Fluoride-Induced Hierarchical Ordering of Mesoporous Silica in Aqueous Acid-Syntheses

نویسندگان

  • Patrick Schmidt-Winkel
  • Peidong Yang
  • David I. Margolese
  • Bradley F. Chmelka
  • Galen D. Stucky
چکیده

The acid-catalyzed synthesis of highly ordered mesostructured materials has led to a variety of twoand three-dimensional periodic symmetries, and has proven to be an effective route for the generation of fibers, spheres, thin films, and other monolithic forms of mesoporous materials. Zhao et al. recently used non-ionic poly(alkylene oxide) block copolymers, under acidic conditions, to prepare well-ordered, hexagonal mesoporous silica, denoted SBA-15, featuring uniform and adjustable large pore sizes combined with thick hydrothermally stable walls. The catalytic effect of fluoride in the synthesis of mesoporous silica at neutral to basic pH has been described by Voegtlin et al. Fluoride has been successfully used to extend the pH range over which anionic silica precursors can be utilized to create organized periodic structures; it has been used to diminish framework defects in zeolites, and to improve the organization in MCM-41 molecular sieves and MSU-X materials. However, to the best of our knowledge, no studies have been reported on the role of fluoride on cationic silica species in the aqueous acid-synthesis of ordered porous silica. In this communication, we describe the hierarchical ordering effects induced by small amounts of fluoride added during the synthesis of SBA-15-type mesoporous silica under acidic aqueous conditions. The non-ionic poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) triblock copolymer EO20PO70EO20 (Pluronic P123) has been employed as the structure-directing agent. At low pH, remarkably well-ordered, hydrothermally stable, large hexagonal mesoporous silica rods with uniform channels extending over micrometer-sized length scales, and with few defects, have been synthesized. The fluoride-induced enhancement of order has enabled the preparation of SBA-15 materials at moderate acidity (~ pH 2.5±3) without compromising the long-range hexagonal symmetry. The mesoporous silicas possess narrow pore-size distributions, hydrothermally stable frameworks, large surface areas, and pore volumes of up to 0.92 cm/g. This work has been motivated by our interest in i) the patterning of mesoporous materials ranging from mesoscopic to macroscopic length scales while retaining molecular-level structural control and ii) understanding the underlying mechanism for the acid-catalyzed mesoporous silica synthesis. Addition of small amounts of fluoride (F:Si molar ratios of 0.008 and 0.03; fluoride source: NH4F or (NH4)2SiF6) during the aqueous acidic SBA-15-type silica synthesis induces substantial ordering that is manifested on different length scales: both the mesoscopic structure and the macroscopic morphology of the mesoporous silicas are significantly improved. Scanning electron microscopy (SEM) has revealed that small amounts of fluoride bring about the formation of large mesoporous silica rods (Fig. 1a) when pre-

برای دانلود متن کامل این مقاله و بیش از 32 میلیون مقاله دیگر ابتدا ثبت نام کنید

ثبت نام

اگر عضو سایت هستید لطفا وارد حساب کاربری خود شوید

منابع مشابه

Aqueous-sensitive reaction sites in sulfonic acid-functionalized mesoporous silicas

Local differences in surface hydrophilicities/hydrophobicities of propyland arene-sulfonic-acid modified mesoporous silica and organosilica catalysts have been compared and correlated with their bulk catalytic properties for aqueous-sensitive organic reactions. Syntheses of propyland arene-SO3H-modified mesoporous silicas and organosilicas yield materials with different hydrophilicities, especi...

متن کامل

In vitro Investigation of Polymer Coated Magnesium Incorporated by Mesoporous Silica Nanocontainers

The idea of smart corrosion inhibition is basis on either inhibitor consumption where it is needed or reducing harmful matrix interaction with it. In addition, applying corrosion inhibitor in a coating causes many problems such as loss of inhibition capability, coating degradation, or both. A useful technique to overcome this problem is applying of inert host systems of nanometer dimensions as ...

متن کامل

Novel modified magnetic mesopouros silica for rapid and efficient removal of methylene blue dye from aqueous media

This reaserch aims at functionalizing magnetic mesoporous silica with methacrylic acid-3-aminopropyltriethoxysilane (Fe3O4@MCM-41@MAA-APTES) applied for removal of methylene blue from aqueous solution. Several variables (such as pH, dye concentration, adsorbent amount and contact time) have been investigated. Under optimum conditions, maximum capacity of 87.71 mg g-1 of MB was obtained for the ...

متن کامل

In vitro Investigation of Polymer Coated Magnesium Incorporated by Mesoporous Silica Nanocontainers

The idea of smart corrosion inhibition is basis on either inhibitor consumption where it is needed or reducing harmful matrix interaction with it. In addition, applying corrosion inhibitor in a coating causes many problems such as loss of inhibition capability, coating degradation, or both. A useful technique to overcome this problem is applying of inert host systems of nanometer dimensions as ...

متن کامل

Synthesized mesoporous silica and calcium aluminate cement fillers increased the fluoride recharge and lactic acid neutralizing ability of a resin-based pit and fissure sealant.

This study evaluated the effect of different types of filler in a resin-based pit and fissure sealant on fluoride release, recharge, and lactic acid neutralization. Resin-based sealant was incorporated with 5% w/w of the following fillers: calcium aluminate cement (CAC), synthesized mesoporous silica (SI), a CAC and SI mixture (CAC+SI), glass-ionomer powder (GIC), and acetic acid-treated GIC (G...

متن کامل

ذخیره در منابع من


  با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید

برای دانلود متن کامل این مقاله و بیش از 32 میلیون مقاله دیگر ابتدا ثبت نام کنید

ثبت نام

اگر عضو سایت هستید لطفا وارد حساب کاربری خود شوید

عنوان ژورنال:

دوره   شماره 

صفحات  -

تاریخ انتشار 1999