A first principle simulation of adsorption behavior of HF, CS2 and COF2 on Au-doped anatase TiO2 (101)

HF, CS2 and COF2 are three kind key partial discharge decomposition gas products of SF6 electrical insulation medium, which could be used for monitoring the type and degree of defect in gas insulated equipment. In this paper, the adsorption property including adsorption entropy change, adsorption distance, density of states, and frontier molecular orbitals, of HF, CS2 and COF2 on Au-doped anatase TiO2 (101) surfaces were simulated and analysis based on density function theory. The results demonstrated that Au-TiO2 incentive upon HF, CS2 and COF2 due to the little conductivity change and low adsorption entropy change, and this material could be not suitable to be used as a gas sensor for three decomposition gas detection in the application of condition monitoring and defect diagnosis in SF6 gas-insulated equipment based on DCA.

Mitigating Global Methane Emissions Using Metal-Organic Framework Adsorbents

Global emission of methane reached a record high in 2020. Furthermore, it is expected that methane emissions will continue to rise in the coming years despite the economic slowdown stemming from the coronavirus pandemic. Adsorbents can be used to reduce methane emissions. However, the question remains as to which adsorbents perform best for enhanced methane capture. In this work, it is demonstrated that metal-organic frameworks (MOFs) exhibited the best methane uptakes at 1 bar and 298 K from experiments as compared to tested carbonaceous materials, polymers, and zeolites. In addition, the adsorption entropy, an important thermodynamic property indicating adsorption capacity and kinetics, is determined on well-defined MOFs using a global predictive equation for porous materials. A correlation was used to describe the effect of translation and rotation of methane in the porous material for methane emission abatement. This information and the entropy of adsorption of methane on MOFs has not been reported before. The predicted results were compared to experimental data obtained from adsorption isotherms. Optimum isosteric heats were calculated by the Bhatia and Myers correlation. Finally, the pre-exponential factor of desorption is determined to aid in the design of materials for global methane emissions mitigation.

Adsorption of geosmin and 2-methylisoborneol onto granular activated carbon in water: isotherms, thermodynamics, kinetics, and influencing factors

Adsorption was found to be an acceptable treatment option to remove geosmin (GSM) and 2-methylisoborneol (2-MIB). It is meaningful to investigate the adsorption capacity of granular activated carbon (GAC) for the two algal odorants in water, and the influences of natural organic material (NOM) and particle size. The adsorption process was studied with the four isotherm models (Langmuir, Freundlich, Temkin, and modified Freundlich), four kinetic models (pseudo first-order, pseudo second-order, Elovich, and intra-particle), and thermodynamics. The results showed that the adsorption of both compounds could be best described by the modified Freundlich isotherm and pseudo second-order model, and the obtained thermodynamic parameters (changes in heat of adsorption, entropy, and Gibbs free energy) revealed that the adsorption was endothermic and spontaneous. Downsizing the particle size of GAC was effective for improving the adsorption capacity and rate. The concentrations of the two odorants could be reduced from 500 ng L−1 to less than 10 ng L−1 with the presence of NOM (<20 mg L−1 total organic carbon, TOC).

Thermodynamic Properties of Water Adsorption on Gaplek Flour Fortified with Red Bead Tree Seed

The moisture sorption isotherm data of gaplek flour fortified with red bead tree seed stored in a chamber, the relative humidity of chamber ranging from 10% to 97% regulated using a saturated salt solution, was determined at three temperatures 25°, 35°, and 45 °C. The experimental data used to determine the thermodynamic functions were isosteric heat of sorption, sorption entropy, and free energy changes. The sorption isosteric heats were determined by the application of the Clausius–Clapeyron equation. Isosteric heats of adsorption increased to maximum level and then declined with increase of moisture content. Adsorption entropy increased to maximum level and then declined with the increase of moisture content. The free energy changes increased with increase in moisture content. The spreading pressure increased with increasing water activity.

Preparation of Acid-Treated Sunflower Straw Powder and Adsorption Behavior of Cr(VI) Ions onto it

The adsorption of Cr6+ions by sulfuric acid -treated sunflower straw powder was investigated under batch mode. The influence of solution pH, adsorbent dosage, adsorbent particle size and temperature was studied. The results have shown that the absorbent was efficient, the removal ratio of Cr6+up to 99.5% with an adsorbent dosage of 8 g•L-1, a pH of 6.0, at 25°C and particle size in 80-100 mesh. The negative changes in free energy (△G) indicate that the adsorption is a spontaneous process, the positive values of the adsorption entropy △S indicate the increased randomness of the Cr6+on straw active carbon surface than in solution.

Copper(II) Adsorptive Removal from Solutions with Sunflower Straw-Modified by Phosphoric Acid

Straw active carbon was manufactured from sunflower straw by phosphoric acid. The adsorption was studied by considering the effects of various parameters on the removal rate of Cu2+ such as the dosage of absorbent, adsorption time, temperature and pH. The results showed that the absorbent was efficient, the removal ratio of Cu2+ up to 98.3% with an adsorbent dosage of 16 g•L-1, a pH of 6.0, at 25°C and absorption time of 4 hours. The Langmuir and Freundlich equations can describe the adsorption equilibrium well. The negative values of the adsorption enthalpy △H and the absolute values>42 kJ•mol-1 indicate the exothermic chemical adsorption character. The negative changes in free energy (△G) indicate that the adsorption is a spontaneous process, The negative values of the adsorption entropy △S indicate the more restricted mobility of the Cu2+ on the carbon surface than in solution.

Adsorption Thermodynamics of Toxin (65 kDa) and Protoxin (130 kDa) from Bacillus thuringiensis by Several Minerals

The adsorption thermodynamics of toxin (65 kDa) and protoxin (130 kDa) from Bacillus thuringiensis (Bt) by several minerals (montmorillonite, kaolinite and silica) were investigated. The adsorption of toxin and protoxin by minerals was a spontaneous process in the range of temperature from 278K to 318K. The ?G0ads values of the toxin adsorption by above minerals ranged from -35.30 to -43.81 kJ mol-1, and the protoxin adsorption ranged from -35.87 to -44.83 kJ mol-1. The adsorption isotherms of both proteins followed Langmuir equation and the maximum adsorbed amount (Nadsmax) of protoxin were lower than those of toxin. The adsorption of Bt proteins on minerals was exothermic process, companying a negative value of ?H0ads. The ?H0ads values of the adsorption of toxin were between -3.85 and -4.98 kJ mol-1 and the protoxin were between -2.60 and -4.53 kJ mol-1. The standard adsorption entropy changes (?S0ads) of toxin ranged from 110.73 to 122.16 J mol-1 K-1, and of protoxin ranged from 122.57 to 132.77 J mol-1 K-1. The positive standard entropy (?S0ads) indicated that the freedom increased when the insecticidal proteins from B. thuringiensis adsorbed minerals. The Kads, ?G0ads and ?S0ads of toxin in value were lower than those of protoxin, suggesting that the spontaneous trend and the affinity between protoxin and minerals were larger than those of toxin.

Experimental and Simulation Study of n-Heptane Adsorption on Rutile

The adsorption of n-heptane on microcrystalline rutile has been studied experimentally by thermodynamic techniques (adsorption isotherms and microcalorimetry) over a wide range of coverage at 303 K and complemented by Grand Canonical Monte Carlo simulations. The differential heat of adsorption exhibited three descending segments corresponding to the adsorption of n-heptane on three types of surfaces. The mean molar adsorption entropy of n-heptane in the monolayer was less than the entropy of the bulk liquid by ca. −23 J/(mol K), thus revealing a hindered state of motion for the n-heptane molecules on the surface of rutile. Simulations of the adsorption of n-heptane were performed on the three most abundant crystallographic faces of rutile. The adsorption isotherm obtained from the combination of the isotherm for each face weighted by the respective abundance was found to be in good agreement with experimental data. A structural characterization of n-heptane near the surface was also conducted which indicated that the substrate strongly perturbed the distribution of the n-heptane conformations relative to the situation found for the gaseous phase. Adsorbed molecules are predominantly orientated with their long axes, with the zig-zag planes of their backbones parallel to the surface and preferentially aligned along the five-fold cus Ti4+ ions of the faces. Fewer gauche conformations were observed for molecules near the surface than was characteristic of the bulk phase.

The adsorption of nitrogen oxides on crystalline ice

The partitioning of nitrogen oxides between ice and air is of importance to the ozone budget in the upper troposphere. In the present study, adsorption of nitrogen oxides on ice was investigated at atmospheric pressure using a chromatographic technique with radioactively labelled nitrogen oxides at low concentrations. The measured retentions solely depended on molecular adsorption and were not influenced by dimerisation, formation of encapsulated hydrates on the ice surface, dissociation of the acids, nor by migration into a quasi-liquid layer or grain boundaries. Based on the chromatographic retention and the model of thermo-chromatography, the standard adsorption enthalpy of -20 kJ mol-1 for NO, -22kJ mol-1 for NO2, -30kJ mol-1 for peroxyacetyl nitrate, -32kJ mol-1 for HON} and -44 kJ mol-1 for HNO3 was calculated. To perform those calculations within the model of thermo-chromatography, the standard adsorption entropy was calculated based on statistical thermodynamics. In this work, two different choices of standard states were applied, and consequently different values of the standard adsorption entropy, of either between -39 kJ mol-1 and -45kJ mol-1, or -164 kJ mol-1 and -169 kJ mol-1 for each nitrogen oxide were derived. The standard adsorption enthalpy was identical for both standard adsorption entropies and thus shown to be independent of the choice of standard state. A brief outlook on environmental implications of our findings indicates that adsorption on ice might be an important removal process of HNO3. In addition, it might be of some importance for HONO and peroxyacetyl nitrate and irrelevant for NO and NO2.