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R. Sukanya Devi et al.
the importance of the photocatalytic reaction is that the semiconductor provides
both oxidation and reduction environment simultaneously. The reaction rate of the
electron and hole is determined by the semiconductor and substrate. The interaction
between the semiconductor and the substrate is dependent on the band gap of the
conduction band, valence band and the redox reactions. The reactions may be of any
of these four ways
1. By Reduction: This occurs as a result of the redox potential of the substrate
becomes lower than that of the redox potential of the conduction band of the
photocatalyst.
2. By Oxidation: This occurs when the redox potential of the substrate becomes
higher than the redox potential in the valence band of the photocatalyst.
3. Neither oxidation nor reduction: This happens while the redox potential of the
substrate becomes greater than conduction band and lower than the valence
band of the photocatalyst.
4. By reduction and oxidation: This happens when the redox potential of the
substrate becomes lower than the conduction band and higher than the valence
band.
The applications of photocatalysts are decolourization of colourants, antifouling
of membranes, antifouling, sterilization, to conserve and store energy self-cleaning
properties, treatment of pollutants in air and water and so on.
Based on appearance of the physical state of the reactants, the photocatalytic
reactions are classified into two types
• Homogeneous photocatalysis: The physical state of the semiconductor and
substrate is of same phase, i.e. solid, liquid or gas.
• Heterogeneous photocatalysis: The physical state of the semiconductor and
substrate is of different phase, i.e. solid, liquid or gas.
The efficiency of the photocatalytic reactions is based on the semiconductors
selected. Several metal oxides are widely studied and used as photocatalyst. In recent
years, the metal oxides are converted to nano particles and are used in photocatalytic
reactions. Similarly, nano plasmons, hybrid nano fibres with nano semiconductors
are extensively used as photocatalyst in laboratory studies.
Metal Oxides
Earlier metal oxides were used in electronics since they can carry charges when
exposed to light. It also has wide application in treatment of wastewater. These
metal oxides are best suitable because of their electronic structure and light absorption characteristics and charge transport properties. Photocatalytic reactions mediated by semiconductor have gained huge importance as the problem related to fast
charge recombination is eliminated. The metal oxides like titanium dioxide and zinc
oxide are widely studied against the dyestuffs belonging to azo dyes Similarly, other
metal oxides like vanadium oxide, tungsten oxide, molybdenum and cerium oxide,
R. Sukanya Devi et al.
the importance of the photocatalytic reaction is that the semiconductor provides
both oxidation and reduction environment simultaneously. The reaction rate of the
electron and hole is determined by the semiconductor and substrate. The interaction
between the semiconductor and the substrate is dependent on the band gap of the
conduction band, valence band and the redox reactions. The reactions may be of any
of these four ways
1. By Reduction: This occurs as a result of the redox potential of the substrate
becomes lower than that of the redox potential of the conduction band of the
photocatalyst.
2. By Oxidation: This occurs when the redox potential of the substrate becomes
higher than the redox potential in the valence band of the photocatalyst.
3. Neither oxidation nor reduction: This happens while the redox potential of the
substrate becomes greater than conduction band and lower than the valence
band of the photocatalyst.
4. By reduction and oxidation: This happens when the redox potential of the
substrate becomes lower than the conduction band and higher than the valence
band.
The applications of photocatalysts are decolourization of colourants, antifouling
of membranes, antifouling, sterilization, to conserve and store energy self-cleaning
properties, treatment of pollutants in air and water and so on.
Based on appearance of the physical state of the reactants, the photocatalytic
reactions are classified into two types
• Homogeneous photocatalysis: The physical state of the semiconductor and
substrate is of same phase, i.e. solid, liquid or gas.
• Heterogeneous photocatalysis: The physical state of the semiconductor and
substrate is of different phase, i.e. solid, liquid or gas.
The efficiency of the photocatalytic reactions is based on the semiconductors
selected. Several metal oxides are widely studied and used as photocatalyst. In recent
years, the metal oxides are converted to nano particles and are used in photocatalytic
reactions. Similarly, nano plasmons, hybrid nano fibres with nano semiconductors
are extensively used as photocatalyst in laboratory studies.
Metal Oxides
Earlier metal oxides were used in electronics since they can carry charges when
exposed to light. It also has wide application in treatment of wastewater. These
metal oxides are best suitable because of their electronic structure and light absorption characteristics and charge transport properties. Photocatalytic reactions mediated by semiconductor have gained huge importance as the problem related to fast
charge recombination is eliminated. The metal oxides like titanium dioxide and zinc
oxide are widely studied against the dyestuffs belonging to azo dyes Similarly, other
metal oxides like vanadium oxide, tungsten oxide, molybdenum and cerium oxide,