Preparation And Properties Of Titanium-based Photocatalytic Materials

Photocatalytic hydrogen production is one of the most promising green technology to solve the issues such as the energy crisis and environmental pollution,which can convert solar energy to hydrogen energy.Titanate material is a suitable candidate for photocatalytic hydrogen production because of its high chemical stability,good resistance to photocorrosion,low cost,lack of toxicity,and negative conduction band.Therefore,through the modification to the titante based photocatalytic materials to improve the photocatalytic hydrogen production performance has become an advanced research emphasis.First,bifunctional CaTiO₃:Ln³⁺?Ln = Eu and Er?nanocrystals were prepared via a sol-gel method and followed by calcination in air.The effect of the concentration of rare earth ions on the phase morphologies,luminescence properties and photocatalytic activity of CaTiO₃ nanocrystals were investigated in detail.As phosphor powder,the luminescence properties CaTiO₃:Ln³⁺ nanocrystals could be controlled by doping with different Ln³⁺ ions,from the emission spectra of the CaTiO₃:Eu³⁺ nanocrystals excited at different excitation wavelengths,the 5D0?7F1?589-602 nm?,5D0?7F2?615-633 nm?,5D0?F3??654 nm?and 5D0?7F4??713 nm?transitions of Eu³⁺ were observed.The emission intensity 5D0?7F2?615?633 nm?of the CaTiO₃:Eu³⁺?17%?nanocrystals was the strongest when the excitation was performed at 397 nm,shows that the CaTiO₃ nanocrystals promoted the europium ion luminescence performance.The upconversion?UC?luminescence spectra of CaTiO₃ nanocrystals with different Er³⁺ concentrations.The spectral peaks correspond to the following transitions:2H11/2?4I15/2??526nm?,4S3/2?4I15/2??544 nm?,4F9/2 ? 4I15/2??662nm?,and the relative intensity of 4F9/2 ? 4I15/2 to 2H11/2/4S3/2?4I15/2 increases with increasing the Er³⁺ content.When Er³⁺ concentration was 10%,the luminescence almost vanished due to luminescence quenching.On the whole,they showed very stable luminescence properties.As photocatalyst,the CaTiO₃:Ln³⁺ nanocrystals exhibited a higher activity for hydrogen production under ultraviolet light irradiation.The CaTiO₃:Er³⁺ nanocrystals display the highest photocatalytic activity,which is up to 461.25 ?mol·h-1·g-1 catalyst,it is higher than that of CaTiO₃:Eu³⁺ nanocrystals and pure CaTiO₃.The UV-vis absorption spectra indicated that the incorporation of Ln³⁺ ions benefits the reduction of the band gap of CaTiO₃ photocatalyst,and the EIS Nynquist plots as well demonstrated that doped Ln³⁺ ions can promote the electron transfer.The as-prepared CaTiO₃:Ln³⁺ nanocrystals exhibit bifunctional performance in the photoluminescence and photocatalytic hydrogen production.Second,an effective photocatalytic hydrogen production catalyst of MgTiO₃/MgTi2O5/TiO2 composite materials were prepared via a hydrothermal method with thermal treatment method.The tri-phase heterogeneous junction was confirmed by XRD,TEM and HRTEM and show that the material is composed of MgTiO₃,MgTi2O5 and TiO2.The photogenerated electrons could transfer from MgTiO₃ to MgTi2Os and then to TiO2 while the holes transfer in the opposite direction,according to the potentials of the conduction and valence bands.This transformation of the tri-phase junction may also prevent back-transfer of the photo-generated electron in the heterojunction interface,thereby promoting charge separation.Furthermore,we investigated the calcination temperature on the effect of the tri-phase heterogeneous junction composites,the result shows that the crystallinity and the photocatalytic hydrogen production activity is best when the calcination temperature is 700 ?.The as-prepared MgTiO₃/MgTi2Os/TiO2 composite materials exhibited very high photocatalytic hydrogen production activity?356.1 ?mol· h-1·g-1 catalyst?and apparent quantum efficiency?50.69%at 365 nm?,which is about twice times higher than that of bare TiO2 nanoblets?189.4?mol·h-1·g-1 catalyst?.Characterization of liner sweep voltage,transient photocurrent,electrochemical impedance spectroscopy and Mott-Schottky plots revealed that the high photocatalytic performance was attributed to the one dimensional structure which possessed excellent charge transportation ability and the MgTiO₃/MgTi2O5/TiO2 materials which could effective drive the charge separation through built-in electric field.This titanate based tri-phase heterogeneous junction photocatalyst preparation and research further enriched the catalyst system of photocatalytic hydrogen production.