Quande Che

Effect of sequential morphology adjustment of hematite nanoplates to nanospindles on their properties and applications

We investigated the marked morphological changes of α-Fe2O3 nanocrystals from nanoplates to nanospindles via an environmentally friendly hydrothermal route. An aqueous Fe salt was used as the precursor and the volume ratio of ammonia to ethylene glycol was varied. The product was uniform and obtained at a high yield. By simply increasing the ratio of the aqueous phase, the morphology could be continuously tuned from nanoplates to nanospindles with the (001) facets gradually disappearing. A fundamental understanding of the shape evolution was obtained via a series of characterizations including X-ray powder diffraction, scanning electron microscopy and transmission electron microscopy. The NO3− ions and NH3 molecules played vital parts at increased temperatures, not only in the phase structure of the iron oxide, but also in the formation of different hematite morphologies with different properties. The decrease in the photocatalytic efficiency in the visible region with the change from nanoplates to nanospindles under the same conditions indicated that the increase in the number of exposed (001) facets promoted the photocatalytic performance. The magnetic and electrochemical properties of typical morphologies were investigated and showed the potential applications of the nanostructures in various fields.

Magic sol–gel silica films encapsulating hydrophobic and hydrophilic quantum dots for white-light-emission

A sol–gel SiO2 film prepared from 3-aminopropyltrimethoxysilane (APS) has been developed as an excellent medium to encapsulate both hydrophobic and hydrophilic quantum dots (QDs). The film was fabricated by spin and dip coating on flat substrates as well as by a spraying approach on various substrates with a 3-dimensional (3D) surface. Pre-heat-treatment of the substrate plays an important role for creating homogeneous films on a 3D surface. In the case of aqueous CdTe and ZnSe0.9Te0.1 QDs, APS did not decrease the photoluminescence (PL) efficiency of the QDs. For hydrophobic QDs, a phase transfer from oil to water phase was first performed through the ligand exchange process between APS and the capping agent. By mixing QDs with different emitting colors, silica gel with white-light emission was obtained. Based on hydrophobic and hydrophilic QDs, white-light-emitting diodes with adjustable chromaticity coordinates were fabricated using a UV-emitting InGaN chip as excitation source. Because of the facile preparation procedure, high stability, and high PL efficiency, the magic film shows great potential for use in white-lighting-emission applications.

Preparation and properties of highly stable quantum dot-based flexible silica films

Highly luminescent hydrophobic CdSe and CdSe/CdxZn1−xS quantum dots (QDs) were synthesized via an organic route. The phase transfer of the QDs was carried out through a ligand exchange from 3-aminopropyltrimethoxysilane (APS) instead of an organic capping agent to get aqueous QDs. A functional sol–gel SiO2 sol with a high QD concentration was obtained from the aqueous QD colloidal solution with APS through the hydrolysis and condensation which subsequently occurred. Flexible inorganic SiO2 films with QDs were fabricated via various methods. The photodegradation experiments of the resulting films were completed. It is surprising that the QDs in films were revealed to be highly stable. Especially, the PL intensity of the films increased dramatically after irradiation by 365 nm UV light. By integrating a thin CdSe QD–silica film on a solar cell, the enhanced current demonstrated that a thin film can facilitate the continuous development of solar cells. Because of their high PL brightness, multicolor emission, flexibility and stability, these films will have great potential applications.

Fabrication and Photocatalytic Activity of Tunable Triangular- and Circular-Like Ag/AgCl Nanoplates

Triangular- and circular-like Ag/AgCl nanoplates with various edge length and thickness have been successfully synthesized by a facile in situ oxidation process. Uniform Ag triangular nanoplates with tunable sizes and thicknesses obtained by adjusting the adding amounts of trisodium citrate and polyvinylpyrrolidone (PVP) were employed as Ag precursors to form triangular- and circular-like Ag/AgCl heterostructures by changing the adding amounts of FeCl3 in the reaction process. The morphological evolution mechanism of Ag nanoplates and Ag/AgCl heterostructures was discussed. It is clear that the morphologies of Ag/AgCl products can be gradually converted from the large and thick triangular-like nanoplates into the small and thin circular-like ones as the AgCl ratio increasing from 5 to 100%, which can be mainly assigned to the synergistic effect of the oxidation of Fe3+ and the etching action of Cl-. The photocatalytic results indicate that Ag/AgCl nanoplates with different ratios of AgCl can exhibit good photocatalytic activity for degradation of methyl orange (MO) pollutant under ultraviolet-light-driven (UVD) and visible-light-driven (VLD) irradiation, respectively. The Ag/AgCl nanoplates with an AgCl ratio of 30% have the superior photocatalytic activity with the photocatalytic efficiency calculated to be 83.5% within 160 min under UVD irradiation and 53.6% within 240 min under VLD irradiation, respectively, owing to the combination of the favorable crystallinity, excellent photoabsorption, and the efficient separation of the photo-induced carriers between Ag and AgCl.