Removal of emerging organic micropollutants via modified-reverse osmosis/nanofiltration membranes: A review

Hazardous micropollutants (MPs) such as pharmaceutically active compounds (PhACs), pesticides and personal care products (PCPs) have emerged as a critical concern nowadays for acquiring clean and safe water resources. In the last few decades, innumerable water treatment methods involving biodegradation, adsorption and advanced oxidation process have been utilized for the removal of MPs. Of these methods, membrane technology has proven to be a promising technique for the removal of MPs due to its sustainability, high efficiency and cost-effectiveness. Herein, the aim of this article is to provide a comprehensive review regarding the MPs rejection mechanisms of reverse osmosis (RO) and nanofiltration (NF) membranes after incorporation of nanomaterials and also surface modification atop the PA layer. Size exclusion, adsorption and electrostatic charge interaction mechanisms play important roles in governing the MP removal rate. In addition, this review also discusses the state-of-the-art research on the surface modification of thin film composite (TFC) membrane and nanomaterials-incorporated thin film nanocomposite (TFN) membrane in enhancing MPs removal performance. It is hoped that this review can provide insights in modifying the physicochemical properties of NF and RO membranes to achieve better performance in water treatment process, particularly for the removal of emerging hazardous substances.

Enhanced Removal of Endocrine-Disrupting Compounds from Wastewater Using Reverse Osmosis Membrane with Titania Nanotube-Constructed Nanochannels

This paper presents a comprehensive study of the performance of a newly developed titania nanotube incorporated RO membrane for endocrine-disrupting compound (EDC) removal at a low concentration. EDCs are known as an emerging contaminant, and if these pollutants are not properly removed, they can enter the water cycle and reach the water supply for residential use, causing harm to human health. Reverse osmosis (RO) has been known as a promising technology to remove EDCs. However, there is a lack of consensus on their performance, especially on the feed concentrations of EDC that vary from one source to another. In this study, polyamide thin-film composite (PA TFC) membrane was incorporated with one-dimensional titania nanotube (TNT) to mitigate trade-off between water permeability and solute rejection of EDC. The characterization indicated that the membrane surface hydrophilicity has been greatly increased with the presence of TNT. Using bisphenol A (BPA) and caffeine as model EDC, the removal efficiencies of the pristine TFC and thin-film nanocomposite (TFN) membranes were evaluated. Compared to TFC membrane, the membrane modified with 0.01% of TNT exhibited improved permeability of 50% and 49% for BPA and caffeine, respectively. A satisfactory BPA rejection of 89.05% and a caffeine rejection of 97.89% were achieved by the TNT incorporated TFN membranes. Furthermore, the greater hydrophilicity and smoother surface of 0.01 TFN membrane led to lower membrane fouling tendency under long-term filtration.

The Influences of 1-Butyl-3-Methylimidazolium Tetrafluoroborate on Electrochemical, Thermal and Structural Studies as Ionic Liquid Gel Polymer Electrolyte

After decades of development, ionic liquid gel polymer electrolytes (ILGPEs) are currently experiencing a renaissance as a promising electrolyte to be used in electrochemical devices. Their inherent tendency towards poor electrochemical properties have limited their applications and commercialization activities. Henceforth, gel polymer electrolyte (GPE) is being introduced to alleviate the abovementioned issues. In this work, the assessment of the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate [BMIM][BF₄] in poly (vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) to form ILGPE was done. The relationship of [BMIM][BF₄] towards the dielectric properties at different wt. % ratios and temperature was ascertained. The results indicated that [BMIM]BF₄ is able to facilitate fast conduction. Moreover, it was found that [BMIM][BF₄] could serve as an effective agent in reducing crystallinity and glass transition temperature of the polymer and thus enhanced the ionic conductivity of the samples. Notwithstanding, the ILGPE sample possessed a high thermal stability up to 300 °C and good electrochemical stability of 4.2 V which are beneficial for operation in electrochemical devices. All in all, the correlation between the ionic liquid chemistry and electrochemical performances could provide a valuable insight to rational selection and design for ILGPE electrolytes.

Cysteine reactivity and oligomeric structures of phospholamban and its mutants

To test models for the pentameric structure of phospholamban (PLB) and study its structure and molecular dynamics in SDS solution, we characterized recombinant PLB and several of its mutants by (a) reactivity of cysteine residues toward DTNB [5, 5'-dithiobis(2-nitrobenzoic acid)] and a thiol-reactive spin label, (b) oligomeric state on SDS-PAGE, and (c) EPR of the spin-labeled proteins. WT-PLB has three cysteine residues (36, 41, and 46), all located in the hydrophobic C-terminal transmembrane region. In SDS at pH 7.5, exhaustive reaction with either sulfhydryl reagent resulted in essentially 2 mol of cysteine reacted/mol of WT-PLB, with only slight destabilization of the native pentameric structure. When WT-PLB was denatured in guanidine at pH 8.1, all three cysteines reacted, disrupting the pentamer, which was restored upon cleavage of the disulfide bonds with DTT. In the tetrameric mutant C41L-PLB, the two remaining cysteine residues reacted, reversibly destabilizing the tetramer. In the monomeric mutant L37A-PLB, all three cysteines reacted. The pentameric double cysteine replacement mutant C36,46A-PLB showed negligible reactivity. We conclude that Cys-41 is the unreactive cysteine in PLB and is located at a crucial site for the maintenance of the pentameric structure. EPR spectra in SDS of spin-labeled WT-PLB and mutants correlate with the oligomeric state on SDS-PAGE; oligomeric proteins show decreased spin-label mobility compared with monomers. Molecular dynamics calculations were used to construct an atomic model for the transmembrane region of the PLB pentamer, constrained by previous mutagenesis results and the results of the present study. We conclude that (a) the mobilities of spin-labels attached to PLB and its mutants are sensitive to oligomeric state and (b) the pattern of cysteine reactivity, spin-label mobility, and oligomeric state supports a structural model for the PLB pentamer in which interactions between each pair of subunits are stabilized by a leucine-isoleucine zipper.

Genomic organization, 5' flanking enhancer region, and chromosomal assignment of the cell cycle gene, p55Cdc

p55Cdc is a mammalian homologue of a family of cell cycle proteins from widely divergent species, which contains WD repeats and has been implicated in cell cycle-regulated ubiquitin-mediated proteolysis. p55Cdc is highly expressed in proliferating but not in differentiated or growth-arrested cells. The expression, phosphorylation, and degradation of this protein have been shown to be cell cycle-regulated. We analyzed a 5.3-kb genomic region that contains the entire rat p55Cdc gene. The gene contains 10 exons ranging in size from 97 to 373 bp. The promoter region has a TAT box, four E-box consensus sequences, and potential binding sites for cell cycle-specific transcription factors. In transient transfection assays, a construct containing a 1000-nucleotide p55Cdc promoter region upstream of the chloramphenicol acetyltransferase reporter gene demonstrated a 12-fold increase in transcriptional activity. Finally, using radiation hybrid mapping techniques, we localized this gene to the human chromosome, 9q13-21.