Lead (II) ions enable the ion-specific effects of monovalent anions on the molecular structure and interactions at silica/aqueous interfaces.

HYPOTHESIS: The adsorption of heavy metal ions such as Pb(II) onto negatively charged minerals such as silica is expected to alter the structure and the interactions at the silica/aqueous interfaces. Besides the solution pH, the inner-sphere sorption of Pb(II) is expected to regulate the surface charge/potential, hypothesized to control the actions of monovalent anions in the aqueous environment. These complex pictures can be probed directly using surface-sensitive sum-frequency generation (SFG) spectroscopy. EXPERIMENTS: The pH-dependent water structure within the double layer at silica/aqueous interfaces under the influence of different ions was examined using SFG. The recorded SFG spectra were deconvoluted into the Stern layer (SL) and diffuse layer (DL) using the maximum entropy method in conjunction with the electrical double-layer theory. FINDINGS: Standalone monovalent sodium salts do not exhibit ion-specific effects on the silica/aqueous interfaces. However, the mixture of Pb(II) species and each of these salts display profound ion-specific effects on the structure of silica/aqueous interfaces, indicating the role of Pb(II) as an enabler of the ion-specificity of the investigated monovalent anions. The interesting effect arises from a complex interplay between the physical processes (i.e., electrostatic interactions, screening effects, etc.) and chemical processes such as the hydrolysis of Pb(II) ions, ion complexation, protonation and deprotonation of the surface silanol group.

Effects of Charged Surfactants on Interfacial Water Structure and Macroscopic Properties of the Air-Water Interface.

Surfactants are used to control the macroscopic properties of the air-water interface. However, the link between the surfactant molecular structure and the macroscopic properties remains unclear. Using sum-frequency generation spectroscopy and molecular dynamics simulations, two ionic surfactants (dodecyl trimethylammonium bromide, DTAB, and sodium dodecyl sulphate, SDS) with the same carbon chain lengths and charge magnitude (but different signs) of head groups interact and reorient interfacial water molecules differently. DTAB forms a thicker but sparser interfacial layer than SDS. It is due to the deep penetration into the adsorption zone of Br- counterions compared to smaller Na+ ones, and also due to the flip-flop orientation of water molecules. SDS alters two distinctive interfacial water layers into a layer where H+ points to the air, forming strong hydrogen bonding with the sulphate headgroup. In contrast, only weaker dipole-dipole interactions with the DTAB headgroup are formed as they reorient water molecules with H+ point down to the aqueous phase. Hence, with more molecules adsorbed at the interface, SDS builds up a higher interfacial pressure than DTAB, producing lower surface tension and higher foam stability at a similar bulk concentration. Our findings offer improved knowledge for understanding various processes in the industry and nature.

Enhancing shear strength and handleability of dewatered clay-rich coal tailings for dry-stacking.

Mineral tailings dams pose high pollution risks to the environment and catastrophic failures. Dry stacking has been identified as a promising alternative to mitigate these risks and offers various benefits to the mining industry but lacks systematic research outcomes. To facilitate dry stacking, coal tailings slurries were dewatered using either filtration or centrifugation methods, resulting in a semi-solid form (cake) that can be safely disposed of. The handleability and disposability of these cakes are greatly influenced by the selection of chemical aids (such as polymer flocculants) and the mechanical dewatering technique employed. The effects of polyacrylamide (PAM) flocculants with a range of molecular weight, charge, and charge density are presented. Coal tailings samples with differences in clay mineralogy were dewatered using press filtration, solid bowl centrifugation, and natural air drying. Handleability and disposability of the tailings were assessed by their rheological properties, including yield stress, adhesive and cohesive stresses, and stickiness. Residue moisture, type of polymer flocculants, and clay mineralogy were found to be crucial factors affecting the handleability and disposability of the dewatered cakes. The tailing yield stress (shear strength) increased as the solid concentration increased. In the semi-solid regime (above 60 wt% solids), the tailings displayed stiff exponential growth. Similar trends were observed for stickiness and adhesive/cohesive energy of the tailings with a steel (truck) surface. Adding polymer flocculants increased the shear strength of the dewatered tailings by 10-15%, thus favouring disposability. However, the polymer selection for coal tailing handling and processing is a trade-off between its disposability and handleability, which requires a multi-criteria decision-making process. The current results also suggested that cationic PAM could be most suitable for dewatering by press filtration, while anionic PAM should be selected for dewatering by solid bowl centrifugation.

Probing interfacial water structure induced by charge reversal and hydrophobicity of silica surface in the presence of divalent heavy metal ions using sum frequency generation spectroscopy.

HYPOTHESIS: Adsorption of divalent heavy metal ions (DHMIs) at the mineral-water interfaces changes interfacial chemical species and charges, interfacial water structure, Stern (SL), and diffuse (DL) layers. These molecular changes can be detected by probing changing orientation and hydrogen-bond network of interfacial water molecules in response to changing local charges and hydrophobicity. EXPERIMENTS: Sum-frequency generation (SFG) spectroscopy was used to probe changes in vibrational resonances of interfacial OH vs. DHMI concentration and pH. SFG spectra were deconvoluted using the measured surface potential and maximum entropy method in conjunction with the electrical double-layer theory for the SL and DL structures and correlated by hydrophobicity. FINDINGS: Three surface charge reversals (CRs) were detected at low (CR1), medium (CR2), and high (CR3) pHs. Unlike CR1, SFG signals were minimized at CR2 and CR3 for DHMIs-silica systems highlighting considerable alterations in the structure of interfacial waters due to the inner-sphere sorption of metal hydroxo complexes. SFG results showed "hydrophobic-like" stretching modes at > 3600 cm-1 for Pb-, Cu-, and Zn-treated silica. However, contact angle measurements revealed the hydrophobization of silica only in the presence of Pb(II), as confirmed by an in-depth SFG analysis of the hydrogen-bond network of the interfacial water molecules in the SL.

Crucial roles of ion-specific effects in the flotation of water-soluble KCl and NaCl crystals with fatty acid salts.

HYPOTHESIS: Flotation of water-soluble KCl and NaCl minerals in brines is significant for K-fertilizer production, but its mechanism is controversial. Dissolved salt ions are expected to change the physicochemical properties of solvents, interfaces, and collector colloids, thereby affecting flotation significantly. EXPERIMENTS: Flotation experiments of KCl and NaCl crystals in brines were conducted using potassium and sodium laurates as collectors. Contact angle (CA) and surface tension measurements, X-ray photoelectron spectroscopy (XPS) analysis, and molecular dynamics simulations (MD) were applied to gain a molecular understanding of changing interfacial properties and crystal-collector colloid interactions in the presence of dissolved ions in terms of salt flotation. FINDINGS: While K+ ions activate the NaCl crystal flotation, Na+ ions depress the KCl crystal flotation, in agreement with the studies of CA, XPS, and MD results with these crystals. XPS results showed no collector adsorption at crystal surfaces which is a requirement of conventional flotation and presents a new theoretical challenge. We argue the crucial role of ion specificity: Na-laurate colloids adsorb at the bubble surface as a monolayer but solvent-separated from KCl crystals, inhibiting their flotation, or in interactive contact with NaCl crystals, enhancing their flotation. Increasing K+ concentration weakens NaCl crystal hydration, increasing Na-laurate colloid attraction with crystals for better flotation. The Contact Interactive Collector Colloid (CICC) and Solvent-separated Interactive Collector Colloid (SICC) hydration states are critical to salt crystal flotation via collector colloid-crystal attraction by dispersion forces.

Flotation surface chemistry of water-soluble salt minerals: from experimental results to new perspectives.

The flotation separation of water-soluble salt minerals has to be conducted under the condition of saturation in brines which represents a challenging but exciting topic of colloid and surface chemistry. Despite several proposals on explaining the success of this industrial application for many decades, our understanding of the flotation separation is still far from complete yet, owing to the complexity of the highly selective collection of salt crystals by air bubbles in brines. Here, we thoroughly review the experimental results for halogen, oxyanion, and double salts and match them with the proposed theories on the flotation of soluble salts to identify the agreed and disagreed cases. The experimental results show that the flotation of these salts varies from collectors (surfactants applied to control the crystal hydrophobicity) to collectors and is strongly affected by the brine ion composition and pH conditions. We find some exceptional flotation results that cannot be simply explained by the crystal surface charge and wettability. Furthermore, we outline several disputes and discrepancies between the experiments and the theories when different collectors are applied. Apart from the extensive consideration of surface hydration, the presence of external ion species exhibits ubiquitous effects on the surface properties of salt crystals and the colloidal properties of collectors. We conclude that the interactions between salt ions, water molecules, collectors, and salt crystals must be considered more thoroughly, and the activity of collectors at the air-liquid interface should also be the focus. Advanced techniques such as molecular dynamics simulation, atomic force microscopy, X-ray photoelectron spectroscopy, and sum-frequency generation spectroscopy are expected to be promising research tools for future studies.

A review on quantifying the influence of lateral capillary interactions on the particle floatability and stability of particle-laden interfaces.

Particle-laden interfaces are critical to the flotation separation of hydrophobic particles using air bubbles. After contacting the particle suspension, the bubble surface is loaded with many hydrophobic particles that can get detached during the bubble rise to the top. While many studies of the capillary stability and detachment of single particles from the clean air-water interface have provided significant insights, the particle floatability, detachment, and stability of the particle-laden interface are not well quantified. This paper provides a critical review of the experimental and theoretical investigations of the lateral capillary interactions on the particle floatability and stability of the particle-laden interfaces. Particularly, we critically analysed, summarized, and commented on asymptotic solutions of the Young-Laplace equation for various particle configurations. Then, we critically assessed the outcomes of both the theoretical and experimental studies of the particle-laden interface stability and related the results to particle-bubble detachment behaviours in flotation applications. This review provides an updated outlook of research perspectives that establish the framework for researchers interested in this fascinating field of flotation and colloid and surface science.

"Nanoreactors" for Boosting Gas Hydrate Formation toward Energy Storage Applications.

Hydrogen and methane can be molecularly incorporated in ice-like water structures up to mass fractions of 4.3% and 13.3%, respectively. The resulting solid structures, called gas hydrates, offer great potential for the efficient storage of hydrogen and natural gas. However, slow gas encapsulation by bulk water hinders this application. Porous structures have been shown to effectively promote gas hydrate formation and are a potential enabler for the development of hydrate-based gas storage technologies. Here, we offer an insightful perspective on using porous structures as nanoreactors for achieving fast gas hydrate formation for gas storage applications. We critically discuss and elucidate the working mechanisms of nanoreactors and identify the criteria for efficient nanoreactors. Based on the concepts founded, we propose a theoretical framework for designing next-generation porous materials for delivering better promoting effects on gas hydrate formation.

The Role of Teacher and Peer Support against Bullying Among Secondary School Students in Vietnam.

Physical bullying is prevalent among secondary school students in Vietnam, and it is thought that support from peers and teachers may make a significant contribution to lessening the problem in the country. The authors aimed to examine the association between peer support, teacher support, and physical bullying among secondary school students in Vietnam, controlling for age and sex. They also tested the moderation effects of sex on peer support, teacher support, and physical bullying. A multiple linear regression analysis was conducted, using a sample of 482 secondary students between 12 and 15 years old from three secondary schools in a big city in the country. Findings of the study revealed that support from peers and teachers was associated with significant attenuation of physical bullying among the sample in the study. Specifically, the more support from peers and teachers that there was, the less likely it was that the participants would get involved in physical bullying behavior. The findings also indicated that sex did not have the moderation effects on the relationship between peer support, teacher support, and physical bullying in the sample. Results of this study have implications for schools, teachers, and secondary school students.

Association between Intrapancreatic Fat Deposition and the Leptin/Ghrelin Ratio in the Fasted and Postprandial States.

BACKGROUND: The clinical relevance of excess intrapancreatic fat deposition (IPFD) is increasingly appreciated. Leptin and ghrelin are key players in the regulation of food intake, energy balance, and body fat mass. The aim was to investigate the associations of the leptin/ghrelin ratio and its components with IPFD. METHODS: All participants underwent magnetic resonance imaging on a 3T scanner to quantify IPFD. Both fasting and postprandial blood samples were analyzed for leptin and acylated ghrelin. Linear regression analysis was conducted, accounting for visceral/subcutaneous fat volume ratio, glycated hemoglobin, and other covariates. RESULTS: A total of 94 participants (32 women) with a median age of 56 (interquartile range 44-66) years were studied. Their median IPFD was 9.6% (interquartile range 8.8-10.4%). In the fasted state, the leptin/ghrelin ratio (ß = 0.354; 95% confidence interval 0.044-0.663; p = 0.025, in the most adjusted model) and leptin (ß = 0.040; 95% confidence interval 1.003-1.078; p = 0.035, in the most adjusted model) were significantly associated with IPFD. Ghrelin in the fasted state was not significantly associated with IPFD. In the postprandial state, the leptin/ghrelin ratio, leptin, and ghrelin were not significantly associated with IPFD. CONCLUSION: Fasting circulating levels of leptin are directly associated with IPFD. Purposely designed mechanistic studies are warranted to determine how high leptin may contribute to excess IPFD.

Clathrate Adhesion Induced by Quasi-Liquid Layer.

The adhesive force of clathrates to surfaces is a century-old problem of pipeline blockage for the energy industry. Here, we provide new physical insight into the origin of this force by accounting for the existence of a quasi-liquid layer (QLL) on clathrate surfaces. To gain this insight, we measure the adhesive force between a tetrahydrofuran clathrate and a solid sphere. We detect a strong adhesion, which originates from a capillary bridge that is formed from a nanometer-thick QLL on the clathrate surface. The curvature of this capillary bridge is nanoscaled, causes a large negative Laplace pressure, and leads to a strong capillary attraction. The microscopic capillary bridge expands and consolidates over time. This dynamic behavior explains the time-dependent increase of measured capillary forces. The adhesive force decreases greatly upon increasing the roughness and the hydrophobicity of the sphere, which founds the fundamental basics for reducing clathrate adhesion by using surface coating.

Factors influencing social work students' motivation to work in drug treatment settings: the role of knowledge and attitudes.

Given the continuing problem of drug use in the United States and the high risk of burnout among substance use treatment staff, this study focuses on examining the relationship between social work students' knowledge and attitudes toward individuals who use drugs and their motivation to work in drug treatment settings. A Multiple linear regression analysis was conducted, using a convenience sample of 229 social work students (age = 21 to 60, female = 82.5%, White = 79.9%, African American = 13.5%, Asian = 2.6%, Hispanic = 3.9%) at a large public university in an eastern state. Results revealed that knowledge and positive attitudes were key factors stimulating social work students' motivation to work with individuals who use drugs, and knowledge was the most influential factor. Social work students are more likely to want to work with individuals who use drugs if they have positive attitudes toward their clients and increased knowledge of drugs and drug-related problems. Interestingly, there is no significant difference in motivation between those who have negative attitudes and other people. Implications for social work education on substance abuse are discussed.

Premelting-Induced Agglomeration of Hydrates: Theoretical Analysis and Modeling.

Resolving the long-standing problem of hydrate plugging in oil and gas pipelines has driven an intense quest for mechanisms behind the plug formation. However, existing theories of hydrate agglomeration have critical shortcomings, for example, they cannot describe nanometer-range capillary forces at hydrate surfaces that were recently observed by experiments. Here, we present a new model for hydrate agglomeration which includes premelting of hydrate surfaces. We treat the premelting layer on hydrate surfaces such as a thin liquid film on a substrate and propose a soft-sphere model of hydrate interactions. The new model describes the premelting-induced capillary force between a hydrate surface and a pipe wall or another hydrate. The calculated adhesive force between a hydrate sphere (R = 300 µm) and a solid surface varies from 0.3 mN on a hydrophilic surface (contact angle, θ = 0°) to 0.008 mN on a superhydrophobic surface (θ = 160°). The initial contact area is 4 orders of magnitude smaller than the cross-sectional area of the hydrate sphere and can expand with increasing contact time because of the consolidation of hydrate particles on the solid surface. Our model agrees with the available experimental results and can serve as a conceptual guidance for developing a chemical-free environmentally friendly method for prevention of hydrate plugs via surface coating of pipe surfaces.

Serum lipid profile as a biomarker of intra-pancreatic fat deposition: A nested cross-sectional study.

BACKGROUND AND AIMS: The relationship between intra-pancreatic fat deposition (IPFD) and lipid profile has been investigated in individuals with obesity and/or type 2 diabetes, but not in healthy non-obese individuals and those after acute pancreatitis. The aim of the study was to investigate the association between serum lipid profile and IPFD in the latter individuals and to determine the effect of abdominal fat distribution and other covariates. METHODS AND RESULTS: A total of 90 individuals with a history of acute pancreatitis as well as 23 healthy non-obese individuals participated in the study. Magnetic resonance imaging was used to quantify IPFD and visceral-to-subcutaneous fat volume ratio, followed by fasting state measurement of high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), total cholesterol (TC), TC/HDL-C ratio, and triglycerides. In healthy non-obese individuals, IPFD was not significantly associated with any of the studied markers. In individuals after acute pancreatitis, IPFD was significantly associated with triglycerides in both unadjusted (ß = 0.360; 95% CI, 0.090-0.629; p = 0.009) and adjusted models, with a ß-coefficient of 0.280 [(95% CI, 0.016-0.545); p = 0.038] in the most adjusted model. Also, IPFD was significantly associated with TC/HDL-C ratio in both unadjusted (ß = 0.336; 95% CI, 0.045-0.626; p = 0.024) and adjusted models, with a ß-coefficient of 0.375 [(95% CI, 0.090-0.660); p = 0.010] in the most adjusted model. Multiple regression yielded triglycerides, but not TC/HDL-C ratio, as a significant marker of IPFD in individuals after acute pancreatitis. CONCLUSIONS: Serum lipid profile is not associated with IPFD in healthy non-obese. Triglycerides, but not other components of lipid profile, is a promising biomarker for IPFD in individuals following acute pancreatitis.

Comprehensive analysis of body composition and insulin traits associated with intra-pancreatic fat deposition in healthy individuals and people with new-onset prediabetes/diabetes after acute pancreatitis.

Current knowledge of biomarkers of intra-pancreatic fat deposition (IFD) is limited. We aimed to analyse comprehensively body composition and insulin traits as biomarkers of IFD in healthy normoglycaemic individuals as well as in individuals with new-onset prediabetes or diabetes after acute pancreatitis (NODAP). A total of 29 healthy individuals and 34 individuals with NODAP took part in this cross-sectional study. The studied biomarkers belonged to the following domains: body composition (anthropometric and MRI-derived variables); indices of insulin secretion; indices of insulin sensitivity; incretins and related peptides; and pancreatitis-related factors. All MRI-derived variables (including IFD) were measured using ImageJ software. Univariate and step-wise regression analyses were conducted to determine variables that best explained variance in IFD. Visceral fat volume and oxyntomodulin were the best biomarkers of IFD in normoglycaemic healthy individuals, contributing to 64% variance. The Raynaud index was the best biomarker of IFD in individuals with NODAP, contributing to 20% variance. Longitudinal studies are warranted to investigate the cause and effect relationship between oxyntomodulin and IFD in healthy individuals, as well as insulin sensitivity and IFD in individuals with NODAP.

Combining Linker Design and Linker-Exchange Strategies for the Synthesis of a Stable Large-Pore Zr-Based Metal-Organic Framework.

A Zr(IV)-based metal-organic framework (MOF), termed reo-MOF-1 [Zr6O8(H2O)8(SNDC)4], composed of 4-sulfonaphthalene-2,6-dicarboxylate (HSNDC2-) linkers and Zr6O8(H2O)8(CO2)8 clusters was synthesized by solvothermal synthesis. Structural analysis revealed that reo-MOF-1 adopts the reo topology highlighted with large cuboctahedral cages (23 Å). This structure is similar to that found in DUT-52 (fcu topology), however, reo-MOF-1 lacks the body-centered packing of the 12-connected Zr6O4(OH)4(CO2)12 clusters, which is attributed to the subtle, but crucial influence in the bulkiness of functional groups on the linkers. The control experiments, where the ratio of H3SNDC/naphthalene-2,6-dicarboxylate linkers was varied, also support our finding that the bulky functionalities play a key role for defect-controlled synthesis. The reo-MOF-1A framework was obtained by linker exchange to yield a chemically and thermally stable material despite its large pores. Remarkably, reo-MOF-1A exhibits permanent porosity (Brunauer-Emmett-Teller and Langmuir surface areas of 2104 and 2203 m2 g-1, respectively). Owing to these remarkable structural features, reo-MOF-1A significantly enhances the yield in Brønsted acid-catalyzed reactions.

Cross-dehydrogenative coupling of coumarins with Csp3-H bonds using an iron-organic framework as a productive heterogeneous catalyst.

The iron-organic framework VNU-20 was utilized as an active heterogeneous catalyst for the cross-dehydrogenative coupling of coumarins with Csp3-H bonds in alkylbenzenes, cyclohexanes, ethers, and formamides. The combination of DTBP as the oxidant and DABCO as the additive led to high yields of coumarin derivatives. The VNU-20 was more active towards this reaction than numerous other homogeneous and heterogeneous catalysts. Heterogeneous catalysis was confirmed for the cross-dehydrogenative coupling transformation utilizing the VNU-20 catalyst, and the contribution of active iron species in the liquid phase was insignificant. The iron-based framework was reutilized many times for the functionalization of coumarins without a remarkable decline in catalytic efficiency. To the best of our knowledge, these reactions of coumarins have not previously been conducted using heterogeneous catalysts.