ABSTRACT
Combination of upconversion nanocrystals (UCNs) with CeO2 is a decent choice to construct NIR-activated photocatalysts for utilizing the NIR light in the solar spectrum. Herein we present a facile approach to deposit a CeO2 layer with controllable thickness on the plate-shaped NaYF4:Yb,Tm UCNs. The developed core-shell nanocomposites display obvious photocatalytic activity under the NIR light and exhibit enhanced activity under the full solar spectrum. For enhancing the separation of photogenerated electrons and holes on the CeO2 surface, we sequentially coat a ZnO shell on the nanocomposites so as to form a heterojunction structure for achieving a better activity. The developed hybrid photocatalysts have been characterized with TEM, SEM, PL, etc., and the working mechanism of such UCN-semiconductor heterojunction photocatalysts has been proposed.
ABSTRACT
ZnO is one of the most promising materials for both photocatalytic and antibacterial applications, but its wide bandgap requires the excitation of UV light which limits their applications under visible and NIR bands. Herein, we demonstrate a facile approach to synthesize core-shell-shell hybrid nanoparticles consisting of hexagonal NaYF4:Yb,Tm, amorphous SiO2 and wurtzite ZnO. The upconversion nanocrystals are used as the core seeds and sequentially coated with an insulting shell and a semiconductor layer. Such hybrid nanoparticles can efficiently utilize the NIR light through the upconverting process, and display notable photocatalytic performance and antibacterial activity under NIR irradiation. The developed NaYF4:Yb,Tm@SiO2@ZnO nanoparticles are characterized with TEM, XRD, EDS, XPS and PL spectra, and their working mechanism is also elucidated.
Subject(s)
Anti-Bacterial Agents/pharmacology , Coated Materials, Biocompatible/chemistry , Fluorides/chemistry , Luminescent Measurements , Nanoparticles/chemistry , Silicon Dioxide/chemistry , Spectroscopy, Near-Infrared , Yttrium/chemistry , Zinc Oxide/chemistry , Bacteria/drug effects , Catalysis/drug effects , Coated Materials, Biocompatible/pharmacology , Fluorides/pharmacology , Microbial Sensitivity Tests , Nanoparticles/ultrastructure , Reactive Oxygen Species/analysis , Silicon Dioxide/chemical synthesis , Spectrophotometry, Ultraviolet , Thulium/chemistry , X-Ray Diffraction , Yttrium/pharmacology , Zinc Oxide/chemical synthesisABSTRACT
High-quality hexagonal NaYF4:Yb,Tm upconversion nanocrystals (UCNs) prepared in organic solutions display uniform sizes and strong UC emissions, but they possess a hydrophobic surface which hinders combining them with various semiconductor nanocrystals (NCs) to form a hybrid NIR-activated photocatalyst. Herein we present a facile approach to modify hydrophobic UCNs with a uniform carbon layer and enable them with hydrophilicity and surface functionalization. The carbon shell provides a good substrate for enriching with metal ions and in situ generation of CdS nanoclusters on the particle surface which can utilize both the upconverted UV and visible emissions. The developed NaYF4:Yb,Tm@C@CdS nanoparticles are characterized with TEM, SEM, XRD, PL and UV-Vis spectra and their formation mechanism is elucidated. The products display good photocatalytic activity under visible light and obviously enhanced performance under Vis-NIR light, due to the efficient utilization of UC emissions and the strong adsorption capacity of the carbon shell. The working mechanism of the hybrid photocatalysts is also proposed.
