Portable photocatalytic air cleaners: efficiencies and by-product generation.

Portable photocatalytic air cleaners were investigated in 24 and 48 m(3) emission test chambers with regard to efficiency and by-product generation. For this purpose, formaldehyde, decane, 1,2-dichlorobenzene, toluene, α-pinene and heptanal were doped at sub-ppm concentration levels into the chambers individually and in mixtures. By way of specified test protocols, efficiencies could be distinguished but were strongly dependant on the choice of test compounds, especially on whether single or multi compound dosing was used, and on long-term effects. Initial clean air delivery rates (CADRs) up to 137 m(3)/h were measured. Typical by-products were found in significant concentrations. The main ones were formaldehyde up to 50 ppb (62 µg/m(3)) and acetone up to 80 ppb (190 µg/m(3)). Other aldehydes were also found, but at smaller levels. The detection of chloroacetone, a strong irritating compound, at concentrations up to 15 ppb (57 µg/m(3)) strengthens the importance of such investigations especially in cases were chloro-organic compounds are involved.

Diaryl-substituted ortho-carboranes as a new class of hypoxia inducible factor-1α inhibitors.

Diaryl-substituted ortho-carboranes 1 were synthesized from the corresponding alkynes by decaborane coupling under microwave-irradiated conditions with a combination of N,N-dimethylaniline and chlorobenzene. Among the compounds synthesized, 1a and 1d exhibited significant inhibition of hypoxia-induced HIF-1 transcriptional activity. Both compounds similarly suppressed hypoxia-induced HIF-1α accumulation in a concentration-dependent manner without affecting HIF-1α mRNA expression.

Decomposition of dichlorobenzene in a dielectric barrier discharge.

This paper presents a decomposition study of 1,2-dichlorobenzene (DCB) using a dielectric barrier discharge (DBD). The discussion is focused on the effects of variations of carrier gases, DCB concentrations and input voltages on the decomposition performance. The DCB conversion was conducted inside a cylindrical reactor consists of silver film as the outside electrode and a spring coil as the inside electrode. Two carrier gases, i.e. air and nitrogen, were introduced to the reactor at a total flow rate of 500 mL/min with DCB concentrations of 100, 300 and 500 ppm. Gaseous products, before and after plasma treatment, were analysed by a gas chromatography and FT-IR spectroscopy, and the consumed power was calculated from Lissajous' figure analysis. In order to improve the decomposition performance, various TiO2-supported catalysts were employed.

Modeling of a combined ultraviolet-biofilter system to treat gaseous chlorobenzene I: model development and parametric sensitivity.

A new type of a combined ultraviolet (UV)-biofilter system for air pollution control is developed. In this paper, two conceptual mathematical submodels of the UV reactor and standalone biofilter are developed. All model parameters have been determined by independent experiments or have been taken from literature. Results from UV and the standalone biofilter submodels are in a good agreement with experimental data. However, the performance of the combined system has significantly deviated from those of the UV or standalone submodels because of the stimulating effects of UV irradiation products on the subsequent biofilter performance. A modified model that considers the stimulating effects has agreed well with experimental data over a wide range of operating conditions. Further analysis of the primary parametric sensitivity of the model has shown that inlet chlorobenzene concentrations, gas empty-bed residence time in the UV reactor, and light intensity are important operating conditions.

Proton resonance for oscillating field of the order of static magnetic field.

A spin decoupling method in nuclear quadrupole resonance spin echo experiment is used to detect the proton magnetic resonance absorption spectrum. The behavior of proton resonance in alpha phase of polycrystalline p-dichlorobenzene as a function of the intensity of the proton decoupling oscillating field (H(2)) is measured. Good agreement between the experimental resonance frequency and Shirley's theory for a non-interacting 1/2 spin system is observed. To our knowledge this is the first time the NMR proton frequency dependence on linear polarized excitation field intensity for H(2)/H(o) as high as 1.8 is measured.

Effects of operation conditions on removal rate constant and quantum yield of gaseous chlorobenzene degradation in a photochemical reactor.

A photochemical reactor with a low-pressure mercury ultraviolet (UV) lamp was established to treat waste gas containing chlorobenzene. Operation conditions such as light intensity, gas humidity, and inlet chlorobenzene concentration were varied. Two significant parameters, the removal rate constant and the quantum yield (relating to removal kinetic and light energy utilization), were investigated under each set of conditions. The experimental results indicated that the removal of chlorobenzene by UV irradiation in the gas phase followed a first-order kinetic model at inlet chlorobenzene concentrations ranging from 200 to 2500 mg x m(-3). With increasing light intensity from 10 to 37 microW x cm(-2), the chlorobenzene removal rate constant rose from 0.004 to 0.011 sec(-1), whereas the quantum yield maintained the same value of 0.60. The effects of gas humidity on the parameters indicated that the highest humidity of 80% could achieve the highest removal rate constant (0.046, 0.029, and 0.015 sec(-1)) and the highest quantum yield (1.91, 1.19, and 0.60) among the tested gas humidities at the inlet concentrations of 400, 1000, and 2500 mg x m(-3), respectively. An increase in inlet chlorobenzene concentration from 200 to 2500 mg x m(-3) resulted in reduction in both removal rate constant (from 0.060 to 0.014 sec(-1)) and quantum yield (from 2.50 to 0.56) that may be attributable to competition between the intermediates and chlorobenzene. On the basis of the quantum yield, the total power expended per mass of chlorobenzene was calculated as 483 kWh x kg(-1) under the conditions of an inlet concentration of 200 mg x m(-3) and an empty-bed residence time of 27 sec.

Titanium dioxide mediated photocatalytic degradation of monochlorobenzene in aqueous phase.

The reaction sequence for the photocatalytic degradation of monochlorobenzene (MCB) in UV/TiO2 process, including substrate adsorption, degradation, and mineralization, was studied. The theoretical maximum quantity of MCB that could be adsorbed onto TiO2 surface in aqueous phase was 0.18+/-0.04 micromol m(-2) of TiO2. In accordance with the upper limit of the relative surface coverage of MCB molecules to surface hydroxyls of TiO2 was around 2.2%, the water molecules as the major adjacent species near TiO2 surface would compete with MCB molecules. Increasing the initial substrate concentration to an appropriate value or enhancing the affinity between the MCB and the TiO2 surface by adjusting the solution pH would promote the photocatalytic degradation. Experimental results revealed that the neutral medium was beneficial for the degradation of MCB. In comparison, the mineralization was most improved at acidic condition. Generally, 90% of the total organic carbon (TOC) was mineralized after 240 min illumination time in the examined pH range except solution pH 11. The suppressed mineralization of MCB at solution pH 11 was ascribed to the lack of adsorption. A simplified 2-step consecutive kinetic model was used to simulate the mineralization.

Efficiency of 1,4-dichlorobenzene degradation in water under photolysis, photocatalysis on TiO2 and sonolysis.

The rate of 1,4-dichlorobenzene (1,4-DCB) degradation and mineralization in the aqueous phase was investigated either under direct photolysis or photocatalysis in the presence of commercial or sol-gel synthesized TiO2, or under sonolysis at 20 kHz with different power inputs. Two lamps, both emitting in the 340-400 nm wavelength range with different energy, were employed as irradiation sources. Photocatalysis ensured faster removal of 1,4-DCB with respect to sonolysis and direct photolysis. The highest degradation and mineralization rate was attained with the combined use of photocatalysis and sonolysis, i.e. under sonophotocatalytic conditions. The efficiency of the employed advanced oxidation techniques in 1,4-DCB degradation is discussed also in relation to their energy consumption, which might be decisive for their practical application.

Neutron response of the chlorobenzene-ethanol-trimethylpentane dosimetry system.

The dosimetric use of the chemical solution chlorobenzene-ethanol-trimethylpentane (CET) is based on the radiolytic formation of hydrochloric acid, which protonates a pH indicator thymolsulphonphthalein. On the basis of the CET solution, an accident and emergency personal dosemeter was designed allowing doses in the range 0.2-15 Gy can be measured. Radiation-chemical yields, G(HCl), for the CET system, and the responses of dosemeters in different neutron fields, ranging from 0.35 to 19.3 MeV mean energy neutrons, are summarised. The relation of G(HCl) to linear energy transfer (LET) of incident heavy charged particles is also evaluated on the basis of the previously published data. The response of the CET system to monoenergetic neutrons was calculated from the measured dependence of the G value upon LET of heavy charged particles and data about the LET distribution for monoenergetic neutrons. A very good agreement between this calculation and the experimental results was obtained. These results enable predictions of the response to be made in radiation fields with the known LET distributions.

Photocatalytic degradation of gaseous organic species on photonic band-gap titania.

The use of photonic band gap (PBG) titania (inverse opal) for the photocatalytic degradation of an organic chemical in air is demonstrated in this study using 1,2-dichlorobenzene. A photonic band gap in the mid-to-high ultraviolet (UV) wavelength range (280-380 nm), normally associated with the optimal photocatalytic activity of anatase titania, is expected to increase the quantum efficiency for the catalyst. To achieve this band gap, porous structures with alternating air and titania spaces with a periodicity of about 150 nm is required. A thin film of porous photonic titania was synthesized in-situ on a quartz glass rod with a sol-gel technique using polystyrene micro-spheres as templates. Scanning electron microscopy images revealed a pore size of about 100 nm and a periodicity of approximately 150 nm, necessary for the desired band gap. X-ray diffraction studies of the coating showed the presence of anatase titania, which is known to exhibit photoactivity. The photocatalytic activity of the coated titania film was verified by measuring the degradation of 1,2-dichlorobenzene vapor in a semi-batch mode in the presence of UV radiation (mid-high UV wavelength) PBG titania showed 248% higher photonic efficiency compared to commercially available P25 titania catalyst. Transmission spectra from the thin films showed high absorbance in the UV range, suggesting a band gap in the region of UV illumination.

Fe(III) homogeneous photocatalysis for the removal of 1,2-dichlorobenzene in aqueous solution by means UV lamp and solar light.

Chlorinated hydrocarbons are widely used in chemical industries as solvents and intermediates for pesticides and dyes manufacture. Their presence was documented in rivers, groundwaters and seawaters. In this work, the oxidation of 1,2-dichlorobenzene in aqueous solutions by means of Fe(III) homogeneous photocatalysis under UV lamp and sunlight irradiations is studied. The results show that the best working conditions are found for pH=3.0 and initial [Fe(III)] concentration equal to 1.0x10(-4) molL(-1) although the investigated system can be utilized even at pH close to 4.0 but with slower abatement kinetics. Some dicholoroderivatives, such as 2,3-dichlorophenol, 3,4-dichlorophenol and 2-chlorophenol, are identified as oxidation intermediates. The values of the kinetic constant for the photochemical reoxidation of Fe(II) to Fe(III) are evaluated by a mathematical model in the range 1.58-3.78 Lmol(-1)s(-1) and 0.69-0.78 Lmol(-1)s(-1) for the systems irradiated by UV lamp and sunlight, respectively.

A reversible molecular switch based on pattern-change in chlorobenzene and toluene on a Si(111)-(7x7) surface.

A reversible molecular switch is proposed, based on an observed change in a physisorbed pattern of chlorobenzene or toluene at Si(111)-(7x7), from "triangles" to "circles". Electronic excitation, at an applied surface voltage of Vs = -2.0 V, caused molecular migration, by one atomic site, from under the tip (switch "off"). Thereafter, the adsorbate pattern reverted thermally from circles to triangles (switch "on") across a measured activation barrier of Ea = 0.3 eV for chlorobenzene and 0.2 eV for toluene.

Effect of additives on photodegradation of 1,3,5-trichlorobenzene in aqueous surfactant solutions.

Photolysis of 1,3,5-trichlorobenzene (TCB) in moderate concentration (0.5 mM) in the presence of several additives was examined in 10 mM of cationic and nonionic surfactant solutions. Additions of small amounts of hydrophobic additives, n-dodecanethiol (1 mM), n-dodecyldimethylamine (<2.5 mM), and N-(n-dodecyl)-N-methylaniline (C12An: <0.5 mM), were effective for photodechlorination of TCB, while the formation of by-products could not be inhibited perfectly. In contrast, exclusive and efficient dechlorination of TCB in cetyltrimethylammonium chloride solution was achieved in the presence of sodium borohydride (<5 mM), which was due to the enhanced local concentration of borohydride anions in cationic micelle surfaces.

Advanced oxidation degradation of dichlorobenzene in water by the UV/H2O2 process.

Through UV/H2O2 photocatalytic advanced oxidation technique the performance, kinetics, pathway, and mechanism of ortho-dichlorobenzene (O-DCB) in water and the effect parameters of degradating reaction were studied systematically. The results showed that the reaction of photocatalytic degradation of O-DCB was fast and accorded well with the pseudo-first-order kinetics. The roles of some parameters, such as the pH, the initial concentrations of O-DCB, H2O2, and some anions in reaction solution, were examined in detail. It was found that weak acidic or neutral environment was favorable to the degradation reaction and some anions slowed down the photocatalytic degradation rate. Input amount of H2O2 possessed the best value under specified condition. The intermediates of O-DCB degradation were also tentatively identified 2,3-dichlorophenol, 3,4-dichlorophenol, formic acid, acetic acid, and oxalic acid mainly adopting GC/MS and ion chromatogram (IC) techniques. According to this, the pathway and mechanism of UV/H2O2 photocatalytic degradation of O-DCB were deduced and led.