Nanoporous spheres

Recently, the LbL technique has been extended from conventional nonporous substrates to macroporous substrates, such as 3DOM materials [58,59], macroporous membranes [60-63], and porous calcium carbonate microparticles [64,65], to prepare porous PE-based materials. LbL-assembly of polyelectrolytes can also be performed on the surface of MS particles preloaded with enzymes [66,67] or small molecule drugs [68], and, under appropriate solution conditions, within the pores of MS particles to generate polymer-based nanoporous spheres following removal of the silica template [69]. 

Tao HC, Huang M, Fan LZ, Qu X (2012b) Interweaved Si SiOx/C nanoporous spheres as anode materials for Li-ion batteries. Solid State Ion 220 1-6... 

Fig. 7.2 Schematic representation of the procedure for the encapsulation of enzyme in PE microcapsules (I) and preparing nanoporous protein particles (II) using MS spheres as templates.

Recently, a new procedure was reported for the preparation of nanoporous polymeric spheres (NPSs) with well-controlled structure via the LbL infiltration and coating of MS spheres with preformed polymers (Figure 7.7) [69]. A main advantage of this approach is that it offers a general and versatile route to the preparation of NPSs of different and tailored compositions, as it is based on electrostatic assembly [69,109]. 

Ho, W., J.C. Yu and S. Lee (2006). Synthesis of hierarchical nanoporous f-doped Ti02 spheres with visible light photocatalytic activity. Chemical Communications 2006(10), 1115-1117. 

Schwertmannite, is a common nanoparticle-product of neutralization of sulfuric acid-rich solutions (Bigham et al. 1994). The original structural analysis indicated that sulfate was contained within tunnels similar to those found in akaganeite (FeOOH). However, recent work by Waychunas et al. (2001) suggests that this is a defective, nanoporous phase and that sulfate occupies inner and outer sphere positions on the surface, and probably on the internal surfaces of defect regions within the structure. 

Bogge et al.. Changeable Pore Sizes Allowing Effective and Specific Recognition by a Molybdenum-Oxide Based Nanosponge En Route to Sphere-Surface and Nanoporous-Cluster Chemistry, Angew. Chem. Int. Ed. Engl. 2002, 41, 3604-3609. 

The polymer template was removed in two different ways, by toluene extraction and by pyrolysis, which resulted in very different types of gold replicas. In the first case the nanoparticles retained their shape, which led to a hierarchical network structure with nanopores between the nanoparticles and macropores from the templating polymer spheres. When the latex was removed by calcination at 300 °C, the gold nanoparticles fused to a dense metal matrix with only macropores. 

A careful X-band Al HYSCORE and W-band H ENDOR analysis showed that from the three Cu species found in Cu-containing Si Al zeolite Y (Si Al = 12 and 5), only one Cu was bound to the framework oxygens [139]. The other species consisted of a copper ion with a complete coordination sphere of water and no direct bonding with the zeolite framework. In a similar way, combined CW-EPR and Al HYSCORE provided evidence of the interaction of Cu with the framework in copper-doped nanoporous calcium aluminate (mayenite) [140]. In mayenite, the positively charged calcium aluminate framework is counter-balanced by extra-lattice O ions. Such free oxide ions are responsible for the ion conductivity of the materials and are readily replaced by various guest anions, such as O2 and OH. A native O2 species could indeed be identihed with EPR in the Cu-doped mayenite materials [140]. 

Figure 4.3 Scanning electron micrc raphs for methyl methacrylate spheres (a), methyl methacrylate sphere covered withTiOa (h), and nanoporous thiol-functionalized titania—silica (c).

The evidence for the formation of a new crystaUine phase is also reinforced by the XRD patterns shown in Fig. 4.4. As can be verified, the methyl methacrylate spheres exhibit some degree of crystallinity. Furthermore, the titania-covered spheres exhibit the same XRD patterns as the uncovered spheres, indicating that the Ti02 coat is amorphous. On the other hand, the nanoporous thiol-functionalized titania-sifica hybrid exhibits a distinct XRD pattern, showing that a new crystaUine phase was formed. By comparison with previously prepared double oxides [13,16] the diffraction peak at 5.5° observed in Fig. 4.2c could be attributed to the 100 diffraction plane of a hexagonal phase. 

While many available molecular simulations of EDLs are based on MD method, MC method has also been used. In particular, MC has been used to model EDLs formed inside nanopores using the restricted primitive model (RPM), in which electrolyte icms are modeled as hard spheres with a point charge placed at their center [7]. 

---