Guanidine‐Functionalized Fluorescent sp² Carbon‐Conjugated Covalent Organic Framework for Sensing and Capture of Pd(II) and Cr(VI) Ions

Abstract

Palladium is a key element in fuel cells, electronic industries, and organic catalysis. At the same time, chromium is essential in leather, electroplating, and metallurgical industries. However, their unpremeditated leakage into aquatic systems has caused human health and environmental apprehensions. Herein, we reported the development of an sp2 carbon‐conjugated fluorescent covalent organic framework with a guanidine moiety (sp2c‐gCOF) that showed excellent thermal and chemical stability. The sp2c‐gCOF showed effective sensing, capture, and recovery/removal of Pd(II) and Cr(VI) ions, which could be due to the highly accessible pore walls decorated with guanidine moieties. The fluorescent sp2c‐gCOF showed higher selectivity for Pd(II) and Cr(VI) ions, with an ultra‐low detection limit of 2.7 and 3.2 nM, respectively. The analysis of the adsorption properties with a pseudo‐second‐order kinetic model showed that sp2c‐gCOF could successfully and selectively remove both Pd(II) and Cr(VI) ions from aqueous solutions. The polymer also showed excellent capture efficacy even after seven consecutive adsorption‐desorption cycles. Hence, this study reveals the potential of fluorescent sp2c‐gCOF for detecting, removing, and recovering valuable metals and hazardous ions from wastewater, which would be useful for economic benefit, environmental safety, human health, and sustainability. The post‐synthetic modification of sp2c‐COF with suitable functionalities could also be useful for sensing and extracting other water pollutants and valuable materials from an aqueous system.

Lanthanide Functionalized Covalent Organic Frameworks Hybrid Materials for Luminescence Responsive Chemical Sensing

“…[86] Besides, some works are reported on the COFs hybrid materials functionalized using small molecule covalent PSM or host-guest assembly. [87][88][89][90][91][92]…”

“…Das et al develop an sp 2 carbon-conjugated luminescent COF with a guanidine moiety (sp 2 c-gCOF) showing effective sensing of Pd 2 + (LOD = 2.7 NM) and CrO 4 2À (LOD = 3.2 nM) ion for its highly accessible pore walls decorated with functionalization. [91] Its extended π-conjugation in the vinylenelinked frameworks embodies the luminescence to be utilized to sense the two ions. Pd 2 + ions significantly reduce the luminescence signals of sp 2 c-gCOF over the other tested metal ions for its stronger binding affinity of its guanidine moiety.…”

“…To presence, the non‐lanthanide functionalized COFs hybrid materials for luminescence responsive chemical sensing mainly focus on the carbon dots (CDs)‐based COFs [80–85] or quantum dots (QDs) nanocomposite systems [86] . Besides, some works are reported on the COFs hybrid materials functionalized using small molecule covalent PSM or host‐guest assembly [87–92] …”

“…Das et al. develop an sp 2 carbon‐conjugated luminescent COF with a guanidine moiety (sp 2 c‐gCOF) showing effective sensing of Pd 2+ (LOD=2.7 NM) and CrO 4 2− (LOD=3.2 nM) ion for its highly accessible pore walls decorated with functionalization [91] . Its extended π‐conjugation in the vinylene‐linked frameworks embodies the luminescence to be utilized to sense the two ions.…”

An Aryl‐ether‐linked Covalent Organic Framework Modified with Thioamide Groups for Selective Extraction of Palladium from Strong Acid Solutions

“…Among these novel adsorption materials, covalent organic frameworks (COFs) are a class of organic porous crystalline materials normally composed of conjugated organic ligands, which possess unique advantages in separation, adsorption, sensing, and catalysis due to their intrinsic porous structure, excellent crystallinity and large surface area [21–23] . However, the reversible linkage represented by imine groups [24–26] inherently limits the chemical stability of COFs, especially in the presence of strong acids and bases [27,28] .…”