Crystal Facet Regulation and Photocatalytic Properties of α-FeOOH: Crystal Facet Effects on the Built-In Electric Fields Coupled with Coordination Adsorption

The α-FeOOH (021) crystal facet has a high density of active sites, and as a reactive facet, it has good adsorption of pollutants and good photocatalytic performance. In this paper, nano α-FeOOH with different (021)/(110) crystal facet ratios was prepared using crystal facet inducers (ethanol, ethylene glycol, and glycerol) via a hydrothermal method, with a (021)/(110) crystal facet ratio reaching 16% in the FG-2 sample. The results of photocatalytic experiments show that this sample’s removal rate of Cr(VI) reaches 60.70% in 4 h, which is 61.00% higher than for FC with unregulated crystal facets, and the apparent normalized photocatalytic reaction rate constant is 8.28 times higher than for FC. Kelvin probe force microscope characterization (KPFM) results and density functional theory (DFT) calculation show that FG-2’s higher rate of removal of Cr(VI) was due in large part to the different electric potentials of the (021) and (110) crystal facets. When the ratio of (021)/(110) crystal facets was changed, different electric fields resulted. Meanwhile, the high site density of the (021) crystal facet created high coordination efficiency and in addition higher reactivity resulted from the chromium ion’s lower adsorption energy that the coupling effect produced.