Pure SiO2 Research Articles

Rapid Probing of Self-Cleaning Activity on Polyester Coated by Titania-Natural Silica Nanocomposite Using Digital Image-Based Colorimetry.

Titania-silica nanocomposites (TiO2-SiO2) show outstanding performance and is very well applied in photocatalysis. In this research, SiO2 extracted from Bengkulu beach sand will be used as a supporting material of the TiO2 photocatalyst for application to polyester fabrics. TiO2-SiO2 nanocomposite photocatalysts were synthesized using the sonochemical method. The coating of the TiO2-SiO2 material on polyester was carried out using the sol-gel-assisted sonochemistry method. The method of determining self-cleaning activity uses a digital image-based colorimetric (DIC) method, which is much simpler than using an analytical instrument. The scanning electron microscopy-energy dispersive X-ray spectroscopy results showed that the sample particles adhered to the fabric surface and the best particle distribution was shown in pure SiO2 and 1:0.5 TiO2-SiO2 nanocomposites. Analysis of Fourier-transform infrared (FTIR) spectroscopy proved the presence of Ti-O and Si-O bonds as well as the typical spectrum of polyester, which indicated that the fabric had been successfully coated with nanocomposite particles. The analysis of the contact angle of the liquid on the polyester surface showed a significant change in the properties of the TiO2 and SiO2 pure coated fabrics, but changes occur only slightly in the other samples. Self-cleaning activity against the degradation of methylene blue dye has been successfully carried out using DIC measurement. The test results showed that the best self-cleaning activity was shown by TiO2-SiO2 nanocomposite with a ratio of 1:0.5 with the degradation ratio reaching 96.8%. Furthermore, the self-cleaning property remains after the washing process, which shows excellent washing resistance.

Rabbit-hair-like SiO2/PI composite nanofibers with super durability for thermal insulation

Flexible composite membrane with strong strength and good thermal performances simultaneously are highly desired in broad fields. Herein, rabbit-hair-like silica/polyimide (SiO2/PI) composite nanofibers with super durability are prepared by a simple electrospinning and impregnating process. The embedded hollow SiO2 microspheres and the bamboo-shaped hollow structure of the composite nanofibers endow the membrane with excellent thermal insulation, while the externally coated thin PI layer provides quite high strength without significantly reducing its thermal stability. The obtained SiO2/PI composite membrane demonstrates high tensile strength (19.7 MPa), good flexibility (withstanding dynamic bending at least 20000 cycles), low thermal conductivity (18.7–42.8 mW m−1 K−1), multi-cycle friction resistance (500 cycles) and abrupt hot/cold alternation stability (near 400 °C). These excellent properties are mainly attributed to the 3D bonding network of the composite membrane and the impregnating-reinforcing effect on single SiO2 nanofiber. This composite membrane not only overcomes the low tensile strength and poor durability of pure SiO2 membrane, but also possesses lightweight and fireproof properties, demonstrating broad prospects in thermal insulation, anti-shock of fire/cold and wearable protective fabrics.

Nanoporous Mg-doped SiO2 nanoparticles with tunable infrared emissivity toward effective radiative cooling coatings

SiO2 is the hotspot radiative cooling material due to its selective radiation or the Mie resonance effect generated by micro/nanospheres of a specific size. Herein, we demonstrate the modulation of the infrared emissivity of the intrinsic SiO2 at the atmospheric window by doping Mg2+ in nanoporous SiO2 nanoparticles via a modified stöber method. The effects of the Mg-doping on the crystallinity, morphology, infrared emissivity of the nanoparticles and the radiative cooling properties of the corresponding coatings are investigated. Results show that the Mg-doping at a level of 0.226–2.26 % can induce cristobalite nanocrystals after sintering at 1000 ℃, transform the morphology from spheres to irregular nanoporous particles, and improve the infrared emissivity up to 0.96. XPS proves the formation of Mg-O bonds and the change of the binding energy of Si 2p and O 1s, supporting the successful doping of Mg2+ in the lattice of SiO2. All-inorganic Mg-doped SiO2 coatings on FTO substrates are prepared via tape casting, which exhibit rough and porous microstructure and high solar reflectivity up to ∼86 %, with the thickness of ∼90 µm. The Mg-doping improves the radiative cooling capacity of the coatings obviously, and the best temperature reduction of 17.8 ℃ compared with the empty space is achieved, 3–5 ℃ lower than the pure SiO2 coating and 4.5 ℃ lower than the commercial SiO2 coating. Our work offers an effective way to modulate the infrared emission of emitter, enriching the technical measures to improve the overall performance of the sub-ambient radiative cooling devices.

Green synthesis of SiO2 from Equisetnm arvense plant for synthesis of SiO2/ZIF-8 MOF nanocomposite as photocatalyst

Equisetnm arvense plant extract was used for preparing amorphous SiO2. For preparing of SiO2/zeolitic imidazolate framework-8 (ZIF-8) nanocomposite by solvothermal method, the synthesized SiO2 was added to synthesis mixture ZIF-8. The photocatalytic activity of SiO2/ZIF-8 was investigated systematically by degrading crystal violet as a cationic dye under UV light irradiation. The photodegradation of crystal violet by SiO2, ZIF-8 and SiO2/ZIF-8 samples was 13.7%, 25.6% and 75.6% during UV-light irradiation for 15 min. Among synthesized samples (SiO2, ZIF-8 and SiO2/ZIF-8), the SiO2/ZIF-8 exhibited highest photocatalytic activity and improved stability compared to pure SiO2 and ZIF-8. As evidenced from SEM and TEM images, ZIF-8 particles without aggregation located over SiO2. The enhancement of the photocatalytic activity is due to the fact that the introduction of insulator SiO2 in SiO2/ZIF-8 composites can modify the surface state of the composite; more importantly, the energy level of SiO2 can help accelerate the separation and transfer of electron-hole pairs of ZIF-8. The SiO2/ZIF-8 photocatalyst did not show any obvious loss of photocatalytic activity during five cycles, which indicate that the heterostructured photocatalyst was stable and can be used repeatedly.

HYDROFLUORIDE PROCESSING OF TAILINGS FROM WET MAGNETIC SEPARATION OF TITANOMAGNETITE TO OBTAIN AMORPHOUS SILICON DIOXIDE

A method for the opening of silicon-containing technogenic feedstock using an aqueous solution of ammonium bifluoride (NH4HF2) with subsequent production of amorphous silica has been developed. In this work we examined wet magnetic separation tailings (WMST) – iron titanium-magnetite ore enrichment rejects that are formed in huge quantities and stored in sludge depositories at concentrating plants. The main rock-forming minerals of WMST are resistant silicates – pyroxene, amphibole, plagioclase and olivine with the total SiO2 content of about 50%. It was established that fluorination of silicon-containing minerals begins during mechanical dispersion of a dry reaction mixture at room temperature. The thermodynamic calculations confirm active interaction of components in the composition of mineral complexes already at 25 ℃, some of the processes being exothermic with entropy reserve. When the temperature increases to 90 ℃ and the duration of leaching to 5 h, the extraction of silicon in the form of soluble ammonium fluorosilicate grows. Insoluble calcium and magnesium fluorides and sparingly soluble under leaching conditions ammonium fluorometallates, as well as a part of unreacted rock are formed in the insoluble residue. Under the most effective desilication conditions (20% NH4HF2 solution, L:S=4:1, 2 h), the residual content of SiO2 decreases to 1–2%. The synthesis of finely dispersed amorphous silica (SiO2) was performed by hydrolytic deposition when the value of рН of clarified ammonium fluorosilicate solution was reduced by adding ammonia. It was shown that gradual introduction of hydrous ammonia (5 ml/h) into diluted fluorosilicate solution with a concentration of less than 5 g/l Si while constant stirring leads to the formation of spherical silica nanoparticles. The degree of silica extraction from tailings in the process of hydrofluorination of 20% NH4HF2 solution at 90 ℃ for 2 h was 98%, and the content of impurities in amorphous silica did not exceed 1–2%. Separation of finely dispersed suspension of insoluble fluorides and hydroxide impurities formed during stepwise hydrolysis of fluorosilicate solution to рН value less than 5 is a necessary condition for producing pure silica SiO2. The final product, similar to “white soot” in properties, is characterized by predominant particle size in the interval of 2-20 nm, a large surface area 230-360 m2/g and a low pycnometric density 1.62 g/cm3. For citation: Medyankina I.S., Pasechnik L.A. Hydrofluoride processing of tailings from wet magnetic separation of titanomagnetite to obtain amorphous silicon dioxide. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2023. V. 66. N 2. P. 70-77. DOI: 10.6060/ivkkt.20236602.6706.

2-Isopropyl-1,3-dimethylimidazolium as a versatile structure-directing agent in the synthesis of zeolites.

An organic cation lacking specificity in its structure-directing action offers the possibility, through the screening of other structure-directing parameters, to synthesize a variety of zeolites. In this work we show that the organic structure-directing agent 2-isopropyl-1,3-dimethylimidazolium (2iPr13DMI) can produce up to seven different zeolite phases depending on water concentration, the presence of inorganic impurities, crystallization temperature and time, and germanium molar fraction. The obtained phases are very different in terms of pore system, connectivity of the zeolite structure and structural units. At the pure SiO2 side, ZSM-12 and SSZ-35 dominate, with ZSM-12 being favored by the presence of potassium impurities and by less concentrated conditions. The introduction of Ge at low levels favors SSZ-35 over ZSM-12 and as the Ge fraction increases it successively affords CSV, -CLO and two distinct UOS zeolites, HPM-11 and HPM-6. These two zeolites have the same topology but distinct chemical compositions and display powder X-ray diffraction patterns that are much different from each other and from that of as-synthesized IM-16 (UOS reference material). They also show different symmetry at 96 K. Rietveld refinements of the three as-made UOS materials mentioned are provided. HPM-6 and HPM-11 are produced in distinct, non-adjacent crystallization fields. The frequent cocrystallization of the chiral STW zeolite, however, did not afford its synthesis as a pure phase. Molecular mechanics simulations of the location of the organic cation and host-guest interactions fail to explain the observed trends, but also considering the intrinsic stability of the zeolites and the effect of germanium help to rationalize the results. The study is completed by DFT calculations of the NMR chemical shifts of 13C in UOS (helping to understand splittings in the spectrum) and 19F in CSV (supporting the location of fluoride inside the new [4452], which is an incomplete double 4-ring).

Double layer chemical encapsulation of SiO2 nanoparticles for interfacial tension reduction under low salinity condition

Recently, rapid growth ofnanotechnologyhas accelerated immensely, and has provided adequate scientific evidence supporting nanoparticles (NPs) as revolutionary agents for oil reservoirs, particularly, for interfacial tension reduction (IFT). For this reason, this paper present synthesis, characterization, and IFT evaluation of new double layer encapsulated SiO2 NPs. The synthesis has been initiated via precursor polyacrylic acid (PAA) to form a first layer intermediate product (SiO2-g-PAA). Subsequently, the SiO2-g-PAA was then individually condensed with Xanthan polymer and 3-aminopropyltriethoxysilane (KH550), to establish double layer products; SiO2-g-PAA-Xanthan and SiO2-g-PAA-KH550, respectively. The products were characterized using Fourier Transform Infrared (FTIR), Field Emission Scanning Electron Microscope (FESEM) and X-ray Diffraction (XRD). Spinning Drop equipment was used to assess the nanofluid’s IFT reduction effects at 0.01, 0.03 & 0.05 % in low salinity (0.3 % NaCl) by comparing with the baseline brine IFT. The FTIR results have confirmed the syntheses of the products, while the FESEM micrographs have described the surface morphologies and average particle size within the nanoscale (36 nm for SiO2-g-PAA-Xanthan & 61 nm for SiO2-g-PAA-KH550). Interestingly, the XRD patterns of all the grafted NPs exhibit amorphous behaviours at 20 θ similar to pure SiO2. The IFT investigations revealed that the brine/oil baseline IFT was recorded to be 9.9 ± 0.07 mN/m, however, upon introducing pure SiO2 NPs into the system at 0.01, 0.03 and 0.05 %, the IFT reduced to a range of 6–8 mN/m (20–33 % efficiency). However, in the presence of SiO2-g-PAA-KH550, extraordinary reduction of the IFT was achieved to a range of 0.5–0.7 mN/m with significant reduction efficiency up to 94 % with respect to a baseline IFT. This is due to the terminal PAA-KH550 on the surface of the SiO2. However, in the case of terminal PAA-xanthan in the SiO2-g-PAA-Xanthan, the polymer did not influence the IFT remarkably, with the IFT reduction efficiency even far lower than the untreated SiO2. Thus, a grafted double layer NPs containing a terminal PAA-KH550 could be an ideal candidate for potential application in chemical EOR due to a remarkable demonstration of IFT reduction which is one of the preconditions governing the successful EOR operation in oil fields.

Embedding Atomically Dispersed Iron Sites in Nitrogen-Doped Carbon Frameworks-Wrapped Silicon Suboxide for Superior Lithium Storage.

Silicon suboxide (SiOx ) has attracted widespread interest as Li-ion battery (LIB) anodes. However, its undesirable electronic conductivity and apparent volume effect during cycling impede its practical applications. Herein, sustainable rice husks (RHs)-derived SiO2 are chosen as a feedstock to design SiOx /iron-nitrogen co-doped carbon (Fe-N-C) materials. Using a facile electrospray-carbonization strategy, SiOx nanoparticles (NPs) are encapsulated in the nitrogen-doped carbon (N-C) frameworks decorating atomically dispersed iron sites. Systematic characterizations including high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and X-ray absorption fine structure (XAFS) verify the existence of Fe single atoms and typical coordination environment. Benefiting from its structural and compositional merits, the SiOx /Fe-N-C anode delivers significantly improved discharge capacity of 799.1mAhg-1 , rate capability, and exceptional durability, compared with pure SiO2 and SiOx /N-C, which has been revealed by the density functional theory (DFT) calculations. Additionally, the electrochemical tests and in situ X-ray diffraction (XRD) analysis reveal the oxidation of Lix Si phase and the storage mechanism. The synthetic strategy is universal for the design and synthesis of metal single atoms/clusters dispersed N-C frameworks encapsulated SiOx NPs. Meanwhile, this work provides impressive insights into developing various LIB anode materials suffering from inferior conductivity and huge volume fluctuations.

Sodium capture mechanism by simulated silica/aluminosilicate slag at high temperatures

• Transition of Al-VI to Al-IV/Al-V in aluminosilicate is a prerequisite for Na capture. • The SCE of pure SiO 2 and Al 2 O 3 is lower than aluminosilicate at high temperatures. • There exist optimal ratios of CaO and MgO in aluminosilicates for Na capture. • The addition of Fe 2 O 3 in aluminosilicates inhibits sodium capture. This paper aims to clarify the sodium capture mechanism by silica/aluminosilicate slag under conditions of cyclone combustion process of high-alkali coal. A series of simulated silica and aluminosilicate slag containing various proportions of SiO 2 , Al 2 O 3 , CaO, MgO, Fe 2 O 3 and NaCl were prepared and exposed in a tube furnace at 1300–1500 °C to simulate a cyclone combustion environment. Results show that the transition from six-coordinated Al (Al-VI) to four- and five-coordinated Al (Al-IV and Al-V) is an essential step for the sodium capture process by molten aluminosilicates. The aluminosilicate with a molar ratio of SiO 2 to Al 2 O 3 (Si/Al) between 3:1 and 10:1 shows the best Na capture performance due to the complete transition of Al in it. Beyond this range, excess Al-VI or SiO 2 will be produced and reduce the sodium capture ability of aluminosilicate. A small amount of CaO or MgO in the aluminosilicates can promote sodium capture efficiency (SCE) due to their fluxing effects. Whereas high content of CaO or MgO will inhibit the Na capture owing to the competing reactions with aluminosilicate between Ca/Mg and Na. The existence of Fe 2 O 3 can strongly inhibit the Na capture, which is probably caused by the fact that the structures of Na-[Fe-O-Si] and Na-[Fe-O-Al] pair are less stable than that of Na-[Si-O-Si] and Na-[Al-O-Si].

Superhydrous aluminous silica phases as major water hosts in high-temperature lower mantle

Water transported by subducted oceanic plates changes mineral and rock properties at high pressures and temperatures, affecting the dynamics and evolution of the Earth's interior. Although geochemical observations imply that water should be stored in the lower mantle, the limited amounts of water incorporation in pyrolitic lower-mantle minerals suggest that water in the lower mantle may be stored in the basaltic fragments of subducted slabs. Here, we performed multianvil experiments to investigate the stability and water solubility of aluminous stishovite and CaCl2-structured silica, referred to as poststishovite, in the SiO2-Al2O3-H2O systems at 24 to 28 GPa and 1,000 to 2,000 °C, representing the pressure-temperature conditions of cold subducting slabs to hot upwelling plumes in the top lower mantle. The results indicate that both alumina and water contents in these silica minerals increase with increasing temperature under hydrous conditions due to the strong Al3+-H+ charge coupling substitution, resulting in the storage of water up to 1.1 wt %. The increase of water solubility in these hydrous aluminous silica phases at high temperatures is opposite of that of other nominally anhydrous minerals and of the stability of the hydrous minerals. This feature prevents the releasing of water from the subducting slabs and enhances the transport water into the deep lower mantle, allowing significant amounts of water storage in the high-temperature lower mantle and circulating water between the upper mantle and the lower mantle through subduction and plume upwelling. The shallower depths of midmantle seismic scatterers than expected from the pure SiO2 stishovite-poststishovite transition pressure support this scenario.

Synthesis and characteristics of Sn-doped SiO2 via plasma-enhanced atomic layer deposition for self-aligned patterning

Sn-doped SiO2 thin films as a spacer for self-aligned patterning were deposited by plasma-enhanced atomic layer deposition and their characteristics were evaluated. This doping research was conducted to improve the mechanical properties of SiO2 films, which have been conventionally used as a spacer material. Because pure SiO2 films have a low Young's modulus, the pattern is stretchable and may collapse as the patterning size decreases. The ratio of the SnO2 and SiO2 deposition cycle was varied from 15(SiO2):1(SnO2) to 3(SiO2):1(SnO2) to modify the film characteristics. X-ray reflectivity (XRR) and time-of-flight secondary ion mass spectrometer analyses revealed whether Sn was doped in SiO2 or became a nanolaminate. The x-ray photoelectron spectroscopy analysis showed that a greater amount of Sn in the SiO2 thin film resulted in a binding energy shift toward the lower binding energy Si2p and Sn3d peaks, and more Si–O–Sn chemical bonding, which increased the number of stiffer ionic bonds as the SnO2 cycle ratio was increased. Therefore, Young's modulus measured by using a nanoindenter increased from 39.9 GPa for SiO2 films to 90.9 GPa for 3(SiO2):1(SnO2) films. However, the hardness results showed a different tendency due to the not well-distributed nanolaminate film structure showing a tendency to decrease and then increase as doping increases. Moreover, the growth rate and film density were evaluated by XRR. The growth per cycle (GPC) of SiO2 was 1.45 Å/cycle and the GPC of SnO2 was 1.0 Å/cycle. The film density of SiO2 was 2.4 g/cm3 and the film density of SnO2 was 4.9 g/cm3. Also, the GPC and film density values of the Sn-doped SiO2 films were in between the values of pure SiO2 and SnO2. The dry etch rate was also measured by reactive ion etching using CF4 plasma with 150 W for 1 min.

Preserving DNA in Biodegradable Organosilica Encapsulates.

A core-shell strategy was developed to protect synthetic DNA in organosilica particles encompassing dithiol linkages allowing for a DNA loading of 1.1 wt %. DNA stability tests involving bleach as an oxidant showed that following the procedure DNA was sandwiched between core particles of ca. 450 nm size and a protective outer layer, separating the DNA from the environment. Rapid aging tests at 60 °C and 50% relative humidity revealed that the DNA protected within this material was significantly more stable than nonprotected DNA, with an expected ambient temperature half-life of over 60 years. Still, and due to the presence of the dithiol linkages in the backbone of the organosilica material, the particles degraded in the presence of reducing agents (TCEP and glutathione) and disintegrated within several days in a simulated compost environment, which was employed to test the biodegradability of the material. This is in contrast to DNA encapsulated following state of the art procedures in pure SiO2 particles, which do not biodegrade in the investigated timeframes and conditions. The results show that synthetic DNA protected within dithiol comprising organosilica particles presents a strategy to store digital data at a high storage capacity for long time frames in a fully biodegradable format.

Atomic-scale and optical investigation of nanostructured Er disilicates in silica

The optical and structural properties of Er-doped Silicon oxide based thin films elaborated by RF magnetron sputtering were investigated as a function of annealing treatment. Atom Probe Tomography and Transmission electron microscopy were used to analyze the position of rare-earth ions as well as the phase separation occurring in the layer in order to provide a complete picture of the nanostructure. The emission properties of Er3+ ions were investigated using cathodoluminescence (CL) spectroscopy. The high doping level of Er ions in silicon oxide matrix leads to a phase decomposition of pure SiO2 and Er2Si2O7 phases with a nanostructure which is influenced by the annealing treatment. It results on different emission intensities in ultraviolet or infrared ranges. The relationship between the nanostructuration observed and the optical properties is discussed in regards of annealing treatment.

Radiation parameterizations and optical characterizations for glass shielding composed of SLS waste glass and lead-free materials

The novelty in the present search, the Soda-Lime-Silica (SLS) glass waste to prepare free lead glass shielding was used in order to limit the accumulation of glass waste, which requires extensive time to decompose. This also saves on the consumption of pure SiO2, which is a finite resource. Furthermore, the combining of BaO with Bi2O3 into a glass network leads to increased optical properties and improved attenuation. The UV–Visible Spectrophotometer was used to investigate the optical properties and the radiation shielding properties were reported for current glass samples utilizing the PhysX/PDS online software. The optical property results indicate that when BaO content increases in glass structure, the Urbach energy ΔE, and refractive index n increases while the energy optical band gap Eopt decreases. The result of the metallisation criteria (M) revealed that the present glass samples are nonmetallic (insulators). Furthermore, the radiation shielding parameter findings suggest that when BaO was increased in the glass structure, the linear attenuation coefficient and effective atomic number (Zeff) rose. But the half-value layer HVL declined as the BaO concentration grew. According to the research, the glass samples are non-toxic, transparent to visible light, and efficient radiation shielding materials. The Ba5 sample is considered the best among all the samples due to its higher attenuation value and lower HVL and MFP values, which make it a suitable candidate as transparent glass shield shielding.

Determining Mechanical Moduli of Disordered Materials with Hierarchical Porosity on Different Structural Levels.

The impact of synthesis parameters and structural properties, respectively, on mechanical properties of porous materials on different structural levels provides valuable information for designing materials for specific applications. Within this study, we apply two nonstandard approaches for determining the mechanical properties of the mesoporous backbone phase in a series of disordered SiO2-based monolithic materials possessing hierarchical meso-macroporosity, that is, deformation upon mercury porosimetry and in situ dilatometry during nitrogen adsorption analysis. By using ordered porous model materials, the latter method has been recently proven to provide reliable mechanical moduli. This concept was now applied to a SiO2 monolith developed for high-performance liquid chromatography exhibiting disordered hierarchical meso- and macroporosity, as well as a series of analogue phenyl-modified meso-macroporous SiO2 monoliths with up to 36.1 at% organic modification. The phenyl group was introduced by adding phenyltrimethoxysilane to the sol-gel mixture. The study aimed at investigating in detail the impact of the organic modification on the morphology of the porous solid and the resulting mechanical properties. The study shows that both Hg porosimetry and in situ dilatometry performed during N2 adsorption at 77 K provide similar and reasonable moduli of compression for the mesoporous backbone of the silica materials investigated. These data were compared with moduli of the macroscopic sample as determined from sound velocity measurements by describing the fully connected macroporous backbone with a foam model. The comparison reveals an otherwise overseen side effect of the organic modification of the silica framework: in contrast to the pure reference SiO2 meso-macroporous monoliths, the hybrid material is composed of a more particulate morphology on the mesoscale, that is, mesoporous particles and corresponding necks between them are formed, which results in significant softening of the porous solid on the macroscale.

Photoluminescent Silica Nanostructures and Nanohybrids.

The complicated photophysics of wide variety of defects existing in silica (SiO2 ) layer of nanometer thickness determines widespread photoluminescence bands of Si/SiO2 based system as well as SiO2 nanoparticles (NPs) for their applications in photovoltaic and optoelectronic devices. This review attempts to summarize different photophysical processes in pure SiO2 NPs. Moreover, these NPs also act as scaffolds for various guest molecules to perform their specific functions. Guest fluorophore molecules when trapped inside pores of SiO2 NPs exhibit a different photodynamics than free state, which opens up several important applications of hybrid SiO2 NPs in artificial photosynthesis, sensing, biology and optical fiber.

(Digital Presentation) Sol – Gel Process of Activated Carbon Based Silica Nanostructure Using Rice Husk Template for Supercapacitor Applications

Rice hulls have portrayed large potential in becoming a sustainable biomass source in producing silica, cellulose, and carbon materials, which garnered well-known interest in the middle of researchers. In recent years, silica-based supercapacitors have emerged as leading energy storage devices that can be mostly used in hybrid electric vehicles, memory devices, etc owing to their unique features like fast charge and discharge rate, long cycle life, high power density, high reliability, etc. The objective of the current study is to determine and compare the specific capacitance of pure silica ( SiO2@SP ) and activated carbon added amorphous silica (SiO2 @SA) nanostructures in rice hulls due to the synergistic effects of the sol-gel process. In this study, we have synthesized pure silica SiO2 and activated carbon added amorphous silica (SiO2 @SA) nanostructures using rice hulls template as a silica source via the simple sol-gel method for supercapacitor applications. XRD, FT-IR, and EDX studies characterize that pure silica(SiO2@SP) is present in amorphous form along with activated carbon having a carbon ballades structure in the prepared SiO2@ SA sample. Further, FE-SEM, TEM observation indicates that the prepared sample is consisting of amorphous silica nanospheres added agglomerated carbon nanoparticles having the size of 20 –30 nm. Cyclic voltammetry and galvanostatic charge/discharge studies characterize the supercapacitive behavior of working electrodes fabricated from prepared SiO2@SP and SiO2@ SA nanostructure. The specific capacitances of SiO2@SP nanostructure are about 36,30,28,26,24,23,22,20 and 12 F/g with the current density value of 4, 6, 8,10,12,14,16,18 and 20 A/g, and the specific capacitances of SiO2@ SA nanostructure are about 85,58,48,46,38,34,32, and 26 F/g with the current density value of 4, 6, 8,10,12,14,16,18 and 20 A/g, respectively. The presence of SiO2@SP species in SiO2@SA nanostructure can provide reactive surfaces for the adsorption/desorption charges and it facilitates the charge storage at the surface of the sample. The above results suggested that the prepared SiO2@SA nanostructure has high potential application for comparison than SiO2@SP nanostructure, making electrochemical supercapacitors.

Plasmon Mediated Electron Transfer and Temperature Dependent Electron-Phonon Scattering in Gold Nanoparticles Embedded in Dielectric Films.

Excitation of localized surface plasmon resonance in metal nanoparticles (NPs) embedded in a glassy matrix generates hot electrons, which can be extracted for different optoelectronic applications. The insights of plasmon relaxation dynamics with varying surrounding dielectric environments and temperature dependence electron-phonon scattering process in gold (Au) NPs are still not very clear. Here, we have employed ultrafast transient absorption (TA) spectroscopy to explore the hot plasmon mediated electron transfer (PMET) and electron-phonon dynamics of photo-excited Au NPs in glassy film matrix with variable SiO2 /TiO2 compositions at cryogenic (5 K) to room temperature (300 K). Herein, we have chosen two pump excitation wavelengths (400 and 700 nm). The 400 nm excitation (d→sp) generates hot electron and the 700 nm excitation (sp→sp) provide information of direct plasmon relaxation. Drastic reduction of the transient signal of Au NPs in the high TiO2 content film as compared to pure SiO2 confirm hot electron transfer (HET) from Au plasmon to TiO2 . Electron-phonon scattering time constant (τe-ph ) of Au NPs in the glassy film is found to be faster in presence of TiO2 due to facile electron transfer/injection. Temperature dependent TA studies suggest that electron-phonon scattering time decreases with temperature. These findings would assist to develop more advanced photo-voltaic, opto-electronic and quantum optic-based devices using the plasmonic metal NPs.

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.

Graphene-supported cobalt nanoparticles used to activate SiO2-based anode for lithium-ion batteries

Although SiO2-based anode is a strong competitor to supersede graphite anode for lithium-ion batteries, it still has problems such as low electrochemical activity, enormous loss of active lithium, and serious volume expansion. In order to solve these problems, we used a graphene network loaded with cobalt metal nanoparticles (rGO–Co) to coat SiO2 porous hollow spheres (SiO2@rGO–Co). The construction of porous hollow structure and graphene network can shorten the lithium-ion (Li+) diffusion distance and enhance the conductivity of the composite, which improves the electrochemical activity of SiO2 effectively. They also alleviate the volume expansion of the anode in the cycling process. Moreover, nano-scale cobalt metal particles dispersed on graphene catalyze the conversion reaction of SiO2 and activate the locked Li+ in Li2O through a reversible reaction, which improves the charge and discharge capacity of the anode. The capacity of SiO2@rGO–Co reaches 370.4 mAh/g after 100 cycles at 0.1 A/g, which is 6.19 times the capacity of pure SiO2 (59.8 mAh/g) under the same circumstance. What is more, its structure also exhibits excellent cycle stability, with a volume expansion rate of only 13.0% after 100 cycles at a current density of 0.1 A/g.