Electronic Supplementary Material A single Au nanoparticle anchored inside the porous shell of periodic mesoporous organosilica hollow spheres Ying Yang 1 ( ), Wen Zhang 1, Ying Zhang 1, Anmin Zheng 2, Hui Sun 1, Xinsong Li 1, Suyan Liu 1, Pengfang Zhang 1, and Xin Zhang 1 ( ) 1 State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Changping, Beijing 102249, China 2 State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Center for Magnetic Resonance, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071, China Supporting information to DOI 10.1007/s12274-015-0840-9 1 Experimental 1.1 Materials Hydrogen tetrachloroaurate (HAuCl 4, Aldrich, >99.9%), poly(vinylpyrrolidone) (PVP, Ourchem), 1,4- bis(triethoxysilyl)ethane (BTEE, 92%), and sodium borohydride (NaBH4, 96%) were commercially acquired. Tetraethylorthosilicate (TEOS), sodium citrate, ascorbic acid, cetyltrimethyl ammonium bromide, 4-nitrophenol, sodium hydroxide, ammonia (25 wt.%), concentrated hydrochloric acid (37 wt.%), and ethanol were of analytical grade and used without further purification. 1.2 Synthesis 1.2.1 Preparation of 2.3 ± 0.3 nm gold seeds A 50 ml aqueous solution containing 5 ml HAuCl 4 (10 mm) and 555.0 mg of PVP was prepared in a conical flask, and stirred at 0 C for 30 min. Then, 5 ml of ice-cold freshly prepared NaBH 4 solution (0.1 M) was added to the solution while stirring. The solution turned pink immediately after adding NaBH 4, indicating particle formation. The resulting gold seed colloidal solution was stored in a refrigerator. 1.2.2 Seeding growth A 35 ml aqueous solution containing 5 ml HAuCl 4 (10 mm) and 555.0 mg of PVP was prepared in a conical flask, and stirred at 0 C for 30 min. Then, 10 ml of seed solution was added while stirring, and stirring was continued for 30 min. Subsequently, 15 ml of freshly prepared ascorbic acid solution (5 mm) was added slowly, and further stirred for 2 h. The resulting gold seed colloidal solution was stored in a refrigerator. Address correspondence to Ying Yang, catalyticscience@163.com; Xin Zhang, zhangxin@cup.edu.cn
1.2.3 Synthesis of Au@SiO 2 Silica coating on PVP-stabilized gold nanoparticles centered at ca. 5.8 nm was achieved through a slightly modified Stöber process. In a typical synthesis, 6 ml of the abovementioned Au colloidal solution was mixed with 18.9 ml of ethanol and 0.84 ml of ammonia, and stirred at room temperature for 5 min. Immediately afterwards, a solution of TEOS (1.19 ml) in 12.8 ml of ethanol was added. The reaction mixture was stirred for an additional 12 h at room temperature, and the resulting gel was stored in a refrigerator. 1.2.4 Synthesis of yolk-shell Au@void@PMO nanospheres First, core-double shell Au@SiO 2 @as-pmo nanospheres were prepared by coating a PMO layer on Au@SiO 2, via CTAB-directed self-assembly of BTEE under alkaline conditions. In the typical synthesis, 0.15 g of CTAB was dissolved in 30 ml of deionized water and stirred for 0.5 h, followed by the addition of 18 ml of Au@SiO 2 colloidal solution. After further stirring for 2 h, 0.15 g of CTAB combined with 0.35 ml of NaOH (2 M) was added, and the resulting mixture was heated to 80 C. Then, 0.17 ml BTEE was added at this temperature and stirring was continued for 24 h. The resulting gel was filtered off and dried at 50 C to yield the Au@SiO 2 @as-pmo hybrid. The structure-directing agent was removed by extraction of the solid with dilute ethanolic HCl solution at 40 C for 5 h (20 ml of 0.5 M ethanolic HCl for 0.5 g of solid). The resulting Au@SiO 2 @PMO was mixed with 5 ml NH 3 H 2 O and 10 ml of ethanol, and stirred at 60 C for 24 h to remove the middle silica layer, thus affording the Au@void@PMO hybrid. 1.3 Comparative synthesis 1.3.1 Preparation of MCM-41 supported Au catalyst, Au-MCM-41 Typically, 0.45 g hexadecyltrimethylammonium bromide (CTAB) was dissolved in 18.5 ml of distilled water, and then, 7.0 ml of ethanol, 6.8 ml of ammonia, and 2.6 ml of tetraethoxysilane (TEOS) were sequentially added to the homogeneous micelle solution. The resulting mixture was further stirred at room temperature for 1 h, transferred into a Teflon-lined stainless steel autoclave, and aged at 100 C for 24 h. After cooling to room temperature, the products were filtered, washed with distilled water repeatedly, and dried overnight at 60 C in air. The structure-directing agent was removed by extraction of the solid with dilute ethanolic HCl solution at 40 C for 5 h (20 ml of 0.5 M ethanolic HCl for 0.5 g of solid), thus affording pure siliceous MCM-41. Then, 0.25 g of MCM-41 was added to 2.7 ml of Au-5 colloidal solution and stirred for 24 h. Further filtration, washing with de-ionized water and ethanol, and drying at 60 C afforded Au-MCM-41. 1.3.2 Preparation of Au@viod@mSiO 2 The procedure and dosage of the reagent used for Au@viod@mSiO 2 synthesis were identical to that for Au@void@PMO synthesis, except that BTEE was used instead of TEOS. 1.3.3 Preparation of PVP-free Au@void@PMO First, PVP-free Au colloidal solution was prepared by a two-stepwise reduction procedure according to the literature method [S1]. Typically, 5 ml of HAuCl 4 (10 mmol L 1 ) was diluted with 45 ml of de-ionized water and stirred for 5 min. Then, 1 ml of aqueous sodium citrate (1 wt.%) was added to the solution rapidly and stirred for 5 min. Subsequently, 1 ml of NaBH 4 (using 1 wt.% of aqueous sodium citrate as the solvent) was added and stirred for further 5 min, to yield PVP-free Au colloidal solution cantered at ca. 6 nm. The following precursor for silica coating, supramolecular assembly, as well as template and silica removal, were identical to those for Au@void@PMO synthesis, finally affording PVP-free Au@void@PMO. www.editorialmanager.com/nare/default.asp
1.4 Characterization SEM analysis was performed on a FEI-Quanta 200F field-emission scanning microscope operated at 15 kv with an EDX detector to determine the morphology of the prepared samples. Transmission electron microscopy (TEM) measurements were carried out on a JEOL JEM-2100 transmission electron microscope with a tungsten filament at an accelerating voltage of 200 kv. HADDF-STEM and elemental mapping were carried out using an FEI Tecnai G2 F20 transmission electron microscope operated at 200 kv. The samples were prepared by placing a drop of the prepared solution on the surface of a copper grid. Powder X-ray diffraction (XRD) analysis was conducted using a D8 Avance (Bruker) diffractometer. Diffractograms were recorded in reflection mode using Ni-filtered CuKα radiation (λ = 0.15406 nm). The samples were scanned over the 2θ range 5 to 60 in steps of 2 min 1. The operation voltage and current were kept at 40 kv and 40 ma, respectively. N 2 adsorption/ desorption isotherms were recorded on a Micromeritics ASAP 2020 automated sorption analyzer. Before the measurements, the samples were outgassed at 120 C for 4 h. The specific surface area was calculated by using the Brunauer- Emmett-Teller (BET) method, and the pore size distributions were measured by using Barrett-Joyner-Halenda (BJH) analysis from the desorption branch of the isotherms. UV-vis spectroscopy was carried out with a PC 456 UV-vis spectrometer. All the measurements were performed at room temperature. Infrared spectra of samples were recorded in KBr disks using a Nicolet Nexus 870 FTIR spectrometer. The 29 Si solid-state NMR experiment was carried out on a Varian Infinityplus-400 spectrometer at a resonance frequency of 79.4 MHz. Spectra were recorded using a 5 mm MAS probe at a spinning rate of 6 khz. 29 Si MAS NMR spectra with high-power proton decoupling were recorded using a π/2 pulse length of 7.2 us and a recycle delay of 80 s. The chemical shift of 29 Si was externally referenced to kaolinite ( 91.5 ppm). Metal content was estimated by inductively coupled plasma atomic emission spectroscopy (ICP-AES) analysis conducted on a Perkin Elmer emission spectrometer. A certain amount of the vacuum-dried material was dissolved in 3 ml of boiling aqua fortis solution. 1.5 ml of hydrofluoric acid was added to dissolve the silica support and then completely evaporated. The residue was acidified with concentrated HNO 3 before dilution to ml with deionized water. Each solution was filtered through a 0.45 μm polyethersulfone filter and submitted for metal analysis. 1.5 Catalytic reduction of 4-nitrophenol The reduction of 4-nitrophenol (4-NP) was carried out in a quartz cuvette and monitored using a UV-vis spectroscopy at room temperature. For comparison, aqueous 4-NP solution (0.01 M) was prepared and subjected to measurements before monitoring the change in absorption. Then, 25 μl of aqueous 4-NP solution was mixed with 2.5 ml of fresh NaBH 4 (0.03 M) solution. Subsequently, a given amount of gold catalyst was added to start the reaction, and UV spectrometry was employed for in situ monitoring of the reduction by measuring the absorbance of the solution at 400 nm as a function of time at intervals of 2.5 min. After completion of the reaction, the mixture was centrifuged, and washed with ethanol and water three times. The resulting catalyst was redispersed in 25 μl of aqueous 4-NP solution and 2.5 ml of fresh NaBH 4 solution, and the test was repeated to investigate the stability. Table S1 Textual properties of Au-containing catalysts Materials S BET (m 2 /g) Pore width (nm) Au@void@PMO 367 4.1, 7.0 PVP-free Au@void@PMO 372 3.9 Au@void@mSiO 2 283 3.7 Au-MCM-41 615 4.0 www.thenanoresearch.com www.springer.com/journal/12274 Nano Research
Table S2 Comparison of the Au content and catalytic performance of various Au-containing catalysts Materials Au loading (wt.%) Catalyst amount (mg) k (min 1 ) K (min 1 mg 1 ) Au@void@PMO 0.0099 3 0.138 473 Au-MCM-41 0.0140 1 0.014 100 Au@void@mSiO 2 0.0100 2 0.050 250 PVP-free Au@void@PMO 0.0973 1 0.020 20 Au-POMA 22 0.0118 (mg) 0.3 ml 0.026 2 24 Au@SiO 2 0.3152 (mg) 1 ml 0.840 3 Au@C 11 0.0118 (mg) 0.3 ml 0.380 32 Au@C 21-5 0.480-10 Au@MgSiO 3-1 0.150 - Au@C 8-5 - - Au@HMSM 23-6.67 umol/l - - Figure S1 UV-vis spectra of Au-2 and Au-5. Figure S2 Au particle size distribution for Au@SiO 2. www.editorialmanager.com/nare/default.asp
Figure S3 SEM image of Au@void@PMO. Figure S4 Hollow radius of Au@void@PMO. www.thenanoresearch.com www.springer.com/journal/12274 Nano Research
Nano Res. Figure S5 TEM images of (a) PVP-free Au@void@PMO, (b) Au@void@mSiO2, (c) Au@void@PMO, and (d) Au-MCM-41, and the corresponding Au size distributions (inset). Figure S6 N2 adsorption/desorption isotherm and the corresponding pore size distribution curve (inset) for PVP-free Au@void@PMO. www.editorialmanager.com/nare/default.asp
Figure S7 N 2 adsorption/desorption isotherm and the corresponding pore size distribution curve (inset) for Au@void@mSiO 2. Figure S8 N 2 adsorption/desorption isotherm and the corresponding pore size distribution curve (inset) for Au-MCM-41. Figure S9 TEM images of irradiated Au@void@PMO. www.thenanoresearch.com www.springer.com/journal/12274 Nano Research
Nano Res. Figure S10 Absorbance wavelength plot for 4-nitrophenol reduction over a (a) Au@void@PMO-containing mixture and (b) filtrate. Heterogeneous reaction check for Au@void@PMO by continuing the reaction after removing the Au@void@PMO by filtration after 5 min. Reaction conditions: 3 mg Au@void@PMO, 0.01 M 4-nitropheol (2.5 μl), 0.01 M NaBH4 (2.5 ml). Figure S11 TEM images of spent Au@void@PMO. Reference [S1] Quinten, M.; Leiner, A.; Krenn, J. R.; Aussenegg, F. R. Electromagnetic energy transport via linear chains of silver nanoparticles. Opt. Lett. 1998, 23, 1331 1333. www.editorialmanager.com/nare/default.asp