Porous Si Nanoparticles Research Articles

Controlled synthesis and characterization of porous silicon nanoparticles for dynamic nuclear polarization.

Si nanoparticles (NPs) have been actively developed as a hyperpolarized magnetic resonance imaging (MRI) contrast agent with an imaging window close to one hour. However, the progress in the development of NPs has been hampered by the incomplete understanding of their structural properties that correspond to efficient hyperpolarization buildup and long polarization decays. In this work we study dynamic nuclear polarization (DNP) of single crystal porous Si (PSi) NPs with defined doping densities ranging from nominally undoped to highly doped with boron or phosphorus. To develop such PSi NPs we perform low-load metal-assisted catalytic etching for electronic grade Si powder followed by thermal oxidation to form the dangling bonds in the Si/SiO2 interface, the Pb centers. Pb centers are the endogenous source of the unpaired electron spins necessary for DNP. The controlled fabrication and oxidation procedures allow us to thoroughly investigate the impact of the magnetic field, temperature and doping on the DNP process. We argue that the buildup and decay rate constants are independent of size of Si crystals between approximately 10 and 60 nm. Instead, the rates are limited by the polarization transfer across the nuclear spin diffusion barrier determined by the large hyperfine shift of the central 29Si nuclei of the Pb centers. The size-independent rates are then weakly affected by the doping degree for low and moderately doped Si although slight doping is required to achieve the highest polarization. Thus, we find the room temperature relaxation of low boron doped PSi NPs reaching 75 ± 3 minutes and nuclear polarization levels exceeding ∼6% when polarized at 6.7 T and 1.4 K. Our study thus establishes solid grounds for further development of Si NPs as hyperpolarized contrast agents.

Molecular Dynamics Modeling of Pulsed Laser Fragmentation of Solid and Porous Si Nanoparticles in Liquid Media.

The production of non-toxic and homogeneous colloidal solutions of nanoparticles (NPs) for biomedical applications is of extreme importance nowadays. Among the various methods for generation of NPs, pulsed laser ablation in liquids (PLAL) has proven itself as a powerful and efficient tool in biomedical fields, allowing chemically pure silicon nanoparticles to be obtained. For example, laser-synthesized silicon nanoparticles (Si NPs) are widely used as contrast agents for bio visualization, as effective sensitizers of radiofrequency hyperthermia for cancer theranostics, in photodynamic therapy, as carriers of therapeutic radionuclides in nuclear nanomedicine, etc. Due to a number of complex and interrelated processes involved in the laser ablation phenomenon, however, the final characteristics of the resulting particles are difficult to control, and the obtained colloidal solutions frequently have broad and multimodal size distribution. Therefore, the subsequent fragmentation of the obtained NPs in the colloidal solutions due to pulsed laser irradiation can be utilized. The resulting NPs' characteristics, however, depend on the parameters of laser irradiation as well as on the irradiated material and surrounding media properties. Thus, reliable knowledge of the mechanism of NP fragmentation is necessary for generation of a colloidal solution with NPs of predesigned properties. To investigate the mechanism of a laser-assisted NP fragmentation process, in this work, we perform a large-scale molecular dynamics (MD) modeling of FS laser interaction with colloidal solution of Si NPs. The obtained NPs are then characterized by their shape and morphological properties. The corresponding conclusion about the relative input of the properties of different laser-induced processes and materials to the mechanism of NP generation is drawn.

Construction of porous Si/Ag@C anode for lithium-ion battery by recycling volatile deposition waste derived from refining silicon

Owing to the rapid advancement of the photovoltaic industry, a lot of photovoltaic (PV) silicon waste will be generated. Thus, the recycling and reuse of waste silicon have become particularly important, both for environmental remediation and economic benefits. In this work, a special structure of porous Si nanoparticles embedded nano-Ag and coated carbon layer (P-SiNPs/Ag@C) was produced by silver-assisted chemical etching (Ag-ACE) the deposited silicon waste. The special porous structure and carbon layer coating can effectively address the volume expansion issues during charge/discharge. The intercalated Ag nanoparticles greatly reduced the transfer impedance and enhanced the electrical conductivity of the anode material. As a result, the novel-designed P-SiNPs/Ag@C anode can maintain a prominent reversible capacity (1521 mAh·g−1 at 0.2 A g−1 after 50 cycles) and outstanding rate performance (1099 mAh·g−1 at 2 A g−1). When the current density at 1 A g−1, the specific capacity still maintains at 706 mAh·g−1 over 300 cycles. The superiority of the prepared P-SiNPs/Ag@C structures was further confirmed by Comsol Multiphysics software. Impressively, the synthesis route provides a novel avenue for value-added utilization of residual silicon waste resources from EB refining silicon and the preparation of high-performance lithium battery silicon-based anode.

Scalable and low-cost synthesis of porous silicon nanoparticles as high-performance lithium-ion battery anode

We design porous silicon (Si) nanoparticles with both nanosize and porous structures via a simple alkaline etching method. The etching at grain boundaries and the anisotropic etching of the different crystal planes of the polycrystalline silicon are responsible for the homogeneous porous nanostructures. After the porous Si nanoparticles are coated with carbon layer, the composite delivering a discharge capacity of 1645.6 mAh g−1 at 0.4 A g−1 after 200 cycles, an outstanding discharge capacity of 861.5 mA g−1 at 4 A g−1 after 800 cycles with a high capacity retention of more than 65%, and a rate capacity of 904.7 mA g−1 at 12.8 A g−1. The porous nanoparticles show both the nanosize (∼100 nm) and the porous structure, which can furthest accommodate the large volume changes of the Si anode, resulting in the good electrochemical performance. The design of porous Si nanoparticles with a high yield of 93% may give a scalable, low-cost, and green approach for commercial silicon-based anodes of lithium-ion batteries.

Synthesis of porous silicon based nanoparticles for applications in surface enhanced Raman spectroscopy

In this work porous Si (PSi) nanoparticles (NPs) were prepared by magnesiothermic reduction of the synthesized SiO2 spheres, and Ag NPs were deposited on the PSi with formaldehyde or HF. In addition, silver NPs were deposited on the porous Si obtained by milling and etching the Si wafer. Silver NPs on SiO2 spheres and particles with Ag core and mesoporous SiO2 shell were also synthesized. SEM analysis showed the Ag NPs size distributions between 30.1 and 64.3 nm. The synthesized samples were quite stable in aqueous media and had zeta potential between −11.5 and −44.3 mV. The samples exhibited reversible physisorption isotherms of type II except for the sample with Ag core and SiO2 (Ag–S) coating, which exhibited a type IVa isotherm accompanied by the hysteresis characteristic of mesoporous adsorbents. The BET surface areas of the samples ranged from 9 to 56 m2g-1, with the mesoporous Ag–S sample having the largest surface area of 378 m2g-1. The surface enhanced Raman spectroscopy (SERS) performance of the synthesized samples was studied by analysing the detection limit of 4-mercaptophenylboronic acid (4-MPBA) as a probe molecule at 532 nm laser excitation. The lowest limit of detection of 1 × 10−5 mol dm−3 was obtained with the sample in which silver NPs were deposited on silica spheres (S–Ag).

The robust carbon shell to improve stability of porous Si anodes for high-performance lithium-ion batteries

Silicon (Si) anode with high theoretical capacity can meet the requirements of high energy density. However, Si anodes suffer from considerable volume expansion and low electron conductivity, resulting in low rate performance and poor cycle stability for Lithium-ion batteries (LIBs). Herein, the carbon coating porous Si (P-Si@C) materials are obtained via decomposition of C2H2 deposition on the surface of porous interconnected Si nanoparticles. Due to the porous structure mitigating Si expansion and the highly robust carbon shell enhancing overall electrical conductivity to improve Li+ diffusivity and ultra-high electron conductivity in Si electrodes. Therefore, the P-Si@C electrodes deliver a high initial Coulombic efficiency (defined as ICE = 83.2%) and long life (high discharge capacity of 1424 mA h/g) at 4 A/g after 600 cycles. As a result, the assembled P-Si@C // LiFePO4 full cell shows a high discharge capacity of 85 mA h/g at 1 C after 200 cycles, corresponding to high retention 88.5%.

Synthesis of porous Si nanoparticles for high performances anode material in lithium-ion batteries

As one of the most promising candidates for anode materials, Si-based electrodes can offer specific capacity an order of magnitude beyond that of conventional graphite. However, Si usually suffers from dramatic volume changes during cycling cause pulverization and capacity fade. The key to improving cycle life is to synthesize Si-based materials with suitable architectures and a rational design. Here, we developed an economical and efficient method to obtain porous Si nanoparticles from coal ash. The Si nanoparticles with several nanometers can significantly shorten ion/electron transportation paths and further avoid the cracking and pulverization induced by large volume changes, and the porous structure makes the penetration of electrolyte easier. After carbonization, the obtained porous Si nanoparticles@C exhibits excellent electrochemical performances, and the special capacity can stable at 750 mAh g−1 at 2.0 A g−1 after 200 cycles. When current density up to 6.0 A g−1, the reversible capacity is 565 mAh g−1. We believe this method will make it possible to facilitate the large-scale and low-cost production of porous Si nanoparticles, and contribute to the development of high-performance Si-based anode materials.

Catalytic parameters and thermal stability of chondroitinase ABCI on red porous silicon nanoparticles

The bacterial enzyme chondroitinase ABC, which digests extracellular chondroitin sulfate proteoglycans, has been shown to enhance axonal regeneration. However, the utilization of this enzyme as therapeutics is notably restricted due to its thermal instability. Therefore, red luminescent porous silicon that hold promise for potential applications in biological/medical imaging was used as a carrying matrix for chondroitinase with the aim of enhancing its stability. Porous Si nanoparticles were prepared by electrochemical etching of silicon wafers in ethanolic HF solution. The size of nanoparticles (210 nm) and the mean pore diameter (8 −20 nm) were determined using dynamic light scattering and scanning electron microscopy. Purified chondroitinase was then incorporated into the silicon pores. Results revealed similar Km and lower Vmax value for the immobilized enzyme when compared with the free enzyme. The immobilized chondroitinase exhibited about a 4 fold increase in stability at 37 °C after 50 min. It is likely possible that, the enzyme was protected inside the pores resulted in higher stability. Moreover, porous silicon was seen to be capable of holding the chondroitinase for repeated cyclic tests for three times. The cell viability assay exhibited no significant cytotoxicity for Psi-chondroitinase up to 24 h.

Coal-based kaolin derived porous silicon nanoparticles as anode materials for Li-ion batteries

Abstract Silicon is an attractive material for the next generation anode material of lithium ion batteries (LIBs), because of the advantages of high energy density, high safety and abundance in earth crust. However, it's the capacity attenuation caused by the volume expansion in lithiation, greatly limited its commercial application. Herein, the porous Si nanoparticles are prepared using abundant coal-based kaolin as raw materials, through ball grinding, calcination, selective leaching and magnesium thermal reduction processes. The porous silicon nanoparticles exhibit excellent electrochemical properties without any further modification, due to the unique porous nanostructures which buffer the volume expansion. The initial CE reaches up to 80.0%. After 100 cycle, the material still remains a discharge capacity of 546 mAh g−1 at 100 mA g−1 and a Coulombic efficiency (CE) of 98.8%. The porous Si nanoparticles are fabricated using abundant raw materials and via a facile procedure that is ready for scale-up to meet the large-scale energy storage application. At the same time, the work provides a value-added solution of coal-based kaolin.

Phosphoric acid induced homogeneous crosslinked phosphorus doped porous Si nanoparticles with superior lithium storage performance

The high volume expansion and low electrical conductivity issues severely limit practical application of Si-based materials for Li ion batteries (LIBs). Here we prepare the homogeneous crosslinked phosphorus (P) doped porous Si nanoparticles (P doped pSi) via magnesiothermic reduction of P contained nanosize SiO2 (P-SiO2). Phosphoric acid (H3PO4) acts as a bifunctional additive to reduce particle size of SiO2 and achieve P doping of porous Si. The employment of this modified nanosize SiO2 as precursor effectively alleviates the agglomeration of Si grains. Besides, the P doping characteristic is quite effective to promote the charge transfer performance of Si anode. Finally, P doped pSi anode displays superior cycle capacity and rate capability in half cells with 1761 mAh g−1 at 0.5 A g−1 after 80 cycles and 700 mAh g−1 at 5 A g−1 even after 400 cycles. Furthermore, the electrochemical performance of P doped pSi//LiFePO4 full cell is also evaluated. All the results indicate that P doped pSi is an excellent competitor to replace traditional graphite anode for LIBs.

Nanoparticles synthesis by Agaricus soil basidiomycetes

We examined the effect of various concentrations of HAuCl4, AgNO3, Na2SeO3, Na2SiO3, and GeO2 on mycelial growth of the soil basidiomycetes Agaricus bisporus and A.arvensis in submerged and solid media. Fungal mycelial extracts and cell-free culture filtrates were able to reduce ions of Au, Ag, Se, Si, and Ge compounds, forming Au0, Ag0, Se0, Si0/SiO2 and Ge0/GeO2 nanoparticles. The physical characteristics of the mycogenic nanoparticles differed depending on the species of Agaricus and the type of extract. Au nanospheres obtained with cell-free culture filtrates were of 2-5nm diameter in A.bisporus and of 2-10nm in A.arvensis. Nanoparticles produced by extracts of mycelia were several times larger and highly heterogenous. Ag nanoparticles produced by cell-free culture filtrates were spherical or irregular-shaped and agglomerated, whereas with extracts of mycelia, small homogenous nanospheres of 1-10nm were formed. Se nanospheres obtained with cell-free culture filtrates were of 100-250nm diameter in A.bisporus and of 150-550nm diameter in A.arvensis. The particles synthesized with extracts of mycelia were of 40-140nm in A.bisporus and of 100-250nm in A.arvensis. Incubation of Na2SiO3 with cell-free culture filtrates resulted in porous Si nanoparticles of 30-65nm in A.bisporus and of 50-200nm in A.arvensis. Ge nanoparticles synthesized by both Agaricus species were mostly spheres of 50-250nm diameter.

Highly porous carbon-coated silicon nanoparticles with canyon-like surfaces as a high-performance anode material for Li-ion batteries

Highly porous carbon-coated Si nanoparticles with canyon-like surfaces exhibit a stable cycle retention of 59.1% after 200 cycles because of sufficient free volume for expansion upon lithiation from their unique canyon-like porous surfaces and cavities formed upon MgO etching.

Facile Synthesis of 3D Anode Assembly with Si Nanoparticles Sealed in Highly Pure Few Layer Graphene Deposited on Porous Current Collector for Long Life Li‐Ion Battery

With its exceptional theoretical charge capacity, silicon holds great promise as an anode material for realization of high energy density Li‐ion batteries. However, extensive volume expansion and poor cycle stability of silicon compromise its actual use. In an effort to tame volume expansion and structural disintegration during cycling, an innovative 3D electrode assembly is fabricated involving continuous layer of graphene coated on porous current collector and Si nanoparticles sealed in as an active material. Graphene deposition and pore formation in metal current collector is achieved in a unique single step synthesis. All the active components like current collector, reacting material, and conducting material are manipulated in a way to produce synergistic architecture in a chemical vapor deposition process. Highly pure graphene deposited in this process enables efficient electron transfer from allover of the surface of silicon nanoparticles and prevents continuous solid electrolyte interphase layer formation. This binder free anode assembly shows extremely stable lithium storage performance for over 1000 cycles with 88% of initial capacity retention and 100% Coulombic efficiency.

CO2 to methanol conversion using hydride terminated porous silicon nanoparticles.

Porous silicon nanoparticles (Si-NPs) prepared via magnesiothermic reduction were used to convert carbon dioxide (CO2) into methanol. The hydride surface of the silicon nanoparticles acted as a CO2 reducing reagent without any catalyst at temperatures above 100 °C. The Si nanoparticles were reused up to four times without significant loss in methanol yields. The reduction process was monitored using in situ FT-IR and the materials were characterized using SEM, TEM, NMR, XPS, and powder XRD techniques. The influence of reaction temperature, pressure, and Si-NP concentration on CO2 reduction were also investigated. Finally, Si particles produced directly from sand were used to convert CO2 to methanol.

Porous Silicon Nanoparticles Prepared By an Alkaline Process As an Anode for Use in Lithium Ion Batteries

INTRODUCTION In future, lithium ion batteries (LIBs) for use in electric cars and other applications will be required to provide greater energy densities. At present, silicon (Si) is a candidate anode material for improved, commercially viable batteries, due to its high theoretical capacity (4200 mAh/g) compared to graphite (372 mAh/g). However, the use of Si-based anodes is still restricted because of two problems; the low electrical conductivity of Si, and the significant volume change during lithiation and delithiation. There has been much research devoted to mitigating the deterioration of Si during charging and discharging and to increasing the conductivity of various anode active materials. Recently, several approaches to the synthesis of porous Si-based anode materials that exhibit good cycling properties have been developed. Some of these techniques are based on wet-chemical etching using hydrofluoric acid (HF) and silver nitrate (AgNO3). Ag-deposited Si nanoparticles are initially fabricated using HF and AgNO3. Subsequently, these particles are immersed in a solution containing HF and hydrogen peroxide (H2O2), producing porous Si nanoparticles. However, since HF is quite hazardous, the fabrication of Ag-deposited Si particles without HF would be an improvement.1,2,3) Herein, we describe the preparation of porous Si nanoparticles intended for use as LIB anode materials via both an alkaline method and an alkaline and HF hybrid method. EXPERIMENTAL A planetary ball mill was used to produce Si nanoparticles. These were ultrasonically dispersed for 30 min in an immersion plating bath containing 2 g/L Si, 0.005 M AgNO3 and 0.010 M EDTA-2Na, adjusted to a pH of 9 to 12 with KOH. The reaction was carried out in a water bath at 30 °C for 1 min. In addition, Si nanoparticles were treated using an alkaline and HF hybrid technique.The porous silicon nanoparticles were collected by suction filtration and dried under vacuum at 80 °C for 2 h. The microstructures of the samples were observed using field emission scanning electron microscopy (FE-SEM). Electrochemical characterizations of samples were performed. The working electrodes were composed of the active material, carbon black and polyvinylidene fluoride (PVdF) as a binder, at a 70:15:15 mass ratio. The mixture was subsequently cast onto copper foil and dried under vacuum at 80 °C for 3 h. Coin-type CR 2032 cells were assembled in an argon-filled glove box using a separator and lithium foil as the counter electrode. The electrolyte was 1 M LiPF6 in a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) (1:1 v/v). The cut off potentials for the charge-discharge processes were 0.02-1.5 V (vs. Li/Li+) and cyclic voltammetry (CV) curves were acquired at room temperature. RESULTS AND DISCUSSION Porous Si nanoparticles were clearly not obtained when using the alkaline method but were fabricated when employing the hybrid approach. Figure 1 shows an SEM image of the nanoparticles resulting from the hybrid method. It is evident that these particles contain numerous nanosized pores. The discharge capacity of these porous Si nanoparticles was much better than that of untreated Si nanoparticles. It is believed that the pores work to mitigate the volume change of the silicon upon insertion. The charge/discharge characteristics of these materials will be detailed in our presentation. Figure 1

In Situ and Ex Situ TEM Study of Lithiation Behaviours of Porous Silicon Nanostructures.

In this work, we study the lithiation behaviours of both porous silicon (Si) nanoparticles and porous Si nanowires by in situ and ex situ transmission electron microscopy (TEM) and compare them with solid Si nanoparticles and nanowires. The in situ TEM observation reveals that the critical fracture diameter of porous Si particles reaches up to 1.52 μm, which is much larger than the previously reported 150 nm for crystalline Si nanoparticles and 870 nm for amorphous Si nanoparticles. After full lithiation, solid Si nanoparticles and nanowires transform to crystalline Li15Si4 phase while porous Si nanoparticles and nanowires transform to amorphous LixSi phase, which is due to the effect of domain size on the stability of Li15Si4 as revealed by the first-principle molecular dynamic simulation. Ex situ TEM characterization is conducted to further investigate the structural evolution of porous and solid Si nanoparticles during the cycling process, which confirms that the porous Si nanoparticles exhibit better capability to suppress pore evolution than solid Si nanoparticles. The investigation of structural evolution and phase transition of porous Si nanoparticles and nanowires during the lithiation process reveal that they are more desirable as lithium-ion battery anode materials than solid Si nanoparticles and nanowires.

Thermally Induced Silane Dehydrocoupling on Silicon Nanostructures

AbstractOrganic trihydridosilanes can be grafted to hydrogen‐terminated porous Si nanostructures with no catalyst. The reaction proceeds efficiently at 80 °C, and it shows little sensitivity to air or water impurities. The modified surfaces are stable to corrosive aqueous solutions and common organic solvents. Octadecylsilane H3Si(CH2)17CH3, and functional silanes H3Si(CH2)11Br, H3Si(CH2)9CH=CH2, and H3Si(CH2)2(CF2)5CF3 are readily grafted. When performed on a mesoporous Si wafer, the perfluoro reagent yields a superhydrophobic surface (contact angle 151°). The bromo‐derivative is converted to azide, amine, or alkyne functional surfaces via standard transformations, and the utility of the method is demonstrated by loading of the antibiotic ciprofloxaxin (35 % by mass). When intrinsically photoluminescent porous Si films or nanoparticles are used, photoluminescence is retained in the grafted products, indicating that the chemistry does not introduce substantial nonradiative surface traps.

Thermally Induced Silane Dehydrocoupling on Silicon Nanostructures.

Organic trihydridosilanes can be grafted to hydrogen‐terminated porous Si nanostructures with no catalyst. The reaction proceeds efficiently at 80 °C, and it shows little sensitivity to air or water impurities. The modified surfaces are stable to corrosive aqueous solutions and common organic solvents. Octadecylsilane H3Si(CH2)17CH3, and functional silanes H3Si(CH2)11Br, H3Si(CH2)9CH=CH2, and H3Si(CH2)2(CF2)5CF3 are readily grafted. When performed on a mesoporous Si wafer, the perfluoro reagent yields a superhydrophobic surface (contact angle 151°). The bromo‐derivative is converted to azide, amine, or alkyne functional surfaces via standard transformations, and the utility of the method is demonstrated by loading of the antibiotic ciprofloxaxin (35 % by mass). When intrinsically photoluminescent porous Si films or nanoparticles are used, photoluminescence is retained in the grafted products, indicating that the chemistry does not introduce substantial nonradiative surface traps.

Porous Silicon Nanoparticle Photosensitizers for Singlet Oxygen and Their Phototoxicity against Cancer Cells

Porous Si nanoparticles, prepared from electrochemically etched single crystal Si wafers, function as photosensitizers to generate (1)O(2) in ethanol and in aqueous media. The preparation conditions for the porous Si nanoparticles were optimized to maximize (1) the yield of material; (2) its quantum yield of (1)O(2) production; and (3) its in vitro degradation properties. The optimal formulation was determined to consist of nanoparticles 146 ± 7 nm in diameter, with nominal pore sizes of 12 ± 4 nm. The quantum yield for (1)O(2) production is 0.10 ± 0.02 in ethanol and 0.17 ± 0.01 in H(2)O. HeLa or NIH-3T3 cells treated with 100 μg/mL porous Si nanoparticles and exposed to 60 J/cm(2) white light (infrared filtered, 100 mW/cm(2) for 10 min) exhibit ∼45% cell death, while controls containing no nanoparticles show 10% or 25% cell death, respectively. The dark control experiment yields <10% cytotoxicity for either cell type.

Investigating individual chromopores within single porous silicon nanoparticles

We use single nanoparticle luminescence microscopy to determine a distribution of individual chromophores present in porous Si nanoparticles. From these distributions, we determine the average number of emitting chromophores in each nanoparticle and the fluorescence emission count rate of a single chromophore within the porous silicon nanoparticle. We also show that the same size nanoparticles prepared under two different electrochemical conditions have different fluorescence peak maxima, and exhibit different chromophore number distributions, consistent with the quantum confinement model for the luminescence in porous silicon.