Magnetite Nanoparticle Decorated Reduced Graphene Oxide Composite as an Efficient and Recoverable Adsorbent for the Removal of Cesium and Strontium Ions

Removal of cesium and strontium for radioactive wastewater by Prussian blue nanorods

In this work, novel Prussian blue tetragonal nanorods were prepared by template-free solvothermal methods to remove radionuclide Cs and Sr. The as-prepared Prussian blue nanorods were identified and characterized by scanning electron microscopy, transmission electron microscope, Fourier transform infrared spectroscopic, thermogravimetric analysis, zeta potential, and surface analysis, and its sorption performance was tested by batch experiments. Our results suggest that Prussian blue nanorods exhibited better adsorption performance than co-precipitation PB or Prussian blue analogue composites. Thermodynamic analysis implied that the adsorption process was spontaneous and endothermic which was described well with the Langmuir isotherm and pseudo-second-order equation. The maximum adsorption capacity of PB nanorod was estimated to be 194.26 mg g^-1 and 256.62 mg g^-1 for Cs⁺ and Sr²⁺(adsorbate concentration at 500 mg L^-1, the temperature at 298 k, pH at 7.0). Moreover, the experimental results showed that the Prussian blue nanorods have high crystallinity, few crystal defects, and good stability under alkaline conditions. The adsorption mechanism of Cs⁺ and Sr²⁺ was studied by X-ray photoelectron spectroscopy, X-ray diffraction, and ⁵⁷Fe Mössbauer spectroscopy. The results revealed that Cs⁺ entered the PB crystal to generate a new phase, and most of Sr²⁺ was trapped in the internal crystal and the other exchanged Fe²⁺. Furthermore, the effect of co-existing ions and pH on PB adsorption process was also investigated. The results suggest that PB nanorods were an outstanding candidate for removing Cs⁺ and Sr²⁺ from radioactive wastewater.

Unexpectedly efficient ion desorption of graphene-based materials

Ion desorption is extremely challenging for adsorbents with superior performance, and widely used conventional desorption methods involve high acid or base concentrations and large consumption of reagents. Here, we experimentally demonstrate the rapid and efficient desorption of ions on magnetite-graphene oxide (M-GO) by adding low amounts of Al³⁺. The corresponding concentration of Al³⁺ used is reduced by at least a factor 250 compared to conventional desorption method. The desorption rate reaches ~97.0% for the typical radioactive and bivalent ions Co²⁺, Mn²⁺, and Sr²⁺ within ~1 min. We achieve effective enrichment of radioactive ⁶⁰Co and reduce the volume of concentrated ⁶⁰Co solution by approximately 10 times compared to the initial solution. The M-GO can be recycled and reused easily without compromising its adsorption efficiency and magnetic performance, based on the unique hydration anionic species of Al³⁺ under alkaline conditions. Density functional theory calculations show that the interaction of graphene with Al³⁺ is stronger than with divalent ions, and that the adsorption probability of Al³⁺ is superior than that of Co²⁺, Mn²⁺, and Sr²⁺ ions. This suggests that the proposed method could be used to enrich a wider range of ions in the fields of energy, biology, environmental technology, and materials science.

A uniformly anchored zirconocene complex on magnetic reduced graphene oxide (rGO@Fe3O4/ZrCp2Cl x (x = 0, 1, 2)) as a novel and reusable nanocatalyst for synthesis of N-arylacetamides and reductive-acetylation of nitroarenes

In this study, a crafted zirconocene complex on rGO@Fe3O4 as a novel magnetic nanocatalyst was synthesized and then characterized using FT-IR, SEM, EDX, VSM, ICP-OES, TGA, BET and MS analyses. Next, catalytic activity of the prepared nanocomposite rGO@Fe3O4/ZrCp2Cl x (x = 0, 1, 2) towards successful reduction of aromatic nitro compounds to arylamines using N2H4·H2O (80%) was investigated. The examined nanocatalyst also showed perfect catalytic activity for reductive-acetylation of aromatic nitro compounds to the corresponding N-arylacetamides without isolation of the prepared in situ amines using the N2H4·H2O/Ac2O system. Furthermore, acetylation of the commercially available arylamines to the corresponding N-arylacetamides was carried out by acetic anhydride in the presence of the rGO@Fe3O4/ZrCp2Cl x (x = 0, 1, 2) nanocomposite. All reactions were carried out in refluxing EtOH as a green solvent to afford the products in high yields. The obtained results exhibited that the nanocomposite of rGO@Fe3O4/ZrCp2Cl x (x = 0, 1, 2) showed a great catalytic activity in comparison to rGO and rGO@Fe3O4 as the parent constituents. Recovery and reusability of rGO@Fe3O4/ZrCp2Cl x (x = 0, 1, 2) were also examined for 8 consecutive cycles without significant loss of the catalytic activity. This establishes the sustainable anchoring of the zirconocene complex on the surface and mesopores of the rGO@Fe3O4 nanohybrid system.

Magnetic Adsorbents for Wastewater Treatment: Advancements in Their Synthesis Methods

The remediation of water streams, polluted by various substances, is important for realizing a sustainable future. Magnetic adsorbents are promising materials for wastewater treatment. Although numerous techniques have been developed for the preparation of magnetic adsorbents, with effective adsorption performance, reviews that focus on the synthesis methods of magnetic adsorbents for wastewater treatment and their material structures have not been reported. In this review, advancements in the synthesis methods of magnetic adsorbents for the removal of substances from water streams has been comprehensively summarized and discussed. Generally, the synthesis methods are categorized into five groups, as follows: direct use of magnetic particles as adsorbents, attachment of pre-prepared adsorbents and pre-prepared magnetic particles, synthesis of magnetic particles on pre-prepared adsorbents, synthesis of adsorbents on preprepared magnetic particles, and co-synthesis of adsorbents and magnetic particles. The main improvements in the advanced methods involved making the conventional synthesis a less energy intensive, more efficient, and simpler process, while maintaining or increasing the adsorption performance. The key challenges, such as the enhancement of the adsorption performance of materials and the design of sophisticated material structures, are discussed as well.

Enhanced phosphate remediation of contaminated natural water by magnetic zeolitic imidazolate framework-8@engineering nanomaterials (ZIF8@ENMs)

The efficient enrichment and reutilization of phosphate from natural water still remains a daunting challenge to satisfy the increasingly stringent phosphate discharge criteria. In response to this problem, the presented study successfully synthesizes a series of magnetic zeolitic imidazolate framework-8@engineering nanomaterials (ZIF8@ENMs) via a two-step hydrothermal and coprecipitation method by facilely growing ZIF8 and/or Fe₃O₄ on various functional ENMs. Structure morphology, chemical composition and hysteresis curve characterizations demonstrate the successful formation of magnetic Fe₃O₄-ZIF8@ENM. Amongst the prepared magnetic ZIF8@ENMs hybrids, the Fe₃O₄-ZIF8@ENMs possessing massive hydroxyl groups is demonstrated to harvest the maximum adsorption capacity of 441.7 mg g^-1 under neutral condition. Such-acquired adsorption capacity evidently surpass state-of-the-art adsorbents. Systematic assessment of the chemical condition effects on phosphate removal, revealing its conspicuous merits of robust pH independence (94.63-98.20%), high selectivity pinpointing phosphate within complex cations, ease-of-separation and satisfactory recycle. The outstanding performance of magnetic ZIF8@ENMs are mainly derived from the formed strong ZnOP, FeOP and electrostatic interactions between phosphate and adsorbents. Along this line, designing magnetic MOFs-based hybrids towards phosphate are anticipated to be promising avenues for advanced treatment of phosphate-like contaminants and efficient recycle in practical applications.

Surface modified and functionalized graphene oxide membranes for separation of strontium from aqueous solutions

Graphene oxide-strontium (GO-Sr) composites prepared under different ambient conditions were characterized using morphological and spectroscopic techniques to optimize the uptake of Sr from aqueous solutions. These studies indicated that interactions among GO and Sr²⁺ ions are highly sensitive to size and aging of GO sheets, as well as pH of the ambience. Further, the extent of Sr uptake on GO sheets was found to be largely influenced by relative fractions of the associated -COOH, -OH, C-O-C functional groups and sp²-C domains. Membranes prepared using various forms of GO were evaluated for their Sr separation ability and, a window of parameters for optimum separation of Sr has been proposed. Among the variety of membranes studied, those made up of fresh and large GO sheets were found to exhibit superior Sr adsorption capacity (~296 mg/g) at limited GO mass. Further, adsorption efficiency of these GO membranes was observed to deteriorate with aging of GO sheets and rise of GO mass on membrane. The membrane based filtration procedure introduced in present work facilitates to provide a lamellar structure of GO sheets with abundant surface area, diverse and accessible sites for Sr²⁺ ion uptake and offer high Sr adsorption efficiencies.

Isotherm and Kinetic Modeling of Strontium Adsorption on Graphene Oxide

In this study, graphene oxide (GO) was synthesized using Hummers method. The synthesized GO was characterized using field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), Fourier transformed infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and Brunauer–Emmett–Teller (BET) nitrogen adsorption. The analyses confirmed the presence of oxygen functional groups (C=O and C-O-C) on the GO surface. These oxygen functional groups act as active sites in the adsorption Sr (II). The BET analysis revealed the surface area of GO of 232 m²/g with a pore volume of 0.40 cm³/g. The synthesized GO was used as an adsorbent for removing Sr (II) from aqueous solutions. The adsorption equilibrium and kinetic results were consistent with the Langmuir isotherm model and the pseudo-second-order kinetic model. A maximum strontium adsorption capacity of 131.4 mg/g was achieved. The results show that the GO has an excellent adsorption capability for removing Sr (II) from aqueous solutions and potential use in wastewater treatment applications.

Adsorptive removal of Sr(II) from aqueous solution by polyvinyl alcohol/graphene oxide aerogel

In this study, a new adsorbent, polyvinyl alcohol (PVA) and graphene oxide (GO), was prepared, characterized and used for the removal of Sr²⁺ from aqueous solution. In PVA/GO composite, the inter-lamellar spacing of adjacent GO layers was dramatically enlarged due to the intercalation of PVA molecules, such a unique architecture significantly mitigated the aggregation of GO layers, which facilitated the accessible exposure of active sites and the mass transfer of strontium ions (Sr²⁺), thus enhancing the adsorption capacity toward Sr²⁺. The adsorption of Sr²⁺ by PVA/GO composite conformed to the pseudo second-order kinetic model (R² = 0.9994), the Langmuir model (R² = 0.9042), and the Freundlich model (R² = 0.9598). The complexation interaction between Sr²⁺ and oxygen atoms/π-electron domain of PVA/GO composite was primarily responsible for the adsorption mechanism, based on the characterization results of X-ray photoelectron spectroscopy (XPS), scanning electron microscope equipped with energy dispersion spectroscopy (SEM-EDS) and powder X-ray diffraction (PXRD).

Mechanism of Cd(II) and Cu(II) Adsorption onto Few-Layered Magnetic Graphene Oxide as an Efficient Adsorbent

Heavy metal contamination caused by industrial discharge is a challenging environmental issue. Herein, an efficient adsorbent based on few-layered magnetic graphene oxide (FLMGO) was fabricated, characterized, and utilized to remove aqueous Cd(II) and Cu(II). Results present that the two components graphene oxide (GO) and Fe₃O₄ of FLMGO promote mutually, enabling FLMGO to outperform either GO or Fe₃O₄. Specifically, FLMGO adsorbs Cd(II) and Cu(II) with adsorption quantities of 401.14 and 1114.22 mg·g^-1 in 5 and 7 min, respectively. Moreover, FLMGO can be readily recovered via magnetic separation using a hand-held magnet. Adsorptions are spontaneous, endothermic, and entropy increasing, which are the best described by the Freundlich and pseudo-second-order model. The interaction mechanism is as follows: lone pair electrons in C=O- and C-O-related groups were coordinated toward Cd(II) and Cu(II) to induce chemical interaction. The high adsorption efficiency endows FLMGO with encouraging application potential in heavy metal remediation.

Efficient removal of Co(II) and Sr(II) from aqueous solution using polyvinyl alcohol/graphene oxide/MnO2 composite as a novel adsorbent

In this study, a novel adsorbent, polyvinyl alcohol/graphene oxide/MnO₂ composite was prepared, characterized and used for efficient removal of Co²⁺ and Sr²⁺ from aqueous solution. Polyvinyl alcohol (PVA) and Mn²⁺ played a synergistic role in the gelation of PVA/GO/Mn²⁺, while Mn²⁺ can be further converted into oxide to achieve functionalized aerogel (PVA/GO/MnO₂). The spectroscopy analysis manifested that hydrogen bonds and electrostatic attraction were responsible for the formation of PVA/GO/MnO₂. The functionalization of MnO₂ enhanced the adsorption capacity for Co²⁺ (2.1 folds) and Sr²⁺ (1.3 folds) by PVA/GO/MnO₂. The composite showed high adsorption capacity at broad pH range of 4.0-9.0. For competitive adsorption test, Ni²⁺/Zn²⁺ exerted the most interfering effect on Co²⁺ adsorption, while Mg²⁺/Ca²⁺ showed severe interfering effect on Sr²⁺ adsorption. Both electrostatic attraction and oxygen-containing groups contributed to the adsorption mechanism. This study may provide a new adsorbent for separation of Co²⁺ and Sr²⁺ from aqueous solution.

Selective adsorption of cesium (I) from water by Prussian blue analogues anchored on 3D reduced graphene oxide aerogel

In this paper, Prussian blue analogues (PBAs) anchored on 3D reduced graphene aerogel (denoted as 3D rGO/PBAs) was prepared, characterized and applied for adsorption of Cs(I) from aqueous solution. The results showed that 3D rGO/PBAs had high specific surface and good hydrophilic property, which was beneficial to the exposure of adsorptive sites and the transfer of adsorbates. The composite exhibited excellent adsorption performance towards Cs(I), and the maximum adsorption capacity was up to 204.9 mg/g, higher than most of reported values. The pseudo second-order kinetic model (R² = 0.999) and the Langmuir isotherm model (R² = 0.997) could fit the adsorption process well, suggesting the nature of homogeneous monolayer chemisorption. High distribution coefficients (k_d) (2.8 × 10⁴ to 5.8 × 10⁴ mL/g), revealed that the composite had good selectivity. Ion-exchange, ion trapping and the complexation interaction might be involved in the process of cesium adsorption, in which ion-exchange may be dominant by characterization results.

Combined use of tannic acid-type organic composite adsorbents and ozone for simultaneous removal of various kinds of radionuclides in river water

Tannic acid-type organic composite adsorbents (PA316TAS, AR-01TAS, PYRTAS, WA10TAS, WA20TAS, and WA30TAS), combined with hydrolyzed and sulfonated tannic acid (TAS) and porous-type strongly basic anion-exchange resin (PA316), benzimidazole-type anion-exchange resin embedded in high-porous silica beads (AR-01), pyridine-type anion-exchange resin (PYR), acrylic-type weakly basic anion-exchange resin (WA10), or styrene-type weakly basic anion-exchange resins (WA20 and WA30) for simultaneous removal of various kinds of radionuclides in river water were successfully synthesized. The adsorption behavior of twelve kinds of simulated radionuclides (Mn, Co, Sr, Y, Ru, Rh, Sb, Te, Cs, Ba, Eu, and I (I^- and IO₃^-)) on these composite adsorbents has been studied in real river water at room temperature. PA316TAS adsorbents showed much higher distribution coefficients (K_d) for all metal ions. TAS structure has more selective adsorption ability for Mn, Co, Sr, Y, Cs, Ba, Eu, and IO₃^-. On the other hand, Y, Ru, Rh, Sb, Te, Eu, I (I^- and IO₃^-) were adsorbed on both PA316 and TAS structures. To evaluate the validity of these mechanistic expectations, the respective chemical adsorption behaviors of Mn, Co, Sr, etc. and PA316TAS adsorbent were examined in river water ranging in temperature from 278 to 333 K. As was expected, one adsorption mechanism for Mn, Co, Sr, Cs, and Ba systems and two types of adsorption mechanisms for Y, Ru, Rh, Sb, Te, Eu, I (I^- and IO₃^-) systems were observed. On the other hand, the precipitation of Mn, Co, Y, Ru, Rh, Te, and Eu was formed by ozonation for river water, that is, ozone can transform Mn, Co, Y, Ru, Rh, Te, and Eu ions into the insoluble precipitates. Hence, one straight line for Sr, Cs, Ba systems and two types of straight lines for Sb, I (I^- and IO₃^-) systems were obtained in river water treated with ozone. The chromatography experiments of Cs, Sr, I (I^- and IO₃^-) were carried out to calculate their maximum adsorption capacities. The obtained maximum adsorption capacities of Cs, Sr, and I^- mixed with IO₃^- were 1.7 × 10^-4 (Cs), 1.8 × 10^-3 (Cs/O₃), 7.8 × 10^-5 (Sr), 5.6 × 10^-4 (Sr/O₃), 5.4 × 10^-2 (I^- and IO₃^-), 3.1 × 10^-2 (I^- and IO₃^-/O₃) mol/g - PA316TAS. It was discovered that the maximum adsorption capacities of I^- and IO₃^- for the composite adsorbent is unprecedented high and the capacity become much greater than an order of magnitude, compared with those of previous reports. This phenomenon suggests the formation of electron-donor-acceptor (EDA) complexes or pseudo EDA complex. Based on these results, it was concluded that the combined use of tannic acid-type organic composite adsorbents and ozone made it possible to remove simultaneously and effectively various kinds of radionuclides in river water in the wide pH and temperature ranges.

Efficacy and Molecular Effects of a Reduced Graphene Oxide/Fe3O4 Nanocomposite in Photothermal Therapy Against Cancer

PURPOSE

Expanded research on the biomedical applications of graphene has shown promising results, although interactions between cells and graphene are still unclear. The current study aims to dissect the cellular and molecular effects of graphene nanocomposite in photothermal therapy against cancer, and to evaluate its efficacy.

METHODS

In this study, a reduced graphene oxide and iron oxide (rGO-Fe3O4) nanocomposite was obtained by chemical synthesis. The nanocomposite was fully characterized by Raman spectroscopy, TEM, VSM and thermal profiling. Cell-nanocomposite interaction was evaluated by confocal microscopy and viability assays on cancer cell line HeLa. The efficacy of the thermal therapy and changes in gene expression of Bcl-2 and Hsp70 was assessed.

RESULTS

The resulting rGO-Fe3O4 nanocomposite exhibited superparamagnetic properties and the capacity to increase the surrounding temperature by 18-20°C with respect to the initial temperature. The studies of cell-nanocomposite interaction showed that rGO-Fe3O4 attaches to cell membrane but there is a range of concentration at which the nanomaterial preserves cell viability. Photothermal therapy reduced cell viability to 32.6% and 23.7% with 50 and 100 µg/mL of nanomaterial, respectively. The effect of treatment on the molecular mechanism of cell death demonstrated an overexpression of anti-apoptotic proteins Hsp70 and Bcl-2 as an initial response to the therapy and depending on the aggressiveness of the treatment.

CONCLUSION

The results of this study contribute to understanding the interactions between cell and graphene and support its application in photothermal therapy against cancer due to its promising results.

Effect of rGO loading on Fe3O4: A visible light assisted catalyst material for carbamazepine degradation

Carbamazepine (CBZ), an anticonvulsant drug, is one of the most recalcitrant pharmaceuticals detected in wastewater. For the photocatalytic degradation of CBZ, visible light assisted heterogeneous Fenton-like hybrid composites were synthesized via a co-precipitation method by anchoring magnetite (Fe₃O₄) with reduced graphene oxide (rGO). The rGO loading not only reduced the aggregation of Fe₃O₄ nanoparticles, but also increased the adsorption capacity of the hybrid composites. The mass ratio of rGO in the composites substantially affected CBZ photocatalytic degradation and a 10 wt% rGO loading (rGF10) provided nearly complete CBZ degradation within 3 h. Moreover, the addition of rGO reduced the charge recombination of the bare Fe₃O₄ nanoparticles and provided more accessible reactive sites, enhancing the degradation capacity. The visible light excited Fe₃O₄ nanoparticles yielded reactive species such as hydroxyl radicals (·OH), holes (h⁺), and superoxide radicals (O₂·^-) during the photodegradation process that were evaluated by using specific scavengers during the degradation experiment. The hybrid catalyst was effective under wide pH ranges (from 3 to 9) and showed faster degradation rates in the acidic condition. The composites were magnetically separable, easily regenerated, and exhibited considerably high photocatalytic activity up to five cycles.