Effects of humidity on photocatalytic oxidation of elemental mercury by rGO-modified CeO2/TiO2: Kinetic analysis and experimental exploration

This study aimed to reveal the interaction between water molecules and the surface of the photocatalyst since the recent trend is moving the selective catalytic reduction downstream of the electrostatic precipitator , which has higher relative humidity . To resolve the issue, we synthesized the reduced graphene oxide (rGO)-modified CeO 2 /TiO 2 (GCT) to photocatalytic oxidize elemental mercury (Hg 0 ). The introduction of rGO successfully enhanced the hydrophobicity of CeO 2 /TiO 2 , preventing the active sites on the surface of GCT photocatalysts blocking by water molecules. Density functional theory calculations and droplet contact angle analyses confirmed the hydrophilicity and hydrophobicity of CeO 2 /TiO 2 and GCT. In-situ ATR-FTIR results indicated that GCT photocatalysts exhibited less rise in the O-H group intensity at 3000–3600 cm −1 compared to CeO 2 /TiO 2 , suggesting the reduction of water adsorption. The kinetic behavior of Hg 0 photocatalytic oxidation reaction was modeled using Langmuir-Hinshelwood, Eley-Rideal, and Mars-van Krevelen mechanisms, revealing that water molecules can either promote or inhibit the photocatalytic oxidation of Hg 0 depending upon Hg 0 concentration. This study systematically investigated the interplay between H 2 O and Hg 0 , demonstrating the potential of rGO-modified CeO 2 /TiO 2 photocatalysts in enhancing the photocatalytic oxidation efficiency of Hg 0 in a humid environment . • DFT calculation confirms competitive adsorption between Hg 0 and H 2 O at active sites. • Modification with rGO could effectively turn hydrophilic CeO 2 /TiO 2 to hydrophobic. • Hg 0 reaction rate is affected by the H 2 O content and regime. • The dependency of the Hg 0 oxidation reaction rate on H 2 O and Hg 0 shows that it follows the L-H mechanism.