Si NPs Research Articles

Study of the Role of Void and Residual Silicon Dioxide on the Electrochemical Performance of Silicon Nanoparticles Encapsulated by Graphene.

Silicon nanoparticles are used to enhance the anode specific capacity for the lithium-ion cell technology. Due to the mechanical deficiencies of silicon during lithiation and delithiation, one of the many strategies that have been proposed consists of enwrapping the silicon nanoparticles with graphene and creating a void area between them so as to accommodate the large volume changes that occur in the silicon nanoparticle. This work aims to investigate the electrochemical performance and the associated kinetics of the hollow outer shell nanoparticles. To this end, we prepared hollow outer shell silicon nanoparticles (nps) enwrapped with graphene by using thermally grown silicon dioxide as a sacrificial layer, ball milling to enwrap silicon particles with graphene and hydro fluorine (HF) to etch the sacrificial SiO2 layer. In addition, in order to offer a wider vision on the electrochemical behavior of the hollow outer shell Si nps, we also prepared all the possible in-between process stages of nps and corresponding electrodes (i.e., bare Si nps, bare Si nps enwrapped with graphene, Si/SiO2 nps and Si/SiO2 nps enwrapped with graphene). The morphology of all particles revealed the existence of graphene encapsulation, void, and a residual layer of silicon dioxide depending on the process of each nanoparticle. Corresponding electrodes were prepared and studied in half cell configurations by means of galvanostatic cycling, cyclic voltammetry and electrochemical impedance spectroscopy. It was observed that nanoparticles encapsulated with graphene demonstrated high specific capacity but limited cycle life. In contrast, nanoparticles with void and/or SiO2 were able to deliver improved cycle life. It is suggested that the existence of the void and/or residual SiO2 layer limits the formation of rich LiXSi alloys in the core silicon nanoparticle, providing higher mechanical stability during the lithiation and delithiation processes.

Direct photoacoustic measurement of silicon nanoparticle degradation promoted by a polymer coating

Nanomaterials with controllable biodegradation properties respond to the main challenge of cancer nanomedicine to minimise side effects and maximise the delivery efficacy to tumours. These biodegradation properties vary from clear aqueous solutions to protein-abundant biological fluids. A photoacoustic method suitable for in vitro quantification of highly scattering colloids with optical absorption properties is introduced and demonstrated by determination of the degradation rate of laser-synthesized silicon nanoparticles (Si NPs) in turbid serum solutions. In vitro screening of a variety of polymer surface-coatings of Si NPs revealed a stand-alone property of polyallylamine (PAA) to accelerate the Si NP dissolution. PAA-coated Si NP half-life was measured ∼ 100-min in aqueous solutions and slowed down to ∼ 24 h in serum. As-produced PAA-coated Si NPs appeared suitable for blockade of the mononuclear phagocyte system. Pre-treatment with PAA-Si NPs caused 1.4-times reduced uptake of magnetic particles by human THP-1 cells in vitro and a 13-fold increase of the magnetic particle delivery to the B16-F1 xenograft tumours in vivo. The demonstrated photoacoustic method is believed to facilitate design and screening of biodegradable materials suitable for in vivo applications such as controlled drug release.

Plasmonic Si@Au core-satellite nanoparticles prepared by laser-assisted synthesis for photothermal therapy

We describe a laser-assisted methodology for the fabrication of Si@Au core-satellite nanostructures for photothermal therapy applications. The methodology consists in laser ablative synthesis of Si and Au NPs in water/ethanol solutions, followed by a chemical modification of the Si NPs by APTMS and their subsequent decoration by the Au NPs. We show that despite a relatively small size (< 40 nm) the formed core-satellites exhibit a strong plasmonic absorption peak centred around 610 nm and having a large tail over 700 nm overlapping with the first optical window of relative tissue transparency. Being relatively small and exempt of any toxic impurity due to ultraclean laser synthesis, the fabricated nanoparticles promise a major advancement of imaging and phototherapy modalities based on plasmonic properties of nanomatererials.

Temperature oscillations during photoinduced heating of aqueous suspensions of silicon nanoparticles

Temperature oscillations (pulsations) were detected in aqueous suspensions of silicon (Si) nanoparticles NPs under laser irradiation with highly absorbed light. The temperature pulsation frequency was found to depend on the NPs concentration in suspension and laser irradiation power. The observed phenomenon is assumed to be caused by the local overheating of Si NPs close to the boiling point of water, while the average heating of the surrounding liquid was insignificant. The observed phenomenon is discussed in view of potential applications in local photo-induced hyperthermia of cancer.

Expandable crosslinked polymer coatings on silicon nanoparticle anode toward high-rate and long-cycle-life lithium-ion battery

Porous and electrically conductive coating on silicon nanoparticles (Si NPs) anode can mitigate the volume expansion during charging or discharging in Li-ion battery (LIB) while conventional protection coating process resulted in non-uniform polymer shell which show low volumetric or areal capacities. Here, we demonstrated that ultra-thin polyacrylonitrile layer can be formed conformally by emulsion-assisted coating process and cross-linked on Si NPs (Si@x-PAN) producing stable and expandable polymer shell which showed a highly stable long-term cycling ability. Areal and specific capacities of Si@x-PAN were an ∼ 2 mAh/cm2 and a 2000 mAh/g, respectively. Importantly, we found that capacity decay was only 5 % after 100 cycles and>75 % of capacity was retained even after 1000 cycles (0.5C/0.5C) with the help of a uniform Li-ion current around the Si NPs during continuous charging and discharging. To our knowledge, this long-term stability at reasonable loading levels is one of the highest levels of performance in pure Si anode systems.

Application of recycled Si from industrial waste towards Si/rGO composite material for long lifetime lithium-ion battery

The photovoltaic industry discards a large amount of Si resources, facing the environmental problem. The reuse of this Si resource helps reduce the cost of waste disposal and utilizes the Si source as an anode for secondary lithium-ion batteries by simple recycling processes. The recycled Si nanoparticles silicon (Si NPs) with rGO in the sponge-like structure of the composite obtains via a freeze-drier aided by the Triton X-100 (TX 100) surfactant. The surfactant also decomposes to form an amorphous carbon shell on the Si surface directly, leading to the protective layer from the volume expansion. The Si/rGO composite obtained from recycled Si exhibits a high initial capacity of 2300 mAh g−1 at a current density of 100 mA g−1, with a stable capacity retention of 72% over 300 cycles at 200 mA g−1. The proposed simple surfactant-assisted self-assembly synthesis confirms that recycled-Si particles sourced from industrial waste are applicable for the production of rechargeable lithium batteries.

Controlling Void Space in Crumpled Graphene-Encapsulated Silicon Anodes using Sacrificial Polystyrene Nanoparticles.

Silicon anodes have a theoretical capacity of 3590 mAh g-1 (for Li15 Si4 , at room temperature), which is tenfold higher than the graphite anodes used in current Li-ion batteries. This, and silicon's natural abundance, makes it one of the most promising materials for next-generation batteries. Encapsulating silicon nanoparticles (Si NPs) in a crumpled graphene shell by spray drying or spray pyrolysis are promising and scalable methods to produce core-shell structures, which buffer the extreme volume change (>300 vol %) caused by (de)lithiaton of silicon. However, capillary forces cause the graphene-based materials to tightly wrap around Si NP clusters, and there is little control over the void space required to further improve cycle life. Herein, a simple strategy is developed to engineer void-space within the core by incorporating varying amounts of similarly sized polystyrene (PS) nanospheres in the spray drier feed mixture. The PS completely decomposes during thermal reduction of the graphene oxide shell and results in Si cores of varying porosity. The best performance is achieved at a 1 : 1 ratio (PS/Si), leading to high capacities of 1638, 1468, and 1179 mAh g-1 Si+rGO at 0.1, 1, and 4 A g-1 , respectively. Moreover, at 1 A g-1 , the capacity retention is 80.6 % after 200 cycles. At a practical active material loading of 2.4 mg cm-2 , the electrodes achieve an areal capacity of 2.26 mAh cm-2 at 1 A g-1 .

Mussel-pearl-inspired design of Si/C composite for ultrastable lithium storage anodes

Silicon (Si) is the most promising anode material for new generation high-performance Lithium-ion batteries (LIBs), but the colossal volume expansion and poor conductivity limit its applications. In this work, we develop a mussel-pearl-inspired Si-embedded carbon/graphite composite (Si/C composite) via a two-step process of ball-milling and subsequent annealing to overcome these obstacles. With this method, Si nanoparticles (Si NPs) are successfully embedded into dual-carbon structure with efficient protection like pearls in mussel. The Si/C composite as anode material shows an ultrastable reversible capacity of 670 mAh g−1 with a superior Initial Coulombic Efficiency (ICE) of 89.4% and an ultrahigh capacity retention of 85% over 850 cycles. Besides, the prepared materials show superior rate capacity at the current density of 5 C. The superior electrochemical performances can be attributed to the excellent structure stability of mussel-pearl structure during cycling, which provides effective protection for Si NPs and accommodate the volume expansion. These results prove that a rational structure design for Si/C composite can present excellent electrochemical performances through a simple and scalable strategy.

Synthesis of orange-emissive silicon nanoparticles as “off-on” fluorescence probe for sensitive and selective detection of l-methionine and copper

Fluorescent silicon nanoparticles (Si NPs) are of great interest as they are free of heavy ions. However, most of Si NPs exhibit blue or green emission, while orange or red-emitting Si NPs are required for an extensive range of applications. Copper ion (Cu2+) and l-methionine (L-Met) detection is critically valuable point since their abnormal level is an indicator of various diseases. In this work, we illustrate an “off-on” method for sensitively and selectively determination of Cu2+ and L-Met using Si NPs as fluorescent probe. The Si NPs emitting orange fluorescence with the quantum yield of 2.23% were prepared via one and easy step of hydrothermal treatment of 3(2-aminoethylamino) propyl (dimethoxymethylsilane) (AEAPDMMS) and 2–aminophenol as precursors. The fluorescence of Si NPs was quenched in the presence of Cu2+ due to the strong metal-ligand coordination and electrostatic interactions between the large amount of amino and hydroxyl groups on the surface of Si NPs and Cu2+. Surprisingly, the resulted non-fluorescent Si NPs-Cu2+ complex displayed a fluorescence “turn-on” toward L-Met, due to the competitive coordination of Cu2+ between L-Met and Si NPs which leads to the unique “off-on” response to L-Met after the release of free Si NPs. The as-proposed approach is fast, simple, low cost and environmental-friendly. More importantly, it has been applied in the determination of Cu2+ and L-Met in water and urine samples, respectively with satisfactory recoveries. Furthermore, the approach could detect Cu2+ and L-Met with detection limit of 0.012 μM and 0.07 μM, which are lower than the level of Cu2+ in drinking water and of L-Met in human urine sample (maximum ~20 μM and ~5.9 μM, respectively).

Flexible Carbon Nanotubes Confined Yolk-Shelled Silicon-Based Anode with Superior Conductivity for Lithium Storage.

The further deployment of silicon-based anode materials is hindered by their poor rate and cycling abilities due to the inferior electrical conductivity and large volumetric changes. Herein, we report a silicon/carbon nanotube (Si/CNT) composite made of an externally grown flexible carbon nanotube (CNT) network to confine inner multiple Silicon (Si) nanoparticles (Si NPs). The in situ generated outer CNTs networks, not only accommodate the large volume changes of inside Si NPs but also to provide fast electronic/ionic diffusion pathways, resulting in a significantly improved cycling stability and rate performance. This Si/CNT composite demonstrated outstanding cycling performance, with 912.8 mAh g−1 maintained after 100 cycles at 100 mA g−1, and excellent rate ability of 650 mAh g−1 at 1 A g−1 after 1000 cycles. Furthermore, the facial and scalable preparation method created in this work will make this new Si-based anode material promising for practical application in the next generation Li-ion batteries.

Color Toning of Mie Resonant Silicon Nanoparticle Color Inks.

An ink of silicon nanoparticles (Si NPs) having the lowest-order Mie resonance in the visible range can generate noniridescent and nonfading structural colors in a wide area through a painting process. However, the strong wavelength dependence of the radiation pattern and the extinction coefficient make the multiple reflection behavior very complicated, and thus, a reliable tool is necessary to predict the hue, saturation, and brightness of the reflection color. In this work, a Monte Carlo simulation to predict the reflection color of Si NP inks is first developed. The simulation takes into account the scattering and absorption cross-sections, a radiation pattern of an individual NP, and multiple scattering in NP dispersion. The simulation shows that the reflection color of a Si NP ink depends strongly on the concentration because of the wavelength dependence of the multiple scattering behavior. To extend the controllable range of the hue, saturation, and brightness of Si NP inks, a mixture ink with light-absorbing carbon black (CB) NPs is developed. It is experimentally demonstrated that the combination of the Kerker-type back scattering of a Si NP and a broad absorption by a CB NP allows us to control the hue, saturation, and brightness in a wide range and to realize vivid reflection colors under room light.

Silicon nanoparticles-based ratiometric fluorescence platform: Real-time visual sensing to ciprofloxacin and Cu2+

In this work, a silicon nanoparticles (Si NPs)-based ratiometric fluorescence sensing platform was conveniently fabricated by simply mixing fluorescent Si NPs as co-ligands and reference signal with lanthanide metal ion Eu3+ as response signal. The introduction of ciprofloxacin (CIP) remarkably turned on the characteristic fluorescence of Eu3+ at 590 nm and 619 nm through the “antenna effect”. At the same time, the blue emission of Si NPs at 445 nm kept comparatively stable. A good linear relationship between the ratio fluorescence intensity and CIP concentration in the range of 0.211–132.4 μM with a limit of detection (LOD) of 89 nM was obtained. In the presence of Cu2+, the fluorescence emission of Eu3+ was sharply turned off because of the stronger coordination ability of Cu2+ with CIP, which guaranteed the sequential detection of Cu2+. Meanwhile, the distinct fluorescent color change from bright blue to red, then back to blue, enabled naked-eye visual detection of CIP and Cu2+ in the solution phase and on paper-based test strip, and was successfully applied to determine the levels of CIP in complicated food samples with high sensitivity.

Hydrophobic versus Hydrophilic Interfacial Coatings on Silicon Nanoparticles Teach Us How to Design the Solid Electrolyte Interphase in Silicon-Based Li-Ion Battery Anodes

Herein, we evaluate the effect of covalently attached molecular coating hydrophobicity on the surface of the silicon nanoparticle (Si NP) active anode material for Li-ion batteries. The experiments are a means to identify the interfacial properties that help minimize electrochemical side reactions during cycling. Preformed coatings on the Si NP surfaces prior to electrode fabrication mimic the ionically conducting and electronically insulating properties of the solid electrolyte interphase (SEI). Hydrophilic oligomers such as polyethylene oxide (PEO) and other related structures are commonly identified as Li+-conducting components of the SEI. Here, we study the effect of such hydrophilic PEO versus hydrophobic alkyl molecular coatings on Si NP anode electrochemical performance. We also study the effect of the PEO oligomer length and the resulting effective thickness of the interfacial coating on the electrochemical performance. We find that PEO oligomers electrochemically isolate Si NPs when the PEO coating thickness approaches the electron tunneling distance of ∼2.5 nm. Surprisingly, the thickness of the PEO-based coatings has a negligible effect on their ability to minimize electrochemical side reactions as measured by Coulombic efficiency. These results reveal how the interfacial coating on silicon anode materials should differ from an operando-formed SEI layer and discuss design strategies for an ideal interfacial active material coating based on these results.

Recycling of the Diamond-Wire Saw Powder Waste to Prepare Silica Nanoparticles

Large amounts of hazardous diamond-wire saw powder (DWSP) waste were generated in the photovoltaic (PV) industry, which not only wasted the valuable resources but also polluted the environment and harmed the human health. In this study, a low-energy and simplified recycling method of the DWSP to prepare the silica nanoparticles (Si NPs) was proposed. The effect of sodium hydroxide concentration, temperature and dwell time on the leaching efficiency was investigated and optimized by the response surface methodology based on the Box-Behnken design (BBD) experiment. The optimal conditions were that the sodium hydroxide concentration of 1.41 mol/L, temperature of 87.16 °C and dwell time of 1.77 h. Under the optimized conditions, the leaching efficiency reached 99.80%, which was almost equal to the theory value predicted by the BBD model (99.68%). Kinetic analysis indicated that the dissolving process of the DWSP was consistent with the second-order homogeneous reaction model, and the apparent activation energy was 69.54 kJ/mol. Moreover, the final product was quite pure amorphous Si NPs with trace amount of absorbed water and sodium chloride impurity. This method is a feasible way to commercially recycle the DWSP in a low-energy and eco-friendly manner.

Effect of Three Nanoparticles (Se, Si and Cu) on the Bioactive Compounds of Bell Pepper Fruits under Saline Stress.

The bell pepper is a vegetable with high antioxidant content, and its consumption is important because it can reduce the risk of certain diseases in humans. Plants can be affected by different types of stress, whether biotic or abiotic. Among the abiotic factors, there is saline stress that affects the metabolism and physiology of plants, which causes damage, decreasing productivity and quality of fruits. The objective of this work was to evaluate the application of selenium, silicon and copper nanoparticles and saline stress on the bioactive compounds of bell pepper fruits. The bell pepper plants were exposed to saline stress (25 mM NaCl and 50 mM) in the nutrient solution throughout the crop cycle. The nanoparticles were applied drenching solution of these to substrate (Se NPs 10 and 50 mg L−1, Si NPs 200 and 1000 mg L−1, Cu NPs 100 and 500 mg L−1). The results show that saline stress reduces chlorophylls, lycopene, and β-carotene in leaves; but increased the activity of some enzymes (e.g., glutathione peroxidase and phenylalanine ammonia lyase, and glutathione). In fruits, saline stress decreased flavonoids and glutathione. The nanoparticles increased chlorophylls, lycopene and glutathione peroxidase activity in the leaves; and ascorbate peroxidase, glutathione peroxidase, catalase and phenylalanine ammonia lyase activity, and also phenols, flavonoids, glutathione, β-carotene, yellow carotenoids in fruits. The application of nanoparticles to bell pepper plants under saline stress is efficient to increase the content of bioactive compounds in fruits.

Single and bi-excitonic characteristics of ligand-modified silicon nanoparticles as demonstrated via single particle photon statistics and plasmonic effects.

Silicon nanoparticles (Si NPs) are of great interest to researchers due to their fluorescence properties, low toxicity, and the low cost of the Si precursor. Recent studies have shown that Si NPs surface-modified with secondary aryl amine ligands emit light at wavelengths ranging from cyan to yellow and with quantum yields of up to 90%. The predominant emitting state in these species has been assigned to a charge-transfer (CT) transition from the ligand to the Si particle as the emission wavelength is determined by the dipolar properties of the ligand rather than the size of the Si core. This contribution focuses on the single-molecule emission properties of Si NPs functionalized with a 1,2,3,4-tetrahydrocarbazole-4-one ligand (Te-On) which have a peak emission wavelength of 550 nm and a quantum yield of 90%. In single-particle dispersed emission spectra, a weak long-wavelength sideband is seen in addition to the dominant yellow emission derived from the CT state. The photon statistical behavior of single Si NPs in the red emission region is consistent with that of a state having collective or bi-excitonic character. In contrast, the yellow emission exhibits predominantly CT character. Deposition of the sample onto a thin gold film causes the CT emission to be quenched whereas that attributed to a bi-exciton state of the Si core is enhanced. These results provide new insights into the mechanism of single-molecule intensity fluctuation in these surface-modified silicon nanoparticles that will benefit proposed applications in biological labeling and as single-photon sources.

Control of Graphene Heteroatoms in a Microball Si@Graphene Composite Anode for High-Energy-Density Lithium-Ion Full Cells

The use of Si and nitrogen-doped graphene to fabricate composite anodes in lithium-ion batteries (LIBs) is attracting intense attention. However, the reported strategies are limited to achieving a cost-effective, scalable, and facile approach. In particular, many reports on Si/N-graphene (N-Gra) anodes cannot achieve a high first discharge capacity while retaining a high Coulombic efficiency (CE). Herein, we report a Si@N-Gra composite with core–shelled microballs of Si NPs and electrochemically exfoliated graphene by NH₃ as a nitrogen source. We use H₂ and NH₃ to control the O and N content and to optimize the anode performance. It is found that N-Gra in the Si@N-Gra composite anode highly improves the electric conductivity and ion mobility. As a result, the microballs structure (Si@N-ECGB) exhibit the highest initial discharge capacity of up to 2604.5 mAh/g with an 85.2% CE. This excellent performance is attributed to efficient lithiation/delithiation that maintains the stability of the Si@N-ECGB. A full cell of Si@N-ECGB||NMC 811 (Ni/Mn/Co = 8:1:1) is demonstrated, from which a high initial capacity (170 mAh/g) and ∼84% retention after 100 cycles are achieved. This work provides a potential strategy for achieving high capacity and stability in LIBs.

Silicon nanoparticle self-incorporated in hollow nitrogen-doped carbon microspheres for lithium-ion battery anodes

In this study, Silicon nanoparticles (Si NPs) were homogeneously self-incorporated into melamine–formaldehyde resin microspheres using a facile hydrothermal technique, followed by annealing the precursors to form hollow nitrogen-doped carbon microspheres (hNC MSs) containing approximately 10.8 wt.% Si NPs (Si@hNC MSs). Melamine was directly polymerized with formaldehyde, providing N and C sources for Li-ion battery anodes. Electrochemical tests demonstrated that the Si@hNC MS anode delivered a high reversible capacity of 872 mAh g–1 at a current density of 200 mA g–1 after 360 cycles. The hNC MSs largely limited the Si volumetric changes caused by repeated charging and discharging, resulting in the high electrochemical stability of the Si anode. This work demonstrates that melamine–formaldehyde resins can be used directly as C and N sources and can effectively mitigate the Si volumetric expansion. Moreover, we believe that this unique resin, an effective C source, has promising potential for improving the electrochemical performance of other metal or metal-oxide anodes.

Productivity of Some Onion Varieties Under Different Silicates Forms in Relation to Thrips (Thrips tabaci L.) Infection

The two field experimentswere carried out at the Experimental Farm, Faculty of Agriculture, Saba Basha, Alexandria University, Alexandria Governorate, Egypt, during the two winter seasons of 2018/2019 and 2019/2020 to study the effect of foilar application of silicon forms on yield, quality and trips population of some onion varieties. This experiment was laid out in split-plot design in three replications in both seasons. The main plot was four onion varieties named; Giza Red, Giza 20, Hybrid Red (Al-Hamra), and Hybrid Yellow (Alabkar), while the subplots were differentsilicon forms (water = control, nano silicon, silicon in tablets, and silicon in powder form) was in both seasons. The obtained results showed that onion varieties differed in the studied characters, foliar application of the different forms of silicon significantly affected yield, and trips population, as well as the interaction between varieties and Si form, was significant in both seasons. Whereas on the other hand, Giza Red recorded the highest values of the studied parameters followed by Giza 20 as compared with the other varieties, also silicon in form nanoparticles (Si NPs)increased growth, yield quality, and decreased population of thrips in onion in both seasons. The interaction between Si forms and onion varieties was significant on all the studied characters, where planting Giza 20 with foliar application of nanoparticles (Si NPs) form recorded the highest values also reduced the population of thrips in the two cropping seasons under the study conditions.

Modification of PET Ion-Track Membranes by Silica Nanoparticles for Direct Contact Membrane Distillation of Salt Solutions.

The paper describes desalination by membrane distillation (MD) using ion-track membranes. Poly(ethylene terephthalate) (PET) ion-track membranes were hydrophobized by the immobilization of hydrophobic vinyl-silica nanoparticles (Si NPs). Si NPs were synthesized by the sol-gel method, and the addition of the surfactant led to the formation of NPs with average size of 40 nm. The thermal initiator fixed to the surface of membranes allowed attachment of triethoxyvinyl silane Si NPs at the membrane surface. To further increase hydrophobicity, ethoxy groups were fluorinated. The morphology and chemical structure of prepared membranes were characterized by SEM, FTIR, XPS spectroscopy, and a gas permeability test. Hydrophobic properties were evaluated by contact angle (CA) and liquid entry pressure (LEP) measurements. Membranes with CA 125–143° were tested in direct contact membrane distillation (DCMD) of 30 g/L saline solution. Membranes showed water fluxes from 2.2 to 15.4 kg/(m2·h) with salt rejection values of 93–99%.