The escalating contamination of water and air by organic pollutants poses a significant threat to environmental and human health. Most of the time, traditional ways of getting rid of pollutants are not very successful or cost-effective. In this situation, nanocomposite materials have become interesting options for breaking down organic pollutants through photocatalysis, especially when visible light is present. Nanocomposites, which combine distinct nanoscale components, offer enhanced photocatalytic activity owing to synergistic effects and tailored properties. This paper provides an overview of the current state-of-the-art in nanocomposite-based photocatalysis, encompassing various types of nanocomposites, including metal-semiconductor, semiconductor-semiconductor, and polymer-semiconductor hybrids. Additionally, the synthesis strategies employed to fabricate these nanocomposites and their implications on photocatalytic performance are discussed. Furthermore, the factors influencing the photocatalytic efficiency of nanocomposites, such as crystallinity, surface area, and charge separation, are elucidated. By elucidating the mechanisms underlying photocatalytic degradation and highlighting recent advancements, this paper aims to underscore the potential of nanocomposites as effective tools for environmental remediation.

Nanotechnology, in its broadest sense, refers to the use of technological means for the purpose of creating and executing nanostructures and nanomaterial applications. Material dimensions (grain size, layer thickness, and materials below 100 nm) that exhibit nanostructures are largely responsible for the growing fascination with nanotechnology (Hornyak et al. 2009). Nanomaterials are unique in their peculiar characteristics due to the size of these particles. According to Chattopadhyay et al. (2009), materials that have a dimension smaller than 100 nm are considered nanomaterials. The chemical, physical, and biological domains are all rich in potential uses for nanotechnology and nanomaterials.

During the 1959 American Physical Society annual meeting, Richard Feynman delivered his now-iconic speech titled "There is a plenty of room at the bottom," marking the beginning of nanotechnology. During the previous twenty years, there have been numerous advancements in the field of nanomaterial manufacturing, including new discoveries and technologies. Innovative nanostructured materials with a broad variety of dimensions and qualities are now within reach, thanks to improved theoretical and experimental synthesis methodologies and procedures for the discovery of novel materials. This innovation paves the way for brand-new areas of study and technological development.

Figure 1: Classification of Nanomaterial under dimensions(Source: Bhattacharya 2014)

There are a number of ways to categorize nanomaterials, but the most common is by their size (Figure 1). Particles of zero-dimensional carbon black made up the first generation of nanomaterials. Nanowires and nanorods, which are typically one-dimensional materials, make up the second generation of nanomaterials. Thin films and coatings are examples of third-generation materials; they only have two dimensions. The fourth generation of materials, carbon nanotubes (CNTs), have three-dimensional structures.

Catalytic Property

Metal oxide dispersions often employ templates such as zeolite, carbon, silica, and alumina as catalysts. Nanoparticle shape and dispersion over a template are notoriously difficult to keep consistent. A controlled reaction with uniform dispersion and particle size can be achieved by using silica as a template on a metal oxide coating. When it comes to SO2 adsorption, Klabunde and colleagues showed that Fe2O3@MgO and Fe2O3@CaO are more efficient than pure metal oxides, MgO, and CaO. The most important factor in these catalytic behaviors is the interaction between the catalyst's shell, core, and reactants.

Stabilization of Colloidal Nanoparticle

Surface modification of Ag, CdSe, Fe₂O₃ and Au over SiO₂ (10- 100 nm thickness) prevents coagulation even with higher concentration salt solution (e.g. 0.15 M NaCl) for a longer time period due to the fact that SiO₂ has lower Hamaker constant than most metals.

The vast array of potential uses for nanotechnology has garnered a lot of interest from both the business world and the academic world in the last 10 years. The commercial sectors, including food and cosmetics, as well as the biomedical, electrical, optical, mechanical, and chemical industries, are finding new uses for nanoscale materials through nanotechnology. Many sectors of the economy are anticipating a resurgence in innovation and discovery thanks to its convergence with IT, biology, and the social sciences.

Semiconductors don't have a continuous range of electronic states like metals do. Instead, they have a void energy area where there are no energy levels to encourage photoactivated electrons and holes to mix again. The band gap is the empty space between the top edge of the full valence band and the bottom edge of the empty conduction band. When a photon hits a semiconductor or photocatalyst, if the photon energy, hω, is equal to or greater than the band gap of the semiconductor or photocatalyst, an electron (e-) is moved from the valence band to the conduction band. At the same time, the valence band makes a hole (h+), which is a positive charge made up of empty electrons (Figure 2).

Figure 2: Band-gap diagram of semiconductor material

Catalysis is an interesting field of study because it has many applications in our daily lives. Catalytic processes are very important in four main areas of the world economy, as shown in Figure 3: making oil and energy, making chemicals and plastics, making food, and cleaning up waste. A lot of people are interested in the idea of using semiconductor-based photocatalysis, which is also called heterogeneous photocatalysis, to clean up trash and make hydrogen fuel from sunshine, which is a clean and plentiful energy source.