| Semiconductor zinc oxide(Zn O) because of its characteristics such as wide band gap width and become a kind of photocatalyst with application prospect. Different modifications of the nanometer Zn O as photocatalyst matrix were studied systematically in this paper. Pure nanometer Zn O was prepared by ultrasound precipitate, Bi/Zn O, Ce/Zn O, Zn O/PVC were prepared by modification, respectively. zeolite loaded Bi/Zn O was prepared, the preparation conditions and application conditions of the Bi/Zn O/zeolite were explored. The Bi/Zn O, Ce/Zn O, Zn O/PVC polypropylene polyhedral sphere were prepared with coupling agent, and their abilities of photocatalytic degradation after loaded were compared. Their structure and performance were explored by a variety of experimental apparatus. Considering the actual application, the ammonia-N and COD of the wastewater of seafood processing were regarded as targets for photocatalytic degradation experiment. The photocatalytic kinetics of Ce/Zn O were studied in this paper. The main research results of this paper are as follows:(1) Pure nanometer Zn O was prepared by ultrasonic precipitation, and the crystal structure and surface morphology were characterized by XRD and SEM. The efficiency of amount of catalyst,catalytic reaction time,initial concentration of ammonia-N and COD, p H value and hydrogen peroxide et al for removal ammonia-N and COD were investigated in detail. The optimum experimental conditions for photo-catalytic degradation of ammonia-N and COD in the wastewater of seafood processing by orthogonal experiment are as follows. For ammonia-N in the, the amount of catalyst is 0.9g/L, the initial concentration of ammonia-N is 140mg/L, the initial concentration of COD is 900/L, the catalytic reaction time 4h, when p H 9, and the maximum degradation rate reaches 65.804%.For COD in the waste water of seafood processing, the amount of catalyst is 0.9g/L,the initial concentration of ammonia nitrogen is 110mg/L, the initial concentration of COD is 600/L, the catalytic reaction time 3h, when p H 9 and the maximum degradation rate reaches 80 %.(2) Ce/Zn O photocatalyst were prepared by precipitation, and the crystal structure, Zn O bonding, crystal shape, particle size, surface morphology, etc were characterized by FTIRs, XRD and SEM. It was found that with the increment of the Ce doping, Ce O2 characteristic peak gradually appear, and the peak position gradually blue shift by observing the infrared spectrogram. With the increase of calcination temperature and calcination time, absorption peak of H-O-H in free water decreased, and the surface of zinc oxide hydroxyl peak first increases then decreases. It was found that catalysts were typical six-party wurtzite, good crystallization and high purity by comparative analysis of the XRD diffraction pattern. Ce element already existed in the composite nanometer catalysts in some form. With the increase of calcination temperature and calcination time, the degrees of crystallinity is higher and higher. The average particle size were between 40 to 50 nm, which means Ce doping doesn’t have much influence on particle size. Their photocatalytic activities were investigated under the conditions of UV light source using the waste water from seafood processing as target pollutant. The results show that the calcination time, calcination temperature, proportion of Ce doped, photocatalyst dosage, reaction time all had function to the degration of COD and ammonia-N. According to the results, the ammonia-N and COD in the waste water from seafood processing were effectively degraded with UV light sources excitation. Doping cerium can improve the photocatalystic ability of Zn O. The influence orders of degradation as follows: calcination temperature> reaction time> photocatalyst dosage> doping ratio≈calcination time for ammonia-N and reaction time> calcination time> calcination temperature> doping ratio> photocatalyst dosage for COD. According to the orthogonal experiment, under the optimum experimental conditions, ammonia-N and COD removal rate can reach 83.4% and 59.1%, respectively.(3) Bi/Zn O photocatalyst were successfully synthesized by sol-gel method. The crystal structure, bonding, crystal shape, particle size, surface morphology, etc were characterized by thermogravimetric analysis, XRD, SEM, FTIRS. It was determined that Bi/Zn O calcination temperature at least higher than 270 ℃by thermogravimetric analysis. By comparing the infrared spectrogram, With the increase of temperature and n(Bi) : n(zinc), the absorption peaks blue shift and with the increase of calcination temperature, the absorption peaks redshift. By XRD diffraction analysis, with the increase of Bi content, calcination temperature and calcination time, particle size increases. The fact was observed by Scanning electron microscopy, with the increase of n(Bi) : n(zinc), calcining temperature, calcining time, The particle sizes relative increase, some even more than nanoscale. Their photocatalytic activities were investigated under the conditions of visible and UV light source using the waste water from seafood processing as target pollutant. According to the results, the ammonia-N and COD in the waste water from seafood processing were effectively degraded within nano-zinc dioxide catalytic system with UV light and visible sources excitation. The influence orders of degradation as follows: reaction time>calcination temperature>calcination time>proportion between bismuth and zinc>photocatalyst dosage for ammonia-N and calcination temperature> proportion between bismuth and zinc>photocatalyst dosage>calcination time>reaction time for COD under UV light. According to the orthogonal experiment, under the optimum experimental conditions, ammonia-N and COD removal rate can reach 86.7% and 76.9%, respectively. Under visible light, the influence orders of degradation were: reaction time>photocatalyst dosage>calcination time>calcination temperature> proportion between bismuth and zinc for ammonia-N and reaction time>calcination time>calcination temperature>proportion between bismuth and zinc>photocatalyst dosag for COD. According to the orthogonal experiment, at the optimum experimental conditions, ammonia-N and COD removal rate can reach 87.1% and 89.33%, respectively.(4) Zn O/PVC photocatalyst were successfully synthesized by two step synthesis method. The crystal structure, bonding, crystal shape, particle size, surface morphology, etc were characterized by thermogravimetric analysis, XRD, SEM, FTIRS. Thermogravimetric analysis was carried that Zn O/PVC composite begin to formate into conjugated polymer around 223 ℃. In the infrared spectrum comparison, Zn O and PVC’s characteristic peaks were observed respectively, and the absorption of Zn-O-C bonding peak was found. At 150 ℃, only Zn O’s peaks in the complex characteristic were apparent, and with the temperatures rise, Zn O’s characteristic peaks gradually disappeared, diffraction peak of Zn O/PVC composite was formed, and their dispersion was higher. Their photocatalytic activities were investigated under the conditions of visible light source using the waste water from seafood processing as target pollutant. According to the results, The influence orders of degradation as follows: proportion between Zn O and PVC> calcination time> calcination temperature> reaction time>photocatalyst dosage for ammonia-N and calcination temperature> calcination time>reaction time>proportion between Zn O and PVC> photocatalyst dosage for COD under visible light. According to the orthogonal experiment, ammonia-N and COD removal rates can reach 77.4% and 66.7%, respectively at the optimum experimental conditions.(5) The nano Ce/Zn O reaction kinetics of ammonia nitrogen and COD in waste water from seafood processing were investigated. According to the basis of dynamic model of Langmuire-Hinshelwood(L-H), four factors such as the catalyst preparation conditions like calcination temperature, calcination time, Ce doping ratio and initial concentration of pollutants were took into consideration. The first order reaction kinetics equation can be used in description.(6) Zeolite, polypropylene polyhedral ball were took into consideration as carriers to load photocatalyst. Bi OCl/Zn O/zeolite catalyst were successful prepared and their structure and surface morphology were characterized by XRD and SEM. The optimization conditions for Bi/Zn O/zeolite catalyst were explored by experiments. The experiments show that the load type photocatalyst has better degradation effects on the low concentration of ammonia-N and COD. The removal rate of ammonia-N and COD were as high as 80.9% and 94.1% respectively under visible light. At the same time, the polypropylene polyhedral ball supported Zn O/PVC, Ce/Zn O, Bi/Zn O were prepared. The results after experiments show that photocatalysts loaded to the polypropylene polyhedral ball still have better removal effect after 6h under the visible light.The degradation of the Bi/Zn O was best, ammonia nitrogen removal rate as high as 68.3% and COD can reach 72.1%. The degradation effect are higher than those of Zn O/PVC and Ce/Zn O. |
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