The Preparation And Photocatalytic Properties Of Brookite TiO₂-based Nanomaterials

With the rapid development of social economy,water pollution has become serious environmental problem.Compared with traditional wastewater treatment methods,photocatalysis use low-cost photocatalysts and relatively simple devices to degrade organic pollutant.TiO₂stands out among many photocatalysts due to its unique advantages of photostability,non-toxicity and low cost.Compared with the anatase and rutile crystal phase,brookite TiO₂has rarely been studied due to its stringent preparation conditions and so on.In addition,brookite TiO₂is a wide band gap semiconductor,which can only be excited under UV light,limiting its photocatalytic activity in practical applications.Therefore,in this paper,brookite TiO₂was taken as the research object,and from the perspective of improving the light capture efficiency and photogenerated charge separation efficiency,different modification methods were adopted to broaden its spectral response range and improve the photogenerated charge separation efficiency,and finally,the photocatalytic degradation properties of brookite TiO₂-based nanomaterials were studied.The main contents and conclusions are as follows:1.The nano-cube brookite TiO₂（named BTN）of the average size～50 nm was synthesized by hydrothermal methods,using TiCl₄as Ti sources;then,the g-C₃N₄/brookite TiO₂nanocomposites with wide spectrum response were synthesized by thermal polymerization under air atmosphere after grinding urea and BTN in a certain proportion.Rhodamine B（Rh B）and methylparaben（MPB）were desorbed under visible light（λ>400 nm）to test the photocatalytic activity of the samples.The phase composition,microstructure and photocatalytic activity of g-C₃N₄/brookite TiO₂nanocomposites were investigated through a series of characterization tests.It was found that when the mass ratio of urea to brookite TiO₂was 25:1,g-C₃N₄was modified on the surface of brookite TiO₂in the form of nanodots（named CND/BTN）;When the mass ratio of urea to brookite TiO₂is 50:1,g-C₃N₄was wrapped in the outer layer of brookite TiO₂in the form of shell（named CNS/BTN）.Under visible light irradiation,the photocatalytic degradation efficiency of MPB by CND/BTN was 2.2 times and 4.5 times that of CNS/BTN and BTN,respectively.Therefore,the g-C₃N₄nanodots and brookite TiO₂form a channel for directional transfer of photogenerated charge,which is promoted the separation of photogenerated charge;however,in CNS/BTN nanocomposites,electron receptors are almost completely covered by g-C₃N₄shells,and most of the active sites are covered by g-C₃N₄,resulting in an increase in the recombination rate of photogenerated charges.Therefore,CND/BTN nanocomposites have high photocatalytic degradation activity.2.The visible light response BiOBr/brookite TiO₂nanocomposite（named BiOBr/BTN）was prepared by modifying BiOBr on the surface of brookite TiO₂nano-cube（BTN）.A series of characterization tests were carried out on BiOBr/BTN nanocomposites to explore the phase composition,microstructure and mechanism of enhanced photocatalytic degradation activity.It was found that when the BiOBr composite amount was 10 mol%,some BiOBr nanodots appeared on the surface of brookite TiO₂;When the compound amount of BiOBr increased to 15 mol%,BiOBr aggregated and fused into a sheet structure,which was attached to the surface of the brookite TiO₂;When the composite amount of BiOBr was further increased to 20 mol%,the size of BiOBr nanosheet gradually increased,presenting the phenomenon of brookite TiO₂nano-cubes attached to its surface.Rhodamine B（Rh B）and methylparaben（MPB）were degraded under visible light（λ>400 nm）to explore the photocatalytic degradation activity of the samples.The results showed that 15%BiOBr/BTN samples had high photocatalytic activity.3.An appropriate amount of NH₄NO₃was added in the preparation process of the precursor of brookite TiO₂nano-cube（BTN）,and nitrogen doped brookite TiO₂nanomaterial（named N-BTN）was prepared by hydrothermal method;and then,Cu-loaded and N-doped brookite TiO₂nanocomposites（named Cu/N-BTN）were prepared by chemical reduction method with different amounts of Cu nanoparticles on N-BTN surface.Rhodamine B（Rh B）and methylparaben（MPB）were desorbed under visible light（λ>400 nm）to test the photocatalytic activity of the samples.The results showed that compared with the original BTN,the photocatalytic degradation activity of N-BTN nanocomposites was only slightly improved,while the photocatalytic degradation activity of Cu/N-BTN nanocomposites was significantly improved,and the degradation efficiency of 5Cu/N-BTN nanocomposites for MPB was 1.9 times and 4.2times that of N-BTN and BTN,respectively.The phase composition,microstructure and photocatalytic activity of Cu/N-BTN nanocomposites were investigated through a series of characterization tests.It is found that the synergistic effect of loaded metal Cu and doped non-metal N can not only broaden the spectral response range of Cu/N-BTN nanocomposites,but also inhibit the recombination of photogenerated charge,thus effectively improving the photodegradation activity of the catalytic system.