| Summary: | 碩士 === 元智大學 === 化學工程與材料科學學系 === 95 === Recent advance in technology has led to serious wasterwater pollution in Taiwan. As a result, many nitrate/nitrite wastewater treatment technologis has been evolved eventually. Therefore, the main objective of this research was to synthesize the nickel (Ni) or zinc (Zn) ferrites (Ni- or Zn-Fe2O4) and to reduce the concentration of nitrate/nitrite contaminants in wastewaters. The current research can be divided into four sections including synthesis of ferrites, application of ferrites on nitrate/nitrite contaminants removal, regeneration, and recycle or reuse of ferrite nanoparticles. Moreover, the kinetic parameters got by pseudo-first-order model equation were also found.
Experimentally, nickel or zinc ferrite nanoparticles were synthesized under hydrothermal conditions (pH = 8.5, T = 453 K, and mixing rate of 1250 rpm) by precipitating from metal nitrates with aqueous ammonia. Synthesized nanopowders were characterized by X-ray powder diffractometer (XRPD), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), BET surface area and porosimeter, electron spectroscopy for chemical analysis (ESCA), Fourier transform infrared spectrometer (FTIR), extended X-ray absorption fine structure (EXAFS), X-ray absorption near edge structure (XANES), ultraviolet-visible spectrophotometer (UV/Vis), and particle size meter. These results showed that the pore sizes of Ni, Zn-Fe2O4 were about 50-100 nm with spinal structure. Ni, Zn-Fe2O4 having strong characteristic peaks at 2θ = 35.66 and 35.24 were investigated by XRPD patterns, respectively. The specific surface area of Ni, Zn-Fe2O4 measured by ASAP isotherms were 100.4 and 170.7 m2/g, respectively. From ESCA spectra, the results showed that the Fe(2p) of Ni, Zn-Fe2O4 were at 711.05 and 711.25 eV respectively, Ni(2p) of NiFe2O4 were at 855.3 eV, Zn(2p) of ZnFe2O4 were at Zn(4) = 1021.95 eV, and Zn(6) = 1023.08 eV, respectively. By using FTIR spectra, the results showed that the characteristic peaks of Ni, Zn-Fe2O4 were about at 571 and 593 cm-1, respectively, the O-H characteristic peaks of Ni, Zn-Fe2O4 were at 1382 and 1380 cm-1, respectively.
The XANES/EXAFS spectra showed that the valencies of the Ni, Zn-Fe2O4 were Ni(II) and Zn(II), respectively. The first shell of Fe-O bonding for Ni, Zn-Fe2O4 with bond distances were 1.95 and 1.94 Å and coordination numbers of 4.03 and 3.81, respectively before hydrogen reduction. Similarly, the first shell of Fe-O bonding for Ni, Zn-Fe2O4 with bond distances were 1.98 and 2.03 Å and coordination numbers of 4.03 and 3.81 respectively after hydrogen reduction at 573 K and 1 atm. The decomposition of nitrate or nitrite contaminants analyzed by UV/Vis was investigated by oxygen-deficient Ni, Zn-Fe2O4 formed by hydrogen reduction at 573 K and 1 atm. As indicated by the results from XRPD, TEM and FE-SEM, the fine structure of Ni, Zn-Fe2O4 did not change after the reaction. In terms of nitrate and nitrite wastewater treatment, the decomposition rates of Zn-ferrites were more efficient than the ones of Ni-ferrites at optimum operating condition at pH = 5 in room temperature. Reaction process described by pseudo-first-order model equation and the k value was increased while the wastewater concentration decreased. The optimized operating conditions were also applied on wasterwater treatment plants, it was found that Zn-ferrites were more efficient than the ones of Ni-ferrite nanoparticles.
As shown by XRPD, TEM and FE-SEM analyses, the structure of Ni, Zn-Fe2O4 is very stable and can be recycled. The recyclibility rates of Ni, Zn-Fe2O4 were 98.25 and 98.36% repectively. Thus, the outcome of this study would be able to be applied on existing wasterwater treatment so as to improve the efficiencies of the processes.
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