Browsing by Author "Brohan, Luc"

Now showing 1 - 3 of 3

(101)-exposed anatase TiO2 nanosheets
(2008-04-08)
Peng, Chih-Wei
;
Ke, Tsung-Yin
;
Brohan, Luc
;
Richard-Plouet, Mireille
;
Huang, Ju-Chun
Chimie Douce Route to Sodium Hydroxo Titanate Nanowires with Modulated Structure and Conversion to Highly Photoactive Titanium Dioxides
(2008-12-09)
Peng, Chih-Wei
;
Richard-Plouet, Mireille
;
Ke, Tsung-Yin
;
Lee, Chi-Young
;
Chiu, Hsin-Tien
Sodium hydroxo titanate nanowires with NaTi(2)O(4)(OH) formulation are fabricated by chimie-douce from TiO(2) powders in a hot concentrated base solution. In the present work, we investigate, in detail, the structure and morphology of the titanate, acid-exchanged materials, and phases formed during dehydration of these compounds; we then discuss the relationship between the initial titanate structure and TiO(2) formation. XRD, ED, HRTEM, EDS, density measurements, and TG/MS results suggest that the titanate and acid-exchanged structures were closely related to the pseudolepidocrocite arrangement ("Cs(2)Ti(6)O(12)" type). The average structure of NaTi(2)O(4)(OH) nanowires consists of noncorrugated Ti(2)O(3)(OH) and NaO layers stacked along the [0 10] direction and an energy minimization was further conducted by theoretical methods. From TEM study, we demonstrated that NaTi(2)O(4)(OH) exhibits a modulated structure (q wave vector equals to 1/7 [001]*), which originates from the misfit between the NaO and Ti(2)O(3)(OH) sublattices. NaTi(2)O(4)(OH) structure has a monoclinic distortion (I2/m space group) with refined unit cell a = 0.37000(6) nm, b = 1.7816(4) nm, c = 2.2077(3) nm, beta = 92.70(1)degrees. Proton exchange followed by heat treatment convert the sodium hydroxo titanate into highly photoactive TiO(2) nanowires. The activity is attributed to the presence of preferentially exposed (001) surface plane which is explained by the topotactic phase transformation of TiO(2)(B) into anatase.
Interconversion of rutile TiO2 and layered ramsdellite-like titanates: New route to elongated mesoporous rutile nanoplates
(2008-10-01)
Peng, Chih-Wei
;
Richard-Plouet, Mireille
;
Tsai, Min-Chiao
;
Lee, Chi-Young
;
Chiu, Hsin-Tien
We report the first soft chemistry synthesis of a new "layered ramsdellite-like" titanate structure, NaTi2O4(OH) (lattice parameters: primitive monoclinic system, a = 4.09 nm, b = 0.29 nm, c = 0.94 nm, and beta = 80 degrees), with high-aspect-ratio, platelike morphology (diameter. 20-200 nm; thickness. 10-40 nm; length. 0.05-5 mu m) from TiO2 rutile. The newly prepared titanate can be transformed back to TiO2 rutile with uniquely shaped mesoporous elongated nanoplate morphology. The reaction proceeds via the disintegration of rutile in NaOH(aq) into NaTi2O4(OH). Ion exchange of Na+ in NaTi2O4(OH) into H+ forms another new layered ramsdellite-like titanate, HTi2O4(OH). A final topotatic condensation of the titanate layers in HTi2O4(OH) by heat treatment at relatively low 673 K produces the mesoporous TiO2 rutile product with highly exposed (110) surfaces.