Synthesis and photocatalytic activity of hexagonal phase NaYF₄:Ho³⁺@TiO₂core–shell microcrystals

Abstract

A β-NaYF 4 :Ho 3+ @TiO 2 core-shell microcrystal photocatalyst was synthesized using a hydrothermal method followed by hydrolysis of tetra-n-butyl titanate (TBOT), with polyvinylpyrrolidone K-30 (PVP) as the coupling agent. X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, fluorescence and Raman spectrometry, ultraviolet-visible diffuse reflectance spectroscopy, and electron spin resonance were used to characterize the photocatalyst. It was found that the core's hexagonal phase NaYF 4 :Ho 3+ microcrystals were evenly coated by a TiO 2 shell and that the average β-NaYF 4 :Ho 3+ microcrystal length was roughly 9 μm with a diameter of about 3.8 μm. After doping which caused a slight increase, the average thickness of the TiO 2 shells was about 50 nm. Because Ho 3+ -single-doped β-NaYF 4 :Ho 3+ @TiO 2 displays strong visible absorption peaks at 450, 537, and 642 nm, we chose 450, 532, and 633 nm to be the excitation wavelengths. We found ultraviolet emission bands at 290 nm ( 5 D 4 → 5 I 8 ) and 389 nm ( 3 K 7 / 5 G 4 → 5 I 8 ). Also, the energy transfer from β-NaYF 4 :Ho 3+ to anatase TiO 2 was confirmed. Rhodamine B (RhB) was used as a model pollutant to investigate the photocatalytic activity of β-NaYF 4 :Ho 3+ @TiO 2 microcrystals under Xe lamp (500 W) irradiation. This investigation showed an advanced visible-light-driven catalyst, with about 67% of the RhB decomposed after 10 h. Compared with the blank experiment, the efficiency was obviously improved. Recycling experiments showed that the β-NaYF 4 :Ho 3+ @TiO 2 composite still presented significant photocatalytic activity after four successive cycles. Finally, we investigated the β-NaYF 4 :Ho 3+ upconversion (UC) mechanism and the β-NaYF 4 :Ho 3+ @TiO 2 core-shell microcrystal visible-light-responsive photocatalytic mechanism. Understanding the visible-light-responsive photocatalytic mechanism will help to improve the structural design and functionality of this new type of catalytic material.

Synthesis of Reduced Grapheme Oxide as A Platform for loading β-NaYF4:Ho3+@TiO2Based on An Advanced Visible Light-Driven Photocatalyst

“…The NaYF 4 :Ho 3+ @TiO 2 core-shell microcrystals were synthesized by referring preliminary work 35 . UV-irradiation of theNaYF 4 :Ho 3+ @TiO 2 -graphene oxide samples was performed using a hydrothermal method.…”

“…Its UC efficiency is limited by NIR radiation source excitation, which is mainly due to its extremely weak absorption in the NIR wavelength range 34 . We conducted researches on core-shell microcrystal of β-NaYF 4 :Ho 3+ @TiO 2 and on the use of Vis as a photocatalyst 35 . This combination takes advantages of Vis and NIR which accounts for ca.…”

The Synthesis of a Core-Shell Photocatalyst Material YF3:Ho3+@TiO2 and Investigation of Its Photocatalytic Properties

“…YF 3 :Ho 3+ @TiO 2 photocatalysis mechanism for RhB degradation (the insets show the transition of Ho 3+ ) Ps: [1] Xu, X. et al Synthesis and intense ultraviolet to visible upconversion luminescence of YF 3 :Ho 3+ nanoparticles. GSA: ground state absorption; ESA: excitation state absorption; UV: ultraviolet; VB: valence band; CB: conduction band.…”

“…It is even worse that most of these contaminants are complex and non-biodegradable, and therefore traditional water treatment methods cannot completely remove them. In recent years, photocatalysis has gained increasing attention due to the discovery of water splitting on a semiconductor electrode [1,2,3,4]. Over the past 20 years, photocatalysis has become a research topic of interest because of its practical applications in air and water remediation, self-cleaning, and self-sterilizing surfaces [5,6].…”

Effect of pH of Precursor on Up/Downconversion and Cathodoluminescence of Gd2O3:Ho3+/Yb3+ Phosphor and Magneto‐Optic Studies

“…The surface composition of Gd 2 O 3 :Ho 3+ /Yb 3+ sample was evaluated using XPS . The XPS spectrum in survey mode has shown in Figure .…”