Silver Cyanide Research Articles

Alternative coatings to cyanide silver coatings with low infrared emissivity for tokamak components

Alternative to cyanide silver coatings with low infrared emissivity for tokamak components were prepared by cyanide-free silver plating on nuclear-grade 304L stainless steel. The surface morphology, coating adhesion and emissivity were characterized and optimized. The experimental results indicate that the developed cyanide-free silver coating is a viable alternative to cyanide silver coating. The adhesion of silver coating was enhanced by the reactivating of nickel plating. The emissivity was reduced by decreasing surface roughness and increasing coating thickness. Both optimizations reach limit at 0.4 μm and 0.6 μm, respectively. Further decrease in surface roughness and increase in coating thickness did not contribute to decreasing emissivity. To sum up, the obtained cyanide-free silver coatings showed sufficient adhesion with emissivity as low as 0.02, thus providing an eco-friendly alternative solution to fusion energy application.

Laser-Induced Activation of N2 and Catalyst-Free Synthesis of HCN

Hydrogen cyanide (HCN) is typically synthesized using ammonia and methane as sources of nitrogen and carbon, respectively, over expensive platinum catalysts at high temperatures. However, continuous high-temperature processing deactivates the catalyst, resulting in limited durability of the process. Besides, there are serious hazards and limitations in the further separation and utilization of HCN. From the perspective of sustainable synthesis and safe utilization, low-cost catalyst or catalyst-free synthesis, mild reaction conditions, and elimination of exposure to toxic reagents are becoming increasingly important. Direct synthesis of HCN from nitrogen (N2) at room temperature without any catalysts and its safe fixation into functional inorganic cyanides are desirable. Here, we report the catalyst-free synthesis of HCN by laser-induced activation of N2 and methanol (CH3OH) at room temperature and then the in situ synthesis of inorganic cyanides (silver and copper cyanides) without purification and separation by reacting the synthetic solution with noble metals. We also establish the possible reaction paths by density functional theory calculations and molecular dynamics simulations to elucidate the thermodynamics and kinetics of the reactions involved in the laser chemistry process, i.e., laser bubbling in liquid (LBL). The high temperature inside the laser-generated bubble overcomes the energy barrier and drives the successful coupling of carbon and nitrogen sources endergonically in the following process. Bubbles experience a rapid quench during the LBL process, resulting in the kinetic control product HCN with high efficiency. The method is viable for the catalyst-free direct synthesis of HCN from N2 and CH3OH at normal conditions for safe fixation into inorganic cyanides.

Nitrogen-Doped Graphene Quantum Dots as “Off–On” Fluorescent Probes in Paper-Based Test Kits for Selective Monitoring of Cyanide in Food

We successfully developed a fluorometric paper-based test kit for the selective and sensitive determination of cyanide using nitrogen-doped graphene quantum dots (N-GQDs) as the fluorescent probe. Citric acid and tris(hydroxymethyl)aminomethane were precursors for the one-step synthesis of N-GQDs via in situ hydrothermal methods, providing a high quantum yield of 57.9%. The proposed mechanism uses a fluorescence turn-on approach. Specifically, the fluorescence of N-GQDs is quenched by the incorporation of Ag+ via a photoinduced electron transfer (PET). During the detection step, sulfuric acid converts cyanide (CN–) into hydrogen cyanide (HCN). The Ag+ species on the N-GQD surface then react with the evolved HCN via a coordination bond to form a silver cyanide complex, resulting in the fluorescence emission of the N-GQDs being turned back on. As a result, the fluorescence emission intensity of N-GQDs linearly increased with increasing CN– concentrations in the range of 0.5–25 mg L–1, with a limit of detection (LOD) of 0.08 mg L–1. Notably, the developed sensor has advantages in terms of simplicity, rapidity, low cost, and high selectivity toward CN–. The analytical performance of the test kit was also validated the performance of the test kit against a conventional precipitation titration method.

Silver Cyanide Powder‐Catalyzed Selective Epoxidation of Cyclohexene and Styrene with its Surface Activation by H2O2(aq) and Assisted by CH3CN as a Non‐Innocent Solvent

AbstractWe undertake silver cyanide (AgCN) powder for its catalytic epoxidation of cyclohexene or styrene in CH3CN with variable substrate‐to‐solvent volume ratios using H2O2(aq) at 60 °C. The reaction mixtures can facilely separate into organic and aqueous layers. Cyclohexene oxide can be produced in the organic layer with 100 % selectivity from the substrate cyclohexene, while styrene oxide was identified with 80 % selectivity against benzaldehyde in styrene oxidation. After reactions, we can recycle the AgCN particles with comparable bulk property clarified via XRD, XPS, XAS, FT‐IR, and 13C‐SS NMR spectroscopy. Using H218O2 as the oxidant, both epoxide products and acetamide are highly enriched with 18O‐atom, indicating that the π bond‐activation is essential for forming the cyclohexene/styrene oxides in the organic and acetamide in the aqueous layers. The oxidation of cyclohexene/styrene catalyzed by AgCN powder through surface activation by H2O2(aq) and assisted by the non‐innocent CH3CN‐originated acetamide can achieve highly selective π‐bond activation with high reactivity.

Assessment of the principal factors influencing the silver cyanidation process by using Plackett-Burman experimental design

For decades, the cyanidation process is frequently used for gold and silver extraction, as well as metal extraction as a sub-product of lead, zinc, and copper metallurgy. The present study focuses on the factors that influence silver extraction efficiency, which represents the rate of silver dissolution in a sodium cyanide solution. The screening design of Plackett and Burman has been performed to investigate the variables that have the most impact on the extraction of metal namely temperature, pH, free cyanide concentration, dissolved oxygen level, pulp density, lead nitrate ratio (Pb(NO3)2ratio), and setting time.To evaluate the meaning of the seven variables, twelve experiments were carried out and the result revealed that for a 95% confidence level, the chosen parameters for the model are meaningful in their whole. The following three factors were significant (P<0.05) when it comes to the silver cyanidation process including, setting time, pulp density, and free cyanide concentration. The variance analysis (ANOVA) using a Fisher test has shown that the setting time was considered to have the most significant effect for a significance level of 1% (Fstatistics=22.8328 > Fc=21.2). Likewise, for a 95% confidence level, both pulp density and free cyanide concentration have a major influence on the response. The Pareto diagram results clearly show that pulp density and setting time represent 20% of factors that have 80% effect on the silver extraction. Model validation verified that no statistically relevant distinction was made between the predicted and experimental results with the determination coefficient R2=0.93, this mean that the metal extraction is better fitted to the model and the predictability of the model is adequate to explain 93% of the variation in the dependent variable as a function of factor variation.

Ag3PO4/Ag nanocomposite for selective and sensitive cyanide determination in food samples through catalytical colorimetry using a paper-based test kit

A paper-based test kit for selective and sensitive determination of cyanide was successfully developed using a Ag3PO4/Ag nanocomposite for catalytic colorimetry. The Ag3PO4/Ag nanocomposite synthesized via a one-step chemical bath method could instantly oxidize the chromogenic substrate ABTS for the color development under acidic conditions without the requirement of H2O2. During the detection step, cyanide in the sample was converted into gaseous hydrogen cyanide (HCN) using sulfuric acid. The HCN species then reacted with the generated Ag+ species via coordinate covalent bonding to form silver cyanide complex ions [Ag (CN2)]-. The amount of Ag+ species used for oxidizing ABTS subsequently decreased and so did the color intensity on the paper-based test kit. Specifically, the color intensity decreased with increasing cyanide concentrations in the range of 2.50–20.0 mg L−1. The limit of detection (LOD) and limit of quantification (LOQ) were 0.48 mg L−1 and 1.59 mg L−1, respectively. The developed test kit showed relatively high selectivity towards cyanide and high tolerance towards other cations and anions present in real samples. When applied to real samples including fruit juices and food products, the performance of the rapid and low-cost test kit was well validated by a conventional precipitation titration method.

Phenyl argentate aggregates [AgnPhn+1]- (n = 2-8): Models for the self-assembly of atom-precise polynuclear organometallics.

Electrospray ionization of phenyl argentates formed by transmetalation reactions between phenyl lithium and silver cyanide provides access to the argentate aggregates, [AgnPhn+1]-, which were individually mass-selected for n = 2-8 in order to generate their gas-phase Ultraviolet Photodissociation (UVPD) "action" spectra over the range 304-399nm. A strong bathochromic shift in optical spectra was observed with increasing size/n. Theoretical calculations allowed the assignment of the experimental UVPD spectra to specific isomer(s) and provided crucial insights into the transition from the 2D to 3D structure of the metallic component with the increasing size of the complex. The [AgnPhn+1]- aggregates contain neither pronounced metallic cluster properties nor ligated metallic cluster features and are thus not superatom complexes. They therefore represent novel organometallic characteristics built from Ag2Ph subunits.

Сжимаемость и электронные свойства цианидов металлов

The compressibility and electronic properties of metal cyanides are investigated within the density functional theory taking into account the dispersion van der Waals interaction. It was shown that gold cyanide has a low linear compressibility (less than 0.1% at a pressure of 1 GPa) and a high linear modulus (~ 1200 GPa) along the -Au-CN-Au-CN- chains. Silver cyanide exhibits negative linear compressibility, which correlates with the compressibility of Ag-N coordination bonds. For sodium cyanide, the linear compressibility along the C - N covalent bonds is greater than for gold and silver cyanides, while the elastic anisotropy is less. Unlike sodium cyanide, for gold and silver cyanides, cation-anionic bonds (Au-N, Au-C and Ag-N, Ag-C) are partially covalent in nature, and the upper valence states correspond mainly to the states of cations. The band gap of gold cyanide is smaller than that of silver and sodium cyanides. The band gap widths of gold and silver cyanides significantly decrease with increasing pressure, which indicates the possibility of metallization at sufficiently high pressures.

Oxidation of Silver Cyanide Ag(CN)2- by the OH Radical: From Ab Initio Calculation to Molecular Simulation and to Experiment.

We investigate the oxidation of silver cyanide in water by the OH radical in order to compare this complex with the free cation Ag+ and to measure the influence of the ligands. High-level ab initio calculations of the model species enable the calibration of molecular simulations and the prediction of the oxidized species: and its absorption spectrum, with an intense band at 292 nm and a weaker one at 390 nm. Pulse radiolysis measurements of the oxidation of by the OH radical in water yields a transient species with a broad, intense band at 290 nm and a weaker band at 410 nm at short times after the pulse and a blue shift of the spectrum at longer times. The prediction of the simulations, that the oxidized complex is formed, is confirmed by thermochemistry. Our calculations also suggest that the formation of the OH-adduct is possible only in very basic solution and that the blue shift observed at long times after the pulse is due to disproportionation of the oxidized complex. We also perform molecular simulations of the oxidation of free Ag+ cations by the OH radical. The results are compared to that of the literature and to the results obtained with the complex.

Investigation of Au-Ag-Cu Alloy Electrodeposition to Electromechanical Systems

Electromechanical systems, which provide electrical power and data connection between moving terminals require high conduction and erosion resistant surfaces. Transfers of electrical power and data are accomplished by the contact of drum and brush wires. The simultaneous electrochemical deposition of desired Au-Ag-Cu alloy compositions, which can be used to coat the brush wires, was investigated in this study. In the scope of the study, the static potential and cyclic voltammetry behaviours of gold, silver and copper cyanide plating baths, as well as the mixtures of binary and ternary baths were investigated to obtain suitable amount of KCN and working potential values. SEM and EDS analyses were conducted in the characterization of coated samples.

Investigation of Au-Ag-Cu Alloy Electrodeposition to Electromechanical Systems

Electromechanical systems, which provide electrical power and data connection between moving terminals, require high conduction and errosion resistant surfaces. Transference of electrical power and data are carried out by the contact of drum and brush wires. The electrochemical deposition of desired Au-Ag-Cu alloy compositions was investigated in this study. In the scope of the study, the static potential and cyclic voltammetry behaviours of gold, silver and copper cyanide plating baths, as well as the mixtures of binary and ternary baths were investigated to obtain suitable amount of KCN and working potential values. Beside SEM and EDS analyses, hardness and friction measurements were conducted in the characterization of coated samples.

Synthesis of silver cyanide without poisonous KCN or NaCN

Highly crystalline silver cyanide (AgCN) was synthesized at room temperature using acetonitrile (CH3CN) as a source of cyanide ion (CN−). The in-situ generation of CN− was assisted by the CCN bond breaking of CH3CN. The reaction was found to be catalyzed by vanadium pentoxide (V2O5) and hydrogen peroxide (H2O2). The process was very simple and effective one as it was possible to extract the white precipitate of AgCN simply by filtration method. The overnight standing of the whole reaction mixture resulted in the 100% conversion of AgNO3 to AgCN. The most significant aspect of the process was that it did not involve any poisonous cyanide compounds like potassium or sodium cyanide; KCN or NaCN. Further, it also did not lead to the formation of any hazardous waste. The present synthetic approach was thus regarded as an alternative and greener route for preparation of pure AgCN directly from AgNO3.

Rapid and sustainable process with low toxicity for cyanation of silver nitrate by DC arc-discharge in presence of acetonitrile

Use of Direct current (DC) arc-discharge in the chemistry reactions is very novel method. In this technique, the DC arc-discharge as a high-energy source conducts reaction to cleaving of the C-CN bond in acetonitrile and causes the cyanation of silver nitrate. This process due to non-use of cyanide ion can be proposed as a green and sustainable method. The obtained Silver cyanide from this procedure was characterized by its spectroscopic data (FT-IR and XRD). [Display omitted]

A closed-loop electrogenerative recycling process for recovery of silver from a diluted cyanide solution.

A closed-loop process for the complete recovery of silver from a diluted silver cyanide solution has been constructed based on an electrogenerative process. It was shown that the reduction of silver was a mass transport controlled process. Under optimal experimental conditions, 100% of silver was recovered from 500 mg L−1 and 100 mg L−1 silver cyanide solutions by using a reticulated vitreous electrode (RVC) as the cathode. The cyanide solution was recycled and reused so that a closed-loop process was obtained. In addition, the RVC in this study can be used repeatedly up to 10 cycles with a calculated relative standard deviation of 1.90%.

A facile and general approach for production of nanoscrolls with high-yield from two-dimensional nanosheets

Nanoscrolls (NSs) assembled from two-dimensional nanosheets have emerged as a novel type of one-dimensional nanomaterials because of their unique topological features and properties. The scale-up preparation of the NSs is crucial for their foundational and applied research. Herein, we report a general and straightforward approach for efficiently converting two-dimensional nanosheets into the NSs with high yield. We demonstrated the converting process by illustrating the formation of the graphene nanoscrolls through characterizing their morphology and structure using a scanning electron microscope, transmission electron microscope, Raman spectra, and X-ray diffraction spectra. The graphene sheets with a few-lay number were converted immediately and entirely into the graphene nanoscrolls when they mixed with an ethanol solution of silver nitrate at room temperature. The as-prepared graphene nanoscrolls were confirmed to be formed via the layer-by-layer assembly of graphene triggered by silver cyanide formed in site. Also, we extended this approach to construct the nanoscrolls of the hexagonal boron nitride, molybdenum disulfide, and tungsten disulfide, respectively, from their corresponding two-dimensional nanomaterials. In a broader context, this approach paves a significant new way for the large production of the NSs with cost-efficiency.

Application of Assaf panel for evaluating throwing power of pulse reverse electroplating on complex geometries

ABSTRACTThe Assaf panel arrangement was used for evaluating pulse reverse plating processes and optimisation of the throwing power (TP) of complex three-dimensional (3D) geometries. Two different electroplating processes were investigated: an acid copper bath and a cyanide silver bath without additives. It has not been possible to establish a direct correlation factor for TP obtained with the Assaf panel and the 3D objects included in the trials. Nevertheless, the Assaf panel was found to be a useful tool for preliminary process parameter optimisation. The copper bath needs agitation to deposit coatings of good quality, whereas the silver bath obtains the best throwing power without agitation. The latter is probably due to inhibition by adsorbed cyanide.

Graphene-catalyzed formation of C\u2261N bonds via cleavage of C-C and N-O bonds in ethanol and nitrate under room temperature

The cleavage of carbon-carbon bonds and the formation of carbon-nitrogen bonds play crucial roles in chemical synthesis. However, these reactions usually proceed at high temperature and involve multiple steps. Herein, we report an unusual and novel reaction catalyzed by graphene. The C-C bond in ethanol and the N-O bond in nitrate can be broken under room temperature, accompanied by the formation of the C≡N bond. We demonstrate these reactions and elucidate their mechanisms by verifying that the product is silver cyanide which was formed when mixing a solution of silver nitrate and ethanol with graphene dispersion in ethanol at room temperature. The pivotal reason for the reaction is the formation of the precipitated silver cyanide. In a broader context, this discovery opens a significant new path for the breakage of the C-C bond in ethanol and the synthesis of nitriles under mild conditions. Also, the graphene was first reported as a catalyst for the room-temperature reaction.

Nghiên cứu dung dịch mạ bạc phốtphát không sử dụng xyanua tự do và các yếu tố ảnh hưởng tới chất lượng lớp mạ

The conditions and chemical composition of the non-freecyanide solution to silver plating had been investigated. The solution is well distributed. The quality of the plating is similar to the plating with free cyanide plating solution. Therefore, non- free cyanide phosphate solution could be replacing by the traditional cyanide silver plating. The appropriate composition and plating conditions are: 15 g/L Ag+; 30 g/L KH2PO4; 140 g/L K2HPO4; current density 0.4 A/dm2; temperature 60÷65oC. The received silver platings are pure, bright and smooth.

Directional growth of Ag nanorod from polymeric silver cyanide: A potential substrate for concentration dependent SERS signal enhancement leading to melamine detection

Attention has been directed to prepare exclusive one-dimensional silver nanostructure from the linear inorganic polymer AgCN. Successive color change from yellow to orange, to red and finally to green reflects the evolution of high yielding Ag nanorods (NRs) from well-known -[Ag-CN]- chains of polymeric AgCN at room temperature. The parental 1D morphology of AgCN is retained within the as-synthesized Ag NRs. So we could successfully exploit the Ag NR for surface-enhanced Raman scattering (SERS) studies for sensing a popular milk adulterant melamine down to picomolar level. We observed interesting concentration dependent selective SERS band enhancement of melamine. The enhanced ~1327cm−1 SERS signal intensity at lower concentration (10−9 and 10−12M) of melamine speaks for the preferential participation of –C–N of melamine molecule with Ag surface. On the other hand, ‘–NH2’ group together with ring ‘N’ participation of melamine molecule onto Ag surface suggested an adsorptive stance at higher (10−3–10−7M) concentration range. Thus the binding modes of the molecule at the Ag surface justify its fluxional behavior.

Use of Ultrasound to Modified Electrodeposited Silver and Silver-Tin Microstructures and Composition without Chemical Additives

Properties of electrodeposited coatings are directly related to their morphology and structure, which are strongly influenced, among others, by the presence of organic additives and electrodeposition parameters (current density, DC vs pulsed current). An attractive possibility results in the use of ultrasound to influence the microstructure without using chemicals, or at least, by reducing their quantity. Ultrasound is expected to have several effects on deposits, by heating the liquid or by generating solution movements that cause convection flows or cavitation bubbles, accompanied by chemical effects. Many works in the literature describe the beneficial effect of ultrasound in plating, reporting finer grains, reduced porosity and increased brightness. Even the penetration of nickel in complex geometric pattern has been reported. In the present study, conventional cyanide silver as well as silver-tin electrolytes were used to examine the effect of current density and ultrasound on the composition, structure and texture of the coatings. Silver-tin alloys were used for such materials as electric contacts because of the excellence in hardness and wear resistance. The goal was to determine the effect of ultrasound (20 kHz and 575 kHz) on sample microstructure and morphology. To insulate the effect of cavitation bubbles from convection flow, all coatings had to be elaborated exactly with the same agitation in absence or presence of ultrasound, at an “equivalent flow” condition. Plotting the silver structures identified by XRD vs. current density in still conditions, two main categories appeared: one poorly structured and the other following the [110] orientation. This is confirmed by SEM and EBSD measurements. When changing from still to mechanically stirred conditions, the value of the current density threshold moves from 2.5mA/cm² to 5mA/cm². This coating microstructure modification threshold is situated at higher current density values when coatings are produced under sonication (575 kHz or 20 kHz), while agitation is kept constant. In both cases, the shift is about 15 mA/cm². It is interesting to note that silver electrodeposits elaborated under 20 kHz ultrasound conditions appear to be less oriented than those obtained under high frequency conditions, with RTChklvalues dropping from 12 to 8 for the [110] orientation. Use of ultrasound during silver coating elaboration, irrespective of hydrodynamic conditions kept otherwise constant, makes it possible to modify significantly the microstructures and morphology of deposits without relying on chemical additives. In the case of silver-tin alloy electrodeposition, it is important to note that the current density variations coupled to the use of ultrasound leads to significant variations in properties of coatings (color, crystalline composition and alloy composition). For equivalent hydrodynamic agitation, silver is predominant at low current density and tin prevails at higher ones. If low frequency ultrasound is applied, Ag3Sn replace the tin, and for high frequency ultrasound, the coating is formed by an intermetallic compound of tin and silver irrespective of the current density. Finally, in all cases, agitation is always beneficial to widen the current density range favourable for structural modifications without the risk of coating deterioration due to burning. Moreover, at the same level of agitation, use of ultrasound offers more advantages because it ensures harder and less structured deposits in increased current density ranges, and offer modifications equally important as in the case of chemical additives use. Figure 1: crystalline orientation of silver deposits at various current densities in presence of ultrasound or at an “equivalent” agitation Figure 2: composition of silver-tin alloy in presence of ultrasound or at an “equivalent” agitation Figure 1