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

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, K_d, 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.