Electrochemical Pretreatment of Polymers with Dilute Nitric Acid Either Alone or in the Presence of Silver Ions

X-ray Photoelectron spectroscopy (XPS) was used to detect major changes to the surface chemistry of polypropylene (PP), high density polyethylene (HDPE) and styrene-butadiene block copolymer (SBS) caused by electrochemical treatment using dilute nitric acid as electrolyte. Large increases in adhesion levels were observed with PP and HDPE. The method has the potential to be a commercial pretreatment that is inexpensive and safe. Further treatments were carried out in which the complex ion (AgNO₃)⁺ was generated electrochemically. Effective pretreatment was achieved even with dilute solutions (0.001 M w.r.t. silver nitrate). Mechanisms are tentatively proposed for the electrochemical treatment when simply using an electrolyte of dilute nitric acid or where the anolyte consists of a solution of silver nitrate in dilute nitric acid.     

Electrochemical recovery of silver from waste aqueous Ag(I)/Ag(II) redox mediator solution used in mediated electro oxidation process

The paper presents a process for the electrochemical recovery of silver(Ag) by electro deposition on the electrode surface from the waste solutions of Ag(I)/Ag(II) redox system in nitric acid medium used for the mediated electrochemical process. Electrochemical recovery was carried out in an undivided cell with DSA-O₂ electrodes at room temperature condition. At an optimized current density of 12 A/dm², 99% of Ag recovery efficiency was achieved with high yield and low energy consumption. Experimental runs were made in order to observe the performance of the Ag recovery process. The operating conditions like current density, temperature and Ag(I) concentration of the electrolyte, the acid concentrations, agitation rate and inter-electrode distance were optimized.     

Pretreatment of polypropylene films for the creation of thin polymer layers,part 1: The use of chemical,electrochemical, and UV methods

The surface of a polypropylene (PP) film was activated with chemical, electrochemical, and physical methods, and the effectiveness of these methods was compared. The effects of PP activation were assessed with attenuated total reflection IR spectroscopy (ATR‐IR), SEM microscopy, and an analysis, based on the liquid contact angle, of the free energy components of the surface. The activation of the PP surface, which was dependent on the oxidizing medium, increased the energy of the PP surface layer and formed new chemical (carbonyl) groups, which were identified by IR (ATR) absorption spectroscopy and confirmed by selective surface dyeing. The treatments were ranked in the following order of increasing effectiveness: UV irradiation < 3M nitric acid < 30% hydrogen peroxide < silver nitrate (electrochemical method) < chromic mixture. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Leaching and electrochemical recovery of copper,lead and tin from scrap printed circuit boards

The recovery of copper, lead and tin from scrap printed circuit boards (PCBs) has been achieved using a combination of leaching, electrochemical ion exchange and electrodeposition. A simple aqueous nitric acid stripping solution, with the concentration range of 1–6 mol dm^?3, has demonstrated the potential for selective extraction of copper and lead from the PCBs. Precipitation of tin as H₂SnO₃ (metastannic acid) occurred at acid concentrations above 4 mol dm^?3. Preliminary galvanostatic electrolysis from simulated leaching solutions has investigated the feasibility of electrodeposition of copper and lead at different concentrations of HNO₃. Cathodic lead deposition, particularly at high electrolyte conditions, resulted in poor current efficiency. This was mainly due to dentritic metal formation and subsequent re‐dissolution. An alternative method investigated for recovering the metal values was the simultaneous electrodeposition of copper at the cathode and lead dioxide at the anode. Electrohydrolysis for acid and base regeneration from the spent nitric acid electrolyte has also been investigated. © 2002 Society of Chemical Industry     

Modeling and optimization of dilute nitric acid hydrolysis on corn stover

BACKGROUND: Because of its high cost, nitric acid has not been widely employed as the catalyst for hydrolysis of lignocellulosic biomass to obtain fermentable sugars. However, recently more and more research results have reported that nitric acid was more effective than other acids for the hydrolysis of lignocellulose. Therefore, it is necessary to find an optimum condition for nitric acid pretreatment and a means of reducing the cost. RESULTS: In this work, low concentrations of nitric acid and short reaction times were considered to optimize the pretreatment process. The kinetic parameters of models to predict the concentrations of xylose, glucose, arabinose, acetic acid and furfural in the hydrolysates were obtained. Applying the kinetic models, the optimum conditions were: 150 °C, 0.6% HNO₃ and 1 min, which yielded a solution containing up to 22.01 g L^?1 xylose, 1.91 g L^?1 glucose, 2.90 g L^?1 arabinose, 2.42 g L^?1 acetic acid and 0.21 g L^?1 furfural, which were consistent with the predicted values. The influence of temperature was also studied using the Arrhenius equation. CONCLUSIONS: A combination of experimental data and model analysis suggested that 96% xylose yield can be achieved by using low concentration nitric acid for a short reaction time, which could greatly reduce the pretreatment cost. Therefore, dilute nitric acid could be considered a good choice for the hydrolysis of corn stover. Copyright © 2010 Society of Chemical Industry     

Desulfurization of gasoline by a new method of electrochemical catalytic oxidation

A new deep desulfurization process for gasoline was obtained by means of electrochemical catalytic oxidation with an electrochemical fluidized-bed reactor on particle group anode. The particle group anode was activated carbon-supported cerium dioxide (CeO₂/C), and the electrolyte was aqueous cerium nitrate solution, and copper pillar was cathode in the electrochemical reactions. The CeO₂/C particle group anode could remarkably accelerate the electrochemical reaction rate and promote the electrochemical catalysis performance for the electrochemical desulfurization reaction. Thermodynamics feasibility analysis clarified that the theoretical decomposition voltage ranged from 0.1–0.5 V in pure acid electrolyte system and desulfurization reactions could not spontaneously carry out, but the reactions were spontaneous when aqueous cerium nitrate solution serves as electrolyte. And the rule of the gasoline desulfurization by the means of electrochemical catalytic oxidation was investigated. The experimental results indicated that the optimal desulfurization conditions were as follows: the cell voltage, concentration of the Ce³⁺ ions, feed volume flow rate and the CeO₂ percentage by weight were 3.2 V, 0.08 mol l⁻¹, 300 ml min⁻¹ and 5.0 wt%, respectively. Under these conditions the concentration of sulfur in gasoline was reduced from 310 to 50 parts per million by weight (ppmw). Based on these experimental results, a mechanism of indirect electrochemical oxidation was also proposed.     

Preparation and Characterization of Antibacterial Ag2O-Coated HDPE Films Obtained by Vacuum Evaporation Technique

To obtain the antibacterial plastics films, the Ag₂O-coated HDPE films were prepared through vacuum evaporation technique via depositing Ag₂O on the substrate of high density polyethylene (HDPE) films pretreated by ion bombardment. The pretreatment made the surface polarity and roughness of the substrates improved. The coating was continuous and dense, being of about 17.2 nm thick, and the content of silver ions in it was 7.0020 µg/cm². The Ag₂O-coated HDPE films exhibited strong antibacterial activity for both gram-negative bacteria (E. coli) and gram-positive bacteria (S. aureus). However, the mechanical properties of the composite films slightly dropped in contrast with the HDPE films.     

Adhesion Improvement by UV Grafting onto Polyolefin Surfaces

High Density Poly(ethylene) (HDPE) and Poly(propylene) (PP) were subjected to several surface treatments, namely UV grafting of hydroxyethylmethacrylate (HEMA), plasma deposition of HEMA and oxygen plasma treatment. Treated surfaces were subjected to two post-treatment routines (extraction with ethanol and high temperature aging). The effect of these treatments on the adhesion of HDPE and PP to epoxy coated studs was evaluated by a pull test. No adhesion at all was recorded on untreated samples. On the other hand, all the treatments yield high bond strength in the case of HDPE: an average bond strength of about 290 kg/cm² and of about 200 kg/cm² was observed after UV grafting and plasma treatments. The treated samples were practically insensitive to post-treatments. As to PP, which undergoes chain scission in plasma, it is best treated by the comparatively milder conditions of UV grafting, which yields an average bond strength similar to that observed on HDPE. O₂ and HEMA-plasma-treated PP show a mean bond strength close to 50 kg/cm², and are deeply affected by the post-treatment routines.     

Cobalt(III)-mediated oxidative destruction of phenol using divided electrochemical cell

Mediated electrochemical oxidation is one of the suitable processes for the destruction of hazardous organic compounds and the dissolution of nuclear wastes at ambient temperature and pressure. The electrochemical oxidation of Co(II) was carried out in an undivided and divided electrochemical cell. The formation of Co(III) was studied in an divided electrochemical cell by varying conditions such as temperature and concentration of nitric acid in a batch type electrochemical reactor in recirculation mode. It was found that the formation of Co(III) increased with increasing nitric acid concentration and decreased with increasing temperatures. The produced Co(III) oxidant was then used for the destruction of phenol. It was noted that phenol could be mineralized to CO₂ and water by Co(III) in nitric acid under different nitric acid concentrations and temperatures. The evolved CO₂ was continuously measured and used for the calculation of destruction efficiency. The destruction was increased with increasing nitric acid concentration as well as the temperature. The maximum efficiency was observed to be 78% based on CO₂ evolution for 5,000 ppm phenol solution at 60 °C in a continuous feed mode. The destruction efficiency was increased 28% by addition of silver at 25 °C.     

The electrochemical behaviour of silver sulphide in sulphuric acid solutions

The electrochemical behaviour of synthetic silver sulphide (acanthite) electrodes in sulphuric acid solutions has been investigated using several techniques including cyclic voltammetry, anodic polarization and constant potential experiments. Under anodic polarization the dissolution has been attributed to the reaction Ag₂S=2Ag⁺+S+2e which occurs in two sequential, single electron transfer steps. A kinetic model for this stepwise anodic dissolution process at lower overpotential, where the current is a function of potential, is provided. At high dissolution rates (i.e. high currents) the slightly soluble silver sulphate salt is formed on the surface due to the saturation of the electrolyte near the Ag₂S interface. This observation is supported by the influence of electrolyte composition on the cyclic voltammetry and the polarization curve. A paralinear film growth model has been found to describe the formation and growth of the silver sulphate product layer indicating an initial region of parabolic kinetics which gradually changes to linear kinetics as the rate of film dissolution approaches that of film formation.     

从废胶片中回收硝酸银

研究了直接用稀硝酸溶液浸渍胶片制取硝酸银 ,考察了浸银的最佳工艺条件。银的浸出率可达 10 0% ,制备的硝酸银纯度可达 99.5 %以上。方法简单可行 ,同时碱解聚酯废料制取对苯二甲酸 (PTA) ,PTA的纯度可达 96 %以上 ,经原子吸收光谱法分析其杂质含量很低     

Novel method for fabrication of PP/HDPE/PP trilayer microporous membrane with a highly orientated structure

In this work, a highly orientated polopropelene/high-density polyethylene/polopropelene (PP/HDPE/PP) trilayer cast film was obtained from viscous encapsulation of HDPE and PP which involved of controlling the molecular factors and processing conditions. Consequently, a stable stratified flow was obtained as a result of phase-segregation through a single screw extruder under a high draw ratio (DR). Microporous HDPE, PP monolayer films as well as PP/HDPE/PP trilayer film have been successfully fabricated after a proper cold and hot stretching. The influence of DR and annealing process on crystalline structure and orientation of monolayer and trilayer membrane was investigated by differential scanning calorimetry, two-dimensional wide-angle X-ray diffraction and Fourier transform infrared. Both crystallinity and crystalline orientation increased with DR and annealing process. Additionally, the crystallinity in PP/HDPE/PP was lower than it in monolayer films but the orientation of PP/HDPE/PP was higher compared to monolayer films. The lamellae structure of HDPE, PP, and PP/HDPE/PP cast films prepared at different DR values and the influence of annealing process was also studied. The lamellae parameters, the long period (L_p ), the thickness of crystalline region (L_c ) and the thickness of amorphous region (L_a ) were obtained via 2D-small angle X-ray scattering. The long period (L_p ) of PP was 35% smaller than HDPE implying tight stacking in PP. The scanning electron microscopy micrographs of the membrane surface morphology and cross-section obtained from the cold and hot stretching of 30% and 150%, respectively. The results showed that the pore size of HDPE was greater than PP. Besides, the pore number and regularity of PP/HDPE/PP at DR = 90, which had a porosity of 0.48, was the best among all samples. The cross-section of PP/HDPE/PP trilayer membrane was found to be a multilayer structure. However, the majority of HDPE phase was in the middle of film while PP phase was absolutely at the edge of the film. The current work may open an entirely novel and simple way to fabricate PP/HDPE/PP trilayer microporous films. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47249.     

Electrochimie du polynitrure de soufre dans les solvants non aqueux—I. Comportement dans l'acetonitrile

The electrochemical behaviour of polysulphur nitride was studied by cyclic voltametry in alkaline and silver salt acetonitrile solutions. In an alkaline salt solution during the cathodic polarization, superficial degradation of (SN)_x probably gives S₇N^? ions. In a silver perchlorate solution silver deposition was observed. It can be dissolved anodically. During the first anodic polarization, oxidation pic occurs. The quantity of electricity involved during this reaction is a function of the association constant of the electrolyte.     

Synthesis,Ion Exchange Properties,and Applications of Amorphous Cerium(III) Tungstosilicate

Abstract

A novel hetropolyacid-based cation exchanger cerium(III) tungstosilicate was synthesized in amorphous form by mixing tungstosilisic acid (TSA) solutions to cerium(III) nitrate solutions at different Ce:TSA ratios. The materials were precipitated from the liquid phase by raising the pH of the solutions using sodium hydroxide. The produced ion exchange powders were characterized using powder X-ray diffractometry, thermogravimetry, infrared spectrometry, inductively coupled plasma and atomic absorption elemental analysis. The materials which were dried at 50°C were found to be stable in water, dilute acids, alkaline solutions, and high temperature up to 1000°C. The Ion exchange properties of the synthesized samples were studied by measuring the distribution coefficients (K_d) for 29 metal ions in demineralized water and nitric acid media. On the basis of K_d values, some quantitative separations such as Co²⁺-Pb²⁺, Cr³⁺-Zr⁴⁺, and Mo⁶⁺- W⁶⁺ are achieved on their columns.     

Electrodeposition of Poly(3-hydroxyaniline) from Acidic Aqueous/Acetonitrile Solution

Electrodeposition of poly (3-hydroxyaniline) on platinum electrode from acidic/acetonitrile medium was carried out using cyclic voltammetry technique. The kinetic parameters were calculated by means of ex-situ microgravimetric and electrochemical data. The experimentally obtained kinetic equations were R_P,W = k_W [acid]^0.91 [monomer]^1.2 [electrolyte]^0.69 from microgravimetric data and R_P,E = k_E[acid]^0.92 [monomer]^0.96 [electrolyte]^0.7 from the values of the anodic current density using cyclic voltammetry technique. The apparent activation energy was calculated by the two techniques and is found to be 145.5 and 143.6 kJ/mol from microgravimetric and electrochemical data, respectively. The mechanism of the electrochemical polymerization reaction has been discussed and thermogravimetric analysis (TGA) is used to confirm the proposed structure and determination of the number of water molecules in the polymeric chain unit.     

Electrochemical study of TiO2 modified with silver nanoparticles upon CO2 reduction

A systematic cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) study on titanium dioxide (TiO₂) and silver–TiO₂ surfaces was performed in order to decouple electrochemical reduction processes of carbon dioxide in aqueous solutions. CV studies indicate cathodic current increase on Ag–TiO₂ compared to bare TiO₂ surfaces. An equivalent circuit based on transmission line model was applied in order to adjust EIS data, and a modification of this model was made to account for Ag particle interaction with the electrolyte solution. Electrochemical processes were then decoupled upon applied potential where the role of TiO₂ surface states was identified and separated from (a) silver reduction, (b) electronic transport on TiO₂, and (c) charge transfer on TiO₂ and Ag surfaces. The Ag–electrolyte interface impedance has considerably lower values than the TiO₂–electrolyte interface, suggesting that the silver particles may be considered as favorable reaction sites for the electrochemical reduction of water and carbon dioxide.     

Development and characterization of silver and zinc doped bioceramic layer on metallic implant materials for orthopedic application

A successful electrodeposition method for preparing silver and zinc modified bioactive calcium phosphate layers onto surgical grade titanium alloy material (Ti6Al4V) was developed. The coatings were deposited on the Ti6Al4V surface by pulse current at 70 °C from an electrolyte containing adequate amounts of calcium nitrate, ammonium dihydrogen phosphate, zinc nitrate and silver nitrate. The corrosion resistivity of the bioceramic coatings was assessed in conventional Ringer׳s solution in a three electrode open cell by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. The results revealed the pure bioactive calcium phosphate (CaP) coated implant materials to possess the highest resistivity to corrosion, while the silver and zinc doped CaP layer showed at least one order of magnitude lower corrosion resistance. These modified CaP coatings can be further considered as antimicrobial coatings with enhanced biocompatibility. The morphology and structure of the coatings were characterized by Scanning electron microscopy (SEM), Energy-dispersive X-ray Spectroscopy (EDX) and X-ray diffraction (XRD) that confirmed the pulse current deposited CaP layer to consist of a mixture of different calcium phosphate phases such as hydroxyapatite (HAp), monetite (dicalcium phosphate, CaHPO₄) as well as other Ca-containing components, portlandite (Ca(OH)₂) and parascholzite (CaZn₂(PO₄)₂(H₂O)₂).     

Photochemical Oxidation of Americium in Dilute Nitric Acid Solution with the Addition of Ozone

Abstract

A trial to oxidize americium (Am) from the trivalent to the hexavalent form in dilute nitric acid solution was undertaken by emitting light from a deuterium lamp as well as by blowing ozone into the solution. It was found out that trivalent Am in dilute nitric acid solution (～0.1 N) can be photooxidized to its hexavalent form by a deuterium lamp which emits lines below 170 nm. Photooxidation, however, cannot be effected unless the oxidation rate exceeds the rate of autoreduction of Am which is caused by radicals and ions formed by alpha radiolysis. Ozone was introduced into the solution to maintain Am in its hexavalent form because ozone, which does not oxidize Am³⁺ to Am⁶⁺ in acid media, readily oxidizes Am^{5 +} to Am⁶⁺ in HNO₃ solution. Photooxidation can be effectively carried out by a combination of photolysis and ozone. Its oxidation rate was about 5%/h in 0.1 N nitric acid solution at 65°C. The oxidation rate decreased with increasing nitric acid concentration.     

Adsorption of Microamounts of Silver on Manganese Dioxide from Acid Solutions

Abstract

Adsorption of microamounts of silver on manganese dioxide from nitric and perchloric acid solutions has been studied and optimized with respect to shaking time, concentrations of electrolyte, adsorbent, and adsorbate. Maximum adsorp- tion (>99.5%) has been achieved from 0.01 mol/dm³ acid solution using 50 mg oxide at 10^?5 mol/dm³ silver concentration after 30 min shaking. The adsorption decreases with increasing concentration of acid and adsorbate from both the acids. The presence of a 10⁴-fold greater concentration of cyanide, thiocyanate, thiosulfate, and Pb(II) than silver reduces the adsorption drastically. The adsorption of silver follows the Freundlich adsorption isotherm over the entire concentration range investigated from 9.27 × 10^?6 to 2.92 × 10^?3 mol/dm³ with a value of A = 49 mmol/g and 1/n = 0.93. Moreover, the Langmuir adsorption isotherm is also valid except at the lowest and highest concentrations. The values of the limiting adsorption concentrtion (C_m ) have been found to be 1 mmol/g and of the equilibrium constant for adsorption 87 dm³/mol at 23 ± 2°C.