Photocatalytic degradation of phenolic compounds with new TiO2 catalysts (original) (raw)
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Applied Catalysis B: Environmental, 2010
Bare TiO 2 photocatalysts made up of polyhedral nanoparticles have been prepared by flame hydrolysis. In order to obtain deeper understanding of the interplay between the properties determining the photocatalytic performance, surface, aggregation and photocatalytic properties have been analyzed and compared. The aggregation of nanoparticles in aqueous solution of NaCl was determined by dynamic light scattering (DLS) technique. The average hydrodynamic diameters of the aggregates investigated under environmentally relevant conditions do not differ significantly in the pH range of 5-6. Zeta potential measurements were also done during DLS analysis, which revealed remarkably low pH IEP values for our flame made samples comparing to the commercial titanias. Furthermore an explicit correlation between the isoelectric points and the synthesis parameters was revealed. O 1s XP spectra for the high activity samples were also recorded and interpreted. Oxygen consumption experiments were used to test the photocatalytic activity in suspensions. The method was found to be not only rapid and inexpensive but also reasonably reproducible. Normalizing the oxygen consumption rate with the specific surface area of the sample and the concentration of the suspension, a good correlation could have been found with the traditionally determined photocatalytic activity. HPLC measurements were used to study the degradation mechanism of phenol via determining the concentration profile of various dihydroxy intermediates, i.e., hydroquinone (HQ) and pyrocatechol (PC). The quality of the photocatalyst strongly affects the maximum ratio of HQ:PC during the photocatalytic degradation process. For our catalysts higher pyrocatechol concentrations were measured than for Degussa P25. TOC measurements were used to follow the complete mineralization. Using our best photocatalysts (e.g., anatase:rutil ratio of 82:18 and mostly polyhedral particles, with 21 m 2 /g BET surface area), phenol concentration decreased faster than for P25, however, the mineralization rate was somewhat lower. This can be attributed to the lower adsorption capacity of our polyhedral particles against PC and carboxylate containing intermediates formed during the more advanced stages of decomposition. These data elucidate, that hydrophilicity, O 2-consumption properties and adsorption/complexation of the target compounds and their degradation products are equally important parameters in determining the photocatalytic performance of catalysts, which otherwise possess similar material properties.
2009
Recent literature reports about several attempts to immobilize TiO 2 powder on different supporting materials [1-21], when titania is used as photocatalyst for the degradation of hazardous organic compounds in air or water. In fact the simple use of powder catalyst, especially in the nanosized form, has the disadvantage of a difficult sedimentation after the photocatalytic process; in addition TiO 2 nanoparticles, dispersed in the surrounding, may be hazardous, due to their potential inflammatory and cytotoxic effects [22]. TiO 2 was generally supported on SiO 2 glass beads [1], rings [2], and reactor tubular walls [3,4]; fiberglass [5,6]; quartz [7,8]; zeolites [9,10]; perlite [11]; pumice [12]; alumina-based ceramic [13]; stainless steel [14,15]; aluminum [16]; polymeric membranes [17-19], etc. Recently natural fibers began to be used as suitable supports and the cotton material was conveniently adapted inside the photoreactors [20,21]. In spite of the different TiO 2 crystalline phases (anatase, rutile and brookite), most of the literature on immobilized catalysts is focused on the use of commercial P25 photocatalyst or of anatase, due to the small average size of the particles (<50 nm); in fact it is expected that the smaller the particle size the higher the surface area suitable for the catalytic activity. No attention, until lately, was directed to the possibility that other properties beside the surface area, like crystal shape and the oxygen source, could be influent. Very recently we demonstrated that the catalytic activity of TiO 2 in the degradation of phenol (PhOH) in water depends on both the average particle size and the type of oxygen donor (O 2 or H 2 O 2). Specifically, when the oxygen donor was H 2 O 2 , the large crystals of pure rutile or rutile-rich mixtures showed the highest activity; oppositely, when using O 2 , anatase and anatase-rich mixtures are the most active [23,24]. This behavior was attributed to the slow recombination rate of the electron-hole couple in rutile large nanocrystals, which controls the catalytic mechanism when the
Journal of Molecular Catalysis A: Chemical, 2009
Nanocrystalline TiO 2 materials produced by an acid-catalyzed sol-gel method are used as catalysts in the photocatalytic degradation of phenol under ultraviolet light. Materials with different crystalline and morphological properties are obtained by controlling the temperature used in the calcination step. Induced light conversion and adsorption have opposite dependencies on the light intensity. The operational parameters (nature of TiO 2 crystal phase, catalyst concentration, pH and initial phenol concentration) have the expected influence in the efficiency of the photocatalytic degradation process. The effect of two different co-oxidants (H 2 O 2 and Na 2 S 2 O 8 ) in the photocatalytic process is also described. A modified Langmuir-Hinshelwood kinetic model is used considering a pseudo-steady state approach in order to explain the dependence of both, the kinetic rate and adsorption equilibrium constants, on light intensity. Hydroquinone and catechol are the main intermediates of the photocatalytic reaction, as result from the reaction of phenol with photogenerated hydroxyl radicals. A possible degradation pathway is advanced.
Photocatalytic degradation of phenol and phenolic compounds
Journal of Hazardous Materials, 2007
Due to the toxicity effects and endocrine disrupting properties of phenolic compounds, their removal from water and wastewater has gained widespread global attention. In this study, the photocatalytic degradation of phenolic compounds in the presence of titanium dioxide (TiO 2) nano-particles and UV light was investigated. A full factorial design consisting of three factors at three levels was used to examine the effect of particle size, temperature and reactant type on the apparent degradation rate constant. The individual effect of TiO 2 particle size (5, 10 and 32 nm), temperature (23, 30 and 37 °C) and reactant type (phenol, o-cresol and m-cresol) on the apparent degradation rate constant was determined. A regression model was developed to relate the apparent degradation constant to the various factors. The largest photocatalytic activity was observed at an optimum TiO 2 particle size of 10 nm for all reactants. The apparent degradation rate constant trend was as follows: o-cresol > m-cresol > phenol. The ANOVA data indicated no significant interaction between the experimental factors. The lowest activation energy was observed for o-cresol degradation using 5-nm TiO 2 particles. A maximum degradation rate constant of 0.0138 min −1 was recorded for o-cresol at 37 °C and a TiO 2 particle size of 13 nm at a D-optimality value of approximately 0.98. The response model adequately related the apparent degradation rate constant to the factors within the range of factors under consideration.
Industrial & Engineering Chemistry Research, 2007
Combined photolysis and predominantly photocatalytic degradation of phenol under UV-C light (λ) 254 nm) with the maximum intensity of 5400 µW/cm 2 was carried out in a batch reactor. The TiO 2 photocatalysts were supported on glass beads, silica gel, and quartz sand using a sol-gel method. The supported TiO 2 catalysts were characterized by XRD, SEM, and EDX analyses. Factors affecting the photocatalytic degradation of phenol such as pH, oxygen supply rate, initial phenol concentration, and H 2 O 2 concentration were investigated. TiO 2 supported on quartz sand gave the highest efficiency with 90% degradation of 50 mg/L phenol solution in 6 h, followed by TiO 2 supported on silica gel and glass beads with 86% and 74%, respectively. The higher photoactivity of supported TiO 2 on quartz sand was ascribed to the high crystallinity and high quantity of Ti, and the absence of ions which could inhibit the crystallization on the catalyst surface. The supported TiO 2 was found to be stable for repeated use. The results suggested that TiO 2 /quartz sand and TiO 2 /glass beads gave very good performances in the phenol degradation reaction. However, with TiO 2 /silica gel, the percentage of degradation decreased to about 11% when used for the second time and then the percentage of degradation decreased slightly when reused again in the third and fourth runs.
Degradation of phenol by TiO 2-based heterogeneousphotocatalysts in presence of sunlight
Journal of Hydro-environment Research, 2009
This paper reports the results of a study on the titanium dioxide Anjatox Ò , which shows very interesting photocatalytic activity. Produced for commercial purposes as a white pigment, its features make it very interesting in the field of heterogeneous photocatalysis. The results obtained with this photocatalyst are compared with the behavior of the well-studied and widely used TiO 2 Degussa P-25 Ò under identical conditions. The degradation experiments showed that the photocatalytic efficiency of Anjatox Ò is comparatively close to that of Degussa P-25 Ò . Both Anjatox Ò and Degussa P-25 Ò show optimum degradation efficiency at a certain loading rate. The particle crystallite size and the BET surface area of the Anjatox Ò TiO 2 are also compared with Degussa P-25 Ò . Moreover the XRD study showed that TiO 2 Anjatox Ò was more crystalline than the TiO 2 Degussa P-25. The particle size histogram of TiO 2 Anjatox Ò was found to be comparatively uniform like TiO 2 Degussa P-25 Ò . The use of TiO 2 Anjatox Ò in heterogeneous photocatalysis is more desirable when high photocatalyst loading is required because of its low cost. The cost of Anjatox TiO 2 was INR.110.00/Kg and the cost of Degussa P-25 was INR 1000/Kg (Jan
Photocatalytic Phenol Degradation by Silica-Modified Titanium Dioxide
Applied Sciences
Titanium dioxide (TiO2) has been widely applied as a photocatalyst for wastewater treatment due to its high photocatalytic activity and it can remove various harmful organic pollutants effectively. Under heated system, however, TiO2 is prone to agglomeration that decrease its abilities as a photocatalyst. In order to overcome the agglomeration and increase its thermal resistance, addition of silica (SiO2) as supporting material is proposed in this research. Silica or silicon dioxide can be extracted from natural resources such as beach sand. Here, we report the application of a composite photocatalyst of TiO2/SiO2 to remove phenolic compounds in wastewater. The photocatalyst was synthesized by adding SiO2 from beach sand onto TiO2 through impregnation methods. The results of the X-ray diffraction (XRD) showed that TiO2 was present in the anatase phase. The highest crystallinity was obtained by TiO2/SiO2 ratios of 7:1. SEM results showed that the shape of the particles was spherical....
2008
Abstract Photocatalytic treatment of water and wastewater is a process which has been introduced since at least a couple of decades ago. But, in spite of its high capabilities, it has not yet reached its real niche among the other treatment methods. Immobilization of TiO2 nano-particles seems to be the key to the industrialization of this process. In this research, an attempt was made to step toward this goal, by immobilizing the successful Degussa P-25 photocatalyst using a very simple and inexpensive method.
Phenol degradation by powdered metal ion modified titanium dioxide photocatalysts
Chemical Engineering Journal, 2012
Conventional water purification and disinfection generally involve potentially hazardous substances, some of which known to be carcinogenic in nature. Titanium dioxide photocatalytic processes provide an effective route to destroy hazardous organic contaminants. This present work explores the possibility of the removal of organic pollutants (phenol) by the application of TiO 2 based photocatalysts. The production of series of metal ions doped or undoped TiO 2 were 52 carried out via a sol gel method and a wet impregnation method. Undoped TiO 2 and Cu doped TiO 2 showed considerable phenol degradation. The efficiency of photocatalytic reaction largely depends on the photocatalysts and the methods of preparation the photocatalysts. The doping of Fe, Mn, and humic acid at 1.0 M% via sol gel methods were detrimental for phenol degradation. The inhibitory effect of initial phenol concentration on initial phenol degradation rate reveals that photocatalytic decomposition of phenol follows pseudo zero order reaction kinetics. A concentration of >1 g/L TiO 2 and Cu doped TiO 2 is required for the effective degradation of 50 mg/L of phenol at neutral pH. The rise in OHat a higher pH values provides more hydroxyl radicals which are beneficial of phenol degradation. However, the competition among phenoxide ion, Cland OHfor the limited number of reactive sites on TiO 2 will be a negative influence in the generation of hydroxyl radical. The dependence of phenol degradation rate on the light intensity was observed, which also implies that direct sunlight can be a substitute for the UV lamps and that photocatalytic treatment of organic pollutants using this technique shows some promise.