Integrating Ultrafiltration Membranes with Flocculation and Activated Carbon Pretreatment Processes for Membrane Fouling Mitigation and Metal Ion Removal from Wastewater.

The presence of metal ions in an aqueous medium is an ongoing challenge throughout the world. Processes employed for metal ion removal are developed continuously with the integration of these processes taking center stage. Herein, an integrated system consisting of flocculation, activated carbon (AC), and an ultrafiltration (UF) membrane was assessed for the removal of multiple metal ions contained in wastewater generated from a university chemistry research laboratory. The quality of the wastewater was established before and further determined after treatment with inductively coupled plasma optical emission spectrometry (ICP-OES) for metal content, total dissolved solids (TDS), turbidity, electrical conductivity (EC), and pH. Assessing the spent AC indicated minimal structural changes, indicating a potential for further reuse; for instance, the BET for both the pristine and spent AC exhibited type I isotherms with a mesoporous structure, indicating no major structural changes due to metal complexation. The relative performance of the integrated system indicated that the use of flocculation improved the water quality of metal-laden wastewater for safe disposal. The integrated treatment systems exhibited high removal efficiencies between 80 and 99.99% for all the metal ions except for Mn (<0.008 mg L-1) and Cr (<0.016 mg L-1) both at ca. 70%, indicative of the positive influence of the polyelectrolyte in the treatment process. The fabricated UiO-66-NH2@GO membranes (Z4 and Z5) exhibited high fouling resistance and reusability potential as well as relatively high pure water flux. Consequently, the integrated process employed for the treatment of laboratory metal-containing wastewater is promising as a generic approach to improving the quality of metal-containing wastewater to meet the standards of discharging limits in South Africa.

Antibacterial studies of Ag@HPEI@GO nanocomposites and their effects on fouling and dye rejection in PES UF membranes.

A series of polyethersulfone membranes containing Ag@HPEI@GO composite was fabricated using non-solvent induced phase separations (NIPS) to mitigate against biofilm causing bacteria and modulate solute rejection. All materials produced and used were fully characterised using a combination of appropriate physicochemical techniques including FTIR, XRD, BET, SEM, AFM. The GO-based fillers exhibited bactericidal activities. The bactericidal activities of GO, HPEI@GO against Escherichia Coli (E. coli) were observed at 8 mg mL-1 whilst Ag@HPEI@GO composites exhibit bactericidal activities against E. coli at 4 mg mL-1. Against Klebsiella pneumonia (K. pneumonia), GO bactericidal activities were observed at 8 mg mL-1, whilst HPEI@GO and Ag@HPEI@GO bactericidal activities on K. pneumonia were observed at 4 mg mL-1. Against Staphylococcus aureus (S. aureus), GO exhibit bactericidal activities at 8 mg mL-1, HPEI@GO and Ag@HPEI@GO composites exhibit bactericidal activities on S. aureus at 4 mg mL-1. The aforementioned microorganisms are among the microorganism that causes biofilm formation on surfaces. The membrane performance was assessed by measuring pure water flux, solute rejections and fouling propensity with three different organic dye molecules and bovine serum albumin (BSA). All composite membranes (GO/PES, HPEI@GO/PES, and Ag@HPEI@GO/PES) exhibited increased hydrophilicity and higher pure water flux compared to the baseline PES membranes with concomitant increase in fouling resistance, The observed flux recovery ratios (FRR) were 80% (GO/PES), 70% (HPEI@GO/PES) and 69% (Ag@HPEI@GO/PES) respectively compared to the 45% FRR observed for the baseline PES membrane after BSA fouling. Congo red (CR) used as an indicator for molecular cut-off of UF membranes was rejected above 95% by all nanocomposite membranes. Furthermore, the nanocomposite membranes-maintained rejection for the positively charged methylene blue (MB) of above 90% whilst rejection observed for amaranth (AR) dye decreased from 80 to 58% with increasing filler content in the PES matrix. The results demonstrate the positive influence of GO, HPEI@GO and Ag/HPEI@GO nanofillers on flux, fouling and solute rejection performance of resultant PES nanocomposite membranes.

Influence of the Zeolite ZSM-22 Precursor on a UF-PES Selective Substrate Layer for Salts Rejection.

Fabrication of the ZSM-22/Polyethersulfone (ZSM-22/PES) membranes as selective salt filters represent a growing membrane technological area in separation with the potential of high economic reward based on its low energy requirements. The incorporation of ZSM-22 zeolite material as additives into the PES polymer matrix has the prospective advantage of combining both the zeolite and polymer features while overcoming the limitations associated with both materials. This work investigated the influence of the nature of the silica precursor on ZSM-22 zeolite hydrothermally synthesised using colloidal (C60) and fumed (C60) silica to Si/Al of 60. The successful synthesis of the highly crystalline zeolitic materials was confirmed through XRD, FTIR, and SEM with EDX. The ZSM-22 additives were directly dispersed into a PES polymeric matrix to form a casting solution for the preparation of the ZSM-22/PES selective substrate layers via a phase inversion method for salts rejection. The polymeric PES was selected as an organic network in which the content of the ZSM-22 zeolite (ranging between 0 and 1.0 wt.%), was obtained and characterised by XRD, FTIR, and SEM analysis, as well as water contact angle (WCA) measurement and dead-end filtration cell. The phase inversion preparation method has induced the resulting ZSM-22/PES NF substrates anisotropy, as attributed to a high water flux to the above 700 L·m-2·h-1; high selectivity and rejection of salts to above 80% is revealed by the obtained results. The materials also exhibited improved antifouling behavior to above 70% flux recovery ratios. As such, the nature of the silica precursor influences ZSM-22 zeolite synthesis as a potential additive in the PES polymer matrix and led to the enhanced performance of the pure PES ultrafiltration membrane.

An In Situ Incorporation of Acrylic Acid and ZnO Nanoparticles into Polyamide Thin Film Composite Membranes for Their Effect on Membrane pH Responsive Behavior.

This paper focuses on an in situ interfacial polymerization modification of polyamide thin film composite membranes with acrylic acid (AA) and zinc oxide (ZnO) nanoparticles. Consequent to this modification, the modified polyamide thin film composite (PA-TFC) membranes exhibited enhanced water permeability and Pb (II) heavy metal rejection. For example, the 0.50:1.50% ZnO/AA modified membranes showed water permeability of 29.85 ± 0.06 L·m-2·h-1·kPa-1 (pH 3), 4.16 ± 0.39 L·m-2·h-1·kPa-1 (pH 7), and 2.80 ± 0.21 L·m-2·h-1·kPa-1 1 (pH 11). This demonstrated enhanced pH responsive properties, and improved water permeability properties against unmodified membranes (2.29 ± 0.59 L·m-2·h-1·kPa-1, 1.79 ± 0.27 L·m-2·h-1·kPa-1, and 0.90 ± 0.21 L·m-2·h-1·kPa-1, respectively). Furthermore, the rejection of Pb (II) ions by the modified PA-TFC membranes was found to be 16.11 ± 0.12% (pH 3), 30.58 ± 0.33% (pH 7), and 96.67 ± 0.09% (pH 11). Additionally, the membranes modified with AA and ZnO/AA demonstrated a significant pH responsiveness compared to membranes modified with only ZnO nanoparticles and unmodified membranes. As such, this demonstrated the swelling behavior due to the inherent "gate effect" of the modified membranes. This was illustrated by the rejection and water permeation behavior, hydrophilic properties, and ion exchange capacity of the modified membranes. The pH responsiveness for the modified membranes was due to the -COOH and -OH functional groups introduced by the AA hydrogel and ZnO nanoparticles.

Antifouling Polyethersulfone-Petrol Soot Nanoparticles Composite Ultrafiltration Membrane for Dye Removal in Wastewater.

Engineered nanoparticles are known to boost membrane performance in membrane technology. Hitherto, tunable properties that lead to improved hydrophilicity due to increased surface oxygen functionalities upon oxidation of petrol soot have not been fully exploited in membrane filtration technology. Herein, the integration of oxidized petrol soot nanoparticles (PSN) into polyethersulfone ultrafiltration membranes produced via phase inversion technique for dye removal in wastewater is reported. The nanoparticles, as well as the composite membranes, were characterized with diverse physicochemical methods, particularly TEM, SEM, BET, AFM, contact angle, etc. The effect of varying the ratio of PSN (0.05-1.0 wt %) on the properties of the composite membrane was evaluated. The composite membranes displayed increased hydrophilicity, enhanced pure water flux, and antifouling properties relative to the pristine membrane. For example, the obtained pure water flux increased from 130 L·m-2·h-1 for base membrane to 265 L·m-2·h-1 for the best composite membrane (M4). The best flux recovery ratio (FRR) observed for the membranes containing PSN was ca. 80% in contrast to 49% obtained with the pristine membrane indicative of the positive influence of PSN on membrane antifouling behavior. Furthermore, the PSN composite membranes displayed relatively selective anionic dye rejection of ˃95% for Congo red and between 50-71% for methyl orange compared with 42-96% rejection obtained for cationic methylene blue dye with increasing PSN content. The successful fabrication of polyethersulfone-PSN composite membranes by a simple blending process opens a novel route for the preparation of economical, functional, and scalable water purification membranes capable of addressing the complex issue of water remediation of organic azo dyes.

Development of ZSM-22/Polyethersulfone Membrane for Effective Salt Rejection.

ZSM-22/polyethersulfone membranes were prepared for salt rejection using modelled brackish water. The membranes were fabricated via direct ZSM-22 incorporation into a polymer matrix, thereby inducing the water permeability, hydrophilicity and fouling resistance of the pristine polyethersulfone (PES) membrane. A ZSM-22 zeolite material with a 60 Si/Al ratio, high crystallinity and needle-like morphologies was produced and effectively used as a nanoadditive in the development of ZSM-22/PES membranes with nominal loadings of 0-0.75 wt.%. The characterisation and membrane performance evaluation of the resulting materials with XRD, BET, FTIR, TEM, SEM and contact angle as well as dead-end cell, respectively, showed improved water permeability in comparison with the pristine PES membrane. These ZSM-22/PES membranes were found to be more effective and superior in the processing of modelled brackish water. The salt rejection of the prepared membranes for NaCl and MgCl2 was effective, while they exhibited quite improved water flux and flux recovery ratios in the membrane permeability and anti-fouling test. This indicates that different amounts of ZSM-22 nanoadditives produce widely divergent influences on the performance of the pristine PES membrane. As such, over 55% of salt rejection is observed, which means that the obtained membranes are effective in salt removal from water.

Antifouling Properties of Silver-Zinc Oxide Polyamide Thin Film Composite Membrane and Rejection of 2-Chlorophenol and 2,4-Dichlorophenol.

The silver-zinc oxide (Ag-ZnO) polyamide thin film composite (PA-TFC) membrane was prepared by interfacial polymerization. The Ag-ZnO/PA-TFC membrane was characterized by attenuated total reflectance fourier-transform infrared spectroscopy (ATR-FTIR) for polyamide functional groups and contact angle for surface hydrophilicity. The Ag-ZnO/PA-TFC membrane was further characterized by Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) for morphology and surface roughness, respectively. The performance of the fabricated membrane was investigated using pure water flux, permeability, rejection, flux recovery, and fouling resistance using low molecular weight organic pollutants, 2-chlorophenol (2-CP) and 2,4-dichlorophenol (2,4-DCP). The results were compared to the neat (PA-TFC) membrane. It was observed that incorporation of Ag-ZnO nanocomposites into the PA-TFC membrane improved hydrophilicity, permeation, rejection, and fouling resistance properties of the membrane. The contact angle decreased from 62.8° to 54° for PA-TFC and the Ag-ZnO/PA-TFC membrane, respectively. The presence of Ag-ZnO enhanced permeability of the membrane from 0.9 (Lm-2h-1bar-1) to 1.9 (Lm-2h-1bar-1). Modification of the membrane with Ag-ZnO further showed an enhanced rejection of 2-CP and 2,4-DCP from 43% to 80% and 58% to 85%, respectively. The 2,4-DCP molecules were rejected more than 2-CP due to enhanced repulsive forces from the extra Cl ion. A high flux recovery of about 95% was achieved for the modified membrane compared to 64% for the neat membrane. The improved flux recovery was an indication of enhanced antifouling propensity.

Adsorptive removal of lead from acid mine drainage using cobalt-methylimidazolate framework as an adsorbent: kinetics, isotherm, and regeneration.

In this work, cobalt-methylimidazolate framework has been used as an adsorbent in the removal of Pb(II) from acid mine drainage in adsorption batch system. X-ray diffraction, Fourier-transform infrared spectroscopy, Brunauer-Emmet-Teller and transmission electron microscope were used for structural, morphological, and surface characteristics of cobalt-methylimidazolate framework. The concentration of heavy metal ions in water samples was measured by inductively coupled plasma optical emission spectrometry. Different experimental factors/variables (such as contact time, dosage, and pH) affecting the adsorption of Pb(II) from acid mine drainage were optimized by response surface methodology based on central composite design. Under optimized experimental parameters, the maximum adsorption capacity of Pb(II) was found to be 105 mg g-1. The nature of the adsorption process was investigated using Langmuir and Freundlich isotherm models. The obtained data best fitted Langmuir isotherm model suggesting a homogeneous adsorption process. Furthermore, the adsorption mechanism was investigated using five kinetic models, that is, pseudo-first order, pseudo-second order, intraparticle diffusion and Elovich model. The adsorption data fitted better to pseudo-second-order followed by intra-particle diffusion kinetic models suggesting that the adsorption mechanism is dominated by both chemical and physical adsorption processes. The adsorbent could be regenerated up to 8 cycles and it was successfully used in the removal of lead in real acid mine drainage samples.

Monolayer-protected clusters of gold nanoparticles: impacts of stabilizing ligands on the heterogeneous electron transfer dynamics and voltammetric detection.

Surface electrochemistry of novel monolayer-protected gold nanoparticles (MPCAuNPs) is described. Protecting ligands, (1-sulfanylundec-11-yl)tetraethylene glycol (PEG-OH) and (1-sulfanylundec-11-yl)poly(ethylene glycol)ic acid (PEG-COOH), of three different percent ratios (PEG-COOH:PEG-OH), 1:99 (MPCAuNP-COOH(1%)), 50:50 (MPCAuNP-COOH(50%)), and 99:1 (MPCAuNP-COOH(99%)), were studied. The electron transfer rate constants (k(et)/s(-1)) in organic medium decreased as the concentration of the surface-exposed -COOH group in the protecting monolayer ligand is increased: MPCAuNP-COOH(1%) (approximately 5 s(-1)) > MPCAuNP-COOH(50%) (approximately 4 s(-1)) > MPCAuNP-COOH(99%) (approximately 0.5 s(-1)). In aqueous medium, the trend is reversed. The surface pK(a) was estimated as approximately 8.2 for the MPCAuNP-COOH(1%), while both MPCAuNP-COOH(50%) and MPCAuNP-COOH(99%) showed two pK(a) values of about 5.0 and approximately 8.0. These results have been interpreted in terms of the quasi-solidity and quasi-liquidity of the terminal -OH and -COOH head groups, respectively. MPCAuNP-COOH(99%) excellently suppressed the voltammetric response of the ascorbic acid but enhanced the electrocatalytic detection of epinephrine compared to the other MPCAuNPs studied. This study reveals important factors that should be considered when designing electrode devices that employ monolayer-protected gold nanoparticles and possibly for some other redox-active metal nanoparticles.

Electrocatalytic sensor devices: (I) cyclopentadienylnickel(II) thiolato Schiff base monolayer self-assembled on gold.

The fabrication of a self-assembled monolayer (SAM) of a cyclopentadienylnickel(II) thiolato Schiff base compound, [Ni(SC(6)H(4)NC(H)C(6)H(4)OCH(2)CH(2)SMe)(eta(5)-C(5)H(5))](2) on a gold electrode is described. Effective electronic communication between the Ni(II) centres and the gold surface was established by electrochemically cycling the Schiff base-doped Au electrode in 0.1M NaOH from -200mV to +600mV. The SAM-modified electrode exhibited quasi-reversible electrochemistry. The integrity of this electrocatalytic SAM, with respect to its ability to block and electro-catalyse certain Faradaic processes, was interrogated using cyclic voltammetric experiments. The formal potential, E degrees ', varied with pH to give a slope of about -30mVpH(-1). The surface concentration, G, of the nickel redox centres was found to be 1.548x10(-11)molcm(-2). By electrostatically doping the SAM using an applied potential of +700mV versus Ag/AgCl, in the presence of horseradish peroxidase (HRP), it was fine-tuned for amperometric determination of H(2)O(2). The electrocatalytic-type biosensor displayed typical Michaelis-Menten kinetics and the limit of detection was found to be 6.25mM.

[2,6-Bis(isopropylthiomethyl)phenyl-kappa3S,C1,S']bromopalladium(II).

The title compound, [PdBr(C(14)H(21)S(2))] or [PdBr[C(6)H(3)(CH(2)S(i)Pr)(2)-2,6]], exhibits square-planar geometry at the Pd centre, with three atoms of the square plane provided by the rigid thiopincer ligand, i.e. 1,3-bis(thiomethyl)benzene.