Chan Zheng

Graphene oxide–noble metal (Au, Pt, and Pd) nanoparticle composites as optical limiters

A series of graphene oxide (GO)/noble metal (Au, Pt, and Pd) nanoparticle (NP) composites were synthesized via a one-step hydrothermal reaction of HAuCl4, H2PtCl6, and Pd(C2H3O2)2 in the presence of GO. The metal NPs with different average sizes and distributions were uniformly deposited onto the GO surface. The GO structure was conserved after loading with Au, Pt, and Pd NPs. The corresponding nonlinear optical (NLO) and optical limiting (OL) properties were investigated using an open-aperture Z-scan technique with nanosecond pulses at 532 nm. The results show that the NLO and OL properties were significantly enhanced after the inclusion of metal NPs on the GO surface because of nonlinear scattering (NLS) effects. These enhancements depend on the type of loading metal NPs. The GO/Au-NP composite exhibits the optimal NLO and OL performances among the studied composites because of the surface plasmon resonance of the Au NPs. Thus, the NLO and OL effects of the two-dimensional GO can be effectively modified by absorbing different metal NPs on its surface. The synthetic NLO and OL properties in the GO/metal NP composites originate from the reverse saturable absorption in the GO sheets and the NLS in metal NPs. All of the results indicate that these composites can be used in optoelectronic applications.

Selective heterogeneous nucleation of gold nanoparticles on one-dimensional cadmium silicate for enhanced nonlinear optical responses

A facile route to uniformly assemble Au nanoparticles (NPs) on the surface of cadmium metasilicate (CdSiO3) nanowires (NWs) via a heterogeneous nucleation process was demonstrated. Transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and UV-visible spectroscopy were performed to investigate the morphology, structure, and linear optical properties of the Au NPs/CdSiO3 NWs hybrid nanostructure. The results revealed that uniform decoration of the Au NPs on the surface of CdSiO3 NWs could be achieved by heterogeneous nucleation. Compared with the infrared bands of the CdSiO3 NWs, weaker characteristic infrared bands were observed upon assembly of the Au NPs on the CdSiO3 NWs due to an electron intraband transfer process in the 6sp band of the Au species. Additionally, the hybrid nanostructure displayed a red-shifted, relatively broader, and weaker surface plasmon resonance band compared with the Au NPs. These changes in the spectral bands could be attributed to the interparticle inter actions absorbed on the surface of the CdSiO3 NWs. The nonlinear optical (NLO) properties of Au NPs/CdSiO3 NWs were characterized using an open-aperture Z-scan technique with 4 ns laser pulses at 532 nm. The Au NPs/CdSiO3 NWs hybrid nanostructure displayed superior NLO responses than a suspension of carbon nanotubes, a benchmark optical limiter. Furthermore, the CdSiO3 NWs noncovalently functionalized with Au NPs offered superior performance over individual CdSiO3 NWs. The enhancement in NLO properties was mainly attributed to the combination of nonlinear scattering and nonlinear absorption induced by surface plasmon resonance effects by the Au NPs.

Fabrication of Silver Shells onto Silica Sphere for Infrared Emissivity

SiO2/Ag core-shell composite microspheres were synthesized by silver-seeding method in this paper. In the process, silver nanoparticles as seeds were deposited by repeating the cycle times for further formation of Ag shell. The effects of reaction power and time on the seeding of silica surfaces and the effect of silver ion on the growth of silver shells were investigated. Structures and properties were measured with TEM, UV, FT-IR and Infrared emissometer. The results showed the Ag nanoparticles on the silica surfaces were uniform in size. And the number density was increased growing with the increase of deposition. It was found that the composite exhibited a lower infrared emissivity value in the wavelength range from 8 to 14 μm than that of pure silica as a result of strong reflection of silver metal.

Nonlinear Absorption Properties of Spherical Gold Colloidal Nanoparticles

Spherical gold colloidal nanoparticles were prepared used traditional liquid phase method and the corresponding nonlinear absorption properties were investigated by open aperture Z-scan technique using 8 ns laser pulses of 532 nm. The gold colloidal nanoparticles exhibited a transform from saturable absorption (SA) to reverse saturable absorption (RSA) at relatively higher irradiation intensities. The SA behavior presumably owes to the bleach of ground-state surface plasmon resonance (SPR) absorption, while the RSA might result from high excited-stated free carrier absorption.

Facile control of metal nanoparticles from isolated nanoparticles to aggregated clusters on two-dimensional graphene to form optical limiters

The aggregation state of Pt and Ni metal nanoparticles (NPs) can be easily controlled from isolated individual NPs to aggregated clusters on two-dimensional reduced graphene oxide (rGO) by one-step chemical reduction. Formation of Pt–Ni NP/rGO and Pt–Ni cluster/rGO depends on the introduction of poly-(vinyl pyrrolidone). In the Pt–Ni cluster/rGO nanohybrid, Pt NPs are encapsulated by Ni NPs to form Pt–Ni clusters on rGO, which significantly changes the surface chemical state of the Pt NPs. The corresponding nonlinear optical (NLO) and optical limiting (OL) properties were investigated by the open-aperture Z-scan technique with nanosecond pulses at 532 nm. The results show that the Pt–Ni cluster/rGO hybrid has stronger NLO and OL effects than the Pt–Ni NP/rGO hybrid in both liquid and solid matrices. The main contributors to the NLO and OL effects in the Pt–Ni/rGO nanohybrids in both the liquid- and solid-state matrices are a combination of nonlinear absorption and nonlinear scattering, although the mechanism in nonlinear scattering is completely different. Transfer of electrons from Pt to Ni owing to the difference in their electronegativities contributes to the enhanced NLO and OL responses in the Pt–Ni cluster/rGO both in suspension and in a gel glass composite. Thus, the NLO and OL responses of two-dimensional GO can be effectively modified by altering the aggregation state of the metal NPs on its surface. This strategy could be easily extended to tailor the optoelectronic properties of graphene-based composites.

Effect of Thermal Treatment on the Texture and Structure of Sol-Gel Derived Carbon Nanotube/Silica Composites

The present work studies the structural and textural evolution of sol-gel derived carbon nanotube(CNT)/silica composites during the process of thermal treatment. The composites were prepared by sol-gel technique, and their structural and textural changes were traced by scanning electron microscopy, Raman spectra, infrared spectra, and thermogravimetric analysis. The results show that doped CNTs have an impact on the structural and textural evolution of CNT/silica composites during the process of thermal treatment and the CNT/silica composites exhibit good thermal stability during the heat treatment process. However, the composites are not densified even after treatment at 1000°C, quite different from the thermal behaviors of pure silica xerogel, due to the existing of guest CNTs.