Ion-imprinted macroporous polyethyleneimine incorporated chitosan/layered hydrotalcite foams for the selective biosorption of U(VI) ions.

In order to prevent uranium pollution and recovery uranium resources, it was necessary to find a highly efficient adsorbent for radioactive wastewater treatment. Herein, U(VI) imprinted polyethyleneimine (PEI) incorporated chitosan/layered hydrotalcite composite foam (IPCL) was synthesized by combining ion-imprinting and freeze-drying techniques. IPCL has a high amino/imino content and an ultralight macroporous structure, making it capable of efficiently adsorbing U(VI) and easy to separate; Especially after ion-imprinting, vacancies matching the size of uranyl ions were formed, significantly improving U(VI) selectivity. The adsorption isotherms and adsorption kinetics were in accordance with the Freundlich model and PSO model respectively, indicating that heterogeneous adsorption of U(VI) by the adsorbents. The adsorption capacity of IPCL-2 for U(VI) reached 278.8. mg/g (under the conditions of optimal pH 5.0, temperature of 298 K, contact time of 2 h, and adsorbent dosage of 0.2 g/L), which is almost double of that for the non-imprinted foam (PCL-2, 138.2 mg/g), indicating that IPCL-2 can intelligently recognize U(VI). The heterogeneous adsorption mechanism of U(VI) by IPCL-2 involves complexation, ion-exchange and isomorphic substitution. The adsorption of U(VI) by IPCL-2 is spontaneous and endothermic. IPCL-2 has excellent adsorption performance for U(VI), and is a promising adsorbent for radioactive pollution control.

Tungsten oxide encapsulated phosphate-rich porous alginate composites for efficient U(VI) capture: Insights into synthesis, adsorption kinetics and thermodynamics.

In this work, novel monoclinic tungsten oxide (WO3)-encapsulated phosphate-rich porous sodium alginate (PASA) microspherical hydrogel beads were prepared for efficient U(VI) capture. These macroporous and hollow beads were systematically characterized through XRD, FTIR, EDX-mapping, and SEM-EDS techniques. The O and P atoms in the PO and monoclinic WO3 offered inner-spherical complexation with U(VI). The in situ growth of WO3 played a significant role inside the phosphate-rich biopolymeric network to improve its chemical stability, specific surface area, adsorption capacity, and sorption rate. The phytic acid (PA) served for heteroatom doping and crosslinking. The encapsulated WO3 mass ratio was optimized in different composites, and WO3/PASA3 (the microspherical beads with a mass ratio of 30.0 % w/w) exhibited remarkable maximum sorption capacity qm (336.42 mg/g) computed through the best-fit Langmuir model (R2 ≈ 0.99) and rapid sorption equilibrium, teq (150 min). The isothermal sorption studies were conducted at different temperatures (298, 303, and 308 K) and thermodynamic parameters concluded that the process of U(VI) sorption using WO3/PASA3 is endothermic and feasible having ΔHo (8.19 kJ/mol), ΔGo (-20.75, -21.38, and - 21.86 kJ/mol) and proceeds with a minute increase in randomness ΔSo (0.09 kJ/mol.K). Tungsten oxide (WO3)-encapsulated phosphate-rich porous microspherical beads could be promising material for uranium removal.

Harmonic and anharmonic studies on THz spectra of two vanillin polymorphs.

Polymorphism commonly exists in organic molecular crystals. The fingerprint features in low-frequency vibrational range are important information reflecting different intermolecular interactions of polymorphs. Interpreting these features is very helpful to understand vibrational property of polymorphs and reveal the thermodynamic stability. In this work, the low-frequency vibrations of form I and II of vanillin are investigated using terahertz time-domain spectroscopy. Static DFT calculation and ab initio molecular dynamics (AIMD) are employed to interpret their low-frequency vibrations of both forms in harmonic and anharmonic ways, respectively. Their low-frequency vibration characteristics in harmonic calculations are discussed, and anharmonic mode couplings between OH bond stretch and the stretching and bending motion of hydrogen bonds are uncovered. Moreover, the thermodynamic energies including electronic potential energy and vibrational/kinetic energy arising from nuclear motions are calculated. The result reveals that the stability order of the two forms is mainly dependent on their electric potential energy difference.

Macroporous and ultralight polyethyleneimine-grafted chitosan/nano-TiO2 foam as a novel adsorbent with antibacterial activity for the efficient U(VI) removal.

The radioactive contamination from the excessive discharge of uranium-containing wastewater seriously threatens environmental safety and human health. Herein, macroporous and ultralight polyethyleneimine-grafted chitosan/nano-TiO2 composite foam (PCT) with antibacterial activity was synthesized, which could quickly remove U(VI) from solution. Among different PCT adsorbents, PCT-2 had the best adsorption performance for U(VI), which could be due to its honeycomb macroporous structures and the presence of abundant amino/imine groups. The kinetics and adsorption isotherms data were found in agreement with the pseudo-second-order model and the Langmuir model, respectively, indicating chemisorption or complexation as the main adsorption mechanism. The saturated adsorption capacity of PCT-2 for U(VI) reaches 259.91 mg/g at pH 5.0 and 298 K. The PCT-2 also presents good selectivity for U(VI) with the coefficient (ßU/M) order of Na+ > K+ > Mg2+ > Ca2+ > Ni2+ > Co2+ > Mn2+ > Al3+ > Fe3+ > Cu2+. The adsorption mechanism was explored using FT-IR and XPS analysis, indicating that amino/imine groups and hydroxyl groups are responsible for U(VI) complexation. Thermodynamic calculations show that U(VI) adsorption is endothermic and spontaneous. The ease of preparation, excellent adsorption performance and environmental friendliness of PCT-2 make it a novel adsorbent with antibacterial activity for radioactive contamination control.

An innovative approach to synthesize graft copolymerized acetylacetone chitosan/surface functionalized alginate/rutile for efficient Ni(II) uptake from aqueous medium.

In this study, an innovative approach is followed to synthesize graft copolymerized chitosan with acetylacetone (AA-g-CS) through free-radical induced grafting. Afterwards, AA-g-CS and rutile have been intercalated uniformly into amino carbamate alginate matrix to prepare its biocomposite hydrogel beads of improved mechanical strength having different mass ratio i.e., 5.0 %, 10.0 % 15.0 % and 20.0 % w/w. Biocomposites have been thoroughly characterized through FTIR, SEM and EDX analysis. Isothermal sorption data showed good fit with Freundlich model as conferred from regression coefficient (R2 ≈ 0.99). Kinetic parameters were evaluated through non-linear (NL) fitting of different kinetic models. Experimental kinetic data exhibited close agreement to quasi-second order kinetic model (R2 ≈ 0.99) which reveals that chelation between heterogeneous grafted ligands and Ni(II) is occurring through complexation. Thermodynamic parameters were evaluated at different temperatures to observe the sorption mechanism. The negative values of ΔG° (-22.94, -23.56, -24.35 and - 24.94 kJ/mol), positive ΔH° (11.87 kJ/mol) and ΔS° (0.12 kJ/molK-1) values indicated that the removal process is spontaneous and endothermic. The maximum monolayer sorption capacity (qm) was figured as 246.41 mg/g at 298 K and pH = 6.0. Hence, 3AA-g-CS/TiO2 could be better candidate for economic recovery of Ni(II) ions from waste effluents.

Mineralogical Properties of a Refractory Tantalum-Niobium Slag and the Effect of Roasting on the Leaching of Uranium-Thorium.

In order to realize sustainable development, it is beneficial to explore an appropriate process to recover the radionuclides contained in tantalum-niobium slag. By micro-mineralogical analysis and roasting experiments, the effect of uranium-thorium leaching from a refractory tantalum-niobium slag is investigated. The uranium and thorium content in the slag is 2.26 × 103 mg/kg and 7.84 × 103 mg/kg, which have large recovery value. As the surface area and pore size of the slag are very small, the leaching agent cannot fully penetrate the particles. Various methods of characterization are used to analyze the mineralogical properties of roasted slag at different temperatures. The leaching ratio of U-Th is 90.84% and 96.62% at the optimum roasting temperature of 500 °C, which are about 39% and 27% higher than original samples. The oxidants Fe3+, O2 and Mn can also promote the conversion of insoluble U(IV) to soluble U(VI). Roasting reduces the content of organic C and S, thereby preventing reduction of U(VI), and increasing pore size as well as specific surface area also promote radionuclide leaching. Thus, the roasting method at 500 °C can destroy the surface wrapping structure of radionuclides, reduce the internal density of minerals, and improve uranium-thorium leaching ratio significantly. It is of great practical significance to reduce the radioactive hazard of waste tantalum-niobium slag and to strengthen the sustainable utilization of resources by suitable process improvement techniques.

Polyethyleneimine incorporated chitosan/α-MnO2 nanorod honeycomb-like composite foams with remarkable elasticity and ultralight property for the effective removal of U(VI) from aqueous solution.

The development of new adsorbents is needed to address the environmental challenges of radioactive wastewater treatment. Herein we reported a novel polyethyleneimine incorporated chitosan/α-MnO2 nanorod honeycomb-like composite (PCM) foam with remarkable elasticity and ultralight property for U(VI) removal. Among different PCM sorbents, PCM-40 possessed the highest sorption capacity for U(VI) due to its highly developed macroporous structure and high content of amine/imine groups. The kinetics were well-simulated by the pseudo-second-order model, indicating chemisorption as the rate-controlling step. The isotherms could be described by the Langmuir model, suggesting mono-layer homogeneous sorption of U(VI). The maximum sorption U(VI) capacity for PCM-40 reaches up to 301.9 mg/g at pH 4.5 and 298 K. The thermodynamic parameters revealed the spontaneous and endothermic nature of the adsorption process. The main sorption mechanism is related to the complexation of uranyl ions with the amine/imine and hydroxyl groups. The high sorption capacity, fast kinetic rate and relatively good selectivity of PCM-40 highlights its promising application in radioactive pollution cleanup.

Selective biosorption of U(VI) from aqueous solution by ion-imprinted honeycomb-like chitosan/kaolin clay composite foams.

The radioactive pollution caused by the discharge of radioactive wastewater poses a serious threat to public health and ecosystem stability owing to its long-term detriments. Herein, the ion-imprinted honeycomb-like chitosan/kaolin clay (ICK) composite foams were successfully fabricated and applied to the selective biosorption of U(VI) from aqueous solution. It was found that the ICK-2 was the best among various ICK foams owing to its well-developed honeycomb-like structure and the presence of abundant functional groups. As compared to the non-imprinted sorbent (NICK-2), the ion-imprinted sorbent (ICK-2) presents higher sorption and better selectivity since it can smartly recognize the target ions. The sorption isotherms was well-fitted with Langmuir model, and the maximum sorption capacity of ICK-2 was evaluated as 286.85 mg/g for U(VI) at 298 K and pH 5.0. The kinetic data could be described by pseudo-second order model. The FTIR and XPS results suggest that both amine and hydroxyl groups are responsible for U(VI) coordination. The ICK-2 presents high sorption capacity, good selectivity and fast kinetic rate, and thus it has potential application for U(VI) separation from radioactive wastewater.

Modified alginate-chitosan-TiO2 composites for adsorptive removal of Ni(II) ions from aqueous medium.

In this study, organo-funtionalization of sodium-alginate has been carried out using phenylsemicarbazide as modifier to graft N, O-donor atoms containing functional groups (amino-carbamate moieties) to offer novel support for TiO2 immobilization. Hybrid composite made of aminocarbamated alginate, carboxymethyl chitosan (CMC) and titanium oxide TiO2 (MCA-TiO2) was prepared for the promising adsorptive remediation of Ni(II). FT-IR, SEM-EDX were employed to characterize MCA-TiO2. The optimization of TiO2 to modified alginate mass ratio was carried out and hydrogel beads with TiO2/MCA mass ratio of 10.0% (2MCA-TiO2) revealed highest sorption efficiency. The produced sorbents were adapted in the form of hydrogel beads for operation. Organic functionalization based on aminocarbamate (OCONHNH2) moieties on linear chains of alginate embedded additional chelating functional sites which enhanced sorption and selectivity. Batch mode experiments were conducted for optimization of pH and sorbent dose. Equilibrium sorption, kinetic and thermodynamic studies were performed to pattern the nature of sorption. Kinetic data was found in close agreement with pseudo-second order rate expression (PSORE). Isothermal equilibrium sorption data was well fitted with Langmuir adsorption model. Maximum sorption capacity was evaluated as 229 mg/g at 298 K and pH = 6.0.

Macroporous ion-imprinted chitosan foams for the selective biosorption of U(VI) from aqueous solution.

The radiological toxicity of uranium in nuclear industrial wastewater poses a long-term threat to environment, thus the effective separation of radionuclide from wastewater is very important for environmental safety. Herein, the macroporous ion-imprinted chitosan foams (ICFs) were synthesized by the combination of the facile freezing-drying and ion-imprinting techniques. Compared with non-imprinted chitosan foam, the ICFs showed much higher adsorption capacities (qm = 248.9-253.6 mg/g) and better adsorption selectivity for U(VI) owing to their smart recognition of the target ions for matching the cavities formed during U(VI)-imprinting process. The adsorption kinetics could be fitted by pseudo-second-order model; whereas the adsorption isotherms could be described by Langmuir model, indicating chemisorption or complexation mechanism. The FT-IR and XPS analysis further confirms that the coordination between U(VI) and the active sites (amine and hydroxyl groups) is the main adsorption mechanism. The thermodynamic parameters suggest that the adsorption of U(VI) is endothermic and spontaneous. This work provides new insights for the design of novel macroporous biosorbents with both high adsorption capacity and excellent adsorption selectivity for U(VI) biosorption from wastewater.

Crystallization Methods for Preparation of Nanocrystals for Drug Delivery System.

Low water solubility of drug products causes delivery problems such as low bioavailability. The reduced particle size and increased surface area of nanocrystals lead to the increasing of the dissolution rate. The formulation of drug nanocrystals is a robust approach and has been widely applied to drug delivery system (DDS) due to the significant development of nanoscience and nanotechnology. It can be used to improve drug efficacy, provide targeted delivery and minimize side-effects. Crystallization is the main and efficient unit operation to produce nanocrystals. Both traditional crystallization methods such as reactive crystallization, anti-solvent crystallization and new crystallization methods such as supercritical fluid crystallization, high-gravity controlled precipitation can be used to produce nanocrystals. The current mini-review outlines the main crystallization methods addressed in literature. The advantages and disadvantages of each method were summarized and compared.