Nanometric hollow spheres made of MSU-X-type mesoporous silica

Submicrometric hollow spheres with mesoporous walls were prepared by applying the synthesis of MSU-X type mesoporous silica at neutral pH. The application of ultrasound in the proper power range, to a mixture of nonionic polyoxyethylene surfactant and unreacted silicon alkoxide (tetraethylorthosilicate) gives a stable emulsion where the cavitation bubbles created by the ultrasound are trapped in the solution. Further hydrolysis and condensation of the silica by the addition of sodium fluoride freezes the structure and gives a powder that exhibits a single reflection in the X-ray diffraction pattern, characteristic of a 3D-wormhole ordered porous framework. Its main feature is a large hysteresis loop in the nitrogen adsorption/desorption isotherm. This hysteresis loop corresponds to the retention of condensed nitrogen within the voids of these particles that can play the role of tanks for volatile compounds.