Preparation Of Pd Loading TiO₂ Nanomaterials And Their Photocatalytic Activities In Hydrogen Production

TiO₂ and its modified nanomaterials have attracted extensive attention due to their excellent performances in photocatalysis,photoelectric catalysis,gas sensor,dye-sensitized solar cell,lithium ion battery,biological antibacterial and other aspects.In this paper,Ti³⁺,N co-doped TiO₂ nanotube arrays(Ti³⁺/N-TiO₂ NTAs)and metal ion doped TiO₂NTAs were prepared by anodic oxidation method.TiO₂ nanoparticles were prepared by a simple one-step hydrothermal method.All of these TiO₂nano-materials were loaded a small amount of precious metals nanoparticles by photodeposition method.The photocatalytic activities of the catalysts were evaluated by the efficiency of photocatalytic hydrogen production in the methanol sacrificial solution,and the photocatalytic reaction mechanism was discussed.The specific contents are as follows:1.In the electrolytic liquid system of ammonium fluoride-water-formamide-glycol,the p H of the electrolyte was adjusted to about 4 by concentrated sulfuric acid,and Ti³⁺/N-TiO₂ NTAs were prepared by anodic oxidation method.Then small amount of noble metal nanoparticles were loaded by photodeposition method.In order to determine the morphology,structure and composition of the samples,a series of characterization including SEM,TEM,XRD,mapping,XPS and UV-Vis absorption spectra were carried out,and the photocatalytic activity of the samples were evaluated by the efficiency of photocatalytic hydrogen production in sacrificial solution.The influence of different reaction conditions on photocatalytic activity of hydrogen production was explored and proposed the mechanism of hydrogen production by water splitting over the Pd loaded Ti³⁺/N-TiO₂ NTAs.The results show that the hydrogen production efficiency of Ti³⁺/N-TiO₂ NTAs in methanol solution was 1.0μmol·cm^-2·h^-1.The photocatalytic hydrogen production activity of Ti³⁺/N-TiO₂ NTAs/Pd 10 was the highest which the hydrogen production efficiency reached 17.6μmol·cm^-2·h^-1,which is 17.6 times higher than the Ti³⁺/N-TiO₂ NTAs.Adding a small amount of KCl to the methanol sacrificial solution or increasing the temperature of the catalytic reaction system can also greatly improve the photocatalytic hydrogen production activity of the samples.The type of sacrificial agent also has a great impact on the hydrogen production activity.2.Ammonium fluoride-water-formamide-glycol electrolyte system was used,in which 0.05 wt%metal nitrate（Na NO₃,KNO₃,Ni（NO₃）₂）was added,the p H of the electrolyte was adjusted to about 4 by concentrated sulfuric acid,and metal ion-doped TiO₂ NTAs was prepared by anodic oxidation method.Due to inhibition of the increase of the tube length and diameter to certain extent resulting from the doping of metal ions,the tube length and diameter were smaller than the undoped samples.HR-TEM and mapping confirmed successful Na ion doping,and the photocatalytic activity of the samples were evaluated by the efficiency of photocatalytic hydrogen production in methanol solution.Compared with un-doped sample,the Na⁺-TiO₂ NTAs/Pd 5 exhibited the higher hydrogen production efficiency(14.4μmol·cm^-2·h^-1),which was 3.4 times higher than that of the undoped sample.3.TiO₂ nanoparticles were prepared by a simple one-step hydrothermal method using tetrabutyl phthalate and acetic acid as raw materials,followed by photodeposition of the Pd nanoparticles with different contents.The photocatalytic activity was measured by the hydrogen production efficiency of the samples in the lactate solution.When the loading amount of Pd nanoparticles was 1.74 wt%,the highest hydrogen production efficiency was 8.0 mmol·g^-1·h^-1.TiO₂ nanoparticles prepared with PVP as auxiliary reagent have the highest hydrogen production activity of 1.00 mmol·g^-1·h^-1 after loading about 0.1 wt%Pd nanoparticles,which was 2.0 times of the samples prepared without auxiliary reagent.The prepared TiO₂ nanoparticles were calcined at high temperature,loaded with about 0.1 wt%Pd nanoparticles,and then tested for hydrogen production by photodegradation of water.The highest activity of hydrogen production by photodegradation of water(1.50mmol·g^-1·h^-1)was obtained at 400℃,which was 3.0 times higher than that of the samples without calcination.