Water-soluble Carbon Nitride Research Articles

Low bandgap carbon nitride nanoparticles incorporated in titania nanotube arrays by in situ electrophoretic anodization for photocatalytic CO2 reduction

We report an in situ electrophoretic anodization process to realize a binary semiconductor heterojunction photocatalyst comprising green-emitting, water-soluble carbon nitride (CN) nanoparticles (NPs) embedded in TiO2 nanotube (TNT) arrays. Embedding CN inside a TiO2 matrix eliminates the possibility of the CNNPs leaching away during photocatalysis or photoelectrochemistry. The synthesized CN exhibits visible light absorption down to 600 nm and an unusually redshifted green emission peak at 527 nm, which are attributed to a carbon rich g-C3N4 composition with a C:N ratio of ∼ 1.9 at the surface. Spectroscopy revealed the excess carbon to be both amorphous and graphitic while the structural features characteristic of g-C3N4 were preserved. Raman spectroscopy, transmission electron microscopy (TEM), electron energy-loss spectroscopy (EELS) and X-ray photoelectron spectroscopy (XPS) analysis verified the formation of the heterostructure as well as indicated strong interaction between the CN and TiO2 in the hybrid. The CNNP@TNT hybrid demonstrated superior performance in sunlight driven photocatalytic CO2 reduction without the need for a sacrificial agent. The CO yield of photoreduction showed a more than threefold improvement for the CNNP@TNT hybrid compared to the stand-alone TNT photocatalyst. The synergistic enhancement of photocatalytic performance emerged due to the formation of a high-quality interface between the constituent semiconductors (TiO2 and CN) that facilitated efficient charge carrier separation. Density functional theory (DFT) calculations showed the feasibility of efficient photogenerated electron-hole pair separation at the heterointerface. Molecular dynamics (MD) simulations validated the facile dispersibility of CNNPs in water and polar solvents.

Water-soluble carbon nitride as phase-convertible adsorbents for removing heavy metals from water

Current adsorption technologies suffer from inferior interfacial mass transfer and slow reaction rates of heterogeneous adsorbents for water decontamination. By far, it remains challenging to explore a solid material with homogeneous dispersion for reusable applications. Herein, we present a proof-of-concept demonstration of using water-soluble carbon nitride (w-C3N4) as a phase-convertible adsorbent, which will combine the advantages of homogeneous adsorption and heterogeneous separation. The w-C3N4 with various hydrophilic and cyano groups exhibit a high Pb2+ adsorption capacity of 302.3 mg/L, together with fast adsorption kinetics, which is much better than bulk g-C3N4 and activated carbon adsorbents. After the adsorption reaction, the soluble adsorbents can be easily separated from water by increasing the ionic strength of the homogeneous solution, which can be effectively regenerated by diluted acid. The creative integration of homogeneous and heterogeneous processes provides a new avenue for breaking through the limits in host–guest interactions of current adsorption technologies by reversible phase conversion.

Water-Soluble Carbon Nitride as Phase-Convertible Adsorbents for Removing Heavy Metals from Water

Water-Soluble Carbon Nitride as Phase-Convertible Adsorbents for Removing Heavy Metals from Water

Photodriven Charge Accumulation and Carrier Dynamics in a Water-Soluble Carbon Nitride Photocatalyst.

Charge accumulation in photoactive molecules and materials holds great promise in solar energy conversion as it allows for decoupling solar‐driven charging from (dark) redox reactions. In this contribution, light‐driven charge accumulation was investigated for a recently reported novel water‐soluble carbon nitride [K,Na‐poly(heptazine imide); K,Na‐PHI] photocatalyst, which exhibits excellent activity and stability in highly selective photocatalytic oxidation of alcohols and concurrent reduction of dioxygen to H2O2 under quasi‐homogeneous conditions. An excellent charge storage ability of the K,Na‐PHI material was demonstrated, showing an optimal density of accumulated electrons (32.2 μmol of electrons per gram) in the presence of 10 vol % MeOH as a sacrificial electron donor. The long‐lived electrons accumulated under anaerobic conditions as K,Na‐PHI.− radical ions were utilized in interfacial electron transfer to O2 or methyl viologen in a subsequent dark reaction. Ultrafast time‐resolved spectroscopy was employed to reveal the kinetics of charge‐carrier recombination and methanol oxidation. Geminate recombination of electrons and holes within approximately 100 ps was followed by trap‐assisted recombination. The presence of methanol as a sacrificial electron donor accelerated the decay of the transient absorption signal when a static sample was used. This behavior was ascribed to the faster charge recombination in the presence of the radical anions generated after hole extraction. The work suggests that photodriven electron storage in the water‐soluble carbon nitride is enabled by localized trap states, and highlights the importance of the effective electron donor for creating long‐lived photo‐generated carbon nitride radicals.

Water-Soluble Carbon Nitride as Phase-Convertible Adsorbents for Removing Heavy Metals from Water

Water-Soluble Carbon Nitride as Phase-Convertible Adsorbents for Removing Heavy Metals from Water

Faceting and Nanostructuring of Gold Surfaces through Cathodic Corrosion: Role of Cationic Electrolyte Species and Water

Gold is one of the most frequently employed electrode materials in electrochemistry due to its exceptional properties such as chemical inertness and high resistance to oxidation and dissolution [1-3]. According to Pourbaix diagrams, gold is regarded stable against degradation under cathodic polarization [4]. In contrast, applying relatively high negative potentials in the presence of alkali metal cations induce notable changes on Au electrode surfaces [5].In this study, cathodic corrosion of polycrystalline gold in different electrolytes of alkali metal hydroxides has been systemically investigated. In comparison to the recent work [5,6], this study provides new findings as a function of the applied parameters for the nanostructuring of gold surfaces. Cell design and the distance between the electrodes have carefully been controlled and optimized. The progression of surface restructuring and corrosion features was investigated using cyclic voltammetry (CV) and scanning electron microscopy (SEM). The results show different corrosion features depending on the nature and the concentration of alkali metal hydroxides, on the applied voltage, and on time. Current-potential curves for the modified electrodes in 0.1 M H2SO4 show characteristic features in the double-layer and oxidation regions. Analyzing the cyclic voltamogramms of the corroded electrodes provides evidence about the preferential orientation of facets and the electrochemical active surface area as a function of the applied parameters. The SEM micrographs show that polarizing the gold surfaces at relatively high negative potentials generates different size and orientation of octahedral nanocrystals using NaOH, spherical nanoparticles and triangular pits using KOH and triangular pits using LiOH. Besides the alkali metal cations, the electrolyte concentration and the applied voltage are important parameters. Furthermore, the role of water in cathodic corrosion of gold has been investigated using mixtures of different mole fraction of water and non-aqueous electrolytes. The absence of corrosion features using water-free non-aqueous electrolytes reveal that water plays a key role in the cathodic corrosion process.In addition, various aqueous mixed electrolytes have been systemically investigated. The results show combined corrosion features according to the mole fraction of different cations. For example, a 1:1 NaOH + LiOH mixture leads to the formation of rectangular pits which are attributed to (100)-facets compared to a 1:1 KOH + LiOH mixture which leads to triangular pits revealing the formation of (111)-facets.By applying alternating current (AC) to Au electrodes in contact with the same electrolytes, colloidal gold nanoparticles could successfully be synthesized. These nanoparticles have been used for the functionalization of water-soluble carbon nitride to enhance its activity for specific photocatalytic reactions such as alcohol oxidation.

Tunable water-soluble carbon nitride by alkali-metal cations modification: Enhanced ROS-evolving and adsorption band for photodynamic therapy

Graphitic Carbon Nitride (g-C3N4) has extensive application prospect of photodynamic therapy (PDT), which can be attributed to the biocompatibility and photosensitivity. However, it suffers from the near-ultraviolet absorption edge and low reactive oxygen species (ROS) release rate. This work exhibits an atomic-thickness water-soluble g-C3N4 with alkali Zn2+ and K+ modification (MCN), whose absorption edge is tuned from 460 nm for GCN to the entire visible-light region (663 nm), and bandgap is reduced to 1.94 eV. Both K+- bridging intercalation and the in-plane Zn-N significantly enhance the photocatalytic performance, as well as inhibit the overexpression of glutathione (GSH) significantly. The synergistic effect make that the release rate of ROS is about 45.16 % (7.95 % for pristine g-C3N4), accomplishing a considerable inactivation efficiency of malignant melanoma A375. This work fundamentally releases the limitation of g-C3N4 as a PDT photosensitizer, revealing its multifunctional promise to cancer therapy.

Water-soluble graphitic carbon nitride as an oxidase-like mimic for calorimetric detection of ascorbic acid

A water-soluble carbon nitride (WSCN) was synthesized through a molten-salt assisted thermal polymerization method. The WSCN has a remarkable red-shifted absorption and could catalytically oxidize 3,3′,5,5′-tetramethylbenzidine (TMB) without exogenous H2O2 to produce a color reaction under λ > 470 nm light illumination. The TMB/WSCN system can be employed for colorimetric detection of ascorbic acid.

In English

As an one of the most promising materials of green energy as a photocatalyst for the production of hydrogen from renewable, natural sources (water, greenhouse gas) and environmental remediation through the degradation of toxic organic pollutants, graphite-like carbon nitride (characterized as a non-toxic and chemically highly resistant material) and its nanostructured and doped (especially by oxygen atoms) derivatives attract special attention. The actual task for expanding the scope of application of g-C 3 N 4 is to improve and optimize its catalytic, electronic and optical properties by increasing both the surface area of graphitic carbon nitride and the number of active centers of the carbon nitride network due to doping of carbon nitride. The use of a mixture of two different precursors ensures the creation of heterojunctions, and as a result, an improvement the photocatalytic characteristics of g-C 3 N 4 . The oxygen-doped carbon nitride (O-g-C 3 N 4 ) and water-soluble carbon nitride oxide (g-C 3 N 4 )O was simultaneously synthesized by the gas phase method under special reaction conditions of pyrolysis of cyanuric acid and urea mixture. Reduction by the hydroquinone of carbon nitride oxide (g-C 3 N 4 )O yields nanostructured reduced carbon nitride (or reduced multilayer azagraphene). Obtained products were characterized by using Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), chemical and X-ray diffraction (XRD) analyses, scanning electron microscopy (SEM). According to the results of XPS and IR spectrometry the chemical bonds between atoms in a heteroatomic plane of reduced carbon nitride (RCN) correspond to the bonds in a synthesized carbon nitride (SCN). However, according to XRD results, reduced carbon nitride (RCN) probably consists of poorly connected heteroatomic azagraphene layers, because it has a significantly larger (on 0.09 nm) interplanar distance between the adjacent nitrogen-carbon layers than interplanar distance between the layers of synthesized carbon nitride (SCN). By SEM characterization it was found that the pyrolysis of a mixture of various precursors (cyanuric acid and urea) yielded a product with smaller crystalline domains (which can improve photocatalytic characteristics) than the pyrolysis of a single precursor (urea only).

Synthesis of reduced carbon nitride at the reduction by hydroquinone of water-soluble carbon nitride oxide (g-C3N4)O

For the first time at the reduction by hydroquinone of water-soluble carbon nitride oxide (g-C3N4)O reduced carbon nitride (or reduced multi-layer azagraphene) is obtained. It is differed from usually synthesized carbon nitride by a significantly large (on 0.09nm) interplanar distance is. At the same time, the chemical bonds between atoms in a heteroatomic plane of reduced carbon nitride correspond to the bonds in a synthesized g-C3N4. The samples of water-soluble carbon nitride oxide were synthesized under the special reactionary conditions of a pyrolysis of melamine and urea. We believe that reduced carbon nitride consists of weakly connected carbon-nitrogen monosheets (azagraphene sheets) as well as reduced (from graphene oxide) graphene contains weakly connected graphene sheets.