Visible light promoted degradation of gaseous volatile organic compounds catalyzed by Au supported layered double hydroxides: Influencing factors, kinetics and mechanism

In this paper, factors of initial concentration, catalyst dosage, irradiation intensity, relative humidity and reaction temperature onto visible light gaseous o-xylene photodegradation by ZnCr layered double hydroxides (ZnCr-LDHs) and Au supported ZnCr LDHs (Au/ZnCr LDHs) were investigated. ZnCr LDHs shows low removal efficiency for o-xylene photodegradation, while Au/ZnCr-LDHs exhibits both excellent photodegradation rate and high TOF values for o-xylene as well as other VOCs including benzene, o-xylene, m-xylene and p-xylene. The kinetic equation and activation energy were calculated for o-xylene photodegradation, which are ln(C/C-0) = -1.143 x 10(4)e(-21.85X103/RT) x [A](0)(013487) x [B](0)(0.1889) x [C](0)(0.3730) x t and 21.85 kJ/mol for ZnCr-LDHln(C/C-0) = -1.315 x 10(3)e(-12.84x103/RT) x [A](0)(0.6201) x [B](0)(0.4962) x [C](0)(0.5382) x t and 12.84 kJ/mol for Au/ZnCr-LDHs. The obvious difference both in kinetic equation and activation energy suggests the reaction mechanism of ZnCr-LDHs and Au/ZnCr-LDHs should be very different. The active species inhabitation experiments show that the major drive of photocatalytic reaction for ZnCr-LDHs is hydroxyl radical, while for Au/ZnCr-LDHs it is the hole and hydroxide radical. It is also proved that the support of Au NPs onto LDHs would result in the transfer of photoexcited electrons from LDHs to Au NPs which results in the enhancement of photocatalytic property as well as photocatalytic mechanism change based on UV-vis, XPS, the contribution of different wavelength ranges of visible light onto photocatalytic efficiency and electrochemical tests.