Avaliação da potencialidade eletroanalítica de biochar, obtido em diferentes temperaturas, em eletrodos modificados para determinação de espécies de interesse

Orientadora : Prof. Dr. Márcio F. BergaminiDissertação (mestrado) - Universidade Federal do Paraná, Setor de Ciências Exatas, Programa de Pós-Graduação em Química. Defesa: Curitiba, 06/03/2015Inclui referências : f. 125-140Resumo: No presente trabalho foram preparadas amostras de biochar a partir de farelo de mamona utilizando diferentes temperaturas de pirólise (200-600ºC). Diversas técnicas foram empregadas para uma geral caracterização do material produzido, sendo estas: termogravimetria (TG), calorimetria exploratória diferencial (DSC), espectroscopia na região do infravermelho por Transformada de Fourier (FTIR), análise elementar (CHNS-O), microscopia eletrônica de varredura (MEV), estimativa de área por B.E.T. e titulações pelo método de Boehm. Depois de caracterizado, o biochar foi empregado como agente modificador na preparação de eletrodos de pasta de carbono modificados (EPCM), os quais foram avaliados para a préconcentração de espécies inorgânicas (íons Pb2+, Cd2+ e Cu2+) e uma espécie orgânica (paraquat). O desempenho voltamétrico dos eletrodos propostos foi avaliado adotando um procedimento de redissolução, em soluções separadas para as etapas de pré-concentração e medida. Todos os estudos foram realizados com a etapa de pré-concentração conduzida em condições de potencial de circuito aberto. A caracterização geral do material mostrou uma alteração significativa das propriedades físicas e químicas de acordo com a temperatura de pirólise utilizada, como a redução de grupos químicos superficiais e aumento da área com o aumento da temperatura de pirólise. O EPCM foi eficiente na pré-concentração dos íons inorgânicos avaliados seguindo a afinidade Pb2+>Cd2+>Cu2+. As melhores respostas voltamétricas foram verificadas para o EPCM preparado com biochar pirolisado em 400 ºC (BC400). Medidas de voltametria de varredura linear permitiram estimar a capacidade de adsorção do biochar para os íons, sendo obtidos os valores de: 15,9 ?g g-1 para Pb2+, 4,29 ?g g-1 para Cd2+ e 2,38 ?g g-1 para Cu2+. O EPCM-BC400 apresentou o melhor desempenho na pré-concentração de paraquat, o que permitiu o desenvolvimento de um método eletroanalítico para a determinação desse analito. Depois de otimizadas as condições experimentais, o procedimento apresentou uma reposta linear para concentrações entre 3,0 x 10-8 e 1,0 x 10-6 mol L-1, com um limite de detecção de 7,6 x 10-9 mol L-1 e um limite de quantificação de 2,5 x 10-8 mol L-1. A influência de espécies concomitantes sobre a resposta voltamétrica foi também avaliada. O método proposto foi aplicado na determinação de paraquat em amostras fortificadas de água potável e de água coco. Valores de recuperação entre 95,8 % e 97,5 % foram encontrados. O teste t-Sudent mostrou boa concordância entre os valores adicionados e recuperados, com 95 % de confiança.Abtract: In the present work biochar samples were prepared from castor cake using different temperature of pyrolysis (200-600ºC). Several techniques were employed to a general characterization of the produced material, such as: thermogravimetry analysis (TGA), differential scanning calorimetry (DSC), Fourier transform infrared (FTIR), elemental analysis (CHNS-O), scanning electron microscopy (SEM), area estimation by B.E.T. method and titrations by Boehm method. After that, biochar was used as modifier agent in the preparation of modified carbon paste electrodes (MCPE) which were evaluated in pre-concentration of organic (paraquat) and inorganic species (Pb2+, Cu2+ and Cd2+ ions). Voltammetric performance of the proposed electrodes has been evaluated adopting a stripping procedure using separate solutions for pre-concentration and measurement steps. Preconcentration step was performed under open conditions potential for all realized studies. The general characterization of the material revealed a significant change in the physical and chemical properties according to the used pyrolysis temperature, eg: decrease of superficial chemical groups and increase of area with increase of pyrolysis temperature. The best voltammetric responses were observed for MCPE prepared using biochar pyrolyzed at 400 ºC (BC400). Linear sweep voltammetry studies allowed an estimation of the biochar adsorption capacity for the ions studied: 15,9 ?g g-1 for Pb2+, 4,29 ?g g-1 for Cd2+ and 2,38 ?g g-1 for Cu2+. The CPME-BC400 has presented the best performance in the preconcentration of paraquat and it was used for development of an electroanalytical method for the determination of this analyte. After optimization of experimental conditions, the procedure showed a linear dynamic range for concentration from 3,0 x 10-8 to 1,0 x 10-6 mol L-1, limit of detection of 7,6 x 10-9 mol L-1 and limit of quantification of 2,5 x 10-8 mol L-1. The influence of concomitant species on the voltammetric response was also evaluated. The t- Student test demonstrated a good concordance between values added and recovered, at 95 % interval confidence

Biochar quimicamente ativado : obtenção, caracterização e aplicação no desenvolvimento de sensores eletroquímicos

Orientador: Prof. Dr. Márcio Fernando BergaminiCoorientador: Prof. Dr. Luiz Humberto Marcolino JuniorTese (doutorado) - Universidade Federal do Paraná, Setor de Ciências Exatas, Programa de Pós-Graduação em Química. Defesa : Curitiba, 29/03/2019Inclui referências: p. 191-211Área de concentração: Química AnalíticaResumo: O biochar é um material carbonáceo obtido pela pirólise de biomassa, e altamente funcionalizado, o que permite sua utilização na sorção ou imobilização de espécies. Com isso, o uso de eletrodos modificados com biochar se torna atrativo na pré-concentração espontânea e determinação voltamétrica de analitos. A quantidade de grupos funcionais do biochar pode ser aumenta por tratamentos químicos superficiais, o que melhora as suas propriedades sortivas. Neste trabalho, o biochar foi obtido a partir de resíduos de farelo de mamona, e foi submetido a diferentes condições de ativação química empregando HNO3 e/ou H2O2. As diferentes amostras foram caracterizadas e avaliadas na determinação de espécies inorgânicas e orgânicas. A amostra N2, tratada com HNO3 50 % (v/v), a 60 ºC por 3 horas, apresentou a melhor resposta, e foi utilizada na construção de EPCM para diferentes metodologias. Primeiramente, foi avaliada a capacidade do EPCM-N2 em pré-concentrar e determinar íons Ni(II), monitorando o par redox Ni(II)/Ni(III) em meio básico. A utilização do eletrodo proposto permitiu a determinação de íons Ni(II) em amostras fortificadas de bioetanol e água residuária. Em seguida, foi avaliada a capacidade de pré-concentração e determinação de ácido cafeico. O EPCM-N2 se mostrou eficiente na préconcentração espontânea da espécie orgânica. O método foi aplicado para a determinação em amostras reais e fortificadas de diferentes tipos de vinho, e apresentou resultados satisfatórios e concordantes ao método espectroscópico, por Folin-Ciocalteu. Outra estratégia avaliada foi a capacidade do biochar em imobilizar NiOOH (EPCM-N2-Ni) na determinação não-enzimática de glicose, reação catalisada pela presença de NiOOH. O eletrodo foi empregado na determinação de glicose em amostras reais e fortificadas de fluídos biológicos em um sistema microfluídico baseado em fios têxteis (?TED), o que permitiu a diminuição de reagentes e resíduos, tornando este um método analítico verde, conforme comprovado por cálculos de Eco-Escala. O EPCM-N2 também foi avaliado para a incorporação simultânea de um mediador redox (azul da Prússia) e enzima glicose oxidase na determinação enzimática de glicose. O biossensor apresentou boa afinidade enzima-substrato e estabilidade após dias sucessivos de medida, e foi aplicado com eficiência na determinação de glicose em amostras de fluídos biológicos. Por fim, o EPCM-N2, em conjunto com outros eletrodos, foi aplicado em uma língua eletrônica voltamétrica, visando a distinção e determinação de catecol, 4-etilcatecol e 4-etilguaiacol. A estratégia permitiu a discriminação e determinação das espécies, empregando ferramentas quimiométricas, PCA e redes neurais. Desta maneira, em virtude da capacidade de interação do biochar, melhorada pela sua ativação química, foi possível a aplicação em diferentes sensores eletroquímicos, com resultados satisfatórios em relação ao eletrodo sem modificação e modificado com biochar precursor (não tratado). Isso demonstra a versatilidade e a viabilidade do uso deste material como modificador para sensores, o que também é interessante do ponto de vista econômico e ecológico. Palavras-chave: biochar ativado, sensores eletroquímicos, níquel, compostos fenólicos, glicose, dispositivo microfluídico, língua eletrônica.Abstract: Biochar is a carbonaceous material obtained by the biomass pyrolysis, and highly functionalized, which allows its use in the sorption or immobilization of species. The use of biochar modified electrodes becomes attractive in the spontaneous preconcentration and voltammetric determination of analytes. The amount of biochar functional groups can be increased by surface chemical treatments, improving the sorption properties. In this work, biochar was obtained from castor oil cake biomass, and subject to different chemical activation conditions using HNO3 and/or H2O2. The different samples were characterized and evaluated in the determination of inorganic and organic species. The sample N2, treated with 50 % (v/v) HNO3 at 60 ºC for 3 hours, presented the best response and was used in the construction of CPME for different methodologies. First, the ability of CPME-N2 to Ni(II) ions preconcentration and determination was monitored by Ni(II)/Ni(III) redox couple in basic media. The use of the proposed electrode allowed the determination of Ni(II) ions in spiked bioethanol and wastewater samples. After, the capacity of caffeic acid preconcentration and determination was evaluated. CPME-N2 was efficient in the spontaneous preconcentration of this organic specie. The method was applied for the determination in real and spiked wine samples, and presented satisfactory and concordant results compared to spectroscopic method, by Folin-Ciocalteu. Another strategy evaluated was the biochar ability for immobilize NiOOH (CPMEN2- Ni) for glucose non-enzymatic determination, a reaction catalyzed by the NiOOH presence. The electrode was used for glucose determination in real and spiked biological fluids samples, in a microfluidic system based on textile threads (?TED), which allowed the reduction of reagents and residues, making this a green analytical method as evidenced by the Eco-Scale score. CPME-N2 was also evaluated for the simultaneous incorporation of a redox mediator (Prussian blue) and glucose oxidase enzyme for the glucose enzymatic determination. The biosensor had good enzyme-substrate affinity and stability after successive measurement days, and was applied efficiently for the glucose determination in biological fluid samples. Finally, CPME-N2, with other electrodes, was applied in a voltammetric electronic tongue, aiming the distinction and determination of catechol, 4-ethylcatechol and 4-ethylguaiacol. The strategy allowed the discrimination and determination of these species, using chemometric tools, PCA and neural networks. In this way, due to the interaction capacity of the biochar, improved by the chemical activation, it was possible to apply different electrochemical sensors, with satisfactory results in relation to the electrode without modification and modified with precursor biochar (untreated). This demonstrates the versatility and feasibility of the biochar use as a sensor modifier, which is also interesting from the economic and ecological point of view. Keywords: Activated biochar, electrochemical sensors, nickel, phenolic compounds, glucose, microfluidic device, electronic tongue

Cenários sobre educação financeira escolar: entrelaçamentos entre a pesquisa, o currículo e a sala de aula de matemática

Neste artigo apresentamos três cenários que buscam problematizar a educação financeira no Brasil e seu papel na promoção de Literacia Financeira no âmbito escolar. Detalham-se ainda aspectos e desafios da educação financeira no contexto da base nacional comum curricular, bem como reflexões sobre a importância do estudo e da abordagem da tomada de decisão, numa perspectiva multidisciplinar, para a concepção, o desenho e a implementação de uma Educação Financeira Escolar (EFE). Por fim, apresenta-se uma síntese de pesquisas que investigaram as relações entre as atividades de livros didáticos com temática financeira e a prática de professores dos anos iniciais sob a ótica da educação matemática crítica. As concepções dos autores e os resultados das pesquisas que as fundamentam apontam para um conjunto de ações para a EFE, incluindo: a necessidade da discussão crítica dos temas, além da mera e exclusiva resolução de exercícios de matemática financeira; a formação do professor e seu papel na mediação e no fomento de discussões e questionamentos dos estudantes; a intenção de desenvolver literacia financeira nas dimensões temporal e espacial, levando em conta o complexo processo de tomada de decisão humana, visando a um agir ético, crítico e convergente com a sustentabilidade do planeta

Voltammetric electronic tongue based on carbon paste electrodes modified with biochar for phenolic compounds stripping detection

Altres ajuts: Marta Bonet-San-Emeterio thanks to AGAUR, Generalitat de Catalunya and to European Social Fund, European Union for FI fellowship. Manel del Valle thanks the support from program ICREA Academia.Biochar is a charcoal produced from the biomass pyrolysis process that presents a highly porous and functionalized surface. In the present work an array of carbon paste electrodes (CPE) made of different forms of carbon (graphite, carbon nanotubes and activated biochar) was evaluated in the development of an electronic tongue for discrimination and stripping voltammetric determination of catechol (CAT), 4-ethylcatechol (4-EC) and 4-ethylguaiacol (4-EG) phenolic compounds. Morphological characterization of carbon materials and electrodes surfaces was performed by scanning electron microscopy (SEM) and semi-quantitative elemental composition by energy dispersive spectroscopy (EDS). Electrochemical Impedance Spectroscopy (EIS) measurements were used for electrochemical characterization of electrodes. Cyclic voltammetry measurements were performed for the phenolic compounds evaluated using different concentrations. Principal component analysis (PCA) was performed to evaluate the qualitative analysis. Quantitative data modeling was done using artificial neural networks (ANN). The proposed sensor array presented analytical potentiality allowing the distinction and determination of CAT, 4-EC and 4-EG by using chemometric processing. The method showed sensibility, reproducibility and a good linearity (R2>0.9940) for three compounds evaluated. Spontaneous preconcentration of three compounds was possible using all three sensors, which can allow the application of these as passive samplers for remote determinations of phenolic compounds in wine and food samples

Novel Additive Manufactured Multielectrode Electrochemical Cell with Honeycomb Inspired Design for the Detection of Methyl Parathion in Honey Samples

The development and increase in the number of crops recently have led to the requirement for greater efficiency in world food production and greater consumption of pesticides. In this context, the widespread use of pesticides has affected the decrease in the population of pollinating insects and has caused food contamination. Therefore, simple, low-cost, and quick analytical methods can be interesting alternatives for checking the quality of foods such as honey. In this work, we propose a new additively manufactured (3D-printed) device inspired by a honeycomb cell, with 6 working electrodes for the direct electrochemical analysis of methyl parathion by reduction process monitoring in food and environmental samples. Under optimized parameters, the proposed sensor presented a linear range between 0.85 and 19.6 μmol L–1, with a limit of detection of 0.20 μmol L–1. The sensors were successfully applied in honey and tap water samples by using the standard addition method. The proposed honeycomb cell made of polylactic acid and commercial conductive filament is easy to construct, and there is no need for chemical treatments to be used. These devices based on 6 working electrodes array are versatile platforms for rapid, highly repeatable analysis in food and environment, capable of performing detection in low concentrations

How to improve sustainability in Fused Filament Fabrication (3D Printing) research?

This review aims to provide an overview of sustainable approaches that can be incorporated into well-known procedures for the development of materials, pre- and post-treatments, modifications, and applications of 3D-printed objects, especially for fused filament fabrication (FFF). Different examples of conductive and non-conductive bespoke filaments using renewable biopolymers, bioplasticizers, and recycled materials are presented and discussed. The main final characteristics of the polymeric materials achieved according to the feedstock, preparation, extrusion, and treatments are also covered. In addition to recycling and remanufacturing, this review also explores other alternative approaches that can be adopted to enhance the sustainability of methods, aiming to produce efficient and environmentally friendly 3D printed products. Adjusting printing parameters and miniaturizing systems are also highlighted in this regard. All these recommended strategies are employed to minimize environmental damage, while also enabling the production of high-quality, economical materials and 3D printed systems. These efforts align with the principles of Green Chemistry, Sustainable Development Goals (SDGs), 3Rs (Reduce, Reuse, Recycle), and Circular Economy concepts

Flexible Label-Free Platinum and Bio-PET-Based Immunosensor for the Detection of SARS-CoV-2

The demand for new devices that enable the detection of severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) at a relatively low cost and that are fast and feasible to be used as point-of-care is required overtime on a large scale. In this sense, the use of sustainable materials, for example, the bio-based poly (ethylene terephthalate) (Bio-PET) can be an alternative to current standard diagnostics. In this work, we present a flexible disposable printed electrode based on a platinum thin film on Bio-PET as a substrate for the development of a sensor and immunosensor for the monitoring of COVID-19 biomarkers, by the detection of L-cysteine and the SARS-CoV-2 spike protein, respectively. The electrode was applied in conjunction with 3D printing technology to generate a portable and easy-to-analyze device with a low sample volume. For the L-cysteine determination, chronoamperometry was used, which achieved two linear dynamic ranges (LDR) of 3.98-39.0 μmol L-1 and 39.0-145 μmol L-1, and a limit of detection (LOD) of 0.70 μmol L-1. The detection of the SARS-CoV-2 spike protein was achieved by both square wave voltammetry (SWV) and electrochemical impedance spectroscopy (EIS) by a label-free immunosensor, using potassium ferro-ferricyanide solution as the electrochemical probe. An LDR of 0.70-7.0 and 1.0-30 pmol L-1, with an LOD of 0.70 and 1.0 pmol L-1 were obtained by SWV and EIS, respectively. As a proof of concept, the immunosensor was successfully applied for the detection of the SARS-CoV-2 spike protein in enriched synthetic saliva samples, which demonstrates the potential of using the proposed sensor as an alternative platform for the diagnosis of COVID-19 in the future

Circular economy electrochemistry: creating additive manufacturing feedstocks for caffeine detection from post-industrial coffee pod waste

The recycling of post-industrial waste poly(lactic acid) (PI-PLA) from coffee machine pods into electroanalytical sensors for the detection of caffeine in real tea and coffee samples is reported herein. The PI-PLA is transformed into both nonconductive and conductive filaments to produce full electroanalytical cells, including additively manufactured electrodes (AMEs). The electroanalytical cell was designed utilizing separate prints for the cell body and electrodes to increase the recyclability of the system. The cell body made from nonconductive filament was able to be recycled three times before the feedstock-induced print failure. Three bespoke formulations of conductive filament were produced, with the PI-PLA (61.62 wt %), carbon black (CB, 29.60 wt %), and poly(ethylene succinate) (PES, 8.78 wt %) chosen as the most suitable for use due to its equivalent electrochemical performance, lower material cost, and improved thermal stability compared to the filaments with higher PES loading and ability to be printable. It was shown that this system could detect caffeine with a sensitivity of 0.055 ± 0.001 μA μM–1, a limit of detection of 0.23 μM, a limit of quantification of 0.76 μM, and a relative standard deviation of 3.14% after activation. Interestingly, the nonactivated 8.78% PES electrodes produced significantly better results in this regard than the activated commercial filament toward the detection of caffeine. The activated 8.78% PES electrode was shown to be able to detect the caffeine content in real and spiked Earl Grey tea and Arabica coffee samples with excellent recoveries (96.7–102%). This work reports a paradigm shift in the way AM, electrochemical research, and sustainability can synergize and feed into part of a circular economy, akin to a circular economy electrochemistry

Circular economy electrochemistry: recycling old mixed material additively manufactured sensors into new electroanalytical sensing platforms

Recycling used mixed material additively manufactured electroanalytical sensors into new 3D-printing filaments (both conductive and non-conductive) for the production of new sensors is reported herein. Additively manufactured (3D-printed) sensing platforms were transformed into a non-conductive filament for fused filament fabrication through four different methodologies (granulation, ball-milling, solvent mixing, and thermal mixing) with thermal mixing producing the best quality filament, as evidenced by the improved dispersion of fillers throughout the composite. Utilizing this thermal mixing methodology, and without supplementation with the virgin polymer, the filament was able to be cycled twice before failure. This was then used to process old sensors into an electrically conductive filament through the addition of carbon black into the thermal mixing process. Both recycled filaments (conductive and non-conductive) were utilized to produce a new electroanalytical sensing platform, which was tested for the cell's original application of acetaminophen determination. The fully recycled cell matched the electrochemical and electroanalytical performance of the original sensing platform, achieving a sensitivity of 22.4 ± 0.2 μA μM-1, a limit of detection of 3.2 ± 0.8 μM, and a recovery value of 95 ± 5% when tested using a real pharmaceutical sample. This study represents a paradigm shift in how sustainability and recycling can be utilized within additively manufactured electrochemistry toward promoting circular economy electrochemistry