Synthesis of Ag₃PO₄ Crystals with Tunable Shapes for Facet-Dependent Optical Property, Photocatalytic Activity, and Electrical Conductivity Examinations

Abstract

This work has developed conditions for the synthesis of AgPO cubes, rhombic dodecahedra, {100}-truncated rhombic dodecahedra, tetrahedra, and tetrapods by tuning the amount of NHNO, NaOH, AgNO, and KHPO solutions added. Use of a minimal amount of AgNO solution can form much smaller rhombic dodecahedra and tetrahedra. Submicrometer-sized AgPO cubes and rhombic dodecahedra with sizes larger than 300 nm do not exhibit the optical size effect, but ∼290 nm rhombic dodecahedra show a smaller band gap value than larger cubes, and tetrahedra show the most blue-shifted absorption edge. The optical facet effect is present in AgPO crystals. AgPO cubes are more photocatalytically active than rhombic dodecahedra toward photodegradation of methyl orange, but tetrahedra are inactive, showing clear presence of photocatalytic facet effects. Electron paramagnetic resonance results confirm much higher production of hydroxyl radicals from photoirradiated AgPO cubes than from rhombic dodecahedra, while tetrahedra yield essentially no radicals. A modified band diagram showing different degrees of band edge bending can explain these observations. All these AgPO crystals show poor electrical conductivity properties, but the {110} faces are slightly more conductive than the {100} faces. As a result, current rectifying I-V curves have been obtained, demonstrating that facet-dependent electrical properties are broadly observable in many semiconductor materials. This work reveals again that facet-dependent optical, photocatalytic, and electrical conductivity properties are intrinsic semiconductor properties.

Facet Effects of Ag3PO4 on Charge‐Carrier Dynamics: Trade‐Off Between Photocatalytic Activity and Charge‐Carrier Lifetime

“…This result agrees with the results of Hsieh et al. that the highest barrier for electron transport exists on the (111) crystal facet of the Ag 3 PO 4 tetrahedron, leading to faster charge recombination than that of the cube …”

“…recently reported that the Ag 3 PO 4 tetrahedron was nearly inert for dye degradation, whereas the Ag 3 PO 4 cube generated the largest amount of hydroxyl radical ( . OH) . Thus, there has been no consensus on which crystal structure of Ag 3 PO 4 is advantageous as a photocatalyst.…”

Density Functional Theory Calculations Revealing Metal‐like Band Structures for Ultrathin Germanium (111) and (211) Surface Layers

“…For example, the same Cu 2 O particle can simultaneously behave like a metal, a semiconductor, and an insulator depending on the measured crystal facets, thereby changing our understanding of semiconductor behavior. Despite the poor electrical‐conductivity responses due to the large energy band gaps of Ag 3 PO 4 , Ag 3 PO 4 crystals still show slight face‐specific electrical‐conductivity differences . Density functional theory (DFT) calculations performed on Cu 2 O, Ag 2 O, and PbS have revealed distinctly different band structures and density‐of‐states (DOS) plots within a few (100), (110), and (111) surface planes, which can be very insightful to understanding the observed electrical‐conductivity differences .…”

Synthesis of size‐tunable zinc blende ZnS nanocrystals

“…Acetic acid was introduced to further tune the ZnS crystal growth rate to achieve particle size control. Previously, a similar strategy to lower the equilibrium toward crystal formation by a precipitation reaction was employed to make Ag 2 O, PbS, and Ag 3 PO 4 crystals with shape control …”