Self-Organized TiO2-MnO2 Nanotube Arrays for Efficient Photocatalytic Degradation of Toluene.

Vertically oriented, self-organized TiO2-MnO2 nanotube arrays were successfully obtained by one-step anodic oxidation of Ti-Mn alloys in an ethylene glycol-based electrolyte. The as-prepared samples were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), UV-Vis absorption, photoluminescence spectroscopy, X-ray diffraction (XRD), and micro-Raman spectroscopy. The effect of the applied potential (30-50 V), manganese content in the alloy (5-15 wt. %) and water content in the electrolyte (2-10 vol. %) on the morphology and photocatalytic properties was investigated for the first time. The photoactivity was assessed in the toluene removal reaction under visible light, using low-powered LEDs as an irradiation source (λmax = 465 nm). Morphology analysis showed that samples consisted of auto-aligned nanotubes over the surface of the alloy, their dimensions were: diameter = 76-118 nm, length = 1.0-3.4 µm and wall thickness = 8-11 nm. It was found that the increase in the applied potential led to increase the dimensions while the increase in the content of manganese in the alloy brought to shorter nanotubes. Notably, all samples were photoactive under the influence of visible light and the highest degradation achieved after 60 min of irradiation was 43%. The excitation mechanism of TiO2-MnO2 NTs under visible light was presented, pointing out the importance of MnO2 species for the generation of e- and h⁺.

Solar photothermochemical reaction and supercritical CO2 work up for a fully green process of preparation of pure p-nitrobenzyl bromide.

It has been reported by us recently that p-nitrobenzyl bromide (PNBBr) can be synthesized from p-nitrotoluene (PNT) in high isolated yield with respect to available bromine in 2:1 Br(-)-BrO3(-) employed as brominating reagent. The reaction was conducted in ethylene dichloride (EDC) and the substrate was taken in excess to suppress dibromo impurity formation. The product was "cold crystallized" from the reaction mass and the mother liquor was recycled in the subsequent batch thereby eliminating organic discharge. The present work attempts to further advance the synthesis of this commercially important molecule employed in protection-deprotection strategies. Herein its successful synthesis employing neat substrate and solar radiation as the sole energy source to drive this photothermochemical reaction is reported. Further, 100% pure PNBBr could be isolated from the solid reaction mass in 87% yield by leaching out the excess substrate through supercritical CO2 (Sc-CO2) extraction. The reaction was therefore accomplished cleanly in all respects and with low carbon footprint.

Polymerization kinetics and reactivity of alternative initiators systems for use in light-activated dental resins.

OBJECTIVES: The purpose of this study was to evaluate the reactivity and polymerization kinetics behavior of a model dental adhesive resin with water-soluble initiator systems. METHODS: A monomer blend based on Bis-GMA, TEGDMA and HEMA was used as a model dental adhesive resin, which was polymerized using a thioxanthone type (QTX) as a photoinitiator. Binary and ternary photoinitiator systems were formulated using 1mol% of each initiator. The co-initiators used in this study were ethyl 4-dimethylaminobenzoate (EDAB), diphenyliodonium hexafluorophosphate (DPIHFP), 1,3-diethyl-2-thiobarbituric acid (BARB), p-toluenesulfinic acid and sodium salt hydrate (SULF). Absorption spectra of the initiators were measured using a UV-Vis spectrophotometer, and the photon absorption energy (PAE) was calculated. The binary system camphorquinone (CQ)/amine was used as a reference group (control). Twelve groups were tested in triplicate. Fourier-transform infrared spectroscopy (FTIR) was used to investigate the polymerization reaction during the photoactivation period to obtain the degree of conversion (DC) and maximum polymerization rate (R(p)(max)) profile of the model resin. RESULTS: In the analyzed absorption profiles, the absorption spectrum of QTX is almost entirely localized in the UV region, whereas that of CQ is in the visible range. With respect to binary systems, CQ+EDAB exhibited higher DC and R(p)(max) values. In formulations that contained ternary initiator systems, the group CQ+QTX+EDAB was the only one of the investigated experimental groups that exhibited an R(p)(max) value greater than that of CQ+EDAB. The groups QTX+EDAB+DPIHFP and QTX+DPIHFP+SULF exhibited values similar to those of CQ+EDAB with respect to the final DC; however, they also exhibited lower reactivity. SIGNIFICANCE: Water-soluble initiator systems should be considered as alternatives to the widely used CQ/amine system in dentin adhesive formulations.

Efficient removal of toluene and benzene in gas phase by the TiO2/Y-zeolite hybrid photocatalyst.

Efficient removal of toluene or benzene molecules thinly diffused in gas phase was achieved by using TiO(2)/Y-zeolite hybrid photocatalysts. TiO(2) of 10 wt% hybridized with a hydrophobic USY zeolite showed higher photocatalytic reactivity as compared to TiO(2) hybridized with hydrophilic H-Y or Na-Y zeolites. This phenomenon can be explained by the fact that the hydrophobic USY zeolite efficiently adsorbs the organic compounds and smoothly supplies them onto the TiO(2) photocatalyst surface. However, the toluene or benzene molecules, which are strongly trapped on the hydrophilic H(+) or Na(+) sites of zeolite, cannot diffuse onto the TiO(2) surfaces, resulting in lower photocatalytic reactivity. Although the adsorption capacity of the pure TiO(2) sample rapidly deteriorated, the TiO(2)/Y-zeolite hybrid system maintained a high adsorption efficiency to remove such aromatic compounds for a long period.

Assembly of Ni(OH)2 nanoparticle films on aqueous surfaces induced by small amounts of toluene, and the study of their unmediated electrocatalytic oxidation toward some small biomolecules.

A simple strategy for the preparation of a Ni(OH)2 nanoparticle film is described. Ni(OH)2 nanoparticles were synthesized in an aqueous solution of Ni2+ and tert-butylamine in the presence of small amounts of toluene, which induced the nanoparticles to assemble a thin film on the aqueous surface. The obtained Ni(OH)2 nanoparticle film was easily transferred onto the electrode surfaces and exhibited stable electrochemical performance. The electrochemical behavior of various small biomolecules, including cysteine, homocysteine, glutathione, histidine, glycine, cystine, methionine, lysine, aspartic acid, glutamic acid, phenylalanine, ascorbic acid, uric acid and dopamine, were studied at the Ni(OH)2 nanoparticle-film-modified electrode. The Ni(OH)2 nanoparticle film exhibits excellent direct, unmediated electrocatalysis toward the oxidation of cysteine, homocysteine and ascorbic acid in a pH 7.4 buffer solution with a low onset potential and a high oxidation signal. This behavior differs from many reports in which small organic molecules are electrocatalyzed indirectly by the Ni(OH)2/NiOOH redox couple in a strongly alkaline solution.

Photocatalytic activity of titanium dioxide nanoparticle coatings applied on autoclaved aerated concrete: effect of weathering on coating physical characteristics and gaseous toluene removal.

Autoclaved aerated concrete has been coated by TiO(2) nanoparticles through a dip-coating (DC) and a novel vacuum saturation (VS) method to investigate the weathering resistance and gaseous toluene removal potential of both coating types. The effect of intensive weathering - corresponding to a period of about 25 years - on the coating characteristics was studied in terms of TiO(2) content, coating thickness and color changes. Toluene removal was investigated in a lab-scale flow-through photoreactor at 24°C and 52% relative humidity, and results obtained immediately after application of the coatings and after two weathering stages were compared. Weathering of the DC and VS coated samples resulted into a decrease of the coating layer thickness of more than 98%, confirmed by a decline in TiO(2) content by more than 99% and 93%, respectively. Surprisingly, toluene removal efficiencies before and after weathering kept constant at about 95% for both coating types, corresponding to an elimination rate of 60-70 mg/(m(2)h) at an initial toluene concentration of 15 ppm(v) and a gas residence time of 3 min. Increasing the toluene load by applying higher toluene inlet concentrations (up to 35 ppm(v)) and lower gas residence times (1 min) did decrease the toluene removal efficiency to 32-41%, but elimination rates increased up to 214 mg/(m(2)h), being a factor of 1.6-4.5 times higher than reported in recent work.

Real-time monitoring of benzene, toluene, and p-xylene in a photoreaction chamber with a tunable mid-infrared laser and ultraviolet differential optical absorption spectroscopy.

We describe the implementation of a mid-infrared laser-based trace gas sensor with a photoreaction chamber, used for reproducing chemical transformations of benzene, toluene, and p-xylene (BTX) gases that may occur in the atmosphere. The system performance was assessed in the presence of photoreaction products including aerosol particles. A mid-infrared external cavity quantum cascade laser (EC-QCL)-tunable from 9.41-9.88 µm (1012-1063 cm(-1))-was used to monitor gas phase concentrations of BTX simultaneously and in real time during chemical processing of these compounds with hydroxyl radicals in a photoreaction chamber. Results are compared to concurrent measurements using ultraviolet differential optical absorption spectroscopy (UV DOAS). The EC-QCL based system provides quantitation limits of approximately 200, 200, and 600 parts in 10(9) (ppb) for benzene, toluene, and p-xylene, respectively, which represents a significant improvement over our previous work with this laser system. Correspondingly, we observe the best agreement between the EC-QCL measurements and the UV DOAS measurements with benzene, followed by toluene, then p-xylene. Although BTX gas-detection limits are not as low for the EC-QCL system as for UV DOAS, an unidentified by-product of the photoreactions was observed with the EC-QCL, but not with the UV DOAS system.

Femtosecond spectroscopy on the photochemistry of ortho-nitrotoluene.

The photo tautomerisations of ortho-nitrotoluene (oNT) and its methylated derivative ortho-ethylnitrobenzene (oENB) have been studied by means of femtosecond spectroscopy and (TD)-DFT computations. In UV/Vis transient absorption spectroscopy a band peaking at 400 nm is seen to rise in a bi-modal manner with time constants of 1-10 ps and 1500 ps. Femtosecond stimulated Raman experiments clearly identify aci-nitro forms as the spectroscopic carriers of the 400 nm band. The assignment of the Raman spectra is based on TD-DFT computations. The quantum yields of the aci-nitro forms after 3 ns are 0.08 (oNT) and 0.3 (oENB). The aci-nitro forms are formed via a singlet channel (1-10 ps) and a triplet channel (1500 ps). There are indications that the triplet channel involves a bi-radical intermediate. In between 3 ns and 1 ms the spectrum of the aci-nitro form shifts from 400 to 390 nm. This could indicate a tautomerisation from Z-aci-nitro to an E form.

Preparation of silver-modified TiO2 via microwave-assisted method and its photocatalytic activity for toluene degradation.

Silver-modified TiO(2) (Ag-TiO(2)) with various Ag/Ti molar ratios were prepared by the microwave-assisted method and characterized by X-ray diffraction (XRD), transmission electron microscope (TEM) and UV-vis diffuse reflectance spectroscopy (UV-vis-DRS). Compared with the hydrothermal method, Ag-TiO(2) of small crystallite size and high crystallinity can be obtained by the microwave-assisted preparation method. When the Ag/Ti molar ratio increased from 0 to 2%, the doping of Ag promoted the phase transformation and inhibited the growth of anatase crystallite. The absorption edge of Ag-TiO(2) shifted to longer wavelength, and the band gap energy of Ag-TiO(2) decreased. However, after increasing the molar ratio Ag/Ti further from 2 to 4%, the anatase content, the crystallite size and the band gap energy of Ag-TiO(2) only increased slightly. In photodegradation gaseous toluene, the photocatalytic activity of Ag-TiO(2) increased with the increase of Ag/Ti molar ratio from 0 to 1%, but declined with the further increase to 2%. The optimal Ag/Ti molar ratio for photocatalytic activity of Ag-TiO(2) was found as 1%, with the content of anatase, rutile and brookite of 71.1, 14.5 and 14.4%, respectively. Compared with TiO(2), Ag-TiO(2) exhibited a better photostability in toluene degradation.

Removal of gaseous toluene by the combination of photocatalytic oxidation under complex light irradiation of UV and visible light and biological process.

Photocatalysis is a promising technology for treatment of gaseous waste; its disadvantages, however, include causing secondary pollution. Biofiltration has been known as an efficient technology for treatment volatile organic compounds (VOCs) at low cost of maintenance, and produces harmless by-products; its disadvantages, include large volume of bioreactor and slow adaptation to fluctuating concentrations in waste gas. A bench scale system integrated with a photocatalytic oxidation and a biofilter unit for the treatment of gases containing toluene was investigated. The integrated system can effectively oxidize toluene with high removal efficiency. The photocatalytic activity of N-TiO(2)/zeolite was evaluated by the decomposition of toluene in air under UV and visible light (VL) illumination. The N-TiO(2)/zeolite has more photocatalytic activity under complex light irradiation of UV and visible light for toluene removal than that of pure TiO(2)/zeolite under UV or visible light irradiation. N-TiO(2)/zeolite was characterized by scanning electron microscopy (SEM), X-ray photoelectron spectrum analysis (XPS), Fourier transform infrared spectroscopy (FT-IR), and as-obtained products were identified by means of gas chromatography/mass spectrometry (GC/MS). Results revealed that the photocatalyst was porous and was high photoactive for mineralizing toluene. The high activity can be attributed to the results of the synergetic effects of strong UV and visible light absorption, surface hydroxyl groups. The photocatalytic degradation reaction of toluene with the N-TiO(2)/zeolite follows Langmuir-Hinshelwood kinetics. Toluene biodegradation rate matches enzymatic oxidation kinetics model.

Efficiency of clay--TiO2 nanocomposites on the photocatalytic elimination of a model hydrophobic air pollutant.

Clay-supported TiO2 photocatalysts can potentially improve the performance of air treatment technologies via enhanced adsorption and reactivity of target volatile organic compounds (VOCs). In this study, a benchtop photocatalytic flow reactor was used to evaluate the efficiency of hectorite-TiO2 and kaolinite-TiO2, two novel composite materials synthesized in our laboratory. Toluene, a model hydrophobic VOC and a common indoor air pollutant, was introduced in the air stream at realistic concentrations, and reacted under UVA (lamda(max) = 365 nm) or UVC (lamda(max) = 254 nm) irradiation. The UVC lamp generated secondary emission at 185 nm, leading to the formation of ozone and other short-lived reactive species. Performance of clay-Ti02 composites was compared with that of pure TiO2 (Degussa P25), and with UV irradiation in the absence of photocatalyst under identical conditions. Films of clay-TiO2 composites and of P25 were prepared by a dip-coating method on the surface of Raschig rings, which were placed inside the flow reactor. An upstream toluene concentration of approximately 170 ppbv was generated by diluting a constant flow of toluene vapor from a diffusion source with dry air, or with humid air at 10, 33, and 66% relative humidity (RH). Toluene concentrations were determined by collecting Tenax-TA sorbent tubes downstream of the reactor, with subsequent thermal desorption--GC/MS analysis. The fraction of toluene removed, %R, and the reaction rate, Tr, were calculated for each experimental condition from the concentrations measured with and without UV irradiation. Use of UVC light (UV/TiO2/O3) led to overall higher reactivity, which can be partially attributed to the contribution of gas phase reactions by short-lived radical species. When the reaction rate was normalized to the light irradiance, Tr/Ilamda,the UV/TiO2 reaction under UVA irradiation was more efficient for samples with a higher content of TiO2 (P25 and Hecto-TiO2), but notfor Kao-TiO2. In all cases, reaction rates peaked at 10% RH, with Tr values between 10 and 50% higherthan those measured under dry air. However, a net inhibition was observed as RH increased to 33% and 66%, indicating that water molecules competed effectively with toluene for reactive surface sites and limited the overall photocatalytic conversion. Compared to P25, inhibition by coadsorbed water was less significant for Kao-TiO2 samples, but was more dramatic for Hecto-TiO2 due to the high water uptake capacity of hectorite.

Effect of TiO2/adsorbent hybrid photocatalysts for toluene decomposition in gas phase.

12 hybrid photocatalysts consisting of titania (TiO(2)) and an adsorbent such as mordenite were investigated for the photocatalytic decomposition of toluene, a major indoor contaminant in indoor air. The highest decomposition rate was obtained with the use of mordenite and silicon dioxide (SiO(2)) as additives to TiO(2). The photocatalytic activities of hybrid photocatalysts in decomposing toluene are 1.33 times as high as pure P25 at the net weight loading of 0.49 mg/cm(2) under the test condition. Scanning electron microscopy (SEM) images confirmed that the hybrid photocatalyst films were very porously distributed; TiO(2) was adsorbed on the surface of mordenite and SiO(2), increasing the reaction area of TiO(2). The unimolecular Langmuir-Hishelwood model and mass-transfer-based (MTB) method were used to evaluate the reaction coefficients and adsorption equilibrium coefficients of hybrid photocatalysts. It is evidenced that the reaction areas of two hybrid photocatalysts were 1.52 and 1.64 times larger than that of P25, respectively, which is the major reason to make the high removal efficiency of toluene.

Preparation and application of visible-light-responsive Ni-doped and SnO2-coupled TiO2 nanocomposite photocatalysts.

A new series of visible-light-driven TiO2 photocatalysts constituting lattice-doped Ni and surface-coupled SnO2 nanocomposites, xNi-TiO2-SnO2 (x=0.1, 0.3, 0.5), were synthesized. TiO2 and xNi-TiO2 were prepared by a sol-gel method while the SnO2 was coupled to these via a ligand exchange reaction and finally the catalysts were thermally treated. The presence of Ni ions in the lattice of the photocatalysts was indirectly confirmed by a red shift in DRS spectra. XRD showed crystalline peaks only assignable to TiO2 anatase phase. XPS analysis confirmed that Sn is present on the surface of the catalysts as SnO2 while Ni(2)O(3) is absent. The xNi-TiO2-SnO2 nanocomposites showed a promising visible-light-responsive photocatalytic activity and were found superior to TiO2, xNi-TiO2 and TiO2-SnO2 for the degradation of toluene in air.

Complete oxidation of acetaldehyde and toluene over a Pd/WO(3) photocatalyst under fluorescent- or visible-light irradiation.

Acetaldehyde was completely oxidized to CO(2) over a Pd/WO(3) photocatalyst under fluorescent-light irradiation in a flow-type reactor, and Pd/WO(3) was also used to completely oxidize toluene to CO(2) in a batch reactor under visible-light irradiation.

Light-controlled supramolecular helicity of a liquid crystalline phase using a helical polymer functionalized with a single chiroptical molecular switch.

Control over the preferred helical sense of a poly(n-hexyl isocyanate) (PHIC) by using a single light-driven molecular motor, covalently attached at the polymer's terminus, has been accomplished in solution via a combination of photochemical and thermal isomerizations. Here, we report that after redesigning the photochromic unit to a chiroptical molecular switch, of which the two states are thermally stable but photochemically bistable, the chiral induction to the polymer's backbone is significantly improved and the handedness of the helical polymer is addressable by irradiation with two different wavelengths of light. Moreover, we show that the chiral information is transmitted, via the macromolecular level of the polyisocyanate, to the supramolecular level of a lyotropic cholesteric liquid crystalline phase consisting of these stiff, rodlike polymers. This allows the magnitude and sign of the supramolecular helical pitch of the liquid crystal film to be fully controlled by light.

Photocatalytic oxidation of organic pollutants on titania-clay composites.

TiO2/Ca-montmorillonite composites were prepared by wet grinding in an agate mill. Positively charged TiO2 nanoparticles are bound to the surface of the negatively charged montmorillonite layers via heterocoagulation; the clay mineral is used as adsorbent and support for the photooxidation process. Aquatic solution of 0.5mM phenol was degraded by irradiation with UV-VIS light (lambda=250-440 and 540-590 nm) in suspensions of TiO2-clay composites and significant photodegradation was observed at 40-60% TiO2/Ca-montmorillonite compositions. Synergistic effect was detected at solid/liquid interface for degradation of phenol and at solid/gas interface in the recycling flow reactors for photooxidation of ethanol and toluene vapors.

Effects of seed aerosols on the growth of secondary organic aerosols from the photooxidation of toluene.

Hydroxyl radical (.OH)-initiated photooxidation reaction of toluene was carried out in a self-made smog chamber. Four individual seed aerosols such as ammonium sulfate, ammonium nitrate, sodium silicate and calcium chloride, were introduced into the chamber to assess their influence on the growth of secondary organic aerosols (SOA). It was found that the low concentration of seed aerosols might lead to high concentration of SOA particles. Seed aerosols would promote rates of SOA formation at the start of the reaction and inhibit its formation rate with prolonging the reaction time. In the case of ca. 9000 pt/cm3 seed aerosol load, the addition of sodium silicate induced a same effect on the SOA formation as ammonium nitrate. The influence of the four individual seed aerosols on the generation of SOA decreased in the order of calcium chloride>sodium silicate and ammonium nitrate>ammonium sulfate.

CEC separation of aromatic compounds and proteins on hexylamine-functionalized N-acryloxysuccinimide monoliths.

Reactive organic polymer monoliths were prepared in fused-silica capillaries by UV-initiated free radical polymerization of N-acryloxysuccinimide (NAS) as reactive monomer, ethylene dimethacrylate as crosslinker, azobisisobutyronitrile as initiator, and toluene as porogen. In a second synthetic step, chemical derivatization of the activated-ester moieties was performed in situ through alkylation reaction with alkylamines to afford monolithic stationary phases with potential reversed-phase properties. A correlation between the synthesis conditions--composition of the reactive solution--chemical characteristics of the reactive polymer monoliths--nitrogen/NAS content--and the reversed-phase separation properties of the functionalized monolithic columns--selectivity towards homologous series of akylbenzenes--was clearly established. This finding offers the possibility of adjusting the experimental conditions with respect to the target applications. The monolithic stationary phases with optimized chemical and porous structures were used for the CEC separation of alkylbenzenes, phenols, anilines, organic acids, amino acids, and proteins. The data indicate that depending on the nature of the analytes (charge, hydrophobic/hydrophilic balance, size) reversed-phase or mixed modes may account for the observed separation.

Mathematical model for photocatalytic destruction of organic contaminants in air.

Photocatalytic oxidation (PCO) was investigated in a bench-scale reactor for the abatement of two airborne organic contaminants: toluene and ethanol. A mathematical model that includes the impacts of light intensity, initial contaminant concentration, catalyst thickness, and relative humidity (RH) on the degradation of organic contaminants in a photocatalytic reactor was developed to describe this process. The commercially available catalyst Degussa-PtTiO2 was selected to compare with the MTU-PtTiO2-350 catalyst, which was synthesized by the sol-gel process, platinized, and calcined at 350 degrees C. For toluene removal using the MTU-PtTiO2-350 catalyst, the degradation rate increased with increases in light intensity from 0.2 to 2.2 mW/cm2 and in catalyst thickness from 0.00037 to 0.00361 cm. However, further increases in light intensity and catalyst thickness had only slight effect on the toluene degradation rate. Increasing the initial concentration from 6.29 to 127.9 microg/L and the RH from 10 to 85% resulted in decreases in the toluene degradation rate. For ethanol removal using the MTU-PtTiO2-350 catalyst, the degradation rate increased more rapidly with an increase in RH from 17 to 56%; the RH had little effect on the ethanol degradation rate while it further increased from 56% to 82%. We discuss applicability of the model to estimate the influence of process variables and to evaluate photocatalyst performance.

Contributions of toluene and alpha-pinene to SOA formed in an irradiated toluene/alpha-pinene/NO(x)/ air mixture: comparison of results using 14C content and SOA organic tracer methods.

An organic tracer method, recently proposed for estimating individual contributions of toluene and alpha-pinene to secondary organic aerosol (SOA) formation, was evaluated by conducting a laboratory study where a binary hydrocarbon mixture, containing the anthropogenic aromatic hydrocarbon, toluene, and the biogenic monoterpene, alpha-pinene, was irradiated in air in the presence of NO(x) to form SOA. The contributions of toluene and alpha-pinene to the total SOA concentration, calculated using the organic tracer method, were compared with those obtained with a more direct 14C content method. In the study, SOA to SOC ratios of 2.07 +/- 0.08 and 1.41 +/- 0.04 were measured for toluene and (alpha-pinene SOA, respectively. The individual tracer-based SOA contributions of 156 microg m(-3) for toluene and 198 microg m(-)3 for alpha-pinene, which together accounted for 82% of the gravimetrically determined total SOA concentration, compared well with the 14C values of 182 and 230 microg m(-3) measured for the respective SOA precursors. While there are uncertainties associated with the organic tracer method, largely due to the chemical complexity of SOA forming chemical mechanisms, the results of this study suggest the organic tracer method may serve as a useful tool for determining whether a precursor hydrocarbon is a major SOA contributor.