3 - Chalcogenides as well as chalcogenides-based nanomaterials and its importance in photocatalysis

Abstract

The rapid expansion of industrialization results in the release of large amounts of poisonous and hazardous chemical contaminants into the surrounding environment. Respiratory and pulmonary diseases due to contaminated air are major health concerns. The idea of photocatalysis is one of the effective approaches utilized widely for environmental detoxication and clean energy generation (H2, CH4 production). The photocatalysts assist in the decomposition of the chemical contaminants (CO, NOx, SOx, etc.) and are also beneficial for the disinfection of bacteria, virus, fungi present in the air. Air purification processes by the absorption of visible-light have led to the significant advancement in photocatalytic material designs. In recent years, the utilization of chalcogenides and their nanosized counterparts in different photocatalysis processes have taken the center-stage, due to their unique but tunable band gaps, excellent charge carrier mobility as well as outstanding structural properties. The origin of quantum size effect due to the reduction in the size of chalcogenides gave birth to exciting features such as high-specific surface area with more active sites, high diffusion length of the charge carriers beneficial for photocatalytic systems in contrast to their bulk counterparts. Upcoming, two-dimensional (2D) chalcogenides are the most prominent ones due to their “layer dependent” optical and electronic characteristics. In addition, 2D system provides more exposed active sites, ultra-high surface area, and suitable band potentials. Chalcogenide materials have several shortcomings such as photocorrosion, instability, poor recyclability, etc., which subsequently affects their efficiency to a greater extent. In this regard, the essence of band gap engineering with the selection of metal/chalcogen, doping/alloying at M site, nanoscaling with surface functionalization (core/shell, dye sensitization, organic molecule/polymer), layer-thickness control or heterostructure (2D/2D’) formation toward the improvement of photocatalytic performance have been discussed. (1) Visible band gap attainment to enhance light absorption for increased charge carrier generation to (2) increased surface area to enhanced adsorption for easy carrier percolation across a network of the nanoparticle to photocorrosion inhibition due to hydrophobicity at a very small size to (3) perfect band gap formation (1L to few-layer chalcogen) for enhanced charge collection (large diffusion length) is offered by a sovereign chalcogen family of materials, free from the idea of noble-metal photocatalyst. This chapter provides a summary of the usefulness of chalcogens and their nanomaterials for photocatalysis (water splitting, reduction of carbon dioxide, etc.); as future guidance for researchers working in the field of chalcogen-based photocatalysis with promising future directions.