Carbon-coated Silica Research Articles

Interface Structure Strengthening of a Mesoporous Silicon/Expanded Perlite Microevaporator for Efficient Solar-Driven Interfacial Evaporation.

Solar-driven interfacial evaporation is one of the cutting-edge technologies for seawater desalination and wastewater purification. Herein, a floating carbon-coated silica microsphere/expanded perlite integrated interfacial microevaporator (HEPCL) is reported. The carbon nanolayer allows the HEPCL to have better broadband light absorption performance than natural graphite and graphene oxide. Through the low density of expanded perlite, HEPCL particles can self-float on the water surface and self-aggregate into an integrated whole under surface tension, which enhances the heat collection capacity. The hierarchical porous structure of the HEPCL has a continuous water absorption capacity. Notably, water molecules adsorbed in the HEPCL have a high desorption energy, which reduces the water evaporation enthalpy (1621 kJ/kg), making it easy to remove with external energy. Thanks to the design merits, the HEPCL achieves a water evaporation rate of 1.551 kg m-2 h-1 (efficiency of 94.85%) under 1 sun irradiation and may inspire a practicable solution of water scarcity.

Carbon-Coated Mesoporous Silica Nano-Quills from Bioderived Cellulosic Templates for Low-Cost Anodes

The escalating global energy demands, driven by population growth and the electrification of transportation, have positioned rechargeable lithium-ion batteries (LIBs) as critical components in phasing out traditional fuel-based technologies. To date, several high-capacity active materials have been developed to replace current graphite-based anodes for boosting the energy density of LIBs. Silicon dioxide (SiO2, or silica) has emerged as a promising alternative, with a high theoretical capacity of 1965 mAh g-1, five times higher than conventional graphite, along with a comparatively smaller volume change than elemental Si during battery cycling. In this study, we report a patented synthesis process that harnesses wood-derived cellulose nanocrystals (CNCs) to craft a unique three-dimensional (3D) silica architecture for developing low-cost LIB anodes. Our cost-effective method yields a mesoporous silica material, termed silica nano-quill (SilicaNQ), with distinctive hollow 1D arms. In addition, we propose a direct annealing strategy for transforming CNC templates into a conformal carbon coating to fabricate SilicaNQ@C powder material. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) provided a detailed exploration of the elemental composition and the bonding states at the atomic level. Anodes comprising SilicaNQ@C active material delivered a stable reversible capacity of 1030 mAh g-1 after cycling at 200 mA g-1 for 200 cycles. We performed X-ray diffraction (XRD) measurements on SilicaNQ@C half cells to identify phase changes at various state-of-charge levels and explore the evolution of interface components over cycling.

Efficient hydrolysis of cellulose into sugars in aqueous systems using fibrous core-shell structure FS@C/HPW

Phosphotungstic acid hydrate (HPW)-doped hydroxyl-rich hydrothermal carbon-coated fibrous silica catalyst (FS@C/HPW) is fabricated to induce the highly efficient hydrolysis of cellulose to sugar in an ultra-low acid aqueous system. The obtained FS90@C/HPW12 owns good thermal stability under 200 °C and the highest specific surface area at 28 m2/g. Owing to its special fibrous microstructures, FS90@C/HPW12 can cause linear damage and structural fragmentation on the surface of cellulose during hydrolysis. Accordingly, rather highly efficient hydrolysis with the cellulose conversion of 100 %, total reducing sugar and glucose yields at 92.2 % and over 85 % is achieved in the aqueous system with FS90@C/HPW12 and 5 mmol/L H2SO4. FS90@C/HPW12 also exhibits good reusability in multiple hydrolysis. This research provides a particular way for the design and synthesis of solid catalysts to induce the highly efficient hydrolysis of cellulose to sugar by chemical catalysis in a full aqueous system.

Carbon-coated silica supported palladium for hydrogen production from formic acid – Exploring the influence of strong metal support interaction

Hydrogen energy is one of the most promising energy carriers to solve the increasingly severe energy crisis. Formic acid decomposition (FAD) solves the storage and transportation problems of hydrogen gas since hydrogen can be produced from aqueous formic acid under mild conditions. To efficiently convert formic acid to hydrogen gas, chemical and structural modification of Pd nanoparticles or supports have been carried out, especially introducing the strong metal support interaction (SMSI). Herein, we synthesized core–shell structured SiO2@SC compounds as the supports to introduce SMIS to Pd/PdO nanoparticles. The relationship between FAD activity and SMSI is investigated. The SMSI between Pd/PdO nanoparticles and SiO2/SC is adjusted by altering the thickness of the carbon layer. The X-ray photoelectron spectroscopy shows that owing to the strong electron-attracting ability SiO2 core contributes to leading the Pd0 active site in an electron-deficient state. The thickness of the carbon layer controls the ratio of Pd0/PdO, which enhances the anti-poisoning ability of the catalyst. Owing to the electron-deficient state of Pd0 and optimal ratio of Pd0/PdO, the hydrogen desorption rate of FAD on Pd is enhanced, and the turn over frequency of Pd/SiO2@SC-1:3 catalyst reaches 1138 h−1, which is ten times higher than that of the pristine Pd/SC catalyst. These results are believed to guide the design and development of highly active Pd-based catalysts for hydrogen generation via FAD.

Electrochemically pre-lithiated SiO2@C nanocomposite anodes for improved performance in lithium-ion batteries

Silica (SiO2)-based materials are a promising alternative anode material due to their high specific capacity, abundance, safety, and environmental friendliness. However, the significant volume expansion and the formation of a solid electrolyte interphase (SEI) with electrolytes cause active lithium loss and result in poor Coulombic efficiency of SiO2-based materials, which hinder their commercial applications. Therefore, pre-lithiation, a method of embedding extra lithium ions in the electrodes prior to cycling, is an effective approach to replenish the largely irreversible lithium loss during cycling and overcomes these challenges. In this study, carbon-coated silica (SiO2@C) nano composite was synthesized via a sol–gel method and the beneficial impacts of using pre-lithiated SiO2@C electrodes in coin cells were investigated. It is shown that the carbon coating onto the surface of the SiO2 particles and the pre-lithiation method led to a distinct improvement in the overall capacity and Coulombic efficiency of the cells due to the pre-formed SEI and the presence of a lithium reservoir within the anode. Furthermore, the anodes exhibited excellent cycling stability and good rate capability up to 2 A g−1.

Development of Microdrip Enzyme Device Using Carbon-Coated Porous Silica Spheres

Carbon-coated porous silica spheres (C/PSSs) are particles with uniform particle and mesopore sizes, on which a thin layer of carbon is uniformly deposited on the surface by chemical vapor deposition. The continuous carbon deposit over the mesopore network allows the C/PSS to be electrically conductive and more chemically stable over its traditional counterparts, such as PSS, porous carbons, and carbon electrodes. As homogeneous particles, C/PSS can also be arranged uniformly on an electrode by screen printing to construct macroscopic networks that facilitate the diffusion of substances. Herein, C/PSS was synthesized and fabricated into a working electrode for a prototype glucose enzyme sensor to perform electrochemical measurements on a sample size of 20 μL. We selected the two enzymes, glucose dehydrogenase (GDH) and glucose oxidase (GOD), and water-soluble mediators, quinoline-5,8-dione (QD), to demonstrate the functionality of the sensor. The GDH sensor achieved a linear response up to 75 mM glucose concentration much higher than commercial sensor strips and the GOD sensor up to 25 mM. The results proved that the response current was mainly controlled by glucose diffusion. We succeeded in developing a sensor chip with C/PSS arranged on the surface with high efficiency by selecting a mediator that can smoothly transfer electrons to and from carbon, which enables various sensing applications. This work is the demonstration of the triple pore structure of the C/PSS electrode for enzyme electrode reactions.

From Rice Husk Ash to Silica-Supported Carbon Nanomaterials: Characterization and Analytical Application for Pre-Concentration of Steroid Hormones from Environmental Waters.

Rice husk (RH) in the rice industry is often air-burnt to obtain energy in the form of heat and RH ash (RHA) residue. In this work, RHA was applied as a starting material to obtain silica-supported carbon nanomaterials, resulting in a new reuse of a globally produced industrial waste product, in a circular economy approach. The preparation involves ultrasound-assisted one-pot oxidation with a sulfonitric mixture followed by wet oven treatment in a closed vessel. A study of oxidation times and RHA amount/acid volume ratio led to a solid material (nC-RHA@SiO2) and a solution containing silica-supported carbon quantum dots (CQD-RHA@SiO2). TEM analyses evidenced that nC-RHA@SiO2 consists of nanoparticle aggregates, while CQD-RHA@SiO2 are carbon-coated spherical silica nanoparticles. The presence of oxygenated carbon functional groups, highlighted by XPS analyses, makes these materials suitable for a wide range of analytical applications. As the main product, nC-RHA@SiO2 was tested for its affinity towards steroid hormones. Solid-phase extractions were carried out on environmental waters for the determination of target analytes at different concentrations (10, 50, and 200 ng L-1), achieving quantitative adsorption and recoveries (RSD < 20%, n = 3). The method was successfully employed for monitoring lake, river, and wastewater treatment plant water samples collected in Northern Italy.

Study on properties of carbon-coated silica prepared by polymer pyrolysis reinforced rubber composites

Silica is an excellent reinforcing material and has been widely used in the rubber tire field. Silica can improve the wet grip performance and reduce rolling resistance. However, the application of silica in high-performance tires have been put forward with higher requirements due to the difficulties of dispersion, high heat generation, temperature sensitivity, and easy gel generation in the mixing process. To solve the above problems, nanocarbon-coated silica (silica@nanocarbon, SN) was proposed as a new reinforcing material in this paper. Nanocarbon coating prepared by pyrolysis of polyethylene. The hydroxyl groups on the surface of SN disappeared. Then, the new material was applied to the rubber composite, and the experimental results show that the curing time (t90) of the SN filled rubber compounds can be shortened. SN can improve the thermal conductivity of rubber compounds, and the compound has better dynamic mechanical properties. It also provides a feasible exploration for the application of modified silica in high-performance tires.

Ni Nanoparticles Grown on SiO2 Supports Using a Carbon Interlayer Sacrificial Strategy for Chemoselective Hydrogenation of Nitrobenzene and m-Cresol

To efficiently increase the dispersity of metal nanoparticles (NPs) of the supported-type catalyst is crucial for promoting their catalytic performance owing to the enlarged amount of exposed active sites and the strengthened metal–support interaction. Therefore, to develop a facile and practical method for preparing a supported-type catalyst with high dispersity is of great significance, but remains a challenge. In this work, inspired by the previously reported non-noble metal sacrificial approach, we report a facile and practical carbon interlayer sacrificial (CIS) strategy for preparing supported Ni NP catalysts on silica rod (10%Ni/r-SiO2-CIS) with high dispersity. This strategy involves two steps: one is depositing carbon on silica rod (r-SiO2) to form the corresponding carbon-coated silica (r-SiO2@C) carrier through a hydrothermal process in the presence of glucose; the other is loading metal precursor on r-SiO2@C through an incipient wetness impregnation (IWI) process followed by hydrogenation for carbon elimination. The method has been extended to the preparation of supported Ni NPs on the silica sphere (10%Ni/s-SiO2-CIS) with high Ni dispersity by using the silica sphere (s-SiO2) as the carrier. For comparison, the conventional-supported Ni NP catalysts (10%Ni/r-SiO2 and 10%Ni/s-SiO2) were also prepared by using a similar method to that for 10%Ni/r-SiO2-CIS and 10%Ni/s-SiO2-CIS except for absence of the carbon-coating process. Owing to the more exposed active sites and the strengthened metal–support resulting from the higher Ni dispersity, both 10%Ni/r-SiO2-CIS and 10%Ni/s-SiO2-CIS catalysts show much superior catalytic properties for the chemoselective hydrogenation of nitrobenzene and m-cresol to their corresponding 10%Ni/r-SiO2 and 10%Ni/s-SiO2. This work opens up an avenue for designing and preparing other outstanding supported metal NP catalysts with high metal dispersity for diverse catalytic transformations.

Carbon-coated mesoporous silica incorporating organoruthenium complexes and its application to hydrosilylation of 1-hexyne

The present article describes the construction of the organoruthenium complex catalyst within carbon-coated mesoporous silica and its application to a heterogeneous catalyst for hydrosilylation reaction. The carbon-coated mesoporous silica (C-MCM-41) was synthesized by carbonization of 2,3-dihydroxynaphthalene (DN) adsorbed on the surface of mesoporous silica, followed by the ligand exchange reaction between [(CH3CN)3RuCp]PF6 (Cp: cyclopentadienyl) and six-membered carbon ring at the surface of C-MCM-41 ([C-MCM-41-RuCp]PF6). X-ray absorption fine structure study for [C-MCM-41-RuCp]PF6 demonstrates that the structure of the constructed ruthenium complex is closely similar to that of a molecular [(C6H6)RuCp]PF6 complex. The [C-MCM-41-RuCp]PF6 behaves as a heterogeneous ruthenium complex catalyst and promotes hydrosilylation of 1-hexyne by triethylsilane in a solid–gas heterogeneous system to give α-vinylsilane as a major product.

Sub-micrometer Nanosecond LA-ICP-MS Imaging at Pixel Acquisition Rates above 250 Hz via a Low-Dispersion Setup

The analytical figures of merit of a low-dispersion (ultrafast) ablation cell geometry within the Cobalt ablation chamber, integrated into a nanosecond laser ablation-inductively coupled plasma-mass spectrometer system, are reported. The system was investigated for its capability for fast high-resolution elemental imaging. A spot of 0.6 μm diameter was achieved on the sample surface by aperture imaging of a 10 μm pinhole. The resulting conical crater (0.6 μm ⌀ × 130 nm↓) morphology in a Au-coated glass target and carbon-coated silica wafer was characterized with atomic force microscopy. The Cobalt ablation chamber is based around a motorized height-adjustable tube cell, which allows modulating the sampling distance, i.e. the distance between the sample surface and the cell inlet, in a dynamic manner. This distance was observed to influence the single pulse response profile. The variation of the average signal intensity at multiple sample heights within a range of 0.5 mm was <3% RSD. Under optimum conditions, single pulse responses with a full width at 10% of the maximum peak intensity (FW0.1M) of ∼1 ms can be achieved for 238U upon ablation of NIST SRM612 glass, effectively opening the way to pixel acquisition rates up to 1 kHz. To demonstrate the potential of this technology, the elemental distribution of Zn in small intestine villi of mice subjected to a Zn-enriched diet was imaged using the 0.6 μm spot size, and rapid imaging of a zircon grain cross-section was performed.

The effects of staged mixing on the dispersion of reinforcing fillers in elastomer compounds

Kinetically mixed reinforcing fillers are dispersed by accumulated strain. Processing conditions such as mixing geometry, intensity and the duration of mixing are key elements that control accumulated strain. A simple method to modify mechanical mixing is the mixing schedule which involves the timing of filler additions to a compound. For example, it is known that simultaneous addition of oil with filler is disadvantageous to dispersion, while the incorporation of oil after filler addition enhances dispersion. The simplest case of mixing schedule involves timed filler additions into an elastomer, for instance in a single stage or in two-stages. This study explores the effects of staged mixing on nanoscale dispersion based on a colloidal model. Dispersion is quantified using a pseudo-thermodynamic approach coupled with ultra-small angle X-ray scattering. It was found that single stage mixing yields optimal nano-dispersion for carbon-coated silica and carbon black in polybutadiene using an internal mixer.

High activity Pd-Fe bimetallic catalysts for aqueous phase hydrogenations

Palladium-iron bimetallic catalysts were synthesized using carbon-coated silica supports that provided high hydrogenation activity relative to monometallic palladium under condensed-phase hydrothermal conditions. The catalysts were applied to the hydrogenation of carbonyl groups in acetone, 2-pentanone, and propionaldehyde. While Fe incorporation independent of Pd-to-Fe ratio gave enhanced activity, the catalysts having more Fe than Pd gave more than a three-fold increase in hydrogenation activity relative to the Pd only counterpart. The activity enhancement appeared to be related to the influence of Fe on the Pd as Fe under the condensed-phase reaction conditions was inert. The catalysts were also tested for hydrogenation of unsaturated carbon-carbon double bond and aromatic rings in which more moderate activity enhancement was observed. Through evaluating the influence of Pd-to-Fe ratio on catalyst properties and catalytic performance for the range of molecules, it is proposed that the turnover frequency enhancement can be attributed to the formation of Pdδ− via Pd-Fe interaction.

Direct inscription and evaluation of fiber Bragg gratings in carbon-coated optical sensor glass fibers for harsh environment oil and gas applications.

In this research work, we show the successful inscription of fiber Bragg gratings into carbon-coated pure silica as well as germanium-doped glass fibers by applying the pulsed laser point-by-point manufacturing technique. First, the parameters used for the Ti:sapphire femtosecond laser process are demonstrated. Without removing the polymeric carbon coating, destruction-free formation of highly reflective Bragg gratings is performed with selected types of hermetically enclosed fibers. We demonstrate the advantage of the carbon coating by long-term exposure to a pure hydrogen atmosphere at an elevated temperature. Such harsh conditions exist in the oil and gas industry, which means there is high application potential for technologically advanced optical sensors. Compared to the also examined standard glass fibers with a distinct signal attenuation, carbon-coated fibers show no significant degradation. Finally, we analyze the mechanical stability of the processed fibers via standardized tensile tests. No substantial decrease in strength occurs among the sensor-integrated samples.

Glass formation and short-range order structures in the BaS + La2S3 + GeS2 system

Infrared (IR) optical materials have enabled a broad range of optical sensing and measurement applications in the mid-wave and long-wave IR. Many IR transmitting glasses are based on covalently-bonded selenides and tellurides, such as As2Se3 and GeTe2, which typically have relatively low glass transition temperatures (Tg) on the order of 200 to 350 °C. Many applications have working temperatures above the Tg of these materials, which compels the development of new IR materials. This work studies the underlying short-range order (SRO) structure and glass formability of a new family of ionically-bonded sulfide glasses, xBaS + yLa2S3 + (1 − x − y)GeS2, to develop high Tg optical materials with a broad IR transmission range. These sulfide glasses were produced by melting sulfide materials inside evacuated and sealed carbon-coated silica ampoules at 1150 °C for 12 h and quenching to room temperature to form glass. Glass samples were then characterized by IR and Raman spectroscopies and differential thermal analysis (DTA). It was found that by increasing the modifier concentration, the predominantly Ge4 SRO units, the superscript defines the number of bridging sulfur (BS) ions in the tetrahedral network found in GeS2 glasses, are ultimately converted to Ge0 units at >40 mol% network modifier content through the generation of non-bridging sulfur (NBS) ions. These molecular ionic units still form a glassy network, with some of the highest reported Tg values to date for a pure sulfide glass. This suggests that this composition has strong ionic bonds between negatively-charged tetrahedral SRO units and the positively-charged modifier cations. While the glass network is depolymerized in the high modifier content glasses though the formation of a high concentration of molecular ionic Ge0 SRO groups, they are, nevertheless, homogeneous glassy materials that exhibit the largest Tg and ΔT (difference between crystallization temperature, Tc, and Tg) values of glasses in this system, making them the optimal glasses for high Tg IR optical components, including, potentially, refractory IR optical fibers.

Preparation of silica-supported carbon by Kraft lignin pyrolysis, and its use in solid-phase extraction of fluoroquinolones from environmental waters

The article describes a carbon-based material for solid-phase extraction (SPE) of fluoroquinolones from waters. It was obtained by pyrolytic deposition of Kraft lignin (LG) on silica particles. Marbofloxacin (MAR) and enrofloxacin (ENR) were chosen as model contaminants. The material was prepared by first adsorbing LG onto silica microparticles, this followed by pyrolytic treatment at 1200 °C for 2 h. Silica-supported carbon was characterized by scanning electron microscopy, surface area measurement (by BET), thermogravimetric analysis, and electron paramagnetic resonance. The carbon-coated silica particles were then tested as a column packing for SPE of MAR and ENR from spiked tap and river waters. Quantitative adsorption was observed at pH values of ~7.5 for both drugs. They were eluted with a 70:30 mixture of aqueous tetrabutylammonium hydroxide and acetonitrile and then quantified by HPLC coupled to fluorescence detection. Samples spiked with MAR and ENR in the range from 10 to 1000 ng·L−1 gave recoveries ranging from 70 to 116% (for n = 3). Good inter-day precision (with RSDs between 7 and 16%) was observed for 20–1000 ng·L−1 spikes, also in natural river water. Sample volumes up to 500 mL provided enrichment factors up to 125, and this makes this material useful for determination of the two drugs at environmentally significant levels which are as low as a few ng·L−1. The batch-to-batch reproducibility was verified for 3 preparations. The sorbent was successfully applied to the determination of these drugs in environmental waters.

Real Understanding of the Nitrogen-Doping Effect on the Electrochemical Performance of Carbon Materials by Using Carbon-Coated Mesoporous Silica as a Model Material.

The main aim of the present work is to precisely understand the sole effect of nitrogen doping on the electrochemical performance of porous carbon materials. To achieve this objective, the whole surface of mesoporous silica (SBA-15) was coated with a thin layer of carbon (about 0.4 nm) with and without N-doping by using acetonitrile and acetylene chemical vapor deposition, respectively. The resulting N-doped and nondoped carbon-coated silica samples have mesopore structures identical to those in the original SBA-15, and they are practically the same in terms of not only the pore size and pore structure but also the particle size distribution and particle morphology, with the exception of N-doping, which makes them unique model materials to extract the sole effect of nitrogen on the performances of electrochemical capacitors and electrocatalytic oxygen reduction. Moreover, the outstanding features of the carbon-coated silica samples allow even a quantitative understanding of the pseudocapacitance induced by nitrogen functionalities on the carbon surface in an acidic aqueous electrolyte.

Dopamine-assisted synthesis of carbon-coated silica for PCR enhancement.

Polymerase chain reaction (PCR) has become one of the most popular methods to identify genomic information on cells and tissues as well as to solve crimes and check genetic diseases. Recently, the nanomaterials including nanocomposite and nanoparticles have been considered as a next generation of solution to improve both quality and productivity of PCR. Herein, taking into these demands, carbon-coated silica was synthesized using silica particles via polymerization of biocompatible dopamine (PD) to form polydopamine (PDA) film and carbonization of PDA into graphitic structures. For further investigation of the effects of as-prepared silica, PDA-coated silica (PDA silica), and carbonized PDA silica (C-PDA silica), two different types of genes were adopted to investigate the influences of them in the PCR. Furthermore, the strong interaction between the nanocomposites and PCR reagents including polymerase and primers enables regulation of the PCR performance. The effectiveness of the nanocomposites was also confirmed through adopting the conventional PCR and real-time PCR with two different types of DNA as realistic models and different kinds of analytical methods. These findings could provide helpful insight for the potential application in biosensors and biomedical diagnosis.

Carbon Overcoating of Supported Metal Catalysts for Improved Hydrothermal Stability

Commercial mesoporous oxides, such as silica, are not stable in liquid-phase reactions, particularly aqueous-phase reactions at elevated temperatures, which are corrosive to oxide supports. We have shown previously that the hydrothermal stability of silica is significantly improved by coating the surface with thin carbon layers. Herein, we show that controlled pyrolysis of sugars also provides a facile approach for coating supported metal catalysts, leading to improved dispersion of the active metal phase in the hydrothermally aged catalyst. The carbon overcoats are synthesized at mild temperatures, resulting in an open structure, as revealed by 13C NMR, which helps explain why the overcoats do not significantly block the active sites. We compare two approaches–depositing Pd on carbon-coated silica and depositing carbon overcoats on Pd/silica. The carbon overcoating approach leads to better performance after hydrothermal aging, as determined by using a probe reaction (CO oxidation) to quantify the number ...

Routes to 3D conformal solid-state dielectric polymers: electrodeposition versus initiated chemical vapor deposition

We show that two distinct methods, electropolymerization and initiated chemical vapour deposition (iCVD), can be adapted to generate ultrathin polymers (30–50 nm thick) at three dimensionally (3D) porous conductive substrates comprising ∼300 μm-thick carbon-coated silica fiber paper (C@SiO2).