Removal Of Three Carcinogenic Inorganic Acid Radical In Water

Malignant tumor has a devastating effect on human health and is one of the majorrisks to life. Nowadays, cancer, cardiovascular diseases and accidents are thethree leading causes of human death. For this reason, the World Health Organization hasmadecuring cancer as one of the prime tasks. Cancer wasalso found by the China’s Health Ministry as the number one cause of Chinese deathsin2005. Incidences of cancer and death rates from cancer have been increasing in the last30years in our country. In the coming twenty or thirty years, cancer incidenceand mortality will continue to show an upward tendency. A growing body of evidence from scientific and medical researchsuggests that most cancer cases are caused by the carcinogenicchemical speciesin the environment, which currently exist in the surface water, ground water and treated drinking water. Thus, the water contaminated with carcinogens must be purified to meet the health requirements. However, the types and amounts of contaminants in water are increasing with the ever-worsening water pollution, and the conventional water treatment techniqueshave lost efficacyin treating these increasingly complex pollutants. Therefore, novel methodsand new materialsfor removing carcinogens from water are needed to meet the future challenge. In the current study, new catalytic and adsorptive materials were developed and found to be highly effective inremoving3major carcinogenicanions from water, namely, nitrate, bromate and arsenite/arsenate.1.A magnetite supported monometallic Pd catalyst was synthesized by a co-precipitation process followed with the reduction in pure hydrogen at453K. The catalyst was composed of ultrafine Pd nanoparticles (-2nm) highly dispersed on the surface of superparamagnetic Fe3O4nanoparticles. The XRD, XPS and TPR measurementsconfirmed thatthe Pd/Fe3O4catalyst meets the three requirementsof denitrification:noble metal, capable of chemisorbing and activating hydrogen, a redox couple, and strong interaction between the noble metal and redox couple.The activity of Pd/Fe3O4catalyst for the reduction of nitrate and nitrite were examinedin lab water spiked with the contaminants. The denitrification activity was found toincrease with increasing Pd content. Inthe denitrification process,nitrite reduction was faster than the reduction of nitrate. XRD and TPR characterization supported the assertion that Pd/Fe3O4acted as thecatalyst in the denitrification process. Aside from its roles as the catalyst support and the magnetic separation medium, Fe3O4was found to be a good promoter for the nitrate reduction, where nitrate was firstly reduced to nitrite by the Fe(Ⅱ)/Fe(Ⅲ) redox couple, and subsequently reduced to nitrogen and ammonium. Further mechanisticstudies demonstrated that besides the Pd sites, active sites for the nitrite reduction also exist on the surface of Fe3O4. Part of the nitrite reduction occurred on the surface of Fe3O4, which may also be attributed to the Fe(Ⅱ)/Fe(Ⅲ) redox couple.Catalyst deactivation was investigated in the recycle experiment. Oxidation of Fe(Ⅱ) on the surface and weaker interaction between Pd and redox couple after catalytic reaction accounted for the catalyst deactivation. Catalyst deactivation induced by oxidation of Fe(Ⅱ) on the surface can be activated by H2reduction at180℃, but the weaker interaction between Pd and redox couple couldnot be recovered.2.A novel quasi-monodispersedsuperparamagneticPd/Fe3O4catalyst was synthesized by solvothermal and aqueous reduction method. The catalyst was made by dispersing nanoparticles of Pd (weight percent up to1%) on the surface of superparamagnetic Fe3O4microspheres with300nm～500nm in diameter and10-20nm in grain size. The existence of Pd nanoparticleson Pd(x)/Fe3O4catalyst surface reduced the mass transport limitation and subsequently facilitated the catalytic reduction of bromate.Most coexisting anions in water except for HCO3-, such as SO422-, NO3-, and Cl-, had only moderate effect on the catalytic reduction ofbromate by the Pd/Fe3O4catalyst. The poisoning effect from HCO3-could be minimized by increasing the Pd nanoparticle size on its surface. The catalyst could be easily recycled and reused, after100time’s recycle, complete catalytic50ppb bromate reduction could occur within only in5min.3.Silica monolith with dual-pore structure was prepared by a sol-gel method. In the monolith,the interconnected macroporesare desirable for liquid transport and the mesopores could serve as the sites for various functions, such as selective adsorption and catalytic active surfaces. The lager pore structure was changed by adjusting temperature and PEO content, whilethe mesopore structure was controlled by the ammonium concentration and solvent thermal conditions.Cerium oxide (CeO2) nanoparticles were integrated onto the silica monolith by a simple impregnation process to create a novel composite arsenic adsorbent (SCO). The SCO has interconnected macropores with high pore volume, large surface area, and CeO2loading up to69wt%after only oneimpregnation. When the cerium CeO2loading amount exceeded67wt%, CeO2nanoparticles precipitated on the surface of the silica skeleton and blockedmacropores.The SCOs served as the adsorption media in continuous column flow tests and demonstrated an exceptional arsenic removal performance. A high breakthrough bed volume of20000bv was achieved at a fast EBCT of4min for the treatment of arsenic-contaminated natural water of～80μg/L to meet the MCL at10μg/L for drinking water. The composite adsorbents required only a simple desorption/regeneration process and demonstrated agood adsorption performance after regeneration,making them attractive for industrial applications in the treatment of arsenic-contaminated water.