Effects of inorganic electrolytes on zeta potentials of ceramic microfiltration membranes

Influence of suspended particles and dissolved organic matters on virus enrichment in reclaimed water by two-step tangential flow ultrafiltration: Phenomena and mechanisms

Enteric virus concentration in large-volume water samples is crucial for detection and essential for assessing water safety. Certain dissolution and suspension components can affect the enrichment process. In this study, tangential flow ultrafiltration (TFUF) was used as an enrichment method for recovering enteric virus in water samples. Interestingly, the bacteriophage MS2 recovery in reclaimed water and the reclaimed water without particles were higher than that in ultrapure water. The simulated reclaimed water experiments showed that humic acid (HA) (92.16% ± 4.32%) and tryptophan (Try) (81.50 ± 7.71%) enhanced MS2 recovery, while the presence of kaolin (Kaolin) inhibited MS2 recovery with an efficiency of 63.13% ± 11.17%. Furthermore, Atomic force microscopy (AFM) revealed that the MS2-HA cluster and the MS2-Try cluster had larger roughness values on the membrane surface, making it difficult to be eluted, whereas MS2-Kaolin cluster had compact surfaces making it difficult to be eluted. Additionally, the MS2-HA cluster is bound to the membrane by single hydrogen bond with SO, whereas both the MS2-Try cluster and the MS2-Kaolin cluster are bound to the membrane by two hydrogen bonds, making eluting MS2 challenging. These findings have potential implications for validating standardized methods for virus enrichment in water samples.

Effects of the Electric Double Layer Characteristic and Electroosmotic Regulation on the Tribological Performance of Water-Based Cutting Fluids

The electroosmosis effect is a complement to the theory of the traditional capillary penetration of cutting fluid. In this study, based on the electric double layer (EDL) characteristics at friction material/solution interfaces, the influences of additives and their concentrations on capillary electroosmosis were investigated, and a water-based cutting-fluid formulation with consideration to the electroosmosis effect was developed. The lubrication performance levels of cutting fluids were investigated by a four-ball tribometer. The results show that the EDL is compressed with increasing ionic concentration, which suppresses the electroosmotic flow (EOF). The specific adsorption of OH- ions or the dissociation of surface groups is promoted as pH rises, increasing the absolute zeta potential and EOF. The polyethylene glycol (PEG) additive adsorbed to the friction material surface can keep the shear plane away from the solid surface, reducing the absolute zeta potential and EOF. The electroosmotic performance of cutting fluid can be improved by compounding additives with different electroosmotic performance functions. Furthermore, electroosmotic regulators can adjust the zeta potential by the electrostatic adsorption mechanism, affecting the penetration performance of cutting fluid in the capillary zone at the friction interface. The improvement in the tribological performance of cutting fluid developed with consideration given to the electroosmosis effect is attributed to the enhancement of the penetration ability of the cutting fluid and the formation of more abundant amounts of lubricating film at the interface.

Oil-in-Water emulsions stabilized by alumina nanoparticles with organic electrolytes: Fate of particles

HYPOTHESIS

Oil-in-dispersion emulsions can be stabilized by like charged particles and surfactant. Surfactant adsorbs at the oil-water interface to reduce the interfacial tension and endow the interface with charge, while particles remain dispersed in the aqueous phase to provide electrostatic repulsion between droplets and particles. Can weakly surface-active organic electrolytes adsorb at the oil-water interface and behave like surfactants in stabilizing oil-in-dispersion emulsions with like charged particles?

EXPERIMENTS

Symmetrical organic electrolytes, tetraalkylammonium bromides (R₄NBr), with either no or very low interfacial activity endowing oil droplets with charge were combined with alumina nanoparticles to stabilize emulsions. The effect of R chain length (varying from methyl to butyl) on the type and stability of emulsions was investigated.

FINDINGS

Mixtures of high concentrations of short chain R₄NBr salts (R = methyl or ethyl) and alumina particles stabilise oil-in-water Pickering emulsions, whereas longer chain (R = propyl or butyl) analogues stabilize oil-in-dispersion emulsions assisted by alumina particles. Tetrapropylammonium and tetrabutylammonium cations adsorb at the oil-water interface reducing the interfacial tension and endowing the interface with charge. The stability of the oil-in-dispersion emulsions is dominated by the electrostatic repulsion between the droplets and between droplets and particles in the continuous aqueous phase.

SERS discrimination of single DNA bases in single oligonucleotides by electro-plasmonic trapping

Surface-enhanced Raman spectroscopy (SERS) sensing of DNA bases by plasmonic nanopores could pave a way to novel methods for DNA analyses and new generation single-molecule sequencing platforms. The SERS discrimination of single DNA bases depends critically on the time that a DNA strand resides within the plasmonic hot spot. In fact, DNA molecules flow through the nanopores so rapidly that the SERS signals collected are not sufficient for single-molecule analysis. Here, we report an approach to control the residence time of molecules in the hot spot by an electro-plasmonic trapping effect. By directly adsorbing molecules onto a gold nanoparticle and then trapping the single nanoparticle in a plasmonic nanohole up to several minutes, we demonstrate single-molecule SERS detection of all four DNA bases as well as discrimination of single nucleobases in a single oligonucleotide. Our method can be extended easily to label-free sensing of single-molecule amino acids and proteins.

Desalination and removal of pesticides from surface water in Mekong Delta by coupling electrodialysis and nanofiltration

The shortage of drinking water is a major problem in the rural areas of the Mekong Delta, especially, when surface water, a main local direct drinking water source is being threatened by pesticide pollution and salinity intrusion. A hybrid process coupling electrodialysis (ED) and nanofiltration (NF) is proposed as an effective process easy to setup in a small plant to treat complex matrix with high salinity and pesticide concentration as is the Mekong Delta surface water. Performance of the ED-NF integration was evaluated with synthetic solutions based on the comparison with a single NF step generally used for pesticide removal. Both energy consumption and water product quality were considered to assess process efficiency. The ED stage was designed to ensure a 50% removal of salinity before applying NF. As expected, the NF rejection is better in the hybrid process than in a case of a single NF step, especially for pesticide rejection. The integration of a NF stage operated with NF270 membrane consumes less energy than that with NF90 membrane but its efficiency was observed not high enough to respect the Vietnamese guidelines. Using NF90, the optimal recovery rate of the NF stage varies from 30 to 50% depending on the salt content in the feed.

The oxidative toxicity of Ag and ZnO nanoparticles towards the aquatic plant Spirodela punctuta and the role of testing media parameters

The toxicity effects of silver (nAg) and zinc oxide (nZnO) engineered nanoparticles (ENPs) on the duckweed Spirodela punctuta were studied to investigate the potential risks posed by these ENPs towards higher aquatic plants. The influence of media abiotic factors on the stability of the ENPs was also evaluated. Marked agglomeration of ENPs was observed after introduction into testing media whereby large particles settled out of suspension and accumulated at the bottom of testing vessels. The high ionic strength (IS) promoted agglomeration of ENPs because it reduced the inter-particle repulsion caused by a reduction in their surface charge. Low dissolution was observed for nAg, reaching only 0.015% at 1000 mg L(-1), whilst improved dissolution was observed for nZnO, only falling below analytical quantification at 0.1 mg L(-1) and lower. The quantification of free radicals namely, reactive oxygen and nitrogen species (ROS/RNS) and hydrogen peroxide (H2O2), indicated the induction of oxidative stress in plants exposed to the ENPs. A definite dose influence was observed for ROS/RNS volumes in plants exposed to nZnO for 14 days, a response not always observed. The total antioxidant capacity (TAC) and superoxide dismutase (SOD) activity in plants indicated varying degrees of oxidative toxicity caused by exposure to ENPs. This toxicity was driven mainly by particulates in plants exposed to nAg, whilst dissolved Zn(2+) was the main driver for toxicity in plants exposed to nZnO. Our findings suggest that the toxicity of nAg and nZnO could be caused by both the particulates and ionic forms, as modified by media properties.

Humic acid removal and easy-cleanability using temperature-responsive ZrO2 tubular membranes grafted with poly(N-isopropylacrylamide) brush chains

New poly(N-isopropylacrylamide) brushes grafted with ZrO2 (PNIPAAm-g-ZrO2) composite membranes, which had been prepared in our laboratory, were used for humic acid (HA) removal. We found that the fluxes associated with such membranes, when compared to those obtained from unmodified ZrO2 membranes, declined slightly at both 25 °C and 35 °C. The PNIPAAm-g-ZrO2 membrane achieved a high rejection, of 98.0%, at a suitable steady flux of 111.9 L m(-2) h(-1) at 25 °C. This membrane exhibited good anti-fouling properties as well as improved membrane performance during filtration of HA. The important role of pH and Ca(2+) concentration in HA removal was also investigated. Lower adsorption fouling and a higher rejection were obtained at higher pH levels. The Ca(2+) ions reduced the electrostatic exclusion and played a cross-linking role between HA and the PNIPAAm-g-ZrO2 membrane surface. Fouling was severe in the presence of Ca(2+). These tests led to the development of an environment-friendly membrane cleaning method, by means of temperature-change water elution around LCST of PNIPAAm-brushes. After the alternate temperature-change (25 °C/35 °C) cleaning, a flux recovery of 98.2% was obtained for the PNIPAAm-g-ZrO2 membrane. Moreover, after four repeated experiments, the anti-fouling and easy-cleaning properties were still maintained. It is implied that PNIPAAm-brushes were firmly "stuck" to the membrane surface, and could not easily be removed by water cleaning or HA filtration. The PNIPAAm-g-ZrO2 membranes exhibited good stability and great potential for HA removal.

Rejection of Bromide and Bromate Ions by a Ceramic Membrane

Effects of pH and the addition of calcium chloride (CaCl(2)) on bromate (BrO(3) (-)) and bromide (Br(-)) rejection by a ceramic membrane were investigated. Rejection of both ions increased with pH. At pH 8, the rejection of BrO(3) (-) and Br(-) was 68% and 63%, respectively. Donnan exclusion appears to play an important role in determining rejection of BrO(3) (-) and Br(-). In the presence of CaCl(2), rejection of BrO(3) (-) and Br(-) ions was greatly reduced, confirming the importance of electrostatic interactions in determining rejection of BrO(3) (-) and Br(-). The effect of Ca(2+) is so pronounced that in most natural waters, rejection of both BrO(3) (-) and Br(-) by the membrane would be extremely small.

Comparative toxicity assessment of CeO2 and ZnO nanoparticles towards Sinorhizobium meliloti, a symbiotic alfalfa associated bacterium: use of advanced microscopic and spectroscopic techniques

Cerium oxide (CeO(2)) and zinc oxide (ZnO) nanoparticles (NPs) are extensively used in a variety of instruments and consumer goods. These NPs are of great concern because of potential toxicity towards human health and the environment. The present work aimed to assess the toxic effects of 10nm CeO(2) and ZnO NPs towards the nitrogen fixing bacterium Sinorhizobium meliloti. Toxicological parameters evaluated included UV/Vis measurement of minimum inhibitory concentration, disk diffusion tests, and dynamic growth. Ultra high-resolution scanning transmission electron microscopy (STEM) and infrared spectroscopy (FTIR) were utilized to determine the spatial distribution of NPs and macromolecule changes in bacterial cells, respectively. Results indicate that ZnO NPs were more toxic than CeO(2) NPs in terms of inhibition of dynamic growth and viable cells counts. STEM images revealed that CeO(2) and ZnO NPs were found on bacterial cell surfaces and ZnO NPs were internalized into the periplasmic space of the cells. FTIR spectra showed changes in protein and polysaccharide structures of extra cellular polymeric substances present in bacterial cell walls treated with both NPs. The growth data showed that CeO(2) NPs have a bacteriostatic effect, whereas ZnO NPs is bactericidal to S. meliloti. Overall, ZnO NPs were found to be more toxic than CeO(2) NPs.