Search Results (18)

Ester collectors have rapidly developed into the main flotation collectors for copper sulfide minerals since they were developed. In this study, the collecting performance of four collectors, O-isopropyl-N-ethyl thionocarbamate ester (IPETC), 3-pentyl xanthate acrylate ester (PXA), O-isobutyl-N-allyl-thionocarbamate (IBALTC), and O-isobutyl-N-isobutoxycarbonyl-thionocarbamate (IBIBCTC), was investigated through microflotation tests, microcalorimetric measurements, and quantum chemical calculations. The results of the microflotation tests show that IBALTC and IPETC have stronger collecting abilities than IBIBCTC and PXA; the order of collecting ability is IBALTC > IPETC > IBIBCTC > PXA. The microcalorimetry test also shows that the adsorption heat of the former two is higher. Quantum chemical calculations show the energy difference between the HOMOs of the collector and the LUMOs of minerals. The electrostatic potential extremum around S atom and the first ionization potential of IPETC and IBALTC are similar and were smaller than IBIBCTC and PXA, which shows that the collecting ability of the former two is similar and stronger than the latter two. Among the collectors, the S atom polarizability, electrophilic, and nucleophilic attack index of IBALTC are the largest, indicating that its electronic deformation capability and nucleophilic properties are the strongest, which results in the strongest coordination interaction with the copper ions in copper sulfide minerals and thus the highest collecting ability. The S atom polarizability, electrophilic, and nucleophilic attack index of PXA are the smallest, indicating that its electronic deformation capability and nucleophilicity are the weakest, and its collecting ability is the weakest. The coordination between collector and mineral surface was analyzed theoretically. The research results are of great help to the design and development of ester collectors. Full article

Mixed matrix lithium adsorbents have attracted much interest for lithium recovery from brine. However, the absence of an interfacial interaction between the inorganic lithium-ion sieves (LISs) and the organic polymer matrix resulted in the poor structural stability and attenuated lithium adsorption efficiency. Here, a novel hollow hemispherical mixed matrix lithium adsorbent (H-LIS) with high interfacial compatibility was constructed based on mussel-bioinspired surface chemistry using a solvent evaporation induced phase transition method. The effects of types of functional modifiers, LIS loading amount, adsorption temperature and pH on their structural stability and lithium adsorption performance were systematically investigated. The optimized H-LIS adsorbent with the LIS loading amount of 50 wt.% possessed the structural merit that the LIS functionally modified by dopamine exposed on both the inner and outer surfaces of the hollow hemispheres. At the best adsorption pH of 12.0, it showed a comparable lithium adsorption capacity of 25.68 mg·g⁻¹ to the powdery LIS within 4 h, favorable adsorption selectivity of Mg/Li and good reusability that could maintain over 90% of lithium adsorption capacity after the LiCl adsorption—0.25 M HCl pickling-DI water cleaning cycling processes for three times. The interfacial interaction mechanism of H-LIS for lithium adsorption was innovatively explored via advanced microcalorimetry technology. It suggested the nature of the Li⁺ adsorption process was exothermic and dopamine modification could reduce the activation energy for lithium adsorption from 15.68 kJ·mol⁻¹ to 13.83 kJ·mol⁻¹ and trigger a faster response to Li⁺ by strengthening the Li⁺-H⁺ exchange rate, which established the thermodynamic relationship between the structure and Li⁺ adsorption performance of H-LIS. This work will provide a technical support for the structural regulation of functional materials for lithium extraction from brine. Full article

The aim is to explore new depressants for achieving the efficient separation of apatite and dolomite. In this work, fucoidan (FD) was examined as an eco-friendly dolomite depressant to separate dolomite from apatite. The depression ability and adsorption mechanisms were investigated. The flotation results indicated that FD selectively depressed dolomite. The flotation difference between dolomite and apatite reached 70% approximately at an FD concentration of 75 mg/L. Meanwhile, the recovery and grade of P₂O₅ reached 89.84% and 32.88% and that of MgO decreased to 1.64% and 34.24% in the artificially mixed minerals test. Wettability, zeta potential, and Fourier transform infrared spectroscopy (FTIR) results revealed that FD tended to adsorb onto dolomite, impeding the interaction of sodium oleate (NaOL) with dolomite, but barely affected that on apatite. Microcalorimetry analysis indicated that the adsorption heat of FD on dolomite was much higher and less time was required to achieve equilibrium. X-ray photoelectron spectroscopy (XPS) results proved that the sulfonic acid radicals within FD chemically interacted with Mg atoms on dolomite while it weakly adsorbed on apatite. Full article

Solid–liquid interfacial phenomena play an essential role in our everyday lives and are often regarded as the outcome of interactions at the solid–liquid interface. However, the intricately intrinsic mechanism underlying interfacial interactions renders in situ simulations and direct measurements challenging. As an effective analytic method for studying solid–liquid interfacial interactions, microcalorimetry can provide the most basic thermodynamic information (including changes in enthalpy, entropy, and Gibbs free energy during solid–liquid binding/separation processes), which is extremely crucial for understanding interaction directionality and limitation. This review is dedicated to highlighting the pivotal role of microcalorimetry in studying solid–liquid immersion and adsorption processes. Specifically, we provide an overview of the commonly employed microcalorimetric methods, including differential scanning calorimetry (DSC), isothermal titration calorimetry (ITC), and immersion microcalorimetry (IM), and delve into the influence factors of enthalpy change, and finally discuss the specific applications of microcalorimetry in studying various solid–liquid binding processes. There remains a vast expanse of thermodynamic information regarding solid–liquid interactions that await exploration via calorimetry. Full article

The physicochemical modification of the filler allows changing the hydrophilic–hydrophobic properties and effectively influencing the processes occurring at the filler–binder interface, on which the physicomechanical characteristics of composites largely depend. The paper presents studies related to the modification of limestone-based filler effect on the degree of its hydrophobicity and wetting with liquids of different polarity, establishing the relationship between the characteristics of hydrophobized mineral powders and the adsorption capacity in relation to water. Using mechanochemical processing with hydrophobic components GF-1 and GF-2, it was possible to obtain fillers with a sufficiently high content of hydrophobic particles (58.2% and 85.9%, respectively). It was found that the results of the contact angle (123.6° and 114.5°, respectively) and the degree of hydrophobicity do not quite correlate with each other. It was noticed that the contact angle on the powder modified with GF-1 decreases with time. Studies of the powders’ thermal effects wetting of different polarity liquids via microcalorimetry allows us to establish that with an increase in the filler hydrophobicity degree, the integral heat of immersion decreases due to a significant decrease in the probability of chemical interactions between water and powder due to the adsorption of applied surfactants molecules on the limestone active centers. The revealed endothermic effects indicate the occurrence of physical interactions due to non-polar dispersion forces. Differences in the nature of heat release and heat absorption in modified fillers indicate significant differences in the composition and mechanism of action of the used surfactants, which affected the efficiency of hydrophobization. At the same time, a linear dependence of the moisture absorption and moisture indicators, determined by independent experiments, on the degree of hydrophobicity was established. Full article

Studying the toxicity of chemical compounds using isothermal microcalorimetry (IMC), which monitors the metabolic heat from living microorganisms, is a rapidly expanding field. The unprecedented sensitivity of IMC is particularly attractive for studies at low levels of stressors, where lethality-based data are inadequate. We have revealed via IMC the effect of low dose rates from radioactive β⁻-decay on bacterial metabolism. The low dose rate regime (<400 µGyh⁻¹) is typical of radioactively contaminated environmental sites, where chemical toxicity and radioactivity-mediated effects coexist without a predominance or specific characteristic of either of them. We found that IMC allows distinguishing the two sources of metabolic interference on the basis of “isotope-editing” and advanced thermogram analyses. The stable and radioactive europium isotopes ¹⁵³Eu and ¹⁵²Eu, respectively, were employed in monitoring Lactococcus lactis cultures via IMC. β⁻-emission (electrons) was found to increase initial culture growth by increased nutrient uptake efficiency, which compensates for a reduced maximal cell division rate. Direct adsorption of the radionuclide to the biomass, revealed by mass spectrometry, is critical for both the initial stress response and the “dilution” of radioactivity-mediated damage at later culture stages, which are dominated by the chemical toxicity of Eu. Full article

Functionalized aluminosilicate materials were studied as catalysts for the conversion of different cyclic carbonates to the corresponding epoxides by the addition of CO₂. Aluminum was incorporated in the mesostructured SBA-15 silica network. Thereafter, functionalization with imidazolium chloride or magnesium oxide was performed on the Al_SBA-15 supports. The isomorphic substitution of Si with Al and the resulting acidity of the supports were investigated via ²⁷Al magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy and NH₃ adsorption microcalorimetry. The Al content and the amount of MgO were quantified via inductively coupled plasma optical emission spectroscopy (ICP-OES) analysis. The anchoring of the imidazolium salt was assessed by ²⁹Si and ¹³C MAS NMR spectroscopy and quantified by combustion chemical analysis. Textural and structural properties of supports and catalysts were studied by N₂ physisorption and X-ray diffraction (XRD). The functionalized systems were then tested as catalysts for the conversion of CO₂ and epoxides to cyclic carbonates in a batch reactor at 100 or 125 °C, with an initial CO₂ pressure (at room temperature) of 25 bar. Whereas the activity of the MgO/xAl_SBA-15 systems was moderate for the conversion of glycidol to the corresponding cyclic carbonate, the Al_SBA-15-supported imidazolium chloride catalysts gave excellent results over different epoxides (conversion of glycidol, epichlorohydrin, and styrene oxide up to 89%, 78%, and 18%, respectively). Reusability tests were also performed. Even when some deactivation from one run to the other was observed, a comparison with the literature showed the Al-containing imidazolium systems to be promising catalysts. The fully heterogeneous nature of the present catalysts, where the inorganic support on which the imidazolium species are immobilized also contains the Lewis acid sites, gives them a further advantage with respect to most of the catalytic systems reported in the literature so far. Full article

Kapok fiber (KF), with the characteristics of a natural hollow structure, light weight, and low density, can be used as acoustic and thermal insulation, buoyancy, adsorption, filling, and composite material. The flame-retardant treatment can expand the functionality and application of KF. In this work, the phosphorylation of KF using phytic acid (PA) in the presence of urea at a high temperature was used to enhance its flame retardancy. The phosphorylation reaction conditions were discussed, and the surface topography, thermal degradation, heat release, and combustion properties of phosphorylated KF were studied. The Fourier transform infrared spectroscopy and ³¹P solid-state nuclear magnetic resonance spectroscopy analyses confirmed the grafting of PA on cellulose by the formation of phosphate ester bonds. Due to the covalent binding of PA, phosphorylated KF exhibited good washing durability. The surface topography, Raman spectroscopy, thermogravimetric (TG), and microcalorimetry analyses revealed the excellent charring ability of phosphorylated KF. In the TG test in nitrogen, the char residue increased to 42.6% of phosphorylated KF from 8.3% of raw KF at 700 °C. In the vertical combustion, raw KF sheet was almost completely burned out within 30 s, while phosphorylated KF was very difficult to catch fire. In the microcalorimetry analysis, the heat release capacity and total heat release of phosphorylated KF decreased to 67 J/g∙K and 3.9 kJ/g, respectively from 237 J/g∙K and 18.1 kJ/g of raw KF. This work suggests that phosphorylated KF is an excellent flame-retardant material. Full article

In this paper, evidence is provided that the model reaction of aqueous dihydroxyacetone (DHA) conversion is as sensitive to the TiO₂ catalysts’ basicity as to their acidity. Two parallel pathways transformed DHA: while the pathway catalyzed by Lewis acid sites gave pyruvaldehyde (PA) and lactic acid (LA), the base-catalyzed route afforded fructose. This is demonstrated on a series of six commercial TiO₂ samples and further confirmed by using two reference catalysts: niobic acid (NbOH), an acid catalyst, and a hydrotalcite (MgAlO), a basic catalyst. The original acid-base properties of the six commercial TiO₂ with variable structure and texture were investigated first by conventional methods in gas phase (FTIR or microcalorimetry of pyridine, NH₃ and CO₂ adsorption). A linear relationship between the initial rates of DHA condensation into hexoses and the total basic sites densities is highlighted accounting for the water tolerance of the TiO₂ basic sites whatever their strength. Rutile TiO₂ samples were the most basic ones. Besides, only the strongest TiO₂ Lewis acid sites were shown to be water tolerant and efficient for PA and LA formation. Full article

Quantitative analyses of cell replication address the connection between metabolism and growth. Various growth models approximate time-dependent cell numbers in culture media, but physiological implications of the parametrizations are vague. In contrast, isothermal microcalorimetry (IMC) measures with unprecedented sensitivity the heat (enthalpy) release via chemical turnover in metabolizing cells. Hence, the metabolic activity can be studied independently of modeling the time-dependence of cell numbers. Unexpectedly, IMC traces of various origins exhibit conserved patterns when expressed in the enthalpy domain rather than the time domain, as exemplified by cultures of Lactococcus lactis (prokaryote), Trypanosoma congolese (protozoan) and non-growing Brassica napus (plant) cells. The data comply extraordinarily well with a dynamic Langmuir adsorption reaction model of nutrient uptake and catalytic turnover generalized here to the non-constancy of catalytic capacity. Formal relations to Michaelis–Menten kinetics and common analytical growth models are briefly discussed. The proposed formalism reproduces the “life span” of cultured microorganisms from exponential growth to metabolic decline by a succession of distinct metabolic phases following remarkably simple nutrient–metabolism relations. The analysis enables the development of advanced enzyme network models of unbalanced growth and has fundamental consequences for the derivation of toxicity measures and the transferability of metabolic activity data between laboratories. Full article

In this study, CeO₂, La₂O₃, and CeO₂-La₂O₃ mixed oxide catalysts with different Ce/La molar ratios were prepared by the soft template method and characterized by different techniques, including inductively coupled plasma atomic emission spectrometry, X-ray diffraction, N₂ physisorption, thermogravimetric analysis, and Raman and Fourier transform infrared spectroscopies. NH₃ and CO₂ adsorption microcalorimetry was also used for assessing the acid and base surface properties, respectively. The behavior of the oxides as catalysts for the dimethyl carbonate synthesis by the transesterification of propylene carbonate with methanol, at 160 °C under autogenic pressure, was studied in a stainless-steel batch reactor. The activity of the catalysts was found to increase with an increase in the basic sites density. The formation of dimethyl carbonate was favored on medium-strength and weak basic sites, while it underwent decomposition on the strong ones. Several parasitic reactions occurred during the transformation of propylene carbonate, depending on the basic and acidic features of the catalysts. A reaction pathway has been proposed on the basis of the components identified in the reaction mixture. Full article

MgAl₂O₄ is used in humidity sensing and measurement, and as a catalyst or catalyst support in a wide variety of applications. For such applications, a detailed understanding of the surface properties and defect structure of the spinel, and, in particular, of the gas interactions at the spinel surface is essential. However, to the best of our knowledge, very limited experimental data regarding this subject is currently available. In this work, four spinel samples with an Al₂O₃ to MgO ratio (n) between 0.95 and 2.45 were synthesized and analyzed using X-ray photoelectron spectroscopy and water adsorption micro-calorimetry. The results showed that the spinel composition and its consequent defect structure do indeed have a distinct effect on the spinel-water vapor surface interactions. The adsorption behavior at the spinel-water interface showed changes that resulted from alterations in types and energetic diversity of adsorption sites, affecting both H₂O uptake and overall energetics. Furthermore, changes in composition following appropriate thermal treatment were shown to have a major effect on the reducibility of the spinel which enabled increased water uptake at the surface. In addition to non-stoichiometry, the impact of intrinsic anti-site defects on the water-surface interaction was investigated. These defects were also shown to promote water uptake. Our results show that by composition modification and subsequent thermal treatments, the defect structure can be modified and controlled, allowing for the possibility of specifically designed spinels for water interactions. Full article

Diffuse reflection infrared Fourier transform (DRIFT) spectra have been quantitatively evaluated to determine unknown extinction coefficients as well as the number of active surface centers and the amount of adsorbed species. Sulfated zirconia with n-butane as probe gas was used as model system. For quantitative evaluation of n-butane adsorption at 323 K, the sulfate band S=O at 1400 cm⁻¹ was chosen. During adsorption, this band is red-shifted to lower wavenumbers accompanied by a structural change of the band indicating isomerization reaction. By analyzing difference spectra and determining the areas of the selected band, the extinction coefficients as well as the number of active centers and the amount of chemisorbed n-butane were calculated. The quantitative evaluation results in a mean internal decadic extinction coefficient of 60 cm⁻¹ µmol⁻¹, an average amount of n-butane adsorbed to the sulfated zirconia of about 4 μmol, and a number of active centers of around 21 μmol/g. These results correspond very well with values from the literature obtained by microcalorimetry. Thus, this method is suggested to be transferred also to unknown systems of interest. Full article

ZrOx/SiO₂ and VOx/ZrO_x/SiO₂ catalysts (5 wt %–25 wt % Zr, 4 wt % V) were prepared by grafting zirconium and vanadium alkoxides on Aerosil 380. All samples were characterized by temperature programmed reduction, N₂ physisorption, X-ray diffraction, Raman spectroscopy, and ammonia adsorption microcalorimetry. Tetragonal ZrO₂ and zircon (ZrSiO₄) were present at 25 wt % Zr, but only amorphous zirconia overlayer existed for lower loadings. At lower Zr loadings (5 wt %–10 wt % Zr), exposed silica surface leads to V₂O₅ crystallites and isolated VO₄ species, although V reducibility behavior changes, from being similar to VOx/SiO₂ (5 wt % Zr) to showing VOx/ZrO₂ behavior at 10 wt % Zr, and a diminished total amount of reducible V. Highly acidic ZrO₂ sites are covered by the vanadium grafting, forming weaker sites (60–100 kJ/mol NH₃ adsorption strength). Catalytic conversion and selectivity for the oxidative dehydrogenation of n-butane (673 K, n-C₄/O₂ = 2.2) over VOx/ZrOx/SiO₂ show that 1,3-butadiene is favored over cis-2-butene and trans-2-butene, although there is some selectivity to the 2-butenes when VOx/ZrO₂ behavior is evident. At low Zr loadings, butadiene formed during reaction acts as the diene species in a Diels–Alder reaction and gives rise to a cyclic compound that undergoes further dehydrogenation to produce benzaldehyde. Full article

Supported nickel catalysts were synthesized, characterized, and employed in the carbon oxides co-methanation process. Five NiO/CeO₂-ZrO₂ mixed oxides, with the same Ni content and different Ce/Zr molar ratios, were prepared by the soft-template method. They were characterized through ICP-AES, N₂ adsorption, XRD, and TPR. Reduced Ni/CeO₂-ZrO₂ catalysts were obtained by submitting the oxide systems to reduction treatment in H₂ at 400 °C. They were characterized by XRD, H₂-TPD, and CO₂ adsorption microcalorimetry and their catalytic performances in the carbon oxides co-methanation were investigated. Catalytic tests were performed in a fixed-bed continuous-flow microreactor at atmospheric pressure. The effect of experimental conditions (reaction temperature, space velocity, reactants molar ratio) was also studied. Almost complete CO conversion was obtained on any catalyst, whereas CO₂ conversion was much lower and increased with Ce content, at least up to Ce/Zr = 1. The beneficial effect of the Ce content could be related to the increased NiO reducibility and to the higher ability to adsorb and activate CO₂. However, at high Ce/Zr ratios, it is probably counterbalanced by an interplay of reactions involving CO and CO₂. Full article