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Electrochemical sensing with carbon nanotubes
No full textIn this chapter we aim at reviewing the most relevant contributions in the development of electrochemical sensors and biosensors based on carbon nanotubes (CNTs). Particular attention will be focused on the different strategies to modified the electrodes for sensing application.
First, we will discuss about the electrochemical properties of nanotubes, their peculiar physical-chemical features that make them very useful for sensing. For instance, CNTs have been incorporated in electrochemical sensors to decrease overpotential and to improve sensitivity. In addition, concerning biosensing, the use of nanotubes enhancing the electrochemical reactivity of important biomolecules by promoting the electron-transfer reactions of biomolecules with catalytic activity.
Different ways of integrating nanotubes and electrodes will be presented: from a bulk modification to a more sensible surface one. After a survey of bulk modification strategies, we will show an in-depth study of the surface modification technique developing the random and oriented choice to modify the surface, especially focusing on the vertical alignment. A structured methodological point of view will be given in this latter section.
We will review the state of the art of sensing and biosensing with CNTs. In the first part of this section we will present how CNTs modified electrodes can act as sensors without any further modification of their structure. In the latter we will first focalize the attention to the functionalization techniques required in order to make CNTs able to detect biological substrates. Therefore we will review how CNTs modified electrodes will detect biological species such as neurotransmitters, proteins, enzymes and proteins enhancing the detection limits obtained using other techniques.
Finally a future perspectives section is provided in which we will analyze the possibility to integrate the CNTs electrochemical devices in microfluidic platforms in order to diminish the average dimensions of the substrates, to enhance the selectivity and other appreciable advantages
Mathematical modeling in chemical engineering: a tool to analyse complex systems
Full text linkMathematical modeling is an attempt to describe a slice of reality in mathematical terms.
In Chemical Engineering, mathematical modeling is used for simulation, control and optimization of a process and it is also a tool to design the industrial devices.
Mathematical modeling is a technique commonly in place also in both theoretical and experimental studies of chemical processes.
In the present chapter mathematical modelling applications to complex systems as a consequence of structure heterogeneity and involved various physical-chemical phenomena are presented. Particular attention will be focused on improving the quantitative understanding of the basic phenomena of a process that can come from the use of mathematical models.
Specific task is also demonstrating how, through the use of information coming from experimental investigations and simulations, it is possible checking on the validity of the assumptions made and fine tuning the predictive mathematical model capability.
The possibility of analyzing and quantifying the role played by each single step of the process is examined in order to define the relevant mathematical expressions. The latter allows getting useful indications about the impact of different operating conditions on the role of each single step and at the very end it gives indication about the efficiency of the process itself.
Next step focuses on the estimation of the significant parameters of the process. In complex systems the determination “a priori” of some parameters is not always feasible and they are therefore determined as a comparison of experimental and simulation data.
The final result is therefore the availability of a tool, the verified and validated (V&V) mathematical model, that can be used for simulation, process analysis, process control, optimization, design.
Specific reference will be made to the use of the proposed methodology on a system whose behaviour, on varying the agitation level, was quantified and validated against the results of an experimental investigation in a pilot plant.
A second application will allow to analyse the effect of transport phenomena in multi-phase heterogeneous systems in order to detect the conditions at which production plant efficiency is improved
Thermal modeling of industrial-scale vanadium redox flow batteries in high-current operations
Full text linkA cell-resolved model that simulates the dynamic thermal behavior of a Vanadium Redox Flow Battery during charge and discharge is presented. It takes into account, at a cell level, the reversible entropic heat of the electrochemical reactions, irreversible heat due to overpotentials, self-discharge reactions due to ion crossover, and shunt current losses. The model accounts for the heat transfer between cells and toward the environment, the pump hydraulic losses and the heat transfer of piping and tanks. It provides the electrolyte temperature in each cell, at the stack inlet and outlet, along the piping and in the tanks. Validation has been carried out against the charge/discharge measurements from a 9kW/27kWh VRFB test facility. The model has been applied to study a VRFB with the same stack but a much larger capacity, operating at 400 A for 8 h, in order to identify critical thermal conditions which may occur in next-generation industrial VRFB stacks capable to operating at high current density. The most critical condition has been found at the end a long discharge, when temperatures above 50°C appeared, possibly resulting in 〖VO〗_2^+ precipitation and battery faults. These results call for heat exchangers tailored to assist high-power VRFB systems
Removal of vegetal tannins from wastewater by electroprecipitation combined with electrogenerated Fenton oxidation
No full textSynthetic solutions containing up to 2000 ppm of gallotannic acid and real wastewater from vegetal tanning processes with values of chemical oxygen demand (COD) exceeding 100 000 ppm were decontaminated by electrolysis using a sacrifical iron anode coupled to either a titanium-platinised or an O2-diffusion cathode. Experiments were performed in the presence of oxidants and oxidation promoters such as air, oxygen and hydrogenperoxide, the latter being directly added to the solution or electrogenerated by the O2-diffusion cathode. COD and UV-visible absorbance evolution showed that tannins are removed from electrolysed solutions down to relatively low values, permitting more than 94% elimination. Partial oxididation of the mother compound generates short-chain by-products (mostly carboxylic acids) responsible for the remaining low COD values. Contaminants (tannins and non-tannins) containedin industrial wastewater were removed by combining electroprecipitation with a Fenton-assisted process; a final oxidation step, carried out on a boron-doped diamond electrode, was performed in order to decerase the COD to very low final values
Electrochemical removal of tannins from aqueous solutions
No full textThe applicability of electrochemical methods to remove tannins from wastewater was investigated. Gallotannic acid was used as the reference substance. Electrochemical experiments were performed using platinum electrodes. Macroscale potentiostatic or galvanostatic electrolyses were carried out with sodium sulfate or sodium chloride as supporting electrolytes, to analyze direct and indirect oxidation processes. Operating variables such as pH and chloride concentration were considered to determine their influence on the efficiency and energy consumption of the process. The simulation of a pilot plant was carried out with a mathematical model, the parameters of which were determined by fitting of experimental profiles. The results of a preliminary investigation on the oxidation−coagulation process using sacrificial electrodes are also reported
Rimozione di tannini mediante elettrocoagulazione: analisi e simulazione del processo in continuo.
No full textBenché l’idoneità dei processi elettrochimici per il trattamento di reflui sia largamente documentata in letteratura, la loro applicabilità è fortemente condizionata dai significativi consumi energetici che li caratterizzano. Incoraggianti prospettive in questo settore sono rappresentate dai processi combinati di ossidazione/coagulazione/precipitazione che permettono da un lato di ottenere elevate rese di abbattimento e dall’altro di contenere i costi associati al trattamento.
Studi precedenti, condotti dagli stessi Autori su apparecchiature da laboratorio, avevano evidenziato l’efficacia del processo di elettrocoagulazione per la rimozione di tannini.
Nel presente lavoro, ai fini della realizzazione di tale processo a livello industriale, ne viene studiato il comportamento su impianto pilota. Sono state dapprima condotte prove in discontinuo con apparecchiature da laboratorio, per individuare le condizioni operative ottimali. Quindi, si è passati allo studio del processo in continuo su impianto pilota, appositamente progettato e realizzato, che opera in ciclo chiuso fino al raggiungimento delle condizioni ottimali di lavoro e successivamente come sistema aperto, in condizioni di stazionarietà.
Modelli matematici formulati per le diverse apparecchiature hanno permesso di simulare l’impianto nelle diverse modalità di funzionamento. Il confronto fra i dati sperimentali ottenuti in condizioni di riciclo totale e quelli teorici hanno confermato l’ottima capacità di previsione dei modelli sviluppati
A Multi-dimensional Vanadium Redox Flow Batteries Performance Model accounting for species crossover
No full text
Enhancement of heterogeneous electron transfer dynamics tuning single-walled carbon nanotube forest height and density
Full text linkElectrochemical sensors are growing in number and importance. Surface modifications could enhance charge transfer properties occurring at the interfaces and carbon nanoassemblies is one of the most used strategy to improve sensitivity to measurements. However, well defined protocols of surface modification are needed in order to fabricate electrochemically effective nanostructured sensors.
Therefore, we aim at investigating the electrochemical properties of single-walled carbon nanotube (SWCNT) forests as a function of height and nanotube surface density. Height of the forests is accurately controlled tuning the oxidation temperatures in the range of 293–313 K of SWCNTs. The surface density of carbon nanotubes was adjusted developing cysteamine/2-mercaptoethanol (CYS/ME) self-assembled monolayers (SAMs) on gold surfaces at different ratios (1:0, 1:3, 1:10, 1:100, 0:1).
Apparent electron transfer rate was analyzed with electrochemical impedance spectroscopy (EIS) and experimental data show that transfer rate constant, kapp, increases from 1 × 10−4 cm/s to 6 × 10−4 cm/s rising oxidation temperatures (i.e. lowering forest height); therefore forests with reduced height show higher electron transfer rate without significant difference in electrodic reversibility. On the other hand, tuning SWCNT surface density, forests obtained with no ME show optimal Δpeak value of 0.087 ± 0.015 V and highest kapp value of 9.15 × 10−3 cm/s. Surprisingly, electrochemical surface area analysis shows that samples with lower amount of cysteamine have an active surface area three times bigger than samples with 1:3 CYS/ME ratio. Low electrochemical efficiency associated with high active surface may be related to unwanted SWCNT bundles adsorbed on the surface for 1:10 and 1:100 CYS/ME ratio samples as confirmed by AFM morphological characterization. Further investigation shows that a transition from a semi-infinite planar diffusion mechanism to a radial diffusion one takes place when SAMs with low chemical affinity to nanotubes are used. Wettability analysis confirms the robustness of the surface chemical modification during the forest development. Altogether these results show that optimal electrochemical properties of carbon modified electrodes require an accurate control of forest fabrication in terms of carbon nanotube structural assembling
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