Multimolecular Layers Research Articles

Unveiling the non-equilibrium process in multilayer mixture adsorption

The Brunauer–Emmett–Teller (BET) theory [S. Brunauer et al., “Adsorption of gases in multimolecular layers,” J. Am. Chem. Soc. 60, 309–319 (1938)] constitutes a cornerstone in gas-adsorption physics. Recently, the kinetic BET equation of single-kind adsorbate has been proposed [H. Yu and X. Zhang, “Molecular-kinetic study of multilayers gas-adsorption in a rarefied gas environment,” Phys. Fluids 34, 123106 (2022)], while its counterpart of mixed adsorbates is currently unknown. Gas mixtures are commonly found in both natural and artificial systems. To address this limitation, we have proposed a kinetic BET theory for adsorbate mixtures in this paper. Moreover, we gave an analytical solution addressing low gas pressure conditions. In this condition, we predicted the “over-adsorption” of one species in the mixture with a higher desorption rate over time, and the “inertia effect” during the crowed-out process of the fast-desorbing species. Further, we also simulated the reciprocal influence of multilayer gas adsorption on the non-equilibrium fluids. Our findings provide valuable insights into gas-adsorption experiments and can facilitate technological advancements.

Reversible surface modification of PAN-based carbon fibers by a ferrocene-based surfactant

The surface of carbon fibers (CFs) was modified by a surfactant (ferrocenemethyl)dodecyldimethylammonium bromide (FDDA) to enhance the interfacial ashesion between the CFs and surrounding matrix. Results showed that it could be electrochemically desorbed by a potentiostatic electro-oxidation method. The FDDA adsorption isotherm was attributed to the formation of multi-molecular layers mainly by non-electrostatic interactions. The adsorption and desorption of FDDA on the CFs have little effect on their tensile strength. The effects of FDDA modification on the interfacial properties of CF/epoxy composites were evaluated by a single-filament fragmentation test. Compared with the un-modified CFs, the FDDA-modified ones had significantly improved interfacial adhesion properties in the composites. This method provides a potential approach for preparing recyclable CF/resin composites.

A study on the adsorption property and mechanism of β-cyclodextrin/polyvinyl alcohol/polyacrylic acid hydrogel for ciprofloxacin

Abstract Polyvinyl alcohol (PVA), acrylic acid (AA), and β-cyclodextrin (β-CD) were used as monomers, and ammonium persulfate was used as an initiator. Orthogonal tests were optimized the experimental condition, and aqueous polymerization was used to prepare poly-β-cyclodextrin/polyvinyl alcohol/polyacrylic acid (β-CD/PVA/PAA) hydrogel. The samples were characterized by FT-IR (Fourier transform infrared), SEM (Scanning electron microscopy), and XRD (X-ray diffraction). β-CD/PVA/PAA hydrogel was analyzed, which influenced external environmental factors on the β-CD/PVA/PAA hydrogel adsorption performance, and the kinetic behavior of β-CD/PVA/PAA hydrogel on ciprofloxacin (CIP) adsorption was explored. The results concluded that the prepared β-CD/PVA/PAA hydrogel has a well-defined three-dimensional network structure. The decrease in the pH of the CIP solution and the adsorption temperature reduces the adsorption reaction of β-CD/PVA/PAA hydrogel on CIP. The kinetics of CIP adsorption by β-CD/PVA/PAA hydrogel confirmed the pseudo-second-order kinetic model (R 2 > 0.997), the maximum equilibrium adsorption amounts is 372.12 mg/g, the removal rate reaches 74.42%. The adsorption process was mainly chemisorption, the adsorption isotherm fits the Freundlich adsorption isotherm model (R 2 > 0.946), and the adsorption process was heterogeneous with multi-molecular layer adsorption. The adsorption process inclined more toward the adsorption of inhomogeneous multi-molecular layers. The β-CD/PVA/PAA hydrogel retained 80% adsorption properties after three adsorption-desorption under optimal conditions.

Thermodynamic characteristics of cotton dyeing with reactive dyes in non-aqueous media

Understanding the dyeing behaviors of reactive dyes onto cotton in non-aqueous media is helpful to facilitate the development of sustainable non-aqueous dyeing. Here, the thermodynamic characteristics of cotton dyeing with reactive dyes in the non-aqueous media of liquid paraffin (LP) and decamethylcyclopentasiloxane (D5), were investigated and compared to those in aqueous medium. The results showed that the adsorption isotherms of the reactive dyes in LP, D5, and water media accorded with the Freundlich model, indicating that the dyeing proceeded via the physical adsorption of multi-molecular layers. Furthermore, the dyeing enthalpy and dyeing entropy of cotton dyeing using reactive dyes in LP and D5 media were positive, which was significantly different from those in an aqueous medium. These properties help to understand and interpret the dyeing properties and behavior of reactive dyes onto cotton in LP and D5 media.

Investigation on the interaction between the lipophilic structure of anionic dispersants and Shenhua non-caking coal in coal water slurry

Three anionic dispersants with different lipophilic structures and hydrophilic ends of sulfonic acid, including sodium lignin sulfonate (SLS), sulfonated acetone formaldehyde condensate (SAF) and naphthalene sulfonate formaldehyde condensate (NSF), were selected to study the effect of different lipophilic structures on the adsorption properties and dispersion mechanism. The results show that NSF and SAF are adsorbed on the surface of Shenhua non-caking coal (SNC) by single-molecular layer while SLS is adsorbed by multi-molecular layers. Through molecular dynamics simulation, the negative value of interaction energy indicates that all three dispersants can be spontaneously adsorbed on the surface of SNC. The dispersant with simple lipophilic structure has small steric hindrance during the adsorption process, which facilitate to rapidly adsorb on the coal surface with a thin layer and more adsorption sites. On the contrary, dispersants with more side chains and complex structure are adsorbed with a relatively thick layer and less adsorption sites. A dispersion mechanism of anionic dispersant on SNC surface has been proposed in this paper.

Physico-chemical characteristics and the adsorption of ammonium of biochar pyrolyzed from distilled spirit lees, tobacco fine and Chinese medicine residues

This paper investigates the physico-chemical characteristics of biochar from three specific waste materials including distilled spirit lees (DSL), tobacco fine (TF) and Chinese medicine residue (CMR) prepared by pyrolysis at 450℃, 550℃ and 650℃. All produced biochars were further analyzed for their ability to adsorb ammonium with initial concentrations of 0−500 mg·L−1. Results showed that all biochars mainly consist of C and O, and possess highly-porous morphology features with pore size of 2.029–6.731 nm. With same feedstock, carbonized DSL, TF and CMR at 650℃ has largest specific surface area of 6.293 m² g−1, 57.485 m² g−1 and 14.668 m² g−1 respectively. The positions of the infrared peaks of biochar derived from same feedstock are similar, but the intensity of some peaks has changed. With same feedstock, DSL450/550, TF650, and CMR450 biochar showed the best performance for ammonium removal with an adsorption capacity of 10.3199–11.8906, 10.4603–13.3511 and 23.2558-24.1546 mg g−1 respectively. The adsorption progress of ammonium by DSL biochar could be well described by both Freundlich and Langmuir adsorption isotherm, while the progress of TF biochar and CMR biochar was best described by Langmuir and Freundlich adsorption isotherm respectively. The fitted results indicate that the adsorption process of NH4+-N by both DSL biochar and TF biochar are uniform monolayer adsorption on the surface, but the adsorption of CMR biochar is mainly in the heterogeneous adsorption mode of multi-molecular layers. In sum, the experiment that was performed as well as the parameters used proved to be feasible for DSL biochar, TF biochar and CMR biochar production as adsorbing medium.

Adsorption Characteristics of Sulfamethazine on Three Typical Porous High-temperature Modified Solid Waste Materials

Three typical porous solid wastes, including livestock manure, crop straw, and coal mining waste, were used as raw materials to prepare cattle manure charcoal, straw charcoal, and coal gangue charcoal by low-oxygen controlling temperature carbonization and calcination. Batch adsorption experiments of sulfamethazine (SMZ) in water were carried out. Adsorption kinetics and isothermal adsorption equilibrium were used to investigate the adsorption characteristics of SMZ on cattle dung charcoal, straw charcoal, and coal gangue charcoal, and the adsorption mechanism was discussed by means of field-electron scanning electron microscope, Fourier transform infrared spectroscopy, Boehm titration, Brunauer-Emmett-Teller measurement, and zeta potentiometric titration. The results showed that the adsorption of SMZ on the three carbon materials reached equilibrium at 24 h. The adsorption kinetics of SMZ on three kinds of carbon materials agreed with the quasi-second-order kinetics equation. R2 ranged from 0.9968 to 0.9999, and the adsorption rate decreased with the decrease in effective adsorption sites on the surface of carbon materials. The adsorption process mainly consists of three steps:membrane diffusion, intraparticle diffusion, and the equilibrium stage. Both intraparticle diffusion and membrane diffusion control the adsorption rate. Isothermal adsorption is more consistent with the Freundlich model. R2 is between 0.9874 and 0.9997. It is mainly physical adsorption and spontaneous exothermic reaction. The maximum adsorption capacity of the three kinds of carbon materials was cattle dung carbon (19.64 mg·g-1) > coal gangue carbon (12.06 mg·g-1) > straw carbon (9.16 mg·g-1). The adsorption mechanism of SMZ on the three kinds of carbon materials mainly includes hydrogen bonding between molecules, surface electrostatic adsorption of multi-molecular layers, and pore filling. Of these, electrostatic adsorption is the main adsorption mechanism. The best adsorption performance of cattle manure charcoal may be due to its rich oxygen-containing functional groups, more negative charges, and larger specific surface area and pore volume.

Adsorptive Removal of Pyridine in Simulation Wastewater Using Coke Powder

Pyridine is a toxic component in industrial wastewater, which is difficult to remove using conventional methods. In this study, the cost-effective coke powder was used to remove pyridine from a pyridine simulation wastewater. The removal efficiency and adsorption capacity of pyridine reached up to 67.32% and 0.4488 mg/g, respectively, at a coke powder concentration of 60 mg/L and an adsorption time of 30 min. The pyridine removal efficiency and adsorption capacity of coke powder reached saturation when the initial concentration was 40 mg/L. The pH of 2–12 in the solution was found to have little effect on the pyridine adsorption process of coke powder, while the coke powder with lower ash content was of better adsorbability for pyridine. The coke powder was regenerated by heat treatment, and reused for pyridine adsorption. It was found that the pyridine removal efficiency slightly decreased after nine times of reuse, in addition to a small cumulative weight loss rate of coke powder. Adsorption isotherm analysis showed that the adsorption of pyridine by coke powder could be well described by the Freundlich isothermal adsorption model, indicating multi-molecular layers mainly dominated the adsorption of pyridine on the surface of coke powder.

The Adsorption Behavior of Atrazine in Common Soils in Northeast China.

The objective of this study was to evaluate the adsorption capacity of atrazine and the effects of different environmental conditions such as temperature, pH, Ca2+ and biochar on the adsorption characteristics of atrazine in different types of soil using the intermittent adsorption method. The kinetic experiment showed that the adsorption of atrazine in albic, black and saline-alkaline soils reached equilibrium within 24h. In the thermodynamics experiment, the Freundlich model effectively described the adsorption characteristics of atrazine in all three types of soil, indicating that the adsorption process forms multi-molecular layers. Lower soil pH conditions were more favorable for the absorption of atrazine. The addition of appropriate concentrations of Ca2+ or biochar could promote the adsorption of atrazine by the soil. Biochar could promote the fixation of atrazine in soils.

A molecular zoom into soil Humeome by a direct sequential chemical fractionation of soil

A Humeomics sequential chemical fractionation coupled to advanced analytical identification was applied directly to soil for the first time. Humeomics extracted ~235% more soil organic carbon (SOC) than by the total alkaline extraction traditionally employed to solubilise soil humic molecules (soil Humeome). Seven fractions of either hydro- or organo-soluble components and a final unextractable humic residue were separated from soil. These materials enabled an unprecedented structural identification of solubilised heterogeneous humic molecules by combining NMR, GC–MS, and ESI-Orbitrap-MS. Identified molecules and their relative abundance were used to build up structure-based van Krevelen plots to show the specific contribution of each fraction to SOC. The stepwise isolation of mostly hydrophobic and unsaturated molecules of progressive structural complexity suggests that humic suprastructures in soil are arranged in multi-molecular layers. These comprised molecules either hydrophobically adsorbed on soil aluminosilicate surfaces in less stable fractions, or covalently bound in amorphous organo-iron complexes in more recalcitrant fractions. Moreover, most lipid molecules of the soil Humeome appeared to derive from plant polyesters rather than bacterial metabolism. An advanced understanding of soil humic molecular composition by Humeomics may enable control of the bio-organic dynamics and reactivity in soil.

低級アルコール粉砕助剤を用いたトルマリンの乾式超微粉砕

The effect of lower alcohol aids on the ultrafine grinding of a tourmaline of a silicate mineral was examined by using a vibration ball mill with a laboratory scale. Lower alcohols used were methanol, ethanol and 1-butanol. All of the experiments were carried out by batch operation, and the change of the specific surface area of tourmaline with grinding time was measured by BET adsorption method. The results showed that the lower alcohols were very effective as grinding aid for ultrafine grinding of tourmaline and especially 1-butanol had the aid effect best. Through various measurements the surface of products ground with lower alcohol aids were found to exhibit hydrophobicity due to the chemisorption of alcohol molecules to the surface. The preferred effect of 1-butanol aid is attributed to efficient monolayer adsorption compared with methanol and ethanol of multimolecular layers adsorption.

Removal of cefalexin using yeast surface‐imprinted polymer prepared by atom transfer radical polymerization

The first use of yeast as a support in the molecular imprinting field combined with atom transfer radical polymerization was described. Then, the as-prepared molecularly imprinted polymers were characterized by Fourier transmission infrared spectrometry, scanning electron microscope, thermogravimetric analysis, and elemental analysis. The obtained imprinted polymers demonstrated elliptical-shaped particles with the thickness of imprinting layer of 0.63 μm. The batch mode experiments were adopted to investigate the adsorption equilibrium, kinetics, and selectivity. The kinetic properties of imprinted polymers were well described by the pseudo-second-order kinetic equation, indicating the chemical process was the rate-limiting step for the adsorption of cefalexin (CFX). The equilibrium data were well fitted by the Freundlich isotherm, and the multimolecular layers adsorption capacity of imprinted polymers was 34.07 mg g(-1) at 298 K. The selectivity analysis suggested that the imprinted polymers exhibited excellent selective recognition for CFX in the presence of other compounds with related structure. Finally, the analytical method based on the imprinted polymers extraction coupled with high-performance liquid chromatograph was successfully used for CFX analysis in spiked pork and water samples.

Kinetics and mechanism studies of p-nitroaniline adsorption on activated carbon fibers prepared from cotton stalk by NH4H2PO4 activation and subsequent gasification with steam

Activated carbon fibers (ACFs) were prepared for the removal of p-nitroaniline (PNA) from cotton stalk by chemical activation with NH(4)H(2)PO(4) and subsequent physical activation with steam. Surface properties of the prepared ACFs were performed using nitrogen adsorption, FTIR spectroscopy and SEM. The influence of contact time, solution temperature and surface property on PNA adsorption onto the prepared ACFs was investigated by conducting a series of batch adsorption experiments. The kinetic rates at different temperatures were modeled by using the Lagergren-first-order, pseudo-second-order, Morris's intraparticle diffusion and Boyd's film-diffusion models, respectively. It was found that the maximum adsorption of PNA on the ACFs was more than 510 mg/L, and over 60% adsorption occurred in first 25 min. The effect of temperature on the adsorption was related to the contacting time and the micropore structure of the adsorbents. And the increase of micropore surface area favored the adsorption process. Kinetic rates fitted the pseudo-second-order model very well. The pore diffusion played an important role in the entire adsorption period, and intraparticle diffusion was the rate-limiting step in the beginning 20 min. The Freundlich model provided a better data fitting as compared with the Langmuir model. The surface micrograph of the ACF after adsorption showed a distinct roughness with oval patterns. The results revealed that the adsorption was in part with multimolecular layers of coverage.

Construction of Mono- and Multimolecular Layers with Electron Transfer Mediation Function and Catalytic Activity for Hydrogen Evolution on a Hydrogen-Terminated Si(111) Surface via Si−C Bond

Organic molecular layers with viologen moiety (i.e., electron acceptor) were constructed on a hydrogen-terminated Si(111) surface via a Si−C bond. Electrochemical characteristics after each synthetic process were measured, and electron mediation capability of the viologen moiety was demonstrated. Incorporation of platinum particles on the viologen-modified Si(111) surface was proved to enhance the hydrogen evolution reaction (HER) rate. Further improvement of the HER rate was achieved by the modification with viologen/Pt multilayers. Photoelectrochemical HER at the p-Si(111) electrode was also significantly accelerated by the modification with mono- and multiviologen/Pt layers.

Ultrathin insulating silica layers prepared from adsorbed TEOS, H2O and NH3 as a catalyst

Homogeneous ultrathin silica films were deposited without need of any expensive equipment and high-temperature processes (t⩽200°C). Repeated adsorption of tetraethoxysilane (TEOS) multimolecular layers and their subsequent reaction with H2O/NH3 mixed vapours at atmospheric pressure and room temperature were used. By preparing the Al/SiO2/N-Si MOS structure conditions were attained for electrical characterisation of the thin oxide layer by capacitance (C–V) and current (I–V) measurements. These measurements confirmed acceptable insulating properties of the oxide, the maximum breakdown field intensity being Ebd=5.4MV/cm. The total defect charge of the MOS structure was positive, affected by a high trap density at the Si–SiO2 interface.

Polymeric films based on long-chain acetylenes as sensors for iodine vapour

Abstract Conducting polymeric thin films can be used as sensors to detect and identify volatile organics. Practically valuable possibilities of obtaining thin conducting layers with a definite topology in the substrate plane are ensured by Langmuir–Blodgett procedure. Orientation of monomer molecules is provided by the procedure of transferring the molecules from the subphase onto the substrate. It is shown that the UV-mediated polymerization of multimolecular layers of the acetylenic alcohol tetracosin-2-ol-1 (C21H43C CCH2OH) results in the trans-configuration with respect to the double bonds formed in polymerization. The conductivity of thus obtained layers is shown to depend on the partial pressure of molecular iodine in the gas phase. A mechanism is proposed that explains a non-linear increase in conductivity accompanying adsorption of iodine vapour.

Adsorption of p-nitrophenol from aqueous solutions onto activated carbon fiber

The adsorption of p-nitrophenol (PNP) onto activated carbon fiber (ACF) was investigated in simulated wastewater in a batch system to evaluate the effects of solution pH, presence of sodium chloride, adsorbent doses and temperature. It was found that PNP adsorption amount depended on pH, sodium chloride content, adsorbent doses and temperature. Langmuir and Freundlich models were applied to describe the adsorption isotherms. Freundlich model agreed with experimental data well, indicating the possibility of more than just one monomolecular layer of coverage. SEM photographs of ACF before and after adsorption revealed that it was in part with multimolecular layers of coverage on ACF surfaces. The change of free energy, enthalpy, and entropy of adsorption were also evaluated for the adsorption process. The pseudo-first-order and pseudo-second-order kinetic models were used to describe the kinetic data. The experimental data fitted very well the pseudo-second-order kinetic model. Attempts were made to desorb PNP from ACF using dilute NaOH solution and water, and desorption efficiency was obtained to the extent of 92.7% with 0.025 M NaOH and water at 368 K.

Photoluminescence from a system of multimolecular layers of the rare earth metal behenates

The conditions for the preparation of the Langmuir–Blodgett (LB) films of individual and mixed europium and terbium behenates are investigated. Spectral characteristics of the luminescence from the obtained films are determined by means of UV and IR spectroscopy. The luminescence of the films of behenic acid, as well as europium and terbium behenates, is studied at the excitation wavelength of λ excit=366 nm. It is stated that the band with λ max≅465 nm corresponds to the T 1→S 0 transition, while more narrow bands (λ≅489, 592, 617 nm) can be attributed unambiguously to the transitions in Eu(III) and Tb(III) ions. The enhancement of the luminescence of Eu(III) by Tb(III) in LB films of the Y type was observed. A mechanism involving excitation and energy transfer in the investigated system is proposed.

The effect of liquid additives on dry ultrafine grinding of quartz

The dry ultrafine grinding of quartz with liquid additives was carried out using a vibration rod mill with a laboratory scale. Liquid additives used were mainly seven alcohols and three glycols with different alkyl groups. All of the experiments were carried out by batch operation, and the variations of specific surface areas of products with grinding time were measured by BET adsorption method. The results showed that alcohol and glycol additives were satisfactorily effective for the ultrafine grinding of quartz. The maximum specific surface area of quartz obtained with an additive was found to increase in proportion to the amount of the additive. The additive molecules of multimolecular layers were supposed to adsorb on the quartz surface when the specific surface area reached the maximum value. The principal effect of additives in ultrafine grinding is considered to be the increase in flowability and the control of reagglomeration of quartz powder due to the alkoxylation of hydroxyl groups on the quartz surface.

Novel alternate layer LB film polymer electrolyte systems

Over the last few years polymer electrolytes have generated much interest as potential components in devices such as batteries and smart windows. Some new systems synthesized recently have proven to be excellent candidates for the preparation of thin films, especially Langmuir-Blodgett films. This technique enables the production of single or multimolecular layers of precisely known thickness. The work in this paper concentrates on the investigation of polyether-alkyl bilayer structures and other components utilising the alternate Langmuir-Blodgett technique. We have demonstrated the viability of producing bilayer structures 19 molecular layers (approximately 45 nm) thick. We have also shown that ions can be taken up from the subphase, with conductivity normal to the layer planes being extremely low in contrast to the higher values obtained using bulk samples. Alkyl chains bearing functional groups are readily blended into the alkyl layers leading to the possibility of creating mixed-function materials. The conductivities of these materials and their blends are discussed.