Synthesis of magnetic rattle-type nanostructures for use in water treatment

Advances in Surface-Enhanced Raman Scattering Sensors of Pollutants in Water Treatment

Water scarcity is a world issue, and a solution to address it is the use of treated wastewater. Indeed, in these wastewaters, pollutants such as pharmaceuticals, pesticides, herbicides, and heavy ions can be present at high concentrations. Thus, several analytical techniques were initiated throughout recent years for the detection and quantification of pollutants in different types of water. Among them, the surface-enhanced Raman scattering (SERS) technique was examined due to its high sensitivity and its ability to provide details on the molecular structure. Herein, we summarize the most recent advances (2021-2023) on SERS sensors of pollutants in water treatment. In this context, we present the results obtained with the SERS sensors in terms of detection limits serving as assessment of SERS performances of these sensors for the detection of various pollutants.

Well-dispersed TiO2 nanoparticles anchored on Fe3O4 magnetic nanosheets for efficient arsenic removal

Magnetic iron-titanium binary oxide as an effective adsorbent for arsenic contaminant is a challenge primarily because of their bulk structure and agglomeration effect. Herein, a novel and uniform sandwich-like magnetic Fe₃O₄@TiO₂ sheets were synthesized by utilizing a facile strategy involving amorphous-to-crystalline transformation and reduction in H₂, to achieve dispersed anatase TiO₂ nanoparticles with a small size of ∼8 nm anchored on Fe₃O₄ sheets. The resultant Fe₃O₄@TiO₂ sheets nanocomposite possessing a high specific surface area of ∼89.4 m² g^-1 and available magnetic susceptibility of ∼20.0 emu g^-1, significantly enhanced the photocatalytic oxidation property of arsenite and considerable adsorption capability for arsenic removal. The adsorption capacities of As(V) and As(III) with UV-assisted from adsorption experimental results were 36.36 and 30.96 mg g^-1, respectively, while the residual concentrations for both As(V) and As(III) were lower than the strict limit of 10 μg L^-1. Adsorption equilibriums were almost reached within 45 min. In addition, the adsorbent exhibited excellent stability over a broad pH range of 3-9 and still maintained great removal efficiency after five time regeneration cycles. Furthermore, except for silicate and phosphate, the extremely weak inhibiting influences of common co-existing ions in arsenic removal process, demonstrated that the developed magnetic Fe₃O₄@TiO₂ sheets with unique nanostructure could be a promising efficient adsorbent for arsenic removal.

Rational design of yolk–shell nanostructures for photocatalysis

Yolk–shell structures provide an ideal platform for the rational regulation and effective utilization of charge carriers because of their void space and large surface areas. Furthermore, the efficiency of charge behavior in every step can be further improved by many strategies. This review describes the synthesis of yolk–shell structures and their effect for the enhancement of heterogeneous photocatalysis.

An overview of recent progress on noble metal modified magnetic Fe3O4 for photocatalytic pollutant degradation and H2 evolution

Noble metal modified magnetic Fe₃O₄ catalysts for photocatalytic pollutant degradation and H₂ evolution are reviewed.

Facile solvothermal preparation of Fe3O4–Ag nanocomposite with excellent catalytic performance

Functional nanocomposites demonstrate excellent comprehensive properties and outstanding characteristics for numerous applications. Magnetic nanocomposites are an important type of composite materials, due to their applications in optics, medicine and catalysis. In this report, a new Fe₃O₄-loaded silver (Fe₃O₄–Ag) nanocomposite has been successfully synthesized via a simple solvothermal method and in situ growth of silver nanowires. The silver nanowires were prepared via the reduction of silver vanadate with the addition of uniformly dispersed Fe₃O₄ nanoparticles. Structural and morphological characterizations of the obtained Fe₃O₄–Ag nanocomposite were carried out using many characterization methods. As a new composite catalyst, the synthesized magnetic Fe₃O₄–Ag nanocomposite displayed a high utilization rate of catalytically active sites in catalytic reaction medium and showed good separation and recovery using an external magnetic field. The facile preparation and good catalytic performance of this Fe₃O₄–Ag nanocomposite material demonstrate its potential applications in catalytic treatment and composite materials.

A new Fe₃O₄–Ag nanocomposite was prepared via solvothermal method, demonstrating potential application in catalytic degradation of wastewater treatment and composite materials.

Synthesis of Core-Shell Structured Porous Nitrogen-Doped Carbon@Silica Material via a Sol-Gel Method

Core-shell structured nitrogen-doped porous carbon@silica material with uniform structure and morphology was synthesized via a sol-gel method. During this process, a commercial triblock copolymer and the in situ formed pyrrole-formaldehyde polymer acted as cotemplates, while tetraethyl orthosilicate acted as silica precursor. The synergetic effect of the triblock copolymer and the pyrrole-formaldehyde polymer enables the formation of the core-shell structure. Herein, the pyrrole-formaldehyde polymer acted as not only the template, but also the nitrogen-doped carbon precursor of the core. The obtained core-shell structured porous material possesses moderate Brunauer-Emmett-Teller specific surface area (410 m² g^-1) and pore volume (0.53 cm³ g^-1). Moreover, corresponding hollow silica spheres or nitrogen-doped porous carbon spheres can be synthesized by calcining the core-shell structured material in air or etching it with HF. The X-ray photoelectron spectroscopy results reveal that the nitrogen states of the obtained material are mainly pyridinic-N and pyridonic-N/pyrrolic-N, which are beneficial for carbon dioxide adsorption. The carbon dioxide uptake capacity of the nitrogen-doped carbon spheres can reach 12.3 wt % at 273 K and 1.0 bar, meanwhile, the material shows good gas adsorption selectivities for CO₂/CH₄ and CO₂/N₂.

Highly Chemiluminescent Magnetic Beads for Label-Free Sensing of 2,4,6-Trinitrotoluene

Until now, despite the great success acquired in scientific research and commercial applications, magnetic beads (MBs) have been used for nothing more than a carrier in most cases in bioassays. In this work, highly chemiluminescent magnetic beads containing N-(4-aminobutyl)-N-ethyl isoluminol (ABEI) and Co²⁺ (Co²⁺/ABEI/MBs) were first synthesized via a facile strategy. ABEI and Co²⁺ were grafted onto the surface of carboxylated MBs by virtue of a carboxyl group and electrostatic interaction. The as-prepared Co²⁺/ABEI/MBs exhibited good paramagnetic properties, satisfactory stability, and intense chemiluminescence (CL) emission when reacted with H₂O₂, which was more than 150 times that of ABEI functionalized MBs. Furthermore, it was found that 2,4,6-trinitrotoluene (TNT) aptamer could attach to the surface of Co²⁺/ABEI/MBs via electrostatic interaction and coordination interaction between TNT aptamer and Co²⁺, leading to a decrease in CL intensity due to the catalytic site Co²⁺ being blocked by the aptamer. In the presence of TNT, TNT would bind strongly with TNT aptamer and detach from the surface of Co²⁺/ABEI/MBs, resulting in partial restoration of the CL signal. Accordingly, label-free aptasensor was developed for the determination of TNT in the range of 0.05-25 ng/mL with a detection limit of 17 pg/mL. This work demonstrates that Co²⁺/ABEI/MBs are easily connected with recognition biomolecules, which are not only magnetic carriers but also direct sensing interfaces with excellent CL activity. It provides a novel CL interface with a magnetic property which easily separates analytes from the sample matrix to construct label-free bioassays.

Photocatalytic degradation of 2-(4-methylphenoxy)ethanol over TiO2 spheres

The photocatalytic TiO₂-assisted decomposition of 2-(4-methylphenoxy)ethanol (MPET) in aqueous solution has been studied for the first time. The intermediate compounds of MPET photodegradation have been also determined. A toxic p-cresol is formed in significant quantities during the photocatalytic reaction. A solvent-exchange approach for a template-free preparation of spherical TiO₂ particles has been described, which is based solely on precipitation of hydrous titania from aqueous titanium peroxo complex by using organic solvents. The proposed method favours the formation of spherical titania particles with a mean size varying from 50 to 260nm depending on the choice of solvent. The procedure for converting nonporous titania spheres into mesoporous material maintaining the same spherical morphology has been developed. The synthesized TiO₂ spheres demonstrate a degree of MPET photo-degradation close to that of the commercial titania Aeroxide P25, besides being successfully recovered and reused for four reaction cycles without loss of photocatalytic activity. The effectiveness of the commercial Aeroxide P25 in MPET photodegradation, on the other hand, suffers 10-time drop during the third reaction cycle, which is attributed to its poor recoverability because the photocatalyst is composed of small particles of 20nm size.

A magnetically recoverable photocatalyst prepared by supporting TiO2nanoparticles on a superparamagnetic iron oxide nanocluster core@fibrous silica shell nanocomposite

A magnetically recoverable photocatalyst was prepared by supporting TiO₂nanoparticles on a superparamagnetic iron oxide nanocluster core@fibrous silica shell nanocomposite.

TiO2 hybrid photocatalytic systems: impact of adsorption and photocatalytic performance

For the past 40 years, titanium dioxide (TiO2) nanomaterials have attracted immense attention because of their potential applications in the photodegradation of organic pollutants, photocatalytic water splitting for H2 generation, and dye-sensitized solar cells. Despite the fact that the potential applications of TiO2 nanoparticles are ubiquitous, they are not problem free, examples include a large interfacial area that causes slow charge carrier transport, a wide optical band gap that leads to limited applications using solar light, and single-phase and nanoscales features that induce fast recombination of photo-reduced carriers. Therefore, this review highlights the development associated with the adsorption photocatalysis hybrid system for treating wastewater. The immobilization of TiO2 photocatalysts in metal oxide, carbon, and ceramic materials to form TiO2 hybrid systems could prevent the problem of particle recovery, adsorption capacity, and the separation process. Such hybrid systems require significant effort of optimizing the specific surface area-to-volume ratio of the supported photocatalysts with its photocatalytic activities.

Nanoparticles with photoinduced precipitation for the extraction of pollutants from water and soil

Nanotechnology may offer fast and effective solutions for environmental clean-up. Herein, amphiphilic diblock copolymers are used to develop a platform of photosensitive core-shell nanoparticles. Irradiation with ultraviolet light removes the protective layer responsible for colloidal stability; as a result, the nanoparticles are rapidly and irreversibly converted to macroscopic aggregates. The associated phase separation allows measuring the partitioning of small molecules between the aqueous phase and nanoparticles; data suggests that interactions are enhanced by decreasing the particle size. Adsorption onto nanoparticles can be exploited to efficiently remove hydrophobic pollutants from water and contaminated soil. Preliminary in vivo experiments suggest that treatment with photocleavable nanoparticles can significantly reduce the teratogenicity of bisphenol A, triclosan and 17α-ethinyl estradiol without generating obviously toxic byproducts. Small-scale pilot experiments on wastewater, thermal printing paper and contaminated soil demonstrate the applicability of the approach.

Plasmonic photocatalyst Ag@AgCl/ZnSn(OH)6: synthesis, characterization and enhanced visible-light photocatalytic activity in the decomposition of dyes and phenol

An efficient VLD photocatalyst, Ag@AgCl/ZSH, was fabricated by ultrasonic assisted precipitation-photoreduction method and its photocatalytic activity was investigated in detail and a possible mechanism was proposed.

Rational design of magnetic nanorattles as contrast agents for ultrasound/magnetic resonance dual-modality imaging

Nanorattles, as promising functional hollow nanomaterials, show considerable advantages in a variety of applications for drug delivery, biosensors, and biomedical imaging because of their tailored ability in both the movable core and shell. In this study, we formulate a facile controllable route to synthesize a monodisperse magnetic nanorattle with an Fe3O4 superparticle as the core and poly(vinylsilane) (PVS) as the outer shell (Fe3O4@air@PVS) using the polymer-backbone-transition strategy. In the process of synthesis, besides acting as the precursor for the PVS shells of nanorattles, organosilica (o-SiO2) plays the role of template for the middle cavities. The structures of nanorattles can be easily formed via etching treatment of NaOH solution. Through encapsulating sensitive perfluorohexane (PFH) in the cavities of Fe3O4@air@PVS, the biocompatible magnetic nanosystem shows a relatively stable ultrasound signal intensity and a high r2 value of 62.19 mM(-1) s(-1) for magnetic resonance imaging (MRI). After intravenous administration of nanorattles to a healthy rat, dramatically positively enhanced ultrasound imaging and negatively enhanced T2-weighted MRI are detected in the liver. Furthermore, when the Fe3O4@PFH@PVS nanorattles are administered to tumor-bearing mice, a significant passive accumulation in the tumor via an electron paramagnetic resonance effect is detected by both ultrasound imaging and MRI. In vivo experiments indicate that the obtained Fe3O4@PFH@PVS nanorattles can be used as dual-modality contrast agents for simultaneous ultrasound and MRI detection.

A novel strategy to fabricate multifunctional Fe3O4@C@TiO2 yolk-shell structures as magnetically recyclable photocatalysts

Using poly(acrylic acid) (PAA) as a template, a novel Fe3O4@C@TiO2 yolk-shell structure derived from heat treatment on Fe2O3@PAA@TiO2 core-shell structures is constructed, where the interior void volume and shell thickness are readily tuned. In this method, the PAA shell between the original spherical α-Fe2O3 nanoparticle (NP) core and the outer TiO2 shell replaces the common SiO2 template leaving out the tedious treatment procedure of the template. After calcination, the α-Fe2O3 core was reduced to the Fe3O4 core providing the NPs with magnetic properties and the middle carbon coating around the magnetic core could avoid the occurrence of photodissolution. Moreover, the obtained Fe3O4@C@TiO2 yolk-shell nanocomposites (NCs) exhibit fine photocatalytic activity for the photodegradation of organic contaminants in waste water.

Recyclable graphene oxide-supported titanium dioxide photocatalysts with tunable properties

A modular synthesis technique was developed for producing graphene-supported titanium dioxide photocatalysts. The modular synthesis allowed for simple tuning of the ratio of particle loading on the graphene oxide (GO) surface as well as good photocatalytic activity of the composite and quick, efficient magnetic separability. GO flakes were used as a support for titanium dioxide nanoparticles and SiO2 insulated nano-sized magnetite aggregates. Different composition ratios were tested, resulting in a catalyst formulation with photocatalytic activity exceeding that of a commercial photocatalyst by a factor of 1.2 as well as excellent recyclability, with the capability to degrade 3 mg/L methylene blue in aqueous solution over 10 consecutive trials with minimal loss in photocatalytic efficiency. Recovery of the catalyst was achieved by simply exposing the nanocomposite to a magnetic field for ∼1 minute. Furthermore, it was found that the catalyst could be regenerated to its initial efficiency through simple UV treatment to provide additional re-use. To highlight the importance of the nanocomposite to the current water treatment industry, we showed rapid degradation of pharmaceutical compounds caffeine and carbamazepine within 60 min. The nanocomposite shows activity exceeding that of commercial photocatalyst P25 with the added benefit of being fully recoverable, reusable, and easy to produce. Overall, a simple technique for producing and tuning an effective magnetically recyclable nanocomposite was developed which should allow easy scalability and industrial production, a factor critical for the implementation of nano-based water treatment techniques.

Formulation design facilitates magnetic nanoparticle delivery to diseased cells and tissues

Magnetic nanoparticles (MNPs) accumulate at disease sites with the aid of magnetic fields; biodegradable MNPs can be designed to facilitate drug delivery, influence disease diagnostics, facilitate tissue regeneration and permit protein purification. Because of their limited toxicity, MNPs are widely used in theranostics, simultaneously facilitating diagnostics and therapeutics. To realize therapeutic end points, iron oxide nanoparticle cores (5-30 nm) are encapsulated in a biocompatible polymer shell with drug cargos. Although limited, the toxic potential of MNPs parallels magnetite composition, along with shape, size and surface chemistry. Clearance is hastened by the reticuloendothelial system. To surmount translational barriers, the crystal structure, particle surface and magnetic properties of MNPs need to be optimized. With this in mind, we provide a comprehensive evaluation of advancements in MNP synthesis, functionalization and design, with an eye towards bench-to-bedside translation.

An optical sensing strategy leading to in situ monitoring of the degradation of mesoporous magnetic supraparticles in cells

Mesoporous magnetic supraparticles (meso-MSPs) as multifunctional targeted drug carriers have attracted much attention, because of their easy magnetic-field manipulation and in situ sensing functionality. In this paper, a Fe(3+)-selective chemodosimeter fluorescent probe (FP-1) was synthesized and loaded inside of the meso-MSPs (meso-MSPs/probe); the meso-MSPs/probe nanocomposites were then used to monitor the degradation of meso-MSPs in cells. In our experiments, strong fluorescence intensity was observed in HeLa cells, because of their acidic intracellular environment, which can quickly degrade the meso-MSPs and then release Fe(3+) ions in cells that, in turn, activate the fluorescence of FP-1. Meanwhile, a very weak fluorescence signal was detected in HEK 293T cells due to the relative neutral intracellular environment of HEK 293T cells, which prevented the Fe(3+) ion from leaching out of meso-MSPs. Moreover, this degradation-luminescence relationship of the meso-MSPs/probe nanocomposites not only assisted us to understand the degradation status of meso-MSPs in cells, but also allowed us to recognize the peculiarity of different cells with various intracellular environments.

Various bismuth oxyiodide hierarchical architectures: alcohothermal-controlled synthesis, photocatalytic activities, and adsorption capabilities for phosphate in water

Controllable synthesis of morphology and composition of functional material through a similar method is very necessary to understand the related properties. In this study, we report a facile solvothermal route to synthesize a series of bismuth oxyiodide compounds, including BiOI, Bi7O9I3, and Bi4O5I2 hierarchical microspheres, under relatively mild conditions through only adjusting the types of alcohols. It was found that the viscosity of alcohol played key roles in determining the morphologies and compositions of the final products. UV-visible diffuse-reflectance spectra and theoretic calculations indicated that bismuth oxyiodides with different ratios of Bi:O:I clearly possessed different light absorption and energy band structures. As a result, the as-synthesized BiOI, Bi7O9I3, and Bi4O5I2 hierarchical microspheres displayed morphology- and composition-dependent photocatalytic activities for the degradation of rhodamine B (RhB) and colorless phenol under visible-light irradiation. On the basis of experimental results, the difference of photocatalytic activity of these bismuth oxyiodide compounds was discussed. Furthermore, hierarchical bismuth oxyiodide microspheres were also evaluated as adsorbents for removing phosphate from aqueous solution. The results showed that Bi7O9I3 and Bi4O5I2 hierarchical microspheres had good adsorption capabilities for phosphate in water because of their larger surface areas and hierarchical porous structures.