Adsorption Of Acetate Research Articles

A facile pretreatment method for efficient immobilization of penicillin G acylase

A facile pretreatment method was developed to obtain high specific activity of PGA from recombinant E. coli cells for preparing immobilized enzyme with high activity, which coupled selective extraction of PGA with butyl acetate and adsorption of butyl acetate with active carbon. Butyl acetate (5%, v/v) led to a 92.0% release of PGA, the specific activity of which in the extracting solution was twice that obtained by sonication. The negative effect on PGA immobilization due to residual butyl acetate in the extracting solution was removed by adding active carbon (8%, w/v). The final PGA solution meets requirement for industrial immobilization while eliminating the high cost of a traditional purification process. This pretreatment method developed in this work is simple, highly performing and cost-effective. It has been employed in a 10 tons/year immobilized PGA production line.

Acetate and phosphate anion adsorption linear sweep voltammograms simulated using density functional theory

Specific adsorption of anions to electrode surfaces may alter the rates of electrocatalytic reactions. Density functional theory (DFT) methods are used to predict the adsorption free energy of acetate and phosphate anions as a function of Pt(1 1 1) electrode potential. Four models of the electrode potential are used including a simple vacuum slab model, an applied electric field model with and without the inclusion of a solvating water bi-layer, and the double reference model. The linear sweep voltammogram (LSV) due to anion adsorption is simulated using the DFT results. The inclusion of solvation at the electrochemical interface is necessary for accurately predicting the adsorption peak position. The Langmuir model is sufficient for predicting the adsorption peak shape, indicating coverage effects are minor in altering the LSV for acetate and phosphate adsorption. Anion adsorption peak positions are determined for solution phase anion concentrations present in microbial fuel cells and microbial electrolysis cells and discussion is provided as to the impact of anion adsorption on oxygen reduction and hydrogen evolution reaction rates in these devices.

Effect of Pd surface structure on the activation of methyl acetate

The activation of methyl acetate (CH 3COOCH 3) has been studied using periodic density functional theory calculations to probe the effect of Pd surface structure on this reaction. The adsorption of methyl acetate, dehydrogenated derivatives including enolate (CH 2COOCH 3) and methylene acetate (CH 3COOCH 2), and dissociation products including acetate, acetyl, ketene, methoxy, formaldehyde, CO, C, O, and H; and the C–H and RCO–OR′ C–O bond dissociation in methyl acetate, enolate, and methylene acetate, are calculated on Pd(1 1 1) terrace, step edge, and kink; and on Pd(1 0 0) terrace and step edge. The adsorption of most species is not strongly affected from (1 1 1)- to (1 0 0)-type surfaces, but is clearly enhanced by step/kink compared to the corresponding terrace. For a given reactant, going both from terrace to step edge and from (1 1 1)- to (1 0 0)-type surfaces stabilizes the transition states of C–O bond dissociation steps. Going from terrace to step edge also stabilizes the transition states of C–H bond dissociation steps, but going from (1 1 1)- to (1 0 0)-type surfaces does not clearly do so. Our results suggest that compared to the Pd(1 1 1) terrace, the Pd(1 0 0) terrace is more selective for the C–O bond dissociation that is desirable for alcohol formation, whereas step edges are more selective for C–H bond dissociation.

Sum-frequency generation of acetate adsorption on Au and Pt surfaces: Molecular structure effects

The reversible adsorption of acetate on polycrystalline Au and Pt surfaces was investigated with broadband sum-frequency generation (SFG) and cyclic voltammetry. Specifically adsorbed acetate as well as coadsorbed sulfuric acid anions are observed for the first time with SFG and give rise to dramatically different SFG intensities on Au and Pt surfaces. While similar coverages of acetate adlayers on Au and Pt surfaces are well established by previous studies, an identification of the interfacial molecular structure has been elusive. However, we have applied the high sensitivity of SFG for interfacial polar ordering to identify different acetate structures at Au and Pt surfaces in contact with HClO(4) and H(2)SO(4) electrolytes. Acetate competes with the formation of surface oxides and shifts the oxidation threshold of both Au and Pt electrodes anodically. Effects of the supporting electrolyte on the formation of acetate adlayers are revealed by comparing SFG spectra in HClO(4) and H(2)SO(4) solutions: Sulfuric acid anions modify the potential-dependent acetate adsorption, compete with adsorbed acetate on Au and coadsorb with acetate on Pt surfaces.

Ethyl Acetate Adsorption onto Activated Carbon

The adsorption and desorption of ethyl acetate on a coconut-based activated carbon has been studied using static and flow adsorption methods at different temperatures from 295 K to 325 K. The adsorbed state of ethyl acetate was studied using nitrogen adsorption at 77 K after the pre-adsorption of ethyl acetate. The adsorption isotherms of ethyl acetate were of Type I in the IUPAC classification, suggesting micropore filling by ethyl acetate molecules. The micropore volume of the activated carbon as evaluated from ethyl acetate adsorption using the liquid density of ethyl acetate agreed well with that from nitrogen adsorption. Nitrogen adsorption after pre-adsorption of ethyl acetate indicated considerably packed molecular states of ethyl acetate molecules within the micropores. Thus, ethyl acetate molecules can migrate to the deeper parts of micropores in the case of static adsorption measurements. However, the specific surface area evaluated from ethyl acetate adsorption was nearly 40% smaller than that ...

Polymeric Fe/Zr pillared montmorillonite for the removal of Cr(VI) from aqueous solutions

Four kinds of pillared montmorillonites were prepared by intercalating poly-hydroxyl iron, poly-hydroxyl iron/zirconium with different Fe/Zr molar ratios (4/1, 1/1) and poly-hydroxyl zirconium into the interlayer space of sodium-saturated montmorillonite (Na-Mt) via ion-exchange, termed Fe-Mt, Fe/Zr 4:1-Mt, Fe/Zr 1:1-Mt and Zr-Mt, respectively. The obtained materials were characterized by X-ray fluorescence (XRF) spectra, X-ray diffraction (XRD) spectra, Fourier transform infrared (FTIR) spectra, point of zero charge measurement and BET analysis. Batch experiments were conducted to investigate the adsorption behavior of Cr(VI) on selected samples. The results showed that the equilibrium uptake of Cr(VI) was highly pH-dependent with an optimal pH range of 3.0–6.0. The kinetics of Cr(VI) adsorption could be described well by the Pseudo-second-order model. The Langmuir adsorption isotherm provided the best correlation of the equilibrium data, and the estimated maximum equilibrium uptake of Cr(VI) of Fe/Zr 4:1-Mt was 22.35 mg/g at pH 3.0, 25 °C, higher than those of other three samples. Also, the thermodynamic parameters demonstrated that the process of Cr(VI) adsorption onto pillared montmorillonites was spontaneous and exothermic in nature. The presence of phosphate, sulphate and tartrate inhibited markedly the adsorption of Cr(VI), whereas nitrate, chlorate and acetate exhibited no significant effect on Cr(VI) adsorption. The analyses combining characterization results with adsorption data revealed that the removal mechanisms of Cr(VI) by these pillared montmorillonites mainly involved electrostatic interaction and ion-exchange. Overall, the regeneration of Fe/Zr-Mt could be achieved using NaOH solution, enabling a promising application for removing Cr(VI) from aqueous solution.

Activation of methyl acetate on Pd(111)

The adsorption and activation of methyl acetate (CH 3COOCH 3), one of the simplest carboxylic esters, on Pd(111) have been studied using self-consistent periodic density functional theory calculations. Methyl acetate adsorbs weakly through the carbonyl oxygen. Its activation occurs via dehydrogenation, instead of direct C–O bond dissociation, on clean Pd(111): It is much more difficult to dissociate the C–O bonds ( E a ≈ 2.0 eV for the carbonyl and acetate–methyl bonds; E a = 1.0 eV for the acetyl–methoxy bond) than to dissociate the C–H bonds to produce enolate (CH 2COOCH 3; E a = 0.74 eV) or methylene acetate (CH 3COOCH 2; E a = 0.82 eV). The barriers for C–H and C–O bond dissociation are directly calculated for enolate and methylene acetate, and estimated for further dehydrogenated derivatives (CH 3COOCH, CH 2COOCH 2, and CHCOOCH 3) based on the Brønsted–Evans–Polanyi linear energy relations formed by the calculated steps. The enolate pathway leads to successive dehydrogenation to CCOOCH 3, whereas methylene acetate readily dissociates to yield acetyl. The selectivity for dissociating the acyl–alkoxy C–O bond, which is desired for alcohol formation, is therefore fundamentally limited by the facility of dehydrogenation under vacuum/low-pressure conditions on Pd(111).

Adsorption and desorption of antimony acetate on sodium montmorillonite

The adsorption of antimony acetate (Sb(OAc) 3) on sodium montmorillonite (Na-MMT) was studied at five different initial concentrations, and data from the adsorption isotherm were modeled using the Langmuir, Freundlich and D–R isotherm equations. The kinetics of adsorption was also discussed using three kinetic models: the pseudo-first-order, the pseudo-second-order and the intraparticle diffusion model. The rate constants of pseudo-first-order, pseudo-second-order and intraparticle diffusion kinetics, and the amount of Sb(OAc) 3 adsorbed at equilibrium were determined. Moreover, the desorption of Sb(OAc) 3 from several kinds of Sb-MMT (Na-MMT was intercalated by antimony acetate) was investigated at room temperature and 180 °C. The results show that according to the maximum amounts of adsorbate and correlation coefficients calculated from the three isotherm equations mentioned above, the corresponding data from adsorption experiments fit fairly well to the Langmuir isotherm. The adsorption data show a good compliance with the pseudo-second-order kinetic model and also follow the intraparticle diffusion model up to 30 min. The equilibrium adsorption capacity of Sb(OAc) 3 on MMT is close to the cation exchange capacity (CEC) of the montmorillonite. The desorption amount of Sb(OAc) 3 is correlated with both the temperature of desorption and the drying temperature of Sb-MMT.

Stability of a cryptomelane catalyst in the oxidation of toluene

The oxidation of toluene over a cryptomelane (K-OMS-2) catalyst was investigated at temperatures between 100 and 300 °C. The catalyst was tested both in temperature-programmed experiments (light-off curves) and in isothermal tests. The carbonaceous deposits retained in the porous structure after the isothermal tests were evaluated by temperature-programmed oxidation. The results show that gradual deactivation occurs at temperatures below 268 °C (which corresponds to the peak maximum in the TPO curves). Furthermore, in a restricted temperature range (252–258 °C), the catalyst shows an unstable behaviour, and oscillations in the conversion into CO 2 occur. TPD experiments after adsorption of toluene at room temperature show that this compound is strongly retained in the porous structure up to high temperatures, which can explain the deactivation and the unstable behaviour. For comparative purposes, TPD after adsorption of ethyl acetate was also carried out, and it was observed that this compound was not retained as much as toluene, no oscillations being detected.

Correction to “DFT and DRIFTS Studies on the Adsorption of Acetate on the Ag/Al2O3 Catalyst”

Correction to “DFT and DRIFTS Studies on the Adsorption of Acetate on the Ag/Al₂O₃ Catalyst”

Adsorption of Copper Acetate onto Pretreated Activated Carbons over a Wide Concentration Range

The commercially available microporous activated carbon Kuraray GC was pretreated in two different ways: one was heated to 950 °C in 5% hydrogen and the other boiled in nitric acid for 5 h. BET surface area measurements and Boehm titrations were done to find the surface area and the numbers of surface functional groups for each carbon. A large range of linearly varying concentrations of aqueous copper acetate solutions was made and stirred with each sample of pretreated carbon. Atomic absorption spectroscopy, titrations, and weight measurements were employed to measure the amount of copper acetate actually adsorbed onto the respective carbon samples. The number of acidic functional groups on the carbon surface as determined by Boehm titrations in the case of the hydrogen treated sample and the nitric acid treated sample do not match with the usual Langmuir parameters both at low and high concentrations. Two distinct isotherm fittings have been obtained for both carbons; double Langmuir isotherms for the hydrogen-treated sample, and a low concentration Langmuir isotherm combined with a high concentration Freundlich isotherm for the nitric acid treated sample. The results have also been compared with the results for untreated Kuraray GC.

Effect of flexibility and polarity of polymer chains on the kinetics of their adsorption from solutions of polymer blends at various adsorbent-to-solution ratios

The kinetics of adsorption of cellulose acetate and poly(butyl methacrylate) with different thermodynamic flexibility parameters at various amounts of adsorbent in binary solutions of polymers and their blends has been studied by IR spectroscopy. For various stages of adsorption, the values of adsorption; the fraction of bound segments; the energy of adsorption interaction; and the diffusion coefficients of macromolecules, which characterize the rate of adsorption, are estimated in relation to the concentrations of solutions and adsorbent-to-solution ratios. The rate of attaining adsorption equilibrium is shown to depend on the polarity and flexibility of macromolecular chains. As the amount of adsorbent is increased, macromolecules of the flexible-chain polymer (poly(butyl methacrylate)) undergo more substantial conformational transformations than macromolecules of stiff-chain polymer (cellulose triacetate) during the formation of equilibrium conformations.

Controlling Shape and Size of TiO2 Nanoparticles with Sodium Acetate

Uniform anatase-type ellipsoidal TiO2 nanoparticles have been prepared by phase transformation of a Ti(OH)4 gel matrix in the presence of sodium acetate as a shape controller. Sodium acetate was found to modify the TiO2 particle shape from cube to ellipsoid in the alkaline solution with the concentration varying from 0 to 0.50 M. A significant reduction of the formation rate of the anatase TiO2 was found due to the adsorption of sodium acetate on their surfaces. Then, the formation of TiO2 nanoparticles could be promoted by the added seeds and the seeding effect also revealed that the particle size could be controlled. Moreover, the results of seeding experiment suggested that the rate-determining step of the gel-sol process was not the dissolution of the hydroxide gel, but the deposition of the monomeric solute onto the preformed particles. Additionally, based on the adsorption experimental results of sodium acetate on the ellipsoidal and cubic particles, the shape transition may be explained in terms of the preferential adsorption of acetate ions onto the specific planes parallel to the c-axis of the tetragonal system and then inhibiting the growth of these planes. Keywords: Titania, shape control, sodium acetate, adsorption, seeding

The reaction of vinyl acetate with Pd(1 1 0) studied with TPD and molecular beams

The adsorption and reaction of vinyl acetate with the clean Pd(110) surface has been investigated using temperature programmed desorption and molecular beam reaction measurements. These show that, under low pressure conditions, the main reaction pathway above 400K is total dehydrogenation to yield hydrogen and carbon dioxide in the gas phase, and surface carbon. This occurs at a steady state, notwithstanding the fact that carbon is being deposited continuously onto the surface. The reaction continues because the vast majority of this carbon is lost from the surface to the bulk of the sample. Between about 320–380K the reaction profile is somewhat different; the molecule dissociates at the CH3COOCHCH2 bond, producing the most stable intermediate, the acetate, and the reaction stops after the build-up of adsorbed acetate and surface carbonaceous species. At ∼300K, the products are very similar to those for acetaldehyde adsorption (namely, methane, CO and some surface carbon), and they evolve in a non-steady state manner due to the build up of adsorbed CO on the surface. Thus the mechanism is dominated here by dissociation at the CH3COOCHCH2 bond, and formation of the acetyl intermediate. Consideration is given to the connection between these data and vinyl acetate synthesis.

The adsorption and reaction of vinyl acetate on Au/Pd(1 1 1) alloy surfaces

The adsorption of vinyl acetate is studied on Au/Pd(1 1 1) alloys as a function of alloy composition using temperature-programmed desorption and reflection–adsorption infrared spectroscopy. Vinyl acetate adsorbs weakly on gold sites on the alloy with a heat of adsorption of ∼55 kJ/mol, which is independent of the size of the gold ensembles. In contrast, adsorption of vinyl acetate on palladium sites is strongly affected by alloying. Vinyl acetate desorbs from isolated palladium sites on the alloy with an activation energy of ∼70 kJ/mol, close to that found on pure Pd(1 1 1). As the palladium coverage, and the number of palladium dimers and larger ensembles in the alloy increases, the heat of adsorption of vinyl acetate increases attaining a maximum of ∼80 kJ/mol at a gold coverage in the alloy of ∼0.5. However, in spite of the larger heat of adsorption on the alloy than on pure Pd(1 1 1), vinyl acetate does not undergo significant thermal decomposition on this alloy surface. This is ascribed to the formation of more distorted vinyl acetate in which the acetate group is more remote from the surface due to the rehybridization of the vinyl group. As the gold coverage decreases to ∼0.35 and lower, thermal decomposition products are found similar to those on Pd(1 1 1).

Optimization of air-borne butyl acetate adsorption on dual-function Ag–Y adsorbent-catalyst using response surface methodology

The low concentration and high flow rate of air-borne butyl acetate (BA) could be effectively removed using combined adsorption-catalytic oxidation system. Ag–Y (Si/Al = 80) dual-function adsorbent was investigated for the adsorption step of 1000 ppm of butyl acetate at gas hourly space velocity of 13,000 h −1 at ambient temperature under dry and humid feeds. A central composite design (CCD) coupled with response surface methodology (RSM) was employed to obtain the optimum process conditions and the interactions between process variables were demonstrated and elucidated. Humidity and increasing organic concentration shortened the adsorption service time. The effect of moisture was more pronounced at low BA concentration. The interactions between the BA concentration and humidity were statistically significant at 95% confidence level. The optimum conditions were found to be at 4500 ppm of BA with 37 min saturation time to give 58 mg BA/g as adsorption capacity. The simulated data fitted the experimental data satisfactorily. The simulated data also correctly demonstrated the overall behaviors of the adsorption process.

Adsorption of butyl acetate in air over silver-loaded Y and ZSM-5 zeolites: Experimental and modelling studies

Adsorption behaviours of butyl acetate in air have been studied over silver-loaded Y (Si/Al = 40) and ZSM-5 (Si/Al = 140) zeolites. The silver metal was loaded into the zeolites by ion exchange (IE) and impregnation (IM) methods. The adsorption study was mainly conducted at a gas hourly space velocity (GHSV) of 13,000 h −1 with the organic concentration of 1000 ppm while the desorption step was carried out at a GHSV of 5000 h −1. The impregnated silver-loaded adsorbents showed lower uptake capacity and shorter breakthrough time by about 10 min, attributed to changes in the pore characteristics and available surface for adsorption. Silver exchanged Y (AgY(IE)) with lower hydrophobicity showed higher uptake capacity of up to 35%, longer adsorbent service time and easier desorption compared to AgZSM-5(IE). The presence of water vapour in the feed suppressed the butyl acetate adsorption of AgY(IE) by 42% due to the competitive adsorption of water on the surface and the effect was more pronounced at lower GHSV. Conversely, the adsorption capacity of AgZSM-5(IE) was minimally affected, attributed to the higher hydrophobicity of the material. A mathematical model is proposed to simulate the adsorption behaviour of butyl acetate over AgY(IE) and AgZSM-5(IE). The model parameters were successfully evaluated and used to accurately predict the breakthrough curves under various process conditions with root square mean errors of between 0.05 and 0.07.

Spectroelectrochemical study of the adsorption of acetate anions at gold single crystal and thin-film electrodes

Acetate adsorption at gold electrodes is studied in perchloric acid solutions by cyclic voltammetry and in-situ infrared spectroscopy. External reflection measurements, performed with gold single crystal electrodes, are combined with Surface Enhanced Infrared Reflection Absorption Spectroscopy experiments under attenuated total reflection conditions (ATR-SEIRAS) carried out with sputtered gold thin-film electrodes. Theoretical harmonic IR frequencies of acetate species adsorbed with different geometries on Au clusters with (1 1 1), (1 0 0) and (1 1 0) orientations have been obtained from B3LYP/LANL2DZ, 6–31 + G* calculations. The theoretical and experimental results confirm that, irrespective of the surface crystallographic orientation, bonding of acetate to the surface involves the two oxygen atoms of the carboxylate group, with the OCO plane perpendicular to the metal surface. DFT calculations reveal also that the total charge of the metal cluster–acetate supermolecule has small effect on the vibrational frequencies of adsorbed acetate species. Both the external and the internal reflection measurements show the co-adsorption of acetate and perchlorate anions. Step-scan measurements carried out with the gold thin-film electrodes have allowed the monitoring of the time-dependent behaviour of perchlorate, acetate and water bands in potential step experiments. Acetate adsorption under those conditions is shown to involve perchlorate desorption and to follow a Langmuir-type kinetics. The step-scan spectra also show the rise and decay of transient water structures with parallel time-dependent shifts of the background intensity in the infrared spectra.

Surface Speciation at Solid/Liquid Interfaces: A Vibrational Sum-Frequency Study of Acetate Adsorption at the Fluorite/Water Interface

Vibrational sum-frequency spectroscopy (VSFS) has been used to investigate the adsorption of acetate at the fluorite/water interface in situ. The bulk pH value was varied to control the composition of the liquid phase in contact with a single crystalline fluorite (CaF2) surface. Spectra were recorded in frequency regions corresponding to vibrational modes of the adsorbate and water. Quantitative information on interfacial water molecules in different states of order was obtained from the present data. Furthermore, the effect of background electrolyte concentration was studied, and it was found that surface hydroxyls play a crucial role for the oriented adsorption of acetate ions at the interface.

Heterogeneity of adsorption mechanisms in chiral normal-phase liquid chromatography: 2-Propanol and ethyl acetate adsorption equilibria

The adsorption equilibria of two commonly employed strong mobile phase modifiers, ethyl acetate and 2-propanol, on a polysaccharide-based chiral stationary phase have been studied by modeling nonlinear perturbation peaks measured after equilibration of the column with hexane (the weak component of the binary mixture). The investigation of adsorption processes from dilute solutions for species that are strongly retained on the stationary phase could be performed by this approach. On the opposite, limits of traditional linear perturbation technique for isotherm determination, in presence of strong interactions, have been evidenced. Alcohol adsorption has been modeled by a single Langmuir isotherm, while the ester has required a BiLangmuir model. These findings have found to be in a semi-quantitative agreement with available spectroscopic data about 2-propanol and ethyl acetate adsorption on thin silica sol–gel films in contact with a weak solvent. Experimental features observed for racemic separation on polysaccharide-based chiral stationary phases, such as the dependence of the separation factor on the amount and type of the employed additive, have been explained in light of these measurements.