Search

Radionuclide contamination has become an urgent problem with the development of nuclear power plants. Herein, chemical-decorated core-shell magnetic manganese dioxide (denoted as Fe3O4@C@MnO2) composites were synthesized via transforming KMnO4 to MnO2 on the carbon-covered magnetite (Fe3O4@C) microsphere surface. It was employed to remove U(VI) and Eu(III) ions from aqueous solution under various conditions. The kinetic adsorption data were well simulated by the pseudo-second-order model and adsorption isotherms were fitted well by Langmuir model. Moreover, the maximum uptake capacities were up to 77.71 mg/g for U(VI) and 51.01 mg/g for Eu(III) at pH = 5.0 and T = 298 K. Adsorption behavior was strongly related to pH values but weakly affected by ionic strength, implying that the interaction of U(VI)/Eu(III) with Fe3O4@C@MnO2 was mainly dominated by inner-sphere surface complexation. XPS analysis illustrated that the interaction of Eu(III)/U(VI) with Fe3O4@C@MnO2 was associated with the strong metal bonds (Mn O), hydroxyl bonded on metal (Mn-OH) and carboxyl groups (-COOH) by surface complexation and zeta potential results implied that the adsorption process was governed by electrostatic attraction. This research highlighted the outstanding performance of Fe3O4@C@MnO2 in eliminating Eu(III)/U(VI) ions from aqueous solutions, which was of great significance in the future application in radionuclides' pollution treatment.

Extraction of Eu(III) from wastewater has recently received extensive attention in environmental water pollution improvement because Eu(III) is the chemical analogue of trivalent lanthanides [Ln(III)] and actinides [An(III)]. In this work, UiO-66-AO with remarkable physicochemical properties was designed through introducing amidoxime groups (C(NOH)NH2) on the surface of UiO-66-CN which was derived from UiO-66-Br through introducing cyano groups (C N). SEM, TEM, BET, FT-IR, XRD, and TGA techniques demonstrated the effective synthesis and excellent structural performances of target materials. The outstanding sorption efficiency of UiO-66-AO (∼253.8 mg/g within 2 h) was verified through kinetic and thermodynamic analyses, showing that the kinetics data were well fitted by pseudo-second-order kinetic model, and the sorption isotherms were effectively fitted by Langmuir model. Based on macroscopic experiments and spectroscopic analyses (FT-IR and XPS), the removal mechanisms of Eu(III) onto UiO-66-AO were electrostatic interaction and inner-sphere surface complexation. In addition, the environmental application assessment had proved that UiO-66-AO owned excellent stability, outstanding selectivity, and remarkable Eu(III) removal percentage in simulated wastewater systems, demonstrating the great potential of UiO-66-AO to remove radionuclides from the actual wastewater.

The binding of metal ions with humic acid (HA) plays an important role in the aggregation of HA and the migration of metal ions in the environments. The effects of common cations (Na+, Mg2+, Ca2+ and Al3+) and heavy metal ions (Ag+, Cd2+, Cu2+, Cr3+ and Eu3+) on the aggregation of HA were investigated systematically by aggregation kinetics, spectroscopic techniques and molecular dynamic (MD) simulations. The critical coagulation concentration (CCC) of mono-, di- and trivalent cations could be predicted by the Schulze-Hardy rule. The aggregation of HA in the presence of Na+ and Ag+ was mainly due to the reduction of repulsive force and the hydrogen bonds between HA molecules. While the complexation of di- and trivalent cations with carboxylic/phenolic groups, or the cation-π interactions enhanced the intra- or inter-molecular bridges in HA and then contributed greatly to the aggregation of HA. Heavy metal ions could easily pass through the electric double-layer of HA compared with common cations. MD simulations further signified the strong aggregation ability of HA molecules in solutions containing high valence metal ions. These findings are important for understanding not only how the influence of metal ions on the aggregation of HA, but also the conditions which ions more efficient for aggregation.

Two-dimensional (2D) nanomaterials have been identified as one of the promising materials due to their great promise for waste treatment. Currently, the investigation of wastewater remediation is highly imperative and still remains challenging. Here, a novel class of 2D MAX@titanate nanocomposites was fabricated by a simple oxidation and alkalization method, and they exhibited different morphologies and impressive elimination performance. The Pb(ii) uptake processes were dramatically affected by the solution pH and reached equilibrium quickly. Abundant functional groups and enhanced specific surface areas endowed T-NTO nanofibers with outstanding adsorption capacity of 328.9 mg g-1 at pH = 5.0 and T = 298 K, which was much higher than that of T-KTO nanoribbons. Moreover, the possible mechanism was expounded with the aid of Raman, FT-IR, XRD and XPS analyses, in which the synergistic effect of surface complexation and ion exchange significantly contributed to the adsorption performance. On the basis of above analyses, this study not only presents a novel and facile strategy for preparing T-NTO and T-KTO nanostructures with superior adsorption capacity, but also broadens the prospective applications of other functional MAX-derived nanostructures in environmental cleanup.

The increased release and accumulation of Bisphenol A (BPA) in contaminated wastewater has resulted in the world wide concerns because of its potential negative effects on human health and aquatic ecosystems. Starting with metal-organic frameworks, we present a simple method to synthesize magnetic porous microcubes (N-doped Fe0/Fe3C@C) with graphitized shell and highly dispersed active kernel via the pyrolysis process under N2 atmosphere. Batch adsorption experimental results showed that N-doped Fe0/Fe3C@C had high adsorption capacity for BPA (∼138 mg g−1 at pH = 7 and 298 K). Degradation of BPA adsorbed on N-doped Fe0/Fe3C@C was further investigated as a function of BPA concentration, persulfate amount, temperature and solution pH. It was found that potassium peroxodisulfate could be activated by N-doped Fe0/Fe3C@C, and a large number of free radicals were generated which was crucial for the degradation of BPA. The concentration of BPA was barely changed in the individual persulfate system. BPA (10 mg L−1) was almost completely degraded within 60 min in the presence of N-doped Fe0/Fe3C@C (∼0.2 g L−1). When the BPA content increased to 25 mg L−1, the removal efficiency of BPA achieved to 98.4% after 150 min. From the XRD, Raman, and XPS analysis, the main adsorption mechanism of BPA was π-π interactions between the π orbital on the carbon basal planes and the electronic density in the BPA aromatic rings. While the superior degradation was attributed to the radical generation and evolution in phenol oxidation. This work not only proved the potential application of N-doped Fe0/Fe3C@C in the adsorption and degradation of BPA, but also opened the new possibilities to eliminate organic pollutants using this kind of magnetic materials in organic pollutants’ cleanup.

Nowadays, more and more researchers pay close attention to the decontamination of radioactive uranium because of its high toxicity and long half-life in the environment. Although many strategies fo...

Graphene oxide (GO) was applied as adsorbent to efficiently eliminate the heavy metal ions from wastewater because of its large amount of functional surface groups and high surface areas. However, the contribution of different functional surface groups on the high preconcentration of heavy metal ions to GO is still unclear. Herein the GO was applied as adsorbent for the efficient preconcentration of Co(II) and the effect of functional surface groups on Co(II) removal was studied by batch sorption experiments. The results showed that the maximum sorption capacities of Co(II) on GO, NGO, MGO and NMGO were 43.6, 27.3, 23.2 and 14.6 mg/g, respectively. The elimination of Co(II) was significantly influenced by ionic strength and pH, indicated that the interaction mechanism was primarily controlled by strong surface complexation. The DFT calculation further evidenced that the oxygen-containing surface groups could form shorter bond distance with Co(II) ions than the nitrogen-containing functional groups, and the calculated adsorption energies (Ead) for GO–COOH–Co (44.05 kcal/mol) and GO–OH–Co (16.44 kcal/mol) were much higher than that for NGO–Co (6.33 kcal/mol). The density of states (DOS) and charge density differences of combined complexes further illustrated the strong surface complexes were formed between Co(II) and the oxygen-containing surface groups of GO surfaces. This work highlighted that the oxygen-containing surface groups played a vital role in the formation of surface complexes with Co(II) on GO, which is crucial for the preparation and application of GO in the radioactive pollution cleanup.

With the widespread application of radionuclide 235U(VI), it is inevitable that part of U(VI) is released into the natural environment. The potential toxicity and irreversibility impact on the natural environment has become one of the most forefront pollution problems in nuclear energy utilization. In this work, rod-like metal-organic framework (MOF-5) nanomaterial was synthesized by a solvothermal method and applied to efficiently adsorb U(VI) from aqueous solutions. The batch experimental results showed that the sorption of U(VI) on MOF-5 was strongly dependent on pH and independent of ionic strength, indicating that the dominant interaction mechanism was inner-sphere surface complexation and electrostatic interaction. The maximum sorption capacity of U(VI) on MOF-5 was 237.0 mg/g at pH 5.0 and T = 298 K, and the sorption equilibrium reached within 5 min. The thermodynamic parameters indicated that the removal of U(VI) on MOF-5 was a spontaneous and endothermic process. Additionally, the FT-IR and XPS analyses implied that the high sorption capacity of U(VI) on MOF-5 was mainly attributed to the abundant oxygen-containing functional groups (i.e., C O and C O). Such a facile preparation method and efficient removal performance highlighted the application of MOF-5 as a candidate for rapid and efficient radionuclide contaminations elimination in practical applications.

Radionuclides with long half-life are toxic, and thereby result in serious threat to human beings and ecological balance. Herein, a simple two-step synthesis method was used to prepare manganese dioxide@polypyrrole (MnO2@PPy) core/shell structures for efficient removal of U(VI) and Eu(III) from aqueous solutions. The adsorption of U(VI) and Eu(III) were investigated under different kinds of experimental conditions. The experimental results suggested that the adsorption of U(VI) and Eu(III) on MnO2@PPy were greatly affected by pH. U(VI) adsorption on MnO2@PPy was independent of ionic strength at pH 6.0. However, Eu(III) adsorption on MnO2@PPy was independent of ionic strength at the whole pH range of experimental conditions. The maximum adsorption capacities ( q max) of U(VI) and Eu(III) were 63.04 and 54.74 mg g−1 at T = 298 K, respectively. The BET, XRD, FTIR and XPS analysis evidenced that high adsorption capacities of U(VI) and Eu(III) on MnO2@PPy were mainly due to high surface area and rich metal oxygen-containing group (i.e., Mn–OH and Mn–O), and the interaction was mainly attributed to strong surface complexation and electrostatic interaction. This study highlighted the excellent adsorption performance of U(VI) and Eu(III) on MnO2@PPy and could provide the reference for the elimination of radionuclides in real wastewater management.

Increasing specific surface area and functional groups are two key ways to improve the adsorption performance of adsorbent materials. Herein, porous Fe2O3 (P-Fe2O3) microcubes composed of fine Fe2O3 nanoparticles (NPs) were facilely synthesized through the simultaneous oxidative decomposition of Prussian blue (PB) microcubes. Owing to their integrated features (i.e., large specific surface area of ∼155 m2 g−1 and large amount of Fe2O3 NPs), the synthesized P-Fe2O3 exhibited excellent adsorption capacities for heavy metal ions (175.5 mg g−1 for Cr(VI) and 97.8 mg g−1 for Pb(II)) and organic contaminants (159.4 mg g−1 for humic acid and 425.9 mg g−1 for methyl blue) from aqueous solutions. Based on the batch experiments, the adsorption isotherms could significantly conform to the Langmuir models. Combined with the microscopic analysis, the results suggested that the enrichment of Pb(II) on P-Fe2O3 was mainly attributed to the chemical binding between the electron donating oxygen ions of P-Fe2O3 surface and Pb(II), while the large available positive charge density could facilitate the effective adsorption of Cr(VI) due to ion exchange and electrostatic attraction. Furthermore, the surface complexation of organic pollutants on P-Fe2O3 was depended on the dipole moment and molar volume of the organic pollutant molecules. The consequences indicated that P-Fe2O3 could be served as a promising material for the decontamination of organic contaminants as well as the elimination of heavy metal ions from aqueous solutions. The findings presented herein played important roles in the purification of inorganic and organic contaminants on the available of inexpensive P-Fe2O3 NPs in natural environmental pollution cleanup applications.

With the rapid expansion of industrialization, it is inevitable that heavy metal ion (such as chromium, Cr(VI)) is released into the ecological systems, which has become a potential threat to public health. Herein, polyvinylpyrrolidone intercalated molybdenum disulfide composites and polyacrylamide intercalated molybdenum disulfide composites were synthesized for the efficient removal of Cr(VI) from aqueous solutions. The sorption of Cr(VI) on the composites was studied by batch technique and the macroscopic sorption results revealed that the removal of Cr(VI) was strongly dependent on ionic strength and pH. The removal capacities of Cr(VI) achieved 142.24 mg/g on PVP/MoS2 and 84.91 mg/g on PAM/MoS2 at pH = 5.0. The thermodynamic study indicated that the interaction was a spontaneous and endothermic process. According to the batch experimental results combined with XPS spectra analysis, it can be considered that the interaction of Cr(VI) with the composites was that Cr(VI) ions were fixed on the composite surfaces by electrostatic attraction and then entered into the interlayer and combined with amide groups at the interlamination of the composites. The findings can provide a new perspective for the rational design of MoS2 composites with high performance and excellent chemical stability for Cr(VI) removal in extreme conditions, which would not cause secondary pollution.

Potentially toxic metals in sewage and industrial effluents pose a serious threat to human health and the environment. Herein, core–shell hollow magnetic polydopamine nanoparticles (denoted as Fe3O4@PDA) were fabricated via a simple one-pot synthesis method and applied for the elimination of Pb(II) and Cu(II) from wastewater. The versatile polydopamine (PDA) layer with abundant functional groups (amine, imine and catechol groups) provided favourable sites to bind metal ions. The experimental results showed that the adsorption processes were significantly affected by the pH values of the suspension. The ionic strength-independent adsorption processes indicated the existence of inner-sphere surface complexes of Pb(II) and Cu(II) on Fe3O4@PDA. The results showed that Fe3O4@PDA exhibited fast removal kinetics for Pb(II) and Cu(II), which achieved equilibrium within 3 h. The adsorption processes were well fitted by the pseudo-second-order kinetic model and Langmuir isotherm model. Furthermore, the removal capacities of Fe3O4@PDA were calculated to be 57.25 mg g−1 for Pb(II) and 86.35 mg g−1 for Cu(II), which were much higher than those of pure Fe3O4 and other materials. Most importantly, the adsorption efficiencies of Pb(II) and Cu(II) on Fe3O4@PDA were still ∼71% and ∼70% after five cycles, respectively. In summary, the hollow Fe3O4@PDA nanoparticles can be used as outstanding materials for the elimination of Pb(II) and Cu(II), which is beneficial to reduce the toxic effects of heavy metal ion contaminated water.

The toxicity and radioactivity of uranium [235,238U(VI)] has resulted in serious environmental issues in recent years. Polyethyleneimine-decorated waste fly ash (FA@PEI) from thermal power plants has been fabricated via a novel and cost-efficient method and applied to the U(VI) elimination from aqueous solutions by batch experiments. The U(VI) removal was found to be dramatically influenced by pH whilst being ionic strength-independent, which indicated that the interaction was primarily controlled by inner-sphere surface complexation. Kinetic studies showed that the FA@PEI had an ultrafast removal rate (1.5 h to achieve adsorption equilibration) for U(VI) and a pseudo-second-order model fitted the adsorption process. The maximum removal capacity of U(VI) by FA@PEI was 70.3 mg g−1 at 298 K and pH 5.0. Based on the thermodynamics data (ΔH° > 0, ΔS° > 0 and ΔG° < 0), the U(VI) removal process is typically spontaneous and endothermic. According to the XPS analysis, the enhanced U(VI) adsorption was mainly attributed to the abundant metal–oxide bonds and amine groups (–NH2, –NH–). Furthermore, the FA@PEI material also demonstrated an outstanding regeneration ability. This paper highlights FA@PEI as an environmentally-friendly and economical alternative for U(VI) elimination from waste water.

Herein, a practical and simple calcination method was used to synthesize layered double oxides (denoted as LDO) and layered double oxides/carbon dots nanocomposites (denoted as LDO-C) for U(VI) efficient removal. The U(VI) adsorption on LDO and LDO-C were investigated under various experimental conditions, and the results indicated that U(VI) uptake on LDO and LDO-C were consumingly dependent on pH and ionic strength at pH > 6, and independent of ionic strength at pH 241 Am(III) than LDO. All in all, the efficient removal performance and superior versatility of LDO-C indicated that it could be applied as promising candidate for efficient immobilization of radioactive pollutant in environmental pollution management.

In the past few decades, uranium (235, 238U(VI)) has turned into a forefront environmental issue due to its extensive use in the nuclear industry and its toxicity and radioactivity. Herein, nanoscale zero valent iron (nZVI), which was supported on Ca–Mg–Al-layered double hydroxide (Ca–Mg–Al-LDH/nZVI), was fabricated via an in situ growth route and employed for U(VI) decontamination from aqueous solutions. Spectroscopy and microscopy (SEM, TEM, FTIR, XRD, BET, and XPS) technologies were applied for the investigation of the properties of Ca–Mg–Al-LDH/nZVI and the U(VI) elimination mechanism. Ca–Mg–Al-LDH/nZVI had a remarkable BET surface (426.8 m2 g−1), abundant functional groups (i.e., Fe–O, Al–O, –OH, etc.), high efficiency (4 h to achieve equilibrium) and large adsorption capacities (Qmax = 216.1 mg g−1) for U(VI) removal. The decontamination process of U(VI) was observed to be pH-dependent and ionic strength-independent, suggesting that the adsorption was predominated by inner-sphere surface coordination. XPS spectroscopy analyses indicated that the reduction and adsorption of nZVI and the adsorption of Ca–Mg–Al-LDH dominated U(VI) elimination on Ca–Mg–Al-LDH/nZVI. The environmentally friendly synthesis method, excellent physicochemical properties and remarkable removal performance suggested that Ca–Mg–Al-LDH/nZVI was applicable as a potential adsorbent for U(VI) decontamination from wastewater in environmental pollution remediation.

Cotton-like graphitic carbon nitride @ layered double hydroxides nanocomposites (g-C3N4@Ni-Mg-Al-LDH) was fabricated using lamellar g-C3N4 and rod-like Ni-Mg-Al-LDH as monomer molecules by one-step hydrothermal synthesis strategy, and it exhibited superior adsorption performance to U(VI) from wastewater based on strong synergistic effects among metal–oxygen functional groups (Mg O, Al O and Ni O) and free-metal functional groups (O C O, C O C, C O, C C and NH2/ NH /= N ). The adsorption of U(VI) on g-C3N4@Ni-Mg-Al-LDH was controlled by outer-sphere surface complexation or ion exchange, which was evidenced with batch adsorption experiments and SEM, EDS, elemental mapping, FT-IR, XRD and XPS characterizations. Moreover, the maximum adsorption capacity of U(VI) on g-C3N4@Ni-Mg-Al-LDH (99.7 mg·g−1) was approximately 1.5 times higher than that of U(VI) on Ni-Mg-Al-LDH (59.8 mg·g−1) and approximately 3.0 times higher than that of U(VI) on g-C3N4 (31.1 mg·g−1) at 298.15 K, and a multilayer adsorption was existed in a low concentration of UO22+, while a monolayer adsorption was appeared in a high concentration of UO22+. The results also showed that the adsorption reaction of U(VI) was a typical endothermic and spontaneous process because of ΔHθ > 0, ΔSθ > 0 and ΔGθ

Hexanuclear zirconium metal–organic frameworks (Zr 6 MOFs) were successfully designed to possess different kinds of defects with various contents and its important influence on the capture of Se(VI) oxyanions was studied. The displaceable ligands (aqua and hydroxy groups) and weak-binding “capping” ligands (Cl − , O 2 C-CH 3 − , O 2 C-CF 3 − or O 2 C-CHF 2 − , HO − and/or H 2 O) on Zr 6 nodes could be substituted by Se(VI) oxyanions via a mechanism of anion-exchange. More efficient and faster uptake of Se(VI) oxyanions was obtained with the increase of the densities of both missing linker defects and missing cluster defects. Experimental findings as well as theoretical density functional theory (DFT) calculations disclosed that smaller HO − , Cl − , or H 2 O compensating ligands can be more easily substituted than the O 2 C-CH 3 − , O 2 C-CF 3 − or O 2 C-CHF 2 − compensating ligands. Based on DFT calculations, the binding energy of Se(VI) oxyanions toward defective UiO-66 is much higher than that of other heavy metals toward MOFs. Moreover, using modulator synthetic strategy in the preparation of Zr 6 MOFs can be a better choice for enhancing the removal capacity than synthesizing them with longer organic linkers which are too complex and expensive. The experimental results and theoretical calculations prefigure the great potentials of defect-tunable MOFs as promising candidates in the application of heavy metal ion remediation because they can be synthesized in large scale at low price and can also be elegantly tailored.

Development of a highly efficient material with large specific area was scientifically and technologically important for simultaneous elimination of inorganic and organic pollutants from wastewater. In this work, layered-double-hydroxides-coated (LDHs-coated) hollow carbon microsphere composites (HCMSs; LDHs/HCMSs) were fabricated using carbon spheres as templates via a hydrothermal method and were then applied for mutual removal of Pb(II) and humic acid (HA) under various experimental conditions, i.e., pH, ionic strength, contact time, addition sequences, and coexisting ions. The results indicated that the copresence of Pb(II) and HA facilitated single target pollutant [Pb(II) or HA] adsorption at pH < 8.0. The adsorbed HA was responsible for the improvement of Pb(II) adsorption, primarily as a result of the formation of HA-Pb-LDHs/HCMSs ternary complexes. Competitive adsorption of Cu(II), Co(II), Pb(II), and Ni(II) ions on LDHs/HCMSs was also investigated, and the LDHs/HCMSs had the affinity in the orde...

Plasma- and chemical-grafted amidoxime/carbon nanofiber hybrids (p-AO/CNFs and c-AO/CNFs) were utilized to remove 238U(VI) and 241Am(III) from aqueous solutions, seawater, and groundwater. Characteristic results indicated more nitrogen-containing groups in p-AO/CNFs compared to c-AO/CNFs. The maximum adsorption capacities of p-AO/CNFs at pH 3.5 and T = 293 K (588.24 mg of 238U(VI)/g and 40.79 mg of 241Am(III)/g from aqueous solutions, respectively) were significantly higher than those of c-AO/CNFs (263.18 and 22.77 mg/g for 238U(VI) and 241Am(III), respectively), which indicated that plasma-grafting was a highly effective, low-cost, and environmentally friendly method. Adsorption of 238U(VI) on AO/CNFs from aqueous solutions was significantly higher than that of 238U(VI) from seawater and groundwater; moreover, AO/CNFs displayed the highest effective selectivity for 238U(VI) compared to the other radionuclides. Adsorption of 238U(VI) onto AO/CNFs created inner-sphere complexes (e.g., U–C shells) as shown ...

A novel low-cost, effective and environmental-friendly laminated carbon nitride decorated with polydopamine (PDA) and grafted with polyethyleneimine (PEI) brush ( l -C 3 N 4 /PDA/PEI 3 ) was successfully synthesized and applied as environmental cleaner for removing U(VI) ions from aqueous solutions under various environmental conditions. The adsorption isotherms fitted well by the Langmuir model, suggesting that the removal of U(VI) on l -C 3 N 4 /PDA/PEI 3 was monolayer coverage. The effects of different PEI contents were also investigated and the results demonstrated that the adsorption capacity of U(VI) on l -C 3 N 4 /PDA/PEI x decreased at higher content of PEI. Typically, various cations (Ca 2+ and Mg 2+ ) and SO 4 2− could inhibit the adsorption through competitive coordination with U(VI), while CO 3 2− promoted U(VI) sorption owing to the formation of indissolvable complexes. The main driving force between U(VI) and l -C 3 N 4 /PDA/PEI 3 was surface complexation with various functional groups (C C, C O, N C C, and C C or C H) and electrostatic attraction. According to the analysis of EXAFS spectra, the occurrence of U-C and U-U shell revealed that inner-sphere complexation and surface co-precipitation dominated the adsorption of U(VI) on l -C 3 N 4 /PDA/PEI 3 at pH 5.0. The composites were also applied to remove 243 Am(III), Cu(II) and Pb(II) ions at different pH values, and similar results were also found for these metal ions. Such a facile synthesis method and efficient removal performance suggested that the l -C 3 N 4 /PDA/PEI 3 materials might be a promising adsorbent for efficient elimination of radionuclides and heavy metal ions in environmental pollution management.

Hierarchical silicon dioxide-@-layered double hydroxide (SiO2@LDH) nanocomposites were synthesized by a facile in situ co-precipitation method, and characterized by XRD, FESEM, FT-IR and XPS in detail. The sorption of uranium (U(VI)) and methyl orange (MO) on SiO2@LDH were investigated as a function of pH, ionic strength, contact time and temperature. The results indicated that the sorption of U(VI) and MO were strongly dependent on pH, and weakly dependent on ionic strength, demonstrating that the interaction of U(VI) was mainly dominated by inner-sphere surface complexation and the sorption of MO was mainly attributed to electrostatic attraction due to the high removal efficiency (∼98% within 4 h for U(VI) ions, and ∼92% within 10 min for MO). The kinetics sorption of U(VI) and MO both followed the pseudo-second-order model well, suggesting that the sorption processes were chemical sorption. The sorption isotherms of U(VI) and MO on SiO2@LDH were well fitted by the Langmuir model, and the maximum sorption capacities of SiO2@LDH were calculated to be 303.1 mg·g−1 for U(VI) and 166.1 mg·g−1 for MO. The thermodynamic parameters revealed that the sorption of U(VI) and MO was spontaneous process. Integrating the experimental result analysis, the hierarchical SiO2@LDH may be a promising material for the efficient elimination of radionuclides and dyes from aqueous solutions in natural environmental pollution cleanup.

The biological toxicity and negative environmental effect of graphene oxide (GO) have attracted wide public concern due to its potential risks. To assess the transport behavior and to reduce the environmental hazardous of GO in natural environment, ZnO and MgO were used as coagulant for GO removal from aqueous solutions. The results indicated that GO coagulation on ZnO and MgO were scarcely affected by ionic strength. At neutral pH, the GO removal capacities could reach 232.8 mg/g on MgO and 210.8 mg/g on ZnO. The high removal capacity and short coagulation time showed the enormous advantages for the high-efficiency removal of GO from aqueous solutions, which were important for the real application of MgO and ZnO in reality. The coagulation mechanisms of GO on ZnO and MgO could be attributed to electrostatic attraction and hydrogen bond, which were further demonstrated by DFT calculations. Considering the cost, efficiency, removal capacity and reusability, one can conclude that metal oxides can be promising materials for GO efficient removal by a simple and rapid coagulation process. The findings can provide critical information about the physicochemical behavior of GO in aquatic natural environment, which is significant to decrease the environmental toxicity of GO.

Humic acid (HA) can markedly change the surface charge of clay minerals and influences the sorption of uranium(U) on clay minerals in aquatic environments. Furthermore, HA can potentially affect the mobility of U(VI) in the natural environment. The effect of HA on the surface charge, aggregation, sorption and bonding properties of attapulgite [(Mg,Al) 4 (Si) 8 (O,OH,H 2 O) 26 ·nH 2 O] was investigated using fluorescence spectroscopy technique in combination with other analytical tools. The UV–vis absorbance spectra and fluorescence peaks obtained in the experiments are attributed to a large number of electron donating substitutes, such as carboxylic acid-like and phenolic acid-like fluorophores, in HA. Electrostatic attraction and ligand exchanges are the primary interaction mechanisms between attapulgite and HA. A significant modification of excitation-emission matrix (EEM) spectra and emission intensity of HA are observed after the interaction, indicating a different binding complex of HA on attapulgite at the molecular level. The sorption kinetics indicate that strong chemical interactions and/or surface complexation primarily contributed to U(VI) sorption. An analysis of U(VI) sorption isotherms and model fitting reveals that the sorption of U(VI) onto attapulgite is a spontaneous and endothermic process. The presence of HA is an important factor that greatly influences the immobilization and removal of U(VI) ions from aqueous solutions.

With the rapid development of industry, heavy metal pollution has become a potential hazard to public health and the ecological system. Herein, molybdenum disulfide coated Mg/Al layered double hydroxide composites (LDHs@MoS2) were prepared via a simple hydrothermal method and applied for the adsorption of Cr(VI) from a water solution. The removal capacity of Cr(VI) on LDHs@MoS2 reached 76.3 mg/g at pH = 5.0, and the removal process relied on ionic strength and pH. The results confirmed that the uptake of Cr(VI) on LDHs@MoS2 followed a spontaneous endothermic process. In contrast to the LDHs, LDHs@MoS2 showed excellent chemical stability, which was beneficial for practical applications. Specifically, the coexisting ions had little influence on the uptake of Cr(VI). The interaction of Cr(VI) with the LDHs@MoS2 composites was mainly controlled by electrostatic attraction and outer-sphere surface complexation. The findings can provide new insights into the uptake of heavy metal ions in a natural aquatic envir...

Herein the novel natural bimetallic oxides of perovskite oxides (CaTiO x ) and calcium aluminum oxides (CaAlO x ) were fabricated by one-step calcination-oxidation process under air conditions and were characterized using zeta potential, FT-IR, SEM, TEM, XRD, and XPS techniques. Porous and cotton-shaped irregular surface morphologies of CaTiO x and CaAlO x could provide excellent active sites and large specific surface area for the removal of U(VI) from wastewater. Based on FT-IR, XRD and XPS analyses, the enrichment of U(VI) was attributed to the abundant adsorption sites (e.g., M-O groups) of CaTiO x and CaAlO x . The consequences demonstrated that the sorption of U(VI) on CaTiO x and CaAlO x were strongly dependent on pH and weakly dependent on ionic strength at pH 4.0. The accordance of sorption kinetic data with the pseudo-second order model suggested that the sorption reaction was multi-stage controlled chemical process. The sorption isotherms of U(VI) can be satisfactorily simulated by the Langmuir model and the maximum monolayer sorption capacities of U(VI) were 241.71 mg·g −1 on CaTiO x and 258.29 mg·g −1 on CaAlO x at 298.15 K. In addition, the thermodynamic results pointed out that the sorption reaction was spontaneous and endothermic process. The sorption mechanism was interpreted as surface complexation and electrostatic interactions. The results demonstrated that CaTiO x and CaAlO x could be widely used as promising and cost-effective materials for the treatment of U(VI) of aqueous solutions in environmental management and pollution prevention and cure.

Novel, efficient, glycerol-modified nanoscale layered double hydroxides (rods Ca/Al LDH-Gl and flocculent Ni/Al LDH-Gl) were successfully synthesized by a simple one-step hydrothermal synthesis route and showed excellent adsorption capacities for U(VI) from aqueous solutions under various environmental conditions. The advanced spectroscopy analysis confirmed the existence of abundant oxygen-containing functional groups (e.g., C–O, O–C═O, and C═O) on the surfaces of Ca/Al LDH-Gl and Ni/Al LDH-Gl, which could provide enough free active sites for the binding of U(VI). The maximum adsorption capacities of U(VI) calculated from the Sips model were 266.5 mg·g–1 for Ca/Al LDH-Gl and 142.3 mg·g–1 for Ni/Al LDH-Gl at 298.15 K, and the higher adsorption capacity of Ca/Al LDH-Gl might be due to more functional groups and abundant high-activity “Ca–O” groups. Macroscopic experiments proved that the interaction of U(VI) on Ca/Al LDH-Gl and Ni/Al LDH-Gl was due to surface complexation and electrostatic interactions. Th...

Graphene oxide and Ni-Al layered double hydroxides (GO@LDH) nanocomposites were synthesized via a one-pot hydrothermal process, and characterized by X-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy in detail. The exploration of U(VI) sorption on GO@LDH surface was performed as a function of ionic strength, solution pH, contact time, U(VI) initial concentrations and temperature. Results of Langmuir isotherms showed that the sorption capacity of GO@LDH (160 mg/g) was much higher than those of LDH (69 mg/g) and GO (92 mg/g). The formed surface complexes between surface oxygen-containing functional groups of GO@LDH and U(VI) turned out to be the interaction mechanism of U(VI) with GO@LDH. According to the thermodynamic studies results, the sorption interaction was actually a spontaneous and endothermic chemical process. The sorption isotherms were better fitted with the Langmuir model compared with other models, which suggested the interaction was mainly dominated by monolayer coverage. The GO@LDH nanocomposites provide potential applications as adsorbents in the enrichment of radionuclides from wastewater in nuclear waste management and environmental remediation.

The interaction mechanism of high effective enrichment of U(VI) on sulfonated graphene oxide (GO) at ultralow pH still remains unclear. The batch characteristic results showed that sulfonated GO presented a variety of functional groups such as hydroxyl ( OH), carboxyl ( COOH) and sulfonyl ( OSO 3 H) groups. The macroscopic results indicated that the sorption of U(VI) on sulfonated GO was independent of ionic strength, and the maximum sorption capacity calculated from Langmuir model was 45.05 mg/g at pH 2.0. The change of relative intensities for S 2p spectra was significantly higher than that of O 1s spectra by XPS analysis. According to EXAFS analysis, the significant splitting of equatorial oxygen (U-O eq ) shell at pH 2.0 was attributed to the electron scattering of the elemental sulfur. The energy of uranyl-sulfonyl (−3198.511 hartree/particle) at pH 2.0 calculated based on theoretical calculations was lower than that of uranyl-carboxyl (−3198.498 hartree/particle), indicating that uranyl-sulfonyl was more stable at ultralow pH. These observations indicated that the sulfonyl of GO was responsible for high effective removal of U(VI) at ultralow pH, which is vital to the application of functionalized GO in the preconcentration of U(VI) in nuclear waste management and the removal of U(VI) from wastewater at low pH values.

The sorption mechanism of Th(IV) on amidoxime/graphene oxide composites was investigated by extended X-ray absorption fine structure (EXAFS) spectra and surface complexation modeling. It was found that amidoxime/graphene oxide composites possessed a variety of oxygen- and nitrogen-containing functional groups such as hydroxyl, carboxyl, carbonyl, amine and imine groups. The sorption kinetics and sorption isotherms of Th(IV) on amidoxime/graphene oxide composites can be satisfactorily fitted by the pseudo-second-order kinetic model and the Langmuir model, respectively. The maximum sorption capacity of Th(IV) on amidoxime/graphene oxide composites calculated from the Langmuir model at pH 2.0 and 293 K was 123.46 mg g−1. According to EXAFS analysis, the presence of a Th–C shell (R = 2.97 A, CN = 4.9) indicated that inner-sphere surface complexation dominated the sorption of Th(IV) on amidoxime/graphene oxide composites at pH 2.0, whereas the occurrence of a Th–Th shell revealed that a surface precipitate dominated the sorption of Th(IV) on amidoxime/graphene oxide composites at pH 5.0. The pH-dependent sorption behaviors of Th(IV) on amidoxime/graphene oxide composites can be satisfactorily simulated by double layer modeling based on two inner-sphere surface complexes and a surface precipitate. These observations revealed that the amidoxime/graphene oxide composites can be regarded as a promising adsorbent to remove tetravalent radionuclides from aqueous solutions in environmental cleanup.

Highly porous zeolitic imidazolate frameworks (ZIFs), with disparate metal ions (ZIF-8 and ZIF-67), disparate organic ligands (ZIF-9 and ZIF-67), single or double central metal atoms (ZIF-8, Zn/Co-ZIF and ZIF-67) were prepared and used in the elimination of typical radionuclide U(VI). The detailed interaction mechanisms were studied by batch experiments, spectral analyses and DFT calculation. Langmuir isotherms model revealed a decreasing tendency to remove U(VI): ZIF-8 (540.4 mg/g) > Zn/Co-ZIF (527.5 mg/g) > ZIF-9 (448.6 mg/g) > ZIF-67 (368.2 mg/g). Based on the effects of pH and foreign ions, FTIR and XPS spectra analyses, the possible interaction mechanisms of U(VI) onto ZIFs were surface complexation and electrostatic interaction. Among them, ZIF-8 with Zn metal center and 2-methylimidazolate organic ligand had the best elimination capacity for U(VI) because of its large surface area, active metal ion and abundant nitrogen-containing groups (e.g., C–N, Zn–N and C N). Specially, the adsorption energy of ZIF-8-Zn2-UO22+ structure was −2.299 eV obtained by DFT calculation, illustrating that U(VI) and N atoms were formed the most stable bidentate coordination compounds. This paper highlights the effects of the hydroxylated metals, the functional groups of the imidazole ring on the elimination of U(VI), which can provide constructive suggestions for further adsorbent materials amelioration.

In this study, chitosan–metal oxide composites (CS–MO) were prepared for graphene oxide (GO) removal from aqueous solutions. The results showed that the GO coagulation on CS–MO was dependent on pH and ionic strength. The maximum GO removal capacities reached 442.5 mg/g on CS–Al2O3, 425.0 mg/g on CS–ZnO and 421.2 mg/g on CS–MgO, respectively, showing a huge advantage in the efficient elimination of GO from natural water system. The coagulation of GO on CS–MO was dominated by electrostatic attraction in acidic conditions and by hydrogen bonds in neutral and alkaline conditions. The findings are helpful to improve the current understanding of the environmental behavior of GO in natural aqueous systems.

With the development and application of graphene oxides (GO), the potential toxicity and environmental behavior of GO has become one of the most forefront environmental problems. Herein, a novel nanoscale layered double hydroxides (glycerinum-modified nanocrystallined Mg/Al layered double hydroxides, LDH-Gl), layered double oxides (calcined LDH-Gl, LDO-Gl) and metallic oxide (TiO 2 ) were synthesized and applied as superior coagulants for the efficient removal of GO from aqueous solutions. Coagulation of GO as a function of coagulant contents, pH, ionic strength, GO contents, temperature and co-existing ions were studied and compared, and the results showed that the maximum coagulation capacities of GO were LDO-Gl (448.3 mg g −1 ) > TiO 2 (365.7 mg g −1 ) > LDH-Gl (339.1 mg g −1 ) at pH 5.5, which were significantly higher than those of bentonite, Al 2 O 3 , CaCl 2 or other natural materials due to their stronger reaction active and interfacial effect. The presence of SO 3 2− and HCO 3 − inhibited the coagulation of GO on LDH-Gl and LDO-Gl significantly, while other cations (K + , Mg 2+ , Ca 2+ , Ni 2+ , Al 3+ ) or anion (Cl − ) had slightly effect on GO coagulation. The interaction mechanism of GO coagulation on LDO-Gl and TiO 2 might due to the electrostatic interactions and strong surface complexation, while the main driving force of GO coagulation on LDH-Gl might be attributed to electrostatic interaction and hydrogen bond, which were further evidenced by TEM, SEM, FT-IR and XRD analysis. The results of natural environmental simulation showed that LDO-Gl, TiO 2 or other kinds of natural metallic oxides could be superior coagulants for the efficient elimination of GO or other toxic nanomaterials from aqueous solutions in real environmental pollution cleanup.

Novel rod-like ternary nanoscale layered double hydroxides (Ca-Mg-Al-LDH) and their bimetal derivatives (Ca-Mg-Al-LDOx, x: 200, 300, 400, 500, and 600 °C) were fabricated with a simple-green hydrothermal and calicination process. The interaction mechanism and adsorption property of U(VI) on Ca-Mg-Al-LDH and Ca-Mg-Al-LDOx were investigated by a batch technique and spectroscopy analysis, and the results indicated that U(VI) could form strong and stable surface complexes on Ca-Mg-Al-LDH and Ca-Mg-Al-LDOx surfaces. The adsorption capacity of U(VI) on various adsorbents could be controlled and adjusted through changing the calcination temperature, which was attributed to the different contents of various metal–oxide bonds (e.g., Ca–O, Mg–O, and Al–O). The adsorption capacities of U(VI) on these adsorbents were in the order of Ca-Mg-Al-LDO500 (486.8 mg/g) > Ca-Mg-Al-LDO600 (373.4 mg/g) > Ca-Mg-Al-LDO400 (292.5 mg/g) > Ca-Mg-Al-LDO300 (260.0 mg/g) > Ca-Mg-Al-LDO200 (223.5 mg/g) > Ca-Mg-Al-LDH (132.5 mg/g), which...

To contribute to the understanding of Eu(III) interaction preperties on hydrous alumina particles in the absence and presence of fulvic acid (FA), the complexation properties of Eu(III) with hydrous alumina, FA and FA-alumina hybrids are studied by batch and time-resolved laser fluorescence spectroscopy (TRLFS) techniques. The continuous increase in the fluorescence lifetime of Eu-alumina and Eu-FA with increasing pH indicates that the complexation is accompanied by decreasing number of hydration water in the first coordination sphere of Eu(III). Eu(III) is adsorbed onto alumina particles as outer-sphere surface complexes of ≡(Al−O)−Eu· (OH)· 7H2O and ≡(Al−O)−Eu· 6H2O at low pH values, and as inner-sphere surface complexes as ≡(Al−O)2−Eu+· 4H2O at high pH. In FA solution, Eu(III) forms complexes with FA as (COO)2Eu+(H2O) x and the hydration water number in the first coordination sphere decreases with pH increasing. The formation of ≡COO−Eu−(O−Al≡)· 4H2O is observed on FA-alumina hybrids, suggesting the formation of strong inner-sphere surface complexes in the presence of FA. The surface complexes are also characterized by their emission spectra [the ratio of emission intensities of 5 D 0→7 F 1 ( λ =594 nm) and 5 D 0→7 F 2 ( λ =619 nm) transitions] and their fluorescence lifetime. The findings is important to understand the contribution of FA in the complexation properties of Eu(III) on FA-alumina hybrids that the clarification of the environmental behavior of humic substances is necessary to understand fully the behavior of Eu(III), or its analogue trivalent lanthanide and actinide ions in natural environment.

Understanding the rate and extent of 63Ni(II) sorption and desorption on/from mineral surfaces are important to predict its mobility performance in the natural environment. We herein systematically investigated the effects of pH, electrolyte cations, humic acid (HA) and temperature on 63Ni(II) sorption/desorption on/from Na-montmorillonite. The results indicated that the sorption/desorption of 63Ni(II) on/from Na-montmorillonite were strongly dependent on pH and electrolyte cations. Desorption abilities of 63Ni(II) were Na+ ≈ K+ > Ca2+ ≈ Mg2+ at the cationic concentration of 0.2 mol/L, which was associated with the clay tactoid size. The kinetic results suggested that 63Ni(II) sorption/desorption initially increased rapidly and remained constant as time increasing. The presence of HA influenced 63Ni(II) sorption clearly and promoted 63Ni(II) desorption as a result of the dissolution of ternary surface complexes. Increasing temperature was favorable for the sorption reaction owing to the formation of strong inner-sphere complexes, however, hampered the desorption reaction because of the increased stability of inner-sphere complexes or the aggregation of montmorillonite. The results are crucial to understand the physicochemical behavior of radionickel in the natural environment.

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 6.0, indicating that the outer-sphere surface complexation dominated the radionuclide adsorption 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...

The competitive sorption of Pb(II), Cu(II) and Ni(II) on the uniform carbonaceous nanofibers (CNFs) was investigated in binary/ternary-metal systems. The pH-dependent sorption of Pb(II), Cu(II) and Ni(II) on CNFs was independent of ionic strength, indicating that inner-sphere surface complexation dominated sorption Pb(II), Cu(II) and Ni(II) on CNFs. The maximum sorption capacities of Pb(II), Cu(II) and Ni(II) on CNFs in single-metal systems at a pH 5.5 ± 0.2 and 25 ± 1 °C were 3.84 (795.65 mg/g), 3.21 (204.00 mg/g) and 2.67 (156.70 mg/g) mmol/g, respectively. In equimolar binary/ternary-metal systems, Pb(II) exhibited greater inhibition of the sorption of Cu(II) and Ni(II), demonstrating the stronger affinity of CNFs for Pb(II). The competitive sorption of heavy metals in ternary-metal systems was predicted quite well by surface complexation modeling derived from single-metal data. According to FTIR, XPS and EXAFS analyses, Pb(II), Cu(II) and Ni(II) were specifically adsorbed on CNFs via covalent bonding. These observations should provide an essential start in simultaneous removal of multiple heavy metals from aquatic environments by CNFs, and open the doorways for the application of CNFs.

The Mg/Al layered double hydroxides (Mg/Al-LDH) as well as Ca/Al-LDH were successfully synthesized by a facile co-precipitation method and were applied as adsorbents for the efficient elimination of graphene oxide (GO) from aqueous solutions. Experimental data showed that the temperature and ionic strength did not play significant role in GO removal. The interaction of GO with Mg/Al-LDH and Ca/Al-LDH achieved interaction equilibrium in less than 1 h. The removal mechanism of GO on Mg/Al-LDH and Ca/Al-LDH could be explained by electrostatic attraction and bridging function between the two materials, and the removal capabilities were Ca/Al-LDH > Mg/Al-LDH. Based on the experimental results, the Ca/Al-LDH could be a very promising material for efficient elimination of GO from aqueous solutions. Results from this study provided critical information for the transport and potential fate of GO in natural environment.

The competitive sorption of As(V) and Cr(VI) on the novel and uniform carbonaceous nanofibers (CNFs) was investigated in single/binary-metal systems. The presence of Cr(VI) showed a greater inhibitory effect on the sorption of As(V) in binary As–Cr system, especially at higher Cr(VI) concentrations. The maximum sorption capacities of Cr(VI) and As(V) on CNFs in single-metal systems at pH 5.0 and 303 K were calculated as 2.36 and 0.67 mmol/g, respectively, by Langmuir equation. XPS results demonstrated that only As(V) species was present at the CNFs surface, whereas both Cr(VI) and Cr(III) species existed on the CNFs surfaces, suggesting the partially reduction of Cr(VI) to Cr(III) by CNFs. According to the macroscopic and spectroscopic analysis, both inner-sphere and outer-sphere surface complexation contributed to the sorption process of Cr(VI), in contrast to the electrostatic outer-sphere sorption of As(V) on CNFs. The inner-sphere Cr complexes might arise from the covalent bonding between Cr(III) and oxygen-containing functional groups of CNFs. The findings herein highlight the higher chemical affinity of CNFs for Cr(VI) relative to As(V), as a consequence of the redox reaction of the strongly toxic Cr(VI) with CNFs.

The effect of Bacillus subtilis ( B. subtilis ) on the adsorption of U(VI) onto sericite was investigated using batch, EXAFS and modeling techniques. The batch adsorption indicated that the increased adsorption of U(VI) on sericite + B. subtilis systems at pH B. subtilis , whereas the inhibited adsorption was observed at pH > 6.0 due to the combination of deprotonated carboxyl groups of B. subtilis with the hydroxyl of sericite. The slightly enhanced adsorption of U(VI) on sericite + B. subtilis with increasing CO 2 contents at pH 2 2+ species) and negatively charged surface of sericite + B. subtilis , whereas the U(VI) adsorption sharply decreased at pH > 7.0 owing to electrostatic repulsion between negatively charged sericite + B. subtilis and negatively charged U(VI) species such as UO 2 (OH) 3 − or UO 2 (CO 3 ) 2 2 − species. According to EXAFS analysis, the increased adsorption mechanism of U(VI) on sericite + B. subtilis at pH 4.0 was attributed to the formation of U–P shell, whereas the bidentate inner-sphere surface complexes was also observed at pH 7.0 due to the formation of U–C shell (2.92 A) and/or U–Si/Al (3.18 A) shell. Under the range of allowable error, the pH-dependent and isothermal adsorption of U(VI) on sericite + B. subtilis can be fitted by surface complexation modeling using ion exchange and surface complexation reaction by using equilibrium parameters obtained from each binary systems. These findings are important to understand the fate and transport of U(VI) on the mineral–bacteria ternary systems in the near-surface environment.

Ozone was used to oxidize graphene oxides (GO) to generate ozonated graphene oxides (OGO) with higher oxygen-containing functional groups. The as-prepared OGO was characterized by Fourier transformed infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Based on the results of potentiometric acid-base titrations, the total carboxylic acid concentration on OGO surface was calculated to be 3.92 mmol/g, which was much higher than that on GO surface. The results of adsorption experiments indicated that the adsorption capacities of OGO for Sr(II) and U(VI) removal were improved significantly after ozonization.

To contribute to the comprehension of Eu(III) sorption properties in oxide-organic material systems, the influence of humic acid (HA) on Eu(III) sorption on bare and HA-bounded γ-Al2O3 is studied using batch experiments and time resolved laser fluorescence spectroscopy (TRLFS). The effect of pH and addition sequences of Eu(III)/HA/Al2O3 on Eu(III) sorption is carried out at different experimental conditions, and the results show that the sorption of Eu(III) is strongly dependent on pH and ionic strength. The sorption of Eu(III) is mainly dominated by ion exchange or outer-sphere surface complexation at low pH, and by inner-sphere surface complexation at high pH values. The presence of HA enhances Eu(III) sorption at low pH, but reduces Eu(III) sorption at high pH values. The addition sequences of Eu(III)/HA to alumina suspensions do not affect Eu(III) sorption, which is also evidenced by the TRLFS measurements. The surface complexes are characterized by their emission spectra [the ratio of emission intensities of 5 D 0 → 7 F 1 (λ = 594 nm) and 5 D 0 → 7 F 2 (λ = 619 nm) transitions] and their fluorescence lifetime. The TRLFS results show clearly that no effect of addition sequences on the sorption and speciation of Eu(III) in HA–Al2O3 hybrids after equilibration. These findings on the effect of humic substances in the complexation properties of Eu(III) indicate that the clarification of the environmental behavior of humic substances is necessary to understand the physicochemical properties of Eu(III), or its analog trivalent lanthanide and actinide ions in the natural environment.

The graphene oxides (GOs) have been studied extensively in multidisciplinary areas owing to their excellent physicochemical properties. The high theoretical surface areas and large amounts of oxygen-containing functional groups at the basal planes and the edge sites ensure their high sorption capacity for heavy metal ions and radionuclides from large volumes of aqueous solutions. Herein, the GOs were applied as adsorbents to remove U(VI) from aqueous solutions at different experimental conditions, and the results showed that the sorption of U(VI) on GOs was strongly dependent on pH and was not affected by ionic strength obviously. The sorption capacity of U(VI) on GOs is calculated to be 1330 mg/g at pH 4.5 and T = 20 °C, which is much higher than any other today’s materials. The interaction mechanism of U(VI) on GOs was simulated by the computational DFT calculations, and the results evidenced that the variation in pH values led to significant changes in the circumstance of functional groups on GOs. As the pH value increased, the weak physical sorption/outer-sphere surface complexation between the GOs and U(VI) at low pH turned into strong chemical sorption/inner-sphere surface complexation with the negative charged –O− or –COO− groups induced by the deprotonation of the functional groups at high pH.

The β-cyclodextrin grafted attapulgite/iron oxides were synthesized and applied for 152+154Eu(III) removal from aqueous solutions. The sorption of 152+154Eu(III) was strongly dependent on pH, and was affected by ionic strength obviously at low pH, and was not influenced by ionic strength at high pH. The sorption was mainly dominated by outer-sphere surface complexation at low pH, and by inner-sphere surface complexation at high pH. The sorption capacity (30.95 mg g−1) was much higher than those of some other materials. Considering the good sorption characteristic and high magnetic separation efficiency, the β-CD/magnetic attapulgite is a promising material for the preconcentration and separation of 152+154Eu(III) in radioactive wastewater treatment.

A novel β-cyclodextrin modified, multifunctional, layer-by-layer graphitic carbon nitride (g-C3N4/β-CD) was successfully synthesized and applied as an effective adsorbent for the removal of methyl orange (MO) and Pb(II) from aqueous solutions under various environmental conditions (e.g., solution pH, solid content, contact time and temperature). The kinetic results indicated that the adsorption was dominated by chemisorption, and the higher adsorption capacity of g-C3N4/β-CD was attributed to it having more oxygen-containing functional groups than g-C3N4. The Langmuir, Freundlich and Sips models were applied to simulate the adsorption isotherms of MO and Pb(II), and the results demonstrated that the adsorption of MO was attributed to multilayer adsorption, while the coverage adsorption of Pb(II) on the g-C3N4/β-CD was monolayer adsorption. The thermodynamic parameters showed that the adsorption of both MO and Pb(II) was spontaneous and endothermic. The DFT calculations further evidenced the surface complexation and electrostatic interaction of Pb(II) on the g-C3N4 and g-C3N4/β-CD, whereas, the interaction of MO with g-C3N4 and g-C3N4/β-CD was mainly attributed to hydrogen bonds and strong π–π interactions. The results demonstrated that g-C3N4/β-CD is a promising material for the efficient removal of organic and inorganic pollutants in environmental pollution remediation.

A magnetic nanocomposite of zero valent iron (ZVI)/poly(amidoxime) (PAO) was prepared by polymerization of acrylonitrile on the ZVI surface, followed by hydroxylamine (NH2OH) treatment to convert the cyano group (–CN) into an amidoxime group (AO). The characterization results showed that PAO-stabilized ZVI magnetic composite (denoted as ZVI/PAO) was prepared successfully. ZVI/PAO was used as an adsorbent for the separation of U(VI) from solutions. The effect of environmental conditions on U(VI) adsorption onto ZVI/PAO was studied in detail. U(VI) adsorption on the ZVI/PAO surface reached equilibrium within 3 h, and the adsorption process is well described by the pseudo-second-order kinetics model. Adsorption isotherms of U(VI) on the ZVI/PAO surface can be well fitted by the Langmuir model, and the maximum adsorption capacity was calculated to be 206 mg g−1 at T = 298 K and pH = 5.0. Experimental results highlighted the application of ZVI/PAO as an adsorbent for the efficient separation of U(VI) and reduction of U(VI) to U(IV) from aqueous solutions.

Potentially toxic metals and dyes commonly coexist in industrial wastewaters, posing a serious threat to public health and the environment and making the treatment more challenging. Herein, we report a novel magnetic polydopamine (PDA)–LDH (MPL) bifunctional material, which is fabricated by an easy and green approach for the simultaneous removal of potentially toxic metals and anionic dyes. In this assembly, both PDA and LDHs are expected to capture these pollutants. In a mono-component system, the removal behaviors showed heterogeneous removal capacities of 75.01, 624.89 and 584.56 mg g−1 for Cu(II), methyl orange (MO) and Congo red (CR), respectively. Interestingly, the presence of CR and MO enhanced the removal of Cu(II) significantly in the Cu(II)–dye binary system. However, the presence of Cu(II) had no significant effect on dyes. Based on the characterization results including X-ray diffraction (XRD) analysis, Fourier transformed infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS) and elemental mapping, the removal of Cu(II) was mainly controlled by bonding with surface functional groups (hydroxyl, catechol, imine and amine groups), coupled with isomorphic substitution and surface precipitation. In summary, such a green and facile synthesis method, efficient removal performance and superior reusability suggest that the MPL assemblies have practical application potential for integrative and efficient treatment of coexisting toxic pollutants.

With the widespread use of graphene oxide (GO), it is inevitable that part of GO is released into the environment and co-exist with heavy metal ions as contaminants and is likely to be co-adsorbed on minerals and oxides. This study, for the first time, demonstrates the individual and mutual removal mechanism of GO and Cu(II) on titanium dioxide (TiO2) by batch experiments, spectroscopic analysis and density functional theory (DFT) computations. Electrostatic interaction and hydrogen bonding are the dominant modes of GO sorption onto TiO2, and the interaction of Cu(II) with TiO2 is mainly dominated by inner-sphere surface complexation. The presence of Cu(II) enhances GO coagulation on TiO2 and vice versa. The experimental results are further verified by DFT sorption energy (Es) calculations in the order (TiO2–GO)–Cu > TiO2–GO for GO interaction and (TiO2–GO)–Cu > TiO2–Cu for Cu(II) interaction. The mutual interaction is favorable for the simultaneous removal of GO and heavy metal ions by surface complexation between Cu(II) and oxygen-containing functional groups. These findings might facilitate better understanding of the co-removal behavior of carbon nanomaterials and heavy metal ions on oxides, which is crucial to decreasing the environmental toxicity of pollutants in the natural environment.