Mesoporous materials

Key points: Mesoporous materials and metal–organic frameworks have ordered pore structures that are defined over the nanoscale; the synthesis of these materials relies upon control of self-assembly; guests can be incorporated into the inorganic host framework for novel applications. An important class of three-dimensionally ordered nanomaterials is mesostructured nanomaterials. Mesoporous materials are well known in heterogeneous catalysis (Chapter 26) and are of great interest because of our ability to tune their pore sizes from 1.5 to 10 nm (Fig. 25.26).

Figure 25.26 A hexagonal mesoporous structure with (a) controlled nanoporosity and (b) functionalized pores.

Mesoporous inorganic nanomaterials are synthesized in a multistep process based on the initial self-assembly of surfactant molecules and block copolymers that self-organize into supramolecular structures (which are liquid crystalline assemblies of cylindrical, spherical, or lamellar micelles; Fig. 25.27). These supramolecular frameworks serve as structuredirecting templates for the growth of mesostructured inorganic materials (often silica or titania). During a solvothermal reaction step, oxide particles (silica, Fig. 25.27) form at the surfaces of the hexagonal rods, assembling around the supramolecular structures. The templating agent can be removed through an acid wash or by calcination to yield inorganic materials having hexagonal pores with uniform and controllable dimensions. This porosity offers unique capabilities for both catalysis and inclusion chemistry. A wide variety of mesostructured and mesoporous inorganic materials have been obtained by varying the choice of templating agent and reaction conditions (Fig. 25.28). For instance, the family known as M41S has silica or alumina-silica inorganic phases and various cationic surfactants leading to three distinct types of structures: hexagonal lamellar (MCM-50), cubic (MCM-48), and hexagonal (MCM-41) (Fig. 25.28).

Figure 25.27 Block-copolymer structure-directing agents self-assemble into micellar rods that form hexagonal arrays that can be removed to yield nanoporous silica matrices for inclusion chemistry and catalysis. (Adapted from M.E. Davis, Chem. Rev., 2002, 102, 3601.) The shape of the surfactant, and the water content used during synthesis controls the resulting nanoarchitecture, as can be seen from the illustration. Surfactants can also be used to tailor the structure. For example, surfactant cetyltrimethylammonium cations (C16TMAC) have been used to fabricate silica nanofibres with hexagonal pores. Mesoporous nanomaterials also offer routes to functionalize pores to increase catalytic activity and selectivity. They have received much attention as host materials for the inclusion of numerous guests such as organometallic complexes, polymers, d-metal complexes, macromolecules, and optical laser dyes. The silica nanofibres shown in Fig. 25.29 can even be used as hosts to grow nanowires of various other oxide materials.

Figure 25.28 Representations of three types of ordered mesoporous solids. (a) Lamellar (layered materials), (b) cubic (complex arrangements), and (c) hexagonal (honeycomb). (Adapted from A. Mueller and D.F. O’Brien, Chem. Rev., 2002, 102, 729.)

Figure 25.29 (a) SEM image of mesoporous silica nanofibres. (b) Lowmagnification TEM image of the nanofibres. (c) High magnification TEM image of one nanofibre. The inset is a selected-area electron diffraction pattern of the nanofibre. (d) High-resolution TEM image recorded at the edge of one nanofibre. (J. Wang, et al., Chem. Mater., 2004, 16, 5169.)

اخر الاخبار

اخبار العتبة العباسية المقدسة

مركز دار العلم للدراسات العقدية والتاريخية يقيم امتحانات نصف السنة الدراسية لطلبته

جامعة الكفيل تنظم سلسلة ورش علمية وتوعوية لتعزيز الوعي الأكاديمي والفكري لدى الطلبة

قسم صناعة الشبابيك يستعرض جهود ورشة صناعة أبواب المراقد المقدسة وشبابيك الأضرحة لملاكات العتبة العباسية المقدسة

شعبة الخطابة الحسينية النسوية تُقيم مسابقة حفظ الخطب الثلاث لطالبات الدورات الصيفية في كربلاء

المزيد

الآخبار الصحية

أول إرشادات غذائية قائمة على الأدلة لمعالجة الإمساك المزمن

صباح بلا إفطار؟.. صحتك في خطر!

هل يمكن للجلد أن يكشف عن صحتك العقلية؟.. دراسة حديثة تجيب

السر في مطبخك.. 6 أطعمة تمنح عظامك قوة الشباب

المزيد

الآخبار التكنلوجية

ناسا تكشف: كوكب الأرض أصبح أقل لمعانا خلال العقود الماضية

دراسة: الوقت الذي تستخدم فيه هاتفك قد يفضح حالتك النفسية

الهنغاري لاسلو كراسناهوركاي يفوز بجائزة نوبل للآداب 2025

رسميا.. إعلان الفائز بجائزة نوبل للسلام لعام 2025

المزيد

مواضيع ذات صلة

Bionanocomposites

Natural and artificial nanomaterials: biomimetics

DNA and nanomaterials

Inorganic–organic nanocomposites

Metal–organic polyhedra and frameworks

Solid-state superlattices

Quantum wells

Two-dimensional control: quantum wells and solid-state superlattices

One-dimensonal control: carbon nanotubes and inorganic nanowires

Supramolecular chemistry and dimensonality

Morphosynthesis

Self-assembly