Preface

Covalent organic frameworks (COFs) provide a molecular platform for the production of predictable ordered and extended 2D or 3D structures with topologically welldefined channels and discrete micropores and/or mesopores, greatly enhancing the possibilities of transforming organic materials into unique properties and functions. The past 17 years have seen tremendous achievements in the design, synthesis and functionalization of COFs to show their promising potential as a class of fascinating organic materials. By way of illustration, this book first summarizes recent advances in the interfacial synthesis of 2D COF films via gas/solid, liquid/liquid, liquid/solid and gas/liquid interface. The COF films obtained exhibit better orientation and fewer defects, endowing them with considerable potential for further applications. Next, recent progress in COFs for photocatalysis in water splitting, CO2 reduction, organic transformation and environmental pollutant degradation is discussed. The latest achievements of COFs as solid ion conductors in energy devices are summarized, the controlled size, topology and interface properties of their ordered pores offering ideal pathways for long-term ion conduction. Finally, the possibility of COFs as emerging platforms in cancer therapy is discussed. Encouragingly, successful cases including chemotherapy, photodynamic therapy, photothermal therapy and immunotherapy have been realized. We believe this book will give readers a broad overview of the design criteria and practical methodologies of COFs in various application fields.

> **Yanan Gao and Fei Lu** Hainan University, Haikou, China

**1**

**Chapter 1**

**Abstract**

**1. Introduction**

Thin Films

*Tao Zhang and Yuxiang Zhao*

chemical bonding, morphology, and crystal structure.

**Keywords:** interfacial synthesis, 2D material, COF, crystal, thin film

Interfacial Synthesis of 2D COF

Two-dimensional covalent organic frameworks (2D COFs) are emerging crystalline 2D organic material comprising planar and covalent networks with long-ranging structural order. Benefiting from their intrinsic porosity, crystallinity, and electrical properties, 2D COFs have displayed great potential for separation, energy conversion, and electronic fields. For the most of these applications, large-area and highly-ordered 2D COFs thin films are required. As such, considerable efforts have been devoted to exploring the fabrication of 2D COF thin films with controllable architectures and properties. In this chapter, we aim to provide the recent advances in the fabrication of 2D COF thin films and highlight the advantages and limitations of different methods focusing on

In 2005, the first covalently bonded crystalline porous polymer was successfully synthesized and named covalent organic frameworks (COFs). In subsequent developments, COFs linked by B∙O, C∙N, C∙C, and other bonds have been reported. The regular network structure of COFs can be fully characterized with the help of existing instruments, which is very beneficial to study the relationship between the performance and structure. COFs can also be divided into two-dimensional (2D) COFs and three-dimensional (3D) COFs according to the specific structure. 2D COFs are emerging crystalline 2D organic material comprising planar and covalent networks with long-ranging structural order [1, 2]. In recent years, 2D COFs have been rapidly developed due to their ease of synthesis and definite structure. Benefiting from their intrinsic porosity, crystallinity, and electrical properties, 2D COFs have displayed great potential for separation [3, 4], energy conversion [5–7], and electronic fields [8]. The preparation of COF materials as thin films is advantageous for most applications. Large-area and highly ordered 2D COFs thin films are widely studied [9–12]. COFs are mostly connected by reversible covalent bonds. If the reaction conditions can be adjusted to make the structure of COFs in a dynamic self-repair process, highly ordered films can be obtained. Clever use of the interface can also give the film a good substrate for growth, and the COFs can be spread out along the interface to produce a smooth film. Common interfaces include gas/solid interface, liquid/liquid interface,

## **Chapter 1**
