Abstract
Nitrogen doped graphene quantum dots (NGQDs) were successfully prepared via a hydrothermal method using citric acid and urea as the carbon and nitrogen precursors, respectively. Due to different post-treatment processes, the obtained NGQDs with different surface modifications exhibited blue light emission, while their visible-light absorption was obviously different. To further understand the roles of nitrogen dopants and N-containing surface groups of NGQDs in the photocatalytic performance, their corresponding composites with TiO2 were utilized to degrade RhB solutions under visible-light irradiation. A series of characterization and photocatalytic performance tests were carried out, which demonstrated that NGQDs play a significant role in enhancing visible-light driven photocatalytic activity and the carrier separation process. The enhanced photocatalytic activity of the NGQDs/TiO2 composites can possibly be attributed to an enhanced visible light absorption ability, and an improved separation and transfer rate of photogenerated carriers.
Highlights
Photocatalytic reactions driven by solar light are a promising method for solving the existing environmental and energy problems
The distinct enhancement of photocurrent under visible-light irradiation is consistent with the PL spectra, demonstrating the vital role of Nitrogen doped graphene quantum dots (NGQDs) in improving carrier separation and transfer rate, N-graphene quantum dots (GQDs) possess good electrical visible-light irradiation is consistent with the PLsince spectra, demonstrating the vital role ofconductivity improving carrier separation and transfer rate, since N-GQDs possess good electrical conductivity [42]
The possible mechanism of the enhanced photocatalytic activity of the NGQDs/TiO2 composites is illustrated in Scheme 1
Summary
Photocatalytic reactions driven by solar light are a promising method for solving the existing environmental and energy problems. In most reported semiconductor quantum dots/TiO2 composites, visible light can be effectively utilized and the recombination of carriers can be inhibited [9,10]. The bonding could promote fast electron transfer in the interfacial region of the GQDs/TiO2 composite structure, inhibiting carrier recombination [16,17,18,19,20] Despite these advantages, the absorption band of GQDs is mainly confined in the UV region, which limits their solar energy utilizing efficiency in photocatalysis. Through adjusting the N doping amounts, different percentages of the C–N configuration in the structure can further influence the electron delocalization and charge carrier density These particular performances have endowed NGQDs with more possibilities in constructing new visible-light driven photocatalysts. To furtherly understand the roles of nitrogen dopants and N-containing surface groups, the photocatalytic degradation activities of different composites under visible light irradiation were measured and are discussed
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