Surface engineered silica mesospheres – A promising adsorbent for CO 2 capture

Quasi-Solid-State SiO2 Electrolyte Prepared from Raw Fly Ash for Enhanced Solar Energy Conversion

Quasi-solid-state electrolytes in dye-sensitized solar cells (DSSCs) prevent solvent leakage or evaporation and stability issues that conventional electrolytes cannot; however, there are no known reports that use such an electrolyte based on fly ash SiO₂ (FA_SiO₂) from raw fly ash (RFA) for solar energy conversion applications. Hence, in this study, quasi-solid-state electrolytes based on FA_SiO₂ are prepared from RFA and poly(ethylene glycol) (PEG) for solar energy conversion. The structural, morphological, chemical, and electrochemical properties of the DSSCs using this electrolyte are characterized by X-ray diffraction (XRD), high-resolution field-emission scanning electron microscopy (HR-FESEM), X-ray fluorescence (XRF), diffuse reflectance spectroscopy, electrochemical impedance spectroscopy (EIS), and incident photon-to-electron conversion efficiency (IPCE) measurements. The DSSCs based on the quasi-solid-state electrolyte (SiO₂) show a cell efficiency of 5.5%, which is higher than those of nanogel electrolytes (5.0%). The enhancement of the cell efficiency is primarily due to the increase in the open circuit voltage and fill factor caused by the reduced electron recombination and improved electron transfer properties. The findings confirm that the RFA-based quasi-solid-state (SiO₂) electrolyte is an alternative to conventional liquid-state electrolytes, making this approach among the most promising strategies for use in low-cost solar energy conversion devices.

The Importance of Precursors and Modification Groups of Aerogels in CO2 Capture

The rapid growth of CO₂ emissions in the atmosphere has attracted great attention due to the influence of the greenhouse effect. Aerogels' application for capturing CO₂ is quite promising owing to their numerous advantages, such as high porosity (~95%); these are predominantly mesoporous (20-50 nm) materials with very high surface area (>800 m²∙g^-1). To increase the CO₂ level of aerogels' uptake capacity and selectivity, active materials have been investigated, such as potassium carbonate, K₂CO₃, amines, and ionic-liquid amino-acid moieties loaded onto the surface of aerogels. The flexibility of the composition and surface chemistry of aerogels can be modified intentionally-indeed, manipulated-for CO₂ capture. Up to now, most research has focused mainly on the synthesis of amine-modified silica aerogels and the evaluation of their CO₂-sorption properties. However, there is no comprehensive study focusing on the effect of different types of aerogels and modification groups on the adsorption of CO₂. In this review, we present, in broad terms, the use of different precursors, as well as modification of synthesis parameters. The present review aims to consider which kind of precursors and modification groups can serve as potentially attractive molecular-design characteristics in promising materials for capturing CO₂.

Sodium silicate-derived aerogels: effect of processing parameters on their applications

Inorganic silica aerogels derived from sodium silicate are voluminous three-dimensional open networks with exceptional properties such as a density as low as ∼100 kg m-3, high porosity (∼99%), low thermal conductivity (∼0.01 W m-1 K-1), high specific surface area (∼1000 m2 g-1), low refractive index (∼1.05) and high optical transmittance (∼95%) depending on their preparation conditions. They are processed through the sol-gel route, which is a reliable methodology to produce high-grade porous materials. Ambient pressure drying has been developed as a low-cost route for the preparation of sodium silicate-derived aerogels, overcoming the difficulties with the use of organosilane precursors and super critical drying. Silica aerogels can be hydrophobic or hydrophilic depending on their synthetic procedure and surface silanol groups. Owing to their unusual properties, these inorganic aerogels have been applied in both commercial and high-tech engineering applications such as thermal insulation, separation, coatings, optics, nuclear particle detection, sensing, and catalysis. This review provides information on the unique features of a wide array of silica aerogels and their potential applications and recent developments in the field of science and technology.

Degree of N-Methylation of Nucleosides and Metabolites Controls Binding Affinity to Pristine Silica Surfaces

Biological molecules interact with silica (SiO₂) surfaces with binding affinities that greatly vary depending on their physical-chemical properties. However, the quantitative characterization of biological compounds adsorbed on silica surfaces, especially of compounds involved in fast, reversible interactions, has been challenging, and the driving forces are not well understood. Here, we show how carbon-13 NMR spin relaxation provides quantitative atomic-detail information about the transient molecular binding to pristine silica surfaces, represented by colloidally dispersed silica nanoparticles (SNPs). Based on the quantitative analysis of almost two dozen biological molecules, we find that the addition of N-methyl motifs systematically increases molecular binding affinities to silica in a nearly quantitatively predictable manner. Among the studied compounds are methylated nucleosides, which are common in epigenetic signaling in nucleic acids. The quantitative understanding of N-methylation may open up new ways to detect and separate methylated nucleic acids or even regulate their cellular functions.

Superswelling Hybrid Sponge from Water Glass for Selective Absorption of Crude Oil and Organic Solvents

A lightweight super hydrophilic hybrid sponge is designed and demonstrated out of water glass and an organic polymer, which has a macroporous flaky nature and is superflexible with an apparent density of 0.069 g cc^-1, ∼97% porosity, and 3000% water uptake. The octadecyltrimethoxy silane-modified hybrid sponge exhibits selective absorption of oil and organic solvents in open water. An absorption capacity in the range 12-23 g g^-1 for the test liquids light crude oil, engine oil, paraffin oil, chloroform, kerosene, and hexane is revealed. Absorption capacity by a weight basis was directly proportional to the density and inversely proportional to the viscosity of test liquids. Trials under both stagnant and turbulent conditions verify selective uptake of oil from sea water. Complete regeneration of the absorbent was possible for ten cycles for the test liquids. The work provides design of an affordable water clean-up material alternative to commonly used polyurethane sponges.

Enhanced CO₂ Adsorption by Nitrogen-Doped Graphene Oxide Sheets (N-GOs) Prepared by Employing Polymeric Precursors

Nitrogen-doped graphene oxide sheets (N-GOs) are prepared by employing N-containing polymers such as polypyrrole, polyaniline, and copolymer (polypyrrole-polyaniline) doped with acids such as HCl, H₂SO₄, and C₆H₅-SO₃-K, which are activated using different concentrations of KOH and carbonized at 650 °C; characterized using SEM, TEM, BET, TGA-DSC, XRD, and XPS; and employed for the removal of environmental pollutant CO₂. The porosity of the N-GOs obtained were found to be in the range 1-3.5 nm when the KOH employed was in the ratio of 1:4, and the XRD confirmed the formation of the layered like structure. However, when the KOH employed was in the ratio of 1:2, the pore diameter was found to be in the range of 50-200 nm. The SEM and TEM analysis reveal the porosity and sheet-like structure of the products obtained. The nitrogen-doped graphene oxide sheets (N-GOs) prepared by employing polypyrrole doped with C₆H₅-SO₃-K were found to possess a high surface area of 2870 m²/g. The N-GOs displayed excellent CO₂ capture property with the N-GOs; PPy/Ar-1 displayed ~1.36 mmol/g. The precursor employed, the dopant used, and the activation process were found to affect the adsorption property of the N-GOs obtained. The preparation procedure is simple and favourable for the synthesis of N-GOs for their application as adsorbents in greenhouse gas removal and capture.

Preparation of stable tetraethylenepentamine-modified ordered mesoporous silica sorbents by recycling natural Equisetum ramosissimum

It is well-known that global warming of the earth is caused by the progressive increase of CO₂ concentration in the environment due to the huge utilization of fossil fuels. As a result, the development of an efficient and economic method to capture CO₂ from large stationary sources, such as coal-fired power plants, cement and steel factories, and so on is urgent. In this study, ordered mesoporous silicas (E-SBA-15) have been prepared by using Equisetum ramosissimum plants as the silica sources and their subsequently incorporating with amino-containing compounds (tetraethylenepentamine, TEPA) and stabilizers (titanium isopropoxide, TIP). A variety of different spectroscopic and analytical techniques, such as nitrogen adsorption-desorption isotherms, low-angle X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier-transformed infrared (FTIR) spectroscopy, and thermogravimetric analysis (TGA) are used to characterize the physicochemical properties of various materials. CO₂ adsorption capacities of prepared sorbents at 75 °C are obtained by TGA at atmospheric pressure. Among all sorbents, TEPA impregnated E-SBA-15 sorbents possess the highest CO₂ sorption capacity (1.60 mmol CO₂ g^-1_sorbent) under ambient pressure using dry 15% CO₂. However, TEPA/TIP incorporated E-SBA-15 sorbents exhibit enhanced durability during repeated sorption-desorption cycles compared to the above-mentioned sorbents. This significant enhancement in the stability of CO₂ sorption-desorption process is most likely due to the decreased decomposition/leaching of TEPA which is restricted via the steric effect of TIP. These synthesized sorbents from inexpensive resources (agricultural waste) exhibit good sorbent capacity and surpassing regenerability, revealing a promising CO₂ sorbent for the cost-effective applications in a cyclic adsorption process.