Facile hydrothermal synthesis of hierarchical porous priceite (Ca4B10O19·7H2O) microspheres as high-efficiency adsorbents for heavy metal ions removal

Abstract

Heavy metal ions have attracted considerable concern for their high toxicity and potential malign effects on the water environment, and adsorption has been regarded as one of the most versatile and effective techniques towards water treatment. In view of this, hierarchical porous carnation-like Ca₄B₁₀O₁₉·7H₂O microspheres self-assembled by two-dimensional (2D) quasi-hexagonal nanoplates are successfully synthesized for the first time as far as we know, by a facile and surfactant ethylenediaminetetraacetic acid disodium salt (EDTA-2Na) assisted hydrothermal approach using CaCl₂·2H₂O, NaOH and H₃BO₃ as the raw materials. The as-obtained carnation-like Ca₄B₁₀O₁₉·7H₂O microspheres exhibit a uniform morphology, ca. 89% of which have a diameter within the range of 8.0–11.0 μm. A probable EDTA-2Na assisted self-assembly formation mechanism has also been proposed based on systematic control experiments. Meanwhile, the carnation-like Ca₄B₁₀O₁₉·7H₂O microspheres demonstrate a transparent characteristic from the ultraviolet to the visible region, a hierarchical porous structure (specific surface area: 32.79 m² g⁻¹, pore volume: 0.151 cm³ g⁻¹, average pore diameter: 3.704 nm) and satisfactory thermal stability. In addition, the carnation-like microspheres are confirmed as great satisfactory adsorbents for heavy metal ion (Pb²⁺) removal with an adsorption capacity q_m of 256.4 mg g⁻¹, which may also be employed as excellent adsorbent candidates for other heavy metal or organic dye removal in water treatment as well as catalyst carriers in heterogeneous catalysis.