Painatuksen UV-stabiilisuuden optimointi fenolihartsatussa paperissa

Tässä diplomityössä tutkittiin painetun paperin ja siitä fenoliformaldehydihartsilla impregnoimalla valmistetun pinnoituskalvon UV-stabiilisuuden parantamis-mahdollisuuksia. Työn kirjallisuusosassa käsitellään painetun pinnoituskalvon valmistusprosessia ja painatuksen UV-valonkestoon vaikuttavia tekijöitä. Painovärin pigmentti, sen määrä ja käsittely, painovärin sideaine sekä fenoliformaldehydihartsi ja sen lisäaineet vaikuttavat pinnoitetun betonoimisvanerin säänkesto-ominaisuuksiin. Erilaisilla epäorgaanisilla valkoisilla pigmenteillä ja kidemuodoilla on erilainen UV-valonkesto ja taitekerroin. Päällystämällä titaanidioksidi esimerkiksi alumiini- tai zirkoniumoksideilla sen UV-valonkestoa voidaan parantaa merkittävästi. UV-hajoaminen voidaan havaita painetun pinnoitteen liituuntumisena. Liituuntumista voidaan pitää veden ja hapen välisenä reaktiona, jota titaanidioksidi ja UV-säteily katalysoivat. Sen takia myös muiden valkoisten epäorgaanisten pigmenttien ominaisuuksia ja käyttöä selvitettiin. Kokeissa käytettiin yhdeksää eri painoväriä, kahta eri paksuista paperia ja kahta eri tyyppistä hartsia. Painovärejä ohennettiin vedellä ja paperin painopuolta vaihdeltiin. Kaikissa painatuksissa käytettiin kolmea eri rasterointiasteen laattaa, jolloin painovärin määrää paperissa saatiin vähennettyä. Painetuista papereista mitattiin densiteetti, värimäärä, pisara-absorptio vedellä ja kontaktikulma hartsilla. Myös painovärin tunkeumaa selvitettiin paperin poikkileikeistä tehtyjen SEM-kuvien avulla. Painetut paperit impregnoitiin fenoliformaldehydihartsilla kalvoksi. Pinnoituskalvot puristettiin vanerin pinnalle laboratoriopuristimella. Koekappaleet altistettiin UV-valolle, sateelle ja pakkaselle sääkaapissa 400 h ajan, mikä vastaa noin 1,5 vuotta ulkona Suomen oloissa. Kappaleista mitattiin kiilto, värinmuutos ja liituuntuminen. Pinnoitteen liituuntumista tapahtui vähiten niissä koepisteissä, joissa painatus oli tehty 30 % rasteroidulla laatallaSäänkestävä TiO2 osoittautui hyväksi, mutta myös ZnO-pigmentillä saatiin hyviä tuloksia. ZnO-koepisteessä liituuntumisreaktio ei ole niin voimakkaasti katalysoitu kuin TiO2-koepisteissä. Paksun paperin painatuspuolella näytti olevan merkitystä säänkestoon. Huopapuolelle painettuna pinnoitteen liituuntuminen oli vähäisempää

Gas-phase photocatalytic oxidation of volatile organic compounds

Substances emitted into the atmosphere by human activities in urban and industrial areas cause environmental problems such as air quality degradation, respiratory diseases, climate change, global warming, and stratospheric ozone depletion. Volatile organic compounds (VOCs) are major air pollutants, emitted largely by industry, transportation and households. Many VOCs are toxic, and some are considered to be carcinogenic, mutagenic, or teratogenic. A wide spectrum of VOCs is readily oxidized photocatalytically. Photocatalytic oxidation (PCO) over titanium dioxide may present a potential alternative to air treatment strategies currently in use, such as adsorption and thermal treatment, due to its advantageous activity under ambient conditions, although higher but still mild temperatures may also be applied. The objective of the present research was to disclose routes of chemical reactions, estimate the kinetics and the sensitivity of gas-phase PCO to reaction conditions in respect of air pollutants containing heteroatoms in their molecules. Deactivation of the photocatalyst and restoration of its activity was also taken under consideration to assess the practical possibility of the application of PCO to the treatment of air polluted with VOCs. UV-irradiated titanium dioxide was selected as a photocatalyst for its chemical inertness, non-toxic character and low cost. In the present work Degussa P25 TiO2 photocatalyst was mostly used. In transient studies platinized TiO2 was also studied. The experimental research into PCO of following VOCs was undertaken: - methyl tert-butyl ether (MTBE) as the basic oxygenated motor fuel additive and, thus, a major non-biodegradable pollutant of groundwater; - tert-butyl alcohol (TBA) as the primary product of MTBE hydrolysis and PCO; - ethyl mercaptan (ethanethiol) as one of the reduced sulphur pungent air pollutants in the pulp-and-paper industry; - methylamine (MA) and dimethylamine (DMA) as the amino compounds often emitted by various industries. The PCO of VOCs was studied using a continuous-flow mode. The PCO of MTBE and TBA was also studied by transient mode, in which carbon dioxide, water, and acetone were identified as the main gas-phase products. The volatile products of thermal catalytic oxidation (TCO) of MTBE included 2-methyl-1-propene (2-MP), carbon monoxide, carbon dioxide and water; TBA decomposed to 2-MP and water. Continuous PCO of 4 TBA proceeded faster in humid air than dry air. MTBE oxidation, however, was less sensitive to humidity. The TiO2 catalyst was stable during continuous PCO of MTBE and TBA above 373 K, but gradually lost activity below 373 K; the catalyst could be regenerated by UV irradiation in the absence of gas-phase VOCs. Sulphur dioxide, carbon monoxide, carbon dioxide and water were identified as ultimate products of PCO of ethanethiol. Acetic acid was identified as a photocatalytic oxidation by-product. The limits of ethanethiol concentration and temperature, at which the reactor performance was stable for indefinite time, were established. The apparent reaction kinetics appeared to be independent of the reaction temperature within the studied limits, 373 to 453 K. The catalyst was completely and irreversibly deactivated with ethanethiol TCO. Volatile PCO products of MA included ammonia, nitrogen dioxide, nitrous oxide, carbon dioxide and water. Formamide was observed among DMA PCO products together with others similar to the ones of MA. TCO for both substances resulted in the formation of ammonia, hydrogen cyanide, carbon monoxide, carbon dioxide and water. No deactivation of the photocatalyst during the multiple long-run experiments was observed at the concentrations and temperatures used in the study. PCO of MA was also studied in the aqueous phase. Maximum efficiency was achieved in an alkaline media, where MA exhibited high fugitivity. Two mechanisms of aqueous PCO – decomposition to formate and ammonia, and oxidation of organic nitrogen directly to nitrite - lead ultimately to carbon dioxide, water, ammonia and nitrate: formate and nitrite were observed as intermediates. A part of the ammonia formed in the reaction was oxidized to nitrite and nitrate. This finding helped in better understanding of the gasphase PCO pathways. The PCO kinetic data for VOCs fitted well to the monomolecular Langmuir- Hinshelwood (L-H) model, whereas TCO kinetic behaviour matched the first order process for volatile amines and the L-H model for others. It should be noted that both LH and the first order equations were only the data fit, not the real description of the reaction kinetics. The dependence of the kinetic constants on temperature was established in the form of an Arrhenius equation.

Photocatalytic Activity of Nanostructured Anatase Coatings Obtained by Cold Gas Spray

This article describes a photocatalytic nanostructured anatase coating deposited by cold gas spray (CGS)supported on titanium sub-oxide (TiO22x) coatings obtained by atmospheric plasma spray (APS) onto stainless steel cylinders. The photocatalytic coating was homogeneous and preserved the composition and nanostructure of the starting powder. The inner titanium sub-oxide coating favored the deposition of anatase particles in the solid state. Agglomerated nano-TiO2 particles fragmented when impacting onto the hard surface of the APS TiO22x bond coat. The rough surface provided by APS provided an ideal scenario for entrapping the nanostructured particles, which may be adhered onto the bond coat due to chemical bonding; a possible bonding mechanism is described. Photocatalytic experiments showed that CGS nano-TiO2 coating was active for photodegrading phenol and formic acid under aqueous conditions. The results were similar to the performance obtained by competitor technologies and materials such as dip-coating P25 photocatalysts. Disparity in the final performance of the photoactive materials may have been caused by differences in grain size and the crystalline composition of titanium dioxide.

A fotocatálise heterogênea e sua aplicação ambiental

This article gives some basic principles of heterogeneous photocatalysis using titanium dioxide as photocatalyst and the state of art of its applications to the abatement of aqueous and atmospheric pollutants.

Dióxido de titânio sol-gel: propriedades e comportamento eletrocrômico

Titanium dioxide was prepared by hydrolysis and polycondensation of titanium tetraisopropoxide. TiO2 films were obtained by spin coating of the precursor solution on ITO substractes (glass covered with indium doped tin oxide). Films were prepared using different temperatures and hydrochloric acid contents. The effect of the drying temperature of the films (100 or 400ºC) was also investigated. TiO2 films were characterized by cyclic voltammetry, chronoamperometry, ultraviolete-visible spectroscopy, scanning electron microscopy and X-ray diffractrometry.

Efeitos dos parâmetros operacionais na fotodegradação do azo corante direct red 23 na interface dióxido de titânio/água

The decolorization and degradation of direct red 23 azo dye have been investigated in aqueous suspension of titanium dioxide under artificial irradiation. The effects of some operational parameters such as azo dye concentration, catalyst loading, and solution pH were investigated at 30.0 ºC and optimized values were obtained. The first-order kinetic model was used to discuss the results. The UV-Vis spectra changes showed that the azo dye sample, collected after 6 h irradiation, was 98% decolorized while the residual total carbon was 97.9% degraded, indicating simultaneous photodecolorization and degradation.

Nanocompósitos semicondutores ZnO/TiO2: testes fotocatalíticos

Titanium dioxide is an efficient photocatalist, being possible to improve its efficiency with better charge separation which occurs when it is coupled with other semiconductors. Nanometric particles of ZnO were used to impregnate TiO2 P25 in order to optimize its photocatalytic properties. ZnO/TiO2 composites were obtained at different proportions and were characterized by X-ray diffraction (XRD), micro-Raman and diffuse reflectance spectroscopies, measurement of surface area (BET) and scanning electron microscopy (SEM). Raman spectroscopy data revealed a change on the TiO2 surface due the presence of ZnO which was observed by an enlargement of TiO2 peaks and a change on the relation rate between anatase and rutile phases of the composites. The photodegradation of azo-dye Drimaren red revealed better efficiency for ZnO/TiO2 3% nanocomposite and for ZnO pure.

Enhanced photocatalytic activity of TiO2 films by modification with polyethylene glycol

Titanium dioxide porous thin films on the Anatase phase were deposited onto glass slides by the sol-gel method assisted with polyethylene glycol (PEG). The dip-coated films were characterized using scanning electron microscopy (SEM), thermogravimetric analysis (TGA and DTG), UV-visible spectroscopy and X-ray diffraction (XRD). The photocatalytic activity of the films was determined by means of methyl-orange oxidation tests. The resultant PEG-modified films were crack-free and developed a porous structure after calcination at 500 °C. Photo-oxidation tests showed the dependency of catalytic activity of the films on the number of layers (thickness) and porosity, i.e. of the interfacial area.

Síntese, caracterização e atividade fotocatalítica de catalisadores nanoestruturados de TiO2 dopados com metais

Titanium dioxide nanostructured catalysts (nanotubes) doped with different metals (silver, gold, copper, palladium and zinc) were synthesized by the hydrothermal method in order to promote an increase in their photocatalytic activity under visible light. The catalysts were characterized by X-ray diffraction, diffuse reflectance spectroscopy, transmission electron microscopy and specific area and pore volume determination. The materials' photocatalytic activity was evaluated by rhodamine B decomposition in a glass batch reactor. Under UV radiation, only nanotubes doped with palladium were more active than the TiO2 P25, but the samples doped with silver, palladium and gold exhibited better results than the undoped samples under visible light.

Efeito da adição de TIO2 nas propriedades térmicas e na cristalinidade do copolímero de etileno/acetato de vinila

We investigated the effect of adding titanium dioxide nanoparticles (TiO2) to ethylene vinyl acetate (EVA) copolymer, containing 28% vinyl acetate groups, on the crystallinity and miscibility of the copolymer. Films of EVA/TiO2 containing 0.25%-1% TiO2, relative to the total weight of EVA, were prepared from their solution. The obtained films were characterized by X-ray diffraction, low-field nuclear magnetic resonance, and differential scanning calorimetry. The addition of TiO2 to the EVA copolymer was proved to cause changes in the crystallinity and mobility of the polymer chains of EVA, due to new intermolecular interactions and nanostructure organization.

INFLUÊNCIA DO TRATAMENTO TÉRMICO NO NANOCOMPÓSITO FOTOCATALISADOR ZnO/TiO2

ZnO/TiO2 nanocomposites were prepared by impregnating zinc acetate dihydrate on the surface of titanium dioxide P25, followed by thermal treatment at 350, 600, 750, and 900 °C, in order to investigate the TiO2 phase and titanate formation and the role of the latter in the photocatalytic activity of the nanocomposite. In the nanocomposites, the anatase-to-rutile transition is favored due to the presence of Zn2+, and the conversion is nearly complete at 750 °C. The presence of zinc metatitanate in the sample heated at 600 °C had no significant effect on the nanocomposite photocatalytic activity.

EVALUATION OF A BUFFERED SOLID PHASE DISPERSION PROCEDURE ADAPTED FOR PESTICIDE ANALYSES IN THE SOIL MATRIX

An evaluation of the pesticides extracted from the soil matrix was conducted using a citrate-buffered solid phase dispersion sample preparation method (QuEChERS). The identification and quantitation of pesticide compounds was performed using gas chromatography-mass spectrometry. Because of the occurrence of the matrix effect in 87% of the analyzed pesticides, the quantification was performed using matrix-matched calibration. The method's quantification limits were between 0.01 and 0.5 mg kg-1. Repeatability and intermediate precision, expressed as a relative standard deviation percentage, were less than 20%. The recoveries in general ranged between 62% and 99%, with a relative standard deviation < 20%. All the responses were linear, with a correlation coefficient (r) ≥0.99.

Surface Modification of Ceramics

Ceramics are widely used in industrial applications due to their advantageous thermal and mechanical stability. Corrosion of ceramics is a great problem resulting in significant costs. Coating is one method of reducing adversities of corrosion. There are several different thin film deposition processes available such as sol-gel, Physical and Chemical Vapour Deposition (PVD and CVD). One of the CVD processes, called Atomic Layer Deposition (ALD) stands out for its excellent controllability, accuracy and wide process capability. The most commonly mentioned disadvantage of this method is its slowness which is partly compensated by its capability of processing large areas at once. Several factors affect the ALD process. Such factors include temperature, the grade of precursors, pulse-purge times and flux of precursors as well as the substrate used. Wrongly chosen process factors may cause loss of self-limiting growth and thus, non-uniformities in the deposited film. Porous substrates require longer pulse times than flat surfaces. The goal of this thesis was to examine the effects of ALD films on surface properties of a porous ceramic material. The analyses applied were for permeability, bubble point pressure and isoelectric point. In addition, effects of the films on corrosion resistance of the substrate in aqueous environment were investigated. After being exposured to different corrosive media the ceramics and liquid samples collected were analysed both mechanically and chemically. Visual and contentual differences between the exposed and coated ceramics versus the untreated and uncoated ones were analysed by scanning electron microscope. Two ALD film materials, dialuminium trioxide and titanium dioxide were deposited on the ceramic substrate using different pulse times. The results of both film materials indicated that surface properties of the ceramic material can be modified to some extent by the ALD method. The effect of the titanium oxide film on the corrosion resistance of the ceramic samples was observed to be fairly small regardless of the pulse time.

Fotokatalyyttinen kalvonpesu

Fotokatalyysillä tarkoitetaan spontaania kemiallista reaktiota, joka tapahtuu fotokatalyytin absorboidessa valoa. Reaktio voi tapahtua joko katalyytin pinnalla tai sen läheisyydessä, mutta fotokatalyytti pysyy reaktiossa muuttumattomana. Ominaisuuksiltaan paras ja eniten tutkittu fotokatalyyttinen materiaali on titaanidioksidi, jolla on säteilytettynä kyky hajottaa orgaanisia molekyylejä hiilidioksidiksi ja vedeksi. Fotokatalyysin käyttömahdollisuuksia tutkitaan membraanikalvojen puhdistamisessa kalvojen käyttöiän ja erotustehokkuuden parantamiseksi. Nykyisin kalvojen puhdistamiseen käytetään useimmiten kemiallista pesua, jonka tuloksena on usein haitallisia yhdisteitä sisältävä liuos. Fotokatalyyttinen puhdistus voisi olla ratkaisu ongelmaan, sillä sen avulla voitaisiin puhdistamisessa käytettävien kemikaalien ja siinä muodostuvien jätteiden määrää vähentää. Tämän työn kokeellisessa osassa tutkittiin polyvinyylideenifluoridikalvon (PVDF) kestävyyttä ja puhdistumista fotokatalyyttisissä reaktioissa. PVDF:n on todettu olevan erinomainen kalvomateriaali, koska se on termisesti stabiili ja se kestää hyvin kemikaaleja, kuten orgaanisia liuottimia, happoja ja emäksiä. Työssä todettiin PVDF-kalvon puhdistuvan UV/TiO2-käsittelyn avulla. Kalvo puhdistui parhaiten, kun käytettiin 0,425 m- % TiO2-liuosta. Puhdistumista havainnoitiin sekä puhtaan veden vuon mittauksilla että värjäämällä käsiteltyjä kalvoja ja mittaamalla niiden värinintensiteetti.