The Preparation Of Bifunctionalized Mesoporous Silica And Their Adsorption Properties For Nonylphenol

Nonylphenol(NP) is an endocrine disrupting chemical. NP may cause disruption of the hormone and the reproductive system by mimicking the structure of female hormone. It has been list as permanent organic pollutant by UNEP.An adsorption method is considered a simple and efficient mtheod toremovalpollutants from water. Ordered mesoporous silicahas attracted great attentionsdue to the highly uniform pore size, high specific surface area, large pore volume, stable chemical properties, and it was considered as an ideal adsorption material. The main drawbacks of am unmodified ordered mesoporous silica were low hyrothemal stability and poor selectivity. So many researchers have focused on the organic surface modification of ordered mesoporous silica to enhance its adsorption capacity or selectivety for organic pollutants. At present, most research mainly focused on the preparation of single functional group adsorbents. However, the selectivity of the monofunctionalized adsorbents is limited in low concentration aqueous solutions. Sohexadecyltrimethoxysilane and aminopropyltrimethosysilanewere used as organicsilane modifier. Bifunctionalized mesoporous silica was successfully prepared in order to efficiently remove NP in the water.Cetyl/amino-SBA-15 was successfully prepared by a post-synthesis grafting method. Cetyl and aminopropyl groups were simultaneously functionalized on the surfaceof SBA-15. The adsorption capacity of bifunctionalized SBA-15 was much higher than the monfunctionalized SBA-15. Fristly,the certain aminopropyl groups facilitated the immobilization of the cetyl groups. Secondly,the cooperative effect of hydrogen bond/electrostatic interaction between 4-nonylphenol(4-NP) and aminopropyl groups and hydrophobic interactions between 4-NP and cetyl groups improved the adsorption capacity of bifunctionalized SBA-15. The adsorption capacity of cetyl/amino-SBA-15 was higher than cetyl/diamino-SBA-15 and cetyl/triamino-SBA-15. Because only one effective amino site in amino-organoalkoxysilanes could work with cetyl groups to cooperatively remove 4-NP. So the effect of amino sites in amino-organoalkoxysilanes is not obvious.In addition,the molecule size of diamino and triamino groups isbigger thanaminopropyl groups,the larger steric hindrance effect of diamino and triamino groups results in a lessergraftedamount. As a result, cetyl/amino-SBA-15 showed thehighestadsorption capacity.The cetyl/amino-SBA-15 with different addition doses and ratios of cetyl/amino were prepared. When the total addition doses of cetyl and amino groups was4 mmol/g, the ratio of cetyl/amino was4:1, the prepared sample exhibited highest adsorption capacity. As the result of element analysis, the mole ratio of grafted cetyl/amino groups of cetyl/amino-SBA-15(3.2/0.8) was almost equal to 1. The results further indicate that the cooperative effect between cetyl and aminopropyl groups is the predominant factor in remarkablyimprovingthe adsorption capacity.The cetyl/amino-SBA-15 exhibited excellent adsorption capacity in p H range from 4 to 9, showed high selectivity for 4-NP against phenol, have excellent and stable adsorption capacity after recycled severaltimes.Three bifunctionalized adsorbents with different pore size were successfully prepared with hexadecyltrimethoxysilane and aminopropyltrimethosysilane as organicsilane modifier, namely cetyl/amino-MCM-41, cetyl/amino-SBA-15 and cetyl/amino-SBA-15(B). The adsorption capacity of three bifunctionalized adsorbents increased with the increase of pore size, cetyl/amino-SBA-15(B) showed the highest adsorption capacity. The three bifunctionalized adsorbents showed high adsorption rate, and the adsorption process could be descripted by pseudo-second dynamic model. The adsorption isotherms conformed to Langmuir adsorption model, the fitted largest adsorption capacity of cetyl/amino-MCM-41, cetyl/amino-SBA-15 and cetyl/amino-SBA-15(B) was146.92, 183.77 and 794.62mg/g, respectively. The result of adorption thermodynamic showed that low temperature was favor the adsorption of NP, and the adsorption of NP on bifuncitonalized adsorbent was aexothemoc and spontaneous process.