Hollow template-free methods

Sun and co-workers developed a novel template-free method to prepare hollow ceria nanocubes with peroxyacetic acid as the oxidant. The formation mechanism was explained as having two steps including the oriented attachment of small nanoparticles to form nanocubes and Ostwald ripening to form the hollow structure dominated by solid-solution-solid mass transportation. 

Among hollow inorganic particles, silica-based particles are the most extensively studied because of their ease of synthesis, structural and compositional diversities, and wide range of applications. Hollow silica particles can be synthesized by either templating or template-free methods. 

This chapter reviewed recent advances in the preparation of hollow oxide nanoparticles by liquid-phase deposition methods. Hollow particles with various compositions, controlled shell structures, and controlled shapes and sizes have successfully been obtained by employing either template or template-free method, and many interesting properties arising from their unique structural features have been reported. Large-scale and low-cost production by environment-friendly processes promises practical applications in many fields. 

Shi, Y, Wang, J.Z., Chou, S.L., Wexler, D., Li, H.J., Ozawa, K., Liu, H.K., Wu, Y.R 2013. Hollow structured Li3V04 wrapped with graphene nanosheets in-situ prepared by one-pot template-free method as anode for lithium ion batteries. Nano Lett. 13 4715-4720. 

Cao, C., Cui, Z., Chen, C., Song, W. and Cai, W. (2010) Ceria hollow nanospheres produced by a template-free microwave-assisted hydrothermal method for heavymetal ion removal and catalysis. Journal of Physical Chemistry C, 114, 9865-9870. 

The cost of the support element and the lengthy steps involved in zeolite film synthesis makes zeolite membranes very expensive compared to the well established polymeric membranes. MFI membranes are relatively expensive and their price (about 5.000 /m2) is typically due by 50% to the support and by 50 % to chemicals. Consequently the development of template-free synthesis on cheaper supports (multi-channels, ceramic foils/plates, capillaries, hollow fibers) is seriously considered, in parallel with the development of continuous, automatic, reliable, and reproducible production methods. 

Hollow silica-alumina composite spheres were prepared by polystyrene (PS) template method as follows. The monodisperse PS particles were prepared by emulsifier-free emulsion polymerization [11], The content of PS particles with the diameter of ca. 200 - 300 nm could be tailored through the addition of ethyl alcohol. Then, 15.0 g of the PS template suspension and 6.75 mL of aqueous L(+)-arginine (0.2325 g, Kanto Chem. Co.) solution were added into 40 mL of ethyl alcohol, and then, 20 mL of aluminium(IV) iso-propoxide (AIP, 0.0057 g, Aldrich) / ethyl alcohol solution was added into the mixed solution, following the addition of 0.1551 mL of tetraethoxysilane (TEOS, Kanto Chem. Co., > 99.9 %). The sol-gel reaction was carried out at 323 K for 17 h, and as-prepared hollow silica-alumina composite spheres could be directly obtained. After drying in a desiccator overnight, the obtained fine powders were calcined at 873 K at heating rate = 0.5 K min ... 

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