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Cataloged from PDF version of article.We propose and demonstrate photocatalytic hybrid nanocomposites that co-integrate TiO(2) and ZnO nanoparticles in the same host resin to substantially enhance their combined photocatalytic activity in the near-UV and visible spectral ranges, where the intrinsic photocatalytic activity of TiO2 nanoparticles or that of ZnO nanoparticles is individually considerably weak For a comparative study, by embedding TiO(2) nanoparticles of ca. 6 nm and ZnO nanoparticles of ca. 40 nm in the sol-gel matrix of acrylic resin, we make thin film coatings of TiO(2)-ZnO nanoparticles (combination of TiO2 and ZnO, each with a mass ratio of 8.5%), as well as the composite films of TiO(2) nanoparticles alone (17.0%), and ZnO nanoparticles alone (17.0%), and a negative control group with no nanoparticles. For all of these thin films coated on polyvinyl chloride (PVC) polyester, we experimentally study photocatalytic activity and systematically measure spectral degradation (recovery obtained by photocatalytic reactions). This spectral characterization exhibits photodegradation levels of the contaminant at different excitation wavelengths (in the range of 310-469 nm) to distinguish different parts of optical spectrum where TiO(2) and ZnO nanopartides are individually and concurrently active. We observe that the photocatalytic activity is significantly improved towards the visible range with the use of TiO(2)-ZnO combination compared to the individual cases. Particularly for the excitation wavelengths of photochemical reactions longer than 400 nm, where the negative control group and ZnO nanoparticles alone yield no observable photodegradation level and TiO2 nanoparticles alone lead to a low photodegradation level of 14%, the synergic combination of TiO(2)-ZnO nanoparticles achieves a photodegradation level as high as 30%. Investigating their scanning electron microscopy (SEM), X-ray diffraction (XRD), and high resolution transmission electron microscopy (HRTEM), we present evidence of the heterostructure, crystallography, and chemical bonding states for the hybrid TiO(2)-ZnO nanocomposite films, in comparison to the films of only TiO(2) nanoparticles, only ZnO nanoparticles, and no nanoparticles. (C) 2011 Elsevier B.V. All rights reserved

Core−shell upconversion nanoparticles (UCNPs) have been intensely studied and are anticipated to affect fields including solar cells and imaging, sensing, and biomedical applications where both optical enhancement and tuning are of great importance. In the case of homoepitaxial core−shell designs, a lack of understanding of the shell's dopant concentration effect on crystal growth is due to difficulties in distinguishing atomistically between the core and shell using experimental approaches.Here we demonstrate the critical role of the homoepitaxial shell's dopant composition on structural and morphological properties which are crucial for upconversion activity. Yb 3+ ion doped (active) and undoped (inert) LaF 3 shell designs are grown on a 20% Yb, 2% Tm codoped hexagonal phase LaF 3 core through a microwaveassisted synthesis route. We further analyzed the crystal ordering through X-ray diffraction analysis and atomic-scale imaging at the core−shell interface with high-angle annular dark field and annular bright field modes of Cs-corrected STEM. The inert shell showed greater optical enhancement than the active shell at all major emission peaks, with the greatest enhancement factors of 13.5 and 7.0 at blue and red emissions, respectively. The tensile strain (+0.23%) of the core is eliminated by the inert shell, which resulted in a −0.05% compressive strain as well as enlargement of the unit cell, whereas the active shell resulted in a tensile strain of +0.53% with a slight increase in unit cell parameters. FFT images are analyzed for further effects, including lattice distortion and directionality of shell growth. The inert shell yields a multifaceted encapsulation resulting in a round morphology with notable distortions, while the active shell with minor distortions has an elongated morphology with sharper edges and preferential growth in the [001] direction. Our work provides direct evidence from the core−shell interface of homoepitaxial upconversion nanoparticles of doped and undoped shell composition and related structural properties.

At nano scale, the size of particles becomes an important parameter that significantly affects the associated quantum processes due to tighter quantum confinement and some of the classical processes due to increasing ratio of surface atoms to bulk atoms as the volume of the particle shrinks. The size effect is evident in the characteristics of commonly known nano structures such as quantum dots and carbon nanotubes. Another class of relatively less known nanostructures where we observe significant influence of the size is titaniumdioxide (TiO 2 ) nanoparticles in photocatalytic activity due to their optical activation process [1]. Such photocatalytic nanoparticles are attractive for different self-cleaning applications such as environmental bio-decontamination for a large variety of organics, viruses, bacteria, fungi and cancer cells, and chemical and biological purification of water [2][3]; and in such applications, the efficiency of the optical activation is critical, for which the nanoparticle size matters. In this work, we optically investigate and characterize the photocatalytic recovery of contaminated TiO 2 nanoparticles of different sizes that are incorporated in solgel films to study the size effect. We demonstrate significant improvement in the optical efficiency of the photocatalytic nanoparticles as we reduce the particle size.Figures 1a and 1b show pictures of our samples that include 21 nm and 6 nm, anatase-type TiO 2 nanoparticles, respectively, both of which are embedded in 10 µm thick acrylic solgel films and contaminated with the same methylene blue solution. Figures 1a and 1b exhibit the self-cleaning effect within the spot size of the activating UV illumination at the centers of the 21 nm and 6 nm samples, respectively, in contrast to the non-activated region around these spots on the samples. Comparing these pictures, we observe that the contaminated region is optically recovered back further towards its original with the use of the size effect. This is due to the increased TiO 2 surface with reducing nanoparticle size, which gives rise to enhancement of the photoefficiency and hence the photocatalytic process. Figure 2a shows the optical transmission spectra of 21 nm TiO 2 samples before and after the methylene blue contamination in the visible range from 400 nm to 700 nm, along with the time evolution of the transmission spectra under UV activation with the optical power of 200 µW at 330 nm after 6 and 16 hours. The methylene blue contamination shifts the optical transmission curve significantly in the visible range. We observe that the optical transmission of the contaminated sample shifts significantly back after the first 6 hours of photoexcitation, but shifts only slightly after the 16 hours of photoexcitation. On the other hand, Fig. 2b plots the optical transmission spectra of 6 nm TiO 2 samples in the same spectral range at the same time intervals under the same UV radiation conditions. In this experiment, we observe that the decontamination process of the 6 nm nanoparticles does n...

We develop optically efficient photocatalytic ZnO nanoparticles that we chemically embed and well disperse into host PVAc thin films and experimentally demonstrate the highest optical efficiency of-70%O in ZnO nanoparticle films, with increasing optical spectral efficiency as the excitation wavelength is swept from 370 nm to 290 nm. ©2007 Optical Society of America OCIS codes: Nanophotonics, (160.4670) Optical materials, (160.4760) Optical properties Nanostructured metal-oxide semiconductors find interesting applications in nanophotonics [1-5]. They exhibit peculiar optoelectronic and photocatalytic properties that make them attractive, for example, for optical decontamination of surfaces, air, and water. For such environmental purposes, we develop photocatalytic ZnO nanoparticles integrated in resin and study their optical spectral efficiency between 290 nm and 370 nm. We experimentally achieve very high optical efficiencies up to 700o in ZnO nanoparticle