Enhanced Visible-light Photocatalytic Activity of g-C 3 N 4 /Nitrogen-doped Graphene Quantum Dots/TiO 2 Ternary Heteroju
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doi: 10.1007/s40242-020-0301-1
Aricle
Enhanced Visible-light Photocatalytic Activity of g-C3N4/Nitrogen-doped Graphene Quantum Dots/TiO 2 Ternary Heterojunctions for Ciprofloxacin Degradation with Narrow Band Gap and High Charge Carrier Mobility CHEN Ting1, ZHONG Lei1, YANG Zhen1, MOU Zhigang1*, LIU Lei1, WANG Yan1, SUN Jianhua1* and LEI Weiwei2* 1. School of Chemistry and Environmental Engineering, Institute of Advanced Functional Materials for Energy, Jiangsu University of Technology, Changzhou 213001, P. R. China; 2. Institute for Frontier Materials, Deakin University, Waurn Ponds, Victoria 3216, Australia Abstract Limited visible-light absorption and high recombination rate of photogenerated charges are two main drawbacks in g-C3N4-based photocatalysts. To solve these problems, g-C3N4/nitrogen-doped graphene quantum dots (NGQDs)/TiO2 ternary heterojunctions were facilely prepared via a one-step calcining method. The morphology, structure, optical and electrochemical properties of g-C3N4/NGQDs/TiO2 were characterized and explored. The optimal g-C3N4/NGQDs/TiO2 composite exhibits enhanced photocatalytic degradation performance of ciprofloxacin (CIP) compared with the as-prepared g-C3N4, TiO2(P25) and g-C3N4/TiO2 heterojunction under visible light irradiation. The apparent rate constant of the composite is around 6.43, 4.03 and 2.30 times higher than those of g-C3N4, TiO2 and g-C3N4/TiO2, respectively. The enhanced photocatalytic efficiency should be mainly attributed to the improvement of light absorption and charge separation and transfer efficiency, originating from the narrow band gap and high charge carrier mobility. The active species trapping experiments results showed that the h + and •O2– were the main active species in the degradation process. A possible photocatalytic reaction mechanism of the g-C3N4/NGQDs/ TiO2 composite for the enhanced degradation of CIP under visible light irradiation was also proposed. Keywords g-C3N4/NGQDs/TiO2; Heterojunction; Photocatalysis; Antibiotic ciprofloxacin
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Introduction
remains a huge challenge in the practical application[3]. More recently, graphite-like environmentally friendly carbon nitride(g-C3N4) is becoming the focus of research in the field of visible-light photocatalysis owing to its tunable electronic structure, relatively narrow band gap(ca. 2.7 eV) and high stability, etc.[4,5]. However, photocatalytic activity for environmental remediation by single g-C3N4 is restricted by the limited visible-light absorption(absorption maximum at 460 nm) and high recombination rate of photogenerated charges[6]. TiO2 is one of the most widely used photocatalysts due to its low cost, nontoxicity, high photoreactivity and chemical stability[7]. P25, as a well-known commercial catalyst containing anatase and rutile phases of TiO2, is widely used in the degradation of many organic pollutants and antibiotics[8,9]. However, it possesses drawbacks of wide band gap(3.2 eV for anatase, 3.0 eV for rutile) and fast recombination of the photo-induced electron hole pairs, which l
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