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Environmental pollution has been widely considered by researchers, especially the heavy metals damage to the human and ecological environment is irreversible. Adsorption is an important method to remove heavy metal ions from the environment. In this paper, humic acid (HA) was functionalized by the improved Hummers method, and its adsorption capacity for Pb(II) was studied. The results of scanning electron microscope (SEM), X-ray diffraction (XRD), Roman, and Brunauer-Emmett-Teller (BET) showed that the thickness of irregular particles decreases to a layered structure during the transformation process. In addition, X-ray photoelectron spectroscopic (XPS) and Fourier transform infrared spectra (FT-IR) spectra showed that the surface of oxidized-biochar (OBC) was rich in reactive oxygen species, which was conducive to the formation of coordination bonds with Pb(II). Further adsorption experiments showed that it was a spontaneous monolayer chemisorption. The results of the DFT calculation showed that -COOH had the lowest adsorption energy for Pb(II), and it was easier to form stable chemical bonds than -OH, -C=O, and -C-O-C-. Because those oxygen-containing functional groups not only can promote electrostatic attraction but also are more favorable for forming a covalent bond with Pb(II). This study had guiding significance for the deep modification and application of weathered coal as a heavy metal ion adsorbent or cation exchanger. [ABSTRACT FROM AUTHOR]

It is a challenge to achieve the harmless treatment and resourceful use of various metal elements in electroplating sludge, and converting them into functional materials has become an important technological direction. Based on the existence of various metal ions in electroplating sludge, sodium oleate intercalated Zn−Cr‐LDHs (Zn−Cr‐layered double hydroxides) were prepared by two‐phase solution heating method. The adsorption process of the prepared LDHs for Congo red (CR) in aqueous solution can be described by Langmuir isotherm model and pseudo‐second‐order kinetic model and the maximum adsorption capacity is 2750.43 mg/g. The results of TEM and XPS show that the adsorption mechanism is dominated by electrostatic adsorption, ion exchange process, hydrogen bonding interaction and surface complexation. Therefore, this paper provides a strategy for recovering metal elements from electroplating sludge to prepare LDHs adsorption materials with ultra‐high adsorption capacity. [ABSTRACT FROM AUTHOR]

The development of high performance magnetic nanomaterials has a good application prospect in wastewater treatment. Herein, Fe3O4/C nanocomposites was synthesized by eco‐friendly hydrolysis‐calcination method using potassium fulvic acid (FA−K) and FeCl3⋅6H2O as raw materials. The morphology of Fe3O4/C nanocomposites exhibited a loose pore structure with uniform size (a diameter ∼ 27 nm). The prepared Fe3O4/C nanocomposites possessed excellent dispersibility and magnetic properties in aqueous solution. The removal efficiency and maximum adsorption capacity of Fe3O4/C nanocomposites were 98% and 64.0 mg g−1, respectively. Moreover, it was confirmed that the adsorption mechanism of Cr(VI) contains electrostatic attraction and redox reaction. In this work, we provide a convenient means for manufacturing Fe3O4/C nanocomposites, and prove that FA−K is a cheap carbon source for manufacturing Fe3O4/C nanocomposites, which makes Fe3O4/C nanocomposites have potential application value in the effective adsorption of Cr(VI). [ABSTRACT FROM AUTHOR]

Heavy metal Cr(VI) in water body has attracted extensive attention due to its carcinogenicity, teratogenicity and mutagenicity. In this study, magnetic walnut shell biochar (Fe 3 O 4 @WSB-n) were prepared from walnut shell (WS) by impregnation (to destroy the wooden structure of walnut shell), alkali activation and hydrothermal synthesis. Not only solved the problem of difficult separation of adsorbent, but also realized the reuse of environmental waste. Results manifest that Fe 3 O 4 @WSB-1 has a hierarchical honeycomb structure with a specific surface area of 914.01 m2 g−1. And the adsorption process of Cr(VI) on Fe 3 O 4 @WSB-1 belongs to monomolecular chemisorption, and the maximum adsorption capacity is reached to 230.63 mg g−1 (0.01 g, 30 mL pH = 2.0, 25 °C). Adsorption capacity of Fe 3 O 4 @WSB-1 for Cr(VI) can still keep 66.85 mg g−1 after 5 cycles. The XPS and FT-IR results show that the oxygen-containing functional groups play a significant role in the adsorption process, and the magnetic centers further promote the reduction of Cr(VI) through reducibility of Fe2+. Due to efficient conversion of hardwood structures, high stability in solution and easy recovery, magnetic biochar is suitable for practical wastewater treatment. [Display omitted] • An efficient method for converting walnut shell hardwood structure into biochar by pyrolysis co-activation. • The composite Fe 3 O 4 @WSB-1 has a hierarchical honeycomb structure with a specific surface area of 914.01 m2 g−1. • Fe 3 O 4 @WSB-1 has excellent adsorption performance (230.63 mg g−1) for hexavalent chromium in wastewater. • Fe 3 O 4 @WSB-1 has strong magnetism and stability, which is beneficial to recovery and reuse of adsorbent. [ABSTRACT FROM AUTHOR]

Highlights: [•] The iron oxide is gained via a facile, green, and economical synthesis process. [•] The promising adsorptive applications in water treatment are investigated. [•] Congo red removal capacity is 253.8mgg−1, and commercial α-Fe2O3 is 42.4mgg−1. [•] The maximum adsorption capacity for Cr(VI) is 17.0mgg−1. [ABSTRACT FROM AUTHOR]