Methods For Adjusting The Interlayer Structure And Improving The Sorption Capacity Of Organobentonite

Organobentonites are increasingly being used to adsorbents owing to their excellent sorption capacity toward organic pollutants. For the long chain organobentonite, the dominant mechanism of the sorption is partitioning. The affinity of organic phase could be enhanced by arranging the model of surfactants within the organobentonites interlayers, and then the sorption capacity of organobentonites might be improved. For the short chain organobentonites, the sorption site for contaminant was the surface of hydrophobic siloxane within the organobentonites interlayers, and the sorption capacity could be enhanced by increasing the exposed area of siloxane.In this study, in order to improve the sorption capacity of organobentonites, many kinds of methods to change the interlayer microstructure of bentonite had been discussed. Thermal treatment could be used to remove the interlayer water in the short carbon chain organobentonite, and then could expose more silicone surface of organobentonite. In addition, a new method was used to preparing organobentonite with low charges for studying the adsorption of organic pollutants. Furthermore, a series of composite-bentonites were synthesized by modifying bentonite simultaneously with surfactant and polymer. Sorption capacities of composite-bentonites toward phenol, heavy metals and dyes were investigated. The main original conclusions of the work are drawn as follows:(1) The interlayer water in the short carbon chain organobentonites can be removed by thermal treatment. So, more hydrophobic silicone surface could be exposed and the adsorption for organic pollutants was improved. In our study, the organobentonite was modified by TMA or CTMA, and then heated at 145 "C for 12 h, further the adsorption capacity of these products toward phenol were compared. The results showed that the adsorption capacity of heated organobentonite modified by TMA increased 18.5% as compared with that by the un-heated product.(2) A new reduced-charge organobentonite with high sorption capacity toward phenol was prepared based on the π-π effect and silicone surface hydrophobic interactions. Benzyltrimethylammonium chloride (BTMA) is an organic cation group with an aromatic ring, modified organobentonite by BTMA could improve the adsorption capacity toward aromatic pollutants (such as phenol) by bond of π-π. Some BTMA+ cations were exchanged into the interlayer of Li-bentonite, and then conducted with thermal treatment. Bentonite pillared by BTMA+ can effectively reduce the collapse of layer structure, which could enhance specific surface area and greater adsorption capacity of bentonite. Compared with the traditional method (i.e., first reducing the charge density and then exchanging BTMA+), the surface area of new reduced-charge BTMA-bentonite increased 1.5 times as that by raw bentonite, and the adsorption capacity for phenol increased by 26.3%.(3) Organobentonite modified by long-chain organic cation (CTMAB) and a cationic polymer chitosan (CTS) was used to remove the hydrophobic organic compounds, heavy metal cations and anionic dyes simultaneously. Compared to the organobentonite modified by CTMAB, the compound modified organobentonite had a better ability in the uptake of those three pollutants. The increase of hydrophobic organic compounds (phenol) adsorbed amount could be attributed to the high charge density of CTS, which could therefore made the arrangement of CTMAB closer. The improved adsorption of heavy metal cations was due to their chelation to the CTS functional groups. Yet the zeta potential of bentonite enhanced by CTS should be the reason behind the promoted removal of anionic dyes.