Shandong University

About: Shandong University is a education organization based out in Jinan, Shandong, China. It is known for research contribution in the topics: Laser & Cancer. The organization has 99070 authors who have published 99160 publications receiving 1625094 citations. The organization is also known as: Shāndōng Dàxué.

Ag@AgCl: A Highly Efficient and Stable Photocatalyst Active under Visible Light

Abstract: Nanoparticles (NPs) of noble metals can strongly absorb visible light because of their plasmon resonance, which is greatly influenced by their morphology and size. The phenomenon of plasmon resonance gives rise to important applications such as colorimetric sensors, photovoltaic devices, photochromic devices, and photocatalysts. Noble metal NPs exhibit characteristic optical and physical properties that are substantially different from those of the corresponding bulk materials. In particular, silver NPs show efficient plasmon resonance in the visible region, which Awazu et al. recently utilized to develop a plasmonic photocatalyst. In their study, TiO2 was deposited on NPs consisting of a silver core covered with a silica (SiO2) shell to prevent oxidation of Ag by direct contact with TiO2. Under UV illumination, this plasmonic photocatalyst exhibits enhanced catalytic activity, which increases with decreasing thickness of the SiO2 shell. To enhance the activity of a plasmonic photocatalyst, it is desirable to deposit silver NPs directly onto the surface of an active dielectric substrate without a protective shell, because the near-field effect of the NPs will be more strongly felt by the substrate. Herein we show that such a photocatalyst can be obtained from silver chloride by exploiting its photosensitivity, and the resulting plasmonic photocatalyst is highly efficient and stable under visible-light illumination. Silver halides are photosensitive materials extensively used as source materials in photographic films. On absorbing a photon, a silver halide particle generates an electron and a hole, and subsequently the photogenerated electron combines with an Ag ion to form an Ag atom. Ultimately, a cluster of silver atoms is formed within a silver halide particle upon repeated absorption of photons. Due to this instability under sunlight, which provides the very basis for chemical photography, silver halides are seldom used as photocatalysts. Nevertheless, there have been reports that under UV/Vis illumination AgCl deposited on a conducting support photocatalyzes O2 production from water in the presence of a small excess of silver ions in solution, and that under UV illumination AgBr dispersed on a silica support photocatalyzes H2 production from CH3OH/H2O solution. [21] In their study on the AgBr/SiO2 photocatalyst, Kakuta et al. [21] observed that Ag species are formed on AgBr in the early stage of the reaction, and AgBr is not destroyed under successive UV illumination. As suggested by Kakuta et al., electron–hole separation may occur smoothly in the presence of Ag species, and the latter may catalyze H2 production from alcohol radicals formed by photo-induced holes. If so, silver NPs formed on silver halide particles might be expected to be a stable photocatalyst under visible-light illumination due to their plasmon resonance. This expectation led us to prepare a new photocatalyst active and stable under visible light, namely, AgCl particles with silver NPs formed on their surface, by first treating Ag2MoO4 with HCl to form AgCl powder and then reducing some Ag ions in the surface region of the AgCl particles to Ag species (for details, see the Experimental Section). For convenience, these are referred to as Ag@AgCl particles. The X-ray diffraction (XRD) pattern of the Ag@AgCl product clearly shows that the cubic phase of Ag with lattice constant a= 4.0861 A (JCPDS file: 65-2871) coexists with the cubic phase of AgCl with lattice constant a= 5.5491 A (JCPDS file: 31-1238; see Figure 1). Scanning electron microscopy (SEM) images of the Ag@AgCl product (Figure 2) reveal that silver NPs with diameters in the range of 20–150 nm are deposited on the surface of AgCl particles with diameters in the range of 0.2–1.3 mm. The UV/Vis diffuse-reflectance spectra of Ag@AgCl, AgCl, and N-doped TiO2 (used as reference photocatalyst) are compared in Figure 3. In contrast to AgCl and N-doped TiO2, Ag@AgCl has a strong adsorption in the visible region which is almost as strong as that in the UV region. This is attributed to the plasmon resonance of silver NPs deposited on AgCl particles. To evaluate the photooxidation capability of Ag@AgCl, we examined the decomposition of methylic orange (MO) dye in solution over the Ag@AgCl sample under visible-light irradiation as a function of time (Figure 4). For comparison, we also carried out decomposition of the MO dye in solution over the N-doped TiO2 reference photocatalyst under visible[*] P. Wang, Prof. Dr. B. Huang, X. Qin, Prof. X. Zhang, Dr. J. Wei State Key Lab of Crystal Materials Shandong University, Jinan 250100 (China) E-mail: bbhuang@sdu.edu.cn Homepage: http://www.icm.sdu.edu.cn/index.php

Fruit and vegetable consumption and mortality from all causes, cardiovascular disease, and cancer: systematic review and dose-response meta-analysis of prospective cohort studies

Abstract: Objective To examine and quantify the potential dose-response relation between fruit and vegetable consumption and risk of all cause, cardiovascular, and cancer mortality. Data sources Medline, Embase, and the Cochrane library searched up to 30 August 2013 without language restrictions. Reference lists of retrieved articles. Study selection Prospective cohort studies that reported risk estimates for all cause, cardiovascular, and cancer mortality by levels of fruit and vegetable consumption. Data synthesis Random effects models were used to calculate pooled hazard ratios and 95% confidence intervals and to incorporate variation between studies. The linear and non-linear dose-response relations were evaluated with data from categories of fruit and vegetable consumption in each study. Results Sixteen prospective cohort studies were eligible in this meta-analysis. During follow-up periods ranging from 4.6 to 26 years there were 56 423 deaths (11 512 from cardiovascular disease and 16 817 from cancer) among 833 234 participants. Higher consumption of fruit and vegetables was significantly associated with a lower risk of all cause mortality. Pooled hazard ratios of all cause mortality were 0.95 (95% confidence interval 0.92 to 0.98) for an increment of one serving a day of fruit and vegetables (P=0.001), 0.94 (0.90 to 0.98) for fruit (P=0.002), and 0.95 (0.92 to 0.99) for vegetables (P=0.006). There was a threshold around five servings of fruit and vegetables a day, after which the risk of all cause mortality did not reduce further. A significant inverse association was observed for cardiovascular mortality (hazard ratio for each additional serving a day of fruit and vegetables 0.96, 95% confidence interval 0.92 to 0.99), while higher consumption of fruit and vegetables was not appreciably associated with risk of cancer mortality. Conclusions This meta-analysis provides further evidence that a higher consumption of fruit and vegetables is associated with a lower risk of all cause mortality, particularly cardiovascular mortality.