g-C3N4 Quantum Dots Research Articles

Graphite-like carbon nitride quantum dot (CNQD)-modified Bi2MoO6 heterostructure with high visible-light photocatalytic activity

Here, g-C3N4 quantum dot (CNQDs)/Bi2MoO6 nanoheterostructures were successfully synthesized. The CNQDs/Bi2MoO6 nanocomposite exhibited enhanced photocatalytic activity.

Microwave growth and tunable photoluminescence of nitrogen-doped graphene and carbon nitride quantum dots

Tunable photoluminescent nitrogen-doped graphene and graphitic carbon nitride (g-C3N4) quantum dots are synthesized via a facile solid-phase microwave-assisted (SPMA) technique utilizing the pyrolysis of citric acid and urea precursors.

Nanoporous 2D semiconductors encapsulated by quantum-sized graphitic carbon nitride: tuning directional photoinduced charge transfer via nano-architecture modulation

A reversed charge transfer pathway in photoredox catalysis has been achieved by rational structure engineering through electrostatically integrating g-C3N4 quantum dots with nanoporous CdS nanosheets.

G-C3N4/B doped g-C3N4 quantum dots heterojunction photocatalysts for hydrogen evolution under visible light

Developing high activity and eco-friendly photocatalysts for water splitting is still a challenge in solar energy conversion. In this paper, B doped g-C3N4 quantum dots (BCNQDs) were prepared via a facile molten salt method using melamine and boron oxide as precursors. By introducing BCNQDs onto the surface of g-C3N4, g-C3N4/BCNQDs heterojunction was constructed via hydrothermal treatment. The resulting g-C3N4/BCNQDs heterojunction exhibits enhanced hydrogen evolution performance for water splitting under visible light irradiation. The mechanism underlying the improved photocatalytic activity was explored and discussed based on the formation of heterojunction between g-C3N4 and BCNQDs with well-matched band structure.

Combination of CuS and g-C3N4 QDs on upconversion nanoparticles for targeted photothermal and photodynamic cancer therapy

Combined therapy with multimodal therapeutic agents based on nanomaterials has been shown as a promising approach to cancer treatment. In this report, a highly efficient multifunctional anti-cancer nanocomposite was fabricated by assembling a photothermal agent (CuS nanoparticles) and a photodynamic agent (g-C3N4 quantum dots) on upconversion nanoparticles (UCNPs) after mesoporous silica coating. Then, the surface modification of the obtained nanocomposite (abbreviated as CUSCs) with polyethylene glycol (PEG) and folic acid (FA) endows the final sample (denoted as CUSCs-PEG-FA) with an excellent cancer cell targeting effect and biocompatibility. In this nanoplatform, CuS nanoparticles are an inorganic substance with low toxicity and high photothermal conversion efficiency. g-C3N4 QDs have excellent biocompatibility and are beneficial for cellular uptake due to their small size. UCNPs can be excited by near-infrared (NIR) light to produce ultraviolet and visible (UV–vis) light emission, which overlaps with the UV absorption peak of high fluorescence g-C3N4 quantum dots (QDs). Therefore, when the nanocomposite is excited by 808 nm NIR light, a synergistic treatment effect will be presented. Since the wavelengths absorbed by the chosen photothermal agent and the photosensitizer are different, sufficient utilization of energy can be achieved. Combining photothermal therapy (high photothermal conversion efficiency of 27.4%) and photodynamic therapy can inhibit cancer more effectively compared to any monotherapy. Moreover, as a result of the inherent performance ability of the doped rare earth ions, excellent applicability for computed tomography (CT), upconversion luminescence (UCL) and magnetic resonance imaging (MRI) has been achieved.

Photoelectrochemical determination of the activity of protein kinase A by using g-C3N4 and CdS quantum dots.

A sensitive and selective photoelectrochemical (PEC) method is described for the detection of protein kinase A (PKA) activity based on the use of graphite-like carbon nitride (g-C3N4) and the CdS quantum dots (QDs). Firstly, a complex was synthesized from g-C3N4 and gold nanoparticles (AuNPs). It was employed as both the PEC-active material and as a support for immobilization of peptides. The latter were assembled on an ITO electrode modified with g-C3N4-AuNPs and subsequently phosphorylated by PKA in the presence of adenosine 5'-[γ-thio]triphosphate (ATP-S). Finally, CdS quantum dots (QDs) were introduced on the ITO in order to increase the PEC response of g-C3N4 based on the Cd-S binding between the QDs and thiol groups. Under the optimal conditions and a typical working voltage of -0.3V, the method has a dynamic range that extends from 0.05 to 50 unit·mL-1, with a 0.017 unit·mL-1 lower detection limit. The method was successfully applied to the quantification of the inhibitory effect of ellagic acid on the activity of PKA, and to monitor enzyme activity in cell lysates. Graphical abstract Schematic of a sensitive and selective photoelectrochemical biosensor for the detection of protein kinase A activity. It is based on the use of graphite-like carbon nitride and CdS quantum dots.

The Ternary Heterostructures of BiOBr/Ultrathin g-C₃N₄/Black Phosphorous Quantum Dot Composites for Photodegradation of Tetracycline.

Herein, we synthesized BiOBr/ultrathin g-C3N4/ternary heterostructures modified with black phosphorous quantum dots using a simple water bath heating and sonication method. The ternary heterostructure was then used for the photocatalytic degradation of tetracycline in visible light, with an efficiency as high as 92% after 3 h of irradiation. Thus, the photodegradation efficiency is greatly improved compared to that of ultrathin g-C3N4, BiOBr, and black phosphorous quantum dots alone. The synthesized ternary heterostructure improves the charge separation efficiency, thus increasing the photodegradation efficiency. This work provides a new and efficient method for the degradation of antibiotics in the environment.

Graphitic-C3N4 quantum dots decorated {001}-faceted TiO2 nanosheets as a 0D/2D composite with enhanced solar photocatalytic activity

Zero-dimensional (0D)/two-dimensional (2D) heterojunctions have attracted great attention in photocatalysis due to their superior interfacial effects. In this work, 0D g-C3N4 quantum dots (CNQDs) were firstly used to modify {001}-faceted 2D TiO2 nanosheets by a simple solvothermal method. During the controlled growth of TiO2 nanosheets with exposed reactive {001} facets, the CNQDs can be simultaneously assembled on the surface of TiO2 nanosheets in a highly dispersive way. The 0D/2D composite containing only 0.5% of CNQDs shows the optimized solar photocatalytic activity for the degradation of rhodamine B and 4-chlorophenol. More importantly, the 0D/2D composite exhibits a better solar photocatalytic activity than the bulk g-C3N4/TiO2 nanosheets composite. This improvement can be ascribed to the close interfacial contact and strong interaction between the highly dispersed CNQDs and the TiO2 nanosheets, which could lead to efficient separation of the photogenerated electron–hole pairs, provide more catalytic active sites, and enhance the absorption of solar light. The 0D/2D composite also shows good stability for its practical applications.

Green synthesis g-C3N4 quantum dots loading h-BN for efficient and stable photocatalytic performance

Many recent advances in constructing green metal-free materials have opened new possibilities in catalysis. To explore and enhance the photocatalytic performance of g-C3N4 quantum dots (CN QDs), the metal-free materials of CN QDs embedded in the h-BN was successfully synthesized by calcination the mixture of melamine and h-BN. The studies proved the CNBN has appeared red-shift due to the quantum size effect and 2D h-BN. The CN QDs were embedded into the h-BN could not only facilitate the separation and transfer, but also the h-BN terminated with OH groups could act as active sites, thus enhanced the photocatalytic performance. Moreover, this work may pave the way for the application of CN QDs and fabricate 2D h-BN composites for green metal-free materials in another field.

Photoelectrochemical aptasensor for sulfadimethoxine using g-C3N4 quantum dots modified with reduced graphene oxide.

A novel photoelectrochemical (PEC) aptasensor with graphitic-phase carbon nitride quantum dots (g-C3N4; QDs) and reduced graphene oxide (rGO) was fabricated. The g-C3N4 QDs possess enhanced emission quantum yield (with an emission peak at 450nm), improved charge separation ability and effective optical absorption, while rGO has excellent electron transfer capability. Altogether, this results in improved PEC performance. The method is making use of an aptamer against sulfadimethoxine (SDM) that was immobilized on electrode through π stacking interaction. Changes of the photocurrent occur because SDM as a photogenerated hole acceptor can further accelerate the separation of photoexcited carriers. Under optimized conditions and at an applied potential of +0.2V, the aptasensor has a linear response in the 0.5nM to 80nM SDM concentration range, with a 0.1nM detection limit (at S/N= 3). The method was successfully applied to the analysis of SDM in tap, lake and waste water samples. Graphical abstract Graphitic-phase carbon nitride(g-C3N4)quantum dots (QDs)and reduced graphene oxide (rGO) were used to modify fluorine-doped SnO2 (FTO) electrodes for use in a photoelectrochemical (PEC) aptasensor. SDM oxidized by the hole on valance band (VB) of g-C3N4 QDs promote the separation of electron in the conductive band (CB), which made the changes of photocurrent signal.

Ultrasensitive detection of heparin by exploiting the silver nanoparticle-enhanced fluorescence of graphitic carbon nitride (g-C3N4) quantum dots.

A composite (Ag-g-CNQDs) was prepared from graphitic carbon nitride quantum dots and silver nanoparticles by water phase synthesis. Aided by metal-enhanced fluorescence, the composite exhibits excitation-dependent red emission with a peak at 600nm with a quantum yield of 21%. If the composite is coated with polyethylenimine (PEI) to form the Ag-g-CNQD/PEI complexe, fluorescence is strongly reduced. Upon addition of heparin, the fluorescence of the system is enhanced because PEI has a higher affinity for heparin than Ag-g-CNQDs. The effect was used to design a fluorometric assay for heparin.The emission at 600nm increases linearly in the 0.025 to 2.5μM heparin concentration range, with a 8.2nM limit of detection. Graphical abstract Schematic illustration for fabricating a composite consisting of silver nanoparticles and graphitic carbon nitride quantum dots (Ag-g-CNQDs). Its redfluorescence is weak in presence of polyethyleneimine but restored on addition of heparin. This forms the basis for anew method for heparin detection.

Density functional theory study on the stability, electronic structure and absorption spectrum of small size g-C3N4 quantum dots

The geometric stabilities, electronic properties as well as ultraviolet–visible (UV–Vis) absorption spectra of the g-C3N4 quantum dots were systematically investigated by density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations. Taking the tri-s-triazine as a basic building unit, three types of planar structures of the g-C3N4 quantum dots were designed. The chain-type g-C3N4 quantum dots are the lowest in energy. The growth pattern of the g-C3N4 quantum dots had been speculated. The absorption spectra of the triangular sheet structure are in good agreement with the experimental results, and the absorption spectra of the (g-C3N4)15 quantum dots with a 3.41 nm lateral size has covered most of the visible light area. These small size g-C3N4 quantum dots are promising to be used as graphitic carbon nitride-based composite materials for energy conversion.

Facile Synthesis of MoS2/g-C3N4/GO Ternary Heterojunction with Enhanced Photocatalytic Activity for Water Splitting

On the basis of a simple ion exchange method, a MoS2/g-C3N4/graphene oxide (GO) ternary nanojunction was constructed as an efficient photocatalyst for hydrogen evolution using solar energy. The confinement effect in MoS2 and g-C3N4 quantum dots enhances their water-splitting redox activities. The designed heterostructure featured a band alignment that facilitates the collection of electrons in MoS2 and holes in g-C3N4, effectively suppressing the recombination of photogenerated charge carriers. Furthermore, the GO with high specific surface area serves as an excellent conductive substrate to transport holes speedily. This study thus provides a novel and facile route of establishing efficient composite photocatalyst with multinary components for energy conversion.

Exploration of Graphitic-C3N4 Quantum Dots for Microwave-Induced Photodynamic Therapy.

Here, we report our new observations on graphitic-phase carbon nitride (g-C3N4) quantum dots (QDs) as agents for microwave induced photodynamic therapy (MIPDT). For the first time, we observed that singlet oxygen is produced in g-C3N4 QDs by microwave irradiation, which can be used for tumor destruction. The results of live/dead staining and flow cytometry show that g-C3N4 QDs based MIPDT can effectively kill cancer cells and promote tumor cell death. In addition, the cell viability and hemolysis tests in vitro indicate that g-C3N4 QDs have very low cell toxicity and possess excellent biocompatibility in the physiological environments. All these indicate that g-C3N4 QDs are promising for MIPDT, a new potential modality for cancer treatment.

Constructing a visible-light-driven photocatalytic membrane by g-C3N4 quantum dots and TiO2 nanotube array for enhanced water treatment

Photocatalytic membranes that driven by visible light are highly desired for water treatment. Here g-C3N4 quantum dots (QDs) assembled into TiO2 nanotube array (TNA) membranes were fabricated for the first time as a visible-light-driven g-C3N4/TNA membrane. Benefiting from the synergistic effect of membrane filtration and photocatalysis, more than 60% of rhodamine B could be removed from water under visible light irradiation. Meanwhile, the g-C3N4/TNA membrane presented an enhanced anti-fouling ability during filtering water containing Escherichia coli under visible light irradiation, and a permeate flux of 2 times higher than that of filtration alone was obtained by integrated process. This study offers a promising strategy for the potential application of the visible-light-driven membranes in water treatment.

Photocatalytic Activity of g-C3N4 Quantum Dots in Visible Light: Effect of Physicochemical Modifications

Graphitic C3N4 (g-C3N4), a newly emerging layered semiconductor, has shown its promising performance for use as a photocatalyst in the hydrogen evolution reaction and as an active layer of solar cells. However, the unfavorable wide band gap seriously restricts its efficiency in this regard. To overcome the limitations, in the present study, we have explored several ways, such as modifying size, substrate, functionalization, and doping of hydrogen-passivated g-C3N4 quantum dots (QDs). Performing extensive density functional theory based calculations, we find that, unlike pristine QDs, proper modification of the electronic nature of the QDs can lead to efficient visible or near-infrared (NIR) light response, making them better functional materials toward solar cell or photocatalytic applications. Interestingly, our studies further suggest that the modified passivated QDs are better catalysts than pristine ones used so far in the H2 evolution reaction. Also, the range of the optical gap these QDs display mak...

Highly efficient photocatalytic activity of g-C 3 N 4 quantum dots (CNQDs)/Ag/Bi 2 MoO 6 nanoheterostructure under visible light

Abstract We have achieved in-situ growth of Ag and g-C3N4 quantum dots (CNQDs) onto the surface of sheet-like Bi2MoO6. The resulting CNQDs/Ag/Bi2MoO6 composite showed significantly enhanced photocatalytic performance (100%) towards degradation of rhodamine B (Rh B) under visible-light irradiation, as compared with pure Bi2MoO6, Ag/Bi2MoO6, and CNQDs/Bi2MoO6. The enhanced performance is attributed to the extended absorption in the visible light region resulting from the CNQDs loading, the high specific surface area, and the efficient separation of electron–hole pairs through a ternary composite system. In addition, the radicals trapping experiments revealed that the holes and O 2 - play the major role in the Rh B decolorization.

Photoelectrochemical immunosensing platform for M. SssI methyltransferase activity analysis and inhibitor screening based on g-C3N4 and CdS quantum dots

DNA methylation is one of the important epigenetics events, and it is responsible for transcription, genomic imprinting and cellular differentiation. Aberrant DNA methylation is always contacted with various diseases. Herein, a simple and low-cost photoelectrochemical (PEC) biosensing method is proposed for detection of DNA methylation, assay of DNA methyltransferase (MTase) activity and screening of MTase inhibitor, which is based on M. SssI MTase-HpaII endonuclease system. The graphite-like C3N4 (g-C3N4) and CdS quantum dots (CdS QDs) are used as photoactive materials. After the double-stranded DNA (dsDNA) was treated with M. SssI MTase in the presence of S-adenosylmethionine, the methylated dsDNA cannot be digested by HpaII endonuclease and dithiol group at the terminal of dsDNA can be retained. As a result, CdS QDs could be coupled successfully with methylated dsDNA between the reaction of CdS QDs with dithiol of dsDNA, achieving the amplification of PEC response. Thus, the photocurrent of PEC biosensor is consistent with the M. SssI activity. The increased photocurrent was in proportion to M. SssI activity in the linear range from 1 to 80U/mL with a detection limit of 0.316U/mL. Furthermore, the effects of atrazine and azamethipos on M. SssI MTase activity were investigated, which might provide useful information on carcinogenic mechanism of pesticide. The PEC biosensor has potential to screen of DNA MTase inhibitor, providing valuable information for anti-cancer drug research and also for cancer therapy.

First principle study of electronic structures and optical absorption properties of O and S doped graphite phase carbon nitride (g-C3N4)6 quantum dots

Graphite phase carbon nitride (g-C3N4) quantum dots have received much attention due to its good stability, water solubility, biological compatibility, non-toxicity as well as strong fluorescence characteristics. In order to enhance the light absorption and improve photocatalytic activities of the g-C3N4 quantum dots, theoretical studies are carried out on the O and S atoms doped (g-C3N4)6 quantum dots. First-principles calculations based on the density functional theory and time dependent density functional theory are performed to investigate the geometries, electronic structures and ultraviolet visible absorption spectra of O and S atoms doped (g-C3N4)6 quantum dots. The results show that the highest electron occupied molecular orbital-the lowest electron unoccupied molecular orbital (HOMO-LUMO) energy gap of doped (g-C3N4)6 quantum dots is significantly reduced though the CN bond lengths closely related to the impurities only change slightly. The calculated formation energies indicate that the O-doped (g-C3N4)6 quantum dots are more stable, and the O atom tends to substitute for N atom at the N3-site, while the S atoms prefer to substitute for N atom at the N8-site. The simulated spectra indicate that the doping of O and S in (g-C3N4)6 could improve the light absorption. Not only the absorption peaks are extended from the UV to the infrared region (e.g. 200-1600 nm), but also the corresponding absorption intensities are enhanced significantly by doping the O or S atoms with the appropriate concentration. The increase of proper impurity concentration will lead to a pronounced red shift in light absorption. The effect of doping site on the optical absorption property of (g-C3N4)6 quantum dots shows that the absorption intensity is mainly affected in the visible range, however, besides the influence on the absorption intensity, the light absorptions of some structures are also affected beyond 800 nm. Overall, the O atoms and S atoms have a substantially similar effect on the light absorption of the (g-C3N4)6 quantum dots, while the effects of these impurity atoms are different in the long wavelength region. Oxygen doping is better than sulfur doping in the absorption of (g-C3N4)6 quantum dots by comparing the doping of O and S. These first-principles studies give us a method to effectively improve the light absorption of g-C3N4 quantum dots, and could provide a theoretical reference for tuning its electronic optical properties and applications.

A facile and one-pot synthesis of fluorescent graphitic carbon nitride quantum dots for bio-imaging applications

Ultrathin g-C3N4 nanosheets and fluorescent g-C3N4 quantum dots are simultaneously prepared via one-pot ethanol-thermal treatment in the presence of KOH.