Urchin-like structured magnetic hydroxyapatite for the selective separation of cerium ions from aqueous solutions

In this study, bio-inspired urchin-like structured hydroxyapatite (UHdA) and its magnetic composite (UHdA@Fe₃O₄) were developed for efficient and easy separation of cerium ions (Ce³⁺) from aquatic waste streams. UHdA and UHdA@Fe₃O₄ exhibited superior Ce³⁺ adsorption capacities of 248.39 and 230.01 mg/g-UHdA respectively, compared to a commercial HdA (141.71 mg/g-HdA) due to their hierarchical mesoporous structure and large specific surface area. The adsorption of Ce³⁺ to UHdA and UHdA@Fe₃O₄ were heterogeneous, pseudo-second-order-kinetic, and the rate-limiting step was external mass transfer and intra-particle diffusion. Moreover, thermodynamic studies revealed that the adsorption process was spontaneous and endothermic nature. The high selectivity towards Ce³⁺ in multi-ionic systems is attributed to the strong affinity between strong Lewis acid (Ce³⁺) and base (PO₄^3- and OH^-) interactions. XRD, FTIR, and XPS analysis demonstrated that the adsorption was mainly attributable to the ion exchange of Ce³⁺ with Ca²⁺ and to surface complexation. The desorption of Ce³⁺ was efficiently accomplished using 0.1 M HNO₃. The results suggest that UHdA and UHdA@Fe₃O₄ could be promising choices for the adsorption and recovery of rare earth elements.

Crown Ether-Immobilized Cellulose Acetate Membranes for the Retention of Gd (III)

This study presents a new, revolutionary, and easy method of separating Gd (III). For this purpose, a cellulose acetate membrane surface was modified in three steps, as follows: firstly, with aminopropyl triethoxysylene; then with glutaraldehyde; and at the end, by immobilization of crown ethers. The obtained membranes were characterized by Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS), through which the synthesis of membranes with Gd (III) separation properties is demonstrated. In addition, for the Gd (III) separating process, a gadolinium nitrate solution, with applications of moderator poison in nuclear reactors, was used. The membranes retention performance has been demonstrated by inductively coupled plasma mass spectrometry (ICP-MS), showing a separation efficiency of up to 91%, compared with the initial feed solution.

Sorption of Ce(III) on magnetic/olive pomace nanocomposite: isotherm, kinetic and thermodynamic studies

Used for various high-tech applications, cerium is an important rare earth element (REE), and its sorption on various solids also is important considering purification and environmental and radioactive waste disposal. In view of the industrial and environmental terms, it is important to remove Ce³⁺ ions from an aqueous solution. Magnetite and magnetic olive pomace nanocomposite were thus fabricated by a partial reduction co-precipitation approach. The structure and morphological properties of the prepared nano-material and nanocomposite were characterized by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-Ray diffraction (XRD), Fourier transform infrared spectrometry (FT-IR), vibrating sample magnetometry (VSM), and BET surface area analysis. The effects of parameters such as solution pH, contact time, initial Ce(III) concentration, and temperature on the sorption efficiency were studied. The maximum sorption capacities of the magnetite (MNP) and magnetic olive pomace nanocomposite (MOP) for Ce(III) ions were found to be 76.92 and 90.90 mgg^-1, respectively. The sorption data fitted well with Dubinin-Radushkevich isotherm model and the pseudo-second-order kinetic model. Thermodynamic parameters indicated that the sorption was non-spontaneous and endothermic. This paper reports the preparation of MNP and novel MOP and their application as efficient, sustainable adsorbents alternative to commercial ones for adsorption of cerium ions from aqueous solution.

Synthesis and Characterization of Cellulose Acetate Membranes with Self-Indicating Properties by Changing the Membrane Surface Color for Separation of Gd(III)

This study presents a new, revolutionary, and easy method for evaluating the separation process through a membrane that is based on changing the color of the membrane surface during the separation process. For this purpose, a cellulose acetate membrane surface was modified in several steps: initially with amino propyl triethoxysilane, followed by glutaraldehyde reaction and calmagite immobilization. Calmagite was chosen for its dual role as a molecule that will complex and retain Gd(III) and also as an indicator for Gd(III). At the contact with the membrane surface, calmagite will actively complex and retain Gd(III), and it will change the color of the membrane surface during the complexation process, showing that the separation occurred. The synthesized materials were characterized by Fourier transform infrared spectroscopy (FT-IR), thermal analysis (TGA-DTA), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy, demonstrating the synthesis of membrane material with self-indicating properties. In addition, in the separation of the Gd(III) process, in which a solution of gadolinium nitrate was used as a source and as a moderator in nuclear reactors, the membrane changed its color from blue to pink. The membrane performances were tested by Induced Coupled Plasma–Mass Spectrometry (ICP-MS) analyses showing a separation process efficiency of 86% relative to the initial feed solution.

Tailored silica nanospheres: an efficient adsorbent for environmental chromium remediation

This manuscript reports the synthesis and characterization of caprylpyrazolone tailored silica nanospheres, synthesized through sol–gel procedure by activating the silica nanospheres with organosilane precursor and grafting with caprylpyrazolone. Its successful attachment to the silica is confirmed by FTIR, TGA and elemental techniques. The feasibility of the synthesized nanospheres as adsorbent was systematically checked by elimination of trace level of Cr(III) from aqueous medium, using radiotracer technique. A number of factors such as effect of pH, agitation time, adsorbent and adsorbate dosage were optimized to guarantee the use of the adsorbent for practical use. Various counter ions were added to the matrix solution to check the selectivity of the synthesized sorbent. Various rate equations and adsorption isotherms such as Freundlich, D-R and Langmuir were employed to suggest the mechanistic pathway of the adsorption process. The Cr(III) extraction was monitored at room and elevated temperatures and thermodynamic parameters such as change in enthalpy, entropy, and Gibbs free energy of the metal ion uptake were computed. The removal of Cr(III) is endothermic (∆H=30.00 J mol−1 K−1) and spontaneous (∆S=105.43 J mol−1 K−1) in nature. Application of the adsorbent to real water samples demonstrated the practical utility of the adsorbent. The sorbent displayed good stability. Its cleaning efficiency is not significantly affected after various adsorption-desorption cycles and so it can be used repeatedly.

Removal of gadolinium, a neutron poison from the moderator system of nuclear reactors

Gadolinium as gadolinium nitrate is used as neutron poison in the moderator system for regulating and controlling the power generation of Pressurized Heavy Water Reactors (PHWR) and proposed to be used in Advanced Heavy Water Reactors (AHWR) owing to its high neutron absorption cross section. Removal of the added gadolinium nitrate (Gd³⁺ and NO₃^-) from the system after its intended use is done using ion exchange resins. In the present investigation, attempts have been made to optimize the ion exchange process for generation of low radioactive waste and maximize utilization of the ion exchange resins by employing different types of resins and different modes of operation. The investigations revealed that use of mixed bed (MB) resin column consisting of Strong Acid Cation (SAC) resin and Strong Base Anion (SBA) resin followed by SAC resin column is efficient in removing the Gd³⁺ and NO₃^- from the system besides maintaining the pH of the moderator system in the desirable regime, where gadolinium does not get precipitated as its hydroxide.

Synthesis, characterization and optimization of heterogeneous catalytic cyclohexene oxidation by tungstophospho(aqua)ruthenate via the fractional factorial design methodology

Keggin-type tungstophospho(aqua)ruthenate (PRuW) was synthesized and supported on acid activated montmorillonite under mild conditions.

Surface adsorption of poisonous Pb(II) ions from water using chitosan functionalised magnetic nanoparticles

In this study, chitosan functionalised magnetic nano-particles (CMNP) was synthesised and utilised as an effective adsorbent for the removal of Pb(II) ions from aqueous solution. The experimental studies reveal that adsorbent material has finer adsorption capacity for the removal of heavy metal ions. Parameters affecting the adsorption of Pb(II) ions on CMNP, such as initial Pb(II) ion concentration, contact time, solution pH, adsorbent dosage and temperature were studied. The adsorption equilibrium study showed that present adsorption system followed a Freundlich isotherm model. The experimental kinetic studies on the adsorption of Pb(II) ions exhibited that present adsorption process best obeyed with pseudo-first order kinetics. The maximum monolayer adsorption capacity of CMNP for the removal of Pb(II) ions was found to be 498.6 mg g-1. The characterisation of present adsorbent material was done by FTIR, energy disperse X-ray analysis and vibrating sample magnetometer studies. Thermodynamic parameters such as Gibbs free energy (ΔG°), enthalpy (ΔH°) and entropy (ΔS°) have declared that the adsorption process was feasible, exothermic and spontaneous in nature. Sticking probability reported that adsorption of Pb(II) ions on CMNP was favourable at lower temperature and sticking capacity of Pb(II) ions was very high.

Central composite design in HPMC granulation and correlations between product properties and process parameters

Combined effects of rpm, binder volume and binder flow rate on granulation yield and flowability properties have been investigated.

Highly efficient ultrasonic-assisted removal of Hg(II) ions on graphene oxide modified with 2-pyridinecarboxaldehyde thiosemicarbazone: Adsorption isotherms and kinetics studies

A novel adsorbent, based on modifying graphene oxide (GO) chemically with 2-pyridinecarboxaldehyde thiosemicarbazone (2-PTSC) as ligand, was designed by facile process for removal of Hg(II) from aqueous solution. Characterization of the adsorbent was performed using various techniques, such as FT-IR, XRD, XPS, SEM and AFM analysis. The adsorption capacity was affected by variables such as adsorbent dosage, pH solution, Hg(2+) initial concentration and sonicating time. These variables were optimized by rotatable central composite design (CCD) under response surface methodology (RSM). The predictive model for Hg(II) adsorption was constructed and applied to find the best conditions at which the responses were maximized. In this conditions, the adsorption capacity of this adsorbent for Hg(2+) ions was calculated to be 309mgg(-1) that was higher than that of GO. Appling the ultrasound power combined with adsorption method was very efficient in shortening the removal time of Hg(2+) ions by enhancing the dispersion of adsorbent and metal ions in solution and effective interactions among them. The adsorption process was well described by second-order kinetic and Langmuir isotherm model in which the maximum adsorption capacity (Qm) was found to be 555mgg(-1) for adsorption of Hg(2+) ions over the obtained adsorbent. The performance of adsorbent was examined on the real wastewaters and confirmed the applicability of adsorbent for practical applications.

Synthesis, characterization and application of cyclam-modified magnetic SBA-15 as a novel sorbent and its optimization by central composite design for adsorption and determination of trace amounts of lead ions

A new, efficient, selective and relatively low cost adsorbent was developed based on Fe₃O₄@cyclam-SBA-15 for adsorption and determination of lead ions.