Flow Microcalorimetry Research Articles

Continuous flow microcalorimetry as a tool for studying catalytic hydrogenations: application to CO2 methanation

Continuous flow microcalorimetry as a tool for studying catalytic hydrogenations: application to CO2 methanation

Combinations of essential oils as effective green stabilizers for single base propellants

AbstractNitrocellulose‐based propellants undergo natural (and inevitable) autocatalytic degradation reactions. The presence of a stabilizer is essential to avoid and reduce the degradation reactions by capturing the NOx molecules. Traditional stabilizers, such as diphenylamine, and ethylcentralite, react with NOx through their amine and/or amide groups, leading to n‐nitroso groups, which are known to have carcinogenic, mutagenic and reprotoxic properties. Molecules that are not prone to form by‐products containing nitrosamines have been studied as substitutes, such as guaiacol and curcumin. However, the aromatic rings on these molecules have their acidity augmented when capturing the NOx groups and, paradoxically, increasing hydrolysis rates. In order to find a solution for the problem, we evaluated the use of essential oils containing terpenes and/or phenolic compounds to introduce a buffering capacity. Several propellant formulations with those compounds were subjected to traditional stability tests (German, Bergman–Junk and Storage tests), Pressure Vacuum Stability Test and Heat Flow Microcalorimetry. Finally, industrial batches were produced for the evaluation of real (ballistic) performance. Results indicated that the usage of essential oils increases stability properties not only through a sum of effects, but also in a synergistic way. Ballistic results were also adequate.

Ion solvation as a predictor of lanthanide adsorption structures and energetics in alumina nanopores

Adsorption reactions at solid-water interfaces define elemental fate and transport and enable contaminant clean-up, water purification, and chemical separations. For nanoparticles and nanopores, nanoconfinement may lead to unexpected and hard-to-predict products and energetics of adsorption, compared to analogous unconfined surfaces. Here we use X-ray absorption fine structure spectroscopy and operando flow microcalorimetry to determine nanoconfinement effects on the energetics and local coordination environment of trivalent lanthanides adsorbed on Al2O3 surfaces. We show that the nanoconfinement effects on adsorption become more pronounced as the hydration free energy, ΔGhydr, of a lanthanide decreases. Neodymium (Nd3+) has the least exothermic ΔGhydr (−3336 kJ·mol−1) and forms mostly outer-sphere complexes on unconfined Al2O3 surfaces but shifts to inner-sphere complexes within the 4 nm Al2O3 pores. Lutetium (Lu3+) has the most exothermic ΔGhydr (−3589 kJ·mol−1) and forms inner-sphere adsorption complexes regardless of whether Al2O3 surfaces are nanoconfined. Importantly, the energetics of adsorption is exothermic in nanopores only, and becomes endothermic with increasing surface coverage. Changes to the energetics and products of adsorption in nanopores are ion-specific, even within chemically similar trivalent lanthanide series, and can be predicted by considering the hydration energies of adsorbing ions.

Connecting Thermodynamics of Alkali Ion Exchange on the Quartz (101) Surface with Density Functional Theory Calculations.

Periodic plane-wave density functional theory (DFT) calculations were performed on the α-quartz (SiO2) (101) surface to model exchange of adsorbed Li+ and either Na+, K+, or Rb+ in inner- and outer-sphere adsorbed, and aqueous configurations, which are charge-balanced with 2 Cl-. SiO- or SiOH groups represented the adsorption surface sites. The SiO- models included 58 H2O and 2 H3O+ molecules to approximate an aqueous environment, whereas the SiOH models had 59 H2O and 1 H3O+ molecules. The goal of this work is to calculate the heats of exchange for these alkali ions and to compare the results with those measured by flow microcalorimetry to ascertain the most probable mechanisms for these cations exchanging on the α-quartz (101) surface. Energy minimizations of each alkali ion adsorbed as outer-sphere complexes on SiOH surface sites, and as inner- and outer-sphere complexes on SiO- surface sites, were used to determine the energy of exchange (ΔEex) with Li+ for comparison with experimentally determined ΔHex values. Here, we present a novel method for calculating ΔEex using the difference in energies of geometry-optimized end member models. The aqueous and surface structures produced are similar to those observed experimentally. Although the trend for the calculated ΔEex values is consistent with those from the heats of exchange measured experimentally, the magnitude of our modeled ΔEex results is significantly larger than select experimental data from the literature [Peng, L. Zeta-Potentials and Enthalpy Changes in the Process of Electrostatic Self-Assembly of Cations on Silica Surface. Powder Technol. 2009, 193(1), 46-49]; we discuss the reasons for this discrepancy herein. The relative energy differences of the various configurations modeled have implications for the measurements of the surface charge via potentiometric titrations due to the more active role of alkali cations in quartz surface chemistry that have been previously considered as inert background electrolytes.

Insights on Alanine and Arginine Binding to Silica with Atomic Resolution.

Interactions of biomolecules with inorganic oxide surfaces such as silica in aqueous solutions are of profound interest in various research fields, including chemistry, biotechnology, and medicine. While there is a general understanding of the dominating electrostatic interactions, the binding mechanism is still not fully understood. Here, chromatographic zonal elution and flow microcalorimetry experiments were combined with molecular dynamic simulations to describe the interaction of different capped amino acids with the silica surface. We demonstrate that ion pairing is the dominant electrostatic interaction. Surprisingly, the interaction strength is more dependent on the repulsive carboxy group than on the attracting amino group. These findings are essential for conducting experimental and simulative studies on amino acids when transferring the results to biomolecule-surface interactions.

Simulation of Heat Flow Curves of NC‐Based Propellants – Part 2: Application to DPA Stabilized Propellants.

AbstractMeasuring of heat flow curves at temperatures near the in‐service range have become a standard for stability and compatibility assessments of nitrocellulose (NC)‐based energetic materials. The typical technique to realise this demand is heat flow microcalorimetry. The heat flow curves are the summarized effect of the rates of all the reaction heats in the mixture. The propellant composition has a significant influence on the shapes of the heat flow curves. To assess the stability on a firmer base, it is of interest to know what contributions to the total heat flow the individual reactions have from the NC decomposition and from the stabilizer reactions. This needs the simulation of the heat flow curves based on the individual reactions with their thermochemical data and their reaction rates. For this, the reaction enthalpies of all relevant reactions must be known. On these prerequisites was reported in part 1. With the data from there, the simulation of the heat flow curve of the ball powder propellant type K6210 was undertaken, using a reaction scheme for the nitrate ester decomposition and the DPA reactions. In principle, the here developed and applied procedure is usable for all types of NC‐based propellants and heat flow curves.

Kinetics and equilibrium adsorption of phosphate on lanthanum oxide supported on activated carbon

Understanding the thermodynamics and kinetics of phosphate adsorption is crucial in the design of packed-bed columns for phosphate removal, particularly in clinical applications such as dialysis, in which limited contact time is available. Studies have shown that the kinetics of phosphate adsorption on metal oxides is a two-step process: rapid initial adsorption that occurs in a few minutes to a few hours is followed by slower adsorption that may last for days. In this work, the thermodynamics and kinetics of phosphate adsorption on lanthanum oxide impregnated on activated carbon (La-AC) are investigated to explain its phosphate adsorption behavior. The phosphate adsorption mechanism was investigated by studying (1) the effects of temperature on phosphate adsorption capacity, (2) the dynamics and enthalpy of adsorption using flow microcalorimetry (FMC), (3) the kinetics of phosphate adsorption, and (4) the relationship between the amount of phosphate adsorbed and the amount of hydroxide released. Phosphate adsorption on La-AC followed the Langmuir isotherm. FMC results indicate that phosphate adsorbed through several mechanisms, principally through the formation of monodentate and bidentate inner-sphere surface complexes. A pseudo-second-order kinetic model is typically used to model phosphate adsorption; however, it was found that a kinetic model developed based on the assumption of two parallel surface adsorption reactions fits the measured adsorption kinetics significantly better than the pseudo-second order kinetic model that is almost universally used to describe phosphate adsorption kinetics. • Lanthanum-impregnated activated carbon was investigated as a phosphate adsorbent. • Phosphate adsorption was well described by the Langmuir isotherm. • Phosphate anions adsorbed on lanthanum surface via a parallel path mechanism. • A kinetic model based on the parallel path mechanism was developed. • Parallel path model fit kinetics much better than the pseudo-2nd-order model.

Interaction of Phosphate with Lithium Cobalt Oxide Nanoparticles: A Combined Spectroscopic and Calorimetric Study.

Adsorption of small ions such as phosphates to the surfaces of metal oxides can significantly alter the behavior of these materials, especially when present in the nanoscale form. Lithium cobalt oxide is a good model system for understanding small-molecule interactions with emerging nanomaterials because of its widespread use in lithium ion batteries and its known activity as a water oxidation catalyst. Here, we present a thermodynamic analysis of phosphate adsorption to LiCoO2 and corroborate the results with additional in situ techniques, including zeta potential measurements and attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy, at pH values relevant to potential environmental release scenarios. Flow microcalorimetry measurements of phosphate interaction with LiCoO2 at pH 7.4 show that there are two distinct exothermic processes taking place. Time-sequence in situ ATR-FTIR with two-dimensional correlation analysis reveals the spectroscopic signatures of these processes. We interpret the data as an interaction of phosphate with LiCoO2 that occurs through the release of two water molecules and is therefore, best described as a condensation process rather than a simple adsorption, consistent with prior studies, demonstrating that phosphate interaction with LiCoO2 is highly irreversible. Additional measurements for over longer times of 5 months show that phosphate adsorption terminates with one surface layer and that continued transformation over longer periods of time arises from H+/Li+ exchange and slow transformation to a cobalt hydroxide, with phosphate adsorbed to the surface only. To the best of our knowledge, this is the first time that flow microcalorimetry and two-dimensional correlation spectroscopy have been applied in tandem to clarify the specific chemical reactions that occur at the interface of solids and adsorbates.

Calorimetric approach to understand pH and salt influence on the adsorption mechanism of lysozyme to a traditional cation exchanger

Built upon our interest in illustrating the complexity of protein adsorption onto chromatographic supports and to understand the rule of nonspecific interactions in the ion exchange adsorption process, a traditional model system (lysozyme – carboxymethyl cellulose) was used to determine the charge influence during biomolecule adsorption. Flow microcalorimetry (FMC) was exploit as a dynamic technique that provides adsorption and desorption heat signals for a specific system, permitting an improved understanding of the driving forces and mechanisms involved during the interaction. For this purpose, measurements were made at pH 8 at both absence and presence of salt (NaCl 50 mM) and compared with previous studies performed at pH 5. Distinct FMC profiles were observed regarding pH. For most of the experiments, two exothermic heat signals are observed at pH 8 while at pH 5 one endothermic and one exothermic peak are shown. This difference was justified with a less energy demanding for desolvation at pH 8. Lysozyme adsorption was shown to be a multi-step process involving desolvation, primary protein adsorption and secondary adsorption after reorientation with distinct contributions to the overall energy. At pH 8, the exothermic contribution to the adsorption process is lower compared to pH 5, which is justified by the lower charge density that lysozyme presents at pH 8 compared to pH 5.

Mobile-Phase Modulators as Salt Tolerance Enhancers in Phenylboronate Chromatography: Thermodynamic Evaluation of the Mechanisms Underlying the Adsorption of Monoclonal Antibodies.

Phenylboronate chromatography has been employed for bioseparation applications though details concerning the mechanisms of interaction between the ligand and macromolecules remain widely unknown. Here, the phenomena underlying the adsorption of an anti-human interleukin-8 (anti-IL8) monoclonal antibody (mAb) onto an m-aminophenylboronic acid (m-APBA) ligandin the presence of different mobile-phase modulators (NaF/MgCl 2 /(NH 4 ) 2 SO 4 ) and under different pH values (7.5/8.5/9.0) is investigated. Flow microcalorimetry (FMC) is applied to measure instantaneous heat energy transfer, providing insights about the role of specific and nonspecific interactions involved in the adsorptive process. Results show that the adsorption of anti-IL8 mAb to m-APBA is enthalpically driven, corroborating the presence of the reversible esterification reaction between boronic acid or boronates and cis-diol-containing molecules. Nevertheless, for all mobile-phase modulators studied, changes in thermogram profiles are observed as well as reductions in the net heat of adsorption when increasing the pH. Overall, FMC and parallel chromatographic experiments data suggest that ligand salt tolerance could be enhanced using mobile-phase modulators, with all salts studied promoting the specific cis-diol interactions and reducing nonspecific interactions. The last feature is more noticeable at pH values above ligand's pK a , mainly due to the ability of NaF and (NH 4 ) 2 SO 4 to diminish electrostatic interactions when compared to the commonly used NaCl.

Antibody Binding Heterogeneity of Protein A Resins.

Protein A affinity chromatography is a core unit operation in antibody manufacturing. Nevertheless, there is not enough understanding of in-column antibody adsorption in the Protein A capture step. This work aims to investigate in situ the establishment of an antibody (trastuzumab) layer during Protein A chromatography both in terms of energetic contributions and uptake kinetics. Flow microcalorimetry is employed as a technique with an in situ operating detector, which provides an understanding of the thermodynamics of the adsorption process. In addition, the antibody uptake rate is also investigated in order to establish a correlation between its diffusion on the stationary phase and the associated thermodynamics. Two resins with different particle size, intraparticle porosity, and a Protein A ligand structure are studied: the synthetically engineered B-domain tetrameric MabSelect SuRe and the synthetically engineered C-domain hexameric TOYOPEARL AF-rProtein A HC. The uptake rate follows a pore diffusion model at low equilibrium time, showing a slower diffusivity after a certain time because of the heterogeneous binding nature of these two resins. In addition, the microcalorimetric studies show that adsorption enthalpy is highly favourable at low isotherm concentrations and evolves toward an equilibrium with increasing surface concentration. These data suggest that the relationship between adsorption enthalpy and the establishment of the antibody layer in the Protein A chain is consistent with heterogeneous adsorption.

Thermodynamics of the adsorption of monoclonal antibodies in phenylboronate chromatography: Affinity versus multimodal interactions

The aim of this work was to investigate the complex phenomena underlying the adsorption of an anti-human IL-8 (anti-IL8) monoclonal antibody (mAb) to m-aminophenylboronate (m-APBA) by Flow Microcalorimetry (FMC) and to understand the role of non-specific interactions in the adsorption process. FMC was exploited as a dynamic on-line method to measure instantaneous heat energy transfers in order to understand the surface phenomena underlying mAb’s adsorption towards the synthetic ligand m-APBA under different pH (7.5, 8.5, 9.0, 9.5 and 10.0) and salt concentrations (0 and 150 mM NaCl). Results showed that the adsorption of anti-IL8 mAb to m-APBA is enthalpically driven (ΔHads<0), as expected for the predominant reversible esterification reaction between boronates and cis-diols-containing molecules. For all the pH conditions studied, thermograms presented a first exothermic peak, characteristic of the reversible esterification reaction between mAb (pI≥9.3) and m-APBA (pKa = 8.8), except at pH 9.0 in the presence of 150 mM NaCl, for which the thermogram presented a first endothermic peak. The heat of adsorption (ΔHads) obtained at conditions where cis-diol interactions were predominant was approximately −243 ± 38 kJ/mol against −82 ± 14 kJ/mol (p-value < 0.05) obtained at pH 9.0 with 150 mM NaCl. The observed shift in the thermogram profile at pH 9.0, 150 mM NaCl, and the consequent decrease of 60–70% in ΔHads were indicative of the promotion of electrostatic interactions between the protein and the ligand. Overall, and whereas the binding of the PBA ligand to mAb molecules has been described for decades as being affinity-based, our study demonstrates the multimodal behaviour of this interaction and contributes towards the understanding of the adsorption thermodynamics.

Kinetics of the base catalysed hydrolysis of methyl paraben revisited: Implications for determination of the effective volume of flow-microcalorimeters used to study cell cultures

The kinetics of hydrolysis of methyl paraben (methyl 4-hydroxybenzoate, MP) by NaOH has been proposed as a reference system to calibrate the effective volume (Veff) of flow-calorimetry vessels that are often used in studies of living cells. This parameter is essential to relate the observed calorimetric signal with a specific cell number or biomass and its determination relies on a rate constant, k, obtained under the assumption of pseudo-first-order kinetics. The significant discrepancies noted between published k values led us to test the reliability of this approximation for different NaOH/MP concentration ratios and at temperatures in a range typically used for living cell studies (292–310K). Kinetic experiments carried out by spectrophotometry, isothermal microcalorimetry, and flow microcalorimetry indicated that the 9/1 NaOH/MP molar ratio typically used for Veff determinations does not ensure the pseudo-first-order kinetic conditions assumed in the Veff calculation model. It is recommended that a NaOH excess of at least 20/1 be used to warrant a<5% error in k, which translates into an identical error in Veff.

Green Carbon Composite-Derived Polymer Resin and Waste Cotton Fibers for the Removal of Alizarin Red S Dye

Phenolic resin and waste cotton fiber were investigated as green precursors for the successful synthesis using a soft template approach of a composite carbon with carbon nanofibers embedded in a porous carbon network with ordered and periodically pore structure. The optimal composite carbon (PhR/NC-1), exhibited a specific surface area of 394 m2∙g−1 with the existence of both microporosity and mesoporosity. PhR/NC-1 carbon was evaluated as an adsorbent of Alizarin Red S (ARS) dye in batch solution. Various operating conditions were examined and the maximum adsorption capacity of 104 mg∙g−1 was achieved under the following conditions, i.e., T = 25 °C, pH = 3, contact time = 1440 min. The adsorption and desorption heat was assessed by flow micro-calorimetry (FMC), and the presence of both exothermic and endothermic peaks with different intensity was evidenced, meaning a partially reversible nature of ARS adsorption. A pseudo-second-order model proved to be the most suitable kinetic model to describe the ARS adsorption according to the linear regression factor. In addition, the best isotherm equilibrium has been achieved with a Freundlich model. The results show that the eco-friendly composite carbon derived from green phenolic resin mixed with waste cotton fibers improves the removal of ARS dye from textile effluents.

ATR-FTIR and Flow Microcalorimetry Studies on the Initial Binding Kinetics of Arsenicals at the Organic-Hematite Interface.

The environmental fate of arsenic compounds depends on their surface interactions with geosorbents that include clays, metal oxides, and natural organic matter (NOM). While a number of batch studies reported that NOM inhibits the uptake of arsenicals, it remains unclear how different classes of organic functional groups affect their binding mechanisms. We report herein the adsorption kinetics of arsenate and dimethylarsinic acid (DMA) with hematite nanoparticles pre-exposed to three types of low molecular weight organics: citrate, oxalate, and pyrocatechol as representatives to the majority of reactive organic functional groups in NOM. These studies were conducted using attenuated total internal reflection Fourier transform infrared spectroscopy (ATR-FTIR) and flow microcalorimetry at pH 7 with an emphasis on the role that electrolytes (KCl, NaCl, and KBr) play in the adsorption process. Results show that (1) negatively charged carboxylate versus hydrophobic phenyl groups influence amounts and initial rates of arsenicals adsorption on hematite nanoparticles to varying degrees depending on the type of complexes they form, (2) the type of electrolytes affects initial adsorption rate of DMA to a greater extent than arsenate when oxalate is present on the surface, and (3) the extent of organics retention by hematite nanoparticles is influenced by the type of the desorbing agent.

Ion Exchange Thermodynamics at the Rutile-Water Interface: Flow Microcalorimetric Measurements and Surface Complexation Modeling of Na-K-Rb-Cl-NO3 Adsorption.

Flow microcalorimetry was used to investigate the energetics associated with Rb+, K+, Na+, Cl-, and NO3- exchange at the rutile-water interface. Heats of exchange reflected differences in bulk hydration/dehydration enthalpies (Na+ > K+ > Rb+, and Cl- > NO3-) such that exchanging Na+ or Cl- from the surface was exothermic, reflecting their greater bulk hydration enthalpies. Exchange heats were measured at pH 2, 3.25, 5.8, and 11 and exhibited considerable differences as well as pH dependence. These trends were rationalized with the aid of a molecularly constrained surface complexation model (SCM) that incorporated the inner-sphere binding observed for the cations on the rutile (110) surface. Explicitly accounting for the inner-sphere binding configuration differences between Rb+, K+, and Na+, as well as accompanying differences in negative surface charge development, resulted in much better agreement with measured exchange ratios than by considering bulk hydration enthalpies alone. The observation that calculated exchange ratios agreed with those measured experimentally lends additional credence to the SCM. Consequently, flow microcalorimetry and surface complexation modeling are a useful complement of techniques for probing the energetics associated with ion exchange and adsorption processes and should also serve to help validate molecular simulations of interfacial energetics.

An integrated flow microcalorimetry, infrared spectroscopy and density functional theory approach to the study of chromate complexation on hematite and ferrihdyrite

An approach to constructing comprehensive predictive models for contaminant interactions with mineral surfaces is to obtain multiples lines of evidence for surface properties and the types of complexes formed under different geochemical conditions. In this study, we used flow adsorption microcalorimetry (FAMC), attenuated total reflection infrared (ATR FTIR) spectroscopy, and density functional theory (DFT) calculations to study chromate complexation on ferrihydrite (FH) and hematite (HT). Under the experimental conditions used, chromate binds via an exothermic inner-sphere complexation on both surfaces, with similar enthalpy values that do not reveal dramatic differences in the sorption mechanism. Due to their underlying surface structure, FH favors more monodentate and HT more bidentate complexation. Chromate complexes were found by ATR and FAMC to be completely reversible, with substantially slower desorption compared to sorption. Both the FAMC and DFT indicated the presence of surface sites with different energetics, whereby lower surface coverages corresponded to higher enthalpies on both FH and HT. Both flow-based ATR and FAMC yielded different surface coverages than batch isotherms under the same conditions, highlighting the need to assess contaminant sorption under realistic conditions. Overall, this integrated approach proved to be an improved paradigm to study ion sorption on mineral surfaces.

Critical Evaluation of the Standard Molar Entropies, Enthalpies of Formation, Gibbs Energies of Formation and Heat Capacities of the Aqueous Trivalent Rare Earth Ions, and the Corresponding Standard Molar Entropies, Enthalpies of Formation and Gibbs Energies of Formation of the Thermodynamically Stable RECl3·7H2O(cr) and RECl3·6H2O(cr)

In an earlier evaluation (F.H. Spedding, J.A. Rard, A. Habenschuss, J. Phys. Chem. 81: 1069–1074, 1977) the standard molar entropies of the aqueous trivalent rare earth ions RE3+(aq) were calculated based on the standard molar entropies of the hydrated rare earth chlorides RECl3·7H2O(cr) (RE = La, Pr) and RECl3·6H2O(cr) (RE = Nd, Gd, Tb, Dy, Ho, Er, Lu) at T = 298.15 K and p = 0.1 MPa, along with their corresponding standard molar enthalpies and Gibbs energies of solution, which are known for nearly all of the RECl3·7H2O(cr) and RECl3·6H2O(cr) including YCl3·6H2O(cr). However, the entropies of these RECl3·7H2O(cr) and of several of the RECl3·6H2O(cr) have large uncertainties because the source heat capacities only extend up to T = 223–262 K and not to T = 298.15 K and the crystals used for these measurements contained some occluded solution (water excess). Simple methods are described to correct these entropies of the RECl3·7H2O(cr) and RECl3·6H2O(cr) and to estimate the standard molar entropies of the RECl3·6H2O(cr) from those of the corresponding anhydrous RECl3(cr). By using these entropies, standard molar enthalpies of solution and revised results for the standard molar Gibbs energy changes to form the saturated solutions, revised and CODATA-compatible values of the standard molar entropies of the RE3+(aq), $$ S_{\text{m}}^{\text{o}} ({\text{RE}}^{3 + } ,\,\,{\text{aq}},\,\,298.15\,\,{\text{K}}) $$ where RE = (La, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y), were evaluated or estimated (RE = Pm). By combining these results with critically-assessed standard molar enthalpies of formation of the RE3+(aq), the standard molar Gibbs energies of formation of these trivalent rare earth aquo ions were calculated, as were the corresponding standard molar Gibbs energies and enthalpies of formation of the thermodynamically stable RECl3·7H2O(cr) and RECl3·6H2O(cr) phases at T = 298.15 K and p = 0.1 MPa. In addition, standard molar heat capacities of most of the RE3+(aq) were evaluated from published results for dilute solutions from flow microcalorimetry.

Relating the Influence of Surface Characteristics of Carbon Electrocatalyst Support to the Performance and Durability of a PEMFC through Calorimetric, Adsorption, Spectroscopic and Electrochemical Measurements

The role played by the surface properties of carbon blacks used as electrocatalyst supports in fuel cell electrodes is crucial in determining the performance and durability characteristics of the final membrane electrode assembly. These key surface properties include the polar character arising from the presence of heteroatoms, and the proportion of the surface area that corresponds to graphitic carbon sites. We have used flow calorimetry to characterise the surface properties of a family of carbon blacks having the same BET surface area (400±10 m2/g), but different pore size characteristics and different properties in terms of polar and graphitic surface sites. The preferential heat of adsorption of n-dotriacontane and n-butanol for basal plane sites and polar sites respectively has been determined for the carbon sites immersed in n-heptane1. The overall hydrophobic character of the carbon surface was evaluated by measuring the heat of adsorption of n-butanol from its aqueous solution2. Platinum nanoparticles prepared by a microwave-assisted polyol method2 were deposited on each of the carbons, and the electrochemical surface area, the mass and specific activity of the Pt/C samples were determined. Membrane-electrode assemblies were prepared using the electrocatalysts at the cathode and they were tested in fuel cell over a range of temperatures and relative humidities, when the observed performance could be related to the relative hydrophobic/hydrophilic properties of the carbons. Further, the stability of the carbons to electrochemical corrosion was assessed by submitting them to high voltage (1.4 V/RHE) and determining the corrosion current and the corresponding mass loss, and the results related to the graphitic character of the carbons determined from flow microcalorimetry and Raman spectroscopy. This understanding will be beneficial in the tuned design of PEMFC electrocatalyst supports for the targeted operation conditions. This work demonstrates the importance of calorimetric methods in characterising carbons for electrochemical applications.

Urinary Tract Infections--Current Innovations in Urine Diagnostics

Urine culture (UC) confirms the diagnosis of urinary tract infection (UTI) and is still considered the diagnostic 'gold standard' for pathogen identification, quantification and resistance testing. However, up to 80% of samples will not yield bacterial growth. Different techniques are currently approved for resistance testing. However, all of them are culture based and have the disadvantage of being very slow. In the field of urology, the development of drug resistance of uropathogens complicates the optimal administration of antimicrobial agents not only in the treatment, but also in the prevention of UTI before endourological and open surgical procedures. In this context, rapid identification of microbiological agents, including timely antimicrobial resistance testing (ART) is desirable. This overview presents alternative techniques (flow cytometry, PCR-based techniques, MALDI-TOF MS and microcalorimetry) to urine culture and discusses their advantages and disadvantages.