The Research Of Rare Earth Upconversion Nanocomposites For Ship Sewage

Ti O2 and g-C3N4 have become two of the most ideally and the most potentially applied semiconductor photocatalyst. However, the bandgap of pure Ti O2 is up to 3.2e V, hence, the ultraviolet(UV) light(λ ≤ 380nm) is necessary to activate it for photocatalytic reaction; Although the bandgap of g-C3N4 is 2.7e V, but can only absorb the visible(Vis) light(λ≤460nm) for photocatalytic reaction. The low-usage of sunlight has been restraining the application for Ti O2 and g-C3N4 photocatalytic in the field of environmental pollution. Many researchers have done quite a lot of research to expand the optical response of the two photocatalysts, but all mostly stay in the visible areas. The near infrared energy in solar energy which is equal to the visible light energy remains untrapped for photocatalysis.The upconversion luminescence is an anti-Stocks phenomenon, it means the rare earth upconversion materials can absorb long wavelengths and then emit short wavelengths. The Yb3+/Tm3+ codoped fluoride can have UV and Vis emissions under the excitation of 980 nm NIR irradiation, then UV and Vis light can been utilized by Ti O2 and g-C3N4 for their photocatalysis. Based on the theory,so we choose the best upconversion efficiency material Na YF4 as matrix, then synthesize β-Na YF4:Yb3+,Tm3+ nanoparticles by thermal decomposition methodand and ivestigated the mechanism of luminescent properties. The near-infrared-driven photocatalyst β-Na YF4:Yb3+,Tm3+@Ti O2 with core@shell structure were successfully synthesized by using PVP as a surface active agent and a binder; β-Na YF4:Yb3+,Tm3+/g-C3N4 with heterostructure were successfully synthesized through ultrasound and magnetic stirring in methanol dispersant. The morphology, crystal structure, chemical composition, luminescence property, etc were investigated with PL, XRD, SEM, TEM etc. The photocatalytic activity and mechanism of β-Na YF4:Yb3+,Tm3+@Ti O2 and β-Na YF4:Yb3+,Tm3+/g-C3N4 were evaluated by the photodegradation of dyes and phenol(simulation of organic ship sewage) under 980 nm NIR irradiation. Terephthalic acid was used to detect the hydroxyl radicals generated by β-Na YF4:Yb3+,Tm3+/g-C3N4 under 980 nm NIR irradiation.Results indicated that β-Na YF4:Yb3+,Tm3+ nanoparticles had hexagonal phase structure and an average diameter of ~20nm with a strong UV and Vis emission property, and then synthesize it into two kinds of near-infrared-driven photocatalysts β-Na YF4:Yb3+,Tm3+@Ti O2 and β-Na YF4:Yb3+,Tm3+/g-C3N4. The degradation rate of dyes and phenol were very high over the two near-infrared-driven photocatalysts under 980 nm NIR irradiation. Through degrade MB with β-Na YF4:Yb3+,Tm3+/g-C3N4 over four times under 980 nm NIR irradiation,the photocatalyst keeps high catalytic activity and stability. Finally,·OH radical generated by photocatalyst were detected in the photocatalytic reaction process, it indicated that the new near-infrared-driven photocatalyst with high catalytic activity. The effective utilization of near-infrared light energy for Ti O2 and g-C3N4 has broad application prospects in the field of water pollution treatment or ship sewage treatment.