Desorption Angle Research Articles

Rapid and selective recycling of Ag(I) from wastewater through an allylrhodanine functionalized micro-filtration membrane

Balance between membrane flux and ion rejection rate of filtration membranes is an important crucial technology to achieve an efficient wastewater treatment. In this work, a polyvinylidene fluoride (PVDF) with 3-allylrhodanine (3-AR) modified composite 3-AR/PVDF membrane was fabricated by non-solvent induced phase separation method. Some parameters, such as water flux, selectivity and rejection, were investigated during the membrane treatment. Morphology characterizations, such as scanning electron microscope (SEM), nitrogen adsorption–desorption and contact angle techniques confirmed 3-AR/PVDF had hydrophilic surface and uniform porous structure with average pore size about 65.67 ∼ 39.32 nm. Surface chemical structure characterizations, such as Fourier transformed infrared (FT-IR) and X-ray photoelectron spectroscopy (XPS) uncovered that the retention of Ag+ was mainly relied on the chemical bonding of C = S and C-S groups on 3-AR. 3-AR/PVDF-0.130 membrane exhibited excellent performance in adsorption (46.42 mg cm−2), water flux (196.04 L m-3 h−1), rejection (8.75 mg), and selectivity (β > 10). Membrane thickness exhibited good linear relationships with water flux and interception (R2 > 0.94), which could be regulated by the thickness of membrane. The membranes maintained excellent stability in wide pH range 1 ∼ 5, and retained >95% rejection and water flux after 6 cycles. Most important, the costs of membrane and operation were assessed during the long-term filtration, which is of significance for practical applications.

Fabrication of a novel surface molecularly imprinted polymer based on zeolitic imidazolate framework-7 for selective extraction of phthalates

In this study, a novel surface molecularly imprinted polymer (MIP) based on zeolitic imidazolate framework (MIP@ZIF-7) was prepared using dibutyl phthalate (DBP) as template via “one-pot” method, which was used for extraction and determination four phthalates (PAEs) in food samples coupled with high performance liquid chromatography (HPLC). The obtained MIP@ZIF-7 was characterized by fourier transform infrared spectrometer (FT-IR), energy dispersive spectrum (EDS), scanning electron microscopy (SEM), nitrogen adsorption–desorption and contact angle tester. The adsorption performance of the prepared ZIF-7, MIP and MIP@ZIF-7 was compared and the results showed that MIP@ZIF-7 exhibited higher adsorption capacity and selectivity for PAEs owing to combining the high specific surface area and excellent stability of ZIF and the specific recognition of MIP. Subsequently, several requisite synthesis and extraction parameters were investigated. Under the optimal conditions, the linear range of the method was 1–100 μg L−1 and the detection limits were in a range of 0.1–0.8 μg L−1. The spiked recovery rate of PAEs from drinking water, carbonated beverages and fruit juices ranged from 77.1 ± 1.5% to 100.7 ± 3.4%, with relative standard deviation of 1.65–4.87% (n = 3). The results indicated that MIP@ZIF-7 could be effectively employed for extraction and determination trace PAEs in food.

Vanadyl acetylacetonate grafted on ordered mesoporous silica KIT-6 and its enhanced catalytic performance for direct hydroxylation of benzene to phenol

Abstract The direct hydroxylation of benzene to phenol under H2O2 is one of the most important research topics in catalytic synthesis and green chemistry. As a conventional and widely available catalyst, vanadyl (IV) acetylacetonate [VO(acac)2] shows remarkable catalytic efficiency for the process, however is a typical homogeneous catalyst. In this work, ordered mesoporous silica (KIT-6) was applied to a new catalytic support to immobilize VO(acac)2. Several chacterization techniques including N2 adsorption–desorption, small and wide angle XRD, TEM, FT-IR, and XPS, have been used to analyze the physiochemical properties of the synthesized materials. VO(acac)2 was solidly immobilized on the amine-functionalized KIT-6 via the formation of Schiff base, while the original ordered mesoporous structure of KIT-6 has been remained after the incorporation of VO(acac)2. In the direct hydroxylation of benzene under H2O2, the KIT-6-NH2-V materials showed catalytic activities. The maximum catalytic yield of phenol obtained at 60 °C was ca. 17%. Furthermore, under the same reaction conditions, the immobilized VO(acac)2 catalyst exhibited superior catalytic activity to the catalysts supported on other two typical ordered mesoporous silicas (SBA-15 and FDU-12).

Hydrothermal stability of different zeolites in supercritical water: Implication for synthesis of supported catalysts by supercritical water impregnation

Supercritical water (SCW) impregnation is an efficient and feasible method that has been used to prepare highly dispersed supported catalysts, but few studies have investigated the stability of support materials in supercritical water. Thus, our aim was to investigate the hydrothermal stability of zeolite supports (ZSM-5, TS-1, ZSM-35, HY, 13X, Beta, SAPO-11 and SAPO-34) as model compounds in supercritical water. Results showed that almost all of zeolites suffered from crystallinity change, structural properties degradation, obvious desilication and dealumination. The decrease of surface areas and the collapse of crystalline structures in HY, 13X, Beta, SAPO-11 and SAPO-34 were more serious compared to ZSM-5, ZSM-35 and TS-1. The micropore areas and acidity of all SCW-treated zeolites were reduced. 13X with lower Si/Al ratio had higher hydrothermal stability than HY due to the formation of extra-framework Al (EFAL). EFAl also generated strong Lewis acid sites determined by ammonia temperature-programmed desorption and 27Al magic angle spinning nuclear magnetic resonance. Desilication and dealumination were simultaneous, and led to the increase of framework Si/Al ratio. ZSM zeolites (ZSM-5, ZSM-35 and TS-1) had higher hydrothermal stability than HY, 13X, Beta, SAPO-11 and SAPO-34 in SCW.

Comparison study between a series of new type functional diatomite on methane adsorption performance

Organosilanes with different head groups and chemical properties, including phenyltriethoxysilane (PTES), aminopropyltriethoxysilane (APTES), and trimethylchlorosilane (TMCS), were used to modify the adsorption properties of diatomite (DE). Characterizations of the as-synthesized samples were investigated by scanning electron microscopy (SEM), infrared spectroscopy (IR), thermogravimetric analysis (TGA), nitrogen adsorption–desorption and solid-state 29Si magic angle spinning nuclear magnetic resonance (MAS NMR). SEM imagines show that the morphology of DE was remained during the modification. IR spectra provide clear evidence that they were indeed modified as intended. The results of TGA show that the weigh losses of all samples were increased after silylation. And the MAS NMR indicated that large amounts of isolated silanols condense with the organolsilanes, which further proved the organic groups have been loaded onto the diatomite. The adsorption experiments of methane by raw and three modified diatomite were also studied. Results showed that the adsorption amount increases constantly with the increasing of pressure and the equilibrium have not been reached at the room temperature. The adsorption data indicate that the sorption of CH4 on modified products and diatomite are dominated by multilayer coverage and they all fit the Freundlich isotherm equation well. The PTES-DE and APTES-DE have excellent CH4 adsorption capacity and they can reach the adsorption target proposed by DOE far below 35 bar, at 3 bar and 7.5 bar respectively. These two materials exhibit excellent adsorption performance for CH4 and have the potential to provide improved methods for reducing greenhouse gas emissions.

Synthesis of three-dimensional carbon felt supported TiO2 monoliths for photocatalytic degradation of methyl orange

Three-dimensional carbon felt supported TiO2 (TiO2@CF) monoliths were synthesized via a solvothermal process. The structural properties of TiO2@CF were characterized by field emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, N2 adsorption–desorption, Raman and contact angle tests. The as-prepared TiO2@CF monoliths exhibited a large surface area, hydrophilic surface as well as a well-defined three dimensional structure. Using methyl orange as a model pollutant, the photocatalytic activity of TiO2@CF monolith was studied. The effects of substrate concentrations, pHs of pollutant solutions and H2O2 concentrations in the degradation of methyl orange were examined. It was revealed that a low pollutant concentration, adequate H2O2 concentration and acidic environment facilitated the degradation of methyl orange. To explore the mechanism, controlled experiments were conducted by adding three scavengers including isopropanol, p-benzoquinone and ethylenediaminetetraacetic acid disodium salt. Mechanistic studies suggested that in the presence of H2O2, hydroxyl radicals played a dominant role in the degradation of methyl orange while the photo-induced holes were mainly responsible in the absence of H2O2. The TiO2@CF monolith catalysts could be easily regenerated via combustion and showed excellent recyclability.

Highly hydrophilic poly(vinylidene fluoride)/meso-titania hybrid mesoporous membrane for photocatalytic membrane reactor in water.

The high hydrophobicity of poly(vinylidene fluoride) (PVDF) membrane remains an obstacle to be applied in some purification processes of water or wastewater. Herein, a highly hydrophilic hybrid mesoporous titania membrane composed of mesoporous anatase titania (meso-TiO2) materials inside the three-dimensional (3D) macropores of PVDF membrane was successfully prepared by using the dual-templated synthesis method combined with solvent extraction and applied as the photocatalytic membrane reactor for the photodegredation of organic dye in water. The structure and the properties of as-prepared hybrid membranes were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), X-ray diffraction (XRD), nitrogen adsorption–desorption and contact angle measurements. It was found that the hydrophilicity of PVDF membrane can be significantly improved by filling mesoporous TiO2 inside the 3D macropores of PVDF membrane. Moreover, such a PVDF/meso-TiO2 hybrid membrane exhibits promising photocatalytic degradation of dye in water due to the existence of mesoporous anatase TiO2 materials inside PVDF membrane. This study provides a new strategy to simultaneously introduce hydrophilicity and some desirable properties into PVDF and other hydrophobic membranes.

The correlation between aging time and pore characteristics in the synthesis of mesoporous Al2O3

Mesoporous alumina powders were synthesized by the evaporation induced self assembly (EVIS) method. Aluminum isopropoxidem, aluminum nitrate and Tri-block copolymer (pluronic P123) were used as inorganic precursors and structuring agent in this study. The prepared sols were aged under 94% relative humidity (RH) for different periods of time. The aged samples were calcined at 400°C for 8h. The effect of aging time on the pore characteristics was studied using Fourier transform infrared spectroscopy (FTIR), nitrogen adsorption–desorption, small and wide angle X-ray diffraction, and high resolution transmission electron microscopy. The results revealed that aging time had a significant impact on the pore size, pore volume, surface area and the degree of pore ordering in the final product. The maximum BET surface area of 307m2/g and the corresponding pore size of about 4nm was obtained for the sol aged for two weeks.

Engineering porous silicon nanostructures as tunable carriers for mitoxantrone dihydrochloride

Nanostructured porous silicon (PSi) thin films, fabricated by the electrochemical anodization of single crystalline Si wafers, are studied as delivery systems for the anticancer drug mitoxantrone dihydrochloride (MTX). The surface chemistry of the PSi carriers was tailored by surface alkylation using thermal hydrosilylation of 1-dodecene and undecylenic acid, followed by physical adsorption or covalent attachment of MTX to the Si scaffold. The nanostructure and the physiochemical properties of the different carriers were characterized by attenuated total reflectance Fourier transform infrared spectroscopy, nitrogen adsorption–desorption and contact angle measurements, demonstrating that surface alkylation results in a pronounced effect on the hydrophobicity/hydrophilicity of the scaffolds and a volumetric gain in pore wall, which in turn results in a decrease in pore diameter (>23%) and available porous volume (>40%). The effect of these key parameters on MTX loading efficacy, release profile, Si scaffold erosion kinetics and in vitro cytotoxicity on human breast carcinoma (MDA-MB-231) cells was studied and compared to the behavior of neat PSi carriers. We show that the chemically modified PSi carriers exhibit sustained release for several days to weeks with minimal to no burst effect, while for the native PSi MTX release was completed within 5h with a substantial burst release of ∼40%. Moreover, our in vitro cytotoxicity experiments have clearly demonstrated that the MTX released from all PSi carriers maintained its cytotoxic effect towards MDA-MB-231 cells, in comparison to the low toxicity of the PSi carriers.

Facile synthesis and catalytic applications of micro-mesoporous molecular sieve ZK-1

A micro-mesoporous molecular sieve ZK-1 was synthesized at 170 °C by a facile one-step hydrothermal method. The structure of ZK-1 can be controlled by the crystallization time. ZK-1(I), the KIT-1 containing ZSM-5 building units in the pore walls, is formed during 2–6 h. ZK-1(II), A mixture of ZSM-5 and KIT-1, is formed after 8 h. The framework structure, porosity, morphology and acidity of the obtained materials were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, Transmission electron microscopy, N2 adsorption, X-ray fluorescence, NH3-temperature programmed desorption and 27Al Magic angle spinning NMR spectroscopy. The samples exhibit good steam stability and better catalytic performances in the isomerization of o-ethyltoluene than KIT-1, suggesting their promising applications in the conversion of large molecules.

Proton conduction in AIII0.5BV0.5P2O7 compounds at intermediate temperatures

Proton conductors capable of operation between 100 and 400 °C are attractive electrochemical materials due to their high utility value in energy and environmental applications. However, such proton conductors have not yet made headway in the marketplace, due to insufficient proton conductivity. Here, we present new types of metal pyrophosphates as promising candidates for intermediate temperature proton conductors. A series of AIII0.5BV0.5P2O7 (AIIIBV = InSb, SbSb, FeSb, GaNb, FeNb, YNb, GaTa, AlTa, FeTa, YTa, BiTa, and SmTa) compounds were synthesized, of which In0.5Sb0.5P2O7, Fe0.5Nb0.5P2O7, and Fe0.5Ta0.5P2O7 exhibited the highest proton conductivities in the temperature ranges of 50–100 °C (0.045 S cm−1@100 °C), 100–200 °C (0.12 S cm−1@150 °C), and 200–400 °C (0.18 S cm−1@250 °C), respectively, in unhumidified air. The proton conductivity of these three compounds was further enhanced by the introduction of AIII or BV deficiency into the bulk. Consequently, Fe0.4Ta0.5P2O7 exhibited the highest proton conductivity of 0.27 S cm−1 at 300 °C in unhumidified air. Such high proton conductivity values were also observed under fuel cell operating conditions. The environments of protons in the bulk of these compounds were monitored using Fourier transform infrared (FT-IR) spectroscopy, temperature-programmed desorption (TPD), and proton magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy. Protons were incorporated into the compounds for charge-compensation of the deficient AIII or BV cations, which results in an increase in the quantity of protons. More importantly, the mobility of the protons was also enhanced. Various electrochemical measurements demonstrate that proton conduction is dominant in these compounds, where the protons migrate according to a hopping mechanism.

Dynamics of collisions of hydroxyl radicals with fluorinated self-assembled monolayers

We present a classical trajectory study of the dynamics of collisions between OH radicals and fluorinated self-assembled monolayers (F-SAMs). The gas/surface interaction potential required in the simulations has been derived from high-level ab initio calculations (focal-point-CCSD(T)/aug-cc-pVQZ) of various approaches of OH to a model fluorinated alkane. The two lowest-energy doublet potential energy surfaces considered in the electronic structure calculations have been averaged to produce a pairwise analytic potential. This analytic potential has been subsequently employed to propagate classical trajectories of collisions between OH and F-SAMs at initial conditions relevant to recent experiments on related systems. The calculated rotational distributions of the inelastically scattered OH agree well with the experiment, which serves to validate the accuracy of the simulations. Investigation of the dynamics of energy transfer for different initial rotational states of OH indicates that an increase in the initial rotation of OH results in increases in both the final average OH rotational and translational energy and in a slight decrease in the amount of energy transferred to the surface. Analysis of the dynamics as a function of the desorption angle of OH from the surface shows that while there is a correlation between the final scattering angle and OH’s amount of final translational energy, the amount of rotational energy in OH is largely independent of the desorption angle. The mechanism of the collisions is found to be mostly direct; in about 90% of most trajectories, OH only collides with the surface once before desorbing, which exemplifies the rigidity of fluorinated monolayer surfaces and their inability to efficiently accommodate gas species.

Mode-dependent coupling between vibration and translation of product CO2 in CO oxidation on Pd(111)

The vibrational temperatures of product CO(2) were measured in CO oxidation on Pd(111) as a function of the desorption angle by means of infrared chemiluminescence. The antisymmetric vibration temperature was separately determined from the other vibrational modes from the normalized chemiluminescence intensity. The product CO(2) desorption is sharply collimated along the surface normal. The antisymmetric vibrational temperature increased from 1300 to 1600 K as the desorption angle increased from 0 degrees to 30 degrees , whereas the averaged vibrational temperature over bending and symmetric modes decreased from 2450 to 1530 K. From these angle dependences, an energy partitioning model in repulsive desorption is proposed.

Angular Dependence of Rotational and Vibrational Energy of Desorbing CO2 in CO Oxidation on Pd Polycrystalline and Pd(111) Surfaces

Abstract Angular dependence of rotational and vibrational temperatures of product CO2 were studied in CO oxidation on a Pd polycrystalline surface by means of chemiluminescence measurements. Rotational temperature (Trot) and vibrational temperature (Tvib) showed minimum values at the surface normal and significantly increased as the desorption angle increased. Trot and Tvib became higher when the ratio of exposure of O2 to that of CO increased. These angular dependences are quite different from those on Pd(111).

Angular dependence of rotational and vibrational energies of product CO2 in CO oxidation on Pd(110)

The rotational and vibrational energies of product CO2 in the CO oxidation on Pd(110) surfaces were measured as functions of desorption angles. The antisymmetric vibrational temperature (Ta) was separately determined from the other vibrational modes from the normalized chemiluminescence intensity. The rotational temperature (Trot) and vibrational temperature averaged over the symmetric and bending modes (Tsb) were then determined by the position and width of spectra by comparison with simulated spectra. On Pd(110)-(1x1), with increases in the desorption angle, Ta, Tsb and Trot decreased in the [001] direction but remained constant in [11[combining macron]0]. However, such anisotropy disappeared when the ratio of exposure of O2 to that of CO decreased, resulting in a gradual decrease of the three temperatures with increases in the desorption angle. On Pd(110) with missing rows, the three temperatures increased in [001] but decreased in [11[combining macron]0], indicating that the transition state changes with the geometry of the substrate. On Pd(110) with missing rows, Ta was significantly lower than Tsb, although Ta was close to or higher than Tsb on Pd(110)-(1x1). However, there was no significant difference in the angular dependence between Ta, Tsb and Trot.

Angle-Resolved Measurements of Rotational and Vibrational Energies of Product CO2 in Catalytic CO Oxidation on Pd Surfaces

Measurements of rotational and vibrational energies of desorbing products in chemical reactions provide useful information on dynamical processes of bond formation and bond rupture and also on structures of transition states. In order to obtain structural information, dependence of these energies on the desorption angle of products should be studied. However, such angle-resolved (AR) measurements of internal energies in thermal surface reactions have long time been lacking due to difficulty of experiments. Recently, measurements of internal energies of AR product CO2 in CO oxidation on Pd surfaces have become possible by detecting extremely weak infrared chemiluminescence from desorbing CO2. Rotational and vibrational energies change depending on polar and azimuth angles and also surface structures, providing new insights into structures of transition states and energy partition dynamics. In this review, recent progress in the above AR measurements is described. [DOI: 10.1380/ejssnt.2008.180]

Internal-energy measurements of angle-resolved product CO2 in catalytic CO oxidation by means of infrared chemiluminescence

Measurements of both vibrational and rotational energies of product CO(2) in CO oxidation on palladium surfaces have been successfully performed as a function of the desorption angle by means of infrared chemiluminescence. The remarkable angle dependences of both energies indicate facile energy partitioning in repulsive desorption and provide new dimensions in the study of surface reaction dynamics as well as additional insights into the product formation site. Details of the apparatus for energy analysis of angle-resolved products are described, especially on how to pick up extremely weak infrared emission signals.

Desorption dynamics of deuterium molecules from the Si(100)-(3×1) dideuteride surface

We measured polar angle (theta)-resolved time-of-flight spectra of D2 molecules desorbing from the Si(100)-(3x1) dideuteride surface. The desorbing D2 molecules exhibit a considerable translational heating with mean desorption kinetic energies of approximately 0.25 eV, which is mostly independent of the desorption angles for 0 degrees<or=theta<or=30 degrees. The observed desorption dynamics of deuterium was discussed along the principle of detailed balance to predict their adsorption dynamics onto the monohydride Si surface.

極角分解ミニチュア飛行時間型イオン質量分析器の製作と評価，電子−イオンコインシデンス分光への応用

Coincidence measurement of energy-selected electrons and mass-selected ions (electron-ion coincidence (EICO) spectroscopy) is a powerful technique to clarify ion desorption mechanism induced by electron transitions, because excited states leading to ion desorption is directly identified. Information on the coincidence ions, however, is limited to the mass and the yield so far. In order to obtain information on kinetic energy and desorption polar angle of ions, we have developed a new polar-angle-resolved miniature time-of-flight ion mass spectrometer (TOF-MS), which can be used for EICO spectroscopy. The TOF-MS consists of a shield for electric field, an ion drift electrode with three meshes, and microchannel plates with three concentric anodes. By using SIMION 3D version 7.0 we simulated ion trajectories of H+ for the TOF-MS with a drift bias of -30 V. The results show that the desorption angles of H+ with a kinetic energy of 3 eV detected by the innermost anode, the intermediate anode, and the outermost anode are 0°17°, 22°48°, and 57°90°, respectively. The performance of the TOF-MS was evaluated by measuring H+ yield spectra and Auger electron-H+coincidence spectra of condensed water (H2O).

Surface Energy Differences in Monolayers Prepared with the Isomers 3- and 4-(12-Mercaptododecyl)phenol

Monolayers of 3-(12-mercaptododecyl)phenol and 4-(12-mercaptododecyl)phenol are prepared to investigate the relationship between the interfacial molecular structure and the surface energy of modified interfaces. These modified interfaces are characterized by reflection absorption infrared spectroscopy, reductive desorption, and contact angle measurements. Contact angle measurements with water (γ = 72.0 mN/m), glycerol (γ = 63.2 mN/m), and ethylene glycol (γ = 48.1 mN/m) show that monolayers of 4-(12-mercaptododecyl)phenol have a higher surface energy (∼42 mN/m) than 3-(12-mercaptododecyl)phenol monolayers (∼31 mN/m). Furthermore, Fowkes analysis of the contact angle data show that only ∼8% of the surface energy of the 4-(12-mercaptododecyl)phenol monolayer arises from dispersive interactions, while ∼30% of the total surface energy of 3-(12-mercaptododecyl)phenol monolayers comes from dispersive interactions. These surface energy results along with the spectral data suggest that the hydroxyl group with monolayers of 4-(12-mercaptododecyl)phenol is oriented away from the substrate and into the adjacent phase more than is found with monolayers of 3-(12-mercaptododecyl)phenol.