The sol-gel process is a wet-chemical technique (chemical solution deposition), which has been widely used in the fields of materials science, ceramic engineering, and especially in the preparation of photocatalysts. Volatile organic compounds (VOCs) are prevalent components of indoor air pollution. Among the approaches to remove VOCs from indoor air, photocatalytic oxidation (PCO) is regarded as a promising method. This paper is a review of the status of research on the sol-gel method for photocatalyst preparation and for the PCO purification of VOCs. The review and discussion will focus on the preparation and coating of various photocatalysts, operational parameters, and will provide an overview of general PCO models described in the literature

Industrial wastewater from galvanization workshops contains high concentrations of copper
(6.5 mg lG1), chromium (60 mg lG1), nickel (283 mg lG1), zinc (63.5 mg lG1) and cyanide (350 mg lG1) which are
violating the Egyptian environmental standards. The wastewater is highly alkaline. The pH value is around 11.7.
Photocatalytic Oxidation using three commercial TiO specimens was investigated in the present study 2
namely, TiO Degussa P25 (80% anatase, 20% rutile), TiO Aldrich (100% anatase) and TiO Aldrich (100% 2 2 2
rutile). The obtained results indicated that TiO Degussa P25 gave the best photocatalytic activity for the 2
removal of cyanide at the following operating conditions: 0.25 g lG1 TiO Degussa P25 photocatalyst, pH 11,
2
Temp. of 298°C and exposure time of 30 min. The efficiency of photocatalytic removal of cyanide was
enhanced by the addition of H O as electron acceptor. 0.3 ml/l H O was added to the photocatalytic reaction. 2 2 2 2
The results indicated that cyanide was not detected and residual heavy metals concentrations were < 0.05 in
the treated effluent. The treated wastewater can be recycled in the industrial processes or disposed safely into
the sewer network.

In this study, the photocatalytic activity of annealed TiN powders and films were examined to clarify the influence of annealing temperature and pressure on the photocatalytic properties under UV and visible light irradiation. TiN films were deposited on stainless steel and quartz substrates by DC magnetron sputtering, and annealed TiN powders were used as a reference material to confirm the effectiveness of TiN oxidation. TiN powders which were annealed at 873-1173K, showed obvious photocatalytic activity, under both UV and visible light irradiation. However, annealed TiN films on the stainless steel substrate showed low photocatalytic activity except for those annealed at 823K and 1.0kPa. This is because film annealed above 923 K consisted of a dominant rutile phase, and the film annealed at 1023K delaminated from the stainless substrate. For the quartz substrate, the dominant phase of the films annealed at 823 and 923 K was anatase, and all films remained completely on the substrate after annealing. In particular, the film which was annealed at 923K and 1.0kPa showed high photocatalytic activity both under UV and visible light irradiation. Thus, good photocatalytic activity can be obtained by annealing TiN with an appropriate temperature, pressure and substrate material.

Objective: To test through various oxidation procedures the
differences in antibacterial activities against Streptococcus mutans (S mutans) of Titanium (Ti) and Titanium silver
(TiAg) metals coated with TiO₂.

Materials
and Methods: This study examined the photocatalytic antibacterial effects on
S mutans of Ti and TiAg ubstrates coated with two
crystalline forms of TiO₂ by thermal and anodic oxidation. A
bacterial suspension of S mutans was pipetted onto TiO₂-coated
metal specimens and uncoated specimens with ultraviolet A (UVA) illumination for
20 to 100 minutes. The same specimen without UVA was used as the control. The
level of colony-forming units of S mutans after UVA illumination was compared with
that of the control.

border=0>Results: The level of colony-forming units of S mutans was significantly lower on
TiO₂-coated Ti and TiAg metal specimens after UVA illumination than
on uncoated Ti and TiAg specimens. The level of colony-forming units of S mutans was significantly lower on the metals
coated by anodic oxidation than on those coated by thermal oxidation. The
TiO₂ coating on TiAg had a significantly higher and more rapid
antibacterial effect than did the TiO₂ coating on Ti.

border=0>Conclusions: The antibacterial effect of a TiO₂ film
formed by anodic oxidation was superior to that formed by thermal oxidation. The
addition of Ag to the Ti specimen indicated a synergistic effect on the
photocatalytic antibacterial property against S mutans.

Abstract

Abstract

Abstract