Guohong Qiu

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.

Characterization of Co-doped birnessites and application for removal of lead and arsenite.

Nanostructured Co-doped birnessites were successfully synthesized, and their application for the removal of Pb(2+) and As(III) from aquatic systems was investigated. Powder X-ray diffraction, chemical analysis, nitrogen physical adsorption, field emission scanning electron microscopy (FE-SEM) and X-ray photoelectron spectroscopy (XPS) were used to characterize the crystal structure, chemical composition, micromorphologies and surface properties of the birnessites. Doping cobalt into the layer of birnessite had little effect on its crystal structure and micromorphology. Both chemical and XPS analyses showed that the manganese average oxidation state (Mn AOS) decreased after cobalt doping. The Co dopant existed mainly in the form of Co(III)OOH in the birnessite structure. Part of the doped Co(3+) substituted for Mn(4+), resulting in the gain of negative charge of the layer and an increase in the content of the hydroxyl group, which accounted for the improved Pb(2+) adsorption capacity. The maximum capacity of Pb(2+) adsorption on HB, CoB5, CoB10 and CoB20 was 2538 mmol kg(-1), 2798 mmol kg(-1), 2932 mmol kg(-1) and 3146 mmol kg(-1), respectively. The total As(III) removal from solution was 94.30% for CoB5 and 100% for both CoB10 and CoB20, compared to 92.03% for undoped HB, by oxidation, adsorption and fixation, simultaneously.

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.

BIRNESSITES WITH DIFFERENT AVERAGE MANGANESE OXIDATION STATES SYNTHESIZED, CHARACTERIZED, AND TRANSFORMED TO TODOROKITE AT ATMOSPHERIC PRESSURE

Todorokite is a common manganese oxide mineral, with a tunnel structure, found in Earth surface environments, and is easily synthesized from layered birnessite. The aim of the current study was to prepare birnessites with different average manganese oxidation states (AOS) by controlling the

Fourier transform infrared spectroscopy study of acid birnessites before and after Pb2+ adsorption

{\rm{MnO}}_4^ - {\rm{/M}}{{\rm{n}}^{2 + }}

Roles of manganese oxides in degradation of phenol under UV-Vis irradiation: Adsorption, oxidation, and photocatalysis

MnO4−/Mn2+ ratio in concentrated NaOH or KOH. A series of (Na,K)-birnessites, Na-birnessites, and K-birnessites with different AOS was synthesized successfully in strongly alkaline media. The (Na,K)-birnessites and Na-birnessites prepared in NaOH clearly contained both large (500–1000 nm) and small (40–400 nm), plate-shaped crystallites. The K-birnessites prepared in KOH media consisted mostly of irregular (100–200 nm), plate-shaped crystallites. The degree of transformation of birnessite to todorokite at atmospheric pressure decreased as the AOS values of (Na,K)-birnessites and Na-birnessites increased from 3.51 to 3.80. No todorokite was present when a Na-birnessite with an AOS value of 3.87 was used as the precursor. Pyrophosphate, which is known to form strong complexes with Mn3+ at a pH range of 1–8, was added to a suspension of (Na,K)-birnessites in order to sequester the available Mn3+ in (Na,K)-birnessites. Removal of Mn3+ from birnessite MnO6 layers by pyrophosphate restricted transformation to todorokite — no (Na,K)-birnessite transformed to todorokite after pyrophosphate treatment. The interlayer K+ initially within (Na,K)-birnessites could not be completely ion-exchanged with Mg2+ to form todorokite at atmospheric pressure. No todorokite was forthcoming from K-birnessites even from those with small AOS values (3.50).

Facile hydrothermal synthesis and electrochemical properties of orthorhombic LiMnO2 cathode materials for rechargeable lithium batteries

Abstract To provide fundamental knowledge for studying the relative content of vacant sites and exploring the mechanism of interaction between Pb2+ and birnessite, Fourier transform infrared spectroscopy (FTIR) of birnessites with different Mn average oxidation states (AOS) before and after Pb2+ adsorption were investigated. The number of absorption bands of FTIR spectra was determined by using the second derivatives of the original spectra. The band at 899-920 cm-1 was assigned to the bending vibration of -OH located at vacancies. The bands at 1059-1070, 1115-1124 and 1165-1171 cm-1 could be attributed to the vibrations of Mn(III)-OH in MnO6 layers, and the intensities of these bands increased with decreasing Mn AOS. The bands at 990 and 1023-1027 cm-1 were ascribed to the vibrations of Mn(III)-OH in the interlayers. Mn(III) in MnO6 layers partially migrated to interlayers during Pb2+ adsorption, which led to an increased intensity of the band at 990 cm-1. The band at 564-567cm-1 was assigned to the vibration of Mn-O located at vacancies. This band could split by coupling of vibrations due to Pb2+ and/or Mn2+ adsorbed at vacant sites. The large distance between the band at 610-626 cm-1 and that at 638-659 cm-1 might reflect small Mn(III) ions located in Mn(III)-rich rows.

Large-scale size-controlled synthesis of cryptomelane-type manganese oxide OMS-2 in lateral and longitudinal directions

Manganese oxides are known as one type of semiconductors, but their photocatalysis characteristics have not been deeply explored. In this study, photocatalytic degradation of phenol using several synthesized manganese oxides, i.e, acidic birnessite (BIR-H), alkaline birnessite (BIR-OH), cryptomelane (CRY) and todorokite (TOD), were comparatively investigated. To elucidate phenol degradation mechanisms, X-ray diffraction (XRD), ICP-AES (inductively coupled plasma-atomic emission spectroscopy), TEM (transmission electronic microscope), N2 physisorption at 77 K and UV-visible diffuse reflectance spectroscopy (UV-Vis DRS) were employed to characterize the structural, compositional, morphological, specific surface area and optical absorption properties of the manganese oxides. After 12 hr of UV-Vis irradiation, the total organic carbon (TOC) removal rate reached 62.1%, 43.1%, 25.4%, and 22.5% for cryptomelane, acidic birnessite, todorokite and alkaline birnessite, respectively. Compared to the reactions in the dark condition, UV-Vis exposure improved the TOC removal rates by 55.8%, 31.9%, 23.4% and 17.9%. This suggests a weak ability of manganese oxides to degrade phenol in the dark condition, while UV-Vis light irradiation could significantly enhance phenol degradation. The manganese minerals exhibited photocatalytic activities in the order of: CRY > BIR-H > TOD > BIR-OH. There may be three possible mechanisms for photochemical degradation: (1) direct photolysis of phenol; (2) direct oxidation of phenol by manganese oxides; (3) photocatalytic oxidation of phenol by manganese oxides. Photocatalytic oxidation of phenol appeared to be the dominant mechanism.

Facile synthesis of birnessite-type manganese oxide nanoparticles as supercapacitor electrode materials.

Pure-phase, LiMn2O4-mixed and aluminum-doped orthorhombic LiMnO2 (o-LiMnO2) cathode materials with high discharge capacity and excellent cyclic stability were prepared by one-step hydrothermal reaction of MnCl2, EDTA, LiOH, AlCl3 and NaClO solutions. Chemical composition and aluminum content were affected by temperature and the concentration of LiOH, NaClO and AlCl3. A mixed phase of Mn3O4 and o-LiMnO2, pure-phase o-LiMnO2, and a mixed phase of o-LiMnO2 and LiMn2O4 were formed with increasing the concentration of NaClO from 0.08 to 0.25 mol L−1 at 180 °C for 24 h. Adding EDTA and NaClO facilitated the formation of o-LiMnO2. Al/Mn molar percent ratios in doped o-LiMnO2 were 0.34, 0.58, 0.91, and 1.22 when Al/Mn molar ratios in hydrothermal system were controlled at 0.05, 0.10, 0.15, and 0.20, respectively. Mixing LiMn2O4 and doping Al improved the discharge capacity and cyclic stability of o-LiMnO2. o-LiMnO2, the mixture with an o-LiMnO2/LiMn2O4 mass ratio of 2.45, and doped o-LiMnO2 with an Al/Mn molar percent ratio of 0.58 exhibited initial discharge capacities of 76, 139, and 82 mA h g−1, and cycling capacities of 124, 144, and 156 mA h g−1 after 100 cycles, respectively. This work facilitates the preparation and electrochemical performance improvement of o-LiMnO2.

Cadmium Removal from Aqueous Solution by a Deionization Supercapacitor with a Birnessite Electrode

A facile method was developed to synthesize size-tunable OMS-2 nanomaterials using a series of saturated fatty carboxylic acids as acid agents and regulators. The particle sizes, from 8.2 to 61.1 nm in width and 35.6 to 1376.1 nm in length, can be precisely controlled by decreasing alkyl chain lengths of carboxylic acids.