Abstract: Bi₂O₂CO₃ nano catalysts were prepared by hydrothermal method, and the effects of ethylene glycol and water on preparation of Bi₂O₂CO₃ were studied by an experiment changing the volume ratio of ethylene glycol to water.XRD, SEM and BET were employed to characterize the properties and structure of the as-prepared samples.At the same time, the mercury removal performance under UV light was experimentally studied.The results showed that it is beneficial for the growth of the pore size of Bi₂O₂CO₃ when ethylene glycol and water acted as common solvent.When the volume ratio of ethylene glycol and water was 2:1, pore diameter reached the maximum, i.e., 33 nm.Furthermore, the mercury photocatalytic oxidation efficiency was positively correlated with the pore diameter.After linear fitting, the slope of the line(k) was 1.64.With the increase of pore diameter, photocatalytic oxidation mercury efficiency increased.When pore diameter reached the maximum(i.e., 32 nm), the mercury photocatalytic oxidation efficiency also reached the maximum, 81%.Studies have shown that the larger pore size will prolong the residence of Hg on the surface of Bi₂O₂CO₃, which is beneficial for photocatalytic removal of element mercury reaction.