A zinc-based coordination polymer as adsorbent for removal of trichlorophenol from aqueous solution : synthesis, sorption and DFT studies

Abstract [Zn(hba)2(tmdp)]n (1), a Zn-coordination polymer (CP), prepared by the reaction of Zn(NO3)2•6H2O, 4-hydroxybenzoic acid (Hhba) and 4,4′- trimethylenedipyridine (tmdp) was reported. The compound was characterised, using CHN, single crystal and powder X-ray diffraction analysis, FT-IR, and TGA techniques. It exhibits a square pyramidal geometry, with the zinc (II) atom coordinated to two nitrogen atoms from two tmdp ligand molecules and to three oxygen atoms from two hba molecules. The zinc (II) carboxylate units are bridged through the N-donor spacer ligand, thereby giving rise to a one-dimensional CP. PXRD analysis confirmed the purity of the bulk of (1). Compound (1) presented an adsorption capacity of 207.8 mg/g for the removal of 2,4,6-trichlorophenol (TCP) from aqueous solution. The adsorption mechanism is governed by π-π stacking and electrostatic interactions, as obtained from DFT studies. The feasibility and exothermic nature of the adsorption process is indicated by the negative binding energy obtained.