The Expanding Of Light Absorption Range And The Enhancement Of Visible Light Photocatalytic Activity Of The Wide-band-gap BiPO₄

Recently, semiconductor photocatalysis has attracted tremendousattention due to its great potential in solving environmental pollution issues andenergy crises. Especially, visible-light-driven semiconductors have been regarded asthe most promising photocatalysts owing to their highly efficient utilization of solarenergy. Except for many pure narrow-band-gap semiconductors that can absorbvisible light and exhibit high photocatalytic activities, a great number ofwide-band-gap photocatalysts only show UV light photocatalytic performances. Inview of the present situation, expanding the visible light absorption range of thewide-band-gap photocatalysts for endowing them visible light activity is animportant and challenging task.As a typical wide-band-gap semiconductor, BiPO4only exhibits superiorphotocatalytic performance under UV light irradiation, which dramatically limits itspractical applications. Therefore，the purpose of this thesis is to broaden the visiblelight absorption region and obtain high visible light induced photocatalyticperformance of BiPO4by surface modification using suitable narrow-band-gapsemiconductors through band matching and structure tuning.The main research contents and important results of this thesis are presented asfollows:(1) A novel visible-light-driven AgI/BiPO4composite was synthesized by a facileroom temperature deposition-precipitation method. The structures, morphologies,components and optical properties of the obtained samples were systematicallycharacterized using XRD, SEM, EDS, TEM, HRTEM, XPS, BET and DRS. Undervisible light (λ>420nm), the as-prepared AgI/BiPO4displayed much higherphotocurrent intensity and enhanced photocatalytic activity for RhB removal thanpure AgI and BiPO4meanwhile maintained good stability. The kappvalue ofAgI/BiPO4for degrading rhodamine B was0.044min-1, which was three times thatof pure AgI. BiPO4acted as an electron trap in the AgI/BiPO4composite with a matching interactive energy band structure, which enhanced the photocatalyticactivity of the composite via promoting the efficient separation of electron-hole pairs,and ensured the stability of AgI/BiPO4by preventing the photoelectrons couplingwith the interstitial Ag+to form metallic Ag0.(2) Ag3PO4quantum dot sensitized BiPO4, a novel p-n junction Ag3PO4/BiPO4photocatalyst, was prepared by co-precipitation hydrothermal method andcharacterized by XRD, SEM, EDS, TEM, HRTEM, XPS and DRS. Ag3PO4/BiPO4exhibited much higher photocatalytic activity than Ag3PO4and BiPO4for thedegradation of methyl orange under visible light (λ>420nm). The enhancedphotocatalytic activity of Ag3PO4/BiPO4could be mainly ascribed to the strongvisible-light absorption originating from the quantum dot sensitization of Ag3PO4and high efficient separation of photogenerated electron-hole pairs through p-nheterojunciton. Moreover, O2and OH were the main reactive species.(3) Novel composite photocatalysts BiPO4/BiVO4with different contents of BiPO4were synthesized by a simple one-pot hydrothermal method under the condition ofpH0.5. The obtained photocatalysts were systematically characterized by XRD,FT-IR, SEM, EDS, TEM, HRTEM, SAED, XPS and DRS. The photocatalyticactivities of BiPO4/BiVO4were evaluated by the degradation of methylene blue,methyl orange and rhodamine B under visible light (λ>400nm). The results showedthat all of BiPO4/BiVO4composites exhibited improved photocatalytic activitiescompared with pure BiPO4and BiVO4. Among the composites,10%BiPO4/BiVO4possessed the best photocatalytic activity. Moreover, the radical scavengers’experiments demonstrated that O2and h+were the main reactive species for themethylene blue degradation under visible light.