SEARCH

SEARCH BY CITATION

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results and Discussion
  6. Conclusions
  7. References

This article presents a facile method to prepare CdS/SiO2 composite microspheres and their good catalytic properties. In our method, monodispersed SiO2 particles bearing amino groups (–NH2) were synthesized at first and then used as carriers to load nanosized CdS particles to form CdS/SiO2 composite microspheres. With the addition of CdAc2 solution to the SiO2 dispersion, Cd2+ was attracted to the surfaces of the SiO2 particles through coordination interaction, and then thioacetamide was added to the dispersion. By heating, S2− released and reacted with the Cd2+, CdS/SiO2 composite microspheres were obtained accordingly. The photocatalytic properties of the as-prepared composite microspheres were investigated as well. It was found that the composite microspheres have excellent photocatalytic activities for the degradation of dyes comparing with the commercial P-25 TiO2 catalysts. After using and recycling for three times, the photocatalytic performance still remained very well.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results and Discussion
  6. Conclusions
  7. References

As a nanostructured material, cadmium sulfide (CdS) nanoparticles exhibit special properties, which could be influenced highly by the shape (1), size (2), microstructure (3), degree of crystallization (4) and crystalline phase (5). For a long time, CdS nanoparticles have been broadly applied in the catalytic (6–8), optical (9,10), electrical (11,12) and many other fields (13–15), because they demonstrate many excellent and unique physicochemical properties, which are resulted from the quantum size effect, surface effect, macroscopic quantum tunneling effect and high specific surface area.

Synthesis of CdS nanoparticles had been developed to various methods. For example, Li et al. (16) employed the composite-molten-salt method to prepare CdS nanoparticles, their method based on the reaction of a metallic salt with a metallic sulfide under a temperature over 125°C, ambient pressure and used a solution of eutectic composite salts without any organic dispersant or capping agent. Moloto et al. (17) adopted a method using the complexes of N,N′-diisopropylthiourea and N,N′-dicyclohexylthiourea cadmium(II) as single-source precursors to prepare CdS nanoparticles. Singh et al. (18) synthesized CdS nanoparticles via the chemical precipitation method involving a reaction between cadmium chloride and sodium sulfide in the presence of cetyl trimethyl ammonium bromide as a cationic surfactant. Andrade et al. (19) obtained CdS nanocrystals in a thiol-functionalized silica-gel matrices, and in their method, a relative high temperature (130°C) was needed. However, one or more of these factors, such as surfactants, long-synthesis time, high temperature or complicated process control may be required for this route.

Recently, the composite material with CdS attached to the organic/inorganic particles is still a hot field of materials research, due to the advantages of components has been successfully combined (20–23). Many materials have been used as carriers to prepare the composite particles. Cheng et al. (24) have prepared the CdS/PS composite particles using polystyrene as carriers. Rajesh et al. (25) have synthesized CdS/polyaniline/CuInSe2 at room temperature via cost effective soft chemical route. Zhou et al. (26) have prepared the CdS/TiO2 nanocomposite making CdS particles deposit onto the surfaces of TiO2 nanotubes. When the composite particles were prepared, the aggregation of nanosized CdS particles could be avoided.

In this article, a novel method to prepare CdS/SiO2 composite particles is presented. SiO2 particles have been used as carriers for nanosized CdS to form CdS/SiO2 composite microspheres at a lower temperature. SiO2 microspheres were prepared via the so-called StÖber method (27), and then –NH2 groups were introduced onto the surfaces of the SiO2 particles. In this step, (3-amincpropy)triethoxysilane (APTES) was employed as a functional component to introduce the –NH2 group on the surfaces, which can attract Cd2+ by coordination to form the desired composite particles. By the addition of TAA under a heating condition, S2- ions were released and reacted with Cd2+ to produce CdS. Eventually, stable CdS/SiO2 composite microspheres were obtained successfully. In the following paragraphs, it will be seen that amino groups played an important role for the formation of CdS/SiO2 composite microspheres. Without APTES, there were few CdS nanoparticles attached on the silica particles. However, when silica particles bearing –NH2 groups were used, almost all the CdS particles were attached onto the silica particles, no further operation was needed to remove the unattached CdS particles. The as-prepared CdS/SiO2 composite microspheres were employed as photocatalyst for the degradation of methylene blue (MB), methyl orange (MO), rhodamine B (RhB) and rhodamine 6G (R6G), and the composite microspheres showed good catalytic activities and recyclability.

Materials and Methods

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results and Discussion
  6. Conclusions
  7. References

Materials.  Tetraethyl orthosilicate (TEOS), ammonia solution, toluene, ethanol (EtOH), thioacetamide (TAA), hydrofluoric acid (HF) and methyl orange (MO) were purchased from Sinopharm Chemical Reagent Co. Cadmium acetate (CdAc2), RhB, R6Gand APTES were purchased from Aladdin Chemistry Co. MB was purchased from Sigma–Aldrich. Photocatalyst, P-25 TiO2 was purchased from Evonik. All the reagents were used as received. Ultrapure water (>17 mΩ cm−1) from a Milli-Q water system was used throughout the experiment.

Preparation of silica particles containing –NH2 groups.  Two methods were used to prepare the monodispersed silica microspheres with –NH2 groups on the surfaces. They are described respectively as follows. Method 1 is named as cohydrolysis, which means that TEOS and APTES were hydrolyzed at the same time. A typical procedure is described as follows. Absolute EtOH (160 g) and an aqueous solution of ammonium hydroxide (50 g) were mixed and charged into a 500 mL two-necked flask. TEOS solution (20.8 g TEOS diluted in 40 g absolute EtOH) was added dropwise into the flask within 1 h, and then 0.52 g APTES was added and cohydrolysis occurred under the catalysis of ammonia to obtain silica particles with –NH2 groups on the surfaces.

Method 2 was a most often used traditional method (28), herein, named as postmodification method. The synthetic procedure is described as follows. Absolute EtOH (160 g) and an aqueous solution of ammonium hydroxide (50 g) were mixed and charged into a 500 mL four-necked flask. TEOS solution (20.8 g TEOS diluted in 40 g absolute EtOH) was added dropwise into the flask within 1 h and reacted for 24 h at 25°C to obtain silica particles, and then the silica particles were centrifuged and washed with deionized water. The silica particles were dispersed in toluene and 0.52 g APTES was added and refluxed for 5 h to modify the as-prepared silica particles with NH2 CH2CH2– groups (by fourier transform infrared spectroscopy [FTIR]). Both of the two methods were shown in Scheme 1.

image

Figure  Scheme 1. .  The possible mechanism of the formation of SiO2 and CdS/SiO2 composite microspheres.

Download figure to PowerPoint

Preparation of CdS/SiO2 composite microspheres.  To prepare CdS/SiO2 composite microspheres, silica particles bearing –NH2 groups were used as carriers. A typical recipe was used as follows: 10 mL aqueous dispersion containing 0.5 g as-prepared NH2 bearing SiO2 particles was charged into a flask containing 130 mL deionized water, pH ≈ 7.3, and heated to 60°C under the continuous stirring. A 10 mL of freshly prepared CdAc2 aqueous solution(1.0 wt%) was added and reacted for 30 min, and then 10 mL of TAA aqueous solution (0.5 wt%) was added once and tested the pH every 30 min. Consequently, the mixture reacted for 2 h, the pH of suspension is about 4.8 finally, and the composite microspheres were obtained and collected for further examination. The mass ratio of CdS to SiO2 was detected; the procedure is described as follows. In a beaker, m1 g of dried CdS/SiO2 composite microspheres, a certain amount of HF acid was added to etch SiO2 microspheres. And then, the CdS particles were washed for three times, the amount of CdS particles, m2 was obtained. The ratio of CdS to SiO2 could be calculated accordingly, and the results were shown in Table 1.

Table 1.   Experimental condition and results of composite particles.
ProductV 1 mL−1V 2 mL−1m 1 g−1m 2 g−1Mass ratio/CdS:SiO2
Theoretical valuesExperimental values
  1. V 1 refers the volume of CdAc2 aqueous solution (1.0 wt%); V2 refers the volume of TAA aqueous solution (0.5 wt%); m1 refers the amount of CdS/SiO2 composite microspheres; m2 refers the amount of CdS particles.

CdS/SiO2110.20230.00241:801:83.29
CdS/SiO2550.22110.01341:161:15.50
CdS/SiO210100.21390.02451:81:7.73
CdS/SiO215150.20010.02901:61:5.90
CdS/SiO220200.20000.03951:41:4.06

When SiO2 obtained by the postmodification method was used as carriers, it could be found that the CdS particles on the silica surfaces were not evenly distributed. However, when the silica particles obtained by method 1 were used as carriers, it could be found that a lot of CdS particles were attracted to the silica particles, and they were distributed evenly on the silica particles.

Obviously, the cohydrolysis method (method 1) was much better than the conventional postmodification (method 2). So, method 1 was chosen to prepare SiO2 in this study.

Photocatalytic properties of CdS/SiO2 composite spheres.  The visible-light photocatalytic properties of the CdS/SiO2 composite microspheres were tested in the photocatalytic degradation of the dyes, such as MB, RhB, R6G and MO. For each run, the reaction suspensions were freshly prepared by adding 20 mg catalyst to 50 mL aqueous dye solution with an initial concentration of 10 mg L−1. The aqueous suspension containing MB and photocatalyst was irradiated by the visible light with constant aeration, and the visible light was obtained by a 300 W Xenon lamps with a 400 nm cut off filter to ensure the desired irradiation light. Four milliliter analytical samples were then taken out every 20 min and immediately centrifuged and then filtered to remove the catalyst. The transparent solution was analyzed by a UV–Vis spectrometer, and the data of the absorbance was measured at the maximum absorption. To record the real photocatalytic activity, the measured solution and the centrifuged particles were poured back into the original beaker to maintain a consistent total amount of the dye in the solution. For comparison, control experiments were performed using commercial P-25 TiO2 powder as photocatayst under identical conditions. The analytical samples of MO were then taken out every 2 min; the data of the absorbance of RhB was measured at 554 nm, the R6G at 527 nm, the MO at 465 nm and the MB at 648 nm.

Characterization.  Transmission electron microscope observation (TEM): A TEM (FEI Tecnai G20) was used to observe the morphology of the obtained particles. The particle dispersion was diluted by water and dropped onto the carbon-coated copper grids and dried for TEM observation.

Scanning electron microscope observation (SEM): A field emitting SEM (FEI Quanta 400 FEG microscopes) was employed to observe the morphology of the obtained particles. The particle dispersions were diluted with water, dried on a silicon slice and sputtercoated with gold prior to examinations.

X-ray photoelectron spectroscopy (XPS): X-ray photoelectron spectroscopy (XPS) analysis was performed on a spectrometer (VG Multilab 2000) using an Al Ka X-ray source (1486.6 eV) and operating at 15 kV under a current of 24 mA. The dispersion of CdS/SiO2 underwent repeated centrifugation/wash operation to remove the possible residual ions. Samples were placed in an ultrahigh vacuum chamber (3 × 10−7 Pa) with electron collection by a hemispherical analyzer with 45° as its angle.

X-ray diffraction (XRD): The powder XRD patterns of CdS/SiO2 were recorded on a Bruker D8 Advance instrument, where using a Cu target Ka-ray was used as X-ray source.

FTIR measurement: Fourier transform infrared spectra were taken on a Nicolet NEXUS 470 spectrometer. The particle dispersions were centrifuged and dried in vacuum at 40°C and then pressed into KBr pellets for FTIR measurement.

UV–Vis measurement: UV–Vis absorption spectra were recorded in aqueous media by using a Shimadzu UV-2450 spectrophotometer.

Results and Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results and Discussion
  6. Conclusions
  7. References

In this study, the Cd2+ ions were absorbed to the surfaces of the SiO2 particles via the coordination between –NH2 and Cd2+. S2- ions were released by heating the TAA, and reacted with Cd2+ to form CdS, the reactions were shown in the following equations:

  • image

The pH of the suspension was about 7.3 before the addition of freshly prepared CdAc2 aqueous solution (1.0 wt%), after adding CdAc2, the pH was ca 7.1, the pH value did not change notably. However, the pH value gradually decreased with reacting to TAA aqueous solution (0.5 wt%), When the reaction occurred for 30 min, the pH was 5.6, at the end of the reaction, the pH reached 4.8. As shown in the above reaction equations, the pH decreased obviously. In this way, the CdS crystal with the average size of 20 nm has been prepared; a typical TEM image of the composite particles was shown in Fig. 1a. The amount of the APTES and the ratio of CdS to silica were important parameters that will affect the morphology and photocatalytic properties of the obtained particles. Their influences will be discussed in the following paragraphs. The possible mechanism of the formation of SiO2 particles with –NH2 groups on the surfaces and consequent CdS/SiO2 composite microspheres was shown in Scheme 1.

image

Figure 1.  TEM images of CdS/SiO2 composite microspheres obtained at different amount of APTES kept the other chemicals constant: (a) 1.04 g, (b) 0.52 g, (c) 0.26 g and (d) 0.13 g. HR-TEM images, the inset in (a), shows the CdS crystal of CdS particles.

Download figure to PowerPoint

The effect of the amount of APTES on the CdS/SiO2 composite microspheres

To obtain monodispersed SiO2 particles, the supplier of –NH2 groups, in our experiment, APTES was added to the reaction after TEOS solution. The amount of APTES acted as a crucial factor for the further usage as carriers to produce CdS/SiO2 composite microspheres. The SiO2 particles prepared with all the ingredients kept unchanged, but APTES were studied. The particle sizes of SiO2 particles did not change notably with the change of the amount of APTES. However, when the same amount of CdAc2 aqueous solution (1.0 wt%) and TAA aqueous solution (0.5 wt%) was employed to prepare CdS/SiO2 composite particles, different results were obtained. Figure 1 shows the TEM images of the CdS/SiO2 composite particles at different amount of APTES.

When the total amount of APTES was increased from 0.13 to 1.04 g, the CdS particles attached onto the surfaces of SiO2 particles increased naturally, which means that with the increase of APTES, the amount of –NH2 on SiO2 particles surfaces increased accordingly, and more –NH2 were introduced on SiO2 particles surfaces, more CdS particles have been attached.

The effect of the amount of Cd2+ and S2− ions on the CdS/SiO2 composite microspheres

The total amount of CdS particles attached onto the surfaces of the SiO2 particles increased remarkably with the increasing of the amount of equimolal CdAc2 aqueous solution and TAA within a certain range. However, when it reached a limit, the total amount of CdS particles almost had not clearly changed with the amount of CdAc2 and TAA continuing to increase. When the amount of CdS was higher, a large number of CdS particles have been attached on the surfaces of SiO2 particles and they almost have formed a shell on the silica. When the amount of CdS was lower than the maximum, all the CdS particles had been attached on the surfaces of SiO2 particles and they were distributed evenly; there was no needed operation to remove the unattached CdS nanoparticles. The mass ratio of CdS to SiO2 had been detected, the results were shown in Table 1, and the theoretical and experimental values are nearly close. It could be seen from Table 1 that the ratio increased with the increase of amount of CdS, but when the CdS was less than 10 mL, the increase of the ratio was very fast, when more than 10 mL, the increase was slower.

The effect of the temperature on the CdS/SiO2 composite microspheres

During the process of the preparation of CdS/SiO2 composite microspheres, the temperature was a key factor. When the amount of all the ingredients was kept unchanged and only adjusted the temperature from 50 to 90°C, and then different results were obtained. Figure 2 shows the TEM images of obtained CdS/SiO2 composite particles at different temperature.

image

Figure 2.  TEM images of CdS/SiO2 composite microspheres obtained at different temperature kept the other chemicals and conditions constant: (a) 50°C, (b) 60°C, (c) 70°C and (d) 90°C.

Download figure to PowerPoint

It could be seen from Fig. 2 that the CdS particles were evenly distributed on the surfaces of silica when the temperature was lower than 60°C (Fig. 2a, b), but when the temperature was higher than 70°C, the distribution was not uniform and the agglomeration occurred (Fig. 2c, d). The reason for this phenomenon might be when the temperature was low (≤60°C), the rate that cadmium absorbed by the surface of silica was slow, which made the adsorption time of cadmium ion longer, so that the cadmium ions had enough time to be uniformly dispersed on the surface of the silica; When the temperature was low, the growth rate of CdS crystal was slow because the release rate of sulfide ions from TAA was slow. So, the CdS/SiO2 composite microspheres with the equally size and uniformly distributed CdS nanocrystal had been obtained.

When the temperature was higher(>60°C), the interaction between the cadmium ions and amino group was enhanced, so the absorbed rate of cadmium ions was accelerated, which lead to the uneven distribution of the cadmium ions. At the same time, the release rate of sulfide ions from TAA increased also, the growth rate became more faster than that under the lower temperature, so the growth of CdS crystal became unstable, the size of CdS nanocrystals prepared under the higher temperature was not very uniform and much of the CdS crystal aggregated during the process of growth.

XPS Measurements and XRD Measurements

Figure 3a–c showed the XPS scans of pure silica, silica with –NH2 groups, and CdS/SiO2 composite microspheres. It indicated that the formation of CdS particles loaded on the SiO2 surfaces by comparison the standard binding energy with –NH2 combined by the surfaces of SiO2 particles (29).

image

Figure 3.  The XPS spectrum: (a) CdS/SiO2 composite microspheres (curve A), SiO2 particles with –NH2 on the surfaces (curve B), SiO2 particles with no –NH2 on the surfaces (curve C). (b) The XPS spectrum of Cd. (c) The XPS spectrum of S and the XRD spectrum: (d) XRD patterns of CdS/SiO2 composite microspheres.

Download figure to PowerPoint

Figure 3d showed the XRD scans of CdS/SiO2 composite microspheres. The XRD spectrum of Cd/SiO2 composite microspheres indicated that the formation of CdS particles on the surfaces of CdS/SiO2 and the CdS crystal.

The XRD performed on the CdS/SiO2 nanocomposites showed broad features at 2θ values on 25.2°, 26.7°, 28.4°, 44.0°, 48.2° and 52.2°, corresponding to the reflections of (100), (002), (101), (110), (103) and (112) crystal planes of the hexagonal CdS structure respectively (JCPDS no. 41-1049; 30), were consistent with the presence of hexagonal CdS as the predominant crystalline phase.

Photocatalytic properties of CdS/SiO2 composite microspheres

Photocatalytic activities of CdS/SiO2 composite microspheres were evaluated by measuring the degradation of dyes in aqueous solution under visible-light irradiation (31). Changes in the concentration of MB were monitored by examining the variations in maximal absorption in UV–Vis spectra at 648 nm (Fig. 4a). The influence of visible-light irradiation was explored and the results were shown in Fig. 5. The degradation of MB was very low (about 1.1%) exposed to simulated light irradiation without photocatalyst. However, when the CdS/SiO2 photocatalyst was used, the degree of the degradation increased notably. When the photocatalyst was used without light irradiation, only 17.6% of degradation was observed. When the photocatalyst and light irradiation were present at the same time, the degradation of MB reached almost 100%. These results suggested that the CdS/SiO2 catalysts have high photocatalytic activity under the light irradiation. For comparison, the tungsten lamp has been used to replace the xenon lamp as the irradiation light, it could be seen the efficiency of the degradation was very low. After 5 h, only 10% of MB could be degraded under the irradiation of a 500 W tungsten lamp.

image

Figure 4.  The UV–Vis spectra of the degradation of pollutants on CdS/SiO2: (A) MB, curve (a) 0 min, curve (b) 20 min, curve (c) 40 min, curve (d) 60 min, curve (e) 80 min, curve (f) 100 min and curve (g) 120 min, (B) RhB, curve (a) 0 min, curve (b) 20 min, curve (c) 40 min, curve (d) 60 min, curve (e) 80 min, curve (f) 100 min and curve (g) 120 min, (C) R6G, curve (a) 0 min, curve (b) 20 min, curve (c) 40 min, curve (d) 60 min, curve (e) 80 min, curve (f) 100 min and curve (g) 120 min, (D) MO, curve (a) 0 min, curve (b) 2 min, curve (c) 4 min, curve (d) 6 min, curve (e) 8 min, curve (f) 10 min, curve (g) 12 min and curve (h) 14 min.

Download figure to PowerPoint

image

Figure 5.  Effect of the light and the photocatalyst on photocatalytic degradation of MB on CdS/SiO2 catalysts (1:8): (a) in the presence of light irradiation and the photocatalyst, (b) in the absence of light irradiation, but in the presence of the photocatalyst and (c) in the presence of light irradiation and no photocatalyst.

Download figure to PowerPoint

Figure 6 shows the results of degradation of MB in the presence of CdS/SiO2 composite microspheres with different CdS to SiO2 mass ratio. The photocatalytic activity of silica without CdS was very low and degradation of MB was about 4.6% (only absorption of MB occurred). When the mass ratio between CdS and SiO2 was 1:16, the degradation of MB reached 60% after 120 min irradiation, with the mass ratio increased to 1:8, the degradation of MB obviously increased and reached 100%; when the mass ratio increased to 1:6, the degradation of MB obviously increased and reached 100% after 80 min irradiation, which means the increase of CdS nanoparticles led to higher catalytic performance. However, the degradation of MB reduced to 91.35% when the mass ratio was 1:4, which could be due to the size of CdS nanoparticles had increased, the increased size led to the reduction of the surface area of CdS nanoparticles, so the reaction sites decreased and the same for the chance that the charge carrier reached the surfaces of the nanoparticles (32).

image

Figure 6.  Effect of the mass ratio of CdS to SiO2 on photocatalytic degradation of MB under visible light irradiation: (a) pure SiO2 particles, (b) 1:16, (c) 1:8, (d) 1:6, (e) 1:4 and (f) P-25 TiO2.

Download figure to PowerPoint

Furthermore, to compare the catalytic activities of the as-prepared CdS/SiO2 composite microspheres with a standard photocatalyst P-25 TiO2, a control experiment was conducted. As stated above, the CdS/SiO2 composite microspheres with the CdS to silica weight ratio of 1:8 and 1:6 were used, the MB was degraded almost 100% within 120 and 80 min, respectively. However, when the degradation was catalyzed under P-25 TiO2, the degradation reached only 88.4% after 2 h. It is clear that the CdS/SiO2 composite microspheres showed much greater activity than that of P-25 TiO2.

To determine whether the as-prepared composite microspheres can catalyze the degradation of other dyes, RhB (26), R6G (19), MO (6) have been tested. Changes of the concentration of RhB were monitored by examining the variations in the maximal absorption in UV–Vis spectra at 554 nm (Fig. 4b), the R6G at 527 nm (Fig. 4c), and the MO at 465 nm (Fig. 4d). The degradation vs time plots are shown in Fig. 7. It could be seen that the degradation of RhB reached 25.9% without light irradiation (Fig. 7a), but under light irradiation the degradation reached 91.2% after 2 h. However, the degradation reached 100% when the standard photocatalyst P-25 TiO2 was used. Figure 7b showed that the degree of the degradation of R6G, without light irradiation, was 10.2% when the as-prepared CdS/SiO2 composite microspheres as the photocatalytic and the degradation reached 66.0% under light irradiation after 2 h, and the degradation reached 100% when P-25 TiO2 was used after 2 h. It could be seen from Fig. 7c that the as-prepared CdS/SiO2 composite microspheres have strong catalytic activities to the degradation of MO in light irradiation. Within 14 min, the MO has been degraded completely, and the degradation reached 96.3% after 2 h when P-25 TiO2 was used. Furthermore, the degradation reached only 42.5% after 2 h when as-prepared CdS/SiO2 composite microspheres was present without light irradiation, this result indicated that the as-prepared CdS/SiO2 composite microspheres have excellent catalytic activities to the degradation of MO.

image

Figure 7.  Effect of the light and the photocatalyst on photocatalytic degradation of pollutants under CdS/SiO2 catalysts (1:8) and P-25 TiO2: (a) RhB, curve (a) under CdS/SiO2 without irradiation, curve (b) under light irradiation and the CdS/SiO2 and curve (c) under light irradiation and P-25 TiO2, (b) R6G, curve (a) under CdS/SiO2 without irradiation, curve (b) under light irradiation and the CdS/SiO2 and curve (c) under light irradiation and P-25 TiO2, (c) MO, curve (a) under CdS/SiO2 without irradiation, curve (b) under light irradiation and the CdS/SiO2 and curve (c) under light irradiation and P-25 TiO2.

Download figure to PowerPoint

To study the reusability and stability of the CdS/SiO2 composite microspheres, the photocatalytic experiments were repeated for three times with the same catalyst. After each experiment, the catalyst was centrifuged, washed, and recycled. The CdS/SiO2 catalyst remained a high photocatalytic activity after three times cycles, and the degradation of MB reached 80.1%. The slight decrease of photocatalytic activity could be due to some CdS particles detached from the SiO2 particles during the recycle of the composite microspheres. This result indicates that the CdS/SiO2 catalysts are fairly photostable and possess the potential of practical application.

Conclusions

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results and Discussion
  6. Conclusions
  7. References

In summary, silica particles with NH2 groups on the surfaces could be synthesized by the cohydrolysis method. Using the as-prepared SiO2 particles as carriers, CdS nanosized particles could be introduced on the surfaces of the silica particles to form composite microspheres. Adjusting the reaction parameters, different composite particles with different morphologies and photocatalytic activities could be obtained. The CdS/SiO2 composite microspheres prepared in this work showed excellent photocatalytic activity and recyclability.

Acknowledgements— The authors would like to thank the support by “Fundamental Research Funds for Central Universities of China” South-central University for Nationalities (no. CZY10005).

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results and Discussion
  6. Conclusions
  7. References
  • 1
    Huang, Y., F. Sun, T. Wu, Q. Wu, Z. Huang, H. Su and Z. Zhang (2011) Photochemical preparation of CdS hollow microspheres at room temperature and their use invisible-light photocatalysis. J. Solid State Chem. 184, 644648.
  • 2
    Esmaili, M. and A. Habibi-Yangjeh (2011) Microwave-assisted preparation of CdS nanoparticles in a halide-free ionic liquid and their photocatalytic activities. Chin. J. Catal. 32, 933938.
  • 3
    Li, B. and Y. Wang (2011) Synthesis, microstructure, and photocatalysis of ZnO/CdS nano-heterostructure. J. Phys. Chem. Solids 72, 11651169.
  • 4
    Huo, Y., X. Yang, J. Zhu and H. Li (2011) Highly active and stable CdS-TiO2 visible photocatalyst prepared by in situ sulfurization under supercritical conditions. Appl. Catal. B: Environ. 106, 6975.
  • 5
    Liu, Z., S. Shen and L. Guo (2012) Study on photocatalytic performance for hydrogen evolution over CdS/M-MCM-41 (M=Zr, Ti) composite photocatalysts under visible light illumination. Int. J. Hydrogen Energy 37, 816821.
  • 6
    Wang, R., D. Xua, J. Liu, K. Li and H. Wang (2011) Preparation and photocatalytic properties of CdS/La2Ti2O7 nanocomposites under visible light. Chem. Eng. J. 168, 455460.
  • 7
    Li, X., Y. Gao, L. Yu and L. Zheng (2010) Template–free synthesis of CdS hollow nanospheres based on an ionic liquid assisted hydrothermal process and their application in photocatalysis. J. Solid State Chem. 183, 14231432.
  • 8
    Yu, X., Q. Wu, S. Jiang and Y. Guo (2006) Nanoscale ZnS/TiO2 composites: Preparation, characterization, and visible-light photocatalytic activity. Mater. Character. 57, 333341.
  • 9
    Murai, H., T. Abe, J. Matsuda, H. Sato, S. Chiba and Y. Kashiwaba (2005) Improvement in the light emission characteristics of CdS:Cu/CdS diodes. Appl. Surf. Sci. 244, 351354.
  • 10
    Pucci, A., M. Boccia, F. Galembeck, C. A. Paula Leite, N. Tirelli and G. Ruggeri (2008) Luminescent nanocomposites containing CdS nanoparticles dispersed into vinyl alcohol based polymers. React. Funct. Polym. 68, 11441151.
  • 11
    Petrella, A., M. Tamborra, P. Cosma, M. L. Curri, M. Striccoli, R. Comparelli and A. Agostiano (2008) Photocurrent generation in a CdS nanocrystals/poly[2-methoxy-5-(2′-ethyl- exyloxy)phenylene vinylene] electrochemical cell. Thin Solid Films 516, 50105015.
  • 12
    Thambidurai, M., N. Muthukumarasamy, D. Velauthapillai, S. Agilan and R. Balasundaraprabhu (2012) Impedance spectroscopy and dielectric properties of cobalt doped CdS nanoparticles. Powder Tech. 217, 16.
  • 13
    Wei, G., M. Yan, L. Ma and H. Zhang (2012) The synthesis of highly water-dispersible and targeted CdS quantum dots and it is used for bioimaging by confocal microscopy. Spectrochim. Acta, Part A 85, 288292.
  • 14
    Saikiaa, D., P. K. Saikiab, P. K. Gogoic, M. R. Dasd, P. Senguptad and M. V. Shelkee (2011) Synthesis and characterization of CdS/PVA nanocomposite thin films from a complexing agent free system. Mater. Chem. Phys. 131, 223229.
  • 15
    Lu, Y., L. Li, Y. Ding, F. Zhang, Y. Wang and W. Yu (2012) Hydrothermal synthesis of functionalized CdS nanoparticles and their application as fluorescence probes in the determination of uracil and thymine. J. Lumin. 132, 244249.
  • 16
    Li, X., C. Hu, X. Wang and Y. Xi (2012) Photocatalytic activity of CdS nanoparticles synthesized by a facile composite molten salt method. Appl. Surf. Sci. 258, 43704376.
  • 17
    Moloto, N., N. Revaprasadu, M. J. Moloto, P. O’ Brien and M. Helliwell (2007) N,N′-Diisopropyl-and N,N′–dicyclohexylthiourea cadmium(II) complexes as precursors for the synthesis of CdS nanoparticles. Polyhedron 26, 39473955.
  • 18
    Singh, V., P. K. Sharma and P. Chauhan (2010) Surfactant mediated phase transformation of CdS nanoparticles. Mater. Chem. Phys. 121, 202207.
  • 19
    Andrade, G. R. S., C. C. Nascimento, E. C. Neves, C. D’. A. E. S. Barbosa, L. P. Costa, L. S. Barreto and I. F. Gimenez (2012) One-step preparation of CdS nanocrystals supported on thiolated silica-gel matrix and evaluation of photocatalytic performance. J. Hazard. Mater. 203, 151157.
  • 20
    Duan, J., Y. Feng, G. Yang, W. Xu, X. Li, Y. Liu and J. Zhao (2009) Novel synthesis and characterization of yellow inorganic/organic composite spheres for electrophoretic display. Ind. Eng. Chem. Res. 48, 14681475.
  • 21
    Biryukov, A. A., T. I. Izaak, E. Y. Gotovtseva, I. N. Lapin, A. I. Potekaev and V. A. Svetlichnyi (2011) Optica properties of CdS/MMA dispersions and CdS/PMMA nanocomposites prepared by one-step, sizecontrolled synthesis. Russ. Phys. J. 53, 849856.
  • 22
    Jiang, L., W. Zhang, Y. Yu and J. Wang (2011) Preparation and charge transfer properties of carbon nanotubes supported CdS/ZnO-NWs shell/core heterojunction. Electrochem. Commun. 13, 627630.
  • 23
    Ge, L. and J. Liu (2011) Efficient visible light-induced photocatalytic degradation of methyl orange by QDs sensitized CdS–Bi2WO6. Appl. Catal. B: Environ. 105, 289297.
  • 24
    Cheng, X., Q. Zhao, Y. Yang, C. T. Sie and K. Y. L. Robert (2008) Graphene–CdS composite, synthesis and enhanced photocatalytic activity. J. Colloid Interface Sci. 32, 61216128.
  • 25
    Rajesh, A. J., S. T. Vidya and S. Ramphal (2012) Growth and characterization of nanostructured CdS/Polyaniline/CuInSe2 thin films for solar cell applications. J. Non-Crystalline Solids 358, 188195.
  • 26
    Zhou, Q., M. Fu, B. Yuan, H. Cui and J. Shi (2011) Assembly, characterization, and photocatalytic activities of TiO2 nanotubes/CdS quantum dots nanocomposites. J. Nanopart. Res. 13, 66616672.
  • 27
    StÖber, W., A. Fink and E. Bohn (1968) Controlled growth of monodisperse silica spheres in the micron size range. J. Colloid Interface Sci. 26, 6269.
  • 28
    Xu, C., C. Xing, W. Jin, H. Jin and J. Xing (2010) Amino functionalized mesoporous silica microspheres with perpendicularly aligned mesopore channels for electrochemical detection of trace 2,4,6-trinitrotoluene. Electrochim. Acta 56, 102107.
  • 29
    Selvaraj, R., H. Sun, V. Selvaraj, K. Younghun, V. Selvaraj, R. Eveliina, K. Arto and S. Mika (2011) CdS microspheres composed of nanocrystals and their photocatalytic activity. J. Nanosci. Nanotechnol. 11, 110.
  • 30
    Spanhel, L., H. Weller and A. Henglein (1987) Photochemistry of semiconductor colloids. 22. Electron injection from illuminated CdS into attached TiO2 and ZnO particles. J. Am. Chem. Soc. 109, 66326635.
  • 31
    Wang, X., H. Tian, Y. Yang, H. Wang, S. Wang, W. Zheng and Y. Liu (2012) Reduced graphene oxide/CdS for efficiently photocatalystic degradation of methylene blue. J. Alloys Compd. 524, 512.
  • 32
    Seoudi, R., A. A. Shabaka, M. Kamal, E. M. Abdelrazek and W. H. Eisa (2012) Dependence of structural, vibrational spectroscopy and optical properties on the particle sizes of CdS/polyaniline core/shell nanocomposites. J. Mol. Struct. 1013, 156162.