Recent progress in g-C3N4 based low cost photocatalytic system: activity enhancement and emerging applications

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Abstract

Noble metal free g-C ₃N ₄ based photocatalysts find promising applications in the fields of photocatalytic H ₂ production, overall water splitting and CO ₂ reduction. Their photocatalytic can be enhanced by depositing non-noble metal co-catalysts and exfoliation to nanosheets.

Abstract

Graphitic C ₃N ₄ (g-C ₃N ₄) has continuously attracted attention since it was reported as a metal-free semiconductor for water splitting. However, its ability to evolve hydrogen from water is significantly dependent on the use of noble metal co-catalyst, mainly Pt. In recent years, good progress has been achieved in developing co-catalysts containing earth abundant elements only for constructing low cost and efficient g-C ₃N ₄ based photocatalytic systems. Besides, exfoliation of bulk g-C ₃N ₄ into two dimensional g-C ₃N ₄ nanosheets offers large surface area and exposed active sites, which are beneficial for activity enhancement. Furthermore, oxygen evolution and CO ₂ photoreduction over g-C ₃N ₄ have gained increasing interests due to the demand to achieve overall water splitting and conversion of CO ₂ into chemicals and fuels. In this mini-review, we will briefly summarize the latest research works on g-C ₃N ₄ based photocatalytic systems during the last three years with emphasis on the progress achieved in enhancing the hydrogen evolution activity of g-C ₃N ₄ by loading noble metal free co-catalysts, exfoliating bulk g-C ₃N ₄ into nanosheets, and applying the g-C ₃N ₄ system in photocatalytic O ₂ evolution and CO ₂ reduction.

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Most cited references 87

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Graphene-Like Carbon Nitride Nanosheets for Improved Photocatalytic Activities

Lili Zhang, Gang Liu, Hui-Ming Cheng … (2012)

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Photocatalytic Reduction of CO2on TiO2and Other Semiconductors

Severin N Habisreutinger, Lukas Schmidt-Mende, Jacek K Stolarczyk (2013)

Rising atmospheric levels of carbon dioxide and the depletion of fossil fuel reserves raise serious concerns about the ensuing effects on the global climate and future energy supply. Utilizing the abundant solar energy to convert CO2 into fuels such as methane or methanol could address both problems simultaneously as well as provide a convenient means of energy storage. In this Review, current approaches for the heterogeneous photocatalytic reduction of CO2 on TiO2 and other metal oxide, oxynitride, sulfide, and phosphide semiconductors are presented. Research in this field is focused primarily on the development of novel nanostructured photocatalytic materials and on the investigation of the mechanism of the process, from light absorption through charge separation and transport to CO2 reduction pathways. The measures used to quantify the efficiency of the process are also discussed in detail.

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Roles of cocatalysts in photocatalysis and photoelectrocatalysis.

Jinhui Yang, Donge Wang, Hongxian Han … (2013)

Since the 1970s, splitting water using solar energy has been a focus of great attention as a possible means for converting solar energy to chemical energy in the form of clean and renewable hydrogen fuel. Approaches to solar water splitting include photocatalytic water splitting with homogeneous or heterogeneous photocatalysts, photoelectrochemical or photoelectrocatalytic (PEC) water splitting with a PEC cell, and electrolysis of water with photovoltaic cells coupled to electrocatalysts. Though many materials are capable of photocatalytically producing hydrogen and/or oxygen, the overall energy conversion efficiency is still low and far from practical application. This is mainly due to the fact that the three crucial steps for the water splitting reaction: solar light harvesting, charge separation and transportation, and the catalytic reduction and oxidation reactions, are not efficient enough or simultaneously. Water splitting is a thermodynamically uphill reaction, requiring transfer of multiple electrons, making it one of the most challenging reactions in chemistry. This Account describes the important roles of cocatalysts in photocatalytic and PEC water splitting reactions. For semiconductor-based photocatalytic and PEC systems, we show that loading proper cocatalysts, especially dual cocatalysts for reduction and oxidation, on semiconductors (as light harvesters) can significantly enhance the activities of photocatalytic and PEC water splitting reactions. Loading oxidation and/or reduction cocatalysts on semiconductors can facilitate oxidation and reduction reactions by providing the active sites/reaction sites while suppressing the charge recombination and reverse reactions. In a PEC water splitting system, the water oxidation and reduction reactions occur at opposite electrodes, so cocatalysts loaded on the electrode materials mainly act as active sites/reaction sites spatially separated as natural photosynthesis does. In both cases, the nature of the loaded cocatalysts and their interaction with the semiconductor through the interface/junction are important. The cocatalyst can provide trapping sites for the photogenerated charges and promote the charge separation, thus enhancing the quantum efficiency; the cocatalysts could improve the photostability of the catalysts by timely consuming of the photogenerated charges, particularly the holes; most importantly, the cocatalysts catalyze the reactions by lowering the activation energy. Our research shows that loading suitable dual cocatalysts on semiconductors can significantly increase the photocatalytic activities of hydrogen and oxygen evolution reactions, and even make the overall water splitting reaction possible. All of these findings suggest that dual cocatalysts are necessary for developing highly efficient photocatalysts for water splitting reactions.

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Author and article information

Journal

Journal ID (publisher-id): CSTAGD

Title: Catalysis Science & Technology

Abbreviated Title: Catal. Sci. Technol.

Publisher: Royal Society of Chemistry (RSC)

ISSN (Print): 2044-4753

ISSN (Electronic): 2044-4761

Publication date Created: 2015

Publication date (Electronic): 2015

Volume: 5

Issue: 12

Pages: 5048-5061

Affiliations

[1 ]School of Chemical & Biomedical Engineering

[2 ]Nanyang Technological University

[3 ]Singapore 637459

[4 ]Energy Research Institute @ NTU

[5 ]SinBeRISE CREATE

[6 ]National Research Foundation

Article

DOI: 10.1039/C5CY00938C

SO-VID: a1a44cb3-26ce-4cd8-abdb-de8e1a84332d

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