Photocatalytic activity of nanocrystalline mesoporous-assembled TiO2 photocatalyst for degradation of methyl orange monoazo dye in aqueous wastewater

In this work, nanocrystalline mesoporous-assembled TiO₂ photocatalyst was synthesized by a sol–gel process with the aid of a structure-directing surfactant and employed for the photocatalytic degradation of methyl orange azo dye (monoazo dye), as compared to various commercially available non-mesoporous-assembled TiO₂ powders. The experimental results showed that the synthesized mesoporous-assembled TiO₂ nanocrystal calcined at 500 °C provided superior decolorization and degradation performance to the non-mesoporous-assembled commercial TiO₂ powders. In addition, several operational parameters affecting the decolorization and degradation of methyl orange, namely photocatalyst dosage, initial dye concentration, H₂O₂ concentration, and initial solution pH, were systematically investigated, using the mesoporous-assembled TiO₂ nanocrystal. The optimum conditions were a photocatalyst dosage of 7 g/l, an initial dye concentration of 5 mg/l, a H₂O₂ concentration of 0.5 M, and an initial solution pH of 4.7, exhibiting the highest decolorization rate of methyl orange.     

Photocatalytic degradation of toluene with ozone addition

The main goal of this study is to analyze the characteristics of photodegradation and photocatalytic activation experimentally with the major parameters such as air flow rate, inlet toluene concentration, ozone concentration, UV light and bead material, etc. In particular, the effects of transmissivity of UV radiation with TiO₂ coated supporter (bead material) and void fraction (bead size) on the photocatalytic degradation are estimated for TiO₂/UV and O₃/TiO₂/UV process. In results, the experiment shows that the UV light transmissivity of 5mm glass bead becomes much higher than that of 6.5 mm alumina bead in spite of lower void fraction inducing the higher photoactivation. The conversion of toluene represents about 96% during reaction time 420 min at the toluene concentration of 100 ppm and ozone concentration of 2.5 ppm, showing a conversion rate of ozone of 95% for O₃/TiO₂/UV process. This paper was prepared at the 2004 Korea/Japan/Taiwan Chemical Engineering Conference held at Busan, Korea between November 3 and 4, 2004.     

Influence of Ozone on the Photocatalytic Oxidation of Organic Compounds

Heterogeneous photocatalytic oxidation processes using titanium oxide as a photocatalyst are widely discussed topics in research for water and waste water treatment. Oxygen fed into the systems is normally used as oxidizing agent. However few investigations exist concerning the use of ozone as an additional oxidant. In this work the influence of ozone on the photocatalytic degradation of organic compounds are described. The results are compared with those by using ozone, UV/O₃ and UV/TiO₂/O₂. The oxidation reactions were performed at pH 3 and 7.

In this research compounds of the different classes were used: glyoxal, pyrrole-2-carboxylic acid, p-toluenesulfonic acid and naphthalene-1,5-disulfonic acid. Depending on the classes of compounds in some cases the elimination rates of the initial compounds is enhanced by using UV/TiO₂/O₃ compared to UV/O₃ or O₃ alone. But in all cases greatest DOC elimination is achieved by using UV/TiO₂/O₃.     

Photocatalytic membrane reactor for degradation of acid red B wastewater

Nano-titanium dioxide (TiO₂) photocatalyst was prepared by acid–sol method using tetrabutyl titanate and ethanol, which appeared to be anatase by XRD analysis. The wastewater containing azo dye acid red B was then subjected to photocatalytic degradation with photocatalyst TiO₂ and UV as light source in a slurry photocatalytic membrane reactor, which included a double layer cylindrical photocatalytic reaction zone and a plate frame membrane separation part. Two kinds of ultrafiltration (UF) membranes PVDF700 and PAN700 were applied and the combined process with photocatalysis was operated by a continuous re-circulating mode during treatment. At first, the adsorption characteristic of the titanium dioxide catalyst under different pH values was analyzed and the optimal operation condition of the photocatalytic process was achieved by changing TiO₂ dose and initial concentration of the dye. Then the performance of photocatalyst separation process by ultrafiltration (UF) was investigated. It was found that the degradation of acid red B was followed by first-order kinetics and the efficiency of photocatalysis can be evaluated by the initial reaction rate. Finally, the conglomeration and hydrophilizion phenomena by TiO₂ in the coupling system and its effect to different ultrafiltration membranes were analyzed.     

Ozone-Based Advanced Oxidation Processes for the Decomposition of N-Methyl-2-Pyrolidone in Aqueous Medium

The present study investigates the decomposition of N-Methyl-2-Pyrolidone (NMP) using conventional ozonation (O₃), ozonation in the presence of UV light (UV/O₃), hydrogen peroxide (O₃/H₂O₂), and UV/H₂O₂ processes under various experimental conditions. The influence of solution pH, ozone gas flow dosage, and H₂O₂ dosage on the degradation of NMP was studied. All ozone-based advanced oxidation processes (AOPs) were efficient in alkaline medium, whereas the UV/H₂O₂ process was efficient in acidic medium. Increasing ozone gas flow dosage would accelerate the degradation of NMP up to certain level beyond which no positive effect was observed in ozonation as well as UV light enhanced ozonation processes. Hydrogen peroxide dosage strongly influenced the degradation of NMP and a hydrogen peroxide dosage of 0.75 g/L and 0.5 g/L was found to be the optimum dosage in UV/H₂O₂ and O₃/H₂O₂ processes, respectively. The UV/O₃ process was most efficient in TOC removal. Overall it can be concluded that ozonation and ozone-based AOPs are promising processes for an efficient removal of NMP in wastewater.     

Statistical optimization of process conditions for photocatalytic degradation of phenol with immobilization of nano TiO<Subscript>2</Subscript> on perlite granules

Response surface methodology (RSM) using D-optimal design was applied to optimization of photocatalytic degradation of phenol by new composite nano-catalyst (TiO₂/Perlite). Effects of seven factors (initial pH, initial phenol concentration, reaction temperature, UV irradiation time, UV light intensity, catalyst calcination temperature, and dosage of TiO₂/perlite) on phenol conversion efficiency were studied and optimized by using the statistical software MODDE 8.02. On statistical analysis of the results from the experimental studies, the optimum process conditions were as follows: initial pH, 10.7; initial phenol concentration, 0.5 mM; reaction temperature, 27 °C; UV irradiation time, 6.5 h; UV light intensity, 250 W; catalyst calcination temperature, 600 °C; and TiO₂/perlite dosage, 6 g/L. Analysis of variance (ANOVA) showed a high coefficient of determination (R²) of 91.8%.     

Application of Response Surface Methodology for Coffee Effluent Treatment by Ozone and Combined Ozone/UV

This paper reports a study using ozone (O₃) and combined ozone/ultraviolet (O₃/UV) processes for color removal and caffeine degradation from synthetic coffee wastewater using a second-order response surface methodology (RSM) with a three-level central composite face-centered (CCF) design. The effects of O₃ concentration, initial pH, and reaction time were examined for both processes. The reaction time and pH were statistically significant for caffeine degradation and color removal. In the ozonation process, higher caffeine degradation and color removal were observed in alkaline pH, indicating that ozone attacks indirectly, consequently generating hydroxyl radicals. Regarding the ozone/UV process, it was observed that lower caffeine degradation and color removal occurred at neutral pH, indicating an adverse effect due to lower ozone dissolution and consequently the production of a smaller amount of free hydroxyl radicals. The achieved results showed that the techniques were efficient for color removal (85% and 99%, respectively) and caffeine degradation (88% and 98%, respectively).     

Decomposition of phenols in aqueous solution by a UV/O3 process

The decomposition of several non‐biodegradable phenols by the UV/O₃ and ozonation processes was studied and compared under various solution pH values, O₃ input mass flow rates and UV intensities to investigate the removal efficiencies of reactants and organic intermediates. The decomposition rate of phenols by the UV/O₃ process was found to increase with increasing O₃ input dosage, light intensity and solution pH value. The mineralization efficiencies of phenols in aqueous solution would be above 98% under adequate reaction conditions within three hours, but would be retarded for alkaline solutions because of the dissolution of CO₂ formed by mineralization of phenols. The increment of ozone input dosage had little effect on the mineralization of organic intermediates at the latter course of the reaction. The order of the decomposition rate of the phenols used in this research was 2,4‐dichlorophenol > 2‐chlorophenol > 2‐nitrophenol for low and neutral pH solutions, whereas they were nearly alike for alkaline solutions. The two‐step consecutive kinetic model was found to fit well in modeling the behavior of species during the decomposition of phenols in aqueous solutions by the UV/O₃ process.     

Effects of microwave,UV, and O3 on propylene gas degradation via photocatalytic reaction with CVD TiO2 films

A microwave/UV/ozone/TiO₂ photocatalyst hybrid process system, which is a combination of various propylene gas treatment techniques, is evaluated for use as an advanced, efficient technology for air pollution treatment. TiO₂ photocatalyst balls were prepared using low-pressure metal-organic chemical vapor deposition. The microwave/UV/TiO₂ photocatalyst hybrid process exhibited the higher degradation efficiency than the microwave/UV/alumina ball hybrid system. The degradation efficiency increased almost linearly with increasing ozone dose. The lower the propylene inlet concentration was the higher degradation efficiency. The double bond of propylene is broken by ozone and OH, resulting in production of CH₄ and C₂H₆. These two intermediate products are mineralized into CO₂, H₂O, and CO. C₂H₄ and C₃H₈ may be produced from CH₄, whereas C₂H₆ and C₃H₆ are produced by microwave irradiation.     

Sulfanilic acid-modified P25 TiO2 nanoparticles with improved photocatalytic degradation on Congo red under visible light

Visible-light-induced titania/sulfanilic acid nano-composite photocatalysts were prepared and characterized by FTIR, XPS, UV-vis, XRD, and SEM. The results indicate that the formation of Ti-O-S bonds after the modification of P25 TiO₂ nanoparticles with sulfanilic acid ligands extends the photoresponse of the photocatalyst from the UV to the visible range. The photocatalytic activity of the nano-composite photocatalyst was examined by degrading Congo red under visible light, in which its effecting factors such as irradiation time, catalyst dosage, solution pH and the addition of H₂O₂, were investigated in detail. The possible mechanism of photocatalytic degradation under visible irradiation has been also presented.     

Phorate degradation by TiO2 photocatalysis: Parameter and reaction pathway investigations

The photocatalytic degradation of phorate in aqueous suspensions was examined with the use of titanium dioxide (TiO₂) as a photocatalyst. About 99% of phorate was degraded after UV irradiation for 60 min. The photodegradation of phorate followed pseudo-first-order kinetics and parameters such as pH of the system, TiO₂ dosage, and presence of anions were found to influence the reaction rate. To obtain a better understanding of the mechanistic details of this TiO₂-assisted photodegradation of phorate with UV irradiation, the intermediates of the processes were separated, identified, and characterized by the solid-phase microextraction (SPME) and gas chromatography/mass spectrometry (GC/MS) techniques. The probable photodegradation pathways were proposed and discussed. To the best of our knowledge, this is the first study that reports the degradation pathways of phorate. The electrical energy consumption per order of magnitude for photocatalytic degradation of phorate was also calculated and showed that a moderated efficiency (E_EO = 96 kWh/(m³ order)) was obtained in TiO₂/UV process.     

Advanced oxidation processes for destruction of cyanide from thermoelectric power station waste waters

Several advanced oxidation processes for the destruction of cyanide contained in waste waters from thermoelectric power stations of combined‐cycle were studied. Thus, oxidation processes involving ozonation at basic pH, ozone/hydrogen peroxide, ozone/ultraviolet radiation and ozone/hydrogen peroxide/ultraviolet radiation have been carried out in a semi‐batch reactor. All these methods showed that total cyanide can be successfully degraded but with different reaction rates, and the decrease in the total cyanide concentration can be described by pseudo‐first order kinetics. The influence of pH and initial concentration of hydrogen peroxide was studied to find the optimal conditions of the oxidation process. Experimental results of the single ozone treatment indicated that total cyanide is destroyed more rapidly at higher pH (12), while ozonation combined with H₂O₂ and/or UV is faster at pH 9.5. The optimum concentration of H₂O₂ was 20.58 × 10^?2 M because an excess of peroxide decreases the reaction rate, acting as a radical scavenger. The total cyanide degradation rate in the O₃/H₂O₂(20.58 × 10^?2 M ) treatment was the highest among all the combinations studied. However, COD reduction, in the processes using UV radiation such as O₃/UV or O₃/H₂O₂/UV was about 75%, while in the processes with H₂O₂ and/or O₃/H₂O₂ was lower than 57% and was insignificant, when using ozone alone. Copyright © 2003 Society of Chemical Industry     

Spectrophotometric evaluation of the photocatalytic degradation of formaldehyde by Fe2O3–TiO2 nano hybrid

Photocatalytic capabilities of sol–gel synthesized Fe₂O₃–TiO₂ nano hybrid was investigated in degradation of formaldehyde in presence of ultra violet and visible irradiation. The reaction stream was evaluated by UV–vis spectrophotometry at 330–500 nm spectral region, using Fluoral-P (4-amino-3-penten-2-one) as a complexing agent. Obtained results confirmed the effective role of Fe₂O₃ phase in nano hybrid for degradation of formaldehyde according to Baeyer–Villiger reaction. On the other hand TiO₂ would play the role of photocatalyst in presence of UV ray. Nano hybrid assisted process was monitored by spectrophotometry, utilizing multivariate curve resolution chemometric technique.     

Inactivation of Escherichia coli using UV/Ag?TiO2/O3‐mediated advanced oxidation: application to ballast water disinfection

BACKGROUND: Ballast water discharge from ships is regarded as one of the four major risk factors that threaten global marine environmental safety, and ballast water treatment is vital to prevent the introduction of potentially invasive species. The UV/Ag? TiO₂/O₃ process has been investigated for its potential use for ballast water treatment using Escherichia coli (E. coli) as an indicator bacterium. Inactivation curves were obtained, and the occurrence of oxidants was studied. RESULTS: Compared with individual unit processes with ozone or UV/Ag? TiO₂, the inactivation of E. coli by the combined UV/Ag? TiO₂/O₃ process was enhanced, and the inactivation efficiency was improved with increasing ultraviolet intensity and ozone dose. The initial total residual oxidant (TRO) concentration was positively correlated with ozone dose, and resulted in faster decay rate for lower initial concentration. Persistence of TRO resulted in a cumulative bacteria mortality in the effluent. CONCLUSION: The UV/Ag? TiO₂/O₃ process was found to be efficient for E. coli inactivation in simulated ballast water. Copyright © 2011 Society of Chemical Industry     

Photodegradation of four fluoroquinolone compounds by titanium dioxide under simulated solar light irradiation

BACKGROUND; In this study, simultaneous photocatalytic degradation of four fluoroquinolone (FQ) compounds (i.e. ofloxacin, norfloxacin, ciprofloxacin and enrofloxacin) was investigated in TiO₂ suspensions under simulated solar light irradiation. Effects of experimental variables including pH, TiO₂ dosage, initial substrate concentration and hydrogen peroxide (H₂O₂) on the degradation processes were also investigated. RESULTS: The antibiotics degradation was pH‐influenced. The photocatalytic reaction followed the pseudo‐first‐order model, with reaction rate constants (k) 0.026, 0.027, 0.022 and 0.026 min^?1 for ofloxacin, norfloxacin, ciprofloxacin and enrofloxacin, respectively. Complete elimination of four FQs was achieved in a reaction system composed of 0.5 g L^?1 of TiO₂ and 82.5 mg L^?1 of H₂O₂ at pH 6 after 90 min irradiation. Mineralization of FQs during TiO₂ photocatalysis was slower than the FQs conversion, and the antibacterial activity of the four FQs was completely removed by TiO₂ under simulated solar light irradiation. CONCLUSION: The four FQs can be simultaneously degraded and mineralized with commercially available TiO₂ under simulated solar light irradiation. Microbiological analysis showed that the antibacterial activity of the four FQs was completely removed. These results are helpful for antibiotics removal in the environment, and for exploring new technology for wastewater treatment. Copyright © 2012 Society of Chemical Industry     

Preparation of TiO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript> composite oxide and its photocatalytic degradation of rhodamine B

The composite semiconductor photocatalyst TiO₂/SiO₂ was prepared by template-hydrothermal method using carbon spheres as the template. The structural and optical properties of TiO₂/SiO₂ were characterized by XRD, SEM, BET, UV–Vis DRS, TG-DTA, PL techniques. The formation of hydroxyl radical on the surface of TiO₂/SiO₂ was studied with terephthalic acid as the probe molecule, combined with fluorescence technique. The results showed that the specific surface area of TiO₂/SiO₂ composite was 327.9 m²/g, and the specific surface area of TiO₂/SiO₂ was larger than that of pure TiO₂. Photocatalytic degradation of rhodamine B showed that TiO₂/SiO₂ composite oxide under visible light illumination 40 min, the degradation rate was 98.6 % and the degradation rate of pure TiO₂ was only 11.9 %. The apparent first-order rate constant of TiO₂/SiO₂ was 33 times that of pure TiO₂ and more than 6 times that of P25 when the molar ratio of Ti to Si was 1:1 under visible light irradiation. Moreover, it’s also as much as 5 times that of pure TiO₂ and is more than 1 times that of P25 under UV light irradiation 25 min. Based on the experimental results, ^·O₂ ^? and h⁺ were suggested to be the major active species which was responsible for the degradation reaction. The increased photocatalytic activity of TiO₂/SiO₂ may be mainly attributed to effectively suppressing the recombination of hole/electron pairs. After the photocatalyst TiO₂/SiO₂ was reused 5 times, the degradation rate of rhodamine B could reach 89.2 % under visible light irradiation. Moreover, The composite semiconductor photocatalyst TiO₂/SiO₂ was selective towards the degradation of rhodamine B.     

Fe2O3/TiO2/Activated Carbon Nanocomposite with Synergistic Effect of Adsorption and Photocatalysis

Fe₂O₃/TiO₂/activated carbon (FT/AC) nanocomposites supported on silica gel beads were synthesized using a sonochemical method and fully characterized. The response surface method was applied to optimize the removal of Pb(II) ions by nanocomposites under visible light. The experiments were conducted by adjusting three parameters, i.e., initial concentration of Pb(II) ions, dosage of Fe₂O₃/TiO₂ (FT) photocatalyst, and pH. The FT/AC nanocomposite showed higher efficiency for Pb(II) ion removal in comparison with FT due to the synergistic effect of activated carbon combined with Fe₂O₃/TiO₂.     

Photocatalytic decolorization of rhodamine B by immobilized TiO2/UV in a fluidized-bed reactor

The photocatalytic oxidation of Rhodamine B (RhB) was studied by using a newly developed immobilized photocatalyst (TiO₂ immobilized by support consisting of a perlite and silicone sealant) and a fluidized-bed reactor. Three 8W germicidal lamps were used as the light source and the reactor volume was 2.8l. When this photocatalyst was employed in a batch process, a total decolorization of the RhB in reaction times lower than 60 min was observed. The optimum dosage of photocatalyst was 33.8 g/l. The initial RhB decolorization rate of the immobilized TiO₂ was higher than that of the suspended TiO₂ and this did not agree with pseudo first-order kinetics because of the adsorption onto the surface of the immobilized TiO₂. This result indicated that the adsorption capacity of the immobilized photocatalyst is very important in photocatalysis.     

UVA-LED assisted persulfate/nZVI and hydrogen peroxide/nZVI for degrading 4-chlorophenol in aqueous solutions

Photocatalytic degradation of 4-chlrophenol (4-CP) using UVA-LED assisted persulfate and hydrogen peroxide activated by the nZVI (Nano Zero Valent Iron) in a batch photocatalytic reactor was investigated. The reaction involved a lab-scale photoreactor irradiated with UVA-LED light emitted at 390 nm. The efficiency of the reaction was evaluted in terms of 4-CP degradation and mineralization degree at different pH of solution, initial concentrations of nZVI, persulfate, hydrogen peroxide and 4-CP. In UVA-LED/H₂O₂/nZVI process, complete degradation of 4-CP (>99%) and 75% mineralization was achieved at pH of 3, hydrogen peroxide concentration of 0.75 mM, nZVI dosage of 1mM and initial 4-CP concentration of 25mg/L at the reaction time of 30 min. The optimum conditions obtained for the best 4-CP degradation rate were at an initial concentration of 25mg/l, persulfate concentration of 1.5mM, nZVI dosage of 1mM, pH of 3 and reaction time of 120min for UVA-LED/persulfate/nZVI process. It was also observed that the 4-CP degradation rate is dependent on initial 4-CP concentrations for both processes. The pseudo-first-order kinetic constant at 25mg/L initial concentration of 4-CP was found to be 1.4×10^?1 and 3.8×10^?2 in UVA-LED/H₂O₂/nZVI and UVA-LED/persulfate/nZVI processes, respectively. Briefly, the UVA-LED/H₂O₂/nZVI process enhanced the degradation rate of 4-CP by 3.67-times in comparison to UVA-LED/persulfate/nZVI process at 30min contact time, which serves as a new and feasible approach for the degradation of 4-CP as well as other organic contaminants containing wastewater.     

Photocatalytic degradation of azo dye using TiO2 supported on spherical activated carbon

TiO₂ supported on spherical activated carbon (TiO₂/SAC) was prepared through an ion-exchange method followed by a heat-treatment process. The adsorption characteristic of TiO₂/SAC was evaluated using azo dye methyl orange (MO) as a target substance, and the photocatalytic degradation of MO under UV irradiation was also discussed. A synergistic effect of both the adsorption capacity of activated carbon and the photoactivity of TiO₂ on the removal of MO from aqueous solution was observed. Experimental results revealed that the photocatalytic degradation of MO improved with increasing photocatalyst dosage and followed a pseudo-first order kinetic. After five-cycle runs, TiO₂/SAC still exhibited relatively high photocatalytic characteristic for the degradation of MO. Besides, the prepared TiO₂/SAC can be helpful in the easy separation of photocatalyst from solution after photocatalysis of MO. Furthermore, the use of liquid chromatography/mass spectrometry (LC/MS) technique, identified three intermediates as degradation products during the photocatalytic reaction of MO with TiO₂/SAC.