Cadmium SulfideâFerrite Nanocomposite as a Magnetically

Article pubs.acs.org/IECR

Cadmium Sulfide−Ferrite Nanocomposite as a Magnetically Recyclable Photocatalyst with Enhanced Visible-Light-Driven Photocatalytic Activity and Photostability Pan Xiong, Junwu Zhu,* and Xin Wang* Key Laboratory for Soft Chemistry and Functional Materials, Nanjing University of Science and Technology, Ministry of Education, Nanjing 210094, China S Supporting Information *

ABSTRACT: We report a facile strategy to fabricate a cadmium sulfide−ferrite (CdS−MFe2O4, M = Zn, Co) nanocomposite with differing ferrite content via a two-step hydrothermal method and demonstrate its application as a magnetically recyclable photocatalyst with enhanced visible-light-driven photocatalytic activity and photostability. The photocatalytic activities of asprepared photocatalysts are evaluated by the degradation of rhodamine B (RhB) and 4-chlorophenol (4-CP) in aqueous solution under visible-light irradiation. Compared with pure CdS, both CdS−ZnFe2O4 and CdS−CoFe2O4 show more broad absorption in the visible-light region, which favors the visible-light utilization for better photocatalytic performance. Moreover, the surface area of cadmium sulfide−ferrite is much higher than that of pure CdS, also resulting in enhanced photocatalytic activity. Furthermore, the synergic effects of CdS and ferrites can reduce the recombination probability of photogenerated electron−hole pairs and enhance the charge separation efficiency, leading to high photocatalytic performance and remarkable inhibited photocorrosion.

1. INTRODUCTION Nowadays, water scarcity and pollution are still one of the most severe public health issues worldwide,1 although tremendous efforts have been dedicated to water treatment research and substantial progress has been made.2 Semiconductor photocatalysis, as a ‘‘green’’ technology, has been widely applied in solar water splitting, purifying air, and eliminating the organic contamination of water.3 However, most of the semiconductor photocatalysts, such as TiO2 and ZnO, require high-energy ultraviolet (UV) radiation for photocatalytic activation because of their wide energy band gap.4 UV light energy accounts for only about 4% of the total energy of the sunlight on the earth, while the visible light contributes to about 43%. Therefore developing efficient visible-light-responsive photocatalysts has been an active research field in recent years. As compared to the wide band gap counterparts, chalcogenide nanomaterials become the promising candidates for the conversion of solar energy into chemical energy under visible-light irradiation.5,6 Especially, CdS is one of the most important II−VI semiconductors having a direct bulk band gap of 2.4 eV at room temperature and being extensively studied for a wide range of applications, particularly for visible-light-driven photocatalysis.7−14 However, the rapid recombination of the excited electron−hole pairs greatly impedes the photocatalytic efficiency of CdS.8 In addition, CdS is susceptible to producing photocorrosion when the photocatalytic reactions are carried out in aqueous media where CdS itself is oxidized by the photogenerated holes.7,9−12 To alleviate these problems, several approaches have been developed, including combination of CdS with other semiconductors,9,13,15 conductive polymers16 or carbon nanomaterials,17,18 and these attempts have proven to be successful in increasing the photoactivity and antiphotocorrosion to some extent. Moreover, heterogeneous photo© 2013 American Chemical Society

degradation reactions are usually carried out either in a slurrytype reactor or in an immobilized-type reactor; therefore, recovery and reuse of photocatalysts after reaction are of great significance in sustainable process management. Recently, spinel-type ferrites with general formula MFe2O4 appear to be even more versatile due to the more complex structure and the resulting many degrees of freedom, and have found many applications such as those in biotechnology,19 catalysts,20 memory devices,21 lithium ion batteries,22,23 water splitting,24,25 and photocatalytic degradation.26−28 Our group has reported that spinel ferrites combined with delocalized conjugated materials such as carbon nanotubes (CNTs),29 graphene,30−32 or conducting polyaniline (PANI)33 showed much higher visible-light photocatalytic activities over pristine ferrites. The significant enhancement in photoactivity is ascribed to the efficient separation of photogenerated carriers in the coupling system and the concerted effects of individual components or their integrated properties. Most recently, Yu et al. reported ZnFe2O4-decorated CdS nanorods with high efficiency for photocatalytic generation hydrogen.34 It is also of great interest to study the cadmium sulfide−ferrite coupling systems and their photocatalytic activity in degradation of organic pollutants. If that can be accomplished, then not only may it be possible to obtain some exceptional properties such as the enhancement of photostability and photoactivity as a result of the concerted effect of the individual components but also the magnetically separable function because of the excellent magnetic properties of ferrites. Received: Revised: Accepted: Published: 17126

July 28, 2013 November 5, 2013 November 13, 2013 November 13, 2013 dx.doi.org/10.1021/ie402437k | Ind. Eng. Chem. Res. 2013, 52, 17126−17133

Industrial & Engineering Chemistry Research

Article

Figure 1. XRD patterns of (a) CdS and CdS−ZnFe2O4 and (b) CdS and CdS−CoFe2O4.

ments were performed by a Micromeritics (ASAP2010 V5.02H) surface area analyzer. The magnetic properties of the nanocomposites were studied by vibrating sample magnetometer (HH-15). The UV−vis diffuse reflectance spectra were acquired on a Shimadzu UV-2550 UV−vis spectrophotometer. The transient photocurrent responses and electrochemical impedance spectra (EIS) were measured on an electrochemical system (CHI-660B) in a three-electrode system with 0.1 M Na2SO4 electrolyte. Pt coil and Ag/AgCl electrode were used as counter and reference electrode, respectively. The working electrodes were prepared as follows: the photocatalysts were dispersed in ethanol and dropped onto the indium tin oxide (ITO) substrates (1 cm × 5 cm), and then the electrodes were dried in nitrogen at 200 °C for 30 min. The visible light (λ > 420 nm) was obtained by a 500 W xenon lamp with a 420 nm cutoff filter (JB 420) to completely remove any radiation below 420 nm. EIS measurements were recorded with an AC voltage amplitude of 5 mV, with a frequency range of 105 to 0.01 Hz at 0 V. 2.3. Photocatalytic Activity Measurement. In all of the photocatalytic degradation experiments, 50 mg of catalyst was added to 100 mL of RhB solution (10 mg/L) or 4-CP solution (10 mg/L). Before irradiation, the suspensions were magnetically stirred in the dark for 1 h in order to reach an adsorption− desorption equilibrium. At a fixed time interval, 5 mL aliquots were sampled and centrifuged to remove the catalyst. The filtrates were analyzed by recording variations in the maximum absorption band using a Shimadzu UV-2550 UV−vis spectrophotometer.

Herein, a simple and straightforward strategy is designed to fabricate a cadmium sulfide−ferrite (CdS−MFe2O4, M = Zn, Co) nanocomposite with differing ferrite content via a two-step hydrothermal method. It is found that the synergic effects of CdS and ferrites can reduce the recombination probability of photogenerated electron−hole pairs and enhance the charge separation efficiency, leading to the higher photocatalytic performance and remarkable inhibited photocorrosion. Ferrite nanoparticles themselves have a strong magnetic property, which can be easily used for magnetic separation after degradation.

2. EXPERIMENTAL SECTION 2.1. Synthesis of the CdS−MFe2O4 (M = Zn or Co) Photocatalysts. All of the reagents used were of analytical reagent grade and were used without further purification. The CdS−MFe2O4 (M = Zn or Co) composites with differing ferrite content were prepared via a two-step hydrothermal method. In the first step, MFe2O4 (M = Zn or Co) nanoparticles were synthesized by the hydrothermal method as in our previous reports.30,31,33 The zinc nitrate and ferric nitrate with a molar ratio of 1:2 were dissolved in ethanol. An appropriate NaOH solution was added until the pH reached 13. Then the mixture was maintained at 180 °C for 20 h in a Teflon-lined stainless autoclave. After filtration and being washed with water, the precipitate was dried to obtain ZnFe2O4 nanoparticles. The CoFe2O4 nanoparticles were prepared by the same method by replacing the zinc nitrate with cobalt nitrate. A typical procedure for the synthesis of CdS−ZnFe2O4 nanocomposite with 5% ZnFe2O4 content is as follows: ZnFe2O4 nanoparticles (0.152 g) and cadmium acetate (0.533 g) were dispersed in 80 mL of dimethyl sulfoxide (DMSO) with ultrasonic vibrations for 30 min to obtain a uniform suspension. Then the mixture was maintained at 180 °C for 12 h in a 100 mL Teflon-lined stainless autoclave. The reaction mixture was allowed to cool to room temperature, and the precipitate was filtered, washed with acetone and alcohol, and dried in a vacuum oven at 60 °C. The product was labeled as CdS−ZnFe2O4(0.05). The CdS−CoFe2O4 nanocomposite was prepared via the same method by replacing the ZnFe2O4 with CoFe2O4. For comparison, the same method was used to synthesize pure CdS without ferrite. 2.2. Characterization. Powder X-ray diffraction (XRD) analyses were performed on a Bruker D8 Advanced diffractometer with Cu Ka radiation, and the scanning angle ranged from 5 to 80° of 2θ. Transmission electron microscopy (TEM) images were taken with a JEOL JEM2100 microscope. The Brunauer−Emmett−Teller (BET) surface area measure-

3. RESULT AND DISCUSSION 3.1. Characterization of the Photocatalysts. X-ray diffraction measurements were performed to study the crystal structure of CdS, CdS−ZnFe2O4, and CdS−CoFe2O4, as shown in Figure 1. The peaks at 2θ = 26.7°, 44.0, and 51.7° correspond to the planes of the (111), (220), and (311) of cubic CdS (JCPDS 80-0019), respectively.5,7 The broad diffraction peaks of CdS nanoparticles are due to DMSO being able to regulate the nucleation rate of CdS particles by slowly releasing S2− ions into solution, resulting in a much smaller crystallite size.35 The XRD patterns of ZnFe2O4 and CoFe 2O 4 are shown in Figure S1 of the Supporting Information. It is obviously seen that almost all of the diffraction peaks of ZnFe2O4 and CoFe2O4 can be assigned to spinel-type ZnFe2O4 (JCPDS 22-1012) and spinel-type CoFe2O4 (JCPDS 22-1086), respectively. In the case of 20− 30% ZnFe2O4 or CoFe2O4 in the nanocomposites, the only peak at 35.2° that corresponds to the (311) plane of ferrite spinel structure for ZnFe2O4 or CoFe2O4 can be observed, 17127

dx.doi.org/10.1021/ie402437k | Ind. Eng. Chem. Res. 2013, 52, 17126−17133


Article

Figure 2. TEM images of (a) CdS−ZnFe2O4 and (b) CdS−CoFe2O4; EDX patterns of (c) CdS−ZnFe2O4 and (d) CdS−CoFe2O4.

tion.27,30,31,33,36−38,43 Although most of RhB can be degraded in 60 min in the presence of pure CdS under visible-light irradiation, the combination of CdS with ZnFe2O4 or CoFe2O4 leads to the dramatically enhanced photocatalytic activity (Figure 3a,b). Among the photocatalysts with differing ferrite content, CdS−ZnFe2O4(0.10) and CdS−CoFe2O4(0.05) exhibited the highest photocatalytic activity for photodegradation of RhB, respectively. Generally, photocatalyst with a high specific surface area would offer more surface active sites and photocatalytic reaction centers, resulting in the enhancement of photocatalytic performance. Thus the higher surface area of CdS−ZnFe2O4 may lead to higher photocatalytic activity, as compared to pure CdS. The photodegradation process can be described by pseudofirst-order kinetics: −ln(C/C0) = kt. Parts c and d of Figure 3 show the pseudo-first-order kinetic rate constants of CdS− ZnFe2O4 and CdS−CoFe2O4, respectively. It is obvious that CdS−ZnFe2O4(0.10) and CdS−CoFe2O4(0.05) show the maximum rate constants (0.13 min − 1 for CdS− ZnFe2O4(0.10) and 0.0822 min−1 for CdS−CoFe2O4(0.05)), which are 4.44 times and 2.82 times as much as that of pure CdS (0.0292 min−1), respectively. In addition to RhB, 4-CP(4-chlorophenol) was also chosen as another representative model pollutant to further evaluate the photocatalytic performance of the as-prepared photocatalysts. As shown in Figure 4, after 6 h of illumination, no noticeable degradation of 4-CP can be observed in the absence of any catalysts. The photocatalytic conversion ratio of 4-CP in the presence of bare CdS under visible light was only about 8%, while approximately 30% and 22% of 4-CP were degraded over CdS−ZnFe2O4(0.10) and CdS−CoFe2O4(0.05), respectively. Table 2 shows the pseudo-first-order kinetic rate constants for the degradation of 4-CP under visible-light irradiation. The rate constants (k) of CdS−ZnFe 2 O 4 (0.10) and CdS−

indicating the low content and poor crystallinity. With decreased content, the ferrite spinel structure was entirely undetectable. Representative TEM images of CdS−ZnFe2O4 and CdS− CoFe2O4 are shown in Figure 2a,b, respectively. The d spacing of 0.34 and 0.25 nm can be assigned to the (111) lattice plane of the cubic CdS and the (311) lattice space of ZnFe2O4 or CoFe2O4, respectively. The composition of the nanocomposites can be further confirmed by EDX analysis (Figure 2c,d), which demonstrates that the CdS−ZnFe2O4 and CdS−CoFe2O4 nanocomposites are composed of O, S, Cd, Zn, Fe, and O, S, Cd, Co, Fe elements, respectively. The BET surface area and pore structure play an important role in improving catalyst performance. It is obvious that the BET surface area remarkably increased after the addition of ZnFe2O4 (Table 1). The presence of ZnFe2O4 may impede crystallization of the CdS, leading to an increase in surface area. Table 1. BET of CdS and CdS−ZnFe2O4 sample

BET surface area (m2/g)

pore volume (cm3/g)

CdS CdS−ZnFe2O4(0.05) CdS−ZnFe2O4(0.10) CdS−ZnFe2O4(0.30)

17.13 103.6 112.7 102.3

0.079 0.134 0.190 0.203

3.2. Enhancement of Photocatalytic Activity. The photocatalytic activities of as-prepared photocatalysts are evaluated by the degradation of RhB in aqueous solution under visible-light irradiation. As can be seen in Figure 3a,b, preliminary blank experiments without any photocatalyst show that no noticeable decomposition of RhB can be observed, indicating that RhB has a good photostability under the visiblelight irradiation. It is known that ZnFe2O4 or CoFe2O4 alone is photocatalytically inactive under visible-light irradia17128



Article

Figure 3. Photodegradation of RhB over (a) CdS, ZnFe2O4, and CdS−ZnFe2O4 and (b) CdS, CoFe2O4, and CdS−CoFe2O4 under visible-light irradiation. Pseudo-first-order kinetic rate constant (k) of (c) CdS, ZnFe2O4, and CdS−ZnFe2O4 and (d) CdS, CoFe2O4, and CdS−CoFe2O4.

3.3. Enhancement of Photostability. The photocatalyst photostability is a very important characteristic with regard to practical application. To evaluate the photostability of CdS, CdS−ZnFe2O4, and CdS−CoFe2O4 photocatalysts, the recycled experiments for the photodegradation of RhB were performed. As shown in Figure 5a, as much as 80% of RhB was degraded when CdS was used for the first cycle; however, a significant decrease in photocatalytic activity was found, and only 30% of RhB was degraded after three cycles, as a result of the photocorrosion of the CdS surface,16 while the recycled use of CdS−ZnFe2O4(0.10) or CdS−CoFe2O4(0.05) for three times did not conspicuously affect the photocatalytic activities (Figure 5a). It is obvious that the photocorrosion effect of CdS was inhibited by ZnFe2O4 or CoFe2O4. XRD measurements show that the crystalline phase structure of CdS was destroyed disastrously after photocatalytic recycles, indicating a severe photocorrosion occurred (Figure 5b), whereas the XRD patterns of CdS−ZnFe2O4 and CdS− CoFe2O4 show that there are no notable differences before and after the photocatalytic recycles (Figure 5c,d), also confirming that the nanocomposites exhibit good photostability and antiphotocorrosion property. The rapid transferring of electron and high separation efficiency of electron−hole pairs are the main reason for the substantially enhanced photoactivity and entirely inhibited photocorrosion.39 Therefore, application of the cadmium sulfide−ferrite nanocomposites for degradation of organic pollutants will not cause secondary pollution. Moreover, as ferrite nanoparticles themselves have a strong magnetic property, CdS−ZnFe2O4 and CdS−CoFe2O4 can be easily separated from the heterogeneous reaction system by a magnet after photocatalysis (see the insets of Figure 5c,d). The magnetic hysteresis loops of ZnFe2O4, CdS−ZnFe2O4, and CoFe 2 O 4 , CdS−CoFe 2 O 4 are shown in Figure S2a,b, respectively, of the Supporting Information . 3.4. Possible Mechanism for the Enhanced Photocatalytic Performances. The UV−vis diffuse reflectance

Figure 4. Photodegradation of 4-CP over CdS, CdS−ZnFe2O4(0.10), and CdS−CoFe2O4(0.05) under visible-light irradiation.

Table 2. Variation of Total Organic Carbon Removal and Photocatalytic Reaction Rate Constants (k) by Degradation of 4-CP under Visible-Light Irradiation sample

pollutants

time (h)

TOC removal (%)

k (min−1)

CdS CdS−ZnFe2O4(0.10) CdS−CoFe2O4(0.05)

4-CP 4-CP 4-CP

6 6 6

1.94 10.9 9.44

0.000181 0.000978 0.000822

CoFe2O4(0.05) are 0.000978 and 0.000822 min−1, which are 5.40 times and 4.54 times as much as that of pure CdS (0.000181 min−1), respectively. Furthermore, to investigate the mineralization degree, the total organic carbon (TOC) removal efficiency is operated and the results are shown in Table 2. Within 6 h after visible-light irradiation, the TOC removal of 4CP over both CdS−ZnFe2O4(0.10) and CdS−CoFe2O4(0.05) is much higher than that of pure CdS. 17129



Article

Figure 5. (a) Photodegradation of RhB over CdS, CdS−ZnFe2O4(0.10), and CdS−CoFe2O4(0.05) for three cycles; XRD patterns of (b) CdS, (c) CdS−ZnFe2O4(0.10), and (d) CdS−CoFe2O4(0.05) before and after photocatalysis. The insets show the solution after magnetic separation using an external magnet.

Figure 6. UV−vis diffuses reflectance spectra of (a) CdS and CdS−ZnFe2O4 and (b) CdS and CdS−CoFe2O4.

Figure 7. EIS spectra of (a) CdS and CdS−ZnFe2O4(0.10) and (b) CdS and CdS−CoFe2O4(0.05) in dark and under visible-light irradiation.

Compared with pure CdS, CdS−ZnFe2O4 and CdS−CoFe2O4 show more broad absorption in the visible-light region. More intuitively, CdS−ZnFe2O4 and CdS−CoFe2O4 become darker

spectra of CdS, CdS−ZnFe2O4, and CdS, CdS−CoFe2O4 are displayed in Figure 6a,b, respectively. It can be observed that the samples are all capable of responding to visible light. 17130



Article

as compared to pure CdS, also indicating more absorbance of visible light, which favors the visible-light utilization for better photocatalytic performance. In the ferrite-coupled CdS systems, the photocatalytic activities were enhanced mainly due to the high efficiency of charge separation induced by the remarkable synergistic effects of CdS and ferrites. Figure 7 shows the EIS responses of CdS, CdS−ZnFe2O4(0.10), and CdS−CoFe2O4(0.05) under dark and visible-light irradiation. The radius of the arc on the EIS Nyquist plot reflects the reaction rate occurring at the electrode surface.40,41 In the dark, both electrodes show a pronounced arc (semicircle portion) at higher frequencies in the EIS plane, the diameter of which corresponds to the electron transfer resistance controlling the kinetics at the electrode interface.41 The radius decreased significantly when CdS was coupled with ZnFe2O4 or CoFe2O4. Under visible-light irradiation, the arc radii on the EIS Nyquist plots become smaller. It is noted that both the CdS−ZnFe2O4(0.10) and CdS−CoFe2O4(0.05) electrodes show smaller arc radius than that of pure CdS, which suggests a more effective separation of photogenerated electron−hole pairs and faster interfacial charge transfer occur on the CdS−ZnFe2O4 and CdS−CoFe2O4 electrodes.40,41 Transient photocurrent measurements can also be useful in helping to understand the photogenerated charge separation process.42 The transient photocurrent responses of CdS, CdS− ZnFe2O4(0.10), and CdS−CoFe2O4(0.05) are recorded via several on−off cycles under visible-light irradiation (Figure 8).

Figure 9. Schematic diagram illustrating the electron−hole separation of CdS−ZnFe2O4(0.10) and CdS−CoFe2O4(0.05) nanocomposites under visible-light irradiation.

CB of ZnFe2O4. Simultaneously, the photogenerated holes in VB of ZnFe2O4 are able to move easily to the VB of CdS. Thus photogenerated electrons and holes move in opposite directions, reducing the recombination probability and enhancing the charge separation efficiency, leading to a higher photocatalytic performance.13,16,43 As a result, photogenerated holes rapidly transferring to the solution leave not enough holes on CdS to cause photocorrosion, resulting in the enhancement of photocurrent responses and the remarkable inhibited photocorrosion.39 The electrons can react with the dissolved oxygen to produce superoxide anion radicals, while the holes are scavenged by the adsorbed water to form hydroxyl radicals. Finally, the active species (holes, superoxide anion radicals, and hydroxyl radicals) oxidize the dye molecules. The theoretical calculations on the inverse spinel structure yield a band gap of 0.80 eV for CoFe2O4, and the conduction band of CoFe2O4 is around 1.2 eV.37 Although the band gap of CdS−CoFe2O4 is much smaller than that of CdS−ZnFe2O4, they have a similar mechanism of the photogenerated electron−hole separation process.

4. CONCLUSION The magnetically recyclable CdS−MFe2O4 (M = Zn, Co) photocatalysts are prepared via a two-step hydrothermal method. The CdS−MFe2O4 (M = Zn, Co) photocatalysts show higher photocatalytic activity and photostability than pure CdS toward the degradation of both RhB and 4-CP under visible-light irradiation. The significant enhancement in photocatalytic performances can be attributed to the higher surface area of the composite and the synergic effect of CdS and ZnFe2O4 (or CoFe2O4), which can lead to more intense adsorption in the visible-light region and more efficient charge separation.

Figure 8. Photocurrent transient responses of CdS, CdS− ZnFe2O4(0.10), and CdS−CoFe2O4(0.05) under visible-light irradiation.

The photocurrents of both the CdS−ZnFe2O4(0.10) and CdS−CoFe2O4(0.05) electrodes were much higher than that of the pure CdS electrode, indicating that the separation efficiency of photoinduced electron−hole pairs was much enhanced. On the basis of the experimental results, a proposed schematic mechanism of the photogenerated electron−hole separation process for CdS−ZnFe2O4 and CdS−CoFe2O4 is illustrated in Figure 9. It is reported that the conduction band (CB) of ZnFe2O4 is more positive than that of CdS, and its valence band (VB) is also more positive than that of CdS,13,27,43,44 so the former can act as a sink for the photogenerated electrons and the later could act as an acceptor for the photogenerated holes in the hybrid photocatalysts.13,44 Both CdS and ZnFe2O4 can be excited by visible light to produce photogenerated carriers and excited holes. The excited-state electrons in CB of CdS can readily inject into

■

ASSOCIATED CONTENT

S Supporting Information *

Figures showing the XRD patterns of ZnFe2O4, and CoFe2O4 and the magnetic hysteresis loops of ZnFe2O4, CdS−ZnFe2O4, CoFe2O4, and CdS−CoFe2O4. This material is available free of charge via the Internet at http://pubs.acs.org.

■

AUTHOR INFORMATION

Corresponding Authors

*Tel.: +86-25-84305667. Fax: +86-25-8431-5054. E-mail: [email protected]. 17131



Article

*Tel.: +86-25-84305667. Fax: +86-25-8431-5054. E-mail: [email protected].

(16) Zhang, H.; Zhu, Y. Significant visible photoactivity and antiphotocorrosion performance of CdS photocatalysts after monolayer polyaniline hybridization. J. Phys. Chem. C 2010, 114, 5822− 5826. (17) Ye, A.; Fan, W.; Zhang, Q.; Deng, W.; Wang, Y. CdS−graphene and CdS−CNT heterostructures as visible-light photocatalysts for hydrogen evolution and organic dye degradation. Catal. Sci. Technol. 2012, 2, 969−978. (18) Xie, G.; Zhang, K.; Guo, B.; Liu, Q.; Fang, L.; Gong, J. R. Graphene-based materials for hydrogen generation from light-driven water splitting. Adv. Mater. 2013, 25, 3820−3839. (19) Liu, J.; Pearce, C. I.; Liu, C.; Wang, Z.; Shi, L.; Arenholz, E.; Rosso, K. M. Fe3−xTixO4 nanoparticles as tunable probes of microbial metal oxidation. J. Am. Chem. Soc. 2013, 135, 8896−8907. (20) Benrabss, R.; Lofberg, A.; Rubbens, A.; Richard, E. B.; Vanniner, R. N.; Barama, A. Structure, reactivity and catalytic properties of nanoparticles of nickel ferrite in the dry reforming of methane. Catal. Today 2013, 203, 188−195. (21) Hu, W.; Qin, N.; Wu, G.; Lin, Y.; Li, S.; Bao, D. Opportunity of spinel ferrite materials in nonvolatile memory device applications based on their resistive switching performances. J. Am. Chem. Soc. 2012, 134, 14658−14661. (22) Fu, Y.; Wan, Y. H.; Xia, H.; Wang, X. Nickel ferrite-graphene heteroarchitectures: Toward high-performance anode materials for lithium-ion batteries. J. Power Sources 2012, 213, 338−342. (23) Jiang, B.; Park, M.; Chae, O. B.; Park, S.; Kim, Y.; Oh, S. M.; Piao, Y.; Hyeon, T. Direct synthesis of self-assembled ferrite/carbon hybrid nanosheets for high performance lithium-ion battery anodes. J. Am. Chem. Soc. 2012, 134, 15010−15015. (24) Xu, X.; Azad, A. K.; Irvine, J. T. S. Photocatalytic H2 generation from spinels ZnFe2O4, ZnFeGaO4 and ZnGa2O4. Catal. Today 2013, 199, 22−26. (25) Rekhila, G.; Bessekhouad, Y.; Trari, M. Visible light hydrogen production on the novel ferrite NiFe2O4. Int. J. Hydrogen Energy 2013, 38, 6335−6343. (26) Fan, G.; Tong, J.; Li, F. Visible-light-induced photocatalyst based on cobalt-doped zinc ferrite nanocrystals. Ind. Eng. Chem. Res. 2012, 51, 13639−13647. (27) Kong, L.; Jiang, Z.; Xiao, T.; Lu, L.; Jonesac, M. O.; Edwards, P. P. Exceptional visible-light-driven photocatalytic activity over BiOBr− ZnFe2O4 heterojunctions. Chem. Commun. (Cambridge, U. K.) 2011, 47, 5512−5514. (28) Fan, G.; Gu, Z.; Yang, L.; Li, F. Nanocrystalline zinc ferrite photocatalysts formed using the colloid mill and hydrothermal technique. Chem. Eng. J. (Amsterdam, Neth.) 2009, 155, 534−541. (29) Xiong, P.; Fu, Y.; Wang, L.; Wang, X. Multi-walled carbon nanotubes supported nickel ferrite: A magnetically recyclable photocatalyst with high photocatalytic activity on degradation of phenols. Chem. Eng. J. (Amsterdam, Neth.) 2012, 195−196, 149−157. (30) Fu, Y.; Wang, X. Magnetically separable ZnFe2O4 graphene catalyst and its high photocatalytic performance under visible light irradiation. Ind. Eng. Chem. Res. 2011, 50, 7210−7218. (31) Fu, Y.; Chen, H.; Sun, X.; Wang, X. Combination of cobalt ferrite and graphene: High-performance and recyclable visible-light photocatalysis. Appl. Catal., B 2012, 111−112, 280−287. (32) Fu, Y.; Chen, H.; Sun, X.; Wang, X. Graphene-supported nickel ferrite: A magnetically separable photocatalyst with high activity under visible light. AIChE J. 2012, 58, 3298−3305. (33) Xiong, P.; Chen, Q.; He, M.; Sun, X.; Wang, X. Cobalt ferrite− polyaniline heteroarchitecture: A magnetically recyclable photocatalyst with highly enhanced performances. J. Mater. Chem. 2012, 22, 17485− 17493. (34) Yu, T. H.; Cheng, W. Y.; Chao, K. J.; Lu, S. Y. ZnFe2O4 decorated CdS nanorods as a highly efficient, visible light responsive, photochemically stable, magnetically recyclable photocatalyst for hydrogen generation. Nanoscale 2013, 5, 7356−7360. (35) Bao, N. Z.; Shen, L. M.; Takata, T.; Domen, K. Self-templated synthesis of nanoporous CdS nanostructures for highly efficient

Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS This investigation was supported by NNSF of China (Grant No. 20171094), NSAF (Grant No. U1230125), STPP of Jiangsu (Grant No. BE 2012151), DFSR (Grant No. A2620110010), the Fundamental Research Funds for the Central Universities (Grant No. 30920130122002), and PAPD of Jiangsu.

■

REFERENCES

(1) Elimelech, M.; Phillip, W. A. The future of seawater desalination: Energy, technology, and the environment. Science 2011, 333, 712−717. (2) Shannon, M. A.; Bohn, P. W.; Elimelech, M.; Georgiadis, J. G.; Marinas, B. J.; Mayes, A. M. Science and technology for water purification in the coming decades. Nature 2008, 452, 301−310. (3) Chong, M. N.; Jin, B.; Chow, C. W. K.; Saint, C. Recent developments in photocatalytic water treatment technology: A review. Water Res. 2010, 44, 2997−3027. (4) Anpo, M.; Takeuchi, M. The design and development of highly reactive titanium oxide photocatalysts operating under visible light irradiation. J. Catal. 2003, 216, 505−516. (5) Li, Q.; Guo, B.; Yu, J.; Ran, J.; Zhang, B.; Yan, H.; Gong, J. Highly efficient visible-light-driven photocatalytic hydrogen production of CdS-cluster-decorated graphene nanosheets. J. Am. Chem. Soc. 2011, 133, 10878−10884. (6) Xie, G.; Zhang, K.; Fang, H.; Guo, B.; Wang, R.; Yan, H.; Fang, L.; Gong, J. R. A photoelectrochemical investigation on the synergetic effect between CdS and reduced graphene oxide for solar-energy conversion. Chem.Asian J. 2013, 8, 2395−2400. (7) Daskalaki, V. M.; Antoniadou, M.; Puma, G. L.; Kondarides, D. I.; Lianos, P. Solar light-responsive Pt/CdS/TiO2 photocatalysts for hydrogen production and simultaneous degradation of inorganic or organic sacrificial agents in wastewater. Environ. Sci. Technol. 2010, 44, 7200−7205. (8) Gao, Z.; Liu, N.; Wu, D.; Tao, W.; Xu, F.; Jiang, K. Graphene− CdS composite, synthesis and enhanced photocatalytic activity. Appl. Surf. Sci. 2012, 258, 2473−2478. (9) Shi, Y.; Li, H.; Wang, L.; Shen, W.; Chen, H. Novel α-Fe2O3/CdS cornlike nanorods with enhanced photocatalytic performance. ACS Appl. Mater. Interfaces 2012, 4, 4800−4806. (10) Nan, Y. X.; Chen, F.; Yang, L. G.; Chen, H. Z. Electrochemical synthesis and charge transport properties of CdS nanocrystalline thin films with a conifer-like structure. J. Phys. Chem. C 2010, 114, 11911− 11917. (11) Kumar, A.; Singhal, A. Optical, photophysical and magnetic behavior of GMP-templated binary (β-Fe2O3/CdS) and ternary (βFe2O3/Ag/CdS) nanohybrids. J. Mater. Chem. 2011, 21, 481−496. (12) Chen, F.; Zhou, R.; Yang, L.; Liu, N.; Wang, M.; Chen, H. Z. Large-scale and shape-controlled syntheses of three-dimensional CdS nanocrystals with flowerlike structure. J. Phys. Chem. C 2008, 112, 1001−1007. (13) Shi, J.; Yan, X.; Cui, H.; Zong, X.; Fu, M.; Chen, S.; Wang, L. Low-temperature synthesis of CdS/TiO2 composite photocatalysts: Influence of synthetic procedure on photocatalytic activity under visible light. J. Mol. Catal. A: Chem. 2012, 356, 53−60. (14) Zhang, J.; Yu, J.; Jaroniec, Mietek.; Gong, J. R. Noble metal-free reduced graphene oxide-ZnxCd1−xS nanocomposite with enhanced solar photocatalytic H2-production performance. Nano Lett. 2012, 12, 4584−4589. (15) Meng, Z.; Peng, M.; Zhu, L.; Oha, W.; Zhang, F. Fullerene modification CdS/TiO2 to enhancement surface area and modification of photocatalytic activity under visible light. Appl. Catal., B 2012, 113− 114, 141−149. 17132



Article

photocatalytic hydrogen production under visible light. Chem. Mater. 2008, 20, 110−117. (36) Senapati, K. K.; Borgohain, C.; Phukan, P. CoFe2O4-ZnS nanocomposite: a magnetically recyclable photocatalyst. Catal. Sci. Technol. 2012, 2, 2361−2366. (37) Xiong, P.; Wang, L.; Sun, X.; Xu, B.; Wang, X. Ternary titaniacobalt ferrite-polyaniline nanocomposite: a magnetically recyclable hybrid for adsorption and photodegradation of dyes under visible light. Ind. Eng. Chem. Res. 2013, 52, 10105−10113. (38) Xu, S.; Feng, D.; Shangguan, W. Preparations and photocatalytic properties of visible-light-active zinc ferrite-doped TiO2 photocatalyst. J. Phys. Chem. C 2009, 113, 2463−2467. (39) Jia, L.; Wang, D. H.; Huang, Y. X.; Xu, A. W.; Yu, H. Q. Highly durable N-doped graphene/CdS heterostructures with enhanced photocatalytic hydrogen evolution from water under visible light irradiation. J. Phys. Chem. C 2011, 115, 11466−11473. (40) Hou, Y.; Li, X. Y.; Zhao, Q. D.; Quan, X.; Chen, G. H. Electrochemically assisted photocatalytic degradation of 4-chlorophenol by ZnFe2O4-modified TiO2 nanotube array electrode under visible light irradiation. Environ. Sci. Technol. 2010, 44, 5098−5103. (41) Zhang, L. W.; Wang, Y. J.; Cheng, H. Y.; Yao, W. Q.; Zhu, Y. F. Synthesis of porous Bi2WO6 thin films as efficient visible-light-active photocatalysts. Adv. Mater. 2009, 21, 1286−1290. (42) Xu, T. G.; Zhang, L. W.; Cheng, H. Y.; Zhu, Y. F. Significantly enhanced photocatalytic performance of ZnO via graphene hybridization and the mechanism study. Appl. Catal., B 2011, 101, 382−387. (43) Zhang, L.; He, Y.; Ye, P.; Wu, Y.; Wu, T. Visible light photocatalytic activities of ZnFe2O4 loaded by Ag3VO4 heterojunction composites. J. Alloys Compd. 2013, 549, 105−113. (44) Zhang, N.; Zhang, Y.; Pan, X.; Yang, M. Q.; Xu, Y. J. Constructing ternary CdS−graphene−TiO2 hybrids on the flat land of graphene oxide with enhanced visible-light photoactivity for selective transformation. J. Phys. Chem. C 2012, 116, 18023−18031.

17133


Cadmium SulfideâFerrite Nanocomposite as a Magnetically

Recommend Documents

Cadmium SulfideâFerrite Nanocomposite as a Magnetically