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Abstract:
This communication presents a comprehensive investigation into the impact of mixing on the synthesis of water-in-water Pickering emulsions. The approach employs commercial-grade oppositely charged nanoparticles within two distinct fluid phases, facilitating self-assembly and the formation of aggregates with variable sizes and compositions. Enhanced interfacial area, achieved through aggregate adsorption at the interface, elevates the Gibbs detachment energy of particles between the two aqueous phases, leading to stable emulsion formation. We further explore the effect of various mixing devices, including high-pressure and sonic wave mixing. Our findings reveal that mixing within the aqueous phase critically influences emulsion size, with sonicator-assisted mixing producing smaller droplets than homogenizer mixing. Both devices yield poly-dispersed droplet size distributions. Interestingly, the droplet size correlates well with the Hinze scale (hd), and the Kolmogorov length scale (ld) exhibits good correspondence within a specific operating range. The proposed method introduces a streamlined, one-step synthesis process for easy preparation, demonstrating excellent stability for a minimum of 30 days. This study pioneers the investigation of mixing effects within an aqueous two-phase system utilizing a Pickering emulsion template.

Abstract:
The increasing groundwater pollution resulting from industrial dyes and pharmaceutical products, which come from various sources, requires urgent attention to implement effective remediation measures. We demonstrate that the rough particles studded with platinum (Pt) nanoparticles can be fabricated at room temperature straightforwardly and in a single step. These rough particles displayed a good catalytic power (100% removal efficiency) against a model industrial dye (methylene blue) and pharmaceutical residue (tetracycline) within a reasonable time scale. Characterization techniques such as X-ray diffraction (XRD), atomic force microscopy (AFM), and field emission scanning electron microscopy (FESEM) confirmed the uniform deposition of Pt nanoparticles on the surface of polystyrene particles, forming dense islands and the roughened surface. Further, we investigated the influence of particle size, concentration, and contact patterns on the performance of rough catalytic particles. The semi-batch conditions favoured the complete decomposition of tetracycline within 40 min, but the batch-wise operation offered a good contacting pattern for methylene blue, yielding a maximal output within 10 min. The kinetics of the heterogeneous catalytic process modelled by Langmuir-Hinshelwood kinetics (r = kKC/1 + KC) predicts that the given methylene blue decomposition reaction induced by the rough particles follows the pseudo-first-order kinetics. The rate constants for the reaction catalyzed by 0.6 and 1.0 m-sized rough particles are 0.048 and 0.032 min, respectively. Furthermore, we established the proof-of-concept using magnetically responsive nanoparticles for real-time applications, including decontamination and recovery of catalyst particles via an externally applied magnetic field in one cycle. Our proposed method helps achieve a near-100% degrading efficiency within 10 to 40 min at minimal catalytic particle concentration, i.e., 200 ppm. Since we can turn the rough particles into super-paramagnetic, we can recover and reuse them for several wastewater treatment cycles without incurring running costs.

Keywords:
Polystyrene (PS), Iron Oxide (IO), Plat- inum nanoparticles, Rough particles, Magnetically- responsive nanoparticles, Methylene blue, Tetracy- cline, Environmental remediation

Abstract:
Nanoplastics pose a significant global environmental concern, as they can accumulate emerging pollutants and enter the food chain, endangering human health and ecosystems. Wastewater treatment plants (WWTPs) have been identified as the primary source of micro and nanoplastic contamination, necessitating the development of effective removal methods. This study investigates the efficacy of electrolysis-assisted flotation (EF) process for removing nanoplastics from synthetic wastewater, using polystyrene-type nanoparticles synthesized from expanded polystyrene waste (EPS) as representative nanoplastic contaminants. Electrolysis experiments were conducted using parallel aluminium electrodes under low-voltage conditions. The study systematically explores the influence of various process parameters, including electrode spacing, salt concentration, nanoplastics concentration, and applied voltage, on the removal efficiency of nanoplastics. The removal efficiency was evaluated using a turbidity meter and dynamic light scattering technique. The derived count rate (DCR) obtained from dynamic light scattering supplements the nephelometric turbidity units (NTU) and provides a reliable estimate of the nanoplastics sample concentration. Under optimized conditions, with a specified electrolyte concentration and pH of 7.2 ± 0.3, the EF process achieved an impressive removal efficiency of nearly 95 % (94 % per DCR). A notable advantage of the proposed method is forming a foamy layer on top of the reactor when nanoplastics and coagulants are mixed, facilitating easy removal by simple scraping. This study provides valuable insights into developing an eco-friendly and sustainable approach for the large-scale removal of nanoplastics. The results contribute to advancing wastewater treatment strategies and addressing the pressing issue of nanoplastic pollution.

Keywords:
Nanoplastics, Polystyrene waste, Electrolysis, Wastewater, Flotation, Removal efficiency

Abstract:
This communication presents a simple yet straightforward method for preparing water-in-water-in-water particle-stabilized double emulsions, also known as Pickering double emulsions. The approach involves using oppositely charged nanoparticles (OCNPs) in two distinct fluid phases, promoting self-assembly and the formation of aggregates with varying sizes and compositions. By enhancing the interfacial area through the adsorption of aggregates at the interface, this method increases the Gibbs detachment energy of particles between the two aqueous phases, forming stable double emulsions. Furthermore, we investigated the impact of the molecular weight of polyethylene oxide and dextran in the respective fluid phases and the mass ratio (M) of the OCNPs on double emulsion formation. The results demonstrate that the molecular weight of the polymers used in the aqueous phase is a critical parameter influencing the structural formation of the emulsion and the generation of double emulsions. Consequently, double emulsions are formed when equal molecular weight polymer mixtures are employed at an appropriate M, with the dispersed phase placed in the highly viscous continuous phase. The proposed method offers a one-step synthesis process, enabling easy preparation, and exhibits excellent stability for at least 30 days. This study represents the first reported approach for the one-step synthesis of multiple emulsions in an aqueous two-phase system utilizing a Pickering emulsion template.

Abstract:
Candle soot (CS) nanoparticles exhibit excellent superhydrophobic and superoleophilic properties, making them an ideal absorbent for separating oil and oil/water mixtures. Although their cost-effectiveness is attractive, the challenges associated with recovering soot nanoparticles after oil absorption and producing secondary pollutants have limited their attention. Our study demonstrates the synthesis of CS nanoparticles embedded polystyrene (PS) nanofibrous membranes with excellent stability, surface-to-volume ratios, and flexibility. CS-incorporated composite membrane with a rough surface showed a water contact angle (WCA) of 156° ± 1.5°, about 20% higher than the smooth pristine PS membrane. The CS-based composite membrane also demonstrated improved performance as an absorbent, owing to its hydrophobic characteristics linked with surface roughness when employed for separating oil from oil/water mixtures. Furthermore, when exposed to four different oils, the CS-based membrane displayed a higher absorption capacity (up to ≈120 g oil/g membrane) than the pristine membrane. Using a gravity-assisted continuous oil/water separation setup, we measured the oil permeate flux using nanofiber mats as a membrane. Compared to the original membrane, the modified membrane showed enhanced oil permeate flux of ~2873 ± 122 L m−2 h−1 and separation efficiency of over 99%.

Keywords:
candle soot, electrospinning, oil/water separation, superhydrophobicity, superoleophilicity

Abstract:
Nanoparticle-stabilized water-in-water (w/w) emulsions, an example of aqueous two-phase systems (ATPS), can produce low-fat food colloids, edible gels, bio-polymer-based bijels, scaffolds for tissue-engineering, and porous materials. This w/w emulsion is made from two thermodynamically incompatible aqueous-polymer solutions, such as polyethylene oxide (PEO) and dextran. Changing the molecular weight of PEO in one aqueous phase stabilizes w/w emulsion. The state diagram we generated using electron and light microscopy provides a novel approach to producing stable emulsion-filled gels and emulsion droplets. The visual examination, brightfield, and fluorescent microscopy studies highlight the role of molecular weight and storage duration. The production of an emulsion-filled gel is ascribed to the “active-filler-particles” arrangement, typically seen when the affinity between droplets stabilized by particles and polymer is substantial. In contrast, we expect the “inactive-filler-particles” arrangement for the samples that undergo phase inversion. The temporal evolution of shear-induced structures recorded using a rheometer demonstrates that these emulsion-filled gels’ viscoelastic properties correspond directly with time, molecular weight, and polymer composition. The emulsion-filled gels generated displayed 90-day storage stability. Our work would help us understand the complex dynamics of w/w emulsion-based formulations that need suitable size, shape, appearance, and shelf life management.

Keywords:
W/W emulsions, ATPS, Emulsion-filled gels, Rheology, Silica nanoparticles