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,  (bismuth oxide layer has six Bi sublayer), which is the thickest times thicker than allamong 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 tointo 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 hydrogen productionmaterial 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.

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The paper "Bi12O17Cl2 with a sextuple Bi-O layer composed of rock-salt and fluorite units and its structural conversion through fluorination to enhance photocatalytic activity" appeared 2 August 2022 in Advanced Functional Materials, with doi: 10.1002/adfm.202204112

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