We report a facile and novel method for the fabrication of Cu2O@PNIPAM core-shell nanoreactors using Cu2O nanocubes as the core. The PNIPAM shell not only effectively protects the Cu2O nanocubes from oxidation, but also improves the colloidal stability of the system. The Cu2O@PNIPAM core-shell microgels can work efficiently as photocatalyst for the decomposition of methyl orange under visible light. A significant enhancement in the catalytic activity has been observed for the core-shell microgels compared with the pure Cu2O nanocubes. Most importantly, the photocatalytic activity of the Cu2O nanocubes can be further tuned by the thermosensitive PNIPAM shell, as rationalized by our recent theory. INTRODUCTIONCu2O is a well-known p-type semiconductor with direct band gap of 2.17 eV. It has a great potential for a wide range of applications, e.g. in solar energy conversion, lithium-ion batteries, gas sensors, photocatalytic degradation of dye molecules, propylene oxidation and photoactivated water splitting. The properties of the Cu2O nanoparticles are strongly dependent on their shape. Hence, there is a growing interest in the synthesis of Cu2O nanostructures with defined shape. [1][2][3][4][5][6] Thus, Cu2O nanocubes, octahedral, nanocages, spheres, nanowires and other highly symmetrical structures have already been reported. 7,8 A main drawback for further applications of Cu2O nanoparticles is that Cu2O is easily oxidized in water and the nanostructure of Cu2O can be destroyed depending on external conditions such as pH or visible light. For this reason, a simple and effective method providing protection of Cu2O-based nanostructures from oxidation is highly desirable. Parecchino et al. successfully improved the chemical stability of a Cu2O layer in water through atomic layer deposition of multiple protective layers of Al-doped zinc and titanium oxide.9,10 Wang's group reported that both CuO and carbon can be used to protect Cu2O films and nanofibers. 11,12 Notably, the aforementioned protection strategies have all been applied to extended one-and two-dimensional phases. However, little has been reported in the literature regarding the effective protection of Cu2O nanoparticles. In this regard, Yang et al. 13 and Su et al. 14 have successfully synthesizedCu2O@SiO2 core-shell nanoparticles, but unfortunately the SiO2 shell makes them aggregate more easily, preventing further study on their surface properties. Recently, shells of poly(N-isopropylacrylamide) (PNIPAM) core-shell microgels have been used to modify inorganic nanoparticles. 15,16 In this way, the nanoparticles encapsulated inside PNIPAM shells can be prevented from aggregation in aqueous solution. 17 For example, Zhao 18 and co-workers reported the fabrication of gold nanoparticles with a thin PNIPAM shell, proposed as a drug delivery system. Of great relevance for catalytic applications is also the fact that the catalytic properties of the embedded nanoparticles can be tuned by the swelling and deswelling of the PNIPAM microgels. [19][20][21][22] In th...
We report a facile method to synthesize anisotropic platelike gibbsite-polymer core-shell particles. Dopamine is self-polymerized on the surface of gibbsite nanoplates and forms a homogeneous layer on it. Transmission electron microscopy characterization of the resulting latexes demonstrates the formation of well-defined platelike core-shell particles. Reaction time and ultrasonification are found to be important factors to control the thickness of the polymer shell and avoid aggregation. Good control over the platelike morphology and 100% encapsulation efficiency have been achieved via this novel route. The resulting well-defined gibbsite-polydamine (G-PDA) core-shell nanoplates show excellent colloidal stability and can form opal-like columnar crystal with iridescent Bragg reflection after modest centrifugation. In addition, G-PDA core-shell nanoplates can serve both as reductant and stabilizer for the generation of Au nanoparticles (NPs) in situ. Au NPs with tunable size have been formed on the G-PDA particle surface, which show efficient catalytic activity for the reduction of 4-nitrophenol and Rhodamine B (RhB) in the presence of borohydride. Such nanocatalysts can be easily deposited on silicon substrate by spin-coating due to the large contact area of platelike G-PDA particles and the strong adhesive behavior of the PDA layer. The substrate-deposited nanocatalyst can be easily recycled which show excellent reusability for the reduction of RhB.
α-Cyclodextrin modified poly(N-vinylcaprolactam) microgels have been applied as “nanoreactors” for the generation of AuNPs with enhanced catalytic activity for the reduction of 4-nitrophenol.
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