Two-Dimensional Porous Silica Nanomesh from ...

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Nanoscience and Nanotechnology Letters Vol. 8, 1028–1032, 2016

Two-Dimensional Porous Silica Nanomesh from Expanded Multilayered Vermiculite via Mixed Acid Leaching Jianming Dan1 3 4 , Xin Huang1 , Panpan Li1 , Yu Zhang2 , Mingyuan Zhu1, Xuhong Guo1 3 4 , Bin Dai1 , Qiang Wang1 2 ∗ , and Feng Yu1 3 4 ∗ 1

Key Laboratory for Green Processing of Chemical Engineering of Xinjiang Bingtuan, School of Chemistry and Chemical Engineering, Shihezi University, Shihezi 832003, P. R. China 2 College of Environmental Science and Engineering, Beijing Forestry University, Beijing 100083, P. R. China 3 Engineering Research Center of Materials-Oriented Chemical Engineering of Xinjiang Production and Construction Corps, Shihezi 832003, P. R. China 4 Key Laboratory of Materials-Oriented Chemical Engineering of Xinjiang Uygur Autonomous Region, Shihezi 832003, P. R. China Porous silica materials with high surface area and excellent pore size have been used world widely in numerous applications. In this contribution, a two-dimensional porous silica nanomesh is prepared from expanded multilayered vermiculite by mixed acid leaching. The silica nanomesh was ∼5.5 nm thick with a surface area of 505 m2 /g, an average pore size of 1.8 nm and a pore volume of 0.406 cm3 /g. The acid treatment of vermiculite for the preparation of silica nanomesh method reported here may provide novel options for the preparation of functional silica nanomesh materials.

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155.69.24.171 Wed, 30 Nov 2016 02:35:41 Keywords: PorousIP:Silica Nanomesh,On: Two-Dimensional, Expanded Multilayered Vermiculite, American Scientific Publishers Microwave,Copyright: Acid Leaching.

1. INTRODUCTION Since the discovery of porous silica synthesized using templates,1 2 the template method has been widely applied extensively to prepare porous silica materials with high surface areas, tunable pore sizes, large pore volumes, rich morphology and environmentally friendly characteristics.3 4 Groundbreaking work by Kresge et al.,5 in 1992 led to the first synthesis of ordered mesoporous silica molecular sieves (i.e., MCM-41) via a liquid-crystal template method. In 1998, Zhao et al.,6 reported a hexagonal mesoporous silica SBA-15. Because of their large surface areas and suitable pore size, there is an urgent need for the use of porous silica materials in widespread application such as catalyst supports,7 hard templates,8 watertreatment adsorbent,9 10 optical devices,11 bio-imaging,12 drug delivery,13 and biomedical applications.14 Porous silicas have attracted significant attention to date in numerous applications. Porous silicas have also been synthesized by alkali etching (e.g., NaOH and KOH) and acid etching (e.g., HF).15 16 Silica-etching provides a simple, facile, and easily scalable route to control the chemical composition ∗

Authors to whom correspondence should be addressed.

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and structural parameters of porous silicas.17 Liu et al.,18 synthesized thiol-functionalized hollow mesoporous silica nanospheres by etching in NaOH and Na2 CO3 solution. Acid leaching has been used to prepare porous silica materials from selective minerals, such as metakaolinite,19 20 montmorillonite,21 kaolin,22 sepiolite,23 talc,24 chrysotile,25 and phlogopite.26 In this contribution, we successfully prepared a twodimensional (2D) porous silica nanomesh with a thickness of ∼5.5 nm, an average pore size of 1.8 nm and a surface area of 505 m2 /g. The porous silica nanomesh was prepared from expanded multilayered vermiculite (EMIVMT) by mixed acid leaching. To our best knowledge, this is the first time that 2D porous silica nanomesh synthesis from EMI-VMT by acid leaching has been reported. VMT is a natural clay mineral (aluminosilicate) and possesses a special layered structure27 28 that could be leached easily by acid according to the work by Temuujin et al.29 and Osaka et al.30 We synthesized the 2D porous silica nanomesh from mixed acid-leached EMI-VMT.

2. EXPERIMENTAL DETAILS The procedure to prepare EML-VMT follows the protocol as described in our previous work.31 After treatment, 1941-4900/2016/8/1028/005

doi:10.1166/nnl.2016.2191

Dan et al.

Two-Dimensional Porous Silica Nanomesh from Expanded Multilayered Vermiculite via Mixed Acid Leaching

hydrated EML-VMT was dried quickly by microwave a Bruker MultiMode8 NanoScope in the tapping mode with standard silicon nitride tips. radiation (800 W for 1 min). The dried EML-VMT was ground and sieved to 0.25–0.42 mm (passed through a 40–60 sieve). The as-obtained EML-VMT precursor (10 g) 3. RESULTS AND DISCUSSION was immersed into 200 mL mixed acid solution at 80 C To understand the formation mechanism of porous silica with 4 h stirring. The mixed dilute acidic aqua regia solu(i.e., SiO2 nanomesh, a schematic illustration is proposed tion (hydrochloric and nitric acid with 3:1 volume ratio) in Figure 1(a), which consists of two main steps. Firstly, was used as the immersion liquid at 1 M, 2 M, 4 M, and raw VMT was immersed in 25% H2 O2 aqueous solution 6 M. The suspension was washed with distilled water to to exfoliate the VMT (Fig. 1(b)), by which the VMT interremove the free acid, and dried at 110 C for 12 h. The layer spacing was increased, and such expansion finally led as-obtained samples were designated as EMT-VMT-nM to the formation of EML-VMT (Fig. 1(c)). Excess water is (n = 1, 2, 4, and 6). then removed by microwave irradiation-assisted rapid heat The chemical composition of samples was determined treatment. Secondly, a porous SiO2 nanomesh (Fig. 1(d)) by X-ray fluorescence (XRF) spectroscopy (Panalytiis formed by immersing ground EML-VMT into mixed cal Axios-mAX). X-ray diffraction (XRD) patterns were acid with subsequent filtration and water washing to determined using a Bruker D8 advanced X-ray diffracneutral. tometer to evaluate the sample structure using monochroTable I shows the chemical compositions, determined matic Cu K radiation ( = 15406 Å) in the range by X-ray fluorescence (XRF), and the porous properties 2 = 2.5–15 and 2 = 10–90. The morphology of samof raw VMT, EML-VMT, and EML-VMT-nM. The chemples was investigated suing scanning electron microscopy ical composition and porous properties of the VMT and (SEM, JEOL JSM-6490LV, Hitachi-SU8010) and transthe EML-VMT samples show no significant change after mission electron microscope (TEM, JEOL JEM-2100F). expansion. However, the EML-VMT-nM samples show Nitrogen (N2 isotherms were obtained at 77 K using a significant changes and the SiO2 contents increase sigsurface area and pore size analyzer (Micromeritics 3Flex). nificantly after mixed acid leaching. After mixed acid The specific surface areas (SSA) were calculated using the treatment, the products were almost pure SiO2 . Porous Brunauer–Emmett–Teller (BET) equation within a relative EML-VMT-6M (i.e., SiO2 nanomesh) had a purity of pressure range (P /P0 of 0.05–0.30. Thebypore volume 99.90%, a specific University surface area of 505 m2 /g and a pore Delivered Ingenta to:was Nanyang Technological 3 determined from the amount of IP: N2 155.69.24.171 adsorbed at the On: high-Wed,volume 0.41 02:35:41 cm /g. 30 Novof2016 est relative pressure of P /P0 =∼0.99.Copyright: The pore diameter American Scientific Publishers The SEM images of the as-obtained VMT, EML-VMT distribution (PSD) was defined by applying the Barrett– and SiO2 nanomesh are shown in Figures 1(e–g). VMT Joyner–Halenda (BJH) model to the desorption isotherm. and EML-VMT exhibit layer structures. The correspondAtomic force microscope (AFM) images were taken using ing reflections of VMT and EML-VMT are attributed

Fig. 1. (a) Schematic illustration of EML-VMT-6M synthesis. Photographs of (b) VMT, (c) EML-VMT, and (d) SiO2 nanomesh. SEM images of (e) VMT, (f) EML-VMT, and (d) SiO2 nanomesh.

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Table I. Chemical composition and porous properties of various samples.

Sample VMT EMT-VMT EML-VMT-1M EML-VMT-2M EML-VMT-4M EMT-VMT-6M (i.e., SiO2 nanomesh)

Chemical composition (mass%)

Surface area (m2 /g)

Pore volume (cm3 /g)

SiO2

MgO

Al2 O3

K2 O

Fe2 O3

CaO

Na2 O

TiO2

1.05 12.1 342 710 511 505

0005 0080 0115 0485 0464 0406

388 408 936 969 998 999

241 217 197 0971 – –

200 208 09 077 – –

622 646 062 045 – –

493 502 148 033 – –

303 289 053 – – –

202 142 033 – – –

0942 0587 0538 0411 0079 –

mainly to the VMT crystal layer (PDF#74-1732) and mica the SiO2 nanomesh, N2 adsorption–desorption isotherms (Fig. 2(c)) were performed. This isotherm profile could be (1M-phlogopite, PDF#10-0495), as shown in Figure 2(a). categorized as type V with a pronounced hysteresis loop, For the VMT, the characteristic diffraction peak at which is visible at a relative pressure of 0.4–0.8. As cal2 = 805 and 8.90 (Fig. 2(b)) correspond to a main culated by the BET method, the SiO2 nanomesh has a interlayer spacing of 1.19 nm and 1.12 nm respectively. SSA of 505 m2 /g and a relatively high pore volume of Compared with VMT, EML-VMT presents the intense 0.406 cm3 /g. Figure 2(d) shows that the average pore size peak at 2 = 890 . This phenomenon illustrates that EML32 33 is 1.8 nm, which confirms the existence of the micropores VMT contains interlayers with a spacing of 1.12 nm. in SiO2 nanomesh. High-resolution AFM images of the After mixed acid etching treatment, diffraction peaks for SiO2 nanomesh are given in Figures 4(a and b). The thickthe layer gaps were missing, which is consistent with ness of SiO2 nanomesh is ∼5.5 nm from AFM width meadelamination of the SiO2 nanomesh (Fig. 1(g)) with amorsurement (Fig. 4(c)). The 2D SiO2 nanomesh that has phous SiO2 phase. been prepared by mixed acid etching has significant The TEM images in Figure 3 show that the SiO2 potential for use as is or in similar inorganic nanostrucnanomesh exhibits a 2D structural morphology. A curly Delivered by Ingenta to: Nanyang Technological University 2D 2016 materials superstructures34 as well as graphene SiO2 nanomesh is visible in Figure 3(a). Amorphous pores IP: 155.69.24.171 On: Wed,tured 30 Nov 02:35:41 35 36 nanomesh, TiO nanomesh,37 carbon nanomesh,38 and of ∼2 nm in diameter are present inCopyright: the SiO2 nanomesh American Scientific Publishers Co3 O4 nanomesh.39 (Fig. 3(d)). To confirm the existence of micropores of

Fig. 2. (a, b) XRD patterns of VMT, EML-VMT, and SiO2 nanomesh. (c) N2 adsorption–desorption isotherm and (d) pore size and distribution.

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Fig. 3.


(a–d) TEM images of SiO2 nanomesh with different magnification.

may offer an additional way to prepare porous SiO2 materials which shows potential for application in many fields. Acknowledgments: This work was financially Delivered by Ingenta to: Nanyang Technological University supported by the Doctor Foundation of Bingtuan IP: 155.69.24.171 On: Wed, 30 Nov 2016 02:35:41 (No. 2014BB004), Copyright: American Scientific Publishersthe Program for Changjiang Scholars Innovative Research Team in University (No. IRT_15R46), the Program of Science and Technology Innovation Team in Bingtuan (No. 2015BD003), and the National Natural Science Foundation of China (No. 21163015).

References and Notes

Fig. 4. width.

(a, b) AFM images of SiO2 nanomesh and (c) corresponding

4. CONCLUSION 2D Porous SiO2 nanomesh was prepared from the EMLVMT by mixed acid ectching. The as-obtained SiO2 nanomesh with a high purity of 99.90% provides an amorphous SiO2 phase with a typical 2D inorganic nanostructured morphology. The thickness and average pore size of SiO2 nanomesh are ∼5.5 nm and 1.8 nm, respectively, which yield a high SSA of 505 m2 /g and a pore volume of 0.406 cm3 /g. The 2D porous SiO2 nanomesh architecture Nanosci. Nanotechnol. Lett. 8, 1028–1032, 2016

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Received: 1 April 2016. Accepted: 10 May 2016.

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