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.

Selective Separation of U(VI) from Pu(IV) by 2,9-Diamide-1,10-phenanthroline Ligands at High Acidity: Extraction and Coordination Chemistry.

During the PUREX process, the separation between U(VI) and Pu(IV) is achieved by reducing Pu(IV) to Pu(III), which is complicated and energy-consuming. To address this issue, we report here the first case of separation of U(VI) from Pu(IV) by o-phenanthroline diamide ligands under high acidity. Two new o-phenanthroline diamide ligands (1,10-phenanthroline-2,9-diyl)bis(indolin-1-ylmethanone) (L1) and (1,10-phenanthroline-2,9-diyl)bis((2-methylindolin-1-yl)methanone) (L2) were synthesized, which can effectively separate U(VI) from Pu(IV) even at 4 mol/L HNO3. The highest separation factor of U(VI) and Pu(IV) can reach over 1000, setting a new record for the separation of U(VI) from Pu(IV) under high acidity. Furthermore, extracted U(VI) can be easily recovered with water or dilute nitric acid, and the extraction performance remains stable even after 150 kGy gamma irradiation, which provides solid experimental support for potential engineering applications. The results of UV-vis titration and single-crystal X-ray diffraction measurements show that the 1:1 complex formed by L1 with U(VI) is more stable than all of the previously reported phenanthroline ligands, which reasonably reveals that the ligand L1 designed in this work has excellent affinity for U(VI). The findings of this work promise to contribute to the facilitation of the PUREX process by avoiding the use of reducing agents. It also provides new clues for designing ligands to achieve efficient separation between U(VI) and Pu(IV) at high acidity.

Complexation and extraction of trivalent actinides over lanthanides using highly soluble phenanthroline diamide ligands with different side chains.

Although phenanthroline diamide ligands have been widely reported, their limited solubility in organic solvents and poor performance in the separation of trivalent actinides (An(III)) and lanthanides (Ln(III)) at high acidity are still clear demerits. In this study, we designed and synthesized three highly soluble phenanthroline diamide ligands with different side chains. By introducing alkyl chains and ester groups, the ligands solubility in 3-nitrotrifluorotoluene is increased to over 600 mmol/L, significantly higher than the previous reported phenanthroline diamide ligands. Based on anomalous aryl strengthening, benzene ring was incorporated to enhance ligand selectivity toward Am(III). Extraction experiments demonstrated favorable selectivity of all the three ligands towards Am(III). The optimal separation factor (SFAm/Eu) reaches 53 at 4 mol/L HNO3, representing one of the most effective separation of An(III) over Ln(III) under high acidity. Slope analysis, single crystal structure analysis, as well as titration of ultraviolet visible spectroscopy, mass spectrometry, and nuclear magnetic resonanc confirmed the formation of 1:1 and 1:2 complex species between the metal ions and the ligands depending on the molar ratio of metal ions in the reaction mixture. The findings of this study offer valuable insights for developing phenanthroline diamide ligands for An(III)/Ln(III) separation.

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.

Effective biosorption of Cu(II) using hybrid biocomposite based on N-maleated chitosan/calcium alginate/titania: Equilibrium sorption, kinetic and thermodynamic studies.

In this research work, a hybrid biocomposite based on N-maleated chitosan, amino-thiocarbamate functionalised calcium alginate and anhydrous Titania nanoparticles (NMC-MCA-TiO2) was fabricated. The study involves the one pot facile synthesis of N-maleated chitosan and amino-thiocarbamate functionalised alginate under moderate conditions. Sorbent was conditioned in the form of hydrogel beads and characterized through FT-IR and SEM analysis. Newly grafted functional groups could act as potential chelating sites for enhanced Cu(II) sorption. Modified biopolymers were organo-functionalised which provided excellent support for immobilization of Titania nanoparticles (TiO2) as inorganic filler. Kinetic data illustrated the manifestation of intrinsic chemisorption instead of simple bulk/film diffusion. Equilibrium sorption data fitted well with Freundlich adsorption model (R2 ≈ 0.99) which designated the heterogeneous nature of sorbent. Maximum sorption capacity of biosorbent was found 192 mg/g at 298 K and pH = 6.0. Standard Gibbs free energy change ∆Go (-21.53, -21.97, and - 22.42 kJ/mol), standard enthalpy change ∆Ho (5.12 kJ/mol) and standard entropy change ∆So (0.09 kJ/mol K-1) values suggested that the sorption process to be spontaneous and endothermic. The sorbent 3NMC-MCA-TiO2 could be competitive candidate for economical and rapid adsorptive removal of Cu(II) from dilute contaminated liquids.

Synthesis of hybrid biosorbent based on 1,2-cyclohexylenedinitrilotetraacetic acid modified crosslinked chitosan and organo-functionalized calcium alginate for adsorptive removal of Cu(II).

The present study is based on the synthesis of a novel hybrid biosorbent using 1,2-cyclohexylenedinitrilotetraacetic acid modified crosslinked chitosan and amino-thiocarbamate moiety functionalized sodium alginate (CDTA-CS/TSC-CA). The fabricated sorbent was employed to investigate the efficient recovery of Cu(II) from aqueous media. CDTA-CS/TSC-CA was characterized using Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM). Analysis confirmed the successful modification of both biopolymers and subsequent loading of Cu(II) ions. CDTA-CS/TSC-CA was casted in the form of hydrogel beads having different CDTA-CS to TSC-CA mass ratios i.e., 10.0-40.0% by mass. The hydrogel beads 4CDTA-CS/TSC-CA with CDTA-CS/TSC-CA mass ratio of 40.0% was found most effective for copper sorption. Equilibrium sorption results showed that initial concentration of copper, medium pH, contact time, sorbent dosage and temperature influenced the sorption capacity (qe). Rate of sorption data was interpreted using different kinetic models and found best fitted with pseudo second order rate expression (R2 ≈ 0.99), illustrating that the rate determining step includes the electron density transfer from sorbent coordination sites to central copper ions. Crank's RIDE equation and Elovich chemisorption model (ECM) revealed the presence of two sorption phases, initially rapid sorption followed by comparatively a slow uptake. Equilibrium sorption data was well depicted by Langmuir model and maximum monolayer adsorption capacity (qm) was computed as 276.53 mg·g-1 at 298 K. Standard Gibbs free energy change, ∆G° (-19.99, -20.18 and -20.36 kJ/ mol), standard enthalpy change, ∆H° (-8.95 kJmol) and standard entropy change, ∆S° (0.04 kJ/mol K-1) values suggested that the adsorption process is spontaneous and exothermic. Hence, 4CDTA-CS/TSC-CA was found efficient biosorbent for copper removal from its dilute effluents.

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.

Fabrication of a novel hybrid biocomposite based on amino-thiocarbamate derivative of alginate/carboxymethyl chitosan/TiO2 for Ni(II) recovery.

A novel hybrid biocomposite based on amino-thiocarbamate derivative of alginate, carboxymethyl chitosan and TiO2 (TiO2/TSC-CMC) was fabricated and characterized using Fourier transform Infrared spectroscopy (FTIR), Scanning electron microscopy (SEM) and Energy dispersive X-ray spectroscopy (EDX). The TiO2/TSC-CMC mass ratio (5.0-30.0%) was optimized and 3TiO2/TSC-CMC (hydrogel beads with TiO2/TSC-CMC mass ratio of 20.0%) was selected as the best sorbent for effective biosorption of Ni(II). Batch sorption experiments were conducted, instantaneous and equilibrium sorption capacities were investigated as function of pH, sorbent dose, initial metal concentration, contact time and temperature. Kinetic data could be well explained through pseudo second order rate equation (PSORE) depicting that the rate determining step involves the transfer of electron density from sorbent functional sites to central metal ion. Langmuir model fitted well with isothermal sorption data and maximum monolayer sorption capacity (qm) was computed as 172 mg/g at pH 6.0 and temperature 298 K. The values of thermodynamic parameters such as standard enthalpy change (16.94 kJ/mol) and standard Gibbs energy change (-18.67, -19.48, -20.57, and -21.38 kJ/mol) and standard entropy change (0.12 kJ/mol·K) concluded that sorption process is endothermic, spontaneous and resulted with increase in randomness. Hence, 3TiO2/TSC-CMC was found efficient and reusable sorbent.

Amino-carbamate moiety grafted calcium alginate hydrogel beads for effective biosorption of Ag(I) from aqueous solution: Economically-competitive recovery.

In present study, pure and amino-carbamate moiety grafted calcium alginate hydrogel beads (CA, PSC-CA) were prepared for their biosorption performance in the recovery of silver ions. The produced sorbents were characterized using FTIR, SEM, EDX and TGA. FTIR and SEM-EDX confirmed the successful modification and loading of silver ions onto hydrogel beads. When compared with CA, PSC-CA showed enhanced sorption but comparable kinetics. Equilibrium sorption studies showed that pH, sorbent dose, contact time and adsorbate concentration influenced the sorption capacity. The uptake kinetic data was well demonstrated by pseudo second order rate equation (PSORE). Elovich equation and the resistance to intra-particle diffusion model (RID) suggested that there were two phases of sorption, first one was rapid followed by relatively slow uptake step. Equilibrium isothermal sorption data was well fitted by Langmuir and Sips models. The separation factor RL was found as 0 < RL < 1 which indicated favourable sorption. The maximum monolayer sorption capacity was computed as 210 mg/g at 298 K. Thermodynamic studies revealed the sorption process to be spontaneous and exothermic. PSC-CA hydrogel beads were found as cost-effective and efficient sorbent for economically-competitive recovery of Ag(I).