Defect Mediation Of Wide Band Gap Photocatalysts And Its Mechanism As Well As Application

Photocatalysis technique depicts promising prospects in environmental, energy and organics transformation related issues. It has always been the key aspect of photocatalysis of research focusing on photocatalytic materials. Despite that many progress has been made, there are still two major barriers that hinder the performance of photocatalysts. One is the low quantum efficiency of the materials, the other is the poor utilization of the solar light. The theme of the present thesis is exploring the possible solution in dealing with the two disadvantages by studying the prevailing defects in photocatalysts.By cold plasma treatment (CPT) technique and dip-coating method, we successfully prepared ZnO bilayer films with oxygen vacancies and interstitial zinc atoms in different locations. The defective films showed promoted photocatalytic activity, with enhanced transportation and good separation of photogenerated charge carriers being the main reasons. The interlayer defects could effectively modulate the activity of ZnO within a certain domain. Also, these metastable defects could be well stabilized and survive the intense oxidative environment by the protection of outerlayer film.To tackle the disadvantages of the relatively low quantum efficiency and the well-known photocorrosion of ZnO, and taking into account the conclusion that defects are desired to work in the near surface to achieve better photocatalytic performance, the ZnO nanoparticles were treated with CPT technique and then coated with a monolayer of PANI. Promisingly, the activity of ZnO was enhanced and its photocorrosion was also inhibited. It was demonstrated that surficial defects and PANI could work synergistically to facilitate the separation of charge carriers, and the monolayer PANI could also efficaciously stabilize the defects on the surface of ZnO in prolonged irradiation. This work may open a new strategy for designing highly efficient photocatalyst with long endurance.Traditional methods like vacuum annealing at high temperatures and high-energy particle bombardment, which base on reduction reactions, have been adopted to create defects. These defects are generally of poor stability. We developed a novel approach to prepare Ti3+ self-doped reduced TiO2 by oxidation of low-valent titanium species. TiO and TiH2, as precursors, were separately treated by solvothermal to obtain bulk Ti3+ self-doped TiO2, which successfully extended the TiO2’s response towards visible-light region. Meanwhile, the UV light activity of the TiO2 was promoted due to the new energy level caused by homogeneous Ti3+ doping. The reduced defective TiO2 displayed remarkably boosted visible light activity in water-splitting as well as photodegradation of dye. Moreover, Au nanoparticles were deposited on TiO2 in situ by the reductive surficial Ti3+. No involving of any foreign reducing agents or stabilizer ensured the intimate contact and rendered strong interaction between semiconductor and Au. Consequently, the activity of TiO2 was further improved.By simply varying the thermal temperature of TiH2 and HC1 mixture, (110) and (111) facets exposed, Ti3+ self-doped rutile was obtained. The abundant bulk Ti3+ species rendered rutile with visible light activity while the synergistic effect between explicit facets facilitated the separation of photogenerated charge carriers. Moreover, the performance of this defect and facet mediated TiO2 in H2 liberation from water under full-solar-spectrum was enhanced by a factor of 40 in comparison with commercial rutile upon normalization of surface area. The present research revealed the interplay of the component and structure of a certain material and shed new light on designing and fabricating efficient photocatalytic materials driven by solar energy.