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Graphical abstract Abstract Potassium humate possesses a wide variety of oxygen-containing functional groups and has good adsorption and complexation properties for many kinds of transition metal ions. In this work, a simple and separable route had been developed to synthesize Fe 3 O 4 /graphene nanocomposite, derived from potassium humate, were employed for the effective adsorption of Cr(VI) in aqueous phase. In addition, the Fe 3 O 4 /graphene nanocomposite prepared at 600 °C (S-600) showed a maximum adsorption capacity of 280.6 mg/g for Cr(VI) and good cycling performance, which was much higher than those reported graphene-based adsorbents and other conventional adsorbents. The adsorptive behavior was well fitted to the Langmuir isotherm model. The adsorption kinetics for removal of Cr(VI) agreed with pseudo-second-order equation, which indicates a kind of chemical adsorption. Its superior adsorption performance might be due to the effective adsorption sites at the surface and formation of FeOH2+ on the surface of Fe 3 O 4 /graphene. This work provided a promising approach for the removal of Cr(VI) from wastewater using a Fe 3 O 4 /graphene nanocomposite, which shows a huge number of application prospects. [ABSTRACT FROM AUTHOR]

Abstract In this work, a novel rhombic dodecahedral structure of Ca-Al-layered double hydroxides (Ca-Al-LDHs) was synthesized by a two-phase solvothermal method. Subsequently, Ca-Al layered double oxides (Ca-Al-LDOs) were obtained by calcinating Ca-Al-LDHs at 600 °C which maintained the rhombic dodecahedral structures well. The morphologies of as-obtained samples were characterized by both transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The phase structure and elemental composition were analyzed by X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDS), respectively. Fourier transformed infrared (FT-IR) spectra were performed to confirm the existence of LDH structures. The Ca-Al-LDOs exhibited high adsorption rates and superb adsorption capacities for removal of Congo red (CR) from aqueous solution. The maximum adsorption capacities of Ca-Al-LDOs towards CR reached to 1536.1 mg g−1, which is extremely higher than most of hydrotalcite-like materials. The adsorption process of Ca-Al-LDHs and Ca-Al-LDOs were described by the Langmuir isotherm model and pseudo-second-order model well. The adsorption mechanisms mainly dominated by electrostatic adsorption, ion exchange process, hydrogen bonding interactions and surface complexation. This general strategy afforded a wide possibility to prepare a novel and advanced LDOs adsorption material for water treatment. Graphical abstract Image 1 Highlights • Ca-Al-LDHs were synthesized via a two-phase solvothermal method. • Ca-Al-LDHs and Ca-Al-LDOs with rhombic dodecahedral morphology. • The Ca-Al-LDOs has the maximum adsorption capacity of 1536.1 mg g−1. [ABSTRACT FROM AUTHOR]

A solvothermal method combining a calcination process was conducted to synthesize Fe 3 O 4 @NiO core–shell hierarchical nanostructures. First, Fe 3 O 4 microspheres were synthesized through a solvothermal method by using ethylene glycol as solvent. Second, Fe 3 O 4 @Ni(OH) 2 core–shell hierarchical nanostructures were prepared through an in situ growing procedure. Third, Fe 3 O 4 @NiO core–shell hierarchical nanostructures were obtained from the Fe 3 O 4 @Ni(OH) 2 precursors by a simple calcination procedure. The results showed that the Fe 3 O 4 core was about 250 nm in diameter and the NiO shell was around 30 nm in thickness. The Fe 3 O 4 @NiO core–shell nanostructures were used as a magnetically separable adsorbent for the removal of Congo red (CR) dye from aueous solution, which exhibited a high adsorption capacity of ~128.9 mg g −1 . Moreover, the Fe 3 O 4 @NiO core–shell nanostructures displayed a superior catalytic property for the epoxidation of styrene with an extremely high selectivity (100%), conversion (99%) and yield (99%). Such Fe 3 O 4 @NiO catalyst could be conveniently recycled from the reaction system by using a magnet and without any noticeable catalytic deactivation even after five cycles. The results indicate that the as-prepared core–shell materials can be used as a recyclable catalyst for the epoxidation of styrene. [ABSTRACT FROM AUTHOR]

A facile pyrolysis-quenching-reroasting process was developed to prepare a sludge-based biochar adsorbent, and its adsorption performance for Cr(VI) ions was investigated. The unquenched biochar (U-BC) and quenched biochar (Q-BC) were systematically compared and characterized. Fourier transform infrared spectroscopy (FTIR) results showed that more carbon and oxygen functional groups such as –COOH and –OH were formed on the surface of Q-BC. These functional groups could be used as active sites during the adsorption process and help to improve the adsorption performance of the material. The results of Brunauer-Emmett-Teller (BET) analysis showed that the specific surface area of U-BC biochar was 523.36 m2/g, while the specific surface area of Q-BC biochar after quenching treatment increased to 785.3 m2/g. The adsorption performance of Q-BC biochar was studied, and the effects of pH, contact time and temperature on the adsorption performance of the material were explored. The pseudo-second-order model and Langmuir isotherm model indicated that the removal of Cr(VI) by Q-BC biochar material was a chemical adsorption-based adsorption process. At a temperature of 298 K and a pH of 1, the maximum Cr(VI) adsorption capacity of the quenched Q-BC biochar is as high as 291.54 mg/g, which was much higher than the maximum adsorption capacity of U-BC biochar (91.46 mg/g). This pyrolysis-quenching-reroasting process to prepare modified biochar provides a new, economical and effective way for the preparation of high-performance adsorption materials from municipal sludge. [Display omitted] • This study provides an idea for the low-cost production of high-performance carbon materials from sludge. • Quenching modification can increase the carbon and oxygen functional groups of biochar. • The maximum adsorption capacity of Cr(VI) on quenched biochar (Q-BC) after quenching was as high as 291.54 mg/g. [ABSTRACT FROM AUTHOR]