Preparation of flexible covalent organic frameworks from a very cheap diamine monomer for highly efficient adsorption of naphthalene and its derivatives

Scheme. 1. Illustration of (a) static procedure and (b) dynamic procedure for analysis of naphthalene and its derivatives. [Display omitted] •MDA was used as a linker monomer to prepare flexible COFs for the first time.•TpMDA showed high removal efficiency to naphthalene and its derivatives.•TpMDA remained well adsorption capacity after 10 times desorption/adsorption cycles.•Possible adsorption mechanisms were discussed in detail.•TpMDA had promising applications in the removal of linear and planar PAHs. In this work, a flexible covalent organic framework (named TpMDA) was prepared by cheap 4,4′-diaminodiphenylmethane (MDA) monomer with flexible methylene groups. TpMDA could realize efficient removal of naphthalene and its derivatives (NAs) from environmental water samples through hydrophobic, π-π and electrostatic interactions. The superior adsorption and desorption performance of TpMDA was confirmed by static and dynamic adsorption/desorption experiments. It can be seen from the fitting results of the adsorption experiments that the adsorption of NAs was a spontaneous, endothermic, and comprehensive adsorption process that included both physical and chemical adsorption. The average removal efficiency of Nap, 1-Anap, 1-Nnap, 1-Naa and Npx by TpMDA from the four batches were 92.1 %, 86.9 %, 93.8 %, 75.3 % and 91.8 %, respectively. The maximum adsorption capacities were 301, 120, 184, 125 and 106 mg/g, respectively. In addition, TpMDA could be reused at least 10 times without degradation of adsorption performance. The selectivity for planar and linear molecules was verified. The feasibility of practical application was verified by static/dynamic adsorption volume experiments and the application of TpMDA in different aqueous environments. In general, this work not only proposes a new idea for the preparation of flexible COFs, but also provides a promising strategy for the removal of NAs in environmental remediation.