Construct Of Hierarchically Porous ZnO Nanostructures For Photocatalysis Application

Considering the increasing serious energy crisis and environmental pollution problems,exploiting and utilizing clean energy to achieve sustainable economic development is becoming more and more urgent.As an ideal green clean technology,photocatalysis has a positive impact on resolving the environmental pollution and relieving the energy crisis.Generally,photocatalytic reaction can convert the light energy into chemical energy in mild reaction conditions?normally at room temperature and pressure?and can realize the direct use of solar energy without additional energy consumption.Due to the advantages mentioned above,photocatalysis is considered as a promising way to effectively solve the currently facing energy crisis and environmental pollutions.Among various photocatalysts,ZnO as a direct band gap semiconductor with wide bandgap?E_g?3.2 eV?,high chemical activity and electron mobility and transparency can effectively avoid the disadvantages of indirect semiconductor materials such as low efficiency of electron transition and low quantum efficiency.However,the relative low efficiency of sunlight utilization and high recombination of photogenerated electron-hole pairs are still the main factors that seriously affect their photocatalytic properties.This leads to the relatively low apparent quantum efficiency and severely restricts ZnO photocatalytic application.To solve the above problems,we have designed and synthesized different novel hierarchically porous ZnO nanostructures and studied their photocatalytic performance and reaction mechanisms.A series of very interesting research results have been obtained as follows:Two dimensional?2D?ZnO mesoporous single-crystal nanosheets?ZnO-MSN?with{0001}polar facets have been designed and prepared via an intriguing colloidal templating approach through controlling the infiltration speed for the suspension of EG-capped ZnO nanoparticles and polymer colloids.We further present the in-depth study of the synthesis mechanism of such special 2D structure and testing its photocatalytic activity on different charged organic molecules.The results show that 2D ZnO-MSN shows highly selective adsorption and significantly higher photodegradation for positively charged rhodamine B with the more exposed O-termination?000-1?polar surfaces.Polar surface exposure and the presence of a single crystal properties not only enhance the electrical properties of different dyes selective adsorption,but also accelerate the photo-generated electron-hole separation and transport,leading to photocatalytic enhancement of ZnO.Highly ordered,dense and continuous ZnO inverse opal?ZnO-IO?films with different air sphere sizes have been successfully prepared by a metal salt-based sol-gel infiltration method.The ZnO-IO films present a photoinduced surface wettability conversion phenomenon and the wettability of the ZnO film can be tuned from superhydrophobicity to hydrophilicity after UV-vis irradiation.ZnO-IO films demonstrate highly enhanced photocatalytic activities due to the hierarchically macro-mesoporous structure via testing the degradation of RhB dyes.By adjusting the angle of the incident light,studying the relative position of reflection peak and the ZnO electronic band gap,investigating the changes of photocatalytic rate,we demonstrate and give the direct evidence of the existence of the slow photon effect.The synergy of the slow photon effect and hierarchically porous structure of inverse opal itself results in the highest photocatalytic activity of ZnO-IO-260 and ZnO-IO-470 at an incident light angle of?=40°.Highly ordered,continuous uniform and high-quality 3D CdS@ZnO core-shell inverse opal nanostructures?CdS@ZnO-csIO?have been successfully prepared via metal salt-based sol-gel infiltration method and successive ion layer absorption and reaction?SILAR?.Due to the hierarchically macro-mesoporous structure,CdS@ZnO-csIO exhibits a high level of photocatalytic hydrogen production performance.We also demonstrate the existence of slow photon effect in 3D CdS@ZnO core-shell inverse opal nanostructures by adjusting the macropore size.The H₂ production results show that CdS@ZnO-csIO-290 showed the highest photocatalytic rate owing to the high light utilization efficiency and field confinement of slow-photon effects happened at blue edge.By comparing the H₂production performance under visible light and simulated solar light irradiation,we can conclude that the synergy of the slow photon effect and Z-scheme water splitting mechanism with the enhancement of light harvesting and the promotion of the charge carriers separation in the inverse opal nanocomposites results in the high photocatalytic rate of H₂ production.Highly ordered,continuous and good quality of 3D CdS@Au@ZnO ternary inverse opal films?CdS@Au@ZnO-csIO?have been successfully prepared via metal in situ photoreduction Au methods based on our previous work.Due to the hierarchically macro-mesoporous structure,CdS@Au@ZnO-csIO films exhibit enhanced light absorption,extended the light responsive region and reduced the recombination rate of charge carriers.These advantages mentioned above result in high water splitting performance.By comparing the different amounts of Au-loaded CdS@Au@ZnO-csIO films for water splitting,the results show that CdS@0.5Au@ZnO ternary inverse opal film with the optimal Au amount demonstrats the best water splitting performance.The synergy of the slow photon effect,Z-scheme water splitting mechanism and SPR effect of Au nanoparticle via enhancing the light absorption efficiency and improving the separation of photo-generated carriers brings CdS@0.5Au@ZnO ternary inverse opal film with the best water splitting performance.