How do pH modifiers modulate the pore environment of polar-neutral bidentate ligated zirconium coordination polymers?

Abstract

Amino acids are having higher chelating nature, which can be easily complexed with various metal ions. Generally, amino acids are considered to be bidentate ligands with amine and carboxylic functional groups. Among all, l-serine is the neutral polar ligand which consists of a hydroxyl functional group. The l-serine is used as an organic ligand in synthesizing Zr-based Coordination Polymers (CPs). During synthesis, Conc. HCl and NaOH are used as additional pH modifiers. The Ser-Zr CPs are synthesized with and without the additional pH modifiers. The pXRD results show that the Ser-Zr CPs possess a short-range ordered network, i.e., amorphous and having qualitatively coarse surface texture. The FTIR spectrum evidences the bonding between the Zr ion and the l-serine ligand through Zr–N bonding at 644 cm−1. The Ser-Zr CPs synthesized with Conc. HCl possesses enhanced BET surface area, average pore diameter, and total pore volume of 760 m2/g, ∼8.28 nm, and 1.563 cm3/g, respectively. Similarly, the Ser-Zr CPs synthesized with Conc. HCl has multilayer bottle-neck type mesopores. However, the thermal stability of all the Ser-Zr CPs is ∼250 °C. The formation of Ser-Zr CPs and the coordination of serine with Zr are further characterized by ICP-OES and CPMAS NMR spectroscopies. The morphology and crystallinity of the Ser-Zr CPs are studied using a high-resolution transmission electron microscope. The amorphous Ser-Zr CPs can be utilized in applications such as gas adsorption and storage, separation, purification, drug delivery, and many more.