Expanding the Applicability of Raman Spectroscopy for Monitoring Photocatalytic Degradation

Compared to other types of wastewater pollutants, dangerous chemical compounds such as pharmaceuticals, pesticides, and herbicides are difficult to remove and consequently being detected (at least in part because detection limits have decreased) in drinking water at increasing concentrations. Photocatalytic degradation degrades harmful compounds to innocuous end products using energy from light. Although it is effective and cost-efficient, the underlying chemical mechanisms are not understood well enough to ensure that dangerous intermediate products are not formed during the degradation process. Raman spectroscopy can be used to analyze photocatalytic degradation reactions in real time, identifying intermediate products based on spectral features. Due to fast data acquisition, Raman studies can identify those intermediate products which are short-lived and could be missed by slower conventional methods. In the current research, colloidal gold nanoparticles were introduced to increase sensitivity via surface-enhanced Raman spectroscopy (SERS), and later modified to maintain signal intensity over a longer period of time. Additionally, an internal standard was introduced for ratiometric determination of analyte concentration. These procedural modifications serve to expand the applicability of Raman spectroscopy for in-situ reaction monitoring

A concept for nanoparticle-based photocatalytic treatment of wastewater from textile industry

Industrial wastewater, such as the effluents from textile and garment companies, may contain toxic organic pollutants, which resist conventional wastewater treatment. Their complete and environmentally friendly degradation requires innovative technologies. Photocatalysis, an advanced oxidation process, can serve this purpose. Since 1972, when the photocatalytic activity of titanium dioxide was first noticed, photocatalysis has drawn the attention of scientists and engineers but it has not yet been widely applied in industrial practice. This is mainly related to the challenges of up-scaling from laboratory experiments to large production sites. The main goal of this thesis is to develop a concept of nanoparticle-based photocatalysis for the treatment of wastewater. Ideally, process parameters should be adjustable and process conditions should be well-defined. These constraints are prerequisite for establishing process models and comparing the photocatalytic efficiency of different photocatalysts or for different pollutants. More importantly, the configuration should be scalable, in order to cover a wide spectrum of applications. In response to these requirements, this thesis introduces a new reactor concept for photocatalytic wastewater treatment, which relies on finely dispersed photocatalysts as well as uniform and defined process conditions with regard to illumination and flow. The concept was realized in a photocatalytic setup with an illuminated flow reactor. The flow channel has a rectangular cross section and meanders in a plane exposed to two dimensional illumination. Crucial process parameters, e.g., volumetric flow rate and light intensity, can be adjusted in a defined manner. This facilitates the study on the photocatalytic degradation of different organic pollutants in the presence of various photocatalytic materials under arbitrary illumination. The thesis provides a comprehensive description of the operational procedures necessary to run photocatalytic reactions in the experimental setup. It includes three main steps: i) dispersion of photocatalysts, ii) equilibration with respect to pollutant adsorption and iii) accomplishing the photocatalytic reaction. Samples are collected in a mixing tank for online or offline analysis. The proceeding decrease in the concentration of organic pollutant is used to assess the activity of the photocatalytic materials. A particular focus lies on the first of these steps, the dispersion of photocatalysts, because it is ignored in most studies. Typically, photocatalysts are in an aggregated state. The thesis demonstrates that type, intensity and energy of dispersion exert a crucial influence on size and morphology of the photocatalyst particles and, thus, on their optical properties and, accordingly, macroscopic photocatalytic behavior. Apart from this, a proper dispersion is necessary to reduce speed of gravitational solid-liquid separation, at best, to prevent catalyst sedimentation and to avoid misleading results. The photocatalytic performance was intensively investigated for the color removal of a model dye substance, methylene blue. Commercial titanium dioxide nanoparticles, widely explored in literature, were used as a photocatalyst. Their characteristics (size, morphology, stability and optical properties) were determined. Photocatalytic experiments were carried out under UV irradiation. Influences of different factors, including the concentration of the photocatalyst, the concentration of the organic compounds, light intensity, optical pathlength and pH were examined. The degradation was quantified via the decrease of methylene blue concentration. This conversion is, however, an immediate result influenced by all process parameters, e.g., the volume, the light intensity, the optical pathlength. Hence, kinetic models on macroscopic and microscopic levels are established. Normalizations with respect to process conditions are proposed. The apparent reaction kinetics are traced back to volume- and intensity-related reaction rate constants, and the reaction rate constant at the illuminated surface of the reactor. Additionally, the model is modified to be used for time-variant UV intensities, as encountered for solar photocatalysis. These achievements allow for a comparison of the experimental results from different laboratories. Moreover, they are prerequisite for the translation of laboratory results into large scale plants. Selected case studies for further applications are introduced. The photocatalytic degradation of different organic molecules (one antibiotic and two commercial dyes) with different photocatalytic materials (commercial nanomaterials and self-synthesized magnetic particles) under artificial or natural light sources was performed. Additionally, photocatalysis was studied in a realistic application. Preliminary tests with dye solutions of a textile company in Danang, Vietnam, impressively showed the feasibility of wastewater treatment by means of photocatalysis. Based on the reported capacity of wastewater in the current treatment plant of the company, the necessary process parameters were assessed. The rough estimation showed that photocatalysis can improve the working ability of the current wastewater treatment plant. In conclusion, this thesis presents a concept for wastewater treatment by slurry photocatalysis. As the process conditions are adjustable and definable, the process can be ideally performed in laboratories for research purposes, where different materials need to be tested and the working volume can be lower than hundreds of milliliters. The photocatalytic configuration is expected to work with a capacity of hundreds of liters, although appropriate experimental evidences are reserved for further up-scaling studies

Příprava a charakterizace fotokatalyticky aktivního oxidu titaničitého

Import 19/10/2011The bachelor thesis is focused on the preparation and characterization of photocatalytically active titanium dioxide. Nanostructured titanium dioxide is outstanding photocatalyst finding a variety of applications from the water treatment to its utilization in energetic. This bachelor thesis focuses on the preparation of the titanium dioxide using the sol-gel method. Titanium tetraisopropoxide was used as a titanium precursor. The samples were prepared in the form of powder as well as in the form of thin layers deposited on the glass substrate. The prepared samples were characterized using methods of chemical and phase analysis, the morphology of the samples was studied using microscopy techniques. The prepared samples were examined for evaluation of their photodegradation activity.Bakalářská práce se zabývá přípravou a charakterizací fotoaktivního oxidu titaničitého. Nanostrukturovaný oxid titaničitý je významným fotokatalyzátorem využívaným v mnoha odvětvích od čištění vody až po jeho využití v energetickém průmyslu. Tato bakalářská práce se zabývá přípravou oxidu titaničitého metodou sol-gel. Jako prekurzor titanu byl použit isopropylalkoholát titaničitý, vzorky oxidu titaničitého byly připraveny ve formě prášku a ve formě tenkých vrstev nanesených metodou dip-coating na skleněných substrátech. Připravené vzorky byly charakterizovány vybranými metodami chemické a fázové analýzy, morfologie vzorků byla studována pomocí mikroskopických technik. U připravených materiálů byla testována jejich fotodegradační aktivita.9360 - Centrum nanotechnologiívýborn

Aprimoramento da fotodegradação de corantes com nanopartículas de SrTiO3 modificadas

Nowadays, thousands of tons of dyes are produced worldwide annually by the industry, and almost one-third of these substances is thrown into effluents. Methylene blue is a widely used dye. Thus, there is a strong need to efficiently remove this pollutant from the aquatic environment. Also, the degradation of this molecule can be used as a model system to understand the degradation of even more complex and toxic molecules. An interesting idea is the use of the Sun’s energy which arrives at Earth’s surface to induce the photodegradation of methylene blue by using photocatalysts. This work aims to propose alternatives for the improvement of the photodegradation of methylene blue and to elucidate the atomic mechanisms existing in these reactions. For that, two different systems based on the modification of commercial SrTiO3 nanoparticles were used. In the first part of the work, SrTiO3 and Ni nanoparticles (synthesized from NiCl2.6H2O precursor) were characterized by X-Ray Diffraction (XRD), Small-Angle X-Ray Scattering (SAXS) and Transmission Electron Microscopy (TEM), obtaining a mean size of 35 nm (SrTiO3), and 3 nm (Ni). Then the Ni nanoparticles were exposed to a thermal treatment in ambient atmosphere at 100 ºC, 300 ºC and 500 ºC. In situ time-resolved X-Ray Absorption Near-Edge Structure (XANES) and in situ Extended X-Ray Absorption Fine Structure (EXAFS) techniques were measured at the Ni K edge during the heating treatments. The analysis shows that the thermal treatment allows tuning the chemical components of Ni nanoparticles (Ni0 and NiO amount). Afterward, 5 wt.% of the Ni nanoparticles were supported on SrTiO3 nanoparticles and used in the photodegradation reaction of methylene blue. Samples heated at 300 ºC and 500 ºC showed an improved activity compared to the sample without thermal treatment. X-Ray Photoelectron Spectroscopy (XPS) measurements at the Ni 2p3/2 region show the major component at the surface is Ni(OH)2 for samples heated up to 300 ºC but NiO appears as the main chemical component for the sample heated at 500 ºC. The XPS measurements at the Ti 2p3/2, Sr 3d and O 1s electronic regions enabled detecting new surface components after the reaction, which are indicative of surface reconstruction of SrTiO3 into TiOx and SrOx terminated surfaces. Density Functional Theory (DFT) results also indicate that the inclusion of Ni induces a change on the electronic density at the p orbitals of Sr and O, which is in agreement with the XPS results. The reason for the improvement in the photodegradation due to the inclusion of Ni nanoparticles treated at 300 ºC is related to the optimization of the metallic Ni amount. Nonetheless, the Ni nanoparticles treated at 500 ºC present a high amount of NiO, possibly forming a NiO/SrTiO3 heterostructure that prevents the electron-hole pair recombination. In the second part of the work, the SrTiO3 nanoparticles were submitted to different fluences of Au7+ ion irradiation in order to create atomic vacancies. The irradiation was carried out in three different fluences: 1 × 1013 ions/cm2 , 5 × 1013 ions/cm2 and 1 × 1014 ions/cm2 . All three samples show improved efficiency on the degradation of methylene blue, even if compared to the best Ni/SrTiO3 system. XRD and UV-Vis measurements show that the SrTiO3 nanoparticles do not suffer noticeable structural and electronic changes upon irradiation and before the photoreaction. XPS measurements at the Sr 3d and Ti 2p3/2 electronic regions were able to detect new surface components after the photoreaction, which may appear due to the vacancy diffusion to the surface region. The improvement in the photodegradation results is related to these extra adsorption sites at the surface.Anualmente, milhares de toneladas de corantes são produzidas pela indústria e aproximadamente um terço dessas substâncias são descartadas nos efluentes. O azul de metileno é um corante amplamente utilizado e, portanto, há uma grande necessidade de removê-lo do meio aquático. Além disso, o estudo da degradação dessa molécula serve como um sistema modelo para entender a degradação de moléculas tóxicas mais complexas. Uma ideia interessante consiste em utilizar a energia solar irradiada sobre a supefície terreste para induzir a degração do azul de metileno por meio de fotocatalisadores. Este trabalho tem como objetivo propor alternativas para o aperfeiçoamento da fotodegradação do azul de metileno e elucidar os mecanismos atômicos da reação. Para isso, foram empregados dois sistemas distintos baseados na modificação de nanopartículas de SrTiO3 comercial. Na primeira parte do projeto, nanopartículas de SrTiO3 e Ni (sintetizadas a partir de um precursor de NiCl2.6H2O) foram caracterizadas por Difração de Raios X (XRD), Espalhamento de Raios X a Baixos Ângulos (SAXS) e Microscopia Eletrônica de Transmissão (TEM), que permitiram obter tamanhos de aproximadamente 35 nm (SrTiO3) e 3 nm (Ni). As nanopartículas de Ni foram expostas a um tratamento térmico em atmosfera ambiente a 100 ºC, 300 ºC e 500 ºC. Medidas de Estrutura de Absorção de Raios X Próxima à Borda (XANES) in situ resolvida no tempo e de Estrutura Fina Estendida de Absorção de Raios X (EXAFS) in situ foram realizadas na borda K do Ni durante o tratamento térmico. A análise mostra que o tratamento térmico permite regular as componentes químicas das nanopartículas de Ni0 para NiO. Posteriormente, 5 % em massa de Ni foi suportado sobre o SrTiO3 e utilizado na reação de fotodegradação do azul de metileno. As amostras aquecidas a 300 ºC e 500 ºC apresentaram uma melhora na atividade comparadas com a amostra sem tratamento térmico. Medidas de Espectroscopia de Fotoelétrons Excitados por Raios X (XPS) na região do Ni 2p3/2 exibiram uma fase majoritária de Ni(OH)2 para as amostras tratadas até 300 ºC, enquanto que na amostra tratada a 500 ºC a fase majoritária é de NiO. As medidas de XPS nas regiões O 1s, Ti 2p3/2 e Sr 3d permitiram a detecção de novas componentes depois da reação que indicam uma reconstrução da superfície de SrTiO3 em TiO2−x e SrOx. Cálculos da Teoria do Funcional da Densidade (DFT) indicam que a inclusão de Ni na superfície do SrTiO3 modificam a densidade de cargas nos orbitais p do O e Sr, e essa mudança pode estar relacionada com uma componente identificada no XPS. A razão do aumento da eficiência de fotodegradação para as nanopartículas de Ni tratadas a 300 ºC está relacionada a otimização da fração de Ni metálico, enquanto que para as nanopartículas de Ni tratadas a 500 ºC está relacionada possivelmente à formação de uma heterojunção NiO/SrTiO3. Na segunda parte do trabalho, as nanopartículas de SrTiO3 foram submetidas a diferentes fluências de íons Au7+, 1 × 1013 ions/cm2 , 5 × 1013 ions/cm2 e 1 × 1014 íons/cm2 , a fim de gerar vacâncias de O. As três amostras apresentaram um aumento na eficiência da degradação do azul de metileno, até mesmo se comparadas à melhor amostra de Ni/SrTiO3. Medidas de XRD e espectroscopia UV-Visível permitiram observar que a estrutura do SrTiO3 não sofre nenhuma mudança estrutural ou eletrônica aparente após a irradiação e antes da fotorreação. No entanto, medidas de XPS nas regiões eletrônicas do Sr 3d e Ti 2p3/2 detectaram novas componentes na superfície após a reação, provavelmente devido à difusão de vacâncias para a superfície do SrTiO3. O aumento da eficiência da fotodegradação, nesse caso, está relacionado ao aumento dos sítios na superfície do SrTiO3 que permitem a adsorção das moléculas na solução

Photocatalytic Degradation of Hazardous Safranin (O) Dye by Using Self Synthesized TIO2 Nanoparticles

The textile industries generates extremely high amount of colour waste water, which are mainly poisons. A traditional biological treatment process is not helpful in treating the dye effluent because of low biodegradability of dyes. The presence of safranin (O) dye causes distinct acute impact on health therefore the removal of this dye from aqueous solution is highly desirable. The aim of this study was to assess the efficiency of photo-degradation of safanin (O) dye with application of nanoparticles of TiO2 as a photocatalyst. For this purpose nanoparticles of TiO2 were synthesized by a very simple sol-gel method with absence of additives and hydrolysing agents. The synthesized nanoparticles of TiO2 were characterized by FTIR, XRD, SEM, BET and UV-vis spectroscopy. It was found that change in polymorphic phase occurs as temperature changes from 600 to 800 0C and also the crystallinity of TiO2 increases with annealing temperature. The application of prepared TiO2 nanoparticles for photocatalytic degradation of safranin (O) dye from aqueous solution was explored. It was determined that anatase phase TiO2 shown highest photo-degradability of safranin (O) dye. The blank tests investigated for light irradiated to safranin (O) dye solution without TiO2 catalyst and for the suspension carrying TiO2 and safranin (O) dye in the dark that revealed both the photocatalyst and light energy were required for the photo-degradation of safranin (O) dye. The effect of several factors such as catalyst dose, initial concentration, pH of solution and temperature, was studied on the photocatalytic degradation of safranin (O) dye and optimized it. Results indicated that photo-degradation of safranin (O) dye increases at higher alkaline pH. The photo-degradation rate was strongly influenced by activation of TiO2 photocatalyst with photon and production of hydroxyl radicals’ hence suggested optimum catalyst dose and initial concentration of dye for photo-degradation process

Nanotechnology in Industrial Wastewater Treatment

Nanotechnology in Industrial Wastewater Treatment is a state of the art reference book. The book is particularly useful for wastewater technology development laboratories and organizations. All professional and academic areas connected with environmental engineering, nanotechnology based wastewater treatment and related product design are incorporated and provide an essential resource. The book describes the application and synthesis of Ca-based and magnetic nano-materials and their potential application for removal/treatment of heavy metals from wastewater

Photocatalysis for Reductive Transformation of Nitrate and Chromate in Drinking Water

abstract: Contamination of drinking water supplies from oxo-anion pollutants necessitates treatment prior to potable use. This dissertation aims to inform and improve light delivery (emission spectra, radiant intensity, reactor configuration) in order to enhance the photocatalytic reduction of hexavalent chromium (Cr(VI)) and nitrate, two common oxo-anions in drinking water, and photocatalytic oxidation of two model organic pollutants (methylene blue, (MB) and para-chlorobenzoic acid (pCBA)). By varying the photon fluence dose, two metrics (contaminant quantum yield (Φ), and electrical energy per order (EEO)) were used to assess photocatalytic reactor performance. A detailed literature review and experimental results demonstrated how different irradiance sources with variable intensity and emission spectra synergistically enhanced contaminant removal by a coupled photolytic/photocatalytic reaction mechanism. Cr(VI) was photocatalytically reduced on TiO2 and formed Cr(OH)3(s) in a large-scale slurry reactor, but Cr(III) was then photolyzed and reformed Cr(VI). UV light also led to photo-aggregation of TiO2 which improved its recovery by the ceramic membrane within the reactor. For nitrate reduction, light source emission spectra and fluence dose delineate the preferred pathways as intermediates were reduced via wavelength-dependent mechanisms. HONO was identified as a key nitrate reduction intermediate, which was reduced photocatalytically (UV wavelengths) and/or readily photolyzed at 365nm, to yield nitrogen gases. Photocatalytic nitrate reduction efficiency was higher for discrete wavelength irradiation than polychromatic irradiation. Light delivery through aqueous media to the catalyst surface limits efficiency of slurry-based photocatalysts because absorption and scattering of light in nanomaterial slurries decreases effective photon transmittance and minimizes photolytic reactions. The use of optical fibers coupled to light emitting diodes (OF-LED) with immobilized catalyst demonstrated higher performance compared to slurry systems. OF-LED increased Φ for MB degradation by increasing direct photon delivery to the photocatalyst. Design of OF-LED reactors using bundled optical fibers demonstrated photocatalytic pCBA removal with high Φ and reduced EEO due to increased surface area and catalytic sites compared to single OF/LED couples. This work advances light delivery as well as the suspension and attachment of nanoparticles in photocatalytic water treatment for selective transformation of oxo-anions and organic compounds to innocuous species.Dissertation/ThesisDoctoral Dissertation Civil, Environmental and Sustainable Engineering 201

Nanoporous carbons from sisal residues and their application in hybrid TiO2/carbon photocatalysts for the removal and degradation of phenol in solution

Tese de doutoramento, Química (Química Tecnológica), Universidade de Lisboa, Faculdade de Ciências, 2016The main aim of this PhD thesis was the development of nanoporous adsorbents and catalysts using industrial by-products of low commercial value as precursors and to investigate their application in advanced remediation technologies for the removal and/or degradation of aromatic pollutants in aqueous solution. The first stage of this study consisted on investigating the valorization of rope industry´s wastes through the analysis of their pyrolytic behaviour. The thermal characterization of the residues confirmed that although most decomposition occurs at 400 ◦C, some pyrolytic reactions take place above 550 ◦C. The yields of the different fractions were 22 wt. % of a carbonaceous residue (char), 50 wt. % tars and a gas fraction at 800 ◦C. From the analysis of the different fractions, it was possible to conclude that the produced oil was rich in hydrocarbons and alcohols, while the gas fraction is mainly composed of CO2, CO and CH4, and the carbonaceous solid residue displayed somewhat porous features, with a more developed porous structure as the pyrolysis temperature increased. Further on, the synthesis of copper-doped activated carbons from sisal residues was explored, using a wet impregnation and low temperature calcination procedure. The incorporation of copper was also performed in a bituminous coal for comparison purposes. The role of copper on the physicochemical and structural features of the materials has shown to be strongly dependent on the nature of the carbon matrix. The dual role of copper on the reactivity of the carbons was observed; on one hand, favouring the development of microporosity in the case of the coal-derived activated carbon, due to the catalysed air gasification of the material at a very low temperature (i.e., 325 °C); on the other hand, the immobilization of copper on the sisal-derived carbon, acted as a combustion retardant during the calcination step, protecting the carbon matrix. In both cases, a homogenous distribution of copper within the carbon matrix, and a good preservation of large textural properties were observed. The incorporation of copper on the carbon material was also carried out through a different approach, via impregnation of the carbon precursor followed by activation. This allowed to obtain carbon materials displaying a well-developed nanoporous texture (although comparatively with a marked inhibition of the textural development), and a homogeneous dispersion of copper particles, predominantly as Cu(II) species. These materials were used in the photocatalytic degradation of phenol from solution under visible light, as hybrid titania/Cu-carbon composites. The photo-oxidation tests showed the outstanding role of copper under visible light, in terms of increased phenol conversion, mineralization degree and degradation rate. Similar overall conversions were obtained with half of the amount of the photoactive semiconductor (1:1 composites). The beneficial effect of copper loading was also observed in the marked regioselectivity of the intermediates, towards the preferential formation of catechol. Furthermore, the copper-loaded photocatalyst was found to be stable upon long irradiation exposure. The nanoporous carbons prepared from the activation of sisal wastes were also used as additives to TiO2 powders. The incorporation of the carbon material in the formulation of the photocatalyst (TiO2/carbon) proved to increase the photocatalytic performance of TiO2 regardless the studied illumination conditions, although the effect was more pronounced at λ > 200 nm. The photocatalytic runs performed using the carbon alone as catalyst confirmed a certain level of self photoactivity under different irradiation conditions (λ > 200 nm or λ > 360 nm). An evident deactivation of the carbon photocatalyst was observed after 60 min of irradiation, most likely due to the consumption of the photoactive sites. As for the photo-oxidation mechanism for the carbon component, a marked regioselectivity towards the ortho-substitution was also observed at high energy photons, confirming the strong effect of both the composition of the catalyst and the illumination conditions on the nature of the degradation intermediates of phenol.O principal objetivo do trabalho que se apresenta nesta tese de doutoramento foi o desenvolvimento de adsorventes e catalisadores nanoporosos usando como precursores subprodutos industriais de baixo valor comercial e avaliar o seu desempenho em tecnologias avançadas para a remediação (remoção e/ou degradação) de poluentes aromáticos em solução aquosa. A primeira etapa do estudo consistiu em investigar a valorização de resíduos de sisal provenientes da indústria de cordoaria. O sisal (Agave sisalana) é uma das fibras naturais de origem lenhinocelulósica mais utilizadas em todo o mundo, devido às suas excelentes características relacionadas com o baixo custo e densidade, boas propriedades mecânicas e ausência de toxicidade. O processo de manufatura de cordas gera uma quantidade elevada de desperdícios, que são claramente subaproveitados, sendo utilizados apenas na produção de cordas de qualidade inferior ou como combustível. Dado o interesse crescente em explorar novas aplicações para estes resíduos, a análise feita neste trabalho relativamente ao seu comportamento pirolítico, permitiu avaliar a potencialidade das fibras de sisal para outras aplicações que não as tradicionais. A caracterização térmica destes desperdícios confirmou que embora a reação de pirólise se inicie a 250 ºC, ocorrendo a maioria da decomposição até 400 ◦C, algumas reações pirolíticas ocorrem acima de 550 ◦C. Os rendimentos obtidos para as diferentes frações foram de 22 % de um resíduo carbonáceo (carbonizado), 50 % de alcatrão e uma fração gasosa a 800 ◦C. A partir da análise das diferentes frações, foi possível concluir que o óleo produzido é rico em hidrocarbonetos e álcoois, enquanto que a fração gasosa é composta maioritariamente por CO2, CO e CH4.e O resíduo sólido exibe alguma porosidade, observando-se um maior desenvolvimento da estrutura porosa com o aumento da temperatura de pirólise. Seguidamente foi explorada a modificação da química superficial de dois carvões ativados resultantes de ativação física dos precursores, resíduos de sisal e carvão betuminoso, com dióxido de carbono e vapor de água, respetivamente. Os carvões foram dopados com cobre através de um processo de impregnação em solução e subsequente calcinação feita a uma temperatura baixa. A influência do cobre sobre as características físico-químicas e estruturais dos materiais mostrou ser altamente dependente da natureza da matriz de carbono. Verificou-se que a influência do cobre na modificação da estrutura depende da reatividade dos carvões, tendo-se constatado que no caso do carvão betuminoso o cobre favorece o desenvolvimento da microporosidade, catalisando a reação de gaseificação do material a uma temperatura muito baixa (325 ° C); enquanto que a imobilização de cobre no carvão derivado de sisal, atuou como um retardante de combustão durante o passo de calcinação, protegendo a matriz de carbono. Em ambos os casos, foi observada uma distribuição homogénea de cobre no interior da matriz de carbono, e uma boa preservação das propriedades texturais. A incorporação de cobre na matriz carbonácea foi também realizada através de uma abordagem diferente, por meio de impregnação do precursor, seguida de ativação. Para tal, impregnaram-se pedaços de sisal primeiro com uma solução de Cu(NO3)2.3H2O (de modo a obter uma concentração de Cu final de 5%) e seguidamente com uma solução de K2CO3, de acordo com a proporção sisal: K2CO3 de 2:1. Os materiais preparados apresentaram uma textura nanoporosa bem desenvolvida, embora para o carvão dopado com cobre se observe uma marcada inibição do desenvolvimento estrutural, comparativamente com o carvão nãodopado. Através da aplicação de diversas técnicas, como espectroscopia fotoeletrónica de raios X, difração de raios X e redução a temperatura programada, foi possível concluir que as partículas de cobre apresentam uma dispersão homogénea na matriz de carbono, e são predominantemente espécies de Cu(II). Estes materiais foram utilizados no processo de fotocatálise heterogénea, uma das tecnologias mais promissoras para a degradação e mineralização de compostos orgânicos recalcitrantes, em meio aquoso. Este processo, que tem sido amplamente estudado na área ambiental, integra os denominados Processos de Oxidação Avançados (POAs), que se baseiam na formação de espécies altamente reativas, como por exemplo, os radicais hidroxilo (•OH), que vão atacar as moléculas orgânicas através de reações sucessivas, até à obtenção de dióxido de carbono e água como produtos finais. Estudou-se a degradação fotocatalítica de fenol, o qual foi escolhido como molécula modelo, uma vez que é frequentemente detetado em águas residuais, nomeadamente em águas provenientes de diversas indústrias. Dada a sua persistência, baixa biodegradabilidade e toxicidade, alguns compostos fenólicos são considerados poluentes prioritários pelas agências ambientais. Inicialmente ensaiou-se a degradação de fenol em solução sob irradiação com luz visível, usando como catalisadorTiO2, o semicondutor mais investigado em processos fotocatalíticos e misturas de dióxido de titânio com carvão dopado com cobre, e com carvão não-dopado. Dada a elevada porosidade apresentada pelos carvões ativados, todos os ensaios fotocatalíticos foram precedidos por uma etapa de pré-adsorção de fenol, de modo a eliminar a contribuição do processo de adsorção na reação de fotocatálise. Os testes de fotooxidação demonstraram o papel fundamental do cobre para, sob irradiação com luz visível, promover o aumento da conversão de fenol, do grau de mineralização Os resultados obtidos mostraram os compósitos 1:1 (i.e. onde se tem apenas metade da quantidade do semicondutor fotoativo da utilizada ao ensaiar apenas o semicondutor) permitem alcançar conversões globais semelhantes. O resultado mais elevado para a mineralização de fenol após 6 h de irradiação foi obtido para o fotocatalisador híbrido TiO2/Cucarvão (cerca de 42 %), quase o dobro da mineralização obtida para o compósito TiO2/carvão não-modificado. O efeito benéfico da presença de cobre foi também observado na regiosselectividade acentuada dos compostos aromáticos intermediários, com a formação preferencial de catecol, considerada um percurso reacional preferencial de oxidação de fenol, em relação à formação de quinonas, uma vez que se gera um menor número de intermediários, sendo assim mais efetiva para alcançar a mineralização completa (conversão em CO2 e H2O). Além disso, o fotocatalisador com cobre mostrou ser estável após um tempo relativamente longo de exposição à irradiação, sem ocorrência de lixiviação ou fotorredução das espécies de cobre. A interpretação dos resultados considerou que as espécies de cobre dispersas na matriz de carbono poderão criar um meio de transferência eletrónica rápida, minimizando a recombinação dos pares eletrão/lacuna criados com a iluminação do semicondutor e também sítios hidrofóbicos, nos quais o oxigénio molecular dissolvido é facilmente adsorvido, o que favorecerá a formação de espécies radicais de oxigénio. Os carvões nanoporosos preparados a partir da ativação dos resíduos de sisal foram também utilizados como aditivos ao TiO2. A incorporação do material de carbono na formulação do fotocatalisador (TiO2/carvão) provou aumentar o desempenho fotocatalítico do TiO2 na degradação e mineralização de fenol, independentemente das condições de iluminação estudadas. Contudo o um efeito é mais pronunciado para λ > 200 nm, dada a presença de fotões mais energéticos e de um fluxo fotónico mais elevado, o qual foi medido por actinometria química. Para estas condições de irradiação a mineralização de fenol com o catalisador TiO2/carvão é 1.5 vezes superior ao que obteve usando apenas TiO2, sendo de salientar que no caso da mistura, a quantidade de TiO2 é apenas metade utilizada para o ensaio com apenas o semicondutor. Os testes fotocatalíticos realizados utilizando como catalisador apenas o carvão confirmaram um certo nível de fotoatividade sob diferentes condições de irradiação (λ > 200 nm ou λ > 360 nm). No entanto, quando a luz é filtrada a λ > 360 nm, após 60 minutos de irradiação é observada uma clara desativação do fotocatalisador, provavelmente devida ao consumo dos locais fotoativos. Quanto ao mecanismo de fotooxidação para o componente de carbono, no caso de fotões de elevada energia foi também observada uma regiosseletividade marcada relativamente à substituição na posição orto, o que confirma a forte influência da composição do catalisador e das condições de iluminação sobre a natureza dos intermediários de degradação de fenol

Functional Photocatalytic Surfaces for Selective Adsorption and Detection of Organic Pollutants

The dissertation focuses on using unique surface wettability properties to remove oil contamination from water. Three main ideas are explored. In Publication 1, a two-step photocatalytic reduction process creates hierarchical Au nanostructures on a TiO2 film, resulting in a stable surface with superhydrophobic properties. This surface is useful for self-cleaning and anti-icing technologies, as well as applications in cell growth and fluid microchips. Publication 2 introduces a "3-in-1" concept, combining a photocatalytic thin film, micro/nanostructuring, and a low surface energy coating. The resulting surface exhibits superhydrophobicity and photocatalytic activity, suitable for oil-water separation, self-cleaning, and water harvesting. The p-V3D3 coating's stability under UV irradiation and atomic oxygen exposure is advantageous. Publication 3 presents a 4N-in-1 hybrid substrate (AgTiO2) for enhanced Raman spectroscopy. This hybrid substrate achieves significant enhancement, high detection sensitivity, superior photocatalytic degradation performance, and long-term reusability.In summary, this dissertation explores the development of surfaces with unique wettability properties for oil-water separation, self-cleaning, water harvesting, and ultrasensitive Raman spectroscopy. The fabricated surfaces demonstrate improved hydrophilicity, superhydrophobicity, and photocatalytic activity, leading to enhanced performance in various applications

Photocatalytic Water and Wastewater Treatment

This book aims to provide an overview of how photocatalysis can be employed in water and wastewater treatment. Each chapter will attend to a different area of interest, starting with an introduction on the fundamentals of photocatalysis. The covered topics include metal organic frameworks (MOFs), photocatalytic reactor types and configurations, landfill leachate treatment, and life cycle assessment (LCA) of solar photocatalytic wastewater treatment. In addition, the final two chapters provide fresh new insight, by analyzing international patents on photocatalytic materials, solar photocatalysis, and nanotechnology