One-Pot Synthesis of Layered Disodium Zirconium Phosphate: Crystal Structure and Application in the Remediation of Heavy-Metal-Contaminated Wastewater.

Abstract

Inorganic ion exchangers offer advantages whenever operation at high temperatures or in oxidizing environments is required. A novel two-dimensional disodium zirconium phosphate, Zr(NaPO4)2·H2O, was reported and investigated as an ion exchanger for heavy metals. The material was synthesized by a novel minimalistic solventless approach, and its solid-state structure was determined from powder X-ray diffraction data. Zr(NaPO4)2·H2O crystallizes in the space group P21/c with cell parameters a = 8.7584(1) Å, b = 5.3543(1) Å, c = 18.1684(3) Å, β = 109.053 (1)°, and Z = 4. Its layered structure is similar to that of α-zirconium phosphate, Zr(HPO4)2·H2O. However, unlike α-zirconium phosphate which is limited in practical applications by its narrow interlayer spacing (d = 7.6 Å), the disodium zirconium phosphate has a larger spacing of 8.6 Å between planes. The material with inherent structural advantages displays excellent sorption for heavy metals such as Pb2+, Cu2+, Cd2+, and Tl+, maintaining its high selectivity with distribution coefficients, Kd, of 104-105 mL/g even in the presence of a large excess of Na+, K+, Mg2+, and Ca2+, which are commonly present in underground water. In particular, the maximum sorption capacity for the highly toxic Tl+ is a record high, 5.07 mmol/g (1036 mg/g). The fast reaction kinetics indicate that the exchangeable positions in Zr(NaPO4)2·H2O are readily accessible, in contrast to Zr(HPO4)2·H2O. The ease of preparation, benign nature, and advantageous ion-exchange properties make Zr(NaPO4)2·H2O a highly promising sorbent for the treatment of water polluted with heavy metals.