Study on Tailings Covering System Constructed by Geological Polymerization of Mine Waste. Part 2: Simulation of Oxidation Inhibition of Overburden on Acid-producing Tailings.

Acid mine drainage (AMD) is a well-recognized environmental issue associated with mining production worldwide. The second part of our study aims to assess the protective effect of using a polymer hard layer (PHL) by conducting sulphur-enriched tailing-based column experiments. An oxygen (O2) barrier was simulated using a designed column device filled with different types of tailings. All experimental columns underwent six drying-wetting cycles, and the chemical properties of the tailings and leachate were detected after every cycle. The permeability coefficient of the PHL was only 1.16 × 10- 5 cm/s. Over the entire experimental period, none of the leachates collected from column 4 using the PHL as an O2 barrier. Moreover, the level of redox potential and pH and the contents of heavy metals such as Cu and Zn were stable in PHL covering system. These results show that a PHL is the optimal covering system.

Study of photogenerated exciton dissociation in transition metal dichalcogenide van der Waals heterojunction A2-MWS4: a first-principles study.

In order to explore the photocatalytic hydrogen production efficiency of the MoS2/WSe2 heterostructure (A2-MWS4) as a photocatalyst, it is highly desirable to study the photogenerated exciton dissociation related to photocatalysis. The electronic properties, optical absorption, and lattice dynamic properties of A2-MWS4 were investigated using a first-principles approach. The results show that the type II energy band alignment of A2-MWS4 facilitates the dissociation of photogenerated excitons (electrons and holes). The highly localized d-state electrons of A2-MWS4 induce the formation of internal potentials that promote the dissociation of photogenerated excitons. The hot carrier diffuses its extra energy into the lattice by scattering with phonons and forms a hot spot in the lattice while releasing phonons, which are dragged away from the hot spot by Ridley decay to promote exciton dissociation. These findings could provide insights for research studies on photochemical reactions and photovoltaic devices.

Study on Tailings Covering System Constructed by Geological Polymerization of Mine Waste, Part 1: Material Characterization and Cover Construction.

Acid mine drainage (AMD) is a serious and persistent environmental pollution problem. At present, many studies have focused on the tailings pond's cover systems. This paper introduced the research results of using tin tailings from Laili mountain to make the covering layer of tailings pond. The first part included a detailed description of tailings characterization and acid production potential. On this basis, the hard layer (HL) was prepared and its feasibility as oxidation barrier was evaluated. It was found that when the proportion of tailings waste was 70%, the immobilization efficiency of heavy metals can reach more than 99.45%, and the pH of leaching solution was about 10.8. Moreover, the beneficial effect of solid waste addition on the HL was also verified. This suggests that HL as a post-mining restorative strategy has strong positive influence on pollution control.

Recent Advances and Future Prospects on the Tailing Covering Technology for Oxidation Prevention of Sulfide Tailings.

Acid mine drainage, produced from sulfur-containing mine waste exposed to air, water, and bacteria, is considered as a serious environmental pollutant because of its extremely low pH and excessive heavy metals. In order to solve the ecological environment problems caused by the acid mine drainage, treatment methods such as neutralization, adsorption, passivation, bio-inhibition, and physical coverage have been developed. Nevertheless, these methods are terminal treatment methods, which are unable to prevent the generation of acid mine drainage at the source. Recently, it is noteworthy that the tailing covering technology is particularly emphasized, owing to its superior source control capability. By reducing the contact with air, water, and bacteria, the oxidation of sulfide tailings is significantly reduced, thus avoiding the production of acid mine drainage. To date, massive research has been studied and parts of technologies have been applied, but the review on the principles, processes, and applications of these technologies are still lacking. Thus, the present review aims to increase the knowledge related to the most relevant application of tailing covering technology with the following aspects: (i) the background, concepts, and performance of tailing covering technology; (ii) the applicable conditions for each tailings coverage system and their advantages and limitations; and (iii) the future perspective of this technology.

Dual-Metal Active Sites Mediated by p-Block Elements: Knowledge-Driven Design of Oxygen Reduction Reaction Catalysts.

In this study, the oxygen reduction reaction (ORR) process of dual-metal active site catalysts (FeMN6-Gra, M = Mn, Ni, Co, or Cu) mediated by p-block elements was investigated using density functional theory calculations. The obtained results demonstrate that, in most cases, the B-doped FeMN6-Gra (M = Mn, Ni, Co, or Cu) catalysts exhibit higher catalytic performance than their undoped counterparts. Among the investigated catalysts, FeNiN6-Gra doping by B modulates the adsorption strength of the metal center on the oxygen-containing intermediates, showing the largest increase in the onset potential (from 0.66 to 0.94 V). Importantly, we found a new law that B-doping affects the total charge of the metal adsorption site and the four surrounding N atoms and that there is a linear relationship between the total charge and the Gibbs free energy. Transition state analysis shows that the energy barrier of the thermodynamic rate-determining step (*OH hydrogenation to H2O) in the FeNiN6B1-Gra-catalyzed ORR process is 0.17 eV, which is smaller than that of the FeNiN6-Gra-catalyzed process (0.28 eV). Overall, the results demonstrate that B-doping can improve the activity of FeMN6-Gra catalysts and provide a new method for the future development of efficient electrocatalysts.

Rational design of M-N4-Gr/V2C heterostructures as highly active ORR catalysts: a density functional theory study.

Inspired by the composites of N-doped graphene and transition metal-based materials as well as MXene-based materials, heterostructures (M-N4-Gr/V2C) of eight different transition metals (M = Ti, Cr, Mn, Fe, Co, Ni, Cu, and Zn) doped with nitrogen-coordinated graphene and V2C as potential catalysts for the oxygen reduction reaction (ORR) using density functional theory (DFT) were designed and are described herein. The calculations showed that the heterostructure catalysts (except for Zn-N4-Gr/V2C) were thermodynamically stable. Ni-N4-Gr/V2C and Co-N4-Gr/V2C showed higher activities towards the ORR, with overpotentials as low as 0.32 and 0.45 V, respectively. Excellent catalytic performance results were observed from the change in electronic structure caused by the strong interaction between V2C and the graphene layers as well as the synergistic effect between the MN4 groups and the graphene layers. This study further provides insights into the practical application of ORR catalysts for MXene systems through the modulation of the electronic structure of two-dimensional materials.

A study on hydrogen storage performance of Ti decorated vacancies graphene structure on the first principle.

The structural properties, formation energy, adsorption energy, and electronic properties of vacancy graphene are studied by first-principles analysis. We found that the formation energy and adsorption energy of double vacancy graphene (DVG-4) are the largest. A single defect in DVG-4 can adsorb at least nine hydrogen molecules, and compared with Ti modified single vacancy graphene (SVG-Ti), the adsorption capacity is increased by 80%. When DVG-4 adsorbs the second, third, and fourth hydrogen molecules, the adsorption energy is greater than 0.7 eV, which is not conducive to the release. Density of state (DOS) and electron density difference (EDIFF) results reveal that charge transfer occurs among hydrogen molecules, Ti atoms, and DVG-4, decreasing the hydrogen adsorption capacity of DVG-4 by 33%. DVG - 4 has the potential to become an excellent hydrogen storage material.

Mechanism for hydrogen evolution from water splitting based on a MoS2/WSe2 heterojunction photocatalyst: a first-principle study.

In this study, density functional theory and hybrid functional theory are used to calculate the work function and energy band structure of MoS2 and WSe2, as well as the binding energy, work function, energy band structure, density of states, charge density difference, energy band alignment, Bader charge, and H adsorption free energy of MoS2/WSe2. The difference in work function led to the formation of a built-in electric field from WSe2 to MoS2, and the energy band alignment indicated that the redox reactions were located on the MoS2 and WSe2 semiconductors, respectively. The binding energy of MoS2 and WSe2 indicated that the thermodynamic properties of the heterogeneous structure were stable. MoS2 and WSe2 gathered electrons and holes, respectively, and redistributed them under the action of the built-in electric field. The photogenerated electrons and holes were enriched on the surface of WSe2 and MoS2, which greatly improved the efficiency of hydrogen production by photocatalytic water splitting.

Synthesis, characterization, and in vitro evaluation of artesunate-ß-cyclodextrin conjugates as novel anti-cancer prodrugs.

A novel series of artesunate-ß-cyclodextrin (ATS-ß-CD) conjugates, in which artesunate (ATS) was coupled covalently to one of the primary hydroxyl groups of ß-cyclodextrin (ß-CD) through amino bond formation, were synthesized and characterized by (1)H NMR, HRMS, 2D NMR (ROESY), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). The results showed that the aqueous solubility of ATS-ß-CD conjugates was 26-45 times better than that of free ATS. The cytotoxicity of the ATS-ß-CD conjugates was evaluated on human colon cancer cell lines HCT116, LOVO, SW480, and HT-29, and the results indicated that ATS-2NßCD exhibited a very high cytotoxicity against HCT116, LOVO, and HT-29 with IC50 values of 0.58, 1.62, and 5.18µmol/L, respectively. In addition, the supposition of better cytotoxicity was further supported by the control experiment of fluorescent cyclodextrin.

Host-guest inclusion system of mangiferin with ß-cyclodextrin and its derivatives.

The characterization, inclusion complexation behavior and binding ability of the inclusion complexes of mangiferin (MGF) with ß-cyclodextrin and its derivatives (hydroxypropyl-ß-cyclodextrin (HPßCD), sulfobutyl ether ß-cyclodextrin (SBEßCD) and mono (6-ethylene-diamino-6-deoxy)-ß-cyclodextrin (ENßCD)) were investigated in both solution and solid state by means of PL spectroscopy, (1)H and 2D NMR, XRD, TG and DSC. The results showed that the water solubility and thermal stability of MGF were significantly increased in the inclusion complex with cyclodextrins. The MGF/CDs complexes will be potentially useful for the design of a novel formulation of mangiferin for herbal medicine.