Shue Song

Synthesis of Magnetite–Graphene Oxide-Layered Double Hydroxide Composites and Applications for the Removal of Pb(II) and 2,4-Dichlorophenoxyacetic Acid from Aqueous Solutions

Magnetic composites consisting of magnetite (Fe3O4), graphene oxide (GO), and Mg3Al-OH layered double hydroxide (LDH), denoted as MGL composites, with varying GO contents (RGO) were synthesized by a mechano-hydrothermal (MHT) route using Fe3O4, Mg(OH)2, and Al(OH)3 as the inorganic starting materials. The application of the synthesized MGLs for removing the heavy-metal Pb(II) and the hydrophobic organic pesticide 2,4-dichlorophenoxyacetic acid (2,4-D) from aqueous solutions was investigated. Chemical bonding among the GO, Fe3O4, and LDH components was observed in the MGLs. The MGL composites showed good water-dispersity, strong magnetic response, and high sorption capacities and removal efficiencies for both Pb(II) and 2,4-D pollutants. The sorption capacities of the MGL for the pollutants significantly increased with an increase in RGO. Increasing pH could increase the removal efficiency for Pb(II) but decrease that for 2,4-D. The MGLs showed more affinity for Pb(II) than for 2,4-D in the competitive sorption. In addition, the MGLs could remain almost constant removal efficiency for the pollutants after reuse over six cycles, indicating their potential use as sorbents in wastewater treatment. Furthermore, a Cs effect was observed in the sorption equilibriums, which could be described using the Langmuir-SCA and Freundlich-SCA isotherms. The removal mechanisms of the MGL for Pb(II) and 2,4-D were discussed. The MHT method provided a simple and environmentally friendly route for synthesizing GO-LDH composite materials.

Synthesis, characterization, and visible-light photocatalytic activity of BiOI hierarchical flower-like microspheres

BiOI hierarchical flower-like microspheres were hydrothermally prepared, using tetrabutylammonium iodide as an iodine source and template. Many BiOI hierarchical structures have been synthesized using KI, NaI, HI or ionic liquids as the iodine source, but the use of alkyl ammonium iodide as the iodine source was not reported in the literature. The so-obtained BiOI samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, nitrogen sorption measurements, and ultraviolet-visible diffuse reflectance spectroscopy. The effects of hydrothermal temperature and time on the BiOI crystal structure and morphology were investigated. The BiOI microspheres were composed of BiOI nanosheets. The photocatalytic performance of the BiOI samples was determined from the degradation of Rhodamine B, under visible light irradiation. BiOI microspheres prepared at 160 °C over 30 h exhibited excellent photodegradation efficiency, which was more than five and seven times higher than those of BiOI nanoplates and N-doped TiO2, respectively. The high photocatalytic performance was attributed to the high specific surface area and low nanosheet thickness. A morphologic factor was proposed to represent the ratio of specific surface area to nanosheet thickness, and correlated to the photodegradation efficiency of the BiOI samples. The photocatalytic efficiency increased with increasing morphologic factor. The BiOI photocatalyst exhibited excellent stability and reusability, and has potential in environment remediation.

A sorbent concentration-dependent Freundlich isotherm

During study of the adsorption isotherms at solid–liquid interfaces, a sorbent concentration effect (Cs-effect) phenomenon was observed. In order to describe the Cs-effect, we proposed a new adsorption model, i.e., surface component activity (SCA) model. It supposes that the interaction between the sorbent particles exists in the real adsorption system, which induces the deviation of a real adsorption system from an ideal one. It is the deviation that induces the emerging of the Cs-effect. Based on the SCA model, the activity coefficient of adsorption sites should be a function of the sorbent concentration (Cs), and a Cs-dependent Freundlich equation (Freundlich-SCA equation) was derived. It was confirmed that the Freundlich-SCA equation can describe the Cs-effect observed in adsorption experiments. Its parameters (nS and KS) can be simulated with experimental adsorption data and are independent of Cs. Thus, these parameters obtained at given Cs values can be used to predict the adsorption behavior of the adsorbate at any Cs value.

Rough glass surface-mediated formation of vesicles from lauryl sulfobetaine micellar solutions.

We report novel vesicles composed of the zwitterionic surfactant lauryl sulfobetaine (LSB), which is a simple single-tailed surfactant (STS). The novel vesicles spontaneously formed from LSB micellar solutions with the mediation of a rough glass surface (RGS) in the absence of any cosurfactants or additives. Importantly, the obtained STS vesicles displayed good stability upon long-term storage, exposure to high temperature, and freeze-thawing after the RGS was removed. The pH of the LSB solution (4.0-9.0) and the presence of NaCl (1.0 × 10(-5) and 1.0 × 10(-4) mol/L) in the LSB solution had no obvious influence on the formation and stability of the vesicles. The adsorption configuration of LSB on the RGS was investigated via water contact angle measurements and atomic force microscope observations. The results showed that LSB adsorption bilayers could form on the RGS, and the bilayer adsorption of LSB on the RGS and the roughness of the solid surface played a key role in the vesicle formation. A possible mechanism for the RGS-mediated formation of LSB vesicles is proposed: LSB micelles and molecules adsorb on the RGS to form curved bilayers, and the curved bilayers are then detached from the RGS and close to form vesicles. To the best of our knowledge, this is the first report of LSB alone forming vesicles. This finding extends our understanding of the nature of vesicle systems.

Formation of simple single-tailed vesicles mediated by lipophilic solid surfaces

Adsorption and aggregation of surfactants at solid-liquid interfaces were fairly well understood, but there was limited knowledge regarding the effect of the presence of a solid surface on aggregate structures in bulk solution. Except for the fatty acid system, most simple single-tailed surfactants (STSs) are well known to form micelles but not vesicles in aqueous solution. Herein, we report a novel phenomenon: with the mediation of lipophilic solid surfaces (LSSs), the zwitterionic STS lauryl sulfobetaine (LSB) formed vesicles from its micellar solution without any additives, producing a mixed solution of vesicles and micelles. More interestingly, the STS vesicles coexisted stably with micelles in the solution and were thermally insensitive even after the removal of LSSs. The quantity of LSB vesicles decreases with the addition of ethanol. The pH effects (4.0-9.0) did not have an obvious influence on the formation and stability of the LSB vesicles. Similar results were obtained from the other STSs, suggesting that the LSS-mediated micelle-to-vesicle transition may be a general phenomenon. We proposed a possible mechanism that adsorption, the matrix effect, and interdigitated bilayer structures were probably crucial for the formation and stability of STS vesicles. We expect this work to provide important insights into the effect of the solid/liquid interface on the self-assembly chemistry of surfactants in bulk solution.