Use of covalent organic framework TpPa(OH)₂ as pH-responsive adsorbent for copper ions from water

For the first time, this study applied the covalent organic framework TpPa(OH)₂ as a pH-responsive adsorbent for copper ions from water. The Langmuir adsorption capacities at pH 7 and 25, 35, and 45 °C are 56.2, 84.8, and 109.9 mg copper ions/g, respectively, an endothermic and entropy-driven process. The adsorption capacity of TpPa(OH)₂ on copper ions at pH −0.2 and 35 °C is reduced to 11.3 mg/g, an 86.7% loss. The layered structures of TpPa(OH)₂ are deteriorated by proton attacks at pH −0.2. The pH-swing (7, −0.2, then 7) increases the Langmuir capacity at pH 7 by 35.5%, contributed by excess sites of the exfoliated layers. The TpPa(OH)₂ can be applied as a pH-responsive adsorbent, adsorbing 109.5 ± 3.2 mg copper ions/g at pH 7 and releasing 82.6% adsorbed copper ions at pH −0.2. © 2023 Elsevier B.V.