Preface

Photocatalysis depicts a remarkable class of chemical transformations. It uses the energy delivered by light and causes hard, sometimes even impossible, reactions to conduct in the darkness. This book deals with a variety of photocatalysis topics.

Chapter 1 by Awwad et al. introduces the principles, opportunities, and applications of photocatalysis. Chapter 2 by Muslim and Ahmad discusses the many applications of metal-organic frameworks (MOFs), including in healing metals and heavy metal cations and for antimicrobial applications and photocatalytic indoor environmental remediation. The commercial exploitation of MOFs in using planet-saving solar energy photocatalysis innovations could be more influential with the assistance of industrial partners and various stakeholders. Chapter 3 by Barci and Hao clarifies the need for raw materials and eco-friendly and cost-effective strategies for detecting and extracting materials to satisfy the semiconductor market and its applications. Since the semiconductor market is increasing progressively, driven mainly by the automotive industry, solar cells, smartphone products, the Internet of Things (IOT), and virtual reality (VR) applications, the demand for raw materials, suppliers, and material manufacturing is also increasing. With scientific progress, more materials, alloys, and intelligent materials are being used and thus we need to consider environmental, moral, and ethical aspects when choosing materials for any product, service, or system. Novel techniques such as light detection and ranging (LiDAR), robotics, autonomous haulage systems, and remote operating and monitoring centers assist in maintaining a suitable equilibrium and enable the increasing semiconductor market trend. Chapter 4 by Mittal discusses the usage of self–cleaning coatings or surfaces, as there is a growing demand for self-disinfected and hygienic surfaces. Self-cleaning coatings can be employed in automobile windshields, textiles, antifouling membranes, paints and building construction materials, optoelectronic devices like solar panels, and the medical device and food industries. This chapter presents an outlook on nano titanium dioxide (TiO2)-based super hydrophilic self-cleaning surfaces by giving a general idea of various systems and approaches that could enhance the self-cleaning manners of TiO2 in the solar spectrum. The exposed crystal facets in TiO2, metal and non-metal doping, and dye sensitization are tailored by the hybrid structure of TiO2, graphene, and graphitic monolayer's TiO2-semiconductor heterojunctions, attributing to visiblelight photocatalytic self-cleaning activity. Chapter 5 by Ezhumalai and Kumaresan focuses on the synthesis methods and applications of g-C3N4 and g-C3N4-based materials in energy storage. g-C3N4-based composites have unique characteristics and a wide range of applications for energy storage and conversion. Chapter 6 by Mohapatra and Park addresses the principal objectives of water purification using a triple-phase catalyst. Under irradiation, charge carriers are formed on the surface of the photocatalyst, and the success of pollutant molecule degradation critically depends on the interaction between the surface and the target molecules. The novel triphasic photocatalytic design with superhydrophobic triphasic interface architecture will allow the immediate delivery of oxygen straight from the air to the reaction interface when compared with state-of-the-art diphasic photocatalytic systems, thus minimizing

electron-hole recombination and resulting in remarkably high efficiency. Recently, a solid surface's super wettability (especially underwater superoleophobicity) has attracted much attention. Chapter 7 by Nguyen et al. examines the use of "green" agents to fabricate materials. The chapter shows that integrating a sufficiently large amount of Fe3O4 will make the composites magnetic enough to separate them from the aqueous solution by an external magnetic field. This characteristic is significant, overcoming the inherent disadvantage of nanomaterials, which disperse too well and are challenging to recover. The summarized research also shows an excellent combination between a magnetic metal oxide and a semiconductor metal oxide, which plays a crucial catalytic role in the photodegradation of pollutant compounds, especially organic pollutants. Chapter 8 by Estrada et al. is an overview of semiconductor photocatalysis, emphasizing carbon and metal sulfide nanocomposites as photocatalysts for wastewater treatment. The coupling of metal sulfides with graphene derivatives platforms has been used synergistically to prevent photo-corrosion of metal sulfide phases and increase the photocatalytic performance of heterostructures. The chapter shows that an increase of graphene or graphene derivative content above a certain value in the hybrid nanostructure decreases the degradation efficiency. Using graphene nanocomposites at a large scale with cost-effective production, high photostability, and high photocatalytic efficiency is challenging. These challenges need to be addressed to guarantee the future commercialization of graphene nanocomposites on a large scale for environmental applications. Chapter 9 by Yoshimoto and Satoshi et al. discusses various types of skin aging, including chronologic aging and photo-aging involving ultraviolet (UV) radiation, visible light, and others. UVA and UVA photocatalysis (involving photosensitizers) contribute to the production of chronically induced skin damage that results in photo-aging, especially wrinkles associated with histopathological actinic elastosis in the dermis. The chapter proposes a screening method to study the effects of antioxidants on UVA photosensitization. It provides new findings for photo-aging prevention by discussing the characteristics of UVA photocatalysts in the skin. Chapter 10 by Dzinun et al. discusses mussel and cockle shells as agricultural wastes for photocatalyst applications. The authors use a solid-state dispersion (SSD) method to prepare a composite photocatalyst in which mussel and cockle are integrated with TiO2 nanoparticles at a ratio of 9:1. It is interesting to note that the prepared composite photocatalyst particle is nanosized to enhance photocatalytic performance. Chapter 11 by Barraza-Jiménez et al. studies anthocyanidins in the gas phase and under the effects of solvents like water, ethanol, n-hexane, and methanol using densityfunctional theory (DFT) and time-dependent density-functional theory (TD-DFT) electronic structure calculations for applications as natural dyes in photocatalysis. Conceptual DFT results show that cyanidin, malvidin, and pelargonidin present good charge transfer properties. Cyanidin presents a lower electron reorganization energy (λe) when water is used as the solvent. TD-DFT is used for excited state calculation, and absorption data shows prominent peaks in a wavelength between 479.1 and 536.4 nm. The chapter discusses the UV–Vis absorption spectra generated and the solvent effects in each case. These pigments are good options for photocatalysis applications, and the best choices for dye sensitization are cyanidin, malvidin, and petunidin, after including the more common anthocyanidins in the analysis. In Chapter 12, Mohammed reviews the research on natural fiber (NFr)-reinforced composites and the constraints that have emerged in their development and serviceability. These constraints must be addressed before NFrs can be utilized successfully. Furthermore, the chapter describes how surface-based photocatalyst nanoparticles (PHNPs) could increase NFr adhesion to their matrix and reduce NFr moisture absorption. Therefore, surface treatments

with PHNPs can modify the characteristics of NFr. Chapter 13 by Mittal discusses the fabrication of advanced nanocomposites and related challenges, such as low efficiency and selectivity towards hydrogen evolution under the illumination of solar energy. This chapter examines recent developments in photocatalysts, and heterojunction fabrication factors influencing the photocatalytic process for the dynamic production of hydrogen. Finally, Chapter 14 by Venkateshwaran et al. discusses the important parameters affecting the activities of both Co3O4 and MnO2, such as phase and morphology engineering, defects and crystal facets engineering, and strains and mixed metal-oxide formations. The chapter also discusses the fundamentals of water oxidation and reduction reactions. Moreover, it investigates the electrochemistry behind MnO2 and Co3O4 for a better understanding of catalyst reactions and mechanisms. This

chapter stresses the importance of MnO2 and Co3O4 as bifunctional catalysts by examining their fundamental electrochemistry, structure-activity relationship, and

This book will inspire readers, researchers, and scientists to further examine newly developed photocatalysts and unlock new potential research tracks for additional novel development. We would like to express our gratitude to the contributing authors for their excellent chapters. We would also like to thank the staff at IntechOpen.

**Dr. Nasser S. Awwad**

Department of Chemistry, King Khalid University, Abha, Saudi Arabia

**Dr. Saleh Saeed Alarfaji** Faculty of Science,

Department of Chemistry, King Khalid University, Abha, Saudi Arabia

> **Dr. Ahmed Alomary** General Manger, Aseer Education, Saudi Arabia

Faculty of Science,

Professor,

future directions in the field of metal-air batteries.

with PHNPs can modify the characteristics of NFr. Chapter 13 by Mittal discusses the fabrication of advanced nanocomposites and related challenges, such as low efficiency and selectivity towards hydrogen evolution under the illumination of solar energy. This chapter examines recent developments in photocatalysts, and heterojunction fabrication factors influencing the photocatalytic process for the dynamic production of hydrogen. Finally, Chapter 14 by Venkateshwaran et al. discusses the important parameters affecting the activities of both Co3O4 and MnO2, such as phase and morphology engineering, defects and crystal facets engineering, and strains and mixed metal-oxide formations. The chapter also discusses the fundamentals of water oxidation and reduction reactions. Moreover, it investigates the electrochemistry behind MnO2 and Co3O4 for a better understanding of catalyst reactions and mechanisms. This chapter stresses the importance of MnO2 and Co3O4 as bifunctional catalysts by examining their fundamental electrochemistry, structure-activity relationship, and future directions in the field of metal-air batteries.

This book will inspire readers, researchers, and scientists to further examine newly developed photocatalysts and unlock new potential research tracks for additional novel development. We would like to express our gratitude to the contributing authors for their excellent chapters. We would also like to thank the staff at IntechOpen.

> **Dr. Nasser S. Awwad** Professor, Faculty of Science, Department of Chemistry, King Khalid University, Abha, Saudi Arabia
