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Thermodynamics Kinetics of Dynamic Systems Part 12

Tham khảo tài liệu 'thermodynamics kinetics of dynamic systems part 12', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Thermodynamics Kinetics and Adsorption Properties of Some Biomolecules onto Mineral Surfaces 319 undergo exchange with some of the cations in the solid lattice leading to the consumption of H ions in suspension. For an oxide or clay there is usually only one ionisable surface group but that is amphoteric so it can take up either a proton or an OH- ion depending on the pH Hunter 2002 SO-H H SOH2 2 SO-H OH- SO- H2O 3 at isoelectric point iep SOH2 SO- 4 where S denotes the surface. When pH is equal pHiep the net charge is zero. This pH corresponds to the presence of equal numbers of oppositely charged groups on the biomolecules. Such a neutral structure of charged groups is called a dipolar ion or zwitterions. The iep of the sepiolite was determined by measuring the zeta potential as a function of pH Fig. 1 . The zeta potential is about 0 mV for sepiolite at around pH 6.6 in this studied pH range of 1.5-10. Fig. 1. The variation of zeta potential with pH of the sepiolite mineral. 3.2 Adsorption capacities as a function of incubation time of sepiolite The adsorptions of casein and catalase on sepiolite were carried out in 0.001 M NaCl and 0.02 M sodium phosphate buffer at pH 7.0 and 22 0C. The initial concentrations of biomolecules were 1.0 mg mL-1 and the solid concentration was 3 g L-1 for sepiolite. Measuring the concentration of biomolecules in solution at different incubation times 320 Thermodynamics - Kinetics of Dynamic Systems generated in a time course of the adsorption. The results are shown in Fig. 2. According toFig. 2 the time required to reach a stationary concentration is about 10 h. 3.3 Adsorption of biomolecules onto sepiolite and zeta Z - potential values Adsorption experiments were carried out at the same conditions with zeta potential experiments in order to correlate the adsorption performance with Z-potential of sepiolite minerals. Fig. 3 shows the variation of zeta potential with biomolecule concentrations of sepiolite minerals in 0.02 M .