Typical Synthesis and Environmental Application of Novel Ti Nanoparticles - Advanced Materials for Agriculture, Food and Environmental Safety - page 422

photocatalysis of TiO 2 materials. Furthermore, photoactivity is highly
dependent on surface area and crystallinity or crystal sizes, which are
inl uenced by the synthetic methods of titania [53, 54].
h e most recent studies show that the addition of small quantities of
Nb 2 O 5 into TiO 2 lattice signii cantly increases the photocatalytic activity
and surface acidity of TiO 2 [55, 56]. Concurrently, Cr(III)- and Fe(III)-
doped photocrystalline titania have also been widely studied in the i eld of
photocatalysis [41, 57-60]. Recently, Han et al. studied the photocatalytic
degradation of 2,4-dichlorophenol with SiO 2 -TiO 2 nanomaterials [61],
and Tiwari et al. synthesized dif erent types of nanomaterial compounds
[62]. h e TiO 2 -based alloy composites [26, 32] also show the photocata-
lytic activity of degradation of dif erent dyes. Nonconventional synthetic
procedures such as chemical vapor deposition [63], hydrothermal [64],
microemulsion [65], sol-gel [66, 67], coprecipitation [68], solid state [39]
and chemical methods [69] were adopted to produce such compositions.
In the present chapter, the recent developments in the syntheses and
characterization of TiO 2 -based noble metals, transitions metals ions and
dif erent TiO 2 -based mesoporous compounds were prepared from a tita-
nium tartarate with triethanol amine precursor by sol-gel or novel chemi-
cal method. h e photocatalytic activity of doped TiO 2 materials upon
visible and UV illumination will be reviewed, summarized and discussed,
in particular, concerning the inl uence of preparation and solid-state
properties of the materials. Reaction mechanisms explaining these ef ects
will be presented and critically evaluated.

15.2 Use of Dif erent Dyes

h e chemical structures of four dyes are presented below. h e degradation
rate of all four dyes shows a pseudo-i rst-order degradation pattern.

15.2.1 Methyl Orange Degradation (MO)

Methyl orange is one of the most important classes of commercial dyes.
It is stable to visible and near-UV light and provides a useful probe for
photocatalytic reactions [70-72]. Because methyl orange turns yellow
in an alkaline solution and red in acidic solution, it is easy to monitor
and analyze by spectrophotometry. h e mineralization, decolorization
and decomposition of methyl orange over TiO 2 have been well studied,
showing a pseudo-i rst-order degradation pattern [72]. h e absorbance