DOI: 10.1002/chem.201406022
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Recycling Nanowire Templates for Multiplex Templating Synthesis: A Green and Sustainable Strategy Jin-Long Wang,[a] Jian-Wei Liu,[a] Bing-Zhang Lu,[a] Yi-Ruo Lu,[a] Jin Ge,[a] Zhen-Yu Wu,[a] ZhiHua Wang,[a] Muhammad Nadeem Arshad,[c] and Shu-Hong Yu*[a, b] templates are always used only one time and wasted after the reactions.[2, 3a,b] From economical and environmental viewpoints, it is highly important to develop a green process for templating synthesis, especially for large-scale templating synthesis for future industrialized production. However, to date, little attention has been paid to the recycling and reproducing of such sacrificial but valuable templates after the chemical reaction. Ultrathin tellurium nanowires (Te NWs) with high aspect ratios have been widely studied[4] and have great potential for fabrication of nanodevices.[5] As a versatile and reactive template, Te NWs can be used as either a chemical transforming template or a physical template to synthesize a family of tellurium-based nanostructures and other 1D nanostructures.[6] For example, a series of metal telluride nanowires (MxTe, M = Ag, Pb, Cd, Bi, Zn, Cu, etc.) and noble metal nanowires such as Pt, Pd, AuPtPd nanowires can be easily synthesized by using Te NWs as the chemical transforming template.[7] In addition, Te NWs can be used as a physical template to fabricate carbon nanofibers (CNFs) with various functionalities.[3a, 8] These metal telluride nanowires and CNFs have widespread applications in diverse fields. However, tellurium nanowire precursor is generally wasted after the templating synthesis, which commonly exists in a form of tellurite in solution.[7f, 9] To date, how to deal with the byproducts of the templating reactions especially for the sacrificial template reactions has been largely ignored. Generally, the most effective way to deal with the byproducts of chemical reactions is to recycle them back to useful products. Herein, we report a new concept on recycling ultrathin tellurium nanowire templates that can be repeatedly used as template to synthesize other 1D nanostructures, such as CNFs, Pt/ Pd@CNFs, Pt nanotubes/nanoparticles composites (NTs@NPs) and Pd NWs. After template synthesis, high-quality Te NWs can be reproduced from the collected solution by adjusting the reaction conditions such as pH and the concentration of the solution. The recycle efficiency is more than 80 % relative to the pristine Te NWs used as template to synthesize Pd NWs, CNFs, 65 % for Pt NTs@NPs and more than 70 % for Pt@CNFs, Pd@CNFs systems in the first recycling process. We anticipate this template recycle strategy will largely decrease the cost of the products derived from tellurium and at the same time avoid contamination of the environment. The recycling procedure for the pristine Te NWs used as template for synthesis of various 1D functional nanomaterials is illustrated in Figure 1 and the typical reactions can be formulated as follows:
Abstract: Template-directed synthesis of nanostructures has been emerging as one of the most important synthetic methodologies. A pristine nanotemplate is usually chemically transformed into other compounds and sacrificed after templating or only acts as an inert physical template to support the new components. If a nanotemplate is costly or toxic as waste, to recycle such a nanotemplate becomes highly desirable. Recently, ultrathin tellurium nanowires (TeNWs) have been demonstrated as versatile chemical or physical templates for the synthesis of a diverse family of uniform 1D nanostructures. However, ultrathin TeNWs as template are usually costly and are discarded as toxic waste in ionic species after chemical reactions or erosion. To solve the above problem, we conceptually demonstrate that such a nanotemplate can be economically recycled from waste solutions and repeatedly used as template.
One dimensional (1D) nanostructures with fascinating properties derived from unique geometric characteristics have been widely studied in electronic, optoelectronic, sensors, and electromechanical fields.[1] Various strategies, including both physical and chemical methods, have been developed to fabricate uniform 1D nanomaterials.[2] Template-directed synthesis, among the various methods, has been one of the most straightforward routes to 1D nanostructure because of its simple, high-throughput procedure and variability in controlling structure and chemical composition of the products.[3] The [a] J.-L. Wang,+ Dr. J.-W. Liu,+ B.-Z. Lu, Y.-R. Lu, J. Ge, Z.-Y. Wu, Z.-H. Wang, Prof. Dr. S.-H. Yu Division of Nanomaterials and Chemistry Hefei National Laboratory for Physical Sciences at Microscale Collaborative Innovation Center of Suzhou Nano Science and Technology Department of Chemistry, University of Science and Technology of China Hefei, Anhui 230026 (P.R. China) E-mail: [email protected] [b] Prof. Dr. S.-H. Yu Institute of Solid State Physics, Hefei Institutes of Physical Science Chinese Academy of Sciences, Hefei 230031 (China) [c] Dr. M. N. Arshad Center of Excellence for Advanced Materials Research Chemistry Department, Faculty of Science King Abdulaziz University, Jeddah 21589 (Saudi Arabia) [+] These authors contributed equally to this work. Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201406022. Chem. Eur. J. 2015, 21, 1 – 6
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Communication in an acid solution with O2 as oxidizing agent, thus pure CNFs were obtained (Supporting Information Figure S1 b). As promising chemical templates, ultrathin Te nanowires are very active and can be easily transformed to telluride materials and 1D noble metal nanomaterials.[6b,c] It has been reported that free-standing Pt NWs membrane fabricated by the multiplex templating route show long-time stability and high specific activity for oxygen reduction reaction (ORR).[13] Te@CNFs with diameter of 30–50 nm (Supporting Information Figure S1 c), in which the Te NWs in the core still have high chemical activity,[14] were first synthesized, then the Te NWs were chemically transformed to the Pt NWs as shown in Figure 1 b. Figure 2 c shows the TEM image of the Pt@CNFs synthesized by a modified method reported before.[13] The XRD pattern in Figure S1d shows that the Pt NWs membrane was of good crystallinity after calcination at 400 8C and was believed to be a good candidate for long-time stable electrocatalyst. As a general method, the Pd@CNFs were also synthesized from the Te@CNFs as shown in Figure 2 d, and the XRD pattern indicates the good crystallinity after calcination at 400 8C (Supporting Information Figure S1 e). Ultrathin noble metal (Pt, Pd) nanowires with large surface area have been intensely studied.[7g, 15] Figure 2 e and f show typical TEM images of the Pd NWs and Pt NTs@NPs synthesized by using pristine Te NWs as template. In this study, we successfully recycled the tellurite from the waste reaction solution to reproduce Te NWs by hydrothermal process.[11] As a promising physical template for synthesis of CNFs, Te NWs were latterly etched out by O2 and transformed to tellurite. Similar to the physical template, the pristine Te NWs were also transformed to tellurite in the chemical templating process oxidized by chloroplatinic acid or palladium chloride. Figure 2 g shows a typical TEM image of the reproduced Te NWs and the X-ray diffraction (XRD) patterns (Supporting Information Figure S2 a) of the pristine and reproduced Te NWs are both in good agreement with the standard literature data (JCPDF card number: 36-1452). The high-resolution TEM (HRTEM) image (Figure S2 b) also indicated the high quality of the reproduced Te NWs. The recycling rate of the different systems for templating synthesis is shown in Figure 2 h, characterized by the inductively coupled plasma mass spectrometry (ICP). Compared with the pristine Te NWs (~ 5.21 mg mL1, 100 %), the relative contents of the reproduced Te NWs were about 81, 76, 71, 82 and 65 % from CNFs, Pt@CNFs, Pd@CNFs, Pd NWs and Pt NTs@NPs, respectively. The UV/Vis spectrum in Figure S3 also demonstrates the relative productivity of recycled Te NWs for the different systems. The yield of Te NWs obtained from the Pt NTs@NPs solution (65 %) was much lower than the other systems, which might be attributed to Pt NTs@NPs absorbing some tellurite, resulting in the low concentration of tellurite in the recycling solution. The XRD patterns in Figure S4 a show that there are a few impurity peaks for the Pt NTs@NPs washed one time compared with those washed three times with alkaline water, which is different from that of the Pd NWs (Supporting Information Figure S4 b); even after several washing steps some telluride still existed that could not be detected by XRD since it was too little compared to the Pt component. By characterization with ICP (Supporting Infor-
Figure 1. Schematic illustration of template synthesis and recycling of Te NWs template. a) Physical template for Te@CNFs synthesis. b) Chemical template for Pt/Pd@CNFs synthesis. c) Chemical template for Pd NWs and Pt NTs@NPs synthesis. d) Reproducing Te NWs using the collected TeO32. O
2 TeðNWsÞ þ glucose ! Te@CNFs ! CNFs þ TeO2 3
H O
2 2 Te@CNFs þ PtCl2 6 =PdCl2 ! Pt=Pd@CNFs þ TeO3
ð1Þ ð2Þ
EtOH
2 TeðNWsÞ þ PdCl2 =PtCl2 6 ! PdðNWsÞ=PtðNTs@NPsÞ þ TeO3
ð3Þ 180 C;3 h
TeO2 3 þ NH3 H2 O þ N2 H4 H2 O ! ! TeðNWsÞ
ð4Þ
Te@CNFs were synthesized by a modified hydrothermal method described previously.[10] In this process, the pristine Te NWs (Figure 2 a and Supporting Information Figure S1 a) synthesized by hydrothermal process[11] with a diameter of 7 nm and length of hundreds of micrometers survived in the products as shown in Figure 2 b. However, CNFs in most cases first undergo a calcination process before further application,[12] during which the Te NWs as core of the nanfibers sublimate to toxic gas into the environment. So, the Te NWs as core of CNFs should be first etched out before calcination by slowly stirring
Figure 2. Various products synthesized using Te NWs as template. a) Pristine Te NWs; b) Te@CNFs; c) Pt@CNFs; d) Pd@CNFs; e) Pd NWs; f) Pt NTs@NPs; g) reproduced Te NWs; h) recycle ratios of reproduced Te NWs compared with pristine Te (A: pristine Te; B: CNFs; C: Pt@CNFs; D: Pd@CNFs; E: Pd NWs; F: Pt NTs@NPs).
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Communication was mainly caused by the small length change of Te NWs which may also appear for pristine Te NWs of different batches.[16] The loss in yield (about 20–30 %) during each recycle process was mainly caused by the separation and washing steps as some tellurite may be washed away with unreacted PdCl2 in ethanol. It might be a constant value that does not change at different scale experiments; this would mean that if the experiment can be scaled up, the recycling ratio would increase as the amount of loss in each recycling process is constant.
mation Table S1), the tellurium element was verified to actually exist after washing three times. For further evaluation of the quality of the reproduced Te NWs after templating synthesis, Te@CNFs with different diameters, Pd NWs and Pt NTs@NPs, as shown in Figure 3 a–d, were synthesized using the reproduced Te NWs as template after some adjustment of the dose of the raw materials according to the concentration of the reproduced Te NWs. CdTe and Ag2Te NWs were also synthesized using the reproduced Te NWs as template, which were recycled from the Te@CNFs system. Figure 3 e and f show the typical TEM images of the CdTe and Ag2Te NWs. The XRD patterns in Figure S5 in the Supporting Information show that the CdTe and Ag2Te are consistent with the standard literature values (JCPDS No. 89-3053) and (JCPDF card: 34-0124). These results demonstrate that irrespective of the small loss during the recycling process, the recovered Te NWs have both good physical and chemical activity for further templating synthesis, underlining that the tellurite as waste in solution can be recovered.
Figure 4. Three recycles for the system of Pd NWs using one pot Te NWs. a, b) TEM images of Te NWs and Pd NWs for the second recycling process. c, d) TEM images of Te NWs and Pd NWs for the third recycling process; e) recycle ratio of three recycles; f) UV/Vis spectra of the Te NWs for the three recycling processes (A: pristine Te NWs; B: 1st recycle; C: 2nd recycle; D: 3rd recycle).
In summary, we demonstrate that a versatile and valuable pristine nanotemplate can be economically recycled from waste solutions and can be repeatedly used as template for multiplex templating synthesis. With ultrathin TeNWs as example, such valuable nanowire template can be recycled from waste solution after different templating processes. The recycled nanowires with considerable yield are of high quality and can be reused as physical or chemical templates for further synthesis of other uniform 1D nanostructures. The present work sheds light on the possibility of recycling valuable but toxic species from residual reaction media after templating synthesis and reaction, which will pave new avenues for optimizing the templating synthetic techniques, and produce functional nanostructures in a more economically and environmentally friendly manner in the future.
Figure 3. TEM images of products synthesized using reproduced Te NWs as templates. a) Te@CNFs (180 nm); b) Te@CNFs (40 nm); c) Pd NWs; d) Pt NTs@NPs; e) CdTe NWs; f) Ag2Te NWs.
Further recycling of one-pot Te NWs for the synthesis of Pd NWs without external addition of tellurite were carried out to investigate the quality of the reproduced Te NWs. Before each recycling experiment, we first made clear the content of tellurium in the collection solution by ICP, then made sure that the raw materials are in the proper proportion in the hydrothermal process. Compared with the first recycling (Figure 2 e and g), the Te NWs produced with the second recycling had good morphology with a recycle ratio of about 52.9 % (Figure 4 a), from which the Pd NWs reproduced (Figure 4 b) were still of good quality. However, for the third recycling, the Te NWs became non-uniform in diameter (Figure 4 c) and so the reproduced Pd NWs (Figure 4 d). This phenomenon became obvious as shown in Figure S6 in the Supporting Information. The recycling ratio for the reproduced Te NWs in three recycles were about 81.2, 52.1 and 22.3 %, respectively, relative to the pristine Te NWs characterized by ICP (Figure 4 e). The UV/Vis spectra of each recycle (Figure 4 f) also indicates the good dispersion and morphology of Te NWs with the two typical absorption peaks located at approximately 260 nm and 630 nm. The peak centered at around 630 nm shifted slightly after recycling; this Chem. Eur. J. 2015, 21, 1 – 6
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Experimental Section All chemicals used were of analytical grade and were used as received without further purification.
Synthesis of pristine Te NWs[10] In a typical synthesis, 0.0922 g Na2TeO3 and 1 g polyvinylpyrrolidone (PVP, MW 40 000) were added into a 50 mL Teflon container. Then 33 mL pure water (R = 18.2 MW) was added. Under vigorous magnetic stirring for several minutes a homogeneous solution was formed. Next, 3.35 mL aqueous ammonia (85 %, w/w %) and 1.65 mL hydrazine hydrate (28 %, w/w %) were put into the container separately. The container was closed and coated by stainless
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After that, the synthesis of the Te NWs was the same as with the process of recycling Te NWs from the CNFs system.
Recycling Te NWs from the Pt/Pd@CNFs nanocables system Synthesis of Te@CNFs[11]
In a typical process, the solution was centrifuged to collect the Pt/ Pd@CNFs noncable and the unreacted H2PtCl6 or PdCl2 was washed away. After that, the synthesis of the Te NWs was the same as with the process of recycling Te NWs from the CNFs system.
Synthesis of Te@CNFs with diameter of 180 nm: Typically, 40 mL of the prepared Te NWs was centrifuged with acetone as sinking agent at 3740 g and washed by water for several times, then the washed Te NWs was dispersed into 320 mL glucose solution (20 g glucose) with vigorous stirring for 15 min. After that, the mixed solution was undergone hydrothermal treatment at 180 8C for 24 h.
Acknowledgements
Synthesis of Te@CNFs with diameter of 40 nm: Typically, 80 mL of the prepared Te NWs was centrifuged with acetone as sinking agent at 3740 g and washed by water for several times, then the washed Te NWs was dispersed into 400 mL glucose solution (8 g glucose) with vigorous stirring for 15 min. After that, such a mixed solution was undergone hydrothermal treatment at 160 8C for 24 h.
We acknowledge funding from the National Basic Research Program of China (Grants 2014CB931800, 2013CB933900), the National Natural Science Foundation of China (Grants 21401183, 91227103, 21431006, 91022032), and Scientific Research Grant of Hefei Science Center of CAS (2015SRGHSC038). This work was funded by the Deanship of Scientific Research (DSR), King Abdulaziz University, under grant No. 89130-35-HiCi.
Synthesis of Pt NTs@NPs/Pd NWs[7f] In a typical experiment, 40 mL of Te NWs was washed with ethanol several times. Then the Te NWs were dissolved in 60 mL ethanol in a conical flask with vigorous stirring at room temperature for 10 min, and 6 mL of H2PtCl6 (77 mm) in ethanol/140 mg PdCl2 was added. The solution was put in an Innova 40 Benchtop Incubator Shaker and reacted at 260 rpm and 50 8C for 13 h.
Keywords: functional nanomaterials · recycling · materials science · tellurium · templating synthesis [1] a) H. Yan, H. S. Choe, S. Nam, Y. Hu, S. Das, J. F. Klemic, J. C. Ellenbogen, C. M. Lieber, Nature 2011, 470, 240 – 244; b) S. Ju, A. Facchetti, Y. Xuan, J. Liu, F. Ishikawa, P. Ye, C. Zhou, T. J. Marks, D. B. Janes, Nat. Nanotechnol. 2007, 2, 378 – 384; c) M. H. Huang, S. Mao, H. Feick, H. Yan, Y. Wu, H. Kind, E. Weber, R. Russo, P. Yang, Science 2001, 292, 1897 – 1899; d) M. Law, L. E. Greene, J. C. Johnson, R. Saykally, P. Yang, Nat. Mater. 2005, 4, 455 – 459; e) Y. Cui, Q. Wei, H. Park, C. M. Lieber, Science 2001, 293, 1289 – 1292; f) Z. L. Wang, J. Song, Science 2006, 312, 242 – 246. [2] Y. Xia, P. Yang, Y. Sun, Y. Wu, B. Mayers, B. Gates, Y. Yin, F. Kim, H. Yan, Adv. Mater. 2003, 15, 353 – 389. [3] a) H. W. Liang, J. W. Liu, H. S. Qian, S. H. Yu, Acc. Chem. Res. 2013, 46, 1450 – 1461; b) H. W. Liang, S. Liu, S. H. Yu, Adv. Mater. 2010, 22, 3925 – 3937; c) B. Mayers, X. Jiang, D. Sunderland, B. Cattle, Y. Xia, J. Am. Chem. Soc. 2003, 125, 13364 – 13365. [4] a) U. K. Gautam, C. N. R. Rao, J. Mater. Chem. 2004, 14, 2530; b) Z. Liu, Z. Hu, Q. Xie, B. Yang, J. Wu, Y. Qian, J. Mater. Chem. 2003, 13, 159 – 162; c) B. Mayers, Y. Xia, J. Mater. Chem. 2002, 12, 1875 – 1881; d) Y. J. Zhu, W. W. Wang, R. J. Qi, X. L. Hu, Angew. Chem. Int. Ed. 2004, 43, 1410 – 1414; Angew. Chem. 2004, 116, 1434 – 1438; e) Q. Lu, F. Gao, S. Komarneni, Adv. Mater. 2004, 16, 1629 – 1632. [5] a) J. Yuan, H. Schmalz, Y. Xu, N. Miyajima, M. Drechsler, M. W. Mçller, F. Schacher, A. H. E. Mller, Adv. Mater. 2008, 20, 947 – 952; b) T. I. Lee, S. Lee, E. Lee, S. Sohn, Y. Lee, S. Lee, G. Moon, D. Kim, Y. S. Kim, J. M. Myoung, Z. L. Wang, Adv. Mater. 2013, 25, 2920 – 2925; c) J. W. Liu, J. H. Zhu, C. L. Zhang, H. W. Liang, S. H. Yu, J. Am. Chem. Soc. 2010, 132, 8945 – 8952; d) Y. Wang, Z. Tang, P. Podsiadlo, Y. Elkasabi, J. Lahann, N. A. Kotov, Adv. Mater. 2006, 18, 518 – 522. [6] a) B. Zhang, W. Y. Hou, X. C. Ye, S. Q. Fu, Y. Xie, Adv. Funct. Mater. 2007, 17, 486 – 492; b) J. W. Liu, F. Chen, M. Zhang, H. Qi, C. L. Zhang, S. H. Yu, Langmuir 2010, 26, 11372 – 11377; c) W. J. Lan, S. H. Yu, H. S. Qian, Y. Wan, Langmuir 2007, 23, 3409 – 3417. [7] a) J.-W. Liu, J. Xu, H.-W. Liang, K. Wang, S.-H. Yu, Angew. Chem. Int. Ed. 2012, 51, 7420 – 7425; Angew. Chem. 2012, 124, 7538 – 7543; b) G. D. Moon, S. Ko, Y. Xia, U. Jeong, ACS Nano 2010, 4, 2307 – 2319; c) K. Wang, H. W. Liang, W. T. Yao, S. H. Yu, J. Mater. Chem. 2011, 21, 15057 – 15062; d) H. W. Liang, S. Liu, Q. S. Wu, S. H. Yu, Inorg. Chem. 2009, 48, 4927 – 4933; e) H. Fan, Y. G. Zhang, M. F. Zhang, X. Y. Wang, Y. T. Qian, Cryst. Growth Des. 2008, 8, 2838 – 2841; f) H. W. Liang, S. Liu, J. Y. Gong, S. B. Wang, L. Wang, S. H. Yu, Adv. Mater. 2009, 21, 1850 – 1854; g) C. Zhu, S. Guo, S. Dong, J. Mater. Chem. 2012, 22, 14851 – 14855; h) H. Yu, P. C. Gibbons, W. E. Buhro, J. Mater. Chem. 2004, 14, 595.
Synthesis of Pt/Pd@C nanocables[13] Typically, one half of the above-purified CNFs products (diameter 30–40 nm) were dispersed in 100 mL of double deionized water with vigorous magnetic stirring. Then 6 mL H2PtCl6 (77 mm) in ethanol or 140 mg PdCl2 was added to the solution. The mixed solution was shaken at a rotation rate of 260 rpm using an Innova 40 Benchtop Incubator Shaker for 12 h at 40 8C.
Recycling Te NWs from the CNFs system First, the CNFs synthesized above were dispersed with 60–80 mL pure water and O2 was bubbled into the solution for about 20 h. After that, the solution was centrifuged to collect the CNFs and the supernatant. Then the product was washed with NaOH solution and the supernatant was collected and put into a flask and rotary evaporated at 70 8C until the solution was about 30 mL or less. Next, the filtrate concentrate was put into a 50 mL Teflon autoclave with 1 g PVP added. After vigorous stirring to form a homogeneous solution, the pH of the solution was adjusted to 9 with HCl and NaOH solution. Then 3.35 mL aqueous ammonia (85 %, w/w %) and 1.65 mL hydrazine hydrate (28 %, w/w %) were put in the container separately. The container was maintained at 180 8C for 3 h. After that, the autoclave was allowed to cool to room temperature.
Recycling Te NWs from the Pd NWs and Pt NTs@NPs reaction systems In a typical process, the product was first centrifuged for 10 min at a speed of 6640 g and washed with ethanol until it was colorless. Then, about 60 mL of pure water was added to disperse the solid, and 0.3–0.5 mL of 2 m NaOH solution was added to adjust the pH to about 10. After that, the solution was centrifuged again to obtain most of the Pd products and the supernate was collected.
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Received: November 8, 2014 Published online on && &&, 0000
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COMMUNICATION & Materials Science
Recyclable nanotemplates: A versatile nanotemplate, so-called ultrathin Te nanowires, can be economically recycled from waste solutions after templating synthesis either as chemical templates or physical templates (see figure). The reproduced tellurium nanowires can be repeatedly used as template for multiplex templating synthesis.
J.-L. Wang, J.-W. Liu, B.-Z. Lu, Y.-R. Lu, J. Ge, Z.-Y. Wu, Z.-H. Wang, M. N. Arshad, S.-H. Yu* && – && Recycling Nanowire Templates for Multiplex Templating Synthesis: A Green and Sustainable Strategy
A versatile and valuable pristine……nanowire template can be economically recycled from waste solutions and can be repeatedly used as template for multiplex templating synthesis; this has been demonstrated conceptually by S.-H. Yu et al. on page && ff. The present work sheds light on the possibility of recycling valuable but toxic species from residual reaction media after templating synthesis and reaction. This will pave new avenues to optimize templating synthetic techniques and produce functional nanostructures in a more economically and environmentally friendly manner in the future.
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Communication
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Recycling Nanowire Templates for Multiplex Templating Synthesis: A Green and Sustainable Strategy Jin-Long Wang,[a] Jian-Wei Liu,[a] Bing-Zhang Lu,[a] Yi-Ruo Lu,[a] Jin Ge,[a] Zhen-Yu Wu,[a] ZhiHua Wang,[a] Muhammad Nadeem Arshad,[c] and Shu-Hong Yu*[a, b] templates are always used only one time and wasted after the reactions.[2, 3a,b] From economical and environmental viewpoints, it is highly important to develop a green process for templating synthesis, especially for large-scale templating synthesis for future industrialized production. However, to date, little attention has been paid to the recycling and reproducing of such sacrificial but valuable templates after the chemical reaction. Ultrathin tellurium nanowires (Te NWs) with high aspect ratios have been widely studied[4] and have great potential for fabrication of nanodevices.[5] As a versatile and reactive template, Te NWs can be used as either a chemical transforming template or a physical template to synthesize a family of tellurium-based nanostructures and other 1D nanostructures.[6] For example, a series of metal telluride nanowires (MxTe, M = Ag, Pb, Cd, Bi, Zn, Cu, etc.) and noble metal nanowires such as Pt, Pd, AuPtPd nanowires can be easily synthesized by using Te NWs as the chemical transforming template.[7] In addition, Te NWs can be used as a physical template to fabricate carbon nanofibers (CNFs) with various functionalities.[3a, 8] These metal telluride nanowires and CNFs have widespread applications in diverse fields. However, tellurium nanowire precursor is generally wasted after the templating synthesis, which commonly exists in a form of tellurite in solution.[7f, 9] To date, how to deal with the byproducts of the templating reactions especially for the sacrificial template reactions has been largely ignored. Generally, the most effective way to deal with the byproducts of chemical reactions is to recycle them back to useful products. Herein, we report a new concept on recycling ultrathin tellurium nanowire templates that can be repeatedly used as template to synthesize other 1D nanostructures, such as CNFs, Pt/ Pd@CNFs, Pt nanotubes/nanoparticles composites (NTs@NPs) and Pd NWs. After template synthesis, high-quality Te NWs can be reproduced from the collected solution by adjusting the reaction conditions such as pH and the concentration of the solution. The recycle efficiency is more than 80 % relative to the pristine Te NWs used as template to synthesize Pd NWs, CNFs, 65 % for Pt NTs@NPs and more than 70 % for Pt@CNFs, Pd@CNFs systems in the first recycling process. We anticipate this template recycle strategy will largely decrease the cost of the products derived from tellurium and at the same time avoid contamination of the environment. The recycling procedure for the pristine Te NWs used as template for synthesis of various 1D functional nanomaterials is illustrated in Figure 1 and the typical reactions can be formulated as follows:
Abstract: Template-directed synthesis of nanostructures has been emerging as one of the most important synthetic methodologies. A pristine nanotemplate is usually chemically transformed into other compounds and sacrificed after templating or only acts as an inert physical template to support the new components. If a nanotemplate is costly or toxic as waste, to recycle such a nanotemplate becomes highly desirable. Recently, ultrathin tellurium nanowires (TeNWs) have been demonstrated as versatile chemical or physical templates for the synthesis of a diverse family of uniform 1D nanostructures. However, ultrathin TeNWs as template are usually costly and are discarded as toxic waste in ionic species after chemical reactions or erosion. To solve the above problem, we conceptually demonstrate that such a nanotemplate can be economically recycled from waste solutions and repeatedly used as template.
One dimensional (1D) nanostructures with fascinating properties derived from unique geometric characteristics have been widely studied in electronic, optoelectronic, sensors, and electromechanical fields.[1] Various strategies, including both physical and chemical methods, have been developed to fabricate uniform 1D nanomaterials.[2] Template-directed synthesis, among the various methods, has been one of the most straightforward routes to 1D nanostructure because of its simple, high-throughput procedure and variability in controlling structure and chemical composition of the products.[3] The [a] J.-L. Wang,+ Dr. J.-W. Liu,+ B.-Z. Lu, Y.-R. Lu, J. Ge, Z.-Y. Wu, Z.-H. Wang, Prof. Dr. S.-H. Yu Division of Nanomaterials and Chemistry Hefei National Laboratory for Physical Sciences at Microscale Collaborative Innovation Center of Suzhou Nano Science and Technology Department of Chemistry, University of Science and Technology of China Hefei, Anhui 230026 (P.R. China) E-mail: [email protected] [b] Prof. Dr. S.-H. Yu Institute of Solid State Physics, Hefei Institutes of Physical Science Chinese Academy of Sciences, Hefei 230031 (China) [c] Dr. M. N. Arshad Center of Excellence for Advanced Materials Research Chemistry Department, Faculty of Science King Abdulaziz University, Jeddah 21589 (Saudi Arabia) [+] These authors contributed equally to this work. Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201406022. Chem. Eur. J. 2015, 21, 1 – 6
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Communication in an acid solution with O2 as oxidizing agent, thus pure CNFs were obtained (Supporting Information Figure S1 b). As promising chemical templates, ultrathin Te nanowires are very active and can be easily transformed to telluride materials and 1D noble metal nanomaterials.[6b,c] It has been reported that free-standing Pt NWs membrane fabricated by the multiplex templating route show long-time stability and high specific activity for oxygen reduction reaction (ORR).[13] Te@CNFs with diameter of 30–50 nm (Supporting Information Figure S1 c), in which the Te NWs in the core still have high chemical activity,[14] were first synthesized, then the Te NWs were chemically transformed to the Pt NWs as shown in Figure 1 b. Figure 2 c shows the TEM image of the Pt@CNFs synthesized by a modified method reported before.[13] The XRD pattern in Figure S1d shows that the Pt NWs membrane was of good crystallinity after calcination at 400 8C and was believed to be a good candidate for long-time stable electrocatalyst. As a general method, the Pd@CNFs were also synthesized from the Te@CNFs as shown in Figure 2 d, and the XRD pattern indicates the good crystallinity after calcination at 400 8C (Supporting Information Figure S1 e). Ultrathin noble metal (Pt, Pd) nanowires with large surface area have been intensely studied.[7g, 15] Figure 2 e and f show typical TEM images of the Pd NWs and Pt NTs@NPs synthesized by using pristine Te NWs as template. In this study, we successfully recycled the tellurite from the waste reaction solution to reproduce Te NWs by hydrothermal process.[11] As a promising physical template for synthesis of CNFs, Te NWs were latterly etched out by O2 and transformed to tellurite. Similar to the physical template, the pristine Te NWs were also transformed to tellurite in the chemical templating process oxidized by chloroplatinic acid or palladium chloride. Figure 2 g shows a typical TEM image of the reproduced Te NWs and the X-ray diffraction (XRD) patterns (Supporting Information Figure S2 a) of the pristine and reproduced Te NWs are both in good agreement with the standard literature data (JCPDF card number: 36-1452). The high-resolution TEM (HRTEM) image (Figure S2 b) also indicated the high quality of the reproduced Te NWs. The recycling rate of the different systems for templating synthesis is shown in Figure 2 h, characterized by the inductively coupled plasma mass spectrometry (ICP). Compared with the pristine Te NWs (~ 5.21 mg mL1, 100 %), the relative contents of the reproduced Te NWs were about 81, 76, 71, 82 and 65 % from CNFs, Pt@CNFs, Pd@CNFs, Pd NWs and Pt NTs@NPs, respectively. The UV/Vis spectrum in Figure S3 also demonstrates the relative productivity of recycled Te NWs for the different systems. The yield of Te NWs obtained from the Pt NTs@NPs solution (65 %) was much lower than the other systems, which might be attributed to Pt NTs@NPs absorbing some tellurite, resulting in the low concentration of tellurite in the recycling solution. The XRD patterns in Figure S4 a show that there are a few impurity peaks for the Pt NTs@NPs washed one time compared with those washed three times with alkaline water, which is different from that of the Pd NWs (Supporting Information Figure S4 b); even after several washing steps some telluride still existed that could not be detected by XRD since it was too little compared to the Pt component. By characterization with ICP (Supporting Infor-
Figure 1. Schematic illustration of template synthesis and recycling of Te NWs template. a) Physical template for Te@CNFs synthesis. b) Chemical template for Pt/Pd@CNFs synthesis. c) Chemical template for Pd NWs and Pt NTs@NPs synthesis. d) Reproducing Te NWs using the collected TeO32. O
2 TeðNWsÞ þ glucose ! Te@CNFs ! CNFs þ TeO2 3
H O
2 2 Te@CNFs þ PtCl2 6 =PdCl2 ! Pt=Pd@CNFs þ TeO3
ð1Þ ð2Þ
EtOH
2 TeðNWsÞ þ PdCl2 =PtCl2 6 ! PdðNWsÞ=PtðNTs@NPsÞ þ TeO3
ð3Þ 180 C;3 h
TeO2 3 þ NH3 H2 O þ N2 H4 H2 O ! ! TeðNWsÞ
ð4Þ
Te@CNFs were synthesized by a modified hydrothermal method described previously.[10] In this process, the pristine Te NWs (Figure 2 a and Supporting Information Figure S1 a) synthesized by hydrothermal process[11] with a diameter of 7 nm and length of hundreds of micrometers survived in the products as shown in Figure 2 b. However, CNFs in most cases first undergo a calcination process before further application,[12] during which the Te NWs as core of the nanfibers sublimate to toxic gas into the environment. So, the Te NWs as core of CNFs should be first etched out before calcination by slowly stirring
Figure 2. Various products synthesized using Te NWs as template. a) Pristine Te NWs; b) Te@CNFs; c) Pt@CNFs; d) Pd@CNFs; e) Pd NWs; f) Pt NTs@NPs; g) reproduced Te NWs; h) recycle ratios of reproduced Te NWs compared with pristine Te (A: pristine Te; B: CNFs; C: Pt@CNFs; D: Pd@CNFs; E: Pd NWs; F: Pt NTs@NPs).
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Communication was mainly caused by the small length change of Te NWs which may also appear for pristine Te NWs of different batches.[16] The loss in yield (about 20–30 %) during each recycle process was mainly caused by the separation and washing steps as some tellurite may be washed away with unreacted PdCl2 in ethanol. It might be a constant value that does not change at different scale experiments; this would mean that if the experiment can be scaled up, the recycling ratio would increase as the amount of loss in each recycling process is constant.
mation Table S1), the tellurium element was verified to actually exist after washing three times. For further evaluation of the quality of the reproduced Te NWs after templating synthesis, Te@CNFs with different diameters, Pd NWs and Pt NTs@NPs, as shown in Figure 3 a–d, were synthesized using the reproduced Te NWs as template after some adjustment of the dose of the raw materials according to the concentration of the reproduced Te NWs. CdTe and Ag2Te NWs were also synthesized using the reproduced Te NWs as template, which were recycled from the Te@CNFs system. Figure 3 e and f show the typical TEM images of the CdTe and Ag2Te NWs. The XRD patterns in Figure S5 in the Supporting Information show that the CdTe and Ag2Te are consistent with the standard literature values (JCPDS No. 89-3053) and (JCPDF card: 34-0124). These results demonstrate that irrespective of the small loss during the recycling process, the recovered Te NWs have both good physical and chemical activity for further templating synthesis, underlining that the tellurite as waste in solution can be recovered.
Figure 4. Three recycles for the system of Pd NWs using one pot Te NWs. a, b) TEM images of Te NWs and Pd NWs for the second recycling process. c, d) TEM images of Te NWs and Pd NWs for the third recycling process; e) recycle ratio of three recycles; f) UV/Vis spectra of the Te NWs for the three recycling processes (A: pristine Te NWs; B: 1st recycle; C: 2nd recycle; D: 3rd recycle).
In summary, we demonstrate that a versatile and valuable pristine nanotemplate can be economically recycled from waste solutions and can be repeatedly used as template for multiplex templating synthesis. With ultrathin TeNWs as example, such valuable nanowire template can be recycled from waste solution after different templating processes. The recycled nanowires with considerable yield are of high quality and can be reused as physical or chemical templates for further synthesis of other uniform 1D nanostructures. The present work sheds light on the possibility of recycling valuable but toxic species from residual reaction media after templating synthesis and reaction, which will pave new avenues for optimizing the templating synthetic techniques, and produce functional nanostructures in a more economically and environmentally friendly manner in the future.
Figure 3. TEM images of products synthesized using reproduced Te NWs as templates. a) Te@CNFs (180 nm); b) Te@CNFs (40 nm); c) Pd NWs; d) Pt NTs@NPs; e) CdTe NWs; f) Ag2Te NWs.
Further recycling of one-pot Te NWs for the synthesis of Pd NWs without external addition of tellurite were carried out to investigate the quality of the reproduced Te NWs. Before each recycling experiment, we first made clear the content of tellurium in the collection solution by ICP, then made sure that the raw materials are in the proper proportion in the hydrothermal process. Compared with the first recycling (Figure 2 e and g), the Te NWs produced with the second recycling had good morphology with a recycle ratio of about 52.9 % (Figure 4 a), from which the Pd NWs reproduced (Figure 4 b) were still of good quality. However, for the third recycling, the Te NWs became non-uniform in diameter (Figure 4 c) and so the reproduced Pd NWs (Figure 4 d). This phenomenon became obvious as shown in Figure S6 in the Supporting Information. The recycling ratio for the reproduced Te NWs in three recycles were about 81.2, 52.1 and 22.3 %, respectively, relative to the pristine Te NWs characterized by ICP (Figure 4 e). The UV/Vis spectra of each recycle (Figure 4 f) also indicates the good dispersion and morphology of Te NWs with the two typical absorption peaks located at approximately 260 nm and 630 nm. The peak centered at around 630 nm shifted slightly after recycling; this Chem. Eur. J. 2015, 21, 1 – 6
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Experimental Section All chemicals used were of analytical grade and were used as received without further purification.
Synthesis of pristine Te NWs[10] In a typical synthesis, 0.0922 g Na2TeO3 and 1 g polyvinylpyrrolidone (PVP, MW 40 000) were added into a 50 mL Teflon container. Then 33 mL pure water (R = 18.2 MW) was added. Under vigorous magnetic stirring for several minutes a homogeneous solution was formed. Next, 3.35 mL aqueous ammonia (85 %, w/w %) and 1.65 mL hydrazine hydrate (28 %, w/w %) were put into the container separately. The container was closed and coated by stainless
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Communication steel autoclave and maintained at 180 8C for 3 h. Then, the autoclave was allowed to cool to room temperature. The product was collected and store in a refrigerator for further application.
After that, the synthesis of the Te NWs was the same as with the process of recycling Te NWs from the CNFs system.
Recycling Te NWs from the Pt/Pd@CNFs nanocables system Synthesis of Te@CNFs[11]
In a typical process, the solution was centrifuged to collect the Pt/ Pd@CNFs noncable and the unreacted H2PtCl6 or PdCl2 was washed away. After that, the synthesis of the Te NWs was the same as with the process of recycling Te NWs from the CNFs system.
Synthesis of Te@CNFs with diameter of 180 nm: Typically, 40 mL of the prepared Te NWs was centrifuged with acetone as sinking agent at 3740 g and washed by water for several times, then the washed Te NWs was dispersed into 320 mL glucose solution (20 g glucose) with vigorous stirring for 15 min. After that, the mixed solution was undergone hydrothermal treatment at 180 8C for 24 h.
Acknowledgements
Synthesis of Te@CNFs with diameter of 40 nm: Typically, 80 mL of the prepared Te NWs was centrifuged with acetone as sinking agent at 3740 g and washed by water for several times, then the washed Te NWs was dispersed into 400 mL glucose solution (8 g glucose) with vigorous stirring for 15 min. After that, such a mixed solution was undergone hydrothermal treatment at 160 8C for 24 h.
We acknowledge funding from the National Basic Research Program of China (Grants 2014CB931800, 2013CB933900), the National Natural Science Foundation of China (Grants 21401183, 91227103, 21431006, 91022032), and Scientific Research Grant of Hefei Science Center of CAS (2015SRGHSC038). This work was funded by the Deanship of Scientific Research (DSR), King Abdulaziz University, under grant No. 89130-35-HiCi.
Synthesis of Pt NTs@NPs/Pd NWs[7f] In a typical experiment, 40 mL of Te NWs was washed with ethanol several times. Then the Te NWs were dissolved in 60 mL ethanol in a conical flask with vigorous stirring at room temperature for 10 min, and 6 mL of H2PtCl6 (77 mm) in ethanol/140 mg PdCl2 was added. The solution was put in an Innova 40 Benchtop Incubator Shaker and reacted at 260 rpm and 50 8C for 13 h.
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Synthesis of Pt/Pd@C nanocables[13] Typically, one half of the above-purified CNFs products (diameter 30–40 nm) were dispersed in 100 mL of double deionized water with vigorous magnetic stirring. Then 6 mL H2PtCl6 (77 mm) in ethanol or 140 mg PdCl2 was added to the solution. The mixed solution was shaken at a rotation rate of 260 rpm using an Innova 40 Benchtop Incubator Shaker for 12 h at 40 8C.
Recycling Te NWs from the CNFs system First, the CNFs synthesized above were dispersed with 60–80 mL pure water and O2 was bubbled into the solution for about 20 h. After that, the solution was centrifuged to collect the CNFs and the supernatant. Then the product was washed with NaOH solution and the supernatant was collected and put into a flask and rotary evaporated at 70 8C until the solution was about 30 mL or less. Next, the filtrate concentrate was put into a 50 mL Teflon autoclave with 1 g PVP added. After vigorous stirring to form a homogeneous solution, the pH of the solution was adjusted to 9 with HCl and NaOH solution. Then 3.35 mL aqueous ammonia (85 %, w/w %) and 1.65 mL hydrazine hydrate (28 %, w/w %) were put in the container separately. The container was maintained at 180 8C for 3 h. After that, the autoclave was allowed to cool to room temperature.
Recycling Te NWs from the Pd NWs and Pt NTs@NPs reaction systems In a typical process, the product was first centrifuged for 10 min at a speed of 6640 g and washed with ethanol until it was colorless. Then, about 60 mL of pure water was added to disperse the solid, and 0.3–0.5 mL of 2 m NaOH solution was added to adjust the pH to about 10. After that, the solution was centrifuged again to obtain most of the Pd products and the supernate was collected.
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Received: November 8, 2014 Published online on && &&, 0000
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COMMUNICATION & Materials Science
Recyclable nanotemplates: A versatile nanotemplate, so-called ultrathin Te nanowires, can be economically recycled from waste solutions after templating synthesis either as chemical templates or physical templates (see figure). The reproduced tellurium nanowires can be repeatedly used as template for multiplex templating synthesis.
J.-L. Wang, J.-W. Liu, B.-Z. Lu, Y.-R. Lu, J. Ge, Z.-Y. Wu, Z.-H. Wang, M. N. Arshad, S.-H. Yu* && – && Recycling Nanowire Templates for Multiplex Templating Synthesis: A Green and Sustainable Strategy
A versatile and valuable pristine……nanowire template can be economically recycled from waste solutions and can be repeatedly used as template for multiplex templating synthesis; this has been demonstrated conceptually by S.-H. Yu et al. on page && ff. The present work sheds light on the possibility of recycling valuable but toxic species from residual reaction media after templating synthesis and reaction. This will pave new avenues to optimize templating synthetic techniques and produce functional nanostructures in a more economically and environmentally friendly manner in the future.
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