Phenol In Aqueous Suspensions Research Articles

Synthesis of protonated titanate nanotubes tailored by the washing step: Effect upon acid properties and photocatalytic activity

Abstract In this work, the acid and photocatalytic properties of titanate nanotubes (NTs) were surveyed. The surface acidity of the NTs was characterized by FTIR with lutidine and pyridine. The photocatalytic degradation of phenol in aqueous suspension was performed to test the photocatalytic properties of the NTs. The results were compared with those obtained from commercial TiO 2 . NTs were prepared by hydrothermal treatment of TiO 2 nanoparticles in a NaOH aqueous solution. During the washing step, three different acid agents (HCl, H 2 SO 4 , and HNO 3 ) were used. TiO 2 nanoparticles were synthesized previously by the sol-gel method. The photocatalytic materials were characterized by FTIR, XRD, XPS, S BET , UV–vis, and HRTEM. It was found that the used acid agent significantly affected the amount and type of acid sites. Bronsted acid sites were favored by the use of HNO 3 . Lewis acid sites were promoted when HCl was employed during the washing step, which is in contrast with the results obtained using the other acids chosen in this work. Besides, the use of HCl promoted the H 2 Ti 3 O 7 phase. The acid phase H 2 Ti 4 O 9 ·H 2 O was favored when HNO 3 was used and H 2 SO 4 formed the H 2 Ti 2 O 4 ·(OH) 2 acid phase. The presence of Cl, S, and N species on the NTs was not found. Furthermore, Na + ions were completely removed from the surface of the NTs, which were exchanged by H + ions. It was found, in general, that the three catalysts presented a relatively high photocatalytic activity to remove phenol. However, NTs washed with HNO 3 (NT-HNO 3 ) displayed the best photocatalytic activity compared to the other NTs. After 200 min, NT-HNO 3 reached a phenol degradation yield close to 100%. Commercial TiO 2 presented a phenol degradation yield close to 60%. It could be concluded that the acid phase (H 2 Ti 4 O 9 ·H 2 O) and concentration of Bronsted acid sites promoted the photocatalytic activity of NT-HNO 3 .

Photocatalytic degradation of phenol using doped titania supported on photonic SiO2 spheres

The photocatalytic degradation of phenol in aqueous suspensions of co-doped TiO2 supported on SiO2 spheres was investigated. A novel photocatalyst was prepared combining iron doped TiO2–SiO2 and reduced TiO2–SiO2 by mechanical milling (MM/TiO2–SiO2). All the particles were characterized by BET. nitrogen adsorption, X-ray diffraction, scanning electron microscopy, UV–visible spectroscopy and elemental analysis. Trough XRD patterns it was calculated that 2 nm rutile crystallites were formed onto SiO2 surface, ICP analysis confirmed Ti content near to nominal, while EDX analysis shows a surface content 10 lower, suggesting that the SiO2 limiting the agglomeration of TiO2 particles allowing a good dispersion. Phenol photodegradation was induced by illuminating the coated spheres in aqueous solution with a visible light source. The synthesized TiO2–SiO2 particles appeared to be 1.3 times more efficient in the phenol conversion, as compared to pure rutile particles. According to characterization results, this improvement could be attributed mainly to three factors: an effective transference of charge carriers trough the grain boundaries present between contact points, a photonic behavior evidenced on an increment on UV–vis absorption intensity and the quantum size effect of rutile crystallites coated on SiO2.

Enhanced adsorption and photodegradation of phenol in aqueous suspensions of titania/graphene oxide composite catalysts

This study uses a hydrothermal method to synthesize titania@graphene oxide (TGO) composite catalysts for the photodegradation of phenol under UV illumination in liquid phase. The graphene oxide (GO) sheets were derived from natural graphite powders using a modified Hummers’ method. One efficient hydrothermal method reinforces the adhesion between GO sheets and titania nanoparticles (T), forming composite catalysts. The adsorption capacities of phenol on T, GO, and TGO composites were experimentally determined, and the order of adsorption efficiency was found to be TGO > GO > T. The photocatalytic performance on the composite catalysts was systematically evaluated by the pseudo first-order kinetic model. Experimental results reveal that the TGO composite exhibits the best photocatalytic activity, including apparent rate constant and equilibrium catalytic ability, among the tested samples. This enhanced performance may be attributed to the well-dispersed titania nanocatalysts that are attached to the GO sheets, which offer homogeneous active sites for phenol adsorption, followed by photodegradation. Accordingly, the robust design of TGO composite catalysts offers an effective route for the treatment of organic wastewater.

Influence of TiO2 optical parameters in a slurry photocatalytic reactor: Kinetic modelling

A kinetic model, based on a proposed reaction photo-mechanism and explicitly dependent on the volumetric rate of photon absorption (VRPA), has been performed and analyzed for the photocatalytic degradation of phenol in aqueous suspensions. UVA–vis simulated solar radiation and three commercial TiO2 powder photocatalysts, with identical chemical structure but with different morphology and hydrodynamic particle size (P25 Aeroxide®, P25/20 VP Aeroperl® and P90 Aeroxide® provided by Evonik) have been used. The effect of TiO2 hydrodynamic particle size on the optical coefficients has revealed that this property is playing an important role on the absorbed radiation evaluation. Radiation profiles inside the photoreactor were determined by solving the radiative transfer equation (RTE), and the corresponding kinetic parameters were obtained.A comparative study of TiO2 loading effect on calculated quantum efficiency (η) revealed P25 was the most photo-efficient catalyst, whereas P25/20 reached similar efficiencies only when higher TiO2 concentrations were used. On the contrary, P90 presented the lowest photo-efficiency with lower photodegradation rates despite absorbing more radiation.The obtained kinetic model has been successfully validated by experimental data, being able to reproduce the evolution of phenol photodegradation at a wide range of catalyst concentrations for the three studied TiO2. In the experimental conditions of this work, low irradiation power conditions can be considered; after simplification, the model adopted a linear dependence on the volumetric rate of photon absorption; showing good agreement between predicted and experimental values, with root-square-mean errors below 5%.

Photocatalytic degradation of phenol by char/N-TiO2 and char/N-F-TiO2 composite photocatalysts

Pyrolytic char/Ν-TiO2 (CTN), pyrolytic char/Ν-F-TiO2 (CTNF) and activated pyrolytic char-TiO2 (ACT) composite catalysts have been successfully prepared by a sol–gel method. TiO2 anatase was the major phase formed in all doped catalysts with a small fraction of brookite phase observed for CTN and ACT. UV–vis diffuse reflectance spectroscopy showed a decrease of band gap energy for all doped CTN and CTNF catalysts. The photocatalytic activity of the studied photocatalysts was systematically investigated under visible light and simulated solar light irradiation, by monitoring the degradation of phenol in aqueous suspensions. CTN and CTNF catalysts showed a better photocatalytic efficiency compared to ACT catalysts. The CTNF composite with a ratio of [pyrolytic char]/[Ν-F-TiO2]=0.2/2 was found to be the most effective catalyst for phenol removal. According to our results, the pyrolytic char presented favorable adsorption characteristics for phenol and acts as an electron-acceptor from doped-TiO2 particles resulting in decreased e− − h+ pair recombination and subsequently in enhanced production of HO. Moreover, it was revealed that Ν-F modification promotes the e− − h+ separation in TiO2 concomitantly with an enhancement in the visible spectral absorbance.

Influence of the Dopant Concentration on the Photocatalytic Activity: Al-Doped TiO2

A set of Al-doped titania x-Al-TiO2 (x = 0.0, 0.1, 0.3, 0.5, 0.7, 0.9, 1.1 wt % Al) has been synthesized by a sol–gel method and tested in the reaction of the photocatalytic degradation of phenol in aqueous suspension. XRD and Raman studies show that the TiO2 samples have a mixed-phase rutile-anatase crystalline structure with linear increase of the anatase fraction from 0.0 wt % for 0.0-Al-TiO2 up to 18 wt % for 1.1-Al-TiO2. A decrease of the particle size from ∼800 to 50 nm and an increase of the specific surface area from 1.7 m2/g up to 28 m2/g with increased content of Al have been observed. The data of XRD, XPS, Raman spectroscopy, and EDS techniques show rather homogeneous aluminum distribution with only the Al(3+) oxidation state of aluminum incorporated in the TiO2 lattice. The bandgap energy Eg = (2.93 ± 0.1) eV corresponding to indirect allowed transitions does not depend on the aluminum content within the 0.0–1.1 wt % Al concentration range. The photocatalytic testing of Al-doped TiO2 samples i...

The influence of Ce doping of titania on the photodegradation of phenol.

Pure and cerium-doped [0.05, 0.1, 0.3, 0.5, and 1.0 Ce nominal atomic % (at.%)] TiO2 was synthesized by the sol-gel method. The obtained catalysts were characterized by X-ray diffraction (XRD), UV-visible diffused reflectance spectroscopy (DRS), Raman, and BET surface area measurement. The photocatalytic activity of synthesized samples for the oxidative degradation of phenol in aqueous suspension was investigated. The content of Ce in the catalysts increases both the transition temperature for anatase to rutile phase transformation and the specific surface area, and decreases the crystallite size of anatase phase, the crystallinity, and the band gap energy value. The material with higher efficiency corresponds to 0.1 Ce nominal at.%. Under irradiation with 350 nm lamps, the degradation of phenol could be described as an exponential trend, with an apparent rate constant of (9.1 ± 0.6) 10(-3) s(-1) (r(2) = 0.98). Hydroquinone was identified as the main intermediate.

Preparation, characterization and photocatalytic performance of pyrolytic-tire-char/TiO2 composites, toward phenol oxidation in aqueous solutions

A pyrolytic char/TiO2 (PC/TiO2) composite material, where PC was derived from recycled tires, was prepared by the sol–gel method. XRD analysis showed formation of TiO2 anatase phase, as well as, a small fraction of brookite phase. UV–vis DRS spectroscopy showed that PC/TiO2 composites have enhanced absorption at visible wavelengths 340–450nm. The photocatalytic activity and the promoting effect of PC/TiO2 composite catalysts were investigated for the degradation of phenol in aqueous suspensions. The photocatalytic degradation followed pseudo-first order kinetics. The ratio TiO2:PC (w:w) largely affected the performance of the composite catalysts. The optimal (w:w=0.1) ratio was found e.g., (0.2g PC, 2g TiO2). An important finding is a significant promoting effect of PC on the photocatalytic performance of TiO2. Electron paramagnetic resonance (EPR) spectroscopy showed that the pyrolytic char acts as a very efficient electron-acceptor from TiO2 particles under UV–vis irradiation. This resulted in decreased electron–hole pair recombination and subsequently in enhanced production of OH-radicals that oxidized phenol. Thus, PC matrix can act as an electron storage matrix for photo-induced electrons from TiO2.

Influence of parameters on the photocatalytic degradation of phenolic contaminants in wastewater using TiO2/UV system

The photocatalytic degradation of phenol in aqueous suspension using commercial TiO2 powder (Degussa P-25) irradiated with UV light was investigated. Photodegradation was compared using a photocatalyst (TiO2 alone), direct photolysis (UV alone) and TiO2/UV in a single batch reactor with mercury lamp irradiation. The study focused on the influence of various operating parameters on phenol treatment efficiency, including catalyst dosage, initial concentration of phenol, temperature, pH and change in pH were systematically investigated. The highest phenol degradation rate was obtained at pH 9.0, temperature 60°C and catalyst dose of 2 g L−1 with higher mineralization efficiency (in terms of TOC reduction). Experimental results showed that under optimized conditions the phenol removal efficiency was 98% and 100% for the TiO2/UV and TiO2/UV/H2O2 system, respectively. No significant effect on addition of chloride and metal ions was observed. Photodegradation of phenol followed first-order kinetics. To test whether the phenol removal was possible for wastewater using a TiO2/UV system, the degradation study was conducted with the real obtained wastewater. The removal of phenol from obtained wastewater and the synthetic wastewater containing phenol was comparable. The TiO2/UV system developed here is expected to be useful for the treatment of wastewater containing phenol.

Preparation and characterization of mesoporous N-doped and sulfuric acid treated anatase TiO 2 catalysts and their photocatalytic activity under UV and Vis illumination

Nitrogen-doped TiO 2 catalysts were prepared by a precipitation method. The samples were calcined at 400 °C for 4 h in air. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), low temperature N 2-adsorption was used for structural characterization and UV-diffuse reflectance (UV-DR) was applied to investigate the optical properties of the as-prepared samples. It was found that microporous N-doped catalysts have solely anatase crystalline structure. Acidic treatment of the calcined samples was performed using sulfuric acid agitation. The crystalline structure remained unchanged due to surface treatment, while the porosity and the surface areas ( a BET S ) were decreased dramatically. Optical characterization of the doped catalysts showed that they could be excited by visible light photons in the 400–500 nm wavelength range ( λ g ,1=∼390 nm, λ g ,2=∼510 nm). It was also established that surface treatment enhances the Vis-light absorption of the N-TiO 2 powders. Finally the catalysts were tested in the photocatalytic degradation of phenol in aqueous suspensions. Two different light sources were used; one of them was a UV-rich high pressure Hg-lamp, while the other was a tubular visible light source. We found that using visible light illumination N-doped, acid treated TiO 2 samples were more catalytically active than non-doped TiO 2 catalysts.

TiO2-Photocatalyzed degradation of phenol in saline media in an annular reactor: hydrodynamics, lumped kinetics, intermediates, and acute toxicity

The photocatalytic degradation of phenol in aqueous suspensions of TiO2 under different salt concentrations in an annular reactor has been investigated. In all cases, complete removal of phenol and mineralization degrees above 90% were achieved. The reactor operational parameters were optimized and its hydrodynamics characterized in order to couple mass balance equations with kinetic ones. The photodegradation of the organics followed a Langmuir-Hinshelwood-Hougen-Watson lumped kinetics. From GC/MS analyses, several intermediates formed during oxidation have been identified. The main ones were catechol, hydroquinone, and 3-phenyl-2-propenal, in this order. The formation of negligible concentrations of 4-chlorophenol was observed only in high salinity medium. Acute toxicity was determined by using Artemia sp. as the test organism, which indicated that intermediate products were all less toxic than phenol and a significant abatement of the overall toxicity was accomplished, regardless of the salt concentration.

Erratum: Effect of Lamp Power and Its Position on Photocatalytic Degradation of Phenol in Aqueous Suspension of TiO2 [e-J. Surf. Sci. Nanotech. Vol. 7, pp. 804-807 (2009)

In the article, Eqs. (8) and (9) should be corrected. In addition, the second legend in Fig. 5 should be corrected. [DOI: 10.1380/ejssnt.2009.836]

Effect of Lamp Power and Its Position on Photocatalytic Degradation of Phenol in Aqueous Suspension of TiO2

The photocatalytic degradation of phenol under irradiation with UV light was investigated in aqueous suspension of nano titanium dioxide (TiO2). The effects of photocatalyst such as TiO2 (anatase) and TiO2-P25 and power of UV-lamp along with position on the photocatalytic degradation of phenol have been studied. The degradation kinetics was analyzed by the change in phenol absorbance employing UV-vis spectrometry as a function of irradiation time. The degradation follows first order kinetics. TiO2-P25 was found to be more reactive than TiO2 (anatase) which is attributed to small crystalline size. Horizontal position of the lamp was found to be better than vertical position of lamp. The degradation was also enhanced with increased in power of UV lamp. [DOI: 10.1380/ejssnt.2009.804]

Photochemical formation of hydroxyl radicals catalyzed by montmorillonite

In this work, the photooxidation of benzene and the formation of phenol in aqueous suspensions of the iron-rich montmorillonite under irradiation of a 250 W metal halide lamp ( λ ⩾ 365 nm) were investigated. We confirmed that hydroxyl radicals ( OH) were produced by illuminating montmorillonite and was responsible for the photooxidation of benzene in aqueous suspensions of montmorillonite. Low pH value facilitated the formation of hydroxyl radicals in the pH range of 2.0–10.0. The OH concentration increased with increasing the concentration of montmorillonite in aqueous solutions in the range of 0–20.0 g l −1. Higher concentration like 25.0 g l −1 montmorillonite inhibited the OH production. Iron, predominantly free iron in the clays, is believed to be one of the most important factors determining OH formation. Structural irons in montmorillonite have contributions to OH formation, especially in the presence of carboxylate ions. The formation of OH from montmorillonite under irradiation of near UV and visible light indicates that clays might play important role not only in transfer through adsorption but also in transformation through oxidation of organic compounds on the surface of clay particles in air, water, soil or even top sediments.

Novel core-shell structured mesoporous titania microspheres: Preparation, characterization and excellent photocatalytic activity in phenol abatement

Thermally stable mesoporous core-shell structured nanocrystallite titanium dioxide (TiO 2) microspheres were prepared by a novel hydro-alcohol thermal method. Anatase powders were synthesized under hydrothermal condition at 368 K from aqueous titania tetrachloride solution with the presence of urea and ammonium sulfate, then the samples were annealed at various temperatures before testing their photocatalytic activity. The morphology and microstructure characteristics of TiO 2 microspheres series were characterized by means of the specific surface area (BET), transmission electron microscopy (TEM), scanning electron microscopy (SEM), differential thermal analysis (DTA), photoluminescence spectra (PLS), X-ray photoelectron spectroscopy (XPS) and X-ray powder diffraction (XRD). The specific microsphere structures were maintained after a heat treatment at 973 K for 3 h, exhibiting a significant thermal stability. The photocatalytic activity was measured in a reactor with ultraviolet lamps. The catalysts show considerably high catalytic activity and recyclability during the photodegradation of phenol in aqueous suspension, the microsphere titania sample calcinated under 733 K for 3 h shows the best photocatalytic activity. The results obtained with this novel photocatalyst are compared with the behavior of the well-studied and widely used Degussa P25 TiO 2 under the same conditions.

Simple fabrication of twist-like helix N,S-codoped titania photocatalyst with visible-light response

Visible-light responsible N,S-codoped titania photocatalyst was fabricated by simple hydrolysis of titania tetrachloride using ammonia in the presence of glacial acetic acid and ammonium sulfate. The N,S-codoped titania materials were fabricated by a template-free route and demonstrated twist-like helix morphology. The morphology and microstructure characteristics of N,S-codoped titania photocatalysts were characterized by means of the N2 adsorption–desorption measurements, thermal gravimetric and differential thermal analysis (TG-DTA), transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), UV–visible diffuse reflectance spectra (DRS) and X-ray powder diffraction (XRD). The unique morphology of N,S-codoped titania materials and mesoporous microstructure were maintained after a heat treatment at 723K for 3h, exhibiting significantly thermal stability. The photocatalytic activity was evaluated by degrading phenol in aqueous suspension under ultraviolet and visible light irradiation. The results obtained with these novel photocatalysts are compared with the behavior of the well-studied and widely used Degussa P25 TiO2 under the same conditions. The N,S-codoped titania samples were more superior than P25 and the sample calcined under 723K for 3h shows the best photocatalytic activity, the higher activity of which could be attributed to its high surface area, large pore volume, well-crystallized anatase, red-shift in adsorption edge and strong absorbance of light with longer wavelength.

Influence of operating parameters on photocatalytic degradation of phenol in UV/TiO2 process

Abstract The use of hydrogen peroxide (H 2 O 2 ) for improved photocatalytic degradation of phenol in aqueous suspension of commercial TiO 2 powders (Degussa P-25) was investigated. Photodegradation was compared using direct photolysis (UV alone), H 2 O 2 /UV, TiO 2 /UV, and H 2 O 2 /TiO 2 /UV processes in a batch reactor with high-pressure mercury lamp irradiation. The effects of operating parameters such as catalyst dosage, light intensity, pH of the solution, the initial phenol, and H 2 O 2 concentrations on photodegradation process were examined. It was shown that photodegradation using H 2 O 2 /TiO 2 /UV process was much more effective than using either H 2 O 2 /UV or TiO 2 /UV process. The effect of the initial phenol concentration on TOC removal was also studied, demonstrating that more than 8 h was required to completely mineralize phenol into water and carbon dioxide. For all the four oxidation processes studied, photodegradation followed the first-order kinetics. The apparent rate constants with 400-W UV ranged from 5.0 × 10 −4 min −1 by direct photolysis to 1.4 × 10 −2 min −1 using H 2 O 2 /TiO 2 /UV process. The role of H 2 O 2 on such enhanced photodegradation of phenol in aqueous solution was finally discussed.

Effect of Ammonia Thermal Treatment on the Structure and Activity of Titanium Oxide Photocatalysts

Different titanium oxide powders (ATiO2, BTiO2) were pretreated in ammonia (NH3) gas at high temperatures. After the pretreatment, the color of the titanium oxide powders changed from white to yellow or gray depending on the pretreatment temperatures. Morphologies and structures of the treated titanium oxide powders were characterized by physical chemical methods. XRD measurements showed that the crystalline structures were mainly mixture of anatase and rutile for the ATiO2 but only anatase for the BTiO2. Stronger absorption of visible light was observed for both types of samples using UV-Vis diffuse reflectance spectra. X-ray photoelectron spectroscopy demonstrated that doped nitrogen existed on the surface TiO2 after ammonia gas pretreatment. The photocatalytic activities of the treated titanium oxide samples were evaluated via the photodegradation of methyl orange and phenol in aqueous suspensions. No obvious improvement in photocatalytic activity was achieved by ammonia pretreatment although it could enhance the absorption of light. Effects of treatment temperatures on photoactivities were complete different for ATiO2 and BTiO2 (i.e. higher treated temperatures yielded higher activities for BTiO2 but lower for ATiO2). All samples yielded lower activity levels after ammonia pretreatment without regard to pretreatment temperature or the reaction light resource.

Determination of phenol in the presence of its principal degradation products in water during a TiO 2-photocatalytic degradation process by three-dimensional excitation–emission matrix fluorescence and parallel factor analysis

This paper describes a simple and rapid way of monitoring a photocatalytic degradation of phenol in aqueous suspensions of TiO 2. A three-way analytical methodology based on fluorescence excitation–emission matrix (EEM) and parallel factor analysis (PARAFAC) was developed to resolve the species present in the reaction mixture and quantify the concentration of phenol and its principal degradation products throughout the degradation. Parameters such as core consistency, fit% and correlation coefficients between recovered and pure spectra were used to determine the appropriate number of factors for the PARAFAC model. The accuracy of the model was evaluated by the root mean square error of prediction (RMSEP). Using a four-factors PARAFAC model, phenol, hydroquinone, resorcinol and catechol, were satisfactorily determined. The proposed method is an interesting alternative to the traditional techniques normally used for monitoring degradation reactions.

TiO2-photocatalyzed degradation of phenol in saline media: lumped kinetics, intermediates, and acute toxicity

The photocatalytic degradation of phenol in aqueous suspensions of TiO2 under different salt concentrations has been investigated. In all cases, complete removal of phenol and mineralization degrees above 90% were achieved. However, the time needed to effectively remove phenol and degrade organics was considerably increased in high salinity medium. The photodegradation of the organics followed a Langmuir–Hinshelwood–Hougen–Watson lumped kinetics, showing rate and adsorption/desorption constants that decrease as salinity increases. From GC/MS analyses, various hydroxylated intermediates formed during oxidation have been identified. The main ones were catechol, hydroquinone, and 4,4′-dihydroxybiphenyl, in this order. It was shown that salinity inhibited catechol formation and promoted 4,4′-dihydroxybiphenyl production. The formation of negligible concentrations of 4-chlorophenol was observed only in high salinity medium. Acute toxicity during degradation process was determined by using Artemia sp. as the test organism, which is suited for saline environments. Intermediate products were all less toxic than phenol and a significant removal of the overall toxicity was accomplished, regardless of the salt concentration.Photocatalytic phenol degradation in the absence of salt and in low salinity media (2gL−1) was quite the same (100% for a 150min irradiation time). However, high salinity media (50gL−1) showed a significant difference (81%). Organic matter mineralization showed a similar behavior regarding the media (94 and 44%, respectively).