Ultrathin Carbon Nitride Research Articles

Solar driven high efficiency hydrogen evolution catalyzed by surface engineered ultrathin carbon nitride

A typical photocatalytic system composed of a light-harvesting center and an active center is presented, showing greatly improved catalytic performance.

Synergy of dopants and defects in ultrathin 2D carbon nitride sheets to significantly boost the photocatalytic hydrogen evolution

Atomically thin 2D carbon nitride sheets (CNs) can improve the photocatalytic performance due to their high specific surface area, exposed active sites, and nano-scaled diffusion path of the charge transferred to surface. However, in practical application, 2D CNs photocatalysts always suffer the low solar absorption. Here, we present a novel approach to achieve the ultrathin 2D CNs photocatalysts with wide spectrum absorption in visible-light range. The new method, i.e. thermal annealing of atomically thin CNs in Se vapor, can dramatically extend the absorption edge of the ultrathin CNs from 418 to 574 nm. Using structural characterization and spin-polarized density functional theory, we identify the loss of the nitrogen atoms at the edges and in situ Se doping into the network of ultrathin CNs, which could change the electronic band structure of the 2D CNs. As a consequence, the ultrathin 2D CNs photocatalyst via Se vapor annealing (Se-CNs) modified by Pt cocatalyst shows a superior photocatalytic hydrogen evolution activity under visible light irradiation. More significantly, the ultrathin Se-CNs photocatalyst also exhibits an impressive photocatalytic hydrogen evolution activity under visible-light irradiation in the absence of Pt cocatalyst. We believe that our study provide a facile and environmentally friendly strategy to realize the utilization of 2D CNs photocatalyst under wide spectrum range of solar radiation to harvest solar energy efficiently, and it can be further applied in various advanced fields, including CO2 photoreduction, organic photosynthesis, and pollutant controls.

Role of Nitrogen on the Mechanical Properties of the Novel Carbon Nitride Nanothreads

Carbon nanothread (C-NTH) is a new ultrathin one-dimensional sp3 carbon nanostructure, which exhibits promising applications in novel carbon nanofibers and nanocomposites. Recently, researchers have successfully developed a new alternative structure - ultrathin carbon nitride nanothread (CN-NTH). In this work, we investigate the mechanical properties of CN-NTHs through large-scale molecular dynamics simulations. Comparing with their C-NTH counterparts, CN-NTHs are found to exhibit a higher tensile and bending stiffness. In particular, because of the bond redistribution, the CN-NTHs in the polymer I group and tube (3,0) group are found to possess a higher failure strain than their C-NTH counterparts. However, the CN-NTH in the polytwistane group has a smaller failure strain compared with the pristine C-NTH. According to the atomic configurations, the presence of nitrogen atoms always leads to stress/strain concentrations for the nanothreads under tensile deformation. This study provides a comprehensive understanding of the mechanical properties of CN-NTHs, which should shed light on their potential applications such as fibers or reinforcements for nanocomposites.

Anchoring single-unit-cell defect-rich bismuth molybdate layers on ultrathin carbon nitride nanosheet with boosted charge transfer for efficient photocatalytic ciprofloxacin degradation

Photocatalysis technology is regarded as a promising way for environmental remediation, but rationally designing photocatalysis system with high-speed interfacial charge transfer, sufficient photoabsorption and surface reactive sites is still a challenge. In this study, anchoring single-unit-cell defective Bi2MoO6 on ultrathin g-C3N4 to form 2D/2D heterostructure system is a triple-purpose strategy for high-performance photocatalysis. The defect structure broadens photo-responsive range. The large intimate contact interface area between two monomers promotes charges carrier transfer. The enhanced specific surface area exposes more reactive sites for mass transfer and catalytic reaction. As a result, the obtained heterostructure displays excellent photocatalytic performance for ciprofloxacin (CIP) (0.0126 min−1), which is 3.32 and 2.93 folds higher than Bi2MoO6 and g-C3N4. In addition, this heterostructure retains high-performance for actual wastewaters treatment, and it displays strong mineralization ability. And this heterojunction also exhibits excellent photostability based on cyclic experiment. Mechanism exploration reveals that hole, superoxide radical, and hydroxyl radical are chief reactive species toward CIP degradation, thereby a Z-scheme charge carrier transfer channel is proposed. In addition, the intermediates and degradation pathways of CIP are tracked by liquid chromatography-triple quadrupole tandem mass spectrometry (LCMS/MS) and three-dimensional excitation-emission matrix fluorescence spectroscopy (3D EEMs). This study paves new way to design and construct atomic level 2D/2D heterojunction system for environment remediation.

Fabrication of 2D/0D Heterojunction Based on the Dual Controls of Micro/Nano‐Morphology and Structure Towards High‐Efficiency Photocatalytic H2 Production

AbstractIt is a keen interest to fabricate heterojunction among semiconductors with different dimensions for improving the photocatalytic performance. Herein, the 2D/0D up‐g‐C3N4/Ni12P5 heterojunctions were prepared by means of anchoring Ni12P5 nanodots on the surface of ultrathin porous carbon nitride (up‐g‐C3N4) nanosheets based on the dual control strategy of micro/nano‐ morphology and structure. The prepared 2D/0D up‐g‐C3N4/Ni12P5 heterojunctions exhibit the far more outstanding photocatalytic H2 production activity in comparison with the up‐g‐C3N4, up‐g‐C3N4/Pt‐3 % and u‐g‐C3N4/Ni12P5‐3 % samples and the superior cycle stability. The prominent photocatalytic H2 production activity and stability originate from the improved visible light harvest ability and separation efficiency of charge carriers owing to the modification effect of Ni12P5 nanodots as cocatalysts on the surface of up‐g‐C3N4 nanosheets through forming the Ni−N bond states.

Ultrathin g-C3N4 with enriched surface carbon vacancies enables highly efficient photocatalytic nitrogen fixation

An ultra-thin carbon nitride with loose structure and more carbon defects on the surface was achieved through high-temperature peeling methods. Its composition, morphological characteristics, surface defect types and electrochemical properties have been measured. After atomic scale structure control and surface defects construction, the photocatalytic activity of prepared g-C3N4-V for ammonia conversion from dinitrogen can be greatly improved in contrast with bulk g-C3N4. Under visible light irradiation, the defective g-C3N4-V can produce 54 µmol/L NH3 within 100 min without any cocatalyst and sacrificial agent. The relationship between morphology characteristics and activity of defective ultrathin g-C3N4 materials was analyzed in detail. Benefiting from thin layer structure and more surface carbon vacancies, the effective charge separation from both bulk and surface can be achieved. Notably, the engineered carbon vacancies greatly facilitate the adsorption and activation of dinitrogen molecule, extremely improving the nitrogen fixation activity for the defective ultrathin g-C3N4-V materials. This work affords novel insights into the design of photocatalyst with defective ultrathin structure towards nitrogen fixation.

Ultrathin Carbon Nitride with Atomic-Level Intraplane Implantation of Graphited Carbon Ring Domain for Superior Photocatalytic Activity in the Visible/Near-Infrared Region

Efficient photocarrier transfer and sufficient light absorption play a crucial role in improving photocatalytic H2 evolution activity. Hence, we report a conceptual design of an ultrathin carbon nitride intraplane implanted with graphited carbon ring domain (CN-GP) via thermal polymerization of polyvinyl butyral and melamine membrane, displaying obvious disparities in the decoration type compared with the adsorption of graphene on the bulk g-C3N4 surface. This unique intraplane heterostructural CN-GP can greatly sheathe the visible/near-infrared light range, expedite electron–hole pair separation, and weaken the barrier of the photocarrier transfer through their suitable energy band structures and in-built electric felds. Consequently, the CN-GP displayed remarkable photocatalytic activity under visible/near-infrared illumination by acquiring a H2 production rate of 11.33 mmol g–1 h–1 and even showed near-infrared-driven photocatalytic activity. This work presents an effective method for the rational fabr...

Layered Heterostructures of Ultrathin Polymeric Carbon Nitride and ZnIn2 S4 Nanosheets for Photocatalytic CO2 Reduction.

The rational construction of heterostructures by using layered semiconductors with two-dimensional (2D) nanosheet configurations is promising to improve the efficiency of CO2 photoreduction. Herein, the fabrication of layered heterojunction photocatalysts (PCN/ZnIn2 S4 ) by in situ growth of 2D ZnIn2 S4 nanosheets on the surfaces of ultrathin polymeric carbon nitride (PCN) layers is presented for greatly enhanced CO2 conversion with visible light. The solution-processed self-assembly strategy renders the building of uniform and intimate junctions between PCN layers and ZnIn2 S4 subunits, which remarkably accelerates the separation and transfer of photogenerated charge carriers. In addition, the layered composites can also promote CO2 adsorption and strengthen the visible-light absorption. Consequently, the optimized PCN/ZnIn2 S4 sheet-shaped composite shows reinforced photoactivity for deoxygenative CO2 conversion, affording a high CO-production rate of 44.6 μmol h-1 , which is 223 times higher than that of the pristine PCN nanosheets. Moreover, the heterojunction photocatalyst also exhibits high stability during repeated runs for five cycles.

Perovskite-type BiFeO3/ultrathin graphite-like carbon nitride nanosheets p-n heterojunction: Boosted visible-light-driven photoelectrochemical activity for fabricating ampicillin aptasensor

Developing effective sensing method for trace analysis of ampicillin (AMP) is urgent and significant due to its residue possess serious threats to human health. Herein, a p-n heterojunction, on the basis of p-type BiFeO3 nanoparticles coupled n-typed ultrathin graphite-like carbon nitride (utg-C3N4) nanosheets, has been designed and synthesized via a simple electrostatic interaction strategy. Such p-n heterojunction has two advantages: one is capable to narrow the band gap of photoactive materials from 2.20 eV of BiFeO3 down to 2.04 eV of BiFeO3/utg-C3N4, leading to improve the efficiency of visible light utilization; and the other is to facilitate the charge separation rate, resulting in the boosted photoelectrochemical (PEC) performance of BiFeO3/utg-C3N4. Under visible light illumination, the photocurrent of the resulted BiFeO3/utg-C3N4 was 7.0-fold enhanced than that of pure BiFeO3 nanoparticles, and indeed 2.3-fold enhanced comparing to BiFeO3/bulk-C3N4. Based on excellent PEC properties of BiFeO3/utg-C3N4, an on-off-on PEC aptasensor was successfully fabricated for ampicillin (AMP) determination with highly selectivity and sensitivity. The fabricated PEC aptasensor exhibited excellent PEC performance with a broad linear in the range from 1 × 10–12 mol L–1 to 1 × 10−6 mol L–1 as well as a low detection limit of 3.3 × 10–13 mol L–1 (S/N = 3), and also good feasibility in real sample. The excellent analytical performance indicated that PEC aptasensor on the basis of the visible light driven BiFeO3/utg-C3N4 heterojunction can provide a promising biosensor platform for sensitive detection AMP in food and environment analysis.

Nanofluidic Ion Transport and Energy Conversion through Ultrathin Free-Standing Polymeric Carbon Nitride Membranes.

Ions transport through confined space with characteristic dimensions comparable to the Debye length has many applications, for example, in water desalination, dialysis, and energy conversion. However, existing 2D/3D smart porous membranes for ions transport and further applications are fragile, thermolabile, and/or difficult to scale up, limiting their practical applicability. Now, polymeric carbon nitride alternatively allows the creation of an ultrathin free-standing carbon nitride membrane (UFSCNM), which can be fabricated by simple CVD polymerization and exhibits excellent nanofluidic ion-transport properties. The surface-charge-governed ion transport also endows such UFSCNMs with the function of converting salinity gradients into electric energy. With advantages of low cost, facile fabrication, and the ease of scale up while supporting high ionic currents, UFSCNM can be considered as an alternative for energy conversion systems and new ionic devices.

Noble metal-free modified ultrathin carbon nitride with promoted molecular oxygen activation for photocatalytic formaldehyde oxidization and DFT study

Modifying the electronic structure of photocatalysts is an important approach for increasing the separation efficiency of photogenerated carriers and activating molecular oxygen into superoxide radical (O2−) for contaminants removal. Herein, based on the density functional theory (DFT) calculations, we found that doping F− can not only narrow the bandgap of graphitic-phase carbon nitride (g-C3N4), but also decrease the electronic localization, extend the π conjugated system and increase the in-planar electron density, resulting in promoting the molecular oxygen activation of g-C3N4. The experiments indicated that the fluorinated ultrathin g-C3N4 was favorable for activating molecular oxygen into O2− under visible light irradiation, which could be ascribed to the relatively higher conduction band position and more negative surface adsorption energy for O2 as well as advantageous charge accumulation on adsorbed O2 as compared to ultrathin g-C3N4. By virtue of the synergic effect of enhanced adsorption ability to O2, effective separation of photogenerated carriers and more reductive photoexcited electrons derived from the ultrathin structure and F− associates, the fluorinated ultrathin g-C3N4 sheets revealed promoted solar driven photocatalytic activity for formaldehyde (HCHO) oxidation. This study could provide new insights into the mechanistic comprehension of molecular oxygen activation reaction and design of low cost noble metal-free modified ultrathin layered photocatalysts with for environmental remediation.

Research on the techniques of ultrasound-assisted liquid-phase peeling, thermal oxidation peeling and acid-base chemical peeling for ultra-thin graphite carbon nitride nanosheets

Graphite phase carbon nitride (g-C3N4) composite structure materials, as a kind of stable compound with graphite-like structure, has attracted more and more attention due to its excellent properties, such as being able to absorb solar energy, stable chemical and optical properties and having a suitable oxidation potential. However, its application in the field of photocatalysis is limited by its small specific surface area and poor dispersibility. To solve this problem, ultra-thin g-C3N4 nanosheets are often prepared using peeling methods. In this paper, the current status and mechanism of thermal oxidation peeling, ultrasound-assisted liquid-phase peeling and acid-base chemical peeling are reviewed in detail. In addition, the future research directions of ultra-thin graphite-like carbon nitride nanosheets are discussed.

A facile and scalable route for synthesizing ultrathin carbon nitride nanosheets with efficient solar hydrogen evolution

Two-dimensional (2D) graphene-like carbon nitride nanosheets (CN-S) with unique photoelectronic properties have received much attention in advanced photocatalysis applications. The challenge for the synthesis of this promising 2D metal-free nanomaterials is to develop a facile but scalable strategy. Herein we for the first time reported a feasible approach to prepare the few-layered CN-S by introduction urea as “bubble template” in the thermal polymerization process. Compared to the bulk carbon nitride (CN-B), the thin-layered CN-S with a thickness of around 4 nm possessed the large specific surface area, enlarge electronic-band structure, fast photogenerated electron-hole transfer capability, and increased charge lifetime. Eventually, the resulting CN-S not only had a relatively high yield of 44.5%, but also exhibited a superior photocatalytic hydrogen evolution activity (1400 μmol g-1 h-1) from water under visible-light irradiation (λ > 420 nm). This work highlights a cost-effective and strategy towards the one-step and large-scale production of high-performance CN-S photocatalysts for efficient solar-to-fuel conversion.

Strongly Coupled Metal Oxide/Reassembled Carbon Nitride/Co-Pi Heterostructures for Efficient Photoelectrochemical Water Splitting.

The photoelectrochemical application of carbon nitride is extremely exciting because of the meta-free components, low cost, nontoxicity, and appropriate band positions. To construct carbon nitride-based heterostructures, a conventional ultrasonic exfoliation method is usually used to fabricate dispersion of ultrathin nanosheets. However, the outstretched structure and the poor dispersity inevitably result in the poor interfacial contact between different materials. To solve this problem, hydrolyzed carbon nitride suspension was used as a homogeneous precursor for the fabrication of composite photoanodes. The in situ reassembly of one-dimensional nanofibers resulted in the formation of uniform and ultrathin carbon nitride nanoarchitectures on the surface of Fe2O3 nanorod arrays. Because of the strongly coupled interfaces and the deposition of Co-Pi water oxidation cocatalysts, the as-synthesized heterostructured photoanodes exhibited three-fold increased photocurrent density and good stability, compared to pristine Fe2O3. The significantly improved photoactivity of the Fe2O3/reassembled carbon nitride/Co-Pi heterostructures was ascribed to the decreased interfacial conductivity and facilitated charge separation. This material designing strategy was further used to construct TiO2/carbon nitride, ZnO/carbon nitride, and WO3/carbon nitride heterostructures. The incorporation of hydrolyzed carbon nitride could remarkably enhance the photoelectrochemical performance of these metal oxide photoanodes. Thus, this work provides a new paradigm for designing carbon nitride-based composite nanostructures for efficient and stable solar fuel production.

Confined Synthesis of Carbon Nitride in a Layered Host Matrix with Unprecedented Solid-State Quantum Yield and Stability.

Fluorescent carbon nanomaterials have drawn tremendous attention for their intriguing optical performances, but their employment in solid-state luminescent devices is rather limited as a result of aggregation-induced photoluminescence quenching. Herein, ultrathin carbon nitride (CN) is synthesized within the 2D confined region of layered double hydroxide (LDH) via triggering the interlayer condensation reaction of citric acid and urea. The resulting CN/LDH phosphor emits strong cyan light under UV-light irradiation with an absolute solid-state quantum yield (SSQY) of 95.9 ± 2.2%, which is, to the best of our knowledge, the highest value of carbon-based fluorescent materials ever reported. Furthermore, it exhibits a strong luminescence stability toward temperature, environmental pH, and photocorrosion. Both experimental studies and theoretical calculations reveal that the host-guest interactions between the rigid LDH matrix and interlayer carbon nitride give the predominant contribution to the unprecedented SSQY and stability. In addition, prospective applications of the CN/LDH material are demonstrated in both white light-emitting diodes and upconversion fluorescence imaging of cancer cells.

Preparation of 2D graphitic carbon nitride nanosheets by a green exfoliation approach and the enhanced photocatalytic performance

In this paper, we reported a new and environment-friendly strategy to exfoliate graphitic carbon nitride (CN) in hot water to obtain ultrathin CN nanosheets (CNNS). By thermal treating, water molecules were intercalated into the interlayer space of bulky CN and further hydrolyzed the bridge-linked N groups between tri-s-triazine units, thereby cutting the CN layers into CNNS. Due to the negative charges on surface (Zeta potential was −13 mV at pH 7), the CNNS colloids were extremely stable. The physicochemical characterization indicated that the as-prepared CNNS had a typical 2D morphology with a ~1.2 nm thickness and numerous –OH groups on surface. Moreover, the high charge separation and transport ability were achieved in CNNS because of the retaining of conjugated CN system. Compared to the bulk CN, the as-prepared ultrathin CNNS exhibited an enhanced photocatalytic performance (four times higher than that of the bulk CN) for degradation of organic dye under visible light irradiation. Additionally, the superior reusability and the excellent generality of CNNS for decomposing other pollutants were also demonstrated. Finally, we proposed a possible mechanism of CNNS based on the examined band structure and the main active species determined by quenching of various active species.

Morphology and defects regulation of carbon nitride by hydrochloric acid to boost visible light absorption and photocatalytic activity

In this work, a hydrochloric acid assisted exfoliation approach to prepare the ultrathin carbon nitride (U-CN) nanosheet and to regulate its morphology and defects was reported. Based on moderate oxidation of hydrochloric acid, bulk carbon nitride (BCN) was just right broken into small pieces with protonation, which is beneficial to the exfoliation of BCN to U-CN nanosheets. Meanwhile, the main structure of CN do not be destroyed. Moreover, hydrochloric acid gives priority to cleave the bridging N atoms with rich elections, leading to the formation of the favorable defects and improving its photocatalytic performance. The obtained U-CN nanosheets prepared in a suitable HCl concentration exhibits enhanced photocatalytic efficiency for hydrogen evolution and Rhodamine B degradation under visible light. Such U-CN nanosheets with simple preparation, low cost, good yield and good photocatalytic activity might shed light on an acid-assisted method for developing high-performance CN photocatalysts.

Bandgap engineering of ultrathin graphene-like carbon nitride nanosheets with controllable oxygenous functionalization

Seeking effective approaches of bandgap engineering with increased carrier lifetime is critical for designing semiconductor photoelectronic devices and photocatalysis systems. Ultrathin graphene-like carbon nitride nanosheets have shown promising prospect in photocatalysis, whereas no preparation strategy for adjusting their bandgap in a wide range has ever been reported. Here in, high yield-rate synthesis of ultrathin two-dimensional carbon nitride nanosheets with controllable oxygenous functionalization (the relative mass ratio of oxygen ranges from 0.523% to 19.9%) was firstly achieved by an improved hummer's method combining concentrated sulfuric acid protonation and potassium permanganate assisted exfoliation, and reduction employing hydrazine hydrate. Protonation and intercalation behavior of different acids in the treatment of bulk-g-C3N4 was elaborated at molecule level for the first time. Introduced oxygenous groups are firstly found to have the capability for adjusting the bandgap of graphene-like carbon nitride nanosheets from 2.54 eV to 3.07 eV and significantly increased the lifetime of the photo carriers. Our strategy may open a new vista for design and construction of various carbon nitride nanocomposites and give detailed instructions in bandgap engineering of other two-dimensional functional materials for wider applications.

A pH Indicator-linked Immunosorbent assay following direct amplification strategy for colorimetric detection of protein biomarkers

A new pH indicator-linked immunosorbent assay (PILISA) reached pg/mL sensitivity based on pH indicator molecules loaded carbon nitride nanosheets as signal enhancer has been developed for colorimetric detection of protein biomarkers. As the secondary antibody binds to the carbon nitride nanosheets, the carbon nitride nanosheets and pH indicator complex as the signal amplification platform for colour change by detecting absorbance of pH indicator. The colour change was resulted from the releasing of pH indicator molecules from carbon nitride nanosheets triggered by alkali solution (AS). In this novel PILISA, the intensity absorbance of pH indicator is proportional to the concentration of the disease marker. The outstanding detection performance of the PILISA can be attributed to the following reasons: (1) ultrathin carbon nitride nanosheets with a larger surface area could adsorb abundant phenolphthalein (PP) molecules through hydrophobic interactions as well as the resulted PP anions can be free easily released into aqueous solution, leading to an obvious allochroic response; (2) the signal intensity is precisely determined by the amount of PP molecules loading onto the carbon nitride nanosheets surface, which ensures simple, low-cost and stable colorimetric detection. As expected, this new PILISA method offered an enzyme-free approach followed enzyme-linked immunosorbent assay format, which showed great promising potential as an innovative robust assay method for practical clinical applications.

Insight into highly efficient simultaneous photocatalytic removal of Cr(VI) and 2,4-diclorophenol under visible light irradiation by phosphorus doped porous ultrathin g-C3N4 nanosheets from aqueous media: Performance and reaction mechanism

Carbon nitride (g-C3N4) has attracted great attention for its wide applications in hydrogen evolution and photocatalytic degradation. In this study, phosphorus doped porous ultrathin carbon nitride nanosheets (PCN-S) were prepared successfully via the element doping and thermal exfoliation method. The prepared PCN-S was characterized by XRD, SEM, TEM, N2-adsorption-desorption measurement, FT-IR, XPS, UV–vis diffuse reflectance spectra, photoluminescence (PL), photocurrent response (I-t) and EIS. The results show that PCN-S owns regular crystal structure of g-C3N4, large specific surface areas and nanosheet structure with lots of in-plane pores on its surface, excellent chemical stability, and broad light response to the whole visible light region, which was attributed to the doping of phosphorus element. Under visible light irradiation, the photocatalytic reduction of Cr(VI) over different samples indicated that the P doping and porous nanosheet structure play an important role for the enhanced performance of PCN-S. The reason was that P element doping can broaden the visible light response region, and large specific surface areas from the porous nanosheet structure can provide quantities of active sites for the photocatalytic reaction. Then the detailed study on the PCN-S for simultaneous photocatalytic reduction of Cr(VI) and oxidation of 2,4-diclorophenol (2,4-DCP) was conducted. The experiments results show that low pH value and enough dissolved oxygen were found to promote Cr(VI) reduction and 2,4-DCP oxidation. The detailed photocatalytic mechanism was proposed. The strategies used in this study could provide new insight into the design of g-C3N4 based materials with high photocatalytic activity, and present potential for the treatment of Cr(VI)/2,4-DCP or other mixed pollutants in wastewater.