PHOTOCATALYTIC CO2 VALORIZATION IN AQUEOUS PHASE OVER Fe–TIO2 AND Fe–PILC: EFFECT OF SUPPORT AND OPERATING CONDITIONS

The photocatalytic valorization of CO 2 is a promising strategy for carbon utilization under mild and sustainable conditions. In this work, iron-modified bentonite and TiO 2 were synthesized via pillaring (Fe–PILC) and sol–gel (Fe–TiO 2 ) methods to investigate the role of the support, irradiation source, and operating conditions on aqueous CO 2 photoreduction. A two-step reaction behavior was identified under 254 nm light irradiation. In the initial stage (<0.17 h) CO 2 conversion is governed by alkaline speciation, leading to the formation of formic acid (FA), acetic acid (AA), and methanol (MeOH). During the second stage, at longer irradiation times, the in-situ formation of H 2 O 2 and the occurrence of hydroxyl radicals (•OH) promote strong oxidative conditions, leading to the degradation of FA and AA, and the rapid consumption of MeOH. Under UV irradiation, 14Fe–TiO 2 exhibited the highest activity, achieving 2 5 0 𝜇 ⁢ 𝑚 ⁢ 𝑜 ⁢ 𝑙 𝑔 − 1 𝑐 ⁢ 𝑎 ⁢ 𝑡 of FA at 293 K in 1 h, which may be associated with the role of TiO 2 as support enhancing charge separation and electron transfer. In contrast, Fe–PILC showed superior performance under visible light irradiation, 𝑐 ⁢ 𝑎 . 1 0 0 𝜇 ⁢ 𝑚 ⁢ 𝑜 ⁢ 𝑙 𝑔 − 1 𝑐 ⁢ 𝑎 ⁢ 𝑡 , in 1h, indicating its potential as an alternative photocatalyst under low-energy light irradiation. Valence band holes are the main species responsible for formic acid depletion, and this causes methanol concentration decreases. The appearance of reactive oxygen species (ROS) also contributes, albeit in less extent, to the depletion of formic acid and methanol through oxidation. These findings demonstrate that understanding the interplay between reductive and oxidative pathways, and their balance is essential to control C 1 –C 2 product stability and selectivity for the sustainable valorization of CO 2 in aqueous phase.