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Cite this: Chem. Commun., 2014, 50, 4931
Facile and rapid growth of Ag2S microrod arrays as efficient substrates for both SERS detection and photocatalytic degradation of organic dyes†
Received 6th January 2014, Accepted 25th March 2014
Qi Cao,a Renchao Che*a and Nan Chenb
DOI: 10.1039/c4cc00107a www.rsc.org/chemcomm
A novel bifunctional substrate derived from well-aligned Ag2S microrod arrays was obtained via a facile and cost-effective solvothermal process rapidly within 1 h. It demonstrates great activity for both SERS detection and photocatalytic degradation of organic dyes, and thus holds great potential for environmental monitoring devices and other applications.
Silver sulfide (Ag2S), as an important narrow band-gap (0.85 eV1) semiconductor, has attracted tremendous research interest for its tunable near-infrared photoluminescence2 and low toxicity3 in its nanoparticle form. In the last few years, application trials of Ag2S have been focused mainly on fabrication of near-infrared fluorescent probes4 and quantum dot solar cells.5 Meanwhile, the activity of Ag2S toward sensitive surface-enhanced Raman scattering (SERS) substrates and efficient photocatalysts for degradation of organic molecules has also been rigorously investigated very recently due to the potential requirement and practical significance for real-time monitoring and subsequently rapid degradation of persistent organic pollutants (POPs). Typically in some cases, SERS-active Ag2S nanoparticles were synthesized by using oleylamine or octadecylamine as both a solvent and a ligand, and further, the degree of charge transfer in the Ag2S–analyte systems was also studied via SERS analysis.6 For photocatalytic applications, various Ag2S-based nanostructures, for example, the Ag2S-encapsulated mesoporous MCM-41 nanoparticles,7 porous Ag2S nanoparticle membranes,8 poly(amidoamine)functionalized carbon nanotube–Ag2S quantum dot nanocomposites9 and the Ag2S–TiO2 donor–acceptor systems10,11 have been designed and fabricated, and finally shown to enhance a
Department of Materials Science, Laboratory of Advanced Materials, Fudan University, Shanghai 200438, People’s Republic of China. E-mail: [email protected] b Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089, USA † Electronic supplementary information (ESI) available: Experimental details, the XRD pattern, the EDS spectrum and element mapping profiles, TEM and HRTEM images, additional SEM images, UV-vis absorbance spectra, the recyclability evaluation part as well as the UV-vis-NIR diffuse reflectance spectra. See DOI: 10.1039/c4cc00107a
This journal is © The Royal Society of Chemistry 2014
photocatalytic activities toward water splitting11 and degradation of POPs such as phenol,10 rhodamine B,8 methyl orange9 and methylene blue.7 Here in this work, for the first time we have obtained novel Ag2S microrod arrays (MRAs) on silver foils via a facile and costeffective solvothermal method using the elemental sulfur powder as a sulfur source and methanol as a solvent. It is worth mentioning that it took as quick as 1 h for the solvothermal process to give well-aligned Ag2S MRAs. The as-obtained Ag2S MRAs consequently demonstrated appreciable SERS as well as photocatalytic activity toward various organic dyes including methyl orange (MO), methylene blue (MB), crystal violet (CV), rhodamine 6G (R6G) and Sudan I (SDI), which endow them with great potential to serve as multifunctional substrates for both detection and in situ degradation of these organic dyes. Since the dyes mentioned above are commonly and intensively utilized in textile, ink, printing and dyeing industries, the dye-containing wastewater may unfortunately result in long-term adverse effects on the aquatic environment,12 and hence would finally jeopardize the health of the people,13 it is believed that this novel Ag2S MRA-based detection and degradation substrate presented in this work would have much potential for the management of the environment as well as human health. The detailed materials and methods are provided in the ESI.† The representative X-ray diffraction (XRD) pattern (Fig. S1(a), ESI†) with all characteristic peaks matching exactly, and the energy dispersive X-ray spectrum (EDS, Fig. S1(b), ESI†), which shows that the mole ratio of Ag and S is approximately 2 : 1, both demonstrate the single and pure Ag2S component of the MRAs. Furthermore, the EDS element mapping of a single rod (Fig. S2, ESI†) and highresolution transmission electron microscope (HRTEM) images of a fragment of the rod (Fig. S3, ESI†) also prove this at single-rod level. The scanning electron microscope (SEM) images recorded at different magnifications and from different angles (Fig. 1) display the overview morphology of as-synthesized Ag2S MRAs. As can be seen clearly, well-aligned arrays of closely packed Ag2S microrods were obtained. The pristine microrods possess a relatively uniform size distribution with a length of about 200 mm and the radial size of about 10 mm. In order to study the effects of the added amount
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Fig. 1 SEM images of as-obtained Ag2S MRAs: (a and b) top-view images at different magnifications; (c) cross-sectional view; (d) side-view image.
of the sulfur powder on the eventual arrangement and size distribution of Ag2S microrods, 0.005 g and 0.02 g of sulfur powder were added, respectively, instead of 0.01 g. SEM images (Fig. S4, ESI†) show that, the Ag2S MRAs derived from 0.005 g of sulfur powder were quite sparse with the rods having a length of about 100 mm and the radial size of less than 10 mm. In the case of 0.02 g of the sulfur powder addition, the average length and radial size of the rods were larger than 400 mm and about 20 mm, respectively, although the distribution of the radial size of the pristine microrods was not so uniform as in the case of 0.01 g. Fig. 2 and Fig. S6(a) (ESI†) show the SERS activity as well as recyclability of the MRA substrates toward five commonly used organic dyes, specifically, MO, MB, CV, R6G and SDI. It is obvious that for all the five types of organic dyes, most of the characteristic peaks which appear in the Raman spectra of the as-purchased dye powders get enhanced distinctly in SERS spectra compared with pristine dilute (10 6 M) solutions. The SERS effect is commonly found in molecular and ionic species absorbed on rough surfaces of metallic or semiconductor nanostructures. The molecular species are subjected to a strong localized field when the supported materials are excited by a laser at the resonance wavelength, thereby producing stronger Raman signals.14 Although the surface plasmon resonance (SPR) of Ag2S which is derived from the conduction band lies typically in the infrared band, the charge transfer resonance between Ag2S MRAs and the investigated dye molecules has made contributions to the distinct enhancement of Raman signals.15 It can be observed that some characteristic peaks in SERS spectra, for instance, the peak located near a wavenumber of 1000 cm 1 for MO in Fig. 2(a), do not have counterparts in their corresponding Raman spectra of the powder forms, and this could just be ascribed to the newly introduced strong localized electromagnetic interactions induced
4932 | Chem. Commun., 2014, 50, 4931--4933
Fig. 2 Raman spectra of as-purchased powders and corresponding 10 6 M solutions, and the SERS spectra of the 10 6 M solutions deposited on Ag2S MRA substrates of different dyes: (a) MO, (b) MB, (c) CV, (d) R6G and (e) SDI. The spectra of MB, CV and R6G were recorded under 785 nm laser excitation while MO and SDI under 633 nm excitation.
by charge transfer resonance between Ag2S MRA substrates and different dye molecules. As shown in Fig. 3, Fig. S5 and S6(b) (ESI†), the photocatalytic activity as well as recyclability of as-obtained Ag2S MRA substrates were evaluated by degradation efficiencies of the same dyes mentioned above. It is obvious that both MO and MB, as the two most widely used model molecules, were degraded almost completely after 60 min of irradiation. And for the other two dyes, CV and R6G, the time taken for complete degradation is 80 and 140 min, respectively. Notably in this work, we selected the SDI dye in addition as another model molecule. Sudan dyes, as potential carcinogens,16 have captivated much attention nowadays since the occurrence of many serious SDI-related food safety incidents. However, the photocatalytic degradation of Sudan dyes still seems to be unheeded, apart from the few studies focused mainly on Sudan IV.17 In the case of SDI degradation by photocatalysis, to the best of our knowledge, the fastest reaction was achieved by using TiO2 films co-doped with iron and nitrogen although it took 4 h to fully complete the degradation.18 Here we achieved 94.3% and 99.9% degradation rates for SDI after 140 and 160 min of the photocatalytic reaction, respectively, in the presence of the Ag2S MRA substrate. Besides, it maintained 84.7% degradation efficiency of SDI after being recycled and reused five times, which further demonstrated the recyclability as well as stability of the Ag2S MRAs as efficient photocatalytic substrates. Additionally, the band-gap data calculated from the
This journal is © The Royal Society of Chemistry 2014
View Article Online
Published on 25 March 2014. Downloaded by University of Michigan Library on 23/10/2014 03:46:54.
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chips or devices, and thus could give an answer to the increasing demand for environmental monitoring and management. This work was financially supported by the National Natural Foundation of China (No. 11274066, 51172047, 50872145 and 51102050) and the Ministry of Science and Technology of China (973 Project No. 2013CB932901 and 2009CB930803). Besides, the authors are grateful to the ‘‘Shu Guang’’ project supported by the Shanghai Municipal Education Commission and the Shanghai Education Development Foundation (09SG01).
Notes and references
Fig. 3 Time-dependent degradation efficiency of (a) MO, (b) MB, (c) CV, (d) R6G and (e) SDI in their 10 6 M solutions under different conditions.
corresponding UV-vis-NIR diffuse reflectance spectra (Fig. S7, ESI†) revealed the band-gap narrowing (BGN) phenomenon of Ag2S MRAs after experiencing photocatalytic reactions. Hence, it can be inferred that the residual degradation products served as surface impurities and consequently led to the BGN19 since it was impossible for us to completely remove them by rinsing. On the other hand, it could be regarded as an indirect proof for the fact that the dye molecules have been well absorbed on the surfaces of Ag2S MRAs. Therefore, the highly efficient photocatalytic degradation could be attributed to not only the inherent narrow band-gap (r0.9 eV) semiconductor properties of Ag2S, but also the large effective absorption areas of dye molecules derived from the close-packed rod arrays and the higher stability of materials on the micrometre scale than on the nanoscale. In conclusion, for the first time we have developed a rapid solvothermal process for the growth of well-aligned Ag2S microrod arrays within 1 h. The involved materials, including Ag foils, sulfur powder and methanol, are both easy to get and cost-effective. The as-obtained Ag2S MRA substrate subsequently demonstrated both SERS and photocatalytic activities as well as recyclability toward various organic dyes including MO, MB, CV, R6G and SDI, and it is especially inspiring that the best ever efficiency of SDI degradation was achieved by utilizing this novel substrate based on Ag2S MRAs. Considering the facile and rapid preparation as well as excellent SERS and photocatalytic performance of Ag2S MRAs, it is believed that this dual-active substrate holds great potential for various environment-related applications such as portable monitoring
This journal is © The Royal Society of Chemistry 2014
1 M. Yarema, S. Pichler, M. Sytnyk, R. Seyrkammer, R. T. Lechner, G. Fritz-Popovski, D. Jarzab, K. Szendrei, R. Resel, O. Korovyanko, M. A. Loi, O. Paris, G. Hesser and W. Heiss, ACS Nano, 2011, 5, 3758. 2 P. Jiang, Z. Q. Tian, C. N. Zhu, Z. L. Zhang and D. W. Pang, Chem. Mater., 2012, 24, 3; P. Jiang, C. N. Zhu, Z. L. Zhang, Z. Q. Tian and D. W. Pang, Biomaterials, 2012, 33, 5130. 3 Y. Zhang, Y. J. Zhang, G. S. Hong, W. He, K. Zhou, K. Yang, F. Li, G. C. Chen, Z. Liu, H. J. Dai and Q. B. Wang, Biomaterials, 2013, 34, 3639; I. Hocaoglu, M. N. Cizmeciyan, R. Erdem, C. Ozen, A. Kurt, A. Sennaroglu and H. Y. Acar, J. Mater. Chem., 2012, 22, 14674. 4 G. S. Hong, J. T. Robinson, Y. J. Zhang, S. Diao, A. L. Antaris, Q. B. Wang and H. J. Dai, Angew. Chem., Int. Ed., 2012, 51, 9818; Y. Zhang, G. S. Hong, Y. J. Zhang, G. C. Chen, F. Li, H. J. Dai and Q. B. Wang, ACS Nano, 2012, 6, 3695. 5 Y. Lei, H. M. Jia, W. W. He, Y. G. Zhang, L. W. Mi, H. W. Hou, G. S. Zhu and Z. Zheng, J. Am. Chem. Soc., 2012, 134, 17392; H. P. Shen, X. J. Jiao, D. Oron, J. B. Li and H. Lin, J. Power Sources, 2013, 240, 8; J. J. Wu, R. C. Chang, D. W. Chen and C. T. Wu, Nanoscale, 2012, 4, 1368. 6 X. M. Hou, X. L. Zhang, W. Yang, Y. Liu and X. M. Zhai, Mater. Res. Bull., 2012, 47, 2579; X. Q. Fu, T. S. Jiang, Q. Zhao and H. B. Yin, J. Raman Spectrosc., 2012, 43, 1191. 7 A. Pourahmad, Superlattices Microstruct., 2012, 52, 276. 8 P. X. Li, Z. Li, L. H. Zhang, E. Z. Shi, Y. Y. Shang, A. Y. Cao, H. B. Li, Y. Jia, J. Q. Wei, K. L. Wang, H. W. Zhu and D. H. Wu, J. Mater. Chem., 2012, 22, 24721. 9 G. M. Neelgund and A. Oki, Appl. Catal., B, 2011, 110, 99. 10 M. C. Neves, J. M. F. Nogueira, T. Trindade, M. H. Mendonca, M. I. Pereira and O. C. Monteiro, J. Photochem. Photobiol., A, 2009, 204, 168. 11 K. Nagasuna, T. Akita, M. Fujishima and H. Tada, Langmuir, 2011, 27, 7294. 12 J. H. Sun, S. Y. Dong, Y. K. Wang and S. P. Sun, J. Hazard. Mater., 2009, 172, 1520; S. Mondal, Environ. Eng. Sci., 2008, 25, 383; F. P. van der Zee and S. Villaverde, Water Res., 2005, 39, 1425; C. Hachem, F. Bocquillon, O. Zahraa and M. Bouchy, Dyes Pigm., 2001, 49, 117. 13 Y. Liu, J. J. Lin, M. M. Chen and L. Song, Food Chem. Toxicol., 2013, 58, 264; M. Lucova, J. Hojerova, S. Pazourekova and Z. Klimova, Food Chem. Toxicol., 2013, 52, 19; S. Srivastava, R. Sinha and D. Roy, Aquat. Toxicol., 2004, 66, 319. 14 S. M. Nie and S. R. Emery, Science, 1997, 275, 1102; R. C. Wang and C. H. Li, Acta Mater., 2011, 59, 822. 15 J. R. Lombardi and R. L. Birke, J. Phys. Chem. C, 2008, 112, 5605; S. K. Islam, M. Tamargo, R. Moug and J. R. Lombardi, J. Phys. Chem. C, 2013, 117, 23372; B. Liu and Z. F. Ma, Small, 2011, 7, 1587. 16 T. M. Fonovich, Drug Chem. Toxicol., 2013, 36, 343; M. Stiborova, V. Martinek, H. Rydlova, P. Hodek and E. Frei, Cancer Res., 2002, 62, 5678. 17 T. Aarthi, P. Narahari and G. Madras, J. Hazard. Mater., 2007, 149, 725; R. B. Pachwarya and R. C. Meena, Energy Sources, Part A, 2011, 33, 1651; C. M. Coates, W. Caldwell, R. S. Alberte, P. D. Barreto and J. C. Barreto, World J. Microbiol. Biotechnol., 2007, 23, 1305. 18 W. B. Liu, J. Deng, Y. B. Zhao, J. S. Xu and L. Zhou, Spectrosc. Spectral Anal., 2009, 29, 1394. 19 A. Morales-Acevedo, J. Appl. Phys., 1991, 70, 3345; S. H. Cho, E. K. Kim and S. K. Min, J. Korean Phys. Soc., 1998, 32, 584.
Chem. Commun., 2014, 50, 4931--4933 | 4933
Published on 25 March 2014. Downloaded by University of Michigan Library on 23/10/2014 03:46:54.
COMMUNICATION
View Journal | View Issue
Cite this: Chem. Commun., 2014, 50, 4931
Facile and rapid growth of Ag2S microrod arrays as efficient substrates for both SERS detection and photocatalytic degradation of organic dyes†
Received 6th January 2014, Accepted 25th March 2014
Qi Cao,a Renchao Che*a and Nan Chenb
DOI: 10.1039/c4cc00107a www.rsc.org/chemcomm
A novel bifunctional substrate derived from well-aligned Ag2S microrod arrays was obtained via a facile and cost-effective solvothermal process rapidly within 1 h. It demonstrates great activity for both SERS detection and photocatalytic degradation of organic dyes, and thus holds great potential for environmental monitoring devices and other applications.
Silver sulfide (Ag2S), as an important narrow band-gap (0.85 eV1) semiconductor, has attracted tremendous research interest for its tunable near-infrared photoluminescence2 and low toxicity3 in its nanoparticle form. In the last few years, application trials of Ag2S have been focused mainly on fabrication of near-infrared fluorescent probes4 and quantum dot solar cells.5 Meanwhile, the activity of Ag2S toward sensitive surface-enhanced Raman scattering (SERS) substrates and efficient photocatalysts for degradation of organic molecules has also been rigorously investigated very recently due to the potential requirement and practical significance for real-time monitoring and subsequently rapid degradation of persistent organic pollutants (POPs). Typically in some cases, SERS-active Ag2S nanoparticles were synthesized by using oleylamine or octadecylamine as both a solvent and a ligand, and further, the degree of charge transfer in the Ag2S–analyte systems was also studied via SERS analysis.6 For photocatalytic applications, various Ag2S-based nanostructures, for example, the Ag2S-encapsulated mesoporous MCM-41 nanoparticles,7 porous Ag2S nanoparticle membranes,8 poly(amidoamine)functionalized carbon nanotube–Ag2S quantum dot nanocomposites9 and the Ag2S–TiO2 donor–acceptor systems10,11 have been designed and fabricated, and finally shown to enhance a
Department of Materials Science, Laboratory of Advanced Materials, Fudan University, Shanghai 200438, People’s Republic of China. E-mail: [email protected] b Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089, USA † Electronic supplementary information (ESI) available: Experimental details, the XRD pattern, the EDS spectrum and element mapping profiles, TEM and HRTEM images, additional SEM images, UV-vis absorbance spectra, the recyclability evaluation part as well as the UV-vis-NIR diffuse reflectance spectra. See DOI: 10.1039/c4cc00107a
This journal is © The Royal Society of Chemistry 2014
photocatalytic activities toward water splitting11 and degradation of POPs such as phenol,10 rhodamine B,8 methyl orange9 and methylene blue.7 Here in this work, for the first time we have obtained novel Ag2S microrod arrays (MRAs) on silver foils via a facile and costeffective solvothermal method using the elemental sulfur powder as a sulfur source and methanol as a solvent. It is worth mentioning that it took as quick as 1 h for the solvothermal process to give well-aligned Ag2S MRAs. The as-obtained Ag2S MRAs consequently demonstrated appreciable SERS as well as photocatalytic activity toward various organic dyes including methyl orange (MO), methylene blue (MB), crystal violet (CV), rhodamine 6G (R6G) and Sudan I (SDI), which endow them with great potential to serve as multifunctional substrates for both detection and in situ degradation of these organic dyes. Since the dyes mentioned above are commonly and intensively utilized in textile, ink, printing and dyeing industries, the dye-containing wastewater may unfortunately result in long-term adverse effects on the aquatic environment,12 and hence would finally jeopardize the health of the people,13 it is believed that this novel Ag2S MRA-based detection and degradation substrate presented in this work would have much potential for the management of the environment as well as human health. The detailed materials and methods are provided in the ESI.† The representative X-ray diffraction (XRD) pattern (Fig. S1(a), ESI†) with all characteristic peaks matching exactly, and the energy dispersive X-ray spectrum (EDS, Fig. S1(b), ESI†), which shows that the mole ratio of Ag and S is approximately 2 : 1, both demonstrate the single and pure Ag2S component of the MRAs. Furthermore, the EDS element mapping of a single rod (Fig. S2, ESI†) and highresolution transmission electron microscope (HRTEM) images of a fragment of the rod (Fig. S3, ESI†) also prove this at single-rod level. The scanning electron microscope (SEM) images recorded at different magnifications and from different angles (Fig. 1) display the overview morphology of as-synthesized Ag2S MRAs. As can be seen clearly, well-aligned arrays of closely packed Ag2S microrods were obtained. The pristine microrods possess a relatively uniform size distribution with a length of about 200 mm and the radial size of about 10 mm. In order to study the effects of the added amount
Chem. Commun., 2014, 50, 4931--4933 | 4931
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Fig. 1 SEM images of as-obtained Ag2S MRAs: (a and b) top-view images at different magnifications; (c) cross-sectional view; (d) side-view image.
of the sulfur powder on the eventual arrangement and size distribution of Ag2S microrods, 0.005 g and 0.02 g of sulfur powder were added, respectively, instead of 0.01 g. SEM images (Fig. S4, ESI†) show that, the Ag2S MRAs derived from 0.005 g of sulfur powder were quite sparse with the rods having a length of about 100 mm and the radial size of less than 10 mm. In the case of 0.02 g of the sulfur powder addition, the average length and radial size of the rods were larger than 400 mm and about 20 mm, respectively, although the distribution of the radial size of the pristine microrods was not so uniform as in the case of 0.01 g. Fig. 2 and Fig. S6(a) (ESI†) show the SERS activity as well as recyclability of the MRA substrates toward five commonly used organic dyes, specifically, MO, MB, CV, R6G and SDI. It is obvious that for all the five types of organic dyes, most of the characteristic peaks which appear in the Raman spectra of the as-purchased dye powders get enhanced distinctly in SERS spectra compared with pristine dilute (10 6 M) solutions. The SERS effect is commonly found in molecular and ionic species absorbed on rough surfaces of metallic or semiconductor nanostructures. The molecular species are subjected to a strong localized field when the supported materials are excited by a laser at the resonance wavelength, thereby producing stronger Raman signals.14 Although the surface plasmon resonance (SPR) of Ag2S which is derived from the conduction band lies typically in the infrared band, the charge transfer resonance between Ag2S MRAs and the investigated dye molecules has made contributions to the distinct enhancement of Raman signals.15 It can be observed that some characteristic peaks in SERS spectra, for instance, the peak located near a wavenumber of 1000 cm 1 for MO in Fig. 2(a), do not have counterparts in their corresponding Raman spectra of the powder forms, and this could just be ascribed to the newly introduced strong localized electromagnetic interactions induced
4932 | Chem. Commun., 2014, 50, 4931--4933
Fig. 2 Raman spectra of as-purchased powders and corresponding 10 6 M solutions, and the SERS spectra of the 10 6 M solutions deposited on Ag2S MRA substrates of different dyes: (a) MO, (b) MB, (c) CV, (d) R6G and (e) SDI. The spectra of MB, CV and R6G were recorded under 785 nm laser excitation while MO and SDI under 633 nm excitation.
by charge transfer resonance between Ag2S MRA substrates and different dye molecules. As shown in Fig. 3, Fig. S5 and S6(b) (ESI†), the photocatalytic activity as well as recyclability of as-obtained Ag2S MRA substrates were evaluated by degradation efficiencies of the same dyes mentioned above. It is obvious that both MO and MB, as the two most widely used model molecules, were degraded almost completely after 60 min of irradiation. And for the other two dyes, CV and R6G, the time taken for complete degradation is 80 and 140 min, respectively. Notably in this work, we selected the SDI dye in addition as another model molecule. Sudan dyes, as potential carcinogens,16 have captivated much attention nowadays since the occurrence of many serious SDI-related food safety incidents. However, the photocatalytic degradation of Sudan dyes still seems to be unheeded, apart from the few studies focused mainly on Sudan IV.17 In the case of SDI degradation by photocatalysis, to the best of our knowledge, the fastest reaction was achieved by using TiO2 films co-doped with iron and nitrogen although it took 4 h to fully complete the degradation.18 Here we achieved 94.3% and 99.9% degradation rates for SDI after 140 and 160 min of the photocatalytic reaction, respectively, in the presence of the Ag2S MRA substrate. Besides, it maintained 84.7% degradation efficiency of SDI after being recycled and reused five times, which further demonstrated the recyclability as well as stability of the Ag2S MRAs as efficient photocatalytic substrates. Additionally, the band-gap data calculated from the
This journal is © The Royal Society of Chemistry 2014
View Article Online
Published on 25 March 2014. Downloaded by University of Michigan Library on 23/10/2014 03:46:54.
ChemComm
Communication
chips or devices, and thus could give an answer to the increasing demand for environmental monitoring and management. This work was financially supported by the National Natural Foundation of China (No. 11274066, 51172047, 50872145 and 51102050) and the Ministry of Science and Technology of China (973 Project No. 2013CB932901 and 2009CB930803). Besides, the authors are grateful to the ‘‘Shu Guang’’ project supported by the Shanghai Municipal Education Commission and the Shanghai Education Development Foundation (09SG01).
Notes and references
Fig. 3 Time-dependent degradation efficiency of (a) MO, (b) MB, (c) CV, (d) R6G and (e) SDI in their 10 6 M solutions under different conditions.
corresponding UV-vis-NIR diffuse reflectance spectra (Fig. S7, ESI†) revealed the band-gap narrowing (BGN) phenomenon of Ag2S MRAs after experiencing photocatalytic reactions. Hence, it can be inferred that the residual degradation products served as surface impurities and consequently led to the BGN19 since it was impossible for us to completely remove them by rinsing. On the other hand, it could be regarded as an indirect proof for the fact that the dye molecules have been well absorbed on the surfaces of Ag2S MRAs. Therefore, the highly efficient photocatalytic degradation could be attributed to not only the inherent narrow band-gap (r0.9 eV) semiconductor properties of Ag2S, but also the large effective absorption areas of dye molecules derived from the close-packed rod arrays and the higher stability of materials on the micrometre scale than on the nanoscale. In conclusion, for the first time we have developed a rapid solvothermal process for the growth of well-aligned Ag2S microrod arrays within 1 h. The involved materials, including Ag foils, sulfur powder and methanol, are both easy to get and cost-effective. The as-obtained Ag2S MRA substrate subsequently demonstrated both SERS and photocatalytic activities as well as recyclability toward various organic dyes including MO, MB, CV, R6G and SDI, and it is especially inspiring that the best ever efficiency of SDI degradation was achieved by utilizing this novel substrate based on Ag2S MRAs. Considering the facile and rapid preparation as well as excellent SERS and photocatalytic performance of Ag2S MRAs, it is believed that this dual-active substrate holds great potential for various environment-related applications such as portable monitoring
This journal is © The Royal Society of Chemistry 2014
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