Effect of different types of organic compounds on the photocatalytic reduction of Cr(VI)

Abstract

The effect of different types of organic compounds (humic acid, oxalate, ethylenediaminetetraacetic acid, nitrilotriacetic acid, phenol) on the photocatalytic reduction of Cr(VI) with illuminated TiO2 was studied in this work with variation of the solution pH, contact time, initial Cr(VI) concentration and type of organic compounds. As the pH increased, the removal efficiency for Cr(VI) decreased. The increase in Cr(VI) removal by UV/TiO2 with decreasing solution pH was due to the increased potential difference between the conduction band of TiO2 and Cr(VI)/Cr(III) as well as the anionic-type adsorption of Cr(VI) on to the TiO2 surface. Removal efficiency for Cr(VI) increased in the presence of organic compound compared with that without organic compound because positive holes in the TiO2 were scavenged by organic additives. The reduction pattern of Cr(VI) was better described by the first-order kinetic model. Finally photocatalytic reaction with illuminated TiO2 can be effectively applied to treat wastewater contaminated with Cr(VI).

Photocatalytic reduction of Cr(VI) over titania suspensions

“…1, Cr(VI) reduction decreases as the solution pH increases from 2.5 to natural pH of 5.1; for instance, the extent of reduction is nearly 100%, 59.7%, 34.4% and 16% after 60 min at pH values of 2.5, 3, 3.5 and 5.1, respectively. In several recent studies [23][24][25], the photocatalytic reduction of Cr(VI) over various TiO 2 suspensions was found to follow a pseudo-first order kinetic expression, i.e. :…”

Cr(VI) remediation from aqueous environment through modified-TiO2-mediated photocatalytic reduction

“…Its better performance was also evident from the consumption of the lowest electrical energy per order of magnitude for photocatalytic reduction of Cr(VI) as compared to that in UV/ZnO and UV/TiO 2 systems [92]. The rate of photocatalytic reduction of Cr(VI) was increased by increasing the photocatalyst dose [154]. Ku et al reported that the combination of ZnO on the surface of TiO 2 at a higher calcination temperature (>500 °C) prevents the transformation of anatase to rutile phase.…”

Application of Semiconductor Photocatalytic Materials for the Removal of Inorganic Compounds from Wastewater

“…The reaction can be accelerated by the addition of organic compounds that act as scavengers of holes or HO•, such as citric acid (Kabra et al 2009;Wang et al 2008), humic acid, oxalate, ethylenediaminetetraacetic acid, nitrilotriacetic acid, phenol (Yang et al 2012b), and isopropyl alcohol (Pifferi et al 2013).…”

“…Table 7.5 describes some recent studies on the removal of Cr (VI) using TiO 2 -modified catalysts. The semiconductor commonly used for the photocatalytic removal of Cr(VI) has been the slurry form of Degussa P25, and the process has been based on the use of UV radiation (Yang et al 2012a(Yang et al , 2012b or solar light (Kabra et al 2009). Very few studies have considered the reduction of Cr (VI) using immobilized TiO 2 nanoparticles.…”