Effect of PAM on Surface Hydrophobicity of Montmorillonite and Difference of Interface Adsorption: An Experimental and Simulation Study

How to realize efficient treatment of coal slime generated by a coal washing operation is an urgent problem to be solved in this industry. The presence of clay minerals, especially highly hydrophilic montmorillonite (MMT), is the key to the poor treatment effect of coal slime. Polyacrylamide (PAM) is very popular as a polymer agent to improve the treatment of coal slime. However, when it is used to treat coal slime with a high content of MMT, the selection of PAM type and the mechanism of action are still lacking. In this study, the effects of different types of PAM on the treatment of coal slime water containing MMT are considered by sedimentation and press filtration tests. The interaction mechanism of PAM on the MMT surface is studied by using ζ-potential, Brunauer–Emmett–Teller (BET) analysis, low-field nuclear magnetic resonance, density functional theory (DFT), and molecular dynamics (MD) simulations. The results show that the three PAM can improve the sedimentation and filtration effect of coal slime water, and the performance is CPAM > NPAM > APAM. The ζ-potential of the MMT (001) surface increases under the action of three PAM, and the effect of CPAM is the most significant. The adsorption of PAM on the MMT (001) surface has the ability to neutralize the surface charge of MMT. The flocculation of MMT particles under PAM results in an increase of particle size and a decrease of specific surface area. Meanwhile, the pore volume of MMT decreases, and the average pore size increases. In addition, PAM mainly removes vicinal water on the MMT surface. The active sites of the MMT surface and PAM are calculated by DFT. The adsorption of three PAM structural units on the MMT Na-001 surface and non-001 surface is nonbonding interaction, and the adsorption energy of CPAM is the largest. And the left shift of εp of the O atom on the MMT surface is conducive to the stable adsorption of CPAM. The MD results show that the concentration of water molecules on the surface of MMT Na-001 decreases after PAM is adsorbed on the MMT Na-001 surface, indicating that PAM can keep water molecules away from the surface of MMT, which means that the hydrophobicity of the MMT surface is enhanced. This study has guiding significance for the selection of PAM and the development of new flocculants in the treatment of coal slime with a high content of MMT

Breakthrough in the Application of a Small Molecule as Dopant-Free Hole-Transport Material in p‑i‑n Perovskite Solar Cells

Dopant-free hole-transport materials (HTMs) with facile synthesis routes and well-matched highest occupied molecular orbital (HOMO) energy levels are paramount for commercialization of perovskite solar cells (pero-SCs). In this article, dopant-free CMT with the nitrogen atom in the center of the simple structure and well-matched HOMO energy levels has been applied in MAPbI3-based p-i-n pero-SCs as the hole-transport layer (HTL). The optimized efficiency achieved turned out to be 20.4%, which is higher than the efficiency of 13.05% obtained when CMT was applied in MAPbI3-based n-i-p pero-SCs, with an open circuit voltage of 1.08 V, a short circuit current of 23.27 mA/cm2, and a fill factor of 81.45%

Aggregation Properties of a Novel Class of Amphiphilic Cationic Polyelectrolytes Containing Gemini Surfactant Segments

A novel class of amphiphilic cationic polyelectrolytes, poly(A-co-G)s, comprising of gemini type surfactant segment 1,3-bis(N,N-dimethyl-N-dodecylammonium)-2-propylacrylate dibromide (G) and acryloyloxyethyl trimethyl ammonium chloride (A), were synthesized. Their aggregation properties were investigated by employing fluorescence spectroscopy, dynamic light scattering, transmission electron microscopy, and ζ-potential measurements. For comparison, a series of polyelectrolytes containing a traditional single alkyl chain surfactant unit (acryloyloxyethyl-N,N-dimethyl-N-dodecylammonium bromide (D)), poly(A-co-D)s, were also synthesized and investigated. It was found that the critical aggregation concentration (cac) of poly(A-co-G)s is much lower than that of poly(A-co-D)s. The huge interpolymer aggregates (with a hydrodynamic radius of >450 nm) occur in poly(A-co-G)s aqueous solution, and the size of aggregates increases with the increase of the molar content of the gemini-type surfmer segment and the concentration of the copolymer. The size of aggregates in poly(A-co-D)s aqueous solution is much smaller than poly(A-co-G)s, which also increases with the increase of the molar content of the single alkyl chain surfmer segment and the concentration of the copolymer. The results of aggregation number and charge density of aggregate in poly(A-co-G)s and poly(A-co-D)s indicate that the copolymers have a strong tendency toward interpolymer aggregation and the aggregates in poly(A-co-G)s are much more compact than those of poly(A-co-D)s. These results are interpreted in terms of the synergistic effects of double hydrophobic chains on the gemini surfactant unit

Selective Reduction of SO₂ in Smelter Off-Gas with Coal Gas to Sulfur over Metal Sulfide Supported Catalysts

A series of metal sulfide supported catalysts were first developed for the SO2 reduction to sulfur by coal gas, and different supports and active components were selected to prepare catalysts through the wet impregnation method. This reduction technology is also a promising desulfurization process of smelter off-gas. Before the calcined supported catalyst was evaluated in a fixed-bed reactor, the presulfidation was performed to get the stronger stability and catalyst ability. The catalysts were characterized by X-ray diffraction, XPS, BET, and SEM analyses. Changes in the catalyst structure and active phase were explored. The acid–base properties of the supports were detected by CO2-TPD, and the reduction ability of the catalyst was evaluated via CO-TPR. The long life of catalyst was evaluated, and the probable catalytic mechanism was proposed

Catalytic Activity and Molecular Behavior of Lanthanum Modified CoS_<i>x</i>/γ-Al₂O₃ Catalysts for the Reduction of SO₂ to Sulfur in Smelter Off-Gas Using CO‑H₂ Mixture as Reductant

In this study, a series of three-component CoSx/γ-Al2O3 catalysts were developed for the reduction of high-content SO2 to sulfur in smelter off-gas. The introduction of a small amount of lanthanum additive greatly improved the catalytic activity and stability of Co-Cu/γ-Al2O3 catalysts using coal gas as reductant. The catalysts were characterized by XRD, XPS, BET, and SEM techniques. H2/CO-TPR was recorded to study redox properties of catalysts. With the use of a CO-H2 mixture with different proportions, a series of parallel experiments were performed to investigate the mutual impact and relation of CO and H2. Under optimum conditions, SO2 conversion of 99% and sulfur selectivity of 99% were obtained. The catalyst remained highly active after a long run of 200 h. Process simulation was used to investigate the molecular behavior of catalyst. Combined with in situ infrared characterization, the catalytic mechanism was put forward and verified