Synthesis of a novel organic-inorganic hybrid of polyaniline/titanium phosphate for Re(VII) removal

Environmental applications and risks of engineered nanomaterials in removing petroleum oil in soil

Oil-contaminated soil posed serious threats to the ecosystems and human health. The unique and tunable properties of engineered nanomaterials (ENMs) enable new technologies for removing and repairing oil-contaminated soil. However, few studies systematically examined the linkage between the change of physicochemical properties and the removal efficiency and environmental functions (e.g., potential risk) of ENMs, which is vital for understanding the ENMs environmental sustainability and utilization as a safety product. Thus, this review briefly summarized the environmental applications of ENMs to removing petroleum oil from complex soil systems: Theoretical and practical fundamentals (e.g., excellent physicochemical properties, environmental stability, controlled release, and recycling technologies), and various ENMs (e.g., iron-based, carbon-based, and metal oxides nanomaterials) remediation case studies. Afterward, this review highlights the removing mechanism (e.g., adsorption, photocatalysis, oxidation/reduction, biodegradation) and the impact factor (e.g., nanomaterials species, natural organic matter, and soil matrix) of ENMs during the remediation process in soil ecosystems. Both positive and negative effects of ENMs on terrestrial organisms have been identified, which are mainly derived from their diverse physicochemical properties. In linking nanotechnology applications for repairing oil-contaminated soil back to the physical and chemical properties of ENMs, this critical review aims to raise the research attention on using ENMs as a fundamental guide or even tool to advance soil treatment technologies.

Toward a mechanistic understanding of Rhenium(VII) adsorption behavior onto aminated polymeric adsorbents: Batch experiments, spectroscopic analyses, and theoretical computations

Rhenium, a rare and critical metal, existing in the industrial wastewater has been aroused extensive interests recently, due to its environmental and resource issues. Chitosan, an easily available, low-cost and eco-friendly biopolymer, was prepared and modified by grafting primary, secondary, tertiary and quaternary amino groups, respectively. Adsorption behaviors and interactions between ReO4- and these four types of aminated adsorbents were investigated through batch experiments, spectroscopic analysis, and theoretical computations. Chitosan modified with secondary amines showed an extremely high uptake of ReO4- with 742.0 mg g-1, which was higher than any reported adsorbents so far. Furthermore, a relatively high adsorption selectivity for Re(VII), as well as the stable and facile regeneration of these aminated adsorbents revealed a promising approach for Re(VII) recovery in full-scale applications. The electrostatic attraction was illustrated to be the main adsorption mechanism by Fourier Transform Infrared Spectroscopy and X-ray Photoelectron Spectroscopy analyses. Significantly, the sub-steps of the adsorption process, encompassing the transformation of binding sites and the subsequent binding between these sites and the adsorbate, have been thoroughly investigated through the density functional theory (DFT) calculation method. This approach was firstly proposed to clearly demonstrate the differences in Re(VII) adsorption behavior onto four types of aminated adsorbents, resulting the importance of not only strong binding energy but also an appropriate binding spatial environmental for effective Re(VII) adsorption.

Tailored metal-organic frameworks facilitate the simultaneously high-efficient sorption of UO22+ and ReO4- in water

The simultaneously efficient extraction of radioactive metal cations and anions from radioactive waste is of great interest for the proper disposal of spent fuel and environmental protection. Modifying metal-organic frameworks (MOFs) into multifunctional materials with controllable and desired properties is an efficient strategy for broadening their practical applications. Herein, poly(ethyleneimine) (PEI) tailored MIL-101(Cr) (MILP) was obtained through an easy operation and low-cost strategy and was utilized to simultaneously extract uranium (UO₂²⁺) and rhenium (ReO₄^-) from water. The effects of PEI coating amounts, system pH, contact time, initial UO₂²⁺/ReO₄^- concentrations, ionic strength, as well as interfering ions were studied to evaluate the sorption performance of MILP composites. The maximum sorption capacity was 416.67 mg/g for UO₂²⁺ at pH 5.5 and 434.78 mg/g for ReO₄^- at pH 3.5, levels that are superior to those of most adsorbents. The sorption of UO₂²⁺/ReO₄^- occurred in a pH-dependent, spontaneous and endothermic manner, which showed preferable modeling by the pseudo-second-order (PSO) kinetic equation and Freundlich isotherm equation. The adsorption of ReO₄^- was inhibited by the coexistence of UO₂²⁺ and high ion strength. Batch experiments and X-ray photoelectron spectroscopy (XPS) results indicate that UO₂²⁺/ReO₄^- sorption was driven by the abundant amino groups and unsaturated metal sites in the MILP-3 composites. MILP-3 also showed excellent recycling performance and maintained high sorption capacities for UO₂²⁺/ReO₄^- in different simulated water samples. This study shows that MILP composites can effectively extract radioactive metal cations and anions from water, and lays a foundation for designing an excellent new category of candidates with versatile functions for wastewater management.

Efficient capture of ReO4- on magnetic amine-functionalized MIL-101(Cr): Revealing from selectivity to mechanism

The efficient decontamination of pertechnetate (⁹⁹TcO₄^-) is an essential task for managing radioactive ⁹⁹Tc in nuclear wastes. Perrhenate, (ReO₄^-), as a nonradioactive analog, exhibits almost identical physicochemical properties as ⁹⁹TcO₄^-. Herein, a novel magnetic amine-functionalized MIL-101(Cr) (NH₂-MIL-101(Cr)@Fe₃O₄) was prepared and used to efficiently remove ReO₄^- from solution for the facile magnetic separation. A series of environmental parameters were considered to investigate the adsorption performance of NH₂-MIL-101(Cr)@Fe₃O₄. Experimental results suggested that NH₂-MIL-101(Cr)@Fe₃O₄ has reached a satisfied adsorption capacity (~401 mg/g) and a very fast adsorption kinetics at pH 7.0. The selectivity for ReO₄^- was maintained even in the presence of interfering anions with relatively high concentrations. ReO₄^- were mainly captured by N-donor sites of the surface-decorated amine via complexation and were trapped in the cavities of modified MIL-101(Cr). NH₂-MIL-101(Cr)@Fe₃O₄ exhibits satisfactory adsorption performance for ReO₄^- and can be conveniently separated from wastewaters after adsorption.

3D Nanoarchitecture of Polyaniline-MoS2 Hybrid Material for Hg(II) Adsorption Properties

We report the facile hydrothermal synthesis of polyaniline (PANI)-modified molybdenum disulfide (MoS2) nanosheets to fabricate a novel organic-inorganic hybrid material. The prepared 3D nanomaterial was characterized by field emission scanning electron microscopy, high-resolution transmission electron microscopy, energy-dispersive X-ray spectroscopy and X-ray diffraction studies. The results indicate the successful synthesis of PANI-MoS2 hybrid material. The PANI-MoS2 was used to study the extraction and preconcentration of trace mercury ions. The experimental conditions were optimized systematically, and the data shows a good Hg(II) adsorption capacity of 240.0 mg g-1 of material. The adsorption of Hg(II) on PANI-MoS2 hybrid material may be attributed to the selective complexation between the-S ion of PANI-MoS2 with Hg(II). The proposed method shows a high preconcentration limit of 0.31 µg L-1 with a preconcentration factor of 640. The lowest trace Hg(II) concentration, which was quantitatively analyzed by the proposed method, was 0.03 µg L-1. The standard reference material was analyzed to determine the concentration of Hg(II) to validate the proposed methodology. Good agreement between the certified and observed values indicates the applicability of the developed method for Hg(II) analysis in real samples. The study suggests that the PANI-MoS2 hybrid material can be used for trace Hg(II) analyses for environmental water monitoring.

Simultaneous removal of U(VI) and Re(VII) by highly efficient functionalized ZIF-8 nanosheets adsorbent

The simultaneously efficient removal of cationic and anionic radionuclides is an important and challenging topic for nuclear waste remediation as well as environmental protection. Herein, monoclinic ZIF-8 nanosheets modified with ethyleneimine polymer (denoted as ZIF-8/PEI) was achieved and used to determine the capture behaviors of both U(VI) oxycations and Re(VII) oxyanions from aqueous solution. ZIF-8/PEI assemblies showed a maximum U(VI) and Re(VII) uptake capacity of 665.3 (pH 5.0) and 358.2 mg/g (pH 3.5), respectively. Experimental, spectroscopic and theoretical calculation results directly unraveled that U(VI) adsorption onto ZIF-8/PEI assemblies was mainly ascribed to the coordination with abundant amino groups and weakly due to the Zn terminal hydroxyl groups, while anion exchange mechanism contributed predominantly to the Re(VII) sequestration. This work not only sheds light on the interaction mechanisms of simultaneous capture of U(VI) and Re(VII) but also highlights the versatile material design of cationic and anionic radionuclide immobilization in radioactive wastewater remediation.

Synthesis of ZnO nanoparticle-anchored biochar composites for the selective removal of perrhenate, a surrogate for pertechnetate, from radioactive effluents

Pertechnetate (TcO₄-) is a component of low-activity waste (LAW) fractions of legacy nuclear waste, and the adsorption removal of TcO₄- from LAW effluents would greatly benefit the site remediation process. However, available adsorbent materials lack the desired combination of low cost, radiolytic stability, and high selectivity. In this study, a ZnO nanoparticle-anchored biochar composite (ZBC) was fabricated and applied to potentially separate TcO₄- from radioactive effluents. The as-synthesized material exhibited γ radiation resistance and superhydrophobicity, with a strong sorption capacity of 25,916 mg/kg for perrhenate (ReO₄-), which was used in this study as a surrogate for radioactive pertechnetate (TcO₄-). Additionally, the selectivity for ReO₄- exceeded that for the competing ions I-, NO₂-, NO₃-, SO₄^2-, PO₄^3-, Cu²⁺, Fe³⁺, Al³⁺, and UO₂²⁺. These unique features show that ZBC is capable of selectively removing ReO₄- from Hanford LAW melter off-gas scrubber simulant effluent. This selectivity stems from the synergistic effects of both the superhydrophobic surface of the sorbent and the inherent nature of sorbates. Furthermore, density functional theory (DFT) calculations indicated that ReO₄- can form stable complexes on both the (100) and (002) planes of ZnO, of which, the (002) complexes have greater stability. Electron transfer from ReO₄- on (002) was greater than that on (100). These phenomena may be because (002) has a lower surface energy than (100). Partial density of state (PDOS) analysis further confirms that ReO₄- is chemisorbed on ZBC, which agrees with the findings of the Elovich kinetic model. This work provides a feasible pathway for scale-up to produce high-efficiency and cost-effective biosorbents for the removal of radionuclides.

Preparation of sulfhydryl functionalized magnetic SBA-15 and its high-efficiency adsorption on uranyl ion in solution

A novel assembly method was used to prepare the sulfhydryl functionalized magnetic SBA-15 (SH-M-SBA-15). The physicochemical properties of SH-M-SBA-15 were characterized by TEM, XRD, EDS, FT-IR, BET, and VSM. Batch adsorption experiments were conducted to investigate the influence of initial uranium concentration, dosage of adsorbent, pH values, contact time, and temperature on the adsorption efficiency and behaviors. The adsorption types were analyzed from the aspects of kinetic, isotherms, and thermodynamic. The results show that the specific surface area of SH-M-SBA-15 is 316.67 m²/g, which is smaller than that of SBA-15 (692.18 m²/g). However, compared with SBA-15, SH-M-SBA-15 has more surface sulfhydryl functional groups. The addition of this group can improve the adsorption of uranyl ions by SH-M-SBA-15. The optimal adsorption conditions were adsorption dosage 40 mg/L, pH 6, temperature 35 °C, contact time 180 min, and initial uranium concentration 35 mg/L. Under this condition, the maximum adsorption amount of uranyl ion by SH-M-SBA-15 can reach 804.79 mg/g, which is much higher than the highest adsorption capacity of uranyl ion by SBA-15 (146.23 mg/g). The adsorption process was better depicted by the Langmuir isotherm model. The process was consistent with the quasi-second-order model. ΔG was negative and ΔH was positive, indicating spontaneous and endothermic adsorption.

Enhanced fluoride removal from water by rare earth (La and Ce) modified alumina: Adsorption isotherms, kinetics, thermodynamics and mechanism

The removal of F^- from aqueous solution using lanthanum and cerium modified mesoporous alumina (La/MA and Ce/MA) was studied, and characteration of the adsorbents by XRD, BET, XRF, FTIR, TEM, XPS and the pH_ZPC measurements were carried out. The adsorption was investigated in both batch and column adsorption systems. Batch experimental results showed that adsorption capacities of adsorbents were recorded in the following order: La/MA > Ce/MA > mesoporous alumina (MA). Besides, adsorption datas were fitted well by Sips isotherm model and Elovich kinetics model, and the maximum adsorption capacity of La/MA was 26.45 mg·g^-1 in Sips model at the dosage of 2.0 g·L^-1 and near neutral condition (pH = 6.0 ± 0.1). Moreover, thermodynamic parameters were illustrated that adsorption process of fluoride ion over La/MA was spontaneous and endothermic. In the adsorption process, the interaction between metal and fluoride, the adsorption capacity was increased due to form the bond of M···F (M = La or Ce). Furthermore, the influence of coexisted anions on F^- removal was investigated, and it was indicated that removal efficiency was slightly affected by the presence of Cl^- and NO₃^-, while SO₄^2- and CO₃^2- caused a sharp fall in removal efficiency. Column experiments results were indicated that time of break-through of La/MA was twice as much as that of MA.

Construction of novel graphene-based materials GO@SiO2@C@Ni for Cr(VI) removal from aqueous solution

A series of novel sandwich-like GO@SiO₂@C@Ni composites were developed. The morphologies and adsorption capacities of the materials sintered at different carbonization temperatures were investigated. The formed GO@SiO₂@C@Ni-400 possessed of wonderful dispersion, large surface area (229.88 m²/g) and high saturation magnetization. Batch experimental results revealed that maximum adsorption capacities of these materials towards Cr(VI) were as follows: GO@SiO₂@C@Ni-400 (299.20 mg/g) > GO@SiO₂@C@Ni-500 (244.05 mg/g) > GO (202.39 mg/g) > Graphene@C@Ni (188.80 mg/g) > GO@SiO₂@C@Ni-600 (165.51 mg/g) > GO@SiO₂@C@Ni-700 (93.36 mg/g). Moreover, the influence of hydrochemistry, such as contact time, pH, co-existing ions and solution temperature, on Cr(VI) adsorption was researched as well. It was demonstrated that GO@SiO₂@C@Ni-400 had remarkable adsorption capacity for Cr(VI) removal under the acidic condition, hardly disturbed by other anions, and showed better adsorption performance at 328 K. Besides, On the base of X-ray photoelectron spectroscopy analysis, mechanisms of adsorption could be explained that Cr(VI) was reduced to Cr(III) by nitrogen dopant, and the complexation was existed between Cr(VI) and oxygen-containing functional groups. Additionally, GO@SiO₂@C@Ni-400 could be easily separated under the external magnetic field and displayed outstanding reusability. Herein, GO@SiO₂@C@Ni-400 opens up the possibility of future practical applications.

Rationally designed core-shell and yolk-shell magnetic titanate nanosheets for efficient U(VI) adsorption performance

The hierarchical core-shell and yolk-shell magnetic titanate nanosheets (Fe₃O₄@TNS) were successfully synthesized by employing magnetic nanoparticles (NPs) as interior core and intercrossed titanate nanostructures (NSs) as exterior shell. The as-prepared magnetic Fe₃O₄@TNS nanosheets had high specific areas (114.9 m² g^-1 for core-shell Fe₃O₄@TNS and 130.1 m² g^-1 for yolk-shell Fe₃O₄@TNS). Taking advantage of the unique multilayer structure, the nanosheets were suitable for eliminating U(VI) from polluted water environment. The sorption was strongly affected by pH values and weakly influenced by ionic strength, suggesting that the sorption of U(VI) on Fe₃O₄@TNS was mainly dominated by ion exchange and outer-sphere surface complexion. The maximum sorption capacities (Q_max) calculated from the Langmuir model were 68.59, 121.36 and 264.55 mg g^-1 for core-shell Fe₃O₄@TNS and 82.85, 173.01 and 283.29 mg g^-1 for yolk-shell Fe₃O₄@TNS, at 298 K, 313 K and 328 K, respectively. Thermodynamic parameters (ΔH⁰, ΔS⁰ and ΔG⁰) demonstrated that the sorption process was endothermic and spontaneous. Based on X-ray photoelectron spectroscopy (XPS) analyses, the sorption mechanism was confirmed to be cation-exchange between interlayered Na⁺ and UO₂²⁺. The yolk-shell Fe₃O₄@TNS had more extraordinary sorption efficiency than core-shell Fe₃O₄@TNS since the yolk-shell structure provided internal void space inside the titanate shell to accommodate more exchangeable active sites. The flexible recollection and high efficient sorption capacity made core-shell and yolk-shell Fe₃O₄@TNS nanosheets promising materials to eliminate U(VI) or other actinides in wastewater cleanup applications.

Metal-organic framework-based materials: superior adsorbents for the capture of toxic and radioactive metal ions

Highly efficient removal of metal ion pollutants, such as toxic and nuclear waste-related metal ions, remains a serious task from the biological and environmental standpoint because of their harmful effects on human health and the environment. Recently, highly porous metal-organic frameworks (MOFs), with excellent chemical stability and abundant functional groups, have represented a new addition to the area of capturing various types of hazardous metal ion pollutants. This review focuses on recent progress in reported MOFs and MOF-based composites as superior adsorbents for the efficient removal of toxic and nuclear waste-related metal ions. Aspects related to the interaction mechanisms between metal ions and MOF-based materials are systematically summarized, including macroscopic batch experiments, microscopic spectroscopy analysis, and theoretical calculations. The adsorption properties of various MOF-based materials are assessed and compared with those of other widely used adsorbents. Finally, we propose our personal insights into future research opportunities and challenges in the hope of stimulating more researchers to engage in this new field of MOF-based materials for environmental pollution management.

Synthesis of a core–shell magnetic Fe3O4–NH2@PmPD nanocomposite for efficient removal of Cr(vi) from aqueous media

The magnetic Fe₃O₄–NH₂@PmPD composites show outstanding Cr(vi) removal performance due to the abundant nitrogen-containing functional groups.

An atomically thick titanium phosphate thin layer with enhancing electrochemical sensitivity toward Pb(ii)

An atomically thick titanium phosphate thin layer is synthesized and used for sensitive electrochemical detection for Pb(ii) with a high sensitivity and low limit of detection.

Efficient removal of U(vi) from aqueous solutions by polyaniline/hydrogen-titanate nanobelt composites

The organic–inorganic hybrid material of polyaniline/hydrogen-titanate nanobelt (PANI/H-TNB) composites was fabricated as a potential adsorbent to remove U(vi) from wastewater.