Chalcopyrite Leaching in the Presence of Isopropanol-The Kinetic and Mechanistic Studies.

Oxidative leaching, as a basic step of the hydrometallurgical process of pure copper production from chalcopyrite, is a slow process in which mineral acids with strong oxidants addition are usually used as a leaching medium. It was found experimentally that the copper leaching from chalcopyrite in the H2SO4-H2O2-H2O system, in the presence of isopropanol (IPA) and under other conditions (H2O2 concentration, rate of mixing and temperature), takes place with satisfactory rate and efficiency. To quantify how much the change of these crucial variables affects the rate of the process, experimentally obtained kinetic curves (conversion over time) were analyzed using a Shrinking Core Model (SCM). The determined values of the copper leaching rate constants (kobs) confirmed the positive influence of increasing IPA and H2O2 concentrations as well as the temperature on the kinetics and efficiency of the leaching. The kinetic studies were also supported by using X-ray diffraction (XRD), 57Fe Mössbauer spectroscopy, scanning electron microscopy (SEM), and adsorption measurements. The positive influence of IPA was explained by its stabilizing role for iron compounds (hematite, magnetite, and pyrite), which are catalysts during the Cu dissolution, as well as H2O2 protection from decomposition during free radical reactions. Finally, the optimal conditions for efficient leaching, the rate-limiting step as well as the mechanism suggestion of the copper dissolution, were given.

The Kinetics of the Redox Reaction of Platinum(IV) Ions with Ascorbic Acid in the Presence of Oxygen.

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.

Determination of the Dielectric Constant of Niobium Oxide by Using Combined EIS and Ellipsometric Methods.

Combining ellipsometric and EIS methods, the dielectric constant ε for the oxide Nb2O5 at room temperature was determined. At first, the linear dependence between anodization voltage and oxide thickness was established in the form d = 2.14 (± 0.05) · U + 12.2 (± 1.7) nm in the range of anodizing potentials 0-50 V. Next, assuming the equivalent circuit corresponds to one, the capacitance C of the dense oxide layer was measured. All results taken together gave the value of dielectric constant ε = 93 ± 5.

Batch Reactor vs. Microreactor System for Efficient AuNP Deposition on Activated Carbon Fibers.

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.

On the Rate of Interaction of Sodium Borohydride with Platinum (IV) Chloride Complexes in Alkaline Media.

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.

Micro Droplet Formation towards Continuous Nanoparticles Synthesis.

In this paper, micro droplets are generated in a microfluidic focusing contactor and then they move sequentially in a free-flowing mode (no wall contact). For this purpose, two different micro-flow glass devices (hydrophobic and hydrophilic) were used. During the study, the influence of the flow rate of the water phase and the oil phase on the droplet size and size distribution was investigated. Moreover, the influence of the oil phase viscosity on the droplet size was analyzed. It was found that the size and size distribution of the droplets can be controlled simply by the aqueous phase flow rate. Additionally, 2D simulations to determine the droplet size were performed and compared with the experiment.

Green method for efficient PdNPs deposition on carbon carrier in the microreactor system.

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.

From dynamic self-assembly to networked chemical systems.

Although dynamic self-assembly, DySA, is a relatively new area of research, the past decade has brought numerous demonstrations of how various types of components - on scales from (macro)molecular to macroscopic - can be arranged into ordered structures thriving in non-equilibrium, steady states. At the same time, none of these dynamic assemblies has so far proven practically relevant, prompting questions about the field's prospects and ultimate objectives. The main thesis of this Review is that formation of dynamic assemblies cannot be an end in itself - instead, we should think more ambitiously of using such assemblies as control elements (reconfigurable catalysts, nanomachines, etc.) of larger, networked systems directing sequences of chemical reactions or assembly tasks. Such networked systems would be inspired by biology but intended to operate in environments and conditions incompatible with living matter (e.g., in organic solvents, elevated temperatures, etc.). To realize this vision, we need to start considering not only the interactions mediating dynamic self-assembly of individual components, but also how components of different types could coexist and communicate within larger, multicomponent ensembles. Along these lines, the review starts with the discussion of the conceptual foundations of self-assembly in equilibrium and non-equilibrium regimes. It discusses key examples of interactions and phenomena that can provide the basis for various DySA modalities (e.g., those driven by light, magnetic fields, flows, etc.). It then focuses on the recent examples where organization of components in steady states is coupled to other processes taking place in the system (catalysis, formation of dynamic supramolecular materials, control of chirality, etc.). With these examples of functional DySA, we then look forward and consider conditions that must be fulfilled to allow components of multiple types to coexist, function, and communicate with one another within the networked DySA systems of the future. As the closing examples show, such systems are already appearing heralding new opportunities - and, to be sure, new challenges - for DySA research.

Kinetic studies of nucleation and growth of palladium nanoparticles.

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.

The influence of the route of administration of gold nanoparticles on their tissue distribution and basic biochemical parameters: In vivo studies.

BACKGROUND: The gold nanoparticles (AuNP's) exhibit interesting chemical and physical properties and for this reason are intensively tested in medicine. However there is a lack of information about toxicity of those nanoparticles as well as their excretion from the body. Thus, the aim of the present study was to investigate the influence of the route of administration of gold nanoparticles to rats on their distribution in tissues and excretion rate. METHODS: The experiment was carried out on male Wistar rats. The colloidal gold suspension containing 0.3619 mg of particles per milliliter, was administered per 1 kg of body weight. Serum levels of alanine aminotransferase, aspartate aminotransferase, total cholesterol, triglycerides, glucose and ferric reducing ability of plasma were measured in all investigated animals. RESULTS: It was shown that after oral administration only a small amount of AuNPs was absorbed. In addition, excretion of the metal during consecutive days after po or iv administration was examined. Moreover, the impact of AuNPs on some biochemical parameters 3 days after intravenous administration was studied. It was shown that the AuNPs are mainly cumulated in the liver, lungs and in spleen after iv administration and only slightly removed from the body in urine and feces. CONCLUSION: Accumulation of those nanoparticles effect in increases of FRAP and glucose level up to 27% and 73%, respectively. This in turn suggests that iv administration of AuNPs may effect in serious medical complications. On the other site, the accumulation in the liver of about 50% of introduced particles to the rats body is promising for phototherapy and it opens "door" for drug transport to this organ.

Tissue distribution of gold nanoparticles after single intravenous administration in mice.

BACKGROUND: Nanoparticles (a part of matter which size is less than 100 nm) have numerous potential applications in biomedicine, due to their unique surface, electronic and optical properties. The goal of the present study was to examine the distribution of gold nanoparticles (GNPs) in mice after single intravenous administration. METHODS: Spherical GNPs were synthesized by chemical reduction of tetrachloroauric acid with ascorbic acid as a reductant. GNPs were stabilized using polyvinyl alcohol (PVA, m.w. = 67000Da) a substance approved for use in the pharmaceutical industry. The size of colloidal gold particles (diameter equals 25 ± 8 nm) was determined using HR SEM and DLS techniques; ζ potential of GNPs was determined using Malvern Zetasizer Nano ZS and it equals -5.2 ± 5.4 mV. An aqueous dispersion of GNPs was administered to mice in a dose of about 10 cm(3)/kg and 24 h later the amount of gold in different organs was determined using the inductively coupled plasma mass spectrometer (ICP MS). Initial concentration of GNPs equals 29.55 mg/l. RESULTS: GNPs after single intravenous administration preferentially accumulated in the liver (12.7% of the applied dose), while the other organs accumulated around 0.1% or less. CONCLUSION: Colloidal GNPs of the used size (about 25 ± 8 nm) provide new potential route for direct delivery system to the liver, which may be important e.g., in liver cancer diagnosis.