New Adsorbent With High Adsorption Capacity For Urea Nitrogen And Creatinine

Urea and creatinine are tow of the major metabolic end products, and the removalof their excess has been a major problem for patients suffering from chronic renalfailure (CRF). Urease (urea amydohydrolyse, EC 3.5.1.5) is a highly efficient enzymethat has been described as specific for conversion urea to ammonium and carbondioxide. The free urease is unstable, and the immobilized urease is stable in thesolution. The reaction occurs between ammonia and aldehyde group of dialdehydecellulose (DAC). The complex reaction occurs between 3,5-dinitrobenzoic acid andcreatinine. According to these reaction theories, the immobilized ureases wereprepaed;and the complex type adsorbent for urea nitrogen, which consisted ofchitosan coated dialdehyde cellulose (CDAC) and immobilized urease in gelatinmembrane (IE), was prepared. Dialdehyde cellulose 3,5-dinitrobenzoate (DNBZ-DAC)containing dialdehyde group and 3,5-dinitrobenzoyl group was prepared, and thisderivative was employed as a new adsorbent for removing urea nitrogen andcreatinine.Chitosan and gelatin with good biocompatibility have been used as carrier forenzyme immobilization. Immobilized urease onto glutaraldehyde cross-linkedchitosan beads, immobilized urease in glutaraldehyde cross-linked gelatin membraneand immobilized urease in gelatin membrane (IE) were prepared. Preparation andproperties of the immobilized urease were compared with each other. Consideringapplication in the adsorbent for urea nitrogen, immobilized urease in gelatinmembrane (IE) with simple preparation and high enzyme activity was used in thiswork.DAC and CDAC were prepared and characterized by FTIR and SEM. Theadsorption of urea nitrogen onto DAC and CDAC under catalysis of IE was studied inbatch system. The equilibrium isotherm of urea nitrogen adsorption onto DAC andCDAC with different degree of oxidation (DO) and the kinetics of adsorption withrespect to the DO of CDAC, the initial urea nitrogen concentration, temperature andDAC/IE and CDAC/IE weight ratio were investigated. Langmuir and Freundlichadsorption models were applied to describe the experimental isotherm and isothermconstants. Equilibrium data fitted very well to the Langmuir model in the entiresaturation concentration range. The effects of DO, initial urea nitrogen concentration,temperature and DCA/IE and CDAC/IE weight ratio on the adsorption of ureanitrogen onto DAC and CDAC, were investigated, and the results indicate theexperiment parameters affected significantly the adsorption capacity. The pseudofirst-order and pseudo second-order kinetic models were used to describe the kineticdata, and the rate constants were evaluated. The experimental data fitted well to thepseudo second-order kinetic model, which indicates that the chemical adsorptionfollows the pseudo second-order kinetic model.The complex type urea nitrogen adsorbent consisting of CDAC and IE wasprepared. The adsorption of urea nitrogen onto the adsorbent in phosphate buffersolution (pH = 7.4) was studied in batch system. The effects of the experimentparameters, which included DO of CDAC, initial urea nitrogen concentration, pH andtemperature, on the adsorption capacity of urea nitrogen onto the adsorbent atCDAC/IE weight ratio 10∶1 were investigated. The results indicate that aboveparameters affected significantly the adsorption capacity. The adsorption capacity ofurea nitrogen onto the adsorbent was 36.7 mg/g at DO of CDAC 88%, initial ureanitrogen concentration 600 mg/L, pH 7.4 and temperature 37 ℃ for adsorption 8 h.DNBZ-DAC was prepared by esterification of DAC and 3,5-dinitrobenzoic chloride(DNBC) in the lithium chloride/N,N-dimethylacetamide (LiCl/DMAc) solvent systemand pyridine as catalyst. It was investigated that the effects of molar ratio of thematerials, the amount of catalyst, reaction temperature and reaction time on the degreeof substitution (DS) of DNBZ-DAC. The product was used as adsorbent for creatinine.The adsorption capacity of creatinine onto DNBZ-DAC was investigated under theexperiment parameters including DS of DNBZ-DAC, initial creatinine concentration,pH and temperature in the phosphate buffer solution. The results suggest that aboveparameters affected significantly the adsorption capacity. The adsorption capacity ofcreatinine onto the adsorbent was 2.71 mg/g at DS of DNBZ-DAC 0.54, initial ureanitrogen concentration 600.1 mg/L, pH 7.4 and temperature 37 ℃ for 8 h.