Precisely tunable thickness of graphitic carbon nitride nanosheets for visible-light-driven photocatalytic hydrogen evolution

Silver sulfide anchored bismuth molybdate p-n heterojunction nano-coating with excellent photo-thermal self-healing performance

In this research, a self-healing nano-coating with excellent photo-thermal response to near-infrared (NIR) laser is prepared. This coating incorporates silver sulfide anchored bismuth molybdate (Ag2S@Bi2MoO6) into a shape memory epoxy resin to achieve for a good photo-thermal conversion capability. The Ag2S@Bi2MoO6 p-n heterojunction could photo-generate more electron-holes pairs under the NIR laser irradiation. Also, it shows a wider absorption range of visible light, leading to effectively absorb the light energy, generate enough heat to induce the shape memory recovery in the coating, and seal the scratch. The results indicate that the temperature of EP-1 % Ag2S@Bi2MoO6 coating has reached about 88 °C, while good self-healing and anti-corrosion properties with a self-healing rate of 88.41 % have been achieved. Furthermore, calculations based on Density Functional Theory and Finite Element Method pointed out that the formation of p-n heterojunction effectively has enhanced the photo-thermal effect. This research opens a new way for developing self-healing coatings with an ultra-fast response time and high self-healing efficiency.

Vacancy-Modified Porous g-C3N4 Nanosheets Controlled by Physical Activation for Highly Efficient Visible-Light-Driven Hydrogen Evolution and Organics Degradation

As a promising photocatalyst material, g-C3N4 has great application potential in energy production and environmental improvement. In this work, surface-modified g-C3N4 nanosheets with excellent stability and high photocatalytic activity were successfully synthesized by physical steam activation. The charge transfer rate of carbon nitride was improved due to the synergistic effect of nitrogen defect and oxygen doping caused by steam activation. Meanwhile, the specific surface area and pore volume of the optimized sample reached 124.3 m2 g-1 and 0.42 cm3 g-1, respectively, which increased the exposed reaction sites of reactants, enhancing the photocatalytic activity of g-C3N4. In addition, this novel g-C3N4 displayed a great H2 evolution rate of 5889.39 μmol h-1 g-1 with a methylene blue degradation rate up to 6.52 × 10-3 min-1, which was 3.7 and 2.1 times of original g-C3N4, respectively. This study provided a simple and economical method to develop a highly efficient g-C3N4 photocatalyst for solar energy conversion.

Engineering of graphitic carbon nitride with simultaneous potassium doping sites and nitrogen defects for notably enhanced photocatalytic oxidation performance

Graphitic carbon nitride (g-C₃N₄) offers exciting opportunities for sustainable photocatalytic oxidation of organic pollutants but suffers from drawbacks of insufficient oxidation driving force and low quantum efficiency. To over the drawbacks, here a simple and effective strategy was developed to engineer g-C₃N₄ with simultaneous interstitially embedded potassium dopant and nitrogen defects, and the process included supramolecular preorganization followed by KOH-assisted thermal polycondensation. In the prepared D_N-K-CN catalysts, potassium doping level and the amount of nitrogen defects were both controllable. With the increment of potassium doping level, the bandgap of the D_N-K-CN became narrow, along with continuously downshifted valence band position. The D_N-K-CN showed greatly enhanced visible-light photocatalytic oxidation performance with respect to g-C₃N₄ in the degradation of emerging phenolic pollutants, acetaminophen and methylparaben; meanwhile, the oxidation performance of D_N-K-CN depended on potassium doping level and the amount of nitrogen defects. Combination of experimental findings and theory calculations it is confirmed that the enhanced photocatalytic oxidation performance of D_N-K-CN was attributed to the synergistic effect of potassium dopant and nitrogen defects, which resulted in the generation of plentiful active oxygen species and the improvement of oxidation driving force of valence holes. The influence of potassium dopant and nitrogen defects on the electronic and band structures of g-C₃N₄ was revealed; simultaneously, mechanism of the enhanced photocatalytic oxidation performance of g-C₃N₄ after the introduction of potassium dopant and nitrogen defects was studied. The present work provided new insights into the electronic and band structure tuning for the improvement of the photocatalytic oxidation performance of g-C₃N₄.

Ultra-small molybdenum sulfide nanodot-coupled graphitic carbon nitride nanosheets: Trifunctional ammonium tetrathiomolybdate-assisted synthesis and high photocatalytic hydrogen evolution

The preparation of nanoscale molybdenum sulfide (MoS₂)-modified graphitic carbon nitride (g-C₃N₄) nanosheets usually contains complex and multiple-step operations, including the separate synthesis of nanoscale MoS₂ and g-C₃N₄ nanosheet, and their subsequent composite process. To effectively overcome the above drawbacks, herein, a facile one-step trifunctional ammonium tetrathiomolybdate ((NH₄)₂MoS₄)-assisted approach has been designed to produce ultra-small MoS_x nanodot-coupled g-C₃N₄ nanosheet photocatalyst, including the first addition of ammonium chloride (NH₄Cl) and (NH₄)₂MoS₄ into melamine precursors and their following one-step calcination. During high-temperature calcination, except for the promoting generation of the g-C₃N₄ nanosheets by produced ammonia (NH₃) and hydrogen sulfide (H₂S) gases, the above (NH₄)₂MoS₄ decomposition not only can efficiently clip the s-heptazine framework to produce more terminal amino groups and cyano groups, but also can produce ultra-small MoS_x nanodots on the resultant g-C₃N₄ nanosheet surface, resulting in the final production of ultra-small MoS_x nanodot-coupled g-C₃N₄ nanosheets. The resultant MoS_x nanodot-coupled g-C₃N₄ nanosheets evidently exhibit increased photocatalytic hydrogen (H₂)-generation rate, about 8-fold increase to the traditional MoS₂-modified g-C₃N₄ photocatalyst. The increased H₂-generation rate can be mainly attributed to the synergism of MoS_x nanodots and cyano group on the g-C₃N₄ nanosheet surface. The current facile technology could open the sights for the preparation of other high-efficiency photocatalysts.

Creation of carbon defects and in-plane holes with the assistance of NH4Br to enhance the photocatalytic activity of g-C3N4

A new holey defect-rich g-C₃N₄ photocatalyst from an NH₄Br-assisted programmed heating method exhibits an enhanced photocatalytic performance.

Effect of carbon and nitrogen double vacancies on the improved photocatalytic hydrogen evolution over porous carbon nitride nanosheets

Both carbon and nitrogen defects are formed in the porous carbon nitride after proper PVP addition and heating in air. It exhibits improved photocatalytic hydrogen evolution performance with increasing carbon to nitrogen atomic ratio.

Colloidal properties of the metal-free semiconductor graphitic carbon nitride

The metal-free, polymeric semiconductor graphitic carbon nitride (g-CN) family is an emerging class of materials and has striking advantages compared to other semiconductors, i.e. ease of tunability, low cost and synthesis from abundant precursors in a chemical environment. Efforts have been done to improve the properties of g-CN, such as photocatalytic efficiency, designing novel composites, processability and scalability towards discovering novel applications as a remedy for the problems that we are facing today. Despite the fact that the main efforts to improve g-CN come from a catalysis perspective, many fundamental possibilities arise from the special colloidal properties of carbon nitride particles, from synthesis to applications. This review will display how typical colloid chemistry tools can be employed to make 'better g-CNs' and how up to now overseen properties can be levered by integrating a colloid and interface perspective into materials chemistry. Establishing a knowledge on the origins of colloidal behavior of g-CN will be the core of the review.

Porous defective carbon nitride obtained by a universal method for photocatalytic hydrogen production from water splitting

For the first time, herein this work, we have developed an effective and adaptable method to introduce defects onto the polymeric carbon nitride by simply grinding urea with urea nitrate which resulting new carbon nitride composite (UNU-C₃N₄) and melamine with urea nitrate which resulting new carbon nitride composite (UNM-C₃N₄). The UNU-C₃N₄ reveals high performance towards photocatalytic hydrogen production and as well as photocatalytic removal of contaminants. The results confirm that the defects enhanced the specific surface area, and improved performance of adsorbed oxygen which beneficial to generate more active radicals and more conducive sties to improve d the overall photocatalytic performance. The high N, H, and O content-enhanced electron polarization effects, by introducing the additional N, H, and O atoms into the g-C₃N₄ matrix, which will increase the charge transfer rate and charge separation efficiency. At the same time, the results of ESR also expression that the new type of as-prepared carbon nitride samples exhibit abundant of hydrogen radical (H) formation, which is also assist to improve the photocatalytic hydrogen production performance. As expected, the H₂ evolution rate of UNU-C₃N₄(or UNM-C₃N₄) underneath simulated solar light irradiation is 9.93 times (13.76 times) than that of U-C₃N₄ (urea as raw material) (or M-C₃N₄ (melamine as raw material)). The high hydrogen evolution rates of UNU-C₃N₄ and UNM-C₃N₄ are 830.94 and 556.79 μmol g^-1  h^-1 under the visible-light irradiation, respectively. Meanwhile, the synthesized UNU-C₃N₄ and UNM-C₃N₄ material are demonstrated an efficient ability to degrade pollutants. In general, this work provides a viable way to introduce defects and hydrogen bands into the structure of carbon nitride.

A curly architectured graphitic carbon nitride (g-C3N4) towards efficient visible-light photocatalytic H2 evolution

The unique curly-like architecture g-C₃N₄ with excellent photocatalytic H₂ evolved activity was reported by a facile precursor-reforming strategy.

Enhancement of photocatalytic activity of g-C3N4 by hydrochloric acid treatment of melamine

Modified g-C₃N₄ samples (g-X, where X corresponds to the number of hours of acid treatment of the melamine) with outstanding photocatalytic performance were prepared by using hydrochloric acid-treated melamine as a precursor and calcining at 550 °C for 2 h. An x-ray diffractometer, field-emission scanning electron microscope, infrared spectrometer, N₂ adsorption-desorption test, x-ray photoelectron spectroscopy, and ultraviolet-visible diffuse-reflectance spectroscopy analysis were carried out to characterize the phase composition, microstructure, chemical structure, specific surface area (SSA), chemical states, elemental composition and optical properties of the samples, respectively. The photocatalytic performance of the samples was evaluated by degrading the Rhodamine B (RhB) aqueous solution. The results showed that the crystal structure and vibration bands of melamine changed due to the reaction with hydrochloric acid. The crystallinity and grain size of g-C₃N₄ in g-X (X = 1, 2, 4, 6, 8, 10) reduced, and the SSA values of g-X increased compared to that of the g-0 sample, which was synthesized from pristine melamine. The g-X samples exhibited excellent photocatalytic activity towards degradation of RhB compared to g-0. The photocatalytic activity of the g-X samples increased gradually as the acid treatment time of the melamine increased from 1 h to 2 h, and then decreased gradually with the extension of the acid treatment time. The rate constant (k) values of g-X are higher than that of g-0. g-2 presented the highest rate constant (k = 0.052 min^-1), which was 5.5 times higher than that of g-0. The improved photocatalytic activity of the g-X samples was attributed to the higher SSA value, the appearance of surface defects, the outstanding photo-carrier separation efficiency and stronger light harvesting ability of g-X, with the last two factors being more significant. Acid treatment of melamine is helpful in the preparation of high performance g-C₃N₄ photocatalyst, and the microstructure and photocatalytic performance of g-C₃N₄ were affected significantly by the acid treatment time.

Three-Dimensional Hierarchical g-C3N4 Architectures Assembled by Ultrathin Self-Doped Nanosheets: Extremely Facile Hexamethylenetetramine Activation and Superior Photocatalytic Hydrogen Evolution

Photocatalytic hydrogen evolution has broad prospects as a clean solution for the energy crisis. However, the rational design of catalyst complex, the H₂ evolution efficiency, and the yield are great challenge. Herein, three-dimensional hierarchical g-C₃N₄ architectures assembled by ultrathin carbon-rich nanosheets (3D CCNS) were prepared via an extremely facile hexamethylenetetramine activation approach at the bulk scale, indicating the validation of scale-up production process. The two-dimensional ultrathin carbon-rich nanosheets were several hundred nanometers in width but only 5-6 nm in thickness and gave rise to a unique 3D interconnected network. The unique composition and structure of the nanosheets endow them with a remarkable light absorption spectrum with the tunable band gap, high electrical conductivity, fast charge separation, and large surface areas with abundant reaction active sites, and thus significantly improved H₂ production performance. As high as ∼7.8%, quantum efficiency can be achieved by irradiating 3D CCNS at 420 nm with a H₂ evolution rate >2.7 × 10⁴ μmol/g/h, which is ∼31.3 times higher than that of the pristine g-C₃N₄. Our work introduces an extremely facile route for mass production of doping modified 3D g-C₃N₄-based photocatalyst with excellent H₂ evolution performances.

Graphitic carbon nitride/CoTPP type-II heterostructures with significantly enhanced photocatalytic hydrogen evolution

CoTPP inhibits the recombination of electron-hole pairs through extracting holes from g-C₃N₄ thus dramatically enhancing photocatalytic hydrogen production under visible light irradiation.

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

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

Facile preparation of graphitic-C3N4 quantum dots for application in two-photon imaging

A novel one-step method for the preparation of g-C₃N₄ QDs for effective two-photon imaging.

One-Step Nickel Foam Assisted Synthesis of Holey G-Carbon Nitride Nanosheets for Efficient Visible-Light Photocatalytic H2 Evolution

Graphitic carbon nitride (g-C₃N₄) with layered structure represents one of the most promising metal-free photocatalysts. As yet, the direct one-step synthesis of ultrathin g-C₃N₄ nanosheets remains a challenge. Here, few-layered holey g-C₃N₄ nanosheets (CNS) were fabricated by simply introducing a piece of nickel foam over the precursors during the heating process. The as-prepared CNS with unique structural advantages exhibited superior photocatalytic water splitting activity (1871.09 μmol h^-1 g^-1) than bulk g-C₃N₄ (BCN) under visible light (λ > 420 nm) (≈31 fold). Its outstanding photocatalytic performance originated from the high specific surface area (240.34 m² g^-1) and mesoporous structure, which endows CNS with more active sites, efficient exciton dissociation, and prolonged charge carrier lifetime. Moreover, the obvious upshift of the conduction band leads to a larger thermodynamic driving force for photocatalytic proton reduction. This methodology not only had the advantages for the direct and green synthesis of g-C₃N₄ nanosheets but also paved a new avenue to modify molecular structure and textural of g-C₃N₄ for advanced applications.

The novel synthesis of a continuous tube with laminated g-C3N4 nanosheets for enhancing photocatalytic activity and oxygen evolution reaction performance

Novel tubular graphitic carbon nitride has been successfully prepared via electrospinning technology, high temperature calcination technology, a vapor deposition reaction method and the method of acid removal, and in this process, Al₂O₃ fibers used as a template can help achieve the controllable preparation of GCNTs.