Guozhu Chen

Institut national de la recherche scientifique, Québec, Quebec, Canada

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Publications (25)71.93 Total impact

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    ABSTRACT: Nano-heterostructures have attracted great attention due to their extraordinary properties beyond those of their single-component counterparts. This review focuses on a specific type of hybrid structures: core-shell structures. In particular, we present and discuss the recent wet-chemical synthesis approaches for semiconductor and metallic core-shell nanostructures, and their relevant properties and potential applications in photovoltaics and catalysis, respectively.
    Chemistry - A European Journal 07/2014; · 5.93 Impact Factor
  • ChemInform 07/2014; 45(26).
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    ABSTRACT: The catalytic properties of ruthenium (Ru) are fairly well known. Nevertheless its shape-controlled synthesis (especially as compared to other noble metals) is still elusive. In this review, we present recent advances in the synthesis of Ru nanomaterials, in particular, spherical nanoparticles, one dimensional nanostructures, nanoplates and hollow structures, as well as other examples. In addition, the catalytic applications of Ru materials are selectively surveyed. Finally, the challenges and perspectives on the controlled synthesis of Ru-based nanomaterials and their catalytic applications are described.
    New Journal of Chemistry 04/2014; 38(5). · 3.16 Impact Factor
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    ABSTRACT: To enhance the catalytic activity of gold nanoparticles (AuNPs) for the hydrogenation of nitro-aromatic chemicals, Pt was introduced into AuNPs to form "bare" PtAu alloy NPs using a physical approach, pulsed laser ablation in liquid (PLAL), on single metal-mixture targets. These PLAL-NPs are deemed to favor catalysis due to the absence of any surfactant molecules on their unique "bare and clean" surface. The PLAL-NPs were facilely assembled onto CeO2 nanotubes (NTs) by simply mixing them without conducting any surface functionalization, representing another advantage of these NPs. Their catalytic activity was assessed in 4-nitrophenol (4-NP) hydrogenation. The reaction catalyzed by alloy-NP/CeO2-NT catalysts demonstrates a remarkably higher reaction rate in comparison with that catalyzed by pure Au and Pt NPs, and other similar Au and Pt containing catalysts reported recently. A "volcano-like" catalytic activity dependence of the alloy NPs on their chemical composition suggests a strong synergistic effect between Au and Pt in the 4-NP reduction, far beyond the simple sum of their individual contributions. It leads to the significantly enhanced catalytic activity of Pt30Au70 and Pt50Au50 alloy NPs, outperforming not only each single constituent, but also their physical mixtures and most recently reported AuNP based nanocatalysts. The favorable d-band center shift of Pt after alloying, and co-operative actions between Pt clusters and nearby Au (or mixed PtAu) sites were proposed as possible mechanisms to explain such a strong synergistic effect on catalysis.
    Nanoscale 11/2013; · 6.73 Impact Factor
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    ABSTRACT: The luminescence switching behavior of CePO4:Tb has been widely studied upon an interfacial oxidation–reduction reaction where KMnO4 and ascorbic acid act as an oxidant and a reductant, respectively. However, the transformation of Mn-involved species derived from KMnO4 during the oxidation–reduction cycle and their effect on the luminescence properties of CePO4:Tb have not been explored so far. Here, we further study this interfacial reaction between CePO4:Tb and KMnO4 through various characterization techniques, such as X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy. We find that an amorphous manganese oxide layer forms on the CePO4:Tb surface along with the partial oxidation of Ce(III) upon addition of KMnO4. In the subsequent reduction, the ascorbic acid not only reduces Ce(IV) to Ce(III) but also dissolves the formed manganese oxide. If manganese oxide is kept on the CePO4:Tb surface during the reduction treatment, the photoluminescence of Tb(III), due to the energy transfer from Ce(III) to Tb(III), would be restrained even if Ce(IV) ions were efficiently reduced. Although the degree of surface oxidation/reduction (Ce(III)/Ce(IV)) was considered to be a key factor for the luminescence quenching/recovery behavior in previous studies, there is a strong indication that the reaction product, e.g. manganese oxide, and associated surface defects generated from the oxidation–reduction reaction can disturb the photoluminescence of Tb(III) when they are not removed.
    The Journal of Physical Chemistry C. 05/2013; 117(19):10031–10038.
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    ABSTRACT: Fluorescent semiconductor quantum dots (QDs) and magnetic nanoparticles are recognized as the most promising nanomaterials for applications in biology and biomedicine. Fluorescent QDs are attracting increased interest mainly as fluorescent platforms that carry multiple diagnostic probes, providing both structural and metabolic information from diseased sites and thus leading to significantly improved imaging for the detection of a variety of human cancers or other diseased states. Magnetic nanoparticles can serve both as magnetic resonance imaging (MRI) agents for the diagnosis of cancers and as vehicles for carrying therapeutic payloads (anticancer drugs, siRNA, etc.) and efficiently delivering them to cancer sites in a target-specific manner. The further combination of QDs and magnetic nanoparticles into a single nanoarchitecture will undoubtedly lead to a new range of potential applications in biological systems. With both fluorescence and superparamagnetic features, these multifunctional nanoparticles can act as multi-dimensional tools in biological applications and are promising to be used in cell sorting, separation, tracking, imaging and drug delivery, which in principle can be easily controlled using magnetic force and monitored with a fluorescent microscope. This review mainly introduces recent developments on the synthesis and surface modification of these fluorescent-magnetic multifunctional nanoparticles, and their potential applications in fluorescence imaging, MRI and drug delivery.
    Reviews in Nanoscience and Nanotechnology. 01/2013; 2(5).
  • Fenfen Zhu, Guozhu Chen, Sixiu Sun, Xuan Sun
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    ABSTRACT: Core–shell (CS) nanoparticles (NPs) have many applications in areas such as catalysis and sensing. The utilization of hollow nanostructured materials as the supports, such as nanotubes (NT), is a growing interest to anchor NPs. Generally, several steps are necessary to prepare CS NP–NT nanocomposites, including: (i) the synthesis of CS NPs; (ii) the preparation of NTs; and (iii) the combination of CS NPs and NTs. Moreover, surface modifications with organic ligands are often involved during the synthesis of CS NPs and/or the step combining CS NPs and supports. Here we report a facile method for in situ growth of Au@CeO2 CS NPs and CeO2 NTs by mixing HAuCl4 and Ce(OH)CO3 nanorods under mild conditions. The formation of Au–CeO2 nanocomposite is due to the interfacial oxidation–reduction reaction between HAuCl4 and Ce(OH)CO3, where Au(III) in HAuCl4 is reduced to Au(0) by Ce(III) in Ce(OH)CO3, while Ce(III) is oxidized into Ce(IV), followed by hydrolysis to generate CeO2. The slow hydrolysis rate of Ce(IV) leads to the coverage of CeO2 on the Au NPs, and on the residual Ce(OH)CO3 surface, developing into Au@CeO2 and Ce(OH)CO3@CeO2 CS structures. Further depletion/dissolution of Ce(OH)CO3 results in Au@CeO2 CS NP–CeO2 NT nanocomposite eventually. The advantages of our synthetic strategy are independent of foreign reducing agents and additional surface modification. And, such CS NP–NT nanocomposite can be obtained in one step, simplifying the synthesis procedures greatly. This method based on interfacial oxidation–reduction may be employed as a unique entry to other nanocomposites.
    J. Mater. Chem. A. 12/2012; 1(2):288-294.
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    ABSTRACT: Ligand-free Ru nanoclusters supported on carbon black have been synthesized in situ for the first time from the reduction of RuCl3 by ammonia-borane concomitantly with its hydrolysis process at room temperature, and their catalytic activity has been investigated. Well dispersed Ru nanoclusters (∼1.7 nm) are stabilized and immobilized by carbon black. Due to the small size and the absence of ligands on the surface, the Ru catalysts exhibit high catalytic activity, which is partly retained after 5 reaction cycles. A kinetic study shows that the catalytic hydrolysis of ammonia-borane is first order with respect to Ru catalyst concentration; the turnover frequency is 429.5 mol H2 min−1 mol−1 Ru. The activation energy for the hydrolysis of ammonia-borane in the presence of Ru/C catalysts has been measured to be 34.81 ± 0.12 kJ mol−1, which is smaller than most of the values reported for other catalysts, including those based on Ru, for the same reaction.
    International Journal of Hydrogen Energy 12/2012; 37(23):17921–17927. · 3.55 Impact Factor
  • Guozhu Chen, Federico Rosei, Dongling Ma
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    ABSTRACT: Interfacial oxidation–reduction reaction is herein developed to prepare hollow binary oxide nanostructures. Ce–Mn nanotubes are fabricated by treating Ce(OH)CO3 templates with KMnO4 aqueous solution, where MnO4− is reduced to manganese oxide and the Ce3+ in Ce(OH)CO3 is simultaneously oxidized to form cerium oxide, followed by selective wash with HNO3. The resulting Ce–Mn binary oxide nanotubes exhibit high catalytic activity towards CO oxidation and show significant adsorption capacity of Congo red. Moreover, guided by the same interfacial-reaction principle, binary oxide hollow nanostructures with different shapes and compositions are synthesized. Specifically, hollow Ce–Mn binary oxide cubes, and Co-Mn and Ce-Fe binary oxide hollow nanostructures are achieved by changing the shape of the Ce(OH)CO3 templates from rods to cubes, by changing the tempates from Ce(OH)CO3 nanorods to Co(CO3)0.35Cl0.20(OH)1.10 nanowires, and by replacing the oxidant of KMnO4 with another strong one, K2FeO4, respectively. This work is expected to open a new, simple avenue for the general synthesis of hollow binary oxide nanostructures.
    Advanced Functional Materials 09/2012; 22(18). · 10.44 Impact Factor
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    ABSTRACT: Hollow Ru nanoparticles with ~14 nm diameter and ~2 nm shell thickness are reported for the first time, by removal of Ni from the delicately designed Ni@Ru core@shell NPs. Such hollow Ru NPs exhibit enhanced catalytic activity in the dehydrogenation of ammonia borane with respect to solid ones.
    Chemical Communications 07/2012; 48(64):8009-11. · 6.38 Impact Factor
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    ABSTRACT: We report the synthesis and characterization of new Ni(x)Ru(1-x) (x = 0.56-0.74) alloy nanoparticles (NPs) and their catalytic activity for hydrogen release in the ammonia borane hydrolysis process. The alloy NPs were obtained by wet-chemistry method using a rapid lithium triethylborohydride reduction of Ni(2+) and Ru(3+) precursors in oleylamine. The nature of each alloy sample was fully characterized by TEM, XRD, energy dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS). We found that the as-prepared Ni-Ru alloy NPs exhibited exceptional catalytic activity for the ammonia borane hydrolysis reaction for hydrogen release. All Ni-Ru alloy NPs, and in particular the Ni(0.74)Ru(0.26) sample, outperform the activity of similar size monometallic Ni and Ru NPs, and even of Ni@Ru core-shell NPs. The hydrolysis activation energy for the Ni(0.74)Ru(0.26) alloy catalyst was measured to be approximately 37 kJ mol(-1). This value is considerably lower than the values measured for monometallic Ni (≈70 kJ mol(-1)) and Ru NPs (≈49 kJ mol(-1)), and for Ni@Ru (≈44 kJ mol(-1)), and is also lower than the values of most noble-metal-containing bimetallic NPs reported in the literature. Thus, a remarkable improvement of catalytic activity of Ru in the dehydrogenation of ammonia borane was obtained by alloying Ru with a Ni, which is a relatively cheap metal.
    Chemistry - A European Journal 04/2012; 18(25):7925-30. · 5.93 Impact Factor
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    ABSTRACT: Core-shell structured Ni@Ru bimetallic nanoparticles are demonstrated as a bifunctional nanoplatform system for the hydrolysis reaction of ammonia-borane and also for magnetic separation.
    Chemical Communications 06/2011; 47(22):6308-10. · 6.38 Impact Factor
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    ABSTRACT: Ceria hollow nanocrystals with single-crystalline-like structure were prepared facilely by solvothermal synthesis free from templates, in which CeCl3 was proposed to hydrolyze with the assistance of poly(vinylpyrrolidone) (PVP) in the water–ethanol mixed solvent. TEM and SEM analyses demonstrated the formation of CeO2 hollow nanocrystals ascribed to a dissolution–recrystallization mechanism. It was found that both the counter ions of the cerium sources (e.g. CeCl3, Ce(NO3)3 or (NH4)2Ce(NO3)6) and the composition of the solvent mixture were critical factors in determining the final morphology of CeO2. The as-prepared CeO2 hollow nanocrystals with high crystallinity exhibited a higher catalytic activity and thermal stability towards COoxidation.
    CrystEngComm 04/2011; 13(8):2904-2908. · 3.88 Impact Factor
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    ABSTRACT: Hollow Cu2O nanocubes have been fabricated under solvothermal condition using N,N -dimethylformamide (DMF) as solvent at 120 °C for 12 h. The products were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray powder diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). Series of experiment confirmed that the amount of water, the reaction time and temperature played important roles in the morphology evolution of hollow Cu2O nanocubes. DMF is a relatively weak alkali solvent and could release a certain amount of OH– under the given conditions. As the release speed of OH– from DMF became substantially slow, the nucleation and growth of Cu2O nanocubes turned into kinetically controlled process. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
    Crystal Research and Technology 07/2009; 44(7). · 1.12 Impact Factor
  • Wei Zhao, Xinyu Song, Guozhu Chen, Sixiu Sun
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    ABSTRACT: ZnWO4 hollow clusters made up of nanorods were successfully prepared through a tripotassium citrate assisted hydrothermal process at 180 °C. The hollow clusters’ diameter was about 400 nm, and these clusters were made up of nanorods with a diameter of about 10 nm and a length of about 50 nm. X-ray power diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) were used to characterize the structure and morphology of the synthesized products. Based on experiments, the growth of these hollow clusters followed an aggregation-Ostwald ripening process. The photocatalytic activities for aqueous Rhodamine B of samples were investigated, and it was seen that ZnWO4 hollow clusters exhibited a strong photocatalytic activity.
    Journal of Materials Science 06/2009; 44(12):3082-3087. · 2.31 Impact Factor
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    ABSTRACT: In this paper, CeO(2) nanotubes based on the Kirkendall effect (for simplicity, this type of nanotubes is denoted as K-type CeO(2) nanotubes) are fabricated through a solid-liquid interface reaction between Ce(OH)CO(3) nanorods and NaOH solutions. Our studies indicate the formation mechanism of K-type CeO(2) nanotubes is quite different from those of CeO(2) nanotubes subjected to template (T-type CeO(2) nanotubes) and lamellar rolling (L-type CeO(2) nanotubes) reported previously by our group. The K-type CeO(2) nanotubes are prepared by congregating Kirkendall voids and subsequent calcinations. The time evolution processes are imaged by TEM, and the results show that as the reaction processes, interior spaces are formed and enlarged in Ce(OH)CO(3) nanorods to form K-type CeO(2) nanotubes. In contrast, the interior space in T-type CeO(2) nanotubes decreases with reaction time. XRD is applied to study the phase transformation in the formation process of K-type CeO(2) nanotubes. Our study also indicates NaOH and reaction temperature are two key factors responsible for formation of K-type CeO(2) nanotubes. Combined with the T- and L-type nanotubes, three types of CeO(2) nanotubes with different formation mechanisms are successfully synthesized in one reaction system, which might afford some guidance for the synthesis of other inorganic nanotubes.
    Inorganic Chemistry 02/2009; 48(4):1334-8. · 4.59 Impact Factor
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    ABSTRACT: In this work, hierarchical PbWO4 spheres assembled by nanorods were successfully synthesized through a tri-potassium citrate assisted hydrothermal process. The samples were studied by powder X-ray diffraction pattern (XRD), field scanning electron microscopy (SEM), and transmission electron microscopy (TEM). It was found that citrate played a key role on the morphology of PbWO4 products. By adjusting concentration of citrate, PbWO4 octahedrons, hierarchical spheres, hierarchical ellipses could be obtained. Based on time-dependent experiments, we found the growth of the hierarchical spheres followed a self-assembly process. The most interesting part was that the hierarchical spheres/ellipses showed a blue emission peak at 440 nm, which differs from the typical green one at 500 nm as reported.
    Materials Letters - MATER LETT. 01/2009; 63(2):285-288.
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    ABSTRACT: A facile, template-free method is reported to prepare Cu2O/Au core–shell nanospheres in aqueous medium at room temperature. In this synthesis, Cu2O nanospheres with definite diameter were first synthesized via the reduction reaction between Cu(NO3)2 and hydrazine (N2H4). Then, the as-prepared Cu2O nanospheres were employed as nucleation centers for deposition of Au shell, resulting in the formation of core–shell nanospheres. The samples obtained at various stages after the addition of the HAuCl4 were studied by TEM observation. These TEM images revealed that the formation hollow interior space between the core and the shell. In addition, UV–vis spectra results indicated that the optical property of the Cu2O/Au core–shell nanospheres was influenced by the size of the hollow interior spaces between the cores and the shells.
    Journal of Crystal Growth 01/2009; 311(9):2742-2745. · 1.55 Impact Factor
  • Wei Zhao, Xinyu Song, Guozhu Chen, Sixiu Sun
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    ABSTRACT: Two kinds of hollow twinning ZnO microstructures were synthesized through a simple hydrothermal method without additional templates or any surfactants. Dumbbell-like and shuttle-like ZnO microstructures with hollows were obtained by changing the materials source. The products were characterized by X-ray power diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). It was found that different precursors may be responsible for the formation of two different morphologies. Based on the time-dependent experiments, we investigated the growth process of these hollow twinning structures and found the “Ostwald-ripening process” played an important role. The interesting point of this growth process was that the interface of the two twinning structure performed as the activate center where the Ostwald-ripening process carried out. We also investigated the luminescent properties of the as-obtained products by photoluminescence (PL) spectroscopy. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
    Crystal Research and Technology 01/2009; 44(4):373-378. · 1.12 Impact Factor
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    ABSTRACT: CeO(2) nanotubes have been synthesized with a simple solid-liquid interface reaction route in the absence of any surfactants. Although the basic reaction principles are similar, two kinds of nanotubes with completely different morphologies and structures can be generated by slightly tuning the postprocessing conditions. The first formation involves employing Ce(OH)CO(3) nanorods as both the physical and chemical templates, and the other requires layered Ce(OH)3 as an anisotropic intermediate species. During this process, NaOH and reaction temperature were demonstrated as the key factors responsible for the formation of Ce(OH)(3) intermediate and final CeO(2) nanotubes with well-defined structures. The structural details were provided by a combination of XRD, SEM, TEM, and HRTEM investigations. Catalytic measurement shows that both nanotubes are very active for CO oxidation, and at 250 degrees C, the conversion rates of CeO(2) nanotubes are 3 times higher than that of the bulk counterpart.
    Inorganic Chemistry 02/2008; 47(2):723-8. · 4.59 Impact Factor