Mechanism And Application Of Nano Zero-valent Iron And Photocatalyst To In-suit Remediate Polluted Water

Groundwater and surface water pollution is a serious problem and the development of suitable in-situ remediation technique is an attractive issue in environmental geochemistry in recent years, which possesses quite significance in both theory and practice. Therefore the author mainly focuses on two aspects of water environmental remediation technology. One is application of nano zero-valent iron（nZVI） to remove the Cr（VI） in the groundwater; the other is using modified TiO₂ to degrade the organic chemicals of benzenes in surface water.The influence of dissolved oxygen（DO） and natural organic matter（NOM） are important significance in the application of removal of Cr（VI） in groundwater by nZVI. So we emphatically discussed the influence and function mechanism of DO and HA（a symbol of NOM） removal of Cr（VI） in water by nZVI. Batch experiments and characterization results showed that the existence of DO can promote the removal of Cr（VI）; but the existence of HA inhibit the reaction especially in the adsorption saturation of HA onto nZVI.In addition, on the basis of laboratory study, we operated a pilot test box to simulate the removing of Cr（VI） in groundwater by nZVI. As the running of pilot test,the Cr（VI） concentration in groundwater has been significantly reduced, which from the original 100 mg/L decreased below the detection limit. The concentration of Cr（VI）in the sand sample was determined at the later period, the results showed that the iron particles could remove and fix chrome well in ground water. After a period of operation, nZVI slurry was injected into the test box, which successfully simulated the injection process of nZVI in the in situ repair.The defects of TiO₂ could hinder the catalytic efficiency when degrade pollutants in surface water using TiO₂. Therefore we have modified TiO₂ to promote the degradation. A novel nanocomposite catalyst of（N, Fe） co-modified TiO₂ nanoparticles loaded on bentonite（B-N/Fe-TiO₂） was successfully prepared for the first time by sol-gel method. The synthesized B-N/Fe-TiO₂ were characterized by multiple techniques. The results showed that B-N/Fe-TiO₂ have big specific surfacearea and highest absorption in UV-visible region. The photocatalytic activity of B-N/Fe-TiO₂ was also the highest, the results of enclosure experiment showed the degradation efficiency of styrene and xylene by B-N/Fe-TiO₂ were 83.2% and 93.1%,respectively in 4 hours. However, B-N/Fe-TiO₂ cannot be recycled although it have high catalytic activity. Therefore a novel nanocomposite catalyst of magnetic Fe2O3 modified TiO₂ loaded with bentonite（Fe2O3-B-TiO₂） was successfully synthesized by a facile sol–gel method. The magnetism of Fe2O3-B-TiO₂ can solve the recycle problem. The preparation process of Fe2O3-B-TiO₂ is simple, and the material have large specific surface area, high visible region optical absorbance, narrow forbidden band and strong magnetic. Batch experiments results showed that the methyl blue was fully degraded by Fe2O3-B-TiO₂ under visible light, and the styrene and p-xylene degradation efficiency was also the highest under sun light.