Ji Ma

A facile, versatile approach to hydroxyl-anchored metal oxides with high Cr(VI) adsorption performance in water treatment

In this study, a facile and versatile urea-assisted approach was proposed to synthesize Chinese rose-like NiO, pinecone-like ZnO and sponge-like CoO adsorbents. The presence of urea during syntheses endowed these adsorbents with high concentration of surface hydroxyl groups, which was estimated as 1.83, 1.32 and 4.19 mmol [OH−] g−1 for NiO, ZnO and CoO adsorbents, respectively. These surface hydroxyl groups would facilitate the adsorption of Cr(vi) species (e.g. HCrO4−, Cr2O72− and CrO42−) from wastewater by exchanging with hydroxyl protons or hydroxide ions, and hence result in extremely high maximum adsorbed amounts of Cr(vi), being 2974, 14 256 and 408 mg g−1 for NiO, ZnO and CoO adsorbents in the pH range of 5.02–5.66 at 298 K, respectively. More strikingly, the maximum adsorbed amounts of Cr(vi) would be greatly enhanced as the adsorbing temperature is increased, and even amount to 23 411 mg g−1 for ZnO adsorbents at 323 K. Based on the kinetics and equilibrium studies of adsorptive removal of Cr(vi) from wastewater, our synthetic route will greatly improve the adsorptivity of the as-synthesized metal-oxide adsorbents, and hence it will shed new light on the development of high-performance adsorbents.

Impact of dispersants on relaxivities of magnetite contrast agents

Particle size is normally thought to be a major factor to evaluate MRI performance of contrast agents in biological systems. In this regard, three size-relevant regimes, including motional averaging regime, static dephasing regime, and echo-limited regime, have been well developed. In this study, we find the dispersant, which is often used as the subordinate additive in MRI measurements, is another key factor that determines the application of these three regimes in real systems. Our results show that the identically sized particle systems can separately exhibit static dephasing and echo-limited behaviors merely by altering the dispersants in aqueous solution.

Discovery of hard-magnetic domains in two-dimensional arrays of soft-magnetic Fe3O4 nanocubes

In this study, abnormal hard-magnetic domains were discovered in Fe3O4@C composite material, in which well-ordered 16-nm-sized Fe3O4 cubes were tightly embedded into carbon sheets of tens of nanometers thick. It was found that ca. 40 columns of Fe3O4 nanocubes magnetically self-assembled into a single strip-type domain with perpendicular magnetic anisotropy. More strikingly, remarkable domain misalignments, which were very similar to common edge dislocations among atomic planes in crystal lattices, were clearly observed and termed as “domain dislocation” in this work. The hard-magnetic properties of Fe3O4@C material, including large coercivity of 2150 Oe, high MR/MS value of 0.9, and strong anisotropy energy of 3.772 × 105 erg/cm3, were further ascertained by carefully designed electromagnetic absorption contrast experiments. It is anticipated that the discovery of hard-magnetic domains and domain dislocations within 2-D arrays of soft-magnetic nanomaterials will shed new light on the development of high-...

Controllable superferromagnetism-induced exchange bias effect in goethite microparticles after zero-field-cooling process

In this study, goethite microparticles (1.5–5 μm in diameter) were used to investigate the abnormal exchange bias effect after zero-field cooling process. It was found that the superferromagnetic mechanism, which is of great relevance for the superparamagnetic hematite impurities, was the root cause of such exchange-bias effect. Most notably, one can readily control this effect by simply regulating the reaction time during synthesis. It is anticipated that this controllable and intriguing superferromagnetism-induced exchange-bias effect may not only open a new direction to re-examine the conventional exchange-bias mechanism but also has practical applications in magnetic tunnel junctions and high-density memories.