Electrocatalytic Investigations of Cu(II) and Fe(III) Complexes of Salophen Derivative Schiff Bases on the Pencil Graphite Electrode

This present study describes a pencil graphite electrode surface covered with Cu(II) and Fe(III) complexes based on Salophen derivative Schiff bases in acetonitrile solution containing LiClO₄ as a supporting electrolyte. Cyclic voltammetry method was used for the surface modification procedure with 25 cycle at a sweep rate of 50 mV s^?1. Some characterization methods were used to identify of the prepared modified surfaces including cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), Ultraviolet‐visible Spectroscopy (UV‐Vis), and Scanning Electron Microscopy/Energy Dispersive X‐ray Spectroscopy (SEM/SEM‐EDX). The catalytic activity of these modified surfaces on the electrochemical oxidation of catechol (CC) was investigated and they compared with each other. The results demonstrated that these modified electrodes showed perfect electrocatalytic activity on the catechol determination, however the modified electrode prepared with the Cu(II) complex has higher catalytic activity than this prepared with the Fe(III) complex thanks to its the lower detection limit.     

XPS and ToF‐SIMS study of a chalcopyrite–pyrite–sphalerite mixture treated with xanthate and sodium bisulphite

We present data from the surface analysis of a mineral mixture of chalcopyrite, pyrite, and sphalerite, elucidating surface reactions occurring during grinding and flotation. Flotation tests are also performed on the mixture, carried out in the presence of collector (SIBX) and also in the absence and presence of sodium bisulphite (NaHSO₃), a gangue sulphide mineral depressant. X‐ray photoelectron spectroscopy (XPS) studies on the ground mineral sample prior to flotation indicate that the mineral feed is heavily oxidised, especially the sphalerite in the mixture. Flotation recovery data clearly shows the effect of this oxidation, with the mineral recoveries of all three phases being lower than those observed in single mineral studies. In addition, the flotation recoveries show the effect of the inadvertent copper activation of pyrite and sphalerite, and the effect of bisulphite in reducing the flotation of sphalerite and pyrite in the mixture. Time of flight secondary ion mass spectrometry(ToF‐SIMS) data indicates that the depressing effect of bisulphite is due to the removal of copper and sulphur‐like species from the surface of pyrite and sphalerite and a consequent increase in the oxidation of these minerals. ToF‐SIMS data also indicates that the low recovery of pyrite and chalcopyrite in the absence of collector is most likely due to precipitation of zinc hydroxide on the surfaces of these minerals, formed in solution due to copper activation of sphalerite. Copyright © 2005 John Wiley & Sons, Ltd.     

Electroreduction of oxygen on copper-containing sulfide minerals

The state of the surface of and the oxygen electroreduction on the naturally occurring minerals bornite, chalcopyrite, and chalcosine are studied in borate buffer solutions using X-ray photoelectron spectroscopy, cyclic voltammetry, and the rotating disk electrode technique. The surface of the minerals in an oxygen-containing atmosphere is covered with compounds of copper and iron in the highest oxidation states, and the oxygen electroreduction occurs on these compounds. Electrocatalytic activity of sulfide minerals during cathodic polarization is presumably due to the participation in the oxygen electroreduction reaction of redox centers, i.e. ions of Fe(II) in bornite and chalcopyrite, and ions of Cu(I) bonded with the sulfide sulfur in each of the minerals.     

Multi-instrument characterization of HiPIMS and DC magnetron sputtered tungsten and copper films

In this work, copper and tungsten were sputtered onto silicon wafers by direct current magnetron sputtering (DCMS) and high-power impulse magnetron sputtering (HiPIMS). The resulting films were characterized by energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM), spectroscopic ellipsometry (SE), and X-ray diffraction (XRD). By EDX and XPS, all the sputtered films showed only the expected metal peaks. By XPS, the surfaces sputtered by DCMS were richer in oxygen than those produced by HiPIMS. By AFM, the surfaces were quite smooth. The root mean square (RMS) roughness values are as follows: 0.83 nm (W, HiPIMS), 1.10 nm (W, DCMS), 0.85 nm (Cu, HiPIMS), and 1.78 nm (Cu, DCMS). By SEM, the HiPIMS films exhibited smaller grain sizes, which was confirmed by XRD. The crystallite sizes estimated by XRD are as follows: 4 nm (W, body-centered cubic, HiPIMS), 13 nm (W, body-centered cubic, DCMS), 7 nm (W, cubic, HiPIMS), 14 nm (W, cubic, DCMS), 25 nm (Cu, HiPIMS), and 35 nm (Cu, DCMS). By SE, the HiPIMS surfaces showed higher refractive indices, which suggested that they were denser and less oxidized than the DCMS surfaces.     

Aluminium preatreatment and the properties of adhesively bonded joints

The influence of metal pretreating on the properties of adhesively bonded joints was investigated. AlMg3 and several pre‐treatment methods were used. The pre‐treated surfaces and the joints were characterized using: SEM/EDX, XPS, EIS, surface tension, DMA, μTA and the determination of mechanical parameters. The highest bond strengths were obtained using anodic oxidation in phosphoric acid as the pre‐treatment method.     

Characterization of transition metal nitride formation in rapid thermal processing (RTP)

The potential of RTP for the preparation of transition metal nitrides by reaction of metal thin films in molecular nitrogen was investigated. The films and the nitridation process were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), energy dispersive x-ray analysis (EDX) in a scanning electron microscope (SEM) and secondary neutral mass spectrometry (SNMS). The chemical states of vanadium at the utmost surface, detected by XPS, are related to V₂O₅ before RTP and to vanadium nitride, oxide and oxynitride after RTP. The deposition of a 3 nm Si top layer prevents V from oxidation and its selective removal before RTP enhances the proportion of nitride determined by XPS after RTP. From comparative experiments in a conventional tube furnace the advantages of RTP became obvious. With short process times of the RTP technique the integral amount of residual oxygen is kept low and oxide formation is largely avoided. The nitrogen content and the different polycrystalline phases formed by varying process time and temperature provide information about reactivity and the nitridation process. The nitrogen to vanadium ratio was determined by EDX and SNMS, revealing that the N content reaches saturation after only 5 seconds at 1100?°C.     

Plasma-assisted oxidation of Cu(100) and Cu(111)

Oxidized copper surfaces have attracted significant attention in recent years due to their unique catalytic properties, including their enhanced hydrocarbon selectivity during the electrochemical reduction of CO₂. Although oxygen plasma has been used to create highly active copper oxide electrodes for CO₂RR, how such treatment alters the copper surface is still poorly understood. Here, we study the oxidation of Cu(100) and Cu(111) surfaces by sequential exposure to a low-pressure oxygen plasma at room temperature. We used scanning tunnelling microscopy (STM), low energy electron microscopy (LEEM), X-ray photoelectron spectroscopy (XPS), near edge X-ray absorption fine structure spectroscopy (NEXAFS) and low energy electron diffraction (LEED) for the comprehensive characterization of the resulting oxide films. O₂-plasma exposure initially induces the growth of 3-dimensional oxide islands surrounded by an O-covered Cu surface. With ongoing plasma exposure, the islands coalesce and form a closed oxide film. Utilizing spectroscopy, we traced the evolution of metallic Cu, Cu₂O and CuO species upon oxygen plasma exposure and found a dependence of the surface structure and chemical state on the substrate''s orientation. On Cu(100) the oxide islands grow with a lower rate than on the (111) surface. Furthermore, while on Cu(100) only Cu₂O is formed during the initial growth phase, both Cu₂O and CuO species are simultaneously generated on Cu(111). Finally, prolonged oxygen plasma exposure results in a sandwiched film structure with CuO at the surface and Cu₂O at the interface to the metallic support. A stable CuO(111) surface orientation is identified in both cases, aligned to the Cu(111) support, but with two coexisting rotational domains on Cu(100). These findings illustrate the possibility of tailoring the oxidation state, structure and morphology of metallic surfaces for a wide range of applications through oxygen plasma treatments.

A low-pressure oxygen plasma oxidized Cu(100) and Cu(111) surfaces at room temperature. The time-dependent evolution of surface structure and chemical composition is reported in detail for a range of exposure times up to 30 min.     

Cryo‐XPS study of xanthate adsorption on pyrite

The adsorption of xanthate on pyrite has been extensively studied. However, the adsorption mechanisms remain a subject of controversy. Formation of both dixanthogen and metal‐xanthate complexes has been suggested. In this study, both room temperature X‐ray photoelectron spectroscopy (XPS) (RT‐XPS) and liquid nitrogen temperature XPS (Cryo‐XPS) were used to study interactions between pyrite and xanthate. While dixanthogen was not detected by RT‐XPS, it was successfully identified through C1s and S 2p peaks using Cryo‐XPS. The impact of pH and copper activation on adsorption of xanthate on pyrite was also investigated. It was found that at low pH, dixanthogen is the dominant species of xanthate adsorption on pyrite. At high pH, metal‐xanthate complexes were found to be prevalent on pyrite surfaces, which are responsible for the surface hydrophobicity. Copper activation showed a significant effect on xanthate adsorption on Cu‐activated pyrite, resulting in mostly the formation of Cu‐xanthate complexes rather than dixanthogen, mainly in the form of Cu(I)‐isopropyl xanthate complex (CuIPX). Copyright © 2012 John Wiley & Sons, Ltd.     

Arsenopyrite and pyrite bioleaching: evidence from XPS, XRD and ICP techniques

In this work, a multi-technical bulk and surface analytical approach was used to investigate the bioleaching of a pyrite and arsenopyrite flotation concentrate with a mixed microflora mainly consisting of Acidithiobacillus ferrooxidans. X-ray diffraction, X-ray photoelectron spectroscopy (XPS) and X-ray-induced Auger electron spectroscopy mineral surfaces investigations, along with inductively coupled plasma-atomic emission spectroscopy and carbon, hydrogen, nitrogen and sulphur determination (CHNS) analyses, were carried out prior and after bioleaching. The flotation concentrate was a mixture of pyrite (FeS₂) and arsenopyrite (FeAsS); after bioleaching, 95% of the initial content of pyrite and 85% of arsenopyrite were dissolved. The chemical state of the main elements (Fe, As and S) at the surface of the bioreactor feed particles and of the residue after bioleaching was investigated by X-ray photoelectron and X-ray excited Auger electron spectroscopy. After bioleaching, no signals of iron, arsenic and sulphur originating from pyrite and arsenopyrite were detected, confirming a strong oxidation and the dissolution of the particles. On the surfaces of the mineral residue particles, elemental sulphur as reaction intermediate of the leaching process and precipitated secondary phases (Fe–OOH and jarosite), together with adsorbed arsenates, was detected. Evidence of microbial cells adhesion at mineral surfaces was also produced: carbon and nitrogen were revealed by CHNS, and nitrogen was also detected on the bioleached surfaces by XPS. This was attributed to the deposition, on the mineral surfaces, of the remnants of a bio-film consisting of an extra-cellular polymer layer that had favoured the bacterial action.     

Fracture‐induced reconstruction of a chalcopyrite (CuFeS2) surface

Two factors contributing to the high binding energy asymmetry of the S 2p XPS peak for virginal chalcopyrite (CuFeS₂) surfaces have been identified. The Cu, Fe and S 2p spectra of freshly fractured surfaces of chalcopyrite have been found to display a loss feature at ～2.6 eV that is attributed to an interband transition S 3p → Fe 3d, from occupied S levels to unoccupied Fe levels. For leached chalcopyrite systems, intensity on that side of the S 2p peak sometimes has been interpreted erroneously in terms of oxidized species such as polysulphides. A second prominent S 2p component has been determined at a binding energy of 161.9 eV and identified as the sulphide dimer S₂^2?. With supporting evidence, a simultaneous surface reconstruction and redox reaction model has been developed for the fracturing of chalcopyrite, leading to an exposed surface phase of about two layers thick with a 50% pyritic content. The pyritic nature of the fractured chalcopyrite surface has implications for understanding the leaching chemistry of chalcopyrite. Copyright © 2003 John Wiley & Sons, Ltd.     

Adsorption states of dialkyl ditelluride autooxidized monolayers on Au(111)

Organic ditellurides (R2Te2 where R = n-butyl (C4), n-octyl (C8), and n-cetyl (C16)) were synthesized, and their adsorption states after oxidation on Au(111) surfaces were studied by X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), theoretical analyses, near-edge X-ray absorption fine structure (NEXAFS) measurements, contact angle measurements, and atomic force microscopy (AFM). The obtained results show that dialkyl ditellurides form autooxidized monolayers (AMs) on the surfaces under ambient conditions and that the oxidation process is accelerated by ambient light. XPS, UPS, and theoretical analyses suggest that the autooxidized ditelluride species consist of polymers or oligomers with Te-O-Te-O network structures stabilized by oxygen bridges between tellurium molecules following the cleavage of tellurium-gold bonds. NEXAFS and contact angle measurements indicate that the average tilt angles of the alkyl chains from the surface normal are smaller for the AMs of dialkyl ditellurides having longer alkyl chains. AFM measurements show defects and roughness features around a few angstroms in height on the surfaces of the dialkyl ditelluride AMs.     

构建稳定的CuO/La2Sn2O7催化剂用于碳烟颗粒燃烧:CuO在La2Sn2O7烧绿石复合氧化物载体上的单层分散行为

柴油车尾气排放的碳烟颗粒造成了日益严重的环境污染.目前催化燃烧是消除碳烟颗粒污染的有效技术.针对金属氧化物负载体系,20世纪70年代末谢有畅教授等人提出了单层分散理论,是指导设计高效负载催化剂的一个重要思想,已被科研工作者们普遍接受.当负载催化剂体系用于某个特定反应时,通常会表现出单层分散阈值效应,即负载的活性组分含量...     

Surface analytical characterisation of Nd:YAG-laser pre-treated Al Mg3 as a preparation for bonding

The contribution summarises results of the surface pre-treatment of Al Mg3 (EN-AW-5754) for bonding applications. Mainly the sheet samples were irradiated with a pulsed solid-state laser in different atmospheres. Afterwards the pre-treated surfaces were analysed by quantitative topographic measurements, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and electrochemical impedance spectroscopy (EIS). The effect of surface pre-treatment on the strength of adhesively bonded specimens was evaluated by tensile lap-shear strength tests. The results were compared with conventional pre-treatment methods, such as anodic oxidation and others.     

Sorption of selenium(IV) and selenium(VI) onto synthetic pyrite (FeS2): spectroscopic and microscopic analyses

Pyrite was hydrothermally synthesized and used to remove Se(IV) and Se(VI) selectively from solution. Surface analyses of pyrite before and after contact with Se(IV) and Se(VI) were conducted using X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and atomic force microscopy (AFM). All solid samples were acquired by allowing 3.1 mmol/L of Se(IV) or Se(VI) to react with 1 g/L of pyrite for 1, 15, or 30 days. The XPS spectra were fitted using the XPSPEAK program that applies a Gaussian Lorentzian function. The fitted spectra indicate that Se(IV) more strongly reacts with the surface-bound S than with the surface-bound Fe of pyrite. However, there is no apparent evidence of surface reaction with Se(VI). Specifically, fitted XPS spectra showed the presence of sulfide and tetrathionate on the surface, indicating that sulfur (S(2)(2-)) at the surface of pyrite can be both oxidized and reduced after contact with Se(IV). This occurs via surface disproportionation, possibly resulting in the formation of surface precipitates. Evidence for the formation of precipitates was seen in SEM and AFM images that showed rod-like particles and a phase image with higher voltage. In contrast, there were no important changes in the pyrite after contact with Se(VI) over a period of 30 days.     

Voltammetry and XPS analysis of a chalcopyrite CuFeS2 electrode

A chalcopyrite CuFeS₂ electrode obtained from the “El Teniente” mine (Chile) has been studied by cyclic voltammetry (CV) in a borax alkaline solution at pH 9.2 and by X-ray photoelectron spectroscopy (XPS) before and after the electrochemical treatment at oxidation and reduction potentials. The voltagram shows two peaks in the positive sweep direction which can be assigned to an oxidation process at the electrode surface that involve the formation of Fe₂O₃ and CuO giving rise to an irregular surface layer of the electrode with islands of different chemical composition. The XPS results confirm the formation of Fe₂O₃ and CuO at the electrode surface and their stability against decomposition at reduction potential. In addition, the formation of FEOOH, CuFeO and CuS species at the electrode surface can be deduced by XPS as well as a covering of the whole electrode surface by species due to carbon–oxygen groups.     

Low-temperature reduction of NO(2) on oxidized Mo(110)

The reactions of nitrogen dioxide (NO(2)) were investigated on oxidized Mo(110) containing both chemisorbed oxygen and a thin film oxide. NO(2) reacts on both oxidized Mo(110) surfaces via a combination of reversible adsorption and reduction to NO, N(2), and trace amounts of N(2)O below 200 K. On the surface containing chemisorbed O, there is some complete dissociation of NO(2) to yield N(a) and O(a). N(2) forms at high temperatures through atom combination. On both surfaces, NO is the predominant product of NO(2) reduction. However, the chemisorbed layer which has a low oxidation state, and hence a greater capacity to accept oxygen, more effectively reduces NO(2). The selectivity for N(2) formation over N(2)O is greater for NO(2) as compared with NO on both surfaces studied. The selectivity changes are largely attributed to an increase in the concentration of Mo=O species and a change in the distribution of oxygen on the surface. Notably, more oxygen, in particular Mo=O moieties, is deposited by NO(2) reaction than by O(2) reaction, indicating that NO(2) is a stronger oxidant. The fact that there are several N-containing species on the surface at low temperatures may also affect the product distribution. On both surfaces, N(2)O(4), NO(2), and NO are identified by infrared spectroscopy upon adsorption at 100 K. All N(2)O(4) desorbs by 200 K, leaving only NO(2) and NO on the surface. Infrared spectroscopy of NO(2) on (18)O-labeled surfaces provides evidence for oxygen transfer or exchange between different types of sites even at low temperatures.     

Wettability interpretation of oxygen plasma modified poly(methyl methacrylate)

Poly(methyl methacrylate) (PMMA) has been modified via a dc pulsed oxygen plasma for different treatment times. The modified surfaces were characterized by X-ray photoelectron spectroscopy (XPS), optical profilometer, zeta potential, and advancing contact angle measurements. The measured advancing contact angles of water decreased considerably as a function of discharge. Several oxygen-based functionalities (carbonyl, carboxyl, carbonate, etc.) were detected by XPS, while zeta potential measurements confirmed an increase in negative charge for the treated PMMA surface. Evaluating the correlation between the concentration of polar chemical species and zeta potential, we found that increase in surface hydrophilicity results from the coeffect due to incorporation of oxygen functional groups and creation of charge states. The electrical double layer (EDL) effect was also considered in contact angle interpretation by introducing an additional surface tension term into Young's equation. We also found that EDL contribution to the solid-liquid interfacial tension is negligible and can be safely ignored for the systems considered here.     

In situ electrochemical characterization of natural pyrite as a galvanic catalyst using single-particle microelectrode technique in ferric sulfate solutions

Ferric reduction on the surface of pyrite, a major factor governing the overall kinetics of pyrite-assisted leaching of chalcopyrite in sulfate solutions, is investigated. In order to study the effect of pyrite on chalcopyrite leaching, four different pyrite samples were used in the leaching process. A single-particle microelectrode technique was employed to investigate the electrochemical and semiconducting properties of different pyrite samples by means of cyclic voltammetry (CV), electrochemical impedance spectroscopy, and Mott–Schottky methods in a solution containing 0.5 mol/L sulfuric acid, 0.005 mol/L ferric sulfate, and 0.005 mol/L ferrous sulfate. During leaching, differences were observed in the behavior of different pyrite samples. CV showed a difference in the magnitude of the ferric reduction reaction peaks. An equivalent analog circuit was used to model the impedance spectra, which led to the conclusion that pyrite samples with lower charge transfer resistance are better catalysts for ferric reduction. Mott–Schottky analysis was used to quantify variations in some semiconductive and electrical properties of pyrite samples from different geographical locations.     

A review of the fundamental studies of the copper activation mechanisms for selective flotation of the sulfide minerals, sphalerite and pyrite

A review of the considerable, but often contradictory, literature examining the specific surface reactions associated with copper adsorption onto the common metal sulfide minerals sphalerite, (Zn,Fe)S, and pyrite (FeS(2)), and the effect of the co-location of the two minerals is presented. Copper "activation", involving the surface adsorption of copper species from solution onto mineral surfaces to activate the surface for hydrophobic collector attachment, is an important step in the flotation and separation of minerals in an ore. Due to the complexity of metal sulfide mineral containing systems this activation process and the emergence of activation products on the mineral surfaces are not fully understood for most sulfide minerals even after decades of research. Factors such as copper concentration, activation time, pH, surface charge, extent of pre-oxidation, water and surface contaminants, pulp potential and galvanic interactions are important factors affecting copper activation of sphalerite and pyrite. A high pH, the correct reagent concentration and activation time and a short time delay between reagent additions is favourable for separation of sphalerite from pyrite. Sufficient oxidation potential is also needed (through O(2) conditioning) to maintain effective galvanic interactions between sphalerite and pyrite. This ensures pyrite is sufficiently depressed while sphalerite floats. Good water quality with low concentrations of contaminant ions, such as Pb(2+)and Fe(2+), is also needed to limit inadvertent activation and flotation of pyrite into zinc concentrates. Selectivity can further be increased and reagent use minimised by opting for inert grinding and by carefully choosing selective pyrite depressants such as sulfoxy or cyanide reagents. Studies that approximate plant conditions are essential for the development of better separation techniques and methodologies. Improved experimental approaches and surface sensitive techniques with high spatial resolution are needed to precisely verify surface structures formed after copper activation. Sphalerite and pyrite surfaces are characterised by varying amounts of steps and defects, and this heterogeneity suggests co-existence of more than one copper-sulfide structure after activation.     

Spectroscopic studies of trimetoxypropylsilane and bis(trimethoxysilyl)ethane sol-gel coatings on aluminum and copper

Trimethoxypropylsilane (TMPS) and bis(trimethoxysilyl)ethane (BTMSE) were used as surface modifiers of metal vie the sol-gel process and dip coating. In addition to the single coating of Al, Cu and Sn, double treatments of Al were also conducted by combining coatings with these sol-gels in different sequences. Reflection and absorption infrared spectroscopy (RAIR) was employed to characterize and to trace the proceeding of the sol-gel process of the films. It was found that the silanol condensation occurs in the coating films on Al and the covalent linkage exists between the TMPS film and copper surface. From the assigned vibration modes, two conformers were identified in pure TMPS, TMPS sol-gel and coated film. A series of dip coating experiments with different concentrations of TMPS sol-gel was conducted, and the results from the collected RAIR spectra of the coated samples suggested that the coated Cu consistently has a better RAIR spectrum than that of the coated Al. The TMPS sol-gel appeared to have a better affinity to Cu than to Al. The temperature effect and the aging effect in the coating films were studied. X-ray photoelectronic spectroscopy (XPS) was employed to characterize the coated film, and the XPS data confirm the formation of the siloxane film from the silane coupling agents (SCA). Electrochemical impedance spectra (EIS) have been collected for bare Al and Cu, BTMSE sol-gel coated Al, and TMPS sol-gel coated Cu in 0.15M NaCl solution. The corresponding electronic circuit parameters have been determined to match the experimental EIS data.