▫$SiO2-Fe_3O_4$▫ hybrid monoliths for photothermal ▫$CO_2$▫ desorption

Elevated CO2 concentrations disrupt the Earth’s carbon cycle, drawing attention to the need for effective carbon management strategies. The widespread adoption of Carbon Capture, Utilization, and Storage (CCUS) technology is hindered by several challenges, The most critical one is the high operational cost, mainly resulting from the energy-intensive capture process (sorption and desorption). Although considerable research has been devoted to enhancing CO₂ capture efficiency, the development of economically viable desorption techniques has lagged, creating a significant gap in the overall process. (1) For now in already used thermal swing desorption method, the entire compartment containing the sorbents needs to be heated, which is very energy consuming. To optimize energy consumption, one of the promising approaches can be localized heating of the sorbents using photothermal (PT) effect. (2) But the first step is to create hybrid materials, e.g. silica-iron oxide. In this composite silica act as capturing material and iron oxide nanoparticles (IONPs) act as photothermally active material. Such hybrid monoliths were prepared via two different methods: (a) Sol-Phase Nanoparticle Dispersion (SPND) where IONPs are added to the sol before it undergoes gelation and (b) Spray coating (SC) of IONPs onto the silica monolith. Initial PTE measurements shows that in the case of SPND method, there is not enough rise in temperature when illuminated by power of 0.1 W (≈ 1 sun). This is due to the “dead” IONPs in the core of monolith, which are not illuminated by light. The significant temperature increase was not observed neither when the monoliths were illuminated with higher power of 1W (≈10 sun). Contrary, in the case of SC monoliths, there is a significant increase in the temperature already for monoliths with the lowest coverage and under low power of 1 sun (≈ 0.1W). The SC prepared hybrid monoliths exhibit hierarchical porosity, with pore sizes ranging from 0.5 nm to few tons of micrometres. Their CO2 uptake reached up to 1.77 mmol/g at 0°C and 0.96 mmol/g at 25°C, which is significantly higher than in the case of pure silica monolith. Thermally programmed desorption revealed that temperature needed for complete CO2 regeneration is ≈100 °C .To investigate the effect of selectively targeting the absorption maximum, PT experiments were conducted using two narrowband light sources: 447 nm, which coincides with the absorption peak of Fe3O4, and 808 nm which does not.