Abstract
In this work, Bi2O3-x with surface oxygen vacancies was prepared through the NaBH4 reduction of Bi2O3. After that, carbon quantum dots (CQDs) were deposited onto the surface of the Bi2O3-x to obtain a series of the CQDs/Bi2O3-x composites. The HRTEM and XPS characterizations of the CQDs/Bi2O3-x composites suggest that the thickness of surface oxygen vacancies could be adjusted by changing the concentration of NaBH4 solution, and the intimate contact between CQDs and the Bi2O3-x is achieved. Acid orange 7 (AO7) was adopted as the target reactant for investigating the photocatalytic degradation activities of the CQDs/Bi2O3-x composites under simulated sunlight and NIR light irradiation. It is found that the photocatalytic activities of the samples are closely related to the concentration of NaBH4 and content of CQDs. The Bi2O3-x samples exhibit enhanced simulated-sunlight-driven photocatalytic activity compared with Bi2O3. Specifically, the optimal degradation efficiency of AO7 is achieved over the 3R-Bi2O3-x (concentration of NaBH4: 3 mmol/L), which is 1.38 times higher than the degradation AO7 efficiency over Bi2O3. After the decoration of the 3R-Bi2O3-x surface with CQDs, the simulated-sunlight-driven photocatalytic activity of the CQDs/Bi2O3-x composite could be further enhanced. Among the samples, the 15C/3R-Bi2O3-x sample reveals the highest photocatalytic activity, leading to an AO7 degradation percentage of ~97% after 60 min irradiation. Different from Bi2O3 and the 3R-Bi2O3-x, the 15C/3R-Bi2O3-x sample also exhibits near-infrared (NIR)-light-driven photocatalytic degradation activity. In addition, the intrinsic photocatalytic activity of CQDs/Bi2O3-x composite was further confirmed by the degradation of phenol under simulated sunlight and NIR light irradiation. The photocurrent response and electrochemical impedance spectroscopy (EIS) measurements confirm the efficient migration and separation of photogenerated charges in the CQDs/Bi2O3-x samples. The •OH and h+ are proved to be the main reactive species in the simulated sunlight and NIR light photocatalytic processes over the CQDs/Bi2O3-x composites. According to the above experiments, the photocatalytic degradation mechanisms of the CQDs/Bi2O3-x composites under simulated sunlight and NIR light illumination were proposed.
Highlights
Bismuth-based photocatalysts have been widely investigated owing to their promising application in wastewater purification [1,2,3,4,5]
The photocatalytic Acid orange 7 (AO7) degradation experiments confirm that the simulated-sunlight-driven photocatalytic performances of the samples are closely related to the concentration of NaBH4 and content of carbon quantum dots (CQDs)
The introduction of surface oxygen vacancies effectively improves the photocatalytic activity of Bi2 O3 under simulated sunlight irradiation
Summary
Bismuth-based photocatalysts have been widely investigated owing to their promising application in wastewater purification [1,2,3,4,5]. The introduction of oxygen vacancies on the surface of photocatalysts is regarded as an important and promising strategy to inhibit the recombination of photogenerated charges and extend the light absorption range [31,32,33,34,35]. Liu et al reported a hydrogenation method to introduce the oxygen vacancies on the surface of Bi2 O3 , improving its photocatalytic activity [30]. Considering the advantages of the above modification methods, it is expected that efficient Bi2 O3 photocatalysts with wide photoresponse regions can be obtained through the synergetic modification of surface oxygen vacancies and CQD decoration.
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