Facile in situ reductive synthesis of both nitrogen deficient and protonated g-C3N4 nanosheets for the synergistic enhancement of visible-light H2 evolution

Enhanced electrochemiluminescence of dual-defect graphite carbon nitride for ultrasensitive detection of CEA

Herein, a dual-defective graphite carbon nitride (DDCN) was prepared by polymerization under N2 atmosphere combined with oxidation treatment. The luminous intensity of dual-defect graphite phase carbon nitride based on defect state luminescence is significantly improved compared to CN-air. On this basis, a biosensor for CEA detection was constructed based on specific immunobinding of antigen-antibody. It is noted that the biosensor exhibits a wide linear range of 1 × 10-5 ∼ 1 × 102 ng•mL-1, a low detection limit of 3.3 × 10-4 pg•mL-1, a recovery of 94 %∼105 % and RSD less than 4.41 %. In addition, there was no significant difference to the clinical results, indicating that this work has good clinical application prospects.

Influence of gadolinium doping on structural, optical, and electronic properties of polymeric graphitic carbon nitride

Polymeric graphitic carbon nitride (gCN) materials have received great attention in the fields of photo and electrocatalysis due to their distinct properties in metal-free systems with high physicochemical stability. Nevertheless, the activity of undoped gCN is limited due to its relatively low specific surface area, low conductivity, and poor dispersibility. Doping Gd atoms in a gCN matrix is an efficient strategy to fine-tune its catalytic activity and its electronic structure. Herein, the influence of various wt% of gadolinium (Gd) doped in melon-type carbon nitride was systematically investigated. Gadolinium-doped graphitic carbon nitride (GdgCN) was synthesized by adding gadolinium nitrate to dicyandiamide during polymerization. The X-ray diffraction (XRD) and transmission electron microscopy (TEM) results revealed that the crystallinity and the morphological properties are influenced by the % of Gd doping. Furthermore, X-ray photoelectron spectroscopy (XPS) studies revealed that the gadolinium ions bonded with nitrogen atoms. Complementary density functional theory (DFT) calculations illustrate possible bonding configurations of Gd ions both in bulk material and on ultrathin melon layers and provide evidence for the corresponding bandgap modifications induced by gadolinium doping.

Highly sensitive and selective demethylase FTO detection using a DNAzyme-mediated CRISPR/Cas12a signal cascade amplification electrochemiluminescence biosensor with C-CN/PCNV heterojunction as emitter

Fat mass and obesity-associated protein (FTO) has gained attention as the first RNA N6-methyladenosine (m6A) modification eraser due to its overexpression being associated with various cancers. In this study, an electrochemiluminescence (ECL) biosensor for the detection of demethylase FTO was developed based on DNAzyme-mediated CRISPR/Cas12a signal cascade amplification system and carboxylated carbon nitride nanosheets/phosphorus-doped nitrogen-vacancy modified carbon nitride nanosheets (C-CN/PCNV) heterojunction as the emitter. The biosensor was constructed by modifying the C-CN/PCNV heterojunction and a ferrocene-tagged probe (ssDNA-Fc) on a glassy carbon electrode. The presence of FTO removes the m6A modification on the catalytic core of DNAzyme, restoring its cleavage activity and generating activator DNA. This activator DNA further activates the trans-cleavage ability of Cas12a, leading to the cleavage of the ssDNA-Fc and the recovery of the ECL signal. The C-CN/PCNV heterojunction prevents electrode passivation and improves the electron-hole recombination, resulting in significantly enhanced ECL signal. The biosensor demonstrates high sensitivity with a low detection limit of 0.63 pM in the range from 1.0 pM to 100 nM. Furthermore, the biosensor was successfully applied to detect FTO in cancer cell lysate and screen FTO inhibitors, showing great potential in early clinical diagnosis and drug discovery.

Accumulation of Long-Lived Photogenerated Holes at Indium Single-Atom Catalysts via Two Coordinate Nitrogen Vacancy Defect Engineering for Enhanced Photocatalytic Oxidation

Visible-light-driven photocatalytic oxidation by photogenerated holes has immense potential for environmental remediation applications. While the electron-mediated photoreduction reactions are often at the spotlight, active holes possess a remarkable oxidation capacity that can degrade recalcitrant organic pollutants, resulting in nontoxic byproducts. However, the random charge transfer and rapid recombination of electron-hole pairs hinder the accumulation of long-lived holes at the reaction center. Herein, a novel method employing defect-engineered indium (In) single-atom photocatalysts with nitrogen vacancy (Nv) defects, dispersed in carbon nitride foam (In-Nv-CNF), is reported to overcome these challenges and make further advances in photocatalysis. This Nv defect-engineered strategy produces a remarkable extension in the lifetime and an increase in the concentration of photogenerated holes in In-Nv-CNF. Consequently, the optimized In-Nv-CNF demonstrates a remarkable 50-fold increase in photo-oxidative degradation rate compared to pristine CN, effectively breaking down two widely used antibiotics (tetracycline and ciprofloxacin) under visible light. The contaminated water treated by In-Nv-CNF is completely nontoxic based on the growth of Escherichia coli. Structural-performance correlations between defect engineering and long-lived hole accumulation in In-Nv-CNF are established and validated through experimental and theoretical agreement. This work has the potential to elevate the efficiency of overall photocatalytic reactions from a hole-centric standpoint.

Chitosan-assisted synthesis of 1D g-C3N4 nanorods for enhanced photocatalysis

1D porous g-C3N4 nanorods were synthesized using chitosan as a template, offering a large surface area and enhanced visible light absorption. These nanorods exhibited a remarkable 8.3-fold increase in H2 generation rate (26.6 μmol h-1) compared to bulk g-C3N4.

Alternating current properties of bulk- and nanosheet-graphitic carbon nitride compacts at elevated temperatures

The investigations of temperature-dependent electrical properties in graphitic carbon nitride (g-C3N4) have been largely performed at/below room temperature on devices commonly fabricated by vacuum techniques, leaving the gap to further explore its behaviors at high-temperature. We reported herein the temperature dependence (400 → 35 °C) of alternating current (AC) electrical properties in bulk- and nanosheet-g-C3N4 compacts simply prepared by pelletizing the powder. The bulk sample was synthesized via the direct heating of urea, and the subsequent HNO3-assisted thermal exfoliation yielded the nanosheet counterpart. Their thermal stability was confirmed by variable-temperature X-ray diffraction, demonstrating reversible interlayer expansion/contraction upon heating/cooling with the thermal expansion coefficient of 2.2 × 10-5-3.1 × 10-5 K-1. It is found that bulk- and nanosheet-g-C3N4 were highly insulating (resistivity ρ ∼ 108 Ω cm unchanged with temperature), resembling layered van der Waals materials such as graphite fluoride but unlike electronically insulating oxides. Likewise, the dielectric permittivity ε', loss tangent tan δ, refractive index n, dielectric heating coefficient J, and attenuation coefficient α, were weakly temperature- and frequency-dependent (103-105 Hz). The experimentally determined ε' of bulk-g-C3N4 was reasonably close to the in-plane static dielectric permittivity (8 vs. 5.1) deduced from first-principles calculation, consistent with the anisotropic structure. The nanosheet-g-C3N4 exhibited a higher ε' ∼ 15 while keeping similar tan δ (∼0.09) compared to the bulk counterpart, demonstrating its potential as a highly insulating, stable dielectrics at elevated temperatures.

Functionalized 2D defect g-C3N4 for artificial photosynthesis of H2O2 and synchronizing tetracycline fluorescence detection and degradation

Artificial photosynthesis of H₂O₂ is a clean production technology, which brings the synergistic effect to photodegradation of pollutants. Inspired by defect engineering, 2D defective carbon nitride (g-C₃N₄) photocatalyst was obtained via potassium ion assisted synthesis. Defective g-C₃N₄ is protonated and applied to photosynthesis of H₂O₂, H₂O₂ concentration produced reached 477.7 μM, which was approximately 5.27 times that by pristine g-C₃N₄. Additionally, defective g-C₃N₄ materials are borrowed to synchronizing tetracycline (TC) fluorescence detection and degradation, suggesting the catalyst existed bifunctional characteristics of TC detection and degradation. Meanwhile, metal impregnation engineering (molybdenum) was borrowed enhancing the electron-trapping ability in local region of defective g-C₃N₄, which takes advantages to the efficient degradation of TC. Furthermore, optical and electrical properties of photocatalysts were investigated in details by advanced material characterization testing. This work provides potential applications in the field of artificial photosynthesis and pollution degradation.

Template-Free Synthesis of Phosphorus-Doped g-C3 N4 Micro-Tubes with Hierarchical Core-Shell Structure for High-Efficient Visible Light Responsive Catalysis

This work reports a new form of tubular g-C₃ N₄ that is featured with a hierarchical core-shell structure introduced with phosphorous elements and nitrogen vacancies. The core is self-arranged with randomly stacked g-C₃ N₄ ultra-thin nanosheets along the axial direction. This unique structure significantly benefits electron/hole separation and visible-light harvesting. A superior performance for the photodegradation of rhodamine B and tetracycline hydrochloride is demonstrated under low intensity visible light. This photocatalyst also exhibits an excellent hydrogen evolution rate (3631 µmol h^-1 g^-1 ) under visible light. Realizing this structure just requires the introduction of phytic acid into the solution of melamine and urea during hydrothermal treatment. In this complex system, phytic acid plays as the electron donor to stabilize melamine/cyanuric acid precursor via coordination interaction. Calcination at 550 °C directly renders the transformation of precursor into such hierarchical structure. This process is facile and shows the strong potential toward mass production for real applications.

TiO2/graphitic carbon nitride nanosheet composite with enhanced sensitivity to atmospheric water

Understanding the fundamentals of transport properties in two-dimensional (2D) materials is essential for their applications in devices, sensors, and so on. Herein, we report the impedance spectroscopic study of carbon nitride nanosheets (CNNS) and the composite with anatase (TiO₂/CNNS, 20 atom% Ti), including their interaction with atmospheric water. The samples were characterized by X-ray diffraction, N₂ adsorption/desorption, solid state ¹H nuclear magnetic resonance spectroscopy, thermogravimetric analysis, and transmission electron microscopy. It is found that CNNS is highly insulating (resistivity ρ ∼ 10¹⁰ Ω cm) and its impedance barely changes during a 20 min-measurement at room temperature and 70% relative humidity. Meanwhile, incorporating the semiconducting TiO₂ nanoparticles (∼10 nm) reduces ρ by one order of magnitude, and the decreased ρ is proportional to the exposure time to atmospheric water. Sorbed water shows up at low frequency (<10² Hz) with relaxation time in milliseconds, but the response intrinsic to CNNS and TiO₂/CNNS is evident at higher frequency (>10⁴ Hz) with relaxation time in microseconds. These two signals apparently correlate to the endothermic peak at ≤110 °C and >250 °C, respectively, in differential scanning calorimetry experiments. Universal power law analysis suggests charge hopping across the 3D conduction pathways, consistent with the capacitance in picofarad typical of grain response. Our work demonstrates that the use of various formalisms (i.e., impedance, permittivity, conductivity, and modulus) combined with a simple universal power law analysis provides insights into water-induced transport of the TiO₂/CNNS composite without complicated curve fitting procedure or dedicated humidity control.

Edge-grafting carbon nitride with aromatic rings for highly-efficient charge separation and enhanced photocatalytic hydrogen evolution

Edge-modification of g-C3N4 induces highly-efficient charge separation through directional transfer of electrons from the center to the edge of the framework.

Investigation of Photocatalyst Composites for Pollutant Degradation in a Microslit Reactor Utilizing High Throughput Screening Techniques

The high-throughput screening investigations on TiO2 based photocatalyst composites presented here have been carried out in a 60-fold parallel photoreactor. Additional catalyst testing was performed in a microslit reactor system with immobilized catalysts. For further enhancing the photocatalytic activity of TiO2 (P25), composites of P25 and, for example, Bi2 O3 , CeO2 , g-C3 N4 , WO3 or ZnO were formulated in different nominal molar ratios. The catalysts' performances were assessed by their conversion of 17α-ethinyl estradiol (EE2) in aqueous solutions, determined by LC-MS. Findings show rapid EE2 conversions in short residence times. The extensive testing of catalysts led to the conclusion that the photocatalytic conversion is rather a function of residence time than a function of the materials utilized. This makes adequate process development seem more important than material development. The novelty of this contribution lies in the unique combination of testing a wide range of composite catalysts in a unique microreactor geometry.

Nitrobenzene inarched carbon nitride nanotube drives efficient directional carriers separation for superior photocatalytic hydrogen production

Carbon nitride (g-C₃N₄) is aussichtsreich for photocatalytic hydrogen evolution, but its photocatalytic activity is not ideal due to the existence of photogenerated electrons and holes in the form of excitons. Herein, a novel nitrobenzene inarched g-C₃N₄ nanotube photocatalyst (CN-DNP) was firstly fabricated via a facial copolymerization method. The aromatic ring in nitrobenzene could enhance the conjugation of carbon nitride to promote electron delocalization. The nitro group enabled electrons to transfer from center to the both ends of g-C₃N₄ nanotube, which drove the separation of photogenerated electrons and holes more effectively. Compared with bulk g-C₃N₄ (CN), CN-DNP had narrower bandgap that can acquire adequate visible light harvesting and improve its photocatalytic performance. Consequently, CN-DNP0.1 displayed an excellent photocatalytic H₂ evolution of 2262.4 μmol g^-1h^-1, which was 11.2 folds higher than that of CN. This strategy provides a new guidance for constructing carbon nitride nanotube materials with carrier directional transfer to enhance the photocatalytic performance.

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.

Design of well-defined shell-core covalent organic frameworks/metal sulfide as an efficient Z-scheme heterojunction for photocatalytic water splitting

Development of a covalent-organic framework (COF)-based Z-scheme heterostructure is a promising strategy for solar energy driven water splitting, but the construction of a COF-based Z-scheme heterostructure with well-defined architecture, large contact area and intimate contact interfaces is scarce. Herein, we fabricated a direct Z-scheme heterostructure COF-metal sulfide hybrid (T-COF@CdS) with shell-core architecture by self-polymerization of 1,3,5-benzenetricarboxaldehyde and 2,4,6-tris(4-aminophenyl)-1,3,5-triazine in situ on CdS. The formed C-S chemical bonding between T-COF and CdS could provide a very tight and stable interface. Owing to the properly staggered band alignment, strong interfacial interaction and large interfacial contact area between T-COF and CdS, a Z-scheme route for charge separation and transfer is realized, resulting in electron accumulation in CdS for H2O reduction. The obtained Z-scheme heterostructure T-COF@CdS-3 exhibits a high apparent quantum efficiency of 37.8% under 365 nm monochromatic light irradiation, and long-term stability arising from shell-core structures in which the T-COF shell protects the catalytic centers of CdS against deactivation, as well as acts as oxidation sites to avoid the photocorrosion of CdS. This work provides a strategy for the construction of a shell-core direct Z-scheme heterostructure photocatalyst for water splitting with high performance.

Fabrication of g-C3N4 Nanosheets Anchored With Controllable CdS Nanoparticles for Enhanced Visible-Light Photocatalytic Performance

Herein, g-C₃N₄/CdS hybrids with controllable CdS nanoparticles anchoring on g-C₃N₄ nanosheets were constructed. The effects of CdS nanoparticles on photocatalytic H₂ production and organic molecule degradation for g-C₃N₄/CdS hybrids were investigated. The maximum rate of H₂ production for g-C₃N₄/CdS sample was 1,070.9 μmol g⁻¹ h⁻¹, which was about four times higher than that of the individual g-C₃N₄ nanosheet sample. The enhanced photocatalytic performance for prepared hybrids could be mainly attributed to the following causes: the formed heterojunctions can contribute to the light absorption and separation of photogenerated electrons and holes, the two-dimensional layered structure facilitates the transmission and transfer of electrons, and high specific surface area could provide more exposed active sites.

Molecular Self-Assembly of Oxygen Deep-Doped Ultrathin C3N4 with a Built-In Electric Field for Efficient Photocatalytic H2 Evolution

Heteroatom-doped carbon nitride (C₃N₄) with a built-in electric field can reinforce the carrier separation; however, the stability will be greatly reduced due to the loss of surface-doped atoms. Here, molecule self-assembly, as a facile bottom-up approach, is explored for the synthesis and oxygen doping of C₃N₄. The obtained C₃N₄ presents a porous and ultrathin structure and oxygen deep-doping, which generate abundant nitrogen vacancies and a stable built-in electric field. Toward photocatalytic hydrogen evolution, the ultrathin and oxygen deep-doped C₃N₄ exhibits a 3.5-fold higher activity than bulk C₃N₄ under simulated sunlight, and 3.6 times higher stability than the oxygen surface-doped counterpart within five cycles. Femtosecond transient absorption spectroscopy indicates the improved carrier separation, and density functional theory (DFT) calculation reveals the promoted H₂O adsorption and activation under the built-in electric field, which contribute to the excellent photocatalytic performance of oxygen deep-doped ultrathin C₃N₄.

Engineering of g-C3N4-based photocatalysts to enhance hydrogen evolution

The technology of photocatalytic hydrogen production that converts abundant yet intermittent solar energy into an environmentally friendly alternative energy source is an attractive strategy to mitigate the energy crisis and environmental pollution. Graphitic carbon nitride (g-C₃N₄), as a promising photocatalyst, has gradually received focus in the field of artificial photosynthesis due to its appealing optical property, high chemical stability and easy synthesis. However, the limited light absorption and massive recombination of photoinduced carriers have hindered the photocatalytic activity of bare g-C₃N₄. Therefore, from the perspective of theoretical calculations and experiments, many valid approaches have been applied to rationally design the photocatalyst and ameliorate the hydrogen production performance, such as element doping, defect engineering, morphology tuning, and semiconductor coupling. This review summarized the latest progress of g-C₃N₄-based photocatalysts from two perspectives, modification of pristine g-C₃N₄ and interfacial engineering design. It is expected to offer feasible suggestions for the fabrication of low-cost and high-efficiency photocatalysts and the photocatalytic mechanism analyses assisted by calculation in the near future. Finally, the prospects and challenges of this exciting research field are discussed.

Nitrogen Vacancy Engineering in Graphitic Carbon Nitride for Strong, Stable, and Wavelength Tunable Electrochemiluminescence Emissions

As an attractive electrochemiluminescence (ECL) emitter, graphitic carbon nitride (CN) still suffers from weak and unstable ECL signals for its poor conductivity and the occurrence of electrode passivation. In this study, a simple nitrogen vacancy (NV) engineering strategy has been developed for the improvement of ECL performances (intensity and stability) for the first time. In comparison to pristine CN (RSD = 51.98% for 10 continuous scan), ca. 60 times amplification in ECL intensity and 70 times enhancement in ECL efficiency for CN modified with NVs (CN-NVs) were obtained. In addition, more stable ECL emissions (RSD = 0.53%) were achieved for CN-NV-550 by thermal treatment of pristine CN in a N₂ atmosphere for another 2 h at 550 °C. The mechanism study for the vital role of NVs on the ECL of CN-NVs revealed that NVs can not only facilitate electron transfer to amplify the ECL intensity but also serve as the electron trap to inhibit electrode passivation. More interestingly, a series of CN-NVs exhibited a tunable ECL wavelength range from 470 to 516 nm with different NV contents. Moreover, their ECL spectra showed an obvious red-shift of the wavelength with their corresponding fluorescence spectra. These findings confirmed that the ECL emissions of CN-NVs were susceptible to the relevant surface states of NVs. Our work may open up a promising pathway for improving ECL performances of CN and create new possibilities for multitarget simultaneous detection based on ECL and construction of color tunable light-emitting devices.

BiOI Particles Confined into Metal-Organic Framework NU-1000 for Valid Photocatalytic Hydrogen Evolution under Visible-Light Irradiation

Herein, a surface site engineering strategy is used to construct a porous Z-scheme heterojunction photocatalyst for photocatalytic hydrogen evolution (PHE) by integration of BiOI in a mesoporous Zr-based metal-organic framework (MOF) NU-1000. Three high-quality and highly dispersed BiOI@NU-1000 heterojunction materials are synthesized, and a set of methods is used to characterize these materials, indicating that the BiOI@NU-1000 heterojunction can retain high porosity and crystallinity of the parent NU-1000. Furthermore, the built-in electric field of the BiOI@NU-1000 composite can effectively tune the band gap, promote the separation of photoinduced charge carriers, improve photocurrent intensity, and reduce photoelectric impedance. Under visible-light irradiation, BiOI@NU-1000-2 showed the best photocatalytic performance in the field of MOF-based photocatalysts for PHE, with a hydrogen production rate of up to 610 μmol h^-1 g^-1. This study will open up opportunities for the construction of Z-scheme photocatalysts based on the highly porous MOF materials to inspire the development of innovative photocatalysts.

Doping of Graphitic Carbon Nitride with Non-Metal Elements and Its Applications in Photocatalysis

This review outlines the latest research into the design of graphitic carbon nitride (g-C3N4) with non-metal elements. The emphasis is put on modulation of composition and morphology of g-C3N4 doped with oxygen, sulfur, phosphor, nitrogen, carbon as well as nitrogen and carbon vacancies. Typically, the various methods of non-metal elements introducing in g-C3N4 have been explored to simultaneously tune the textural and electronic properties of g-C3N4 for improving its response to the entire visible light range, facilitating a charge separation, and prolonging a charge carrier lifetime. The application fields of such doped graphitic carbon nitride are summarized into three categories: CO2 reduction, H2-evolution, and organic contaminants degradation. This review shows some main directions and affords to design the g-C3N4 doping with non-metal elements for real photocatalytic applications.