•Polystyrene-alt-(N-4-benzoylglycine-maleamic acid), cumene terminated polymer was synthesized.•Polysulfone blend ultrafiltration membrane was successfully fabricated via phase inversion method.•The ...membrane showed outstanding capability towards heavy metal ions (Pb2+ and Cd2+) removal by adsorption.•Membrane recycled by simple acid wash.
A simple, scalable, novel polymer was synthesized by the aminolysis of poly(styrene-co-maleic anhydride) cumene terminated (PSMAC) using p-aminohippuric acid. The main objective was to perceive the effect of blend ratio of polysulfone (PSF) and polystyrene-alt-(N-4-benzoylglycine-maleamic acid) cumene terminated (PAH) on morphology and permeation properties of the membranes. The PSF/PAH blend membranes unveiled enriched hydrophilicity, porosity, zeta potential, water uptake and permeability owing to the existence of the hydrophilic PAH. However, the contact angle was not diminished over 20% of PAH ratio as there was an increase of hydrophobic alkyl group density. Differential scanning calorimetry (DSC) was employed for the determination of the glass transition temperature of the blends and the results revealed that the polymer blend is miscible in nature. Moreover, the M-3 membrane was screened for the heavy metal ion removal and achieved removal of 91.5% of Pb2+ and 72.3% of Cd2+ ions, respectively. The adsorption parameters indicated that the Langmuir isotherm model fits well for both Pb2+ and Cd2+ ions adsorption on M-3 membrane. The adsorption capacity attained from Langmuir isotherm model was 19.35 and 9.88 mg/g for Pb2+ and Cd2+ ions correspondingly.
Physiochemical methods have generally been used to "open-up" biomass substrates/pulps and have been the main method used to fibrillate cellulose. However, recent work has shown that canonical ...cellulase enzymes such as endoglucanases, in combination with "amorphogenesis inducing" proteins such as lytic polysaccharide monooxygenases (LPMO), swollenin and hemicellulases, are able to increase cellulose accessibility. In the work reported here different combinations of endoglucanase, LPMO and xylanase were applied to Kraft pulps to assess their potential to induce fibrillation at low enzyme loading over a short time period. Although gross fiber properties (fiber length, width and morphology) were relatively unchanged, over a short period of time, the intrinsic physicochemical characteristics of the pulp fibers (e.g. cellulose accessibility/DP/crystallinity/charge) were positively enhanced by the synergistic cooperation of the enzymes. LPMO addition resulted in the oxidative cleavage of the pulps, increasing the negative charge (~100 mmol kg
) on the cellulose fibers. This improved cellulose nanofibrilliation while stabilizing the nanofibril suspension (zeta potential ζ = ~60 mV), without sacrificing nanocellulose thermostability. The combination of endoglucanase, LPMO and xylanases was shown to facilitate nanofibrillation, potentially reducing the need for mechanical refining while resulting in a pulp with a more uniform nanofibril composition.
We have reported on the potential use of membrane distillation (MD) to remove emerging pollutants from wastewater as an alternative to other biological and chemical treatments. For every successful ...application of MD, the fouling and scaling associated with membrane wetting must be reduced to minimize the deterioration in performance. Here, we have hypothesized that the effectiveness of the antibiotic removal from wastewater can be significantly influenced by the interfacial interaction between the antibiotics and the membrane surface. To verify this, we investigated the applicability of the direct contact MD (DCMD) to treat the antibiotics, including positively-charged tobramycin (TOB), negatively-charged cefotaxime (CTX), and neutral ciprofloxacin (CFX). DCMD tests were performed with negatively-charged commercial polyvinylidene fluoride (PVDF) membranes, with the observance of a significant decline in flux and wetting issues during the MD treatment of TOB. The PVDF membrane exhibited a stable flux (CTX: 19.76 LMH and CFX: 19.81 LMH), with almost 100% rejection of the CTX and CFX due to electrostatic repulsion. Optical coherence tomography (OCT) further elucidates the in-situ fouling development for TOB, CTX and CFX.
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•Membrane distillation showed a high potential for antibiotic removal.•Electronic interfacial interaction significantly influenced membrane distillation performance.•Positively charged antibiotic attached on negatively charged membrane.•pH adjustment improved both water flux and antibiotic rejection.•Fouling behavior was revealed by optical coherence tomography.
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•Zeta potential of cellulose nanocrystals is explored as a function of additives.•Hofmeister-type specific ion effects modulate ion adsorption.•Surfactant adsorption can increase or ...reverse surface charge.•Film roughness from cellulose nanocrystals depends on suspension zeta potential.
The zeta potential of cellulose nanocrystal (CNC) aqueous dispersions was studied as a function of solution conditions, including changing pH and different electrolyte identities and concentrations. A range of electrolytes that spans typical Hofmeister/hydrophobic effects was explored, along with both cationic and anionic surfactants. A subtle interplay of electrostatic and hydrophobic effects in ion adsorption was uncovered, including evidence of charge reversal and supercharging when hydrophobic surfactants are added to aqueous CNC dispersions. The apparent effects of zeta potential on dispersion stability were explored by using atomic force microscopy (AFM) to determine the roughness of resulting CNC films. The root mean square roughness (RMS) of these cellulose films was unaffected by the presence of surfactants (achieving a constant value of ∼9nm), but scaled inversely and non-linearly with the zeta potential of the CNC suspension while using the ionic salts from ∼2nm to 10nm, indicating a facile method for the control of cellulose film roughness.
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Pyrrhotite (Fe(1–x)S; 0 < × ≤ 0.125) is a complex sulfide gangue mineral in base metal mining operations, having several superstructures. Of these, magnetic/4C (Fe7S8) and ...non-magnetic/5C (Fe9S10) superstructures are commonly found together and have demonstrated different flotation behaviour both in lab-scale and industrial settings. Currently, much of the literature data supports the theory that non-magnetic pyrrhotite is more floatable than magnetic pyrrhotite. The present study aimed at assessing the differences between the superstructures by investigating their zeta potentials (pH 2–11), n-amyl xanthate collector adsorption (pH 7, 8.5, and 10), and microflotation (pH 7–11) response (with and without sonication pre-treatment). Overall, zeta potential analysis demonstrated similar superstructure behaviour (minerals alone and in the presence of Ni2+, Cu2+, and xanthate collector) when their surfaces are “fresh” (i.e. minimal contact with oxygen). The results also supported xanthate adsorption by an initial physisorption mechanism. Collector adsorption studies demonstrated that xanthate uptake was much higher for magnetic than non-magnetic pyrrhotite for all pH conditions tested (7, 8.5, and 10). Based on this, it was proposed that different proportions of Fe(OH)SX and Fe(OH)SX2 (dixanthogen) are present on the superstructures and that non-magnetic pyrrhotite likely contains more dixanthogen. Microflotation investigations showed that when surface oxidation products have been removed (via sonication) and sufficient xanthate is present (permitting adequate dixanthogen), magnetic and non-magnetic pyrrhotite superstructures behave virtually the same. It was acknowledged that in real systems (i.e. industrial operations) where surface oxidation is inevitable, superstructure flotation will differ significantly due to their different reactivities towards oxygen.
The objective of this study is to investigate the interaction between graphene oxide (GO) laminate and salt solutions. The well-aligned GO laminates are distributed on the top surface of a ...polyvinylidene fluoride-polyacrylic acid (PVDF-PAA) microporous layer via vacuum filtration. The PVDF-PAA layer is formed after being cast on a non-woven support and immersed in a water coagulation bath. We illustrate herein how the inter-layer spacing of the GO laminate membrane is varied due to contact with salt solutions or water, which results in tunable ionic sieving effect. It is assumed that the water permeation through the GO composite membrane follows a modified Hagen-Poiseuille's law. The GO inter-layer spacing is calculated, and this spacing is shrunken to 2.8 nm in the presence of MgSO4 and enlarged to 6.1 nm with Na2SO4 from the initial 4.8 nm of water-swollen GO. The permeance values of the filtrate from Na-solutions are unexpectedly higher than those of pure water. The strong GO-Mg2+ interaction causes the surface zeta potential toward a neutral charge, which results in low rejections (<12%) for MgSO4 and MgCl2 solutions. The intermediate GO-Na+ interaction maintains the negative zeta potential of the GO layer, which readily rejects Na2SO4 (79%). The cations can modulate surface zeta potential and inter-layer spacing, which in turn directly impact the anion permeation and salt rejection behaviors. Overall, GO-salt interaction plays an important role in tailoring GO membrane characteristics. These GO-cation behaviors have potential applications in water filtration, desalination, molecular separation, and ion sensing and detection.
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•Synthesis of non-woven/PVDF-PAA/GO composite membrane for a water desalination.•We illustrate how the inter-layer spacing of the GO laminate membrane is varied via contact with salt solutions or water.•The water permeation through the GO composite membrane follows a modified Hagen-Poiseuille's law.•GO zeta potential has a direct impact on the anion permeation and salt rejection behaviors.
Inspired by a famous identity of Ramanujan, we propose a general formula linearizing the convolution of Dirichlet series as the sum of Dirichlet series with modified weights; its specialization ...produces new identities and recovers several identities derived earlier in the literature, such as the convolution of squares of Bernoulli numbers by Dixit et al., or the Fourier expansion of the convolution of Bernoulli–Barnes polynomials by Komori et al.
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This study explores the potential use of amine cross-linked reed (ACR) for removing nitrate, phosphate and Cr(VI) from aqueous in a fixed-bed column. Characteristics (surface area, ...pore structure, FTIR, Raman spectra, XPS, zeta potential and solid NMR) of ACR as well as anions laden samples were intensively investigated. Results indicated that FTIR, Raman and XPS of nitrate and phosphate laden ACR were quite different from those of Cr(VI) laden samples, which corresponded well to their adsorption properties. Tertiary amine group played the main role in uptake of nitrate and phosphate by electrostatic attraction. Characteristics of Cr(VI) laden samples indicated that a reduction of Cr(VI) to Cr(III) occurred on surface of ACR (this was also proved by the zeta potential analysis). However, the main adsorption mechanism for Cr(VI) onto ACR was still based on electrostatic attraction. The maximum dynamic adsorption capacity of ACR for nitrate, phosphate and Cr(VI) was estimated to be 118.9mg/g, 103.1mg/g and 135.3mg/g. The nitrate/phosphate adsorption capacities of spent ACR after 3 cycles of adsorption–desorption were recovered with 97.3–98.4%. In contrast, only 49.2% of Cr(VI) recovery was achieved, partially due to the destruction of the functional groups on surface of ACR during the Cr(VI) adsorption.
•Two Zr(IV)-based MOFs can remove cationic dyes more effectively than anionic dyes.•UiO-66 has higher selectivity for cationic dyes after modification with NH2.•The mechanism for adsorption ...selectivity is rationally proposed.
Herein, two zirconium(IV)-based MOFs UiO-66 and UiO-66-NH2 had been successfully prepared by a facile solvothermal method and were characterized by X-ray diffraction (XRD), field emission transmission electron microscopy (FETEM), N2 adsorption–desorption (BET), X-ray photoelectron spectroscopy (XPS), and zeta potential. They exhibit small size, large surface area, and can remove cationic dyes from aqueous solution more effectively than anionic dyes. This adsorption selectivity is due to the favorable electrostatic interactions between the adsorbents and cationic dyes. Furthermore, owing to the individual micropore structure of UiO-66-NH2 and its more negative zeta potential resulted from the charge balance for the protonation of –NH2, UiO-66-NH2 displays much higher adsorption capacity for cationic dyes and lower adsorption capacity for anionic dyes than UiO-66.
Despite the broad range of interest and applications, controls on calcite surface charge in aqueous solution, especially at conditions relevant to natural systems, remain poorly understood. The ...primary data source to understand calcite surface charge comprises measurements of zeta potential. Here we collate and review previous measurements of zeta potential on natural and artificial calcite and carbonate as a resource for future studies, compare and contrast the results of these studies to determine key controls on zeta potential and where uncertainties remain, and report new measurements of zeta potential relevant to natural subsurface systems.
The results show that the potential determining ions (PDIs) for the carbonate mineral surface are the lattice ions Ca2+, Mg2+ and CO32−. The zeta potential is controlled by the concentration-dependent adsorption of these ions within the Stern layer, primarily at the Outer Helmholtz Plane (OHP). Given this, the Iso-Electric Point (IEP) at which the zeta potential is zero should be expressed as pCa (or pMg). It should not be reported as pH, similar to most metal oxides.
The pH does not directly control the zeta potential. Varying the pH whilst holding pCa constant yields constant zeta potential. The pH affects the zeta potential only by moderating the equilibrium pCa for a given CO2 partial pressure (pCO2). Experimental studies that appear to yield a systematic relationship between pH and zeta potential are most likely observing the relationship between pCa and zeta potential, with pCa responding to the change in pH. New data presented here show a consistent linear relationship between equilibrium pH and equilibrium pCa or pMg irrespective of sample used or solution ionic strength. The surface charge of calcite is weakly dependent on pH, through protonation and deprotonation reactions that occur within a hydrolysis layer immediately adjacent to the mineral surface. The Point of Zero Charge (PZC) at which the surface charge is zero could be expressed as pH, but surface complexation models suggest the surface is negatively charged over the pH range 5.5–11.
Several studies have suggested that SO42− is also a PDI for the calcite surface, but new data presented here indicate that the value of pSO4 may affect zeta potential only by moderating the equilibrium pCa. Natural carbonate typically yields a more negative zeta potential than synthetic calcite, most likely due to the presence of impurities including clays, organic matter, apatite, anhydrite or quartz, that yield a more negative zeta potential than pure calcite. New data presented here show that apparently identical natural carbonates display differing zeta potential behaviour, most likely due to the presence of small volumes of these impurities. It is important to ensure equilibrium, defined in terms of the concentration of PDIs, has been reached prior to taking measurements. Inconsistent values of zeta potential obtained in some studies may reflect a lack of equilibration.
The data collated and reported here have broad application in engineering processes including the manufacture of paper and cement, the geologic storage of nuclear waste and CO2, and the production of oil and gas.
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•The IEP should be expressed as pCa or pMg; not pH. The PZC can be expressed as pH•Ca2+ and Mg2+ behave identically and zeta potential varies linearly with pCa and pMg•pH varies linearly with pCa irrespective of sample type or solution ionic strength•pSO4 may affect zeta potential by moderating the equilibrium pCa•It is important to ensure equilibrium has been reached prior to taking measurements
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