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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]

Al 2 O 3 /carbon (Al 2 O 3 /C) composites obtained from the alkaline wastewater of oil refinery and acid wastewater of aluminum anodizing factory have been studied with the principle of “using waste to treat waste”. The process includes these steps: (1) acid-alkali neutralization, (2) evaporation, (3) calcination, (4) washing and drying. The Al 2 O 3 /C composites prepared by calcinating the precursors under Ar atmosphere are used as high-capacity adsorbents for removal of Pb(II) and Cd(II) from aqueous solutions. For Pb(II), the adsorptive behavior satisfies the Langmuir assumptions and the maximum adsorption capacity reaches to 709.2 mg g −1 . For Cd (II), the adsorptive behavior satisfies the Freundlich assumptions and the equilibrium adsorption capacity is up to 1299.4 mg g −1 . For single adsorption of Pb(II) and Cd(II), the adsorption kinetics follows Pseudo-second-order model well. This route shows a possible way of reducing emissions to the environment, recovering resource as a valuable material, and providing a novel strategy for wastewater treatment. [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]

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]

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]

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]