Novel preparation of SiO2/C foams with tailored porosity by emulsion template method and SiO2 sol-gel technology

SiO₂/C foams with carbon particles as raw material were prepared using emulsion template combined with SiO₂ sol-gel technology. One significant hurdle lies in achieving scalable and cost-effective fabrication of bulk materials endowed with customized porosity, along with an optimal blend of attributes such as high mechanical strength, super-hydrophilicity, thermal insulation, and effective absorption of electromagnetic waves. SiO₂/C foams with varied pore sizes and porosities were synthesized by manipulating the water-oil volume ratio in the raw materials. The impact of pore size and porosity on the compressive strength, thermal insulation, super-hydrophilicity and electromagnetic wave absorption property of SiO₂/C foam materials were thoroughly investigated. The gel reaction involving inorganic SiO₂ not only could fix the bubbles in situ and impart sufficient mechanical properties but also confer super-hydrophilic characteristics to the SiO₂/C foam materials. The SiO₂/C foams exhibited adjustable porosity levels ranging from 57% to 78%.The SiO₂/C foams, characterized by a uniform pore size of approximately 8.33 μm, demonstrated low thermal conductivity. Additionally, the compressive strength of SiO₂/C foam with a porosity of 57% was measured at 3.5 MPa. For sample S4, the minimum reflection loss (RL_min) of -48 dB with an effective absorption bandwidth spanning 5.76 GHz, observed at a matching thickness of 2.2 mm. Due to their outstanding performances, characteristics, and the ease of scalable fabrication, the SiO₂/C foams developed in this study showcase significant potential for diverse applications.