Preparation Of NaYF₄:Ho³⁺@TiO₂-rGO Ternary Photocatalyst And Their Photocatalytic Activity

TiO₂ is a kind of environmental functional material with excellent performance,which is friendly to the environment,it's also stable in quality and cheap in price.However,due to the wide band gap of TiO₂,it can only be excited by ultraviolet light,so it's utilization rate of solar light is very low;on the other hand,the TiO₂ electron hole recombination rate is high,leads to the low light quantum efficiency.So that the wide application of TiO₂ has been affected and restricted.Based on the analysis of the existing photocatalyst modification technology that the graphene platform "upconversion?UC?technology" and "TiO₂ photocatalytic technology" is a promising treatment technology.The samples prepared by hydrothermal method of rare earth ions doped UC material ?-NaYF₄:Ho₃₊,sol-gel preparation of ?-NaYF₄:Ho₃₊@TiO₂ core-shell photocatalyst,and UV reduction of GO preparation of ?-NaYF₄:Ho₃₊@TiO₂ ternary photocatalyst.And the photocatalyst's structure,morphology,luminescent properties,and photocatalytic properties were studied in the next.The main contents and conclusions of the paper are as follows:?1?The X ray diffraction?XRD?and scanning electron microscopy?SEM?results showed that ?-NaYF₄:Ho₃₊ was hexagonal.The average microcrystal length is roughly 9.0 um,with a diameter of about 4.0 um.The spectrum analysis?EDS?and X-ray photoelectron spectroscopy?XPS?results show that Ho₃₊ had successful incorporation of rare earth ions into the ?-NaYF₄ host matrix.The TEM and STEM-EDS results show that the UC microcrystals are uniformly coated by a TiO₂ layer,and the average thickness of the TiO₂ shells is about 50 nm.In the ?-NaYF₄:Ho₃₊@TiO₂-rGO ternary photocatalytic system,the rGO exhibits in the excellent sheet structure,and the morphology and structure of the composites are not changed.?2?The UV-Vis absorbance spectra?UV-Vis DRS?showed that the ?-NaYF₄:Ho₃₊ has obviously three absorption peaks,450,532 and 633 nm.The fluorescence spectrum?PL?results show that the UC phenomenon can occur under the excitation of Vis,which emits UV light of 290 nm under the excitation of 450 nm can be strongly quenched by being absorbed by TiO₂.The dependence of luminescence intensity on excitation power results shows that these transitions were all transitions of two-photon UC processes.After coating ?-NaYF₄:Ho₃₊ with TiO₂,notable spectral differences were observed.The intense emission peak at 290 nm almost disappeared.For rGO-assisted ?-NaYF₄:Ho₃₊@TiO₂,the low emission intensity can be ascribed to the fact that the lights were absorbed by the composite with the help of rGO.?3?The FTIR,Raman,XPS,and UV-Vis DRS results showed that the existence of rGO in ternary photocatalytic system.Moreover,the existence of Ti-O-C bond indicates the existence of chemical bond force between rGO and TiO₂,and such chemical bond is beneficial to the red shift of absorbed wavelength.The photoelectrochemical three-dimensional fluorescence spectroscopy,and electron spin resonance?ESR?results showed that the introduction of rGO can effectively enhance the electron transfer capability,which is beneficial to improve the separation of electrons and holes.Brunauer-Emmett-Teller surface area measurement?BET?showed that the introduction of rGO can enlarge surface area and pore volume,are beneficial for the ?-NaYF₄:Ho₃₊@TiO_<sub>2-rGO composite contacting with organic contaminants,?4?Rhodamine B was used in a series of degradation experiments to evaluate the photocatalytic activity of ?-NaYF₄:Ho₃₊@TiO₂-rGO.The results showed that with the increase of the amount of photocatalyst,the photocatalytic degradation effect increased at frist and then decreased,and decolorization rate of RhB is up to 95% within 10 h when the photocatalyst dosage is 0.15 g.The initial concentration was inversely proportional to the decolorization rate,and completely bleached of RhB within 10 h when the initial concentration of RhB was 4.0 mg/L.When the light intensity increased,the decolorization rate of RhB on the photocatalyst showed an upward trend.When the light intensity was 100600 lx,the decolorization could be achieved by 6 h.The degradation of Rh B by ?-NaYF₄:Ho₃₊@TiO₂-rGO ternary photocatalyst was consistent with the zero order kinetic equation of Langmuir-Hinshelwood.Considering the factors of the photocatalyst dosage?mcata?,the initial concentration of RhB?C0?and light intensity?E?,the dynamic model is:...