Graphitic Carbon Nitride Nanotubes Research Articles

Halloysite-derived mesoporous g-C3N4 nanotubes for improved visible-light photocatalytic hydrogen evolution

Abstract Hydrogen evolution via visible-light photocatalytic water splitting is an ideal solution to the worldwide energy and environmental crisis, while the key challenge is to develop efficient and cheap photocatalysts. Here, mesoporous graphitic carbon nitride (g-C3N4) nanotubes were synthesized using modified halloysite as template via a facial vapor deposition method. The halloysite-derived mesoporous g-C3N4 nanotubes exhibited an excellent photocatalytic hydrogen evolution efficiency of 633 μmol g−1 h−1 under visible light irradiation, which was 14.3 times that of bulk g-C3N4. The improvement of photocatalytic activity mainly benefits from the enlarged specific surface area and the reduced recombination rate of photoinduced electron-hole pairs of the mesoporous g-C3N4 nanotubes. The strategy established here may be valuable for synthesizing efficient g-C3N4 photocatalysts with other tailor nanostructures utilizing diverse raw clay minerals.

Bimetallic Ag-Cu Supported on Graphitic Carbon Nitride Nanotubes for Improved Visible-Light Photocatalytic Hydrogen Production.

This work, for the first time, reports visible-light active bare graphitic carbon nitride nanotubes (C3N4 NTs) for photocatalytic hydrogen generation, even in the absence of any cocatalyst. Upon uniform dispersion of the cocatalysts, Ag-Cu nanoparticles, on the well-ordered bare C3N4 NTs, they exhibit twice the H2 evolution rate of the bare C3N4 NTs. The improved activity is attributed to their unique tubular nanostructure, strong metal-support interaction, and efficient photoinduced electron-hole separation compared to their bare and monometallic counterparts, evidenced by complementary characterization techniques. This work reveals that the H2 production rates correlate well with the oxidation potentials of the sacrificial reagents used. Triethylamine (TEA) outperforms other sacrificial reagents, including triethanolamine (TEOA) and methanol. Mechanistic studies on the role of various sacrificial reagents in photocatalytic H2 generation demonstrate that irreversible photodegradation of TEA into diethylamine and acetaldehyde via monoelectronic oxidation contributes to the improved H2 yield. Similarly, TEOA is oxidized to diethanolamine and glycolaldehyde, whereas methanol is unable to quickly capture the photoinduced holes and remains intact due to the low oxidation potential.

Phosphorus-Doped Graphitic Carbon Nitride Nanotubes with Amino-rich Surface for Efficient CO2 Capture, Enhanced Photocatalytic Activity, and Product Selectivity.

Phosphorus-doped graphitic carbon nitrides (P-g-C3N4) have recently emerged as promising visible-light photocatalysts for both hydrogen generation and clean environment applications because of fast charge carrier transfer and increased light absorption. However, their photocatalytic performances on CO2 reduction have gained little attention. In this work, phosphorus-doped g-C3N4 nanotubes are synthesized through the one-step thermal reaction of melamine and sodium hypophosphite monohydrate (NaH2PO2·H2O). The phosphine gas generated from the thermal decomposition of NaH2PO2·H2O induces the formation of P-g-C3N4 nanotubes from g-C3N4 nanosheets, leads to an enlarged BET surface area and a unique mesoporous structure, and creates an amino-rich surface. The interstitial doping phosphorus also down shifts the conduction and valence band positions and narrows the band gap of g-C3N4. The photocatalytic activities are dramatically enhanced in the reduction both of CO2 to produce CO and CH4 and of water to produce H2 because of the efficient suppression of the recombination of electrons and holes. The CO2 adsorption capacity is improved to 3.14 times, and the production of CO and CH4 from CO2 increases to 3.10 and 13.92 times that on g-C3N4, respectively. The total evolution ratio of CO/CH4 dramatically decreases to 1.30 from 6.02 for g-C3N4, indicating a higher selectivity of CH4 product on P-g-C3N4, which is likely ascribed to the unique nanotubes structure and amino-rich surface.

Carbon Nanotube–Graphitic Carbon Nitride Hybrid Films for Flavoenzyme‐Catalyzed Photoelectrochemical Cells

AbstractIn green plants, solar‐powered electrons are transferred through sophistically arranged photosystems and are subsequently channelled into the Calvin cycle to generate chemical energy. Inspired by the natural photosynthetic scheme, a photoelectrochemical cell (PEC) is constructed configured with protonated graphitic carbon nitride (p‐g‐C3N4) and carbon nanotube hybrid (CNT/p‐g‐C3N4) film cathode, and FeOOH‐deposited bismuth vanadate (FeOOH/BiVO4) photoanode for the production of industrially useful chiral alkanes using an old yellow enzyme homologue from Thermus scotoductus (TsOYE). In the biocatalytic PEC platform, photoexcited electrons provided by the FeOOH/BiVO4 photoanode are transferred to the robust and self‐standing CNT/p‐g‐C3N4 hybrid film that electrocatalytically reduces flavin mononucleotide (FMN) mediator. The p‐g‐C3N4 promotes a two‐electron reduction of FMN coupled with an accelerated electron transfer by the conductive CNT network. The reduced FMN subsequently delivers the electrons to TsOYE for the highly enantioselective conversion of ketoisophorone to (R)‐levodione. Under light illumination (>420 nm) and external bias, (R)‐levodione is synthesized with the enantiomeric excess value of above 83%, not influenced by the scale of applied bias, simultaneously exhibiting stable and high current efficiency. The results suggest that the biocatalytic PEC made up of economical materials can selectively synthesize high‐value organic chemicals using water as an electron donor.

Self-assembled synthesis of defect-engineered graphitic carbon nitride nanotubes for efficient conversion of solar energy

High-yield and uniform-size graphitic carbon nitride nanotubes (g-C3N4 nanotubes) with abundant nitrogen defects are synthesized for the first time by a green and acid-alkali-free synthesis using a sole melamine precursor. This approach utilizes the slow in-situ conversion of part of melamine into cyanuric acid and consequent molecular self-assembly with the rest of melamine to form supramolecular intermediate. The following pyrolysis converts the supramolecular intermediate to g-C3N4 nanotubes with abundant nitrogen defects. The morphology thus resulted preferable performance than the traditional molecular self-assembly in which the mixture of melamine and cyanuric acid is used as precursors. The g-C3N4 nanotubes with orderly tubular morphology of length-diameter ratio of 30–70 exhibit excellent hydrogen evolution rate (118.5 μmol h−1), which is obviously superior to the bulk g-C3N4. The apparent quantum efficiency of g-C3N4 nanotubes under irradiation at 420 nm is achieved at 6.8%, which is among the top of one dimensional (1D) g-C3N4 structure, such as g-C3N4 nanotubes, nanowires and nanorods. The improved photocatalytic performance benefits from the tubular structure and the nitrogen defects, which lead to the improved optical absorption, more exposed active edges, nitrogen defects active sites, enhanced charge transfer and separation efficiency, higher surface area, fast and long-distance electron transport, and longer fluorescence lifetime. Beside hydrogen evolution reaction, the g-C3N4 nanotubes also have broad applications in environmental treatment and photoelectrochemical detection of organic dyes.

Noble metal-free g-C3N4/TiO2/CNT ternary nanocomposite with enhanced photocatalytic performance under visible-light irradiation via multi-step charge transfer process

A noble metal-free photocatalyst, consisting of graphitic carbon nitride (g-C3N4), TiO2 and carbon nanotubes (CNT) was synthesized by a facile hydrothermal method and its application for the photocatalytic decolouration of methylene blue (MB) dye under visible light irradiation has been demonstrated. The microstructure, morphology, structural and optical properties of the synthesized nanocomposites was systematically studied using TEM, SEM, XRD, RAMAN, FTIR and UV–Vis DRS techniques. The g-C3N4/TiO2/CNT ternary nanocomposite exhibits five times higher photocatalytic activity compared to bare g-C3N4 under visible light irradiation. Enhanced photocatalytic performance of the ternary nanocomposite has been attributed to the synergistic effects of three components: Multistep charge transfer between heterojunction formation at g-C3N4/TiO2 interface and CNT, enhanced visible-light absorption and effective charge separation. A possible reaction mechanism has been proposed and scavenger experiment has been carried out to find the role of active radical species responsible for the dye decolouration. Additionally, the g-C3N4/TiO2/CNT photocatalyst retained excellent stability even after several cycles. This study offers a promising way of developing a highly efficient, noble metal-free, stable and visible-light-driven photocatalyst to promote the utilization of solar energy for environmental purification.

Enhanced photocatalytic conversion of greenhouse gas CO2 into solar fuels over g-C3N4 nanotubes with decorated transparent ZIF-8 nanoclusters

The atmospheric concentration of CO2 as the dominant greenhouse gas continues to rise and has become a global environmental issue. Photocatalytic CO2 reduction into solar fuels has been regarded as an ideal solution to reduce CO2 emissions and to use solar energy. Graphitic carbon nitride (g-C3N4) is one of the most promising visible-light-driven photocatalysts for CO2 reduction. Unfortunately, the CO2 reduction performance of g-C3N4 based photocatalyst is normally limited by the inferior charge separation ability and limited CO2 adsorption capacity. In this study, two cooperative strategies, that is, combined host nanostructural design and surface guest grafting, are adopted to overcome the aforementioned drawbacks. Specifically, holey graphitic carbon nitride (g-C3N4) nanotubes were firstly fabricated to modify the light-harvesting ability, the redox potential as well as the charge separation efficiency. And then, the as-prepared tubular g-C3N4 was decorated with suitable amount of transparent zeolitic imidazolate framework-8 (ZIF-8) nanoclusters to further increase CO2 capture capacity without sacrifice of light absorption capacity. Because of the cooperative effects of nanostructural design and surface grafting, the optimized ZIF-8 modified tubular g-C3N4 photocatalysts exhibit a great enhancement in photocatalytic CH3OH production efficiency by more than 3 times, relative to the bulk g-C3N4 (BCN) photocatalyst synthesized by conventional pyrolysis of melamine. This work will enlighten a promising strategy to construct efficient photocatalyst for greenhouse gas CO2 resourcing, by taking advantage of the cooperative effects of semiconductor nanostructures and surface metal-organic framework grafters.

Hierarchical Porous O-Doped g-C3 N4 with Enhanced Photocatalytic CO2 Reduction Activity.

Artificial photosynthesis of hydrocarbon fuels by utilizing solar energy and CO2 is considered as a potential route for solving ever-increasing energy crisis and greenhouse effect. Herein, hierarchical porous O-doped graphitic carbon nitride (g-C3 N4 ) nanotubes (OCN-Tube) are prepared via successive thermal oxidation exfoliation and curling-condensation of bulk g-C3 N4 . The as-prepared OCN-Tube exhibits hierarchically porous structures, which consist of interconnected multiwalled nanotubes with uniform diameters of 20-30 nm. The hierarchical OCN-Tube shows excellent photocatalytic CO2 reduction performance under visible light, with methanol evolution rate of 0.88 µmol g-1 h-1 , which is five times higher than bulk g-C3 N4 (0.17 µmol g-1 h-1 ). The enhanced photocatalytic activity of OCN-Tube is ascribed to the hierarchical nanotube structure and O-doping effect. The hierarchical nanotube structure endows OCN-Tube with higher specific surface area, greater light utilization efficiency, and improved molecular diffusion kinetics, due to the more exposed active edges and multiple light reflection/scattering channels. The O-doping optimizes the band structure of g-C3 N4 , resulting in narrower bandgap, greater CO2 affinity, and uptake capacity as well as higher separation efficiency of photogenerated charge carriers. This work provides a novel strategy to design hierarchical g-C3 N4 nanostructures, which can be used as promising photocatalyst for solar energy conversion.

Ab initio study of aspirin adsorption on single-walled carbon and carbon nitride nanotubes.

Using density functional theory, we investigate the adsorption properties of acetylsalicylic acid (aspirin) on the outer surfaces of a (10,0) carbon nanotube (CNT) and a (8,0) triazine-based graphitic carbon nitride nanotube (CNNT). The adsorption energies for the CNNT and CNT are 0.67 and 0.51 eV, respectively, and hence, the aspirin molecule binds more strongly to the CNNT. The stronger adsorption energy for the binding to the CNNT is ascribed to the high reactivity of its nitrogen atoms with high electron affinity. The CNNT exhibits local electric dipole moments that cause strong charge redistribution in the adsorbed aspirin molecule. The influence of an external electric field on the adsorption of aspirin on the nanotubes is explored by examining modifications in their electronic band structures, partial densities of states, and charge distributions. An electric field applied along a particular direction is found to induce molecular states of aspirin that lie within the in-gap region of the CNNT. This implies that the CNNT can be potentially utilized for the detection of aspirin.

Tunable thermal, flame retardant and toxic effluent suppression properties of polystyrene based on alternating graphitic carbon nitride and multi-walled carbon nanotubes

Significant improvements in thermal and flame retardant properties of polymeric materials at low loadings hold tremendous promise for fire safety materials.

Porous and low-defected graphitic carbon nitride nanotubes for efficient hydrogen evolution under visible light irradiation

Porous and low-defected g-C3N4 nanotubes with high SBET and optimized optical and electronic properties exhibit enhanced photocatalytic activity.

Transparent half metallic g-C4N3 nanotubes: potential multifunctional applications for spintronics and optical devices.

Multifunctional material brings many interesting issues because of various potential device applications. Using first principles calculations, we predict that the graphitic carbon nitride (g-C4N3) nanotubes can display multifunctional properties for both spintronics and optical device applications. Very interestingly, armchair tubes (n, n) with n = 2, 3, 4, 5, 6 and (5, 0) zigzag tubes are found to be half metallic, while zigzag tubes (n, 0) with n = 4, 6 show an antiferromagnetic ground state with band gaps. However, larger zigzag tubes of (7, 0), (8, 0), and (10, 0) are turned out to be half metallic. Along with the half metallic behavior of the tubes, those tubes seem to be optically transparent in the visible range. Due to these magnetic and optical properties, we suggest that the g-C4N3 nanotubes (CNNTs) can be used for both ideal spintronics and transparent electrode materials. We also explored the stability of magnetic state and nanotube structure using ab initio molecular dynamics. The CNNTs were found to be thermally stable and the magnetic moment was robust against the structural deformation at 300 K. Overall, our theoretical prediction in one dimensional CNNTs may provide a new physics in spintronics and also in other device applications because of potential multifunctional properties.

Graphitic Carbon Nitride Nanotubes As Li-Ion Battery Materials: A First-Principles Study

First-principles calculations based on density functional theory are carried out to investigate the Li storage capability of graphitic carbon nitride nanotubes. The porous nanotubes provide unprecedented opportunity for energy storage due to their uniform size of pores in the wall and doubly bonded nitrogen at the edges of the pore. The calculations predict that the Li atoms can easily access the interior of the nanotube through the pores in the wall because of the low energy barrier and thus be stored both inside and outside of the nanotubes. The exothermic intercalation of Li further shows that g-C3N4 nanotubes are suitable for Li storage. The Li density in bundles of nanotubes is predicted to be up to 0.57 (Li4C3N4). The porous graphitic carbon nitride nanotubes are applicable in Li-ion battery with high density and stability.

First-principles study on hydrogen storage by graphitic carbon nitride nanotubes

First-principles calculations based on density functional theory were carried out to investigate the hydrogen storage capacity of graphitic carbon nitride nanotubes. Graphitic carbon nitride nanotubes could be attractive hydrogen sorbent for two reasons: firstly, its porous structure allows easy access of hydrogen into the interior of the nanotubes; and secondly, the doubly bonded nitrogen at its pore edges provides active sites for either the adsorption of hydrogen (chemically and physically), or functionalization with metal catalysts. Our calculations show that an isolated nanotube can uptake up to 4.66 wt. % hydrogen, with an average overall hydrogen adsorption energy of about −0.22 eV per H atom. In the form of a bulk bundle, the hydrogen storage capacity is enhanced due to the increased availability of space among the tubes. We predict that the hydrogen storage capacity in the bundle is at least 5.45 wt. %. Importantly, hydrogen molecules can easily access the tube’s interior due to the low energy barrier (∼0.54 eV) for their passage through the pores, indicating a fast uptake rate at relatively low pressure and temperature. Our findings show that graphitic carbon nitride nanotubes should be applicable to practical hydrogen storage because of the high gravimetric capacity and fast uptake rate.

Metal-functionalized single-walled graphitic carbon nitride nanotubes: a first-principles study on magnetic property.

The magnetic properties of metal-functionalized graphitic carbon nitride nanotubes were investigated based on first-principles calculations. The graphitic carbon nitride nanotube can be either ferromagnetic or antiferromagnetic by functionalizing with different metal atoms. The W- and Ti-functionalized nanotubes are ferromagnetic, which are attributed to carrier-mediated interactions because of the coupling between the spin-polarized d and p electrons and the formation of the impurity bands close to the band edges. However, Cr-, Mn-, Co-, and Ni-functionalized nanotubes are antiferromagnetic because of the anti-alignment of the magnetic moments between neighboring metal atoms. The functionalized nanotubes may be used in spintronics and hydrogen storage.

Ab Initio Study on a Novel Photocatalyst: Functionalized Graphitic Carbon Nitride Nanotube

A novel nanomaterial, graphitic carbon nitride nano-tube, was designed and studied for its application to photocatalyst by first-principles calculations. This nanomaterial is semiconducting with size-dependent bandgap and stable in an extreme environment. Most interestingly, its electronic structure with adjustable bandgap can be easily modified by functionalizing with metal atoms. The calculated electronic and optical properties of functionalized nanotube evidence the narrowed bandgap and optical gap, and enhanced mobility, satisfying basic prerequisites as a new class of high efficiency photocatalysts for water splitting and other avenues of solar energy utilization. The functionalized nanotubes may enable efficient solar energy conversion in a variety of industrial and environmental applications.