Photodeposition of lanthanum on titanium oxide for photocatalytic removal of 2,4-dichlorophenoxyacetic acid

Abstract

Hazardous and toxic compounds, such as 2,4-dichlorophenoxyacetic acid (2,4-D) herbicides, can affect environmental and human health through the water stream [1]. Among the studied photocatalysts, titanium oxide (TiO2) [2-4] has been modified with other transition metal ions and oxides [5] to give complete mineralization of 2,4- D [6,7]. However, lanthanum modified TiO2 nanoparticles for the removal of 2,4-D herbicide has been not yet reported so far. Therefore, we highlight the improvement of photocatalytic activity of 2,4-D using photocatalysts prepared from UV photodeposition method of lanthanum oxide on TiO2. Lanthanum nitrite hyxahydrate (0.1-1 mol%) as a precursor of lanthanum oxide in ethanol at 30 ºC was successfully deposited on TiO2 under UV irradiation (8 Watt, 254 nm). The resulting La/TiO2 photocatalysts were investigated for photocatalytic decomposition of 2,4-D under UV irradiation (8 Watt, 254 nm) for 1 h using high performance liquid chromatography. The 0.1La/TiO2 photocatalyst exhibited the highest photocatalytic activity of 24% which was 1.3 times higher that the unmodified TiO2. Scavenger study using tertbutyl alcohol, ammonium oxalate and silver nitrate revealed that holes play the most important role to remove 2,4-D on the photocatalysts. This study demonstrated that the photocatalytic activity of TiO2 could be increased with modification by La, which acted as an electron trapper that may supress electron-hole recombination without blocking the emission sites of the TiO2 as shown from the decreasing of fluorescence intensities at 276 nm upon excitation at 218 nm when the amount of La was optimized.