Hydrothermal Synthesis Of Doped Porous Titania From Industrial Titanyl Sulfate Solution And Its Fromation Mechanism

Porous titania has superior physical and chemical propeties because of its high specificsurface area, order pore structure and easily recyclable, and it has been widely applied inmany fields, such as sewage treatment, air purification, solar cell, antibiosis, etc. In thisdissertation, porous titania with highly specific surface area has been synthesized fromindustrial TiOSO₄solution derived from sulfate process by hydrothermal hydrolysis, andin-situ doped with Fe and S ion carried by TiOSO₄solution. The effects of hydrothermalreacting time and temperature, titanium concentration, calcination temperature and time, andso on, on the structure and property of the doped porous titania were investigated, formationprocess and mechanism of porous titania were also researched, and its photocatalyticapplication and catalyst life were evaluated. The as-prepared samples were characterized byXRD, SEM, TEM, FT-IR, XPS, N2absorption and desorption, particle size distribution, etc.,and its photocatalytic activity were evaluated by degradation of methylene blue （MB）. Themain studies results are as follows.The synthesis conditions have played an important role on the photocatalytic activity ofthe doped porous titania.（1） As prolonging of hydrothermal reacting time, the photocatalyticdegradation rate of MB first increased and then dropped, the sample shows the highestphotocatalytic activity at hydrothermal reacting time of3h.（2） Reducing hydrothermalreacting temperature is good for forming fine and uniform titania particles, in favour ofenhanceing its photocatalytic activity.（3） Elevating titanium concentration （below215g/L） isbeneficial to improve its photocatalytic activity.（4） F value, feed time, bottomwater andtitanium volume ratio has small effect on photocatalytic degradation of MB.（5） Reducingcalcination temperature （above450℃） and prolonging calcination time （below1h） arebeneficial to maintain the balance between the specific surface area and crystallinity of titania,resulting in its high photocatalytic activity.Hydrothermal crystallization of industrial metatitanic acid can improve thephotocatalytic activity of the porous titania. With prolonging the hydrothermal treatment time,the degradation rate first increased and then dropped, wiht hydrothermal treatment for2h thebest, whose degradation ratewas higher8.01%than the untreated one.All the metatitanic acid precipitate had porous structure in the process of hydrothermalsynthesis, with average porous size about4nm, and its specific surface area up to214m2/g.The formation of porous due to two reasons, on the one hand metatitanic acid particlesaggregated to form porous structure, on the other hand water molecule were encapsulated bymetatitanic acid particled and porous structure was formed after water removed by drying. Doping of Fe ion in porous titania resulted from the replacment of Ti in TiO₂crystal andabsorption on the metatitanic acid surface. While doping S ion resulted from SO₄^2-absorptionand bonding with TiO₂, introducing into metatitanic acid to for solid superacid.Doped porous titania were synthesized with the optimal synthesis conditions, and itsphotocatalytic application and catalyst life were investigated.（1） The synthesized dopedporous titania showed nearly the same photocatalytic activity contrast wiht Degussa P25, andits degradation rate is higher than P25in the first ten minutes.（2） Doped porous titaniacalcined at450℃exhibited the highest activity in selective catalytic reduction of NO, withthe degradation rate of84.14%.（3） Catlyst life experiments showed that the photocatalyticdegradation rate of doped porous titania gradually reduced as increasing the reusing time, butwith little change.