Conversion of CO₂ in Exhaust Gas to Formic Acid and Formamides with Wasted Silicon Recovered from End-of-Life Solar Panels

Recycling end-of-use solar panels faces significant challenges due to the high volume of discarded panels. The recycling of Si wafers recovered from these panels has drawn attention. In this study, we combined the recycling of waste silicon wafers with the conversion of CO2 in exhaust gas from a thermal power plant. The reduction of CO2 using silicon wafers as a reducing agent produced formic acid and formamides in high yields. The exhaust gas was directly introduced from the power plant to the reactor. The reactions were effective in the presence of a tetrabutylammonium fluoride catalyst. Among the four silicon samples recovered from solar panels, those with higher surface aluminum content showed lower reactivity; however, pretreatment with aqueous HCl significantly enhanced their reactivity. Detailed characterization of the Si samples before and after the reaction was conducted by using X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscopy, and N2 adsorption–desorption isotherms.