Efeitos tridimensionais no escoamento em torno de cilindros confinados

Mestrado em Engenharia Química

Capacidade antioxidante de cervejas comerciais

Mestrado em Engenharia Química

Basic dyestuffs removal from textile effluents using feathers: equilibrium, kinetic and column studies

This research work has been focused in the study of gallinaceous feathers, a waste that may be valorised as sorbent, to remove the Dark Blue Astrazon 2RN (DBA) from Dystar. This study was focused on the following aspects: optimization of experimental conditions through factorial design methodology, kinetic studies into a continuous stirred tank adsorber (at pH 7 and 20ºC), equilibrium isotherms (at pH 5, 7 and 9 at 20 and 45ºC) and column studies (at 20ºC, at pH 5, 7 and 9). In order to evaluate the influence of the presence of other components in the sorption of the dyestuff, all experiments were performed both for the dyestuff in aqueous solution and in real textile effluent. The pseudo-first and pseudo-second order kinetic models were fitted to the experimental data, being the latter the best fit for the aqueous solution of dyestuff. For the real effluent both models fit the experimental results and there is no statistical difference between them. The Central Composite Design (CCD) was used to evaluate the effects of temperature (15 - 45ºC) and pH (5 - 9) over the sorption in aqueous solution. The influence of pH was more significant than temperature. The optimal conditions selected were 45ºC and pH 9. Both Langmuir and Freundlich models could fit the equilibrium data. In the concentration range studied, the highest sorbent capacity was obtained for the optimal conditions in aqueous solution, which corresponds to a maximum capacity of 47± 4 mg g-1. The Yoon-Nelson, Thomas and Yan’s models fitted well the column experimental data. The highest breakthrough time for 50% removal, 170 min, was obtained at pH 9 in aqueous solution. The presence of the dyeing agents in the real wastewater decreased the sorption of the dyestuff mostly for pH 9, which is the optimal pH. The effect of pH is less pronounced in the real effluent than in aqueous solution. This work shows that feathers can be used as sorbent in the treatment of textile wastewaters containing DBA.

Determinação da tensão interfacial do sistema Água - Tolueno - Acetona

Mestrado em Engenharia Química. Ramo de Optimização Energética na Indústria Química

Voltammetric oxidation of drugs of abuse I. Morphine and metabolites

A detailed study of the electrochemical oxidative behavior of morphine in aqueous solution is reported. Through the synthesis of several metabolites and derivatives, pseudomorphine, morphine N-oxide, normorphine, dihydromorphine and 2-(N,N-dimethylaminomethyl)morphine, and their voltammetric study it was possible to identify the oxidation peaks for morphine. The anodic waves are related with the oxidation of phenolic and tertiary amine groups. It is also possible to verify that a poorly defined peak observable during morphine oxidation is not a consequence of further oxidation of pseudomorphine but due to formation of a dimer during phenolic group oxidation. The results obtained and especially those regarding the formation of a new polymer based on a C O coupling could be useful for clarifying the discoloration phenomenon occurring during storage of morphine solutions as well as leading to a better understanding of its oxidative metabolic pathways.

Voltammetric oxidation of drugs of abuse III. Heroin and metabolites

The oxidative behavior of heroin in aqueous solution is reported. In order to identify its oxidation peaks, several metabolites, 6-monoacetylmorphine, 3-monoacetylmorphine and norheroin, were synthesized and their electrochemical behavior studied using differential pulse voltammetry. The anodic waves observed for heroin correspond to the oxidation of the tertiary amine group and its follow-up product (secondary amine), and to the oxidation of the phenolic group obtained from hydrolysis, at alkaline pHs, of the 3-acetyl group. The results enabled a new oxidative mechanism for heroin to be proposed in which a secondary amine, norheroin, and an aldehyde are obtained. The voltammetric behavior of 6-monoacetylmorphine and morphine was found to be similar demonstrating that the presence of an acetyl substituent on the 6-hydroxy group does not have a relevant influence on the peak potential of the wave resulting from oxidation of the 3-phenolic group.

DNA-based biosensor for the electrocatalytic determination of antioxidant capacity in beverages

Reactive oxygen species (ROS) are produced as a consequence of normal aerobic metabolism and are able to induce DNA oxidative damage. At the cellular level, the evaluation of the protective effect of antioxidants can be achieved by examining the integrity of the DNA nucleobases using electrochemical techniques. Herein, the use of an adenine-rich oligonucleotide (dA21) adsorbed on carbon paste electrodes for the assessment of the antioxidant capacity is proposed. The method was based on the partial damage of a DNA layer adsorbed on the electrode surface by OH• radicals generated by Fenton reaction and the subsequent electrochemical oxidation of the intact adenine bases to generate an oxidation product that was able to catalyze the oxidation of NADH. The presence of antioxidant compounds scavenged hydroxyl radicals leaving more adenines unoxidized, and thus, increasing the electrocatalytic current of NADHmeasured by differential pulse voltammetry (DPV). Using ascorbic acid (AA) as a model antioxidant species, the detection of as low as 50nMof AA in aqueous solution was possible. The protection efficiency was evaluated for several antioxidant compounds. The biosensor was applied to the determination of the total antioxidant capacity (TAC) in beverages.

Optical fiber sensor for Hg(II) based on carbon dots

An optical fiber sensor for Hg(II) in aqueous solution based on sol–gel immobilized carbon dots nanoparticles functionalized with PEG200 and N-acetyl-l-cysteine is described. This sol–gel method generated a thin (about 750 nm), homogenous and smooth (roughness of 2.7±0.7 a˚ ) filmthat immobilizes the carbon dots and allows reversible sensing of Hg(II) in aqueous solution. A fast (less than 10 s), reversible and stable (the fluorescence intensity measurements oscillate less than 1% after several calibration cycles) sensor system was obtained. The sensor allow the detection of submicron molar concentrations of Hg(II) in aqueous solution. The fluorescence intensity of the immobilized carbon dots is quenched by the presence of Hg(II) with a Stern-Volmer constant (pH = 6.8) of 5.3×105M−1.

Green production of zero-valent iron nanoparticles using tree leaf extracts

The interest in zero-valent iron nanoparticles has been increasing significantly since the development of a green production method in which extracts from natural products or wastes are used. However, this field of application is yet poorly studied and lacks knowledge that allows the full understanding of the production and application processes. The aim of the present work was to evaluate the viability of the utilization of several tree leaves to produce extracts which are capable of reducing iron(III) in aqueous solution to form nZVIs. The quality of the extracts was evaluated concerning their antioxidant capacity. The results show that: i) dried leaves produce extracts with higher antioxidant capacities than non-dried leaves, ii) the most favorable extraction conditions (temperature, contact time, and volume:mass ratio) were identified for each leaf, iii) with the aim of developing a green, but also low-cost,method waterwas chosen as solvent, iv) the extracts can be classified in three categories according to their antioxidant capacity (expressed as Fe(II) concentration): >40 mmol L−1; 20–40 mmol L−1; and 2–10 mmol L−1; with oak, pomegranate and green tea leaves producing the richest extracts, and v) TEManalysis proves that nZVIs (d=10–20 nm) can be produced using the tree leaf extracts.

Electrochemical oxidation of tamoxifen revisited

Tamoxifen is a selective estrogen receptor modulator that is used as an adjuvant and/or chemotherapeutic agent for the treatment of all stages of hormone-dependent breast cancer. Currently there is a deep interest in the study of tamoxifen biotransformation and identification of metabolites since they can significantly contribute to the overall pharmacological or adverse effects of the drug. Accordingly, the study of the electrochemical behavior of tamoxifen in aqueous solution is reported. To clarify the occurring oxidative process and to assess the influence of the functional groups on the oxidation mechanism, the voltammetric assessment was extended to the study of tamoxifen’s analogues (E)-tamoxifen and dihydrotamoxifen, and to its main phase I oxidative metabolite, N-desmethyl tamoxifen. The data found shows that the oxidative processes occurring in tamoxifen are essentially related with the two chemical moieties present in the molecule: the substituted aromatic nucleus and the tertiary amine group. Moreover, the results obtained suggest that the ethylenic linkage is not critical for tamoxifen’s oxidation although it could play an important role in the course of the oxidation process. These results could contribute to highlight some remaining questions regarding tamoxifen’s metabolic behavior and to the development of new analytical strategies, based on electrochemical approaches.

Preparação de adsorventes mesoporosos para a adsorção de poluentes em águas

Mestrado Engenharia Química. Ramo Tecnologias de Protecção Ambiental

Remediação de solos contaminados por compostos farmacêuticos

O recente surgimento de nanopartículas de ferro valente-zero (nFZV), um material com elevada capacidade de remediação de solos por via de reacções de oxidação/redução pode ser uma opção viável para a remoção de fármacos do solo. A sua aplicação já é uma realidade em alguns tipos de solos contaminados por compostos específicos e, com este trabalho, procura-se estudar a sua capacidade de remediação de solos contaminados por compostos farmacêuticos, recorrendo-se a uma tecnologia “verde” de síntese destas nanopartículas. Esta tecnologia é bastante recente, ainda não aplicada no campo de trabalho, que se baseia no uso de folhas de certas árvores para produzir extratos naturais que reduzem o ferro (III) a ferro zero valente, formando nFZV. Desta forma procedeu-se, à escala laboratorial, ao estudo da eficiência das nFZV na degradação de um fármaco – paracetamol – e comparou-se com a eficiência demonstrada por oxidantes, muito utilizados hoje em dia em casos de remediação in situ como o permanganato de potássio, o peróxido de hidrogénio, o persulfato de sódio e o reagente de Fenton. O estudo foi efectuado em dois meios diferentes: solução aquosa e solo arenoso. De forma muito sucinta, o estudo baseou-se na introdução dos oxidantes/nFZV em soluções/solos contaminados com paracetamol e consequente monitorização do processo de remediação através de cromatografia líquida de alta eficiência. Nos ensaios com soluções aquosas contaminadas com paracetamol, o permanganato de potássio e o reagente de Fenton revelaram capacidade para degradar o paracetamol, atingindo mesmo um grau de degradação de 100%. O persulfato de sódio também demonstrou uma capacidade de degradação do paracetamol, chegando a atingir 99% de degradação, mas apenas recorrendo ao uso de um volume de oxidante elevado quando comparado com os outros dois oxidantes já referidos. Por outro lado, o peróxido de hidrogénio não demonstrou qualquer capacidade de degradação do paracetamol, pelo que o seu uso não passou desta fase. Verificou-se também que o uso de ferro granulado para o tratamento de água contaminada com paracetamol revelou resultados diferentes dos observados no uso de nFZV, obtendo-se eficiências de 87%. Existiram dificuldades analíticas na quantificação do paracetamol, especificamente relacionadas com o uso do extracto de folhas de amoreira, cuja composição continha substâncias que causaram dificuldades acentuadas na análise dos cromatogramas. Por fim, um pequeno teste de combinação do reagente de Fenton com os fenómenos de biodegradação resultantes dos microrganismos presentes em folhas do extracto de chá preto demonstrou que este pode ser uma área que pode e deve ser mais estudada. Desta forma, a utilização das nFZV para o tratamento de água contaminada com paracetamol não permitiu a retirada de conclusões seguras sobre a capacidade que as nFZV produzidas com extractos de folhas de amoreira e de chá preto têm de degradação do paracetamol. Nos testes de remediação de solos contaminados os resultados demonstraram que, mais uma vez, tanto o permanganato de potássio como o reagente de Fenton se revelam como os melhores oxidantes para a degradação do paracetamol, obtendo-se a degradação total do paracetamol. Por outro lado, voltou a ser necessário uma elevada quantidade de persulfato de sódio quando comparada com os dois anteriores, para que ocorra a degradação desta mesma quantidade de paracetamol, demonstrando mais uma vez que, apesar de não ideal, o persulfato demonstra capacidade de degradação do paracetamol.

MIP-graphene-modified glassy carbon electrode for the determination of trimethoprim

A novel sensitive electrochemical sensor was developed by electropolymerization of pyrrole(PY)and molecularly imprinted polymer (MIP)which was synthesized onto a glassy carbon electrode (GCE) in aqueous solution using cyclic voltammetry in the presence of Trimethoprim (TMP) as template molecules. Furthermore,a previous electrode modification was performed by deposition of a suspension of graphene on the electrode's surface. The performance of the imprinted and non-imprinted (NIP) films was evaluated by impedance spectroscopy (EIS) and cyclic voltammetry (CV) of a ferric solution. The molecularly imprinted film exhibited a high selectivity and sensitivity toward TMP. The sensor presented a linear range, between peak current intensity and logarithm of TMP concentration between 1.0x10-6 and 1.0x10-4 M. The results were accurate (with recoveries higher than 94%), precise (with standard deviations less than 5%) and the detection limit was 1.3x10-7 M. The new sensor is selective, simple to construct and easy to operate. The MIP sensor was successfully applied to quantify TMP in urinesamples.

Imunossensores Eletroquímicos para o Diagnóstico Precoce e Descentralizado do Cancro da Mama

O cancro é uma das principais causas de morte em todo o mundo. Entre as mulheres, o cancro da mama é o mais frequente. A deteção precoce do cancro é de extrema importância na medida em que pode aumentar as possibilidades de cura dos pacientes e contribuir para a diminuição da taxa de mortalidade desta doença. Um método que tem contribuído para a deteção precoce do cancro é a análise de biomarcadores. Biomarcadores associados ao cancro da mama, como o Recetor 2 do Fator de Crescimento Epidérmico Humano (HER2) e o Antigénio Carbohidratado 15-3 (CA 15-3), podem ser detetados através de dispositivos como os biossensores. Neste trabalho foram desenvolvidos dois imunossensores eletroquímicos para a análise de HER2 e CA 15-3. Para ambos os sensores foram utilizados, como transdutores, elétrodos serigrafados de carbono. A superfície destes transdutores foi nanoestruturada com nanopartículas de ouro. Foram realizados imunoensaios não-competitivos (do tipo sandwich) em ambos os imunossensores, cuja estratégia consistiu na (i) imobilização do respetivo anticorpo de captura na superfície nanoestruturada dos elétrodos, (ii) bloqueio da superfície com caseína, (iii) incubação com uma mistura do analito (HER2 ou CA 15-3) e o respetivo anticorpo de deteção biotinilado, (iv) adição de estreptavidina conjugada com fosfatase alcalina (S-AP; a AP foi utilizada como marcador enzimático), (v) adição de uma mistura do substrato enzimático (3-indoxil fosfato) e nitrato de prata, e (vi) deteção do sinal analítico através da redissolução anódica, por voltametria de varrimento linear, da prata depositada enzimaticamente. Com as condições experimentais otimizadas, foi estabelecida a curva de calibração para a análise de HER2 em soro, entre 15 e 100 ng/mL, obtendo-se um limite de deteção de 4,4 ng/mL. Para o CA 15-3 a curva de calibração (em solução aquosa) foi estabelecida entre 15 e 250 U/mL, obtendo-se um limite de deteção de 37,5 U/mL. Tendo em conta o valor limite (cutoff value) estabelecido para o HER2 (15 ng/mL) pode-se comprovar a possível utilidade do imunossensor desenvolvido para o diagnóstico precoce e descentralizado do cancro da mama. No caso do CA 15-3 serão necessários estudos adicionais para se poder avaliar a utilidade do imunossensor para o diagnóstico do cancro da mama.