Insight into structure evolution of carbon nitrides and its energy conversion as luminescence

A series of carbon nitride(CN)materials represented by graphitic carbon nitride(g-C_(3)N_(4))have been widely used in bioimaging,biosensing,and other fields in recent years due to their nontoxicity,low cost,and high luminescent quantum efficiency.What is more attractive is that the luminescent properties such as wavelength and intensity can be regulated by controlling the structure at the molecular level.Hence,it is time to summarize the related research on CN structural evolution and make a prospect on future developments.In this review,we first summarize the research history and multiple structural evolution of CN.Then,the progress of improving the luminescence performance of CN through structural evolution was discussed.Significantly,the relationship between CN structure evolution and energy conversion in the forms of photoluminescence,chemiluminescence,and electrochemiluminescence was reviewed.Finally,key challenges and opportunities such as nanoscale dispersion strategy,luminous efficiency improving methods,standardization evaluation,and macroscopic preparation of CN are highlighted.

First-principles studies of the vibrational properties of amorphous carbon nitrides

Raman spectra of amorphous carbon nitride films （a-C：N） resemble those of typical amorphous carbon （a-C）, and no specific features in the spectra are shown due to N doping. The present work provides a correlation between the microstructure and vibrational properties of a-C：N films from first principles. The six periodic model structures of 64 atoms with various mass densities and nitrogen contents are generated by the liquid-quench method using Car-Parinello molecular dynamics. By using Raman coupling tensors calculated with the finite electric field method, Raman spectra are obtained. The calculated results show that the vibrations of C=N could directly contribute to the Raman spectrum. The similarity of the Raman line shapes of N-doped and N-free amorphous carbons is due to the overlapping of C=N and C=C vibration bands. In addition, the origin of characteristic Raman peaks is also given.

The origins of the broadband photoluminescence from carbon nitrides and applications to white light emitting

Carbon nitrides synthesized by thermal polycondensation of melamine at 700 ~C exhibit photoluminescence （PL） ranging from 400 to 650 nm. This broad PL is attributed to band to band transitions and bandtail transitions of lone pair （LP） states of intra-tri-s-triazine and inter-tri-s-triazine nitrogens. The proposed PL mechanism is further confirmed by diffusion reflectance spectroscopy, as well as time-resolved and temperature-dependent PL. This intense fluorescence is stable at different pH and resistant to UV exposure, suggesting that this inexpensive broadband luminescent material could be significant for white- light-emitting （WLE） applications. Thus, quasi-WLE films and membranes with designed patterns are fabricated by embedding the carbon nitrides into polymethyl methacrylate. Moreover, even broader PL （400 to 740 nm） is acquired in com- posite films composed of carbon nitrides, further suggesting that the carbon nitrides are robust candidates for WLE.

Molecular engineering of carbon nitrides for overall photosynthesis of H_(2)O_(2)

Artificial photocatalysis offers a promising strategy to sustainably produce hydrogen peroxide(H_(2)O_(2))that is one of the most valuable multifunctional chemicals.Among various photocatalysts,polymeric carbon nitride(pCN)has drawn continuous attention in non-sacrificial H_(2)O_(2)production.However,the poor activ-ity of half reactions,ie.,the oxygen reduction reaction(ORR)and water oxidation reaction(WOR),greatly restricts the efficiency of photocatalytic H_(2)O_(2) production.In this highlight,we discuss the significant ad-vances in molecular engineering of carbon nitrides for H_(2)O_(2) photosynthesis and the importance of the deep understanding of the photocatalysis process for rational design and reaction pathways of organic conjugated polymers to address the growing H_(2)O_(2)demand.Furthermore,we summarize the emerging applications of photocatalytic H_(2)O_(2)productions beyond energy and environment.

Semi-heterogeneous photo-Cu-dual-catalytic cross-coupling reactions using polymeric carbon nitrides

A merger of copper catalysis and semiconductor photocatalysis using polymeric carbon nitride(PCN)for multi-type cross-coupling reactions was developed.This dual-catalytic system enables mild C-H arylation,chalcogenation,and C-N cross-coupling reactions under visible light irradiation with a broad substrate scope.Good-to-excellent yields were obtained with appreciable site selectivity and functional group tolerance.Metal-free and low-cost PCN photocatalyst can easily be recovered and reused several times.

Novel multifunctional epoxy based graphitic carbon nitride/silanized TiO_(2)nanocomposite as protective coatings for steel surface against corrosion and flame in the shipping industry

The chemical compound 3-(N-ethylamino)isobutyl)trimethoxysilane(EAMS)modified titanium dioxide(TiO_(2)),producing EAMS-TiO_(2),which was encased in graphitic carbon nitride(GCN)and integrated into epoxy resin(EP).The protective properties of mild steel coated with this nanocomposite in a marine environment were assessedusing electrochemical techniques.Thermogravimetric analysis(TGA)and Cone calorimetry tests demonstrated thatGCN/EAMS-TiO_(2)significantly enhanced the flame retardancy of the epoxy coating,reducing peak heat release rate(PHRR)and total heat release(THR)values by 88%and 70%,respectively,compared to pure EP.Salt spray testsindicated reduced water absorption and improved corrosion resistance.The optimal concentration of 0.6 wt%GCNEAMS/TiO_(2)yielded the highest resistance,with the nanocomposite achieving a coating resistance of 7.50×10^(10)Ω·cm^(2)after 28 d in seawater.The surface resistance of EP-GCN/EAMS-TiO_(2)was over 99.9 times higher than pure EP after onehour in seawater.SECM analysis showed the lowest ferrous ion dissipation(1.0 nA)for EP-GCN/EAMS-TiO_(2)coatedsteel.FE-SEM and EDX analyses revealed improved breakdown products and a durable inert nanolayered covering.Thenanocomposite exhibited excellent water resistance(water contact angle of 167°)and strong mechanical properties,withadhesive strength increasing to 18.3 MPa after 28 d in seawater.EP-GCN/EAMS-TiO_(2)shows potential as a coatingmaterial for the shipping industry.

Hybrid 2D/3D Graphitic Carbon Nitride-Based High-Temperature Position-Sensitive Detector

Ultraviolet position-sensitive detectors(PSDs)are expected to undergo harsh environments,such as high temperatures,for a wide variety of applications in military,civilian,and aerospace.However,no report on relevant PSDs operating at high temperatures can be found up to now.Herein,we design a new 2D/3D graphitic carbon nitride(g-C_(3)N_(4))/gallium nitride(GaN)hybrid heterojunction to construct the ultraviolet high-temperature-resistant PSD.The g-C_(3)N_(4)/GaN PSD exhibits a high position sensitivity of 355 mV mm^(-1),a rise/fall response time of 1.7/2.3 ms,and a nonlinearity of 0.5%at room temperature.The ultralow formation energy of-0.917 eV atom^(-1)has been obtained via the thermodynamic phase stability calculations,which endows g-C_(3)N_(4)with robust stability against heat.By merits of the strong built-in electric field of the 2D/3D hybrid heterojunction and robust thermo-stability of g-C_(3)N_(4),the g-C_(3)N_(4)/GaN PSD delivers an excellent position sensitivity and angle detection nonlinearity of 315 mV mm^(-1)and 1.4%,respectively,with high repeatability at a high temperature up to 700 K,outperforming most of the other counterparts and even commercial silicon-based devices.This work unveils the high-temperature PSD,and pioneers a new path to constructing g-C_(3)N_(4)-based harsh-environment-tolerant optoelectronic devices.

Microwave-Assisted Confining Growth and Liquid Exfoliation of sp^(3)-Hybrid Carbon Nitride Nano/Micro-Crystals

As one promising carbon-based material,sp^(3)-hybrid carbon nitride has been predicted with various novel physicochemical properties.However,the synthesis of sp^(3)-hybrid carbon nitride is still limited by the nanaoscale,low crystallinity,complex source,and expensive instruments.Herein,we have presented a facile approach to the sp^(3)-hybrid carbon nitride nano/micro-crystals with microwave-assisted confining growth and liquid exfoliation.Actually,the carbon nitride nano/micro-crystals can spontaneously emerge and grow in the microwave-assisted polymerization of citric acid and urea,and the liquid exfoliation can break the bulk disorder polymer to retrieve the highly crystalline carbon nitride nano/micro-crystals.The obtained carbon nitride nano/micro-crystals present superior blue light absorption strength and surprising photoluminescence quantum yields of 57.96% in ethanol and 18.05%in solid state.The experimental characterizations and density functional theory calculations reveal that the interface-trapped localized exciton may contribute to the excellent intrinsic light emission capability of carbon nitride nano/micro-crystals and the interparticle staggered stacking will prevent the aggregation-caused-quenching partially.Finally,the carbon nitride nano/micro-crystals are demonstrated to be potentially useful as the phosphor medium in light-emitting-diode for interrupting blue light-induced eye damage.This work paves new light on the synthesis strategy of sp^(3)-hybrid carbon nitride materials and thus may push forward the development of multiple carbon nitride research.

Advances in Polymeric Carbon Nitride Photocatalysts for Enhanced CO_(2)Reduction

Photocatalysis has emerged as a promising alternative for converting and utilizing CO_(2).Polymeric carbon nitride(PCN),typically synthesized through the one-step thermal polycondensation of nitrogen-rich precursors,has shown considerable promise due to its adjustable band structure and inherent safety.Over the past five years,significant literature in this field has identified five primary methods for modifying PCN:morphology modulation,element doping,defect induction,co-catalyst loading,and heterojunction construction.A detailed discussion on how each modification method influences light absorption,charge separation,and surface reaction efficiencies in photocatalysis is provided.Based on these findings,several future directions for the development of PCN-based materials are proposed,such as designing tailored PCN structures for specific photocatalytic reactions and using theoretical calculations to verify and correct results from current characterization methods.Despite the challenges associated with the large-scale synthesis of PCN materials with controllable structures and satisfactory performance,this work offers valuable insights for advancing photocatalytic PCN-based systems for large-scale solar fuel production.

Enhanced visible-light photocatalytic activity of Z-scheme graphitic carbon nitride/oxygen vacancy-rich zinc oxide hybrid photocatalysts

With the objectives of enhancing the stability,optical properties and visible-light photocatalytic activity of photocatalysts,we modified oxygen vacancy-rich zinc oxide（Vo-ZnO） with graphitic carbon nitride（g-C3N4）. The resulting g-C3N4/Vo-ZnO hybrid photocatalysts showed higher visible-light photocatalytic activity than pure Vo-ZnO and g-C3N4. The hybrid photocatalyst with a g-C3N4 content of 1 wt% exhibited the highest photocatalytic degradation activity under visible-light irradiation（λ≥ 400 nm）. In addition,the g-C3N4/Vo-ZnO photocatalyst was not deactivated after five cycles of methyl orange degradation,indicating that it is stable under light irradiation. Finally,a Z-scheme mechanism for the enhanced photocatalytic activity and stability of the g-C3N4/Vo-ZnO hybrid photocatalyst was proposed. The fast charge separation and transport within the g-C3N4/Vo-ZnO hybrid photocatalyst were attributed as the origins of its enhanced photocatalytic performance.

Vanadium supported on graphitic carbon nitride as a heterogeneous catalyst for the direct oxidation of benzene to phenol

A series of graphitic carbon nitride supported vanadium catalysts（xV/g-C3N4） with different vanadium contents（x/%） were prepared by impregnation.XRD,FT-IR,TEM,TG-DTG,nitrogen adsorption and XPS characterizations were conducted which revealed a strong interaction between the vanadium species and g-C3N4 support.8V/g-C3N4 exhibited the highest activity and showed stable recyclability in the benzene hydroxylation reaction with a benzene conversion of 24.6%and phenol selectivity of 99.2%under the optimized conditions.The excellent catalytic performance of xV/g-C3N4 was due to the integration of vanadium species with high catalytic activity and the g-C3N4support in their interaction with the benzene substrate.

DFT‑Guided Design and Fabrication of Carbon‑Nitride‑Based Materials for Energy Storage Devices:A Review

Carbon nitrides(including CN,C2N,C3N,C3N4,C4N,and C5N)are a unique family of nitrogen-rich carbon materials with multiple beneficial properties in crystalline structures,morphologies,and electronic configurations.In this review,we provide a comprehensive review on these materials properties,theoretical advantages,the synthesis and modification strategies of different carbon nitride-based materials(CNBMs)and their application in existing and emerging rechargeable battery systems,such as lithium-ion batteries,sodium and potassium-ion batteries,lithium sulfur batteries,lithium oxygen batteries,lithium metal batteries,zinc-ion batteries,and solid-state batteries.The central theme of this review is to apply the theoretical and computational design to guide the experimental synthesis of CNBMs for energy storage,i.e.,facilitate the application of first-principle studies and density functional theory for electrode material design,synthesis,and characterization of different CNBMs for the aforementioned rechargeable batteries.At last,we conclude with the challenges,and prospects of CNBMs,and propose future perspectives and strategies for further advancement of CNBMs for rechargeable batteries.

Enhanced photochemical oxidation ability of carbon nitride by π-πstacking interactions with graphene

A one-pot method for the preparation of g-C3N4/reduced graphene oxide（rGO） composite photocatalysts with controllable band structures is presented.The photocatalysts are characterized by Fouirer transform infrared spectroscopy,X-ray diffraction,scanning electron microscope,transmission electron microscope,and Mott-Schottky analysis.The valance band（VB） of g-C3N4 exhibits a noticeable positive shift upon hybridizing with rGO,and thus results in a strong photo-oxidation ability.The g-C3N4/rGO composites show a higher photodegradation activity for 2,4-dichlorophenol（2,4-DCP） and rhodamine B（RhB） under visible light irradiation（λ≥420 ran）.The g-C3N4/rGO-1sample exhibits the highest photocatalytic activity,which is 1.49 and 1.52 times higher than that of bulk g-C3N4 for 2,4-DCP and 1.52 times degradation,respectively.The enhanced photocatalytic activity for g-C3N4 originates from the improved visible light usage,enhanced electronic conductivity and photo-oxidation ability by the formed strong π-π stacking interactions with rGO.

Thermal nitridation of triazine motifs to heptazine-based carbon nitride frameworks for use in visible light photocatalysis

A thermal nitridation route for the assembly and polymerization of molecular triazine units to heptazine-based covalent frameworks has been successfully established. The obtained conjugated carbon nitride polymers feature nanostructures that show enhanced photocatalytic reactivity for hydrogen production under visible light irradiation.

Enhanced visible-light photo-oxidation of nitric oxide using bismuth-coupled graphitic carbon nitride composite heterostructures

Pure bismuth（Bi） metal-modified graphitic carbon nitride（g-C3N4） composites（Bi-CN） with a pomegranate-like structure were prepared by an in situ method.The Bi-CN composites were used as photocatalysts for the oxidation of nitric oxide（NO） under visible-light irradiation.The inclusion of pure Bi metal in the g-C3N4 layers markedly improved the light absorption of the Bi-CN composites from the ultraviolet to the near-infrared region because of the typical surface plasmon resonance of Bi metal.The separation and transfer of photogenerated charge carriers were greatly accelerated by the presence of built-in Mott-Schottky effects at the interface between Bi metal and g-C3N4.As a result,the Bi-CN composite photocatalysts exhibited considerably enhanced efficiency in the photocatalytic removal of NO compared with that of Bi metal or g-C3N4 alone.The pomegranate-like structure of the Bi-CN composites and an explanation for their improved photocatalytic activity were proposed.This work not only provides a design for highly efficient g-C3N4-based photocatalysts through modification with Bi metal,but also offers new insights into the mechanistic understanding of g-C3N4-based photo catalysis.

High selectivity to p-chloroaniline in the hydrogenation of p-chloronitrobenzene on Ni modified carbon nitride catalyst

A nanocomposite composed of Ni modified carbon nitride was synthesized and used in the hydro- genation of p-chloronitrobenzene. H/D exchange demonstrated that the hydrogen chemisorbed on the surface of this nanocomposite catalyst had a hydrogen atom density of 0.65/nm2. It was active for hydrogenation but its activity was inferior to the hydrogen adsorbed on a Ni/Al2O3 catalyst. Catalytic tests showed that this catalyst possessed a lower activity than Ni/AhO3 but the selectivity towards p-chloroaniline was above 99.9%. Even at high conversion, the catalyst maintained high selectivity, which was attributed to the unique surface property of the catalyst and the absence of a site for the adsorption ofp-chloronitrobenzene, which prevents the C-Cl bond from breaking.

Interfacial engineering of graphitic carbon nitride(g-C_3N_4)-based metal sulfide heterojunction photocatalysts for energy conversion: A review

As one of the most appealing and attractive technologies, photocatalysis is widely used as a promising method to circumvent the environmental and energy problems. Due to its chemical stability and unique physicochemical, graphitic carbon nitride (g-C3N4) has become research hotspots in the community. However, g-C3N4 photocatalyst still suffers from many problems, resulting in unsatisfactory photocatalytic activity such as low specific surface area, high charge recombination and insufficient visible light utilization. Since 2009, g-C3N4-based heterostructures have attracted the attention of scientists worldwide for their greatly enhanced photocatalytic performance. Overall, this review summarizes the recent advances of g-C3N4-based nanocomposites modified with transition metal sulfide (TMS), including (1) preparation of pristine g-C3N4,(2) modification strategies of g-C3N4,(3) design principles of TMS-modified g-C3N4 heterostructured photocatalysts, and (4) applications in energy conversion. What is more, the characteristics and transfer mechanisms of each classification of the metal sulfide heterojunction system will be critically reviewed, spanning from the following categories:(1) Type I heterojunction,(2) Type II heterojunction,(3) p-n heterojunction,(4) Schottky junction and (5) Z-scheme heterojunction. Apart from that, the application of g-C3N4-based heterostructured photocatalysts in H2 evolution, CO2 reduction, N2 fixation and pollutant degradation will also be systematically presented. Last but not least, this review will conclude with invigorating perspectives, limitations and prospects for further advancing g-C3N4-based heterostructured photocatalysts toward practical benefits for a sustainable future.

Highly crystalline carbon nitride hollow spheres with enhanced photocatalytic performance

Graphitic carbon nitride(g-C_(3)N_(4))has emerged as a remarkably promising photocatalyst for addressing environmental and energy issues;however,it exhibits only moderate photocatalytic activity because of its low specific surface area and high recombination of carriers.Preparation of crystalline g-C_(3)N_(4) by the molten salt method has proven to be an effective method to improve the photocatalytic activity.However,crystalline g-C_(3)N_(4) prepared by the conventional molten salt method exhibits a less regular morphology.Herein,highly crystalline g-C_(3)N_(4) hollow spheres(CCNHS)were successfully prepared by the molten salt method using cyanuric acid-melamine as a precursor.The higher crystallization of the CCNHS samples not only repaired the structural defects at the surface of the CCNHS samples but also established a built-in electric field between heptazine-based g-C_(3)N_(4) and triazine-based g-C_(3)N_(4).The hollow structure improved the level of light energy utilization and increased the number of active sites for photocatalytic reactions.Because of the above characteristics,the as-prepared CCNHS samples simultaneously realized photocatalytic hydrogen evolution with the degradation of the plasticizer bisphenol A.This research offers a new perspective on the structural optimization of supramolecular self-assembly.

Copper and platinum dual-single-atoms supported on crystalline graphitic carbon nitride for enhanced photocatalytic CO_(2) reduction

Single-atom Pt catalysts are designed to promote efficient atom utilization,whereas effective decrease of Pt loading and improvement of photocatalytic activity in monoatomic Pt-deposited systems is still ongoing.Atomically dispersed metal species in crystalline carbon nitride are still challenging owing to their high crystallization and structural stability.In this study,we developed a novel single-atomic Pt-Cu catalyst for reducing noble metal loading by combining Pt with earth-abundant Cu atoms and enhancing photocatalytic CO_(2)reduction.N-vacancy-rich crystalline carbon nitride was used as a fine-tuning ligand for isolated Pt-Cu atom dispersion based on its accessible functional N vacancies as the seeded centers.The synthesized dimetal Pt-Cu atoms on crystalline carbon nitride(Pt Cu-cr CN)exhibited high selectivity and activity for CO_(2)conversion without the addition of any cocatalyst or sacrificial agent.In particular,we demonstrated that the diatomic Pt-Cu exhibited high mass activity with only 0.32 wt% Pt loading and showed excellent photocatalytic selectivity toward CH_(4)generation.The mechanism of CO_(2)photoreduction for Pt Cu-cr CN was proposed based on the observations and analysis of aberration-corrected high-angle annular dark-field scanning transmission electron microscopy images,in situ irradiated X-ray photoelectron spectroscopy,and in situ diffuse reflectance infrared Fourier transform spectroscopy.The findings of this work provide insights for abrogating specific bifunctional atomic metal sites in noble metal-based photocatalysts by reducing noble metal loading and maximizing their effective mass activity.

The embedded CuInS2 into hollow-concave carbon nitride for photocatalytic H2O splitting into H2 with S-scheme principle

It is still a great challenge to effectively optimize the electronic structure of photocatalysts for the sustainable and efficient conversion of solar energy to H2 energy.To resolve this issue,we report on the optimization of the electronic structure of hollow-concave carbon nitride(C3N4)by deviating the sp2-hybridized structure of its tri-s-triazine component from the two-dimensional plane.The embedded CuInS2 into C3N4(CuInS2@C3N4)demonstrates an increased light-capturing capability and the promoted directional transfer of the charge carrier.Research results reveal that the hollow structure with an apparent potential difference between the concave and convex C3N4 drives the directional transfer of the photoinduced electrons from the Cu 2p orbital of CuInS2 to the N 1s orbital of C3N4 with the S-scheme principle.The H2 evolution efficiency over CuInS2@C3N4 is up to 373μmol?h^-1 g^-1 under visible irradiation,which is 1.57 and 1.35 times higher than those over the bulk g-C3N4 with 1 wt%Pt(238μmol?h^-1 g^-1)and g-C3N4 with 3 wt%Pd(276μmol?h^-1 g^-1),respectively.This suggests that the apparent potential difference of the hollow C3N4 results in an efficient reaction between the photogenerated electrons and H2O.This work supplies a new strategy for enhancing the sustainable solar conversion performance of carbon nitride,which can also be suitable for other semiconductors.