Photoreduction of Cr(vi) using hydroxoaluminiumtricarboxymonoamide phthalocyanine adsorbed on TiO2

Abstract

Hydroxoaluminiumtricarboxymonoamide phthalocyanine (AlTCPc) adsorbed at different loadings on TiO(2) Degussa P-25 was tested for Cr(vi) photocatalytic reduction under visible irradiation in the presence of 4-chlorophenol (4-CP) as sacrificial donor. A rapid reaction takes place in spite of the presumable aggregation of the dye on the TiO(2) surface. The removal of Cr(vi) is fairly negligible under visible-light irradiation, either without photocatalyst or in the presence of bare TiO(2). The fast capture of conduction band electrons by Cr(vi), which forms a surface complex with TiO(2), inhibits the formation of reactive oxygen species in the reductive pathway. This fact and the easier oxidation of 4-CP as compared to AlTCPc hinder the photobleaching of the dye and make feasible Cr(vi) reduction under visible irradiation. The consumption of Cr(vi) follows a pseudo-first order kinetics; the decay constant depends, in the studied range, on the photocatalyst mass, but it is barely affected by dye loading. The presence of 4-CP is essential, but its concentration has no effect on the Cr(vi) decay rate. Oxidation products of 4-CP, such as hydroquinone, catechol or benzoquinone, are not observed. Direct evidence of the one-electron reduction of Cr(vi) to Cr(v) was obtained by EPR spectroscopy using citric acid as Cr(v) trapping agent. In this case, disappearance of Cr(v) also follows a first order decay, but conduction band electrons do not seem to be involved. The fact that oxidation products of 4-CP are not observed is consistent with the fast dark removal of reaction intermediates by Cr(v), proved by EPR.

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

“…The sensitized TiO 2 -PFT was evaluated for both Cr (VI) reduction and phenol oxidation, and the reduction efficiency of Cr (VI) reached a maximum of 50 % at pH 3 (Qiu et al 2012). AlTCPc adsorbed on Degussa P25 TiO 2 was tested for Cr(VI) reduction in the presence of 4-chlorophenol (4-CP) as a sacrificial donor (Meichtry et al 2009). Additionally, the photoreduction of Cr(VI) over anatase TiO 2 nanoparticles was achieved through surface modification with small-molecular-weight organic acids (SOAs), such as tartaric acid, as sacrificial organic compounds.…”

“…The removal effectiveness is nearly 100 % at initial Cr concentrations below 53.7 mg L À1 after 3 h of solar radiation. An effective visible light active sensitization of TiO 2 has been achieved using poly(fluorene-co-thiophene) (PFT) as a surface adsorbate (Qiu et al 2012), sensitized with hydroxoaluminiumtricarboxymonoamide phthalocyanine (AlTCPc) (Meichtry et al 2009) and modified with small-molecular-weight organic acids (Wang et al 2010). The sensitized TiO 2 -PFT was evaluated for both Cr (VI) reduction and phenol oxidation, and the reduction efficiency of Cr (VI) reached a maximum of 50 % at pH 3 (Qiu et al 2012).…”

Photocatalytic Semiconductors

“…An effective visible light active sensitization of TiO 2 has been achieved using poly(fluorene-co-thiophene) (PFT) as a surface adsorbate (Qiu et al 2012), sensitized with hydroxoaluminiumtricarboxymonoamide phthalocyanine (AlTCPc) (Meichtry et al 2009) and modified with small-molecular-weight organic acids (Wang et al 2010). The sensitized TiO 2 -PFT was evaluated for both Cr (VI) reduction and phenol oxidation, and the reduction efficiency of Cr (VI) reached a maximum of 50 % at pH 3 (Qiu et al 2012).…”

Photoelectrocatalytic degradation of blistering agent sulfur mustard to non-blistering substances using pPy/NiOBPC nanocomposite

“…The complete oxidation of sulfur-containing compounds (using metal oxide and semiconductor oxide), before discharging them into waterways, was suggested to be a possible solution for environmental pollution problems [23][24][25][26]. As an alternative to inorganic semiconductors, metallophthalocyanines (MPcs) were used to produce photocatalytic systems [27][28][29][30]. PCs and their derivatives have attracted much attention due to their extraordinary electronic, optical and structural properties in photosensitization, [31] nonlinear optics, [32] catalysis, [33] photodegradation [34] and sensing [35] applications.…”