| Chronic renal failure is a disease of high incidence and high mortality. Removinggastrointestinal uremic toxins with oral adsorbent is an effective method of treatment. sinceoral adsorbent is easy for application, low cost and easily accepted by patients, this therapyhas gradually become an important way for the treatment of chronic renal failure. Medicinalactivated carbon has the advantages of non-toxicity, low cost, strong adsorption ability, inaddition, it is hard to digest or be decomposed by bacteria, and the prototype can be out of thebody with feces. In the clinical treatment of acute poisoning and infectious gastrointestinaldiseases, it was suggested that activated carbon has a good curative effect. Removinggastrointestinal uremic toxins in patients(mainly creatinine toxins) with chronic renal failure byoral activated carbon adsorbent will reduce the incidence of end-stage renal failure and prolongthe lives of patients. Still, there are many disadvantages in commercial activated carbon,including wide range of pore size distribution, low selective adsorption and small adsorptioncapacity, thus the research work of enhancing the selectivity and increasing the adsorptionquantity to creatinine toxins on activated carbon has important significance. The main researchcontents and results are as follows:1. Research of the relations hip between adsorption properties of creatinine and porestructure characteristics of activated carbonActivated carbons with different pore structure were prepared with steam, CO2and KOH,respectively. The relationship between adsorption properties to creatinine and pore structurecharacteristics of activated carbon was studied. The results showed that: the adsorptioncapacity of creatinine on activated carbon increased as the increase of BET surface area. Whenthe specific surface area was similar, activated carbon with higher micropore volume had betteradsorption property to creatinine. Meanwhile, the adsorption process of ceratinine on activatedcarbon belongs to microporous adsorption, micropores between1nm and2.5nm did benefit to the adsorption, and the adsorption capacity of creatinine on activated carbon with an averagepore diameter of2.2nm could reached103.8mg/g. Conclusively, adsorption of creatinine wasinfluenced by BET surface area, pore volume and micropore ratio; activated carbons with highsurface area, big pore volume and high micropore ratio had best adsorption property tocreatinine.2. Directional regulation for pore structure of coconut shell activated carbon andadsorption to creatinineCO2secondary activation and high temperature reforming were used to regulate porestructure of coconut shell activated carbon. Results showed that:(1) The pore size of activatedcarbon was obviously expanded by CO2secondary activation. Compared with prolongingsecondary activation time, improving secondary activation temperature was more significanteffect of adsorption to creatinine, and the adsorption capacity of creatinine increased by28.87mg/g after treated by CO2secondary activation.(2) The carbon skeleton was shrinkaged afterhigh temperature treatment, and pore diameter distribution concentrated in micropore, thus themicropore ratio increased. Additionally, the adsorption properties of iodine, methylene blue andcreatinine were improved significantly after high temperature reforming, and the adsorptioncapacity to ceratinine was reached to more than93mg/g.(3) FT-IR analysis showed thatsurface functional groups on coconut shell activated carbon after being treated had a greatchange: the former increased by hydroxyl, lactone, carboxyl and other acidic oxygen functionalgroups; while high temperature reforming lead to a substantial increase of free hydroxyl, inaddition, phenolic hydroxyl and lactone also increased.3. Surface modification of coconut shell activated carbon and adsorption properties tocreatinineHydrochloric acid was used as surface modification agent, single factor experiment andL16(44) orthogonal experiment were investigated. The molar concentration of hydrochloric acid,the volume of hydrochloric acid, modified temperature and modified time was four conditions,and the best modification process was obtained finally. The results showed that: The influence on adsorption quantity of creatinine in the order of modification temperature, time, molarconcentration and volume of hydrochloric acid. The optimal technology were as follows:60℃,10ml/g,3mol/L,6h and the adsorption capacity of creatinine increased by16.6%after modified by hydrochloric acid. FT-IR analysis showed that acidic oxygen functionalgroups such as phenolic hydroxyl and carboxyl increased significantly after modified byhydrochloric acid, and the more intense of modification conditions, the larger increasedproportion of functional groups. The amount of acid functional group were increased obviouslyafter modified by hydrochloric acid, which increased the hydrophilicity of the activatedcarbon surface, thereby enhanced the adsorption of polar molecules creatinine.4. Effect of adsorption conditions on adsorption of creatinine and kinetics studyAccording to the results of the foregoing experiments, activated carbon with bestadsorption performance was chose to be adsorbent. The adsorption behavior of creatinine oncoconut shell activated carbon was studied, including activated carbon dosage, adsorption time,initial solution concentration, reaction temperature and pH. Meanwhile, the adsorption datawas treated according to pseudo-first-order, pseudo-second-order and intraparticle diffusionkinetic models, and the parameters of equations were determined. The results showed that theadsorption equilibrium was reached within6h and its equilibrium adsorption capacity was95.14mg/g, which is far higher than oxidized cellulose and oxidized starch (adsorptioncapacity is about20~30mg/g). The adsorption to creatinine increased as the increase of initialsolution concentration of creatinine. There was no significant effect in adsorption while pHwas from2to12. The adsorption to creatinine on activated carbon is endothermic process,improving the adsorption temperature could enhanced adsorption capacity of creatinine, whichsuggested that there was chemical adsorption in this process. The adsorption kinetics followedpseudo-second-order kinetic model, which proved that the adsorption of creatinine on activatedcarbon was a chemisorption process. |
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