Influence of Synthesis Conditions on Properties of Ethane-Bridged Periodic Mesoporous Organosilica Materials as Revealed by Spin-Probe EPR

A thorough investigation of the formation mechanism and surface properties of periodic mesoporous organosilicas (PMOs) is of crucial importance for further tuning and improving of the structural characteristics and applications of these promising meso-structured materials. In the present paper, the effects of the synthesis conditions on the properties of ethane-bridged PMOs were studied by means of spin-probe electron paramagnetic resonance (EPR) spectroscopy complemented with standard characterization techniques for porous materials. When spin probes were dissolved in the synthesis mixture, the influence of the precursor type on the formation kinetics of ethane-bridged PMOs could be tested. The use of the precursor 1,2-(tris­(tri­ethoxy­silyl)­ethane instead of bis­(tri­methoxy­silyl)-ethane significantly slows the pore formation, leading to materials with larger pore diameters. Furthermore, different spin probes with varying sizes and polarities were adsorbed onto two types of ethane-bridged PMOs synthesized at room temperature or at 95 °C. The effect of surface polarity, surface water, and pore size on the incorporation and mobility of molecules in the PMO pores was thus monitored. Ethane-bridged PMO materials synthesized at room temperature were found to have a smaller pore size and a larger amount of physisorbed water than those synthesized at 95 °C, influencing strongly the insertion of molecules in the pores as observed by spin-probe EPR.