Synthesis Of Several Nanoflower-like Heterostructures Based On TiO₂ With Exposed {001} Facets For Enhancement Of Photocatalytic Performances

Facing increasingly environmental pollution and energy crisis situation,the heterogeneous photocatalysis based on various oxide semiconductors,such as TiO₂ photocatalytic process,is an ideal technique for remedying environmental pollution and hydrogen production by solar energy,which has become one of the most active research field in recent years.In this thesis,the author firstly reviews the current research status of TiO₂-based nanostructured photocatalysts on improving their photocatalytic activities at home and abroad,points out the existing problems at present,and proposes several corresponding improvement strategies.Then,the author systematically summarizes the research work carried out during her master degree study entitled“Synthesis of several nanoflower-like heterostructures based on TiO₂with exposed{001}facets for enhancement of photocatalytic performances”in which the main research contents and results are as following two aspects:1)In the first aspect,we design and fabricate a new three-dimensional（3D）nanoflower-like TiO₂ nano-architecture with almost 100%exposed{001}facets by a facile hydrothermal method.And on this basis,we selected p-type narrow band-gap binary compound semiconductor NiS as a modifier to futher decorate on such n-type TiO₂ with exposed{001}facets for forming nanoflowers-like NiS/TiO₂ p-n heterostructures.A series of test results show that the built-in electric field between NiS and TiO₂ interface can directly drive the charge separation and transfer through the electric field force,thus enhancing the photocatalytic reactions.It is found that such photocatalyst of nanoflower-like NiS/TiO₂ p-n heterostructures with exposed{001}facets can possess excellent photocatalytic activity for degradation of methyl orange（MO）,the photodegradation efficiency up to 98%within 20 min,10 times higher than that of pure TiO₂ nanoflowers.Further analysis indicates that the synergy effects between the high efficient charge separation and transfer driven by the built-in electric field at interfaces of NiS/TiO₂ p-n heterostructures,and the high photocatalytic activity of exposed high energy{001}facets would be the major factors that offer the enhanced photocatalytic performance.This research would provide a promising strategy for design and construction of high efficient photocatalytic devices based on TiO₂ nanostructures.2)In the second aspect,on the ground of above work,we further decorate the 3D NiS/TiO₂ p-n heterostructures mentioned above with thin crumpled and entangledβ-Ni（OH）₂ for forming a new 3D flower-like ternary p-n-p heterostructureβ-Ni（OH）₂/NiS/TiO₂ by a straight forward chemical bath deposition method.As a new photocatalystic device,it is ideally suited for both removal of anionic dye methyl orange（MO）,and release of hydrogen from the MO solution driven by photoelectric conversion without the need for using noble metals.The formation structure with optimal molar ratio 0.01-β-Ni（OH）₂/0.001-NiS/TiO₂ shows superior photocatalytic activity for removal of anionic dye MO and releasing hydrogen,its removal efficiency is as high as 98%in 15 minutes with a degradation rate of 0.146 min^-1 under simulated sunlight irradiation.And in the meanwhile,the photocatalytic H₂-production rate can achieve about 18.78 umol.h^-1 and 7.28 umol.h^-1 in the noble-metal-free system and MO aqueous solution,respectively.Further analysis indicates that in addition to the synergies mentioned above,the modifierβ-Ni（OH）₂,as an assistant sacrificial agent,plays an important role of holes transfer for the charge transport balance in the oxidation-reduction process,and the generated active species NiOOH also has a beneficial effect on degrading MO and releasing hydrogen.Furthermore,this study would offer a new idea for design and construction of high efficient photocatalytic devices to have the best of both worlds for degradation pollutants and hydrogen production.