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In this work, UV-Vis spectrophotometry, High Resolution Scanning Transmission Electron Microscopes and selected experimental conditions were used to screen the colloidal system. The obtained results complement the established knowledge regarding the mechanism of nanoparticle formation. The process of gold nanoparticles formation involves a two-step reduction of Au ions to Au(0); atom association and metastable cluster formation; autocatalytic cluster growth; ultra-small particle formation (1–2 nm, in diameter); particle growth and larger particles formation; and further autocatalytic crystal growth (D > 100 nm). As a reductant of Au(III) ions, a cinnamon extract was used. It was confirmed that eugenol as one of the cinnamon extract compounds is responsible for fast Au(III) ion reduction, whereas cinnamaldehyde acts as a gold-particle stabilizer. Spectrophotometry studies were carried out to track kinetic traces of gold nanoparticle (D > 2 nm) formation in the colloidal solution. Using the Watzky—Finke model, the rate constants of nucleation and autocatalytic growth were determined. Moreover, the values of energy, enthalpy and entropy of activation for stages related to the process of nanoparticle formation (Index 1 relates to nucleation, and Index 2 relates to the growth) were determined and found to be E1 = 70.6 kJ, E2 = 19.6 kJ, ΔH1 = 67.9 kJ/mol, ΔH2 = 17 kJ/mol, ΔS1 = −76.2 J/(K·mol), ΔS2 = −204.2 J/(K·mol), respectively. In this work the limitation of each technique (spectrophotometry vs. HRSTEM) as a complex tool to understand the dynamic of the colloidal system was discussed. [ABSTRACT FROM AUTHOR]

In this work, the kinetics of the redox reaction between platinum(IV) chloride complex ions and ascorbic acid is studied. The reduction process of Pt(IV) to Pt(II) ions was carried out at different reagent concentrations and environmental conditions, i.e., pH (2.2–5.1), temperature (20–40 °C), ionic strength (I = 0.00–0.40 M) and concentrations of chloride ions (0.00–0.40 M). The kinetic traces during the reduction process were registered using stopped-flow spectrophotometry. Based on the kinetic traces, the rate constants were determined, and the kinetic equations were proposed. It was shown that in the mild acidic medium (pH = 2.5), the reduction process of Pt(IV) to Pt(II) ions is more complex in the presence of oxygen dissolved in the aqueous solutions. For these processes, the values of the enthalpy and entropy of activation were determined. Moreover, the mechanism of the reduction of Pt(IV) to Pt(II) ions was proposed. The presented results give an overview of the process of the synthesis of platinum nanoparticles in the solution containing oxygen, in which the reduction process of Pt(IV) to Pt(II) ions is the first step. [ABSTRACT FROM AUTHOR]

In this paper, a novel method for the synthesis of Pt nanoparticles (PtNPs) using a microwave autoclave reactor is proposed. For benchmarking, the obtained results are compared with the traditional, batch method. A novel process window is proposed, which is the application of high-temperature and high-pressure. The main finding is that this only brings advantage, when the ionic strength of the system is enough low. It is explained, that at high pressure and high temperature, water behaves like only a slightly polar solvent, approaching a subcritical state. This reduces the electrostatic stabilization of the particles. Moreover, a change in the Pt particle shape is observed under high pressure and temperature conditions, suggesting that additional physical–chemical processes are involved. [ABSTRACT FROM AUTHOR]

This work presents a detailed description of a commonly used and low-cost evaluation process that is simply based on the nonlinear fitting of concentration-, time- and temperature-dependent surface plasmon resonance (SPR) sensorgrams in order to provide kinetic and thermodynamic characterization of a biologically relevant interaction. Regardless of type, this evaluation proceeding is maximally suitable to manage the time-dependent sensor signals of other quasi two-dimensional sensor techniques, like quartz crystal microbalance (QCM) or optical waveguide lightmode spectroscopy (OWLS). Based on the hypothetic reaction schemes, the SPR signals have been fitted by the analytical solutions of the rate equations using optional spreadsheet software. Statistical tests of the goodness of nonlinear fits confirm the application of a reversible, pseudo first order kinetic model, in this way the apparent (k obs), the association (k a) and the dissociation (k d) constants as well as the equilibrium constants (K A) and the Gibbs free energy change (ΔG) have been calculated at six different temperatures. The enthalpy (ΔH 0 ), entropy (ΔS 0 ) and heat capacity changes (ΔC p) have also been estimated using nonlinear regression analysis. The sign and values of the state functions approve the presence of a salt bridge between a model polypeptide fragment of human glutamate receptor (ANYT) and kynurenic acid (KYNA) which was confirmed by molecular docking calculations as well. • Surface plasmon resonance based, in-situ biomimetic modelling and monitoring • Evaluation process for concentration-, time- and temperature-dependent sensorgrams • Kinetic and thermodynamic characterization of a biologically relevant interaction • Confirmation of predicted salt bridge between the kynurenic acid and receptor model [ABSTRACT FROM AUTHOR]

Abstract In this paper process of gold(III) chloride adsorption from an aqueous and semi-aqueous system was described. It was found, that the adsorption of gold(III) ions from aqueous solutions leads to a metallic gold formation at the surface of activated carbon. The size of the particles after adsorption is significant and can be seen with the naked eye. In all studied cases, if the adsorption was carried out from an aqua solution, more than 95% of the gold was removed from the solution. In the case of the semi-aqueous system, also metallic gold was obtained, however, the particles size is in the nanometric scale. Moreover, an equilibrium in the system was observed. Highlights • Activation parameters for the gold adsorption process were determined. • It was shown that the water take part in the reaction. • Presence on neutral salt changes shape of formed gold structure. • Kinetic of the process is under mixed control. [ABSTRACT FROM AUTHOR]

• Kinetics of cis – trans complex isomerization during Pd – azocompound complex formation. • Metal-organic frameworks formation in the aging process. • TD-DFT calculations was using as a tool for Pd-MO complexes structure confirmation. In this work, we follow the process of metalorganic complex formation between Pd(II) ions and 4-[4-(D imethylamino) phenylazo ]benzenesulfonic acid sodium salt (methyl orange) in the area of its tautomeric equilibrium. Using UV–Vis spectrophotometry we followed intermediate stages related to inorganic complex association, ligand exchange, cis – trans complex isomerization, and bonding of metal to nitrogen and carbon in the phenyl ring. Obtained double kinetic curves registered at 470 and 273 nm suggest, that the process of complex formation and the cis – trans isomerization is first order in respect to methyl orange. For the process of metalorganic complex formation the activation parameters like energy, enthalpy, and entropy were determined (E A = 45.69 k J m o l , Δ H ≠ = 43.1 ± 1.8 k J m o l , Δ S ≠ = − 172.6 J / (mol · K) , respectively) using Arrhenius and Eyring dependencies. Moreover, based on obtained results coming from spectrophotometric study and DFT calculations, the mechanism and molecular structure of the intermediates and products during the process of metalorganic complex formation, were proposed. It was shown, that process takes place in four stages. The two first are related to N – Pd and Pd – C bond formation, and the next one is associated with H- shaped bridge formation. As the last one is aging leading to more complex structure building and finally to metal-organic frameworks formation. [ABSTRACT FROM AUTHOR]

The process of noble metals ions recovery and the removal small fraction of nanoparticles from waste solution is an urgent topic not only from the economic but also ecology point of view. In this paper, the use of activated carbon fibers (ACF) as a "trap" for gold nanoparticles obtained by a chemical reduction method is described. The synthesized nanoparticles were stabilized either electrostatically or electrosterically and then deposited on carbon fibers or activated carbon fibers. Moreover, the deposition of metal on fibers was carried out in a batch reactor and a microreactor system. It is shown, that process carried out in the microreactor system is more efficient (95%) as compared to the batch reactor and allows for effective gold nanoparticles removal from the solution. Moreover, for similar conditions, the adsorption time of the AuNPs on ACF is shortened from 11 days for the process carried out in the batch reactor to 2.5 min in the microreactor system. [ABSTRACT FROM AUTHOR]

[Display omitted] • Selective Pd(II) ions determination using methyl orange. • Aging of cyclopalladated complex allows for efficient methyl orange removal. • {PdCl(dmso)} 2 (µ-azb) complex for ultra-small amount of Pd(II) determination. The proper determination of Pd(II) ions in the presence of Pt(IV) ions in a waste solution is an intricate analytical issue. Having the knowledge about waste composition, we are able to properly design processes and their selective separation and recovery. Other important aspect is related to the dyes removal coming from textile industry, which is still not resolved. To solve these issues, in this work, we propose the twin solution, which describes a specialized method allowing for both selective Pd(II) ions determination and methyl orange removal. These processes take place in the range of tautomeric equilibrium of methyl orange (pH = 3 – 5). In order to follow the process of cyclopalladated compounds formation, UV–Vis spectra were registered at different conditions, i.e. pH, temperature as well as in the presence of different anions: Cl ̅ and ClO 4 ̅ and cations: Na+, K+, Pt4+, Pt2+, Co2+, Ni2+, Zn2+, Cu2+. The developed method of Pd(II) ions determination is distinguished by high sensitivity and selectivity, even in the presence of Pt(IV) ions. Moreover, the palladium content can be determined using UV–Vis spectroscopy at two wavelengths, i.e. at 560 and 702 nm at 50°C. This extends the possibility of metal detection in the presence of cations having spectra in similar wavelength ranges. It is also concluded, that the process of removal of methyl orange is possible only in water: obtained product is unstable and forms an easy-filtratable blue/purple coloured precipitate. [ABSTRACT FROM AUTHOR]

Highlights: [•] The reaction reduction of Pt(IV) ions with NaBH4 is zero order reaction. [•] Kinetic equation allowed for establish of microreactor parameters: flow rate, length. [•] 3.5–5nm platinum nanoparticles are synthesized in microreactor. [•] The catalyst consists of PtNPs was deposited on ACFs in one microreactor cycle. [ABSTRACT FROM AUTHOR]

Highlights: [•] Gold nanoparticles synthesis and deposition on a graphene oxide sheet in microflow reactor was investigated. [•] Size and size distribution can be controlled by the flow rate. [•] Application of strong reductant (DMAB) leads to the formation of very small nanoparticles of size about 3nm. [•] Graphene oxide sheets plays an important role as a stabilizing agent for gold nanoparticles. [Copyright &y& Elsevier]

Abstract: The synthesis of gold nanoparticles consists of several stages, i.e. reduction, nucleation and growth. The most important step in particles formation process is the reduction reaction of Au(III) ions to Au(I). The rate of such reaction determines the rate of nuclei formation, i.e. reduction reaction of Au(I) to Au(0) and thus the rate of nanoparticles formation. In this paper, the kinetics and mechanism of redox reaction between gold(III) chloride complex ions and l-ascorbic acid in the aqueous solution have been carried out using spectrophotometric technique. From the experimentally obtained kinetic curves the rate constants of reaction at different conditions of initial concentrations of reactants, pH, temperature, ionic strength and concentration of chloride ions, were determined. It was found that in strong acidic solution (pH 1.3), the values of enthalpy (ΔH ‡) and entropy (ΔS ‡) of activation were 38.5kJ/mol and −89.5kJ/molK, respectively and at higher pH (pH 2.5) the values of ΔH ‡ and ΔS ‡ were 42.0kJ/mol and −64.5kJ/molK, respectively. Using obtained results, the kinetic equation was determined and corresponding mechanism of reaction was suggested. Obtained data can be useful for calculating time of nuclei formation and consequently for better size control and size distribution of particles, e.g. in a microreactor. [Copyright &y& Elsevier]

In this work, sodium borohydride was used as a strong reductant of traces of platinum complex ions. The investigations of the kinetics of redox reaction between platinum(IV) chloride complex ions and sodium borohydride were carried out. For the first time, the kinetic experiments were carried out in a basic medium (pH~13), which prevents NaBH4 from decomposition and suppresses the release of hydrogen to the environment. The rate constants of Pt(IV) reduction to Pt(II) ions under different temperatures and concentrations of chloride ions conditions were determined. In alkaline solution (pH~13), the values of enthalpy and entropy of activation are 29.6 kJ/mol and –131 J/mol K. It was also found that oxygen dissolved in the solution strongly affects kinetics of the reduction process. Using collected results, the reduction mechanism was suggested. For the first time, the appearance of diborane as an intermediate product during Pt(IV) ions reduction was suggested. Moreover, the influence of oxygen present in the reacting solution on the rate of reduction reaction was also shown. [ABSTRACT FROM AUTHOR]

The synthesis of palladium nanoparticles and conditions of their deposition on active carbon fibers in the microreactor was described. All processes related with metal ion reduction, nucleation, and autocatalytic growth of particles as well as their deposition were carried out in the microreactor in only one cycle. Synthesis of palladium nanoparticles was carried out under different conditions, i.e., changing the initial concentration of metal ions and the reductant, at 40 °C. Depending on the conditions imposed, the nanoparticles of different size (hydrodynamic radius change from 12 to 37 nm) and shape (spherical, cube, pyramid) were obtained. It was also shown that flow conditions allow for much more efficient Pd deposition on active carbon fibers than the process carried out in the batch. It was observed that for concentrations of Pd(II) ions higher than 0.2 mM, the degree of fiber surface coverage increased significantly in comparison with the batch process. [ABSTRACT FROM AUTHOR]

The selective determination of metals in waste solutions is a very important aspect of the industry and environmental protection. Knowledge of the contents and composition of the waste can contribute to design an efficient process separation and recovery of valuable metals. The problematic issue is primarily the correct determination of metals with similar properties such as palladium and platinum. Thus this paper focuses on the development of a selective method that enables Pd(II) determination in the presence of Pt(IV) ions using the azo-dye tropaeolin OO (TR). For this purpose, the process of the metalorganic complex formation and Pd(II) ions determination were studied by using UV–Vis spectrophotometry under different conditions: solvents (water and B-R buffer), pH (2.09–6.09), temperature (20–60 °C), anions and cations concentrations. The formed metalorganic complex between Pd and tropaeolin OO allows for distinguishing Pd(II) ions from both platinum complexes, i.e. Pt(II), Pt(IV). Moreover, the proposed method can be applied to solutions containing both chloride and chlorate ions. The obtained characteristic spectrum with two maxima allows the determination of palladium even in the presence of other cations (Na, K, Mg, Zn, Co, Ni, Al) and changed concentrations of Pt(IV) ions. Furthermore, the developed spectrophotometric method for the Pd(II) ions determination using tropaeolin OO is characterized by high selectivity towards palladium ions. [ABSTRACT FROM AUTHOR]

In this paper, the kinetic studies of nucleation and growth processes of palladium nanoparticles formation are presented. As a palladium precursor the chloride complex of Pd(II) and as a reductant l -ascorbic acid, were used. Kinetic studies were conducted under different experimental conditions such as initial concentration of metal ions, ascorbic acid, chloride ions as well as at different temperature and ionic strength. Using Finke–Watzky model kinetic rate constants were established and discussed. The value of activation enthalpy and entropy have also been determined using Eyring–Polanyi equation. For all obtained colloids, plasmons and values of hydrodynamic radius were registered. [ABSTRACT FROM AUTHOR]

Abstract: Kinetics of gold(III) chloride complex ions reduction with dimethylamine borane and precipitation of gold nanoparticles was investigated. The influence of concentrations of reductant, gold(III) chloride complex ions, neutral salt and chloride ions as well as temperature on the process was reported. Experimental results were used to determine parameters in the Arrhenius equation. A set of reactions occurring in the system was proposed. Rate equations were presented and verified. It was proposed that state of the catalytic surface of gold particles play a crucial role in the mechanism of the reaction and competition between AuCl4 − adsorption and AuCl4 − reduction on the metal particles exists in the system. Microscopic observations as well as analysis of the particles were also performed. [Copyright &y& Elsevier]

In this paper precisely controlled silver nanoparticles synthesis method using microdroplets as a reactor was shown. It was confirmed that the application of microdroplets effects in a decrease in particles size and size distribution in comparison with a typical batch reactor from 4.8 ± 1.3 nm to 2.5 ± 0.5 nm. This decrease of particles size distribution is directly related to the fact, that thanks to the application of microdroplets as reactors the mass transfer limits were eliminated. [ABSTRACT FROM AUTHOR]

Abstract: In these studies, the flow microreactor system was used as a valuable tool for controlled synthesis of gold nanoparticles (AuNPs) with the narrow size distribution. As a method of synthesis, the reduction of gold(III) chloride complex ions using glucose as a reducing agent was carried out. Synthesis was performed in the presence of different amount of PVP (polyvinylpyrrolidone) as a stabilizing agent. The optimal conditions inside the microreactor system (concentrations and the flow rate of components) were established as a results of kinetic measurements in the batch reactor. In these studies the rate constants of AuNPs formation (nucleation and growth) as a function of different reductant concentration as well as temperature were determined using UV–Vis spectrophotometry and Dynamic Light Scattering (DLS) method. Experimentally obtained kinetic data gave us the chance to formulate the rate law of AuNPs formation which further was used to establish synthesis conditions. Applying T-type geometry of microchannels connection, for different reactant and PVP flow rates the injection of PVP at the proper time of AuNPs growth was done. It was found that applied method is promising one for the stabilization and preparation of gold nanoparticles with well-defined shape (spheres) and with narrow size distribution. [Copyright &y& Elsevier]

• Diffusion impact on the silver nanoparticles crystal structure is shown. • Hexagonal crystal structure 4H and 2H of Ag nanoparticles were synthesized. • 4H and 2H crystals transform to more dense packed FCC. • Mass synthesis of 4H and 2H structure is possible. In this paper diffusion impact on the silver nanoparticles synthesis and their crystal structure is shown. For this purpose, comparative studies between continuous flow two-phase microdroplets systems vs. two-phase batch reactor were performed. Such two-phase configuration of the investigated system makes it possible to study the impact of mass transfer phenomenon on the nanoparticles formation process. In the case of two-phase microdroplets system, diffusion is replaced by convection, accelerated by interphase friction between water droplets and a continuous organic phase. It was concluded that under diffusion control it was possible to obtain silver nanoparticles with a hexagonal crystal structure. Moreover, for the first time using a chemical method, and diffusion rate-limiting step, the hexagonal structure 4H and 2H of Ag nanoparticles were synthesized. We suggest, that such hexagonal crystals can be applied as a smart drug delivery system, where the drug releases can be controlled by short light impulse. In effects, thermodynamically unstable 4H and 2H crystals transform to more dense-packed FCC structure. [ABSTRACT FROM AUTHOR]