Robert P. Socha

Photocatalytic Activity of Titanium Dioxide Modified by Silver Nanoparticles

Photocatalytic activity of Ag/TiO(2) composites obtained by photoreduction treatment (PRT) was investigated. The composite materials, containing various ratio of silver nanoparticles (0.6-3.7 wt %) were obtained by depositing silver on the Evonic-Degussa P25 titania surface. Selected samples whose color varied between light rose and purple brown were examined by SEM, TEM, XPS, DRS, and BET techniques. Flat band potential was determined using Roy method. TEM analysis showed spherically shaped silver nanoparticles of the diameter 4-12 nm. The XPS measurements revealed that silver particles were obtained mainly in metallic form. DRS spectra and photovoltage measurements showed that silver nanoparticles modified the P25 spectral properties but they changed neither the band gap nor the location of flat band potential. The photocatalytic activity of Ag/P25 composite was compared to the photocatalytic activity of pure P25 in the photooxidation reaction of an important potable water contaminant humic acid (HA) and two model compounds, oxalic acid (OxA) and formic acid (FA). The photodecomposition reaction was investigated in a batch reactor containing aqueous suspension of a photocatalyst illuminated by either UV or artificial sunlight (halogen lamp). The tests proved that a small amount of silver nanoparticles deposited on the titania surface triggers the increase in photocatalytic activity; this increase depends, however, on the decomposed substance.

Electrochemical investigation of the codeposition of SiC and SiO2 particles with nickel

The use of electrochemical impedance spectroscopy (EIS) for the in situ control of the electrolytic codeposition of Ni/SiO2 and Ni/SiC was investigated. An attempt was made to clarify why silica particles hardly codeposit in comparison to silicon carbide particles. It was found that the presence of SiO2 and SiC particles influences the metal deposition process in different ways. SiC particles that are being embedded in the growing metal layer cause an apparent decrease in the electrode surface area, probably due to blocking off a part of the surface by partly engulfed particles. In the case of SiO2 particles, which embed in the metal matrix to a very limited extent, no blocking was observed. It was found that the presence of particles in the solution causes an apparent increase in the electrode surface area, probably due to increased surface roughness.

Synthesis and antimicrobial activity of monodisperse copper nanoparticles.

Metallic monodisperse copper nanoparticles at a relatively high concentration (300 ppm CuNPs) have been synthesized by the reduction of copper salt with hydrazine in the aqueous SDS solution. The average particles size and the distribution size were characterized by Dynamic Light Scattering (DLS), Nanosight-Nanoparticle Tracking Analysis (NTA). The morphology and structure of nanoparticles were investigated using Scanning Electron Microscopy (SEM). The chemical composition of the copper nanoparticles was determined by X-ray Photoelectron Spectroscopy (XPS). Monodisperse copper nanoparticles with average diameter 50 nm were received. UV/vis absorption spectra confirmed the formation of the nanoparticles with the characteristic peak 550 nm. The antimicrobial studies showed that the copper nanoparticles had high activity against Gram-positive bacteria, standard and clinical strains, including methicillin-resistant Staphylococcus aureus, comparable to silver nanoparticles and some antibiotics. They also exhibited antifungal activity against Candida species.

Influence of the surface properties of silicon carbide on the process of SiC particles codeposition with nickel

The influence of different treatment of SiC particle surface on the rate of codeposition of SiC particles with nickel in the process of SiC/Ni composite preparation was investigated. The hydrophobicity of SiC surface was characterized by contact angle measurements in the system SiC/liquid (water or plating bath)/air. Simultaneously the surface oxidation of SiC was investigated by XPS. The hydrophobic properties of SiC and its susceptibility to codeposition with nickel were compared with those of silica, a strongly hydrophilic substance. It was found that oxidation of the SiC surface, also due to the contact of its surface with plating bath, decreases significantly its hydrophobicity, diminishing at the same time the ratio of codeposition with nickel. However SiC does not oxidize easily and aggressive oxidation (long contact with concentrated H2O2 solution) is required to attain the hydrophilicity of the surface comparable to silica. At moderate oxidizing conditions, intermediate oxidation products (SiOxCy) appear at the SiC surface, which make the surface only partly hydrophilic.

Modification of niobium surfaces using plasma electrolytic oxidation in silicate solutions

Herein, a study of the plasma electrolytic oxidation (PEO) of niobium in an anodising bath composed of potassium silicate (K2SiO3) and potassium hydroxide (KOH) is reported. The effects of the K2SiO3 concentration in the bath and the process voltage on the characteristics of the obtained oxide layers were assessed. Compact, barrier-type oxide layers were obtained when the process voltage did not exceed the breakdown potential of the oxide layer. When this threshold was breached, the morphology of the oxide layer changed markedly, which is typical of PEO. A significant amount of silicon, in the form of amorphous silica, was incorporated into the oxide coatings under these conditions compared with the amount obtained with conventional anodising. This surface modification technique led to an improvement in the corrosion resistance of niobium in Ringer’s solution, regardless of the imposed process conditions.

Electrodeposition of thin metallic layer for solar cell electrodes

Purpose – The paper aims to show application of the electrochemically deposited coatings for thickening of the screen printed electric paths potentially applied in photovoltaic cells. Design/methodology/approach – The electric paths were screen printed with the use of silver-based paste. The paths were thickened by electrodeposition of thin copper layer in potentiostatic regime from surfactant-free plating bath. The morphology and surface quality of the paths were studied by imaging with scanning electron microscopy. Findings – The electric paths can be thickened successfully, but quality for the screen printed substrate determines quality of deposited layer. The EDX analysis confirmed that the deposited copper layer covered uniformly the printed paths. Research limitations/implications – The adhesion of the copper-covered path to the silicon wafer surface depends on adhesion of the original screen printed path. Originality/value – This paper confirms that electrodeposited copper can be applied for screen...

Electrochemically deposited nanocrystalline InSb thin films and their electrical properties

We present an electrochemical route to prepare nanocrystalline InSb thin films that can be transferred to an industrial scale. The morphology, composition, and crystallinity of the prepared uniform and compact thin films with a surface area of around 1 cm2 were investigated. The essential electrical characteristics such as conductivity, Seebeck coefficient, the type, concentration and mobility of charge carriers have been examined and compared with InSb nanowires obtained in the same system for electrochemical deposition (fixed pulse sequence, temperature, electrolyte composition, and system geometry). Moreover, obtained thin films show much higher band gap energy (0.53 eV) compared to the bulk material (0.17 eV) and InSb nanowires (0.195 eV).

Tuning the polarity of charge transport in InSb nanowires via heat treatment

InSb nanowire (NW) arrays were prepared by pulsed electrodeposition combined with a porous template technique. The resulting polycrystalline material has a stoichiometric composition (In:Sb = 1:1) and a high length-to-diameter ratio. Based on a combination of Fourier transform infrared spectroscopy (FTIR) analysis and field-effect measurements, the band gap, the charge carrier polarity, the carrier concentration, the mobility and the effective mass for the InSb NWs was investigated. In this preliminary work, a transition from p-type to n-type charge transport was observed when the InSb NWs were subjected to annealing.

Copper deposition on screen printed electrical paths for solar cell application

Purpose – The aim of this paper is to present results of investigations carried out on the front electrode of solar cells. Nowadays, most worldwide solar cell production is dominated by monocrystalline and polycrystalline silicon as a base material. In such cells, the electrical carriers are collected by the system of metallic paths fabricated on a silicon surface. One possible way to increase cell efficiency and reduce the production costs of solar modules is to replace the expensive silver by cheaper copper in front metallic electrodes. Design/methodology/approach – The paper presents results of investigations performed on the front electrode of the solar cell. The investigations were focused on the modification of typical screen printing fabrication of the thin electrical finger paths of the front solar cell electrode. The resulting contacts were characterized morphologically (the dimensions and geometry of the front contacts) by scanning electron microscopy. The composition of finger path covered with...

Kinetic Studies of Gold Recovery from Diluted Chloride Aqueous Solutions Using Activated Carbon Organosorb 10 CO

The kinetic studies of gold(iii) chloride complex ions recovery from acidic solution using activated carbon (AC) were carried out using spectrophotometry. AC samples were characterized in terms of surface area, porosity, and zeta potential. The surface functional groups were also identified. It was found that adsorption of AuCl4– onto AC was followed by reduction of the ions to the metallic form. The process obeyed the first order reaction model, but the reaction was controlled by diffusion. Arrhenius and Eyring–Polanyi equations were used for determination of the activation parameters. Distribution of gold across the AC pellets was also determined and discussed according to the porous material theory.