Small Amounts Research Articles

Deformational and metasomatic transformations of detrital gold in the course of placer formation

The richest gold placers periodically mined since 1838 are known in the north of the Republic of Tyva, within the basin of the Amyl and Sistig-Khem rivers. Ag-Au gold is the most common, and cuprous and mercuric varieties are presented in small quantities. Lode gold occurrences are confined to quartz veins and have no economic value. Detrital gold in the placer deposits has the typical typomorphic features of placer gold: roundness, compositional heterogeneity, the presence of rims and intergranular veinlets of high-fineness gold, and particle deformation structures. We have considered the transformation mechanisms of detrital gold within the mentioned placers due to the deforming interaction of transported particles in the sedimentogenic environment at the stage of motogenesis, as well as crystallophysical effects at the stage of syngenesis – early diagenesis during heterogeneous metasomatic recrystallization of endogenous gold under conditions of differential mobility of the main mineral-forming elements of gold, Au, Ag,
 Cu, and Hg. As a result, compositionally polyphase structures formed in the particle, they are high-fineness rims along the periphery of the particles, intergranular veins of high-fineness gold, deformation structures, and increased fineness in the particle kernels.

Geochemical evolution of geothermal waters in the Pearl River Delta region, South China: Insights from water chemistry and isotope geochemistry

The Pearl River Delta (PRD) region in South China is abundant of geothermal water resources whereas geochemical evolution of the geothermal water is still poorly understood. In this study, geothermal water is sampled to investigate the provenance of CO2 and sulphate, residence time, recharge elevation, circulation depth, and water-interaction processes by analyzing chemistry of major ions and isotope geochemistry. The range of δ13C and content of bicarbonate reveal multiple sources of soil CO2, carbonate rocks, and small amounts of mantle CO2. The δ34S ratio and sulphate concentration are attributed to evaporites dissolution, input of atmospheric sulphur, seawater intrusion, and oxidation of pyrite. The residence time of up to 21.01 ka for geothermal water likely suggests the earliest precipitation recharge during the Late Pleistocene. Mountains or/and hills at an altitude of 300–760 m in north PRD region are currently the major recharge areas for the geothermal water which can circulate at the depths of up to 3000–4800 m along regional structures. The isotopic and hydrochemical analysis confirms that extensive water interaction with silicate rock, carbonate rock and evaporite, evaporation-crystallization process, and cation exchange are the key mechanisms that control the geochemical evolution of geothermal water in the PRD geothermal system.

Hybrid composite with WC/Y–TZP–Al2O3 ceramic matrix and dispersed Hadfield steel particles

Low-temperature and short-time sinter-forging has been used to obtain a dense WC/Y–TZP–Al2O3 hybrid ceramic–matrix composite with dispersed Hadfield steel with high fracture toughness. The hardness and К1С fracture toughness were 13.7 ± 0.3 GPa and 7.4 ± 0.4 MPa m1/2, respectively. The composite contained phases such as Y–TZP–Al2O3 eutectics and hypereutectic grains, WC agglomerates, γ-Fe particles as well as small amounts of Al2(WO4)3 and MnFe2O4. No t-ZrO2→m-ZrO2 transformational toughening occurred during mechanical loading so that enhanced fracture toughness resulted from forming a dense microstructures with ductile metallic interlayers between ceramic and tungsten carbide grains.

Bromination of 2D materials

The adsorption, reaction and thermal stability of bromine on Rh(111)-supported hexagonal boron nitride (h-BN) and graphene were investigated. Synchrotron radiation-based high-resolution x-ray photoelectron spectroscopy (XPS) and temperature-programmed XPS allowed us to follow the adsorption process and the thermal evolution in situ on the molecular scale. On h-BN/Rh(111), bromine adsorbs exclusively in the pores of the nanomesh while we observe no such selectivity for graphene/Rh(111). Upon heating, bromine undergoes an on-surface reaction on h-BN to form polybromides (170–240 K), which subsequently decompose to bromide (240–640 K). The high thermal stability of Br/h-BN/Rh(111) suggests strong/covalent bonding. Bromine on graphene/Rh(111), on the other hand, reveals no distinct reactivity except for intercalation of small amounts of bromine underneath the 2D layer at high temperatures. In both cases, adsorption is reversible upon heating. Our experiments are supported by a comprehensive theoretical study. DFT calculations were used to describe the nature of the h-BN nanomesh and the graphene moiré in detail and to study the adsorption energetics and substrate interaction of bromine. In addition, the adsorption of bromine on h-BN/Rh(111) was simulated by molecular dynamics using a machine-learning force field.

Oxygen Release Suppression and Electronic Conductivity Enhancement for High Performance Li‐ and Mn‐Rich Layered Oxides Cathodes by Chalcogenide Redox Couple and Oxygen Vacancy Generations

AbstractLi‐ and Mn‐rich layered oxides (LMROs) are promising cathode materials for next‐generation lithium‐ion batteries (LIBs) due to their high capacity and high energy density. However, they suffer from severe capacity and voltage fading during cycling, where the irreversible oxygen release during cycle is deemed to a severe factor. Herein, this put forward a general oxygen release suppression strategy by introducing small amounts of sodium chalcogenides during cathode slurry preparation. The formed unstable surface peroxide ions O22− of LMRO during charging is reduced to stable O2− by chalcogen ion and couples the formation of sodium chalcogenic oxides, which is reduced to sodium chalcogenides and O2− during discharging. As a result, the oxygen release is significantly suppressed and the structural stability of LMRO is greatly enhanced. Meanwhile, abundant surface oxygen vacancies are generated coupling with evidently increased carrier concentration and mobility, thus enhancing electronic conductivity significantly. The Li1.2Ni0.13Co0.13Mn0.54O2 cathode with 3 wt% Na2Se shows a capacity retention as high as 96.2% and a capacity of 225 mAh g−1 after 500 cycles at 1 C, coupling with a high capacity of 135 mAh g−1 at 10 C. The relevant mechanism for the improved electrochemical properties is revealed, which is hopefully helpful for novel strategy design to high‐performance LMRO cathodes.

H2 production by solar photoreforming of plastic materials using SiC-g-C3N4composites

The photoreforming of polyethylene terephthalate and bisphenol A was here investigated using uncommon photocatalysts (SiC-g-C3N4 composites). The results showed as the addition of small amounts of g-C3N4 on SiC promoted an efficient charge carriers separation and a good interaction between the two materials, leading to a H2 production rate of 18 and 12 μmolH2/gcat∙h for the photoreforming of polyethylene terephthalate and bisphenol A, respectively. The accurate selection of different g-C3N4 precursors, combined with the appropriate control of the key reaction parameters (pH and plastic materials pretreatments) allowed to optimize the performance of the SiC-g-C3N4 composites for the photocatalytic H2 production.

Modeling and Simulation of Community Group Buying Warehousing and Distribution Center Based on Flexsim

With the continuous increase in the demand for small quantities, diverse varieties, and high-efficiency goods distribution, there is a growing customer need for short-cycle products. In this context, leveraging Flexsim software platform, this paper models the warehousing and distribution center for community group-buying goods. The modeling encompasses key operational aspects such as product supply, storage, picking and grouping, as well as loading and unloading, and distribution. Through simulation, the results are analyzed and optimized, yielding the optimal layout scheme for the community group-buying warehousing and distribution center model.

Electrospun polymeric nanohybrids with outstanding pollutants adsorption and electroactivity for water treatment and sensing devices

Graphene oxide (GO) and carbon nanotubes (CNTs) were loaded at different mutual ratios into poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-co-HFP) matrix and electrospun to construct mats that were assessed as smart sorbents for decontaminating water from methylene blue (MB) pollutant, while ensuring the additional possibility of detecting the dye amounts. The results revealed that sorption capacity enhances upon increasing GO content, which is beneficial to wettability and active area. Equilibrium adsorption of these materials is precisely predicted by the Langmuir isotherm model and the maximum capacities herein achieved, ranging from 120 to 555 mg/g depending on the formulation, are higher than those reported for similar systems. The evolution of the structure and properties of such materials as a function of dye adsorption was studied. The results reveal that MB molecules prompted the increase of electrical conductivity of the samples in a dose-dependent manner. Mats containing solely CNTs, while displaying the worst sorption performance, showed the highest electrical performances, displaying interesting changes in their electrical response as a function of the dye amount adsorbed, with a linear response and high sensitivity (309.4 µS cm−1 mg−1) in the range 0–235 µg of dye adsorbed. Beyond the possibility to monitor the presence of small amounts of MB in contaminated water and the saturation state of sorbents, this feature could even be exploited to transform waste sorbents into high-added value products, including flexible sensors for detecting low values of pressure, human motion, and so on.Graphical Multifunctional materials for dye absorption and detection, pressure sensing, fabricated by integrating GO and CNTs into PVDF-HFP matrix via electrospinning.

Metal Activation Produces Different Reaction Environments for Intermediates during Oxidative Addition.

Commercial zinc metal powder requires activation for consistent and reliable use as a reductant in the formation of organozinc reagents from organohalides, and for the avoidance of supplier and batch-to-batch variability. However, the impact of activation methods on the reaction environments of subsequent intermediates has been unknown. Herein, a fluorescence lifetime imaging microscopy (FLIM) method is developed to bridge this knowledge gap, by imaging and examining reaction intermediates on zinc metal that has been activated by pretreatment through different common methods (i. e., by chemical activation with TMSCl, dibromoethane, or HCl; or by mechanical activation). The group of chemical activating agents, previously thought to act similarly by removing oxide layers, are here shown to produce markedly different reaction environments experienced by subsequent oxidative-addition intermediates from organohalides - data uniquely available through FLIM's ability to detect small quantities of intermediates in situ coupled with its microenvironmental sensitivity. These different microenvironments potentially give rise to different rates of formation, subsequent solubilization, and reactivity, despite the shared "[RZnX]" molecular structure of these intermediates. This information revises models for methods development for oxidative addition to currently sluggish metals beyond zinc by establishing diverse outcomes for pretreatment activation methods that were previously considered similar.

Reaction of NaBH4 and NaB(OH)4 as a way to increase the yield of hydrogen in catalytic hydrolysis of sodium borohydride by water

In this work, sodium tetrahydroxoborate (NaB(OH)4) that is the main product of the hydrolysis reaction of NaBH4 with a relatively small excess of water is studied in the reaction with sodium borohydride in the presence of a catalyst and without it. It was found, that mixtures consisting of NaB(OH)4 and NaBH4 begin to melt at 70 °C with the formation of a liquid phase without destroying the close coordination environment for both types of boron atoms. When a cobalt-based catalyst is added to mixtures, significant hydrogen evolution is observed. The resulting products are hydrogen and amorphous borates with a gross composition close to [NaBO2·0.75H2O].Carrying out the catalytic hydrolysis of borohydride in the system of initial composition H2O:NaBH4:catalyst under the conditions same to that the catalytic reaction of NaBH4 and NaB(OH)4 was observed is a promising way to produce H2 since it provides a high yield of hydrogen at small amounts of catalyst and atmospheric pressure. Catalytic hydrolysis carried out in the temperature range 80–120 °C with initial molar ratios H2O:NaBH4 = 3 and 2.7, and atmospheric pressure demonstrates a hydrogen yield of 8.3 wt% and NaBH4 conversion of 96 % at only 2.3 wt% of CoCl2 as catalyst. Since the resulting final composition of borates is close to [NaBO2·0.66H2O], the potential mass yield of hydrogen in this process can reach 9.3 wt%.

A two‐stage solution method for the design problem of medium‐thick plates in steel plants

AbstractThe medium‐thick plate is an important type of steel product widely used in construction and engineering machinery. The orders are usually characterised by multiple specifications and small quantities. The plate design is an important part in the production process of medium‐thick plate, which includes the combination of sub‐plates and the size design of the motherboard. A multi‐objective model for medium‐thick plate design is proposed based on the 2D bin packing model, comprehensively considering spatial and size constraints of the plate production. A two‐stage genetic algorithm (TSGA) is developed to solve the proposed model. In the first stage, an improved GA is used to optimise the corresponding relationship between the sub‐plates and the slab, as well as the size of the motherboard. In the second stage, an exact algorithm based on the integer programming model is applied to calculate the order layout to minimise the surplus materials. To validate the proposed method, computational experiments are conducted based on actual production data from a steel plant. The experimental results show the effectiveness of the TSGA algorithm in solving the plate design problem.

Pyrite-activated persulfate to degrade 3,5,6-trichloro-2-pyridyl in water: Degradation and Fe release mechanism

TCP (3,5,6-trichloro-2-pyridinol), the main recalcitrant degradation product of chlorpyrifos, poses a high risk to human health and ecological systems. This study provided a comprehensive exploration of the pyrite-activated persulfate (PS) system for the removal of TCP in water and placed particular emphasis on the pyrite oxidation process that releases Fe. The results showed that the pyrite-activated PS system can completely degrade TCP within 300 min at 5.0 mmol/L PS and 1000 mg/L pyrite at 25 °C, wherein small amounts of PS (1 mmol/L) can effectively facilitate TCP removal and the oxidation of pyrite elements, while excessive PS (>20 mmol/L) can lead to competitive inhibitory effects, especially in the Fe release process. Aimed at the dual effects, the evident positive correlation (R2 > 0.90) between TCP degradation (kTCP) and Fe element release (kFe), but the value of k (0.00237) in the pyrite addition variable experiment was less than that in the PS experiment (k = 0.00729), further indicating that the inhibition effect of excessive addition consists of PS but not notably pyrite. Moreover, the predominant free radicals and non-free radicals produced in the pyrite/PS system were tested, with the order of significance being •OH < Fe (Ⅳ) < SO4•- < •O2− < 1O2, wherein 1O2 emerged as the principal player in both TCP degradation and Fe release from the pyrite oxidation process. Additionally, CO32− can finitely activate PS but generally slows TCP degradation and inhibit pyrite oxidation releasing Fe process. This study provides a theoretical basis for the degradation of TCP using pyrite-activated PS.

Flexible Cages Enable Robust Supramolecular Elastomers.

Advances in modern industrial technology continue to place stricter demands on engineering polymeric materials, but simultaneously possessing superior strength and toughness remains a daunting challenge. Herein, a pioneering flexible cage-reinforced supramolecular elastomer (CSE) is reported that exhibits superb robustness, tear resistance, anti-fatigue, and shape memory properties, achieved by innovatively introducing organic imide cages (OICs) into supramolecular networks. Intriguingly, extremely small amounts of OICs make the elastomer stronger, significantly improving mechanical strength (85.0MPa; ≈10-fold increase) and toughness (418.4MJm-3; ≈7-fold increase). Significantly, the cooperative effect of gradient hydrogen bonds and OICs is experimentally and theoretically demonstrated as flexible nodes, enabling more robust supramolecular networks. In short, the proposed strengthening strategy of adding flexible cages effectively balances the inherent conflict between material strength and toughness, and the prepared CSEs are anticipated to be served in large-scale devices such as TBMs in the future.

Toward Eco‐Friendly E‐Waste Recycling: New Perspectives on Ozone‐Assisted Gold Leaching

Global demand for more effective methods to reclaim gold from electronic waste (E‐waste) has never been greater. Alternatives to hydrometallurgical methods, such as cyanide, are still limited. This work examines utilizing ozone and chlorides to recycle Au from E‐waste. It is started with a fundamental investigation of Au dissolution processes on the extended surface of Au polycrystalline and Au nanoparticulated electrodes. An online electrochemical scanning flow cell coupled with inductively coupled plasma mass spectrometry quantifies the rates and amounts of Au leaching. Identical‐location scanning electron microscopy (IL‐SEM) further correlates dissolution events with electrode morphological changes. It is demonstrated that ozone in the electrolyte imposes an anodic potential on the electrode, leading to anodic Au dissolution. Passivation disappears when small amounts of chlorides are added to the electrolyte, significantly enhancing the leaching yield. IL‐SEM images of gold nanoparticles (NPs) before and after exposure to ozone reveal heterogeneity in NP size‐dependent dissolution, showing higher dissolution for smaller particles. An effective Au leaching procedure is further demonstrated in a lab‐scale reactor using real E‐waste where almost complete recovery of Au is achieved. This research suggests that with engineering optimization in reactor applications based on ozone‐stimulated gold, dissolution can pave the way for environmentally friendly gold recycling.

A Continuous-Wave EPR Investigation into the Photochemical Transformations of the Chromium(I) Carbonyl Complex [Cr(CO)4bis(diphenylphosphino)]+ and Reactivity with 1-hexene.

Chromium complexes containing a bis(diphenylphosphino) ligand have attracted significant interest over many years due to their potential as active catalysts for ethylene oligomerisation when combined with suitable co-catalysts such as triethylaluminium (TEA) or methylaluminoxane (MAO). While there has been considerable attention devoted to the possible reaction intermediates and the nature of the Cr oxidation states involved, the potential UV photoactivity of the Cr(I) complexes has so far been overlooked. Therefore, to explore the photoinduced transformations of bis(diphenylphosphino) stabilized Cr(I) complexes, we used continuous-wave (CW) EPR to study the effects of UV radiation on a cationic [Cr(CO)4(dppp)]+[Al(OC(CF3)3)4]- complex (1), where dppp represents the 1,3 bis-(diphenylphosphino)propane ligand, Ph2P(C3H6)PPh2. Our preliminary investigations into the photochemistry of this complex revealed that [Cr(CO)4(dppp)]+ (1) can be readily photo-converted into an intermediate mer-[Cr(CO)3(κ1-dppp)(κ2-dppp)]+ complex (2) and eventually into a trans-[Cr(CO)2(dppp)2]+ complex (3) in solution at room temperature under UV-A light. Here, we show that the intermediate species (2) involved in this transformation can be identified by EPR at much lower temperature (140 K) and at a specific wavelength (highlighting the wavelength dependency of the reaction). In addition, small amounts of a 'piano-stool'-type complex, namely [Cr(CO)2(dppp-η6-arene)]+ (4), can also be formed during the photoconversion of [Cr(CO)4(dppp)]+ using UV-A light. There was no evidence for the formation of the [Cr(L-bis-η6-arene)]+ complex (5) in these UV irradiation experiments. For the first time, we also evidence the formation of a 1-hexene coordinated [Cr(CO)3(dppp)(1-hexene)]+ complex (6) following UV irradiation of [Cr(CO)4(dppp)]+ in the presence of 1-hexene; this result demonstrates the unprecedented opportunity for exploiting light activation during Cr-driven olefin oligomerisation catalysis, instead of expensive, difficult-to-handle, and hazardous chemical activators.

Self-Assembled Monolayer-Based Hole-Transporting Materials for Perovskite Solar Cells.

Ever since self-assembled monolayers (SAMs) were adopted as hole-transporting layers (HTL) for perovskite solar cells (PSCs), numerous SAMs for HTL have been synthesized and reported. SAMs offer several unique advantages including relatively simple synthesis, straightforward molecular engineering, effective surface modification using small amounts of molecules, and suitability for large-area device fabrication. In this review, we discuss recent developments of SAM-based hole-transporting materials (HTMs) for PSCs. Notably, in this article, SAM-based HTMs have been categorized by similarity of synthesis to provide general information for building a SAM structure. SAMs are composed of head, linker, and anchoring groups, and the selection of anchoring groups is key to design the synthetic procedure of SAM-based HTMs. In addition, the working mechanism of SAM-based HTMs has been visualized and explained to provide inspiration for finding new head and anchoring groups that have not yet been explored. Furthermore, both photovoltaic properties and device stabilities have been discussed and summarized, expanding reader's understanding of the relationship between the structure and performance of SAMs-based PSCs.

Phytoplankton ecology in the early years of a boreal oil sands end pit lake

BackgroundBase Mine Lake (BML) is the first full-scale end pit lake for the oil sands mining industry in Canada. BML sequesters oil sands tailings under a freshwater cap and is intended to develop into a functional ecosystem that can be integrated into the local watershed. The first stage of successful reclamation requires the development of a phytoplankton community supporting a typical boreal lake food web. To assess the diversity and dynamics of the phytoplankton community in BML at this reclamation stage and to set a baseline for future monitoring, we examined the phytoplankton community in BML from 2016 through 2021 using molecular methods (targeting the 23S, 18S, and 16S rRNA genes) and microscopic methods. Nearby water bodies were used as controls for a freshwater environment and an active tailings pond.ResultsThe phytoplankton community was made up of diverse bacteria and eukaryotes typical of a boreal lake. Microscopy and molecular data both identified a phytoplankton community comparable at the phylum level to that of natural boreal lakes, dominated by Chlorophyta, Cryptophyta, and Cyanophyta, with some Bacillariophyta, Ochrophyta, and Euglenophyta. Although many of the same genera were prominent in both BML and the control freshwater reservoir, there were differences at the species or ASV level. Total diversity in BML was also consistently lower than the control freshwater site, but consistently higher than the control tailings pond. The phytoplankton community composition in BML changed over the 5-year study period. Some taxa present in 2016–2019 (e.g., Choricystis) were no longer detected in 2021, while some dinophytes and haptophytes became detectable in small quantities starting in 2019–2021. Different quantification methods (qPCR analysis of 23S rRNA genes, and microscopic estimates of populations and total biomass) did not show a consistent directional trend in total phytoplankton over the 5-year study, nor was there any consistent increase in phytoplankton species diversity. The 5-year period was likely an insufficient time frame for detecting community trends, as phytoplankton communities are highly variable at the genus and species level.ConclusionsBML supports a phytoplankton community composition somewhat unique from control sites (active tailings and freshwater lake) and is still changing over time. However, the most abundant genera are typical of natural boreal lakes and have the potential to support a complex aquatic food web, with many of its identified major phytoplankton constituents known to be primary producers in boreal lake environments.

Amino-grafted basic mesoporous silicas: a type of highly performant catalysts for the green synthesis of 2-amino-4H-chromenes

Novel series of amino-grafted mesoporous silica materials applied to the green and efficient synthesis of 2-amino-4H-chromenes, from salicylaldehydes and ethyl cyanoacetate, under mild and free-solvent conditions, is herein reported for the first time. These catalysts are easily prepared by using the post-synthetic method, by functionalizing the SBA-15 silica with the corresponding amino silanes. The observed catalytic performance is mainly controlled by the type and concentration of basic sites. The methodology herein reported could be considered as an environmentally friendly alternative for the selective chromene synthesis, which allows to achieve high yields in short reaction times using notably small amounts of the catalysts. The experimental results are also supported with theoretical calculations, which suggest that the amine groups at the silica surface are behind the observed catalytic performance with the assistance of the silica matrix.

Sodium Carbonate Pulping of Wheat Straw—An Alternative Fiber Source for Various Paper Applications

European paper mills are currently facing the question of whether recovered paper, their main raw material, will be available in sufficient quantities and an acceptable quality in the future. An alternative to recovered paper or wood fiber is the use of agricultural residues such as wheat straw. Sodium carbonate-based straw pulping processes have the advantage of not requiring recausticizing for chemical recovery, which reduces investment and operating costs. With the addition of oxygen, delignification can be significantly improved to provide pulps suitable for bleaching. This study compares the pulping of wheat straw using sodium carbonate, sodium carbonate + oxygen, and sodium carbonate + sodium hydroxide + oxygen. Pulping parameters such as temperature, retention time, and chemical charge were varied, and their influence on pulp properties was studied. The use of sodium carbonate alone produced pulps with high yields of up to 72% and comparably high burst and compressive strength. The addition of oxygen and small amounts of sodium hydroxide produced pulps with a high initial brightness of 42 %ISO and a low kappa number (18), still at high pulp yields of 62%. These pulps were two-stage bleached to achieve brightness levels of up to 73 %ISO.

Enzyme model-catalyzed oxidative polymerization of 5-cyano-2-methoxyphenol, a new phenolic monomer with cyano substituent

Abstract Oxidative polymerization of 5-cyano-2-methoxyphenol was achieved with high C–O coupling selectivity by an enzyme model-catalyst as the first example of a cyano-substituted phenol. The electron-withdrawing/donating interaction of the substituents would lead to high reactivity and selectivity. Surprisingly, the resulting polymer showed a very narrow molecular weight distribution. The polymer consisted of a linear unit with small amounts of branched and bent units, in which C=O structure was slightly detected but could be reduced by lowering the reaction temperature.