCCN are optimized to extend its optical absorption and enhance separation efficiency of photo-generated charge carriers. With these changes, NDCCN displays high photocatalytic activity for hydrogen evolution under visible light illumination (111 μmol h−1), which is 4.6 times of that over pristine CN. This finding opens up a new window to simultaneously decrease nitrogen composition and increase crystallinity of carbon nitride for higher solar-light-driven hydrogen production efficiency.

Visible-light-driven photoreduction of CO2 to CO over porous nitrogen-deficient carbon nitride nanotubes

The solar energy-driven photoreduction of CO2 with H2O to hydrocarbon fuels is an interesting but challenging topic.