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

Na-mediated carbon nitride realizing CO2 photoreduction with selectivity modulation

The depressed directional separation of photogenerated carriers and weak CO2 adsorption/activation activity are the main factors hampering the development of artificial photosynthesis. Herein, Na ions are embedded in graphitic carbon nitride (g-C3N4) to achieve directional migration of the photogenerated electrons to Na sites, while the electron-rich Na sites enhance CO2 adsorption and activation. Na/g-C3N4 (NaCN) shows improved photocatalytic reduction activity of CO2 to CO and CH4, and under simulated sunlight irradiation, the CO yield of NaCN synthesized by embedding Na at 550°C (NaCN-550) is 371.2 μmol g-1 h-1, which is 58.9 times more than that of the monomer g-C3N4. By means of theoretical calculations and experiments including in situ fourier transform infrared spectroscopy, the mechanism is investigated. This strategy which improves carrier separation and reduces the energy barrier at the same time is important to the development of artificial photosynthesis.

Effect of Functional Group Modifications on the Photocatalytic Performance of g-C3 N4

In recent years, photocatalysis has received increasing attention in alleviating energy scarcity and environmental treatment, and graphite carbon nitride (g-C₃ N₄ ) is used as an ideal photocatalyst. However, it still remains numerous challenges to obtain the desirable photocatalytic performance of intrinsic g-C₃ N₄ . Functional group functionalization, formed by introducing functional groups into the bulk structure, is one of the common modification techniques to modulate the carrier dynamics and increases the number of active sites, offering new opportunities to break the limits for structure-to-performance relationship of g-C₃ N₄ . Nevertheless, the general overview of the advance of functional group modification of g-C₃ N₄ is less reported yet. In order to better understand the structure-to-performance relationship at the molecular level, a review of the latest development of functional group modification is urgently needed. In this review, the functional group modification of g-C₃ N₄ in terms of structures, properties, and photocatalytic activity is mainly focused, as well as their mechanism of reaction from the molecular level insights is explained. Second, the recent progress of the application of introducing functional groups in g-C₃ N₄ is introduced and examples are given. Finally, the difficulties and challenges are presented, and based on this, an outlook on the future research development direction is shown.

Photocatalytic concrete for degrading organic dyes in water

Since the advent of photocatalytic degradation technology, it has brought new vitality to the environmental governance and the response to the energy crisis. Photocatalysts harvest optical energy to drive chemical reactions, which means people can use solar energy to complete some resource-consuming activities by photocatalysts, such as environmental governance. In recent years, researchers have tried to combine photocatalyst TiO₂ with building materials to purify urban air and obtained good results. One of the important functions of photocatalysts is to degrade organic pollutants in water through light energy, but this technology has not been reported in the practical application areas. To extend this technology to practical application areas, photocatalytic concrete for degrading pollutants in waters was proposed and demonstrated for the first time in this paper. The photocatalytic concrete proposed based on the K-g-C₃N₄ shows a strong ability to degrade the organic dyes. According to the experiment results, the angle of light source plays an important role in the process of photocatalytic degradation, while waters with pH value of 6.5-8.5 hardly influenced the degradation of organic dyes. When the angle of light source is advantageous for photocatalytic concrete to absorb more visible light, more organic dyes will be degraded by photocatalytic concrete. The degradation rate of methylene blue could reach about 80% in ½ hour under desirable conditions and is satisfied compared with that of reported works. This study implicates that photocatalytic concrete can effectively degrade organic dyes in water. The influences of changes in the water environment hardly affect the degradation of organic pollutants, which means photocatalytic concrete can be widely used in green infrastructures to achieve urban sewage treatment.

One-pot hydrothermal synthesis of a double Z-scheme g-C3N4/AgI/β-AgVO3 ternary nanocomposite for efficient degradation of organic pollutants and DPC-Cr(VI) complex under visible-light irradiation

The Z-scheme photocatalytic system provides a promising way to achieve significant photodegradation efficiency. The work embodied here describes the synthesis of highly efficient double Z-scheme g-C₃N₄/AgI/β-AgVO₃ (g-CNAB) ternary nanocomposite using a one-pot hydrothermal route. The optical properties, phase structure, and morphology of the synthesized samples were investigated using UV-visible diffuse-reflectance spectroscopy (UV-Vis DRS), X-ray diffraction, and scanning electron microscopy, respectively. The transmission electron microscopy investigation revealed that synthesized composite material represents close interfacial interactions. X-ray photoelectron spectroscopy analysis confirms the presence of all the elements in the synthesized ternary nanocomposite materials. The photocatalytic performance of as-prepared photocatalysts has been systematically investigated using the photodegradation of a variety of pollutants, including Rhodamine B, Ciprofloxacin, and 1,5-diphenylcarbazide-Cr(VI) [DPC-Cr(VI)] complex under visible-light irradiation. Among all synthesized materials, such as g-C₃N₄, AgI, β-AgVO₃, and ternary nanocomposites with varying loading of β-AgVO₃ [g-CNAB_{(0.5, 1.0, 1.5, 2.0)}], the photocatalyst g-CNAB_(1.5) nanocomposite achieved a remarkably high photocatalytic efficiency. The quenching impact of several scavengers revealed that reactive species such as superoxide anion radical (O₂^·-) and hydroxyl radical (·OH) are significant in the degradation of various contaminants. Based on the characterization and application, a plausible photocatalytic mechanism has been sketched out to determine the reaction pathways involved in the degradation of pollutants present in the aqueous medium.

Enhancing Photocatalytic Hydrogen Production of g-C3N4 by Selective Deposition of Pt Cocatalyst

Graphitic carbon nitride (g-C₃N₄) has been widely studied as a photocatalyst for the splitting of water to produce hydrogen. In order to solve the problems of limited number of active sites and serious recombination rate of charge-carriers, noble metals are needed as cocatalysts. Here, we selectively anchored Pt nanoparticles (NPs) to specific nitrogen species on the surface of g-C₃N₄ via heat treatment in argon–hydrogen gas mixture, thus achieving g-C₃N₄ photocatalyst anchored by highly dispersed homogeneous Pt NPs with the co-existed metallic Pt⁰ and Pt²⁺ species. The synergistic effect of highly dispersed metallic Pt⁰ and Pt²⁺ species makes the catalyst exhibit excellent photocatalytic performance. Under the full-spectrum solar light irradiation, the photocatalytic hydrogen production rate of the photocatalyst is up to 18.67 mmol·g⁻¹·h⁻¹, which is 5.1 times of the catalyst prepared by non-selective deposition of Pt NPs.

A comparison study of sodium ion- and potassium ion-modified graphitic carbon nitride for photocatalytic hydrogen evolution

It is well known that modifying graphitic carbon nitride (GCN) is an imperative strategy to improve its photocatalytic activity. In this study, Na-doped and K-doped graphitic carbon nitride (GCN-Na and GCN-K) were prepared via the simple thermal polymerization of a mixture of melamine and NaCl or KCl, respectively. The structure characterization showed that both Na⁺ and K⁺ intercalation could reduce the interlayer distance of GCN and introduce cyano defects in GCN, while K⁺ apparently had a stronger influence on the structure variation of GCN. The chemical composition data showed that both Na⁺ and K⁺ could easily interact with GCN, while K-doping caused a greater change in the C/N ratio than Na-doping. Moreover, compared to GCN-Na-5 (5 represents weight ratio of alkali halide to melamine), the conduction and valence bands of GCN-K-5 both shifted upward based on the electronic and optical measurements. Consequently, GCN-K-5 yielded an H₂ evolution rate around 4 times higher than that of GCN-Na-5 under visible light irradiation (>420 nm). The cation size effect on GCN was proposed to be mainly responsible for the variation in the structure, optical and electronic properties of ion-doped GCNs, and hence the enhanced photocatalytic H₂ evolution. The current work can provide new insight into optimizing photocatalysts for enhanced photocatalytic performances.

The ion size effect on graphitic carbon nitride is responsible for variations in its structure, optical and electronic properties, and hence the enhancement in photocatalytic hydrogen evolution.

g-C3N4 Modified by meso-Tetrahydroxyphenylchlorin for Photocatalytic Hydrogen Evolution Under Visible/Near-Infrared Light

A new photocatalyst denoted as mTHPC/pCN was prepared by modifying protonated graphitic carbon nitride (pCN) by meso-tetrahydroxyphenylchlorin (mTHPC). Relevant samples were characterized via various methods including zeta potential measurements, X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, N₂ adsorption–desorption, transmission electron microscopy, ultraviolet-visible–near-infrared spectroscopy, electrochemical impedance spectroscopy, photocurrent response measurements, electron spin resonance spectroscopy, and phosphorescence spectroscopy. Compared with pCN, mTHPC/pCN shows enhanced absorption in the visible and near-infrared regions and thus higher photocatalytic activity in hydrogen evolution. A possible mechanism for mTHPC/pCN is proposed.

Construction of 1D Ag-AgBr/AlOOH Plasmonic Photocatalyst for Degradation of Tetracycline Hydrochloride

In this work, the highly efficient and low-cost Ag-AgBr/AlOOH plasmonic photocatalyst is successfully prepared via a simple and mild wet-chemical process and used for degrading high concentration methylene blue (MB) and tetracycline hydrochloride (TCH). The optimized 6-Ag-AgBr/AlOOH sample showed a 79% decomposition of TCH in 2 h, which is almost two times higher than that of bare AgBr (37%). For degrading MB, the photocatalytic activity of 6-Ag-AgBr/AlOOH (decomposing 84% in 2 h) showed a large enhancement as compared to bare AgBr (only 57%). The TEM, HRTEM, XRD, DRS, and XPS characterization results confirm that Ag-AgBr is a composite catalyst formed by loading Ag nanoparticles onto AgBr surfaces and then loaded on to AlOOH. The possible mechanism proposed is that •O 2 - and •OH radicals produced under sun light are the main active species for degrading MB and TCH. It is hoped that this work will open a new gateway to the synthesis of highly efficient and low-cost Ag-AgBr/AlOOH plasmonic photocatalysts for degrading organic pollutants.