Phenyl-Bridged Graphitic Carbon Nitride with a Porous and Hollow Sphere Structure to Enhance Dissociation of Photogenerated Charge Carriers and Visible-Light-Driven H2 Generation

Simple defect engineering of carbon nitride using mixed precursors for enhanced photocatalysis

Remarkable improvements in the morphological and photophysical properties of the carbon nitride (CN) photocatalyst are achieved by simply mixing two different precursors, which partially terminates the co-polymerization of heptazine units and induces a defective structure. This defective CN is rich in mesopores, offering abundant reaction sites and exhibiting enhanced photoconductivity.

Dual-site and carbon-ring moiety modulation of polymeric carbon nitride for improved cooperative photocatalysis

The conjugated structure of graphitic polymeric carbon nitrides (GPCNs) has low efficiency in the photocatalytic hydrogen peroxide (H2O2) production, due to the electronic properties, band structure, and surface-active-sites. Herein, boron and carbon-ring modified GPCNs were synthesized with via a thermal condensation method, using melamine and phenylboronic acid as raw materials. The introduced boron atom, conjugated to the carbon atom in the heptazine moiety, and the adjacent nitrogen vacancy (VN) formed a dual-site, which not only modified the electronic properties but also promoted the adsorption and activation of molecular dioxygen; The carbon-ring introduced altered the band structure and electron distribution, which was proved by density functional theory (DFT) calculations. The co-modification promoted the conversion of dioxygen molecule to H2O2, coupled with oxidation of benzyl alcohol (BA) to benzaldehyde (BAD). The optimal activity was achieved over CN-B3 (1.87 mmol/(g·h)), which was about 4-fold higher than that of PCN (0.49 mmol/(g·h)). More interestingly, mechanism study revealed that the photocatalytic H2O2 generation was realized via a photon energy transfer route, that is, O2 molecule firstly was converted to a highly active singlet oxygen (1O2) intermediate, which was reduced by electrons to superoxide anions (O2-) and coupled with proton to form H2O2. This method provides a novel strategy to improve photocatalytic H2O2 and high value-added chemical production by regulating the microstructure and electronic structure of GPCNs through heteroatom and moiety co-modification.

Bridging engineering of polymeric carbon nitride for boosting photocatalytic CO2 reduction

The inherent electron localized heptazine structure of carbon nitride (CN) derived from intrinsic tertiary N (N3C) bridging structure makes the photogenerated charge separation rather difficult, which severely limits photocatalytic CO2 activity of CN. Therefore, modulation of N3C bridging structure of CN is highly desirable to enhance the charge separation efficiency of CN. Herein, we reported a novel thiophene-bridged CN (BTCN) with intramolecular donor-π-acceptor (D-π-A) systems synthesized by nucleophilic substitution and Schiff base reaction to improve the photogenerated charge separation efficiency. The experimental and density functional theory (DFT) results indicate that this BTCN exhibits a high π-electron delocalization range and enhanced photogenerated charge transfer efficiency, which mainly account for the enhanced photocatalytic activity. The optimal BTCN photocatalyst exhibits enhanced charge separation efficiency and higher photocatalytic CO2 reduction activity with a CO yield of 23.02 μmol·g-1·h-1, which was higher than those of CN and edge-modified CN (ETCN) counterpart. This work highlights the importance of regulation of π-electron delocalization for the design of highly active CN photocatalysts via the rational substitution of N3C bridging structure with π-spacer molecular linkages for photocatalytic CO2 reduction.

Diiodo-BODIPY Sensitizing of the [Mo3S13]2- Cluster for Noble-Metal-Free Visible-Light-Driven Hydrogen Evolution within a Polyampholytic Matrix

We report on a photocatalytic setup that utilizes the organic photosensitizer (PS) diiodo-BODIPY and the non-precious-metal-based hydrogen evolution reaction (HER) catalyst (NH₄)₂[Mo₃S₁₃] together with a polyampholytic unimolecular matrix poly(dehydroalanine)-graft-poly(ethylene glycol) (PDha-g-PEG) in aqueous media. The system shows exceptionally high performance with turnover numbers (TON > 7300) and turnover frequencies (TOF > 450 h^-1) that are typical for noble-metal-containing systems. Excited-state absorption spectra reveal the formation of a long-lived triplet state of the PS in both aqueous and organic media. The system is a blueprint for developing noble-metal-free HER in water. Component optimization, e.g., by modification of the meso substituent of the PS and the composition of the HER catalyst, is further possible.

Plasmon Au/K-doped defective graphitic carbon nitride for enhanced hydrogen production

Knowledge of the photocatalytic H₂-evolution mechanism is of critical importance for water splitting, and for designing active catalysts for a sustainable energy supply. In this study, we prepared plasmon Au-modified K-doped defective graphitic carbon nitride (Au/KCNx) and then applied it in photocatalytic hydrogen-production tests. The hydrogen-production rate of the Au/KCNx photocatalyst (8.85 mmol g^-1 h^-1) was found to be almost 104 times higher than that of Au/g-C₃N₄ (0.085 mmol g^-1 h^-1), together with an apparent quantum efficiency of 12.8% at 420 nm. It could significantly improve the photocatalytic activities of the Au/KCNx sample, which was attributed to the synergistic effects of the plasmon effect, potassium doping, and nitrogen vacancy. In addition, the Au/KCNx photocatalyst had a large surface area, which was beneficial for photogenerated carrier separation and transfer. The novel strategy proposed here is a potential new method for the development of graphitic carbon nitride photocatalysts with obviously enhanced activities.

Template-free preparation of carbon nitride hollow spheres with adjustable sizes for photocatalytic hydrogen generation

Carbon nitride hollow spheres (CNHS) with adjustable sizes were successfully fabricated via a template-free supramolecular pre-assembly strategy, in which melamine-cyanuric acid (MCA) hollow spheres were constructed through hydrogen bonds. A feasible formation mechanism was proposed, which coupled an inside-out Ostwald ripening with the supramolecular pre-assembly process. Interestingly, the sizes of MCA could be manipulated by changing the pre-assembly temperature. Consequently, the sizes of CNHS were adjustable. The optimal CNHS exhibited excellent photocatalytic hydrogen evolution rate (98.6 μmol/h) in the visible-light region, which was approximately 11 times higher than that of bulk carbon nitride calcined by melamine. The significantly improved performance was due to the contributions including: the unique architectures with remarkable light absorption ability, high electrical conductivity, relatively narrowed band gap, fast charge separation. This work provides a facile template-free supramolecular pre-assembly strategy to fabricate carbon nitride hollow spheres with adjustable sizes for the first time.

Construction of double-functionalized g-C3N4 heterojunction structure via optimized charge transfer for the synergistically enhanced photocatalytic degradation of sulfonamides and H2O2 production

Herein, supporting g-C₃N₄ embedded with benzene-ring (BCN) on P-modified g-C₃N₄ (PCN) successfully synthesized the homogeneous photocatalyst BCN/PCN (PBCN) via a simple thermal polymerization reaction. Under blue-light (LED) irradiation, the optimized PBCN (0.448 min^-1) demonstrated excellent photocatalytic performance, attaining over 74 times the degradation rate for sulfisoxazole (SSZ) in contrast to non-functionalized g-C₃N₄ (CN, 0.006 min^-1). Theoretical calculations revealed that the substitution of heterocyclic rings in the g-C₃N₄ triazine networks with benzene-rings enabled them to serve as electron donors, while promoting photoinduced spatial charge dissociation. Further, the carrier PCN tended to serve as electron acceptors to form electron-rich corner-phosphorous sites. Reactive species experiments demonstrate that the O₂˙^- and h⁺ constituted the primary photocatalytic mechanism of SSZ degradation. The potential SSZ degradation routes were predicted based on the transformation products via mass spectrometry. Finally, the composite materials also exhibited excellent photocatalytic activity in the conversion of solar energy to chemical energy (H₂O₂). This study guides the rational modification of g-C₃N₄-based semiconductors to achieve green energy production and beneficial ecological applications.

Intramolecular π-conjugated channel expansion achieved by doping cross-linked dopants into carbon nitride frameworks for propelling photocatalytic hydrogen evolution and mechanism insight

PYM as a cross-linked bridge in CN frameworks via a multi-bonding mode expedites the transfer and separation of intramolecular photoproduced electron–hole pairs by π-conjugated channel expansion to improve the PHE activity.

Tandem ZnCo-porphyrin metal–organic frameworks for enhanced photoreduction of CO2

A bimetallic ZnCo-porphyrin metal–organic framework (ZnCo-BMOF) nanosheet comprised of photosensitizers (Zn porphyrin) and catalysts (Co porphyrin) was developed for efficient photoreduction of CO2 to CO.

Constructing porous intramolecular donor–acceptor integrated carbon nitride doped with m-aminophenol for boosting photocatalytic degradation and hydrogen evolution activity

A porous intramolecular D–A integrated carbon nitride with boosted photocatalytic activity was constructed via thermal melting followed by thermal copolymerization of m-aminophenol with urea.

Instantaneous Sonophotocatalytic Degradation of Tetracycline over NU-1000@ZnIn2S4 Core-Shell Nanorods as a Robust and Eco-friendly Catalyst

The universal pollution of diverse water bodies and declined water quality represent very important environmental problems. The development of new and efficient photocatalytic water treatment systems based on the Z-scheme mechanisms can contribute to tackling such problems. This study reports the preparation, full characterization, and detailed sonophotocatalytic activity of a new series of hybrid NU@ZIS nanocomposites, which comprise a p-n heterojunction of 3D Zr(IV) metal-organic framework nanorods (NU-1000) and photoactive ZnIn₂S₄ (ZIS) nanostars. Among the obtained materials with varying content of ZIS (5, 10, 20, and 30%) on the surface of NU-1000, the NU@ZIS20 nanocomposite revealed an ultrahigh catalytic performance and recyclability in a quick visible-light-induced degradation of the tetracycline antibiotic in water under sonophotocatalytic conditions. Moreover, increased activity of NU@ZIS20 can be ascribed to the formation of a p-n heterojunction between NU-1000 and ZIS, and a synergistic effect of these components, leading to a high level of radical production, facilitating a Z-scheme charge carrier transfer and reducing the recombination of charge carriers. The radical trapping tests revealed that ^•OH, ^•O₂^-, and h⁺ are the major active species in the sonophotocatalytic degradation of tetracycline. Possible mechanism and mineralization pathways were introduced. Cytotoxicity of NU@ZIS20 and aquatic toxicity of water samples after tetracycline degradation were also assessed, showing good biocompatibility of the catalyst and efficacy of sonophotocatalytic protocols to produce water that does not affect the growth of bacteria. Finally, the obtained nanocomposites and developed photocatalytic processes can represent an interesting approach toward diverse environmental applications in water remediation and the elimination of other types of organic pollutants.

Ternary multifunctional catalysts of polymeric carbon nitride coupled with Pt-embedded transition metal oxide to enhance light-driven photothermal catalytic degradation of VOCs

Light driven photothermal catalysis has been carried out by converting the light energy into heat to reach the light-off temperature of the reaction. Herein we have synthesized the ternary multifunctional catalysts of polymeric carbon nitride coupled with Pt-embedded transition metal oxide (Pt-Co_x/CN), for the catalytic degradation of toluene. Under the condition of space velocity of 30,000 mL/(gh) and concentration of 210 ppm, toluene conversion and CO₂ mineralization can reach 90% and 83% over Pt-Co₂₀/CN, respectively. The introduction of an appropriate proportion of CoO enhances the light absorption of nanocomposites and improves the adsorption for toluene. Meanwhile, CoO promotes the proportion and mobility of adsorbed oxygen on the surface, which are conducive to the catalytic oxidation reaction according to the Mars-van Krevelen mechanism. The results also suggest that light irradiation serves as a source of heat to initiate photo-induced chemical reactions and promote photothermal catalytic oxidation by promoting the activation of lattice oxygen.

Incorporation of Nonmetal Group Dopants into g-C3N4 Framework for Highly Improved Photocatalytic H2 Production

The incorporation of nonmetal group dopants into a graphitic carbon nitride (g-C₃N₄) framework is fabricated by adding a small amount of hexamethylenetetramine during the thermal polymerization process. The material shows an excellent visible-light photocatalytic H₂ production performance that is eight times higher than bulk g-C₃N₄. This outstanding performance is ascribed to the introducing of N-doped carbon, which not only enhances the light absorption and favorsa narrower band gap, but also upshifts the conductionband (CB) potential, resulting in a better reduction ability of electrons. This discovery has potential significancefor the designing of high performance, economic, and environmental friendly photocatalyst for solar energy conversion.

Insight into the influence of donor-acceptor system on graphitic carbon nitride nanosheets for transport of photoinduced charge carriers and photocatalytic H2 generation

The rapid recombination of photogenerated charges is one of the main restriction for promoting the photocatalytic H₂ generation of graphitic carbon nitride (CN) material. Herein, donor-acceptor (D-A) system was introduced into CN nanosheets by oxygen and/or phenyl doping (DA-CN) strategy to facilitate the transport of photoinduced charge carriers and H₂ generation. Experimental and theoretical results revealed that the nanosheet structure of DA-CN shortened the photoexcited charges transport length to the surface, and the D-A system embedded in DA-CN provided the dipole-induced internal electric field for charges transport. As a consequence, compared with pristine CN, DA-CN samples performed the improved transport of photogenerated charges and photocatalytic H₂ evolution. Notably, DA-CN-OP (oxygen and phenyl co-doping) with the strongest dipole-induced internal electric field originated from D-A system displayed the highest photocatalytic H₂ evolution rate at 7.394 mmol g^-1h^-1, which was 7.67 times as that of pristine CN (0.964 mmol g^-1h^-1). This work not only provides a simple strategy to construct highly efficient CN nanosheet photocatalyst with D-A system, but also promote the deep insight into the effect of molecular dipole originated from D-A system on the transport of photoinduced charge carriers and photocatalytic activity for CN material.

Experimental study on bone defect repair by BMSCs combined with a light-sensitive material: g-C3N4/rGO

Bone marrow mesenchymal stem cells (BMSCs), as seed cells, have played an important role in bone defect repair. However, efficiently amplifying and inducing BMSCs in vitro or vivo remains an urgent problem to be solved. Electrical stimulation has been beneficial to the proliferation and differentiation of BMSCs, but current electrical stimulation methods have a critical disadvantage in that they usually burn the skin. g-C₃N₄/rGO, a new photosensitive material, can produce photocurrent under natural light irradiation, thus reducing energy consumption. Our purpose was to explore whether this photocurrent can promote the proliferation and differentiation of BMSCs. g-C₃N₄/rGO synthesised under high temperature and pressure had negligible cytotoxicity as confirmed by methyl thiazolyl tetrazolium to BMSCs. Better osteogenesis was found in the blue light material group than in the light-shielding material group, exhibited by alizarin red staining, alkaline phosphatase activity, Western-Blot, and RT-qPCR. Animal experiments showed that the bone repair potential of the material group was significantly higher than that of the non-material group. Overall, we conclude that g-C₃N₄/rGO is a new non-toxic photosensitive material which can rapidly induce BMSCs into osteoblasts, accelerating bone regeneration and providing us with a feasible method of rapid bone repair.