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Related Concept Videos

Network Covalent Solids02:18

Network Covalent Solids

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Network covalent solids contain a three-dimensional network of covalently bonded atoms as found in the crystal structures of nonmetals like diamond, graphite, silicon, and some covalent compounds, such as silicon dioxide (sand) and silicon carbide (carborundum, the abrasive on sandpaper). Many minerals have networks of covalent bonds.
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Metallic solids such as crystals of copper, aluminum, and iron are formed by metal atoms. The structure of metallic crystals is often described as a uniform distribution of atomic nuclei within a “sea” of delocalized electrons. The atoms within such a metallic solid are held together by a unique force known as metallic bonding that gives rise to many useful and varied bulk properties.
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Updated: Jun 21, 2025

Microfluidic-based Synthesis of Covalent Organic Frameworks COFs: A Tool for Continuous Production of COF Fibers and Direct Printing on a Surface
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High-Performance Piezoelectric Two-Dimensional Covalent Organic Frameworks.

Qianfeng Gu1, Xiangqian Lu2, Cailing Chen3

  • 1Department of Materials Science and Engineering, City University of Hong Kong, Tat Chee Avenue 83, Kowloon, Hong Kong SAR, 999077, P. R. China.

Angewandte Chemie (International Ed. in English)
|July 8, 2024
PubMed
Summary
This summary is machine-generated.

New organic piezoelectric nanogenerators (PENGs) use fluorinated covalent organic frameworks (COFs) to achieve record-high output voltages, advancing self-powering technologies.

Keywords:
covalent organic frameworksfluorinated alkyl chainpiezoelectric nanogeneratorpiezoelectricity

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Area of Science:

  • Materials Science
  • Nanotechnology
  • Energy Harvesting

Background:

  • Organic piezoelectric nanogenerators (PENGs) offer potential for mechanical energy harvesting but are limited by low output open circuit voltage.
  • Developing efficient organic materials is crucial for advancing self-powering systems.

Purpose of the Study:

  • To develop novel two-dimensional (2D) covalent organic frameworks (COFs) for high-performance PENGs.
  • To enhance the piezoelectric properties of organic materials for improved energy harvesting.

Main Methods:

  • Synthesized two fluorinated 2D COFs: CityU-13 and CityU-14.
  • Fabricated PENGs using these COFs.
  • Characterized the piezoelectric properties, including polarization, piezoelectric coefficient (d33), and output voltage/current.

Main Results:

  • CityU-13 and CityU-14 COFs exhibited strong piezoelectricity, confirmed by switchable polarization and high d33 values.
  • PENGs demonstrated record-high open circuit voltages: 60 V for CityU-13 and 50 V for CityU-14.
  • The devices showed stable performance with excellent short-circuit current and durability over 600 seconds.

Conclusions:

  • Fluorinated 2D COFs (CityU-13 and CityU-14) significantly enhance PENG performance.
  • These COFs offer the highest output voltages among reported organic materials for PENGs.
  • The study presents a promising pathway for developing advanced self-powering devices.