High-purity monoclinic pyrrhotite derived from natural pyrite with excellent removal performance for Cr (VI) and its mechanism.

Pyrrhotite, especially the monoclinic type, is a promising material for removing Cr (VI) from wastewater and groundwater due to its high reactivity. However, the purity of the preparation monoclinic pyrrhotite from heated natural pyrite is not high enough, and the role of possible sulfur vacancies in pyrrhotite's crystal structure has been largely ignored in the removal mechanism of Cr (VI). In this work, we characterized the phase composition changes of annealed pyrite in inert gas and prepared high-purity (~ 96%) monoclinic pyrrhotite at the optimal condition. We found that it could remove 18.6 mg/g of Cr (VI) by redox reaction, which is the best value reported of natural pyrite-derived materials so far. As the reactive media material of simulated permeable reactive barrier, the service life of the high-purity monoclinic pyrrhotite column is 297 PV, which is much longer than that of the pyrite column (50 PV). A new founding is that S2- and S vacancy play the essential role during the redox reaction of pyrrhotite and Cr (VI). Monoclinic pyrrhotite had more S vacancy than hexagonal pyrrhotite and pyrite, which explained its superior Cr (VI) removal performance.

Submersed macrophytes Vallisneria natans and Vallisneria spinulosa improve water quality and affect microbial communities in sediment and water columns.

Healthy aquatic ecosystems are essential for human beings. However, anthropogenic activities severely worsen water quality. In this study, using assembling mesocosms, we developed an efficient and easy-to-handle method to monitor the water quality by measuring the electrical conductivity (EC) of water. Our data demonstrate that the growth of two submersed macrophytes, Vallisnerianatans and Vallisneria spinulosa, improves water quality by decreasing EC. Furthermore, using high-throughput DNA sequencing, we analyzed the microbial community abundance and structure in sediment and water columns with or without plant growth. We generated 33,775 amplicon sequence variants from 69 samples of four sediment groups (BkM, CtM, VnR, and VsR) and three water column sample groups (CtW, VnW, and VsW). The results show that the relative abundance of bacteria was higher in the sediment than in the water column. Moreover, the diversity and composition of microbiomes were altered by Vallisneria spp. growth, and the α-diversity of the microbial communities decreased due to submersed macrophytes in both the sediment and water columns. The ß-diversity of the microbial communities also varied significantly with or without Vallisneria spp. growth for both the sediment and water columns.

Gemological characteristics and inclusions of green rutilated quartz from Huanggangliang, Inner Mongolia.

Normally, various minerals exist in quartz as inclusions. In this study, methods such as gem microscopy, polarizing microscopy, Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, and electron probe microanalysis (EPMA) were used to systematically study the gemological characteristics and inclusions in green rutilated quartz from Inner Mongolia. Results show that the sample appears green due to the chaotic distribution of green inclusions in the shape of hair filaments. Combined with the chemical composition, the inclusions are Ca-Fe-rich amphiboles with compositions very close to those of the end-member ferro-actinolite. According to the principle of amphibole nomenclature, the inclusions are named ferro-actinolite in the subclass of calc-alkaline amphiboles with a few named ferro-hornblende. Results suggested that the inclusions in green rutilated quartz were formed during the late stage of quartz crystallization. This work provides a new theoretical basis for the study of green rutilated quartz in Huanggangliang, Inner Mongolia.

Controlling the Fluorescence Behavior of Hydrophobic Pigments by Supramolecular Self-Assembling on Organic Layered Silicate Minerals.

This research focused on the supramolecular self-assembly of organic fluorescent molecules on organically modified layered silicate minerals to design and prepare layered nanocomposites with excellent fluorescence properties. Aromatic hydrocarbons are hydrophobic and poorly loaded on the hydrophilic surface of layered silicate minerals, but they are easily captured by an organically modified mineral surface. Montmorillonite (MMT) and saponite (SAP), typical 2:1 type layered silicate minerals with different octahedral cations, were modified with the cationic surfactant octadecyl trimethylammonium chloride (OTAC) and loaded with pyrene (an aromatic hydrocarbon dye) with different molar ratios to the cationic surfactant by supramolecular self-assembling to construct fluorescent nanocomposites. The effect of pyrene concentration and the octahedral cation of the 2:1 type layered silicate minerals on photoluminescence properties was investigated. The fluorescence spectra of the nanocomposites prepared under low pyrene concentrations showed two bands at around 400 and 470 nm, corresponding to the monomer and excimer emissions; the band intensity of the excimer shoots up with the increase of pyrene concentration, reflecting different contributions from monomer and dimer species and the formation of radical aggregates. The excellent heat resistance of the layered silicate structure can effectively protect pyrene molecules from external environmental influences.

Highly Reversible Chevrel Phase Mo6Se8 Cathode with Low Voltage Hysteresis for Rechargeable Aluminum Batteries.

Rechargeable aluminum (Al) batteries have attracted considerable interest as potential large-scale energy storage technologies due to the abundance, high theoretical capacity, and high safety of Al. We report here a highly reversible Al-Mo6Se8 prototype cell with low discharge-charge hysteresis (approximately 50 mV under 30 mA g-1 at 50 °C), ultra-flat discharge plateau, and exceptional cycle stability: the reversible capacity retaining at a steady 77 mA h g-1 after more than 1800 cycles. The Al intercalation-extraction mechanism is probed with ex situ and operando XRD techniques, revealing the reversible intercalation reaction from Mo6Se8 to Al4/3Mo6Se8. The stable electrochemical performance and unambiguous intercalation mechanism of the Al-Mo6Se8 system provide an alternative for beyond-lithium battery technologies.

Vacancy-Enhanced Self-Reduction of Eu in Pyrophosphate Phosphor.

The self-reduction mechanism in pyrophosphate phosphors is currently explained through nonequivalent substitution for charge compensation. Nevertheless, the impact of oxygen vacancies on the self-reduction enhancement requires further investigation. Herein, heterovalent Ba1-xZn1-yP2O7:xEu2+/3+, yMg phosphors with rigid structures were prepared through conventional solid-phase technology in air. The cation substitution strategy leads to different chemistry electronegativity and adjustable crystal field environments and creates vacancy defects. Crystal structure and component analysis indicate the gradual phase segregation change from BaZnP2O7 to BaMgP2O7 with increasing Mg2+ content. The CIE coordinates that are tuned from (0.514, 0.334) to (0.326, 0.152) and realize color-tunable emission from red-orange to blue-violet can be used as multicolor functional materials. Besides, the phosphor demonstrates its maximum Sa of 0.4725% K-1 (498 K) and Sr of 1.376% K-1 (423 K). These results demonstrate that the phosphors have the potential for contactless optical temperature measurement and anticounterfeiting. This work not only investigates the self-reduction of the Eu3+ → Eu2+ phenomenon but also provides a supplementary explanation and data support to complete the effect of the oxygen vacancy on self-reduction.

Mechanistic insight into lead immobilization on bone-derived carbon/hydroxyapatite composite at low and high initial lead concentration.

The contamination of heavy metal lead has a serious impact on the natural environment and organisms. Among various materials for lead removal, animal bone derived hydroxyapatite has received extensive attention. However, there are different opinions among researchers regarding the mechanism of lead removal by hydroxyapatite, possibly due to varying initial lead concentrations used in different studies and lack of accuracy in the study of lead removal mechanisms. In present work, we synthesized a carbon-containing hydroxyapatite (CHAP) through pyrolysis of bovine bone with excellent lead removal efficiency, and further investigated the lead removal mechanism of CHAP under high and low initial lead concentrations by combining XRD Rietveld refinement, FTIR, XPS, HRTEM etc. methods. The results showed that under low initial Pb2+ concentration condition, the main mechanism of lead removal by CHAP was chemical precipitation (94.1 %), with small contributions of lead complexation with carbon functional groups and cation-π interactions on the amorphous carbon in CHAP, and surface adsorption on the precipitates. Under high initial Pb2+ concentration condition, chemical precipitation remained the main mechanism (74.68 %), but the contributions of the other three mechanisms increased, and ion exchange appeared in the later stage of the removal process. This study provides new insights on the lead immobilization mechanism by CHAP at different initial Pb2+ concentrations in water.

Magnetic Field-Enhanced Performance of Superparamagnetic LiMn2 O4 -Based Composite Slurry Electrode for Semisolid Flow Battery.

Semisolid flow batteries are expected to be applied to large-scale energy storage fields due to the combination of the high energy density of rechargeable batteries and the flexible design of flow batteries. However, electronic conductivity, specific capacity, and viscosity of slurry electrodes are generally mutually restrictive. Here, a new concept of semisolid flow batteries based on magnetic modification slurry electrode is proposed and the electrochemical performance of the semisolid electrode is expected to be improved by close contact and enhanced electronic conductivity between the active particles with the aid of external magnetic field. This concept is further demonstrated using superparamagnetic LiMn2 O4 -Fe3 O4 -carbon nanotube composite as semisolid cathode. It achieves a capacity of 113.7 mAh g-1 at a current density of 0.5 mA cm-2 with the aid of external magnetic field (about 0.4 T), which is about 21% higher than that without external magnetic field. Simulation study also reveals this improvement mainly resulted from the increase of the conductive paths of electrons after the rearrangement of the active particles under the external magnetic field. It is believed that this strategy gives a new and effective method for controlling the viscosity and electronic conductivity of the slurry electrodes and related flowable electrochemical energy storage systems.

Enhanced Electrochemical Performance of Metallic CoS-Based Supercapacitor by Cathodic Exfoliation.

Two-dimensional nanomaterials hold great promise as electrode materials for the construction of excellent electrochemical energy storage and transformation apparatuses. In the study, metallic layered cobalt sulfide was, firstly, applied to the area of energy storage as a supercapacitor electrode. By a facile and scalable method for cathodic electrochemical exfoliation, metallic layered cobalt sulfide bulk can be exfoliated into high-quality and few-layered nanosheets with size distributions in the micrometer scale range and thickness in the order of several nanometers. With a two-dimensional thin sheet structure of metallic cobalt sulfide nanosheets, not only was a larger active surface area created, but also, the insertion/extraction of ions in the procedure of charge and discharge were enhanced. The exfoliated cobalt sulfide was applied as a supercapacitor electrode with obvious improvement compared with the original sample, and the specific capacitance increased from 307 F∙g-1 to 450 F∙g-1 at the current density of 1 A∙g-1. The capacitance retention rate of exfoliated cobalt sulfide enlarged to 84.7% from the original 81.9% of unexfoliated samples while the current density multiplied by 5 times. Moreover, a button-type asymmetric supercapacitor assembled using exfoliated cobalt sulfide as the positive electrode exhibits a maximum specific energy of 9.4 Wh∙kg-1 at the specific power of 1520 W∙kg-1.

Improvement of magnetite adsorption performance for Pb (II) by introducing defects.

Surface defect engineering is an efficient strategy to enhance the adsorption properties of materials. After calcination in argon, the adsorption capacity of natural magnetite to Pb (II) is significantly improved. The Rietveld refinement, Mössbauer spectrum, and XPS were used to prove the existence of oxygen and cation vacancies in the crystal structure of magnetite after calcination, and it is found that the vacancy content is linearly related to the adsorption amount of Pb (II). This indicates that the increase in the adsorption performance of magnetite after calcination is determined by the vacancy. The adsorption capacity increases from 8 to 26 mg/g when the calcination temperature reaches 700°C. The equilibrium adsorption process of Pb (II) on magnetite can be well fitted to the Langmuir model, and the kinetic adsorption followed a pseudo-second-order mechanism. The improvement of the adsorption performance of magnetite is mainly due to the change in its structure, which depends on the oxidation degree and surface effect of magnetite in the calcination process. This work also provides a theoretical basis for the broad application of magnetite as environmental material.

Mimicking Photosynthesis: A Natural Z-Scheme Photocatalyst Constructed from Red Mud Bauxite Waste for Overall Water Splitting.

All-solid-state Z-Scheme photocatalysts have attracted significant attention due to their great potential for solar fuel production. However, delicately coupling two individual semiconductors with a charge shuttle by a material strategy remains a challenge. Herein, we demonstrate a new protocol of natural Z-Scheme heterostructures by strategically engineering the component and interfacial structure of red mud bauxite waste. Advanced characterizations elucidated that the hydrogen-induced formation of metallic Fe enabled the effective Z-Scheme electron transfer from γ-Fe2 O3 to TiO2 , leading to the significantly boosted spatial separation of photo-generated carriers for overall water splitting. To the best of our knowledge, it is the first Z-Scheme heterojunction based on natural minerals for solar fuel production. Thus our work provides a new avenue toward the utilization of natural minerals for advanced catalysis applications.

Synergistic Transition-Metal Selenide Heterostructure as a High-Performance Cathode for Rechargeable Aluminum Batteries.

We synthesize and characterize a rechargeable aluminum battery cathode material composed of heterostructured Co3Se4/ZnSe embedded in a hollow carbon matrix. This heterostructure is synthesized from a metal-organic framework composite, in which ZIF-8 is grown on the surface of ZIF-67 cube. Both experimental and theoretical studies indicate that the internal electric field across the heterostructure interface between Co3Se4 and ZnSe promotes the fast transport of electron and Al-ion diffusion. As a result, the heterostructured Co3Se4/ZnSe demonstrates superior specific capacity and cycle stability compared to the single-phase Co3Se4 and ZnSe cathode materials.

Water characterization and structural attribution of different colored opals.

The structure type and water content of opal will affect its stability and value. When the structure is Opal-A type, its value is higher. When the water content is high, its stability will decrease. The structural attribution and water distribution of pink, yellow, green, blue and purple opal have been investigated by several methodologies like powder X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and Fourier transform near infrared spectroscopy (FT-NIR). The results show that all the opal samples are CT type, among which the green sample has the highest crystallinity. The water contents of the opals range from 3.06 to 8.78%. The distribution and quantity of molecular water (H2Omol) and silanols (H2OSiOH) are calculated semi-quantitatively according to intensity of 4500 cm-1 and 5200 cm-1 peaks in the near infrared region, and it is found that the water in all the samples is basically composed of molecular water. The precipitation mechanism for opal formation results in different structural types, and the difference in structural composition leads to different water contents. This work provides a theoretical basis for the future study of the opal metallogenic environment.

Hydrological isolation affected the chemo-diversity of dissolved organic matter in a large river-connected lake (Poyang Lake, China).

The transportation processes during aquatic systems regulate the ultimate chemistry of dissolved organic matter (DOM), and in recent years, climate changes and human activities have altered the hydrological patterns of many rivers and lakes, which generated some severe issues, such as hydrological isolation. However, how hydrological isolation affects variations of DOM chemistry in large lake systems is still poorly understood. Here, optical properties and molecular compositions of DOM samples derived from a large river-connected lake (Poyang Lake, China) and its nearby seasonal sub-lakes (formed by hydrological isolation) were characterized using Fourier transform ion cyclotron resonance mass spectrometry (FT ICR MS) and ultraviolet-visible (UV-Vis) spectroscopy. The results revealed more abundance of organic matter in sub-lakes than that in the main lake according to high dissolved organic carbon (DOC) concentrations and absorption coefficients (a254 and a280). Large proportions of CHOS formulas were identified by FT ICR MS in sub-lakes DOM, which were produced through Kraft reactions (sulfide/bisulfide + lignin CHO → CHOS) in the interface of sediment/water, and greatly contributed to aliphatic compounds. In addition, obvious variations of compounds (such as polyphenols, highly unsaturated and aliphatic compounds) and lability of DOM were observed between sub-lakes and main lakes, which were mainly caused by the different degradation pathways of DOM (photodegradation in sub-lakes while biodegradation in the main lake). Our results demonstrated that hydrological isolation has significant impacts on DOM chemistry, and provides an improved understanding of the DOM biogeochemistry process in Poyang Lake and supports the management of the large lake systems.

Study of the mechanism of color change of prehnite after heat treatment.

The most common color of prehnite is green, while yellow prehnite is rare and precious. Heat treatment is usually an effective way to improve the color of gemstones, but whether heat treatment can improve the color of prehnite remains to be explored. In this paper, yellow-green prehnite samples were heat-treated under oxidizing and reducing atmospheres, and the composition, structure and chromogenic mechanism of the prehnite samples before and after the heat treatment were analyzed and summarized by means of X-ray Fluorescence Spectroscopy (XRF), X-ray diffractomer (XRD), in situ high temperature XRD, Fourier Transform Infrared Spectroscopy (FTIR), Micro-Raman Spectroscopy, UV-Vis Spectroscopy, and X-ray photoelectron spectroscopy (XPS). The results show that the change of the relative content and occupation position of Fe2+ and Fe3+ is the main reason for the color change of yellow-green prehnite. When the yellow-green prehnite is heated to 800 °C, in an oxidizing atmosphere, some of the Fe2+ is oxidized to Fe3+, the content of Fe3+ increases, and the color becomes brownish yellow; in a reducing atmosphere, some of the Fe3+ is reduced to Fe2+, the content of Fe2+ increases, and the color becomes grayish white. The UV-Vis absorption spectra of the oxidized and reduced samples at this temperature further showed that the absorption broadband at 520-700 nm caused by the charge transfer between Fe2+ and Fe3+ disappeared, resulting in a great change in the color of the prehnite. Our experimental model provides ideas and experimental data for the further study of prehnite heat treatment.

Mineralogical Characteristics and Luminescent Properties of Natural Fluorite with Three Different Colors.

Fluorite is rich in mineral resources and its gorgeous colors and excellent luminescence characteristics have attracted the attention of many scholars. In this paper, the composition, structure, luminescent properties, and the potential application value of three fluorites with different colors and are systematically analyzed. The results show that REE and radioactive elements have effects on the structure, color, and luminescence of fluorite. Radioactive elements Th and U will aggravate the formation of crystal defects in fluorite. The green color is related to Ce3+ and Sm2+. Colloidal calcium and F- center are responsible for the blue-purple color of fluorite. There are many luminescent centers, such as Eu, Pr, Dy, Tb, Er, and Sm, in fluorite. The blue fluorescence is mainly caused by 4f7-4f65d1 of Eu2+. In addition, it is found that fluorite has certain temperature sensing properties in the temperature range of 303-343 K.

Structure and Photoluminescence Properties of Dy3+ Doped Phosphor with Whitlockite Structure.

Whitlockite has the advantages of a low sintering temperature, high stability, and a low fabrication cost, and it is widely used as the host for luminescent material. In this study, Ca1.8Li0.6La0.6-x(PO4)2:xDy3+ phosphor was prepared by the high-temperature solid-state method, and its structure, composition, and luminescence properties were systematically studied. The results showed that a new whitlockite type matrix was prepared by replacing Ca2+ in whitlockite with monovalent and trivalent cations. The prepared phosphors belonged to a hexagonal crystal system with a particle size in the range of 5-20 µm. Under the excitation of 350 nm UV light, the samples emitted white light, and there were mainly two stronger emission peaks at 481 nm in the blue band and 573 nm in the yellow band, which correspond to the electron transitions at 4F9/2→6H15/2 and 4F9/2→6H13/2 of Dy3+, respectively. The optimal doping concentration of Dy3+ in Ca1.8Li0.6La0.6(PO4)2 matrix was 0.03 (mol%). The main mechanism of concentration quenching in the sample was dipole-dipole energy transfer. When the temperature was 130 °C, the luminescence intensity of the samples was 78.7% of that at 30 °C, and their thermal quenching activation energy was 0.25 eV. The CIE coordinates of the sample at 30 °C were (0.2750, 0.3006), and their luminescent colors do not change with temperature. All the results indicate that Ca1.8Li0.6La0.6-x(PO4)2:xDy3+ phosphor is a luminescent material with good luminescence performance and thermal stability, which shows a promising application in the field of LED display.

A Calibration Method for a Self-Rotating, Linear-Structured-Light Scanning, Three-Dimensional Reconstruction System Based on Plane Constraints.

This paper proposes a calibration method for a self-rotating, linear-structured-light (LSL) scanning, three-dimensional reconstruction system based on plane constraints. The point cloud of plane target collected by the self-rotating, LSL scanning, 3D reconstruction system should be constrained to the basic principle of the plane equation; it can quickly and accurately calibrate the position parameters between the coordinate system of the LSL module and the coordinate system of the self-rotating, LSL scanning, 3D reconstruction system. Additionally, the transformation equation could be established with the calibrated optimal position parameters. This paper obtains the above-mentioned position parameters through experiments and uses the calibrated self-rotating, LSL scanning, 3D reconstruction system to perform three-dimensional scanning and reconstruction of the test piece. The experimental results show that the calibration method can effectively improve the measurement accuracy of the system.

Aptamer-Integrated Scaffolds for Biologically Functional DNA Origami Structures.

The manufacture of DNA origami nanostructures with highly ordered functional motifs is of great significance for biomedical applications. Here, we present a robust strategy to produce customized scaffolds with integrated aptamer sequences, which enables direct construction of functional DNA origami structures. As we demonstrated, aptamers of various numbers and types were efficiently and stably integrated in user-defined positions of the scaffolds. Specifically, two different thrombin aptamer sequences were simultaneously inserted into the M13mp18 phage genome. The assembled functional DNA origami structures from this aptamer-integrated scaffold exhibited increased binding efficiency to thrombin and displayed more than 10-fold stronger resistance to exonuclease degradation than that produced using the traditional staple extension method. Additionally, a scaffold integrated with the platelet-derived growth factor aptamer was produced, and the assembled DNA origami structures showed significant inhibitory effect on breast cancer cells MDA-MB-231. This scalable method of creating design-specific scaffolds opens up a new way to construct more stable and functionally robust DNA origami structures and thus provides an important basis for their broader applications.

High Performance Aqueous Li-Ion Flow Capacitor Realized Through Microstructure Design of Suspension Electrode.

Suspension electrode is the core of flowable electrochemical energy storage systems, which are considered suitable for large-scale energy storage. Nevertheless, obtaining suspension electrodes with both low viscosity and high conductivity is still a big challenge. In present work, spinel LiMn2O4 was chosen as an example to make suspension with low viscosity and high conductivity through microstructure morphology control of solid particles and the contact mode between active materials and conductive additives in suspension electrode. By coating a thin layer of polyaniline on the surface of spherical spinel LiMn2O4, the resulting suspension showed much higher electronic conductivity (about 10 times) and lower viscosity (about 4.5 times) as compared to irregular and bare spinel LiMn2O4-based suspension counterpart. As a result, the Li-ion flow capacitor based on LiMn2O4 and activated carbon suspensions exhibited a record energy density of 27.4 W h L-1 at a power density of 22.5 W L-1 under static condition to date, and can be smoothly work under an intermittent-flow mode. The strategy reported in this work is an effective way for obtaining suspension electrodes with low viscosity and high electronic conductivity simultaneously. It can not only be used in the flow capacitors, but also can be extended to other flowable electrochemical energy storage systems.