The search for active semiconductor photocatalysts that directly split water under visible-light irradiation remains one of the most challenging tasks for solar-energy utilization. Over the past 30 years, the search for such materials has focused mainly on metal-ion substitution as in In(1-x)Ni(x)TaO(4) and (V-,Fe- or Mn-)TiO(2) (refs 7,8), non-metal-ion substitution as in TiO(2-x)N(x) and Sm(2)Ti(2)O(5)S(2) (refs 9,10) or solid-solution fabrication as in (Ga(1-x)Zn(x))(N(1-x)O(x)) and ZnS-CuInS(2)-AgInS(2) (refs 11,12). Here we report a new use of Ag(3)PO(4) semiconductor, which can harness visible light to oxidize water as well as decompose organic contaminants in aqueous solution. This suggests its potential as a photofunctional material for both water splitting and waste-water cleaning. More generally, it suggests the incorporation of p block elements and alkali or alkaline earth ions into a simple oxide of narrow bandgap as a strategy to design new photoelectrodes or photocatalysts.
We recently reported that Ag(3)PO(4) exhibits excellent photooxidative capabilities for O(2) evolution from water and organic dye decomposition under visible-light irradiation. However, very little is known about the shape and facet effects of Ag(3)PO(4) crystals on their photocatalytic properties. Herein we have developed a facile and general route for high-yield fabrication of single-crystalline Ag(3)PO(4) rhombic dodecahedrons with only {110} facets exposed and cubes bounded entirely by {100} facets. Moreover, studies of their photocatalytic performance have indicated that rhombic dodecahedrons exhibit much higher activities than cubes for the degradation of organic contaminants, which may be primarily ascribed to the higher surface energy of {110} facets (1.31 J/m(2)) than of {100} facets (1.12 J/m(2)).
Herein, we have developed a facile and general method for the high-yield fabrication of AgX/Ag(3)PO(4) (X = Cl, Br, I) core-shell heterostructures with an unusual rhombic dodecahedral morphology, which exhibit much higher photocatalytic activities, structural stabilities and photoelectric properties than pure Ag(3)PO(4) crystals in environment and energy applications.
A strategy of reaction-environment modulation was employed to change the surface property of a semiconductor photocatalyst to enhance its photocatalytic performance. Surface alkalinization induced by a high alkalinity of the solution environment significantly shifted the surface energy band of a SrTiO(3) photocatalyst to a more negative level, supplying a strong potential for H(2)O reduction and consequently promoting the photocatalytic efficiency of H(2) evolution. This mechanism is also applicable for visible-light-sensitive La,Cr-codoped SrTiO(3) photocatalyst, which hence, could achieve a high apparent quantum efficiency of 25.6% for H(2) evolution in CH(3)OH aqueous solution containing 5 M NaOH at an incident wavelength of 425 ± 12 nm.
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