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Influence of Hydrogenation on Morphology, Chemical Structure and Photocatalytic Efficiency of Graphitic Carbon Nitride.

ABSTRACT: In this contribution, the effect of hydrogenation conditions atmosphere (temperature and time) on physicochemical properties and photocatalytic efficiency of graphitic carbon nitride (g-C3N4, gCN) was studied in great details. The changes in the morphology, chemical structure, optical and electrochemical properties were carefully investigated. Interestingly, the as-modified samples exhibited boosted photocatalytic degradation of Rhodamine B (RhB) with the assistance of visible light irradiation. Among modified gCN, the sample annealed at 500 °C for 4 h (500-4) in H2 atmosphere exhibited the highest photocatalytic activity-1.76 times higher compared to pristine gCN. Additionally, this sample presented high stability and durability after four cycles. It was noticed that treating gCN with hydrogen at elevated temperatures caused the creation of nitrogen vacancies on gCN surfaces acting as highly active sites enhancing the specific surface area and improving the mobility of photogenerated charge carriers leading to accelerating the photocatalytic activity. Therefore, it is believed that detailed optimization of thermal treatment in a hydrogen atmosphere is a facile approach to boost the photoactivity of gCN.

SUBMITTER: Baranowska D

PROVIDER: S-EPMC8657794 | biostudies-literature | 2021 Dec

REPOSITORIES: biostudies-literature

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Influence of Hydrogenation on Morphology, Chemical Structure and Photocatalytic Efficiency of Graphitic Carbon Nitride.

Baranowska Daria D Kędzierski Tomasz T Aleksandrzak Małgorzata M Mijowska Ewa E Zielińska Beata B

International journal of molecular sciences 20211203 23

In this contribution, the effect of hydrogenation conditions atmosphere (temperature and time) on physicochemical properties and photocatalytic efficiency of graphitic carbon nitride (g-C<sub>3</sub>N<sub>4</sub>, gCN) was studied in great details. The changes in the morphology, chemical structure, optical and electrochemical properties were carefully investigated. Interestingly, the as-modified samples exhibited boosted photocatalytic degradation of Rhodamine B (RhB) with the assistance of visi ...[more]

PMID: 34884900

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Project description:Graphitic carbon nitride (g-C3N4) is a metal-free photocatalyst used for visible-driven hydrogen production, CO2 reduction, and organic pollutant degradation. In addition to the most attractive feature of visible photoactivity, its other benefits include thermal and photochemical stability, cost-effectiveness, and simple and easy-scale-up synthesis. However, its performance is still limited due to its low absorption at longer wavelengths in the visible range, and high charge recombination. In addition, the exfoliated nanosheets easily aggregate, causing the reduction in specific surface area, and thus its photoactivity. Herein, we propose the use of ultra-thin porous g-C3N4 nanosheets to overcome these limitations and improve its photocatalytic performance. Through the optimization of a novel multi-step synthetic protocol, based on an initial thermal treatment, the use of nitric acid (HNO3), and an ultrasonication step, we were able to obtain very thin and well-tuned material that yielded exceptional photodegradation performance of methyl orange (MO) under visible light irradiation, without the need for any co-catalyst. About 96% of MO was degraded in as short as 30 min, achieving a normalized apparent reaction rate constant (k) of 1.1 × 10-2 min-1mg-1. This represents the highest k value ever reported using C3N4-based photocatalysts for MO degradation, based on our thorough literature search. Ultrasonication in acid not only prevents agglomeration of g-C3N4 nanosheets but also tunes pore size distribution and plays a key role in this achievement. We also studied their performance in a photocatalytic hydrogen evolution reaction (HER), achieving a production of 1842 µmol h-1 g-1. Through a profound analysis of all the samples' structure, morphology, and optical properties, we provide physical insight into the improved performance of our optimized porous g-C3N4 sample for both photocatalytic reactions. This research may serve as a guide for improving the photocatalytic activity of porous two-dimensional (2D) semiconductors under visible light irradiation.

Project description:Metal-doped graphitic carbon nitride (MCN) materials have shown great promise as effective photocatalysts for the conversion of acetic acid to carbon dioxide under UV-visible irradiation and are superior to pristine carbon nitride (g-C3N4 , CN). In this study, the effects of metal dopants on the physicochemical properties of metal-doped CN samples (Fe-, Cu-, Zn-, FeCu-, FeZn-, and CuZn-doped CN) and their catalytic activity in the photooxidation of acetic acid were investigated and discussed for their correlation, especially on their surface and bulk structures. The materials in the order of highest to lowest photocatalytic activity are FeZn_CN, FeCu_CN, Fe_CN, and Cu_CN (rates of CO2 evolution higher than for CN), followed by Zn_CN, CuZn_CN, and CN (rates of CO2 evolution lower than CN). Although Fe doping resulted in the extension of the light absorption range, incorporation of metals did not significantly alter the crystalline phase, morphology, and specific surface area of the CN materials. However, the extension of light absorption into the visible region on Fe doping did not provide a suitable explanation for the increase in photocatalytic efficiency. To further understand this issue, the materials were analyzed using two complementary techniques, reversed double-beam photoacoustic spectroscopy (RDB-PAS) and electron spin resonance spectroscopy (ESR). The FeZn_CN, with the highest electron trap density between 2.95 and 3.00 eV, afforded the highest rate of CO2 evolution from acetic acid photodecomposition. All Fe-incorporated CN materials and Cu-CN reported herein can be categorized as high activity catalysts according to the rates of CO2 evolution obtained, higher than 0.15 μmol/min-1, or >1.5 times higher than that of pristine CN. Results from this research are suggestive of a correlation between the rate of CO2 evolution via photocatalytic oxidation of acetic acid with the threshold number of free unpaired electrons in CN-based materials and high electron trap density (between 2.95 and 3.00 eV).

Dataset Information

Influence of Hydrogenation on Morphology, Chemical Structure and Photocatalytic Efficiency of Graphitic Carbon Nitride.

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Influence of Hydrogenation on Morphology, Chemical Structure and Photocatalytic Efficiency of Graphitic Carbon Nitride.

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