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Solar photocatalytic process & solar photocatalytic reactors

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Solar photocatalytic process & solar photocatalytic reactors

  1. 1.  SOLAR PHOTOCATALYTIC PROCESS & SOLAR PHOTOCATALYTIC REACTORS.
  2. 2. CONTENTS:  Introduction  Mechanism of solar photocatalysis  Solar photocatalytic reactors  Advantages  Disadvantages  Applications  conclusion
  3. 3. 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.
  4. 4. 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.
  5. 5. 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.
  6. 6. 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.
  7. 7.  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”.
  8. 8.  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.
  9. 9. Reactions in photocatalysis:
  10. 10. 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.
  11. 11. 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.
  12. 12. 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
  13. 13. 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.
  14. 14. 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.
  15. 15. 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.
  16. 16. 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.
  17. 17. 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
  18. 18. 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.
  19. 19. 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.
  20. 20. 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.

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