This thesis presented the study of carbon-based materials for ultra-sensitive molecular sensing. Reduced Graphene Oxide (rGO), a 2-dimensional one-atomic layer thick carbon material, had the advantage of low-cost, aqueous and industrial-scalable production route. Using rGO as the transducer platform could potentially lower the cost of sensors down to a few dollars per chip. However, there were still limitations in rGO that prevented its widespread usage as a biosensor transducer or in electronics: its low electrical conductivity and large electrical deviations. This thesis was structured to understand and solve these problems for transducer application. The thesis could be broken down into 3 parts: The first part of the thesis presented the critical review of the background and limitations of graphene research, followed by the background and importance of biosensor developments for the detection of sweat sodium ions and circulatory Interleukin-6 proteins. The second part of the thesis tested the hypothesis that the rGO limitations could be eliminated to create a highly sensitive biosensor transducer via (A) improving rGO synthesis (B) pristine Carbon Nanotubes-rGO hybrid film and (C) growth of rGO. The mechanism of ultra-large graphene oxide synthesis and graphene oxide growth was also elucidated in this section. The third part of the thesis then presented the fabrication and test of the practical and homogenous carbon-based biosensor using the transducer synthesized earlier. The thesis showed that through proving the hypothesis correct, it enabled the synthesis of an all organic sodium ion sensor with integrated pump and an ultra-sensitive interleukin-6 bio-sensor. Both of these novel sensors were able to detect the respective molecules in their physiological ranges.

The Graphene term has become synonymous with layered carbon sheets having thicknesses ranging from the monolayer to stacks of about ten layers. For bulk volume production, graphite chemical exfoliation is the preferred solution. For this reason, much interest has congregated around different processes to oxidize and peel off graphite to obtain graphene oxide (GO) and its counterpart, reduced GO (rGO). The community at-large has quickly adopted those processes and has been intensively using the resulting (r)GO as active materials for a myriad of applications. Yet, partially given the absence of comparative studies in synthesis methodologies, a lack of understanding persists on how to best tailor these carbon materials for a given application. In this dissertation, the effect of using different chemical oxidation-reduction strategies for graphite, namely the impact on the structure and chemistry of GOs and rGOs is systematically discussed. Added to this, it is demonstrated that the drying step of the powdered materials cannot be neglected. Its influence is demonstrated in studies such as the optimization of capacitance of rGOs touted as electrochemical energy storage materials (Chapter 4). It is concluded that, in order to maximize the performance of GO and rGO materials for any particular application, there must be a judicious choice of their synthesis steps. Obvious as it may be for anyone working in Chemistry, this point has been surprisingly overlooked for too long by the vast majority of those working with these carbon materials.

Over the last decade, two dimensional (2D) materials have attracted considerable attention from both the scientific and engineering community due to their unique properties. One important advance of 2D materials is that they can be exfoliated into nanosheets suspended in a liquid phase and that this allows the formulation of 2D nanomaterials inks. Such inks can be deposited as functional components through low-cost inkjet printing techniques. Many 2D materials based inks have been produced over the years. This thesis investigates the use of inkjet printing to deposit 2D materials such as graphene oxide (GO) and black phosphorus (BP).GO, a derivative of graphene, has been widely used to produce graphene-based conductors via inkjet printing owing to its good stability in readily available solvents such as water. In this work, highly conductive reduced graphene oxide (rGO) films with bulk conductivity in excess of 2 × 10^4 Sm-1 have been prepared by inkjet printing a GO aqueous ink, with mean flake size 35.9 micro metre, through a 60 micro metre inkjet printing nozzle followed by a reduction step. Experimental results showed that individual GO flakes up to 200 micro metre diameter can be successfully printed with no instances of nozzle blocking or poor printing performance. The mechanism by which this occurs is believed to be GO sheet folding during drop formation followed by elastic unfolding during drop impact and spreading. In addition, the influence of GO flake size on rGO film conductivity has been investigated. It was found that the rGO film conductivity increased about 60% when the mean flake size of the GO flakes in the ink increases from 0.68 micro metre to 35.9 micro metre. The drying behaviour of printed GO droplets has been studied on eight GO aqueous inks in which the mean flake size of GO was varied over a range from 0.68 to 35.9 micro metre. It was found that the coffee ring effect (inhomogeneous drying of a droplet to leave a ring like deposit) of dried droplets of the GO ink weakened and disappeared when the flake size increasing. It was found that, with a printed deposit around 340 micro metre in diameter, the coffee ring effect (CRE) was suppressed with the mean flake size > 10.3 micro metre. The critical flake size for CRE suppression reduced to 5.97 and 3.68 micro metre when the substrate temperature was 40 and 50 °C, respectively. It was further found that the CRE weakened with decreasing printed drop size, with the critical flake size reducing to 1.58 micro metre with a printed drop diameter of 30 micro metre.The interaction between BP nanometre thickness flakes and humid atmospheres was investigated using an inkjet printed BP sensor. The BP sensor showed was very sensitive to changes in humidity with a response time of a few seconds and the effect is reproducible in minutes. However, long term exposure to humid air with a relative humidity (RH) > 11% leads to a significant chemical change in the BP films, with Fourier transform infra-red spectroscopy (FTIR) indicating partial hydrolysis of the BP to form phosphate and phosphonate ions. Low temperature heat treatment of BP films under dry conditions after exposure to elevated RH leads to a partial recovery of the impedance response and reversion to a chemical state similar to that before exposure to a humid environment. The recovery of BP properties is most complete after exposure to lower humidity environments (RH < 11%), although exact replication of the original impedance response and FTIR spectrum was not possible.

Submitted by Rosivalda Pereira (mrs.pereira@ufma.br) on 2017-06-02T20:23:35Z No. of bitstreams: 1 RitaSousaCarvalho.pdf: 1881186 bytes, checksum: 0d50276b7867c21064584927762057dc (MD5) / Made available in DSpace on 2017-06-02T20:23:35Z (GMT). No. of bitstreams: 1 RitaSousaCarvalho.pdf: 1881186 bytes, checksum: 0d50276b7867c21064584927762057dc (MD5) Previous issue date: 2016-07-29 / A novel and selective electrochemical sensor for the determination of the butylated hydroxyanisole (BHA) and tert-butylhydroquinone (TBHQ) antioxidants employing the differential pulse voltammetry (DPV) was developed. In this sense, a glassy carbon electrode (GCE) modified with a copper tetrasulfonated phthatocyanine (CuTSPc) adsorbed on reduced graphene oxide (rGO) showed excellent response for the TBHQ and BHA oxidation with a decrease in the overpotentials about 130mV vs Ag/AgCl and anodic peak currents about 4 times higher than the observed responsesat an electrode unmodified. The increase of the oxidation reaction rates for TBHQ and BHA was attributed to the efficient electron transfer between the studied species and the immobilized materials on surface of the GCE.The materials rGO, CuTSPc and rGO/CuTSPc were characterized by Fourier transform infrared spectroscopy (FTIR) and the analytical response of the sensor for the analytes was studied by cyclic voltammetry (CV) and linear scan voltammetry (LSV) techniques. After optimization of the experimental parameters, the analytical curves for determination of BHA and TBHQ by DPV technique demonstrated an excellent linear response from 0.1 to 500µmol L-1 with detection limit of 0.045 µmol L-1 for TBHQ and 0.036 µmol L-1 for BHA. Finally, the proposed method was successfully applied in the simultaneous determination of BHA and TBHQ in six biodiesel samples, and the results obtained were found to be similar to those obtained using the HPLC method with agreement at 95 % confidence level. The addition and recovery studies have shown that the proposed method has good accuracy with recovery values between 99.5 and 100.5 % forTBHQ and 99.1 and 100.2 for BHA. / Um novo e seletivo sensor eletroquímico para a determinação dos antioxidantes butilato de hidroxianisol (BHA) e terc-bultil-hidroquinona (TBHQ) empregando a Voltametria de Pulso Diferencial (VPD) foi desenvolvido. Neste sentido, um eletrodo de carbono vítreo (ECV) modificado coma ftalocianina tetrassulfonada de cobre (CuTSPc) adsorvida sobre óxido de grafeno reduzido (OGr) mostrou uma excelente resposta para as oxidações de TBHQ e BHA com uma diminuição nos sobrepotenciais cerca de 130 mV vs Ag/AgCl e correntes de pico anódicas cerca de 4 vezes maiores do que as respostas observadasem um eletrodo não modificado. O aumento nas velocidades das reações de oxidação de TBHQ e BHA foi atribuído à eficiente transferência de elétrons entre as espécies estudadas e os materiais imobilizados na superfície do ECV. Os materiais OGr, CuTSPc e OGr/CuTSPc foram caracterizados por espectroscopia no infravermelho com transformada de Fourrier (FTIR) e a resposta analítica do sensor para os analitos foi estudada pelas técnicas voltametria cíclica (VC) e voltametria de varredura linear (VVL). Após a otimização dos parâmetros experimentais e operacionais, as curvas analíticas para a determinação individual e simultânea de BHA e TBHQ, pela técnica VPD, demonstraram uma excelente resposta linear de 0,1 a 500 µmol L-1 com limite de detecção de 0,045 µmol L-1 para TBHQ e 0,036 µmol L-1 para BHA. Finalmente, o sensor proposto foi utilizado com sucesso para a determinação TBHQ e BHA em seis amostras de biodiesel e os resultados foram similares aos obtidos pelo método HPLC com um nível de concordância de 95 %. Os estudos de adição e recuperação mostraram que o método proposto apresenta boa exatidão com valores de recuperação entre 99,5 e 100,5% para TBHQ e 99,1 e 100,2 para BHA.

The efficacy of dispersed reduced graphene oxide (rGO) as a nucleation site for the growth of mesophase in an isotropic pitch was investigated and quantified in this study. Concentrations of rGO were systematically tested in an isotropic petroleum and coal-tar pitch during thermal treatments and compared to pitch without rGO. The mesophase content of each thermally treated pitch was quantified by polarized light point counting. Further characterization of softening temperature and insolubles were quantified. Additionally, the pitches with and without rGO were melt spun, graphitized, and tensile tested to determine the effects of rGO on graphitized fiber mechanical properties and fiber morphology.

abstract: Thiol functionalization is one potentially useful way to tailor physical and chemical properties of graphene oxides (GOs) and reduced graphene oxides (RGOs). Despite the ubiquitous presence of thiol functional groups in diverse chemical systems, efficient thiol functionalization has been challenging for GOs and RGOs, or for carbonaceous materials in general. In this work, thionation of GOs has been achieved in high yield through two new methods that also allow concomitant chemical reduction/thermal reduction of GOs; a solid-gas metathetical reaction method with boron sulfides (BxSy) gases and a solvothermal reaction method employing phosphorus decasulfide (P4S10). The thionation products, called "mercapto reduced graphene oxides (m-RGOs)", were characterized by employing X-ray photoelectron spectroscopy, powder X-ray diffraction, UV-Vis spectroscopy, FT-IR spectroscopy, Raman spectroscopy, electron probe analysis, scanning electron microscopy, (scanning) transmission electron microscopy, nano secondary ion mass spectrometry, Ellman assay and atomic force microscopy. The excellent dispersibility of m-RGOs in various solvents including alcohols has allowed fabrication of thin films of m-RGOs. Deposition of m-RGOs on gold substrates was achieved through solution deposition and the m-RGOs were homogeneously distributed on gold surface shown by atomic force microscopy. Langmuir-Blodgett (LB) films of m-RGOs were obtained by transferring their Langmuir films, formed by simple drop casting of m-RGOs dispersion on water surface, onto various substrates including gold, glass and indium tin oxide. The m-RGO LB films showed low sheet resistances down to about 500 k&#937;/sq at 92% optical transparency. The successful results make m-RGOs promising for applications in transparent conductive coatings, biosensing, etc. / Dissertation/Thesis / Ph.D. Chemistry 2013

Orientadores: Ana Flávia Nogueira, Flávio Leandro de Souza / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Química / Made available in DSpace on 2018-08-27T13:00:11Z (GMT). No. of bitstreams: 1 Carminati_SaulodoAmaral_M.pdf: 3434559 bytes, checksum: 5dc1e86f14ccc0bccd7264ae9b28c11e (MD5) Previous issue date: 2015 / Resumo: O Resumo poderá ser visualizado no texto completo da tese digital / Abstract: The Abstract is available with the full electronic digital document / Mestrado / Quimica Organica / Mestre em Química

Orientador: Juliano Alves Bonacin / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Química / Made available in DSpace on 2018-08-27T15:22:06Z (GMT). No. of bitstreams: 1 Santos_PamylaLayenedos_M.pdf: 4212017 bytes, checksum: 32d8be4cbad15f721c18e5490e98cb35 (MD5) Previous issue date: 2015 / Resumo: O azul da Prússia (AP) é um dos mais antigos compostos de coordenação e pode ser utilizado na modificação de sensores eletroquímicos para a detecção de H2O2, o AP pode catalisar a redução do peróxido e por isso é conhecido como "artificial peroxidase". Entretanto, filmes de AP não apresentam boa estabilidade eletroquímica e alternativas como a obtenção de nanocompósito baseados em AP e grafeno podem ser utilizadas para contornar o problema. O grafeno é um material com alta condutividade, flexibilidade e resistência à tração, pode ser obtido pelo método de Hummers que consiste na redução do óxido de grafeno e neste caso é chamado de óxido de grafeno reduzido. Assim, o objetivo deste trabalho é a obtenção fotoquímica de um nanocompósito baseado em azul da Prússia (AP) e óxido de grafeno reduzido (rGO) que permite uma combinação das propriedades eletrocatalíticas do AP e condutoras do rGO para a aplicação em sensores eletroquímicos. Além disso, espera-se uma maior estabilidade eletroquímica deste material. Os materiais óxido de grafeno reduzido e azul da Prússia foram obtidos separadamente pelos métodos químicos e fotoquímicos com a utilização de LEDs. Os resultados mostraram vantagens do método fotoquímico como o controle da morfologia e do tamanho dos cristais de azul da Prússia. O grau de redução dos materiais baseados em grafeno foi controlado com o tempo de irradiação no LED e isso foi refletido em suas propriedades eletroquímicas, com uma resposta linear da corrente de pico em função do grau de redução. O nanocompósito foi obtido pelo método fotoquímico in situ, e isso foi comprovado pelas técnicas DRX, espectroscopias Raman e UV-Vis. As micrografias obtidas por FEG-SEM mostraram a presença de cubos de AP sobre toda a superfície do óxido de grafeno reduzido. Espera-se que a interação entre o AP e rGO permita uma maior estabilidade eletroquímica do material que será testado no sensoriamento de H2O2 / Abstract: Prussian blue is one of the oldest coordination compounds and can be used on the modification of electrochemical sensors for the detection of H2O2, PB can catalyze the reduction of hydrogen peroxide and, for that, it is known as "artificial peroxidase". However, PB films do not show good electrochemical stability and alternatives such as the obtention of nanocomposites based on PB and graphene can be used to work around this problem. Graphene is a material with high conductivity, flexibility and tensile strength. Graphene can be obtained by Hummers method, which consists of reducing graphene oxide, in which case it is called a reduced graphene oxide. The goal of this work is photochemically obtaining a nanocomposite based on Prussian blue (PB) and reduced graphene oxide (rGO) that allows a combination of the electrocatalytical properties of PB and high conductivity of rGO for use in electrochemical sensors. In addition, we expect a higher electrochemical stability of this material. Reduced graphene oxide and Prussian blue were obtained separately by chemical and photochemical methods using LED. The results show the advantages of photochemical method to control the morphology and size of Prussian blue crystals. The reduction extent of graphene-based material was controlled by the irradiation time of the LED and this was reflected in its electrochemical properties, with a linear response of the peak current depending on the reduction extent. The nanocomposite was obtained by in situ photochemical method, and this was confirmed by XRD techniques, Raman and UV-Vis. The micrographs obtained by FEG-SEM showed the presence of PB cubes on the entire surface of the reduced graphene oxide. It is expected that the interaction between the PB and rGO allowing greater electrochemical stability of the material to be tested in H2O2 sensing / Mestrado / Quimica Inorganica / Mestra em Química

Water splitting through photoelectrochemical reaction is widely regarded as a major method to generate H2 , a promising source of renewable energy to deal with the energy crisis faced up to human being. Efficient exploitation of visible light in practice of water splitting with pure TiO2 material, one of the most popular semiconductor material used for photoelectrochemical water splitting, is still challenging. One dimensional TiO2 nanotubes is highly desired with its less recombination with the short distance for charge carrier diffusion and light-scattering properties. This work is based on TiO2 NTPC electrode by the optimized two-step anodization method from our group. A highly crystalized p-type Cu2O layer was deposited by optimized pulse potentiostatic electrochemical deposition onto TiO2 nanotubes to enhance the visible light absorption of a pure p-type TiO2 substrate and to build a p-n junction at the interface to improve the PEC performance. However, because of the real photocurrent of Cu2O is far away from its theoretical limit and also poor stability in the aqueous environment, a design of rGO medium layer was added between TiO2 nanotube and Cu2O layer to enhance the photogenerated electrons and holes separation, extend charge carrier diffusion length (in comparison with those of conventional pure TiO2 or Cu2O materials) which could significantly increase photocurrent to 0.65 mA/cm2 under visible light illumination (>420 nm) and also largely improve the stability of Cu2O layer, finally lead to an enhancement of water splitting performance.

Groundwater (GW) accounting for most of the freshwater available around the World, finding sustainable techniques to depollute it is of crucial importance for safe drinking water supply. The extensive use of fertilizers in the agriculture, as well as other anthropogenic activities, are contributing to the excessive nitrate levels in some aquifers. These levels need to be reduced to obtain potable water. Bioelectrochemical systems (BES), using microorganisms to catalyze a desired electrochemical reaction, recently proved to be a very promising technology for water remediation. Groundwater denitrification using Microbial Electrolysis Cell (MEC) needs to be improved for further scaled-up on-site system. The advantages conferred by fluidized bed reactor (FBR), as well as the outstanding electrochemical properties of reduced graphene oxide (rGO), are two potential enhancements of such bioelectrochemical denitrification system that were investigated in this thesis. Some essential parameters could be determined during the preliminary steps' experiments. The fluidization trials gave us a clear insight that Coconut-based Activated Carbon (CAC) particles were resistant carrier particles, nicely fluidized within a 39.27cm3 circular cathodic chamber for a flow rate ranging between 450ml/min to 590ml/min. For the same flow rate of 500ml/min, we could obtain CAC particles fluidization for the upstream fluidized configuration, and still bed particles for the fixed bed downstream configuration, which would be very useful for later unbiased comparison. The denitrifying bacteria showed during their enrichment, a nitrate removal rate of up to 1.986ppm NO3-N/h in serum bottles, with an average of 0.38ppm NO2-N/h accumulation. The parallel running of fixed bed versus fluidized bed denitrifying reactor in order to compare their denitrification performances, was planned, but could not be performed due to COVID-19. The graphene oxide (GO) batch experiments showed a good biocompatibility between GO/rGO and our autotrophic denitrifying bacteria. A change of morphology within about 20 hours was observed, probably suggesting the reduction of GO to rGO by the bacteria. During a first test, the presence of GO led to a 2.7 folds less efficient denitrification performance as compared with the GO/rGO-free condition, likely due to the competition between nitrate and GO for being reduced. However, the denitrification rate in presence of GO/rGO increased up to 1.873ppm NO3-N/h after the second pulse of groundwater and flush with H2/CO2 gas, which is almost 2.3 folds higher than initially in the same condition. This suggests that GO needs some time to get fully reduced to rGO, and the denitrification rate might reach the same or higher levels as in the GO/rGO-free conditions, when GO is fully reduced. Improved denitrification would indicate that rGO facilitates the electron transfer between bacteria and nitrate, as it can be expected from its electrochemical properties previously studied. This would be worth being investigated in the scope of a longer experience. / Grundvatten (GW) som står för det mesta av det sötvatten som finns tillgängligt runt om i världen och att hitta hållbara tekniker för att förorena det är av avgörande betydelse för en trygg dricksvattenförsörjning. Den omfattande användningen av gödselmedel i jordbruket, liksom andra antropogena aktiviteter, bidrar till de överdrivna nitratnivåerna i vissa vattenfiskare. Dessa nivåer måste sänkas för att erhålla dricksvatten. Bioelektrokemiska system (BES), med användning av mikroorganismer för att katalysera en önskad elektrokemisk reaktion, visade sig nyligen vara en mycket lovande teknik för sanering av vatten. Grundvatten denitrifikation med hjälp av Microbial Electrolysis Cell (MEC) måste förbättras för att ytterligare skala upp systemet på plats. Fördelarna med fluidiserad bäddreaktor (FBR) såväl som de enastående elektrokemiska egenskaperna hos reducerad grafenoxid (rGO) är två potentiella förbättringar av ett sådant bioelektrokemiskt denitrifikationssystem som undersöktes i denna avhandling. Vissa väsentliga parametrar kan bestämmas under de preliminära stegens experiment. Fluidiseringsstudierna gav oss en klar insikt om att kokosnötbaserade aktiverade kolpartiklar (CAC) -partiklar var resistenta bärarpartiklar, trevligt fluidiserade i en cirkulär katodisk kammare på 39,27 cm3 för en flödeshastighet mellan 450ml/min till 590ml/min. För samma flödeshastighet på 500ml/min kunde vi få CAC-partikelfluidisering för uppströms fluidiserad konfiguration och stillbäddspartiklar för den fixerade bädden nedströms konfiguration, vilket skulle vara mycket användbart för senare opartisk jämförelse. De denriffriserande bakterierna visade under deras anrikning en nitratborttagningshastighet av upp till 1,986 ppm NO3-N/h i serumflaskor, med ett genomsnitt på 0,38 ppm NO2-N / h ackumulering. Den parallella körningen av denitrifierande reaktorn med fast bädd kontra fluidiserad bädd för att jämföra deras denitrifikationsprestanda planerades, men kunde inte utföras på grund av COVID-19. Diagramexperimenten av grafenoxid (GO) visade en god biokompatibilitet mellan GO/rGO och våra autotrofiska denitrifierande bakterier. En förändring av morfologin inom cirka 20 timmar observerades, vilket antagligen antydde att bakterierna minskade GO till rGO. Under ett första test ledde närvaron av GO till 2,7 gånger mindre effektiv denitrifikationsprestanda jämfört med GO/rGO-fritt tillstånd, troligtvis på grund av konkurrensen mellan nitrat och GO för att ha minskat. Denitrifikationsgraden i närvaro av GO/rGO ökade emellertid upp till 1,873 ppm NO3-N/h efter den andra grundvattenspulsen och spolades med H2/CO2-gas, vilket är nästan 2,3 gånger högre än ursprungligen i samma tillstånd. Detta antyder att GO behöver lite tid för att helt reduceras till rGO, och denitrifikationsgraden kan nå samma eller högre nivåer som i GO/rGO-fria förhållanden, när GO är helt reducerad. Förbättrad denitrifikation skulle indikera att rGO underlättar elektronöverföring mellan bakterier och nitrat, som det kan förväntas av dess elektrokemiska egenskaper som tidigare studerats. Detta skulle vara värt att undersökas inom ramen för en längre upplevelse.