Mingming Liu

Innovative chemically bonded ionic liquids-based sol-gel coatings as highly porous, stable and selective stationary phases for solid phase microextraction.

In this work, two allyl-functionalised ionic liquids (ILs), 1-allyl-3-methylimidazolium hexafluorophosphate and 1-allyl-3-methylimidazolium bis(trifluoromethanesulphonyl)imide, were used as selective coating materials to prepare chemically bonded ILs-based organic-inorganic hybrid solid phase microextraction fibres. These fibres were prepared with the aid of γ-methacryloxypropyltrimethoxysilane as bridge using sol-gel method and free radical cross-linking technology. The underlying mechanisms of the sol-gel reaction were proposed, and the successful binding of these functional ILs to the sol-gel substrate was confirmed by Fourier transform infrared spectroscopy. These IL-based sol-gel coatings had porous surface structure, high thermal stability, a wide range of pH stability, strong solvent resistance and good coating preparation reproducibility. They also had high selectivity and sensitivity towards strong polar phenolic environmental estrogens (PEEs) and aromatic amines due to the strong electrostatic interactions, hydrogen bonding and π-π interactions provided by the special molecular structure of these imidazolium ILs. Moreover, their characteristics were somewhat different depending on the type of anions in the IL structure. The practical applicability of these IL-based sol-gel coatings was evaluated through the analysis of PEEs in two real water samples. The detection limits were quite low, varying from 0.0030 to 0.1248 μgL(-1). The linearity was very good in the range of 0.1 to 1000 μgL(-1) for most analytes, and the relative standard deviation values were below 6%. The relative recoveries were between 83.1 and 104.1% for lake water and between 89.1 and 97.1% for sewage drainage outlet water.

Thermally stable ionic liquid-based sol-gel coating for ultrasonic extraction-solid-phase microextraction-gas chromatography determination of phthalate esters in agricultural plastic films.

A novel sol-gel-coated ionic liquid-based ([AMIM][N(SO(2)CF(3))(2)]-OH-TSO) fiber was successfully applied for the determination of phthalate esters (PAEs) in agricultural plastic films by ultrasonic extraction (UE) combined with solid phase microextraction-gas chromatography (SPME-GC) due to its high thermal stability, specific selectivity and extraction efficiency. The extractant for UE and the adsorption time for SPME were optimized to achieve higher extraction efficiency. The desorption temperature and time were also optimized to avoid the carryover effect of previous extraction, and ultimately improve the precision and accuracy of the method. The [AMIM][N(SO(2)CF(3))(2)]-OH-TSO fiber showed comparable, or even higher response to most of the investigated PAEs than the commercial PDMS, PDMS-DVB and PA fibers. The carryover problem, often encountered when using commercial fibers, had been eliminated when desorption was performed at 360°C for 8 min. The proposed SPME-GC method showed good linearity over three to four orders of magnitude, and low limits of detection ranged from 0.003 to 0.063 μg L(-1). The relative standard deviation values obtained were below 10%, and the recoveries were in the ranges of 90.2-111.4%. Some of the PAEs studied were detected at very high concentration in these agricultural plastic film samples, resulting in a potential risk of crop damage, environmental contamination and human health exposure.

Sorption of tetracycline on organo-montmorillonites

Tetracycline (TC) is a veterinary antibiotic that is frequently detected as pollutant in the environment. Powerful adsorbents are required for removing TC. The present paper compares the TC adsorption capacity of Na-montmorillonite (Na-mont) with six organo-montmorillonites (organo-monts). Three quaternary ammonium cations (QACs) with different alkyl-chain lengths were used as modifiers. Powder X-ray diffraction indicated that the d(001) values of organo-monts increased with increasing the QACs loading and alkyl-chain length. The CECs of the organo-monts were substantially lower than that of Na-mont and decreased with QACs chain length and increased loading. The modeling of the adsorption kinetics revealed that the processes of TC adsorption on the tested samples could be well fitted by the pseudo-second-order equation. The maximum adsorption capacities of TC on the organo-monts (1000-2000mmol/kg) were considerably higher than that on Na-mont (769mmol/kg). Both the Langmuir and Freundlich model could fit the adsorption isotherms. The TC adsorption to the organo-monts increase significantly with decreasing the pH below 5.5 because of the electrostatic interaction, and a high QACs loading performed better than a low loading at around pH 3.

Co2+-exchange mechanism of birnessite and its application for the removal of Pb2+ and As(III).

Co-containing birnessites were obtained by ion exchange at different initial concentrations of Co(2+). Ion exchange of Co(2+) had little effect on birnessite crystal structure and micromorphology, but resulted in an increase in specific surface areas from 19.26 to 33.35 m(2)g(-1), and a decrease in both crystallinity and manganese average oxidation state. It was due to that Mn(IV) in the layer structure was reduced to Mn(III) during the oxidation process of Co(2+) to Co(III). The hydroxyl groups on the surface of Co-containing birnessites gradually decreased with an increase of Co/Mn molar ratio owing to the occupance of Co(III) into vacancies and the location of large amounts of Co(2+/3+) and Mn(2+/3+) above/below the vacant sites. This greatly accounted for the monotonous reduction in Pb(2+) adsorption capacity, from 2538 mmol kg(-1) for the unmodified birnessite to 1500 mmol kg(-1) for the Co(2+) ion-exchanged birnessite with a Co/Mn molar ratio of 0.16. The amount of As(III) oxidized by birnessite was enhanced after ion exchange, but the apparent initial reaction rate was greatly decreased. The present work demonstrates that Co(2+) ion exchange has great influence on the adsorption and oxidation behavior of inorganic toxic metal ions by birnessite in water environments.

Adsorption-Desorption of Myo-Inositol Hexakisphosphate on Hematite

Abstract Adsorption, desorption, and precipitation reactions at environmental interfaces impact the bioavailability, mobility, and fate of organic phosphates in terrestrial and aquatic environments. Myo-inositol hexakisphosphate (IHP) is the most abundant organic phosphate in soils. The adsorption/desorption characteristics of IHP on/from hematite were studied using batch adsorption and desorption experiments, Zeta (&zgr;) potential measurement, and in situ attenuated total reflectance Fourier transform infrared spectroscopy. The experiments were also conducted with phosphate (Pi) for comparison. Adsorption of both IHP and Pi has an initial rapid uptake followed by a slow adsorption process. The adsorbed amounts of IHP and Pi on hematite were 0.67 and 1.78 &mgr;mol m−2 at pH 5, respectively, decreasing with increasing pH. At all pH levels between 3 and 10, the surface of IHP adsorbed hematite was highly negative charged, leading to increasing IHP adsorption with ion strength. The desorption of IHP/Pi decreased sharply with the increasing desorption cycle and decreasing preadsorption amount. The desorption curves of IHP/Pi by 0.02 mol L−1 KCl or H2O can be well fitted by an exponential equation, whereas those for citrate followed a linear equation. Readsorption occurred in the later stage of Pi desorption by H2O, which was not observed in case of IHP probably because of the greater steric hindrance of IHP with the larger molecular size. In combination with adsorption-desorption characteristics, &zgr; potential measurements, and attenuated total reflectance Fourier transform infrared spectroscopy analysis, it is suggested that each adsorbed IHP molecule binds on hematite in the form of inner-sphere surface complexes via two phosphate groups.

Preparation and characterization of biocompatible molecularly imprinted poly(ionic liquid) films on the surface of multi-walled carbon nanotubes

A series of novel protein molecularly imprinted polymers (MIPs) were synthesized through a surface molecular imprinting technique by using bovine serum albumin (BSA) as a template, acrylamide modified multi-walled carbon nanotubes (MWCNTs-AAm) as substrates, and allyl-functionalized ionic liquids (ILs) as monomers. The MWCNTs@BSA-MIPILs synthesized under different monomer/template/cross-linker ratios were characterized by FTIR, SEM and BET analyses. The adsorption kinetics and isotherm, imprinting effect, selectivity and competitiveness, reusability, and practical applicability were evaluated in detail. The influence of the outside diameters of MWCNTs and the anion types of ILs on the imprinting effect of the MWCNTs@BSA-MIPILs was also studied. The MWCNTs with smaller diameters (<8 nm and 10–20 nm) were more beneficial for the preparation of the surface imprinted polymers. The MIPs prepared with IL monomers composed of anions with low nucleophilicity and hydrogen bond basicity (PF6−), and high steric effect (CF3SO3−) were found to have a better imprinting effect in comparison with those prepared with Cl− and BF4−-based IL and the traditional acrylamide monomers. They also exhibited higher selective recognition ability for BSA than for human serum albumin, lysozyme, trypsin and bovine hemoglobin. The imprinting and selectivity factors were greatly improved in a binary protein solution containing BSA and bovine hemoglobin. The developed MWCNTs@BSA-MIPILs were also successfully used for the purification of BSA from bovine calf serum. These results indicated that the PF6− and CF3SO3−-based ILs, for their important role in stabilizing biomacromolecules, will be ideal functional monomers for the development of biocompatible MIPs for protein molecules.

STRUCTURAL CONTROLS ON THE CATALYTIC POLYMERIZATION OF HYDROQUINONE BY BIRNESSITES

The role of Mn oxide in the abiotic formation of humic substances has been well demonstrated. However, information on the effect of crystal structure and surface-chemical characteristics of Mn oxide on this process is limited. In the present study, hexagonal and triclinic birnessites, synthesized in acidic and alkali media, were used to study the influence of the crystal-structure properties of birnessites on the oxidative polymerization of hydroquinone and to elucidate the catalytic mechanism of birnessites in the abiotic formation of humic-like polymers in hydroquinone-birnessite systems. The intermediate and final products formed in solution and solid-residue phases were identified by UV/Visible spectroscopy, atomic absorption spectrometry, Fourier-transform infrared spectroscopy, X-ray diffraction, solid-phase microextraction-gaschromatography-mas ss pectrometry, ion chromatography, and ultrafiltration. The degree of oxidative polymerization of hydroquinone wasenhanced with increase in the interlayer hydrated H+, the average oxidation state (AOS), and the specific surface area of birnessites. The nature of the functional groups of the humic-like polymers formed was, however, almost identical when hydroquinone was catalyzed by hexagonal and triclinic birnessites with similar AOS of Mn. The results indicated that crystal structure and surface-chemistry characteristics have significant influence on the oxidative activity of birnessites and the degree of polymerization of hydroquinone, but have little effect on the abiotic formation mechanism of humic-like polymers. The proposed oxidative polymerization pathway for hydroquinone isthat, asit approachesthe birnessite, it formsp recursor surface complexes. Asa strong oxidant, birnessite accepts an electron from hydroquinone, which is oxidized to 1,4-benzoquinone. The coupling, cleavage, polymerization, and decarboxylation reactionsaccompany the generation of 1,4-benzoquinone, lead to the release of CO2 and carboxylic acid fragments, the generation of rhodochrosite, and the ultimate formation of humic-like polymers. These findings are of fundamental significance in understanding the catalytic role of birnessite and the mechanism for the abiotic formation of humic substances in nature.

Rapid determination of the Mn average oxidation state of Mn oxides with a novel two-step colorimetric method

The Mn average oxidation state (Mn AOS) of Mn oxides has a significant impact on their reactivity towards trace metals and organic contaminants via sorption, catalysis and oxidation processes. Accurate determination of the Mn AOS is a key step to understanding the structures, composition, physicochemical properties, environmental behaviors and potential applications of Mn oxides. Here, a rapid two-step colorimetric method was developed to determine the Mn AOS of various Mn oxides, and it was tested on several Mn oxides (vernadite, acid birnessite and hausmannite). We also determined the Mn AOS of these Mn oxides with the conventional oxalic acid–permanganate back titration method and X-ray absorption near-edge spectroscopy (XANES) for comparison. In this rapid two-step colorimetric method, leucoberbelin blue I (LBB) and formaldoxime colorimetry were employed to obtain the oxidation numbers of high-valent Mn and total Mn, respectively, which were then used to calculate the Mn AOS. The colorimetric measurements are of considerable color stability and high sensitivity, thus enabling rapid, convenient and highly accurate determination of the Mn AOS compared with conventional methods. In addition, the required sample amount is greatly reduced (from ∼0.05 g to ∼0.005 g), making the proposed method an appropriate strategy for micro-volume samples.

Distribution, Species and Interfacial Reactions of Phytic Acid in Environment

myo-inositol-1,2,3,4,5,6-hexakisphosphate is called phytic acid or phytate,and commonly abbreviated as IHP or myo-IP6.IHP is the most abundant organic phosphorus in most soils.The mobility,cycling,transport,bioavailability to plants and environmental impact of soil phosphorus are affected by the interfacial reactions of IHP in the environment.This paper briefly summarized the distribution and species of phytic acid in the environment,and interfacial reactions,which including adsorption and desorption of IHP by soil components,such as iron and aluminum oxides,clays,calcium carbonate and so on,complexation reactions and precipitation with polyvalent cations.The transport and bioavailability of IHP are affected by its adsorption on soil minerals.The adsorption capacity of minerals for IHP is much greater than that for orthophosphate.The adsorption capacity of amorphous Fe/Al-(hydr)oxides for IHP is generally higher than that of crystalline Fe/Al-(hydr)oxides.In addition,the effects of environmental conditions,such as the type of minerals,pH,temperature and coexisted ions on the above interfacial reactions are discussed.The impacts of adsorbed IHP on surface charge,particle size and stability against aggregation of the minerals,and the application of IHP for remediation of metal-contaminated soils as well are also involved.Finally,hot spots for future research of IHP in the environment are proposed.