Tetrachloroaurate Anion Research Articles

Two-Step Electrochemical Au Nanoparticle Formation in Polyaniline.

In this work, we use a two-step cyclic electrochemical process to insert Au into polyaniline (PANI). It was suggested previously that this method would lead to the formation of atomic Au clusters with controlleds number of Au atoms without providing morphological proof. In each cycle, tetrachloroaurate anions (AuCl4-) are attached on the protonated imine sites of PANI, followed by a controlled reduction using cyclic voltammetry (CV). In contrast to previous work, we demonstrate that the reduction leads to the nucleation and growth of an Au nanoparticle (NP) whose density and size dispersion depend on the Au loading in PANI. Adding more deposition cycles increases the Au NP density and size. Transmission electron microscopy (TEM) and corresponding energy dispersive X-ray spectroscopy (EDS) indicate a homogeneous distribution of Au elements in the PANI matrix before CV reduction, while Au elements are aggregated and clearly localized in the NPs positions after CV reduction. We further use Rutherford backscattering spectrometry (RBS) to quantify the Au uptake in PANI. The Au distribution is verified to be initially homogeneous across the PANI layer whereas the increasing number of deposition cycles leads to a surface segregation of Au. We propose a two-step growth model based on our experimental results. Finally, we discuss the results with respect to the formation of atomic Au clusters reported previously using the same deposition method.

Selective Extraction of Tetrachloroaurate Anion from a Model Leachate Using Alcohols

Selective Extraction of Tetrachloroaurate Anion from a Model Leachate Using Alcohols

Electrostatic Self-Assembly Approach to Fabricate Architectures of Carboxyl Functionalized Gold-Aryl Nanoparticles and Graphene Oxide Platforms

Graphene oxide (GO) was decorated with gold-aryl (Au-C) nanoparticles AuNPs-COOH by sodium borohydride reduction of aryldiazonium tetrachloroaurate(III) salt at room temperature in aqueous solutions. Brunauer-Emmett-Teller measurements supported GO anchoring by AuNPs modified with COOH; surface area dropped significantly. Morphology of AuNPs-COOH/GO nanocomposite (NC) was probed using AFM and TEM, showing NC’s surface roughness and wrinkling. XPS results suggest the clear reductive reaction of tetrachloroaurate anion into metallic gold in AuNPs-COOH/GO along with detailed interpretations of functional groups’ nature. Molecular dynamics calculations endowed support of favorable wrinkling at the edges and carboxyl intercalation to GO surface of types π- π, hydrogen bonding, and hydrophobic interactions. Solvent accessible surface area calculations of GO showed a decrease in total surface area. Environmental nanoremediation of the catalytic reduction of 4-nitrophenol, a priority pollutant listed by USEPA, was investigated. The apparent rate constants Kapp of four catalytic reduction cycles of nitrophenol were measured. The highest value is 1.17 × 10-1 min-1 for the first cycle which decreased to 4.49 × 10 -2 min -1 for the fourth cycle. The variations in rate constants were measured with different conditions, including NaBH 4 concentrations, NC loadings and NC incubating time in NaBH4.

Selective Recovery and Detection of Gold with Cucurbit[n]urils (n = 5-7).

Environmentally benign methods for gold recovery and detection are highly desirable for a sustainable future. Herein, we demonstrate a selective recovery and detection strategy of gold with cucurbit[n]urils (Q[n = 5-7]) by means of outer-surface interactions. Tetrachloroaurate anion ([AuCl4]-) is able to be rapidly precipitated with Q[n] in forms of supramolecular adducts. X-ray crystallography of four Q[n = 5-7]·[AuCl4]- complexes reveal that strong outer-surface interactions between Q[n = 5-7] and [AuCl4]- are the major driving force for the formation of Q[n = 5-7]·[AuCl4]- complexes. Impressively, each Q[6] macrocycle is surrounded by 12 [AuCl4]- anions. Each of these 12 [AuCl4]- anions is connected to four adjacent [AuCl4]- anions, leading to the formation of a three-dimensional supramolecular framework with tubular channels. In addition, we found an interesting inclusion complex [Au(OH2)4]3+⊂Q[7] in the Q[7]·[AuCl4]- complex, which is the first example of hydrated metal cation encapsulated inside the cavity of Q[n]. Spectroscopic data suggest that Q[n = 5-7] possess a high affinity and selectivity for [AuCl4]- even in the presence of other transition-metal ions. Q[n] modified electrodes are found to be an effective material for the detection of trace gold in dilute solutions.

Evaluation of diazonium gold(III) salts in forensic chemistry: Latent fingerprint development on metal surfaces

Evaluation of diazonium salts in forensic chemistry will vastly benefit in the design of novel developers for latent fingerprints on metal surfaces used as crime tools. We used the easily reducible aryldiazonium salt stabilized with tetrachloroaurate anion of the formula [NO2-4-C6H4N≡N]AuCl4. Localized elemental analysis, after 2 h of contact with the aryldiazonium salt, using X-ray fluorescence (XRF) and energy dispersive spectroscopy (EDS) showed the deposition of gold on the fingerprints collected on copper, lead and aluminum. Poor development obtained from the non-gold aryldiazonium salt [NO2-4-C6H4N≡N]BF4, in addition the temporal evolution of the deposition over 24 h showed images of poor contrast and scattered minor deposits. It can be noticed from the images collected using scanning electron microscopy (SEM) and stereomicroscope that the grafted film was not filling the grooves but selectively adhered to the eccrine prints on copper and lead however showed indiscriminate deposition on aluminum surface at high concentrations. Obliteration of developed fingerprints was not observed on all surfaces. The degraded contrast on aluminum after the visible overflow of the trenches is a limitation of diazonium on highly reactive metal surfaces according to the electrochemical series. It can be concluded that copper surface is the most successful among the three metals. The gold film aided to visualize the three levels of primary, secondary and tertiary fingermarks at high level of details. Reduced gold on fingerprints can be beneficial in archiving and future analysis.

Adsorption Synthesis of Iron Oxide-Supported Gold Catalyst under Self-Generated Alkaline Conditions for Efficient Elimination of Carbon Monoxide

Goethite- and hematite-supported highly dispersed gold catalysts for carbon monoxide oxidation were synthesized by gold precursor adsorption onto the support materials in self-generated alkaline solutions. The support materials were prepared by reacting iron nitrate with excess sodium hydroxide. The residual minor alkali incorporated into the support could provide suitable alkaline conditions at approximately pH 8 for the hydrolysis of tetrachloroaurate anions and the subsequent adsorption process. Gold species underwent autoreduction to achieve activation during the synthesis. An increase in pH or temperature to 80 °C decreased the gold loading of the catalysts. The optimal catalysts could achieve complete oxidation of carbon monoxide at −20 °C.

Highly sensitive and simple liquid chromatography assay with ion-pairing extraction and visible detection for quantification of gold from nanoparticles

A simple isocratic HPLC method using visible detection was developed and validated for the quantification of gold in nanoparticles (AuNP). After a first step of oxidation of nanoparticles, an ion-pair between tetrachloroaurate anion and the cationic dye Rhodamine B was formed and extracted from the aqueous media with the help of an organic solvent. The corresponding Rhodamine B was finally quantified by reversed phase liquid chromatography using a Nucleosil C18 (150mm × 4.6mm, 3µm) column and with a mobile phase containing acetonitrile and 0.1% trifluoroacetic acid aqueous solution (25/75, V/V) at 1.0mLmin−1.and at a wavelength of 555nm. The method was validated using methodology described by the International Conference on Harmonization and was shown to be specific, precise (RSD < 11%), accurate and linear in the range of 0.1 – 30.0µM with a lower limit of quantification (LLOQ) of 0.1µM. This method was in a first time applied to AuNP quality control after their synthesis. In a second time, the absence of gold leakage (either as AuNP or gold salt form) from nanostructured multilayered polyelectrolyte films under shear stress was assessed.

Influence of pH and aurate/amino acid ratios on the tuneable optical features of gold nanoparticles and nanoclusters

Blue- and green-emitting gold nanostructures have been synthesized by spontaneous interactions of the tetrachloroaurate anions (AuCl4−) with L-histidine (His) and L-tryptophan (Trp) at 37°C in aqueous medium. The dominant role of AuCl4−/amino acid molar ratios as well as the pH in the formation of gold nanoparticles (Au NPs) or nanoclusters (Au NCs) was confirmed by numerous spectroscopic techniques. We demonstrate that without additional reducing agents the His and Trp show different reduction behaviour with AuCl4− which supports the fact that the unique optical features originate from diverse structures. Because of the pH-dependent complexation and reduction capability of the studied amino acids the dominant presence of polynuclear fluorescent gold(I) complexes (quantum yield (QY%) ∼4%) with a well-ordered structure is presumable for His-directed Au system confirmed by mass spectrometry, X-ray diffraction and infrared experiments. The existence of d=8 nm-sized Au NPs or subnanometer-sized (d<2nm) Au NCs (Au3-Au5) that have tuneable blue or green photoluminescence (λemission=470–500nm) was identified in the samples containing Trp depending on the applied AuCl4−/Trp ratios. The blue-emitting Au/His nanohybrid system as potential bioimaging agent was used to visualize fluorescently albumin- and chitosan-based carrier composite particles.

Electrochemically Controlled Atom by Atom Deposition of Gold to Polyaniline

Polyaniline (PANI) has been an effective matrix for hosting and preserving metal nanoclusters. In the case of gold, the tetrachloroaurate anion has a high affinity for the imine sites of PANI. Upon contact with PANI, is spontaneously reduced to metallic gold, but the size of the formed Au clusters cannot be precisely controlled. Herein, we report on the electrochemical method of controlled deposition of one atom by one atom of gold per imine site of PANI. By controlling the potential, we keep PANI in an oxidized state while exposing it to a solution of to form a complex, which is reduced to atomic gold by sweeping the potential negative. This frees up the imine sites of PANI again and makes them accessible for the next Au deposition cycle. The repeated deposition of Au atoms follows a cyclic pathway. The amount of gold deposited using this method is consistent for each repeated cycle.

Synthesis and some sorption properties of anion exchangers with guanidyl ligands

The results of synthesis of anion exchangers with guanidyl end groups are presented in this paper. Reaction of primary amino groups attached to resins with S-methylthiourea gave the anion exchangers with up to 2.6 mmol of ligands per gram of resin. The best anion exchangers with guanidyl ligands are these having porous structure and ligands derived from diethylenetriamine. These exchangers sorb about 45 mg of gold/g from 50 ppm dicyanoaurate solution and more than 100 mg of gold/g from tetrachloroaurate solutions. The anion exchangers with guanidyl ligands are selective towards tetrachloroaurate anions. From AuCl 4 - solution containing also Fe(II), Zn(II), Ni(II) and Cu(II) in 0.1 M HCl they sorb practically tetrachloroaurate anions only. When the ratio of metal ions is higher than amine groups, anion exchangers sorb high amount of metal ion from the acetate solution, for example about 700 mg/g of cobalt.

Anion exchangers with alkyl substituted guanidyl groups: Gold sorption and Cu(II) coordination

Two methods of introducing guanidyl groups into polymer matrix were investigated in this work: the reaction of cyanamide (alkyl substituted cyanamides) and carbodiimides with amino groups in modified polystyrene. The new anion exchangers (AEG) with alkyl substituted guanidyl groups contain 1.5–2.3 mmol/g of ligands and exhibit high selectivity towards Au(CN) 2 − anions. From the solution containing 2 ppm of gold the sorption is as high as 30 mg/g. Furthermore, AEG reveal high affinity towards tetrachloroaurate anions. The log K in diluted solution is about 5. The values of gold sorption as dicyanoaurate or tetrachloroaurate anions on AEG with alkyl substituted hydrogen atoms in guanidyl groups is two–four times higher than sorption on anion exchangers synthesized previously by exchange of chlorine with guanidine or aminoguanidine. The EPR studies of Cu(II)-loaded AEG were undertaken to correlate the structural properties of the formed complexes with the nature of the ligands, the ligand concentration, water regain of the resins and pH.

Modification of Malonamide Ion-Exchange/Chelating Resins Using the Fields–Kabatschnik Reaction and Their Application to Metal Ion Removal from Aqueous Solutions

A resin containing 2-aminoethyl-substituted amides of malonic acid was modified in the Fields–Kabatschnik reaction using diethyl phosphite. The resultant ion-exchange/chelating resins have aminomethylphosphonate groups. Modification proceeds almost quantitatively, giving a resin with P=1.97 mmol/g, N=4.20 mmol/g, and water regain of 0.44 g/g. It can be selectively hydrolyzed by treatment with trimethylchlorosilane/potassium bromide in dry acetonitrile. Both acidic and ester forms of the resin were used in the removal of Cu(II), Cd(II), Ni(II), and Zn(II) from their diluted 1×10−4N solutions in 0.2 M acetate buffer at pH 3.7 and 5.6. The affinity of the resin in an acid form toward divalent metal cations is high, and at pH 5.6 the log Kd is 7.54, 3.97, 3.41, and 3.98, respectively. The resins are selective and the presence of an excess of sodium ions does not influence the uptake of metal ions. The type of complexes formed between the resins and Cu(II) ions was studied using EPR spectroscopy. The ester form of the resin was used in the removal of tetrachloroaurate anions from hydrochloric acid solution. It has been found that the log Kd is in the range of 3.14–3.94 for the uptake of AuCl−4 from 5.0–0.5 M HCl solutions.

Interaction of protonated retinal Schiff base with N-methylacetamide: an FT-IR investigation

The complexation of protonated retinal Schiff bases of tert-butylamine (HClO 4 and HAuCl 4 salt, respectively) with N-methylacetamide were studied in CD 2Cl 2 solution by Fourier transform- infrared (FT-IR) spectroscopy. The N-methylacetamide forms complexes with the protonated Schiff base in which the NH and CO bonds are involved and in which the N-methylacetamide isomerises from the trans to the cis configuration. The formation of these complexes is strongly influenced by the types of anion present. The tetrachloroaurate anion interacts with the N +H group of the Schiff base and consequently influences the nature of the retinal residue. No complexation occurs with N, N-dimethylacetamide.