In the present work, we report the preparation and photocatalytic properties of TiO2@yeast-carbon with raspberry-like structure using a pyrolysis method. The products are characterized by field emission scanning electron microscopy (FE-SEM), energy dispersive spectrometry (EDS), X-ray diffraction (XRD), thermal gravimetric and differential thermal analysis (TGA-DTA), Fourier transformed infrared spectroscopy (FT-IR), and ultraviolet visible spectroscopy (UV-VIS), respectively. The results show that the hybrid TiO2@yeast-carbon microspheres have ordered elliptic shapes of uniform size (length =
In the past few years, raspberry-like composite particles with well-defined structures have become the subject of rapidly growing interest due to their high surface roughness and potential applications [
The high surface area, large pores (macroporosity), and the presence of surface hydroxyl groups make carbon substance an ideal catalyst support [
The yeast-carbon is a porous and amorphous solid carbon material, which is derived mainly from baker’s yeast. For instance, Nacoo and Aquarone [
The powdered yeast was purchased from Angel Yeast Company. Photocatalyst was TiO2 from Degussa and was used without further purification. In all preparations, absolute ethanol and double-distilled water were used. Methylene blue (MB) and congo red (CR) were analytic grades and were used as the model pollutants in present work.
In a typical synthesis procedure, 125.0 mg yeast powder was washed with distilled water and absolute ethanol for three times, respectively. The yeast was dissolved in 20.0 mL of distilled water and stirred vigorously for 30 minutes. The pH was adjusted to approximately 3 by adding drop wise sulfuric acid. Further, 10.0 mg TiO2 was dispersed in 20.0 mL of distilled water, using ultrasonic vibration for 1.0 minute. The pH was adjusted to approximately 9-10 with sodium hydroxide and stirred for 30.0 min. Then the suspended TiO2 and yeast were gathered by centrifugation from their own suspensions and redistributed in 20.0 mL of distilled water. Afterwards, TiO2 and yeast suspensions were mixed and magnetically stirred for 1.5 h at room temperature and left for 3.0 h without further stirring or shaking to ensure the formation of TiO2@yeast particles. Thus, the mixture was centrifuged in three or more cycles to remove the undesired components and finally desiccated at 353 K for 1.0 h. Subsequently the TiO2@yeast particles were calcined at 573 K for 1.0 h in a nitrogen pipe furnace and cooled to room temperature. After that, the TiO2@yeast-carbon composite microspheres were obtained.
Philips XL-30 field emission scanning electron microscope (FE-SEM) was used to observe the morphology of samples. X-ray diffraction (XRD) patterns were collected on X. Pert Pro diffractometer using Cu K
The methylene blue (MB) dye and congo red (CR) are widely used in dye industry. Therefore, the elimination of these compounds is becoming an increasingly important environmental problem. Photocatalytic degradation of MB and CR was evaluated under UV irradiation in an aqueous media. The initial concentration of MB and CR was set as 2~3 mg/L, respectively. The amount of photocatalysts including yeast-carbon and TiO2@yeast-carbon were kept at 0.25 g/L. Before UV irradiation, the suspension containing photocatalyst, MB, and CR was deposited within 50.0 min to establish adsorption-desorption equilibrium. Then the suspension was irradiated under a UV lamp (the intensity of irradiation is 60 W). The concentration of MB and CR was traced by UV-VIS spectroscopy. The absorbance characteristic at bands 666.4 nm and 499.0 nm was taken to determine MB and CR concentration by using a calibration curve, respectively.
The shape and structure of the samples are shown in Figure
SEM images of (a) the naked yeast, (b) general observation of the raspberry-like TiO2@yeast precursor, (c) the yeast-carbon, (d) the overall view of the raspberry-like TiO2@yeast-carbon microspheres, (e) the selected raspberry-like TiO2@yeast-carbon microspheres, and (f) typical raspberry-like TiO2@yeast-carbon microspheres observed under high magnification.
XRD patterns of yeast, yeast-carbon, TiO2@yeast-carbon, and TiO2 are displayed in Figure
XRD patterns of (a) the prepared yeast-carbon, (b) the premier yeast, (c) the 80% of TiO2@yeast-carbon, (d) the 40% of TiO2@yeast-carbon, and (e) the pure TiO2.
In Figure
TGA-DTA curves of the yeast and the TiO2@yeast-carbon.
After pyrolysis entirely, the raspberry-like TiO2@yeast-carbon microspheres can be attained, which has been proved by SEM analysis. The connection between the guest particles TiO2 and the host particles of the yeast-carbon can be elaborated further by FT-IR analysis. FT-IR spectra of the yeast, yeast-carbon, TiO2@yeast precursor, TiO2 and TiO2@yeast-carbon composites are presented in Figure
FT-IR spectrum of (a) the original yeast, (b) the TiO2 nanoparticle, (c) the TiO2@yeast precursor, (d) the yeast-carbon, (e) the 80% TiO2@yeast-carbon, and (f) the 40% TiO2@yeast-carbon.
Based on the characterization discussed above, the following mechanism that appeared in Scheme
Schematic illustration for the formation of the raspberry-like TiO2@yeast-carbon and their synergistic effect in the removal of dyes aqueous solutions.
Figure
UV-VIS diffuses reflectance spectra of the yeast-carbon, TiO2 nanoparticles, and the obtained raspberry-like TiO2@yeast-carbon samples ((a) the yeast-carbon, (b) the TiO2 nanoparticles, and (c) the hybrid TiO2@yeast-carbon).
The raspberry-like TiO2@yeast-carbon microspheres containing an incompletely covered surface of yeast-carbon may possess unique properties for getting rid of water pollutants. The rich pore structure of yeast-carbon might promote adsorption of organic dyes, while the outer TiO2 nanoparticles can be in charge of the photocatalytic degradation of the dyes [
From the results shown in Figure
Photocatalytic activities of yeast-carbon and TiO2@yeast-carbon under UV irradiation.
The adsorption constant for MB and CRwas listed in Table
Comparison of the adsorption constant for MB and CR.
Dyes |
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Langmuir isotherm | Freundlich isotherm | ||||
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1/ |
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MB | 1.00 | 0.23 | 1.53 | 1.25 | 0.99 | 0.78 | 0.94 | 0.83 |
2.00 | 0.56 | |||||||
3.00 | 0.87 | |||||||
4.00 | 1.17 | |||||||
5.00 | 1.18 | |||||||
| ||||||||
CR | 3.00 | 0.12 | 1.15 | 0.33 | 0.98 | 0.39 | 0.13 | 0.82 |
5.00 | 0.34 | |||||||
7.00 | 0.59 | |||||||
9.00 | 0.74 | |||||||
11.00 | 0.75 |
In summary, we prepared hybrid raspberry-like TiO2@yeast-carbon utilizing pyrolysis method. The as-synthesized hybrid TiO2@yeast-carbon had ordered elliptic shapes of uniform size
This work was financially supported by China Postdoctoral Science Special Foundation, Scientific Research Foundation for the Returned Overseas Chinese Scholars, the National Natural Science Foundation of China (no. 21176031), Shaanxi Provincial Natural Science Foundation of China (no. 2011JM2011), and Fundamental Research Funds for the Central Universities (no. 2013G2291015).