As a common intermolecular interaction force, hydrogen bonds play a significant role in physical, chemical and biological processes. And this so-called "weak interaction" has long been studied extensively. Thanks to its unique orientation and specificity of bonding, hydrogen bonding effect can regulate molecular aggregation perfectly, which has been widely applied in synthesis of crystal materials. Especially, the hydrogen bonds formed with the assist of ion or charge, namely the charge-assisted hydrogen bonds (CAHB), exhibit a binding strength stronger than ordinary hydrogen bond, and equivalent to covalent bond, which has aroused numerous interests of researchers. Different from ordinary hydrogen bonds, there is a charge distribution between the two substances that form the CAHB. Actually, just the distribution of charge in a given resonance structure dominant the formation of the relatively strong CAHB. In addition, there is also Coulomb interaction between the amphoteric ion component and the carrier carrying the opposite charge. The existence of two energy-equivalent valence bond resonance forms result in the stronger binding CAHB. Specifically, (+)CAHB is formed between the positive charge on the proton donor atom; and (-)CAHB is formed between the formal negative charge on the proton accepting group. It has been also found that CAHB, as a kind of low-resistance hydrogen bond or a salt bridge similar to a cation bridge, is ubiquitous in environmental processes. They possess not only bonding strength much stronger than ordinary hydrogen bonds, but also characteristics similar to covalent bonds, which is beneficial to the self-assembly process of many environmental media. The super macromolecular structure formed by CAHB is the main form of natural organic matter (NOM) in the environment. Adsorption is commonly used to remove the dissociable amphoteric organic pollutants in water environments. The electrostatic interaction between carbon-based adsorbents and ionic compounds may be the main adsorption mechanism for the removal of these ionic compounds. However, a number of other studies have noted that individual electrostatic interaction alone is not able to explain the effect of pH on the adsorption of dissociated ionic contaminants. Apparently, there exists additional physical or chemical interaction mechanisms that need to be further investigated. While CAHB can be well used to explain some abnormal phenomena in adsorption experiments, such as the strong interaction between the negatively charged adsorbates and the adsorbents. In this article, the key formation mechanism of CAHB in the environment and their environmental effects are summarized. Combining with some experimental data, the important mechanism of natural organic matter (including humic substances and dissolved organic matter) conjugating and forming supramolecules via CAHB is discussed with emphasis. Finally, the environment behavior of ionic compounds affected by natural organic matter under the complex water quality conditions with the participation of CAHB is mentioned. The selection and preparation of carbon-based adsorbents for the removal of ionic compounds are also suggested. © 2019, Materials Review Magazine. All right reserved.
