In this study, Ce x Zr 1−x O 2 solid-solution oxide (x = 0.7) was prepared using hydrothermal method , and the obtained Ce 0.7 Zr 0.3 O 2 nanoparticles were modified with wood–based carbon quantum dots (CQDs). Furthermore, we report a composite photocatalyst of vacuum heat-treated CQDs/Ce 0.7 Zr 0.3 O 2 for degrading methylene blue. The structural properties and photocatalytic activity of CQDs/Ce 0.7 Zr 0.3 O 2 were systematically studied after vacuum heat treatment. Herein, a part of the functional groups present on CQD surfaces changed through high–temperature heating during vacuum heat treatment. The dominant structures sp 2 hybrid carbon atoms and amorphous carbon were transformed to defect states of sp 3 hybrid oxygen atoms, thus increasing the surface oxygen vacancy concentration. The high activity and excellent stability of vacuum heat-treated CQDs/Ce 0.7 Zr 0.3 O 2 system can be attributed to increased surface oxygen vacancy concentration, modification of CQDs, and the protruding structure of Ce 0.7 Zr 0.3 O 2 , contributing to efficient charge transfer. This study provides potential systems of CQD-modified photocatalysts and also reveals the substantial effect of vacuum heat treatment on enhancing the photocatalytic properties of composites.
Gao Xing,Gong Xinchao,Nguyen Tat Thang,Du Wenxin,Chen Xueqi,Song Zihui,Chai Rusong,Guo Minghui
In this study, a luminescent material of wood-based carbon quantum dots (CQDs)/Ce 0.7 Zr 0.3 O 2 with a regular, uniform shape, and a high color purity was synthesized by a facile method. Ce x Zr 1− x O 2 solid-solution oxides ( x = 0.7) were prepared by a hydrothermal method, and CQDs were adsorbed on the as-obtained Ce 0.7 Zr 0.3 O 2 nanoparticles. The crystal structure was identified by powder X-ray diffraction and Rietveld refinement. In addition, the effect of adsorbed CQDs on the luminescence properties of Ce 0.7 Zr 0.3 O 2 was systematically investigated by Raman spectroscopy, elemental analysis, electron spin resonance spectroscopy, and photoluminescence spectroscopy, as well as decay curve and quantum yield (QY) measurements. Herein, a promising strategy of surface engineering, that is, reduction of the surface defect concentration in Ce 0.7 Zr 0.3 O 2 by the adsorption of CQDs to decrease the nonradiative transition processes at defect sites was described. As expected, the adsorption of CQDs decreased the Ce–O bond length and the surface defect concentration of Ce 0.7 Zr 0.3 O 2 , thereby effectively decreasing the nonradiative transition processes and suppressing fluorescence quenching. Hence, CQDs/Ce 0.7 Zr 0.3 O 2 with a perfect cubic structure exhibits a performance improvement in terms of the luminescence and QY value. Furthermore, a light-emitting diode device was fabricated using as-synthesized CQDs/Ce 0.7 Zr 0.3 O 2 , emitting apparent yellow light with a high color purity (93.3%), with International Commission on Illumination coordinates of (0.5239, 0.4531), and a low correlated color temperature (2271 K) under a driven current of 60 mA, suggesting that CQDs/Ce 0.7 Zr 0.3 O 2 exhibits potential for practical applications.
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