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Chemical sensors are molecular receptors that transform their chemical information into analytically useful signals upon binding to specific guests. These sensors are attracting attention owing to their potential for easy detection and quantification of the pollutant species in many fields of application, such as waste management, environmental chemistry, clinical toxicology, and bioremediation of radionuclides.[1-6] Among these, the sensitive detection of heavymetal ions, such as mercury and lead, is critical for monitoring the environment as they are highly toxic and common environmental pollutants. Although instrumental analyses such as atomic absorption or atomic emission spectroscopy are currently used in applications relevant to the detection of toxic metal ions, there is still a need to develop inexpensive and easy methods for the detection of these toxic ions. In view of these sophisticated experimental methods, emphasis is currently being placed on the development of sensor materials for the detection of toxic ions that offer high sensitivity,

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Nanostructure composite silica monoliths (HOM-n) with three-dimensional (3-D) structures and controllable pore size were fabricated by using microemulsion lyotropic liquid crystal mesophase as templates under acidic conditions. By addition of alkanes with different molecular size (C6 -C19 alkyl chains) into the primary lyotropic liquid crystal mesophase of Brij 56 (C16EO10), quaternary microemulsion liquid crystal phases formed and the mesophase topology of the surfactant was significantly enhanced with 3-D structures. Hydrocarbon molecular size and the degree of solubilization significantly influenced the amphiphilic phase behavior and the mesopore morphological structure. The phase transitions between the different cubic symmetries could be controlled by using a different solubilizing agent in the microemulsion phases of Brij 56 amphiphile. Thereby, the phase transition of primary liquid crystal mesophases in the microemulsion systems were used to fabricate well-defined highly ordered mesoporous silica monoliths HOM-n, including hexagonal P6mm (HOM-2), 3-D hexagonal P63/mmc (HOM-3), primitive-centered cubic Pn3m (HOM-7), Pm3n (HOM-9), and Pm3m (HOM-4) symmetries and body-centered cubic Im3m (HOM-1), bicontinuous cubic Ia3d (HOM-5), and face-centered cubic Fm3m (HOM-10) materials. In these systematic trends, the transitions were primarily governed by the interfacial curvature surface of the amphiphile aggregates. The interactions between alkanes and aggregates substantially influenced the interfacial surface curvatures of micelles, thereby affecting the preferable mesophase structures. However, the primitive cubic (Pm3n) and face-centered cubic (Fm3m) monoliths were the most stable phases among all mesophases, indicating that surfaces with high interfacial curvature were obtained by the addition of long hydrocarbon chain lengths (C10 -C19 range). The addition of short lengths, hexane (C6) and heptane (C7), to the aggregate did not significantly affect the shape geometry of the phases, with the exception of the microemulsion lamellar phases formed in the 2-D hexagonal silica monoliths (HOM-2). Our results show that domains with highly curved interfaces were favored in these microemulsion systems. A tailored pore size was obtained within the transition between the 3-D phases with all mesophases. The extent of transition between the phases with enlarged pore dimensions was further studied by varying the amount of solubilizing agent in the microemulsion composition. Large 3-D monoliths of millimeter-sized particles had a wide range of uniform pore size between 30 and 80 Å, high surface area up to 900 m2/g, and thick walls of about 100 Å. Such properties will allow a wide range of mesoscopic applications.

Mesoporous silica with large pores varying widely in size and with three-dimensional (3D) architectures are potential candidates for numerous applications.[1±5] Enlarging the pore size of mesoporous silica materials is an area that is actively researched. However, considerable attention has also been devoted to synthetic strategies for tailoring mesoporous silica dimensions in the 20±500 range through the use of various surfactant molecules, auxiliary chemicals, and synthetic conditions.[6±15] Furthermore, 3D mesoporous structures have been prepared through the phase transition of cylindrical phase assemblies by adding auxiliary molecules at ambient synthesis conditions. [7] The mesoporous silicates produced had an enlarged pore size; however, a loss of long-range order over the array was often observed, as revealed by the less well-resolved X-ray diffraction spectra and the broadening of the high-intensity peaks. In general, powdery mesoporous silica in micrometer-sized particles (1±2 lm) has been obtained; the formation of large, uniform monoliths was limited.[14±19]Furthermore, the utilization of a dilute surfactant in the synthesis of the mesoporous silica severely limited the ability to predict the mesophase topologies, because the primary phase of an amphiphile is affected by the interactions between the surfactant assemblies and the inorganic precursors.[5±7]Sol±gel synthesis of silica in a bulk lyotropic liquid-crystalline phase allows the inorganic precursors to precipitate in the synthesis solution during the solidification (i.e. rational precipitation), thereby allowing fabrication of large monoliths of the desired size and shape.[20±22] The use of a high template concentration (> 30 %) preserves the pre-existence of liquidcrystalline phases prior to solidification of the silica network, and thus allows a high degree of control over the amphiphilic phase domains and morphological organization of the mesopores. [21] However, even in these syntheses, the pore size is limited to a maximum of 40 by the type and composition of the amphiphiles.[20±23]Here, we developed a simple and versatile method that uses a lyotropic microemulsion of Brij 56 (C 16 EO 10 ) as a template for the synthesis of highly ordered silica monoliths (designated as HOM-n) with a large caged, cubic structure, a uniform pore size up to 80 , a high surface area (900 m 2 g ±1 ), and thick silicate walls of 100 . Furthermore, the long-range order of the structure was maintained. This direct templating method was successfully used here to fabricate well-defined, highly ordered 3D HOM-n monoliths of desired size and shape, such as spherical cubic Im3m (HOM-1), 3D hexagonal P6 3 /mmc (HOM-3), cubic Ia3d (HOM-5), cubic Pn3m (HOM-7), cubic Pm3n (HOM-9), novel cubic Fm3m (HOM-10), and cubic Pm3m (HOM-4). The phase transitions between the different cubic symmetries represent a significant feature during the synthesis of HOM-n monoliths in these microemulsion systems.Our microemulsion liquid-crystal phases were formed by mixing alkanes of various...