Controllable Synthesis And Performance Study Of Metal Chalcogenide Nanocrystals With Different Phase Structures

According to current studies of phase-selective synthesis and the phase structure-dependent properties of metal chalcogenide nanocrystals(MC NCs),we have designed some simple solid-liquid phase chemical routes to controllably synthesize some different phase structure of MC NCs via different precursors,addition modes or reducing reagents.These MC NCs include Cu-based chalcogenide NCs(e.g.hexagonal phase CuSe,cubic phase Cu2-xSe and monoclinic phase Cu2Se),Zn-based chalcogenide NCs(hexagonal phase ZnSe,cubic phase ZnSe),Ge-based chalcogenide NCs(monoclinic phase GeSe2,orthorhombic GeSe).The compositions,surface states and microstructures of these MC NCs have been characterized by EDS,Mapping,XRD,XPS,UV,TG-DTA,FT-IR,FE-SEM,TEM and HRTEM.A series of control experiments have been conducted to investigate the growth mechanisms.Moreover,the properties of Surface-enhanced Raman scattering(SERS),electrogenerated chemiluminescence(ECL)and photoelectrochemical(PEC)were investigated.We have speculated the relationship between the phase structure and their corresponding properties,and achieved some interesting results.The details are shown below:(1)A simple and facile approach was developed to the fabrication of monoclinic Cu2Se and Cu2Se/Pd heterostructure.[(C2H5)4N]2[CuCl4]was employed as copper source and SeO2-terpineol as Se(-?)precursor,generating the hexagonal CuSe and cubic Cu2-xSe through the "hot injection" and "one pot method",respectively.Both CuSe and Cu2-xSe could transform into monoclinic Cu2Se via heat treatment using TOP at 220 ?.Further,the Cu2Se/Pd as well as CuSe/Pd and Cu2-xSe/Pd heterostructures was obtained easily by simple mixing copper selenides and Pd(NO3)2 in 2-propanol solution.Transmission electron microscopy and high-resolution transmission electron microscopy analysis displayed the Pd nanoparticles grew and distributed on the surface of copper selenides.The effect of certain reaction parameter on the formation of copper selenides was studied.It was found that the amounit of the used terpineol played an important role in phase-selective synthesis of CuSe and cubic Cu2-xSe.Using more amount of the terpineol was beneficial to the formation of Cu2-xSe even in the "hot injection" mode.Owing to the strong synergistic effects between the Cu2Se and Pd,Cu2Se/Pd shown the more excellent SERS performance than pure Pd and Cu2Se.Moreover,the Cu2Se/Pd heterostructure exhibited the best SERS sensitivity to 4-Mpy and a detection limit as low as 1.0×10-9 M compared with the other two copper selenides/Pd heterostructures,revealing the phase-dependent characteristic.This novel Cu2Se/Pd heterostructure would have potential applications in chemical and biological sensing fields.(2)The ZnSe NCs with different phase structure were prepared in the reaction system of ZnCl2,SeO2,borane-tert-butylamine complex(BTBC)using 1-octadecene as solvent.BTBC was employed as directing agent to modify the growth kinetics of nanocrystals and control the phase structure of products.It was found that the addition of BTBC would make cubic ZnSe transform into hexagonal ZnSe NCs.After surface functionalization with carboxylic groups,the amphiphilicity and biocompatibility of the two kinds of ZnSe NCs have been improved significantly.ECL tests revealed that the hexagonal ZnSe has a strong,stable and excellent reversibility,indicating it can be used as a potential ECL sensor for Cd2+ detection with a detection limit as low as 0.8 p.M.All the results showed that ZnSe would be used as a promising luminophore in the development of novel ECL biosensors for trace metal ion analysis due to the low cytotoxicity,low cost and excellent solubility.(3)3D germanium selenides,including monoclinic GeSe2,mixed-phase GeSe2-GeSe and orthorhombic GeSe,can be synthesized by the reactions of GeI4 with selenourea in the presence of BTBC and oleylamine(OLA)via "one pot method".to the best of our knowledge,this is the first time to realize the phase-controlled synthesis of 3D germanium selenides.Here OLA acted as the solvent,surfactant,and coreductant,and BTBC served as a reductant.For well understanding the optoelectronic properties of germanium selenides,their optical band structure was evaluated in tetrabutylammonium hexafluorophosphate(TBAPF6)dissolved in acetonitrile as supporting electrolyte.The PEC tests indicated that monoclinic GeSe2 exhibited a strong and stable photoresponse under 530 nm laser excitation compared with orthorhombic GeSe and mixed-phase GeSe2-GeSe.With good biocompatibility and low toxicity under the long wavelength laser excitation compared with CdSe and PbSe,GeSe2 shows excellent performance in PEC,and it can be used as a new kind of photoactive material in photoelectrochemical biosensors.