| Perchlorate contamination of drinking water has become a major concern formany people. USA added perchlorate to the pollutant’s list of drinking water, andJapan listed it as the first category contaminant. A pollution survey in China shownthat, perchlorate has been detected in drinking water, dairy p roducts, grains, and evenin human breast milk. The perchlorate contamination results in great threat to thehealth of people. Perchlorate competitively inhibits iodide at the level of the sodiumiodide supporter, so the main health concern regarding perchlorate is its ability tointerfere with iodine uptake by the thyroid gland, resulting in a decreasing productionof the thyroid hormones. It has been linked to anemia and fetal brain damage.Perchlorate is one of the most stable pollutants in nature. Perchlorate salts are highlysoluble in water and dissolved perchlorate anions do not tend to partition fromaqueous to gas phase. Perchlorate salts also have low vapor pressure and hence itcannot volatilize under ambient conditions. It is very difficult to re move perchloratefrom water once contaminated because it is a persistent pollutant. Hence, obtaining anadsorbent that assure the effectively removal of perchlorate contaminants fromaqueous solution is important and urgent.The coconut activated carbon (GAC) was nitrogen functionized used to do thetest. As we all known, with a high the adsorption capability of activated carbonprepared from coconut is usually high. The process of ammoniation can improve theadsorption capacity for perchlorate. In this study, the modified GAC was treated bythree steps in turn; they were pretreatment, ammoniation and methylation. In the thirdchapter, the modified activated carbons were treated by one or two or three steps. Thecharacteristics of the modified activated carbons were analyzed by scanning electronmicroscopy (SEM), laser particle size analyzer and specific surface area tests (BET),pH detection, and X-ray photoelectron spectroscopy (XPS). The static adsorption oflow concentration perchlorate contaminants from aqueous solution was study. Theresult indicated that the surface character of modified activated, which was with theprocess of carbon pretreatment, ammoniation and methylation, has been changed asfollow: first, the nitrogen-functionalized GAC had a BET surface area of370.38m2/g,micropore volume of0.103cm3/g; second, the pH value of it was9.65, it wasindicated that there were many basic groups on the surface; third,nitrogen-functionalized GAC was fixed more nitrogen functions, pyridine structure percentage was45.88%. It was found that nitrogen-functionalized GAC wouldachieve as much as5.3-fold improvement in perchlorate adsorption.In the fourth chapter, the impacts of pretreatment on the surface chemistry and poresize properties of nitrogen functionalized GACs were studied. In this paper, granularactivated carbon (GAC) from coconut shell was pretreated by HNO3, H2O2andurea-formaldehyde resin, respectively. The characteristics of nitrogen-functionalizedGACs were analyzed by scanning electron microscopy (SEM), laser particle sizeanalyzer and specific surface area tests (BET), electrophoretic mobilities, Fouriertransform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS).The result shown that, the nitrogen-functionalized which pretreated byurea-formaldehyde caused a drastically decrease in surface area and microporosity.N-CH3group and C=N groups were detected on the surfaces of these three kinds ofmodified GACs. The modified GAC which pretreated by urea-formaldehyde resinintroduced more pyridine structure and the potential values of it was45.2, the virginactivated carbon only was-0.04338, it was indicated that there were more surfacecharge on the surface. The perchlorate adsorption of nitrogen-functionalized GACwhich pretreated by urea-formaldehyde resin was more than that of the others twopretreatment methods. The perchlorate adsorption mechanism onnitrogen-functionalized GAC was researched. The perchlorate sorption may involve:(1) metal exchange with chloride anion, attributing to co-precipitation, the chlorideanion was substituted with the perchlorate anion, until saturation occurs;(2) physicaladsorption of the activated carbon surface;(3) attracted by the positive charge;(4)precipitation.In the fifth chapter, the remove of perchlorate by nitrogen-functionalized GACwhich treated by different ammoniated condition. The result shown thatnitrogen-functionalized GAC had the highest perchlorate absorption capacity whichwas heated to700°C, and stayed at this temperature for60min. In this chapter, theregeneration of nitrogen-functionalized GAC was also researched. The result ofthermal regeneration showed that the perchlorate absorption capacity ofnitrogen-functionalized GAC which was regenerated three times was4500, itachieved as much as4.5-fold improvement in perchlorate adsorption. So, this productwas preferably regenerate peculiarity.It can be concluded through the front research that the nitrogen-functionalizedgranular activated carbon was effectively in the removal of low concentrationperchlorate which treated by three steps in turn： GAC was pretreated by urea-formaldehyde resin，than the obtained materials were ammoniated treatment forone hour at700℃，the last, the materials methylation. It achieved as much as5.3-foldimprovement in perchlorate adsorption, at the same time, it can be regeneration. |
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