Xiong-Fei Zhang

Acid-promoted synthesis of UiO-66 for highly selective adsorption of anionic dyes: Adsorption performance and mechanisms

UiO-66 was modulated by addition of acetic acid or HCl in the precursor solution. The resulting acetic acid-promoted UiO-66has more regular octahedral structures and high surface areas of 892-1090m2/g. Anionic dyes (methyl orange (MO) and Congo red (CR)) and cationic dyes (methylene blue (MB) and rhodamine B (RhB)) were examined for the selective dye adsorption on various UiO-66. The acid-promoted UiO-66 exhibits an excellent selective adsorption to anionic dyes, where the adsorption capacities of MO and MB are 84.8 and 13.2mg/g, respectively. However, UiO-66 prepared without acid shows similar adsorption to both anionic dye MO (70.4mg/g) and cationic dye MB (67.5mg/g). Mixed dyes (MO/MB and MO/RhB) adsorption on acid-promoted UiO-66 further proves the selective adsorption to anionic dyes. The adsorption mechanism was studied by testing the Zeta potential of acid-promoted UiO-66, and more positive Zeta potential (hydrogen ions) of UiO-66 is beneficial to the anionic dye adsorption.

Facile stir-dried preparation of g-C3N4/TiO2 homogeneous composites with enhanced photocatalytic activity

g-C3N4/TiO2 composites with homogeneous well-combined structures were prepared by a simple stir-dried method, using dicyandiamide (DICY) and tetrabutyl orthotitanate (TBOT) as the precursors, followed by high-temperature calcination. Various characterization techniques including XRD, FTIR, nitrogen adsorption–desorption, SEM and XPS confirm the formation of an interconnected structure between g-C3N4 and TiO2 in the composites. g-C3N4/TiO2 composites exhibit much higher photocatalytic activity than that of pure g-C3N4 and TiO2 in the degradation of methylene blue under visible light. In particular, the CT-5 composite prepared with DICY/TBOT at a mass ratio of 5 : 1, exhibited a photodegradation activity that is about 3.8 times that of TiO2 and 2.9 times that of pure g-C3N4. The homogeneous g-C3N4/TiO2 composite CT-5 can be repetitively used without significant loss of activity. The strong synergistic effect between g-C3N4 and TiO2 achieved by this preparation method greatly improves the separation efficiency of photo-generated electrons and holes, thus offering enhanced photocatalytic performances.

Alginate-based attapulgite foams as efficient and recyclable adsorbents for the removal of heavy metals

Floatable and porous foam adsorbents constructed by encapsulating attapulgite (ATP) in sodium alginate (SA) were fabricated via a freeze-drying and post cross-linking method, and both attapulgite and sodium alginate possessed adsorptive sites. These adsorbents were characterized by XRD, FTIR, and SEM to investigate their crystal structures, surface properties, size and morphology. In the adsorption tests, the adsorption capacity was derived from the Langmuir isotherm model, and the maximal adsorption capacity of as-prepared adsorbents was 119.0 mg g-1 for Cu(II) and 160.0 mg g-1 for Cd(II). In addition to the remarkable adsorptive performances, these adsorbents presented strong chemical stability and were readily recyclable because of their floatability in water solution. These aforementioned advantages highlight that the alginate-encapsulated attapulgite foams are potential scalable adsorbents for heavy metal ions removal from polluted water, and such a structure design could intrigue the development of novel adsorptive materials.

In-situ gelation of sodium alginate supported on melamine sponge for efficient removal of copper ions

Sodium alginate-melamine sponge composites were fabricated by in-situ gelation of sodium alginate supported on the commercial melamine sponge (MS). MS serves as the three-dimensional skeleton for alginate coating and can effectively avoid the shrink of alginate, and thus makes the alginate-MS composites user-friendly and facile to recover. In the adsorption test, the adsorption process is pseudo-second order and matches the Langmuir model with the maximum adsorption capacity of 90.1mg/g for copper ions. The alginate-MS is recyclable and presents enhanced mechanical properties compared with those of pristine MS. All these properties make such alginate-MS a promising candidate as an adsorbent for heavy metal removal.

Constructing Cd 0.5 Zn 0.5 S@ZIF-8 nanocomposites through self-assembly strategy to enhance Cr(VI) photocatalytic reduction

A novel and highly efficient photocatalyst of Cd0.5Zn0.5S@ZIF-8 nanocomposite has been developed by a facile self-assembly strategy. This is the first report on the application of CdxZn1-xS and metal-organic framework (MOF) nanocomposite as photocatalysts for the reduction of Cr(VI). The resulting Cd0.5Zn0.5S@ZIF-8 exhibited higher photocatalytic activity than that of pristine Cd0.5Zn0.5S and ZIF-8. Particularly, the CZS@Z60 composite with 60 wt% of ZIF-8 exhibited a photocatalytic activity that is about 1.6 times as high as that of Cd0.5Zn0.5S. The dominant reason for the improved photocatalytic reduction potential is proved to be the newly-formed interfacial SZn bonds that firmly connect Cd0.5Zn0.5S and ZIF-8 and substantially improve the separation efficiency of photo-excited electrons and holes. The newly-formed chemical bonds are confirmed by XPS analyses, and the prolonged lifetime of photo-excited electrons is evidenced by the electrochemical measurement of photocurrent, which shows that the photocurrent on Cd0.5Zn0.5S@ZIF-8 is much higher than that of Cd0.5Zn0.5S and ZIF-8. This study clearly demonstrates that the MOF-based composite nanomaterials hold great promises for applications in the field of environmental remediation and for design of novel photocatalytic materials.

Temperature-induced formation of cellulose nanofiber film with remarkably high gas separation performance

Abstract Free-standing cellulose nanofiber (CNF) films were prepared by a specially designed oven-drying approach. For the first time, the evaporation rate was carefully controlled to enhance the gas separation performance of the CNF film with the highest H2/N2 and H2/O2 selectivities of 159.4 and 218.2, respectively. The dense structure formed by the CNFs and the intra- and inter-fibrillar hydrogen bonds are believed to contribute to the separation property. Particularly, the specific role of floating-shape film precursor formed at the rapid evaporation stage (stage I) and the mechanism for film formation were investigated. This study demonstrated that the evaporation rate controlled by the heating temperature exhibited significant influence on surface, uniformity and gas separation of the CNF films.

Isomerization of Styrene Oxide to Phenyl Acetaldehyde over Different Modified Beta Zeolites

The catalytic performance of the isomerization of styrene oxide to phenyl acetaldehyde was investigated over different modified beta catalysts under gas-phase atmosphere free of solvents. The physicochemical properties were characterized by a combination of X-ray diffraction (XRD), N2 adsorption, Fourier transform infrared spectroscopy (FT-IR), Magic Angle Spinning Nuclear Magnetic Resonance (MAS-NMR), NH3-Temperature programmed desorption (NH3-TPD) and thermo gravimetric analysis (TGA), etc. Acid sites with stronger strength are responsible for the formation of condensation products and fast deactivation of catalysts. The obtained results also demonstrate that the introduction of boron atoms can create suitable acid strength and acid distribution without significantly destroying its microporous structures. Therefore, BAl-BEA sample is highly active and selective for the rearrangement of styrene oxide as well as very stable to deactivation.Graphical Abstract

Facilitated Transport of CO2 Through the Transparent and Flexible Cellulose Membrane Promoted by Fixed-Site Carrier

Facilitated transport cellulose membranes with different zinc ion loadings are fabricated via a facile and green solvent system (zinc chloride/calcium chloride solution). Zn2+ ions lower the pristine hydrogen bonds that normally reinforce the cellulose chains, and Ca2+ ions facilitate interactions among the Zn-cellulose chains to form nanofibrils. The strategy provides an effective route to immobilize zinc species into membrane matrix and constructs facilitated transport pathway for CO2 molecules. The self-standing membranes are transparent, flexible and demonstrate ultraselective CO2 permeation. The optimum separation performance is achieved over CM-0 with the highest zinc content (22.2%), and it exhibits a CO2 permeability of 155.0 Barrer, with selectivity ratios of 27.2 (CO2/N2) and 100.6 (CO2/O2). The excellent separation performance is assigned to the π complexation mechanism between Zn2+ and CO2.