Screening of Zirconium-Based Metal–Organic Frameworks for Efficient Simultaneous Removal of Antimonite (Sb(III)) and Antimonate (Sb(V)) from Aqueous Solution

Seven kinds of zirconium-based metal–organic frameworks (Zr-MOFs) with different aperture size and organic linkers functionalized with different functional groups (−NH₂, −OH, and −SO₃H) were screened for their ability to remove antimonite (Sb­(III)) and antimonate (Sb­(V)) anions from water. Zr-bound hydroxides in Zr-MOFs can simultaneously remove both Sb­(III) and Sb­(V) via a mechanism of anion exchange. For antimony removal by UiO-66-NH₂, the anion exchange seemed to be strengthened due to the Lewis acid–base interactions between the −NH₂ groups on the BDC ligand and the antimony oxyanions. Among seven kinds of Zr-MOFs selected here, NU-1000 exhibited fast adsorption kinetics and high removal capacity for both Sb­(III) (136.97 mg/g) and Sb­(V) (287.88 mg/g), which was much higher than many antimony adsorbents described to date. Uptake of antimony at low concentrations of 100 μg/L (with a remaining antimony concentration of only ∼2 μg/L in 10 min) disclosed that current U.S. Environmental Protection Agency standards for antimony can be reached by using NU-1000 as an adsorbent. Additionally, the effects of coexisting anions such as As­(III), As­(V), PO₄^3–, SO₄^2–, NO₃^–, and F^– on the antimony adsorption onto NU-1000 were also studied. Finally, the Sb adsorption mechanism of NU-1000 was studied via X-ray photon spectroscopy and attenuated total reflection infrared spectroscopy techniques to explore the important characteristics that make NU-1000 a compelling candidate for wastewater management

Highly Efficient Enrichment of Radionuclides on Graphene Oxide-Supported Polyaniline

Graphene oxide-supported polyaniline (PANI@GO) composites were synthesized by chemical oxidation and were characterized by SEM, Raman and FT-IR spectroscopy, TGA, potentiometric titrations, and XPS. The characterization indicated that PANI can be grafted onto the surface of GO nanosheets successfully. The sorption of U­(VI), Eu­(III), Sr­(II), and Cs­(I) from aqueous solutions as a function of pH and initial concentration on the PANI@GO composites was investigated. The maximum sorption capacities of U­(VI), Eu­(III), Sr­(II), and Cs­(I) on the PANI@GO composites at pH 3.0 and <i>T</i> = 298 K calculated from the Langmuir model were 1.03, 1.65, 1.68, and 1.39 mmol·g^–1, respectively. According to the XPS analysis of the PANI@GO composites before and after Eu­(III) desorption, nitrogen- and oxygen-containing functional groups on the surface of PANI@GO composites were responsible for radionuclide sorption, and that radionuclides can hardly be extracted from the nitrogen-containing functional groups. Therefore, the chemical affinity of radionuclides for nitrogen-containing functional groups is stronger than that for oxygen-containing functional groups. This paper focused on the application of PANI@GO composites as suitable materials for the preconcentration and removal of lanthanides and actinides from aqueous solutions in environmental pollution management in a wide range of acidic to alkaline conditions

Interaction between Eu(III) and Graphene Oxide Nanosheets Investigated by Batch and Extended X-ray Absorption Fine Structure Spectroscopy and by Modeling Techniques

The interaction mechanism between Eu­(III) and graphene oxide nanosheets (GONS) was investigated by batch and extended X-ray absorption fine structure (EXAFS) spectroscopy and by modeling techniques. The effects of pH, ionic strength, and temperature on Eu­(III) adsorption on GONS were evaluated. The results indicated that ionic strength had no effect on Eu­(III) adsorption on GONS. The maximum adsorption capacity of Eu­(III) on GONS at pH 6.0 and <i>T</i> = 298 K was calculated to be 175.44 mg·g^–1, much higher than any currently reported. The thermodynamic parameters calculated from temperature-dependent adsorption isotherms suggested that Eu­(III) adsorption on GONS was an endothermic and spontaneous process. Results of EXAFS spectral analysis indicated that Eu­(III) was bound to ∼6–7 O atoms at a bond distance of ∼2.44 Å in the first coordination shell. The value of Eu–C bond distance confirmed the formation of inner-sphere surface complexes on GONS. Surface complexation modeling gave an excellent fit with the predominant mononuclear monodentate >SOEu²⁺ and binuclear bidentate (>SO)₂Eu₂(OH)₂²⁺ complexes. This paper highlights the application of GONS as a suitable material for the preconcentration and removal of trivalent lanthanides and actinides from aqueous solutions in environmental pollution management

Cr(VI) Reduction and Immobilization by Core-Double-Shell Structured Magnetic Polydopamine@Zeolitic Idazolate Frameworks‑8 Microspheres

A well-defined core-double-shell structured magnetic polydopamine@zeolitic idazolate frameworks-8 (MP@ZIF-8) hydrid microsphere consisting of the core of magnetic Fe₃O₄ nanoparticles, the inner shell of a polydopamine layer, and the outer shell of a porous ZIF-8 nanocrystal was prepared through a facile and green approach to achieve synergistic reduction and adsorptive removal of Cr­(VI). The microsphere property was characterized methodically. The batch adsorption experiments showed that the MP@ZIF-8 exhibited high efficiency in the Cr­(VI) removal from aqueous solutions, affording Cr­(VI) removal capacity of 136.56 mg g^–1, surpassing pristine MP (92.27 mg g^–1). The pseudo-second-order model fitted the Cr­(VI) removal kinetics well. Cr­(VI) removal on the MP@ZIF-8 relied highly on pH values. More significantly, with the reduction of nitrogen atom group on ZIF-8 and PDA, Cr­(VI) was easily converted into low toxicity Cr­(III) and then immobilized on the MP@ZIF-8. Thus, the hybrid microspheres provided excellent adsorptive activity in treating Cr-contaminated wastewater

Interaction Mechanism of Re(VII) with Zirconium Dioxide Nanoparticles Archored onto Reduced Graphene Oxides

Zirconium oxide archored onto reduced graphene oxides (ZrO₂@rGO) was fabricated via a hydrothermal method and used for Re­(VII) removal from aqueous solutions. Scanning electron microscopy, Fourier transferred infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, and X-ray photoelectron spectroscopy were used to characterize the as-prepared ZrO₂@rGO. The results indicated that ZrO₂ was successfully decorated on rGO. The maximum sorption capacity of ZrO₂@rGO toward Re­(VII) was 43.55 mg/g. ZrO₂@rGO exhibited enhanced sorption capacity for Re­(VII) in comparison with bare ZrO₂ or rGO. The sorption kinetics could be described by the pseudo-second-order equation. The sorption process of Re­(VII) on ZrO₂@rGO was endothermic and spontaneous. X-ray photoelectron spectroscopy indicated the formation of an ionic bond of Zr–O with Re­(VII). According to the density functional theory calculations, O_Re–Zr bonds on the surface of the monoclinic ZrO₂ plane (m-ZrO₂) (111) plane and tetragonal ZrO₂ (t-ZrO₂) (111) plane were formed when Re­(VII) sorbs. The sorption energy of Re­(VII) onto the t-ZrO₂ (111) plane was 3.87 eV, being higher than that of Re­(VII) onto m-ZrO₂ (1.26 eV)

Amino Siloxane Oligomer Modified Graphene Oxide Composite for the Efficient Capture of U(VI) and Eu(III) from Aqueous Solution

Poly 3-aminopropyltriethoxysilane is a highly reactive high-molecular polymer because of the existence of abundant amino groups, which presents a strong affinity toward different metal cations. In view of this, the novel poly amino siloxane oligomer modified graphene oxide composite (PAS–GO) was fabricated by a facile cross-linking reaction and applied to capture U­(VI)/Eu­(III) ions from aqueous solution. The interaction mechanisms between the PAS–GO and U­(VI)/Eu­(III) were elaborated. The modification by NH₂ increased the sorption sites and improved the sorption capacities because of the synergistic effect of chelation with U­(VI)/Eu­(III). X-ray photoelectron spectroscopy revealed that nitrogen groups are involved in the removal of U­(VI)/Eu­(III) since nitrogen atoms of amine groups provided the lone pair of electrons with U­(VI)/Eu­(III) species. The maximum sorption capacity of U­(VI) and Eu­(III) on the PAS–GO at 298 K calculated by the Langmuir isotherm model was 310.63 and 243.90 mg/g, respectively. The PAS–GO could be repeatedly used for more than five cycles with slight degradation of sorption. High sorption efficiency and excellent reusability make the PAS–GO composite an ideal candidate for the capture of U­(VI)/Eu­(III) from aqueous solution

New Synthesis of nZVI/C Composites as an Efficient Adsorbent for the Uptake of U(VI) from Aqueous Solutions

New nanoscale zerovalent iron/carbon (nZVI/C) composites were successfully prepared via heating natural hematite and pine sawdust at 800 °C under nitrogen conditions. Characterization by SEM, XRD, FTIR, and XPS analyses indicated that the as-prepared nZVI/C composites contained a large number of reactive sites. The lack of influence of the ionic strength revealed inner-sphere complexation dominated U­(VI) uptake by the nZVI/C composites. Simultaneous adsorption and reduction were involved in the uptake process of U­(VI) according to the results of XPS and XANES analyses. The presence of U–C/U-U shells demonstrated that innersphere complexation and surface coprecipitation dominated the U­(VI) uptake at low and high pH conditions, respectively. The uptake behaviors of U­(VI) by the nZVI/C composites were fitted well by surface complexation modeling with two weak and two strong sites. The maximum uptake capacity of U­(VI) by the nZVI/C composites was 186.92 mg/g at pH 4.0 and 328 K. Additionally, the nZVI/C composites presented good recyclability and recoverability for U­(VI) uptake in regeneration experiments. These observations indicated that the nZVI/C composites can be considered as potential adsorbents to remove radionuclides for environmental remediation

Spectroscopic Investigation of Enhanced Adsorption of U(VI) and Eu(III) on Magnetic Attapulgite in Binary System

The coadsorption of uranium and europium on magnetic attapulgite (M-ATT) was explored through batch experiments and spectroscopic tests. The adsorption processes of U­(VI) and Eu­(III) onto M-ATT were highly affected by the solution pH but not by the ionic strength, indicating that the adsorption of the two metals was predominated through inner-sphere surface complexation. Adsorption isotherms demonstrated that the maximum adsorption capacities of U­(VI) on M-ATT in the single-solute system (e.g., 60.48 mg g^–1 at pH 6.0) were lower than that in the binary-solute system (e.g., 63.03 mg g^–1 at pH 6.0), and the same trend was noticed for Eu­(III) adsorption due to their synergistic effect. The existence of U­(VI) and U­(IV) species evidenced the partial reduction of adsorbed U­(VI) to U­(IV) by M-ATT based on XPS tests. Hence, the enhanced adsorption of U­(VI) in the existence of Eu­(III) is ascribed to the primary coadsorption and then the redox of adsorbed U­(VI) to U­(IV) by M-ATT, as well as the formation of new sorbent active sites derived from reductive coprecipitation (e.g., UO_2+<i>x</i>(s)), which also increased the Eu­(III) adsorption on M-ATT. The findings are significant for coadsorption of radionuclides by magnetic adsorbents in environmental pollution management

Direct Synthesis of Bacteria-Derived Carbonaceous Nanofibers as a Highly Efficient Material for Radionuclides Elimination

Bacteria-derived carbonaceous nanofibers (CNFs) can be directly synthesized by the pyrolysis of bacterial cellulose pellicles under N₂ atmosphere. The batch adsorption experiments showed that the bacteria-derived CNFs displayed the excellent adsorption performance for radionuclides. The maximum adsorption capacities of the CNFs calculated from the Langmuir model at pH 4.5 and 293 K were 67.11 mg/g for Sr­(II) and 57.47 mg/g for Cs­(I). The adsorption of Cs­(I) and Sr­(II) on the CNFs decreased with increasing ionic strength at pH < 5.0, whereas no effect of ionic strength was observed at pH > 6.0, indicating that the outer-sphere surface complexation dominated the radionuclide adsorption at pH < 5.0 whereas the adsorption was attributed to inner-sphere surface complexation at pH > 6.0. The further evidence of surface complexation modeling indicated that Sr­(II) and Cs­(I) adsorption on the CNFs can be satisfactorily fitted by a double diffuse layer model with an outer-sphere (SOHSr²⁺/SOHCs⁺) and an inner-sphere complexes (SOSr⁺/SOCs). The X-ray photoelectron spectroscopy analyses demonstrated that the adsorption of Sr­(II) and Cs­(I) on the CNFs were ascribed to the combination of the oxygenated functional groups of the CNFs. These observations indicated that the CNFs, as inexpensive and available carbon-based nanomaterials, can be regarded as a promising adsorbent for the removal of radionuclides from aqueous solutions in environmental pollution cleanup

Biochar Derived from Sawdust Embedded with Molybdenum Disulfide for Highly Selective Removal of Pb²⁺

Surface interactions between the adsorbents and heavy metal ions play an important role in the adsorption process, and appropriately decorating the material’s surface can significantly improve the removal capacity of the adsorbents. So, the objective of this study is to modify biochar by coating with molybdenum disulfide (MoS₂) for enhancing the adsorption of Pb²⁺. The biochar pyrolyzed at 600 °C was chosen as the base to combine the flowerlike MoS₂ (MoS₂@biochar) by solvothermal reaction, in which the abundant S-containing functional groups may promote the elimination of Pb²⁺. The prepared MoS₂@biochar exhibits excellent adsorption capacity (189 mg/g) to Pb²⁺ in water solution. The adsorption of Pb²⁺ maintains a high level under the circumstance of coexisting ions (Mg²⁺, Ca²⁺, Co²⁺, and Cd²⁺), suggesting the high selectivity for Pb²⁺. The adsorption mechanism of Pb²⁺ on MoS₂@biochar is mainly ascribed to the inner-sphere surface complexation, in particular, metal–sulfur chemical complexation. The easily recycled MoS₂@biochar still has high adsorption capacity for Pb²⁺. This work demonstrates that the MoS₂@biochar is an excellent candidate of adsorbent for Pb²⁺ removal