Solar TiO2 Photocatalysis Research Articles

Solar photocatalytic degradation of total organic halogen in water using TiO2 catalyst

Disinfection byproducts (DBPs) in treated wastewater effluents pose environmental and health risks during water reuse. Solar-TiO2 photocatalysis is a promising technology for degrading organic pollutants in treated effluents. In this study, total organic halogen (TOX) was used as an analytical tool to determine the efficiency of solar-TiO2 photocatalytic process for the dehalogenation of DBPs in water. Natural solar photocatalytic experiments using TiO2 particles were conducted to evaluate dehalogenation kinetics of different TOX groups formed by fulvic acid including total organic chlorine (TOCl), bromine (TOBr) and iodine (TOI). The results showed that the mixed phase TiO2 (Aeroxide P25) was much more effective at TOX removal than the anatase (Hombikat UV-100) and rutile (TiOxide) TiO2 particles. The TOX photocatalytic degradation rates of different halogen substituents ranked as TOI > TOCl (NH2Cl) > TOBr > TOCl (Cl2). The TOX removal followed first-order kinetics with half-lives of 42.8, 11.0, 5.0 and 2.7 min for TOCl (Cl2), TOBr, TOCl (NH2Cl), and TOI, respectively, at the 100 mg L−1 TiO2 dose. The TOX dehalogenation was enhanced at pH 9 compared to pH 5, and the addition of hydrogen peroxide had limited improvement in the TOX removal. Hydrophobic and molecular weight (MW) > 1 kDa fractions of TOCl (Cl2) were more susceptible to the solar photocatalytic process than the hydrophilic and MW < 1 kDa fractions. The solar-TiO2 photocatalytic process also effectively removed TOX in chlorinated and chloraminated wastewater samples. The results of this study suggest that the solar-TiO2 photocatalysis is an effective treatment technology for TOX removal in water reuse.

Degradation of hormones in tap water by heterogeneous solar TiO2-photocatalysis: Optimization, degradation products identification, and estrogenic activity removal

Hormones are one of the most hazardous classes of Contaminants of Emerging Concern (CEC) found in tap water, being significantly recalcitrant regarding traditional water treatment processes. In this work, the hormones estrone, 17β-estradiol, 17α-ethinylestradiol, and estriol, present in tap water, were degraded by heterogeneous solar photocatalysis in a flat-plate photochemical reactor (recycle mode) using TiO2 (P25, Evonik) as the photocatalyst. A fully automated analytical method based on online SPE and LC-UV was developed and validated for monitoring those molecules. For a fixed amount of sample (125 μL), the limit of quantification was 10 μg L−1 (for all four hormones) with coefficients of variation smaller than 20%, and accuracy between 80% and 120%, all of which are acceptable figures for this kind of determination. The reactional system was optimized with the aid of a 22 factorial design. At optimized conditions (pH ≈ 6.8, flow rate 250 mL min−1), the removal of the four hormones (250 μg L−1 each) was approximately 85% after 3 h of treatment. However, even after 9 h of treatment, it was not possible to completely remove the estrogenic activity (MCF-7 cells) of the treated tap water. The structures of some degradation products were proposed.

Raw Industrial Wastewater Treatment Using Fenton, Photo Fenton and Photo Catalytic: A Comparison Study

This work implemented solar TiO2 photocatalysis, Fenton, and photo-Fenton separately for treating raw petroleum refinery wastewater (PRW) in terms of its COD and TOC removal. The effect of irradiation and reaction time along with initial pH on the degradation profiles was assessed and compared. The experimental work then revealed that maximum removal efficiency of COD and TOC by solar TiO2 photocatalysis was 48.2 and 53.3%, respectively while photo-Fenton reached 54.1 and 59.1%, respectively. Photo-assisted process was found significantly better than dark mechanism, especially for TiO2 catalysis. In addition, employing acidic condition in the range of 3 to 5 in both photocatalysis and photo-Fenton processes resulted in the obvious improvement of pollutant degradation. Eventually, the kinetic study indicated that the degradation of COD and TOC is suitable to pseudo-first-order pattern by reaching high R2 values.

Comparative Study of Advanced Oxidation Processes to Treat Petroleum Wastewater

AbstractThis study was carried out to compare the performance of different oxidation processes, such as solar photo-Fenton reaction, solar photocatalysis by TiO2, and the combination of the two for the treatment of petroleum wastewater from Sohar Oil Refinery by a central composite design with response surface methodology. The degradation efficiency was evaluated in terms of chemical oxygen demand (COD) and total organic carbon (TOC) reductions. Solar photocatalysis by the TiO2/Fenton method improved the performance of the photocatalyst at neutral pH for petroleum wastewater without the need to adjust the pH during this treatment. Under acidic conditions, the solar photo-Fenton process is more efficient than solar TiO2photocatalysis while it is less efficient under alkaline conditions. The TiO2dosage and pH are the two main factors that improved the TOC and COD reductions in the solar photocatalysis using combined TiO2/Fenton and the solar TiO2photocatalysis processes while the pH and H2O2concentration are the two key factors that affect the solar photo-Fenton process.

Comparison of solar TiO2 photocatalysis and solar photo-Fenton for treatment of pesticides industry wastewater: Operational conditions, kinetics, and costs

Solar photo-Fenton and solar TiO2 photocatalysis processes were investigated for degradation of pesticides from real industrial wastewater. Chlorpyrifos, lambda-cyhalothrin, and diazinon were the major contaminants found in the wastewater. The effect of initial pH, chemical dosing, and irradiation time on the removal efficiency of pesticides and chemical oxygen demand (COD) were assessed. The maximum removal of COD by photo-Fenton process was 90.7%, while by TiO2 photocatalysis was 79.6%. Moreover, the photo-Fenton process was more efficient for degradation of pesticides fractions. Employing of H2O2 in photocatalysis process (UV/H2O2/TiO2) improved the removal of COD (84%) and the degradation of pesticides. The kinetic study showed that the degradation of pesticides fractions follows pseudo-first-order pattern. Amortization and operating costs of full scale solar oxidation plant were estimated. The estimated costs for photocatalysis and photo-Fenton processes were 8.69 and 5.2€/m3, respectively.

Disinfection of urban effluents using solar TiO2 photocatalysis: A study of significance of dissolved oxygen, temperature, type of microorganism and water matrix

The enhancement of current technologies used to treat polluted water is one of the most important challenges in water research. The application of physico-chemical treatments could reduce the load of chemical and biological pollutants present in WW reducing the pressure over water requirements, allowing the reclaim of the treated water. Advanced Oxidation Processes (AOPs) and, in particular, photocatalysis using titanium dioxide (TiO2) have shown a great potential for chemicals removal as well as for pathogens reduction in water. Moreover, the use of solar Compound Parabolic Collectors (CPC) reactors has been also shown to be very effective for water treatment purpose by solar photocatalysis. Nevertheless, the effects of some key parameters in photocatalytic disinfection have not been already investigated at pilot scale in solar reactors; like dissolved oxygen concentration, water temperature, water matrix composition and the type of microorganism. The roles of these parameters in photocatalytic processes are individually known for chemicals degradation, but their relative significance in water photocatalytic disinfection has been never studied at pilot scale. The aim of this work was to investigate the influence of these parameters on the disinfection efficiency using a solar 60L-CPC reactor with suspended TiO2 (100mg/L). The following variables were experimentally evaluated: injection of air in the reactor (160L/h); different controlled temperatures (15, 25, 35 and 45°C); two very different models of water pathogen, Escherichia coli (model of fecal water contamination) and Fusarium solani spores (a highly phytopathogenic fungus); and the chemical composition of the water comparing urban WW effluents (UWWE) and simulated urban WW effluent (SUWWE). The increase of water temperature (from 15 to 45°C) had a benefit on the disinfection rate for both pathogens in all the experimental conditions evaluated. The air injection led to an important enhancement on the inactivation efficiency, which was stronger for F. solani spores, the most resistant microorganisms to TiO2 photocatalysis. The composition of the water matrix significantly affected the efficiency of the photocatalytic treatment, showing a better inactivation rate in SUWWE than for UWWE.

Recent Progress in TiO2-Mediated Solar Photocatalysis for Industrial Wastewater Treatment

The current paper reviews the application of TiO2-mediated solar photocatalysis for industrial wastewater treatment, starting with a brief introduction on the background of industrial wastewater and the development of wastewater treatment processes, especially advanced oxidation processes (AOPs). We, then, discuss the application of solar TiO2photocatalysis in treating different kinds of industrial wastewater, such as paper mill wastewater, textile wastewater, and olive mill wastewater. In the end, we compare solar TiO2photocatalysis with other AOPs in terms of effectiveness, energy, and chemical consumption. Personal perspectives are also given, which may provide new insights to the future development of TiO2photocatalysis for industrial wastewater.

Sacrificial Hydrogen Generation from Formaldehyde with Pt/TiO2 Photocatalyst in Solar Radiation

In this work, solar TiO2 photocatalysis was used for sacrificial hydrogen generation from formaldehyde. Platinum was loaded onto a TiO2 photocatalyst by a solar photodeposition method to suppress the electron/hole recombination process. The photocatalyst inside the reactor was irradiated from the top with a solar simulator. Photocatalytic hydrogen generation from formaldehyde was influenced by the solution pH, platinum loading (wt %) on TiO2, catalyst concentration, light intensity, and initial formaldehyde concentration. A Langmuir-type model fitted well with the experimental data, and the values of surface reaction rate constant, k, and the adsorption equilibrium constant, K, are 2.3598 × 10–6 mol min–1 and 17.73 M–1, respectively. Apparent quantum yield (QY) was higher for the UV light-driven hydrogen generation (10.91%) compared to the solar light-driven hydrogen generation (1.24%).

Optimization of mild solar TiO2 photocatalysis as a tertiary treatment for municipal wastewater treatment plant effluents

The appropriate catalyst concentration for industrial wastewater treatment is several hundred milligrams per liter in solar photoreactors. Nonetheless, when the purpose of eliminating emerging contaminants in municipal wastewater treatment plant effluents is for reuse of the water, and they are present at extremely low concentrations, a tertiary treatment with a much lower photocatalyst concentration might be possible. TiO2 concentrations of only tens of mgL−1 were selected to evaluate the influence of catalyst load, initial hydrogen peroxide dose and radiation intensity on the degradation rate of five emerging contaminants (100μgL−1 of ofloxacin, sulfamethoxazole, flumequine, carbamazepine, and 2-hydroxy-biphenyl) spiked in a real municipal wastewater treatment plant effluent. Response surface methodology based on a spherical central composite design was used to optimize the parameters to find the maximal degradation rate. The experiments were carried out using an Evonik P-25 titanium dioxide suspension in a Suntest solar simulator. It has been demonstrated that the use of hydrogen peroxide is highly recommendable for working with TiO2 at low concentrations and high photon flux must be avoided. It has also been demonstrated that too low (less than 40mgL−1) TiO2 concentration is not recommendable.

Degradation of trinitrophenol by sequential catalytic wet air oxidation and solar TiO2 photocatalysis

Catalytic wet air oxidation (CWAO) and solar TiO2 photocatalysis were investigated as advanced oxidation processes to degrade trinitrophenol (TNP) in model aqueous solutions. An activated carbon (AC) treated with sulphuric acid of different concentrations (5, 10 and 18M) at two different temperatures (353 and 423K) was investigated as a metal-free CWAO catalyst, while a commercially available P25 TiO2 powder was used as a photocatalyst. CWAO experiments were conducted at 448K, 0.7MPa oxygen pressure (4.7MPa of total pressure), 1.3gL−1 AC loading and 270mgL−1 TNP concentration, while photocatalytic experiments were conducted at ambient temperature, 1gL−1 photocatalyst loading, 500–1000Wm−2 irradiance provided by a solar simulator and 32–270mgL−1 TNP concentration. Treatment efficiency was assessed by measuring the concentrations of TNP and nitrates, total organic carbon (TOC) and biochemical oxygen demand (BOD5). Up to 90% TNP degradation was attained during CWAO over 120min, from an initial concentration of 270mgL−1. For the same TNP concentration, TiO2 photocatalysis gives only 13% conversion over the same 120min. However, for TNP concentrations below 144mgL−1, photocatalysis can be effectively used: 100 and 80% TNP degradation obtained in 120min of irradiation for initial TNP concentrations of 64 and 144mgL−1, respectively. In this respect, CWAO and photocatalysis were employed sequentially to treat TNP; complete TNP conversion being achieved after 120min of CWAO followed by 60min of photocatalysis at 1000Wm−2 irradiance, and this was accompanied by 82% TOC reduction, as well as an increase of BOD5/TOC ratio from 0 to 2.28.

Comparative Study of Phenolics Degradation Between Biological and Photocatalytic Systems

Phenol and phenol compounds are toxic organics that can be found in many industrial wastewaters. Biological wastewater treatments are considered to be the most convenient methods owing to their efficiency and low economic cost. Nonetheless, many organic pollutants are refractory to bacterial degradation. Photocatalytic methods can be an interesting alternative as pretreatment to improve biodegradability and reduce toxicity of industrial effluents. The goal of this study was to compare and combine TiO2-photocatalysis with constructed wetlands to obtain a low-cost method for the treatment of phenolic wastewater. The degradation of phenol was studied by means of TiO2-photocatalysis (solar and UV-lamp) in batch reactors. The degradations of phenol and two of its photocatalytic degradation intermediates, catechol and hydroquinone, were studied in wetland reactors with and without two wetland plants: common reed (Phragmites australis) and papyrus (Cyperus alternifolius). The application of pseudo first-order kinetics to the elimination of phenol in the wetland reactors provided high correlation coefficients (R2=0.85–0.99), allowing the comparison of the biological and photocatalytic methods. Although higher concentrations of phenol (250–400mg∕l) could be treated, the elimination of 50ppm was usually accomplished in batch experiments in less than 15h, the time in which low or nil solar radiation is available for TiO2-photocatalysis. As a consequence, this concentration can be considered to be the upper limit for the wetland influent. The degradations of catechol and hydroquinone showed higher rate constants (0.2–0.4h−1) than that of phenol (about 0.15h−1), particularly in the reactor with common reed (1–2h−1). The degradation of phenol by the photocatalytic methods was three to four times faster than those obtained with the wetland reactors. By using solar TiO2-photocatalysis, concentrations of phenol up to 100ppm were reduced down to 16ppm and 27ppm of phenol and hydroquinone, respectively, in about 7h. However, it was toxic. When this sample was continuously (38ml∕min) added to wetland reactors with common reed, phenol and hydroquinone concentrations were below their detection limits (1ppm and 2ppm, respectively). Solar TiO2-photocatalysis is a promising technique for the treatment of phenol but its application is limited to daytime periods with appropriate weather conditions. Constructed wetlands can also eliminate phenol and phenolic compounds without these limitations, but the toxicity of the influent must be as low as possible. The combination of both methods can provide a low-cost method for the treatment of phenolic wastewater.

Increased biodegradability of UltracidTM in aqueous solutions with solar TiO2 photocatalysis

A study of solar TiO(2) photocatalytic degradation of the insecticide Ultracidtrade mark, a commercial formulation containing methidathion as the active ingredient, is described. Total elimination of methidathion can be achieved in less than 2h of irradiation, although longer solar exposures are needed for complete mineralisation of the solution (7-8h). Activated sludge respirometry shows that when methidathion is eliminated, the solution is detoxified, so further irradiation does not seem necessary. A Zahn-Wellens test also indicates improved biodegradability of the treated sample after abatement of the active ingredient. Finally, analysis of the ions formed indicates that the thiophosphate moiety of the molecule is preferentially attacked in the early stages of the reaction, while the thiadiazole ring is more sluggish to the effect of TiO(2)-photocatalysis.

TiO 2-photocatalysis as a tertiary treatment of naturally treated wastewater

Solar TiO 2-photocatalysis was applied to waters from a natural wastewater treatment plant located in the Universidad de Las Palmas de Gran Canaria. Degussa P-25 TiO 2 and its mixture with activated carbon (AC–TiO 2) were used as catalysts. The presence of ozone and certain ions such as phosphates on the photocatalytic degradation of organic matter was also studied. Disinfection experiments have provided interesting results, particularly when using the catalyst AC–TiO 2 and ozone, since total disinfection was achieved in less than 60 min. No bacterial reappearance at 24 or 48 h was observed. Additionally, this catalyst gave important TOC and some ions concentrations reductions. Studies in catalyst reuse revealed that the catalyst AC–TiO 2 showed almost no deactivation.

Solar Photocatalytic Destruction of p-Nitrophenol: A Pedagogical Use of Lab Wastes

In this article we propose the destruction of p-nitrophenol wastes obtained in a previous lab experiment, to generate a new lab experiment. The recommended destruction technique is solar TiO2-photocatalysis. When the effects of TiO2 and sunlight are tested separately, a slight decrease of p-nitrophenol is observed; but when TiO2 and sunlight are employed together p-nitrophenol disappears in 1 or 2 h. These experiments do not require sophisticated equipment or special lab training for the students. Groups of students tested different experimental conditions, such as the effect of different light intensities and sources (800-W UV-lamp, sunlight on sunny days, and sunlight on a cloudy day) or the addition of H2O2. p-Nitrophenol is degraded under the three light sources but at different rates. The addition of H2O2 to the TiO2-plus-sunlight system enhances p-nitrophenol degradation kinetics when compared with the TiO2 plus sunlight and H2O2 plus sunlight combinations.

Incidence of pretreatment by potassium permanganate on hazardous laboratory wastes photodegradability

In this paper we present the results of the application of conventional and photocatalytic methods for the treatment of hazardous laboratory wastes. Liquid wastes from the spectrophotometric determination of NH + 4 as indophenol have been chosen as model samples. The waste composition is rather heterogeneous, as phenol, ethanol, nitroprusside and citrate can be found, among others. High organic carbon contents (thousands of ppm) are found, part of which is volatile organic carbon (VOC) up to 68%. Three different photocatalytic methods have been tested: TiO 2-photocatalysis, photoFenton reaction and the combination of H 2O 2-UV light. The degradation process was monitored by Total Organic Carbon (TOC) reduction. The effect of experimental parameters, such as pH and TiO 2, H 2O 2 and Fe 2+ concentrations, has been investigated. The strongest TOC reduction was achieved employing the photoFenton reaction with 2.5 mM Fe 2+ and 8 mM H 2O 2. The effect of solar TiO 2-photocatalysis and the photoFenton reaction was also studied. TOC reductions of 76.6 and 46.8% were achieved by the photoFenton reaction and TiO 2-photocatalysis, respectively. The mineralization of individual components of the samples: nitroprusside, phenol and citrate (1000 ppm of C) was also attempted by KMnO 4 and the three photomethods. Nitroprusside was the most resistant component to be mineralized. PhotoFenton and the combination of H 2O 2–UV light gave the best results for nitroprusside degradation. Due to the high TOC content of the samples, an oxidative pretreatment with KMnO 4 before the photocatalytic treatment was also investigated. KMnO 4 pretreatment gave reductions of initial TOC as high as 90% and VOC reductions from 30 to 77%. The remaining solution must be treated with KMnO 4 if the photocatalytic methods are to be applied later. If the sample is not previously treated with KMnO 4, not one of the photomethods tested is able to reduce the remaining non-purgeable (NPOC) organic carbon of the sample. This suggests that KMnO 4 oxidizes the organic pollutants to other organics compounds that can be more readily mineralized by photodegradation. The recommended method for the treatment of these wastes consists of a pretreatment with KMnO 4, followed by the photocatalytic treatment by means of photoFenton reaction.