In recent decades, there have been remarkable developments in the chemical synthesis and study of the properties of colloidal inorganic nanocrystals. Despite seminal research and several important previous studies, this scientific topic has gained impetus in the period since the 1990s. In addition to consolidated knowledge on the chemical synthesis of colloidal particles, more powerful characterization techniques and computational tools have emerged, associated with new chemical strategies to produce new materials. Several strategies now available are based on reproducible chemical methods for controlling morphology and particle size, taking advantage of the diversity of nanomaterials with different length scales and shapes. In this way, unique properties can be designed and explored for new applications and functional devices. Although this knowledge is founded on well-established procedures at the chemistry level for the synthesis and characterization of colloidal systems, various innovative approaches have emerged since then, framed by a new paradigm associated with nanotechnology. To a great extent, this scientific framework required multidisciplinary synergies for exploring fundamental properties of matter, aimed ultimately at the manufacture of new functional systems based on objects such as nanocrystals, the nanometric dimensions of which enable new properties to be developed. It is noteworthy that such properties not only depend on the nanoscale characteristics of the particles but may also result from their assembly into complex hierarchical nanostructures and hybrid materials. The relevance of the nature of the surface of nanocrystals in defining their properties and implications in terms of the interfaces that are established with the surrounding environments was also soon realized. On the other hand, the inherent difficulty in investigating nanosurfaces was no great surprise, as in conventional solid materials surface aspects are generally more complex to study than the bulk properties. In this context, what emerges as particularity relevant in colloidal nanocrystals is the fact that their surface area per unit volume is higher, so that surface phenomena acquire greater relevance in defining their properties and mediating their interaction with the surroundings.

In this book, different classes of inorganic materials are approached as illustrative examples underlying the important concepts depending on the properties and applications of colloidal nanocrystals. We are aware that by opting for this approach, the surface chemistry of each of the different nanocrystalline systems is not covered exhaustively and with the depth needed by specialists. We instead favour those readers who intend, in a first stage, to acquire a general insight into the relevant scientific literature in one of the topics of the surface chemistry of colloidal nanocrystals, be it the scientist who is seeking a new research line or the graduate student who is starting their doctoral studies. The first introductory chapter (Chapter 1) presents a brief historical perspective and provides a brief overview of the aspects that will be addressed in the subsequent chapters. The following two chapters highlight fundamental concepts at the level of the surface chemistry of colloidal nanocrystals of different nature. Chapter 2 is dedicated to colloidal particles of different materials that are stable in an aqueous medium, and Chapter 3 focuses on nanocrystals with hydrophobic surfaces, with the main emphasis on semiconductor materials. The next three chapters are devoted to more practical aspects of surface chemical modification and chemical tailoring of interfaces. Chapter 4 addresses the interaction of nanocrystals with polymers and resulting nanocomposites, Chapter 5 reviews important literature on the formation and properties of biointerfaces and, finally, Chapter 6 highlights the relevance of the nature of the surface of colloidal nanocrystals in the fabrication of nanotechnological devices and applications in different fields.

This book also mirrors the thematics approached in our research activities. The experience acquired over the years in the scientific supervision of students has largely guided the planning of the book. The perspectives put forward in the different chapters would certainly have been different, despite the scientific truth inherent to the same facts, if the circumstances in which we have developed our research activities had been different. Therefore, we thank all those colleagues and students who collaborated with us and helped us along our scientific path. We express our deep gratitude to our most direct collaborators, tireless companions over the years in the daily activities of the nanoLAB research laboratory. We thank Professor João Rocha for encouraging us to write a book on this topic, whose thematic affinity with our scientific activities in the frame of the CICECO – Aveiro Institute of Materials he felt important to reinforce. We also thank Francisco Trindade for generating some of the figures presented in the book, following our specific requests.

The world was hit by the Covid-19 pandemic while we were writing a substantial part of this book. In this context, with tragic consequences for humanity and still with no end in sight at the present time, society turns to Science, asking for immediate solutions, with many citizens wanting to know what a virus is and how it works. Although virology is a subject that is far from the expertise of the present authors, it appears pertinent to refer to it in a personal context. Although of a different nature, the new corona virus is an example of a self-assembled nano-object, with dimensions typical of a nanoparticle whose surface mediates the way in which it interacts with its surroundings. For example, its inactivation under external exposure such as during hand washing can be achieved by dissolving the protective lipid bilayer of the virus using amphiphilic molecules that exist in soap. This is an actual example, among many others, highlighting the relevance of understanding the surface chemistry of structures with nanometric dimensions.

The scientific literature on the topics addressed in this book has increased exponentially in recent years, which makes it very difficult to present exhaustive citations of all the relevant studies. Nevertheless, the reader is encouraged to consider the cited literature sources as a frame for our writing, bearing in mind their guidance towards further reading in special thematics. A great motivation for writing this book was the attempt to integrate different aspects regarding the surface chemistry of colloidal nanocrystals, which we feel are well documented in the state of the art while being dispersed in the literature sources. We hope that this book will contribute to filling this gap in terms of the scientific literature in the field of nanosciences, but of course only the reader will be able to judge whether such an endeavour had been successful. We conclude by wishing you pleasant reading when going through the pages of this book.

Ana L. Daniel-da-Silva

Tito Trindade

Aveiro