Gold Ions Research Articles

A novel S,N-rich MOF for efficient recovery of Au(III): Performance and mechanism

A novel S,N-rich MOF with adenine and 4,4′-thiodiphenol as organic ligands was synthesized via the one-step solvothermal method, and used for gold recovery. The pH impact, adsorption kinetics, isotherms, thermodynamics, selectivity, and reusability were investigated accordingly. The adsorption and desorption mechanism were also explored comprehensively. The electronic attraction, coordination, and in situ redox account for the Au(III) adsorption. The Au(III) adsorption is affected strongly by the pH of solutions, and best at pH of 2.57. The MOF exhibits exceptional adsorption capacity as high as 3680 mg/g at 55 °C, fast kinetics with 8 min for 9.6 mg/L Au(III), and excellent selectivity for gold ion in real e-waste leachates. The adsorption process of gold on the adsorbent is endothermic and spontaneous, and influenced visibly by temperature. The adsorption ratio still maintained 99% after seven adsorption-desorption cycles. The column adsorption experiments show that the MOF has outstanding selectivity for Au(III) with 100% of removal efficiency in a complex solution containing Au, Ni, Cu, Cd, Co, and Zn ions. A glorious adsorption with a breakthrough time of 532 mins was obtained for the breakthrough curve. This study not only provides an efficient adsorbent for gold recovery, but also guidance for designing new materials.

One-pot green synthesis of gold nanoparticles using Sarcophyton crassocaule, a marine soft coral: Assessing biological potentialities of antibacterial, antioxidant, anti-diabetic and catalytic degradation of toxic organic pollutants

Marine bio-resources are being extensively researched as a priceless supply of substances with therapeutic potential. This work report the first time attempt made towards the green synthesis of gold nanoparticles (AuNPs) using the aqueous extract of marine soft coral (SCE), Sarcophyton crassocaule. The synthesis was conducted under optimized conditions and the visual coloration of reaction mixture changed from yellowish to ruby red at 540 nm. The electron microscopic (TEM, SEM) studies exhibited spherical and oval shaped SCE-AuNPs in the size ranges of 5–50 nm. The organic compounds present in SCE were primarily responsible for the biological reduction of gold ions validated by FT-IR while the zeta potential confirmed the overall stability of SCE-AuNPs. The synthesized SCE-AuNPs exhibited variety of biological efficacies like antibacterial, antioxidant and anti-diabetic in nature. The biosynthesized SCE-AuNPs demonstrated remarkable bactericidal efficacy against clinically significant bacterial pathogens with inhibition zones of mm. Additionally, SCE-AuNPs exhibited greater antioxidant capacity in terms of DPPH: 85 ± 0.32% and RP: 82 ± 0.41%). The ability of enzyme inhibition assays to inhibit α-amylase (68 ± 0.21%) and α-glucosidase (79 ± 0.2%) was quite high. The study also highlighted the spectroscopic analysis of the biosynthesized SCE-AuNPs' catalytic effectiveness of 91% in the reduction processes of the perilous organic dyes, exhibiting pseudo-first order kinetics.

Super-stable mineralization of multiple heavy metal ions from wastewater for utilization in photocatalytic CO2 reduction and trace precious metal recovery

The treatment and recycling of heavy metal pollutants are vital for the restoration of the ecological environment and the recovery and reuse of resources. Herein, we report an atomic-economic method to synthesize a novel CaCr-layered double hydroxide (LDH) by extracting toxic Cr3+ (more than 1000 mg/L) from industrial wastewater, by which the wastewater can be purified to discharge standards. The obtained CaCr-LDH can be reused for the super-stable mineralization of multiple heavy metal ions with a high capacity, and the removal capacities of Ni, Co, Cu and Zn ions are 306.7 mg/g, 578.0 mg/g, 657.9 mg/g, and 352.1 mg/g, respectively. Furthermore, CaCr-LDH has the advantages of a large treatment range, anti-interference, alkali corrosion resistance, low cost, and less sludge. In the above mineralization process, CaCr-LDH converts to MCaCr-LDH (M = Co, Ni, Cu, and Zn) through an isomorphous substitution process. The obtained NiCaCr-LDH products show excellent performance in photocatalytic CO2 reduction with a high CH4 selectivity of 34.8% under visible light. The MCaCr-LDH products can selectively adsorb gold ions with approximately 90% adsorption efficiency and reduce them with approximately 80% reduction efficiency from printed circuit board leaching wastewater, offering promising functionalities for improving environmental pollution, resource waste, and energy crises.

Apigenin-coated gold nanoparticles as a cardioprotective strategy against doxorubicin-induced cardiotoxicity in male rats via reducing apoptosis

AimsCardiotoxicity is associated with doxorubicin (DOX), an effective anticancer drug. Apigenin has cardioprotective properties; it may be employed as a capping and reducing agent in synthesizing gold nanoparticles (AuNPs). This study examined the cardioprotective impact of AuNPs synthesized with apigenin (Api) in DOX-induced cardiotoxicity (DIC). Main methodsApi-AuNPs were synthesized in a single pot without needing additional reagents for reducing gold ions or stabilizing the NPs. The cytotoxicity of Api-AuNPs on H9c2 heart cells was subsequently determined using the MTT assay. In the animal investigation, 40 male rats were randomly assigned to one of four groups: control, cardiotoxicity (DOX), DOX treated with apigenin (DOX + Api), or DOX treated with Api-AuNPs (DOX + Api-AuNPs). To examine heart function, echocardiography was conducted. Blood samples were obtained to evaluate injury indicators (Lactate dehydrogenase (LDH), creatine kinase MB (CK-MB), Cardiac Troponin I (cTn-I), Alanine transaminase (ALT), and Aspartate transaminase (AST)). The heart was removed under general anesthetic, weighed, and preserved in formalin solution. Six micrometer-thick cardiac tissue sections were stained with hematoxylin, eosin (H&E), and immunohistochemistry to identify cardiomyocyte apoptotic markers (Bax, Bcl-2, and caspase3). Key findingsApi-AuNPs have an average size of 21.4 ± 11.6 nm and are stable in physiological environments. Api-AuNPs therapy substantially reduced body and heart weight loss compared to the DOX group. Injury indicators were reduced dramatically by Api-AuNPs treatment. Api-AuNPs inhibited myocardial apoptosis via modulating Bax, caspase3, and Bcl-2 and ameliorating tissue damage caused by DOX. SignificanceApi-AuNPs' anti-apoptotic activities provide cardioprotection against DIC. It has the potential to reduce cardiotoxicity and boost myocardial performance.

Covalent organic polymers with azido group for efficient recovery of gold from gold-bearing waste

BackgroundGold is a rare precious metal. Efficient and selective adsorption of Au(III) is of great significance for gold recovery. MethodsA covalent organic polymer with azido group (N3-COP) was synthesized utilizing enaminone covalent organic polymer and Ts-N3 as raw materials. Significant FindingsThe adsorption capacity of N3-COP for gold ions was up to 1220 mg·g−1 under the condition that the adsorption process took place at room temperature and at a pH value of 4. The results of adsorption thermodynamic and adsorption kinetic experiments illustrated that the adsorption process of N3-COP for the trivalent gold ion is consistent with the Langmuir adsorption model and Quasi second-order adsorption model. Additionally, this adsorbent has high adsorption selectivity when it is used to adsorb trivalent gold ion from effluent containing gold (III), cadmium (II), nickel (II), cobalt (II), and copper (II) ions. This adsorbent also has good reusability for it maintains excellent adsorption performance after five consecutive adsorption operations.

A Novel Insight into the Ullmann Homocoupling Reactions Performed in Heterogeneous Catalytic Systems.

The Ullmann reaction has been reported to be the first cross-coupling reaction performed by using a transition metal catalyst. This reaction has been initially considered as the copper-catalyzed homocoupling of aryl halides, leading to the formation of symmetrical biaryl compounds via the generation of novel C-C bonds. Although this reaction has been extensively studied in recent decades and valuable results have been achieved, there are still considerable efforts focused on the development of novel catalytic systems, mild reaction conditions, and extended substrate scope. The mechanistic aspects of the Ullmann homocoupling reaction have also been investigated, as related to the introduction of new sustainable strategies and green procedures. The application of recyclable heterogeneous catalysts has been found to overcome most of the limitations associated with the harsh reaction conditions of the original Ullmann reaction. More recently, copper-based catalytic systems have also been replaced by palladium nanoparticles, ionic palladium species, gold nanoparticles, and palladium-gold bimetallic systems. In this review, current results reported on the Ullmann homocoupling reaction are discussed, with an emphasis on the development of novel catalytic systems, which can be efficiently used under heterogeneous conditions.

Gold-containing liposomes and glucose-coated gold nanoparticles enhances the radiosensitivity of B16F0 melanoma cells via increasing apoptosis and ROS production

AimTo increase the effectiveness of radiation therapy, metals with high Z number are used as radiosensitizers. In this regard, the effectiveness of various gold nanoparticles as radiosensitizer has been proven. Therefore, this study aimed to evaluate the effects of liposomes containing gold ions (Gold-Lips) and glucose-coated gold nanoparticles (Glu-GNPs) on radiation sensitivity of B16F0 melanoma cells. Main methodsNaked GNPs, Glu-GNPs and Gold-Lips were synthesized and their physicochemical properties were evaluated using DLS. The cytotoxicity and sensitivity of the nanoparticles to radiation were evaluated using MTT and colony formation assay, respectively. Flow cytometry was performed to evaluate the apoptotic effect of nanoparticles on B16F0 cells. The intracellular ROS levels and mRNA expression of Bax, Bcl-2, p53, Caspase-3, and Caspase-7 genes were also evaluated. Finally, caspase 3/7 activity was determined using a luminescence assay kit. Key findingsThe results revealed that GNPs, Glu-GNPs, and Gold-Lips had a desired size and zeta potential. Results from the colony assay showed that the all non-toxic concentrations of Gold-Lips significantly increased cell death in B16F0 cells compared with the Glu-GNPs (p > 0.05). Flow cytometry and Caspase-3/-7 activity confirmed the results of the colony assay and showed that increasing the sensitivity of cells to radiation increases apoptosis. Moreover, we found that Gold-Lips increased the mRNA expression of p53, Bax, and Caspase-3/-7, and decreased the Bcl-2 mRNA expression. SignificanceOverall, both Gold-Lips and Glu-GNPs enhanced the radiosensitivity of B16F0 cells, however, Gold-Lips had better effects, which could make them a promising tools in cancer radiotherapy.

Adsorption of gold and silver glycinate on graphene and graphene oxide surface: A DFT study

The non-toxicity and efficiency of glycinate make it an attractive alternative for cyanide in the extraction of gold and silver from ores. In this study, the adsorption behavior of gold and silver complexes with cyanide and glycinate anions on graphene and graphene oxide surfaces was investigated based on the density functional theory calculations. Contrary to cyanide complexes, glycinate complexes prefer parallel orientation to graphene and graphene oxide surfaces. Based on the obtained adsorption energies, interaction of all complexes with graphene oxide surface is stronger than with graphene surface. The adsorption energies of Au(gly)2- and Ag(gly)2- on the graphene surface are −1.46 and −1.11 eV, whereas Au(CN)2- and Ag(CN)2- adsorb on this surface with energies of −0.62 and −0.51 eV. PDOS diagram analysis confirms that the hydroxyl group is responsible for strong interaction between complexes and graphene oxide surface. The adsorption energies of Au(gly)2- and Ag(gly)2- complexes on the GO2 and GO3 surfaces are −2.19 and −1.85 eV, respectively, which implies the applicability of graphene oxide surface at recovering gold and silver ions from the leaching solution. Charge density difference and Mulliken population analyses show charge transfer occurs from the adsorbed complex to the surface which is intensified by adding functional groups to the surface.

Preparation of gold nanoparticles using monoolein cubic phase as a template

MO cubic phase containing gold nanoparticle (GNP) was prepared by hydrating MO melt with gold ion solution to synthesize GNP of different sizes and shapes. A TEM microscopy and an elemental mapping analysis disclosed that GNP could be formed within the cubic phase. GNP prepared in an aqueous solution (GNP(W)) exhibited its surface plasmon resonance (SPR) spectrum in the visible light region with the peak around 528 nm and it was a sphere of which diameter was 10–30 nm. Besides a SPR spectrum in the visible light region, GNP formed in the cubic phase (GNP(CP)) showed its SPR spectrum spanning from the far-red to the near-infrared region, indicating GNP(CP) was gold particles of different sizes and shapes. In fact, non-spherical particles, including tetrahedron, decahedron, and rod, were found on the TEM photo of GNP(CP) and were larger than GNP(W). Furthermore, GNP(CP) exhibited the inherent lattice constant of gold, confirmed by a high-resolution TEM microscopy and an X-ray diffraction spectroscopy, indicating that various gold particles of different sizes and shapes could be formed in the cubic phase, maintaining its intrinsic crystalline structure.

Gold drugs as colistin adjuvants in the fight against MCR-1 producing bacteria.

The emergence and rapid spread of the mobile colistin resistance gene mcr-1 among bacterial species and hosts significantly challenge the efficacy of "last-line" antibiotic colistin. Previously, we reported silver nitrate and auranofin serve as colistin adjuvants for combating mcr-1-positive bacteria. Herein, we uncovered more gold-based drugs and nanoparticles, and found that they exhibited varying degree of synergisms with colistin on killing mcr-1-positive bacteria. However, pre-activation of the drugs by either glutathione or N-acetyl cysteine, thus releasing and accumulating gold ions, is perquisite for their abilities to substitute zinc cofactor from MCR-1 enzyme. X-ray crystallography and biophysical studies further supported the proposed mechanism. This study not only provides basis for combining gold-based drugs and colistin for combating mcr-1-positive bacterial infections, but also undoubtedly opens a new horizon for metabolism details of gold-based drugs in overcoming antimicrobial resistance.

Solvation Structure and Dynamics of Aqueous Solutions of Au+ Ions: A Molecular Dynamics Simulation Study

Although gold (Au) as an element is precious and noble, its elemental as well as ionic form is of huge scientific importance in view of its applications in electrochemistry, nano-electronics and other related fields. We have studied structure and dynamics of aqueous solutions of gold ions (Au+) using molecular dynamics simulations. Using a modified LJ parameter set for the Au+ ions in water in our molecular dynamics simulations, we have established the hydration structure and dynamics of Au+ ions in terms of radial distributions, orientations and residence time of the nearest neighbours. Our results on peak position, height and coordination numbers are in much better agreement with those from the recent CPMD simulations. Relative orientation of the neighbours as obtained from the angular distributions suggests octahedral or trigonal bi-pyramidal structure of the solvation shell. Orientational distributions of dipoles and other molecular orientational vectors indicate that the hydrogen atoms of the water molecules are away from the central Au+ ion. The residence time calculated from the corresponding time correlation function is found to be reasonably high, indicating less exchange of water molecules between the first and second solvation shells of the Au+ ion. In essence, the present results are in much better agreement with the CPMD results as compared to other QM/MM and classical force-field-based simulations.

Integration of Gold Nanoparticles into Crosslinker-Free Polymer Particles and Their Colloidal Catalytic Property.

This work demonstrates the incorporation of gold nanoparticles (AuNPs) into crosslinker-free poly(N-isopropylacrylamide), PNIPAM, particles in situ and the examination of their structural and catalytic properties. The formation process of the AuNPs across the crosslinker-free PNIPAM particles are compared to that of crosslinked PNIPAM particles. Given the relatively larger free volume across the crosslinker-free polymer network, the AuNPs formed by the in situ reduction of gold ions are detectably larger and more polydisperse, but their overall integration efficiency is slightly inferior. The structural features and stability of these composite particles are also examined in basic and alcoholic solvent environments, where the crosslinker-free PNIPAM particles still offer comparable physicochemical properties to the crosslinked PNIPAM particles. Interestingly, the crosslinker-free composite particles as a colloidal catalyst display a higher reactivity toward the homocoupling of phenylboronic acid and reveal the importance of the polymer network density. As such, the capability to prepare composite particles in a controlled polymer network and reactive metal nanoparticles, as well as understanding the structure-dependent physicochemical properties, can allow for the development of highly practical catalytic systems.

Selective Recovery of Gold from Electronic Waste by New Efficient Type of Sorbent.

Modular connectors are applied by computer users, and they can be metallic secondary sources containing metals such as gold and copper. Because gold is a micro-component, the solution obtained after the pin digestion contains a low concentration of gold(III) ions, and efficient and selective sorbent should be used for gold(III) ion recovery. The selective removal of small amounts of gold(III) from 0.001-6 M hydrochloric acid solutions using pure and solvent-impregnated macroporous polystyrene crosslinked with divinylbenzene sorbents (Purolite MN 202 and Cyanex 272) is presented. Gold(III) ions were recovered effectively from the chloride solution after the digestion of the modular connector RJ 45 (8P8C) using Purolite MN 202 after the impregnation process. The dependence of the recovery percentage (R%) of gold(III) on the contact time was determined. The highest value of gold(III) ion sorption capacity (259.45 mg·g-1) was obtained in 0.001 M HCl for Purolite MN202 after the Cyanex 272 impregnation. The results can be applied to gold recovery from e-waste. The presented method of gold recovery does not generate nitrogen oxides and does not require the use of cyanides.

Porous organic polycarbene nanotrap for efficient and selective gold stripping from electronic waste

The role of N-heterocyclic carbene, a well-known reactive site, in chemical catalysis has long been studied. However, its unique binding and electron-donating properties have barely been explored in other research areas, such as metal capture. Herein, we report the design and preparation of a poly(ionic liquid)-derived porous organic polycarbene adsorbent with superior gold-capturing capability. With carbene sites in the porous network as the “nanotrap”, it exhibits an ultrahigh gold recovery capacity of 2.09 g/g. In-depth exploration of a complex metal ion environment in an electronic waste-extraction solution indicates that the polycarbene adsorbent possesses a significant gold recovery efficiency of 99.8%. X-ray photoelectron spectroscopy along with nuclear magnetic resonance spectroscopy reveals that the high performance of the polycarbene adsorbent results from the formation of robust metal-carbene bonds plus the ability to reduce nearby gold ions into nanoparticles. Density functional theory calculations indicate that energetically favourable multinuclear Au binding enhances adsorption as clusters. Life cycle assessment and cost analysis indicate that the synthesis of polycarbene adsorbents has potential for application in industrial-scale productions. These results reveal the potential to apply carbene chemistry to materials science and highlight porous organic polycarbene as a promising new material for precious metal recovery.

Light-Assisted Synthesis of Silver and Gold Nanoparticles by New Benzophenone Derivatives.

Benzophenone derivatives were evaluated as new photoinitiators in combination with triethylamine (TEA) and iodonium salt (Iod) for very rapid and efficient formation of metal nanoparticles in an organic solvent, by which silver and gold ions were reduced under light at 419 nm (photoreactor) with an irradiation intensity of 250 microwatts/cm2. The new benzophenone derivatives combined with TEA/Iod salt showed good production of metal nanoparticles (Au0 and Ag0) and a small size of nanoparticles of around 4-13 nm. The photochemical mechanisms for the production of initiating radicals were studied using cyclic voltammetry, where a negative ΔG of around -1.96 eV was obtained, which made the process favorable. The obtained results proved the formation of amine and phenyl radicals, which led to the reduction of gold III chloride or silver ions to the gold and silver NPs. The UV-vis spectroscopy technique was used as a very beneficial tool for the surface plasmon resonance band detection of metal nanoparticles. To sum up the results, we have observed that nanoparticles (NPs) were distributed differently in different photoinitiator systems and the particle size also changed by changing the system of initiation. In comparison to the system alone, not only were the nanoparticles smaller but they were also generated within a shorter period of irradiation time for the system BP\Iod\TEA. Finally, the quenching process of benzophenone fluorescence by the gold and silver nanoparticles was investigated.

Machine Learning Analysis of Reaction Parameters in UV-Mediated Synthesis of Gold Nanoparticles

Gold nanoparticles represent an important class of functional nanomaterials for optoelectronics, biomedical applications, and catalysis. Therefore, controllable synthesis of nanoparticles with specified size and shape is important. Though reduction of gold ions is quite a simple process and may be performed with many different protocols, the reproducibility of the results and transfer of protocols between independent research groups remains a challenging task. Machine learning analysis based on statistical approaches is hardly applicable to the published data, since most of the researchers report only successful syntheses. In this work, we apply uniform sampling of the reaction parameter space. The concentrations of gold precursor, reducing agent, and surfactant were varied via an improved Latin hypercube sampling, and each run was performed under in situ UV–vis control. Based on the resulting set of optical spectra, we address the relevant chemical questions about nanoparticle formation, their shape, and period of growth. Our work demonstrates a data driven approach applied to the space of reaction parameters in a limited available set of experiments.

Coordination of Noble Metals in Poly(vinyl mercaptoethanol) Particles Prepared by Precipitation/Emulsion Polymerization

AbstractS‐Vinyl monomers react readily in radical polymerizations resulting in polymers with interesting features such as enhanced refractive indices, increased thermal stability, or the ability to coordinate various metals. Among them, vinyl mercaptoethanol (VME) can be produced in industrial scale, but the poor solubility of the resulting homopolymer limits its application. In this contribution, polymerizations of the monomer are investigated in water forming a heterogeneous system. The good solubility of the monomer in water imparts the system with mixed characteristics between a precipitation and an emulsion polymerization. Evaluating various surfactants, only polyvinyl alcohol (PVA) is found to create stable dispersions, although micrometer‐sized particles are formed with a broad size distribution. Nevertheless, the particles are able to coordinate silver or gold ions. Attempts to reduce the noble metal ions by commercial reducing agents fail. However, exposure to sunlight unexpectedly results in a controlled reduction of the metal ions and the formation of composite particles. Silver ion‐containing dispersions demonstrate strong antibacterial properties, while the effect is diminished in the corresponding composite. Overall, the precipitation/emulsion polymerization of VME represents a promising pathway to stable sulfur‐rich polymer dispersions with the ability to coordinate metal ions or form reactive metal composites.

Promoting plasmonic photocatalysis with ligand-induced charge separation under interband excitation.

Plasmonic nanoparticles have been demonstrated to enhance photocatalysis due to their strong photon absorption and efficient hot-carrier generation. However, plasmonic photocatalysts suffer from a short lifetime of plasmon-generated hot carriers that decay through internal relaxation pathways before being harnessed for chemical reactions. Here, we demonstrate the enhanced photocatalytic reduction of gold ions on gold nanorods functionalized with polyvinylpyrrolidone. The catalytic activities of the reaction are quantified by in situ monitoring of the spectral evolution of single nanorods using a dark-field scattering microscope. We observe a 13-fold increase in the reduction rate with the excitation of d-sp interband transition compared to dark conditions, and a negligible increase in the reduction rate when excited with intraband transition. The hole scavenger only plays a minor role in the photocatalytic reduction reaction. We attribute the enhanced photocatalysis to an efficient charge separation at the gold-polyvinylpyrrolidone interface, where photogenerated d-band holes at gold transfer to the HOMO of polyvinylpyrrolidone, leading to the prolonged lifetime of the electrons that subsequently reduce gold ions to gold atoms. These results provide new insight into the design of plasmonic photocatalysts with capping ligands.

Synthesis of aminated three-layered hollow mesoporous organosilica spheres and in-situ loading gold nanoparticles

• atHMOSs with amino groups were synthesized by a sol-gel method and a subsequent hydrothermal treatment procedure. • The prepared atHMOSs exhibited well-defined three-layered hollow structure and uniform mesopores. • The amino group in atHMOS gives it the ability to load large amounts of gold nanoparticles. Hollow mesoporous spheres with hierarchical structure and functional groups were considerably interest in separation, catalysis, and biomedicine. In this work, aminated three-layered hollow mesoporous organosilica spheres (atHMOSs) are synthesized for the first time by successively co-assembling multiple organosilanes with surfactant and a subsequent hydrothermal treatment procedure. Electron microscopy shows that the prepared atHMOSs have a well-defined three-layered hollow structure with a monodisperse diameter (440 nm) and a uniform mesopores (4.1 nm). Importantly, owing to the doped amino groups successfully, the atHMOSs can effectively coordinate with gold ions, and thus gold nanoparticles loaded in atHMOSs are further prepared after reducing the adsorbed gold ions.

Synthesis of an ethylene diamine modified tannin polymer and recovery of gold(iii) ions from electronic wastes

Recycling of precious metals in electronic waste, especially gold, is important because of the high amount of ore grade. This study focuses on the usability of tannins, a natural and economical polyphenol, in gold recycling.