TiO2 photocatalysis and related surface phenomena

http://publicationslist.org/data/meng.chong/ref-18/sdarticle.pdf

Recent Developments in Photocatalytic Water Treatment Technology: A Review

The photocatalytic degradation of azo dyes containing different functionalities has been reviewed using TiO2 as photocatalyst in aqueous solution under solar and UV irradiation. The mechanism of the photodegradation depends on the radiation used. Charge injection mechanism takes place under visible radiation whereas charge separation occurred under UV light radiation. The process is monitored by following either the decolorization rate and the formation of its end-products. Kinetic analyses indicate that the photodegradation rates of azo dyes can usually be approximated as pseudo-first-order kinetics for both degradation mechanisms, according to the Langmuir–Hinshelwood model. The degradation of dyes depend on several parameters such as pH, catalyst concentration, substrate concentration and the presence of electron acceptors such as hydrogen peroxide and ammonium persulphate besides molecular oxygen. The presence of other substances such as inorganic ions, humic acids and solvents commonly found in textile effluents is also discussed. The photocatalyzed degradation of pesticides does not occur instantaneously to form carbon dioxide, but through the formation of long-lived intermediate species. Thus, the study focuses also on the determination of the nature of the principal organic intermediates and the evolution of the mineralization as well as on the degradation pathways followed during the process. Major identified intermediates are hydroxylated derivatives, aromatic amines, naphthoquinone, phenolic compounds and several organic acids. By-products evaluation and toxicity measurements are the key-actions in order to assess the overall process.

TiO2-assisted photocatalytic degradation of azo dyes in aqueous solution: kinetic and mechanistic investigations A review

Fujishima and Honda (1972) demonstrated the potential of titanium dioxide (TiO2) semiconductor materials to split water into hydrogen and oxygen in a photo-electrochemical cell. Their work triggered the development of semiconductor photocatalysis for a wide range of environmental and energy applications. One of the most significant scientific and commercial advances to date has been the development of visible light active (VLA) TiO2 photocatalytic materials. In this review, a background on TiO2 structure, properties and electronic properties in photocatalysis is presented. The development of different strategies to modify TiO2 for the utilization of visible light, including non metal and/or metal doping, dye sensitization and coupling semiconductors are discussed. Emphasis is given to the origin of visible light absorption and the reactive oxygen species generated, deduced by physicochemical and photoelectrochemical methods. Various applications of VLA TiO2, in terms of environmental remediation and in particular water treatment, disinfection and air purification, are illustrated. Comprehensive studies on the photocatalytic degradation of contaminants of emerging concern, including endocrine disrupting compounds, pharmaceuticals, pesticides, cyanotoxins and volatile organic compounds, with VLA TiO2 are discussed and compared to conventional UV-activated TiO2 nanomaterials. Recent advances in bacterial disinfection using VLA TiO2 are also reviewed. Issues concerning test protocols for real visible light activity and photocatalytic efficiencies with different light sources have been highlighted.

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A review on the visible light active titanium dioxide photocatalysts for environmental applications

https://opus.lib.uts.edu.au/bitstream/10453/33344/4/A%20review%20on%20the%20occurrence%20of%20micropollutants%20in%20the%20aquatic%20environment%20and%20their%20fate%20and%20removal%20during%20wastewater%20treatment.pdf

A review on the occurrence of micropollutants in the aquatic environment and their fate and removal during wastewater treatment

Decontamination and disinfection of water by solar photocatalysis: Recent overview and trends

Particulate suspensions of TiO2 irradiated with natural solar light in a large experimental plant catalyze the oxidation of a typical organic contaminant: pentachlorophenol (PCP). The addition of oxidants, concentration of which is kept constant during treatment, such as hydrogen peroxide, peroxymonosulphate (oxone) and peroxydisulphate increases the rate of photodegradation of PCP in the following order: S2O2−8>Oxone>H2O2. Peroxydisulphate (10 mM), selected as the best oxidant studied, has been applied to the development of a solar photocatalytic plant for the treatment of commercial pesticide rinsates found in the wastewater produced by a pesticide container recycling plant, which includes the correct treatment of this highly contaminating effluent. The first results, without process or hardware optimisation, show that peroxydisulphate enhances the photocatalytic mineralization rate at least five times.

Enhancement of the rate of solar photocatalytic mineralization of organic pollutants by inorganic oxidizing species

In the context of an upcoming energy crisis due to the decline of the Oil Era, water problems are expected to substantially worsen. And vice versa, due to the close relationship between water and energy issues, water problems are also expected to contribute to increased energy problems. Furthermore, environmental considerations, such as global warming, will surely add significant pressure. In this scenario, renewable energies are rapidly increasing their contribution to the global mix, with solar energy clearly having the greatest potential, and in view of the worldwide coincidence that where there is water stress and/or scarcity, there are also good solar radiation levels, the conclusion seems clear suitable technologies must be developed to permit the use of solar energy to simultaneously help solve energy and water problems. The main solar energy applications for water processes presented in this paper are: (i) solar desalination; (ii) solar detoxification and; (iii) solar disinfection.

M. I. Maldonado

Papers

Decontamination and disinfection of water by solar photocatalysis: Recent overview and trends

Enhancement of the rate of solar photocatalytic mineralization of organic pollutants by inorganic oxidizing species

Review of feasible solar energy applications to water processes

Solar photocatalytic degradation of some hazardous water-soluble pesticides at pilot-plant scale.

Solar photocatalytic degradation and detoxification of EU priority substances