Photoreduction of Cr(VI) Ions in Aqueous Solutions by UV/ Photocatalytic Processes

Abstract

This study discussed the photoreduction of Cr(VI) ions in aqueous solutions by UV/TiO 2 photocatalytic processes under various operational factors. Experimental results showed that the removal rate of Cr(VI) increased with decreasing solution pH values and with increasing dosages of organic compounds, indicating that the recombination rate of electrons and h + can be retarded in the reaction systems by the addition of the scavenger, thus raising the reaction rate of Cr(VI). The relationship of the chemical reaction rate of Cr(VI), TiO 2 dosage, and changes of Cr(VI) concentration was expressed by the pseudo-first-order kinetic equation. Comparing the experimental results of two different doping metals in modified TiO 2 photoreduction systems, the removal rate of Cr(VI) by the Ag/TiO 2 process is larger, possibly because the electron transferring ability of Ag is superior to that of Cu. However, the photoreduction rates of Cr(VI) by modified UV/TiO 2 processes are worse than those by a nonmodified commercial UV/TiO 2 process.

A Study on the Photocatalytic Reduction of Some Metal Ions in Aqueous Solution Using UV- Titanium Dioxide System

“…ions in solution and therefore are not easily adsorbed on the negatively charged TiO 2 surface at basic pH. This result cor with the finding of [6], who stated that during the photocatalytic removal of Cr (VI), the reduction rate of dichromate ions gradually decreased because the increase in pH value redu adsorption of dichromate ions on the surface of the photocatalyst; similarly, at high pH value, Cr(OH) 3 covered the surface active position of TiO 2 so that the trivalent chromium from their solution at basic medium, for instance, ions precipitate out of solution to form ions precipitate to Cd(OH) 2 . As a result, the metals are not detected when the resulting solution is analysed by AAS instrument.…”

Photoreduction Processes over TiO2 Photocatalyst

“…Hence, detoxification of the toxic Cr(VI) can be carried out by reduction method. Photoreduction of Cr(VI) over TiO 2 photocatalyst has been frequently reported [18][19][20][21][22][23] with satisfaction result. Further, the Cr 3+ ions can precipitate into undissolved Cr(OH) 3 in basic condition that is remediable by solidification/stabilization technique:…”

“…This is a reduction path. The use of the electrons from TiO 2 for some reducible metal ions such as Ag(I) [5][6][7][8][9][10][11][12][13], Au(III) [13][14][15][16][17], Cr(VI) [18][19][20][21][22][23], Cu (II) [24][25][26], Hg(II) [27,28], and U(VI) [29,30] has also been developed.…”

Heterogeneous photocatalysis in flow chemical reactors

“…They suggested that as the placement in the light or dark had no influence, the static mixers and photochemical reactors could be sep- arated into individual components of a flow system, providing process intensification without complicated reactor designs, trying to incorporate large irradiation surface areas and static mixing in a single unit. The mechanism for select examples of photocatalytic pollutant degradation in water have been studied in detail and are represented in Figure 19, along with a schematic of the flow system used in the study [284][285][286][287].…”

“…A) Suggested mechanisms for the aqueous pollutant degradation by TiO 2 in a slurry flow reactor[284][285][286][287]. B) Flow schematic of the slurry reactor and C) more detailed schematic of the irradiated reactor with a static mixer in the dark silicone tubing (dashed arrow) or an irradiated quartz tube (solid arrow).…”