Aqueous Streams Research Articles

Extraction of salicylic acid from wastewater using ionic liquid-based green emulsion liquid membrane: COSMO-RS prediction and experimental verification

Salicylic acid is an important component in cosmetics and skincare products and is widely found in aqueous streams as waste material. The present study reported the extraction of salicylic acid from wastewaters using a new technique termed as ‘ionic liquid-based emulsion liquid membrane’ (IL-ELM). Ionic liquids were introduced as carriers in IL-ELMs to enhance the emulsion stability. COSMO-RS simulation tool was employed to identify the effective IL among the 45 ILs composed of different cations and anions. It was found that IL [TMAm][Cl] (tetramethylammonium chloride) was found to be the most effective extracting agent for the extraction of salicylic acid that possesses the higher capacity, selectivity and lower activity coefficient towards analyte molecules. The COSMO-RS prediction results were in good agreement with the experimental data. Furthermore, this study optimized several operating conditions, including surfactant concentration, stripping agent concentration, IL concentration, emulsification time, homogenization speed and extraction time that affected the extraction efficiency. Overall, the proposed IL-ELM showed 90.04% extraction efficiency for salicylic acid under the optimized conditions of 0.005 M NaOH as stripping agent, 1.0 wt% Span-20 as emulsifier, 0.2 wt% [TMAm][Cl], 4000 rpm homogenization speed, 3:1 treat ratio and 25 min of extraction time.

Photocatalytic MIL101(Fe)/ZnO chitosan composites for adsorptive removal of tetracycline antibiotics from the aqueous stream

Antibiotics are widely used to treat bacterial infections in humans and animals. Among different classes of antibiotics, tetracycline (TC) is the most used, and its elimination from the environment has become a serious concern. The present study focused on the facile synthesis of zinc oxide (ZnO) nanoflowers, Matériaux de l' Institut Lavoisier 101 (MIL-101(Fe)) and MIL101(Fe)/ZnO chitosan composite beads for the adsorptive removal and photocatalytic degradation of TC. The effect of various operational parameters such as adsorbent dosage, TC concentration, pH and time was investigated. The MIL101(Fe)/ZnO chitosan composite beads were characterized by XRD, TGA, SEM, BET surface area and FT-IR. The MIL101(Fe)/ZnO chitosan composite beads showed high thermal stability up to 250 °C and the highest adsorption capacity of 31.12 mg g−1. The PSO adsorption kinetics and Langmuir adsorption isotherm were found the best fit. The adsorption of TC on the MIL101(Fe)/ZnO chitosan composites was attributed to the π -π interaction between the aromatic rings of TC and the adsorbent. The adsorption of the TC was confirmed using the SEM and FT-IR; the TC was visible on the bead's surface that showed the affinity of the synthesized beads towards the adsorption of the TC. The beads were regenerated with high efficiency in the presence of sunlight. The photo-excitation was due to MIL101(Fe) and ZnO, which created the electrons (e−) and holes (h+) in the structure. The beads showed a removal efficiency of more than 90% up to 5 cycles. Therefore, the MIL101(Fe)/ZnO chitosan composite beads can be used and reused for a long period.

Adsorption of hexavalent chromium from aqueous stream by maghemite nanoparticles synthesized by the microemulsion method

The magnetic nanoparticles maghemite were synthesized by the co-precipitation reaction and then used for the removal of hexavalent chromium from the synthetic aqueous stream. The maghemite nanoparticles were synthesized by the co-precipitation reaction of ferric and ferrous salts with oleic acid and into a water-in-oil micro emulsion using Sodium dioctyl sulfosuccinate surfactant. Dynamic light scattering and X-ray diffraction were used for the characterization of formed nanoparticles. The nanoparticles thus obtained were used as adsorbent for the adsorption of hexavalent chromium from the synthetic aqueous stream in a batch experiment and subsequently the adsorption kinetic mechanism of hexavalent chromium uptake was investigated. The uptake of hexavalent chromium was also found to be pH dependent. Experimental values of hexavalent chromium adsorption were fitted with Freundlich, Langmuir, Sips, Redlich-Peterson and Koble-Corrigan isotherms models. The best possible fits were yielded through five error functions. Adsorption thermodynamics was also studied.

Mercapto-functionalized ordered mesoporous silica-modified PVDF membrane for efficiently scavenging Cd2+ from water

In this study, (3-mercaptopropyl) triethoxysilane (MPTMS)-modified ordered mesoporous silica (OMS) materials were prepared using a post-grifting method, with MPTMS as the organic functionalized reagent. The OMS materials were analyzed by FT-IR spectra, N2 sorption, and small angle X-ray scattering to evaluate their potential for scavenging Cd2+ from water. Moreover, a (3-mercaptopropyl) triethoxysilane-functionalized ordered mesoporous silica modified polyvinylidene fluoride (MPTMS-OMS/PVDF) membrane was synthesized using the solvent phase inversion method to remediate wastewater containing heavy metal ions. The MPTMS-OMS was characterized by a maximum specific surface area of 422 m2/g, high surface hydrophilicity, and high pure water flux. The MPTMS-OMS/PVDF exhibited a dynamic adsorption capacity for Cd2+ in water. At an MPTMS-OMS content of 5 wt%, the Cd2+ removal efficiency was 90%, whereas the pure PVDF showed no Cd2+ adsorption capacity. These results highlight the potential of the MPTMS-OMS/PVDF membrane to eliminate Cd2+ during the decontamination of aqueous streams containing low-concentrations of contaminants.

Mass transfer analysis and kinetic modeling for process design of countercurrent membrane supported reactive extraction of carboxylic acids

Countercurrent membrane supported reactive extraction (MSRE) was studied for removal of carboxylic acids from aqueous streams with a PTFE capillary membrane. Analysis of the mass transfer rates was performed to support modeling of the process. Total mass transfer coefficients ranging from 2.0·10-7 to 4.0·10-7 m/s were obtained when extracting lactic acid with 20 wt% tri-N-octyl amine in 1-decanol with membrane thicknesses of 260 µm and 80 µm. The limiting mass transfer resistance in all experiments was in the membrane phase. The developed model based on mass transfer and reaction in parallel allows to predict countercurrent extraction. Experimental validation with 5, 7 and 12 m long membrane modules showed excellent accordance for two acids, validating the model simulations. Simulated membrane contactor lengths required for single, two and three countercurrent stages varied between 10 and 39 m/stage for lactic, mandelic, succinic, itaconic and citric acid, depending on acid, membrane, and diluent.

Phase behavior and pH modelling for ammonia-MEA-water mixtures for corrosion control in water utility applications

We present thermodynamic models for ammonia-MEA-water mixtures and evaluate the pH of the aqueous streams for the purpose of corrosion control in water-utility applications. In particular, (1) An equation of state (EOS) model using Peng-Robinson EOS with the asymmetric Huron-Vidal (HV) mixing rule for aqueous subsystems is developed and calibrated against experimental data; and (2) As an outcome, a modeling workflow is developed to estimate the pH as a function of the temperature and the composition of the aqueous streams. Such studies are important for various chemical and manufacturing industries. Furthermore, the methodologies developed through this work can be applied to wider ranges of pressures and temperatures for water utilities, reactor plants, and refineries.

A Review on the Nanofiltration Process for Treating Wastewaters from the Petroleum Industry

Activities and/or processes in different segments of the petroleum industry, including upstream and downstream, generate aqueous waste streams containing oil and various contaminants that require treatment/purification before release/reuse. Nanofiltration (NF) technology has been approved as an efficient technology for treating wastewater streams from the petroleum industry. The primary critical issues in an NF treatment process can be listed as mitigation of membrane fouling; selection of appropriate pre-treatment process; and selection of a suitable, cost-effective, non-hazardous cleaning strategy. In this study, NF separation mechanisms, membrane fabrication/modification, effective factors on NF performance, and fouling are briefly reviewed. Then, a summary of recent NF treatment studies on various petroleum wastewaters and performance evaluation is presented. Finally, based on the gaps identified in the field, the conclusions and future perspectives are discussed.

Highly efficient degradation of organic pollutant mixtures by a Fe(III)-based MOF-catalyzed Fenton-like process in subcritical water

Propylene glycol monomethyl ether acetate (PGMEA) photoresist solvent and monoaromatics are typical organic pollutants found in the wastewater discharged from semiconductor manufacturing processes. Conventional treatment technologies, however, remain mostly ineffective to eliminate these pollutants from aqueous streams. Herein, we developed a novel strategy for highly efficient degradation of PGMEA and archetypal monoaromatics (i.e., benzene, toluene, xylene, phenol, and cresol) in aqueous solution by heterogeneous Fenton-like process with a flexible Fe-MOF (MIL-88B) under mild subcritical water (SCW) condition (100 °C). The as-synthesized MIL-88B(Fe) microbipyramids possess large pore channels (∼32 nm) and open iron sites. The results showed that the SCW-mediated heterogeneous Fenton-like process at 100 °C with an optimal catalyst loading of 1 wt% exhibited a remarkable degradation performance toward target organic pollutants in a multicomponent system, affording a 92% total organic carbon (TOC) removal in 60 min. This mineralization efficiency was found to be notably superior to those of traditional homogeneous Fenton (FeSO4/H2O2; ∼54%) and Fenton-SCW (∼60%) processes. The practicability of this approach was demonstrated using real world water samples (i.e., river water, fishpond water, and wastewater) with >80% TOC removal efficiency. This study showed that the heterogeneous Fenton-like process utilizing an inexpensive, nontoxic, and reusable MIL-88B(Fe) MOF under mild SCW conditions is a promising strategy for treating semiconductor waste effluents and environmental water matrices containing toxic recalcitrant organics in an eco-friendly and efficient manner.

Microfluidic synthesis of magnetic nanoparticles in droplet-based microreactors

Microfluidic devices have been widely used to achieve highly controlled synthesis of various nanomaterials including inorganic materials, polymers and composite materials via continuous microreactors. Here, droplet-based continuous microreactors generated in a microfluidic device are used to synthesize magnetic nanoparticles (Fe3O4) via simple coprecipitation method. The chip is composed of multifunctional units, including T-junction for droplet generation, Y-junction and S-channels for droplet fusion and rapid mixing as well as the observation of the formation process of nanoparticles. The size of water-in-oil droplets was inspected by tuning the flow rate of aqueous and oil phase. By changing the temperature and flow rate of aqueous and oil streams, we investigated the variation of the morphology, size, saturation magnetization and coercivity of nanoparticles. This work presents that chemical reaction can be initiated by fusing two aqueous droplets due to the hydrodynamic coupling, which is superiorly efficient compared to the conventional coprecipitation method for synthesizing Fe3O4 nanoparticles of high saturation magnetization and low coercivity.

Current status and future prospects of membrane separation processes for value recovery from wastewater

Resource constraints and deteriorating environment have made it necessary to look for intensification of the industrial processes, to recover value from spent streams for reuse. The development of reverse osmosis has already established that water can be recovered from aqueous streams in a cost-effective and beneficial manner to the industries. With the development of several membrane processes and membrane materials, the possibility of recovering value from the effluents looks like a workable proposition. In this context, the potentialities of the different membrane processes in value recovery are presented. Among the pressure-driven processes, reverse osmosis can be used for the recovery of water as value. Nanofiltration has been used for the recovery of several dyes including crystal violet, congo red, methyl blue, etc., while ultrafiltration has been used in the fractionation of different solute species using membranes of different pore-size characteristics. Diffusion dialysis is found useful in the separation of acids from its salt solutions. Bipolar membrane electrodialysis has the potential to regenerate acid and base from salt solutions. Thermally driven membrane distillation can provide desalinated water, besides reducing the temperature of hot discharge streams. Passive membrane processes such as supported liquid membranes and membrane-assisted solvent extraction have been found useful in separating minor components from the wastewater streams. The details are discussed to drive home that membrane processes can be useful to achieve the objectives of value recovery, in a cost-effective manner through process intensification, as they are more compact and individual streams can be treated and value used seamlessly.

Targeted Lead and Copper Removal from Aqueous Streams Using Carbon Electrodes in an Electrochemical Filter

Lead contamination in drinking water is a pervasive health problem across the US, brought into the public spotlight by the 2014 water crisis in Flint, Michigan. The Environmental Protection Agency (EPA) established The Lead and Copper Rule in 1991 to limit exposure of these elements and set the action level to 15 ppb; however, there is no safe level of lead consumption.1 Despite corrosion prevention measures taken by public water authorities, lead concentrations in drinking water are routinely elevated nationwide.2 A reliable long-lasting water filter that can specifically target lead and other metals is currently lacking in the marketplace. Metals removal from wastewater is also a major concern for many industries, where water reuse is becoming commonplace, regulations are getting more stringent, and discharge limits must be met. Much of this current work has focused on lead and copper removal from drinking water and industrial wastewater, with a specific focus on commercializing a technology that can provide clean water in a sustainable manner. Applying this technology to other metals of interest has also been demonstrated.Conventional and electrochemical methods for metals removal from water cannot effectively distinguish between many dissolved species and behaves more as a bulk removal process. In order to obtain a purified or concentrated stream of a desired metal, additional separation steps need to be used, making the overall process more expensive and complicated. PowerTech Water has developed carbon electrodes in an electrochemical filter that can target specific metals in a water stream to either remove or recover them, depending on the application. The device uses activated carbon electrodes and a small applied voltage (<2.0 V) to induce Faradaic reactions at both the carbon-based anode and cathode within the cell. By tuning the device configuration and operating parameters, a targeted metal will precipitate out of solution, generally according to its Pourbaix diagram, and be trapped within the porous electrode matrix.Electrochemical water treatment was performed at a constant applied voltage with lead spiked tap water, achieving >90% removal of the target metal, while leaving other species (eg. Na+ and Ca2+) in solution. SEM and EDX analysis of the used anodes and cathodes confirmed the presence of lead species (Figure 1, right panel). To further understand the mechanisms at play, the near electrode pH and voltage distribution were measured. By varying the applied potential, the pH and voltage at the anode and cathode were recorded, along with the concentration of lead at the inlet and outlet. This information, when combined with the Pourbaix diagram, can be used to help identify the lead speciation at each electrode and optimize device performance. Additional experiments were performed with copper spiked tap water, demonstrating the versatility of the electrochemical filter described here.

Electrochemical Valorization of Biomass-Derived Feedstocks: Levullinic Acid to 4-Hydroxyvaleric Acid

Fossil fuel-based sources of energy are being gradually replaced by renewable electricity (such as solar, wind, etc), while there is a rising interest in biomass as a sustainable platform to produce fuels and other carbon-based chemicals.1,2 Electrochemistry is thus an attractive approach for the valorization of biomass-derived feedstocks. This approach has shown some advantages compared to traditional thermal- or bio-based chemical conversion such as the amenability to operate directly on aqueous biomass hydrolysate streams, and operability near ambient conditions, which also facilitates distributed scale production.2 This work discusses the electrochemical conversion of levulinic acid (LA) to 4-hydroxyvaleric acid (HVA). HVA is a versatile compound that can be used as a monomer for the production of biodegradable and biocompatible polyesters, in addition to diverse commodities and fine chemicals.3,4 It is projected that the biopolymers industry will reach a global market size of USD 27.9 billion by 2025.5 While prior work has demonstrated that LA can be electrochemically converted into valeric acid (VA) and γ-valerolactone (GVL), among other compounds,2, HVA has only previously been fund as a trace-level intermediate of LA electrochemical reduction into GVL.Here, we show a maximum HVA production rate higher than 40 g L-1 h-1 (i.e., 200 kg L-1 m-2 h-1) at 100% selectivity, and conversion and faradaic efficiency of 81%, while complete LA conversion could also be achieved under lower rates. Our characterization indicates this can further be optimized by reactor design (particularly the mass transport properties) and electrolyte engineering. Though evaluation of different pHs, aqueous supporting electrolytes, temperature, electrode potential, stirring rates, and initial concentration of LA we also elaborate on mechanistic underpinnings of the reaction selectivity, proposing that the formation of VA and GVL is through surface-mediated reactions, while HVA is formed via an outer sphere electron transfer (OSET) route (Fig.1). References (1) npj Clim. Atmos. Sci. 2019, 2 (1), 35.(2) ACS Energy Lett. 2021, 1205–1270. https://doi.org/10.1021/acsenergylett.0c02692.(3) . J. Biotechnol. 2015, 210, 38–43.(4) J. Agric. Food Chem. 2019, 67 (9), 2540–2546.(5) Global Bioplastics & Biopolymers Market Outlook 2020-2025 https://www.globenewswire.com/news-release/2020/04/17/2017839/0/en/Global-Bioplastics-Biopolymers-Market-Outlook-2020-2025.html (accessed April 22, 2021). Figure 1

Adsorption of cupric, cadmium and cobalt ions from the aqueous stream using the composite of iron(II,III) oxide and zeolitic imidazole framework-8

Abstract In recent research, the composite of Fe3O4 and metal-organic frameworks have shown great potential in removing potentially toxic metals from water. We conducted the adsorption studies of potentially toxic metal ions (Cu2+, Co2+ and Cd2+) using the composite of Fe3O4 and zeolitic imidazole framework-8 (Fe3O4@ZIF-8) for the first time. The solvothermal technique was used to synthesize the Fe3O4. The magnetic ZIF-8 offers high thermal stability, greater adsorption surface, good removability, and high chemical and thermal stability. Characterization techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared spectroscopy (FTIR) were used to characterize the synthesized samples. The SEM and XRD results revealed the high purity and structural integrity of ZIF-8 crystallites. To remove potentially toxic metals (Cu2+, Co2+ and Cd2+), the influence of adsorbent dosage, contact time, pH, and adsorbate concentration on the adsorption performance of Fe3O4@ZIF-8 was investigated. The Langmuir isotherm accurately represented the adsorption processes, with absorption magnitudes of Fe3O4@ZIF-8 determined to be 46.82 mg g−1, 71.29 mg g−1 and 54.49 mg g−1 for Cu2+, Co2+ and Cd2+, respectively. According to the adsorption mechanism analysis, the primary Cu2+, Co2+ and Cd2+ removal methods of Fe3O4@ZIF-8 were ion exchange and coordination bonds. The uptake capacity of Cu2+, Co2+ and Cd2+ solution by Fe3O4@ZIF-8 were not significantly affected by the presence of counter ions. The material exhibited superior regenerative properties for Cu2+, Co2+ and Cd2+ ions from water for up to three cycles. This study concluded that the Fe3O4@ZIF-8 could be a viable candidate for eliminating potentially toxic metals (Cu2+, Co2+ and Cd2+).

Regression models of adsorbing nickel (II) ions by carbon sorbents

Abstract: The use of inexpensive materials such as sorbents increases the competitive advantages of removing heavy metal ions, including nickel (II) ions, from aqueous solutions and wastewater. Such materials include active carbons – carbon sorbents. The oxidized carbon sorbent AD-05-2 and its original analogue have been used as the object of this research. The oxidation of carbon sorbent AD-05-2 was conducted using a solution of nitric acid and urea following a conventional method. Oxidation resulted in improvement of the textural characteristics of the carbon sorbent. The total pore volume increased, including the volume of micropores, which had a positive effect on the sorption properties of the obtained sample. This article studies the adsorption of nickel (II) ions by the oxidized carbon sorbent AD-05-2 and its original analogue. For both models, the total time of establishing adsorptive equilibrium in the system adsorbate–adsorbent was 4 hours, pH = 9,6, and the range of temperatures – 298–338 K. The obtained experimental data on the nickel (II) ion adsorption are processed in the software package Statgraphics Plus. Adsorption isotherms are described using parabolic regression models, which cover 98.86–99.99% of the experimental data. The adsorption of nickel (II) ions increases with temperature, as indicated by a higher value of the first derivative dA/dCp, apparently, due to accelerated external diffusion. A significant steep rise of the isotherms corresponds to the temperature of 338 K, which indicates the diffusion effect on the adsorption process. The estimates of the accuracy of regression models are provided by the mean square σ and absolute Δ errors. Autocorrelation of experimental data is estimated using Durbin – Watson (DW) test. The obtained regression models can be applied for calculating the optimum parameters of nickel (II) ions’ adsorption from aqueous solutions and process stream using the oxidized carbonic sorbent AD-05-2 and its original analog.

Hydrothermal treatment as a complementary tool to control the invasive Pampas grass (Cortaderia selloana)

The rapid spread of invasive Pampas grass (PG) is having not only ecosystems impact, but also significant economic and social effects. The tonnes of bulky waste from the plant disposal require proper treatment to avoid seed dispersal, greenhouse gas emissions and landscape damage. In the pursuit of zero-waste management, hydrothermal treatment (HT) appears as a challenging alternative. The possibility of mobile HT systems offers an alternative to accomplish on-site both the PG waste management and the application of the resulting by-products within a circular framework. As a first step, this research shows that, without a prior drying step, the hydrothermal treatment at 100-230 °C under autogenous water vapor pressure for only 30 min allows safe seeds inertization, while a stable carbon-enriched solid and an aqueous stream are generated. Prolonging the process for 2 h has no profitable effects. As the reaction temperature increases, the PG residue is converted into a material with 49–58 wt% of carbon, 41–32 wt% of oxygen and 3–4 wt% of ash. The pH (~6.3), low electrical conductivity (1.21–0.86 dS/m), high carbon content, open porosity (5–8 m2/g) and improved performance in seed germination and in the early growth test suggest the potential of HT-solids derived at 100–120 °C as amendment to sequester carbon in the soil and improve its physico-biological properties. The phytotoxicity detected in the peat/lignite-like solids obtained at 200–230 °C limits its application in soil, but calorific values of 22–24 MJ/kg indicate their suitability as CO2-neutral fuel. The agrochemical analysis of the liquid by-products indicates poor value on their own, but their use supplemented with compost may be an option.

Developing spherical activated carbons from polymeric resins for removal of contaminants from aqueous and organic streams

Developing spherical activated carbons from polymeric resins for removal of contaminants from aqueous and organic streams

Ion Exchange Membranes for Reverse Electrodialysis (RED) Applications - Recent Developments

The innovative membrane-based technology called reverse electrodialysis (RED) is capable of producing electrical power from the controlled mixing of two aqueous streams of different salinity. There has been tremendous progress so far in the development of RED process in terms of system development, spacer design, membranes properties and operational conditions optimization. Among those, characteristics of the ion exchange membranes are found to be the critical element affecting the performances of RED process. In this respect, a brief overview of the latest developments in ion exchange membranes were presented in this review, focussing on their properties and performances in RED applications. The recent developments of nanocomposite and ion selective membranes, particularly pore filling ion exchange membranes due to their high performances and inexpensive fabrication cost were also summarized. Shortly, fouling problem for the ion exchange membranes employed in the RED system was mentioned.

Time dependent zero valent iron oxidation and the reductive removal of pertechnetate at variable pH

Elemental iron Fe0 is a promising reductant for removal of radioactive technetium-99 (Tc) from complex aqueous waste streams that contain sulfate, halides, and other inorganic anions generated during processing of legacy radioactive waste. The impact of sulfate on the kinetics of oxidation and reduction capacity of Fe0 in the presence of Tc has not been examined. We investigated the oxidative transformation of Fe0 and reductive removal of TcO4- in 0.1 M Na2SO4 as a function of initial pH (i.e., pHi 4, 7, and 10) under aerobic conditions up to 30 days. Tc reduction was the fastest at pHi 7 and slowest at pHi 10 (Tc reduction rate pHi 7 > 4 > 10). Aqueous fraction of Tc was measured at 0.4% at pHi 7 within 6 h, whereas ≥ 97% of Tc was removed from solutions at pHi of 4 and 10 within 24 h. Solid phase characterization showed that magnetite was the only oxidized crystalline phase for the first 6 h regardless of initial pH. Lepidocrocite was the most abundant oxidized product for pHi 10 after 5 days, but was not observed at pH of 4 or 7.

Development and optimization of ionic liquid-based emulsion liquid membrane process for efficient recovery of lactic acid from aqueous streams

Development of ionic liquid-based emulsion membranes (ILEMs) has emerged as potential alternatives to organic solvent-based emulsion membranes for the extraction and recovery of biologically active compounds from aqueous streams. Hence, present study aims to develop novel ILEMs for the removal of bioactive lactic acid (LA) from aqueous streams using 100% vegetable oil as diluent. A series of ILEMs were prepared using three different ionic liquids (ILs) namely tetramethylammonium chloride [TMAm][Cl], tetramethylammonium acetate [TMAm][Ac] and tributylmethylammonium chloride [TBMAm][Cl] as a carrier. Besides, olive oil used as diluent, NaOH used as stripping agent, Tween 80 and Span 20 were employed as emulsifier in ILEMs preparation. The visual static stability of ILEMs was observed and the ILEM extraction efficiency was fully optimized in terms of various process parameters. The results showed that short-chain acetate based quaternary ammonium IL [TMAm][Ac] provided greater efficiency compared to chloride based ILs [TMAm][Cl] and [TBMAm][Cl]. A maximum of 94.50% LA removal was obtained with [TMAm][Ac] at optimized conditions of 0.05 M LA, 1.0 wt.% Span 20, 0.3 M NaOH, 0.3 wt.% [TMAm][Ac], 0.3 ratio of internal phase to diluent phase and 3:1 treat ratio (ratio of external phase to membrane phase) at a stirring speed of 250 rpm for 25 min. The emulsion was found stable for 134 min at the optimized conditions. Overall, this newly developed ILEM could be effectively used for the LA removal and other bioactive compounds from aqueous streams.

Experimental and Computational Analysis of Mixing Inside Droplets for Microfluidic Fabrication of Gold Nanoparticles

Emulsions formed by mixing reactant streams inside microdroplets are efficient microscale reactors for the synthesis of nano/microparticles/crystals due to small quantities of reagents confined within each droplet and the separation of droplet contents from the reactor walls. In this work, the synthesis of size-tunable gold nanoparticles (AuNPs) within emulsion droplets generated in a three-phase glass capillary microfluidic device was investigated experimentally and numerically using computational fluid dynamics (CFD). AuNPs were produced by micromixing two aqueous streams, 1.15 mM HAuCl4 containing the 1% poly(vinylpyrrolidone) capping agent and 20 mM ascorbic acid solutions, inside monodispersed droplets created by three-dimensional (3D) counter-current flow focusing in a medium-chain triglyceride. The mean particle size of AuNPs was tunable in the range between 26 and 56 nm and depended on the degree of premixing of the reactant streams shortly before droplet generation, and the mixing efficiency within droplets, which was controlled by hydrodynamic conditions within the microfluidic device. The CFD results were compared and validated against experimental observations and revealed the presence of a recirculation zone near the outer wall of the injection capillary tip. The mixing efficiency was higher at smaller droplet size causing a reduction in the particle size of the AuNPs.