Adsorption Density Research Articles

Investigation of the enhanced oil recovery potential of sodium cocoyl alaninate: an eco-friendly surfactant

Amino acid-based surfactants (AASs) and other novel surfactants have recently gained attention to provide a favorable environmental image (“green”) in surfactant application. Yet their potential in enhancing oil recovery is not well investigated. Only a few works have been reported on their potential enhanced oil recovery (EOR) application with less satisfactory results. Here in, sodium cocoyl alaninate (SCA), an acylated amino acid with excellent properties that facilitate its application in other fields, is investigated for its EOR potential. Its effectiveness in lowering the interfacial tension and the emulsifying crude oil–brine mixture were studied. The ability to alter rock surface wettability and its adsorption behavior on the sand surface were studied as well. Then, its oil recovery potential was confirmed through a core displacement experiment. All studies were performed in comparison with conventionally deployed sodium dodecyl sulfate (SDS). The critical micelle concentrations for SCA (CMC = 0.23 wt%) and SDS (CMC = 0.21 wt%) were close, which serves as a good basis for comparing their EOR potential. SCA proved to be more effective in IFT reduction attaining a minimum IFT of 0.069 mN/m (i.e., ~ 98.8% IFT reduction) compared to 0.222 mN/m of SDS (i.e., ~ 96.2% IFT reduction) at the same concentration. Salinity showed a synergistic effect on the interfacial properties of both SCA and SDS but had a more significant impact on SDS interfacial properties than SCA due to low salt tolerance of SDS. The low IFT attained by SCA yielded enhanced emulsion formation and stable emulsion both at 25 °C and 80 °C for a period of one week. SCA also altered quartz surface wettability better via reduction of contact angle by 94.55% compared to SDS with contact angle reduction of 87.51%. The adsorption data were analyzed with the aid of various adsorption isotherm models. The adsorption behavior of SCA and SDS could be best described by the Langmuir model. This means a monomolecular surfactant layer exists at the aqueous–rock interface. SDS also exhibited more severe adsorption on the sand surface with the maximum adsorption density of 15.94 mg/g compared to SCA with the maximum adsorption density of 13.64 mg/g. The core flood data also confirmed that SCA has a better oil recovery potential than SDS with an additional oil recovery of 29.53% compared to 23.83% of SDS. This additional oil recovery was very satisfactory compared to the performance of other AAS that have been studied. This study therefore proves that SCA and other AAS could be outstanding alternatives to conventional EOR surfactants owing to their excellent EOR potential in addition to their environmental benign nature.

Insights into shale gas adsorption and an improved method for characterizing adsorption isotherm from molecular perspectives

• The specific multiscale inter-connected pore models of shale are proposed. • The dependences of diverse media properties and pore size on CH 4 adsorption behaviors are clearly examined by GCMC simulations. • An improved method for calibrating isothermal adsorption experimental result is proposed. Gas adsorption behavior in shale complex porous media is of great importance to gas in place (GIP) evaluation and exploration. At present, the mechanism of methane adsorption has not been adequately investigated in multi-size nanoscale space via experimental and simulation methods. In this work, the specific multi-size inter-connected pore models are proposed to study the adsorption isotherm and density profiles based on the veritable pore structure characterizations of shale samples. The grand canonical Monte Carlo (GCMC) simulations are utilized to give insight into methane adsorption behavior in organic matter and inorganic clay minerals with multi-size pores at reservoir conditions. Based on the proposed models, the effects on adsorption behaviors of methane molecules under the simultaneous action of diverse media surfaces and variable pore sizes are carefully examined. In addition, the adsorbent-adsorbate interactions, which involve the cation exchange and the isosteric heat variations with media surfaces, are carefully investigated to reveal complex adsorption behaviors in shale nanopores. Considering the identified factors influencing methane adsorption and the shortcomings of experimental test, an improved method for calibrating the gas adsorption isotherms in shale is proposed from a molecular perspective, which takes into account several factors, including i) the accessible volume of methane molecules, ii) the pore size distribution in shale, and iii) the composition of organic matter and clay minerals. The GCMC simulation results are integrated into the process of calibrating experimental results in a case study with a shale sample from the Longtan Formation in the Sichuan Basin, China. The findings of this study advance the in-depth understanding of gas adsorption mechanisms in complex nanoporous structure and provide a reliable approach to evaluate the GIP in shale.

Purification of biflavonoids from Selaginelladoe derleinii Hieron by special covalent organic polymers material

Herein, a novel covalent organic polymers (COP) material based on acylhydrazone bond (AB-COP) was prepared as an efficient extraction material for enriching natural medicine biflavonoids from Selaginella doederleinii Hieron. The obtained AB-COP structure was characterized in detail. And it was the first time to investigate the effect of AB-COP on the adsorption of biflavonoids. The effects of initial concentration of solution, adsorption temperature, solid-liquid ratio, adsorption time on the adsorption of biflavonoids were studied. In addition, adsorption kinetic model, adsorption thermodynamic model and density functional theory (DFT) were also investigated to evaluate the adsorption mechanism. At the same time, the static desorption and reusability of AB-COP were investigated. Finally, the dynamic enrichment effect of AB-COP for biflavonoids was investigated. The results showed that AB-COP was successfully synthesized by Fourier transform infrared spectroscopy (FT-IR), solid state nuclear magnetism (NMR), X-ray diffraction (XRD), thermogravimetric analysis (TG), scanning electron microscopy (SEM), laser particle size analysis and Brunner Emmet Teller (BET) specific surface area test. The optimized adsorption parameters of AB-COP were initial concentration of 0.5 mg/mL, temperature of 45 °C, solid-liquid ratio of 10:10 (mg/mL), adsorption time of 60 min. The Langmuir adsorption isotherm could effectively describe the adsorption process, the pseudo-secondary adsorption model could accurately explain the adsorption mechanism, and the DFT calculations revealed that the interaction forces of AB-COP and biflavonoids were π-π stacking and hydrogen bonding. In addition, AB-COP successfully resolved biflavonoids through urea-methanol (1.3 mol/L), and the material can be reused at least four times. Finally, the solid phase extraction (SPE) chromatographic column prepared by AB-COP was successfully applied to the enrichment of biflavonoids from S. doederleinii, and the effect was significantly better than traditional chromatography materials, andthis method was also successfully applied to the enrichment of flavonoids in other plant extracts including Flos sophorae, Pericarpium viride, Lophatheri herba, Herba cuscutae. These results provide references for further purification of bioactive ingredients from plant extracts by using AB-COP.

Biocompatible surface functionalization architecture for a diamond quantum sensor

Quantum metrology enables some of the most precise measurements. In the life sciences, diamond-based quantum sensing has led to a new class of biophysical sensors and diagnostic devices that are being investigated as a platform for cancer screening and ultrasensitive immunoassays. However, a broader application in the life sciences based on nanoscale NMR spectroscopy has been hampered by the need to interface highly sensitive quantum bit (qubit) sensors with their biological targets. Here, we demonstrate an approach that combines quantum engineering with single-molecule biophysics to immobilize individual proteins and DNA molecules on the surface of a bulk diamond crystal that hosts coherent nitrogen vacancy qubit sensors. Our thin (sub-5 nm) functionalization architecture provides precise control over the biomolecule adsorption density and results in near-surface qubit coherence approaching 100 μs. The developed architecture remains chemically stable under physiological conditions for over 5 d, making our technique compatible with most biophysical and biomedical applications.

Supercritical CO2 adsorption and desorption characteristics and pore structure controlling mechanism of tectonically deformed coals

Characteristics of supercritical CO2 adsorption/desorption on coals are the key scientific problems for CO2 geological sequestration in deep coal seams. The differences in pore structures of tectonically deformed coals will affect their adsorption/desorption characteristics. Isothermal adsorption/desorption experiments of CO2 on five medium rank coal samples with different tectonic deformations were carried out at 45℃ and 0–16 MPa. Characteristics of adsorption/desorption, including isotherm, adsorption extremes, desorption deviation and negative adsorption, were investigated. Based on mercury intrusion porosimetry, low temperature N2 and CO2 adsorption experiments, pore structure and fractal characteristics were analyzed. Finally, effects of pore structure on characteristics of adsorption/desorption and adsorption mechanism were investigated. Results show that CO2 adsorption and desorption isotherms shows the “two-stage” variation with multiple extremes and negative adsorption. The adsorption peak values at low pressure stage are mainly affected by pore specific surface area of transition pores, while the adsorption capacity at high pressure stage is mainly controlled by the development of ultra-micropores, especially for ductile deformed coals. As the coal deforms from weak to strong, the desorption deviation shows the change trend of “premature desorption - reversible desorption - premature desorption”, which is controlled by fractal characteristics of pores (D1 and D3). Extraction of small organic molecules by supercritical CO2 has been considered as a possible cause for increase in density of bulk free phase and negative adsorption.

Trimetallic CoNiFe-layered double hydroxides: Electronic coupling effect and oxygen vacancy for boosting water splitting

Developing cost-effectively bifunctional electrocatalysts with high activity sites and optimized intrinsic activity is still an enormous challenge. Here, a trimetallic CoNiFe-layered double hydroxide (LDH) hollow superstructure grown on carbon cloth is ingeniously fabricated through an aging and etching-coprecipitating method. Remarkably, electron cloud density of active sites and adsorption for reaction intermediate are optimized by the strong electronic coupling effect and the abundant oxygen vacancies, which can endow catalysts with marvelous intrinsic activity for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). As a consequence, the trimetallic CoNiFe-LDH catalyst requires low overpotentials toward HER (143 mV at 10 mA cm−2) and OER (219 mV at 20 mA cm−2) in 1.0 M KOH, enabling an alkaline electrolyzer to deliver a low cell voltage of 1.56 V at 10 mA cm−2 that are superior to most reported LDH catalysts. This work reports a high activity bifunctional OER/HER electrocatalysts, which may open numerous opportunities to the development of trimetallic LDH catalysts in hydrogen production.

Recovery of milk whey proteins by foam separation

Milk whey proteins recovery was conducted with foam separation. Experiments were conducted by batch mode in pH 4–8. The separation rate was evaluated by the rate constant of the first-order kinetic equation. Both recovery efficiency and separation rate were highest at pH 7. Overall equilibrium adsorption constant, K, and saturated adsorption density, Xs, were determined from a proposed estimating method using data obtained in batch mode. At pH 7, K and Xs were determined using the data obtained in continuous mode. K and Xs determined by both operation modes were agreed well. Adsorption parameters of the major proteins in milk whey (bovine serum albumin (BSA), α-lactalbumin (LA), and β-lactoglobulin (LG)) were estimated by the proposed estimating method in pH 4–7. Xs is largest at pH 5 and the K of LG over pH 5 was larger, which suggested that LG was the most hydrophobic species among them.

Adsorption mechanism and flotation behavior of ammonium salt of N-Nitroso-N-phenylhydroxyamine on malachite mineral

The adsorption mechanism between malachite and a specific organic ligand of the ammonium salt of N-Nitroso-N-phenylhydroxyamine (NBH) with the NH4+ group and nitrosamine polar group has been studied. The tapping mode atomic force microscopy (AFM) imaging illustrated that irregular protrusions were covered on malachite surface at the nanoscale when malachite was treated in NBH solutions under alkaline conditions at pH 9.5. It indicated that the NBH displayed an excellent affinity to malachite, and the adsorption density was correlated with the concentration of NBH. Based on copper ammine theory and the results of Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS), the intermediate transition process of the interaction between malachite and NBH can be summarized as activation, diffusion and reduction, combination, and redeposition. The copper ions removed from the ammonia-activated malachite surface combined with the NBH resonating structures to form the bidentate and monodentate complexes. Eventually, those microscopic analyses are confirmed by the macroscopic flotation test. The flotation recovery illustrated the formation of ligand–Cu complex strengthened the hydrophobicity of malachite in a three-phase system. Therefore, it is feasible using NBH as collector to selectively separate malachite from gangue minerals in flotation experiments.

Experimental investigation of the adsorption process of the surfactant-nanoparticle combination onto the carbonate reservoir rock surface in the enhanced oil recovery (EOR) process

Nowadays, the application of materials, such as surfactants and nanoparticles in enhanced oil recovery (EOR) projects has been widely studied. So, the adsorption process of these substances is one of the important methods to increase the oil recovery factor from carbonate oil reservoirs. However, understanding how the surfactant-nanoparticle combination interacts through the adsorption process onto the carbonate reservoir rocks surface is not well discussed. In this paper, the adsorption process of saponin extracted from the Glycyrrhiza glabra plant as a natural non-ionic surfactant (GG surfactant) with the presence of hydrophilic titanium dioxide nanoparticles (HITNPs) onto the carbonate reservoir rock (adsorbent) surface has been investigated for mobilizing the crude oil remaining to increase the oil recovery factor. Hence, this study highlights the equilibrium adsorption rate and the adsorption kinetics of these materials in aqueous solutions for chemical EOR schemes. Also, analyses of X-ray diffraction (XRD) spectrometry, scanning electron microscopy (SEM), and Fourier transform infrared (FTIR) spectroscopy have been applied to confirm and determine the physicochemical changes and properties of materials. To evaluate the adsorption rate and the relationship between surfactant concentration with the presence of nanoparticles and adsorption density on the adsorbent surface in the aqueous phase, batch adsorption tests under atmospheric conditions at different concentrations and times have been used to comprehend the impact of adsorbate dose on the sorption efficiency. Therefore, the electrical conductivity (EC) technique was used for measuring the adsorption rate of surfactant with the presence of HITNPs in the aqueous phase on the adsorbent surface. The adsorption kinetics process was experimentally investigated at laboratory temperature (25 °C) by monitoring the uptake of solutions on the adsorbent surface as a function of time. The experimental adsorption data were also examined by different equilibrium and kinetic models of adsorption. Hence, the adsorption parameters were determined for each model. Langmuir isotherm was the best model according to the higher values of the correlation coefficient (R2) for GG surfactant and surfactant nanofluid solutions on the adsorbent surface. Furthermore, the pseudo-second-order kinetic model could satisfactorily estimate the adsorption kinetics of GG surfactant and surfactant nanofluid solutions on the adsorbent surface. Results indicated that the adsorption process of GG surfactant and surfactant nanofluid solutions on the adsorbent surface is characterized by a short period of rapid adsorption, followed by a long period of slower adsorption. Moreover, the results of the IFT experiment of these materials showed that GG surfactant and surfactant nanofluid solutions could significantly reduce the IFT value between oil and water system. Finally, the results obtained from this study can help in selecting appropriate surfactants and metal oxide nanoparticles for the design of EOR projects, especially reservoir simulation schemes and chemical flooding processes for carbonate oil reservoirs.

Shell-to-core ratio dependence on modulating interactions between core-shell composite nanoparticles at an air-aqueous interface

The current study examined the shell-to-core ratio (λ) dependence on modulating interactions between core-shell composite particles (CPs) at the air-aqueous interface. The CPs were prepared by physical adsorption of poly(vinylpyrrolidone) (PVP) on the surface of silica nanoparticles (NPs). The λ value increases with increasing PVP adsorption density and PVP molecular weight. The resulting CPs are referred to as CPs8, CPs40, CPs360, and CPs1300 respectively, depending on the molecular weight of PVP that being used. The 8 kDa PVP shell is thin, and the CPs8 behave more like hard spheres at the interface. Hence, great shear and compressional elasticities of the CPs8-laden interface were measured. Whereas, higher values of λ (thicker PVP shells) induce a stronger steric barrier, which dominates the self-assembly of the CPs and modulates the microstructure of the CPs-laden interface into more complex and non-hexagonal phases (i.e. anisotropic chains), e.g. for the CPs360 and CPs1300 cases. The enhanced steric repulsion between the polymer shells makes significant contributions in building up the surface pressure before the solid particle cores being sufficiently compressed, which reduces the apparent particle surface coverage, lubricates the CPs-CPs interaction, and facilitates the rearrangement of the CPs under compression and shear, resulting in interfacial films with weak viscoelasticity. The CPs40, however, showed a transition behavior between the “hard” CPs8 and the “softer” CPs360 and CPs1300 at the air-aqueous interface.

Prediction of the adsorption properties of liquid at solid surfaces with molecular scale surface roughness via encoding-decoding convolutional neural networks

Molecular dynamics (MD) simulation can effectively analyze the transport properties of liquid at the solid surface with different nanoscale roughness, while high computational costs are required. Herein, a deep learning encoding-decoding convolutional neural network is proposed to predict the adsorption density distribution of atomic and organic liquids under different molecular scale surface roughness. Compared with the previous deep learning studies focusing on simple macro adsorption parameters, our deep learning method realizes the prediction and visualization of micro scale adsorption behavior with very high accuracy. The data-driven deep learning algorithm replaces the MD extensive sampling and simplifies the operation process, which improves the computational efficiency of a single model 36000-fold. This study proves the good coupling between MD and deep learning method, which is helpful for designing surface geometry to obtain desirable interfacial transport properties of molecular liquid and complementing the nanoscale model system enabling the interactive visualization.

Bacillus licheniformis a potential bio-collector for Barite-Quartz selective separation

Employing microorganisms and their metabolites as a potentially low-cost and environmentally friendly alternative for the synthetic compounds in many of the current mineral beneficiation techniques is receiving increasing attention. For the first time, the influence of the Bacillus licheniformis cells and its metabolites for selective flotation of barite from quartz was studied. The maximum adsorption density of 1.33 × 1010 cells/g was achieved at pH = 3 for barite, six times higher than quartz. Flotation experiments revealed that cell-assisted separation was more effective than metabolite-facilitated flotation, either for single mineral or the mixed sample (barite mixed with quartz). Barite was recovered up to 87% (at pH = 3) in sole-mineral flotation experiments, and flotation of the mixed sample, also, proved a successful selective separation of barite (76% recovery) from quartz at the bio-collector dosage of 6.55 × 103 cells/ml. Adsorption kinetics study showed that the pseudo second-order model could represent cell adsorption densities for both minerals, while the Langmuir model simulated adsorption isotherms. Finally, it was shown that B. licheniformis cells could selectively enhance particles hydrophobicity and successfully be utilized as a bio-collector.

Investigations of CO2 storage capacity and flow behavior in shale formation

CO2 storage, CO2 stimulation, CO2-enhanced oil recovery (EOR), and CO2-enhanced gas recovery (EGR) in shale reservoirs have recently attracted attention. Thorough investigations mimicking high pressure and high-temperature subsurface conditions are necessary to understand the interaction between CO2 and organic-rich shales, advance the fundamental understating of flow mechanisms in unconventional reservoirs, and successfully implement a field project. Most of the previous work focused on one aspect of adsorption, flow behavior, and reservoir numerical simulation. We suggest that a single approach investigation may lead to incomplete conclusions of CO2 injection in shales. This work comprehensively evaluates CO2 storage potential and injectivity in the Bakken Formation through various approaches. Samples are tested from the Lower Bakken Shale (LBS), the Middle Bakken (MB), and the Upper Bakken Shale (UBS). In terms of absolute and Gibbs/excess, adsorption isotherms of these two types are both measured, and the adsorbate density is estimated. We differentiate two adsorption isotherms and emphasize the correct use of the isotherm in the current commercial reservoir simulator, which is relatively obscure in the existing literature body. Nuclear magnetic resonance (NMR) confirms a portion of bitumen/absorption mobilization because of CO2 exposure. In the compositional simulations of CO2 injection in shales, several novel conclusions are obtained regarding analyzing main control factors; the most important one is that adsorption outweighs molecular diffusion in determining CO2 injection rate.

Ab initio studies of the electronic structure induced by the CO and N2 adsorptions on graphene and on graphite slab

In this paper, we present an Ab initio study on the electronic properties of graphene and graphite slabs, using band structure and density of states calculations. The calculations are based on the use of GPAW (Grid-based Projector-Augmented Wave) and ASE (Atomistic Simulation Environment) methods. Our study also focuses on the adsorption mechanism of CO and N2 molecules, deposited on adsorbents such as graphene and graphite slabs. The main results of our work are the optimization of the energies of CO (optimal energy equals −14.67 eV) and N2 (optimal energy equals −15.80 eV) molecules, as well as the calculation of the optimal adsorption distance of these molecules on the adsorbents namely d(C0-graphene) = 4.69 Å, d(N2-graphene) = 6.03 Å, d(C0-graphite) = 4.69 Å and d(N2-graphite) = 5.36 Å. The calculated changes in adsorption energies and density of state of the adsorbent could be exploited as an application for gas sensors. Simulated surface/gas tunneling microscopy (STM) observations are also reported. They allow to highlight the change of electronic structure of the surface when the gas is absorbed. All results contribute to the optimization of the potential realization of a gas sensor. Our paper provides interesting information for the theoretical and experimental communities working on this research area. It contributes to the debate on the adsorption of CO and N2 molecules on graphene and on a graphite slab.

The structural feature of Ni–Al-LDH nanosheets and their adsorption performance for ethyl mercaptan from methane gas

The adsorption of ethyl mercaptan (EM) on Ni–Al layered double hydroxide nanosheets (Ni–Al-LDH-NS) was investigated by an adsorption experiment on a fixed bed adsorption apparatus and density functional theory calculations (DFT).

Ti3C2TxMXenedoped by W atoms for full-spectrumphotofixation of nitrogen

Full-spectrum photofixation of N2 with remarkable NH3 production rate of 228 μmol/(g·h) was achieved by W atoms doped Ti3C2TxMXene (W/Ti3C2Tx-U) catalyst without sacrificial agents at room temperature. The effects of W doping and ultrasonic intercalation of Ti3C2TxMXene were studied. Scanning transmission electron microscope, electron spin resonance spectra, X-ray photoemission spectroscopy, UV-Vis spectrophotometer, temperature programmed adsorption analyzer and density functional theory calculation were used to characterize the obtained catalysts. Results showed that Ti3C2TxMXene harvested ultraviolet-visible and near-infrared light to generate hot electrons. In addition, the doped W atoms played an effective role in adsorbing and activating N2 molecules by donating electrons to the anti-bonding orbitalof N2 molecules to elongate the bond length of N≡N.

Nanoscale gas accumulation at solid-liquid interfaces: a molecular dynamics study.

The development of the interfacial gas enrichment layer at the solid-liquid interface is coupled with the stability of surface nanobubbles. Depending upon the concentration of gas molecules, solid-liquid-gas interaction strengths, and other thermodynamic parameters, gas molecules can take several different forms such as dense gas layer, bulk and surface nanobubble, and other gaseous domains. Using molecular dynamics simulations we study the characteristics of gas accumulation into a dense gas layer, surface nanobubble and local gas aggregation at the graphene-water interface with no pinning sites. We find that gas molecules can migrate over the solid surface and can collect together to take the morphological form of a surface nanobubble. The developed nanobubble is mobile and can move over the homogeneous hydrophobic solid surface without losing its shape. We find that the gas adsorption on surfaces in the presence of a solvent is strongly affected by the wetting characteristics of the solid. In the absence of a solvent, gas adsorption is found to be universal for all surface types. Individual gas adsorption is found to be prominent and occurs in a short period, and is essential for the stability of the formed gaseous domains. Simulation results show gas adsorption density on surfaces to have a strong dependence on the solid-liquid interaction parameter than on solid-gas interaction strength.

Comparative study of the interaction mechanisms between galena, cerussite and anglesite with benzohydroxamate and octanohydroxamate in aqueous solution

• The interaction mechanisms between lead ores with hydroxamate anions were suggested. • The identity of the formed metal complexes was determined by FTIR . • A lower BHA adsorption density on the lead active sites was found compared to OHA. • The collector anions are chemically adsorbed in most of the studied conditions. • Both anionic collectors are physisorbed onto anglesite conditioned at pH 5. Chelating agents have currently received particular attention in the search for reagents to improve the separation of oxidized minerals by froth flotation. Among chelating reagents, the hydroxamic acids outstand because they have shown a higher performance without the health, safety and environmental (HSE) concerns associated with the xanthates. In this study, the chemical adsorption of benzohydroxamic acid (BHA) and octanohydroxamic acid (OHA) onto galena (PbS), cerussite (PbCO 3 ) and anglesite (PbSO 4 ) surfaces was evaluated making use of infrared spectroscopy. Likewise, zeta potential measurements were carried out to determine the surface charge of the mineral particles before and after conditioning with the surfactant. Finally, the interaction mechanisms between galena, cerussite and anglesite with hydroxamate anions in aqueous solution were suggested; these mechanisms present the global reactions and help to understand the interaction of BHA and OHA with lead ores. It is suggested that the bezohydroxamate and octanohydroxamate anions are chemically adsorbed on the lead mineral surface in most of the studied conditions, except on the anglesite conditioned at pH 5, where the referred anions are physisorbed. The results obtained from infrared spectroscopy and zeta potential measurements suggest that P b 2 + dissolves from the crystal lattice and reacts with the anions to precipitate Pb–benzohydroxamate or Pb–octanohydroxamate, which are physically readsorbed on the anglesite surface vicinity. Additionally, the identity of the formed metal complexes was determined.

Adsorption and sensing performances of transition metal (Ag, Pd, Pt, Rh, and Ru) modified WSe2 monolayer upon SF6 decomposition gases (SOF2 and SO2F2)

In this study, we explored the adsorption of SF6 decomposition products (SOF2 and SO2F2) on transition metal (Ag, Pd, Pt, Rh, and Ru) modified WSe2 (with adatom and TM-substitution) using DFT calculations. The adsorption energy, charge transfer, electrostatic potential, and density of states of the adsorption structures between the target gas molecules and TM-WSe2 were studied. The calculation results show that the conductivity of the WSe2 monolayer modified with metal atoms is improved. And the adsorption energy of these gases on Ag-WSe2 (with adatom), and SO2F2 on Pd, Pt modified WSe2 (with TM-substitution) is very small. The density of states analysis indicates that Ag-WSe2 (with TM-substitution) shows weak sensing property to SO2F2 molecule. Therefore, these five modified systems are not suitable for gas-sensing equipment. For other modified systems, the conductivity decreases to different degrees after the adsorption of gas. Therefore, the gases can be detected according to the different change rule of conductivity after adsorption. In addition, these adsorption structures have a reasonable recovery time. The results not only have important significance for explaining the sensing mechanism of TM modified WSe2 adsorption to SF6 decomposition products, also provide a potential material for the further development of gas-sensing sensors.

Insights into the influence of temperature on the adsorption behavior of sodium oleate and its response to flotation of quartz

Temperature affects the flotation of quartz in the calcium/sodium oleate (NaOL) system, while there is a lack of understanding of its potential mechanism. Therefore, in this work, the flotation response of quartz to temperature was investigated via micro-flotation experiments, interface property analyses, and theoretical calculations. Flotation results demonstrated that increasing temperature contributed to higher flotation recovery of quartz, which enhanced the removal of quartz from hematite. Surface tension results revealed that higher temperatures lowered the critical micelle concentration (CMC) and surface tension of the NaOL solution, and thus enhanced its surface activity. Solution chemistry calculations and X-ray photoelectron spectroscopy (XPS) measurements confirmed that the increased content of Ca(OH)+ achieved by increasing temperatures enhanced the adsorption amounts of calcium species (acting as activation sites) on the quartz surface. Dynamic light scattering (DLS) measurements verified that the association degree of RCOO− to form (RCOO)22− was strengthened. Furthermore, adsorption density measurements and molecular dynamics (MD) simulations confirmed that increasing the temperature facilitated NaOL adsorption toward the surface of the quartz, which was attributed to the stronger interaction between NaOL and the calcium-activated quartz surface at higher temperatures. As a result, quartz flotation was improved by increasing temperatures. Accordingly, a possible adsorption model was proposed.