Pristine CN Research Articles

Nickel Ammine Complex‐derived NiO Modified g‐C3N4 Composites with Enhanced Visible‐light Photocatalytic H2 Evolution Performance

AbstractIn this paper, NiO/g‐C3N4 (NiO/CN) composites were successfully prepared by the wetness impregnation method using nickel ammine complex solution as NiO source. As photocatalysts, NiO/CN composites showed enhanced visible‐light photocatalytic hydrogen evolution activities in the presence of triethanolamine as sacrificial agent. The effects of NiO content and annealing temperature for NiO/CN composites on the photocatalytic H2 evolution activities were investigated. Furthermore, NiO/CN composite with 10.0% NiO content after annealing at 450 °C exhibited optimal photocatalytic H2 evolution rate of 90.05 μmol⋅h−1⋅g−1 which is about 17 times higher than that of pristine CN (5.22 μmol⋅h−1⋅g−1). Moreover, the experimental results demonstrated that amorphous NiO as co‐catalyst not only offered active sites for H2 evolution but also benefited the efficient separation of the photogenerated charge carries. In addition, NiO/CN composite displayed the superior photocatalytic stability during the photocatalytic process.

In-situ phosphating to synthesize Ni2P decorated NiO/g-C3N4 p-n junction for enhanced photocatalytic hydrogen production

Photocatalysis is a promising method to obtain hydrogen without any pollution. The key to improve the efficiency of photocatalytic reaction is to design an excellent catalyst structure which can effectively promote the separation and transfer of photogenerated electrons and holes. In this work, a novel photocatalyst, Ni2P decorated NiO/g-C3N4 p-n junction (NiO/Ni2P/CN, abbreviating g-C3N4 as CN) is successfully developed by a one-step in-situ phosphating of Ni(OH)2/CN. The optimized NiO/Ni2P/CN exhibits an impressive photocatalytic H2 evolution rate of 5.04 μmol h−1 under visible-light irradiation (λ > 420 nm) without any noble metal as co-catalyst, which is 126 times higher than that of pristine CN. This high photocatalytic performance is mainly based on the intimated contact of the three components (Ni2P, NiO and CN), where the photogenerated holes on the valence band (VB) of CN can be transferred to the VB of NiO due to the internal-built electric field created by p-n junction, while the photoexcited electrons on the conduction band (CB) of CN can be migrated to Ni2P co-catalyst with a low overpotential, thus the separation and transfer of charge carriers are significantly promoted, and finally the photocatalytic activity of NiO/Ni2P/CN for the hydrogen evolution from water splitting is enhanced. This work may enlighten on the design of photocatalysts with high efficiency by constructing p-n junction and metal phosphide co-catalyst with low overpotential.

Efficient visible light driven degradation of sulfamethazine and tetracycline by salicylic acid modified polymeric carbon nitride via charge transfer

Photocatalysis has been widely studied as a promising technique for removal of organic pollutants in wastewater. A modified carbon nitride has been designed for this purpose. In this study, a facile method to synthesize distorted carbon nitride by simply copolymerizing urea and salicylic acid (SA) has been explored. The incorporation of SA induced the structure change from planar structure to distorted curls structure. Compared to pristine CN, the CN-SA shows wide light absorption, which is attributed to the n → π* transition at the nitrogen atoms with lone pair electrons of heptazine units. The photoelectrode of CN-SA exhibited higher photocurrent and lower charge resistance than that of pristine CN electrode, indicating that the photogenerated charge carriers of CN-SA are more efficiently separated. As a result, the optimal CN-SA shows 2-fold enhancement in degradation of tetracycline (TC) as compared to pristine CN. Furthermore, we found that the degradation rate of sulfamethazine (SMZ) was 0.0823 min−1 using the CN-SA photocatalyst, which is three times higher than that of pristine CN (0.0293 min−1). In addition, the CN-SA shows good stability without structural change or loss of photocatalytic performance after four cycles. According to the radical species trapping experiments and electron spin resonance analyses, O2− and h+ were the main active species involved in the degradation of organic pollutants. The developed strategy provides a novel approach to design the tunable band structure of organic semiconductor materials for various applications.

Crystallization, cyanamide defect and ion induction of carbon nitride: Exciton polarization dissociation, charge transfer and surface electron density for enhanced hydrogen evolution

Exciton polarization dissociation, charge transfer and surface electron density in photocatalysts are crucial for photocatalytic hydrogen evolution reactions (HERs). In this study, crystalline carbon nitride with cyanamide defect edges (crystalline CCN) was synthesized by one step polymerization of urea in the presence of KCl. The texture and electronic band structure of carbon nitrides could be facilely tailored by changing KCl dosage. The light absorption edge of crystalline CCN extended to 736 nm due to n→π* electron transition. The enhanced dielectric constants of crystalline carbon nitrides promoted exciton polarization dissociation. The small effective electron mass (me*) in crystalline CCN facilitated me* diffusion. The efficient separation of electrons and holes benefited the formation of internal electric field, showing an 8.56-fold promotion in electron transfer compared to pristine CN. Significantly, femtosecond time-resolved transient absorption demonstrated that the surface electron density on crystalline CCN was enhanced in the presence of salt ions (NaCl). As a result, crystalline CCN exhibited 14.9 times higher HER rate than pristine CN under visible light irradiation. The apparent quantum yield for H2 evolution on crystalline CCN reached to 42% at 420 nm and 9% at 500 nm. This study gets a comprehensive understanding of photocatalytic HERs using carbon nitride photocatalysts.

Novel CoAl-LDH/g-C3N4/RGO ternary heterojunction with notable 2D/2D/2D configuration for highly efficient visible-light-induced photocatalytic elimination of dye and antibiotic pollutants.

In this study, we fabricate a novel ternary heterojunction comprising CoAl-layered double hydroxide, g-C3N4, and reduced graphene oxide (LDH/CN/RGO) with a notable 2D/2D/2D configuration using a simple one-step hydrothermal method. The visible-light-induced LDH/CN/RGO ternary heterojunctions displayed significantly enhanced photocatalytic performance towards the degradation of aqueous Congo red (CR, dye) and tetracycline (TC, antibiotic) contaminants, which is far superior to that observed for pristine CN (base material), LDH, P25 (reference), and binary CN/RGO and LDH/CN heterojunctions. In particular, the LDH/CN/RGO ternary heterojunction with RGO and LDH contents of 1 wt.% and 15 wt.%, respectively, exhibited the highest degradation activity among all the fabricated catalysts, and it also displayed exceptional stability during recycling experiments. The significant enhancement in the photocatalytic performance and good stability of existing LDH/CN/RGO ternary heterojunctions were primarily attributed to the large intimate interfacial contact between constituent CN, LDH, and RGO prompted by their exceptional 2D/2D/2D arrangement, which accelerates the interfacial charge-transfer processes to effectively hinder the recombination of photoexcited charge carriers. The present study provides new insights into the rational design and fabrication of novel g-C3N4-based 2D/2D/2D layered ternary heterojunctions as high-performance photocatalysts, and promotes their application in addressing diverse energy and environmental issues.

Bio-inspired carbon doped graphitic carbon nitride with booming photocatalytic hydrogen evolution

In this work, kapok fiber (KF), known as a versatile biomass, has been mixed with melamine to produce carbon modified graphitic carbon nitride (CCN) by one-step pyrolysis. The bio-char ribbon edges formed after the decomposition of KF act as the substrate for the epitaxial growth of CCN. The photocatalytic activity in hydrogen (H2) generation from water splitting has been investigated. Nash Equilibrium from Game Theory has been firstly applied in the analysis of the H2 generation rates among catalysts. The bio-char ribbon edges at the thin CN layers after carbon doping from KF decomposition improve the charge separation and transfer for the surface H2 generation reaction. The CCN exhibits superior visible-light-driven photocatalytic activity and the H2 evolution rate (18.89 μmol/h) is 67.5 times higher than that of the pristine CN (0.28 μmol/h). The apparent quantum yields are calculated to be 4.1%, 1.4%, 0.66% for monochromatic light λ = 420, λ = 470 and λ = 550 nm, respectively.

Domestic LED light driven methylene blue degradation by g-C3N4-CaCu3Ti4O12 composite

We report a successful synthesis of the composite of quadruple perovskite, CaCu3Ti4O12 (CCTO) with graphitic carbon nitride (g-C3N4; CN) that is shown to be highly active for methylene blue (MB) degradation in aqueous medium in the presence of H2O2 activator under domestic LED light irradiation. Comparison of activity behavior of the composite with the respective pristine materials, CCTO and CN, shows the onset of a synergistic effect beyond 5 wt% loading of CN. Notably, the 10 wt% CN loaded CCTO (CN10CCTO) shows excellent enhancement in photocatalytic activity (achieving MB removal ∼96%). The pristine CCTO was prepared via a citrate combustion route, while g-C3N4 was prepared by a thermal heat treatment method. The composite materials have been synthesized by low temperature (∼150 °C) thermal treatment of an intimate physical mixture of the components in desired composition (w/w). The materials are characterized by using powder X-ray diffraction (P-XRD), Fourier transform infrared (FTIR) spectroscopy, UV–Vis diffuse reflectance spectroscopy, photoluminescence (PL) spectroscopy, transient photoresponse, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The mechanism of photodegradation is studied by performing the oxidation in presence of various types of scavengers, which have revealed the involvement of multiple types of radicals in the degradation process with first order kinetics. The scavenger-fluorescence study have strengthen the findings on mechanism of degradation. The enhanced activity of the composite material is ascribed to the easy availability of the charge carriers in the composite as evidenced from the band energy diagram suggested on the basis of cyclic voltammetry measurement. The recycling test clearly indicates the uninterrupted performance of the material without losing its activity.

Black phosphorus supported Ni2P co-catalyst on graphitic carbon nitride enabling simultaneous boosting charge separation and surface reaction

Rational design and engineering of highly active co-catalysts made of stable and earth-abundant elements is essential to boost the photocatalytic water splitting performances. This paper reports a 2D-black phosphorus (BP) supported Ni2P (2D-Ni2P@BP) as a non-precious heterostructure co-catalyst coupled with a 2D porous graphitic carbon nitride nanosheet (CN NSs) photocatalyst to induce visible light photocatalytic hydrogen production. The resulting 2D-Ni2P@BP/CN composite structure exhibits a remarkable visible light photocatalytic H2 evolution activity of 858.2 μmol h−1 g−1, revealing ∼50- and ∼5-fold enhancement compared to that of a pristine CN reference and Pt/CN sample, respectively. The dramatic advancement in H2 evolution could be ascribe to the superior hydrogen evolution reduction (HER) activity of Ni2P@BP. The excellent HER activity arises from the synergetic effect between BP and Ni2P in which BP, with its superior electron mobility, is believed to accelerate the charge separation/transfer by mediating the photogenerated electrons from CN NSs to the surface of the catalytically active sites of Ni2P, while Ni2P promotes the surface reduction reaction by lowering the H2-evolution overpotential. It is considered that this work provides a new paradigm for designing advanced, stable, and cost-effective photocatalyst systems for the practical implementation of solar hydrogen production.

Li-Decorated Fullerenes: A DFT Study

Density functional calculations have been applied to study the structure, stability and aromaticity of Li-decorated non-IPR fullerene cages, Cn with n = 44, 46, 48, and 50, and IPR fullerene cages, Cn with n = 60, 70, 76, and 84. Based on our results, the binding energies per Li atom for Li12Cn clusters depend on the type and size of the cages. As of Li-decorated IPR fullerenes, where pentagons are isolated, there is virtually no interaction between the Li atoms, so that the binding energies for the Li-decorated IPR Cn fullerenes are obtained to be larger than those for the Li-decorated non-IPR ones. The C–C bond lengths in the pentagons of Li12Cn clusters are enlarged relative to those of pristine Cn clusters. Based on NBO analysis, charge transfer (~ 0.5e) from Li to the fullerene cage makes the Li atoms positively charged. NICS data suggest that the degree of aromaticity in C60, C76, and C84 cages increases upon formation of the Li-decorated Cn clusters while more positive NICS values are obtained for C70 and the smaller fullerenes with Li decoration of the cages.

Graphitic carbon nitride nanosheets anchored with BiOBr and carbon dots: Exceptional visible-light-driven photocatalytic performances for oxidation and reduction reactions

The aim of this work is the fabrication of very efficient visible-light-driven photocatalysts through anchoring carbon dots and BiOBr over nanosheets of graphitic carbon nitride. Hence, a series of g-C3N4 nanosheets/Carbon dots/BiOBr (denoted as CNNS/CDs/BiOBr) nanocomposites with different amounts of BiOBr were synthesized by refluxing route. The resultant photocatalysts were characterized by XRD, EDX, SEM, TEM, HRTEM, AFM, XPS, FT-IR, UV–vis DRS, TGA, BET, and PL instruments. Among the photocatalysts, the CNNS/CDs/BiOBr (20%) nanocomposite exhibited the highest photocatalytic performance for degradations of RhB, MB, and MO under visible light, which is about 129, 29.8, and 20.5 times as superior as the CN powder, respectively. Also, photoreduction of Cr(VI) to Cr(III) over the ternary nanocomposite with 20% of BiOBr showed high photoactivity, which was 21.7-folds higher than that of the pristine CN. Reactive species trapping experiments revealed that superoxide anion radicals and hydroxyl radicals played significant role in degradation reaction of RhB. The utilized photocatalyst was recycled with negligible loss in the activity, which is important in photocatalytic processes. Finally, by studying the electrochemical behavior, the band alignments of the semiconductors were obtained and the preliminary mechanism was suggested as a direct Z‐scheme system for the enhanced interfacial charge separation and transfer, which leads to the exceptional photocatalytic performance.

Highly crystalline sulfur-doped carbon nitride as photocatalyst for efficient visible-light hydrogen generation

Heteroatom-doping is an efficient approach to extend optical absorption beyond 460 nm, which, however, often reduces crystallinity to cause a concomitant detrimental effect on photocatalytic activity. In the present study, we developed a facile approach to synthesize S-doped g-C3N4 with a high crystallinity by self-assembling melamine and tri-thiocyanuric acid, followed by calcination. The resultant optimal S-doped carbon nitride (MTCN-6) exhibited a super-high H2-generation rate of 1511.2 μmol g−1 h-1 (about 11 times higher than that of the pristine CN) under visible light excitation (λ > 420 nm) and an excellent AQE of 3.9% at 420 nm.

Two-dimensional mesoporous g-C3N4 nanosheet-supported MgIn2S4 nanoplates as visible-light-active heterostructures for enhanced photocatalytic activity

A series of novel visible-light-driven MgIn2S4/g-C3N4 (MISCN) heterostructures were fabricated in situ by a simple one-pot hydrothermal method. The synthesis of the MgIn2S4 (MIS) nanoplates and the construction of intimate interfacial contacts by loading MIS nanoplates onto mesoporous g-C3N4 (CN) nanosheets were achieved simultaneously in a hydrothermal environment. Systematic characterization, including powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), UV–vis diffuse reflection spectroscopy (UV–vis DRS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), Brunauer–Emmett–Teller (BET), X-ray photoelectron spectroscopy (XPS), and photoelectrochemical measurements were employed to analyze the phase structure, chemical composition, absorption properties, microstructure, and photocatalytic mechanism. The as-prepared MISCN photocatalysts exhibit improved photocatalytic activity for 4-nitroaniline (4-NA) reduction and methyl orange (MO) degradation as compared with pure MIS nanoplates and pristine CN nanosheets under visible light irradiation. The enhancement of photocatalytic performance can be attributed to faster charge separation and transport benefitting from the construction of tight heterogeneous interfaces and band offset structure between MIS nanoplates and mesoporous CN nanosheets. This investigation may be extended to explore and fabricate the novel and highly efficient visible-light-driven g-C3N4-based heterostructures for organic transformations and pollutant removal.

Insight into the Enhanced Photocatalytic Activity of Potassium and Iodine Codoped Graphitic Carbon Nitride Photocatalysts

Potassium and iodine codoped graphitic carbon nitride (CN-KI) photocatalysts were prepared via thermal polymerization of a mixture prepared by dissolving dicyandiamide into a KI solution. Several techniques were employed to characterize the CN-KI photocatalysts and elucidate the mechanisms of the K and I codoping. Compared to pristine CN, CN-KI exhibited a red shift in optical absorption edge, and the electron spin resonance analysis revealed that the enlargement of the visible light response mostly originated from I doping. Then, photoluminescence spectra showed that recombination of photogenerated carriers in CN-KI was retarded compared to that in pristine CN, and electrochemical impedance spectroscopy measurements suggested that the decrease in carrier recombination resulted from K doping because the doping with K into the CN network improved the charge transportation efficiency. Consequently, the K and I codoped g-C3N4 sample with an optimal mass fraction of KI exhibited superior photocatalytic activi...

Enhanced mechanical strength and ductility of metal-repaired defective carbon nanotubes: A density functional study

Metal atoms are filled into the defective sites of single-walled carbon nanotube (SWCN) containing vacancy defects, resulting in a stable repaired SWCN. The tensile deformation of the repaired SWCN is investigated by spin-polarized density functional theory. Compared to the defective SWCN, the repaired CN shows significant enhancements in mechanical strength and ductility that are close to those of pristine CN. The underlying physics of these behaviors are analyzed by the structural transformation, electronic structures, and spin and charge distributions during the tensile tests. A strong magnetomechanical coupling effect is found to be responsible for the enhanced mechanical behaviors of metal-CN hybrid structures.

Properties of Boron-Substituted Heterofullerenes

On the basis of a succinct description of geometrical configurations for giant fullerenes, the electronic properties and structural distortions of heterofullerenes CN-1B(N = 60, 180, 240, 420, 540, 720, 780) are analyzed by the extended Su-Schrieffer-Heeger model. In comparison with their pristine fullerenes CN, local distortions and mid-gap states are found to occur in boron-doped giant fullerenes.