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Query: KEGG:D01931 (TiO2)
 11,320 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The possibility of entrapping polycrystalline TiO2 in a polymeric support, in order to couple the two unit operations, i.e. ultrafiltration and photodegradation of organic pollutants in aqueous solutions, was investigated. To this aim, polymeric membranes for ultrafiltration with entrapped TiO2 were prepared, characterised and tested. The polymeric support chosen was commercial polysulfone (PSf). The membrane preparation was carried out with the technique referred to as phase inversion. A three-component system, with a polymer, a solvent and a non-solvent was used. The best operative conditions were determined in order to obtain the desired membrane morphology. Permeability measurements and photostability tests were also carried out by using a system under pressure. Finally, a preliminary investigation was performed in order to evaluate the photocatalytic activity of the membranes with entrapped TiO2 for the oxidation of 4-nitrophenol as a model molecule in aqueous solutions.
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PMID:Preparation and characterisation of membranes with entrapped TiO2 and preliminary photocatalytic tests. 1138 36

Degradation tests in a photocatalytic membrane system have been carried out using TiO2 (Degussa P25) as catalyst and humic acid, organic dyes, 4-nitrophenol as pollutants. The influence of UV radiation and initial concentration of pollutant on the photodegradation rate were investigated in discontinuous and continuous systems. Experimental results showed that it is possible to obtain an efficient photocatalytic membrane process, but various parameters (e.g. pH) should be optimised to obtain high reaction rate and high membrane rejection of pollutants and their by-products.
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PMID:Photocatalytic membrane processes for degradation of various types of organic pollutants and micropollutants in water. 1138 45

This article describes a method for treating aqueous 4-nitrophenol by mixing with TiO2-SnO2 coupled particles. The reactivity of single photocatalysis (TiO2 and SnO2 all as 1.2 g/L) is compared with that of mixing TiO2-SnO2 (0.6 g/L + 0.6 g/L) coupled particles. Aqueous 4-nitrophenol was treated by single photocatalysis or coupled semiconducting particles in a double-layer glass batch reactor using a 15W UV fluorescent tube at 25 degrees C and 300 rpm for mixing. The results demonstrated that pH and the concentration of TiO2 were the factors that most influenced the degradation characteristics, and that the system of TiO2-SnO2 coupled particles improved the efficiency of removal of refractory organic pollutants by 15%, by the inter-particle electron transfer (IPET) effect. The results showed that the degradation of aqueous 4-nitrophenol was 75% when coupled particles were used--better than the 60% obtained using single photocatalysis--with a reaction time of 120min.
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PMID:Effect of coupled semiconductor system treating aqueous 4-nitrophenol. 1533 73

The photocatalytic degradation of methyl parathion was carried out using a circulating TiO2/UV reactor. The experimental results showed that parathion was more effectively degraded in the photocatalytic condition than the photolysis and TiO2-only condition. With photocatalysis, 10mg/l parathion was completely degraded within 60 min with a TOC decrease exceeding 90% after 150 min. The main ionic byproducts during photocatalysis were measured. The nitrogen from parathion was recovered mainly as NO3-, NO2- and NH4+, 80% of the sulfur as SO4(2-), and less than 5% of the phosphorus as PO4(3-). The organic intermediates 4-nitrophenol and paraoxon were also identified, and these were further degraded. Two different bioassays (Vibrio fischeri and Daphnia magna) were used to test the acute toxicity of solutions treated by photocatalysis and photolysis. A Microtox test using V. fischeri showed that the toxicity, expressed as the relative toxicity (%), was reduced almost completely after 90 min under photocatalysis, whereas only an 83% reduction was achieved with photolysis alone. Another toxicity test using D. magna also showed that the relative toxicity disappeared after 90 min under photocatalysis, whereas there was a 65% reduction in relative toxicity with photolysis alone. The pattern of toxicity reduction parallels the decrease in parathion and TOC concentrations.
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PMID:Degradation mechanism and the toxicity assessment in TiO2 photocatalysis and photolysis of parathion. 1605 12

The solar photocatalytic degradation of methyl parathion was investigated using a circulating TiO2/solar light reactor. Under solar photocatalysis condition, parathion was more effectively degraded than solar photolysis and TiO2-only conditions. With solar photocatalysis, 20 mg/L of parathion was completely degraded within 60 min with a TOC decrease of 63% after 150 min. The main ionic byproducts during photocatalysis recovered from parathion degradation were mainly as NO3-, NO2- and NH4+, 80% of the sulphur as SO4(2-), and 5% of phosphorus as PO4(3-). The organic intermediates 4-nitrophenol and methyl paraoxon were also identified, and these were further degraded in solar photocatalytic condition. Two different bioassays (Vibrio fischeri and Daphnia magna) were used to test the acute toxicity of solutions treated by solar photocatalysis and photolysis. The Microtox test using V. fischeri showed that the toxicity expressed as EC50 (%) value increased from 5.5% to >82% in solar photocatalysis, indicating that the treated solution is non-toxic, but only increased from 4.9 to 20.5% after 150 min in solar photolysis. The acute toxicity test using D. magna showed that EC50 (%) increased from 0.05 to 1.08% under solar photocatalysis, but only increased to 0.12% after 150 min with solar photolysis, indicating the solution is still toxic. The pattern of toxicity reduction parallels the decrease in TOC and the parathion concentrations.
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PMID:Parathion degradation and toxicity reduction in solar photocatalysis and photolysis. 1660 11

Aqueous 4-nitrophenol solutions containing TiO2 or Al2O3 nanoparticles were irradiated with electron beam. 4-Nitrophenol was decomposed by the ionizing radiation process in the absence of the nanoparticles. The addition of TiO2 or Al2O3 (2 g l(-1)) before irradiation improved the removal of 4-nitrophenol, total organic carbon (TOC) but also nitrogen (TN). To identify the origin of the loss (catalysis or simply adsorption), TiO2 or Al2O3 nanoparticles were added after irradiation. Experiments show that the effect of the presence of TiO2 or Al2O3 during irradiation is just due to adsorption.
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PMID:Radiolysis of aqueous 4-nitrophenol solution with Al2O3 or TiO2 nanoparticles. 1711 29

The simultaneous photocatalytic degradation of phenol and 4-nitrophenol and reduction of metal ions like copper (Cu2+) and chromium (Cr6+) was studied with solution combustion synthesized nanoanatase TiO2 (CS TiO2) and commercial titania, Degussa P-25. The presence of metal ion reduces the rate of degradation of phenol and 4-nitrophenol. It was found that Cu2+ reduction to Cu+ is accelerated in the presence of phenol. In the case of Cr6+, CS TiO2 enhances the initial adsorption of Cr6+ and complete reduction is achieved within the first 10 min of UV irradiation. The presence of phenol or 4-nitrophenol also enhances the initial adsorption of Cr6+ and its reduction. The metal ion reduction in the presence of CS TiO2 is compared with that of Degussa P-25. The rate of reduction of metal ions in presence of Degussa P-25 is twice as slow as that of CS TiO2 in presence of both phenol and 4-nitrophenol. The presence of Cu2+ and Cr6+ also induces the formation of the intermediates which were not observed for the phenol-CS TiO2 system. The formation and consumption of the intermediates are modeled with a simple series reaction mechanism. A detailed dual-cycle, multistep reaction mechanism of TiO2 photocatalysis for the simultaneous degradation and reduction is proposed and the model is developed following the network reduction technique. The kinetic rate constants in the model are evaluated for the systems studied.
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PMID:Kinetics of simultaneous photocatalytic degradation of phenolic compounds and reduction of metal ions with nano-TiO2. 1832 22

Poor selectivity of titania (TiO2) photocatalysis is unfavorable to photocatalytic removal of highlytoxic low-level organic pollutants in polluted waters in the presence of other less toxic high-level pollutants. A new strategy of increasing this selectivity is the surface modification of TiO2 via coating a thin layer of molecular imprinted polymer (MIP), which provides molecular recognition ability toward the template molecules. By using 2-nitrophenol and 4-nitrophenol as target pollutants, MIP-coated TiO2 photocatalysts were prepared via surface molecular imprinting and were observed to have high activity and selectivity toward the photodegradation of the targets. In the presence of bisphenol A (50 mg L(-1)) as a nontarget pollutant, the apparent rate constant for the photodegradation of the target 2-nitrophenol and 4-nitrophenol (1.8 mg L(-1)) over the corresponding MIP-coated TiO2 was 10.73 x 10(-3) and 7.06 x 10(-3) min(-1), being 2.46 and 4.61 times of that (4.36 x 10(-3) and 1.53 x 10(-3) min(-1)) over neat TiO2, respectively. The enhanced photocatalytic selectivity was increased when the concentration of the target was decreased and/or when the difference in both the chemical structure and molecule size between the target and nontarget molecules was increased. The increased selectivity was mainly attributed to the special interaction between the target molecules and the footprints polymer via the functional groups (-OH and -NO2).
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PMID:Enhanced photocatalytic degradation and selective removal of nitrophenols by using surface molecular imprinted titania. 1844 21

Here we report an a novel approach, the marriage of photocatalytic degradation and electrochemical oxidation, to wastewater remediation based on the use of bifunctional electrodes. To illustrate this innovative technique, TiO2/Ti/ Ta2O5-IrO2 bifunctional electrodes were prepared using a facile thermal decomposition technique and employed in this study. The TiO2 photocatalyst was coated on one side of the Ti substrate, while the Ta2O5-IrO2 electrocatalytic thin film was coated on the other side. The fabricated bifunctional electrodes were characterized by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The performance of the bifunctional electrodes was tested using both 4-nitrophenol (4-NPh) and 2-nitrophenol (2-NPh) as model pollutants. Our study demonstrates that the prepared bifunctional electrodes exhibit high efficiency for both 4-NPh and 2-NPh degradation. In the degradation of 4-NPh a rate constant of 1.06 x 10(-2) min(-1) was created and a rate constant of 1.93 x 10(-2) min(-1) was produced for 2-NPh by the combination of the photochemical and electrochemical oxidation on the novel bifunctional electrodes, quadruple the rate constant created by the individual photochemical and photoelectrochemical methods. The innovative approach described in this study provides a very promising and energy efficient environmentally friendly technology for water purification and waste effluent treatment.
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PMID:A new approach to wastewater remediation based on bifunctional electrodes. 1967 13

Heterogeneous photocatalysis on metal oxide semiconductor particles is an advanced oxidation technology (AOT), which has been effective means of removing organic pollutants from water streams as it utilizes ultraviolet light with semiconductors acting as photocatalyst and leads to complete mineralization of pollutants to environmentally harmless compounds. In the present investigation, the photo-catalyzed degradation studies of p-Nitrophenol (PNP) were carried out in laboratory scale immersion well UV photo-reactor using semiconductor photo-catalyst TiO2 in suspension. For this purpose, low pressure 12 W mercury lamp was used and the effect of (i) time of irradiation, (ii) dose of TiO2, (iii) initial concentration of PNP and (iv) the addition of H2O2 to the system was studied to arrive at optimum process parameters for the complete degradation and decolorization of PNP. Simple UV irradiation could not achieve significant degradation of PNP. But UV+aeration+TiO2+ H2O2 combination achieved almost complete degradation of PNP. The spectrophotometric analysis showed that the rate of degradation of PNP was very fast in initial two hours and the maximum degradation was achieved in 5 hours. The degradation was found to increase in the order UV < UV + aeration < UV + aeration + TiO2 < UV + aeration + TiO2+ H2O2, and the degradation was found to be almost 100% for UV + aeration + TiO2 + H2O2, 91% for UV + aeration + TiO2, 43% for UV + aeration and only 26% for UV irradiation.
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PMID:Photo-catalyzed degradation of p-nitrophenol employing TiO2 and UV radiations. 1969 65


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