A nanocomposite of carbon quantum dots and TiO₂nanotube arrays: enhancing photoelectrochemical and photocatalytic properties

Abstract

A novel nanocomposite of carbon quantum dots (CQDs) and TiO 2 nanotubes was fabricated and its enhanced photocatalytic and photoelectrochemical properties were demonstrated. Carbon quantum dots were obtained by electrochemical-etching graphite electrodes and TiO 2 nanotubes arrays were prepared by anodization methods. Subsequently, CQDs were assembled on the surface of vertically aligned TiO 2 nanotube arrays (CQDs/TiO 2 nanotubes) and the as-prepared samples were characterized by field-emission scanning electron microscopy, X-ray diffraction, UV-vis diffuse reflectance spectroscopy, photoelectrochemical and photocatalytic measurements. XPS measurement shows the presence of carbon species which come from CQDs. A red shift of light absorption edge and more absorption in the visible light region were observed for the resulting samples from the UV-vis diffuse reflectance spectra. An enhanced photocurrent and photopotential were demonstrated for the CQDs sensitized TiO 2 nanotubes under visible light irradiation and the photocurrent density was 2.7 times larger than that of pristine TiO 2 nanotubes. A solar cell was fabricated for further verifying the sensitization of CQDs over TiO 2 nanotubes. Moreover, the photocatalytic activity of CQDs/TiO 2 nanotubes towards the degradation of methylene blue was demonstrated and about 14% enhanced degradation efficiency was obtained with the presence of CQDs. This work developed a simple method to fabricate CQDs and demonstrated the introduction of CQDs to be a new approach for improving the utilization of visible light for TiO 2 nanotube arrays.

Charge and energy transfer interplay in hybrid sensitized solar cells mediated by graphene quantum dots

“…The open circuit potential (V oc ) is 0.48 V when GQDs were loaded on TiO 2 , a four time increase with respect to the reference cell. These values are in accordance with those of the previously reported GQD-based DSSCs [26][27][28][29].…”

“…In ultraviolet spectral range, GQDs have extinction coefficients ranging from 10 to 200·10 3 M -1 cm -1 [24], larger than that of common fluorophores, and comparable to those of semiconductor quantum dots (QDs) [25]. Due to this fact, GQDs can be physically included in a photoanode to act as a sensitizer in quantum dot -sensitized solar cells (QDSSC), but only very low efficiencies have been reported to this point, albeit different GQDs synthesis methods or different architectures of TiO 2 electrode were proposed [26][27][28][29]. The explanation for the rather low efficiencies of the GQDs sensitized solar cells resides in the limited spectral range of absorption as well as in their low quantum yield compared with the standard fluorophores or semiconducting QDs.…”

Improving the contact properties of CdS-decorated TiO2 nanotube arrays using an electrochemical/thermal/chemical approach

“…The experimental impedance data were curve-fitted and analyzed using the EQUIVCRT program and the electric equivalent circuit (eec) shown in the inset of Fig. 8 [38,39], where R s is the electrolyte resistance, R f is the charge transport resistance in the internal film (TiO 2 or CdS/TiO 2 ), Q dl is a Fig. 7 a Absorbance spectra and b d(ln(F(R)hv)/d(hv) vs. hv curves obtained from diffuse reflectance spectra using the method proposed by Chakrabarti et al [34], for TNAs with CdS coupled by electrochemical/ thermal/chemical method (CdS/TNAs, M1-M3) using 1000 (M1), 2000 (M2), and 3000 (M3) cycles in the electrodeposition of cadmium precursor particles; TNAs with CdS coupled by SILAR method (SICdS/TNAs); and cadmium-free TNAs following the same thermal (TTNAs) and chemical treatment (TS-TNAs) constant phase element (CPE) associated with the doublelayer capacitance, R ct is the charge transfer resistance between the electrode surface and the electrolyte, and Q sc is a CPE associated with the space charge capacitance.…”

In situ fabrication of TiO 2 nanotube arrays sensitized by Ag nanoparticles for enhanced photoelectrochemical performance

“…Therefore, the in situ preparation of Ag nanoparticles on TiO 2 NTs to promote the electron transfer efficiency is still challenging and demanding. Herein, we described a simple way of preparing Ag nanoparticles to sensitize TiO 2 NTs using ascorbic acid as the reducing agent, and the chemical linking roles of ascorbic acid promote the uniform coverage of 3 Ag nanocrystals on the top and inner surface of TiO 2 NTs. The TiO 2 NTs/Ag exhibited high activities for the photocurrent response and the degradation of MO and RhB dyes.…”