Abstract
The aggregation of zinc oxide nanoparticles leads to an increased absorbance in the ultraviolet-visible region by an induced light scattering effect. Herein, we demonstrate the inhibition of photoconversion activity in ZnO-graphene core-shell quantum dots (QD) (ZGQDs) agglomerated by 4-aminophenol (4-AP) used as a linker. The ZnO-graphene quantum dots (QD) aggregates (ZGAs) were synthesized using a facile solvothermal process. The ZGAs revealed an increased absorbance in the wavelengths between 350 and 750 nm as compared with the ZGQDs. Against expectation, the calculated average photoluminescence lifetime of ZGAs was 7.37 ns, which was 4.65 ns longer than that of ZGQDs and was mainly due to the high contribution of a slow (τ2, τ3) component by trapped carriers in the functional groups of graphene shells and 4-AP. The photoelectrochemical (PEC) cells and photodetectors (PDs) were fabricated to investigate the influence of ZGAs on the photoconversion activity. The photocurrent density of PEC cells with ZGAs was obtained as 0.04 mA/cm2 at 0.6 V, which was approximately 3.25 times lower than that of the ZGQDs. The rate constant value of the photodegradation value of rhodamine B was also decreased by around 1.4 times. Furthermore, the photoresponsivity of the PDs with ZGAs (1.54 μA·mW−1) was about 2.5 times as low as that of the PDs with ZGQDs (3.85 μA·mW−1). Consequently, it suggests that the device performances could be degraded by the inhibition phenomenon of the photoconversion activity in the ZGAs due to an increase of trap sites.
Highlights
Zinc oxide nanoparticles (ZnO NPs) are known to be environmentally friendly substances, which have an excellent photo conversion activity, good photo responsibility in the UV-visible range, and unique physical properties
We demonstrate the synthesis of the zinc oxide graphene quantum dot aggregates (ZGAs) using 4-aminophenol (4-AP) as a linker by a facile solvothermal method
The aggregation mechanism of ZnO-graphene quantum dots (QD) aggregates (ZGAs) can be described by several chemical reactions as follows (Figure 1b): (1) the activated carboxyl groups of ZnO-graphene core-shell quantum dots (ZGQDs) react with the amine groups of 4-AP to form amide bonds at a high temperature of 140 ◦ C [15], (2) the hydroxyl groups remaining in 4-AP form ester bonds with the carboxyl groups of another graphene surface by the esterification reaction, (3) the amine groups of 4-AP react with epoxy groups on the graphene nanoshell through the ring-opening reaction [17], and (4) the noncovalent interaction between graphene shells of ZGQDs and aromatic molecules of 4-AP [18]
Summary
Zinc oxide nanoparticles (ZnO NPs) are known to be environmentally friendly substances, which have an excellent photo conversion activity, good photo responsibility in the UV-visible range, and unique physical properties. Owing to these outstanding properties, they have been. The large-sized ZnO NPs are limited to improving photo conversion activity due to relatively low light scattering resulting from reduced internal surface area. Using our approach it is possible to form aggregates of ZnO quantum dots which are individually graphene wrapped. We demonstrate the synthesis of the zinc oxide graphene quantum dot aggregates (ZGAs) using 4-aminophenol (4-AP) as a linker by a facile solvothermal method. We fabricated the ZGA- and ZGQD-based photodetectors (PDs), and a photoelectrochemical (PEC) cell to demonstrate the role of the suggested materials
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