Nitrogen-Doped Graphene: The Influence of Doping Level on the Charge-Transfer Resistance and Apparent Heterogeneous Electron Transfer Rate

Three nitrogen-doped graphene samples were synthesized by the hydrothermal method using urea as doping/reducing agent for graphene oxide (GO), previously dispersed in water. The mixture was poured into an autoclave and placed in the oven at 160 °C for 3, 8 and 12 h. The samples were correspondingly denoted NGr-1, NGr-2 and NGr-3. The effect of the reaction time on the morphology, structure and electrochemical properties of the resulting materials was thoroughly investigated using scanning electron microscopy (SEM) Raman spectroscopy, X-ray powder diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), elemental analysis, Cyclic Voltammetry (CV) and electrochemical impedance spectroscopy (EIS). For NGr-1 and NGr-2, the nitrogen concentration obtained from elemental analysis was around 6.36 wt%. In the case of NGr-3, a slightly higher concentration of 6.85 wt% was obtained. The electrochemical studies performed with NGr modified electrodes proved that the charge-transfer resistance (Rct) and the apparent heterogeneous electron transfer rate constant (Kapp) depend not only on the nitrogen doping level but also on the type of nitrogen atoms found at the surface (pyrrolic-N, pyridinic-N or graphitic-N). In our case, the NGr-1 sample which has the lowest doping level and the highest concentration of pyrrolic-N among all nitrogen-doped samples exhibits the best electrochemical parameters: a very small Rct (38.3 Ω), a large Kapp (13.9 × 10-2 cm/s) and the best electrochemical response towards 8-hydroxy-2'-deoxyguanosine detection (8-OHdG).

Band structure engineering of polymeric carbon nitride with oxygen/carbon codoping for efficient charge separation and photocatalytic performance

The high charge recombination efficiency and weak visible-light absorption of polymeric carbon nitride (CN) severely suppress its photocatalytic performance. To overcome these defects, oxygen/carbon codoped CN (OCN) was prepared firstly using acrylamide as the additive. OCN exhibits much enhanced visible light absorption, charge separation and transfer, and thus photoactivity in hydrogen production and environmental remediation. OCN exhibits a ~6-fold higher photocatalytic hydrogen production rate (~2626 μmol h^-1 g^-1) than CN, comparable to most of nonmetal-doped CN, and an apparent quantum yield of ~16.3% (420 nm). OCN is also much better at producing singlet oxygen than CN. The significantly enhanced charge separation for OCN arises from the O/C codoping structure which forms an impurity level above the valence band edge in the bandgap, i.e., works as a hole-capture center. This work affords a simple and effective strategy to synthesize modified CN for photoactivity enhancement, clarifies the doping mechanism, and may guide research on other nonmetal doped organic semiconductor photocatalysts.

The enhanced photodegradation of bisphenol A by TiO2/C3N4 composites

A new photocatalyst of TiO₂/C₃N₄ composite (TiO₂/g-C₃N₄) was synthesized by the hydrothermal method. The characterization showed that TiO₂/g-C₃N₄ extended absorption light range and enhanced generation efficiency of photo-induced electron. Under the simulated solar irradiation, the photodegradation rate of bisphenol A (BPA) by TiO₂/g-C₃N₄ was twice as fast as that of g-C₃N₄. Furthermore, TiO₂/g-C₃N₄ presented the good stability and excellent selectivity for BPA degradation. The high degradation rate of BPA by TiO₂/g-C₃N₄ was demonstrated to be superoxide radical (·O₂^-) and singlet oxygen (¹O₂) by radical quenching experiment, which was further evidenced by EPR, XPS, DRS and PL analysis. These findings revealed that TiO₂/g-C₃N₄ can be used as a potential photocatalyst for removing organic pollutants in actual environmental remediation.

The Improvement of Photocatalysis H2 Evolution Over g-C3N4 With Na and Cyano-Group Co-modification

Na and cyano-group co-modified g-C₃N₄ was easily synthesized and its physicochemical property was completely analyzed. The results manifested that Na and cyano-group modification could heighten visible light absorbed ability and accelerate photoinduced charge separation. When resultant Na and cyano-group co-modified g-C₃N₄ was splitting water H₂ evolution, its H₂ evolution rate was obviously improved. Furthermore, it also kept excellent stable capacity of H₂ evolution and stability of chemical structure. Hence, this present study does not only develop an efficient strategy to boost photocatalytic property of g-C₃N₄ based catalysts, but also provides useful guidance for designing more effective photocatalysts.

Ag loaded B-doped-g C3N4 nanosheet with efficient properties for photocatalysis

Three material engineering strategies in the form of doping (Boron-doping), nanostructuring (nanosheet (NS) formation) and decorating with plasmonic nanoparticles (loading with Ag metal), were integrated to improve the photocatalytic activity of graphitic carbon nitride (gC₃N₄). Concentrations of B-doping and Ag-loading were optimized to maximize the catalytic performance in the final nanocomposite of Ag-loaded B-doped gC₃N₄ NS. Combined effect of all three strategies successfully produced over 5 times higher rate towards degradation of organic dye pollutant, when compared to unmodified bulk gC₃N₄. Detailed characterization results revealed that incorporation of B in gC₃N₄ matrix reduces the band gap to increase the visible light absorption, while specific surface area is significantly enhanced upon formation of NS. Decoration of Ag nanoparticles (NPs) on B-doped gC₃N₄ NS assists in fast transfer of photogenerated electrons from gC₃N₄ to Ag NPs owing to the interfacial electric field across the junctions and thus reduces the recombination process. Investigations on individual strategies revealed that decoration of Ag NPs to induce better charge separation, is the most effective route for enhancing the photocatalytic activity.

Controlling the secondary pollutant on B-doped g-C3N4 during photocatalytic NO removal: a combined DRIFTS and DFT investigation

The mechanisms of enhanced photocatalysis efficiency and suppression of toxic intermediate production during photocatalytic NO oxidation on B-doped g-C₃N₄ were revealed.

Crystal-Face Tailored Graphitic Carbon Nitride Films for High-Performance Photoelectrochemical Cells

Graphitic carbon nitride (g-CN) has been widely studied as a promising candidate for water splitting, owing to its metal-free nature, moderate band gap, and low cost. However, its photocurrent density is still very low for photoelectrochemical cell applications. In this work, a crystal face tailored g-CN photoelectrode has been fabricated by a facile thermal vapor deposition method. We use the melamine formaldehyde resin as a new precursor and have successfully fabricated g-CN films. The intensity ratio between two typical peaks (100) and (001) of g-CN is very different from that in the existing literature. The water splitting photocurrent density is as high as 228.2 μA cm^-2 , which is 126.8 times higher than pure g-CN (1.8 μA cm^-2 ) at 1.23 V vs. reversible hydrogen electrodes under one sun illumination without sacrificial reagents and co-catalysts. The electrode shows the best performance, compared with the previously reported g-CN photoelectrodes.

Advanced bi-functional CoPi co-catalyst-decorated g-C3N4 nanosheets coupled with ZnO nanorod arrays as integrated photoanodes

In this work, a CoPi-decorated type II heterojunction composed of one-dimensional (1D) ZnO nanorod arrays (NRAs) coated with two-dimensional (2D) carbon nitride (g-C₃N₄) was successfully prepared and used as photoanode.

Boosted visible light photodegradation activity of boron doped rGO/g-C3N4 nanocomposites: the role of C–O–C bonds

Boron doping is an effective way to promote the chemical interaction between rGO and g-C₃N₄.

WS2/g-C3N4 composite as an efficient heterojunction photocatalyst for biocatalyzed artificial photosynthesis

A heterogeneous WS₂/g-C₃N₄ composite photocatalyst was prepared by a facile ultrasound-assisted hydrothermal method.

Preparation of phenyl group functionalized g-C3N4 nanosheets with extended electron delocalization for enhanced visible-light photocatalytic activity

Phenyl group functionalized g-C₃N₄ shows an improved light utilization and charges separation rate due to extended conjugation system, leading to a superior catalytic activity in a variety of photocatalytic systems.