Pickering emulsions prepared by layered niobate K₄Nb₆O₁₇ intercalated with organic cations and photocatalytic dye decomposition in the emulsions

Recent advances in the design and use of Pickering emulsions for wastewater treatment applications

Pickering emulsions have recently emerged as versatile systems capable of targeting many applications of wastewater treatment. The unique properties, which include high emulsion stability, easy preparation, low toxicity, and stimuli-responsiveness, pave the way for advances in common pollutant control processes. This review aims to provide a comprehensive overview on different aspects in the Pickering emulsion design focusing on the key structural relations and their implications in specific applications. The first section is dedicated to the critical parameters governing the Pickering emulsion type, droplet size and stability. Furthermore, a section describing methods for demulsification and particle recovery is included, in which various stimuli have been explored. Finally, the most potent applications of Pickering emulsions such as photocatalytic degradation, adsorption, extraction, and separation of common wastewater pollutants are presented and discussed with a great deal of attention towards the efficacy, current limitations, and future potential. Recognizing the rise of innovative Pickering emulsion solutions is expected to induce profound effects facilitating the technology transfer to industrial processes.

Soap-Free Emulsion Composed of Polymer Solutions and an Aqueous Clay Suspension

Novel emulsification was found in the system of aqueous suspension of a clay mineral (a synthetic hectorite) and a solution of polyvinyl butyral in 1-butanol without using surface-active agents. Droplets of the oil phase exhibited different sizes depending on the concentration of polyvinyl butyral solution and aqueous clay suspension. Shearing force produced from the high viscosity of the clay suspension was a factor to lead oil droplets to size smaller. The clay mineral was confirmed to be in the water phase, not at the oil and water interface. The emulsion showed useful thermal stability up to 80 °C. The present emulsion was successfully applied as a platform of the photochromic reaction of spiropyran.

Facile preparation of protonated hexaniobate nanosheets and its enhanced photocatalytic activity

Exfoliated hexaniobate nanosheets E-H₂K₂Nb₆O_17-x (E-HKNO) with broad light absorption (up to 850 nm) and high adsorption properties were prepared via ion exchange and transient annealing processes with micron-size K₄Nb₆O₁₇ powders as the precursor. The as-prepared E-HKNO nanosheets show excellent visible light photodegradation performances when compared to degussa P25, which was evaluated in terms of degradation of Rhodamine B (Rh B). High adsorption and broad light absorption characteristics could be attributed to the exfoliation behavior and the reduction of surface Nb⁵⁺ to Nb⁴⁺, which was confirmed by x-ray photoelectron spectroscopy (XPS) and Raman spectra. From the Mott-Schottky analysis, the E-HKNO is an n-type semiconductor and has a higher flat band voltage (-0.46 V versus RHE at pH = 7), compared with K₄Nb₆O₁₇. In addition, the electrochemical impedance spectroscopy (EIS) indicates that the E-HKNO nanosheets have an increased semiconductor-electrolyte charge transfer resistance, which is not conducive to the separation of photogenerated carriers (e^--h⁺). Accordingly, a small amount of holes scavenger (EDTA) was added to improve the photodegradation performance of the E-HKNO, since the holes scavenger can inhibit the recombination of the photogenerated carriers. This work provides not only a facile method for the preparation of an efficient E-HKNO nanosheets photocatalyst, but also new insights for further enhancing the photodegradation performance by adding trace scavenger.

Exploring optoelectronic properties and mechanisms of layered ferroelectric K4Nb6O17 nanocrystalline films and nanolaminas

Two-dimensional layered K₄Nb₆O₁₇ (KN) was easily formed as a secondary phase caused by the volatilization of alkali metal ions, when preparing ferroelectric K_xNa_1−xNbO₃ based ceramics and films. In this work, it was believed that KN film is with weak ferroelectricity and has a little effect on the ferroelectric properties of K_xNa_1−xNbO₃ based films. Moreover, temperature dependent (77–500 K) dielectric functions of KN film have been firstly extracted by fitting ellipsometric spectra with the Adachi dielectric function model and a four-phase layered model. The high-frequency dielectric constant linearly increases and optical band gap slightly decreases with increasing the temperature. We also research its photoelectrochemical properties and its application in high-efficient light-induced H₂ evolution. In addition, X-ray photoelectron spectroscopy, Raman scattering, temperature dependent transmittance and infrared reflectance spectra, and first-principles calculation were conjointly performed to further reveal the intrinsic optoelectronic features and relevant mechanisms of KN.

Boosted adsorption–photocatalytic activities and potential lithium intercalation applications of layered potassium hexaniobate nano-family

We demonstrated that the KN nano-family (including KN nanolaminas and nano hollow spheres) can be derived from the same Nb₂O₅-based hydrothermal reaction.

Self-assembled nanoparticle-stabilized photocatalytic reactors

The efficiency of nanostructured photocatalysts continues to improve at an impressive pace and is closing in on those needed for commercial applications; however, present-day reactor strategies used to deploy these nanostructures fail to achieve the sufficient areas (>1 m(2)) needed for solar application. Here we report the Self-assembled Nanoparticle-stabilized Photocatalytic Reactor (SNPR), a fully-scalable reactor strategy comprised only of nanoparticles adsorbed at the fluid-fluid interfaces of oil-in-water emulsions, water-in-oil emulsions, and CO2-in-water foams. We show that SNPRs naturally disperse over open water and need no physical substrate, requiring only photocatalysts and fluid. In environmental applications the SNPR provides more than double the reaction rate of a comparable single-phase reactor. In continuous mode, the SNPR achieves 100% photocatalyst retention and processes 96% of the stream over 20 hours; in contrast, the performance of a comparable aqueous suspension declines to zero over this interval, losing all photocatalyst to the outlet stream. We further characterize the photoactivity of individual photocatalytic droplets, with reactants in both the continuous and dispersed phases. These results demonstrate SNPRs as a robust and flexible reactor strategy and a route-to-scale for nanomaterials.

Effects of variables on the dispersion of cationic–anionic organomontmorillonites and characteristics of Pickering emulsion

Montmorillonites were modified with different amounts of cationic and anionic surfactants by variable steps; characteristics of cationic–anionic organomontmorillonites and Pickering emulsion were further investigated.

Detection of zinc finger protein (EGR1) based on electrogenerated chemiluminescence from singlet oxygen produced in a nanoclay-supported porphyrin environment

Early growth response protein 1 (EGR1), as a characteristic example of zinc finger proteins, acts as a transcription factor in eukaryotic cells, mediating protein-protein interactions. Here, a novel electrochemiluminescence (ECL)-based protocol for EGR1 assay was developed with a new eco-friendly emitter: singlet oxygen produced in the vicinity of nanoclay-supported zinc proto-porphyrin IX (ZnPPIX). Its electrochemical reduction stimulates an intense monochromic CL irradiation at 644 nm from the dissolved oxygen as endogenous coreactant in the aqueous solution. This ECL derivation was rationalized via hyphenated spectroscopy and theoretical calculation. To promote hydrophilicity and solid-state immobilization of porphyrins, the lamellar artificial laponite was employed as a nanocarrier owning to its large specific area without the blackbody effect. The facile exfoliation of laponite produced quality monolayered nanosheets and facilitated the adsorption and flattening of PPIX upon the surface, resulting in a highly efficient ECL emission. Based on the release of Zn(2+) in zinc finger domains of EGR1 upon contact with the ECL-inactive PPIX, which was monitored by circular dichroism and UV-absorption, a sensitive Zn(2+)-selective electrode for the "signal-on" detection of EGR1 was prepared with a detection limit down to 0.48 pg mL(-1) and a linearity over 6 orders of magnitude. The proposed porphyrin-based ECL system thus infused fresh blood into the traditional ECL family, showing great promise in bioassays of structural Zn(II) proteins and zinc finger-binding nucleotides.

Ti/ZnO–MxOy composites (M = Al, Cr, Fe, Ce): synthesis, characterization and application as highly efficient photocatalysts for hexachlorobenzene degradation

A series of novel organic–inorganic nanoscale layered materials were synthesized by intercalating the Ti-containing Schiff base complex into the interlayer of the ZnM layered double hydroxides (LDHs, M = Al, Cr, Fe, Ce).

g-C3N4 hybridized with AgVO3 nanowires: preparation and its enhanced visible-light-induced photocatalytic activity

The g-C₃N₄/AgVO₃ nanowires composite was fabricated and developed into an efficient visible-light-induced photocatalyst for eliminating organic pollutants.

A novel p–n junction Ag3PO4/BiPO4-based stabilized Pickering emulsion for highly efficient photocatalysis

This study demonstrates a new kind of photocatalytic system via utilization of the superior specific properties inherent in Pickering emulsions.

Recent advances in synthesis and applications of clay-based photocatalysts: a review

Clay-based photocatalysts with high adsorbability and special structures have attracted extensive attention because of their applications in environment and energy fields.

Versatile fabrication of nanocomposite microcapsules with controlled shell thickness and low permeability

Novel ethyl phenylacetate (EPA)-loaded nanocomposite microcapsules with polyurea (PU) /poly (melamine formaldehyde) (PMF) shells were facilely and fabricated: by using silica nanoparticle-stabilized oil-in-water (o/w) emulsion template and subsequent interfacial reaction and in situ polymerization. SiO2 nanoparticles absorbed at the interface between oil and water to stabilize the o/w emulsions. The oil droplets containing EPA, isophorone diisocyanate (IPDI) and tolylene 2,4-diisocyanate-terminated poly (propylene glycol) (PPG-TDI) were subsequently reacted with MF prepolymer (pre-MF) dissolved in water phases. The interfacial reaction between pre-MF and IPDI produced interior PU walls. Meanwhile, the in situ polymerization of pre-MF generated exterior PMF walls. It was found that these in/out double walls were compact together. The resulting capsules had spherical shapes and rough exterior surfaces, and could be easily isolated, dried, and redispersed in epoxy resins. The size of the produced microcapsules was dependent on the concentration of SiO2 nanoparticles. The dynamic thermal gravimetric analysis (TGA) demonstrated that the capsules showed excellent thermal stability with little weight loss when exposed at 150 °C for 2 h. Interestingly, with a double PU/PMF shell, these capsules exhibited an extra-low permeability. Moreover, these microcapsules can also demonstrate exceelent magnetic responsiveness after introducing magnetic nanoparticles inside. We believe our microcapsules could be potential candidates in microcapsule engineering, self-healing composites, and drug-carrying systems.