Photocatalyst nanomaterials are a class of materials that have gained significant attention in recent years due to their unique properties and potential applications in a wide range of fields. These materials are typically composed of nanoparticles with sizes ranging from a few nanometers to several hundred nanometers and are designed to absorb light and convert it into chemical energy.
One of the key advantages of photocatalyst nanomaterials is their high surface area-to-volume ratio, which makes them highly effective at catalyzing chemical reactions. This property is particularly useful in applications such as water purification, where photocatalysts can be used to break down organic contaminants and other pollutants.
Some common examples of photocatalyst nanomaterials include titanium dioxide (TiO2), zinc oxide (ZnO), and cadmium sulfide (CdS). These materials can be synthesized using a variety of methods, including sol-gel, hydrothermal, and microwave-assisted synthesis, and their properties can be tuned by adjusting factors such as particle size, shape, and composition.
While photocatalyst nanomaterials have shown great promise in a range of applications, there are also some potential concerns associated with their use since these materials may be toxic to certain organisms, and their long-term environmental impact is not yet fully understood. As such, further research is needed to fully understand the potential benefits and risks associated with the use of photocatalyst nanomaterials.
The photocatalytic mechanism is a complex process that involves several steps. The basic principle behind photocatalysis is that when a photocatalyst material is exposed to light, the energy from the light can excite electrons in the material, creating electron-hole pairs. Such excited electrons or holes can diffuse to the surface and create two oxidation reactants – hydroxyl radicals .OH and superoxide anion O2-. These reactants decompose toxic organic substances to non-toxic organic compounds such as carbon, water, ammonium, nitrates and chloride ions. The specific steps involved in the photocatalytic mechanism depend on the material being used, as well as the type of reaction being catalyzed.
Steps involved in the photocatalytic process:
Absorption of light: The photocatalyst material absorbs light energy, which excites electrons in the material to higher energy levels.
Generation of electron-hole pairs: The excited electrons leave behind positively charged "holes" in the material, creating electron-hole pairs.
Surface reactions: The electron-hole pairs can then participate in surface reactions with adsorbed molecules on the surface of the photocatalyst material. For example, in the case of a pollutant such as organic contaminants, the electron-hole pairs can react with the adsorbed molecules to break them down into smaller, less harmful compounds.
Electron transfer: In some cases, the electron-hole pairs can transfer electrons to or from other molecules in the system, such as in a redox reaction.
Recombination: Eventually, the electron-hole pairs will recombine, releasing energy in the form of heat or light. This can limit the efficiency of the photocatalytic process, and researchers often aim to design materials that can minimize recombination and maximize the number of active electron-hole pairs.
Thus, the basic idea is to use light energy to drive chemical reactions and break down pollutants, making it a promising approach for environmental remediation and other applications.
There are many examples of nano photocatalyst materials that have been developed and studied for various applications. Some common examples include:
Titanium dioxide (TiO2): TiO2 is one of the most widely studied photocatalyst materials and is used in applications such as air and water purification, self-cleaning surfaces, and solar cells. TiO2 nanoparticles can be synthesized in a variety of sizes and shapes, and their photocatalytic properties can be tuned by controlling the crystal structure and surface area.
Zinc oxide (ZnO): ZnO is another commonly studied photocatalyst material, with applications in areas such as wastewater treatment, air purification, and photovoltaic devices. Like TiO2, the photocatalytic properties of ZnO nanoparticles can be modified by controlling different factors such as crystal structure, doping, and surface modification.
Cadmium sulfide (CdS): CdS is a semiconductor material with photocatalytic properties that has been studied for applications such as hydrogen production and environmental remediation.
Graphene oxide (GO): GO is a 2D material with unique properties that make it an attractive photocatalyst material. GO has been studied for applications such as water purification, air purification, and photocatalytic degradation of organic pollutants.
Metal-organic frameworks (MOFs): MOFs are a class of materials that consist of metal ions or clusters coordinated with organic ligands. MOFs have been studied as photocatalysts for applications such as hydrogen production, carbon dioxide reduction, and water purification.
Each material has its own unique properties and advantages, and the choice of material will depend on the specific application and desired performance characteristics.
The transition metal oxide semiconductor TiO2 photocatalyst is one of the most popular and widely studied photocatalytic materials for several reasons. TiO2 is an essential and a widely used material in most industrial products like sunscreen, paints, coatings, and self-cleaning glasses because of its high photoactive ability. Besides, more research works are going on TiO2materials because of their abundant, non-toxic, economically cheap, and thermally and chemically stable in nature. Catalytic oxidation and reduction processes are one of the possible remediations to solve the environmental pollution issues. TiO2 semiconductor photocatalyst is a well-known commercially available catalyst material. Still, the wider bandgap (3.2eV), high energy requirement for exciton generation & faster rate of recombination of excitons of TiO2 photocatalyst hold back its extended benefits in the fields of photocatalytic and photovoltaic applications.
Some of the key advantages of TiO2 photocatalyst include:
High efficiency: TiO2 has a high quantum yield, meaning that it can convert a large proportion of absorbed photons into chemical energy. This makes it an efficient photocatalytic material for a variety of applications.
A stable material that is resistant to corrosion and degradation, making it suitable for use in harsh environments and over long periods of time.
Biocompatible material, due to its non-toxicity, is more useful in biomedical applications, such as drug delivery and tissue engineering.
Abundant and low-cost material thus becomes an attractive option for large-scale applications.
Easily synthesized using a variety of methods, including sol-gel, hydrothermal, and microwave-assisted synthesis.
Band structure of Cu doped TiO2
Photocatalysis has a wide range of potential applications in areas such as environmental remediation, energy production, and biomedical engineering.
Degrades organic pollutants and disinfects wastewater and air. i.e., Environmental remediation
These materials can be used in applications such as water treatment plants, air purifiers, and self-cleaning surfaces.
Used to generate hydrogen fuel through the water splitting reaction. This process involves using sunlight to split water molecules into hydrogen and oxygen. E.g., CdS and TiO2
In Self-cleaning surfaces, it breaks down organic contaminants and maintains their cleanliness. These surfaces can be used in applications such as building exteriors, car paints, and clothing.
Used to make more efficient solar cells, like dye-sensitized solar cells.
Also, used for drug delivery, tissue engineering, and sterilization. Basically, it is used to trigger drug release or degrade unwanted biomolecules.