Cu2O/Cu hollow spheres are prepared using one-pot template-free solvent-thermal synthesis route with (CH3COO)2Cu·H2O as a precursor. With the reaction time increasing gradually from 2 h to 20 h, the morphology of the Cu2O/Cu evolves from nanoparticle to hollow nanosphere. The hollow structure is obtained when the cooling rate falls down to 0.7°C/min. And the content of Cu in the hollow spheres also can be easily controlled by adjusting the solvent-thermal synthesis time. Using photocatalytic degradation of phenol as the probe molecules under visible-light illumination, we have investigated the influence of hollow structure on the photocatalytic activity of Cu2O/Cu. The prepared hollow sphere Cu2O/Cu particles exhibited a higher photodegradation capability than nanoparticles and solid spheres. When the content of Cu lies in the range of 11–86 wt%, the samples exhibit higher photocatalytic performance, indicating that the Cu2O/Cu particles with hollow structure are promising candidates for the processing of pollutants.
Semiconductor-based photocatalysts, activated by illumination at room temperature, are used for degradation of organic pollutants by redox reaction. The technique is environmentally clean and thus attracts more and more attention [
As is well known, the maximum irradiation of sunlight lies in the visible range, and only photocatalysts with corresponding band gap could sufficiently use solar energy. The band gap of Cu2O is 2.0~2.2 eV, and the component elements are inexpensive and abundantly available, making it a promising candidate for photocatalysts. Numerous reports have shown the superior performance of Cu2O on solar energy conversion [
A simple and green one-pot in situ synthetic route for nanosized Cu2O/Cu hollow nanospheres is introduced here. The synthesis of Cu2O/Cu is developed with a template-free solvent-thermal route to control its morphology and phase composition. More importantly, the hollow structure of Cu2O/Cu can be obtained by adjusting the reaction conditions. A possible formation mechanism was proposed to account for the production of hollow structures. The effect of reaction time and cooling rate on its morphology was investigated. The adsorption and photocatalytic activity of samples were evaluated by the photocatalytic degradation of phenol under visible light illumination.
All the chemicals were analytical grade regents used without further purification. In a typical preparation, copper acetate ((CH3COO)2Cu
Experimental conditions, phase composition, and characterized parameters of different samples, where
Sample | Reaction time (h) | Cu wt% | Cu2O wt% |
|
|
|
---|---|---|---|---|---|---|
S1 | 2 | — | 100 | 12.5 | 2.162 | 0.0131 |
S2 | 6 | 11 | 89 | 17.4 | 1.688 | 0.0161 |
S3 | 10 | 31 | 67 | 18.9 | 1.774 | 0.0154 |
S4 | 14 | 61 | 39 | 19.3 | 2.088 | 0.0304 |
S5 | 20 | 86 | 14 | 19.1 | 2.134 | 0.0234 |
The samples were characterized by X-ray powder diffraction (XRD) using a Rigaku 12 kW X-ray diffractometer with Cu
The adsorption behavior and photocatalytic activity of the Cu2O/Cu were evaluated by the degradation of the solution of phenol at a concentration of 10 mg/L. 0.030 g Cu2O/Cu NCs powder was dispersed in a 50 mL probe molecular aqueous solution. Before illumination, the suspension was stirred in the dark for more than 120 min to achieve an adsorption/desorption equilibrium of organic molecules on the surface of Cu2O/Cu. The photocatalytic reaction was carried out at room temperature by using a 100 W tungsten lamp as a visible light source. At different time intervals during the experiment, 5 mL of solution was sampled each time for analysis. After centrifugation at 11000 rpm for 10 min, the absorbance of solution was measured using a UV-visible spectrophotometer (TU-1901).
Sample S4 (precursor concentration is 0.02 M, reaction time is 14 h, and cooling rate is 0.7°C/min) possesses the typical morphology of all, whose TEM images are shown in Figure
(a) TEM images of sample S4; (b) XRD patterns of sample S4.
To study the formation process of the Cu2O hollow spheres, samples were collected at different reaction time and were characterized by the TEM analysis (Figure
The effect of reaction time on the formation of Cu2O/Cu hollow nanospheres: (a) 2 h; (b) 4 h; (c) 10 h; and (d) 20 h.
In this experiment, the authors found that the cooling rate has great impact on the formation of hollow structure. Figure
The cooling rate-dependent morphology: (a) quenched in ice water; (b) 3°C/min; and (c) 0.7°C/min.
Figure
Schematic illustration of the formation hollow spheric nanostructures.
Figure
Powder XRD patterns of hollow nanospheres synthesized with different reaction times: (S1) 4 h; (S2) 6 h; (S3) 10 h; (S4) 14 h; and (S5) 20 h.
Figure
SEM images of Cu2O/Cu composites obtained in different precursor concentrations: (a) 0.02 M; (b) 0.05 M.
Figure
N2 adsorption-desorption BET isotherms of samples S1 and S4. The inset shows the pore size distribution.
Phenol is transparent to visible light and very hard to mineralize due to its resonance stability. The strong absorption peak at about 269 nm is selected to monitor the photocatalytic degradation process. With longer irradiation time, this characteristic peak becomes weaker and weaker, indicating the degradation of phenol. No new adsorption peaks appear and no obvious shift of the characteristic peak is observed, indicating the degradation of phenol.
In order to understand the hollow structure in enhancing the photocatalytic performance of Cu2O, pure Cu2O nanoparticles, nanospheres, and hollow nanospheres are prepared and the photocatalytic activity is studied. Shown in Figure
Relative concentration (
Figure
Relative concentration (
Consider
Hollow spheric Cu2O/Cu photocatalysts have been synthesized by following a one-pot solvent-thermal synthesis route without using any templates and additives. The reaction time and cooling rate have a strong effect on the formation of the hollow Cu2O/Cu nanospheres. The hollow spheric structure is formed at a reaction time in the range of 4 h to 20 h and low cooling rate 0.7°C/min. The content of Cu increases with increasing reaction time. As visible-light-driven photocatalysts, the hollow spheric Cu2O/Cu exhibit better photocatalytic performance than the nanoparticles and solid spheres. Our route offers an effective way to control the synthesis of Cu2O/Cu hollow spheres and may shed light on the design of simple route for one-pot synthesis of metal oxide nano-heterojunction, other well defined complex nanostructures.
The authors declare that there is no conflict of interests regarding the publication of this paper.
This research work is funded by the National Science and Technology Support Program of China (no. 2013BAE04B03 and no. 2013BAE04B02) and the National Natural Science Foundation of China (no. 10674034).