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• Co-MOF was synthesized in aqueous solution. • Co-MOF was positively charged at pH lower than 11.8. • Electrostatic and π–π stacking interactions contributed to the favorable adsorption of CR on Co-MOF. • Co-MOF had excellent recyclable performance. Wastewater discharged from the dye production and consumption process has a high chemical oxygen demand, high chroma, and complex structure. In this study, a boat shaped flaky cobalt-based metal–organic framework (Co-MOF) was synthesized in aqueous solution by using a green one-step precipitation strategy. This strategy exhibited favorable efficiency for the removal of Congo red (CR). Furthermore, ZIF-67 with a rhombic dodecahedral shape was synthesized in anhydrous methanol solvent through a one-step precipitation strategy. The effects of the contact time, adsorbent dosage, initial CR concentration, and pH value on the adsorption of CR were also investigated. Results indicated that the adsorption of CR by Co-MOF and ZIF-67 fitted well with the Langmuir model and pseudo-second-order kinetic model. The maximum adsorption capacities obtained for Co-MOF and ZIF-67 with the Langmuir model were 1019.06 and 1044.58 mg/g at 25 °C, respectively. The obtained equilibrium time was less than 5 min. Moreover, Co-MOF and ZIF-67 had the same removal capacities for CR. The adsorption mechanism was attributed to the strong electrostatic and π–π stacking interactions of CR with Co-MOF and ZIF-67. Thus, the proposed method is a facile and green method to synthesize Co-MOF for the efficient removal of organic dyes from aqueous solutions. [ABSTRACT FROM AUTHOR]

Discharging phosphorus (P)-contaminated water directly into the aquatic environment leads to resource loss and eutrophication. Thus, removing P from waste streams is imperative. In this study, calcium-decorated biochar (Ca-BC) in different mass ratios of Ca to BC was designed to effectively adsorb P from solution. Ca-BC was characterized through X-ray diffraction (XRD) analysis, followed by isotherm and kinetic adsorption experiments. The decorated Ca on the BC surface was found to have preferred P adsorption ability. A design of calcium hydroxide (Ca(OH) 2 ) to flour in a mass ratio of 2:1 was found to have a maximum adsorption capacity of 314.22 mg g −1 for P. The Langmuir and pseudo-second-order models fit the sorption process adequately. XRD analysis indicated that the preferable adsorption ability to P was due to the reaction of Ca(OH) 2 and PO 4 3− , forming the hydroxylapatite (Ca 5 (PO 4 ) 3 (OH)) crystal. The P in solution was transformed to the crystal. Thus, Ca-BC is an environmental friendly and low-cost sorbent for P removal. [ABSTRACT FROM AUTHOR]

Uranium containing radioactive wastewater is seriously hazardous to the natural environment if it is being discharged directly. Herein, nano-flake like Fe loaded sludge carbon (Fe-SC) is synthesized by carbothermal process from Fe-rich sludge waste and applied in the immobilization of uranium in aqueous. Batch isotherm and kinetic adsorption experiments are adopted to investigate the adsorption behavior of Fe-SC to uranium in aqueous. XPS analyses were conducted to evaluate the immobilized mechanism. It was found that the carbonized temperature played significant role in the characteristics and immobilization ability of the resulted Fe-SC. The Fe-SC-800 carbonized at 800 °C takes more advantageous ability in immobilization of uranium from aqueous than the commercial available AC and powder zero valent iron. The adsorption behavior could be fitted well with the Langmuir isotherm adsorption model and pseudo-second order model. The equilibrium adsorption amount and rate for Fe-SC-800 is high to 148.99 mg g −1 and 0.015 g mg −1 min −1 , respectively. Both reductive precipitation and physical adsorption are the main mechanisms of immobilization of uranium from aqueous by Fe-SC-800. [ABSTRACT FROM AUTHOR]

In this work, rice straw was modified by succinic acid to improve its adsorption ability for uranium. Infrared analysis indicated that carboxylic acid groups and ester groups were grafted on rice straw surface. Scanning electron microscope showed that the appearance of rice straw had become thinner, more dispersed, and rolled-up like dead leaves after modification, implying that its structures got looser and its inner pores increased, resulting in its reactive surface area being notably extended. Effects of reaction time, adsorbent dosage, temperature, pH, and initial uranium concentration on adsorption of uranium were also investigated. Results showed that the adsorption efficiency of modified rice straw increased from 55% to 95% at 10 mg/L uranium solution, adsorption equilibrium was achieved within 1.5 h, and kinetic data could be well described by pseudo-second-order kinetic model. Adsorption isotherms followed the Langmuir and Freundlich models, and maximum adsorption amount of uranium onto the rice straw calculated from Langmuir equation rose from 19.7628 to 24.0385 mg/g at 35°C after modification. In addition, infrared analysis depicted that the adsorption of uranium by modified straw mainly depended on the complexation of carboxylic acid groups and ester groups with uranium. [ABSTRACT FROM AUTHOR]

Highlights: [•] Hierarchical porous sludge char were fabricated by pyrolysis at 500°C. [•] A stronger Si–O bond (1.83Å and 1.87Å) between the carboxyl and SiO2 was found. [•] Quantum chemistry calculation confirmed the interaction of Si–O and H–O bonds. [•] Multiple model (Q T = Q A + K PCe) was presented in the sludge char sorption process. [ABSTRACT FROM AUTHOR]

Highlights: [•] Sludge-derived char is prepared by pyrolysis at 500°C. [•] Hierarchical pores are fabricated by coupling citric acid and ZnCl2 activation. [•] Sludge-derived char performs hydrophobic surface. [•] Char has superior adsorption ability to toluene for pore and partition adsorption. [ABSTRACT FROM AUTHOR]

Background There is growing interest in employing sludge-based carbons ( SC) from waste treatment as adsorbents. However, the application of SC is limited by its poor porosity caused by large amounts of minerals blocking the pores. It is thus, highly desirable to develop a post-washing process to remove the minerals in SC. Results In this paper, SC was washed with deionized water ( DW), hydrochloric acid ( HCl), citric acid ( CA) and a mixed solution of hydrochloric acid and citric acid ( HCl-CA), respectively. Results showed that HCl-CA washing had the highest demineralization efficiency (63%), so that HCl-CA washed SC had the lowest ash content (32%) and largest total pore volume (0.455 m3 g-1), and presented the highest adsorption capacities of 319 mg g-1 for acid orange II ( AOII) and 250 mg g-1 for methylene blue ( MB). Conclusion HCl-CA washing has the highest demineralization efficiency. The high efficiency is attributed to the synergetic effects of both protonation and chelation. Demineralization has a strong influence on the development of pore structures, which further influences adsorption capacity. © 2012 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Water contamination caused by radionuclides is a major environmental issue. Uranium (U) belongs to the actinide group of elements. Hexavalent uranium (U(VI)) is radioactively and chemically harmful and highly mobile in the environment and wastewater stream. Therefore, developing highly efficient materials for minimizing the environmental impact of U(VI) is essential. To achieve this goal, we successfully synthesized a novel material, namely graphene oxide (GO)/hydroxyapatite (HAP), by directly assembling GO and HAP through a facile hydrothermal method, which exhibits effective U(VI) removal and immobilization. The GO/HAP composite has an outstanding sorption capacity for U(VI) (i.e., 373.00 mg/g) within 5 min at a pH of 3.0. The parameters from thermodynamic analysis indicated that the GO/HAP composite absorbed U(VI) through a process of spontaneous and exothermic adsorption. XPS, XRD, and FT-IR results revealed that the composite's phosphate group was mainly responsible for U(VI) retention and incorporation. The GO/HAP composite's enhanced U(VI) sorption capacity is most likely ascribed to the synergistic effect after functionalizing with nano HAP. The current findings may greatly facilitate the creation of rational design strategies to develop highly efficient materials that can treat radioactive wastewater. Image 1 • Abundant of HAP nanoparticles were successfully grafted and coated homogeneously on the surfaces of GO nanosheets. • The processing parameters influencing U(VI) adsorption were thoroughly investigated. • The GO/HAP composite is promising for the remediation of U(VI) contaminated sites. • The interaction mechanism between U(VI) and GO/HAP composite was revealed. [ABSTRACT FROM AUTHOR]

Adsorption of uranium (U) from real mine contaminated water (U 1.652 mg/L) by phosphate rock apatite (PRA) was investigated in the batch experiment and flow column test system. In batch experiment, the equilibrium adsorption amount is 0.1133 mg/g with the highest uranium removal efficiency of 76.89% under the ratio of solid to liquid (1:100) in 15 h. And the pH of wastewater became neutral (pH 7.51) from acidic (pH 3.88) after adsorption equilibrium. The saturated adsorption amount (0.2021 mg/g) in batch experiment is higher than the maximum accumulative adsorption amount (0.0684 mg/g) in column experiment. Langmuir model and pseudo-second order kinetic model are fitted well and, indicating that PRA is a favorable adsorbent with monolayer coverage and a chemisorption for uranium. Moreover, the surface morphology of the adsorbent by SEM confirmed the surface changes after uranium adsorption. XRD spectra showed that two new mineral phase of Metaankoleite [K(UO 2 )(PO 4 )·3H 2 O], Chernikovite [H 2 (UO 2 ) 2 (PO 4 ) 2 ·8H 2 O] have been generated on PRA after uranium adsorption, but which were trace for relatively low uranium concentration in tested polluted water. In addition, the FT-IR spectra results confirmed the uranium in contaminated water was adsorbed onto the PRA in the form of (O = U = O) 2+ with the participation of the PO 4 3– in binding of it. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract Aluminum hydroxide and oxide have been widely used for decontamination due to their environmentally friendly nature and cost effectiveness. Aluminum (hydro) oxides are the main phases of aluminum-derived environment materials. Herein, the solvent-free hydrothermal synthesis of gamma-aluminum oxide (γ-Al 2 O 3) nanoparticles and phase transformation of AlOOH into γ-Al 2 O 3 are reported. Hydrothermal treatment of NH 3 ·H 2 O-induced aluminum precipitate resulted in the formation of AlOOH, which was an intermediate product of γ-Al 2 O 3. AlOOH was transformed into highly crystalline 20-nm γ-Al 2 O 3 particles through calcination at 500 °C due to dehydration. The transformation was confirmed through X-ray diffraction (XRD) and thermogravimetric (TG) analyses. The resulting γ-Al 2 O 3 had superior adsorption ability for the anionic Congo red (CR) dye than for the cationic methylene blue (MB) and malachite green (MG) dyes. The selective adsorption ability of CR instead of MB was attributed to the electrostatic attraction and hydrogen bonds between the amino group and azo double bond of CR, and between the amino group and hydroxyl group in γ-Al 2 O 3. Thus, this study investigated crystalline phase transformation into γ-Al 2 O 3 and selective adsorption capacity of CR, which provides important information regarding the synthesis of crystalline γ-Al 2 O 3 adsorbent, with selective adsorption ability for decontamination applications. [ABSTRACT FROM AUTHOR]

The interactions between uranium(VI) and phosphate are known to be critical in governing the mobility of uranium(VI). However, only using phosphate compounds to remove uranium(VI) in aqueous solution is often unsatisfactory owning to insufficient active sites on their surface. The enhancement of the adsorption ability of phosphate compounds is timely important. In this study, we successfully modified a typical type of natural phosphate rock with chitosan and applied this product to remove uranium(VI). The effects of initial uranium(VI) concentration, contact time and adsorbent dosage on uranium(VI) removal behavior were systematically investigated via a series of batch experiments. The uranium(VI) adsorption on chitosan modified phosphate rock can reached equilibrium after 5 h at acidic pH (pH 2.5). The uranium(VI) removal efficiency was greatly enhanced after phosphate rock was modified by chitosan. Adsorption mechanism of uranium(VI) on modified phosphate rock was proved by FT-IR, XRD, and SEM. After modification, a new group (–NH 2 ) and a crystalline phase of ammonium calcium hydrogen phosphate (NH 4 CaHP 2 O 7 ) were generated. Being adsorbed uranium(VI), the morphology of adsorbents (i.e., chitosan modified phosphate rock and phosphate rock) changed markedly. XRD results showed that certain diffraction peaks for newly generated crystal structures after chitosan modification, besides these diffraction peaks became weakened and even disappeared after uranium(VI) adsorption. As to the adsorption mechanism of this modify adsorbent, results from isotherm and kinetic analyses demonstrated that uranium(VI) adsorption was more related to Freundlich model and pseudo second order equation. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ni-Co LDO could be obtained by calcination of Ni-Co LDH. • The morphology of the Ni-Co LDO can be adjusted by the calcination temperature. • The Ni-Co LDO-500 prefer removing uranium to Ni-Co LDH. • Electrostatic attraction, surface complexation and memory effect contributed to U(VI) recovery. • Ni-Co LDO-500 showed good stability and excellent regeneration ability. The utilization and development of nuclear energy has resulted in the discharge of uranium-containing wastewater. Layer double hydroxides (LDHs) and oxides (LDOs) were reported for efficient extracting U(VI) from wastewater. In this work, nickel–cobalt layered double oxide (Ni-Co LDO-X, X represents the calcination temperature) with excellent electrostatic attraction and complexation was synthesized via calcination of nickel–cobalt layered double hydroxide (Ni-Co LDH) under air atmosphere for extracting U(VI) comparing to Ni-Co LDH. Scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and zeta potential analysis were conducted to characterize the Ni-Co LDO-X. Batch adsorption experiments were carried out to investigate the U(VI) extraction properties. The U(VI) adsorption capacity on Ni-Co LDO-500 increased over 3 times compared to that of Ni-Co LDH. The process of uranium removed by Ni-Co LDO-500 conforms to the Langmuir model, the calculated maximum adsorption capacity is 707.91 mg/g. The results suggested that the excellent U(VI) adsorption ability on Ni-Co LDO-500 mainly dominated by the memory effect, electrostatic interaction, and complexation on the outer-sphere surface. Ni-Co LDO-500 has excellent regeneration ability in five adsorption/desorption experiments. The Ni-Co LDO-500 had favorable ability in removing uranium in actual wastewater with the residual concentration being lower than 0.05 mg/L. The above results highlight that the Ni-Co LDO-500 is promising to be used for the decontamination of uranium in actual uranium-containing wastewater. [ABSTRACT FROM AUTHOR]

With the wide application of nuclear energy and the rapid development of mining, a great quantity of uranium (U(VI)) containing wastewater is inevitably generated. In this work, a facile environmental-friendly coprecipitation method was proposed for the green synthesis of binary layered double hydroxides (Ni–Co LDH W -7), which could be used to efficiently adsorb U(VI) from wastewater. Pseudo-second-order kinetic model and Dubinin-Radushkevich model fitted well with the adsorption of U(VI) on Ni–Co LDH W -7, the maximum adsorption capacity of U(VI) on Ni–Co LDH W -7 was 201.09 mg/g calculated by the Langmuir model. Adsorption equilibrium reached after 30 min, which is a spontaneous and endothermic process. Fourier Transform Infrared Spectrometer (FTIR) and X-ray Photoelectron Spectroscopy (XPS) measurements manifested that the favorable U(VI) extraction on Ni–Co LDH W -7 is mainly ascribed to inner-layer surface electrostatic interaction and complexation, which is dominated by abundant oxygen-containing M-OH and interlayer OH− ions. Briefly, this work provides a facial and environmental-friendly Ni–Co LDH W -7 for removing U(VI) in actual uranium-containing wastewater. [Display omitted] • A facile environmental-friendly coprecipitation method was proposed for green synthesis of Ni–Co LDH W -7. • Adsorption capacity of uranium reached 201.09 mg/g calculated by Langmuir model at pH = 6 and 298 K. • Metal hydroxyl group configuration and the hydroxyl groups contributed to U(VI) binding on Ni–Co LDH W -7. • Ni–Co LDH W -7 showed good stability. [ABSTRACT FROM AUTHOR]

[Display omitted] • Al-rich minerals have phase-dependent effect of on the sequestration of U(VI). • Cations and anions for U(VI) sequestration upon α/γ-Al 2 O 3 were investigated. • PO 4 3− can significantly facilitating the U(VI) sequestration on α/γ-Al 2 O 3. • HA can promote or inhibit the sequestration of U(VI) under acidic or alkaline conditions. Uranium and uranium-containing pollutants are excessively released into the environment, leading to serious water and soil contamination. Minerals such as alumina are naturally abundant and frequently affect the fate and migration behavior of uranium ions. A thorough understanding of the migration and immobilization behavior of uranium on Al-rich minerals (e.g., α-alumina [α-Al 2 O 3 ] and γ-alumina [γ-Al 2 O 3)]) is essential for unraveling numerous environmental issues. We performed a systematic comparative analysis of U(VI) retention by α-/γ-alumina. The effects of coexisting ions and natural organic matter were explored. Solution pH contributed critically to the retention of U(VI) by α-/γ-alumina. The adsorption rate of γ-Al 2 O 3 for U(VI) removal was faster than that of α-Al 2 O 3 , reaching equilibrium within 15 min with a high removal efficiency of 94.43%. PO 4 3− ions significantly promoted U(VI) adsorption, especially for the case of α-Al 2 O 3. The addition of phosphate resulted in a 15-fold enhancement in adsorption capacity. Humic acid promoted U(VI) removal by γ-Al 2 O 3 under acidic conditions while strong inhibition on both α-Al 2 O 3 and γ-Al 2 O 3 in basic conditions. The removal mechanism of U(VI) by alumina is mainly ascribable to electrostatic interaction and surface complexation from various oxygenated functional groups. The present findings are pivotal to the understanding of uranium migration and immobilization in the environment. [ABSTRACT FROM AUTHOR]