Pristine Carbon Nitride Research Articles

Performance and mechanism insights into S-doped superhydrophilic carbon nitride for photocatalytic hydrogen evolution and degradation

Carbon nitride (CN) photocatalyst possesses great potential in alleviating energy and environmental crisis, while the insufficient active sites exposure, limited light harvest and poor charge behavior, as well as inferior dispersibility in water limit its photocatalytic activity. In this research, a loose porous crimp S doped CN photocatalyst with superhydrophilicity was tailored via facile one-pot thermal-melting followed thermal induce copolymerization of urea with 2-mercaptonicotinic acid. The dope of 2-mercaptonicotinic acid leads to the significant enhancement of specific surface area, range/intensity of visible-light harvest and charge behavior, as well as hydrophilicity of CN. The photocatalytic hydrogen evolution rate achieves a remarkable improvement of 7.61 times compared to CN alone, reaching 88.14 μmol h−1. Additionally, the photodegradation of tetracycline is enhanced by approximately 3.96 times compared to pristine CN, resulting in a degradation efficiency of 90.5 %. Via active species capture tests, ESR, LC-MS, toxicity prediction and DFT calculations, the main active species, degradation pathway, intermediates toxicity and promoted mechanism of photocatalytic performance are explored. This study presents a straightforward and cost-effective approach to enhance the intrinsic activity of CN-based photocatalysts by simultaneously regulating their active sites exposure, light absorption and charge behavior for addressing environmental and energy concerns.

Phosphorus-doped carbon nitride for enhanced supercapacitor performance and energy storage applications

Exploiting the advantages of graphitic carbon nitride doped with phosphorus (xP-CN) electrodes were designed for high-performance hybrid asymmetric supercapacitor via facile hydrothermal and thermal decomposition techniques. The structural, surface chemistry, functional and morphological characterizations evidence depict successful phosphorus incorporation in Carbon Nitride (CN). X-ray photoelectron spectroscopy analysis shows that phosphorus (P) atoms have replaced corner carbon atoms in the CN structure. These findings clearly demonstrate that the presence of phosphorus doping improves the electrochemical activity of the electrodes. The designed three-electrode system has a specific capacitance of 189.36 F/g with a current density of 1 A/g. Phosphorus doping has been discovered to play a significant role in improving both specific capacitance and cycling stability. The capacitance retention of the two-electrode solid-state device has 97.2 % after 5000 cycles. These electrochemical evaluations reveal that the xP-CN electrode exhibits superior electrochemical performances than pristine CN. This doping strategy for CN presents a novel and efficient approach for crafting high-performance supercapacitors.

Surface Nanojunction Enabled by Vapor‐Assisted π‐Conjugation Modification of Carbon Nitride for Enhanced Photocatalytic Water Splitting

The unsatisfied visible light harvesting, slow charge separation, and limited practical surface area of carbon nitride (CN) constrain its performance in photocatalytic water splitting and environmental remediation. Herein, the thermal vapor‐assisted π‐conjugation modification of CN by grafting with p‐aminophenoxy groups was developed to tune the photophysical properties of CN to enhance its photocatalytic activity. Besides extending the light absorption, the surface modification constructed a nanojunction across the depth direction, which leads to facilitated charge separation and transfer. In addition, the thermal vapor modification process thermally etches and trims the pristine CN to be highly holey structure, resulting to >10 times increase in specific surface area. Photocatalysis results showed that the obtained modified CN yielded hydrogen from photocatalytic water splitting at a rate of 7.82 mmol/g/h, over 7‐folds as that of pristine CN, with quantum yield of 3.28% at 400 nm. The π‐conjugation modified CN also demonstrated enhanced photocatalytic environmental remediation application, exemplified by much faster photodegradation of tetracycline hydrochloride. This work provides the thermal vapor surface chemical modification of CN as a promising integrated pathway of multiple favorable photophysical properties towards efficient photocatalysis application.

At least five: Benefit origins of potassium and sodium co-doping on carbon nitride for integrating pharmaceuticals degradation and hydrogen peroxide production

Benefit origins of potassium (K+) and sodium (Na+) co-doping on carbon nitride for integrating pharmaceutical degradation and hydrogen peroxide (H2O2) production was investigated. K+ and Na+ co-doped carbon nitride (CN-K/Na) with modified crystallinity and surface structure was synthesized by ionothermal polymerization of urea. The CN-K/Na exhibited an apparent quantum yield of 26.2% in H2O2 photosynthesis at 400nm (isopropanol as proton donor), and it was better at extracting proton from pharmaceutical-laden wastewater to produce H2O2 than pristine carbon nitride. These superior performances are attributed to the benefits directly or indirectly caused by the co-doping: i) Na+ optimizes in-plane charge transfer, ii) K+ builds channel for interplane charge transfer, iii) cyano group as Lewis acid site adsorbs and activates oxygen, iv) amino group as Lewis base site extracts and releases protons, v) increased visible-light absorption. This work offers significant insights into designing polymeric photocatalysts for environmental management and energy conservation.

Synergy of P doping and crystallinity modulation in carbon nitride for enhancing photocatalytic uranyl reduction

Doping modification is a useful way to promote the catalytic activity of carbon nitride (CN). However, most doped CNs have lower structural symmetry and several edge defects, which hinder the transfer of charge carriers. This work reports a P-doped crystalline carbon nitride (crystalline PCN) for the efficient photoreduction of uranyl. The thermal polymerization and salt post-treatment convert the amorphous PCN into crystalline PCN. Compared to the pristine CN, the crystalline PCN has over 1620 % higher activity for uranyl (U(VI)) reduction, reaching a 97.8 % reduction rate in 60 min. Furthermore, the 2-PCN shows excellent stability and a U(VI) removal efficiency >85.7 % in the pH range of 5–8. Characterization analysis reveal that both the P doping and crystalline modulation do not obviously change their morphology, light absorption property and energy band structure, but markedly promote the delocalization of electrons around the doped P atoms, thereby severely inhibit direct electron-hole recombination. Thus, the more efficient separation of charge carriers generates more reactive specials to participate in the photocatalytic uranyl reduction reaction. This study demonstrates a dual-modification strategy for the rational synthesis of highly active metal-free CN-based photocatalysts for uranyl reduction.

Polychloride and benzene ring synergistically boosting photocatalytic degradation and nitrogen fixation performances of carbon nitride

The limited active site exposure, insufficient light absorption and poor charge behavior of carbon nitride (CN) limit its application in environmental remediation and clean energy production. In this study, ultrathin porous CN with enhanced photocatalytic activity was constructed by doping 2,2′,5,5′-Tetrachlorobenzidine (TB) into CN framework. The synergistic effect of polychloride and benzene rings on CN leads to the significant enhancement of range/intensity of visible-light harvest and charge behavior, as well as specific surface area. The optimal sample achieves 100% tetracycline photodegradation efficiency with a rate constant approximately 9 times of pristine CN, and total organic carbon removal efficiency reaches 78.2%. Moreover, photocatalytic ammonia production rate is 7 times of pristine CN. Through active species trapping experiments, ESR, LC-MS, toxicity prediction and DFT calculations, the main active species, degradation pathway, intermediates toxicity and enhanced mechanism of photocatalytic activity are investigated. This work provides a reference for simultaneously regulating the morphology, light absorption and charge behavior of CN-based photocatalyst for addressing environmental and energy concerns.

Construction of dual driving force in carbon nitride for highly efficient hydrogen evolution: Simultaneously manipulating carriers transport in intra- and interlayer

Photocatalytic hydrogen evolution is widely recognized as an environmentally friendly approach to address future energy crises and environmental issues. However, rapid recombination of photo-induced charges over carbon nitride in lateral and vertical direction hinder this process. Herein, we proposed an effective strategy involving the embedding of benzene rings and the intercalation of platinum atoms on carbon nitride for a controlled intralayer and interlayer charges flow. Modified carbon nitride exhibits a significant higher hydrogen evolution rate (6288.5 μmol/g/h), which is 42 times greater than that of pristine carbon nitride. Both experiments and simulations collectively indicate that the improved photocatalytic activities can be attributed to the adjustment of the highly symmetric structure of carbon nitride, achieved by embedding benzene rings to induce the formation of an intralayer build-in electric field and intercalating Pt atoms to enhance interlayer polarization, which simultaneously accelerate lateral and vertical charges migration. This dual-direction charges separation mechanism in carbon nitride provides valuable insights for the development of highly active photocatalysis.

Molecular Terpyridine-Lanthanide Complexes Modified Carbon Nitride for Enhanced Photocatalytic CO2 Reduction.

Molecule/semiconductor hybrid catalysts, which combine molecular metal complexes with semiconductors, have shown outstanding performances in photocatalytic CO2 reduction. In this work, we report two hybrid catalysts for the selective photoreduction of CO2 to CO. One is composed of carbon nitride and a terpyridine-Lu complex (denoted as LutpyCN), and the other is composed of carbon nitride and a terpyridine-Ce complex (denoted as CetpyCN). Compared with pristine carbon nitride, the hybrid catalysts LutpyCN and CetpyCN display a noteworthy increase in CO generation, boosting the yield by approximately 176 times and 106 times, respectively. Mechanistic studies demonstrate that such significant enhancement in photocatalysis is primarily due to more efficient separation of photogenerated carriers for hybrid catalysts after modifying CN with molecular terpyridine-lanthanide species.

Bidirectional heterojunctions photocatalyst engineered with separated dual reduction sites for hydrogen evolution

Photocatalytic technology is identified as one of the most clean and sustainable routes for hydrogen generation. Nonetheless, inadequate photoinduced carrier separation limits photocatalytic performance. Rationally designing bidirectional heterojunctions that leverage single/two-photon co-excitation pathways and dual reduction sites, thereby inhibiting recombination of the photoinduced carriers and exposing active sites to increase photocatalytic activity. This study proposes bidirectional heterojunctions consisting of 0D carbon dots (CDs) and nickel phthalocyanines co-modified sulfur-doped multivesicular carbon nitride tubes (denoted as 7CDs/SMVCTs/Ni0.5 %). The as-prepared photocatalyst displays a remarkable yield of 16,363.62 μmol g−1 h−1, with a rate 23.2 times that of pristine carbon nitride (denoted as PCN, 704.23 μmol g−1 h−1). The improvement of photocatalytic performance is attributed to the efficient separation and transportation of photoexcited electron-hole pairs induced by the coexistence of single/two-photon excitation pathways and dual reduction sites. The efficient combination of lateral and vertical heterostructures plays an essential role in the photocatalytic process and is exhaustively studied using catalyst rational design and modification technology.

Important role of carbon doping in photocatalytic peroxymonosulfate activation of carbon nitride for efficient 4-Chlorophenol degradation

In order to improve the photocatalytic activity of pristine carbon nitride while maintaining its metal-free property to achieve the activation of peroxymonosulfate (PMS), a series of carbon-doped g-C3N4 (BCN) with different carbon contents were synthesized in this paper by adding benzotriazole to urea. The catalyst obtained by this approach significantly promoted PMS activation and enhanced the degradation efficiency of 4-chlorophenol (4-CP). Experiments and theoretical calculations showed that the introduction of carbon not only narrowed the band gap, but also accelerated the separation of photoinduced electron-hole pairs, which greatly improved the photocatalytic activity of g-C3N4. In the degradation of pollutants, free radicals and non-free radicals acted simultaneously, with non-free radicals playing a dominant role. This study explained the origin of 1O2 by Density functional theory (DFT) calculations, visible light excited photocatalysts to form holes, while carbon introduction decreased the valence-electron density around the area, inducing electron transfer from PMS toward g-C3N4 directed to generate 1O2. The 1O2-dominated degradation process improved the application of the catalysts in complex aqueous matrices. In addition, we proposed 4-CP degradation pathways, and the toxicity of intermediates derived from 4-CP degradation process reduced.

Significant augmentation of hydrogen and benzaldehyde production through mediator-free in-situ synthesis of CuNi/CN photocatalysts for benzyl alcohol splitting

Amidst growing concerns surrounding global warming and energy scarcity, there is an urgent demand for more efficient and environmentally friendly methods of hydrogen production. In response, we introduce a novel mediator-free in-situ approach for synthesizing CuNi/CN composite photocatalysts. This method entails the synthesis of copper and nickel complexes to fabricate bimetallic Cu and Ni nanoparticles on carbon nitride (CN). These catalysts are deployed for the photocatalytic dehydrogenation of benzyl alcohol, resulting in the generation of hydrogen and benzaldehyde. The CuNi bimetal-loaded CN structure provides ample active sites and demonstrates a low hydrogen reduction overpotential, thereby enhancing both charge separation and surface hydrogen reduction processes. In comparison to pure CN, the composite photocatalyst exhibits significantly improved photocatalytic activity. Notably, the composite 2 % Cu1Ni1/CN photocatalyst achieves a record-high hydrogen production rate of about 80 μmol g-1h−1, representing an impressive increase of approximately 533 times compared to pristine CN. Moreover, the catalyst offers cost-effectiveness, ease of preparation, and reusability, ensuring stable hydrogen production efficiency over multiple cycles. This precious metal-free composite photocatalyst not only facilitates the synthesis of valuable compounds but also promotes sustainable advancements in efficient hydrogen energy generation.

Introducing Br, K, and cyano group into carbon nitride for efficient photocatalytic hydrogen peroxide production then in situ tetracycline mineralization

In this work, Br, K-doped and cyano group-rich carbon nitride (CN) were prepared via pyrolysis of molten urea and 6-Bromopyridine-3-carbaldehyde, followed by re-calcination with potassium thiocyanate. The hydrogen peroxide (H2O2) evolution and in situ tetracycline (TC) mineralization performances of the prepared samples were studied. The optimal sample could produce 9127 μmol g–1 h–1 H2O2 from 10 vol% ethanol solution and air atmosphere, which was 10.9 times higher than that of pristine CN. With addition of 4 mg L–1 Fe2+ ions, 97.2% of TC (10 mg L–1) and 98.7% of total organic carbon were removed in 30 min under the actions of holes, hydroxyl and superoxide radicals. The high H2O2 yield and TC mineralization ratio were attributed to the increased light absorption, efficient electrons-holes separation, enhanced surface O2 adsorption (0.3878 mmol g−1), and accelerated conversion from Fe3+ to Fe2+ ions. Meanwhile, the system possessed good reusability in H2O2 evolution and TC removal. It is expected that this work can provide new ideas to design CN-based photo-Fenton system to treat wastewater.

Synergy of sodium doping and nitrogen defects in carbon nitride for promoted photocatalytic synthesis of hydrogen peroxide

Photocatalytic synthesis of hydrogen peroxide has gradually become a promising method for in-situ production of hydrogen peroxide, which relies on sustainable solar energy. However, the commonly used photocatalyst, i.e., carbon nitride (CN), still suffers from the drawbacks of narrow light absorption range and fast charge recombination. Here, we report a facile method to introduce nitrogen defects into carbon nitride together with sodium ion. By adjusting the ratio of sodium dicyandiamide, the band gap of carbon nitride can be controlled, while the carrier separation and transfer ability of carbon nitride is improved. The modified CN with sodium doping and nitrogen defect (SD-CN) demonstrates outstanding H2O2 production performance (H2O2 yield rate of 297.2 µmol L−1 h−1) under visible light irradiation, which is approximately 9.8 times higher than that of pristine CN. This work deepens the understanding of the coordinated effect of structural defect and element doping of carbon nitride on the photocatalytic H2O2 production performance, and provides new insight into the design of photocatalytic system for efficient production of H2O2.

Defect Engineering Simultaneously Regulating Exciton Dissociation in Carbon Nitride and Local Electron Density in Pt Single Atoms Toward Highly Efficient Photocatalytic Hydrogen Production.

The high exciton binding energy (Eb) and sluggish surface reaction kinetics have severely limited the photocatalytic hydrogen production activity of carbon nitride (CN). Herein, a hybrid system consisting of nitrogen defects and Pt single atoms is constructed through a facile self-assembly and photodeposition strategy. Due to the acceleration of exciton dissociation and regulation of local electron density of Pt single atoms along with the introduction of nitrogen defects, the optimized Pt-MCT-3 exhibits a hydrogen production rate of 172.0µmolh-1 (λ ≥ 420nm), ≈41 times higher than pristine CN. The apparent quantum yield for the hydrogen production is determined to be 27.1% at 420nm. The experimental characterizations and theoretical calculations demonstrate that the nitrogen defects act as the electron traps for the exciton dissociation, resulting in a decrease of Eb from 86.92 to 43.20meV. Simultaneously, the stronger interaction between neighboring nitrogen defects and Pt single atoms directionally drives free electrons to aggregate around Pt single atoms, and tailors the d-band electrons of Pt, forming a moderate binding strength between Pt atoms and H* intermediates.

Carbon nitride coupled with carbon nanohorns for improved photocatalytic hydrogen production and dyes degradation

In the present study we attempted to develop photoactive nanocomposites via the facile coupling of carbon nitride (CN) with single walled carbon nanohorns (CNHs). Photocatalytic activity was evaluated for the degradation of Rhodamine B (RhB) and the production of H2. The CNHs content noticeably affected the photoactivity of the nanocomposites and the best performing material exhibited a 3-fold increase in photocatalytic H2 production compared to pristine CN using 1 wt% Pt as co-catalyst. A systematic study was undertaken to explain the mechanistic aspects of the photo-reaction process. The active species responsible for the photodegradation of RhB were identified using reference reactions. Such species were further studied using in-situ spin-trap EPR experiments. Photoluminescence and time-resolved fluorescence decay kinetics suggested faster transfer of photogenerated electron/hole pairs resulting in reduced charge recombination phenomena in the nanocomposites. The combined photocatalytic application and characterization of the prepared materials revealed that the promotion of the redox reactions in based on improvements on the charge separation efficiency.

Oxygen vacancy-rich CoMoO4/Carbon nitride S-scheme heterojunction for boosted photocatalytic H2 production: Microstructure regulation and charge transfer mechanism

Developing highly efficient S-scheme photocatalysts is a subject of immense interest for harnessing solar energy towards sustainable hydrogen production. Herein, a novel S-scheme heterojunction of oxygen vacancy-rich CoMoO4/CN (CMO/CN) photocatalyst was rationally constructed through loading CoMoO4 nanorods on carbon nitride (CN) nanosheets via a direct one-pot calcination method. The CMO/CN S-scheme heterojunction exhibited enhanced surface area, fine CN dispersion, rich oxygen vacancies, and accelerated charge separation/transfer efficiency, which were conducive to improving photocatalytic H2 evolution performance. Of note, the optimal 3 %CMO/CN sample displayed the highest H2 production rate of 8.35 mmol g−1 h−1, which is 4.6 folds that of pristine CN. In situ irradiated X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) characterizations confirmed the S-scheme charge transfer path between CN and CMO, which greatly promoted spatial charge separation. Density functional theory (DFT) calculations together with contact angle tests revealed the reduced activation energies for H2O dissociation and enhanced hydrophilicity of the CMO/CN. The CMO/CN photocatalysts also presented high stability and fine reusability. This work may provide insights into the combination of defect engineering and heterojunction designing for high-efficiency solar-to-chemical energy conversion.

Enhanced hydrogen peroxide production and organic substrates degradation using atomically dispersed antimony P-doped carbon nitride photocatalysts

In this work atomically dispersed antimony P-doped carbon nitride was prepared with the aim of producing hydrogen peroxide under visible light irradiation and of obtaining organic contaminants degradation. The conjugation of the P-doping can induce significant increase in visible light harvesting, narrowing of band gap energy and shift of the upper edge of the VB to less positive value and the introduction of Sb can efficiently trap oxygen molecules in the Sb-OO end-on structure and at the same time accumulate electrons which act as the photoreduction sites for O2 via a 2e− ORR pathway. Pristine C3N4 and P-doped C3N4 were prepared as references using melamine and ammonium dihydrogen phosphate as precursors and different amount of Sb were added (x = 0.5, 1, 3, 5 mmol) to synthetize Sbx P-doped C3N4. All materials were characterized with multiple techniques, tested for the hydrogen peroxide production and for the degradation of carbamazepine. The pristine C3N4 led to a H2O2 poor production but with the introduced modifications the yield increased and an upward trend during the time was observed. The optimum amount of Sb was found to be 1 mmol and it led to the production of more than 7 times the amount produced by pristine carbon nitride. The degradation of carbamazepine using only visible radiation required prolonged timescales but when we expand the light spectrum to include near-UV, the abatement of the pollutant is achieved in a few hours. The efficiency of the synthesized materials in hydrogen peroxide production suggests possible future developments that take advantage of the excellent peroxide production of atomically dispersed antimony P-doped carbon nitride photocatalysts in Fenton-like processes or involve the use of peroxidase enzymes to achieve enhanced degradative performances.

Synergizing copolymerization and thermal induction for carbon nitride: Reinforcing photocatalytic performance and mechanism insight

Structure optimization of photocatalyst graphitic carbon nitride (CN) is still a key endeavor. CN nanosheets were prepared via a facile one-pot copolymerization process, incorporating electron-withdrawing groups 5-cyanopyrimidine (CPM) and melamine under calcination. The synergistic effect of molecular doping and thermal induction effectively modulates the intrinsic electronic and band structure of CN. The post-optimized sample (CNMCPM0.03–700) exhibits a higher reduction potential, reduced nanosheet thickness, stronger crystallinity, and enhanced electron-holes separation efficiency, compared to pristine CN (CNM). Notably, significant morphological and textural alterations were observed in the modified CNMCPMX-T samples. Consequently, a remarkable enhancement in visible-light photocatalytic H2 evolution and CO2 reduction performance was achieved. Specifically, the CNMCPM0.03–700 retained an H2 evolution rate of 166.4 µmol·h−1, which was 14.8-fold higher than that of CNM (11.3 µmol·h−1), along with a 31.6-fold increase in CO evolution efficiency. Molecular and textural engineering demonstrate their universal applicability for different comonomers. This study showcases the feasibility of synergizing thermal induction and copolymerization strategies for synthesizing high-efficiency CN-based photocatalysts with unique topology and structural precision.

Defect and nanostructure engineering of polymeric carbon nitride for visible-light-driven CO2 reduction

Sunlight-induced photocatalytic carbon dioxide (CO2) reduction to energy-rich chemicals by metal-free polymeric carbon nitride (CN) semiconductor is a promising tactic for sustained solar fuel production. However, the reaction efficiency of CO2 photoreduction is restrained seriously by the rapid recombination of photogenerated carriers on CN polymer. Herein, we incorporate 2-aminopyridine molecule with strong electron-withdrawing group into the skeleton edge of CN layers through a facile one-pot thermal polymerization strategy using urea as the precursor, which renders a modified carbon nitride (ACN) with extended optical harvesting, abundant nitrogen defects and ultrathin nanosheet structure. Consequently, the ACN photocatalyst with desirable structural features attains enhanced separation and migration of photoexcited charge carriers. Under visible light irradiation with Co(bpy)32+ as a cocatalyst, the optimized ACN sample manifests a high CO2 deoxygnative reduction activity and high stability, providing a CO yielding rate of 17 μmol h−1, which is significantly higher than that of pristine CN. The key intermediates engaged in CO2 photoreduction reaction are determined by the in situ diffuse reflectance infrared Fourier transform spectroscopy, which sponsors the construction of the possible photocatalytic CO2 reduction mechanism on ACN nanosheets.

Enhancing the Photoluminescence and Electroluminescence of Graphitic Carbon Nitride via Atomic and Molecular Co-modification.

Graphitic carbon nitride (g-CN) materials exhibit attractive optoelectronic physical properties; however, their low photoluminescence quantum yields (PLQYs) limit their applications in luminescent devices. Here, boron-doped aromatic carbon nitride (B-PhCNx) was synthesized for the first time via direct thermal polymerization of 2,4-diamino-6-phenyl-1,3,5-triazine and boric acid. The impact of B doping and phenyl modifying on the structural and optical characteristics of the samples was investigated in detail. The highest PLQY of 40.7% was achieved in B-PhCN20, which is 6.8 times that of pristine carbon nitride (p-CN). The B-PhCN20-based light-emitting diode demonstrates a maximum luminance of 1494 cd m-2 and a maximum external quantum efficiency of 1.03%, which are 3.5 and 4.9 times that of the p-CN-based device, respectively. Our findings will provide a reference for rationally designing low-cost and high-performance carbon-nitride-based optoelectronic devices.