Formation of hollow silica nanospheres by reverse microemulsion

Greening the pathways: a comprehensive review of sustainable synthesis strategies for silica nanoparticles and their diverse applications

Silica nanoparticles (SiNPs) have emerged as a multipurpose solution with wide-ranging applications in various industries such as medicine, agriculture, construction, cosmetics, and food production. In 1961, Stöber introduced a ground-breaking sol-gel method for synthesizing SiNPs, which carried a new era of exploration both in academia and industry, uncovering numerous possibilities for these simple yet multifaceted particles. Inspite of numerous reported literature with wide applicability, the synthesis of these nanoparticles with the desired size and functionalities poses considerable challenges. Over time, researchers have strived to optimize the synthetic route, particularly by developing greener approaches that minimize environmental impact. By reducing hazardous chemicals, energy consumption, and waste generation, these greener synthesis methods have become an important focus in the field. This review aims to provide a comprehensive analysis of the various synthetic approaches available for different types of SiNPs. Starting from the Stöber' method, we analyze other methods as well to synthesis different types of SiNPs including mesoporous, core-shell and functionalized nanoparticles. With increasing concerns with the chemical methods associated for environmental issues, we aim to assist readers in identifying suitable greener synthesis methods tailored to their specific requirements. By highlighting the advancements in reaction time optimization, waste reduction, and environmentally friendly precursors, we offer insights into the latest techniques that contribute to greener and more sustainable SiNPs synthesis. Additionally, we briefly discuss the diverse applications of SiNPs, demonstrating their relevance and potential impact in fields such as medicine, agriculture, and cosmetics. By emphasizing the greener synthesis methods and economical aspects, this review aims to inspire researchers and industry professionals to adopt environmentally conscious practices while harnessing the immense capabilities of SiNPs.

Nanoparticle-mediated dsRNA delivery for precision insect pest control: a comprehensive review

Nanoparticle-based delivery systems have emerged as powerful tools in the field of pest management, offering precise and effective means of delivering double-stranded RNA (dsRNA), a potent agent for pest control through RNA interference (RNAi). This comprehensive review aims to evaluate and compare various types of nanoparticles for their suitability in dsRNA delivery for pest management applications. The review begins by examining the unique properties and advantages of different nanoparticle materials, including clay, chitosan, liposomes, carbon, gold and silica. Each material's ability to protect dsRNA from degradation and its potential for targeted delivery to pests are assessed. Furthermore, this review delves into the surface modification strategies employed to enhance dsRNA delivery efficiency. Functionalization with oligonucleotides, lipids, polymers, proteins and peptides is discussed in detail, highlighting their role in improving stability, cellular uptake, and specificity of dsRNA delivery.This review also provides valuable guidance on choosing the most suitable nanoparticle-based system for delivering dsRNA effectively and sustainably in pest management. Moreover, it identifies existing knowledge gaps and proposes potential research directions aimed at enhancing pest control strategies through the utilization of nanoparticles and dsRNA.

One-pot, degradable, silica nanocarriers with encapsulated oligonucleotides for mitochondrial specific targeting

Mutations in nuclear and mitochondrial genes are responsible for severe chronic disorders such as mitochondrial myopathies. Gene therapy using antisense oligonucleotides is a promising strategy to treat mitochondrial DNA (mtDNA) diseases by blocking the replication of the mutated mtDNA. However, transport vehicles are needed for intracellular, mitochondria-specific transport of oligonucleotides. Nanoparticle (NP) based vectors such as large pore mesoporous silica nanoparticles (LP) often rely on surface complexation of oligonucleotides exposing them to nucleases and limiting mitochondria targeting and controlled release ability. In this work, stable, fluorescent, hollow silica nanoparticles (HSN) that encapsulate and protect oligonucleotides in the hollow core were synthesized by a facile one-pot procedure. Both rhodamine B isothiocyanate and bis[3-(triethoxysilyl)propyl]tetrasulfide were incorporated in the HSN matrix by co-condensation to enable cell tracing, intracellular-specific degradation and controlled oligonucleotide release. We also synthesized LP as a benchmark to compare the oligonucleotide loading and release efficacy of our HSN. Mitochondria targeting was enabled by NP functionalization with cationic, lipophilic Triphenylphosphine (TPP) and, for the first time a fusogenic liposome based carrier, previously reported under the name MITO-Porter. HSN exhibited high oligonucleotide incorporation ratios and release dependent on intracellular degradation. Further, MITO-Porter capping of our NP enabled delayed, glutathione (GSH) responsive oligonucleotide release and mitochondria targeting at the same efficiency as TPP functionalized NP. Overall, our NP are promising vectors for anti-gene therapy of mtDNA disease as well as many other monogenic disorders worldwide.

Probing nearby molecular vibrations with lanthanide-doped nanocrystals

The photoluminescence (PL) of lanthanide-doped nanocrystals can be quenched by energy transfer to vibrations of molecules located within a few nanometers from the dopants. Such short-range electronic-to-vibrational energy transfer (EVET) is often undesired as it reduces the photoluminescence efficiency. On the other hand, EVET may be exploited to extract information about molecular vibrations in the local environment of the nanocrystals. Here, we investigate the influence of solvent and gas environments on the PL properties of NaYF4:Er3+,Yb3+ upconversion nanocrystals. We relate changes in the PL spectrum and excited-state lifetimes in different solvents and their deuterated analogues to quenching of specific lanthanide levels by EVET to molecular vibrations. Similar but weaker changes are induced when we expose a film of nanocrystals to a gas environment with different amounts of H2O or D2O vapor. Quenching of green- and red-emitting levels of Er3+ can be explained in terms of EVET-mediated quenching that involves molecular vibrations with energies resonant with the gap between the energy levels of the lanthanide. Quenching of the near-infrared-emitting level is more complex and may involve EVET to combination-vibrations or defect-mediated quenching. EVET-mediated quenching holds promise as a mechanism to probe the local chemical environment-both for nanocrystals dispersed in a liquid and for nanocrystals exposed to gaseous molecules that adsorb onto the nanocrystal surface.

An experimental workflow to assess the applicability of microemulsions for conformance improvement in oil-bearing reservoir

A comprehensive workflow approach is necessary to link multiple experimental tasks and identify microemulsion (ME) formulations with 'optimal' stability, displacement behavior and technical feasibility in the petroleum industry. In this paper, a systematic approach is described with the aid of a case study which involves the formulation of an anionic sodium dodecyl sulfate-based microemulsion. The design of such ME systems requires a proper methodology, substantial laboratory work, and functional assessment from research/industrial viewpoints. The surfactant has been screened in terms of its micellization potential, followed by phase behavior analysis and Winsor classification of prepared microemulsions. The desired composition(s) are characterized via several tools to determine droplet size, morphology, oil/water solubilization potentials and salinity scan results. The suitability of the microemulsion system for conformance improvement technology (CIT) is proposed to be assessed via physicochemical evaluation studies encompassing two attributes: rheology and stability. For a favorable 'conforming' drive, the microemulsion must exhibit phase stability, sufficient injectivity, and moderate-to-high viscosity under shear. Technical assessment by the industry and research team must also include factors related to cost, availability of chemicals, environmental degradation, and reservoir considerations. The article demonstrates a comprehensive all-inclusive workflow methodology to design and formulate surfactant-stabilized microemulsions via case study analysis for application in CIT. This represents a sound approach to identifying efficient, cost-effective injection fluid systems and provides a framework to identify useful parameters for ME formulation design and employ the proposed (effective) strategy for conformance control.

Confining the Sol-Gel Reaction at the Water/Oil Interface: Creating Compartmentalized Enzymatic Nano-Organelles for Artificial Cells

Living organisms compartmentalize their catalytic reactions in membranes for increased efficiency and selectivity. To mimic the organelles of eukaryotic cells, we develop a mild approach for in situ encapsulating enzymes in aqueous-core silica nanocapsules. In order to confine the sol-gel reaction at the water/oil interface of miniemulsion, we introduce an aminosilane to the silica precursors, which serves as both catalyst and an amphiphilic anchor that electrostatically assembles with negatively charged hydrolyzed alkoxysilanes at the interface. The semi-permeable shell protects enzymes from proteolytic attack, and allows the transport of reactants and products. The enzyme-carrying nanocapsules, as synthetic nano-organelles, are able to perform cascade reactions when enveloped in a polymer vesicle, mimicking the hierarchically compartmentalized reactions in eukaryotic cells. This in situ encapsulation approach provides a versatile platform for the delivery of biomacromolecules.

An insight into the green synthesis of SiO2 nanostructures as a novel adsorbent for removal of toxic water pollutants

Green synthesis of nanomaterials is a sustainable, biologically safe, reliable, and eco-friendly approach. Green synthesis is beneficial to reduce the devastating effects of the traditional chemical synthesis methods and particularly aims at decreasing the usage of toxic chemicals. This review deals with the green synthesis of silica nanoparticles (SiO₂ NPs) with emphasis on the engineering surface properties for enhanced adsorption capability and their applications as novel nano-adsorbents for water pollutants removal. Green synthesized SiO₂ NPs have shown excellent adsorption properties with higher adsorption capacity of 150-200 mg/g and more than 95% removal for various toxic water pollutants along with reusability for more than 5 cycles. These SiO₂ NPs show fascinating physical and chemical properties i.e. tunable size (5 nm to more than 100 nm), low toxicity, biocompatibility, high porosity, higher specific surface area (500--700 m²/g) making them attractive/suitable for several applications in biomedical, agriculture, catalysis, construction, water treatment, etc. Commonly, highly pure SiO₂ NPs are synthesized from organic chemicals (very expensive and highly toxic in nature) as a precursor that led to high production costs, high energy consumption, and environmental hazards. On the other hand, green synthesis of SiO₂ NPs from natural resources like biomass that includes rice husk, bamboo leaves/stem, sugarcane bagasse, corn cobs, wheat straw, etc. is cost-effective, less toxic, and eco-friendly which has been discussed in detail. Furthermore, the effect of key synthesis parameters (i.e., temperature, time, concentration, pH, etc.) on the morphology, size, purity, and specific surface area of SiO₂ NPs have been summarized. Finally, the applications of SiO₂ NPs as nano-adsorbents for the removal of toxic water pollutants (i.e., heavy metal cations, anions, dyes, etc.) including the adsorption mechanisms along with the future scope, challenges, and suggestions have been discussed.

A practical strategy for fabrication of transparent, robust and environmentally friendly superhydrophobic surfaces for toys and games

Abstract

This work presents a practical strategy for fabrication of transparent, robust and environmentally friendly superhydrophobic surfaces for toys and games by a one-step spray coating method. A type of commercial stringed silica nanoparticles (NPs) is chemically modified by a mixture of two fluorine-free silanes, tetraethyl orthosilicate (TEOS) and dodecyltrimethoxysilane (DDTMS) via a sol–gel process with the aid of ammonia as a basic catalyst and a small amount of water in ethanol, resulting in the formation of an amphiphilic solution, suitable for coating a variety of substrate materials such as glass, ceramics, wood, metal, plastics and paper and so on. Polyarylic acid (PAA) is used as a binder to improve the mechanical robustness of the superhydrophobic coating. Effects of silica NPs concentration, mixing order, TEOS/DDTMS ratio, PAA amount and catalyst on the transparency, uniformity, mechanical robustness and superhydrophobicity of the resultant coatings deposited on the glass slides are investigated. The mechanisms for the superhydrophobicity and water-resistance as well as the effects of catalyst and mixing order are discussed. Furthermore, an example of the superhydrophobic surfaces as toys is presented. This work will pave the way for expanding wide applications of the superhydrophobic surfaces towards toys and games.

Article Highlights

Effect of (3-aminopropyl)triethoxysilane on dissolution of silica nanoparticles synthesized via reverse micro emulsion

Silica nanomaterials have been studied based on their potential applications in a variety of fields, including biomedicine and agriculture. A number of different molecules have been condensed onto silica nanoparticles' surfaces to present the surface chemistry needed for a given application. Among those molecules, (3-aminopropyl)triethoxysilane (APS) is one of the most commonly applied silanes used for nanoparticle surface functionalization to achieve charge reversal as well as to enable cargo loading. However, the colloidal stability of APS-functionalized silica nanoparticles has not been thoroughly studied, which can be problematic when the high reactivity of amine groups is considered. In this study, four different types of silica nanoparticles with varied location of added APS have been prepared via a reverse micro emulsion process, and their colloidal stability and dissolution behavior have been investigated. Systematic characterization has been accomplished using transmission electron microscopy (TEM), silicomolybdic acid (SMA) spectrophotometric assay, nitrogen adsorption-desorption surface area measurement, and aerosol ion mobility-mass spectrometry to track the nanoparticles' physical and chemical changes during dissolution. We find that when APS is on the interior of the silica nanoparticle, it facilitates dissolution, but when APS is condensed both on the interior and exterior, only the exterior siloxane bonds experience catalytic hydrolysis, and the interior dissolution is dramatically suppressed. The observation and analyses that silica nanoparticles show different hydrolysis behaviors dependent on the location of the functional group will be important in future design of silica nanoparticles for specific biomedical and agricultural applications.

In Situ Dielectric Spectroscopy Monitoring of Silica Nanoparticle Synthesis in Cationic Water-in-Oil Microemulsions

In situ monitoring of microemulsion-based nanoparticle synthesis is significant for understanding the particle formation mechanism and for advancing controlled nanoparticle synthesis by this means. In this study, the processes of silica nanoparticle synthesis in a CTAB/n-hexanol/cyclohexane/ammonia microemulsion were monitored via dielectric spectroscopy in situ and in real time, with the influences of the water content and precursor concentration being considered. Two dielectric relaxations in addition to a water-induced one were observed in the frequency range of 1 MHz to 3 GHz, which persist throughout the synthesis processes. It is suggested that the lower-frequency relaxation is ascribed to interfacial polarization and the higher-frequency one is caused by the orientational polarization of the ion pair consisting of a counterion and a surfactant polar group. The latter and water-induced relaxations were found to be barely changed during the synthesis processes, while the former changes obviously with synthesis time. The evolution of the lower-frequency relaxation and direct current conductivity with synthesis time are presented and discussed, on the basis of which the particle formation process is inspected from a dielectric spectroscopic point of view.

Emerging Applications of Silica Nanoparticles as Multifunctional Modifiers for High Performance Polyester Composites

Nano-modification of polyester has become a research hotspot due to the growing demand for high-performance polyester. As a functional carrier, silica nanoparticles show large potential in improving crystalline properties, enhancing strength of polyester, and fabricating fluorescent polyester. Herein, we briefly traced the latest literature on synthesis of silica modifiers and the resultant polyester nanocomposites and presented a review. Firstly, we investigated synthesis approaches of silica nanoparticles for modifying polyester including sol-gel and reverse microemulsion technology, and their surface modification methods such as grafting silane coupling agent or polymer. Then, we summarized processing technics of silica-polyester nanocomposites, like physical blending, sol-gel processes, and in situ polymerization. Finally, we explored the application of silica nanoparticles in improving crystalline, mechanical, and fluorescent properties of composite materials. We hope the work provides a guideline for the readers working in the fields of silica nanoparticles as well as modifying polyester.

A Comprehensive Study of Drug Loading in Hollow Mesoporous Silica Nanoparticles: Impacting Factors and Loading Efficiency

Although hollow mesoporous silica nanoparticles (HMSNs) have been intensively studied as nanocarriers, selecting the right HMSNs for specific drugs still remains challenging due to the enormous diversity in so far reported HMSNs and drugs. To this end, we herein made a comprehensive study on drug loading in HMSNs from the viewpoint of impacting factors and loading efficiency. Specifically, two types of HMSNs with negative and positive zeta potential were delicately constructed, and three categories of drugs were selected as delivery targets: highly hydrophobic and lipophobic (oily), hydrophobic, and hydrophilic. The results indicated that (i) oily drugs could be efficiently loaded into both of the two HMSNs, (ii) HMSNs were not good carriers for hydrophobic drugs, especially for planar drugs, (iii) HMSNs had high loading efficiency towards oppositely charged hydrophilic drugs, i.e., negatively charged HMSNs for cationic molecules and vice versa, (iv) entrapped drugs would alter zeta potential of drug-loaded HMSNs. This work may provide general guidelines about designing high-payload HMSNs by reference to the physicochemical property of drugs.

In Situ Study of the Wet Chemical Etching of SiO2 and Nanoparticle@SiO2 Core-Shell Nanospheres

The recent development of liquid cell (scanning) transmission electron microscopy (LC-(S)TEM) has opened the unique possibility of studying the chemical behavior of nanomaterials down to the nanoscale in a liquid environment. Here, we show that the chemically induced etching of three different types of silica-based silica nanoparticles can be reliably studied at the single particle level using LC-(S)TEM with a negligible effect of the electron beam, and we demonstrate this method by successfully monitoring the formation of silica-based heterogeneous yolk-shell nanostructures. By scrutinizing the influence of electron beam irradiation, we show that the cumulative electron dose on the imaging area plays a crucial role in the observed damage and needs to be considered during experimental design. Monte-Carlo simulations of the electron trajectories during LC-(S)TEM experiments allowed us to relate the cumulative electron dose to the deposited energy on the particles, which was found to significantly alter the silica network under imaging conditions of nanoparticles. We used these optimized LC-(S)TEM imaging conditions to systematically characterize the wet etching of silica and metal(oxide)-silica core-shell nanoparticles with cores of gold and iron oxide, which are representative of many other core-silica-shell systems. The LC-(S)TEM method reliably reproduced the etching patterns of Stöber, water-in-oil reverse microemulsion (WORM), and amino acid-catalyzed silica particles that were reported before in the literature. Furthermore, we directly visualized the formation of yolk-shell structures from the wet etching of Au@Stöber silica and Fe3O4@WORM silica core-shell nanospheres.

Aqueous core and hollow silica nanocapsules for confined enzyme modules

The development of enzyme modules by coupling several enzymes in confinement is of paramount importance to artificial biological reaction systems for efficient enzymatic reactions. Silica nanocapsules are ideal candidates for loading enzymes. Aqueous core silica nanocapsules have relatively been rarely reported due to the crux of difficulty in forming dense silica shells by interfacial sol-gel reactions. Herein we suggest a one-step synthesis of hollow silica nanocapsules with an aqueous core containing enzymes via a template-free and interfacial condensation method for developing enzyme modules with coupled enzymatic reactions. As a proof-of-concept, we developed enzyme modules for three useful purposes by encapsulating a couple of enzymes: (i) development of a miniature glucose sensor, (ii) protection of living cells, and (iii) regeneration of nicotinamide adenine dinucleotides (NADs). By the modulation of enzymes using silica nanocapsules, more efficient coupled reactions, separation of enzymatic reactions from surroundings, and easy handling of several enzymes by using a single module could be achieved. Therefore, our silica nanocapsules for enzyme modules can be promoted as general platforms for developing artificial nanoreactors.

Preparation of Sub-50 nm Colloidal Monodispersed Hollow Siloxane-Based Nanoparticles with Controlled Shell Structures

Hollow siloxane-based nanoparticles (HSNs) have attracted significant attention because of their promising unique properties for various applications. For advanced applications, especially in catalysis, drug delivery systems, and smart coatings, high dispersibility and monodispersity of HSNs with precisely controlled shell structures are important. In this study, we established a simple method for preparing colloidal HSNs with a uniform particle size below 50 nm by the reaction of colloidal silica nanoparticles with bridged organoalkoxysilane [1,2-bis(triethoxysilyl)ethylene: (EtO)₃Si-C₂H₂-Si(OEt)₃, BTEE] in the presence of a cationic surfactant. Upon the formation of organosiloxane shells by hydrolysis and polycondensation of BTEE, the core silica nanoparticles were spontaneously dissolved, and a part of the silicate species was incorporated into the organosiloxane shells. The size of the colloidal silica nanoparticles, the amount of BTEE added, and the pH of the reaction mixture greatly affected the formation of HSNs. Importantly, colloidal HSNs having micropores and mesopores in the shells were successfully prepared using silica nanoparticles (20, 30, and 40 nm in diameter) at pH values of 9 and 11, respectively. These HSNs are potentially important for applications in drug delivery systems and catalysis.

Recent Trends in Morphology-Controlled Synthesis and Application of Mesoporous Silica Nanoparticles

The outstanding journey towards the investigation of mesoporous materials commences with the discovery of high surface area porous silica materials, named MCM-41 (Mobil Composition of Matter-41) according to the inventors' name Mobile scientists in the United States. Based on a self-assembled supramolecular templating mechanism, the synthesis of mesoporous silica has extended to wide varieties of silica categories along with versatile applications of all these types in many fields. These silica families have some extraordinary structural features, like highly tunable nanoscale sized pore diameter, good Brunauer-Emmett-Teller (BET) surface areas, good flexibility to accommodate different organic and inorganic functional groups, metals etc., onto their surface. As a consequence, thousands of scientists and researchers throughout the world have reported numerous silica materials in the form of published articles, communication, reviews, etc. Beside this, attention is also given to the morphology-oriented synthesis of silica nanoparticles and their significant effects on the emerging fields of study like catalysis, energy applications, sensing, environmental, and biomedical research. This review highlights a consolidated overview of those morphology-based mesoporous silica particles, emphasizing their syntheses and potential role in many promising fields of research.

In Situ and Real-Time Monitoring of Nanoparticle Formation in Microemulsion by Means of Dielectric Spectroscopy

Dielectric spectroscopy was employed, for the first time, to monitor the formation process of silica nanoparticles in a nonionic surfactant-based microemulsion in situ and in real time. Two dominant relaxations were observed in the frequency range of 1 MHz-3 GHz during this process. The relaxation at the lower frequency range was confirmed to be mainly ascribed to interfacial polarization, whose relaxation parameters, together with the electrical property of the synthesis system, were used to characterize the evolution of this dynamic formation process. Four evolution stages are distinctively revealed, including an induction stage, a nucleation dominant stage, an early particle growth stage, and a late growth stage. The dynamic features at each evolution stages were discussed in terms of the dielectric characteristics of the system. It is strongly suggested that dielectric spectroscopy is an effective tool for the in situ mechanistic study of nanoparticle formation in microemulsion.

A Nano-Rattle SnO2@carbon Composite Anode Material for High-Energy Li-ion Batteries by Melt Diffusion Impregnation

The huge volume expansion in Sn-based alloy anode materials (up to 360%) leads to a dramatic mechanical stress and breaking of particles, resulting in the loss of conductivity and thereby capacity fading. To overcome this issue, SnO₂@C nano-rattle composites based on <10 nm SnO₂ nanoparticles in and on porous amorphous carbon spheres were synthesized using a silica template and tin melting diffusion method. Such SnO₂@C nano-rattle composite electrodes provided two electrochemical processes: a partially reversible process of the SnO₂ reduction to metallic Sn at 0.8 V vs. Li⁺/Li and a reversible process of alloying/dealloying of Li_xSn_y at 0.5 V vs. Li⁺/Li. Good performance could be achieved by controlling the particle sizes of SnO₂ and carbon, the pore size of carbon, and the distribution of SnO₂ nanoparticles on the carbon shells. Finally, the areal capacity of SnO₂@C prepared by the melt diffusion process was increased due to the higher loading of SnO₂ nanoparticles into the hollow carbon spheres, as compared with Sn impregnation by a reducing agent.

Surfactant-Stabilized Spontaneous 3-(Trimethoxysilyl) Propyl Methacrylate Nanoemulsions

Nanoemulsions are a versatile means to create a variety of consumer products and complex materials. Producing nanoemulsions with a high volume fraction of the dispersed phase is generally limited to mechanically intensive processes, such as high-pressure homogenization, and often results in polydisperse droplet size distributions. Low-energy methods, such as spontaneous emulsification, can produce monodispersed droplets, but the volume fraction of the dispersed phase is usually much lower. Here, we report on the spontaneous emulsification of 3-(trimethoxysilyl) propyl methacrylate (TPM) into an alkaline aqueous phase (pH > 10.0) that contains surfactants (Tween 20, sodium dodecyl sulfate (SDS), or cetyltrimethylammonium bromide (CTAB)). The nanoemulsions are monodisperse with droplet diameters that range between 15 and 500 nm. The small droplet size is due to the presence of surfactants that stabilize the droplets against coalescence. The spontaneous emulsion process can produce emulsions with a dispersed volume fraction of up to 10% in CTAB solutions and up to 30% using Tween 20 and SDS. After the emulsification process, the TPM droplets can be polymerized to produce nanoparticles. Using dynamic light scattering and scanning electron microscopy, we characterize the relationship between the surfactant concentration and the size of the droplets in the nanoemulsions. We find that the droplet diameter is primarily determined by the molar ratio of oil to surfactant. We also find that the pH in the aqueous phase also modulates the droplet diameter when using an ionic surfactant. This work expands the spontaneous emulsification of TPM in the absence of stabilizing particles to the nanoscale while producing one of the highest volume fractions of nanoemulsion droplets obtained via a low-energy mechanism.

Nano/Microstructured Silicon-Carbon Hybrid Composite Particles Fabricated with Corn Starch Biowaste as Anode Materials for Li-Ion Batteries

Silicon has a great potential as an alternative to graphite which is currently used commercially as an anode material in lithium-ion batteries (LIBs) because of its exceptional capacity and reasonable working potential. Herein, a low-cost and scalable approach is proposed for the production of high-performance silicon-carbon (Si-C) hybrid composite anodes for high-energy LIBs. The Si-C composite material is synthesized using a scalable microemulsion method by selecting silicon nanoparticles, using low-cost corn starch as a biomass precursor and finally conducting heat treatment under C₃H₆ gas. This produces a unique nano/microstructured Si-C hybrid composite comprised of silicon nanoparticles embedded in micron-sized amorphous carbon balls derived from corn starch that is capsuled by thin graphitic carbon layer. Such a dual carbon matrix tightly surrounds the silicon nanoparticles that provides high electronic conductivity and significantly decreases the absolute stress/strain of the material during multiple lithiation-delithiation processes. The Si-C hybrid composite anode demonstrates a high capacity of 1800 mAh g^-1, outstanding cycling stability with capacity retention of 80% over 500 cycles, and fast charge-discharge capability of 12 min. Moreover, the Si-C composite anode exhibits good acceptability in practical LIBs assembled with commercial Li[Ni_0.6Co_0.2Mn_0.2]O₂ and Li[Ni_0.80Co_0.15Al_0.05]O₂ cathodes.

Recent experimental explorations of non-classical nucleation

This work provides a clearer picture for non-classical nucleation by revealing the presence of various intermediates using advanced characterization techniques.

Synthesis of microporous silica nanoparticles to study water phase transitions by vibrational spectroscopy

Silica can take many forms, and its interaction with water can change dramatically at the interface. Silica based systems offer a rich tapestry to probe the confinement of water as size and volume can be controlled by various templating strategies and synthetic procedures. To this end, microporous silica nanoparticles have been developed by a reverse microemulsion method utilizing zinc nanoclusters encapsulated in hydroxyl-terminated polyamidoamine (PAMAM-OH) dendrimers as a soft template. These nanoparticles were made tunable within the outer diameter range of 20-50 nm with a core mesopore of 2-15 nm. Synthesized nanoparticles were used to study the effects of surface area and microporous volumes on the vibrational spectroscopy of water. These spectra reveal contributions from bulk interfacial/interparticle water, ice-like surface water, liquid-like water, and hydrated silica surfaces suggesting that microporous silica nanoparticles allow a way to probe silica water interactions at the molecular scale.

Preparation of Colloidally Stable Positively Charged Hollow Silica Nanoparticles: Effect of Minimizing Hydrolysis on ζ Potentials

Silica nanoparticles have received great attention as versatile nanomaterials in many fields such as drug delivery, sensing, and imaging due to their physical and chemical flexibility. Specifically, the silanol groups at the surface of silica nanoparticles have enabled various surface modifications and functionalization to tailor the nanoparticles for each application. Chemical tailoring to switch from negative to positive surface charge has been one important strategy to enhance cell internalization and biodistribution of the nanoparticles. However, efficient surface charge modification that is sustained upon dispersion is difficult to achieve and has not been well characterized though it can be a critical requirement for successful nanoparticle performance. In this study, solid spherical silica nanoparticles and hollow spherical silica nanoparticles around 45 nm in diameter were synthesized, both possessing tunable positive ζ potentials in aqueous colloidal suspension, to investigate the relationship between time-dependent ζ potential changes and their morphologies. A set of three different particles showing varied ζ potentials of approximately 5, 20, and >30 mV in both morphologies were prepared, and their colloidal surface electric potential fluctuations were measured. These studies reveal that the hollow morphologies are much more effectively able to maintain positive ζ potentials for 7 days of aqueous incubation, whereas the magnitude of the ζ potential of the solid silica spheres decreases uncontrollably, largely due to hydrolysis of the interior siloxane bonds, resulting in adsorption of the released silicic acid onto the nanoparticle surface.

Reversibly responsive microemulsion triggered by redox reactions

HYPOTHESIS

Stimuli-responsive surfactants (also known as switchable surfactants) can undergo reversible conversions between active and inactive forms under particular stimuli, affecting surface and interfacial activity, aggregation structure, emulsification and solubilisation. Selenium-containing surfactants are of reversibly redox-responsive. Hence, microemulsions (MEs) stabilized by selenium-containing surfactants should reversibly respond to redox reactions.

EXPERIMENTS

The formation of MEs, consisting of sodium dodecylselanylpropyl sulfate (reduced form, SDSePS-Re) or its oxidized form (SDSePS-Ox), n-butanol, n-heptane, and water, was verified based on a pseudo-ternary phase diagram. Changes in molecular structure between SDSePS-Re and SDSePS-Ox were verified by nuclear magnetic resonance spectrometry and electrospray ionization mass spectrometry. The transition between SDSePS-Re- and SDSePS-Ox -based MEs was systematically characterized through electrical conductivity measurements, cryo-transmission electron microscopy and dynamic light-scattering.

FINDINGS

Both SDSePS-Re and SDSePS-Ox could stabilize the mixture of n-butanol-n-heptane-water to form MEs. A reversible transition between an SDSePS-Re-based ME and the corresponding SDSePS-Ox-based ME was achieved, which was realized by the oxidation of SDSePS-Re with H₂O₂ and then reduction with N₂H₄. Compared with SDSePS-Re, SDSePS-Ox has a lower surface activity, resulting in a difference in solubilization capacity of the oil between SDSePS-Re- and SDSePS-Ox -based MEs. After oxidation with H₂O₂, phase separation could be observed in some SDSePS-Re-based MEs; however, the SDSePS-Re-based MEs could be recovered after reduction of SDSePS-Ox-based MEs with N₂H₄.

Understanding the role of co-surfactants in microemulsions on the growth of copper oxalate using SAXS

SAXS study for evaluating the effect of variation of co-surfactants on the shape of reverse micelles and growth of copper oxalate nanostructures.

Nanostructured silver decorated hollow silica and their application in the treatment of microbial contaminated water at room temperature

Effect of silver decoration on hollow silica and its antimicrobial properties.

All-Silica Submicrometer Colloidosomes for Cargo Protection and Tunable Release

Colloidosomes have received considerable attention for the controlled delivery of active ingredients in medicine, agrochemicals, and cosmetics. However, most reported colloidosomes are highly permeable and size is larger than 1 μm. All silica colloidosomes have now been prepared with adjustable size, compact shell and low permeability. Our approach is based on the formation of inverse water-in-oil (w/o) emulsions stabilized solely by hydrophobic silica nanoparticles and subsequent locking of the particle at the oil-water interface by a simple sol-gel reaction of silica precursor at room temperature. The colloidosomes obtained display a robust and closed shell, ensuring a long-term retention of small hydrophilic molecules such as Methylene Blue. Remarkably, unlike all other reported silica colloidosomes, a timely and stepwise release of the encapsulated cargo can be triggered by adding ethanol or surfactant without destroying the capsule shell.

From a silane monomer to anisotropic buckled silica nanospheres: a polymer-mediated, solvent-free and one-pot synthesis

The morphology of particles, along with other particle attributes, has been shown to affect the biological fate of particles administered into the body. Particles with collapsed surfaces or shells (dimpled, buckled or crumpled) can have different appearances, under the microscope, that resemble many things encountered in our daily life, such as apples/cherries, doughnuts, and bowls. Recent studies have demonstrated that they are not just particles with interesting geometries, but they can also be used as functional blocks for assembled complex materials. Since previous research focus has been on micron-sized particles and organic solvents were often used, it is of particular interest to synthesize the nanosized counterpart with a buckled surface using a purely aqueous method. Herein we report a facile method for rapid synthesis of buckled silica nanoparticles (SiNPs) based on S-nitrosothiol chemistry in a solvent-free reaction. 3-Mercaptopropyl trimethoxysilane (MPTMS) was used as a single silane source in a one-pot aqueous solution containing sodium nitrite and polyvinyl alcohol (PVA). Upon the addition of HCl, S-nitrosation and condensation of MPTMS occur simultaneously and the reaction system undergoes a rapid transition from a clear solution to a solution containing nanoparticles with a lag time controlled mainly by the amount of HCl added. The experimental parameters were systematically studied to determine the optimal concentration of each component. For a typical reaction, sub-100 nm nanoparticles can be produced in less than 1 h, and the best result can be obtained within 2 to 4 h. Remarkably, the nanoparticle exhibits buckled surface morphologies under TEM and SEM. The average size is about 60 nm in diameter. Moreover, the solid-state Si-NMR data show that T² and T³ silicon species are rapidly evolved with slight dynamic changes over the reaction time. Further, PVA is shown to control the surface buckling as well as to stabilize the formed particles. The as-prepared SiNPs can be used as a nitric oxide (NO) carrier with the potential to release NO in an apparent zero-order manner. In conclusion, the study demonstrates the feasibility of employing an aqueous route for efficiently preparing SiNPs with multifarious surface cavities based on S-nitrosothiol chemistry.

Confined Nucleation and Growth of PdO Nanocrystals in a Seed-Free Solution inside Hollow Nanoreactor

This paper reports a novel and adaptable hollow nanoreactor system containing a solution of cucurbituril (CB) inside a silica nanoparticle (CB@h-SiO₂) which enables the nucleation and formation of nanocrystals (NCs) to be confined at the seed-free interior solution inside the cavity. The above nanospace confinement strategy restricted the volume of medium available for NC formation to the solution inside the cavity to a few tens of nanometers in size and allowed homogeneous NC nucleation to be examined. Harboring of CB@h-SiO₂ in a Pd²⁺ complex solution confined the nucleation and formation of PdO NCs to the well-isolated nanosized cavity protected by the silica nanoshell, allowing the convoluted formation of clustered PdO NCs to be thoroughly examined. The corresponding temporal investigation indicated that PdO NC clusters evolved via a distinct pathway combining dendritic growth on early nucleated seed NCs and attachment of small intermediate clusters. In addition, the explored strategy was used to fabricate a recyclable nanocatalyst system for selective catalytic oxidation of cinammyl alcohols, featuring a cavity-included Fe₃O₄/PdO nanocomposite.

Continuous, size and shape-control synthesis of hollow silica nanoparticles enabled by a microreactor-assisted rapid mixing process

Hollow silica nanoparticles (HSNPs) were synthesized using a microreactor-assisted system with a hydrodynamic focusing micromixer. Due to the fast mixing of each precursor in the system, the poly(acrylic acid) (PAA) thermodynamic-locked (TML) conformations were protected from their random aggregations by the immediately initiated growth of silica shells. When altering the mixing time through varying flow rates and flow rate ratios, the different degrees of the aggregation of PAA TML conformations were observed. The globular and necklace-like TML conformations were successfully captured by modifying the PAA concentration at the optimized mixing condition. Uniform HSNPs with an average diameter ∼30 nm were produced from this system. COMSOL numerical models was established to investigate the flow and concentration profiles, and their effects on the formation of PAA templates. Finally, the quality and utility of these uniform HSNPs were demonstrated by the fabrication of antireflective thin films on monocrystalline photovoltaic cells which showed a 3.8% increase in power conversion efficiency.

PtNi/NiO Clusters Coated by Hollow Sillica: Novel Design for Highly Efficient Hydrogen Production from Ammonia-Borane

Ammonia-borane (NH₃·BH₃; AB) has been considered as an excellent chemical material for hydrogen storage. However, developing highly efficient catalysts for continuous hydrogen generation from AB is still a challenge for future fuel cell applications. The combination of Pt with Ni is an effective strategy to achieve active bimetallic nanocatalyst, and the particle size has proved to play a crucial role in determining its final activity. However, the synthesis of PtNi bimetallic catalyst in the size of highly dispersed clusters has always been a challenge. In this report, PtNi/NiO clusters coated by small-sized hollow silica (R-PtNi/NiO@SiO₂) were designed for efficient hydrogen generation from the hydrolysis of ammonia-borane. The newly designed catalysis system showed extremely high activity with the initial turnover frequency value reaching 1240.3 mol of H₂·mol^-1 of Pt·min^-1, which makes it one the most active Pt-based catalysts for this reaction. Detailed characterization by means of scanning transmission electron microscopy, X-ray photoelectron spectroscopy, energy-dispersive X-ray spectroscopy element mapping, etc. revealed that the excellent performance of R-PtNi/NiO@SiO₂ is derived from the highly dispersed PtNi/NiO clusters and the reduction of extra Pt⁴⁺ on the surface of PtNi/NiO clusters to Pt⁰ at relatively low temperature.