Photodegradation of Organic Pollutants Coupled with Simultaneous Photocatalytic Evolution of Hydrogen Using Quantum-Dot-Modified g-C₃N₄ Catalysts under Visible-Light Irradiation

Abstract

Carbon quantum dots/CdS quantum dots/g-C3N4 (CDs/CdS/GCN) photocatalysts have been designed and prepared. Systematic characterization such as XRD, SEM, TEM, UV, and XPS, were done to confirm the composite catalysts of CDs/CdS/GCN. The simultaneous photocatalytic production of hydrogen coupled with degradation of organic contaminants (p-chlorophenol, bisphenol A, and tetracycline, called 4-NP, BPA, and TTC, respectively) was efficiently realized over the resultant CDs/CdS/GCN composites. The as-prepared 3%CDs/10%CdS/GCN exhibits high efficiency of photocatalytic hydrogen evolution from water splitting and photodegradation rates of organic pollutants in aqueous solutions of 4-NP, BPA, and TTC under visible-light illumination since the formation of interfaces between CdS quantum dots and GCN nanosheets leads to an efficient charge separation efficiency. Furthermore, as compared to that in a pure water system, the photocatalytic evolution rate of H2 over the 3%CDs/10%CdS/GCN catalyst in the presence of 4-NP solution is decreased, while the H2 evolution rates increase when BPA or TTC solution were used instead of 4-NP solution under visible-light irradiation. Consequently, 4-NP shows higher photodegradation efficiency than do BPA and TTC in the simultaneous photocatalytic oxidation and reduction system. Aiming at making clear the relationship between the photocatalytic H2 production and the photocatalytic pollutants degradation, density functional theory (DFT) calculations, and liquid chromatography mass spectrometry (LC-MS) were used for a systematic investigation. The present work reports a plausible mechanism of photodegradation of different organic contaminants with synchronous photocatalytic H2 evolution from water and the photocatalytic enhancement of the CDs/10%CdS/GCN catalysts.

A Review on Quantum Dots Modified g-C3N4-Based Photocatalysts with Improved Photocatalytic Activity

“…The highest H 2 production rate was 116.1 µmol h −1 , which was two-fold higher than that of pure CNNS (37.8 µmol h −1 ). Jiang et al [105] prepared CDs/CdS QDs/g-C 3 N 4 (CDs/CdS/GCN) composites through a combination of solvothermal and physical coprecipitation methods. The XRD pattern (Figure 8b) exhibits that the introduction of CDs would not affect the crystal phase and structure of CdS/GCN heterojunctions.…”

“…These active species could directly degrade TC. Jiang et al [105] prepared CDs/CdS QDs/g-C 3 N 4 (CDs/CdS/GCN) photocatalysts. The UV-vis diffuse reflectance spectra for 3%CDs/CdS/GCN exhibited optimal absorption intensity in the visible region and marked red-shifts due to the good light absorption property of CDs and CdS QDs.…”

“…Sunlight-driven photocatalytic technologies provide a promising method to solve these problems [4][5][6]. As a novel strategy to take advantage of solar energy, semiconductor photocatalysts are becoming a scientific research focus due to its environmentally-friendly and energy-efficient characteristics, as compared [102,105]. Copyright American Chemical Society, 2018; Elsevier, 2016; respectively).…”

“…Transient photocurrent responses of (a) g-C3N4 and CDs/g-C3N4 (10 wt.%), (b) CM3 and 0.5CCM3, (c) GCN, GCN nanosheet, PM CdS/GCN, 10%CdS/GCN and 3%CDs/10%CdS/GCN, (d) g-C3N4, HpCN and CQDs/HpCN (reproduced with permission from[92,100,105,106]. Copyright Royal Society of Chemistry, 2017; Elsevier, 2018; American Chemical Society, 2018; Elsevier, 2016; respectively).…”

“…Photoluminescence (PL) emission spectra of (a) g-C 3 N 4 , (1-10%) MoO 3 /C 3 N 4 composites, and 0.5CCM3 at an excitation wavelength of 300 nm, (b) GCN, GCN nanosheets, PM CdS/GCN, 10%CdS/GCN and 3%CDs/10%CdS/GCN at an excitation wavelength of 325 nm (reproduced with permission from[100,105]. Copyright Elsevier, 2018; American Chemical Society, 2018; respectively).…”