benzofurans and titanium-dioxide

Photocatalysis is applied increasingly in addressing and solving environmental and energy-related problems. Especially the TiO₂-derived catalysts attract attention because of their catalytic efficiency, wide range of applications, ease in use, and low cost (it costs about 150 Yuan a kilogram in China). This review first describes the principles of photocatalytic destruction by semiconductors and then focuses on degradation rates and reaction mechanisms in a variety of photocatalytic uses of modified TiO(2). Finally, these concepts are illustrated by selected examples relating to the photocatalytic degradation of organic persistent pollutants, such as polychlorinated benzenes (PCBz), biphenyls (PCB) and dibenzo-p-dioxins and dibenzofurans (PCDD/Fs). And some approaches towards industrial application are analyzed.

Topics: Benzofurans; Catalysis; Environmental Pollutants; Environmental Restoration and Remediation; Hydrocarbons, Cyclic; Hydroxyl Radical; Metal Nanoparticles; Photochemical Processes; Polychlorinated Biphenyls; Polychlorinated Dibenzodioxins; Semiconductors; Titanium

dl-3-n-butylphthalide (dl-NBP) is a powerful antioxidant compound with profound neuroprotective effects in stroke and brain injury. However, its role in Parkinson's disease (PD) is not well known. Traumatic brain injury (TBI) is one of the key factors in precipitating PD like symptoms in civilians and particularly in military personnel. Thus, it would be interesting to explore the possible neuroprotective effects of NBP in PD following concussive head injury (CHI). In this chapter effect of nanowired delivery of NBP together with mesenchymal stem cells (MSCs) in PD with CHI is discussed based on our own investigations. It appears that CHI exacerbates PD pathophysiology in terms of p-tau, α-synuclein (ASNC) levels in the cerebrospinal fluid (CSF) and the loss of TH immunoreactivity in substantia niagra pars compacta (SNpc) and striatum (STr) along with dopamine (DA), dopamine decarboxylase (DOPAC). And homovanillic acid (HVA). Our observations are the first to show that a combination of NBP with MSCs when delivered using nanowired technology induces superior neuroprotective effects in PD brain pathology exacerbated by CHI, not reported earlier.

Topics: Benzofurans; Brain Injuries, Traumatic; Humans; Mesenchymal Stem Cells; Neuroprotection; Parkinson Disease; Titanium

In the present study, we report on the co-occurrence of persistent organic pollutants (POPs) adsorbed on nanoparticular titanium dioxide (TiO2). We report on the finding of polychlorinated dibenzodioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and polychlorinated biphenyls (PCBs) on the surface of commercially available TiO2 nanoparticles, being formed during the fabrication process of the TiO2. Thereby, the samples comprise PCBs with higher congener numbers or, in the absence of PCBs, a high concentration of PCDDs and PCDFs. This new class of POPs on an active catalytic surface and the great range of applications of nanoparticular TiO2, such as in color pigments, cosmetics, and inks, give rise to great concern due to their potential toxicity.

Topics: Benzofurans; Dibenzofurans, Polychlorinated; Nanoparticles; Polychlorinated Biphenyls; Polychlorinated Dibenzodioxins; Titanium

Gaseous 1,2-dichlorobenzene (1,2-DCBz) was catalytically decomposed in a fixed-bed catalytic reactor using composite copper-based titanium oxide (CuOx/TiO2) catalysts with different copper ratios. Carbon nanotubes (CNTs) were introduced to produce novel CuOx/TiO2-CNTs catalysts by the sol-gel method. The catalytic performances of CuOx/TiO2 and CuOx/TiO2-CNTs on 1,2-DCBz oxidative destruction under different temperatures (150-350 °C) were experimentally examined and the correlation between catalyst structure and catalytic activity was characterized and the role of oxygen in catalytic reaction was discussed. Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) generation during 1,2-DCBz catalytic oxidation by CuOx/TiO2-CNTs composite catalyst was also examined. Results indicate that the 1,2-DCBz destruction/removal efficiencies of CuOx (4 wt%)/TiO2 catalyst at 150 °C and 350 °C with a GHSV of 3400 h(-1) are 59% and 94% respectively and low-temperature (150 °C) catalytic activity of CuOx/TiO2 on 1,2-DCBz oxidation can be improved from 59 to 77% when CNTs are introduced. Furthermore, oxygen either in catalyst or from reaction atmosphere is indispensible in reaction. The former is offered to activate and oxidize the 1,2-DCBz adsorbed on catalyst, thus can be generally consumed during reaction and the oxygen content in catalyst is observed lost from 39.9 to 35.0 wt% after reacting under inert atmosphere; the latter may replenish the vacancy in catalyst created by the consumed oxygen thus extends the catalyst life and raises the destruction/removal efficiency. The introduction of CNTs also increases the Cu(2+)/Cu(+) ratio, chemisorbed oxygen concentration and surface lattice oxygen binding energy which are closely related with catalytic activity. PCDD/Fs is confirmed to be formed when 1,2-DCBz catalytically oxidized by CuOx/TiO2-CNTs composite catalyst with sufficient oxygen (21%), proper temperature (350 °C) and high concentration of 1,2-DCBz feed (120 ppm).

Topics: Adsorption; Benzofurans; Catalysis; Chlorobenzenes; Copper; Dibenzofurans, Polychlorinated; Nanotubes, Carbon; Oxidation-Reduction; Polychlorinated Dibenzodioxins; Temperature; Titanium

The photocatalytic film Ce doped VxOy/TiO2 was loaded on cordierite honeycomb (CHC), and this composite was prepared by sol-gel and dipping method, with Ce, oxides of V and TiO2 as dopant and key substances, respectively. Using gaseous 1,2-dichlorobenzene to replace dioxin as target pollutant, dual degradation experiments at 140-280 °C were carried out (thermal decomposition and photodegradation), and the effects of preparation conditions on catalytic activity were investigated: doping amount of Ce, dipping time in the gel, the concentration of ammonium metavanadate (NH4VO3) solution, dipping time in NH4VO3 solution, sintering temperature. The gaseous samples were taken before and after the reactor and analyzed by gas chromatography. According to the results, the optimal preparation conditions were determined, and the corresponding removal rate was above 95% after 90 min of degradation at 280 °C. The composite was examined by ultrasonic to analyze the adhesive strength between the film and CHC, and further characterized by XRD and SEM. Furthermore, flue gas from waste incinerator was chosen as target pollutant, which contained PCDD/Fs, the industrial sidestream degradation experiment was carried out and showed excellent removal efficiency of the composite, the removal rate of PCDD/Fs reached ca. 90% after 90 min of degradation.

Topics: Benzofurans; Catalysis; Ceramics; Cerium; Chlorobenzenes; Dioxins; Gases; Incineration; Polychlorinated Dibenzodioxins; Temperature; Titanium; Vanadium Compounds

The mixture of V2O5-WO3/TiO2 catalyst and two kinds of Activated Carbons (AC) (AC-1: based on lignite; AC-2: based on coconut shell) was used to destroy gas phase PCDD/Fs with high concentration (9. 80 ng.m-3, evaluated by international toxic equivalence quantity (I-TEQ) under low thermal temperature (160°C) based on a dioxin generating system. After mixing with AC, removal efficiency (RE) and destruction efficiency (DE) of PCDD/Fs increased by 20% compared with only catalyst condition. In comparison with mixture of AC based on coconut shell, mixture of AC based on lignite had lower RE-values and higher DE-values. The adjustments of the ratio of catalyst and AC could cause the different degradation effects, and RE-values increased and DE-values decreased with increasing proportions of catalyst. When the volume fraction of oxygen was 0% in experimental atmosphere, catalyst could lose its activity and most PCDD/Fs were not oxidized but adsorbed by the mixture. RE and DE-values increased with increasing content of oxygen. The addition of ozone (concentration of 200 mg.m-3) could improve catalytic oxidation effects to a certain degree. However, ozone might react with AC, which could influence the lifetime of the mixture. Under 200°C, the mixture with proportion of AC: catalyst = 1:1 and in the present of 200 mg.m-3 ozone conditions, the highest RE and DE-value were obtained with 98. 0% and 94. 8% respectively, and the concentration of PCDD/Fs residual in off-gas was only 0. 51 ng.m-3 evaluated by I-TEQ.

Topics: Adsorption; Benzofurans; Catalysis; Charcoal; Oxidation-Reduction; Oxides; Ozone; Polychlorinated Dibenzodioxins; Polymers; Titanium; Tungsten; Vanadium Compounds

The catalytic oxidation of PCDD/Fs (polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans) vapors was studied in a temperature range of 180-220°C on a honeycomb V2O5-TiO2-based catalyst, in the presence and the absence of ozone. A stable dioxin-generating system was established to support the experimental program and this system could adjust the concentration of PCDD/Fs by injecting appropriate mother liquors. At 220°C the removal efficiency(1) (RE) of PCDD/Fs reaches up to 97% and the degradation efficiency (DE) up to 90%. Both values diminish at lower operating temperatures. In the presence of ozone, however, these values rise to 99% and 98% at 220°C. Especially at low temperatures the effect of ozone is obvious. Catalytic oxidation with ozone thus offers a low-temperature solution to achieve higher rates and low activation energies. The morphology and microstructure of the catalysts changes after ozone treatment and some of their characteristics seem closely related with DE-values.

Topics: Benzofurans; Catalysis; Dibenzofurans, Polychlorinated; Environmental Pollutants; Oxidation-Reduction; Ozone; Polychlorinated Dibenzodioxins; Temperature; Titanium; Vanadium Compounds

Titania supported vanadium oxide is a renowned catalyst for the abatement of polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs) from gas effluents. To develop more active formulations, researchers mainly rely on lab-scale experiments on "PCDD/Fs-mimicking substances", like (chloro)-benzene. Using such model compounds is convenient whereas handling PCDD/Fs in the laboratory is potentially hazardous and complicated. Recent studies, however, challenged some foremost conclusions of model compound based studies, starting from the observation that different model compounds gave contrasted results. Thus the present work aims at confronting some of these dubious conclusions with direct experimental tests on PCDD/Fs. One reference V(2)O(5)/TiO(2) catalyst and three modified formulations (V(2)O(5)/TiO(2)-SO(4), V(2)O(5)-MoO(3)/TiO(2), and V(2)O(5)-WO(3)/TiO(2)) have been evaluated. A dedicated apparatus was used which allows safe and reliable tests on a mixture of PCDD/Fs congeners. Some of the previously proposed catalyst improvement strategies actually prove to be disadvantageous in the removal of PCDD/Fs. In particular, MoO(3)- and WO(3)-modified catalysts were significantly less active than the reference catalyst. These observations show that conclusions from model compound based studies must be drawn with care and should ideally be confronted with tests on the actual target pollutants.

Topics: Air Pollutants; Air Pollution; Benzofurans; Catalysis; Dibenzofurans, Polychlorinated; Oxidation-Reduction; Polychlorinated Dibenzodioxins; Reproducibility of Results; Titanium; Vanadium; Waste Management

The gaseous photocatalytic degradation of dibenzofuran, dioxins-like substance, was investigated by using TiO2, Ce3+/TiOs and Fe3+/TiO2 as photocatalysts. The batch-type photocatalytic reaction experiments were conducted, and the effects of initial concentration of reactant, humidity, circulation flow rate and light intensity on the photocatalytic degradation of dibenzofuran were studied. And the models and methods for estimating photocatalytic reaction constants and Langmuir adsorption constants were proposed. Results showed that the photocatalytic activity of the TiO2 photocatalyst was obviously improved after doping with Fe3+ and Ce3+, and the photocatalytic activity of Fe3+/TiO2 was the best in three photocatalysts. The degradation rate of dibenzofuran increased with the increase of the initial concentration of gaseous dibenzofuran in the batch-type photocatalytic reaction system. The photocatalytic degradation of gaseous dibenzofuran was enhanced when proper quantities of water vapor existed. However, it would be inhibited if there was excessive water vapor. As the circulation flow rate and the light intensity increased, the photocatalytic degradation rate of gaseous dibenzofuran also increased. The photocatalytic reaction rate coefficients of dibenzofuran on the photocatalysts TiO2, Ce3+/TiO2 and Fe3+/TiO2 were 34.54 x 10(-5), 36.23 x 10(-5) and 37.95 x 10(-4) mg x (min x m2)(-1) respectively.

Topics: Air Pollutants; Benzofurans; Catalysis; Cerium; Ferric Compounds; Models, Theoretical; Photochemical Processes; Titanium

Development of effective PCDD/F (polychlorinated dibenzo-p-dioxin and dibenzofuran) control technologies is essential for environmental engineers and researchers. In this study, a PCDD/F-containing gas stream generating system was developed to investigate the efficiency and effectiveness of innovative PCDD/F control technologies. The system designed and constructed can stably generate the gas stream with the PCDD/F concentration ranging from 1.0 to 100ng TEQ Nm(-3) while reproducibility test indicates that the PCDD/F recovery efficiencies are between 93% and 112%. This new PCDD/F-containing gas stream generating device is first applied in the investigation of the catalytic PCDD/F control technology. The catalytic decomposition of PCDD/Fs was evaluated with two types of commercial V(2)O(5)-WO(3)/TiO(2)-based catalysts (catalyst A and catalyst B) at controlled temperature, water vapor content, and space velocity. 84% and 91% PCDD/F destruction efficiencies are achieved with catalysts A and B, respectively, at 280 degrees C with the space velocity of 5000h(-1). The results also indicate that the presence of water vapor inhibits PCDD/F decomposition due to its competition with PCDD/F molecules for adsorption on the active vanadia sites for both catalysts. In addition, this study combined integral reaction and Mars-Van Krevelen model to calculate the activation energies of OCDD and OCDF decomposition. The activation energies of OCDD and OCDF decomposition via catalysis are calculated as 24.8kJmol(-1) and 25.2kJmol(-1), respectively.

Topics: Air Pollutants; Air Pollution; Benzofurans; Catalysis; Dibenzofurans, Polychlorinated; Dioxins; Gases; Oxides; Polychlorinated Dibenzodioxins; Temperature; Titanium; Tungsten; Vanadium Compounds; Water

Supported transition metal oxides and vanadium-containing multi-metallic oxides were investigated to develop new catalysts for the catalytic destruction of highly toxic polychlorinated aromatic pollutants such as polychlorinated benzenes, polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), and/or biphenyls (PCBs) from waste gases. The decomposition of 1,2-dichlorobenzene (Cl2Bz) was chosen as a model reaction. Titania-supported vanadium catalyst (VOx/TiO2) showed the highest activity and stability among the binary oxides tested even in the presence of water vapor. The optimum loading of vanadia was 5 wt %, corresponding to half a monolayer, suggesting that the active species are tetrahedral vanadyl species on titania. Characterizations of the VOx/TiO2 catalysts were carried out with XRD, laser Raman spectroscopy, and TPR. Multi-metallic VOx/TiO2 catalysts prepared by incorporating Mo, W, or Cr showed enhanced activities for Cl2Bz oxidation. Among the tested catalysts, V-Mo-Ox/TiO2 catalysts wash-coated on the cordierite honeycomb showed a good activity for the decomposition of the toxic PCDDs/PCDFs in the flue gas emitted from a municipal solid waste incinerator (MSWI).

Topics: Air Pollution; Benzofurans; Catalysis; Dibenzofurans, Polychlorinated; Environmental Pollutants; Incineration; Oxidants; Oxides; Polychlorinated Biphenyls; Polychlorinated Dibenzodioxins; Refuse Disposal; Soil Pollutants; Titanium; Vanadium Compounds

Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/DFs) formation by the thermal reactions of phenols with CuCl2 under oxygen flux were carried out in relation to their formation mechanisms. To evaluate the effect of photocatalytic degradation of titanium dioxide (TiO2) thin film prepared by the sol-gel method, the photocatalysis of PCDD/DFs in acetonitrile/water solution by batch-recycle system was conducted. For the thermal reaction system of powder mixtures of 2,4,5-trichlorophenol (2,4,5-TCP) and CuCl2, the formation rates were 8.1 microg/g-2,4,5-TCP/min for total PCDD/DFs and 6.9 microg/g-2,4,5-TCP/min for PCDDs, and total PCDD/DF rate was higher by approximately 40 fold compared to phenol vapor/oxygen/CuCl2 powder system. For the system of 2,4,5-TCP, PCDDs were mainly formed via ortho-phenoxyphenols (POP) intermediate by the condensation of 2,4,5-trichlorophenate. For PCDD/DF photocatalytic degradations, most PCDD congeners photodecomposed rapidly and the rates presented more than 70% (as dechlorination rates of 76% for PCDDs) at 24 h after irradiation, using PCDD/DFs formed with 2,4,5-TCP. The rate constants were in the order of 4.8-6.1 x 10(-3) min(-1), assuming the pseudo-first-order reactions for their low levels.

Topics: Air Pollutants; Benzofurans; Catalysis; Coloring Agents; Incineration; Phenols; Photochemistry; Polychlorinated Dibenzodioxins; Refuse Disposal; Soil Pollutants; Temperature; Titanium