Hydrogen production via photocatalytic water splitting using sunlight has enormous potential in solving the worldwide energy and environmental crisis. The key challenge in this process is to develop efficient photocatalysts which must satisfy several criteria such as high chemical and photochemical stability, effective charge separation and strong sunlight absorption. The combination of different semiconductors to create composite materials offers a promising way to achieve efficient photocatalysts because doing so can improve the charge separation, light absorption and stability of the photocatalysts. In this review article, we summarized the most recent studies on semiconductor composites for hydrogen production under visible light irradiation. After a general introduction about the photocatalysis phenomenon, typical heterojunctions of widely studied heterogeneous semiconductors, including titanium dioxide, cadmium sulfide and graphitic carbon nitride are discussed in detail.

During the last few years, the presence of pharmaceuticals in the aquatic environment, classified as so-called emerging contaminants, has attracted attention from the scientific community.

The over-exploitation of fossil fuels means that research into alternative sustainable energy sources is crucial for the scientific community. The harvesting of solar energy via photocatalysis is a key approach to developing these alternatives. Furthermore, photocatalytic materials show great promise for degradation of pollutants. However, limitations in incident light utilization and charge separation are major drawbacks that restrict the activity of current artificial photosystems. Construction of hollow nano-sized photocatalysts is emerging as a promising approach to fabricating novel and effective materials, as hollow photocatalysts possess unique properties that may be exploited to overcome these challenges. This review gives a concise overview of the advantages of hollow structures for this purpose, the methodology used to prepare hollow photocatalysts, and the current state-of-the-art in the development of hollow structure photocatalysts for energy production and environmental applications.

Photocatalysis is a multifunctional phenomenon that can be employed for energy applications such as H₂ production, CO₂ reduction into fuels, and environmental applications such as pollutant degradations, antibacterial disinfection, etc. In this direction, it is not an exaggerated fact that TiO₂ is blooming in the field of photocatalysis, which is largely explored for various photocatalytic applications. The deeper understanding of TiO₂ photocatalysis has led to the design of new photocatalytic materials with multiple functionalities. Accordingly, this paper exclusively reviews the recent developments in the modification of TiO₂ photocatalyst towards the understanding of its photocatalytic mechanisms. These modifications generally involve the physical and chemical changes in TiO₂ such as anisotropic structuring and integration with other metal oxides, plasmonic materials, carbon-based materials, etc. Such modifications essentially lead to the changes in the energy structure of TiO₂ that largely boosts up the photocatalytic process via enhancing the band structure alignments, visible light absorption, carrier separation, and transportation in the system. For instance, the ability to align the band structure in TiO₂ makes it suitable for multiple photocatalytic processes such as degradation of various pollutants, H₂ production, CO₂ conversion, etc. For these reasons, TiO₂ can be realized as a prototypical photocatalyst, which paves ways to develop new photocatalytic materials in the field. In this context, this review paper sheds light into the emerging trends in TiO₂ in terms of its modifications towards multifunctional photocatalytic applications.