Aqueous Ammonium Sulfate Research Articles

Water activity and surface tension of aqueous ammonium sulfate and D-glucose aerosol nanoparticles

Abstract. Water activity (aw) and interfacial energy or surface tension (σ) are key thermodynamic parameters to describe the hygroscopic growth of atmospheric aerosol particles and their ability to serve as cloud condensation nuclei (CCN), thus influencing the hydrological cycle and climate. Due to size effects and complex mixing states, however, these parameters are not well constrained for nanoparticles composed of organic and inorganic compounds in aqueous solution. In this study, we determined aw and σ by differential Köhler analysis (DKA) of hygroscopic growth measurement data for aerosol particles smaller than 100 nm composed of aqueous ammonium sulfate (AS), D-glucose (Gl), and their mixtures. High-precision measurements of hygroscopic growth were performed at relative humidities (denoted RH) ranging from 2.0 % to 99.6 % with a high-humidity tandem differential mobility analyzer (HHTDMA) in three complementary modes of operation: hydration, dehydration, and restructuring. The restructuring mode (hydration followed by dehydration) enabled the transformation of initially irregular particles into compact globules and the determination of mass equivalent diameters. The HHTDMA-derived growth factors complemented by DKA allows for determination of water activity and surface tension from dilute to highly supersaturated aqueous solutions that are not accessible with other methods. Thus, for mixed AS / Gl nanoparticles with mass ratios of 4:1 and 1:1, the upper limit of solute mass fraction (Xs) was 0.92 and 0.98, respectively. For pure AS and Gl, the DKA-derived aw is in good agreement with electrodynamic balance and bulk measurement data. For AS particles, our aw data also agree well with the Extended Aerosol Inorganics Model (E-AIM III) over the entire concentration range. In contrast, the UNIFAC model as a part of AIOMFAC (Zuend et al., 2011) was found to overestimate aw in aqueous Gl particles, which can be attributed to unaccounted intermolecular interactions. For mixed AS and Gl nanoparticles, we observed a non-monotonic concentration dependence of the surface tension that does not follow the predictions by modeling approaches constructed for mixed inorganic/organic systems. Thus, AS / Gl particles with a 1:1 mass ratio exhibited a strong decrease of σ with increasing solute mass fraction, a minimum value of 56.5 mN m−1 at Xs≈0.5, and a reverse trend of increasing σ at higher concentrations. We suggest that D-glucose molecules surrounded by ammonium sulfate ions tend to associate, forming non-polar aggregates, which lowers the surface tension at the air–droplet interface. We analyzed the uncertainty in the DKA-derived water activity and surface tension, related to the instrumental errors as well as to the morphology of the nanoparticles and their phase state. Our studies have shown that under optimal modes of operation of HHTDMA for moderate aqueous concentrations, the uncertainty in aw and σ does not exceed 0.2 %–0.4 % and 3 %–4 %, respectively, but it increases by an order of magnitude in the case of highly concentrated nanodroplet solutions.

Direct recovery of electro-synthesized ammonia from low-concentration nitric oxide using pulse electrodeposited Cu/C catalyst in a catholyte-free system

Electrochemical production of ammonia (NH3) from nitric oxide (NO) offers a sustainable and environmentally friendly way to convert a nitrogenous pollutant into a valuable chemical feedstock and energy carrier. However, practical challenges in the electrochemical NO-to-NH3 conversion stem from mass transport limitations due to low NO concentrations in real-world streams and the need for post-purification of synthesized NH3. In this study, by synergistically developing an electrocatalyst (pulse-electrodeposited copper) and implementing a catholyte-free cell configuration with advantages of (i) facile NO transport, (ii) inhibited side reaction, and (iii) direct NH3 recovery in an external acid, we showcase an NH3 Faradaic efficiency of 85.6 % and a production rate of 53.4 μmol cm−2h−1 starting from 500 ppm NO. Crucially, the electro-synthesized NH3 was directly recovered as a high-purity aqueous ammonium sulfate solution comparable to industrial-grade quality. This approach opens the door to transforming waste into resources in a more energy-efficient and straightforward manner.

Extraction of phenolic compounds from walnut green husk (Juglans regia L.) by Salting-Out extraction method

Some factors in the salting-out extraction (SOE) method play a major role. The aim of this study was to investigate the interaction effects of the phase forming components and consequently select the best conditions to achieve a highly efficient recovery of phenolic compounds from walnut green husks (Juglans regia L.) using mixtures of ethanol and aqueous ammonium sulfate solutions. According to the results that were analyzed by response surface methodology, the optimal extraction conditions were obtained at ethanol: salt: water ratio of 34.8: 15.1: 54.4 (w/w) at a pH of 6–6.5 and 25 °C. At the optimal conditions, the overall phenolic and flavonoid content, and antioxidant activity were significantly higher than obtained by the conventional method. In addition, at a higher scale (i.e., 5 kg), similar results were obtained. Thus, it can be concluded that SOE has the potential to be scaled up for the simultaneous separation and purification of compounds from plant biomass. This paper is addressing extraction techniques, measurement, and characterization of new natural phenolic compounds from an agricultural by-product and valorization of waste.

Optical manipulation and fusion of aqueous droplets containing inorganic and organic solutes in air using the dual-beam laser trapping technique.

The comparative evaluation of two aerosol droplets of different chemical compositions using the dual-beam laser trapping technique can be employed for highly sensitive and accurate measurements of the water activities of such droplets. However, it is technically difficult to load droplets of different chemical compositions into adjacent optical traps that are only a few tens of micrometers apart. To overcome this challenge, a chamber with an overhanging roof was created. This roof prevented the initially trapped droplets from being contaminated by aerosol droplets that were subsequently introduced into the chamber. Herein, we report the simultaneous laser trapping of an aqueous ammonium sulfate (AS) droplet and an aqueous succinic acid (SA) droplet in air using the dual-beam laser trapping technique. Two droplets were successfully fused through optical manipulation to form a mixed inorganic/organic droplet in air. This experimental approach is advantageous because it forms mixed inorganic/organic droplets under constant relative humidity (RH) conditions. However, in previous studies, it was necessary to compensate for changes in RH prior to and after droplet fusion. To assess the validity of theoretical predictions of the water activity of droplets containing AS and SA, the equilibrium radii of the droplet were compared with those calculated using certain theoretical models.

Effect of uni-divalent electrolyte in the interaction associated with solubility for the predominant form of L-isoleucine and L-serine in aqueous media

The study aimed to measure the solubilities of L-serine and L-isoleucine in an aqueous ammonium sulfate [(NH4)2SO4] solution at different temperatures (288.15 to 308.15 K) using a gravimetric technique. In pure aqueous media L-serine solubility is 4.1218 in mol•kg−1 of water while for L-isoleucine is 0.3094 mol•kg−1 at 298.15 K. The obtained solubility data was used to estimate the thermodynamic properties of the amino acids, such as the standard Gibbs free energy and standard entropy change during the solvation process. The analysis involved investigating the short range chemical interactions between the amino acids and the electrolyte solution, which significantly influenced the solvation thermodynamics. The study found that L-serine exhibited a salting in effect, meaning its solubility increased in the presence of ammonium sulfate, while L-isoleucine experienced a salting out effect, resulting in decreased solubility with the electrolyte. Additionally, solubility parameters were employed to assess the chemical strength of the amino acids and understand their solute–solvent interactions and relative solubilities in the solution. Overall, this experimental investigation provided valuable insights into the solvation behavior and chemical characteristics of L-serine and L-isoleucine in the presence of an electrolyte solution.

Non-evaporative solid phase ammonium sulfate separation from ammonia-stripped sulfuric acid solution by solvent-driven fractional crystallization

Manifold ammonia separation and recovery processes, such as adsorption, ion exchange, air stripping, membrane stripping, and electrochemical stripping, have been developed to harvest ammonia from waste streams. The separated ammonia was mostly stored in sulfuric acid as aqueous ammonium sulfate, an excellent fertilizer supplying nitrogen and sulfur. This aqueous phase of the ammonium sulfate, however, hindered the direct application of the recovered ammonia, due to low purity and large volume. Evaporative crystallization had been employed to promote its value, but its comprehensive obstacles include high operating costs, slow reaction kinetics, and low-purity end-products. We herein employed solvent-driven fractional crystallization (SDFC), also known as antisolvent crystallization, to crystallize recovered ammonia as sulfate salt (i.e., (NH4)2SO4) from the model ammonia-stripped sulfuric acid solution using methanol, ethanol, and acetone without energy-intensive evaporation. At 20 °C, the SDFC technique represented rapid crystallization, which reached equilibrium within only 5 min, and over 80 % of crystallization efficiency when 4-fold of the organic solvents were added. SDFC exclusively produced ammonium sulfate under various ammonium-to-sulfate molar ratios (ASR), whereas the evaporative crystallization produced a substantial amount of an unfavorable product, letovicite (i.e., (NH4)3H(SO4)2) at a low ASR. These features highlight the promise of SDFC as an alternative to the conventional evaporative crystallization. This study demonstrates the SDFC technique to improve the purity and usability of recovered ammonia in an acid stripping solution, thereby improving the potential of existing ammonia recovery technologies and their applicability in the environmental industry.

Highly stretchable porous regenerated silk fibroin film for enhanced wound healing.

Silk fibroin (SF) has received interest in tissue engineering owing to its biocompatibility, biodegradability, and favorable mechanical properties. However, the complex preparation, brittleness, and lack of pores in the structure of the silk fibroin film limit its application. Herein, we show that facile dissolution of SF in aqueous phosphoric acid followed by regeneration in aqueous ammonium sulfate ((NH4)2SO4) could afford highly stretchable films with nano-pores formed in the nonsolvent-induced phase separation process. The named phase separation, which determines the morphology and mechanical properties of the regeneration silk fibroin (RSF) films, is highly dependent on the (NH4)2SO4 concentration as well as the initial concentration of the SF solution. Therefore, the RSF films exhibit a tunable pore size ranging from 230 to 510 nm and excellent stretchability with tensile strain up to 143 ± 16%. Most interestingly, the RSF films were shown to support the proliferation of human skin fibroblasts in vitro as well as speed up full-thickness skin wound healing in a rat model. This work establishes an easy and feasible method to access porous RSF membranes that can be used for wound dressing in clinical settings.

Does liquid-liquid phase separation impact ice nucleation in mixed polyethylene glycol and ammonium sulfate droplets?

Particles can undergo different phase transitions in the atmosphere including deliquescence, liquid-liquid phase separation (LLPS), melting, and freezing. In this study, phase transitions of particles/droplets containing polyethylene glycol with a molar mass of 400 g mol-1 (PEG400) and ammonium sulfate (AS), i.e., PEG400-AS particles/droplets, were investigated at different organic-to-inorganic dry mass ratios (OIRs) under typical tropospheric temperatures and water activities (aw). The investigated droplets (60-100 μm) with or without LLPS in the closed system froze through homogeneous ice nucleation. At temperatures lower than 200 K, multiple ice nucleation events were observed within the same individual droplets at low aw. Droplets with and without LLPS shared similar lambda values at the same OIR according to the lambda approach indicating they form ice through the same mechanism. A parameterization of lambda values was provided which can be used to predict freezing temperature of aqueous PEG400-AS droplets. We found that adding AS reduces the temperature dependence of aw in aqueous PEG400 droplets. Assuming incorrectly that aw is temperature-independent for a constant droplet composition leads to a deviation between the experimental determined ice nucleation rate coefficients for droplets at OIR > 1 and the predicted values by the water-activity-based ice nucleation theory. We proposed a parameterization of temperature dependence of aw to minimize the deviations of the measured melting temperatures and nucleation rate coefficients from the corresponding predictions for aqueous PEG400-AS system.

Design of novel temperature-resistant and salt-tolerant acrylamide-based copolymers by aqueous dispersion polymerization

ABSTRACT Development of polymer-based flooding technology to improve oil recovery efficiency, water dispersion copolymerization of acrylamide, cationic monomer methacryloxyethyltrimethyl ammonium chloride (METAC), and anionic monomer acrylic acid (AA) were carried out in aqueous ammonium sulfate solution with polyvinyl pyrrolidone (PVP) as the stabilizer. The copolymers were characterized by 1H-NMR, FT-IR, TG, and SEM to confirm that they were prepared successfully and exhibited excellent salt-resistant property. Moreover, the effect of the aqueous solution of ammonium sulfate (AS) concentration, stabilizer concentration, and initiator concentration on the viscosity and size were systematically investigated. To further improve the thermal endurance properties of copolymer, hydrophobic monomers with different alkyl chain lengths were added to the above system. The acrylamide-based quadripolymer possessed prominent thermal and salt endurance properties by utilizing the advantages of zwitterionic structure and hydrophobic monomer. With the temperature rising, the viscosity retention could reach 70.2% in the water and 63.8% in the saline. This work had expected to provide a new strategy to design polymers with excellent salinity tolerance and thermal-resistance performances.

Solubility and solvation thermodynamics of glycine, dl-alanine and l-threonine in pure aqueous and aqueous (NH4)2SO4 solution

In this article the equilibrium saturated solubility of glycine, dl-alanine and l-threonine in aqueous ammonium sulphate media at various temperatures were estimated. The standard transfer Gibbs free energies and different thermodynamic parameters were also estimated. Different interactions were analysed for the solvation of the amino acids in the experimental media to explain the mechanism of solvation. For dl-alanine and l-threonine, salting-in effect is observed at lower electrolyte concentration while at higher electrolyte concentration salting-out effect is observed at a particular temperature. The chemical stability of the amino acids in aqueous electrolyte mixture was explained to justify the experimental results.

Hygroscopicity of Microplastic and Mixed Microplastic Aqueous Ammonium Sulfate Systems.

A growing body of research suggests the presence and long-range transport of microplastics in the atmosphere. However, the interactions between these microplastics and atmospheric aerosol are poorly understood. Environmental microplastics vary in color, morphology, and chemical composition and become oxidized over time by UV, mechanical, and biological action. Once introduced to the atmosphere, these microplastics will likely become mixed with atmospheric aerosol. Determining how microplastics interact with aerosol particles and how they may alter aerosol physical properties, including water uptake and loss, is necessary to understand the impact of these microplastics on our environment. Herein, we investigate the effect of microplastics on the water activity of bulk water and ammonium sulfate solutions. We compare a variety of plastic compositions and microplastic morphologies including plastics that have been aged by UV irradiation and mechanical forces in the lab. In addition, we investigate the water uptake and loss in microplastic samples through dynamic vapor sorption. We find an increase in total water sorption for UV-aged plastics compared to pristine plastics. Finally, we investigate the effect of fractional surface coverage on the equilibration time scale.

Electrochemically exfoliated graphene sheets as electrode material for aqueous symmetric supercapacitors

Abstract In this work, we have demonstrated a prompt anodic electrochemical exfoliation of graphite into graphene sheets (GS) in aqueous media. For the synthesis of GS, a constant potential of +10 V has been applied between two identical graphite sheets in 0.1 M aqueous ammonium sulfate. The exfoliated GS were characterized via standard analytical tools such as Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), Raman, X-ray photoelectron spectroscopy (XPS), and field emission scanning electron microscopy with energy dispersive spectrum (FE-SEM with EDS). Further, the electrochemical performance of GS coated Ni foam (GS/Ni foam) was assessed by cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS) techniques in 2 M KOH. The quasi-rectangular shaped voltammograms and triangular shaped GCD curves in a three-electrode system was evidenced the double-layer capacitance of GS/Ni foam, which exhibited maximum specific capacitance of 84.82 and 40. 83 F/g at 2 mV/s, and 0.1 A/g of current density, respectively. Moreover, the symmetric two-electrode performance of GS/Ni foam was also examined, which showed good energy density (3.03 Wh/kg) and power density (562.5 W/kg). This study proves that the anodically exfoliated GS can act as a good symmetric supercapacitor in KOH.

Selective Sulfur Dioxide Absorption from Simulated Flue Gas Using Various Aqueous Alkali Solutions in a Polypropylene Hollow Fiber Membrane Contactor: Removal Efficiency and Use of Sulfur Dioxide.

Hollow fiber membrane contactors (HFMCs) provide a large specific surface area. Thus, their significantly reduced volume provides an advantage compared to the conventional gas–liquid contactor. In this study, the selective removal efficiency of flue gas, in which sulfur oxide (SO2) and carbon dioxide (CO2) coexist, was measured using a polypropylene (PP) HFMC with such advantages. To increase the selective removal efficiency of SO2, experiments were conducted using various alkaline absorbents. As a result, with 0.05 M ammonia solution, the removal efficiency of 95% or more was exhibited with continuous operation for 100 h or more. We confirmed that the absorbent saturated by the once-through mode was aqueous ammonium sulfate ((NH4)2SO4) solution and could be used as a fertilizer without additional processing.

Mixed-acid intercalation for synthesis of a high conductivity electrochemically exfoliated graphene

Precise control of electrochemical intercalation and exfoliation conditions provides a method for tuning graphene properties. A systematic evaluation of the defects induced in graphene for varying intercalation times and intercalant composition is done using a sulphuric and phosphoric acid mixtures. Intercalation was performed in a concentrated mixture of sulphuric and phosphoric acid, followed by anodic exfoliation in aqueous ammonium sulphate solution. Multi-atom-doped graphene with primarily “boundary-type” defects is obtained, and the ratio of the defect-activated Raman modes showed a unique characteristics at 1600 s intercalation, irrespective of the intercalant composition. Careful selection of intercalation time is required to control the graphene defects. Phosphorus and nitrogen-doping increased with phosphoric acid content, influencing graphene properties. Interestingly, extending intercalation times beyond 1600 s deteriorated the electrical conductivity but enhanced the thermal stability with higher phosphoric acid content. We attribute this to loss of the sp2 graphitic structure at higher intercalation times which dominates over contributions from the dopants. The highest electrical conductivity of ∼14,000 S m−1 was two orders of magnitude higher than graphene obtained with pure sulphuric-acid intercalation. By adding phosphoric acid into the intercalant, the energy consumption and exfoliation time was reduced by 34% and by a factor of 3 respectively.

Valorization of Carbohydrates of Agricultural Residues and Food Wastes: A Key Strategy for Carbon Conservation

The complete conservation of the carbon, hydrogen, and oxygen atoms of cellulose and starch can theoretically be achieved by their conversion to levulinic and formic acids. Similarly, hemicellulose can be converted to furfural and water with 100% atom economy. The valorization of carbohydrates of agricultural residues (banana-, orange-, and potato-peels, corn leaf and root, and rice husk), potential components of raw food wastes (corn, rice, potato, lettuce, onion, leek, vegetable, bean, and tomato), and cooked food wastes (rice noodle, spaghetti, risotto, noodle, bread, and biscuit) was demonstrated in the presence of sulfuric acid at 130 °C in γ-valerolactone as the green solvent to yield levulinic and formic acids as the two main products. Levulinic acid was also produced from furfural by its transfer hydrogenation with formic acid to furfuryl alcohol in the presence of Shvo’s catalyst followed by its acid catalyzed conversion to levulinic acid. Neutralization of the sulfuric acid in the reaction mixture with ammonium hydroxide resulted in an aqueous ammonium sulfate phase and a γ-valerolactone rich organic phase. Due to the salting out effect of the ammonium sulfate in the aqueous phase, levulinic acid and formic acid partitioned to the γ-valerolactone rich organic phase at >99.8% and >97.1%, respectively. The transfer hydrogenation of levulinic acid with formic acid in the presence of the Shvo’s catalyst resulted in the formation of 4-hydroxyvaleric acid, which readily underwent dehydration to yield γ-valerolactone, a green and sustainable liquid. The possibility of converting C₅- and C₆-carbohydrates to levulinic acid or γ-valerolactone is a great opportunity for carbon conservation with a carbon-economy higher than that for butanol or ethanol.

Infrared Nanospectroscopy at the Graphene-Electrolyte Interface.

We present a new methodology that enables studies of the molecular structure of graphene-liquid interfaces with nanoscale spatial resolution. It is based on Fourier transform infrared nanospectroscopy (nano-FTIR), where the infrared (IR) field is plasmonically enhanced near the tip apex of an atomic force microscope (AFM). The graphene seals a liquid electrolyte reservoir while acting also as a working electrode. The photon transparency of graphene enables IR spectroscopy studies of its interface with liquids, including water, propylene carbonate, and aqueous ammonium sulfate electrolyte solutions. We illustrate the method by comparing IR spectra obtained by nano-FTIR and attenuated total reflection (which has a detection depth of a few microns) demonstrating that the nano-FTIR method makes it possible to determine changes in speciation and ion concentration in the electric double and diffuse layers as a function of bias.

Influence of Ions and Temperature on Aqueous Biphasic Systems Containing Ionic Liquid and Ammonium Sulfate

Recently, ionic liquids (ILs) were widely used to form aqueous biphasic systems (ABSs). In this study, a systematic investigation involving various ILs was studied to provide more information on fo...

Thermodynamic Modeling of CaSO4–(NH4)2SO4–NH3–H2O Quaternary System with Asymmetric E-NRTL Model

Ammonium sulfate [(NH4)2SO4], an undesired byproduct in the caprolactam process, can be converted into recyclable NH3 by the substitution reaction with lime milk to reduce the ammonia consumption and produce high-quality gypsum. However, the thermodynamic mechanism of this process has not been clarified, which results in the unpredictable crystal phase of calcium sulfate products. In this work, a thermodynamic model for the CaSO4–(NH4)2SO4–NH3–H2O quaternary system with the asymmetric E-NRTL activity coefficient model was developed to understand the thermodynamic behavior. The modeling works involved the data fitting of binary solubility, osmotic coefficient, enthalpy of solution, and heat capacity data as well as ternary solubility data. It was shown that the model could predict the solubility of ammonia and calcium sulfate in aqueous ammonium sulfate solution with temperature ranging from 0 to 160 °C and pressure up to 1.0 MPa. Furthermore, the constructed model for the quaternary system was proved to b...

Aqueous Intercalation of Graphite at a Near-Neutral pH

Graphite has been extensively studied as a battery electrode, but few investigations have explored its behavior in water at neutral pH. Here, we investigate graphite intercalation in an aqueous ammonium sulfate electrolyte with a pH of 6. We identified potentials at which bisulfate intercalation and deintercalation compete with water oxidation. In situ X-ray diffraction revealed that the interlayer space of graphite expands during intercalation, reaching a stage-two graphite intercalation compound. Irreversible changes to the graphite occurred during intercalation, as demonstrated by the appearance of sp3-type carbon, hydroxyl, and carbonyl groups in Raman and X-ray photoemission spectra. Our findings indicate that intercalation of graphite in aqueous media at a near-neutral pH and modest potentials is possible, but improved chemical and structural stability of the graphite and electrolyte are required to achieve long-term operation.

Particle acidity and sulfate production during severe haze events in China cannot be reliably inferred by assuming a mixture of inorganic salts

Abstract. Atmospheric measurements showed rapid sulfate formation during severe haze episodes in China, with fine particulate matter (PM) consisting of a multi-component mixture that is dominated by organic species. Several recent studies using the thermodynamic model estimated the particle acidity and sulfate production rate, by treating the PM exclusively as a mixture of inorganic salts dominated by ammonium sulfate and neglecting the effects of organic compounds. Noticeably, the estimated pH and sulfate formation rate during pollution periods in China were highly conflicting among the previous studies. Here we show that a particle mixture of inorganic salts adopted by the previous studies does not represent a suitable model system and that the acidity and sulfate formation cannot be reliably inferred without accounting for the effects of multi-aerosol compositions during severe haze events in China. Our laboratory experiments show that SO2 oxidation by NO2 with NH3 neutralization on fine aerosols is dependent on the particle hygroscopicity, phase-state, and acidity. Ammonium sulfate and oxalic acid seed particles exposed to vapors of SO2, NO2, and NH3 at high relative humidity (RH) exhibit distinct size growth and sulfate formation. Aqueous ammonium sulfate particles exhibit little sulfate production, in contrast to aqueous oxalic acid particles with significant sulfate production. Our field measurements demonstrate significant contribution of water-soluble organic matter to fine PM in China and indicate that the use of oxalic acid in laboratory experiments is representative of ambient organic dominant aerosols. While the particle acidity cannot be accurately determined from field measurements or calculated using the thermodynamic model, our results reveal that the pH value of ambient organics-dominated aerosols is sufficiently high to promote efficient SO2 oxidation by NO2 with NH3 neutralization under polluted conditions in China.