Title: Metal-free-based photocatalytic materials: Advances and future perspectives for environmental and energy purposes

Abstract

The contemporary world is facing energy shortages and environmental problems, which hinder the evolution of human civilization giving rise to various types of crises. The huge energy consumption and environment pollution related to the traditional industrial processes, along with the increasing need of synthetic chemicals to satisfy the current society requirements, are urgent issues to be addressed for the development of the new foundations for a sustainable future. These critical challenges need solutions which require an important upgrade in energy sources and the conception of new generation processes and manufacturing technologies. Researchers, over the past few decades, have been studying several methods to understand how to overcome these problems. In this context, heterogeneous photocatalysis appears as one of the useful technologies to help these urgent efforts, and it can make a contribution to solve environmental problems and manage the conversion of solar energy into chemical energy in a sustainable way. Among the semiconductors to be used as photocatalysts, metal-free materials, such as graphene, nitrides, carbides, and conjugated organic polymers, have gained extensive research interest due to their earth abundance, cost-effectiveness, good electrical conductivity, and environmental friendliness. These semiconductors are active for photocatalytic H2 generation, CO2 reduction, and for environmental applications, not only for photocatalytic abatement of pollutants, both in gas-solid and liquid-solid regimes, but also for the valorization of substances obtained from biomass to obtain high added value chemicals. All of these applications of the photocatalytc technology are carried out in green conditions, by using water as solvent, at room temperature and atmospheric pressure by using natural solar irradiation as energy source. In the present work the recent progress from our laboratory research on metal-free photocatalysis will be systematically presented and also compared with the literature research. Opportunities and challenges on metal-free photocatalysts to enhance their activity under natural solar irradiation will be presented. Based on the aforementioned discussions, suitable future research directions and perspectives for the design and development of potential metal-free photocatalysts will be provided.