Effects of inorganic anions on cadmium sorption behaviours on titanate nanotube surfaces.

This manuscript describes the characterization of as-synthesized titanate nanotube (TNT) and its sorption behaviours on cadmium with the interactions of inorganic anions. The X-ray diffraction and transmission electron microscopy found that the nanotube is in sodium titanate crystal phase (Na2Ti3O7) and the pores of TNT are bimodally distributed with nominal pore sizes of 3 and 15 nm. In the binary systems between TNT and anions, the binding affinity is fluoride > phosphate > sulphate with sulphate being the least preferred. The order is similar to that of their first acidity constants, pKa1. In the presence of cadmium ions, slight decreases in fluoride and sulphate uptakes were observed. Phosphate uptake was, however, synergistically improved when cadmium was introduced. In the same ternary systems, it was found that these anions decreased the cadmium uptakes by TNT with the effect of sulphate being the most prominent.

A hierarchically assembled mesoporous ZnO hemisphere array and hollow microspheres for photocatalytic membrane water filtration.

A mesoporous ZnO hemisphere array has been prepared via a topotactic transition of Zn(4)(OH)(6)CO(3)·H(2)O (ZCHH) by chemical bath deposition. Each hemisphere is comprised of a radially oriented nanoflake shell grown on the hemispherical interior. Reaction time-dependent SEM analysis shows that the morphological formation of ZCHH involves a deposition-growth-secondary growth-redeposition procedure. Upon calcination, ZCHH readily decomposes to nanocrystalline wurtzite-phase ZnO without significant change in morphology, and the release of CO(2) and H(2)O from ZCHH creates an additional mesoporous structure in both hemispherical interior and nanoflake shell. A similar process but without using a substrate has been developed for synthesis of mesoporous ZnO hollow microspheres in powder form. Both the elaborated superstructured photocatalysts consisting of mesoporous nanoflakes have been demonstrated to exhibit excellent performances in the photocatalytic membrane filtration.

Selective sorption of divalent cations using a high capacity sorbent.

This manuscript describes the application of a novel sorbent, sodium titanate nanotube (STN) on partitioning of various divalent cations. Seven divalent cations, from alkaline earth, transition and post-transition groups, were used to determine the capacity and selectivity of STN. At pH 3 ± 0.02 and 0.1M ionic strength, STN displayed high capacity for Pb and Cd (1.27 and 0.39 mmol/g, correspondingly). The affinity of divalent cations was in the order Pb ≫ Cd>Cu>Zn>Ca>Sr>Ni. For six of the tested cations, their sorption capacity can be linearly correlated to its hydrolysis constant and electronegativity. STN has unusually low affinity for Ni and correlations of sorption capacity of Ni falls outside the 95% confidence intervals. Furthermore, it exhibited sorption behavior similar to alkaline earth cations, significant uptakes occurred only when pH>point of zero charge. In competitive sorption tests, STN preferentially sorb Cd over other metals (Zn, Ni, Ca and Sr) which coexist in industrial wastewater. As such STN is a potential novel sorbent useful for partitioning Cd from other metals in industrial wastewater.

Sequestration of cadmium ions using titanate nanotube.

In this manuscript, titanate (Na(2)Ti(3)O(7)) nanotubes synthesized from alkali hydrothermal route, with high BET surface area (206 m(2)/g), were used as an effective sorbent to remove cadmium ions from water. Sorption capacity (q(m,Langmuir) = 1.1 mmol/g at pH 7) was higher than other sorbents. X-ray photoelectron spectroscopy (XPS) analyses performed on fresh and cadmium-sorbed samples reveal intensities of Na 1s peak decreased after sorption indicating ion-exchanging between cadmium and sodium ions occurred at interlayer of nanotubes. However kinetic study did not show a stoichiometrically equivalent amount of Na(+) being released suggesting Cd uptake was not due solely to ion-exchange mechanism. Batch tests also showed that cadmium uptake was not significantly affected by variation in ionic strength, signifying cadmium ions form an inner-sphere complexation with surface hydroxyl groups. Finally, surface complexation modeling was performed based on charge distribution multisite ion complexation (CDMUSIC) model. It was found that CDMUSIC was able to fit the experimental data best when inner-sphere complexation and ion-exchange were applied together.