“Switch-Off-On” Detection of Fe3+ and F− Ions Based on Fluorescence Silicon Nanoparticles and Their Application to Food Samples

An approach to the detection of F− ions in food samples was developed based on a “switch-off-on” fluorescence probe of silicon nanoparticles (SiNPs). The fluorescence of the synthetic SiNPs was gradually quenched in the presence of Fe3+ ion and slightly recovered with the addition of F− ion owing to the formation of a stable and colorless ferric fluoride. The fluorescence recovery exhibited a good linear relationship (R2 = 0.9992) as the concentration of F− ion increased from 0 to 100 μmol·L−1. The detection limit of the established method of F− ion was 0.05 μmol·L−1. The recovery experiments confirmed the accuracy and reliability of the proposed method. The ultraviolet–visible spectra, fluorescence decays, and zeta potentials evidenced the fluorescence quenching mechanism involving the electron transfer between the SiNPs and Fe3+ ion, while the fluorescence recovery resulted from the formation of ferric fluoride. Finally, SiNPs were successfully applied to detect F− ions in tap water, Antarctic krill, and Antarctic krill powder.

Synthesis and characterization of novel thermo- and salt-sensitive amphoteric terpolymers based on acrylamide derivatives

A novel linear amphoteric terpolymers based on neutral monomer — N-isopropylacrylamide (NIPAM), ani- onic monomer — 2-acrylamido-2-methyl-1-propanesulfonic acid sodium salt (AMPS), and cationic mono- mer — (3-acrylamidopropyl) trimethylammonium chloride (APTAC) were synthesized by free-radical polymerization in aqueous solution and characterized by methods of 1H NMR and FTIR spectroscopy, TGA, GPC, Dynamic light scattering (DLS) and zeta-potential. The thermal and salt sensitivity of amphoteric ternary polymers of various compositions, particularly, [NIPAM]:[AMPS]:[APTAC] = 90:2.5:7.5; 90:5:5; 90:7.5:2.5 mol.% were studied in aqueous and aqueous-salt solutions in the temperature range from 25 to 60 C and at the NaCl ionic strength  interval from 10–3 to 1M. It was found that due to hydrophobic/hydrophilic balance, the temperature dependent conformational and phase change of macromolecular chains becomes sensitive to salt addition and allows the fine-tuning of the phase transition. In aqueous and aqueous-salt solutions, the average hydrodynamic size of amphoteric terpolymers is varied from 8 to 300 nm exhibiting bimodal distribution at room temperature. The number average (Mn) and weight average (Mw) molecular weights, polydispersity index (PDI), and zeta-potentials of amphoteric terpolymers in aqueous solu- tions were determined

Multi-physics study of acoustofluidic delivery agents' clustering behavior

Acoustofluidicly manipulated microbubbles (MBs) and echogenic liposomes (ELIPs) have been suggested as drug delivery systems for the ‘on demand’ release of drug in target tissue. This requires a clear understanding of their behaviour during ultrasonication and after ultrasonication stops. The main focus of this study is to investigate the behaviour of MBs and ELIPs clusters after ultrasonication stops and the underlaying cause of cluster diffusion considering electrostatic repulsion, steric repulsion and Brownian motion. It also examines the capability of existing models used to predict MBs’ attraction velocity due to secondary radiation force, on predicting ELIPs’ attraction velocity. Tunable resistive pulse sensing (TRPS) and phase analysis light scattering (PALS) techniques were used to measure zeta potentials of the agents and the size distributions were measured using TRPS. The zeta potentials were found to be -2.43 mV and -0.62 mV for Definity™ MBs, and -3.62 mV and -2.35 mV for ELIPs using TRPS and PALS, respectively. Both agents were shown to have significant cluster formation at pressures as low as 6 kPa. Clusters of both agents were shown to diffuse as sonication stops at a rate that approximately equals the sum of the diffusion coefficients of the agents forming them. The de-clustering behaviours are due to Brownian motion as no sign of electrostatic repulsion was observed and particles movements were observed to be faster for smaller diameters. These findings are important to design and optimise effective drug delivery systems using acoustofluidically manipulated MBs and ELIPs.

Manganese Assisted Waterflooding Processes for Enhanced Oil Recovery in Carbonates

Modifying the wettability of carbonate formations through divalent foreign metal incorporation can become a cost-effective practical method for enhanced oil recovery (EOR) applications. The addition of manganese ions to both high salinity water (HSW) and tailored SmartWater at dilute concentrations is exploited in this study to maximize the interfacial potential and promote water-wet conditions in carbonate reservoirs. In this experimental investigation, the impact of manganese ions on zeta-potentials at calcite/brine and crude oil/brine interfaces is first determined by measuring zeta-potentials in calcite suspensions and oil emulsions. Two different water chemistries representative of HSW (~60,000 ppm TDS) and a low salinity tailored SmartWater (~6,000 ppm TDS) were used. The measurements were then extended to carbonate rocks and reservoir cores by performing contact angle and spontaneous imbibition tests at reservoir conditions. The oil-water interfacial tensions are also measured to understand the interactions of manganese ions at the oil/brine interface. The zeta potential results showed a positive consistent trend, with the addition of 100-1,000 ppm of Mn+2 ions in the form of MnSO4 to the high salinity water, to impact the wetting transition towards water-wet conditions in carbonates. The addition of Mn+2 ions at a concentration of 100-1,000 ppm to HSW enhanced the electrokinetic interactions to favorably alter surface charges at both oil/brine and calcite/brine interfaces. These findings based on eletrokinetic interactions demonstrated good agreement with contact angle data wherein manganese ions in HSW were able to drastically decrease the contact angles from 156 to 88°. Conversely, insignificant changes in oil-water interfacial tensions were observed due to manganese ions. The manganese assisted spontaneous imbibition oil recoveries were increased by about 10% in HSW. Mn+2 ions showed the ability to increase the negative potentials at both calcite/brine and oil/brine interfaces. The obvious trend of such enhanced electrical potential due to Mn+2 addition at the calcite interface supports the claim that Mn+2 selectively gets incorporated into the calcite crystal to modify its surface chemistry. This is expected to increase the surface charges of same polarity at the two opposing interfaces and promote the electrostatic repulsion to inherently change the surface preference towards water-wet conditions. This work for the first time identified the favorable impact of incorporating Mn+2 ions under optimized conditions to enhance the wetting transition in carbonate reservoirs. Such new knowledge gained from this experimental study highlights the practical significance of Mn+2 ions as cheap and sustainable wettability modifiers for EOR applications in carbonate reservoirs.

Steric Effects on Electroosmotic Nano-Thrusters under High Zeta Potentials

Here, space electroosmotic thrusters in a rigid nanochannel with high wall zeta potentials are investigated numerically, for the first time, considering the effect of finite size of the ionic species. The effect, which is called a steric effect, is often neglected in research about micro/nano thrusters. However, it has vital influences on the electric potential and flow velocity in electric double layers, so that the thruster performances generated by the fluid motion are further affected. These performances, including thrust, specific impulse, thruster efficiency, and the thrust-to-power ratio, are described by using numerical algorithms, after obtaining the electric potential and velocity distributions under high wall zeta potentials ranging from −25.7 mV to −128.5 mV. As expected, the zeta potential can promote the development of thruster performances so as to satisfy the requirement of space missions. Moreover, for real situation with consideration of the steric effect, the thruster thrust and efficiency significantly decrease to 5–30 micro Newtons and 80–90%, respectively, but the thrust-to-power ratio is opposite, and expends a short specific impulse of about 50–110 s.

A Novel Zein-Based Composite Nanoparticles for Improving Bioaccessibility and Anti-Inflammatory Activity of Resveratrol

A microbial transglutaminase-induced cross-linked sodium caseinate (MSC) was used to stabilize zein nanoparticles, and the study was to investigate whether zein-MSC nanoparticles (zein-MSC NPs) can be used as an encapsulation carrier for resveratrol. A group of resveratrol-loaded zein-MSC nanoparticles (Res-zein-MSC NPs) with varying zein to Res mass ratios was first prepared. The particle sizes and zeta-potentials were in the ranges from 215.00 to 225.00 nm and from −29.00 to −31.00 mV. The encapsulation efficiency (EE) of Res was also influenced by the zein to Res mass ratio, and the encapsulated Res existed in an amorphous form. The major interactions between Res and zein-MSC NPs were hydrogen bonding and hydrophobic interaction. Furthermore, compared with free Res, the photo-stability and bioaccessibility of Res-zein-MSC NPs were significantly improved. The cellular studies also showed that Res-zein-MSC NPs exhibited lower cytotoxicity and desirable anti-inflammatory activity.

Electrophoresis of tightly fitting spheres along a circular cylinder of finite length

Electrophoresis of a tightly fitting sphere of radius $a$ along the centreline of a liquid-filled circular cylinder of radius $R$ is studied for a gap width $h_0=R-a\ll a$ . We assume a Debye length $\kappa ^{-1}\ll h_0$ , so that surface conductivity is negligible for zeta potentials typically seen in experiments, and the Smoluchowski slip velocity is imposed as a boundary condition at the solid surfaces. The pressure difference between the front and rear of the sphere is determined. If the cylinder has finite length $L$ , this pressure difference causes an additional volumetric flow of liquid along the cylinder, increasing the electrophoretic velocity of the sphere, and an analytic prediction for this increase is found when $L\gg R$ . If $N$ identical, well-spaced spheres are present, the electrophoretic velocity of the spheres increases with $N$ , in agreement with the experiments of Misiunas & Keyser (Phys. Rev. Lett., vol. 122, 2019, 214501).

Influence of flow rate on the transport of nTiO2 and phosphate and its modeling

We studied Zeta potentials of nanoparticles titanium dioxides （nTiO2） in different concentration of NaNO3 and phosphate (P) solutions. In addition, the effect of flow rate on the transport of nTiO2 in P was investigated at pH＝6.5. Experimental results show that the Zeta potential of nTiO2 is compressed with the increasing ion concentration (IC) of NaNO3 at pH＝6.5. The negative charge increases with the augment of P. Therefore, the high P and low NaNO3 induce the stabilization of nTiO2 aggregates. The transport experiments suggest that the rapid flow rate is favorable for the transportability of nTiO2 and soluble phosphate. The breakthrough transport curves (BTCs) of nTiO2 in sand columns can be fitted well with two-site kinetic attachment model. The modeling results suggest that the values of first-order attachment rate coefficients (k2) and detachment rate coefficients (k2d) on site 2 and first-order attachment rate coefficients (k1) on site 1 are responsible to the attaching efficiency of nTiO2 on sands and their transportability.

Sedimentation of nanoparticle titanium dioxide in the presence of ammonium

Due to its physicochemical properties, nanoparticles titanium dioxide (nTiO2) is being put into mass production and widespread applications, which inevitably results in their increasing exposure to the water body. After it entering the water body, the chemical properties of nTiO2 can be influenced by ion compositions, ion strength and pH, which affects their ecological risk. Excess of ammonium (NH4+) fertilizer has contaminated soil and water environments. In this paper, the Zeta potentials and hydrodynamic radius of nTiO2 were studied in NH4+ solution compared to those in Na+ solution. In addition, the sedimentation rate of nTiO2 was also investigated. The experiment results show that high pH inhibits the sedimentation of nTiO2. Moreover, NH4+ increases the stability of nTiO2 more than Na+ at the same IS, which was attributed the more negative Zeta potentials and the smaller hydraulic radius. Our results provide a theoretical basis for evaluating the ecological risk of nTiO2 in aqueous solution containing NH4+.

Synthesis and characterization of nanoscale composite particles formed by 2D layers of Cu-Fe sulfide and Mg-based hydroxide

Two-dimensional phenomena are attracting enormous interest at present and the search for novel 2D materials is very challenging. We propose here the layered material valleriite composed of altering atomic sheets of Cu-Fe sulfide and Mg-based hydroxide synthesized via a simple hydrothermal pathway as particles of 50-200 nm in the lateral size and 10-20 nm thick. The solid products and aqueous colloids prepared with various precursor ratios were examined using XRD, TEM, EDS, X-ray photoelectron spectroscopy (XPS), reflection electron energy loss spectroscopy (REELS), Raman, Mössbauer, UV-vis-NIR spectroscopies, magnetic, dynamic light scattering, zeta potential measurements. The material properties are largely determined by the narrow-gap (less than 0.5 eV) sulfide layers containing Cu+ and Fe3+ cations, monosulfide and minor polysulfide anions but are strongly affected by the hydroxide counterparts. Particularly, Fe distribution between sulfide (55-90%) and magnesium hydroxide layers is controlled through insertion of Al into the hydroxide part and by Cr and Co dopants entering both layers. Room-temperature Mössbauer signals of paramagnetic Fe3+ transformed to several Zeeman sextets with hyperfine magnetic fields up to 500 kOe in the sulfide layers at 4 K. Paramagnetic or more complicated characters were observed for valleriites with higher and lower Fe concentrations in hydroxide sheets, respectively. Valleriite colloids showed negative zeta potentials, suggesting negative electric charging of the hydroxide sheets, and optical absorption maxima between 500 nm and 700 nm, also depended on the Fe distribution. The last features observed also in the REELS spectra may be due to localized surface plasmon or, more likely, quasi-static dielectric resonance. The tunable composition, electronic, magnetic, optic and surface properties highlight valleriites as a rich platform for novel 2D composites promising for numerous applications.