A novel electro-driven membrane for removal of chromium ions using polymer inclusion membrane under constant D.C. electric current

Fabrication and characterisation of novel chitosan-based polymer inclusion membranes and their application in environmental remediation

Several water and wastewater technologies have been implored for the removal of dyes during wastewater treatments; however; different types have been reportedly found in surface and groundwater systems. Hence, there is a need to investigate other water treatment technologies for the complete remediation of dyes in aquatic environments. In this study, novel chitosan-based polymer inclusion membranes (PIMs) were synthesized for the removal of malachite green dye (MG) which is a recalcitrant of great concern in water. Two types of PIMs were synthesized in this study, the first PIM (PIMs-A) was composed of chitosan, bis-(2-ethylhexyl) phosphate (B2EHP), and dioctyl phthalate (DOP). While, the second PIMs (PIMs-B) were composed of chitosan, Aliquat 336, and DOP. The physico-thermal stability of the PIMs was investigated using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA), both PIMs demonstrated good stability with a weak intermolecular force of attraction amongst the various components of the membranes. The effects of the initial concentration of MG, pH of the MG solution, stripping solution, and time were investigated. At optimum conditions, both membranes (PIM-A and B) recorded the highest efficiencies of 96 % and 98 % at pH 4 and initial contaminants concentration of 50 mg/L, respectively. Finally, both PIMs were used for the removal of MG in different environmental samples (river water, seawater, and tap water) with an average removal efficiency of 90 %. Thus, the investigated PIMs can be considered a potential suitable technique for the removal of dyes and other contaminants from aquatic matrices.

Efficient separation of arsenic species of oxyanion As (III) and As (V) by using effective polymer inclusion membranes (PIM)

The heavy metal contaminant arsenic exist in the form of arsenite (As(III)) and arsenate (As(V)) ions. These ions are highly carcinogenic that are usually present in the ground water. To date, most of the designed polymer inclusion membrane (PIM) involved only about separation without differentiating the oxidation states. Thus, there is a research gap on separation of element with different oxidation states. Thus, this study addresses such research gap which have been not explored previously. To extract such ions from water, the present study involves fabrication of PIM by varying the compositions of the base polymer, carrier and plasticizer. Also effect of the strip solution, and transport properties were studied. High performance membrane was obtained with 50% (w/w) Aliquat 336 and 50% (w/w) Cellulose triacetate (CTA). The production of 1 m² of PIM may cost approximately 0.08-0.16$. Also, we have combined the separation capacity of polymer inclusion membrane (PIM) with the sensitivity and elemental detection using atomic absorption spectrometry (AAS) to detect and separate As(III) and As(V). AAS is limited to detecting only elemental arsenic (As) and does not distinguish between As(III) and As(V). Further, to address such limitations in this current study we were able to separate As(V) from As(III) within 5 h. In addition, to provide sole solution a device was fabricated to extract As(V) in the field studies which displayed outstanding efficiency of 99.7 ± 0.2%. The extracted samples was tested in AAS to differentiate between oxidation states of the arsenic species and these important results are supportive in finding out the redox potential of water and for other geochemical explorations.

An electromembrane microextraction-based green method for the determination of trace copper in natural waters

Driven by the search for an environmentally-friendly methodology, electromembrane extraction (EME) has recently emerged as a green and versatile tool for the analysis of trace pollutants in water samples, being mainly applied to the preconcentration and determination of organic compounds. Recently, EME has also shown its applicability to the analysis of inorganic species, allowing a considerable reduction in both reagent consumption and extraction times, and without loss of efficacy, in comparison with other liquid phase microextraction techniques. In this study, an EME system for trace copper analysis in natural waters has been optimised by the modified simplex method. A chemical modifier, di-2-pyridyl ketone benzoylhydrazone (dPKBH) was synthesized and dissolved in 1-nonanol, to be used as an organic phase impregnated into the pores of a polymeric hollow fibre. With only 15 min of extraction, an enrichment factor of 77.1 ± 10.8 was obtained for a wide salinity range (0-35), allowing its application in a variety of different waters, including seawater. Optimum operating conditions were a sample pH of 6.26, an electric potential of 95 V, 0.08 M nitric acid as the acceptor phase, 4.01 mM dPKBH in 1-nonanol as the organic phase and a stirring rate of 1500 rpm. A LOD of 0.004 μg L^-1 was obtained, and the system was successfully applied to the analysis of several water samples containing copper at low ppb levels (tap water and river water) or even at sub-ppb levels (seawater).

Synthesis of a new magnetic Sulfacetamide-Ethylacetoacetate hydrazone-chitosan Schiff-base for Cr(VI) removal

In this study, a novel magnetic organic-inorganic composite was fabricated. Where, Chitosan, sulfacetamide and ethylacetoacetae were used to prepare a new Sulfacetamide-Ethylacetoacetate hydrazone-chitosan Schiff-base (SEH-CSB) with a variety of active sites that capable of forming coordinate covalent bonds with Cr(VI). This was followed by modification of the formed SHE-CSB with NiFe₂O₄ to obtain the magnetic Chitosan-Schiff-base (NiFe₂O₄@SEH-CSB). NiFe₂O₄@SEH-CSB was characterized using FTIR, zeta potential, SEM, VSM and XPS. Results clarified that SHE played a crucial role in the removal of Cr(VI). The removal of Cr(VI) on NiFe₂O₄@SEH-CSB was found to be more fitted to pseudo-2nd order kinetics model and Freundlich isotherm. Besides, the maximum adsorption capacity of NiFe₂O₄@SEH-CSB for Cr(VI) was found to be 373.61 mg/g. The plausible mechanism for the removal of Cr(VI) on NiFe₂O₄@SEH-CSB composite suggested coulombic interaction, outer-sphere complexation, ion-exchange, surface complexation and coordinate-covalent bond pathways. The magnetic property enabled easy recycling of NiFe₂O₄@SEH-CSB composite.

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.

Catalytic properties of transition metals modified nanoscale zero-valent iron for simultaneous removal of 4-chlorophenol and Cr(VI): Efficacy, descriptor and reductive mechanisms

Since chlorophenols (CPs) and Cr(VI) are two types of common pollutants in the environment, developing an effective approach to remove these contaminants has important benefits for public health. However, few efforts have been made so far. In this study, we prepared nanoscale zero-valent iron (nZVI) and a series of bimetallic nanoparticles (transition-metal modified nZVI) to investigate their catalytic properties for the simultaneous removal of 4-chlorophenol (4-CP) and Cr(VI). While nZVI enabled a fast removal of Cr(VI), it had a poor dechlorination ability. However, effective simultaneous removal of 4-CP and Cr(VI) was achieved with the transition metal modified nZVI, especially in the Pd/Fe bimetallic system. The enhanced catalytic activity of transition metal modified nZVI was primarily attributed to the formations of numerous nano-galvanic cells and atomic hydrogen species that facilitated electron transfer in the reaction system and played a key role in triggering the C-Cl bond cleavage, respectively. According to the dechlorination ability, the transition-metal catalysts examined in this study can be divided into three groups in descending order: the first being Pd and Ni, the second including Cu and Pt, while the last consisting of Au and Ag. The catalytic hydrodechlorination activity of bimetals can be well described by the volcano curve and rationally explained by the hydrogen adsorption energies on the metals, and was severely impaired by increasing Cr(VI) concentrations. Characterization results validated the formations of Fe(III)-Cr(III) hydroxide/oxyhydroxide on the bimetals surface after reacting with 4-CP and Cr(VI). This work provides the first insight into the catalytic properties of transition-metal modified nZVI for the effective removal of combined pollutants.

Investigation of a novel high-efficiency ion-permselective membrane module based on the electrochemically switched ion exchange scheme

Electric field-accelerated ion-permselective membrane (EISM) separation has attracted significant attention in recent years. Thus, herein, to further investigate the ion transport mechanism and optimize the separation efficiency, five types of ion-permselective membrane modules (IPMM I–V) based on the electrochemically switched ion exchange (ESIX) scheme were designed. Compared with the traditional ion separation systems, the in situ membrane-based ion separation system was set up with an extra pulse potential applied to the PPy/PSS/SSWM (polypyrrole/polystyrenesulfonate/stainless steel wire mesh) membrane. The continuous permselective separation of K⁺ as target ions was performed from dilute aqueous solution through the IPMM system. The pulse potential combined with the regulated cell voltage was functionalized synergistically to create an “ion-sieving effect” and effectively guide the target cations from the source cell to the receiving cell. Moreover, the formation of an equal potential volume in IPMM-V suppressed the reverse migration of the target ions and the detected ion flux across the membrane was 100 times that of the IPMM-I system. The ion transport mechanism was also analyzed in detail based on the equivalent circuit of the system, and the optimized operation parameters were obtained for the high-efficient ion separation system. These results can provide some beneficial information for the design and practical operation of novel EISM systems.

Novel ion permselective membrane modules based on the ESIX scheme.

Mobility and transformation of Cr(VI) on the surface of goethite in the presence of oxalic acid and Mn(II)

Goethite is an effective adsorbent for hexavalent chromium (Cr(VI)). Oxalic acid and other organic acids will affect the release, immobilization, and bioavailability of Cr(VI) in nature on the mineral surface. Mn(II) can accelerate the reduction of Cr(VI) with oxalic acid. Herein, the effects of oxalic acid and Mn(II) on the mobilization and transformation of adsorbed Cr(VI) on the surface of goethite were investigated in this study. The results revealed that Mn(II) could increase the adsorption of Cr(VI) by increasing the positive charge on the surface of goethite. The complexation of oxalic acid with the surface of goethite caused the adsorbed Cr(VI) to be released into the solution. Moreover, oxalic acid could undergo redox with adsorbed Cr(VI) through electron conduction on the surface of goethite, thereby resulting in the transformation of adsorbed Cr(VI) to Cr(III). During the reaction in the presence of oxalic acid, the concentration of Cr(III) increased from 0 to 13.9 mg/L. In addition, Mn(II), oxalic acid, and Cr(VI) could form unstable ester-like species in the solution, which accelerated the reduction of Cr(VI) to Cr(III). These findings of this study may enrich our understanding of the behaviors of Cr(VI) in the coexistence of goethite, oxalic acid, and Mn(II).

New Type Biomembrane: Transport and Biodegradation of Reactive Textile Dye

In traditional separation processes, there are environmental risks still because of the presence of toxic agents. Thus, a novel biomembrane microreactor named eco-green biomembrane (EgBM) was developed to perform the transport, biodegradation, and cleaning of a textile dye aqueous solution (3 mg/L) from the donor (i.e., textile dye) to the acceptor (i.e., laccase enzymes) phases. In the present work, Morchella esculenta pellets were used as carriers and degraders instead of using the traditional chemical carriers. The optimized EgBM was made of cellulose triacetate (16.1%) as a base polymer, 2-nitrophenyl octyl ether (25.2%) as a plasticizer, and M. esculenta fungus pellets (58.7%) as both carriers and degraders. A decoloration percentage of 98.6% ± 0.8 in 60 h was attained, which was due to two mechanisms: biosorption (15.4% ± 0.1) on fungal mycelium and biodegradation (83.2% ± 0.6) by laccase enzymes. The EgBM was achieved not only by the transport of reactive textile dyes used in the donor phase but also by the biodegradation and biosorption of the dyes.

Electro-membrane extraction of cadmium(II) by bis(2-ethylhexyl) phosphate/kerosene/polyvinyl chloride polymer inclusion membrane

The development of the electroplating and battery industries has increased the environmental problems and the needs for resource recovery of Cd(II). In this study, the Electro-membrane extraction (EME) behaviour of Cd(II) was investigated by using polymer inclusion membrane with bis(2-ethylhexyl) phosphate as carrier and polyvinyl chloride as base polymer(PD-PIM) at 0-80 V. Results showed that the EME of Cd(II) by PD-PIM can be obtained in the feed phase with pH 3-8 and stripping phase of dilute acid. Voltage is the main factor to increase the mass transfer rate of Cd(II). The applied electric field reduced the mass transfer activation energy of Cd(II) by PD-PIM and weakened the mass transfer interference of Cd(II) on the background material of the feed phase. After using kerosene-stabilised PD-PIM for operation at pH5, 60 V for 120 h, Cd(II) in the 1 L solution reduced from 15 mg/L to 0.08 mg/L, and the enrichment factor was 9.79.

Sustaining the efficiency of the Fe(0)/H2O system for Cr(VI) removal by MnO2 amendment

This study aims to provide new knowledge regarding the effect of MnO₂ co-presence on efficiency of Cr(VI) removal with Fe(0). Non-disturbed batch experiments (≤40 days) were conducted using two types of Fe(0) (milli- and micro-sized), two Cr(VI) concentrations (5 and 100 mg/L), in three different systems ("Fe(0) only", "MnO₂ only", and "Fe(0) + MnO₂"), at an initial pH value of 6.9. Compared to "Fe(0) only" system, the efficiency and rate of Cr(VI) removal were highly promoted in "Fe(0) + MnO₂" system; moreover, while for the "Fe(0) only" system removal of Cr(VI) was severely hindered by increasing Cr(VI) concentration, in "Fe(0) + MnO₂" system comparable high efficacies were noticed both at low and high concentration. Recycling experiments indicated that total Cr(VI) removal capacity of "Fe(0) + MnO₂" system was up to 48.1 times greater than of the "Fe(0) only" system. Enhanced removal of Cr(VI) with Fe(0) was achieved at low doses of MnO₂, with an optimal mass ratio Fe(0):MnO₂ of 4:1. The favorable synergistic effect observed in "Fe(0) + MnO₂" system was ascribed to capacity of MnO₂ to accelerate Fe(0) oxidative dissolution, and to generate supplementary amounts of secondary adsorbents/reductants with removal ability towards Cr(VI). This study provides compelling evidence that "Fe(0) + MnO₂" system could represent a highly efficient and cost-effective alternative for the abatement of Cr(VI) aqueous pollution.

Efficient removal of Cr(VI) from water by quaternized chitin/branched polyethylenimine biosorbent with hierarchical pore structure

A novel chitin-based biosorbent (QCP) was synthesized by cross-linking quaternized chitin and branched polyethylenimine with the aid of epichlorohydrin for efficient removal of Cr(VI) from water. Because it possessed both quaternary ammonium groups and amino groups as well as the hierarchical pore structure, QCP presented a maximum adsorption capacity of 387.7 mg/g according to the Langmuir isotherm at 25 °C. The biosorption of QCP achieved the equilibrium within 40 min and followed the pseudo-second-order kinetic model. QCP worked well even in the solution with high pH and high content of competing anions and, it exhibited an excellent reusability. The main Cr(VI) uptake mechanism was confirmed to be electrostatic attractions between Cr(VI) anions and quaternary ammonium groups as well as the protonated amino groups, and followed by partial reduction of Cr(VI) to Cr(III) by amines and hydroxyls. This work may provide a potential for Cr(VI) removal by chitin-based biosorbents.