Zirconium Phosphate and Phosphonate Nanoparticles for Phosphate Removal from Water: An Aquarium Life Support System Application

In aquatic environments, phosphorus is known as the “limiting nutrient.” It combines with nitrogen and photosynthetic processes to produce plant and algal growth. Phosphorus in marine life support systems exists in either a particulate or dissolved phase. While particulate sources may be removed during filtration or fractionation, the dissolved form persists. In a typical marine environment (pH 8), dissolved phosphorus is almost all hydrogen phosphate ion (HOPO3), also known as inorganic or orthophosphate. Here we report the synthesis and use of zirconium phosphate ( -ZrP, Zr(O3POH)2·H2O) and zirconium methylenediphosphonate (ZrMDP, Zr[O3P(CH2)PO3]) nanoparticles for phosphate removal from water. Sodium phosphate solutions (0.5-10.0 mg/L) are exposed to nanoparticle suspensions (10 mg/mL) and phosphate uptake is measured by ion chromatography. In all cases, high phosphate removal is observed. For example, the 5.00 mg/L sodium phosphate solution experiences 99.9% removal after exposure to -ZrP. After treatment phosphate concentration drops to 0.005 mg/L! This is well below the algal growth threshold (0.01-0.05 mg/L). Future work will explore the particles’ phosphate removal capacity, their regeneration, and the ability to engineer a robust filtration media where the particles are anchored to a silica (sand) surface. Introduction Phosphates are common in nature. They exist as the polar hydrophilic head groups in the phospholipid bilayers of cell walls and in micelles. They are also prevalent in nucleic acids (RNA and DNA), and in the cell’s “energy molecule” adenosine triphosphate (ATP). Phosphate minerals in rock like calcium hydroxyphosphate and calcium fluorophosphate are also natural sources. Phosphorus is dissolved in water primarily as the phosphate ion (PO4). Natural or background concentrations of phosphate in water, also known as inorganic or orthophosphate, are in the range 0.005-0.05 mg/L. Periodic algal blooms may be observed at phosphate concentrations between 0.08-0.10 mg/L. Long term eutrophication can be avoided when phosphate levels are kept below 0.5-0.05 mg/L (Dunne and Leopold, 1978). In marine systems, phosphorus is the