Search

Hydroxyl radicals ( • OH) generated in the photocatalytic process are crucial to the conversion of methane (CH 4 ) to value-added methanol (CH 3 OH) at room temperature. However, utilizing noble metal-free catalysts and low-energy photons of solar light, such as visible and near-infrared light (vis-NIR), is difficult to provide more electron states to form • OH radicals. Here, we developed FeOOH/Li 0.1 WO 3 core-shell nanorods via a two-step in/out co-modification of hexagonal tungsten oxide (h-WO 3 ): (1) lithium ions intercalating into the hexagonal tunnels of h-WO 3 to form Li 0.1 WO 3 nanorods and (2) using FeOOH-wrapped Li 0.1 WO 3 to obtain FeOOH/Li 0.1 WO 3 core-shell nanorods. Introduction of lithium induces polaron transition in Li 0.1 WO 3 , enabling the absorption of vis-NIR light. Interestingly, FeOOH-based Fenton-like reaction when H 2 O 2 is selected as an oxidant favors the generation of more • OH radicals available for CH 4 oxidation to CH 3 OH. Meanwhile, FeOOH with Fe III as an "electron sink" highly improves the separation of photoinduced electrons and holes in Li 0.1 WO 3 . Eventually, efficient selective formation of CH 4 OH is achieved with remarkable generation rates up to ∼342 and ∼160 μmol g -1 at visible light (420-700 nm) and NIR light (≥800 nm), respectively. Our finding opens up new possibilities for developing noble metal-free catalysts for solar energy-driven CH 4 conversion to CH 3 OH under ambient conditions.

Plasmon enhancement of optical properties is both fundamentally important and appealing for many biological and photonic applications. Although metal-enhanced two-photon excitation fluorescence has been demonstrated in the solid substrates, there is no report on metal enhanced overall two-photon excitation fluorescence in the colloid system. Here we systematically investigated gold nanorod enhanced one- and two-photon excitation fluorescence of a porphyrin molecule, T790. The separation distance between the metal core and T790 was varied by adjusting the silica shell thickness from 13 to 42 nm. One- and two-photon excitation fluorescence intensities of T790 were found to strongly depend on the thickness of silica shell that separates gold nanorod and T790. The optimum one- and two-photon excitation fluorescence enhancement was found to occur at shell thicknesses of 34 and 20 nm, with enhancement factors of 2.1 and 11.8, respectively. Fluorescence lifetime of T790 steadily decreased as the shell thickness decreased. The observed two-photon excitation fluorescence enhancement is ascribed to a combination effect of local electric field amplification and competition between increased radiative and non-radiative decay rates. Core-shell nanoparticles that displayed enhanced two-photon excitation fluorescence were also found to exhibit significantly improved singlet oxygen generation capability under two-photon excitation. The applications of these nanoparticles as effective agents for two-photon cell imaging and nano-photosensitizers for two-photon photodynamic therapy with improved efficiency have also been demonstrated in HepG2 cancer cells. The combined advantages of enhanced two-photon excitation fluorescence and two-photon induced singlet oxygen generation make these core-shell nanoparticles as attractive agents for two-photon imaging guided two-photon photodynamic therapy.

Gold nanorods with three different aspect ratios were prepared and their dual capabilities for two-photon imaging and two-photon photodynamic therapy have been demonstrated. These gold nanorods exhibit large two-photon absorption action cross-sections, about two orders of magnitude larger than small organic molecules, which makes them suitable for two-photon imaging. They can also effectively generate singlet oxygen under two-photon excitation, significantly higher than traditional photosensitizers such as Rose Bengal and Indocyanine Green. Such high singlet oxygen generation capability under two-photon excitation was ascribed to their large two-photon absorption cross-sections. Polyvinylpyrrolidone (PVP) coated gold nanorods displayed excellent biocompatibility and high cellular uptake efficiency. The two-photon photodynamic therapy effect and two-photon fluorescence imaging properties of PVP coated gold nanorods have been successfully demonstrated on HeLa cells in vitro using fluorescence microscopy and indirect XTT assay method. These gold nanorods thus hold great promise for imaging guided two-photon photodynamic therapy for the treatment of various malignant tumors.

Radially oriented anthracene nanowires and their self-assembled concentric ring arrays were prepared through a facial solvent-evaporation method. The successful growth of anthracene nanowires can be attributed to a combined mechanism of molecular self-assembly facilitated by strong π-π intermolecular interactions together with evaporation-induced capillary flow and fingering instability. Their radial orientation is determined by the capillary flow; their shape (either straight or curved nanowires) is governed by the competition between the capillary and Marangoni convectional flows. The self-assembly of nanowires into large-scale concentric ring arrays can be interpreted in terms of the repeated slipping-and-sticking motions of the contact line. The high-quality crystalline anthracene nanowire arrays exhibit size-dependent fluorescence emission with high-degree anisotropy.

Novel multifunctional nanoparticles that combine two functionalities (a gold nanorod core and a porphyrin-doped mesoporous silica shell) into one entity were synthesized. Due to the encapsulation of mesoporous silica, the porphyrin can be well protected against the external bioenvironment. In addition, the generated singlet oxygen by porphyrin molecules can be easily released from the silica. We have demonstrated that these multifunctional nanoparticles can generate singlet oxygen with relatively higher yield compared to free porphyrin. These multifunctional nanocomposites are attractive candidates for simultaneous photosensitization and two-photon imaging as well as imaging guided therapy.

Poly-copper tetraaminophthalocyanine (CuTAPc) nanotubes were successfully fabricated on porous alumina templates by electropolymerization. Their high surface area and simple preparation protocol made them potential candidates as the modification layer of electrodes for sensor application. High sensitivities and improved linear ranges were obtained through different measurements such as differential pulse voltammetry (DPV), differential potential amperometric (DPA) and electrochemical impedance spectroscopy (EIS). Detection limits as low as 10 nM were demonstrated in common voltammetric analysis with ultra-high response current in the microA range.