Initial Stage Of Adsorption Research Articles

Outlining the Roles of Membrane-Foulant and Foulant-Foulant Interactions in Organic Fouling During Microfiltration and Ultrafiltration: A Mini-Review.

Membrane fouling remains a notorious problem in microfiltration (MF) and ultrafiltration (UF), and a systematic understanding of the fouling mechanisms is fundamental for solving this problem. Given a wide assortment of fouling studies in the literature, it is essential that the numerous pieces of information on this topic could be clearly compiled. In this review, we outline the roles of membrane-foulant and foulant-foulant intermolecular interactions in MF/UF organic fouling. The membrane-foulant interactions govern the initial pore blocking and adsorption stage, whereas the foulant-foulant interactions prevail in the subsequent build-up of a surface foulant layer (e.g., a gel layer). We classify the interactions into non-covalent interactions (e.g., hydrophobic and electrostatic interactions), covalent interactions (e.g., metal-organic complexation), and spatial effects (related to pore structure, surface morphology, and foulants size for instance). They have either short- or long-range influences on the transportation and immobilization of the foulant toward the membrane. Specifically, we profile the individual impacts and interplay between the different interactions along the fouling stages. Finally, anti-fouling strategies are discussed for a targeted control of the membrane-foulant and foulant-foulant interactions.

Nanoclusters and amorphous ice flakes built from water dimers

The water-solid interaction is fundamentally important for understanding and controlling the structures of interfacial water. Here we study the initial stage of water adsorption and nucleation on a Cd(0001) surface, through a combination of low temperature scanning tunnelling microscopy (STM) experiments and first-principles density-functional theory (DFT) calculation. Water is found to aggregate into various clusters with the dominant of water dimers. Particularly, the amorphous ice nanoflakes are built exclusively from water dimers. Driven by the electric field from a STM tip, the water dimers can hop across the surface, detach from a cluster with subsequent attaching to another, or rotate or diffuse within the amorphous ice nanoflakes. DFT calculations demonstrate that the ultrahigh stability of water dimers results from the adsorption-induced enhancement of dipole moment of water.

Water adsorption on vanadium oxide thin films in ambient relative humidity.

In this work, ambient pressure x-ray photoelectron spectroscopy (APXPS) is used to study the initial stages of water adsorption on vanadium oxide surfaces. V 2p, O 1s, C 1s, and valence band XPS spectra were collected as a function of relative humidity in a series of isotherm and isobar experiments. Experiments were carried out on two VO2 thin films on TiO2 (100) substrates, prepared with different surface cleaning procedures. Hydroxyl and molecular water surface species were identified, with up to 0.5 ML hydroxide present at the minimum relative humidity, and a consistent molecular water adsorption onset occurring around 0.01% relative humidity. The work function was found to increase with increasing relative humidity, suggesting that surface water and hydroxyl species are oriented with the hydrogen atoms directed away from the surface. Changes in the valence band were also observed as a function of relative humidity. The results were similar to those observed in APXPS experiments on other transition metal oxide surfaces, suggesting that H2O-OH and H2O-H2O surface complex formation plays an important role in the oxide wetting process and water dissociation. Compared to polycrystalline vanadium metal, these vanadium oxide films generate less hydroxide and appear to be more favorable for molecular water adsorption.

Magnetic hybrid gels for emulsified oil adsorption: an overview of their potential to solve environmental problems associated to petroleum spills.

Hydrogels (HGs) based on gelatin and crosslinked with gum Arabic have been prepared by the thaw-freezing method, employing two different concentrations of gum Arabic (15 and 50% w/w). Magnetic gels or ferrogels (FGs) were prepared by applying the breath in method to incorporate iron oxide magnetic nanoparticles to the HG matrix. The obtained HG and FG were characterized by XRD, FTIR, and SEM, and the FG composition was estimated by atomic absorption spectroscopy in terms of Fe content. The adsorption of crude oil onto HG and FG was explored achieving very satisfactory results. FG was regenerated by washing with toluene, maintaining efficiency of almost 90% after the fourth cycle. Equilibrium studies were performed to determine the capacity of the prepared FG for adsorption of crude oil from seawater synthetic solutions. The experiments were carried out as a function of different initial concentrations of oil residue (24 to 240 mg/L) exploring different contact times. Equilibrium data were found to fit very well with the Sips models. The kinetic data adsorption of oil onto the FG-15 was better fitted by a pseudo-second-order kinetic indicating that at the initial stages of adsorption, external mass transfer could control the whole rate of the crude oil uptake while intraparticle diffusion controlled the global rate of adsorption at later stages. The obtained results showed that the FG prepared by employing 15% of gum Arabic as the crosslinker (FG-15) has a high removal efficiency of crude oil reaching 1.53 g/g of FG at pH 5.5 and 0.59 g/g for oil/water emulsions in the order of 0.1 g/L. The magnetic properties extend its application. The reached data suggest that the materials presented here may be useful to further the design of systems or devices intended for the remediation of petroleum spills and/or its derivatives in marine water as well as other surfaces such as polluted rocks or soil.

Experimental Study on the Kinetics of Adsorption of CO2 and CH4 in Gas-Bearing Shale Reservoirs

Knowledge of the kinetics of adsorption of CO2 and CH4 on shale is essential for the optimization of the technique of enhanced gas recovery by CO2 injection. In this paper, the experiments of adsorption kinetics of CO2 and CH4 on marine Wufeng (WF) shale and continental Yanchang (YC) shale at 318 K, 338 K and 358 K over the pressure range of 3.0-8.0 MPa were conducted by volumetric method. Results show that the adsorption processes of CH4 and CO2 on shale can be described as initial rapid adsorption stage and slow sorption stage. The unipore model can simulate the kinetics data of CO2 and CH4 well. The diffusion coefficient (D) of gas increases with the increase of pressure. High temperature will help to improve the diffusivities of CO2 and CH4. The order of magnitude of D of CO2 and CH4 on two samples is 10-11 m2/s. The diffusion activation energies (Ea) of CO2 and CH4 on YC shale are 3.37 kJ/mol and 10.15 kJ/mol, respectively, and Ea of CO2 and CH4 on WF shale are 1.33 kJ/mol and 3.56 kJ/mol, respective...

Effect of applied electric field on growth morphology of copper phthalocyanine thin films

The effect of electric field on the initial stages of copper phthalocyanine adsorption on the SiO2 substrate was studied experimentally. The external electric field was applied during thermo-vacuum evaporation of CuPc. Using atomic-force microscopy and scanning electron microscopy, it was found that in the presence of an electric field, the film morphology changes. Instead of randomly oriented elongated crystallites, new form bend-shaped ones are formed on the substrate surface. The paper provides an explanation of the experimentally observed effect of the electric field on the structure of the growing film.

Study of pre-treatment of quinoline in aqueous solution using activated carbon made from low-cost agricultural waste (walnut shells) modified with ammonium persulfate.

Activated carbon made from agricultural waste (walnut shells) was investigated as a suitable adsorbent for effectively removing quinoline from industrial wastewater. The activated carbon was treated with phosphoric acid and oxidized by ammonium persulfate and its ability to adsorb pyridine and quinoline in aqueous solution was investigated. Kinetic parameters for the adsorption process were determined through pseudo-first-order and pseudo-second-order kinetic models and intraparticle diffusion models. Equilibrium experiments and adsorption isotherms were analyzed using Langmuir and Freundlich adsorption isotherms. After reaching equilibrium, the activated carbon adsorbed quinoline in preference to pyridine: the equilibrium adsorptions from individual aqueous solutions (200 μL L-1) of quinoline and pyridine were 166.907 mg g-1 and 72.165 mg g-1, respectively. Thermodynamic studies of quinoline adsorption were conducted at different temperatures and indicated that quinoline adsorption was an endothermic and spontaneous process. The column-adsorption of quinoline and pyridine was consistent with the Thomas model and the Yoon-Nelson model. The removal efficiency of quinoline reached more than 97% for a velocity of 6 mL min-1 at the initial adsorption stage.

Adsorption kinetics of halloysite nanotube and modified halloysite at the Palm oil-water interface and Pickering emulsion stabilized by halloysite nanotube and modified halloysite nanotube

In this study, the interfacial tension behavior of halloysite nanotube (HNT) as a hydrophilic nanoparticle and modified APTES-HNT as a hydrophobic nanoparticle at the palm oil-water interface was investigated. The result of this study was used to determine the stability and potential formation of Pickering emulsion as a novel dispersed system. The diffusion coefficients at the initial and late stages of adsorption were obtained. The results indicated that the interfacial tension of palm oil-water decreased with increasing the nanoparticles concentration. The diffusion coefficient at the different concentrations (0.1 g/L to 0.5 g/L) for the short time was obtained to be within the range of 1.4480 ×10-14- 6.1408 ×10-13 (m2/s) and for the longer times was within the range of 4.8065 ×10-16-7.4476 ×10-15 m2/s. The results indicated that the HNT and APTES-HNT produced significant surface and interfacial tension reductions, which confirmed their ability for stabilization of Pickering emulsion. The measured contact angle for HNT and APTES-HNT were determined to be 29.14 ° and 97 °, respectively. Stable oil-in-water and water-in-oil emulsion were obtained for HNT and APTES-HNT, respectively. The emulsions exhibited no coalescence over a period of 4 weeks.

Experimental study on adsorption of Hg(II) with microwave-assisted alkali-modified fly ash

Microwave alkali-modified fly ash was prepared as an adsorbent for mercury (II) in aqueous solution and its adsorption kinetics and mechanism are reported in this paper. The adsorption isotherm could be predicted by the Langmuir isotherm model and the saturated adsorption capacity was 2.6663 mg·g−1, which indicated that it was monolayer adsorption. It was also found that the quasi-second-order kinetic model could describe the entire process of adsorption, while the quasi-first-order kinetic equation could only reflect the initial stage of adsorption. The adsorption rate was also affected by intra-particle diffusion and by liquid film diffusion or other membrane diffusion.

Crystal violet adsorption by oppositely twisted heat-treated halloysite and pecoraite nanoscrolls

Present study focuses on crystal violet adsorption by mineral halloysite and synthetic pecoraite nanoscrolls. Being scrolled in opposite directions, these two materials serve both as good adsorbents and model objects to understand the dye adsorption mechanism. Heat treatment of the nanoscrolls allowed us to track the adsorption process features by changing the structure and surface state of the particles. Structural transitions were observed by complementary techniques including X-ray diffraction, thermal analysis, electron microscopy, N2 adsorption and ς-potential measurements. By a fast UV/VIS study of adsorption kinetics, it became possible to take a closer look at the very initial steps of the process. Intraparticle diffusion governs the overall adsorption kinetics of the dye by halloysite and pecoraite nanoscrolls. The presence of OH-groups on the nanoscrolls' surface strongly facilitates the initial stage of adsorption. Structural transition at around 600 °C increases adsorption rate and performance of synthetic pecoraite due to ς-potential sign change.

Flow field evolution during gas depletion considering creep deformation

Unsteady creep of coal seams and the resultant abnormal flow of coal seam gas are the main reasons for dynamic disasters in deep mines. In this study, for investigating the evolution of gas depletion in deep mines, the flow field evolutions during gas adsorption and desorption were simulated first based a multi-field (coal deformation field, diffusion field and seepage field) coupling model considering the creep deformation. Firstly, a laboratory experiment was performed to validate the mathematical model. Then, spatial and temporal evolutions of matrix and fracture gas pressures, coal permeability and equivalent stress during gas adsorption and desorption were analyzed. The results show that in the initial stage of adsorption, gas pressure in fractures increases rapidly under the action of pressure gradient. As the gas gradually diffuses into matrix pores, gas pressure in the matrix goes up, which results in swelling deformation of coal matrix and alters the fracture aperture. Accordingly, coal permeability and equivalent stress were affected. During the desorption process, gas pressure in fractures drops rapidly at first, and then it falls at a lower rate. The diffusion of gas into fractures gradually leads to matrix shrinkage and enhances coal permeability. With a decrease in fracture gas pressure, the equivalent stress of coal declines rapidly first, followed by a slow rise induced by the diffusion of gas in the matrix. Furthermore, changes in the amount of gas desorption was analyzed by fitting the experimental test data in a specific time, which verified rationality of the mathematical model. The study can provide theoretical guidance for prevention and control of dynamic disasters in coalmines and the gas pre-drainage through borehole in deep mines.

Amine-impregnated carbon aerogels with ultra-high pore volume synthesized by pH adjusting for efficient CO2 Capture

Carbon aerogels with ultra-high pore volume and meso/macro pores were successfully synthesized by using silica hard templating combined sol–gel method by controlling the pH value of the initial reaction solution. High loadings (65–80 wt%) of TEPA (tetraethylenepentamine) and PEI (polyethyleneimine) were impregnated into CA with a high pore volume of 5.7 cm3/g for CO2 adsorption, respectively. The effects of amine loading, CO2 concentration, adsorption temperature, and moisture on the CO2 adsorption performance of the amine-loaded CA sorbents were comparatively investigated. The results showed that the CA with ultra-high pore volume enabled excellent CO2 adsorption capacity and fast kinetics (5.93 mmol/g and 4.70 mmol/g within 2.5 min for the case of TEPA and PEI respectively at 75 °C under 10% dry CO2). The sorbents exhibited good recycle-ability both in dry and humid conditions. Under humid conditions, the diffusion resistance of the sorbents at the initial stage of CO2 adsorption was observed. This study suggests that CA with large pore size could be utilized as promising amine sorbent for post-combustion CO2 capture.

Explaining water adsorption in one-dimensional channels in AlPO4-5 on molecular scale

Abstract The adsorption of water in one-dimensional channels in porous aluminophosphate material AlPO4-5 has been studied by a combination of gravimetric analysis techniques, neutron and X-ray diffraction and neutron spectroscopy. Molecular structure of AlPO4-5 consists of 12-membered rings of alternating, corner-sharing AlO4 and PO4 tetrahedra connected by oxygen bridges into sheets in the (a, b) plane. The sheets are connected by oxygen bridges along the c crystal axis and form one-dimensional channels of which the largest, formed by the 12-membered rings, have a van der Waals diameter of about 8.3 A. Gradually increasing the amount of adsorbed water we could follow the evolution of the confined water mobility in a systematic way and identify the molecular mechanism of water adsorption. We focused particularly on the range of low and medium relative pressures up to p/p0 = 0.32, where a change from a hydrophobic behavior to a steep, capillary condensation like water intake has been observed. At the initial adsorption stages water occupies positions close to the pore walls causing the contraction of channels in the (a, b) plane and the prolongation of the channels along c axis in AlPO4-5. With the progressing intake water molecules form chains along the main channels. The cooperative interactions between water molecules lead to the onset of phonon-like cooperative modes and, surprisingly, to the increase of diffusive-like motion, which slow down only in the final adsorption stages when AlPO4-5 channels are completely filled.

The initial stage of OH adsorption on Ni(111)

The adsorption of OH on Ni(111) has been investigated by a combination of density functional theory and classical molecular dynamics. At low coverage, the adsorption is strong, the adsorbate carries almost unit negative charge, and interacts strongly with water. Because of their high charges, adsorbed OH species repel each other, and adsorption becomes less favorable with increasing coverage. Adsorption on Ni(111) is contrasted with that on Pt(111).

Study on the mechanism of SO2 removal by activated carbon

SO2 removal mechanism by activated carbon was investigated in a fixed bed reactor. The effects of SO2, O2 and H2O concentration and adsorption temperature on SO2 adsorption were studied. The results show that SO2 initial adsorption rate increases with SO2 concentration increasing, but decreases with adsorption temperature increasing. The reaction order for SO2 is 0.896 when SO2 is adsorbed at 65 °C. SO2 initial adsorption rate constant and the reaction order for SO2 decrease gradually with adsorption temperature increasing, and the activation energy in SO2 initial adsorption stage is -16.344 kJ /mol, indicating that SO2 adsorption on activated carbon is unfavorable at higher temperature and SO2 adsorption is the rate controlling step.

Characterization of extracellular polysaccharide/protein contents during the adsorption of Cd(II) by Synechocystis sp. PCC6803.

Cyanobacteria have been proven to be cheaper and more effective for the removal of metallic elements in aqueous solutions. In this study, the living cyanobacteria Synechocystis sp. PCC6803 was used to adsorb Cd(II) and its extracellular polymeric substances (EPS) were investigated in the adsorption process. The initial stage of adsorption of Cd(II) was a rapid process, and then increase slowly accompanied with the increases of biomass. The final adsorption percentage could achieve 86% when the Cd(II) concentration was 0.5mg/L. It proved that Synechocystis sp. PCC6803 has a good adsorption capacity for heavy metal ions. EPS was extracted to investigate the secretion of which was dynamic and the maximum extracellular polysaccharides and proteins were 134.2 and 100.9mg/g, respectively. Furthermore, the real-time PCR (RT-PCR) results of genes (slr0977 and exoD) involved in EPS synthesis and secretion indicated that the EPS production was firstly increased and then decreased slightly. Transmission electron microscope (TEM) observation revealed that heavy metal ions were absorbed into EPS layer. Fourier transform infrared spectrum (FT-IR) analysis showed that EPS was rich in functional groups which could combine with heavy metal ions, such as -OH and -NH groups. All the results obtained show that the secretion of EPS by cyanobacteria was one of the ways to resist heavy metal stress. And it shows a trend of rising first and then decreasing, the change regulation of which was consistent with adsorptive behavior.

Species formed during NO adsorption and NO + O2 co-adsorption on ceria: A combined FTIR and DFT study

Adsorption of NO and co-adsorption of NO and O2 on ceria have been re-investigated by FTIR spectroscopy. To provide unambiguous assignments of the IR bands, adsorption of 15NO and co-adsorption of 14NO + 15NO isotopic mixtures have also been studied and DFT calculations performed. At the initial adsorption stages mainly symmetric nitrite species (2472, 1304, ca. 1160 and 822 cm‐1) and trans-hyponitrites ([N2O2]2−, ca. 1100 cm‐1) are simultaneously produced as a result of NO disproportionation. At further stages non-symmetric NO2− species (1393 and 1014 cm‐1), N2O (2240, 1252 cm‐1) and small amount of nitrates are formed. Nitrates are the only surface products of the thermal decomposition of the nitrites and hyponitrites. In the presence of small amounts of oxygen, the hyponitrites are very easily oxidized. In contrast, all nitrites increase in concentration after addition of small amount of O2 to the NO/CeO2 system but are gradually oxidized in the presence of higher amount of oxygen giving rise to different surface nitrates.

Equilibrium and dynamic surface properties of cationic/anionic surfactant mixtures based on bisquaternary ammonium salt

The interaction behavior and the process of mixed micellization for binary mixtures of bisquaternary ammonium salt (BQAS) and sodium dodecyl sulfate (SDS) were investigated using the surface tensionmeter, and the synergistic properties of these mixtures were evaluated. The interaction parameters and thermodynamic parameters of BQAS/SDS mixtures were calculated based on the regular solution theory. Moreover, the dynamic surface tension curves of these mixtures were examined using bubble profile analysis method, and the corresponding kinetic parameters were obtained. Results indicate that the critical micelle concentrations of the BQAS: SDS mixtures with the molar ratios of 3:7, 5:5, and 7:3 are 4.0 × 10−5 mol/L, 5.0 × 10−5 mol/L and 6.0 × 10−5 mol/L, respectively, which are two orders of magnitude lower than that of either component. Despite the mixing ratios vary from 3:7 to 7:3, these mixtures have almost equal surface tensions. Consequently, the component of adsorption layer is dominated by the catanionic surfactant complexes, rather than the mixing ratios in the bulk phase. The interaction parameters βσ and βm of binary systems with the BQAS: SDS molar ratios of 5:5 are −18.11 and −15.56, respectively, indicating the strong synergistic effects in the reduction of surface tension and the formation of micelle. The thermodynamic parameters suggest that the formation of micelles is an exothermic and entropy increase process. Moreover, results of dynamic surface tension indicate that the BQAS/SDS mixtures exhibit a faster adsorption process than either pure component, resulting from the enhanced hydrophobicity of catanionic surfactant complexes. In addition, the initial stage of adsorption of BQAS/SDS mixtures exhibits a mixed kinetic-diffusion mechanism.

Cooperative Formation of Long-Range Ordering in Water Ad-layers on Fe3 O4 (111) Surfaces.

The initial stages of water adsorption on magnetite Fe3 O4 (111) surface and the atomic structure of the water/oxide interface remain controversial. Herein, we provide experimental results obtained by infrared reflection-absorption spectroscopy (IRAS) and temperature-programmed desorption (TPD), corroborated by density functional theory (DFT) calculations showing that water readily dissociates on Fetet sites to form two hydroxo species. These act as an anchor for water molecules to form a dimer complex which self-assembles into an ordered (2×2) structure. Water ad-layer ordering is rationalized in terms of a cooperative effect induced by a hydrogen-bonding network.

Direct observation of the initial adsorption stage of stearic acid on HOPG/aqueous interface using in-situ atomic force microscopy

Direct observation of the initial adsorption stage of stearic acid on graphite surfaces by Atomic Force Microscopy (AFM) imaging has been investigated. The adsorbed aggregates of the stearic acid (C17H35COOH) at the graphite/aqueous interface were observed with PeakForce Tapping® mode in air and in liquid. Initial adsorption stage of the stearic acid on Highly Oriented Pyrolytic Graphite (HOPG) has been identified. At a low stearic acid concentration, the adsorption initially occurred only along the cleavage edge and few on the basal plane of the graphite in a straight line or in a random individual distribution, which might be due to the higher surface energy at the edge and the oxidation or defects on the plane. At a high concentration, wormlike aggregates increased on the basal plane, which might be attributed to the semi-micelle adsorption of stearic anion on the plane. The initial adsorption at very low concentration may play a role to identify the area of oxidation or defects on graphite and graphene surfaces.