Adsorption-Photocatalytic Oxidation Performance Of TiO₂ Based Nanotubes In Elemental Mercury Removal

Mercury is one of the most hazardous air pollutants for its neurological toxicity, volatility, persistence, and bioaccumulation, which poses a great threat to both human health and organism security. Among human activities, coal combustion made the greatest contribution to anthropogenic source of mercury emission, which might lead to global mercury pollution through long distance transmission. Therefore, removal of Hg0 emitted from the flue gas has been a great challenge to environmental protection. Adsorption is one of the useful ways to capture mercury, but the high cost and secondary pollutions limit its application. Recently, the progress in absorption-photocatalytic oxidation gave us a new sight. We originally applied titania-based nanotubes to remove Hg0 in coal combustion by absorption-photocatalytic oxidation mode. This reasearch was focused on the reaction mechanism and modification of the titania nanotubes (TNTs).The TNTs, which have a special nanotube structure, were synthesized by hydrothermal method. The morphology and structure of the TNTs, calcined at different temperatures, were characterized by XRD, SEM, TEM, XPS and BET-BJH methods. The huge surface area and porosity of TNTs enhanced the synergy effect between absorption and photocatalytic oxidation, thus TNTs'removal efficiency of Hg0 was increased. A high removal efficiency (>90%) was observed in a 100 h experiment. Moreover, pores of the TNTs gradually collapsed and transformed into rod-like structure with the increasing calcination temperature. The TNTs which were treated at 500℃obtained the best removal performance.Furthermore, the properties and structure of the carbon doped titania nanotubes (C/TNTs) were studied. Meanwhile, the Hg0 removal performances of the C/TNTs were investigated. It was found that carbon doping could protect the damage of nanotubes to a certain extent in thermal treatment, but its transformation to rod-like structure couldn't be hold back absolutely. C/TNTs was a good photocatalyst & adsorbent, which had a admirable Hg0 removal efficiency (nearly 100%).To enhance the adsorption-photocatalytic oxidation ability of TNTs, the noble mental doped TNTs were prepared by photo-reduction method. The results showed that the synergy effect between adsorption and photocatalytic oxidation was significantly promoted by the combined actions of noble mental particles and TNTs, thus an excellent Hg0 removal efficiency was observed.