and surfactant/polymer-free methods for the morphology control of TiO 2
nanostructures. Anatase TiO 2 nanorods have been synthesized via a simple
two-step method: a hydrothermal treatment of the commercial P25 TiO 2
nanoparticles in a composite-hydroxide eutectic system of 1:1 M KOH/NaOH,
followed by acid posttreatment (Hafez 2009). The obtained TiO 2 nanorods have a
good crystallinity with the dimensions of 200–300 nm length and of 30–50 nm
diameter. Furthermore, they are mesoporous with an average pore size of 6.2 nm and
have a BET specific area of 85 m
2 /g. Compared to their precursor anatase/rutile TiO 2
P25 and the titanate nanotubes, the pure anatase TiO 2 nanorods are more efficient for
the photodegradation of the commercial cibacron red (FN R) textile dye under UV
irradiation. Hierarchical rutile TiO 2 superstructures made of nanorods assembled at a
water-dichloromethane interface have been prepared by a hydrothermal treatment of
dichloromethane solution of TiCl 4 (Wang et al. 2009). Size and shape of
nanostructures were easily modified by varying the H 2 O/TiCl 4 molar ratio. The
resulting TiO 2 hierarchical superstructures showed higher photocatalytic property
to decompose methylene blue under UV light irradiation in aqueous solution (92%
in 30 min) compare to that of commercial P25 (47% in 30 min). The hydrothermal
synthesis route based on a water-dichloromethane interface has allowed obtaining
TiO 2 nanostructures as powder or as freestanding film. The film is composed of
greater crystallites, has a lower specific surface area, and shows lower photocatalytic
efficiency; however, it offers an easier handling. The synthesis of TiO 2 nanorods has
been also realized by a rapid microwave-assisted polyol route from titanium
glycolate followed by water treatment under microwave irradiation or calcination
at 500
C (Gerasimova et al. 2016). Following this route or a conventional polyol
route, the synthesized nanorods are micro-mesoporous. The post-synthesis water
treatment under microwave allowed forming anatase nanocrystallites of 5.4 nm size
and increasing specific surface area. The as-synthesized TiO 2 nanorods show a better
photocatalytic activity for the removal of rhodamine B (97% decomposition of
rhodamine B after 30 min of UV light irradiation). The post-synthesis calcination
at 500
C has resulted in the formation of mesoporous nanorods with bigger anatase
crystallites (19.3 nm), a lower specific surface area, and a lower capacity of dye
adsorption but having higher photocatalytic efficiency (98% decomposition of
rhodamine B after 15 min of UV light irradiation).
Titania nanotubes (TNT) have been also considered for the removal of dyes from
aqueous solutions (Lai et al. 2014). The three general approaches in preparing TNT are
alkaline hydrothermal route, anodization techniques, and chemical (template) synthesis. The hydrothermal synthesis is recognized as a facile and low-cost method and
leads after a first step to titanate nanotubes that can be transformed into anatase TNT by
acid posttreatment and calcination (Xu et al. 2011). The obtained mesoporous anatase
TNT photocatalyst has shown a good photocatalysis efficiency toward the degradation
of acid orange 7 dye. Recently, a single post-acid treatment after hydrothermal
synthesis of titanate nanotubes in highly concentrated NaOH solution was reported
to be sufficient to obtain anatase nanotubes with high surface OH density (Tsai et al.
2017). The resulting materials are active photocatalysts for the decomposition of
Congo red and crystal violet dyes due to their high dye pre-adsorption capacity.
2 Dyes Depollution of Water Using Porous TiO 2 -Based Photocatalysts
55
nanostructures. Anatase TiO 2 nanorods have been synthesized via a simple
two-step method: a hydrothermal treatment of the commercial P25 TiO 2
nanoparticles in a composite-hydroxide eutectic system of 1:1 M KOH/NaOH,
followed by acid posttreatment (Hafez 2009). The obtained TiO 2 nanorods have a
good crystallinity with the dimensions of 200–300 nm length and of 30–50 nm
diameter. Furthermore, they are mesoporous with an average pore size of 6.2 nm and
have a BET specific area of 85 m
2 /g. Compared to their precursor anatase/rutile TiO 2
P25 and the titanate nanotubes, the pure anatase TiO 2 nanorods are more efficient for
the photodegradation of the commercial cibacron red (FN R) textile dye under UV
irradiation. Hierarchical rutile TiO 2 superstructures made of nanorods assembled at a
water-dichloromethane interface have been prepared by a hydrothermal treatment of
dichloromethane solution of TiCl 4 (Wang et al. 2009). Size and shape of
nanostructures were easily modified by varying the H 2 O/TiCl 4 molar ratio. The
resulting TiO 2 hierarchical superstructures showed higher photocatalytic property
to decompose methylene blue under UV light irradiation in aqueous solution (92%
in 30 min) compare to that of commercial P25 (47% in 30 min). The hydrothermal
synthesis route based on a water-dichloromethane interface has allowed obtaining
TiO 2 nanostructures as powder or as freestanding film. The film is composed of
greater crystallites, has a lower specific surface area, and shows lower photocatalytic
efficiency; however, it offers an easier handling. The synthesis of TiO 2 nanorods has
been also realized by a rapid microwave-assisted polyol route from titanium
glycolate followed by water treatment under microwave irradiation or calcination
at 500
C (Gerasimova et al. 2016). Following this route or a conventional polyol
route, the synthesized nanorods are micro-mesoporous. The post-synthesis water
treatment under microwave allowed forming anatase nanocrystallites of 5.4 nm size
and increasing specific surface area. The as-synthesized TiO 2 nanorods show a better
photocatalytic activity for the removal of rhodamine B (97% decomposition of
rhodamine B after 30 min of UV light irradiation). The post-synthesis calcination
at 500
C has resulted in the formation of mesoporous nanorods with bigger anatase
crystallites (19.3 nm), a lower specific surface area, and a lower capacity of dye
adsorption but having higher photocatalytic efficiency (98% decomposition of
rhodamine B after 15 min of UV light irradiation).
Titania nanotubes (TNT) have been also considered for the removal of dyes from
aqueous solutions (Lai et al. 2014). The three general approaches in preparing TNT are
alkaline hydrothermal route, anodization techniques, and chemical (template) synthesis. The hydrothermal synthesis is recognized as a facile and low-cost method and
leads after a first step to titanate nanotubes that can be transformed into anatase TNT by
acid posttreatment and calcination (Xu et al. 2011). The obtained mesoporous anatase
TNT photocatalyst has shown a good photocatalysis efficiency toward the degradation
of acid orange 7 dye. Recently, a single post-acid treatment after hydrothermal
synthesis of titanate nanotubes in highly concentrated NaOH solution was reported
to be sufficient to obtain anatase nanotubes with high surface OH density (Tsai et al.
2017). The resulting materials are active photocatalysts for the decomposition of
Congo red and crystal violet dyes due to their high dye pre-adsorption capacity.
2 Dyes Depollution of Water Using Porous TiO 2 -Based Photocatalysts
55