Adriana Zaleska

Mechanism of phenol photodegradation in the presence of pure and modified-TiO2: A review

In recent years, the application of heterogeneous photocatalytic water purification processes has gained wide attention due to its effectiveness in degrading and mineralizing the recalcitrant organic compounds as well as the possibility of utilizing the solar UV and visible-light spectrum. By far, titania has played a much larger role in this scenario compared to other semiconductor photocatalysts due to its costly effectiveness, inert nature and photostability. A substantial amount of research has focused on the enhancement of TiO(2) photocatalysis by modification with metal, non-metal and ion doping. This paper aims to review and summarize the recent works on the titanium dioxide (TiO(2)) photocatalytic oxidation of phenol and discusses various mechanisms of phenol photodegradation (indicating the intermediates products) and formation of OH radicals. Phenol degradation pathway in both systems, TiO(2)/UV and doped-TiO(2)/Vis, are described.

Surface Properties and Photocatalytic Activity of KTaO3, CdS, MoS2 Semiconductors and Their Binary and Ternary Semiconductor Composites

Single semiconductors such as KTaO3, CdS MoS2 or their precursor solutions were combined to form novel binary and ternary semiconductor nanocomposites by the calcination or by the hydro/solvothermal mixed solutions methods, respectively. The aim of this work was to study the influence of preparation method as well as type and amount of the composite components on the surface properties and photocatalytic activity of the new semiconducting photoactive materials. We presented different binary and ternary combinations of the above semiconductors for phenol and toluene photocatalytic degradation and characterized by X-ray powder diffraction (XRD), UV-Vis diffuse reflectance spectroscopy (DRS), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) specific surface area and porosity. The results showed that loading MoS2 onto CdS as well as loading CdS onto KTaO3 significantly enhanced absorption properties as compared with single semiconductors. The highest photocatalytic activity in phenol degradation reaction under both UV-Vis and visible light irradiation and very good stability in toluene removal was observed for ternary hybrid obtained by calcination of KTaO3, CdS, MoS2 powders at the 10:5:1 molar ratio. Enhanced photoactivity could be related to the two-photon excitation in KTaO3-CdS-MoS2 composite under UV-Vis and/or to additional presence of CdMoO4 working as co-catalyst.

Nanoparticles Preparation Using Microemulsion Systems

A wide range of techniques have been developed for the preparation of nanomaterials. These techniques include physical methods such as mechanical milling (Arbain et al., 2011) and inert gas condensation (Perez-Tijerina et al., 2008), along with chemical methods such as chemical reduction (Song et al., 2009), photochemical reduction (Ghosh et al., 2002), electrodeposition (Mohanty, 2011), hydrothermal (Hayashi & Hakuta, 2010), and sol-gel synthesis (Sonawane & Dongare, 2006). Among all chemical methods the microemulsion has been demonstrated as a very versatile and reproducible method that allows to control over the nanoparticle size and yields nanoparticles with a narrow size distribution (LopezQuintela, 2003).

Preparation and characterization of Au/Pd modified-tio 2 photocatalysts for phenol and toluene degradation under visible light—: the effect of calcination temperature

Rutile loaded with Au/Pd nanoparticles was prepared using a water-in-oil microemulsion system of water/AOT/cyclohexane followed by calcination. The effect of calcination temperature (from 350 to 700°C) on the structure of Au/Pd nanoparticles deposited at rutile matrix and the photocatalytic properties of Au/Pd-TiO2 was investigated in two model reactions (toluene degradation in gas phase and phenol degradation in aqueous phase). Toluene was irradiated over Au/Pd-TiO2 using light emitting diodes (LEDs, λmax = 415 nm). The sample 0.5 mol% Pd/TiO2 exhibited the highest activity under visible light irradiation in gas and aqueous phase reaction among all photocatalysts calcined at 350°C, while the sample modified only with gold nanoparticles showed the lowest activity. The Au/Pd-TiO2 sample calcinated at 350°C possesses the highest photocatalytic activity when degrading phenol under visible light, which is 14 times higher than that of the one calcinated at 450°C. It was observed that increasing temperature from 350 to 700°C during calcination step caused segregation of metals and finally resulted in photoactivity drop.

Photocatalytic Air Purification

Titanium dioxide represents an effective photocatalyst for destruction of volatile organic compounds (VOC), NO x and SO 2 in indoor and outdoor air. The mechanism of selected pollutants removal as well as the dependence of reaction rate on some key influencing factors are discussed. Recent papers and patents considering photocatalysts preparation and immobilization techniques including type of supports, surface pretreatment procedure are reviewed. Photocatalytic reactors are designed in order to provide strictly controlled conditions for photocatalytic air purification. Some reactors can be utilized in commercial applications as a part of HVAC systems (Heating, Ventilation and Air Conditioning) but most of them are used in laboratories to measure the activity of different types of photocatalysts applied for gas streams treatment. Examples of photoreactors used for gas phase treatment are presented.

Destruction of chlorinated pesticides in TiO2-enhanced photochemical process

Aqueous solutions containing 200mg/dm3 of lindane, p,p´-DDT and methoxychlor were photodegraded for 60 min in UV/TiO2/O2 system. Sparged air was introduced into the reactor environment. Titanium dioxide supported on glass, hollow microsphers served as the photocatalyst. Pesticides destruction ratio was evaluated and oxidation products were identificated by gas chromatography with thermionic specific detector (GC-TSD) and mass spectroscopy detector (GC-MS). The concentration of pesticides after reaction was determined in the liquid phase, in the solid phase (adsorbed on the photocatalyst) and in the gas phase. The experimental data indicates that pesticide removal with the gas phase was insignificant, therefore it was neglected in the assessment of the photodegradation efficiency. From 14% to 58% of investigated pesticides remained adsorbed on catalyst surface after photodegradation. High content of pesticides in the solid phase after reaction resulted from their low solubility in water and indicates significant adsorption ability of the pesticides by TiO2.

The Photocatalytic Conversion of (Biodiesel Derived) Glycerol to Hydrogen - A Short Review and Preliminary Experimental Results Part 1: A Review

Abstract The paper presents a short review of published results about different methods of waste glycerol conversion to the various chemicals and energy carriers as well the preliminary experimental results of the photocatalytic glycerol conversion into hydrogen. The first part of the paper presents literature data pertaining to the glycerol utilization, including thermal methods (incineration, pyrolysis, gasification and reforming), catalytic oxidation, chemical and biochemical conversion and photoconversion into hydrogen, are presented. The mechanism of selected processes and reaction conditions are also discussed. The second part of the paper presents the results of the hydrogen production over irradiated aqueous glycerol solution containing TiO2-based photocatalysts (TiO2- modified W, Mn, Cr, Ni, Co, Pt, Pd, Au and Ag). The test runs were performed in the batch and semi-batch reactors equipped with Xe lamps as a light source. Much higher hydrogen productivity was observed for the titania modified by noble metals than for transition metal used for modification. The highest hydrogen productivity (24.2 mmol H2·gcat-1·h-1) was reached in the presence of Pt/TiO2, when glycerol concentration in the solution equaled to 4.5 wt.% and the photocatalysts loading in the suspension was ~ 0.042 wt.%.

The Photocatalytic Conversion of (Biodiesel Derived) Glycerol to Hydrogen - A Short Review and Preliminary Experimental Results Part 2: Photocatalytic Conversion of Glycerol to Hydrogen in Batch and Semi-batch Laboratory Reactors

Abstract The paper presents a short review of published results about different methods of waste glycerol conversion to the various chemicals and energy carriers as well the preliminary experimental results of the photocatalytic glycerol conversion into hydrogen. The first part of the paper presents literature data pertaining to the glycerol utilization, including thermal methods (incineration, pyrolysis, gasification and reforming), catalytic oxidation, chemical and biochemical conversion and photoconversion into hydrogen, are presented. The mechanism of selected processes and reaction conditions are also discussed. The second part of the paper presents the results of the hydrogen production over irradiated aqueous glycerol solution containing TiO2-based photocatalysts (TiO2-modified W, Mn, Cr, Ni, Co, Pt, Pd, Au and Ag). The test runs were performed in the batch and semi-batch reactors equipped with Xe lamps as a light source. Much higher hydrogen productivity was observed for the titania modified by noble metals than for transition metal used for modification. The highest hydrogen productivity (24.2 mmol H2·gcat-1·h-1) was reached in the presence of Pt/TiO2, when glycerol concentration in the solution equaled to 4.5 wt.% and the photocatalysts loading in the suspension was ~ 0.042 wt.%.

UV/VIS LIGHT-ENHANCED PHOTOCATALYSIS FOR WATER TREATMENT AND PROTECTION

Applied research data on advanced photocatalytic methods aimed at treatment of contaminated aqueous phase is presented. Phenol and chloroorganic pesticides (as model compounds) besides actual wastewater samples were UV- photodegraded using suspended TiO2 or UV/H2O2/air systems. Titanium dioxide catalysts modified with non-metal elements were used to photodegrade phenols in visible light. Laboratory and pilot scale reactors were used and the effect of process scale-up investigated.