Boosting performance with a dash of rock salt

Kyoto, Japan -- The layered development of photocatalytic technology that has evolved since the 1970s has led to a crystal-clear structural picture of bismuth oxychloride.

Now, researchers have revealed the chemical structure of this extensively studied photocatalyst. Unlike conventional oxyhalide photocatalysts with bismuth-oxide-fluorite-based layers, bismuth oxychloride is layered with corrugated bismuth oxides separated by chlorine layers.

"This structure has two unique features," explains lead author Daichi Kato of Kyoto University.  "First, the thickness of bismuth-oxide layer n is six, which is the thickest among all known layered oxyhalides."

"Second, the inner region contains one-dimensional rock-salt units in the fluorite matrix along a single axis, causing in-plane corrugation."

This corrugation is removed when topochemical fluorination causes the bismuth-oxygen layer in bismuth oxychloride to transform into a bismuth oxyfloride layer. In effect, these fluorinated samples show higher photocatalytic activity than bismuth oxychloride due to the loss of corrugation.

"We were surprised by the structural change due to fluoridation showing the original bismuth-oxygen layer with alternating rock salt and fluorite units," says the author.

The team has found that these structural layers can be manipulated together to harness improved photocatalytic activity, which presents a future potential for material designs.

"The very unique solid crystal structures of layered bismuth oxychloride with fluorite layers contribute to materials science as well and are what also interest us on a pure chemistry level," Kato concludes.

FLUORINATION OF CORRUGATED BI₁₂O₁₇CL₂ WITH ROCK SALT AND FLUORITE UNITS TO YIELD UNCORRUGATED BI₁₂O₁₄FCL