Selective transport and removal of Cr(VI) through polymer inclusion membrane containing 5-(4-phenoxyphenyl)-6H-1,3,4-thiadiazin-2-amine as a carrier

Technical design and optimisation of polymer inclusion membranes (PIMs) for sample pre-treatment and passive sampling - A review

This review reports on the increasing interest in technical designs, calibration, and application of PIM-based devices in sample pre-treatment and passive sampling in environmental water monitoring from 2010 to 2021. With regards to passive sampling, devices are calibrated in a laboratory setup using either a dip-in or flow-through approach before environmental application. In sample preparation, the device set-ups can be offline, online or in a continuous flow separation device connected to a flow injection analysis system. The PIMs have also demonstrated potential in both these offline and online separations; however, there is still a draw-back of low diffusion coefficients obtained in these PIM set-ups. Electro-driven membrane (EME) extraction has demonstrated better performance as well as improved analyte flux. Critical in electro-driven membrane extraction is applying correct voltage that may not compromise the PIM performance due to leaching of components to the aqueous solutions. Further, besides different PIM configurations and designs being developed, PIM based extractions are central to PIM components (base polymer, carrier and plasticizer). As such, recent studies have also focused on improving PIM stability by investigating use of various PIM components, incorporating nano additives into the PIM composition, and investigating novel green PIM synthetic routes. All these aspects are covered in this review. Further, some recent studies that have demonstrated the ability to eliminate effects of flow patterns and membrane biofouling in PIM based applications are also included.

A Comparative Study on Hexavalent Chromium Adsorption onto Chitosan and Chitosan-Based Composites

Chitosan (Cs)-based composites were developed by incorporating silica (Cs-Si), and both silica and hydroxyapatite (Cs-Si-Hap), comparatively tested to sequester hexavalent (Cr(VI)) ions from water. XRD and FT-IR data affirmed the formation of Cs-Si and Cs-Si-Hap composite. Morphological images exhibits homogeneous Cs-Si surface, decorated with SiO2 nanoparticles, while the Cs-Si-Hap surface was non-homogeneous with microstructures, having SiO2 and Hap nanoparticles. Thermal analysis data revealed excellent thermal stability of the developed composites. Significant influence of pH, adsorbent dose, contact time, temperature, and coexisting anions on Cr(VI) adsorption onto composites was observed. Maximum Cr(VI) uptakes on Cs and developed composites were observed at pH 3. The equilibration time for Cr(VI) adsorption on Cs-Si-Hap was 10 min, comparatively better than Cs and Cs-Si. The adsorption data was fitted to pseudo-second-order kinetic and Langmuir isotherm models with respective maximum monolayer adsorption capacities (qm) of 55.5, 64.4, and 212.8 mg/g for Cs, Cs-Si, and Cs-Si-Hap. Regeneration studies showed that composites could be used for three consecutive cycles without losing their adsorption potential.

On-Line Separation and Determination of Trivalent and Hexavalent Chromium with a New Liquid Membrane Annular Contactor Coupled to Inductively Coupled Plasma Optical Emission Spectrometry

We describe a new on-line sensitive and selective procedure for the determination of trivalent and hexavalent chromium in liquid samples by a tailor-made contactor (TMC), specifically a liquid membrane annular TMC, coupled with inductively coupled plasma with optical detection. The TMC was designed and developed to integrate the extraction and stripping phases of the analyte in one module to minimize the membrane solvent’s consumption and maximize the speed of transport through the liquid membrane. Moreover, the particular geometry studied, which consists of two coaxial hollow fibers, allows the TMC to be used for both separating and preconcentrating purposes. Both (−)-N-dodecyl-N-methylephedrinium bromide (30 mM) in dichloroethane and HNO3 (0.75 M) were used as the liquid membrane and receiving solution, respectively. The proposed method’s performance was evaluated in terms of the hexavalent chromium extraction efficiency and the coefficient of variation percentages; these were higher than 85% and less than 5%, respectively. In addition, the proposed procedure was applied to two real samples: a tap water sample and an eluate from solid urban waste. In both cases, the analytical performances were good and comparable to those obtained using synthetic standard solutions.

Carrier-mediated extraction: Applications in extraction and microextraction methods

The present review is mainly focused on the overview of carrier mediated extraction (principles and applications) being reported over the last two decades and discusses the extraction process through carriers in various extraction methods such as Bulk liquid membranes, supported liquid membranes, emulsion liquid membranes and polymer inclusion membranes. Several types of carriers such as neutral, anionic, cationic, macrocyclic and supramulecular carriers are discussed. Also their application for metal, anions, drugs and environmental compounds are investigated. Carriers have been demonstrated to be useful for the selective extraction and recovery of numerous cations and anions enhancing the extraction properties of traditional solvent extraction and ion-exchange processes. Several types of carriers have different transport mechanisms. In these mechanisms, transport configurations are addressed and emphasized and the detailed information on the type of carrier are presented along with their specific separation modes. The performance of different carriers in terms of selectivity as well as efficiency are also discussed. Finally, the application of different carriers for the extraction of various compounds are compared and reviewed. To our best knowledge no reviews have been published on carrier-mediated extraction methods.

Hexavalent chromium removal from aqueous solution by adsorption on modified zeolites coated with Mg-layered double hydroxides

In this study, MgAl-LDHs and MgFe-LDHs were synthesized via co-precipitation method and in situ coated on pre-washed zeolites through dipping process in beaker. The obtained modified zeolites and original zeolites were utilized as substrates of constructed rapid infiltration systems (CRIS) to remove hexavalent chromium (Cr(VI)) in wastewater. Micro-morphology features and chemical composition of zeolites before and after modification were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray fluorescence spectrometer (XRF). The SEM, XRD, and XRF results demonstrated the feasibility of LDHs coated on the surface of the original zeolites. Purification experiments in simulated CRIS showed that the Cr(VI) removal rates of zeolites/MgAl-LDHs increased by 110.03% on average every concentration (0.5-16 mg L^-1) compared with the original zeolites under 24-h HRT. The adsorption capacity of zeolites/MgAl-LDHs reached 66.98 mg kg^-1 at 32 mg L^-1 initial Cr(VI) concentration, which is nearly twice that of the original zeolites (33.24 mg kg^-1) and 1.5 times higher than that of zeolites/MgFe-LDHs (42.01 mg kg^-1). Isothermal adsorption tests showed that the Freundlich isotherm equations gave better fitting to the adsorption process. And zeolites/MgAl-LDHs showed a best fit with pseudo-second-order model which meant that the adsorption of Cr(VI) by zeolites/MgAl-LDHs was dominated by chemisorption. Thermodynamic parameters showed that the process of adsorption for the three substrates was spontaneous and endothermic intrinsically. Zeolites/MgAl-LDHs also displayed nearly 60% desorption rate with low concentration eluent (0.01 mol L^-1 NaCl). Therefore, zeolites/MgAl-LDHs were chosen out as an optimal substrate for removing Cr(VI) from wastewater in CRIS. Graphical Abstract.

The Influence of the Morphology and Mechanical Properties of Polymer Inclusion Membranes (PIMs) on Zinc Ion Separation from Aqueous Solutions

The transport of Zn(II) ions across polymer inclusion membranes (PIMs) with acetylacetone (ACAC) or di(2-ethylhexyl)phosphoric acid (D₂EHPA) as carriers was studied. Polymeric membranes consisting of polyvinylchloride (PVC) as the support, bis(2-ethylhexyl)adipate (DAO) as plasticizer, and ACAC or D₂EHPA as ion carriers were investigated. The highest recovery factors for Zn(II) ions were observed in the case of a membrane containing 20% acac (99.6%) and 60% D₂EHPA (56.3%). The prepared PIMs were examined using atomic force microscopy (AFM) techniques. Their mechanical properties were also determined. The influence of membrane morphology and mechanical properties on the zinc transport process was discussed.

Preparation and characterization of functionalized silica spheres for removal of Cu(ii), Pb(ii), Cr(vi) and Cd(ii) from aqueous solutions

Functionalized silica spheres (SMS) with mesoporous structure were fabricated through a facile and environmentally benign route, and exhibited remarkable removal efficiency for metal ions from aqueous solutions.