Fabrication Of Iron-Containing Novel Photocatalysts And Their Enhanced Photocatalytic Performances For Organic Pollutants Degradation

Photocalysis technology has been a research hotspot in the field of clean energy production and environment purification since photocatalysts are able to transform solar energy into chemical energy.Nowadays,how to improve photocatalysts'quantum efficiency,how to promote photocatalysts'response to longer wavelength light and how to further study the photocatalytic mechanism have been the three key points in the fiels of photocatalysis technology.Iron-containing semiconductors are usually able to be modicated by visible light even infrared light.However,defects always exist in the ferrum contained materials,which result in the poor separation of electrons and holes.In order to overcome the problems mentioned above,we fabricated several ferrum contained materials,which are modified by heterojunction fabrication,SPR effect modification and iron substitution doping.The modification and photocatalytic mechanism were deeply studied and discussed.The main research work and results are listed as follows:?1?A novel AgFeO₂/g–C₃N₄ composite with enhanced photocatalytic activity was fabricated by a simple precipitation method.The g–C₃N₄ sheet with thickness of 2⁴nm was successfully loaded on the surface of the AgFeO₂ nanoparticles.As compared to pure AgFeO₂ and pure g–C₃N₄,the as prepared AgFeO₂/20%g–C₃N₄ photocatalysts exhibited surperior visible light photocatalytic performance.Besides,the photocatalytic activity of the AgFeO₂/20%g–C₃N₄ sample was well maintained as well as its structure even after six recycles.According to DFT calculation result and Mott Schottky plot,AgFeO₂ is p type semiconductor,with O 2p dominated valance band and Fe 3d dominated conductive band.When AgFeO₂ was connected to g–C₃N₄n type semiconductor,the photo-generated electrons in the p-n heterojunction would transfer from AgFeO₂ to g-C₃N₄,forming Z-scheme route.The holes and electrons with stronger oxidation and reduction potentials are maintained and participate in the pollutant degradation reaction.?2?Ag⁰/AgFeO₂ nanocatalysts were synthesized by ethanol assisted ultrasonic reduction method.The obtained product is consisted of hexagonal AgFeO₂ and cubic metal Ag.The Ag⁰ nanoparticles well dispersed on the surface of cocoon like AgFeO₂nanoparticles.The?111?face of Ag⁰ and the?101?face of AgFeO₂ are connected.The Ag-2/AgFeO₂ typical sample exhibited surperior photocatalytic performance,with pseudo-first-order rate constant of 0.040 min^-1,which is 2.2 times bigger than that by AgFeO₂/20%g-C₃N₄.The inducement of the prominently enhanced photocatalytic activity of Ag⁰/AgFeO₂ was deeply analyzed.The SPR effect of metal Ag⁰ not only improved the Ag⁰/AgFeO₂ photocatalyst's absorption ability to light???500 nm?,but also promoted the separation of photo-induced electrons and holes as compared to that of AgFeO₂.Moreover,the electrostatic potentials of Ag metal?111?and AgFeO₂?101?surfaces were calculated to further study the photo-generated electron transfer route.The e^–transferred from AgFeO₂ to Ag⁰ while the free h⁺in the valance band of AgFeO₂ was confirmed as the dominant active species for the pollutant degradation.?3?The SPH and SPH-Ag photocatalysts with spheniscidite structure?[NH₄]⁺[Fe₂?OH??H₂O??PO₄?₂]·2H₂O?were firstly synthesized by one step hydrothermal method.Typically,the SPH-Ag material was modified by Ag⁺substitution doping.The SPH-Ag photocatalyst is equipted with pure spheniscidite structure and enhanced photocataltic performance.Furthermore,its photocatalytic property was highly maintained as well as its structure after five recycles.Ag⁺is demonstrated to enter into the spheniscidite cavities and substitute 1/4 of NH₄⁺without destroying the structure.The DFT calculation further confirmed that the SPH-Ag-1 is much more stable than SPH and SPH-Ag-2.Noteworthy,compared to SPH,the pure phase SPH-Ag catalyst equipped with larger specific surface area,broader visible light response region,stronger oxidizing ability and lower recombination rate of electrons and holes.Meanwhile,the valence electrons are rearranged and the unoccupied Ag 5s orbital hybridizes with Fe 3d and O 2p orbitals at valance band,which greatly improves the ability of gaining electrons and the separation of photo generated charge carriers over SPH-Ag.?4?The Fe³⁺doped IOMS-2 semiconductor catalysts were synthsed by one step hydrothermal method under different temperatures.The IOMS-120 typical sample with pure cryptomelane phase was obtained under 120 ^oC.The specific surface area of the IOMS-120 sample is 143.73 m²/g,which is more than 7 times than that of the OMS-2.Under vis-NIR light irradiation,about 360 ppm of formaldehyde,127 ppm of ethanol and 43 ppm of acetone were almost totally degradaded simultaneously to CO₂ and H₂O by 0.05 g of the IOMS-120 sample,whose catalytic activity was much superior to that of OMS-2 and IOMS-2 samples.Besides,its absorbency for light?1800 nm???200 nm?was greatly promoted by Fe³⁺doping.The oxygen vacancy content in the IOMS-120 is about two times of OMS-2.Interestingly,the doped Fe³⁺more tends to replace the lattice Mn under higher preparation temperature.As for the IOMS-120,87%of the doped Fe³⁺replaced the lattice Mn,while the rest substituted the K⁺in the tunnels.Under this condition,the lattice oxygen was much more active than that in the catalyst whose doped Fe³⁺all replaced lattice Mn ions,which was demonstrated by DFT calculation.According to the results of the degradation experiments,DFT calculation and characterization,the orbital electrons in the O 2p,Mn 3d and Fe 3d of the IOMS-120 were motivated by absorbing photons,which resuting in the formation of active species with strong oxidizability.Meanwhile,the IOMS-120 transferred the absorbed light into heat,which motivated the lattice oxygen into avtive O^*.Thereafter,the formaldehyde adsorbed on the surface of the catalyst was degradaded by the active species and O^*.This work may provide certain theoretical basis and research ideas on the synthesis of cheap,efficient and environmental friendly iron-containing photocatalysts,as well as their photocatalytic mechanisms.