Photocatalytic Discoloration of Dyes: Relation between Effect of Operating Parameters and Dye Structure

Abstract

The process of TiO 2 /UV photocatalytic discoloration of wastewaters containing organic dyes is influenced by a number of variables. In this paper, the effects of some of these parameters, i.e., mass of catalyst, initial dye concentration, and pH, were related to the structural nature of the dyes investigated, azo and anthraquinone dyes, two families that are representative of about 75 % of the dyes marketed nowadays. Both bibliographical and own experimental data were used to analyze and discuss the photocatalytic discoloration in terms of dye structure and degradation pathways. It is shown that azo dyes (Methyl Orange, Metanil Yellow, Acid Orange 7, and Reactive Red 120) are more easily discolored than Reactive Blue 19 (anthraquinone dye), due to the higher molecular stability of the latter. It is also shown that azo dye discoloration is more influenced by the initial dye concentration, whereas recalcitrant anthraquinone dyes (Reactive Blue 19) mainly demand for basic pH values to generate enough OH . radicals. Concerning TiO 2 loading, both the bibliographical and current research data showed no effect of this variable in the experimental range analyzed.

Improving the photo‐reduction of CO2 to fuels with catalysts synthesized under high pressure: Cu/TiO2

“…An ad hoc designed experimental set‐up described elsewhere, was used for the synthesis of photocatalysts in supercritical CO 2 . The installation operated in discontinuous mode and comprised two main subsystems: a pumping section and a reaction chamber.…”

Preparation of TiO2-based catalysts with supercritical fluid technology: characterization and photocatalytic activity in CO2reduction

“…The photocatalytic reduction of CO 2 is a procedure long studied, titanium dioxide (TiO 2 ) being the most commonly used catalyst so far due to its excellent properties. Some of them are a high light absorption efficiency, low band gap energy (3.03–3.23 eV), photostability and chemical inertness, environmental friendly nature, low cost and low toxicity . As can be observed in Fig.…”

“…Supercritical technology has been traditionally applied to the extraction of natural products but, over the years its application range has expanded. Thus, a number of studies have demonstrated improved properties in catalysts synthesized in supercritical media . Generally speaking, the properties of supercritical fluids are very attractive for particle generation and precipitation, since they allow control of particle properties (e. g. morphology, structure, particle size, particle size distribution) that are very important for the final application of the product …”

Greenhouse Effect Mitigation Through Photocatalytic Technology

“…There are examples where the lamp is located parallel to the reactor [82] (Fig. 7a) or placed in an inner radiation cell [83,84] (Fig. 7b).…”

“…A first ad hoc experimental setup consisted in a fluidized bed reactor (glass cylindrical flask, inner volume 1 L) and an UV radiation source (150-W medium pressure mercury UV lamp) was used [59,83] (Fig. 7b).…”