Morphology Controlled Synthesis Of Two Kinds Of Typical Photocatalysts To Fabricate Heterostructure Interface With Enhanced Photocatalytic Activity

Photocatalysis technology has been widely concerned and studied in recent years due to its unique advantages in environmental governance and clean energy.The key problems in this field gradually get clear,including the photon absorption,charge carrier separation and transfer,and surface reaction activity.Meanwhile,the corresponding effective strategies have been proposed and verified,such as band structure engineering,crystal facets control,heterostructure fabrication and cocatalyst loading.Among them,several key factors,such as facets,cocatalysts and heterostructure,play multiple and interrelated roles during the photocatalytic reaction.Extensive basic researches show that the active facet is the key factor to improve the activity for the monocomponent of photocatalyst.In multicomponent system,the heterostructure and cocatalysts can separate the charge carrier at the interface and activate the reaction on the surface,respectivily,which lead to the change of properties at interfacial facets.In turn,the carrier driving force and activation function also depend on the crystal facets at the interface.Therefore,the research on the crystal facets at multicomponent interface is the key approach to enhance the separation and transfer of carrier and activation efficiency.This work focus on the facets control at multicomponent interface to enhance the reactive efficiency.Two kinds of methods,selectivity of sites and facets at multicomponent interface,are proposed to investigate two kinds of photocatalysts,Zn O and Ag₃PO₄,respectively.In the first part,the morphology evolution of porous ZnO nanosheets synthesized by hydrothermal reaction and the corresponding photocatalytic activity are investigated.Then relation between the selective photocorrosion and the stability is presented,followed by the revelation of its reason through the process of adsorption and degradation.Based on the function of active facets during the selective photocorrosion,the correlation between the active facets and the corroded sites is established,which can be validated in the hexagonal sheets and other morphology of ZnO.It is found that the selective photocorrosion of porous ZnO nanosheets with excellent photocatalytic activity can be observed,which results in a significant decease of the unit activity attributed to the loss of the active crystal facets.At the same time,the similar competitive relationship between the same kinds of dye molecules are exhibited in the adsorption and reaction process.It indicates that the selective adsorption and the specific active facets loss make the jointly efforts on the selective photocorrosion,due to the?002?crystal plane in Zn O acts as polar crystal face and active face.It is also verified that the selective photocorrosion of Zn O with hexagonal and hexagonal bowl-like morphology in the Rhodamine B solution take place on the?002?,where the polarity results in the selective adsorption and activity leads to the degradation reaction.Following the investigation of active facets,two kinds of cocatalysts are loaded on porous ZnO nanosheets to observe the deposition sites,explore their selectivity,analyze the influence of the selectivity on spacial charge separation efficiency and reveal the different impacts of Zn O facets at the deposited interface on photocatalytic activity.The results turn out to be challenging,including the numerous factors-induced distribution,disadvantage on degradation activity,undiscovered properties in oxygen evolution,and so on.Meanwhile,based on the porous Zn O nanosheets,the selectively and randomly distributed ZnO/CdS heterostructures are designed and synthesized,followed by the measurement of photoelectrical properties and hydrogen evolution activity.Then,the above results are compared to present the advantage of selective heterostructure.It shows that the H₂ evolution rate of Zn O/CdS-S2 reaches 384?mol·g^-1·h^-1,which is 14 times higher than that(25?mol·g^-1·h^-1)of CdS.More importantly,the H₂ evolution rate of ZnO/CdS-S2is higher than that of Zn O/CdS-R2,which indicates more efficient charge separation and higher hydrogen evolution are achieved for ZnO/Cd S-S compared with Zn O/CdS-R.Thus,the facets at the heterostructure interface are revealed to be vital and significant for the photocatalytic reaction efficiency.In the second part,the factors related to morphology of Ag₃PO₄ are mainly studied on by on with controlled variables.It is found that the morphology of Ag₃PO₄ is both influenced by dynamics and thermodynamics.In detail,the dynamic factors include adding approach?adding rate and order?,ionic concentration ratio,total ionic concentration,saturation and pH,etc.in the system,while thermodynamics mainly rely on temperature change induced the ionic concentration ratio and saturation.Of course,these factors determine the morphology via various way but not individually.It is noted that some growth conditions can be coupling without obvious disturbance to morphology,such as temperature and ionic concentration ratio.Thus,it can provide the chance and approach to fabricate the multicomponent interface with different facets of Ag₃PO₄ crystal.According to how these factors determine facets growth,three methods are used to synthesize Ag₃PO₄-based heterostructures,including one-step mixing,ion exchange and heterogeneous nucleation.In Ag₃PO₄/TiO₂ compound prepared by one-step mixing,the self-corrosion in dark is observed and the corresponding chemical environment change of Ag differs from that in photocorrosion.It is revealed that the self-corrosion attributes to the deceased degradation activity under visible light but no obvious effect under ultraviolet light.In Ag₃PO₄/AgBr and Ag₃PO₄/Ag₂CN₂ heterojunctions synthesized through ion exchange,AgBr nanoparticles and Ag₂CN₂ nanosheets are both out control during synthesis.In Ag₃PO₄/Ag₂CN₂ heterojunction and Ag₃PO₄?1?/Ag₃PO₄?2?homojunction,the growth condition of each component can be coupled without obvious disturbance to morphology.Thus,two components with specific morphology can be coupled to form heterostruture interface with corresponding facets through heterogeneous nucleation,which give a chance to explore the function of specific facets at heterostruture interface for Ag₃PO₄.