Preparation of halloysite@graphene oxide composite and its application for high-efficient decontamination of U(VI) from aqueous solution

Construction of 3D-Printed Sodium Alginate/Chitosan/Halloysite Nanotube Composites as Adsorbents of Methylene Blue

In this study, sodium alginate/chitosan/halloysite nanotube composites were prepared by three-dimensional printing and characterized in terms of morphology, viscosity, thermal properties, and methylene blue (MB) adsorption performance. The high specific surface area and extensively microporous structure of these composites allowed for effective MB removal from wastewater; specifically, a removal efficiency of 80% was obtained after a 60 min treatment at an adsorbent loading of 1 g L-1 and an MB concentration of 80 mg L-1, while the maximum MB adsorption capacity equaled 376.3 mg g-1. Adsorption kinetics and isotherms were well described by quasi-second-order and Langmuir models, respectively. The composites largely retained their adsorption performance after five adsorption-desorption cycles and were concluded to hold great promise for MB removal from wastewater.

Study on uranium ion adsorption property of porous glass modified with amidoxime group

In this paper, we prepared three types of porous glasses (PGs) with specific surface areas of 311.60 m2/g, 277.60 m2/g, and 231.38 m2/g, respectively, via borosilicate glass phase separation. These glasses were further modified with amidoxime groups (AO) using the hydroxylamine method, yielding adsorbents named 1.5-PG-AO, 2-PG-AO, and 3-PG-AO. The adsorption performance of these adsorbents under various conditions was investigated, including sorption kinetics and adsorption mechanisms. The results reveal that the number of micropores and specific surface area of PG are significantly reduced after AO modification. All three adsorbents exhibit similar adsorption capabilities. Particularly, pH has a pronounced effect on U (VI) adsorption of PG-AO, with a maximum value at pH = 4.5. Equilibrium adsorption is achieved within 2 h, with a maximum adsorption capacity of 129 mg/g. Notably, a uranium removal rate of 99.94% is attained. Furthermore, the adsorbents show high selectivity in uranium solutions containing Na+ or K+. Moreover, the adsorbents demonstrate exceptional regeneration ability, with the removal rate remaining above 80% even after undergoing five adsorption-desorption cycles. The adsorption reaction of uranium on PG-AO involves a combination of multiple processes, with monolayer chemisorption being the dominant mechanism. Both the complex adsorption of AO and the ion exchange and physical adsorption of PG contribute to the adsorption of uranyl ions on the PG-AO adsorbents.

Phosphorylation improved the competitive U/V adsorption on chitosan-based adsorbent containing amidoxime for rapid uranium extraction from seawater

A novel chitosan-based porous composite adsorbent with multifunctional groups, such as phosphoric acid, amidoxime, and quaternary ammonium groups, was prepared to improve the adsorption rate and competitive uranium‑vanadium adsorption of amidoxime group adsorbents. The maximum uranium adsorption capacity of PACNC was 962.226 mg g^-1 at 308 K and pH = 7. The maximum adsorption rate constant of PACNC for uranium was 2.83E-2 g mg^-1 min^-1, which is 2.38 times that of ACNC (1.19E-2 g mg^-1 min^-1). Moreover, the adsorption equilibrium time was shortened from 300 (ACNC) to 50 (PACNC) min. In simulated and real seawater, the K_d and adsorption capacity of PACNC for uranium were approximately 8 and 6.62 times those for vanadium, respectively. These results suggest that phosphorylation significantly improved the competitive adsorption of uranium‑vanadium and uranium adsorption rate. PACNC also exhibited good recycling performance and maintained stable adsorption capacity after five cycles. DFT calculations were used to analyze and calculate the possible co-complex structure of PACNC and uranium. The binding structure of phosphate and amidoxime is the most stable, and its synergistic effect effectively improves the competitive adsorption of uranium-vanadium of amidoxime. All the results demonstrated that PACNC has substantial application potential for uranium extraction from seawater.

Efficient extraction of U(VI) from uranium enrichment process wastewater by amine-aminophosphonate-modified polyacrylonitrile fibers

The enrichment and recovery of U(VI) from low-level radioactive wastewater in the process of uranium enrichment is important for the sustainable development of nuclear energy and environmental protection. Herein, a novel amine-aminophosphonate bifunctionalized polyacrylonitrile fiber (AAP-PAN), was prepared for the extraction of U(VI) from simulated and real uranium-containing process wastewater. The AAP-PAN fiber demonstrated a maximum adsorption capacity of 313.6 mg g^-1 at pH = 6.0 and 318 K in the batch experiments. During the dynamic column experiment, over 99.99% removal of U(VI) could be achieved by the fiber using multi-ion simulated solution and real wastewater with an excellent saturation adsorption capacity of 132.0 mg g^-1 and 72.5 mg g^-1, respectively. It also exhibited an outstanding reusability for at least 5 cycles of adsorption process. The mechanism for U(VI) removal was studied by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analysis in the assist of simulation calculation. It suggested that the amine and aminophosphonate groups can easily bind uranyl ions due to U(VI) is more likely to combine with oxygen atoms of CO and PO, respectively.

Bioapplication of cyclodextrin-containing montmorillonite

Recent progresses in the integration of CDs and montmorillonite, as well as applications of CD-containing montmorillonite hybrid host systems are summarized in this review. Several efficient synthesis strategies, such as ion exchange, metal coordination, supramolecular strategies, polymerizations and organic synthesis methods, have been discussed during the preparation of CDs/montmorillonite hybrid composites. In particular, diverse instrumental techniques were highly recommended for characterizing the as-obtained hybrid systems, including their chemical composition and structures, crystallinity, surface/self-assembled morphologies, as well as other particular physiochemical properties, providing a direct guide for promoting the desired structures and exploring various applications. It should be noted that the introduction of functional groups, as well as the integration of CDs and montmorillonite granted the thus obtained CD-containing montmorillonite hybrid host systems a lot of unique features, providing great opportunities for expanding the practical applications to a series of biological and environmental areas, such as biosensors, sorption and decontamination of bio/environmental hazardous materials, biostudies about aqueous dispersity, stability and biocompatibility, drug loading and target delivery, controlled and sustained drug release, as well as antibacterial.

Amidoximated wooden solar evaporator for high-efficiency nuclear wastewater treatment

The efficient removal of uranium (VI) (UO₂²⁺) is of great significance to the ecological environment. However, there is still a lack of efficient adsorption materials to remove UO₂²⁺ in wastewater economically. Because natural basswood has high porosity, natural hydrophilicity, and abundant surface functional groups, wood as a support material has a good application prospect in water treatment. In the present work, the amidoxime functional group (AO) is grafted to the hydroxyl group of the wood fiber (AO-wood). A carbon layer is formed on the surface of the basswood by heating, and some Ag nanoparticles with good optothermal effect are added to the wood tunnel (Ag-C-AO-wood). Ag-C-AO-wood is used for efficient wastewater treatment under light conditions. The adsorption kinetic of Ag-C-AO-wood is 4.6 h under one irradiation, which is 7 times faster than AO-wood. It has approached or even surpassed some traditional carbon materials with stirring. This method is expected to break the traditional stirring method. Ag-C-AO-wood can not only remove uranium up to 82% but also have a good removal efficiency (27%) on iodide ions. More importantly, due to basswood characteristics, it is possible to large-scale preparation and explore its potential application value in wastewater.

High-Capacity Amidoxime-Functionalized β-Cyclodextrin/Graphene Aerogel for Selective Uranium Capture

Uranium extraction from seawater is a grand challenge of mounting severity as the energy demand increases with a growing global population. An amidoxime-functionalized carboxymethyl β-cyclodextrin/graphene aerogel (GDC) is developed for highly efficient and selective uranium extraction via a facile one-pot hydrothermal process. GDC reaches equilibrium in 1 h, and the maximum adsorption capacity calculated from Langmuir model is 654.2 mg/g. Benefiting from the chelation and complexation reaction, the obtained GDC has an excellent selectivity even when the competitive cations, anions, and oil pollutants exist. In addition, the aerogel possesses great mechanical integrity and remains intact after 10 compression cycles. Meanwhile, the GDC can be easily regenerated and maintains a high reusability of 87.3% after 10 adsorption-desorption cycles. It is worthwhile to mention that GDC exhibits an excellent extraction capacity of 19.7 mg/g within 21 days in natural seawater, which is greatly desired in uranium extraction from seawater.

Nano-sized architectural design of multi-activity graphene oxide (GO) by chemical post-decoration for efficient uranium(VI) extraction

The introduction of organic groups onto graphene oxide (GO) platelets can supply additional active sites for adsorption of uranium(VI) (U(VI)) to improve the adsorption capacity. However, as a result of the existence of stabilizing π-conjugation system, a facile and effective modification method remains a challenge. Therefore, a novel strategy is exploited by nano-sized architectural design of multi-activity GO through post-decoration with amidoxime functionalized diaminomaleonitrile (DM-AO). The post-modification of DM-AO successfully activated the inert sites in GO platelets. Meanwhile, the amidoxime group in DM-AO can improve the adsorption selectivity. Adsorption amount of U(VI) on the as prepared GO-DM-AO reached at 935 mg g^-1, which is increased by 209% increment compared with that of pristine GO at the same concentration. The adsorption efficiency of GO-DM-AO is greatly improved, and the time to reach the adsorption equilibrium is half of that of GO. Excitingly, the excellent removal efficiency could still maintained even after 5 cycles of adsorption-desorption. The outstanding adsorption amount, short adsorption equilibrium time, and excellent removal efficiency can provide a theoretical guidance for further immobilization of U(VI) from seawater.

Preparation, Characterization and Adsorption Potential of Grainy Halloysite-CNT Composites for Anthracene Removal from Aqueous Solution

Grainy Hal-CNT composites were prepared from powder halloysite nanoclay (Hal) and carbon nanotubes (CNTs). The effect of the amount and type of CNTs, as well as calcination temperature on morphology and properties of Hal-CNT composites and their adsorption capacity of anthracene (ANT), were studied. The surface topography of granules was heterogenous, with cracks and channels created during granulation of powder clay and CNTs. In FTIR, spectra were exhibited only in the bands arising from halloysite, due to its dominance in the granules. The increase in the heating temperature to 550 °C resulted in mesoporosity/macroporosity of the granules, the lowest specific surface area (SSA) and poorest adsorption potential. Overall, SSA of all Hal-CNT composites were higher than raw Hal, and by itself, heated halloysite. The larger amount of CNTs enhanced adsorption kinetics due to the more external adsorption sites. The equilibrium was established with the contact time of approximately 30 min for the sample Hal-SWCNT 85:15, while the samples with loading 96:4, it was 60–90 min. Adsorption isotherms for ANT showed L1 type, which is representative for the sorbents with limited adsorption capacity. The Langmuir model described the adsorption process, suggesting a monolayer covering. The sample Hal-SWCNT 85:15 exhibited the highest adsorption capacity of ANT, due to its highest SSA and microporous character.

Synthesis of Mesoporous/Macroporous Microparticles Using Three-Dimensional Assembly of Chitosan-Functionalized Halloysite Nanotubes and Their Performance in the Adsorptive Removal of Oil Droplets from Water

Halloysite nanotubes (HNTs) were assembled into mesoporous/macroporous microparticles (c-g-HNTs MPs) using Pickering template-assisted approach. To unravel the stabilization mechanism in Pickering emulsion form, several emulsions and microparticles were prepared at various conditions and visualized using confocal laser scanning microscopy. The prepared c-g-HNTs MPs were used to treat emulsified oil solutions resulting in a maximum removal efficiency of 94.47%. The kinetics data of oil adsorption onto c-g-HNTs MPs was best fitted by the pseudo-second-order kinetic model ( R² = 0.9983). The maximum monolayer adsorption capacity of oil onto c-g-HNTs MPs as predicted by the multilayer Brunauer-Emmett-Teller model was found to be 788 mg/g. Compared with pristine HNTs, c-g-HNTs MPs exhibited higher self-settleability rates in aqueous solutions as well as in emulsified oil solutions, demonstrating their candidacy for practical water treatment applications. The c-g-HNTs MPs were repeatedly used for five adsorption-desorption cycles with minimal losses noticed in their performance.

Efficiency and mechanism of adsorption of low concentration uranium in water by extracellular polymeric substances

Extracellular polymeric substances (EPS) of uranium adsorbent was first extracted from the aerobic activated sludge of municipal wastewater treatment plant as raw material. The structure and surface morphology of EPS was characterized by FTIR, SEM-EDX, 3D-EEM, and XPS. The 3D-EEM spectra of EPS revealed that there are Tryptophan-like protein and Humus which can adsorb uranium in the EPS. The results of XPS indicated that the EPS surface contained active functional groups (COOH,CONH₂,-H₂PO₄,OH,NH₂ and so on) which all react with uranium, and the C, N, O elements play an important role in the reaction. The static batch test was used to study the adsorption behavior of uranium on the EPS, and the effects of pH, dosage of EPS and initial concentration of the solution on the removal of uranium by EPS were investigated. The adsorption isotherm, thermodynamics and kinetic models were used to match the mechanism of the interaction between EPS and uranium. Batch adsorption experiments revealed that the pH value had a great influence on the adsorption effect of EPS, and the optimal solution pH for uranium adsorption was around 6.0 with the removal efficiency of uranium was about 93% in the condition of neutral. Freundlich (R² ≈ 0.997) and Langmuir (R² ≈ 0.9931) models can get a good fitting effect, indicating that the adsorption of uranium by EPS had both monolayer adsorption and multilayer adsorption. EPS and uranium were combined disorderly and ion exchange mechanism could be involved. In this study, the active groups on the surface of EPS were also involved in the chemisorption process of uranium adsorption. The maximum adsorption capacity of EPS by Langmuir fitting was 333.3 mg/g. We conclude EPS is a potential adsorbent for radionuclide treatment.

Halloysite nanotubes in analytical sciences and in drug delivery: A review

Halloysite (HNT) is a natural inorganic mineral that has many applications in manufacturing. This review (with 192 references) covers (a) the chemical properties of halloysites, (b) the effects of alkali and acid etching on the loading capacity and the release behavior of halloysites, (c) the use of halloysite nanotubes in analytical sciences and drug delivery, and (d) recent trends in the preparation of magnetic HNTs. Synthetic methods such as co-precipitation, thermal decomposition, and solvothermal method are discussed, with emphasis on optimal magnetization. In the analytical field, recent advancements are summarized in terms of applications of HNT-nanocomposites for extraction and detection of heavy metal ions, dyes, organic pollutants, and biomolecules. The review also covers methods for synthesizing molecularly imprinted polymer-modified HNTs and magnetic HNTs. With respect to drug delivery, the toxicity, techniques for drug loading and the various classes of drug-halloysite nanocomposites are discussed. This review gives a general insight on the utilization of HNT in analytical determination and drug delivery systems which may be useful for researchers to generate new ideas. Graphical abstract Schematic presentation of the structure of halloysite nanotubes, selected examples of modifications and functionalization, and represetative field of applications.

Investigation of uranium (VI) adsorption by polypyrrole

The purpose of this study was to investigate the adsorption of uranium (VI) ions on the polypyrrole adsorbent. Polypyrrole was synthesized by a chemical method using polyethylene glycol, sodium dodecylbenzenesulfonate, and cetyltrimethylammonium bromide as the surfactant and iron (III) chloride as an oxidant in the aqueous solution. The effect of various surfactants on the synthesized polymers and their performance as the uranium adsorbent were investigated. Adsorbent properties were characterized by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) techniques. The effect of different parameters such as pH, contact time, initial metal ion concentrations, adsorbent dose, and the temperature was investigated in the batch system for uranium adsorption process. It has been illustrated that the adsorption equilibrium time is 7min. The results showed that the Freundlich model had the best agreement and the maximum adsorption capacity of polypyrrole for uranium (VI) was determined 87.72mg/g from Langmuir isotherm. In addition, the mentioned adsorption process was fast and the kinetic data were fitted to the Pseudo first and second order models. The adsorption kinetic data followed the pseudo-second-order kinetic model. Moreover, the thermodynamic parameters ΔG⁰, ΔH⁰ and ΔS⁰ showed that the uranium adsorption process by polypyrrole was endothermic and spontaneous.