丁基黄药在CuO表面吸附的二维连续在线原位ATR-FTIR光谱研究

运用连续在线原位衰减全反射傅里叶变换红外光谱(ATR-FTIR)技术测定了纳米CuO表面对丁基黄药的吸附行为. 在FTIR 谱图中发现有峰的红移现象,吸收峰由1200 cm^-1偏移到1193 cm^-1,用超纯去离子水脱附,峰强度只有微小的变化,可判断丁基黄药在CuO表面发生了很强的化学吸附. 通过对吸附行为进行二维(2D)红外光谱分析,分辨出吸附过程中光谱强度的变化顺序. 二维异步相关光谱测定结果表明,1265 cm^-1处振动吸收峰最先引起光谱强度的变化,1265 cm^-1处吸收峰可归因为表面反应生成的双黄药和黄药分子聚集体的复合峰. 根据1200 cm^-1处黄药特征吸收峰强度的变化,进行吸附动力学模拟,得出CuO对丁基黄药的最大吸附量为529 mg·g^-1,且吸附符合拟二级吸附动力学过程.     

连续在线原位ATR-FTIR技术测定介孔CuAl2O4对黄药的吸附

以丁胺和正十二醇为混合模板剂, 采用共沉淀法制备了介孔纳米CuAl₂O₄. 用X射线粉末衍射(XRD)、傅里叶变换红外(FTIR)光谱、N₂吸附-脱附对产物的结构进行了表征. 采用连续在线原位衰减全反射傅里叶变换红外(ATR-FTIR)光谱技术研究了水溶液中丁基和辛基黄药在介孔CuAl₂O₄表面的吸附. 随着吸附时间的延长,1200 和1040 cm^-1两处黄药特征峰的高度逐渐增加, 根据1200 cm^-1处C-O-C伸缩振动峰的变化来评价黄药在CuAl₂O₄表面的吸附动力学过程. 结果表明, 介孔纳米CuAl₂O₄对黄药有很强的吸附能力, 在100 min 的时间内, CuAl₂O₄样品对丁基和辛基黄药的吸附量分别达到了236 和300 mg·g^-1, 且属于化学吸附. 对实验数据进行理论模拟, 发现吸附过程更接近于拟二级吸附动力学方程.     

土壤中正丁基黄原酸钾与铅离子的吸附特性研究

通过静态试验研究了土壤对正丁基黄原酸钾的吸附性能和影响因素,以及正丁基黄原酸钾-铅复合污染体系的吸附平衡与动力学特征。结果表明,土壤对正丁基黄原酸钾的吸附过程遵循Lagergren二级动力学模型,等温吸附可用Freundlich模型拟合,提高温度有利于吸附,土壤对正丁基黄原酸钾的吸附属于内扩散控制过程;土壤吸附正丁基黄原酸钾最佳p H范围为5~9,p H较低时正丁基黄原酸钾易被酸解,碱性环境(p H10)将抑制土壤对正丁基黄原酸钾的吸附;正丁基黄原酸钾与Pb2+形成难溶络合物而严重影响了Pb2+在土壤中的吸附,使Pb2+的吸附速率常数由38.319g/(mg·min)提高到70.350g/(mg·min),平衡吸附量(qe)由1.909mg/g降低到1.385mg/g,且影响程度随着Pb2+浓度的升高而减弱。     

Ordered adsorption of coagulation factor XII on negatively charged polymer surfaces probed by sum frequency generation vibrational spectroscopy

Electrostatic interactions between negatively charged polymer surfaces and factor XII (FXII), a blood coagulation factor, were investigated by sum frequency generation (SFG) vibrational spectroscopy, supplemented by several analytical techniques including attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), quartz crystal microbalance (QCM), ζ-potential measurement, and chromogenic assay. A series of sulfonated polystyrenes (sPS) with different sulfonation levels were synthesized as model surfaces with different surface charge densities. SFG spectra collected from FXII adsorbed onto PS and sPS surfaces with different surface charge densities showed remarkable differences in spectral features and especially in spectral intensity. Chromogenic assay experiments showed that highly charged sPS surfaces induced FXII autoactivation. ATR-FTIR and QCM results indicated that adsorption amounts on the PS and sPS surfaces were similar even though the surface charge densities were different. No significant conformational change was observed from FXII adsorbed onto surfaces studied. Using theoretical calculations, the possible contribution from the third-order nonlinear optical effect induced by the surface electric field was evaluated, and it was found to be unable to yield the SFG signal enhancement observed. Therefore it was concluded that the adsorbed FXII orientation and ordering were the main reasons for the remarkable SFG amide I signal increase on sPS surfaces. These investigations indicate that negatively charged surfaces facilitate or induce FXII autoactivation on the molecular level by imposing specific orientation and ordering on the adsorbed protein molecules. Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users.     

Molecular macrocluster formation on silica surfaces in phenol-cyclohexane mixtures

The adsorption of phenol, an aromatic compound with a hydrogen-bonding group, onto a silica surface in cyclohexane was investigated by colloidal probe atomic force microscopy (AFM), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), and adsorption isotherm measurements. ATR-FTIR measurements on the silica surface indicated the formation of surface macroclusters of phenol through hydrogen bonding. The ATR-FTIR spectra were also measured on the H-terminated silicon surface to observe the effect of the silanol groups on the phenol adsorption. The comparison of the ATR-FTIR spectra for both the silicon oxide and H-terminated silicon surfaces proved that the silanol groups are necessary for the formation of phenol clusters on the surface. The surface force measurement using colloidal probe AFM showed a long-range attraction between the two silica surfaces in phenol-cyclohexane mixtures. This long-range attraction resulted from the contact of the adsorbed phenol layers for the phenol concentrations below 0.6 mol %, at which no significant phenol clusters formed in the bulk solution. The attraction started to decrease at 0.6 mol % phenol due to the exchange of the phenol molecules between the clusters in the bulk phase and on the surface. The surface density of phenol in the adsorbed layer was calculated on the basis of the long-range attraction and found to be much smaller than the liquid phenol density. The plausible structure of the adsorbed phenol layer was drawn by referring to the crystal structure of the bulk phenol and orientation of the phenol molecules on the surface, estimated by the dichroic analysis of ATR-FTIR spectroscopy. The investigation of the phenol adsorption on the silica surface in a nonpolar solvent using this novel approach demonstrated the effect of the aromatic ring on the surface packing density.     

Adsorption of alpha amino acids at the water/goethite interface

The adsorption of amino acids onto mineral surfaces plays an important role in a wide range of areas, e.g., low-temperature aqueous geochemistry, bone formation and protein-bone interactions. In this work, the adsorption of three alpha aminoacids (sarcosine, MIDA and EDDA) onto goethite (alpha-FeOOH) was studied as a function of pH and background electrolyte concentration at 25.0 degrees C, and the molecular structures of the surface complexes formed were analyzed by means of ATR-FTIR spectroscopy. The results showed that adsorption of alpha amino acids were strongly dependent on the functionality and structure of the ligands. No adsorption was detected for the zwitterionic sarcosine indicating that simple alpha amino acids without other ionizable and/or functional groups display insignificant affinity for mineral surfaces such as goethite. With respect to the more complex amino acids, which are surface reactive, the number and relative positions of carboxylate and amine groups determine the types of surface interactions. These interactions range from non-specific outer-sphere to specific inner-sphere interactions as shown by the MIDA and EDDA results, respectively. The results presented herein suggest that isomerically-selective adsorption might only occur for amino acids that are capable of specific surface interactions, either through site-specific hydrogen bonding or inner-sphere complexation.     

Cryo‐XPS study of xanthate adsorption on pyrite

The adsorption of xanthate on pyrite has been extensively studied. However, the adsorption mechanisms remain a subject of controversy. Formation of both dixanthogen and metal‐xanthate complexes has been suggested. In this study, both room temperature X‐ray photoelectron spectroscopy (XPS) (RT‐XPS) and liquid nitrogen temperature XPS (Cryo‐XPS) were used to study interactions between pyrite and xanthate. While dixanthogen was not detected by RT‐XPS, it was successfully identified through C1s and S 2p peaks using Cryo‐XPS. The impact of pH and copper activation on adsorption of xanthate on pyrite was also investigated. It was found that at low pH, dixanthogen is the dominant species of xanthate adsorption on pyrite. At high pH, metal‐xanthate complexes were found to be prevalent on pyrite surfaces, which are responsible for the surface hydrophobicity. Copper activation showed a significant effect on xanthate adsorption on Cu‐activated pyrite, resulting in mostly the formation of Cu‐xanthate complexes rather than dixanthogen, mainly in the form of Cu(I)‐isopropyl xanthate complex (CuIPX). Copyright © 2012 John Wiley & Sons, Ltd.     

Highly Sensitive Determination of Butyl Xanthate in Surface and Drinking Water by Headspace Gas Chromatography with Electron Capture Detector

A highly sensitive and convenient method for the determination of butyl xanthate in surface water and drinking water was developed by headspace gas chromatography with electron capture detector (HS–GC–ECD). The analytical method was based on the decomposition of butyl xanthate under an acidic condition, generating carbon disulfide, which could be sensitively detected by gas chromatography with electron capture detector. The signal of CS₂ from the decomposition of potassium butyl xanthate was directly proportional to the concentration of potassium butyl xanthate over the range 0.7–100 ng/mL. The detection limit at a signal-to-noise ratio of three (S/N = 3) for potassium butyl xanthate was 0.3 ng/mL (~1.6 × 10⁻⁹ mol/L), which was more than two orders of magnitude lower than the popular UV methods and close to one order of magnitude lower than the similar headspace gas chromatography–mass spectroscopy method. The relative standard deviation (R.S.D.) within a day and in 3 days for potassium butyl xanthate at both 5 and 50 ng/mL was less than 4.7 %, suggesting good analytical performance of the present method. Good recoveries from 93.3 to 104.7 % were obtained from spiked surface and drinking water samples, indicating that the proposed HS–GC–ECD method was applicable for the quantification of butyl xanthate in surface and drinking water. Compared with other reported methods, the present method is highly sensitive, without sample preparation, and easily extended to the analysis of other xanthates.

     

Surface stoichiometry of zinc sulfide and its effect on the adsorption behaviors of xanthate

ABSTRACT: In this paper, the surface stoichiometry, acid-base properties as well as the adsorption of xanthate at ZnS surfaces were studied by means of potentiometric titration, adsorption and solution speciation modeling. The surface proton binding site was determined by using Gran plot to evaluate the potentiometric titration data. Testing results implied that for stoichiometric surfaces of zinc sulfide, the proton and hydroxide determine the surface charge. For the nonstoichiometric surfaces, the surface charge is controlled by proton, hydroxide, zinc and sulfide ions depending on specific conditions. The xanthate adsorption decreases with increasing solution pH, which indicates an ion exchange reaction at the surfaces. Based on experimental results, the surface protonation, deprotonation, stoichiometry and xanthate adsorption mechanism were discussed.     

An ATR-FTIR spectroscopic study of the competitive adsorption between oxalate and malonate at the water-goethite interface

The competitive adsorption between oxalate and malonate at the water-goethite interface was studied as a function of pH and total ligand concentrations by means of quantitative adsorption measurements and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. The results obtained show that ATR-FTIR spectroscopy resolves the individual spectroscopic features of oxalate and malonate when adsorbed simultaneously at the water-goethite interface. The characteristic peaks of all four types of predominating surface complexes existing in the single ligand systems were identified, namely one inner sphere and one outer sphere surface complex for each ligand. The quantitative adsorption data showed that oxalate partially out-competes malonate at the water-goethite interface. Evaluation of the peak area variations as a function of pH indicated that the stronger oxalate adsorption can be ascribed to the more stable inner sphere surface complex of oxalate, which in turn is related to the oxalate five-member chelate ring structure yielding a more stable complex compared to the six-member ring of malonate.     

Surface analysis of pyrite applying ESCA

Summary X-ray photoelectron spectroscopy (ESCA) has been applied to investigate the adsorption of xanthate on pyrite immersed in potassium ethyl xanthate solution at different pH values. The xanthate adsorption complex on the pyrite surface was confirmed as the precursor of dixanthogen.     

Functionalization of regenerated cellulose membrane via surface initiated atom transfer radical polymerization for boron removal from aqueous solution

In this study, an adsorptive membrane was prepared for efficient boron removal. Poly(glycidyl methacrylate) was grafted on the surfaces of the regenerated cellulose (RC) membrane via surface-initiated atom transfer radical polymerization, and N-methylglucamine was used to further react with epoxide rings to introduce polyhydroxyl functional groups, which served as the major binding sites for boron. The pristine and modified membranes were characterized by X-ray photoelectron spectroscopy (XPS), attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR), dynamic water contact angle measurement, and scanning electron microscopy. It was shown that the designed functional groups were successfully grafted onto the RC membrane, and surface modification contributed to higher boron binding capability. The optimal pH range for boron adsorption was 4-8. Under a neutral pH condition, the maximum adsorption capacity of the modified membrane was determined to be 0.75 mmol/g, which was comparable with those of commercial resins. Studies of electrolyte influence indicated the formation of inner-sphere surface complexes on the membrane surface. The ATR-FTIR and XPS analyses showed that secondary alcohol and tertiary amine groups were mainly involved in boron adsorption, and tetrahedral boron complexes were found on the membrane surface.     

ATR-FTIR studies of phospholipid vesicle interactions with α-FeOOH and α-Fe2O3 surfaces

Prior infrared spectroscopic studies of extracellular polymeric substances (EPS) and live bacterial cells have indicated that organic phosphate groups mediate cell adhesion to iron oxides via inner-sphere P–OFe surface complexation. Since cell membrane phospholipids are a potential source of organic phosphate groups, we investigated the adhesion of phospholipidic vesicles to the surfaces of the iron (oxyhydr)oxides goethite (α-FeOOH) and hematite (α-Fe₂O₃) using attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy. l-α-Phosphatidylcholine (PC), phosphatidylethanolamine (PE) and phosphatidic acid (PA) were used because they are vesicle forming phospholipids representative of prokaryotic and eukaryotic cell surface membranes. Phospholipid vesicles, formed in aqueous suspension, were characterized by transmission electron microscopy (TEM), multi-angle laser light scattering (MALS) and quasi-elastic light scattering (QELS). Their adhesion to goethite and hematite surfaces was studied with ATR-FTIR at pH 5. Results indicate that PC and PE adsorption is affected by electrostatic interaction and H-bonding (PE). Conversely, adsorption of PA involves phosphate inner-sphere complexes, for both goethite and hematite, via P–OFe bond formation. Biomolecule adsorption at the interface was observed to occur on the scale of minutes to hours. Exponential and linear increases in peak intensity were observed for goethite and hematite, respectively. Our ATR-FTIR results on the PA terminal phosphate are in good agreement with those on EPS reacted with goethite and on bacterial cell adhesion to hematite. These findings suggest that the plasma membrane, and the PA terminal phosphate in particular, may play a role in mediating the interaction between bacteria and iron oxide surfaces during initial stages of biofilm formation.     

Phase diagram for the adsorption of weak polyelectrolytes at a soft charged surface

We have experimentally studied the adsorption of polyelectrolytes at oppositely charged surfaces. A weak flexible polyelectrolyte, poly(acrylic acid), was adsorbed from dilute solutions on a Langmuir film of a cationic amphiphile, dimethyldioctadecylammonium bromide. The polymer surface coverage, Gamma, at equilibrium was measured by two reflectivity techniques-ellipsometry and polarization modulated infrared reflection absorption spectroscopy (PM-IRRAS)-as a function of the surface charge density, sigma, and of the polymer ionization degree, alpha. Different adsorption regimes were evidenced. For weakly charged surfaces, sigma < sigma sat, Gamma increases with sigma and with 1/alpha, as expected for a neutralization of the surface by the adsorbed polymers. For highly charged surfaces, sigma > sigma sat, the adsorption of polyelectrolytes saturates. The mean orientation of the adsorbed chains also depends on the value of sigma: it is parallel to the surface for sigma < sigma (< sigma sat) and orthogonal to the surface for sigma > sigma. We have measured the values of sigma sat and sigma as a function of alpha and compared the results with existing theories.     

Vibrational Spectroscopy Study of Selenate and Sulfate Adsorption Mechanisms on Fe and Al (Hydr)oxide Surfaces

The coordination and speciation of selenate (SeO(4)) and sulfate (SO(4)) on goethite and Al oxide were studied using Raman and ATR-FTIR spectroscopy. Raman spectra were collected from pastes of suspensions containing 4 mM SeO(4) or SO(4). For SO(4), complementary data were collected by ATR-FTIR spectroscopy in goethite systems with 1 mM SO(4) and in Al oxide systems with 4 mM SO(4). The combined data set of Raman and ATR-FTIR spectra indicate that both inner- and outer-sphere surface complexes of SeO(4) and SO(4) occur on these metal (hydr)oxide surfaces. These spectral data show that SeO(4) and SO(4) have a similar complexation behavior on the same adsorbent. On goethite, these form predominantly monodentate inner-sphere surface complexes at pH <6, while at pH >6 these anions exist predominantly as outer-sphere surface complexes. On Al oxide, in contrast, these anions exist predominantly as outer-sphere surface complexes, but a small fraction is also present as an inner-sphere complex at pH <6. A comparison of the spectral intensities of these anions on goethite and Al oxide shows that complexation of these anions with Al oxide is weaker than with Fe oxide. Copyright 2000 Academic Press.     

An in situ ATR-FTIR study of polyacrylamide adsorption at the talc surface

The adsorption of a low molecular weight unmodified polyacrylamide (Polymer-N) and a hydroxyl-substituted polyacrylamide (Polymer-H) onto talc was studied using in situ particle film ATR-FTIR spectroscopy in the multiple internal reflection mode. Spectra of the adsorbed polymer were collected as a function of increasing concentration and as a function of time. Measurement of the peak intensities of the adsorbed polymer allowed adsorption isotherms and adsorption kinetics to be determined for both polymers. Langmuir adsorption isotherm analysis of in situ data yielded Gibbs free energies of adsorption (deltaG0(ads)) for Polymer-N and Polymer-H of -44.5 and -45.7 kJ/mol, respectively, which correlate well with similar values determined from ex situ adsorption isotherms. Kinetic analysis indicated that the adsorption of both polymers was a pseudo-first-order process. The apparent rate constants for Polymer-N and Polymer-H were 0.10 and 0.15 min(-1), respectively. Absence of spectral shifts in the spectra of adsorbed polymer is indicative of a hydrophobic interaction between the polyacrylamides and the talc surface.     

Azo Derivatives of Phenol and 1-Naphthol as Flotation Collector of Sulfide Ore of Non-Ferrous Metals

Nine heterocyclic and aromatic azo derivatives of phenol and 1-naphthol were studied as flotation collectors of sulfide ores of non-ferrous metals. The constants of acid dissociation of compounds in aqueous solutions and their solubility in alkaline media are determined. It has been established that the adsorption of reagents on the surface of sulfide copper-nickel ore has a physical character. The adsorption constants are calculated. It is shown that the reagents under study exhibit collective properties with respect to the sulfide minerals of copper, cobalt and nickel. The use of mixtures of azo compounds with potassium butyl xanthate leads to an increase in both the recovery degree and the quality of the concentrate for nickel and copper in comparison with a single butyl xanthate.     

Hydrogen-bonded macrocluster formation of ethanol on silica surfaces in cyclohexane(1)

Adsorption of ethanol onto silica surfaces from ethanol-cyclohexane binary liquids was investigated by a combination of colloidal probe atomic force microscopy, adsorption excess isotherm measurement, and FTIR spectroscopy using the attenuated total reflection (ATR) mode. An unusually long-range attraction was found between the silica (glass) surfaces in the presence of ethanol in the concentration range of 0.1-1.4 mol % at room temperature. At 0.1 mol % ethanol, the attraction appeared at a distance of 35 +/- 3 nm and turned into a repulsion below 3.5 +/- 1.5 nm upon compression. Half of the attraction range agreed with the adsorption layer thickness estimated from the adsorption excess amount by assuming that the adsorption layer was composed only of ethanol. This indicated that the observed long-range attraction was caused by the contact of opposed adsorption layers of ethanol on the silica surfaces and that the sharp increase of repulsion at shorter distance was caused by the overlap of structured ethanol clusters adjacent to the surface. ATR-FTIR spectra demonstrated that ethanol adsorbed on the silica (silicon oxide) surfaces formed hydrogen-bonded clusters (polymers). Practically no ethanol clusters were formed on the hydrogen-terminated silicon surface. These results indicated that the cluster formation involved hydrogen-bonding interactions between surface silanol groups and ethanol hydroxyl groups in addition to those between ethanol hydroxyl groups. At higher temperatures (30-50 degrees C), the range and the strength of attraction decreased owing to the decrease in the hydrogen-bonded clusters monitored by FTIR spectroscopy, reflecting the nature of hydrogen bonding. The range and the strength of the attraction also changed when the ethanol concentration increased: The long-range attraction started to decrease at 0.6 mol % ethanol at room temperature and disappeared at 1.4 mol % while the adsorption excess amount remained almost constant as did the FTIR peak intensity of the hydrogen-bonded OH group of adsorbed ethanol. In the bulk solution, ethanol clusters appeared at 0.5 mol % ethanol; thus, this change in the attraction could be accounted for in terms of the exchange of ethanol molecules between the surface clusters and bulk clusters. The novel self-assembled structure of alcohol on the surface, found in this study may be called a "surface molecular macrocluster" because the hydrogen-bonded clusters extend to distances of ca. 20 nm longer than the typical sizes of common clusters, 2-4 nm, of alcohol (e.g., ethanol).     

Adsorption behavior of human serum albumin on ATR crystal studied by in situ ATR/FTIR spectroscopy and two-dimensional correlation analysis

The time-dependent adsorption behavior of human serum albumin (HSA) onto an ATR (ZnSe) crystal was investigated by two-dimensional (2D) correlation analysis and in situ ATR-FTIR spectroscopy following the secondary structural changes in the amide I region. The two major advantages of the generalized 2D correlation spectroscopy were first tested. New extra bands have been resolved by 2D correlation analysis, but they are either artifacts or a result of uncertainty on band position in generalized 2D correlation spectroscopy. The sequence of the intensity variations of the three sub-bands under the amide I band profile deduced from the 'sequential order' rules is contradictory to the experimental observation, which supports our argument on the 'sequential order' rules in generalized 2D correlation spectroscopy (H. Huang, Anal. Chem., 2007, 79, 8281-8292). Subsequent detailed analysis on the in situ ATR-IR spectra shows that the adsorption process of HSA on the ATR (ZnSe) crystal in aqueous solutions can be divided into three stages: no obvious conformational transitions in the first 25 min of adsorption of HSA molecules; large structural rearrangement from α-helix to random coil and short extended chain structures in a fully cooperative way from 25 to 50 min of adsorption; and further slight conformational transformation of short extended chain and turn structures into random coil with no sequential order after 50 min of adsorption.