Study Of Nanoscale Mixed Crystal TiO₂ Synthesizing And Photo-catalytic Degradation Methylene Blue Characteristic And Influencing Factors

Nanoscale titania is a photo-catalyst applicated most comprehensively, which can be utilized to photo-degrade waste water and exhaust. It has two main crystal types—anatase and rutile. The futile content in nanosized titania play a important role on its photocatalytic effficiency. Nanoscale mixed crystal titania synthesizing and characterization have important significance on photocatalytic research of nanosized titania.Through homogeneous hydrolysis method, using tetrachloride titanium, ethanol, acetic acid as raw material, utilizing toluene-p-sulfonic acid (TSA) or citric acid (CA) as additive, titania with controllable rutile content were synthesized. The outer surface of titania were measured using BET method. The surface appearances of titania were observed using SEM. The photocatalytic efficiency of synthesized nanoscale titania is demonstrated through photodegrading methylene blue solution. The photodegradation ratio of methylene blue were demonstrated by testing the absorbility of methylene blue in different reaction time. The influencing factors of photodegradation of titania were discussed, such as the rutile content in titania and initial pH of methylene blue(MB) solution etc. The main results are shown as below:With improved homogeneous hydrolysis method, calcined in 450℃and TSA accession ratio increase from 0.0 to 0.14 (the mol ratio of TSA v. s. acetic acid is from 0.0 to 0.14 ), synthesized nanoscale TiO₂ contain 0% rutile; Calcined in 550℃, TSA accession ratio increase from 0.0 to 0.05, synehesized TiO₂ contain 0% rutile. TiO₂ contain 16.2% rutile content with 0.10 accession ratio of TSA. When TSA accession ratio goes up to 0.14, TiO₂ contains 24.4% rutile; Calcined in 600℃, synthesized TiO₂ contains 28.9% rutile without accession of TSA. Along with the accession ratio of TSA increase, rutile content in synthesized TiO₂ has a increase trend. Synthesized TiO₂ contains 93.0% rutile with 0.18 accession ratio of TSA; Calcined in 700℃, synthesized TiO₂ contains 80.6% rutile with 0.0 accession ratio of TSA. When accession ratio of TSA increase from 0.10 to 0.18, the rutile content of synthesized TiO₂ all are 100%. Calcineing temperature increase can induce the rutile formation in TiO₂.Using CA as additive, calcined in 450℃, the accession ratio of CA goes up from 0.0 to 0.10, synthesized TiO₂ contain 0% rutile. Synthesized TiO₂ contain 15.8% rutile with 0.15 accession ratio of CA; Calcined in 500℃, the accession ratio of CA increase from 0.0 to 0.05, synthesized TiO₂ contain 0% rutile. The synthesized TiO₂ contain 26.8% rutile with 0.10 accession ratio of CA. The synthesized TiO₂ contain 54.4% rutile content with 0.15 accession ratio of CA. The synthesized TiO₂ contain 59.4% rutile with 0.25 accession ratio of CA. So the rutile content of synthesized TiO₂ goes up along with the increase of accession ratio of CA.The photocatalytic efficiencies of synthesized nanoscale titania are significantly influenced by crystal types of titania. The nanosized titania containing some rutile has prominent photocatalytic efficiency. It can be concluded: nanocrystal TiO₂ containing 20%-35% rutile content may be synthesized under the condition that being calcined in 500℃-600℃and with 0.0-0.05 accession ratio of TSA, which has best photocatalytic efficiency among all synthesized nanoscale titania samples, it's 2h photodegradation rate of MB is 37.53%. Otherwise the 2h photodegradation rates of MB of the TiO₂ sample containing 100% anatase and the TiO₂ sample containing 93.0% rutile are 25.56% and 3.53% respectively.Two synthesized titania samples, TSA00-500(calcined in 500℃, 32.9% rutile content), CA025-500(calcined in 500℃, without rutile) and P25 (with about 20.4% rutile content), were utilized to photo-degrade 100 mg·L^-1 MB solution respectively. The photo reactions were according with the charateristic of first order dynamic reaction. Their photodegradation rate constants(min^-1) in order were P25 (0.00869)〉TSA00-500 (0.00273)) CA025-500 (0.00226).The initial pH of MB solution has important influence on photodegradation of MB. The synthesized TiO₂ sample TSA00-550(calcined in 550℃, without rutile ) and P25 were used to photodegradate 100mg·L^-1 MB under the condition of various pH. It can be concluded: the MB 1 h photodegradation rates of the two titania samples are least at pH 5, the photocatalysis efficencies of the two titania samples are better at pH 3 than that at pH 5, the two samples' photocatalysis efficencies have a enhancement trend along with alkalinity increase of MB solution. The MB 1 h photodegradation rate of TSA00-550 attained maximum--62.66% at pH 11; The MB 1 h photodegradation rate of P25 reached maximum--71.97% at pH 9.