Photocatalytic Reduction of Cr(VI) in an Aqueous Suspension of Surface-Fluorinated Anatase TiO₂ Nanosheets with Exposed {001} Facets

Abstract

In the present work, reduction of Cr(VI) induced by UV–visible light in aqueous solution was investigated. The aqueous medium contained TiO2 nanosheets and no additional reducing agents or hole scavengers. A hydrothermal method was used to synthesize fluorinated TiO2 nanostructures with various percentages of exposed {001} facets and initial F/Ti ratios. Fluorine-free TiO2 nanosheets were obtained by washing the TiO2 samples with NaOH solution. The surface fluorination facilitates the adsorption process by increasing the number of surface OH groups generated. Moreover, fluorination efficiently inhibits the recombination of photogenerated electron–hole pairs. The {001} facets have an indirect role in the photocatalytic reduction of Cr(VI) because oxidative dissolution of H2O occurring on {001} facets and Cr(VI) reduction occurring on {101} facets are simultaneous reactions. The optimal ratio of exposed {001} to {101} was found to be ∼72:18.

The selective deposition of silver nanoparticles onto {1 0 1} facets of TiO 2 nanocrystals with co-exposed {0 0 1}/{1 0 1} facets, and their enhanced photocatalytic reduction of aqueous nitrate under simulated solar illumination

“…Thus, it would be desirable to selectively deposit noble metal nanoparticles onto {1 0 1} facets of anatase TiO 2 nanocrystals with co-exposed {0 0 1} and {1 0 1} facets, which could combine the advantages from both the crystal facet effect and noble metal modification to initiate the oriented migration of photogenerated electrons and further enrich their presence onto the surface of TiO 2 for the enhanced photocatalytic reduction activity. Although limited reports were available on the selective deposition of noble metals onto anatase TiO 2 with exposed facets [34][35][36], few studies had been conducted on the photocatalytic reduction activity of TiO 2 with noble metal modifications on selected facets.…”

Rapid and efficient photocatalytic reduction of hexavalent chromium by using “water dispersible” TiO2 nanoparticles

“…When the "water dispersible" TiO 2 nanoparticles is used instead of P25, the photocatalytic reduction efficiency of Cr(VI) ions can be increased by 3.8 times. In order to quantitatively describe the activities of the photocatalysts, the reaction rate constant (k) of photoreduction of Cr(VI) ions over the "water dispersible" TiO 2 nanoparticles and P25 was evaluated according to the pseudo-first-order model, respectively [20].…”

Photocatalytic Degradation of Salicylic Acid and Reduction of Cr(VI) using TiO2

“…Theoretically, the photocatalytic reduction of Cr(VI) on TiO 2 should be more efficient in the metal-organic-TiO 2 system than in the single system due to the accelerating effect by the preferential photocatalytic oxidation of the organics. In such metal-organic-TiO 2 system, the organic compound receives holes from valence band directly or indirectly, and is oxidized [21]. Thus increasing the photoreduction efficiency of Cr(VI) by suppressing the electron-hole recombination.…”