A comparative study of micro- and nano-structured di-nuclear Co(II) complex, designed to produce efficient nano-sorbent of Co3O4 applicable in the removal of Pb2+

A di-nuclear inorganic complex, formulated as [Co2(H2O)5(pdc)2]·2H2O (1) that pdc2− is pyridine-2,6-dicarboxylato has been synthesized under hydrothermal condition and sonochemical irradiation. Depending on the synthetic conditions, different morphology has been obtained for complex 1. Complex 1 hydrothermal (hc) which obtained as single crystal is a micro-structured compound and was characterized by single crystal X-ray diffraction. Complex 1 ultrasound (uc) is a nano-structured compound and obtained as precipitate. Structural comparison of hc and uc by Fourier-transform infrared spectroscopy (FT-IR), powder X-ray diffraction, and scanning electron microscopy (SEM) revealed that both synthesized complexes have the same structure with different particles size and morphology. In this study, a new synthetic route has been developed to prepare Co3O4 nanoparticles for environmental catalytic applications. Effective sorbents Co3O4-hc and Co3O4-uc were prepared by thermolysis of dinuclear cobalt complexes and characterized by FT-IR, SEM, XRD, and Brunauer–Emmett–Teller specific surface area. Co3O4-hc and Co3O4-uc were used as nano-sorbents for the removal Pb(II) from aqueous solution. Detailed sorption studies showed that both synthetic sorbents are valuable to remove Pb(II) from wastewater. The effective catalytic performance of the as-prepared sorbents can be attributed to the physicochemical features of synthetic catalysts, such as mesoporous nature, homogenous dispersion of the active phase, small particle size and high surface area. The effects of contact time, pH, Pb(II) and adsorbent dosage to remove Pb(II) were investigated. Maximum adsorption percent of Co3O4-hc and Co3O4-uc at room temperature were found to be 90 and 92.2%, respectively. The selectivity of the as-prepared catalysts toward metal ions Pb(II), Co(II), Cr(III), Cu(II), Fe(II), Hg(II), Mn(II) and Ni(II) exhibited that Co3O4 catalysts have the highest selectivity toward Pb(II). Also, the synthetic catalysts Co3O4-hc and Co3O4-uc showed an excellent cycling performance for Pb(II) removal up to 85.3 and 83.4% recovery over five cycles.