Abstract: Pillared montmorillonite (P-MMT), organic montmorillonite (O-MMT), layered double hydroxide (LDH) and layered double oxide (LDO) were prepared. Their adsorption performance on Cr (VI) was measured.
The result shows that adsorbent capability (AC) of P-MMT and O-MMT is 8.9 and 3.7 mg/g respectively; both of them can be attributed to physical adsorption. Their surface characters, i.e., hydrophilic P-MMT
versus hydrophobic O-MMT, are quite possibly responsible for the difference in AC. LDO’s AC on Cr (VI) is 73 mg/g at room temperature, much higher than that of the other materials. After the adsorption,
LDO’s XRD pattern changes apparently, similar to the one of LDH. This demonstrates that LDO took anions from the solution to recover the crystal structure of LDH, and that the adsorption is chemical
one. Theoretical AC of LDO on Cr (VI) calculated from the reaction formation is 152 mg/g. pH variation during the adsorption was observed. pH of the solution increased rapidly at the first few minutes,
slowly from 5 to 180 minute, decreased a bit after that. The first two phases indicate the adsorbing progress, and the last one is quite possibly related with the interference of dissolved CO₂. There
are two ways to restrain the activity of CO₂, increasing Cr (VI) content and/or decreasing CO₂ content. In the solution being boiled and isolated from air, LDO’s AC on Cr (VI) can be as high as 157.1 mg/g.
The part above the theoretical AC can regard as the contribution of physical adsorption.

Key words: compounds with layered structure, layered double oxide, Cr （VI） anion, adsorption performance