- Nano Express
- Open Access
Fabrication of TiO2 Nanosheet Aarrays/Graphene/Cu2O Composite Structure for Enhanced Photocatalytic Activities
© The Author(s). 2017
Received: 8 March 2017
Accepted: 18 April 2017
Published: 26 April 2017
TiO2 NSAs/graphene/Cu2O was fabricated on the carbon fiber to use as photocastalysts by coating Cu2O on the graphene (G) decorated TiO2 nanosheet arrays (NSAs). The research focus on constructing the composite structure and investigating the reason to enhance the photocatalytic ability. The morphological, structural, and photocatalytic properties of the as-synthesized products were characterized. The experimental results indicate that the better photocatalytic performance is ascribed to the following reasons. First, the TiO2 NSAs/graphene/Cu2O composite structure fabricated on the carbon cloth can form a 3D structure which can provide a higher specific surface area and enhance the light absorption. Second, the graphene as an electron sink can accept the photoelectrons from the photoexcited Cu2O which will reduce the recombination. Third, the TiO2 nanosheet can provide more favorable carrier transportation channel which can reduce the recombination of carriers. Finally, the Cu2O can extend the light absorption range.
Recently, application of semiconductor photocatalyst titanium dioxide (TiO2) in environmental purification has attracted great attention owing to its tremendous advantages, such as stability, nontoxicity, and low cost [1–3]. Based on the fact that photocatalytic reactions mainly take place on the surfaces of the photocatalysts, the morphology is the crucial factor to determine the efficiency . Up to now, many efforts have been made to fabricate TiO2 nanocrystals, nanowires, nanorods, and nanotubes [5–8]. However, the application of TiO2 nanosheet arrays with larger specific surface area in photocatalytic degradation is rarely reported. Especially, TiO2 nanosheet arrays grown on the carbon cloth can construct three-dimensional (3D) structures to improve the specific surface area.
Unfortunately, the wide bandgap of TiO2 limits the effective absorption of visible light . In order to overcome the shortcoming, one strategy is to modify TiO2 with narrow bandgap semiconductors [10–12]. Among them, cuprous oxide (Cu2O) with narrow bandgap can be a promising candidate for expanding the absorption spectra range. [13–18] Moreover, the built-in electric field between P-type Cu2O and N-type TiO2 can accelerate the separation of carriers.
However, the poor interfacial feature between different semiconductors directly influences the separation efficiency of carriers. Therefore, the interfacial optimization is an effective way to enhance photocatalytic degradation efficiency [19, 20]. The previous researches indicate that graphene (G) shows excellent interfacial optimization function between different semiconductors due to its high conductivity and two-dimensional structure, which facilitates the interfacial contact and carrier transportation [21–25]. However, it is difficult to make graphene well disperse between different semiconductors. In this paper, a modified method is applied to fabricate the homogeneously dispersed G between TiO2 nanosheet and Cu2O.
Preparation of TiO2 NSAs/G/Cu2O
The fabrication of TiO2 NSAs is the following. TiO2 sol was prepared using a previously reported method . In brief, TiO2 seed layer was deposited on carbon cloth (2 cm × 3 cm) by immersing in TiO2 sol for 10 min. Then, the seed layer was calcined at 400 °C for 1 h. The Teflon-lined stainless steel autoclave (100 mL in volume) filled with 40 mL of aqueous solution of 10 M NaOH and 0.2 g of activated carbon was placed in an oven at 180 °C for 24 h. After the autoclave cooled down to room temperature, the prepare samples were rinsed with DI water to remove the residual activated carbon, followed by soaking with 0.1 M hydrochloric acid for 1 h, then washed to neutral with DI water.
For the composite structure of TiO2 NSAs/G, 0.2 g of graphene replacing activated carbon was added into the Teflon-lined stainless steel autoclave ethanol solution.
Cu2O layer was deposited by the following procedures. 2.3 mmol of Cu(CH3COO)2 and 2.3 mmol of CH3CONH2 were dissolved into 100 mL of diethylene glycol (DEG) under ultrasonication to prepare the reaction solution. Then, TiO2 NSAs or TiO2 NSAs/G substrate was immersed into the solution. Subsequently, it was heated to 120° under magnetic stirring and kept at this temperature for 6 h. After cooling down to room temperature in air, TiO2 or TiO2 NSAs/G substrate coated with Cu2O was washed with absolute ethanol and DI water for five times in sequence and dried in air.
The morphologies of the samples were investigated by a field emission scanning electron microscopy (FE-SEM, Quanta FEG250). The crystal structure of samples was examined by X-ray diffraction (XRD, D8 Advance) with Cu K α at λ = 0.15406 nm radiation. XPS spectra were recorded on a Thermo Fisher ESCALAB 250Xi system with Al Kα radiation, operated at 150 W. The absorption spectrum of the samples was measured using a UV–vis spectrophotometer (TU-1901). The Raman spectrum of the sample was characterized by Raman spectroscopy (LabRAM HR800).
Photocurrent density was measured using an electrochemical workstation (CS2350) in a three-electrode electrochemical cell with 1 M Na2SO4 as the electrolyte, in which the as-prepared samples were acted as the working electrode, Pt and Ag/AgCl electrode were used as the counter and reference electrodes, respectively. The I–t curve was recorded under Xe lamp (153 mW/cm2) irradiation.
Measurement of Photocatalytic Activity
The photocatalytic activity was evaluated toward the photodegradation of RhB. A 500 W Xe lamp was used as the light source. The samples with same size 2 cm × 3 cm were placed into 20 ml RhB solution (10 mg/L). After irradiation for a designated time (30 min), 3 mL of RhB solution was taken out to identify the concentration of RhB using UV–vis spectrophotometer (TU-1901). All of these measurements were carried out at room temperature.
Results and Discussion
The improved photocatalytic property of TiO2 NSAs/G/Cu2O may be attributed to the following factors. First, the introduction of Cu2O can extend the light absorption range, and thus, the photocatalytic activities are enhanced. Second, the limitation of carrier recombination is a key factor to enhance the photocatalytic property. The graphene as an electron sink can accept the photoelectrons from the photoexcited Cu2O which will reduce the recombination. Besides, TiO2 nanosheet structure can provide more favorable carrier transportation channel. Third, the better photocatalytic property can take advantage of large specific surface area. TiO2 NSAs/G/Cu2O structure fabricated on the carbon cloth can form a 3D structure which can provide a higher specific surface area. The high surface area of the 3D structure allows not only more surfaces to be reached by the incident light but also more sites on the surface for the adsorption and photodegradation of RhB, which results in enhanced photocatalytic performance. Finally, the 3D structure can enhance the photon utilization efficiency. The structure allows a great number of the photons to penetrate deep inside the photocatalyst, and most photons are trapped within the 3D structure until being completely absorbed.
In summary, the novel 3D TiO2 NSAs/G/Cu2O structure is prepared via a simple and efficient method. Importantly, the composite structure exhibits excellent photocatalytic degradation properties. The enhanced performance can be ascribed to its extended light absorption range, large specific surface area, enhanced photon utilization efficiency, improved charge transfer efficiency and suppressed photoelectron-hole recombination. Furthermore, the photocatalysts grown on carbon cloths make the collection and recycle of photocatalysts much easier.
This work was supported by the Natural Science Foundation of Shandong Provience (Grant Nos. ZR2016FM30, ZR2016JL015), the Science-Technology Program of Higher Education Institutions of Shandong Province (Grant No. J14LA01), the Graduate Innovation Foundation of University of Jinan, GIFUJN, (Grant No. YCXS15006), the Open Project Program of Key Laboratory for Photonic and Electric Bandgap Materials, Ministry of Education, Harbin Normal University (Grant No. PEBM201505), and National Natural Science Foundation of China (Grant Nos. 51672109, 61504048, 21505050).
Y.N.N. and H.J.Z. designed the experiments. Y.N.N. and F.K. performed the experiments. D.X.L. performed the SEM observations. Y.N.N., H.J.Z., D.X.L., and W.M.Z. discussed and commented on the experiments and results and wrote the paper. All authors read and approved the final manuscript.
The authors declare that have no competing interests.
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