Photocatalysis

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PHOTOCATALYSIS

• Introduction, Advantages and Applications 

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Definition of photocatalysis

• Photocatalysis is a process in which light energy
  is used to drive pairs of chemical reactions. 
• Through the absorption of light, an excited
  electron/hole pair is produced. Due to their
  activated state, the electron and hole perform
  chemical reduction . 
• In typical photocatalytic reactions, catalysts or
  substrates are activated by photons or light
  radiation, such as ultraviolet or visible light
  of suitable wavelengths

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PHOTOCATALYST

• photocatalysts are materials that change the rate
  of a chemical reaction on exposure to light.
• The term photocatalyst is a combination of two
  words photo related to photon and catalyst.
• e.g.  Titanium dioxide (TiO2) 
• In the picture photons from a light source
  are absorbed by the surface of the TiO2 disc
  exciting electrons within the material.

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Types of photocatalysis

• There are two types of photocatalysis - 
•  1. Heterogeneous  2.  Homogeneous 
• Heterogeneous  photocatalysis -  Photocatalyst
  and reactant is in different phase.
• TiO2, a wide band-gap semiconductor, is a common
  choice for heterogeneous catalysis. Inertness to
  chemical environment and long-term photostability
  has made TiO2  an important material in many
  practical applications. 

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2. Homogeneous catalysis-  In homogeneous
photocatalysis, the reactants and the
photocatalysts exist in the same phase .  The
process by which the atmosphere self-cleans and
removes large organic compounds is a gas phase
homogenous photocatalysis reaction. The ozone
process is often referenced when developing many
photocatalysts 2O3(g) H2O(g)     ?    O2(g)
2OH Most homogeneous photocatalytic reactions
are aqueous phase, with a transition-metal
complex photocatalyst .The wide use of
transition-metal complexes as photocatalysts is
in large part due to the large band gap and high
stability of the species. Homogeneous
photocatalysts are common in the production of
clean hydrogen fuel production, with the notable
use of cobalt and iron  complexes.
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• Plasmonic antenna-reactor photocatalysis
• Another  category of photocatalysis is known as
  plasmonic antenna-reactor photocatalysis.
• A plasmonic antenna-reactor photocatalyst is a
  photocatalyst that combines a catalyst with
  attached antenna that increases the catalyst's
  ability to absorb light, thereby increasing its
  efficiency.
• A SiO2 catalyst combined with an Au light
  absorber accelerated hydrogen sulfide-to-hydrogen
  reactions. The process is an alternative to the
  conventional Claus process that operates at
  8001,000 C.
• A Fe catalyst combined with a Cu light absorber
  can produce hydrogen from ammonia (NH3) at
  ambient temperature using visible light.
  Conventional Cu-Ru production operates at
  6501,000 C .

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APPLICATION 0F PHOTOCATALYSIS

• Photoactive catalysts have been introduced over
  the last decade, such as TiO2  and ZnO nanorodes.
  Most suffer from the fact that they can only
  perform under UV irradiation due to their band
  structure. Other photocatalysts, including a
  graphene-ZnO nanocompound counter this problem.
  Important applications of 
• Photocatalysis are
• Self-cleaning surfaces
• Air and water purification 
• Sterilization
• Hydrogen evolution
• Photoelectrochemical conversion

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Photoelectrochemical conversion

• Photoelectrochemical (PEC) CO2 conversion can be
  considered as an artificial photosynthesis
  technique that produces formate, formaldehyde,
  formic acid, methane, methanol, ethanol, etc.

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SELF CLEANING SUFACES

• When original building materials are coated with
  a photocatalyst, a protective film of titanium
  provide self-cleaning building by becoming
  antistatic, super oxidative and hydrophilic.

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Water purification

• Photocatalyst coupled with UV light can oxidize
  organic pollutants into nano toxic material such
  as CO2 , water and can disinfect certain
  bacteria.
• This technology is very effective at removing
  further hazardous organic compounds and
  at killing a variety of bacteria and some
  viruses in secondary wastewater treatment.

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DEGRADATION OF DYES USING TiO2
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Water Splitting

• The utilization of solar energy for water
  splitting paves a way for environmentally
  friendly H2 generation. Photocatalytic water
  splitting for H2 production is done with
  conjugated polymers, g-C3N4, graphene, other
  carbon-based photocatalysts, earth-abundant
  metal-based photocatalysts and co-catalysts.

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Advantages of photocatalysis

•  Reliable and green
•  Non-toxic
• Cost-effective
• Reducing CO2
• Environment-friendly

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THANK YOU !