| Summary: | 碩士 === 國立中興大學 === 土壤環境科學系所 === 103 === Tetracyclines (TCs) are commonly used as feed supplements to enhance animal growth or to treat diseases derived from microbial infections. Because TC cannot be completely metabolized in vivo, about 30-90 % TCs are excreted via the feces and urine as integral. As a result, TC has been found in many soils and natural waters, particularly in those areas near the farmlands. Inorganic colloids, such as clay minerals, distribute widely in the environments which may perform as a good adsorbent for TC or other pollutants because these minerals exhibit unique properties of small particle size and large surface area. Bentonite, one of the soil minerals consisting mainly of montmorillonite, can be a scavenger for environmental pollutants; however, the hydrophilic surfaces of bentonite may limit its application for removing less or non-polar organic molecules. Therefore, a cationic surfactant, such as alkyl amines, had been used to convert the bentonite surfaces becoming more hydrophobic to promote its adsorption capacity of non-polar molecules. Cationic surfactant exhibits a higher bio-toxicity, and this kind of surfactant may lead to a poison while being used as an antibiotic carrier. In this study, a non-ionic surfactant, i.e., Brij30, was used to modify bentonite, and its interaction with TC over a pH range of 3-8 was investigated. Results showed that TC adsorption on bentonite/or Brij30 modified bentonite could be described by the Langmuir model. However, Brij30 would inhibit TC adsorption on bentonite due probably to the blockage of the adsorptive sites of bentonite by Brij30. At pH 3, each bentonite sample exhibited a better adsorption ability of TC, attributing to the electrostatic attractions between TC and bentonite. The results of pH and ionic strengthen effects indicated that TC adsorption on Brij30-modified bentonite was more favorable at pH 8 than that at pH 5. This may be attributed to the hydrophobic interactions of TC molecules with Brij30. Besides, XRD diagram indicated that the d-spacing of TC-loading bentonite exhibited the highest at pH 8 which suggested that TC molecules may associate each other, probably through hydrophobic forces, prior to entering the interlayer of bentonite. FTIR spectra showed that the C=O from A ring and O=C-NH2 group may play an important role in TC adsorption.
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