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In this study, an anion exchange material obtained by chemically modifying granulated polyvinyl chloride with urea was examined. To study the structural morphology of the anion exchanger, polymer PVC‐based anion exchange resin second type (PPE‐2), we applied different characterization techniques including X‐ray diffraction (XRD), Fourier‐transform infrared (FTIR), scanning electron microscopy (SEM), and water vapor adsorption analysis. Moreover, PPE‐2 was used to remove hexavalent chromium ions from aqueous media. A pseudo‐second order model was used to describe sorption kinetics as well as the adsorption mechanism. The Langmuir isotherm and the pseudo‐second order kinetic model led to the most consistent results in describing ion removal from solution. In the case of hexavalent chromium ions, the maximum adsorption capacity was 148.4 mg g−1. The Dubinin‐Radushkevich (D‐R) free energy of adsorption (ED) was >16 kJ mol−1, which indicates chemical interaction between the ion exchange material and Cr(VI) ions. The Gibbs energy ΔG, enthalpy ΔH, and entropy ΔS changes during binding showed that the sorption process is spontaneous and involves chemical sorption through endothermic ion exchange reactions. In addition, the results demonstrate that the anion exchanger (PPE‐2) very efficiently removed hexavalent chromium ions from industrial wastewater. [ABSTRACT FROM AUTHOR]

A new adsorbent with chromium removal function was synthesized by carbon thermal method using iron-containing waste Fenton sludge and carbon-containing solid waste fly ash to treat high pH scoring wastewater generated from industrial processes. The results showed that the adsorbent used T = 273.15 K, pH = 10, t = 1200 min, C0 = 100 mg/L, had a removal rate of Cr(VI) of more than 80%, and the adsorption capacity could reach 393.79 mg/g. The characterization results show that the synthesized mesoporous nitrogen-doped composite material has a large specific surface area and mesoporous structure, and the surface of the material is rich in oxygen-containing functional groups and active sites. Compared with other studies, the adsorption capacity of the material is larger, which indicates that the removal effect of Cr(VI) in this study is better. The adsorption kinetic results show that the adsorption follows a pseudo second kinetic model, and the adsorption process is a chemisorption involving electron sharing or electron exchange. This experiment designed a simple method to synthesize mesoporous nitrogen-doped composites using industrial solid waste, with raw materials from cheap and easily available industrial solid waste, and solved the dual problems of heavy metals in wastewater and solid waste, providing a new idea for the resource utilization of Fenton sludge while not producing secondary pollution. [ABSTRACT FROM AUTHOR]

Porous carbon, which can be functionalized, is considered as a potential carbon material. Herein, two-dimensional (2D) nitrogen-doped magnetic Fe 3 C/C (NMC) was prepared by a simple carbonization method using potassium humate (HA-K) as raw material. Remarkably, two templates, g -C 3 N 4 and KCl, were formed in situ during the carbonization process, which provide the necessary conditions for the formation of 2D NMC. The NMC was comprehensively studied by different characterization methods. The results show that NMC has a large surface area and mesoporous structure. The prepared NMC-0.50 was used to test the removal performance of Cr(VI). The effects of pH value, coexisting ions and time on Cr(VI) removal performance were investigated, and the adsorption kinetics, isotherm and thermodynamics were studied. The results showed that the adsorption isotherm model of NMC-50 accorded with the Langmuir model, and the maximum adsorption capacity was 423.73 mg g−1. The reaction mechanism of Cr(VI) is adsorption and redox reaction. In addition, NMC-0.50 exhibit high selectivity, separability and regeneration performance. A convenient means for the synthesis of NMC was designed in this work, and demonstrate that NMC has practical value as an adsorbent. The reaction mechanism of Cr(VI) is redox reaction and adsorption behavior, and the redox reaction is dominant. Image 1 • Synthesis of 2D nitrogen-doped magnetic Fe 3 C/C by one-step carbonization. • In situ formation of double templates during carbonization. • The adsorption of Cr(VI) is achieved via redox reactions and adsorption process. • 2D nitrogen-doped magnetic Fe 3 C/C has maximum adsorption capacity (423.73 mg g−1) for Cr(VI). The 2D nitrogen-doped magnetic Fe 3 C/C was applied to efficiently adsorb Cr(VI). [ABSTRACT FROM AUTHOR]

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]

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]

Microbial reduction of hexavalent chromium (Cr (VI)) shows better efficiency and cost-effectiveness. However, immobilization of Cr (III) remains a challenge as there is a limited supply of electron donors. A greener and cleaner option for donating external electrons was using bioelectrochemical systems to perform the microbial reduction of Cr(VI). In this system, we constructed a polydopamine (PDA) decorated Shewanella oneidensis MR-1 (S. oneidensis MR-1) bioelectrode with bidirectional electron transport, abbreviated as PDA@ S. oneidensis MR-1. The conjugated PDA distributed on the intracellular and extracellular of individual S. oneidensis MR-1 has been shown to accelerate electron transfer by outer membrane C-type cytochromes and flavin-bound MtrC/OmcA pathway by various electrochemical analyses. As expected, the PDA@ S. oneidensis MR-1 biofilm achieved 88.1% Cr (VI) removal efficiency (RE) and 58.1% Cr (III) immobilization efficiency (IE) within 24 h under the autotrophic conditions at the optimal voltage (−150 mV) compared with the control potential (0 mV). The PDA@ S. oneidensis MR-1 biofilm showed increased RE activity was attributed to the shortening of the distance between individual bacteria by PDA. This research provides a viable strategy for in situ bioremediation of Cr(VI) polluted aquatic environment. [Display omitted] • A bidirectional electron transfer bioelectrode composed of polydopamine-decorated S. oneidensis MR-1 was constructed. • Cr (VI) removal efficiency of 99.2% were achieved at the optimal voltage (−150 mV). • Cr (III) immobilization efficiency of 58.1% was attained by autotrophic biofilm. • Polydopamine accelerated the electron transfer from the cathode to Cr(VI). [ABSTRACT FROM AUTHOR]

Biochar derived from municipal sludge can be applied to adsorption. But it usually requires activation and pickling due to the generation of impurities such as metal oxide particles, which is uneconomical. Here, a facile strategy, acidification-one-step calcination, was developed and sludge-based Fe–C materials with good Cr(VI) removal effect were obtained by regulating the amount of hydrochloric acid. The results show that the adsorption capacity of Fe/C-5 (the best sample) for Cr(VI) was 150.84 mg g−1. According to the Langmuir isotherm and pseudo-second-order kinetic model, the removal of Cr(VI) by Fe/C-5 is spontaneous and endothermic chemisorption process. In addition, Fe/C-5 has good ability to remove Cr(VI) under the interference of coexisting ions, and has good cycle stability. The removal of Cr(VI) by Fe/C-5 is considered to be synergistic process of adsorption and reduction. The Fe atoms were highly dispersed in Fe/C-5 and tightly bonded with C atoms, which not only strengthened the Cr(VI) adsorption by electrostatic attraction, but also activated the C atoms in the biochar material, so that the C atoms can reduce Cr(VI) to Cr(III) under acidic conditions. This may be due to the fact that acid pretreatment converted the iron in municipal sludge in the form of Fe–O/OH to free Fe3+ and entered the C lattice during the calcination process. In this work, Fe–C materials with excellent Cr(VI) adsorption capacity were prepared by one-step calcination method, which has important reference significance for the resource utilization of municipal sludge. [Display omitted] • Fe/C materials were prepared by one-step calcination of acidified municipal sludge. • The Fe3+ are highly dispersed in Fe/C-5 rather than in the form of cluster. • Fe/C materials removed Cr(VI) by adsorption and reduction synergistically. [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]