Acta Phys. -Chim. Sin. ›› 2018, Vol. 34 ›› Issue (6): 708-718.doi: 10.3866/PKU.WHXB201710162

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Improving the Efficiency of Carbon Quantum Dots as a Visible Light Photosensitizer by Polyamine Interfacial Modification

Shaohai LI,Bo WENG,Kangqiang LU,Yijun XU*()   

  • Received:2017-07-27 Published:2018-03-20
  • Contact: Yijun XU
  • Supported by:
    The project was supported by the National Natural Science Foundation of China(U1463204);The project was supported by the National Natural Science Foundation of China(21173045);the Award Program for Minjiang Scholar Professorship, China, the Natural Science Foundation (NSF) of Fujian Province for Distinguished Young Investigator Rolling Grant, China(2017J07002);the Independent Research Project of State Key Laboratory of Photocatalysis on Energy and Environment, China(2014A05);the 1st Program of Fujian Province for Top Creative Young Talents, the Open Research Project of State Key Laboratory of Physical Chemistry of Solid Surfaces of Xiamen University, China(201519);the Program for Returned High-Level Overseas Chinese Scholars of Fujian Province, China


Carbon quantum dots (CQDs) are emerging as the new-generation light absorber for solar energy conversion. However, the low photosensitization efficiency of CQDs is one of the current bottlenecks impeding their large-scale practical applications in photocatalysis. Therefore, developing a facile approach for the engineering and functionalization of CQDs-based composites to improve the photosensitization efficiency of CQDs is highly desirable. On account of the abundant functional groups, especially oxygen-containing functional groups such as carbonyl, carboxyl, and hydroxyl present on their surface, CQDs can be readily combined with various organic molecules or polymers as a surface passivation component to reduce the nonradioactive surface recombination of photo-generated charge carriers, thus enabling the CQDs to exhibit strong photoluminescence in the visible and near-infrared spectral regions. Consequently, polymer passivation has been demonstrated as an ideal strategy to make it accessible for improving the sensitization efficiency of CQDs in photocatalytic applications. Branched polyethylenimine (BPEI) is one of polymers that contains a high density of amine groups and exhibits high electron mobility, which can be used as an electron injection material at the interface of nanomaterials. Besides, the BPEI polymer with amino groups exhibiting positive charge has been utilized for designing heterogeneous catalysts by an electrostatic self-assembly strategy. Therefore, BPEI is expected to modify the surface of inorganic oxides semiconductor to enhance the photosensitization efficiency of CQDs under visible light. However, to date, the study in this regard has been still unavailable. In this work, we developed a facile approach to engineer well-distributed CQDs via electrostatic interaction on BPEI passivated TiO2 composites (BTC) as photocatalysts. The BTC composites with an optimal loading of 5% (w, mass fraction) CQDs outperformed the TiO2/CQDs (TC) composite and referential BPEI/SiO2/CQDs (BSC) composites for the photoreduction of 4-nitroaniline under visible light irradiation. The structure of the fabricated BTC composites was systematically investigated by the combined use of structural and spectral characterizations, demonstrating that the photosensitizer CQDs contacted well with the BPEI modified TiO2 nanoparticles. The comparison characterizations revealed that BPEI facilitated the dissociation and transfer of excitons as an electron transfer channel. The as-prepared BTC composites benefited from the favorable interfacial contact and effective transfer of photo-generated charge carriers, and thus manifested superior photocatalytic activity to the TC composite. It is expected that this strategy would be extended to other wide band gap semiconductor photocatalyst systems and open up new possibilities in designing efficient CQDs-based semiconductor artificial light harvesting systems by interfacial optimization.

Key words: Carbon quantum dots, Sensitization, Branched polyethylenimine, Photocatalysis, Semiconductor