Clean Gold Research Articles

Time and frequency spillovers and drivers between rare earth and energy, metals, green, and agricultural markets

This study investigates the time and frequency return and volatility spillover relationship between rare earth markets and oil, clean energy, gold, base metal, green bond, ESG, and agricultural markets by adopting the spillover indices introduced by Diebold and Yilmaz (2014) and Baruník and Křehlík (2018). As a more comprehensive view of the spillover relationship between rare earth and these industries, this study fills the gap in the existing literature on the relationship between rare earth and energy, metals, or green-related markets. Moreover, we conduct a regression analysis to reveal the drivers of the connectedness network. The empirical results suggest that the rare earth metals (REM) market is a net spillover receiver from the base metal, clean energy, and ESG markets, which are the top three net risk emitters. The network connectedness results shed light on the connections and strengths at different time horizons throughout the sample. The regression results indicate that financial condition and investor sentiment play the most significant roles in driving connectedness and have different effects at different frequencies. Furthermore, severe financial stress may increase short-term risk spillover, which indicates that investors sell out risky assets in stressful times. However, financial stress decreases long-term spillover, which implies that it damages the long-term operation of the financial market. The results could guide investors holding REM assets to balance risk and return and also provide references for policymakers to monitor market conditions and adopt policies to foster the health of the REM market.

Short- and long-run determinants of the price behavior of US clean energy stocks: A dynamic ARDL simulations approach

This paper aims to identify factors that drive US clean-energy stock price movements in the short and long term, using a wide range of variables representing the carbon emission market, non-green financial assets, non-renewable commodities, macroeconomic fundamentals, investor attention and sentiment, and global stress and uncertainty. The empirical investigation is carried out in the context of the elastic-net regularization (ENET) approach and dynamic simulations of the autoregressive distributed lag (DYNARDL) model, with proper consideration to the potential presence of structural changes. From among 26 candidate variables, the ENET selects the clean technology market, public attention to clean energy, oil, and gold as the primary factors contributing the most to the behavior of clean-energy stock prices. The estimation results of the DYNARDL model suggest that the clean technology market and oil are vital determinants in the short and long run, while public attention and gold tend to affect clean-energy stock prices only in the short run. Furthermore, the respective magnitudes of influence of the four variables are larger in the short term than in the long term. Our findings offer practical implications for socially responsible investors and policymakers.

Precious metals as safe-haven for clean energy stock investment: Evidence from nonparametric Granger causality in distribution test

The study aims to examine the connectedness between clean energy stocks and precious metals prices under the different market episodes. We employ the Granger causality-in-the distribution test proposed by Candelon and Tokpavi (2016) to investigate the presence of a causality relationship between the variables for the whole distribution because the test has superior power even if the sample size is small. WilderHill Clean Energy Index is considered a benchmark for the clean energy stock market and gold, silver, platinum, and palladium prices are used for the precious metals. By using daily data from January 1, 2001, to December 12, 2021, we find that there is a unidirectional causal link running from the clean energy stock returns to the precious metal prices in the center and the left tail of the distribution. On the other hand, there is strong feedback between the variables in the right tail of the distribution. These results show that clean energy stock prices have an edge in affecting precious metal prices and precious metals cannot be used to hedge the downside risk of clean energy stock investments.

Development of electrochemical biosensor: Voltammetric analysis of lymphocytes and indication activation of complement system

This work reports the development of an electrochemical biosensor after immobilization of the lymphocytes to detect the reaction between antibodies and specific HLA antigens present in the serum samples. A clean homemade gold electrode with voltammetric polycrystalline characteristics was used. Lymphocytes were immobilized and tested with positive and negative human serum and complements on the gold electrode. The experiments were carried out in a cell with three electrodes: working - gold, reference - Ag/AgCl/sat. KCl and auxiliary - platinum. The cyclic voltammetric analyses of immobilized lymphocytes on the gold surface presented anodic current equal to 1.78 μA at c.a. 0.50 V vs. Ag/AgCl/sat. KCl. The electrochemical responses of the serum (positive and negative) and complement do not show signs of oxidation or reduction in the potential range used. The electrodes with cells and positive serum showed the amplified current signal in the oxidation potential of the cells. The electrode was developed to verify the antigen antibody reaction, present lymphocyte cell and human serum samples. The electrode was qualitatively efficient when compared to the methods of flow cytometric analysis and complement dependent cytotoxicity, being able to be used with operational and economic advantages.

The reaction of thiols on a model gold catalyst leads to the formation of thiolates capable of self-coupling and of displacing carboxylic acids

The pathways of heterogeneous catalytic reactions depend on the adequate stability of reagents and intermediates on the catalyst. The development of efficient, selective catalysts require an understanding of such stability and it may differ from the one observed in the gas phase. Herein, we report the enhanced acidity of ethanethiol and benzenethiol (with respect to the gas-phase acidity) on an oxygen-covered gold surface as a model catalyst. This increased acidity is caused by the strong affinity of sulfur towards gold and leads to a facile dehydrogenation, even on a clean gold surface. The resulting thiolate species undergo further reactions through β-H elimination in ethanethiol and to coupling products for both thiols. Remarkably, this acidity is sufficient to displace formic acid and trifluoroacetic acid, confirming the increased surface stability of thiolates on gold. Nevertheless, the displacement of ethanethiol by benzenethiol shows that other effects, such as the van der Waals interactions, can add to the stability of intermediates. This study contributes to the understanding of the affinity of sulfur with gold and its impact on its catalytic activity.

A clean, green haven?—Examining the relationship between clean energy, clean and dirty cryptocurrencies

Is clean energy a safe haven for cryptocurrencies, or vice versa? In this paper, we investigate the hedge and safe haven property of a wide range of clean energy indices against two distinct types of cryptocurrencies based on their energy consumption levels, termed “dirty” and “clean”. Statistical evidence shows that clean energy is not a direct hedge for either of types. However, it serves as at least a weak safe haven for both in extreme bearish markets. Moreover, clean energy is more likely to be a safe haven for dirty cryptocurrencies than clean cryptocurrencies during increased uncertainty. We further study the spillover patterns among clean energy, cryptocurrency, stock, and gold markets. Weak connectedness is found between clean energy and cryptocurrencies which implies the potential use of clean energy as a hedge and diversification tool for cryptocurrencies in the future.

Relationships among the Fossil Fuel and Financial Markets during the COVID-19 Pandemic: Evidence from Bayesian DCC-MGARCH Models

This study examined how the relationships among the fossil fuel, clean energy stock, gold, and Bitcoin markets have changed since the COVID-19 pandemic took place for hedging the price change risks in the fossil fuel markets. We applied the Bayesian Dynamic Conditional Correlation-Multivariate GARCH (DCC-MGARCH) models using US daily data from 2 January 2019 to 26 February 2021. Our results suggest that the fossil fuel (WTI crude oil and natural gas) and financial markets (clean energy stock, gold, and Bitcoin) generally had negative relationships in 2019 before the pandemic prevailed, but they became positive for a while in mid-2020, alternating between positive (0.8) and negative values (−0.8). As it is known that negative relationships are required among assets to hedge the risk of price changes, this implies that stakeholders need to be cautious in hedging the risk across the fossil fuel and financial markets when a crisis like COVID-19 occurs. However, our study also revealed that such negative relationships only lasted for three to six months, suggesting that the effects of the pandemic were short term and that stakeholders in the fossil fuel markets could cross hedge with the financial markets in the long term.

Making untreated carbon effective in cleaner thiosulfate system: A new and high-efficiency method including gold adsorption and desorption

Compared with the cyanide method, the thiosulfate method is a green and clean gold production method, while gold recovery from thiosulfate solution is pending. Although the activated carbon adsorption method has been highlighted, current studies cannot avoid the complexity of activated carbon modification. This study used thiosemicarbazide (TSC) as the additive of the gold solution, investigating the gold recovery performance of pristine activated carbon and its adsorption mechanism. As a result, even for containing gold 100 mg/L, gold adsorption percentage close to 100% could be achieved on original carbon within 12 h when adding 0.02 g TSC. Next, under the optimal conditions, gold loading amount of 42.6 kg/t was attained after five-stage adsorption. Characterization via XPS, FT-IR, BET, and UV–vis verified the gold adsorption mechanism was related to TSC's decomposition into SCN− under activated carbon's catalysis, the formation of Au(SCN)2- and whose adsorption on the surface of original carbon. Furthermore, it was found that this method exhibited well gold recovery ability (99%) for gold in both Cu2+-en-S2O32− and Cu2+-NH3-S2O32− solutions; Additionally, well gold recovery performance (99%) was also achieved for two leaching solutions (Au: 35 and 42 mg/L, Cu2+: 3178 mg/L) of an actual ore. Last, gold desorption studies indicated that a good gold desorption rate of 95.3% was achieved within 24 h for carbon containing 5 kg/t of gold when using N, N-dimethylformamide (DMF) as desorbent. This paper gifted untreated activated carbon with excellent adsorption ability towards gold in thiosulfate system for the first time, which is meaningful for the cleaner production gold.

Polarization Spectroscopy of Anisotropic Plasmons in Self‐Oriented Nanoclusters of Gold on Monolayer of Nitrogen Atoms Chemisorbed at GaAs(001) Surface

Herein, the formation of Au nanoclusters on nitridized GaAs(001) surface is described, as well as the structure diagnostics and spectroscopic studies which reveal a strong anisotropy of the plasmons localized on the clusters. Principal aspects of the work are the following. Technologically, structures of Au/N/GaAs are fabricated with a monolayer of nitrogen atoms chemisorbed preliminary onto GaAs substrate to prevent its reaction with subsequently deposited Au film. Annealing of the structures Au/N/GaAs results in the appearance of anisotropic nanoclusters of chemically clean gold on GaAs surface. Experimentally, the existence of in‐surface anisotropy of Au clusters is verified with the atomic force microscopy and it is investigated with the resonant optical spectroscopies of anisotropy reflectance and polarized reflection. All the methods are applied jointly for the detailed study of anisotropic plasmons revealed in gold nanocluster arrays. Theoretically, the plasmon‐conditioned features observed in optical polarized spectra are interpreted using an optical model of in‐surface anisotropic plasmons in Au nanospheroids. As a result, the macroscopic anisotropy and orientation of gold nanoclusters and their plasmons relative to the crystallographic axes of GaAs substrate are unambiguously established and reliably specified.

Eco-friendly and reagent recyclable gold extraction by iodination leaching-electrodeposition recovery

Although iodination gold leaching is a clean, non-toxic and efficient non-cyanide gold leaching process, it still has the problems of high reagents cost and difficult leaching solution treatment. To solve these problems, a process of iodination leaching-electrodeposition recovery was proposed. Thermodynamic analysis confirmed the feasibility of iodination gold leaching, and the influence of different factors on gold leaching was studied. The result shows that roasting could effectively improve the gold leaching effect, the concentration of initial iodine and initial iodide ion had a significant effect on the gold leaching, and the gold leaching could be achieved under normal temperature and neutral conditions. The kinetic analysis shows that the gold leaching process conforms to the shrinkage kinetics model, and the control step was the solid film diffusion control. The apparent activation energy of this reaction was 8.642 kJ/mol, and the reaction order of initial iodine concentration and initial iodide ion concentration were 0.72 and 0.52, respectively. Gold was recovered from the leaching solution by electrodeposition with a recovery percentage of more than 99%. More importantly, the iodine was formed in the anode area, in other words, the reagents used for gold leaching were enriched in the anode area during the gold recovery process. The recovery percentage of iodine in the anode area reached 83%, and the anolyte could be recycled. This process fundamentally solves the problem of high cost of iodination leaching.

Glucosamine to gold nanoparticles binding studied using Raman spectroscopy

The binding of glucosamine to gold in water solutions of glucosamine hydrochloride mixed with clean colloidal gold nanoparticles obtained by laser ablation in liquid was studied using surface-enhanced Raman scattering (SERS), dynamic light scattering (DLS) and UV–VIS spectroscopy. The purpose of this study was to establish whether the binding of charged aminogroup to gold nanoparticles (AuNPs) is taking place, and if it does, how can it be identified by means of SERS.The average size of dried gold nanoparticles was (20 ± 4) nm determined by averaging the sizes observed in transmission electron microscopy micrographs, which is smaller than the average size of gold nanoparticles in water solution as determined by DLS: (52 ± 2) nm. Upon adding the glucosamine solutions to gold colloid, average hydrodynamic diameter of ions was slightly larger for 0.1 mM glucosamine solution (55 ± 2 nm), while it increased to (105 ± 22) nm in the case of 1 mM solution, and was (398 ± 54) nm when 10 mM glucosamine solution was added.Most prominent Raman bands observed both for 0.1 mM and 1 mM glucosamine solutions were located at 1165 cm−1, 1532 and 1586 cm−1 and assigned to C-N coupled with C-C stretching, and C-NH3+ deformation angles bending. In SERS spectrum of 1 mM GlcN+ solution, two strong bands at 999 and 1075 cm−1 were found and attributed to C-Oring stretching coupled with C-NH3+ bending (999 cm−1) and to dominantly C-O stretching vibration. The differences in SERS spectra are attributed to different number of glucosamine molecules that attach to gold nanoparticles and their orientation with respect to the metal particle surface, partly due to presence of beta anomers protonated at anomeric oxygen position. The assignment of glucosamine bands was further corroborated by comparison with vibrational spectra of alpha and beta glucose and of polycrystalline powder of glucosamine hydrochloride. For all three substances comprehensive calculation of vibrational density of states was conducted using density functional theory. Benchmark bands for polycrystalline glucose anomers distinction are 846 and 915 cm−1 for alpha glucose, and 902 cm−1 for beta glucose. However, the bands observed in SERS spectra of 0.1 mM glucosamine solution at 831, 899, and 946 cm−1 or in 1 mM solution at 934 cm−1 cannot be easily identified as belonging either to alpha or beta glucosamine anomer, due to complexity of atomic motions involved. The identification of vibrational bands associated with –CNH3+ group will aid SERS studies on amino acids, especially in cases when several atomic groups could possibly bind to AuNPs.

Electrokinetic Streaming Current Method to Probe Polycrystalline Gold Electrode-Electrolyte Interface Under Applied Potentials

We developed a method, by combining electrochemical and electrokinetic streaming current techniques to study ion distribution and ionic conductivity in the diffuse part of electrochemical double layer (EDL) of a metal-electrolyte interface, when potential is applied on the metal by a potentiostat. We applied this method to an electrochemically clean polycrystalline gold (poly Au)-electrolyte interface and measured zeta potential for various applied potentials, pH, and concentration of the electrolyte. Specific adsorption of chloride ions on poly Au was studied by comparing measurements of zeta potential in KCl and KClO4 electrolytes. In absence of specific adsorption, zeta potential was found to increase linearly with applied potential, having slope of 0.04–0.06. When Cl− adsorption occurs, zeta potential changes the sign from positive to negative value at ∼750 mV vs Ag/AgCl applied potential. Complementary cyclic voltammetry and X-ray photoelectron spectroscopy studies were conducted to determine a degree of chloride ion adsorption on a poly Au. A correlation was observed between the applied potential at which zeta potential is zero and potential of zero charge for poly Au. Ion-distribution and ionic conductivity in the diffuse layer were calculated from the measured zeta potential data using nonlinear Poisson-Boltzmann distribution.

Immunosensor incorporating half-antibody fragment for electrochemical monitoring of amyloid-β fibrils in artificial blood plasma

In this report, an electrochemical immunosensor for the selective and sensitive monitoring of Aβ1-42 fibrils is presented. The sensing platform was prepared by the formation of a 4,4′-thiobisbenzenethiol (TBBT) self-assembled monolayer on a clean gold surface followed by the covalent entrapment of gold nanoparticles (AuNPs). The half-antibody fragments of the Anti-Amyloid Fibrils antibody were immobilized on AuNPs via S-Au covalent bonds. Each step of immunosensor fabrication was characterized with cyclic voltammetry and electrochemical impedance spectroscopy. The biosensor was successfully used for the sensing of Aβ1-42 fibrils in both phosphate saline buffer (PBS) and artificial blood plasma (ABP). The immunosensor sensitivity estimated based on calibration slopes was better in the presence of APP in the comparison to PBS. The LOD values obtained for both measuring media were of 0.6 pM level. The moderate response towards Aβ1-42 oligomers demonstrated the immunosensor selectivity.

Measuring and Controlling the Local Environment of Surface-Bound DNA in Self-Assembled Monolayers on Gold When Prepared Using Potential-Assisted Deposition

DNA self-assembled monolayers (SAMs) were prepared using potential-assisted deposition on clean gold single-crystal bead electrodes under a number of conditions (constant or square-wave potential perturbations in TRIS or phosphate immobilization buffers with and without Cl-). The local environment around the fluorophore-labeled DNA tethered to the electrode surface was characterized using in situ fluorescence microscopy during electrochemical measurements as a function of the underlying surface crystallography. Potential-assisted deposition from a TRIS buffer containing Cl- created DNA SAMs that were uniformly distributed on the surface with little preference to the underlying crystallography. A constant (+0.4 V/SCE) or a square-wave potential perturbation (+0.4 to -0.3 V/SCE, 50 Hz) resulted in similar DNA-modified surfaces in TRIS immobilization buffer. Deposition using a square-wave potential without Cl- resulted in lower DNA surface coverage. Despite this, the local environment around the DNA in the SAM appears to be densely packed. This implies the formation of clusters of densely packed DNA in the SAM. This effect was also demonstrated when depositing from a phosphate buffer. DNA clusters were significantly reduced when Cl- was present in the buffer. Clusters were most prevalent on the low-index plane surfaces (e.g., {111} and {100}) and less on the higher-index planes (e.g., {210} or {311}). A mechanism is proposed to rationalize the formation of DNA-clustered regions for deposition using a square-wave potential perturbation. The conditions for creating clusters of DNA in a SAM or for preventing these clusters from forming provide an approach for tailoring the surfaces used for biosensing.

Price spillovers between rare earth stocks and financial markets

We study price transmission between rare earth stocks and the base metals, gold, clean energy, oil and global MSCI stock markets. Using a Markov switching vector autoregressive model that accounts for different volatility regimes, our empirical findings reveal that price connectedness between rare earth (RE) and other stock markets differs across volatility regimes. Specifically, in a low-volatility regime: (a) RE stocks are linked to the base metals market, receiving and transmitting sizeable price spillovers, and (b) RE stocks are weakly connected with clean energy, gold, oil and general stock markets. In contrast, in a high-volatility regime, there is increased RE price co-movement with price oscillations in the clean energy, oil and general stock markets. These findings have implications for hedging risk associated with positions in RE companies using other financial assets.

Carbon-neutral medical conferences should be the norm

Carbon-neutral medical conferences should be the norm

Orientational and Crystalline Order of Copper–Phthalocyanine Films on Gold: the Role of Substrate Roughness and Cleanliness

Although metal phthalocyanines are widely used in optoelectronic devices, e.g., as hole-transport and electron-blocking layers, or as UV-stable dyes, their multilayer growth on metal substrates has surprisingly not been studied very systematically. Even for CuPc, one of the most widely studied representatives of phthalocyanines, contradictory structures are reported for films grown on gold, a common electrode material, suggesting that the influence of actual substrate surface properties on film growth has not been sufficiently considered. In this study, we analyze the growth of CuPc films on gold substrates for thicknesses ranging from the initial seed layer to thick multilayers (50 nm) by combining near-edge X-ray absorption spectroscopy with atomic force microscopy and X-ray diffraction. To study the influence of surface roughness, we compare the formation of CuPc films on well-ordered Au(111) and sputter-deposited polycrystalline gold substrates and also investigate the influence of surface contamination by exposing these gold surfaces to air before film growth. While on clean gold substrates, CuPc molecules exclusively adopt a recumbent orientation and form (112̅)-oriented films, they also grow in an upright orientation on contaminated gold surfaces. On Au(111), this leads to the coexistence of (112̅)- and (100)-oriented regions, whereas only (100)-oriented films are formed on contaminated polycrystalline gold. Remarkably, the (112̅)-oriented films consist of extended but isolated crystalline islands, resulting in large overall roughness, whereas the (100)-oriented films consist of rather small domains but have significantly lower film roughness.

Surface Oxide-Derived Nanoporous Gold Catalysts for Electrochemical CO2-to-CO Reduction

Electrochemical CO2 reduction (ECR) has become a viable option as the cost of renewable energy continues to decrease. One of the major obstacles that prevents its widespread use is the lack of efficient ECR catalysts due to our only slowly emerging understanding of catalyst design. Here, we report on a surface oxide-derived nanoporous gold catalyst prepared by one-step electrochemical dealloying that shows an extremely low overpotential (Faradaic efficiency for CO exceeds 90%) of 0.185 V (−0.3 V vs RHE) for CO2-to-CO conversion in 0.1 M KHCO3 solution. We demonstrate that surface oxide-derived nanoporous gold shows improved ECR performance with higher Faradaic efficiency compared to clean nanoporous gold which is the consequence of its smaller overpotential for CO2-to-CO reduction and simultaneous suppression of hydrogen evolution.

Reducing global mercury pollution with simultaneous gold recovery from small-scale mining tailings

Author Summary: The increasing population on planet Earth has many impacts—one is a strong influence on the amount of mercury released to the environment. The worst influence stems from the rapidly increasing number of small-scale gold miners in Asia, Africa, Central and South America, who presently provide food on the table for tens of millions of households. Small-scale gold miners use vast amounts of mercury to capture the gold, and much of this mercury is released directly to the environment. A large part evaporates to the atmosphere and the rest is transported downstream in rivers ending up in the oceans. The amount of mercury released is phenomenal: an estimated 3000 tons of mercury is released annually by small-scale gold miners alone. A vast proportion enters the food chain in fish and sea mammals, as well as in rice polluted by spillage waters which enters irrigation pathways. Human consumption of polluted fish and/or rice already today has a crippling impact on human health in some countries, and this will have even more severe consequences if the current situation is not changed radically and rapidly. It is of particular concern if mercury-intoxicated women become pregnant, because the foetus extracts mercury from the mother. The human foetus is much more sensitive to mercury intoxication and thus has a high risk of being born with brain damage as well as physical disabilities. Over just one generation this will cause reduced intelligence for exposed children. Through such organisations as the United Nations Environment Programme (UNEP), the World community has become acutely aware of the rapidly increasing global mercury pollution. The treaty designed to protect human health and nature, the “Minamata Convention” has today been signed by the majority of world countries. Signatory countries are hereby obliged to start initiatives to reduce and even stop mercury use. This grim outlook has prompted a group of international concerned researchers and small-scale gold miners from Philippines to start teaching small-scale gold miners to work without the use of mercury and simultaneously to find ways to clean mercury-polluted gold mining tailings, which are one of the main polluting agents. This latter will have an immediate positive economic effect for the communities involved, which should be a significant motivation to change to non-mercury recovery processes. We here describe the specific technological drive to be able to go mercury free.

Electrodepositing DNA Self-Assembled Monolayers on Au: Detailing the Influence of Electrical Potential Perturbation and Surface Crystallography.

The preparation of DNA self-assembled monolayers (SAMs) on single-crystal gold bead electrodes using an applied potential is evaluated with in situ electrochemical fluorescence microscopy. Applying a constant deposition potential or a square-wave potential perturbation during the formation of DNA SAMs is compared for two different modification methods: DNA SAM formation on a clean gold surface followed by alkythiol backfilling (as is typically done in the literature) or via thiol-exchange on an alkylthiol-modified gold surface. DNA SAMs prepared from a chloride-containing deposition buffer were not significantly different when using either square-wave potential perturbation or at a constant applied potential even when considering different surface crystallographies. Greater variations were observed when applying more positive potentials for both DNA thiol-exchange and DNA adsorption on clean Au. Our results suggest that using either a constant potential or a square-wave potential perturbation for 5 min both create defects by weakening the gold-thiol interaction. When the deposition is performed with the adsorption of chloride ions from the electrolyte, the electrodeposition results in a similar increase in DNA coverage when compared to depositions performed at open circuit potentials.