Construction of Layered Double Hydroxides/Hollow Carbon Microsphere Composites and Its Applications for Mutual Removal of Pb(II) and Humic Acid from Aqueous Solutions

Development of a highly efficient material with large specific area was scientifically and technologically important for simultaneous elimination of inorganic and organic pollutants from wastewater. In this work, layered-double-hydroxides-coated (LDHs-coated) hollow carbon microsphere composites (HCMSs; LDHs/HCMSs) were fabricated using carbon spheres as templates via a hydrothermal method and were then applied for mutual removal of Pb(II) and humic acid (HA) under various experimental conditions, i.e., pH, ionic strength, contact time, addition sequences, and coexisting ions. The results indicated that the copresence of Pb(II) and HA facilitated single target pollutant [Pb(II) or HA] adsorption at pH < 8.0. The adsorbed HA was responsible for the improvement of Pb(II) adsorption, primarily as a result of the formation of HA-Pb-LDHs/HCMSs ternary complexes. Competitive adsorption of Cu(II), Co(II), Pb(II), and Ni(II) ions on LDHs/HCMSs was also investigated, and the LDHs/HCMSs had the affinity in the order of Co(II) < Ni(II) < Cu(II) < Pb(II). Interestingly, in binary/quaternary systems, the results showed that the presence of Cu(II), Co(II), and Ni(II) ions exhibited slight inhibition on Pb(II) adsorption. However, the total amounts of heavy metal ions adsorbed on LDHs/HCMSs increased with the increase of the heavy metal ions. Results of X-ray photoelectron spectroscopy and Fourier transformed infrared spectroscopy indicated that outer-sphere surface complexation mainly dominated the adsorption of Pb(II) on LDHs/HCMSs, while the adsorption of HA was attributed to surface complexation of the disassociated HA on LDHs/HCMSs. The findings highlighted the novel synthesis of LDHs/HCMSs and its potential application for simultaneous removal of different metal ions and natural organic contaminants from wastewater in environmental pollution cleanup.