This document discusses solar photocatalysis and solar photocatalytic reactors. It introduces photocatalysis as accelerating photoreactions using a catalyst and light. Titanium dioxide is commonly used as the photocatalyst due to its efficiency, stability, low cost and non-toxic properties. Solar photocatalytic reactors bring photons, photocatalyst and reactants into contact to produce reactions. The two main types are slurry reactors, which provide high surface area but require catalyst separation, and immobilized reactors, which don't require separation but have lower surface area. Applications include water treatment, sterilization and oil decomposition.

2.  SOLAR PHOTOCATALYTIC
PROCESS & SOLAR
PHOTOCATALYTIC
REACTORS.

3. CONTENTS:
 Introduction
 Mechanism of solar photocatalysis
 Solar photocatalytic reactors
 Advantages
 Disadvantages
 Applications
 conclusion

4. Introduction:
What is solar photocatalysis:
Photocatalysis is the
acceleration of a photoreaction
in the presence of a catalyst.
Both light and catalyst are
necessary to achieve or to
accelerate a chemical reaction.

5. Photocatalytic activity:
 Ability of some nano materials
e.g. TiO2
Which is also called photocatalyst is
used to speed up a certain
reaction as a catalyst
in combination with light.

6. Why TiO2 is mostly used as a
photocatalyst:
TiO2 is mostly used as a
photocatalyst
due to its:
 High efficiency.
 Photochemical stability.
 Non-toxic in nature.
 Low cost.

7. Mechanism of solar
photocatalytic process:
When photocatalyst titanium
dioxide absorbs Ultra violet
radiation from sun light or
illuminated light source, it will
produce a pair of electrons and
holes.
The electron of the valance band
titanium dioxide becomes excited
when illuminated by light.

8.  The excess energy of this excited electron
promoted the electron to the conduction band
of titanium dioxide therefore creating the
negative-electron(e-) and positive-hole(h+)
pair. This stage is reffered to as the
semiconductors photo-excited state.
 The energy difference between the valence
band and conduction band is known as the
“Band Gap”.

9.  The positive-hole of titanium dioxide breaks
apart the water molecule to form hydrogen gas
and hydroxyl radical. The negative-electron
reacts with oxygen molecule to form super
oxide anion.This cycle continues when light is
available.

11. Reactions in photocatalysis:

12. Solar photocatalytic reactors:
 The implementation of most
photocatalytic processes at an effective
scale requires the use of a photoreactor.
 Photoreactor:
A device which brings photons, a
photocatalyst and reactants into contact,
as well as collecting the reaction products.

13. Photocatalytic reactors:
 Photocatalytic reactors can be classified
based on the two state of the photocatalyst
i.e.
Suspended or attached. Photocatalytic
reactors can use either UV or solar
radiation.
Types of photocatalytic reactors:
 Slurry reactor.
 Immobilized TiO2 reactors.

14. Slurry reactors:
 TiO2 slurry reactors are most commonly
type used in water treatment.These
reactors show the largest photocatalytic
activity.
 They provide a high total surface area of
photocatalyst per unit volume.
 These reactors require sepration of the
sub-micron TiO2 particles from the
treated water which complicates the
treatment process

16. Immobilized TiO2 reactors:
Photocatalytic reactors with
immobilized TiO2 are those in
which catalyst is fixed to support
via physical surface forces or
chemical bonds.
These reactors extend the benefit
of not requiring catalyst recovery
and permit the continuous use of
the photocatalyst.

17. The photocatalytic membrane reactors
can be generalized in two categories:
1. Irradiation of the membrane module.
2. Irradiation of feed tank containing
photocatalyst in suspension.

18. Drawback of immobilized
reactors:
 These posses low surface area to
volume ratios, catalyst fouling and
significant pressure drop.
 The other draw back is that
membrane photocatalytic reactors is
the diffusion of organic compounds
to the catalyst surface which is slow
particularly when the organic
compound concentration is low.

19. Advantages of solar
photocatalysis:
 The process is used for waste water
treatment.
 This process is applied for both slurry
and immobilized reactor.
 The photocatalyst used is of low cost.
 The photocatalyst used in this process
is re-used and re-cycled.

20. Disadvantages of solar
photocatalysis:
The reactor used in this process
is of high cost.
The photocatalytic degradation
of organic compound can be
affected by pH value

21. Applications of solar
photocatalysis:
This process is used for:
Sterilization of surgical
instruments and removal of
unwanted fingerprints from
sensitive electrical and optical
components.
 Decomposition of crude oil with
TiO2 photocatalyst.

22. Decontamination of water with
photocatalysis and adsorption: the
removal and destruction of organic
contaminants in groundwater can be
addressed through the impregnation of
adsorbents with photoactive catalysts.

23. Conclusion :
The photocatalysis of organic compounds in water
with titanium dioxide is a promising technology.
Decontamination of water effluents is one of
the most successful photochemical applications of
solar photons . This process is best way to remove
impurities from water . No doubt that detoxifying
the water by photocatalysis is full of promise.