Supporting Information. Nanoscale Kirkendall Growth of Silicalite-1 Zeolite Mesocrystals with. Controlled Mesoporosity and Size

Transcription

1 Electronic Supplementary Material (ESI) for ChemComm. This journal is The Royal Society of Chemistry 2015 Supporting Information Nanoscale Kirkendall Growth of Silicalite-1 Zeolite Mesocrystals with Controlled Mesoporosity and Size Tian-Lu Cui, Xin-Hao Li,* Li-Bing Lv, Kai-Xue Wang, Juan Su and Jie-Sheng Chen* School of Chemistry and Chemical Engineering, Shanghai Jiao Tong University, Shanghai , P. R. China. * (XHL), (JSC)

2 Methods Synthesis of mesoporous silicalite-1: Colloidal silica (Ludox, 40 wt.% in H 2 O) and tetrapropyl ammonium hydroxide (TPAOH, 25 wt.% in H 2 O) with a molar ratio of 8:1 (SiO 2 :TPAOH) were evaporated at 70 C to remove the water under stir. The asobtained dry gels (2 g) were mixed with 0.2 ml of water (dry gel/h 2 O = 10/1) and then transferred to a Teflon-lined autoclave with a volume of 15 ml for further crystallization at 130 C for h to survey the evolution of mesoporous silicalite- 1. After crystallization, the products were washed with distilled water and then heated at 550 C in air for 6 h to remove organic components. The amount of TPAOH and water can be tuned to control the porosity and size of the samples. Detailed conditions were depicted in Figure 3 with the amount of Ludox and other synthetic parameters fixed (130 C, 48 h). Synthesis of bulk silicalite-1: Bulk silicalite-1 was synthesized from a clear precursor sol composed of TEOS, TPAOH and distilled water at the following molar compositions: 10TEOS/3TPAOH/350H 2 O. After crystallization at 170 C for 3 days, the as-synthesized samples were washed with distilled water and heated at 550 C in air for 6 h to remove organic components. Characterizations The powder X-ray diffraction (XRD) patterns were recorded on a Rigaku D/ Max 2550 X-ray diffractometer with Cu Kα radiation (λ= Å) with a tube current of 30 ma and a tube voltage of 40 kv. The scanning electron microscope (SEM) images were taken on a JEOL JSM-6700F field emission scanning electron microscope. Transmission electron microscopy (TEM) images were obtained on a JEM-200CX transmission electron microscope. The nitrogen adsorption/desorption measurements were performed on an ASAP 2020 Accelerated Surface Area and Porosimetry (Micromeritics Inc., USA) and NOVA 2200e Accelerated Surface Area and Porosimetry (Quantachrome Inc., USA). The surface areas were calculated by the Brunauer-Emmett-Teller (BET) method, the pore size distributions of micropores and mesopores were calculated by the Horvath-Kawazoe (HK) and Barret-Joyner-Halenda (BJH) methods, respectively. The Infrared (IR) spectroscopic analyses were carried

3 out by Nicolet 6700 Fourier transform infrared spectrometer (USA) in the range of cm -1. The UV-vis absorption spectra were recorded on a Shimadzu UV spectrometer. Adsorption Characterizations Adsorption frequencies of methylene blue over zeolites were obtained by measuring their concentrations before and after adsorption. 50 mg of meso-silicalite-1 and bulk-silicalite-1 were added into a conical flask, and then 40 ml of methylene blue (4 mg/l) was added quickly. After that, these suspensions were stirred vigorously at room temperature. The concentration of adsorbate was measured by UV-Vis spectra.

4 Figures Figure S1 SEM images of mesoporous silicalite-1 samples obtained after various crystallization periods: (a) 0 h, (b) 4 h, (c) 8h, (d) 48 h.

5 Adsorbed volume (cc/g, STP) (a) Relative pressure (P/P 0 ) dv/dd (cc/nm/g) (b) Pore width(nm) Figure S2 N 2 adsorption-desorption isotherm and pore size distribution of dried Ludox.

6 Adsorbed volume (cc/g, STP) (a) Relative pressure (P/P 0 ) dv/dd (cc/nm/g) (b) Pore Width (nm) Figure S3 N 2 adsorption-desorption isotherm and pore size distribution of silica intermediates (dried mixture of Ludox and TPAOH).

7 Transmittance (a.u.) silicalite-1 silica intermediates Ludox 5-rings Wavenumber (cm -1 ) Figure S4 IR spectra of various samples: Ludox (black), silica intermediate (red), silicalite-1 (blue). It is obviously that the as synthesized silicalite-1 shows band at 550 cm -1 which specifically assigned to five-ring structures in pentasil zeolites, while no band existed in that of the initial Ludox. Interestingly, a relatively weaker band at 550 cm -1 can be observed in the silica intermediate, while precursor obtained by conventional method exhibits similar intensity to the silicalite-1 sample. This is to say that the chemistry of silica and TPAOH here is similar to the dissolution process in conventional methods, whilst the diffusion manner of as-formed silica intermediates was however different as described in the main text. The key difference is the form of water in the whole synthetic system, that is, vapor in our Kirkendall method and liquid in conventional methods.

8 without water 48 h 144 h 48 h 8 h 4 h 0 h theta (degree) Figure S5 XRD patterns of mesoporous silicalite-1 samples obtained after various crystallization periods under standard conditions and the control sample (grey) without the addition of water. It is obvious that the crystallization of silicalite-1 could not proceed without the presence of water, excluding the possibility of psedo-solidstate reaction here.

9 Adsorbed volume (cc/g, STP) (a) 4 h Relative pressure (P/P 0 ) Adsorbed volume (cc/g, STP) (b) 8 h Relative pressure (P/P 0 ) Adsorbed volume (cc/g, STP) (c) 48 h Relative pressure (P/P 0 ) Adsorbed volume (cc/g, STP) (d) 144 h Relative pressure (P/P 0 ) Figure S6 N 2 adsorption-desorption isotherm curves of mesoporous silicalite-1 samples obtained after various crystallization periods: (a) 4 h, (b) 8 h, (c) 48 h and (d) 144 h.

10 Cumulative Pore Volume (cc/g) Cumulative Pore Volume (cc/g) h Pore width (nm) h (a) (c) Pore width (nm) dv/dd (cc/nm/g) dv/dd (cc/nm/g) Cumulative Pore Volume (cc/g) Cumulative Pore Volume (cc/g) (b) 8 h Pore width (nm) (d) 144 h Pore width (nm) dv/dd (cc/nm/g) dv/dd (cc/nm/g) Figure S7 Cumulative pore volumes (dark line) and pore size distributions (dotted line) of mesoporous silicalite-1 samples obtained after various crystallization periods: (a) 4 h, (b) 8 h, (c) 48 h and (d) 144 h. It should be noted that the mesopores with a size between 5-10 nm shown in (a) were mainly originated from the Ludox aggregations (Figure S2-3), whilst the contribution of the intra-particle pore volume of the nanocrystals (size: 95 nm) to the total volume of mesopores was negligible here.

11 Figure S8 Particle size distribution (a), pore size distribution (b) and corresponding pore volume of large mesopores (> 18 nm) (c) of mesoporous samples obtained after various crystallization periods. These results unambiguously confirmed the formation of Kirkendall mesopores with larger size (18 nm) during the crystallization process. Also, the fact that pore volume of the sample obtained at 4 h with particles size around 95 nm is negligible further excluded obvious contribution of inter particle porosity to the total pore volume of our samples.

12 1.25:1 Dry gel / H 2 O 2.5:1 5:1 10:1 20: Pore width (nm) Pore volume (cc/g) Pore volume (cc/g) Figure S9 Mesopore size distribution (left) and pore volume of corresponding mesopores (right) in mesoporous silicalite-1 nanocrystals prepared with different weight ratios of dry gel/h 2 O.

13 Figure S10 SEM images of mesoporous silicalite-1 samples obtained with different weight ratios of dry gel/h 2 O: (a) 20/1, (b) 5/1, (c) 2.5/1 and (d) 1.25/1.

14 Table S1 Yields of zeolite via various methods. Synthetic method Si/TPAOH/H 2 O T ( o C) Yield (%) Ref. Conventional method 3~1/1/10~ Kirkendall method 8/1/0.4~ This work Conventional method-modified 8/1/ ~1