All You Need to Know About Photocatalytic Reaction

It is defined as the reaction carried out in the presence of photon and catalyst; hence it is known as the photocatalytic reaction. Photocatalysis is one of the essential processes in various industries and for R&D purposes. This unique process ensures the reactants altered, without having any effect on its original form.

This process is designed to accelerate the photo-reaction with the help of a catalyst. As the photoreaction takes place, the chemical reaction requires the light to be absorbed by one or more reactants. The catalyst accelerates the photo-reaction by noticeably decreasing the activation energy.

Fundamentals of Photocatalytic Reaction

In general, a photocatalytic reaction uses light energy to modify the state of the reactants in the photocatalysis. Even though the catalyst is essential to accelerate photoreaction, it does not lose its original state as it is not directly involved in inducing the rate of reaction. Light radiation is necessary for an ideal photocatalytic substance. The light may be UV or visible range.

A simple example of an ideal photo-catalyst is chlorophyll, the natural substance found in all plant leaves. In the photosynthesis process, the chlorophyll turns to water and captured sunlight to generate energy. However, in the artificial, nano-sized photo-catalyst materials (TiO2) work to develop a strong oxidation agent as well as create electronic holes. It is essential to modify the organic matter to carbon dioxide and water, with the help of light and water.

Types of Photocatalytic Reactions

There are mainly two types of photocatalytic reactions:

  • Homogenous photocatalytic reaction and
  • Heterogeneous photocatalytic reaction

Homogenous Photocatalytic Reaction

In the homogeneous process, the photo-catalysts and reactants are present in the same phase.

In this process, ozone produces hydroxyl radicals in two ways; however the efficiency of the Fenton system photocatalytic reaction is considerably higher. It is owing to several factors, such as the concentration of hydrogen peroxide, the intensity of the ultraviolet (UV) light as well as the pH levels. This type of photocatalysis has proven to be comparatively more useful as it utilizes natural sunlight and can withstand light sensitivity up to 450 nm. It works to lower the cost of utility (electric) bills and the cost of buying an industrial-grade UV lamp for photoreaction.

On the other hand, the downside of this process is that a considerably lower level of pH needs to maintained for efficient precipitation and removal of iron particles.

Heterogeneous Photocatalytic Reaction

In heterogeneous photocatalytic reaction, the reactant and catalyst are present in different phases. It is a versatile photoreaction and includes dehydrogenation, metal depositing, removal of gaseous pollutants, water detoxification, mild/complete oxidations, hydrogen transfer as well as the exchange of deuterium-alkane isotopes, among others.

Most commonly-used heterogeneous photo-catalysts are semiconductors and transition metal oxides, as these have unique properties. As semiconductors have a band gap, it can create an excited electron or ‘exciton.’ It achieved by bombarding the semiconductor with a photon having energy equal to, or greater than the semiconductor’s band gap.

These excitons are essential for reacting with the oxidants present in the reactants to reduce the substance, or to oxidize the substance.

Applications of Photocatalytic Reactions

There are several industries and R&D niches where the photocatalytic reaction is an essential process. These are the several top presents and potential applications of photocatalysis reactions:

  • Photocatalytic water-splitting
  • Using TiO2 in self-cleaning glass
  • Disinfecting water/water treatment using SODIS (Solar Water Disinfection) method
  • Using TiO2 in self-sterilizing coatings
  • Oxidation of organic contaminants in the presence of UV light and magnetic field
  • Sterilizing medical equipment
  • Cleaning fingerprints off of sensitive electronic sensors and devices
  • Using TiO2 to decontaminate water using photocatalysis