The Application of 2,6-Bis(4-Methoxybenzoyl)-Diaminopyridine in Solvent Extraction and Polymer Membrane Separation for the Recovery of Au(III), Ag(I), Pd(II) and Pt(II) Ions from Aqueous Solutions.

The work describes the results of the first application of 2,6-bis(4-methoxybenzoyl)-diaminopyridine (L) for the recovery of noble metal ions (Au(III), Ag(I), Pd(II), Pt(II)) from aqueous solutions using two different separation processes: dynamic (classic solvent extraction) and static (polymer membranes). The stability constants of the complexes formed by the L with noble metal ions were determined using the spectrophotometry method. The results of the performed experiments clearly show that 2,6-bis(4-methoxybenzoyl)-diaminopyridine is an excellent extractant, as the recovery was over 99% for all studied noble metal ions. The efficiency of 2,6-bis(4-methoxybenzoyl)-diaminopyridine as a carrier in polymer membranes after 24 h of sorption was lower; the percentage of metal ions removal from the solutions (%Rs) decreased in following order: Ag(I) (94.89%) > Au(III) (63.46%) > Pt(II) (38.99%) > Pd(II) (23.82%). The results of the desorption processes carried out showed that the highest percentage of recovery was observed for gold and silver ions (over 96%) after 48 h. The results presented in this study indicate the potential practical applicability of 2,6-bis(4-methoxybenzoyl)-diaminopyridine in the solvent extraction and polymer membrane separation of noble metal ions from aqueous solutions (e.g., obtained as a result of WEEE leaching or industrial wastewater).

Gold(III) recovery from aqueous solutions by raw and modified chitosan: A review.

Chitosan, a prestigious versatile biopolymer, has recently received considerable attention as a promising biosorbent for recovering gold ions, mainly Au(III), from aqueous solutions, particularly in modified forms. Confirming the assertion, this paper provides an up-to-date overview of Au(III) recovery from aqueous solutions by raw (unmodified) and modified chitosan. A particular emphasis is placed on the raw chitosan and its synthesis from chitin, characteristics of raw chitosan and their effects on metal sorption, modifications of raw chitosan for Au(III) sorption, and characterization of raw chitosan before and after modifications for Au(III) sorption. Comparisons of the sorption (conditions, percentage, capacity, selectivity, isotherms, thermodynamics, kinetics, and mechanisms), desorption (agents and percentage), and reusable properties between raw and modified chitosan in Au(III) recovery from aqueous solutions are also outlined and discussed. The major challenges and future prospects towards the large-scale applications of modified chitosan in Au(III) recovery from aqueous solutions are also addressed.

Facile cross-link method to synthesize chitosan-based adsorbent with superior selectivity toward gold ions: Batch and column studies.

The recovery of gold from wastewater has received significant attention in the last years due to its high economic value and low availability. A novel chitosan-based adsorbent (CS-GTU) was successfully synthesized by using formaldehyde as a crosslinker between chitosan and guanylthiourea, and applied for selective adsorption of AuIII from an aqueous medium. Through batch experiments, the maximum adsorption capacity of CS-GTU for AuIII could reach up to 695.63 mg/g at pH 5.0, and the adsorption process followed the Pseudo-second-order kinetic and Langmuir isotherm models, indicating that the monolayer chemisorption possibly occurred on the adsorbent surfaces. The adsorption was an enthalpy driven and spontaneous chemical process based on thermodynamic analysis. Furthermore, the adsorbent has demonstrated outstanding selectivity toward AuIII from multi-metallic solutions, and five cycled experiments of adsorption-desorption showed that CS-GTU could be efficiently regenerated. Experimental breakthrough curves were successfully simulated by using the Thomas model, which can fit the experimental data with the correlated curve (R2 > 0.9) well. This improvement in adsorption was a consequence of the complexation and electrostatic attraction of gold ions with the abundant sulfur/nitrogen-containing groups. The CS-GTU beads can be considered as a suitable and efficient adsorbent for gold ions in aqueous solutions.

Increased Recovery of Gold Thiosulfate Alkaline Solutions by Adding Thiol Groups in the Porous Structure of Activated Carbon.

Thiosulfate leaching combined with ion-exchange resins is an innovative alternative for gold recovery. According to the properties of activated carbon, it could replace resins in the gold recovery process, improve efficiency, and reduce operating cost. In this research, the adsorption process of gold thiosulfate complex on thiol-modified activated carbon was studied. Thioglycolic acid (ATG) was impregnated in activated carbon, and its adsorption ability was tested with synthetic solutions of gold and sodium thiosulfate (Au 10 mg·L-1, Na2S2O3 0.1 mol·L-1, pH = 10.0). Carbon was characterized by infrared spectroscopy, SEM-EDS, PZC titration, hardness number measures, and proximal analysis. Synthetic solutions were also characterized by UV-vis spectroscopy and cyclic voltammetry. The percentage of volatile material increased from 10.0 to 13.9% due to the impregnation process of ATG. Infrared spectra show characteristic bands of C-H, S-H, and C-S bonds. In the adsorption tests, the ATG-impregnated carbon achieved 91% of gold recovery, while the same amount of ATG in the liquid phase stirred with unmodified activated carbon reached 90% of gold recovery. The 44.9% of gold recovered with activated carbon impregnated with ATG was eluted with sodium cyanide ([NaCN] = 0.2 mol·L-1; [NaOH] = 0.25 mol·L-1; [CH3CH2OH] = 30% V/V; pH = 12.0; t = 24 h). These results suggest the gold transferred from the thiosulfate complex to a new gold thiolate complex.

Selective Gold Recovery from Homogenous Aqueous Solutions Containing Gold and Platinum Ions by Aromatic Amino Acid-Containing Peptides.

There is increasing interest in the development of noble metal separation/recovery processes, especially for applications to "urban mining". Common separation/recovery processes for noble metals use a solvent (liquid-liquid) extraction technique in hydrometallurgy. However, these processes are time-consuming and not environmentally friendly, because they use organic solvents for sequential metal ion extractions. Electrowinning is an alternative approach for selective metal precipitation that involves controlling the redox potentials of electrodes but requires specialized equipment and generates hydrogen as a byproduct at the cathode surface under dilute conditions. In the present study, we investigated selective gold recovery from a homogenous aqueous solution containing a mixture of dilute HAuCl4 and H2PtCl6 (5.0 × 10-5 M each) and aromatic amino acid-containing peptides (2.0 × 10-4 M each). Gold selectivity was determined by analyzing the compositions of the solids and supernatants obtained from the reaction mixtures. A much higher gold selectivity (gold/platinum (Au/Pt) atomic ratio = 7.5) was obtained using an anthracene-containing peptide compared to peptides containing one or two naphthalene ring(s). Our proposed approach is applicable to the sequential separation of several noble metal ions, such as Au, palladium (Pd), Pt, iridium (Ir) and rhodium (Rh), and simply requires developing aromatics suitable for each noble metal of interest.

Adsorption behavior and mechanism of Au(III) on caffeic acid functionalized viscose staple fibers.

A novel fibrous adsorbent (DAVSF-CA) was synthesized via grafting caffeic acid (CA) onto dialdehyde viscose staple fiber (DAVSF), and used to selectively adsorb Au(III) from simulated wastewater. Fourier Transform Infrared (FTIR), X-ray Photoelectron (XPS) and Nuclear Magnetic Resonance (NMR) spectra confirmed that caffeic acid was successfully grafted on DAVSF through condensation reaction. Adsorption experiments revealed that the adsorption of Au(III) on DAVSF-CA was extremely dependent on pH values and temperatures, and the maximum adsorption capacity of 3.71 mmol/g for Au(III) was obtained at pH 3.0 and 333 K according to the Langmuir fitting. High temperature was favorable for Au(III) adsorption because the adsorption of Au(III) on the DAVSF-CA was endothermic. The competitive adsorption demonstrated that DAVSF-CA had a good preference to Au(III) adsorption in the presence of some coexisting pollutants. The adsorption isotherm data of Au(III) were well-described by the Langmuir model, while the kinetic data were fitted well by the Pseudo-second-order equation. The major reaction involving the reduction of Au(III) to Au(0) was identified by XPS and XRD analysis. Namely, Au(III) was first captured on protonated functional groups via electrostatic adsorption, and then reduced to its elemental form and formed the nano-particles on the adsorbent surfaces.

SEC hyphenated to a multielement-specific detector unravels the degradation pathway of a bimetallic anticancer complex in human plasma.

The bimetallic metal complex Titanocref exhibits relevant anticancer activity, but it is unknown if it is stable to reach target tissues intact. To gain insight, a pharmacologically relevant dose was added to human blood plasma and the mixture was incubated at 37 °C. The obtained mixture was analyzed 5 and 60 min later by size-exclusion chromatography hyphenated to an inductively coupled plasma atomic emission spectrometer (SEC-ICP-AES). We simultaneously detected several titanium (Ti), gold (Au) and sulfur (S)-peaks, which corresponded to a Ti degradation product that eluted partially, and a Au degradation product that eluted entirely bound to plasma proteins (both time points). Although ~70% of the intact Titanocref was retained on the column after 60 min, our results allowed us to establish - for the first time - its likely degradation pathway in human plasma at near physiological conditions. These results suggest that ~70% of Titanocref remain in plasma after 60 min, which supports results from a recent in vivo study in which mice were treated with Titanocref and revealed Ti:Au molar ratios in tumors and organs close to 1:1. Thus, our stability studies suggest that the intact drug is able to reach target tissue. Overall, our results exemplify that SEC-ICP-AES enables the execution of intermediate in vitro studies with human plasma in the context of advancing bimetallic metal-based drugs to more costly clinical studies.

Toolkit Development for Cyanogenic and Gold Biorecovery Chassis Chromobacterium violaceum.

Chromobacterium violaceum has been of interest recently due to its cyanogenic ability and its potential role in environmental sustainability via the biorecovery of gold from electronic waste. However, as with many nonmodel bacteria, there are limited genetic tools to implement the use of this Gram-negative chassis in synthetic biology. We propose a system that involves assaying spontaneous antibiotic resistances and using broad host range vectors to develop episomal vectors for nonmodel Gram-negative bacteria. These developed vectors can subsequently be used to characterize inducible promoters for gene expressions and implementing CRISPRi to inhibit endogenous gene expression for further studies. Here, we developed the first episomal genetic toolkit for C. violaceum consisting of two origins of replication, three antibiotic resistance genes, and four inducible promoter systems. We examined the occurrences of spontaneous resistances of the bacterium to the chosen selection markers to prevent incidences of false positives. We also tested broad host range vectors from four different incompatibility groups and characterized four inducible promoter systems, which potentially can be applied in other Gram-negative nonmodel bacteria. CRISPRi was also implemented to inhibit violacein pigment production in C. violaceum. This systematic toolkit will aid future genetic circuitry building in this chassis and other nonmodel bacteria for synthetic biology and biotechnological applications.

Adsorptive recovery of Au(III) from aqueous solution using crosslinked polyethyleneimine resins.

Resin adsorption is considered as a promising method to recover gold ions from wastewater, but further reduction reaction is required to convert gold ions into particles. In this study, a crosslinked polyethyleneimine resin (CPEIR) was developed via a suspension polymerization of polyethyleneimine (PEI) and ethylene glycol diglycidyl ether (EGDE) for gold recovery. The Au(III) adsorption capacities of CPEIR were significantly impacted by solution pH and initial Au(III) concentrations but unaffected by co-existing metal ions. Compared with commercial anion-exchange resin IRA400, the CPEIR exhibited higher sorption amount and selectivity for Au(III) due to its high density of amine and hydroxyl groups on the surfaces. The adsorption isotherm of Au(III) on CPEIR was well described by the Langmuir equation, and the maximum uptake amount of Au(III) was high up to 943.5 mg/g, much higher than the reported sorbents. The adsorption kinetic data on the CPEIR were fitted well by the Pseudo-second-order equation, and the intraparticle diffusion was found to be the rate-controlling process of Au(III) adsorption. X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) analysis confirmed that Au(III) ions were adsorbed on the CPEIR via electrostatic attraction and chelating interaction, and subsequently the partial loaded Au(III) ions were reduced to elemental gold whereas the hydroxyl groups of CPEIR were oxidized to carbonyl groups.

One pot preparation of magnetic chitosan-cystamine composites for selective recovery of Au(III) from the aqueous solution.

A novel magnetic chitosan adsorbent (CDF-CS) was synthesized by inserting magnetic particles into the crosslinked compound of chitosan (CS) and cystamine based on one-step method for selectively recovering Au(III) from aqueous solution. The characterization and adsorption mechanism of CDF-CS were studied by SEM-EDS, VSM, FT-IR and XPS, respectively. The experimental results show that the adsorption capacity of CDF-CS is still large in a wide range of pH values (from 1 to 7) and has a higher adsorption capacity for Au(III) than the raw chitosan, the maximum adsorption capacity of CDF-CS for Au(III) was 478.47 mg/g about 6 h at pH = 7.0. The adsorption behavior is most consistent with this pseudo-second-order kinetic model. The adsorption process of gold ions by CDF-CS follows the Langmuir adsorption isotherm. Furthermore, the thermodynamic parameter indicates that the adsorption reaction of gold ions by CDF-CS is an endothermic chemisorption. CDF-CS has great potential for removing gold ions from aqueous solutions due to the excellent repeatability and selectivity. Finally, the adsorption mechanism is that chelation reaction and ion exchange mainly occurred between CDF-CS and Au(III). Therefore, CDF-CS is very promising in recovery of Au(III) from aqueous solutions.

High separation efficiency of gold nanomaterials of different aspect ratio and size using capillary transient isotachophoresis.

Two modes of capillary electrophoresis (CE), capillary zone electrophoresis (CZE) and capillary transient isotachophoresis (ctITP), were compared for the detection and separation of spherical gold nanoparticles (AuNPs) and gold nanorods (AuNRs). The development of ctITP using two different leading ions is described. Overall, when compared to traditional capillary zone electrophoresis (CZE), ctITP resulted in improved peak shape and peak efficiency. Specifically, the number of theoretical plates for AuNR samples increased by a factor of 2-2.5 depending on the choice of leading ion. Further, using ctITP two AuNRs differing by aspect ratio were baseline resolved, whereas the same AuNRs could not be separated using CZE or other techniques like single particle inductively coupled plasma mass spectrometry (spICP-MS) and asymmetric flow field-flow fractionation (AF4). The results of this study demonstrate that ctITP is an efficient on-line technique for the improved detection and separation of gold nanomaterials in CE.

Biogenic Au@ZnO core-shell nanocomposites kill Staphylococcus aureus without provoking nuclear damage and cytotoxicity in mouse fibroblasts cells under hyperglycemic condition with enhanced wound healing proficiency.

The aim of the present study is focused on the synthesis of Au@ZnO core-shell nanocomposites, where zinc oxide is overlaid on biogenic gold nanoparticles obtained from Hibiscus Sabdariffa plant extract. Optical property of nanocomposites is investigated using UV-visible spectroscopy and crystal structure has been determined using X-ray crystallography (XRD) technique. The presence of functional groups on the surface of Au@ZnO core-shell nanocomposites has been observed by Fourier transforms infrared (FTIR) spectroscopy. Electron microscopy studies revealed the morphology of the above core-shell nanocomposites. The synthesized nanocomposite material has shown antimicrobial and anti-biofilm activity against Staphylococcus aureus and Methicillin Resistant Staphylococcus haemolyticus (MRSH). The microbes are notorious cross contaminant and are known to cause infection in open wounds. The possible antimicrobial mechanism of as synthesized nanomaterials has been investigated against Staphylococcus aureus and obtained data suggests that the antimicrobial activity could be due to release of reactive oxygen species (ROS). Present study has revealed that surface varnishing of biosynthesized gold nanoparticles through zinc oxide has improved its antibacterial proficiency against Staphylococcus aureus, whereas reducing its toxic effect towards mouse fibroblast cells under normal and hyperglycaemic condition. Further studies have been performed in mice model to understand the wound healing efficiency of Au@ZnO nanocomposites. The results obtained suggest the possible and effective use of as synthesized core shell nanocomposites in wound healing.

Efficient prevention of nanomaterials transport in the porous media by treatment with polyelectrolytes.

Contamination of soil by engineered nanomaterials (ENM) is an emergent environmental problem that urges the development of robust treatment protocols to prevent ENM transport through soil. We developed a method for efficient entrapment and retention of ENM in solid porous media of quartz sand with grain size of 300-500 µm used as a simple model of soil and studied the transport properties of multi-walled carbon nanotubes, fullerenes, silica and gold nanoparticles through the sand-packed column by UV-vis and fluorescent spectroscopy. The treatment of ENM-contaminated porous media with a mixture of oppositely charged polyelectrolytes, cationic poly(diallyldimethylammonium chloride) and anionic poly(acrylic acid) sodium salt, dissolved in NaCl solution followed by dilution in the column results in strong electrostatic interaction between the polyelectrolytes and a formation of inter-polyelectrolyte complexes (IPEC) that induce flocculation of ENM and adsorption to the surface of sand. The method demonstrates excellent ENM entrapment efficiency (>90%) and high capacity of several grams of ENM per 1 g of polyelectrolytes. The IPEC network formed after the treatment also serves as an efficient protection barrier for newly added ENM contaminants. The method is universal for various types of ENM (carbon ENM, metal and oxide nanoparticles) and equally efficient for distilled water, tap water, or lake water eluents.

Analysis of metallic nanoparticles and their ionic counterparts in complex matrix by reversed-phase liquid chromatography coupled to ICP-MS.

Developing quantification and characterization methodology for metallic nanoparticles (MNPs) and their ionic component in complex matrix are crucial for the evaluation of their environmental behavior and health risks to humans. In this study, reversed phase high performance liquid chromatography combined ICP-MS was established for the characterization of MNPs in complex matrix. The ionic component could be separated from NPs with the optimized parameters of aqueous mobile phase. Good linear relationship between average diameter and retention time of NPs was obtained using HPLC-ICP-MS and the size smaller than 40 nm could be determined with this method, the detected results were in accordance with TEM results. The low detection limit of AuNPs and Au(Ⅲ) (both in sub-µg/L level) showed that this method was promising for the characterization of AuNPs and Au(Ⅲ) in environmental water. The mass concentration of ionic Au(Ⅲ) in environmental water could be detected using the proposed HPLC-ICP-MS and the concentration of AuNPs was obtained by subtracting the Au(Ⅲ) concentration from the total Au (The concentration of total Au was detected by ICP-MS after microwave digestion). Furthermore this proposed HPLC-ICP-MS method and single particle-ICPMS (SP-ICP-MS) was used for the analysis of the Ag speciation in commercial antibacterial products.

Sorption-reduction coupled gold recovery process boosted by Pycnoporus sanguineus biomass: Uptake pattern and performance enhancement via biomass surface modification.

Biorecovery is emerging as a promising process to retrieve gold from secondary resources. The present study aimed to explore the uptake pattern of Pycnoporus sanguineus biomass for gold, identify the effective functional groups in gold recovery process, and thus further intensify the process via microbial surface modification. Results showed that P. sanguineus biomass could effectively recover gold with the formation of highly crystal AuNPs without any exogeneous electron donor. Under the conditions of various initial gold concentrations (1.0, 2.0, and 3.0 mM), biomass dosage of 2.0 g/L, solution pH value of 4.0, and incubation temperature of 30°C, the uptake equilibrium established after 4, 8, and 12 h, respectively. The uptake process could be well described by pseudo-second order kinetics model (R2  = 0.9988) and Langmuir isotherm model (R2  = 0.9958). The maximum uptake capacity of P. sanguineus reached as high as 358.69 mg/g. Further analysis indicated that amino, carboxyl and hydroxyl groups positively contributed to the uptake process. Among them, amino group significantly favored the uptake of gold during recovery process. When P. sanguineus biomass was modified by introduction of amino group, the gold uptake process was successfully intensified by shortening the uptake period and enhancing the uptake capacity. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 33:1314-1322, 2017.

Simultaneous AuIII Extraction and In†Situ Formation of Polymeric Membrane-Supported Au Nanoparticles: A Sustainable Process with Application in Catalysis.

A polymeric membrane-supported catalyst with immobilized gold nanoparticles (AuNPs) was prepared through the extraction and in situ reduction of AuIII salts in a one-step strategy. Polymeric inclusion membranes (PIMs) and polymeric nanoporous membranes (PNMs) were tested as different membrane-support systems. Transport experiments indicated that PIMs composed of cellulose triacetate, 2-nitrophenyloctyl ether, and an aliphatic tertiary amine (Adogen 364 or Alamine 336) were the most efficient supports for AuIII extraction. The simultaneous extraction and reduction processes were proven to be the result of a synergic phenomenon in which all the membrane components were involved. Scanning electron microscopy characterization of cross-sectional samples suggested a distribution of AuNPs throughout the membrane. Transmission electron microscopy characterization of the AuNPs indicated average particle sizes of 36.7 and 2.9 nm for the PIMs and PNMs, respectively. AuNPs supported on PIMs allowed for >95.4 % reduction of a 0.05 mmol L-1 4-nitrophenol aqueous solution with 10 mmol L-1 NaBH4 solution within 25 min.

Separation, Sizing, and Quantitation of Engineered Nanoparticles in an Organism Model Using Inductively Coupled Plasma Mass Spectrometry and Image Analysis.

For environmental studies assessing uptake of orally ingested engineered nanoparticles (ENPs), a key step in ensuring accurate quantification of ingested ENPs is efficient separation of the organism from ENPs that are either nonspecifically adsorbed to the organism and/or suspended in the dispersion following exposure. Here, we measure the uptake of 30 and 60 nm gold nanoparticles (AuNPs) by the nematode, Caenorhabditis elegans, using a sucrose density gradient centrifugation protocol to remove noningested AuNPs. Both conventional inductively coupled plasma mass spectrometry (ICP-MS) and single particle (sp)ICP-MS are utilized to measure the total mass and size distribution, respectively, of ingested AuNPs. Scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDS) imaging confirmed that traditional nematode washing procedures were ineffective at removing excess suspended and/or adsorbed AuNPs after exposure. Water rinsing procedures had AuNP removal efficiencies ranging from 57 to 97% and 22 to 83%, while the sucrose density gradient procedure had removal efficiencies of 100 and 93 to 98%, respectively, for the 30 and 60 nm AuNP exposure conditions. Quantification of total Au uptake was performed following acidic digestion of nonexposed and Au-exposed nematodes, whereas an alkaline digestion procedure was optimized for the liberation of ingested AuNPs for spICP-MS characterization. Size distributions and particle number concentrations were determined for AuNPs ingested by nematodes with corresponding confirmation of nematode uptake via high-pressure freezing/freeze substitution resin preparation and large-area SEM imaging. Methods for the separation and in vivo quantification of ENPs in multicellular organisms will facilitate robust studies of ENP uptake, biotransformation, and hazard assessment in the environment.