Showing papers on "Silica gel published in 2020"

Surface characterization of carbonated recycled concrete fines and its effect on the rheology, hydration and strength development of cement paste

Abstract: Carbonation treatment can effectively improve the performance of recycled concrete aggregate and fines due to the reactions of CO2 with CH and C–S–H gel of cement paste. To better understand the mechanisms involved in the performance improvement, the surface properties of carbonated recycled cement paste powder (CRP) and its effect on the rheology, hydration and strength development of cement paste was studied. The results showed that during the carbonation, the surface of CRP was covered by a layer of amorphous silica gel. The generated CaCO3 was wrapt by the silica gel and seldom exposed. The silica layer led to the poor flowability of CRP-cement paste due to that the silica gel on the surface of CRP has a strong affinity for H2O. During the very early hydration, the silica gel dissolved and then CaCO3 was exposed. CaCO3 is capable of chemically absorbing Ca2+, which facilitated the nucleation of C–S–H nuclei and stabilized the C–S–H phase. As a result, the C–S–H grew densely, uniformly and perpendicularly on the surface of CRP. In addition, the chemically absorbing Ca2+ enabled the chemical bond to be formed between CaCO3 and C–S–H. Due to increased C–S–H resulted from reactions of silica gel with CH at the interface and the stronger bond formed between CaCO3 and C–S–H, the interface between CRP and hydration products was much stronger than that between recycled cement paste powder (RP) and hydration products.

Experimental study on thermophysical and porous properties of silica gels

Abstract: Porous silica gel (SG) has been extensively used as an adsorbent in adsorption cooling, dehumidification, and desalination applications. Specific heat capacity (Cp) of SG with temperature variation is not experimentally investigated yet. Therefore, this study focuses on the experimental investigation of Cp along with the porous properties of six types of different particle size silica gels. Adsorbed phase Cp of SG is also determined with 10% and 20% water uptake. The experimental Cp is measured within 30 to 100 °C, and the Cp values vary from 0.8 to 1.10 kJ kg–1 K–1 in the measurement temperature range. RD silica gel of the smallest particle size shows the highest Cp values, whereas indicator type silica gel shows the lowest Cp. The Green-Perry model fits well with the experimental Cp data. The porosity analysis shows that RD silica gels of large particle size (D > 0.7 mm) possess the highest surface area (≈ 770 m2/g), and type B silica gels have the largest pore volume (≈ 0.8 cm3/g) along with larger mesopores. A relationship between pore volume and Cp is also reported. The measured data are novel and essential for rigorous performance prediction of adsorption cooling, dehumidification, and desalination systems.

A Generalized Procedure for the Production of High-Grade, Porous Biogenic Silica

Abstract: Biomasses are a sustainable, CO2 neutral source used in biorefining. Si-accumulating plants can be used for the production of biogenic silica in a biomass valorisation process. This study examines the production of high-grade porous silica from different plant parts like rice, oat and spelt husk, rice straw and horsetail using a generalized procedure for all. The silica materials were produced by a 2-step method. First, the biomasses were pretreated with water and then subjected to leaching with citric acid. As a second step, a sequential burning program was applied. The characterization of the untreated biomasses was carried out by X-ray fluorescence (XRF) analysis and thermal analysis (TG–DTA). The biogenic silica samples were subjected to XRF, carbon content analysis, low temperature nitrogen physisorption, scanning and transmission electron microscopy as well as X-ray diffraction. Independent of the initial composition of the plant part, the established method resulted in amorphous, biogenic silica with up to 99.7% purity, mesopores between 2 and 30 nm with pore volumes of up to 0.46 cm3 g−1 and specific surfaces of up to 303 m2 g−1. It was shown that the generalized method developed works not only for all the biomasses separately, but also if treated in the same batch. The produced biogenic silica can be considered as sustainable alternative to other silica products like precipitated silica, silica gel and fumed silica which are produced in highly energy consuming processes.

Preparation of hydrophobic hierarchical pore carbon-silica composite and its adsorption performance toward volatile organic compounds.

Abstract: Carbon-silica materials with hierarchical pores consisting of micropores and mesopores were prepared by introducing nanocarbon microspheres derived from biomass sugar into silica gel channels in a hydrothermal environment. The physicochemical properties of the materials were characterized by nitrogen physical adsorption (BET), scanning electron microscopy (SEM), and thermogravimetric (TG), and the adsorption properties of various organic waste gases were investigated. The results showed that microporous carbon materials were introduced successfully into the silica gel channels, thus showing the high adsorption capacity of activated carbon in high humidity organic waste gas, and the high stability and mechanical strength of the silica gel. The dynamic adsorption behavior confirmed that the carbon-silica material had excellent adsorption capacity for different volatile organic compounds (VOCs). Furthermore, the carbon-silica material exhibited excellent desorption characteristics: adsorbed toluene was completely desorbed at 150°C, thereby showing superior regeneration characteristics. Both features were attributed to the formation of hierarchical pores.

Cu(II)-Hydrazide Coordination Compound Supported on Silica Gel as an Efficient and Recyclable Heterogeneous Catalyst for Green Click Synthesis of β-Hydroxy-1,2,3-triazoles in Water.

Abstract: A hydrazone ligand, (E)-6-(2-((2-hydroxynaphthalen-1-yl)methylene)hydrazinyl)nicotinohydrazide (H2L), was synthesized and characterized by spectroscopic methods. The reaction of H2L with CuCl2·2H2O in methanol gave Cu(II) coordination compound, [Cu(HL')(Cl)]·CH3OH (1), which was characterized by elemental analysis and spectroscopic methods (Fourier transform infrared (FT-IR) and UV-vis). The structure of 1 was also determined by single-crystal X-ray analysis. Structural studies confirmed the formation of esteric group during the synthesis of 1. Compound 1 was immobilized on 3-aminopropyltriethoxysilane (APTS)-functionalized silica gel through the amidification reaction and the obtained heterogeneous coordination compound was utilized as a catalyst for the three-component azide-epoxide-alkyne cycloaddition reaction in water as a green solvent. The structural properties of the heterogeneous catalyst were characterized by a combination of FT-IR, UV-vis, thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and energy-dispersive spectrometry (EDS) analyses. The effect of the amount of catalyst and temperature on the cycloaddition reaction was studied, and the obtained 1,2,3-triazoles were characterized by spectroscopic studies and single-crystal X-ray analysis. The catalytic investigations revealed that this catalytic system has high activity in the synthesis of β-hydroxy-1,2,3-triazoles. It was also found that the aromatic and aliphatic substituents on the alkyne and epoxide together with the reaction temperature have considerable effects on the activity and regioselectivity of this catalytic system.

Characterization of silica gel-based composites for adsorption cooling applications

Abstract: In this study, adsorption characteristics of water vapor onto several silica gel-based composites have been investigated experimentally. Adsorbent samples under investigation are silica gel powder (SGP), 98wt% SGP with 2wt% Polyvinylpyrrolidone (PVP) binder, 93wt% SGP, 2wt% PVP binder with 5wt% EG500 and 93wt% SGP, 2wt% PVP binder with 5wt% EG100. The three composite samples have been named as (S1-PVP), (S2-EG500) and (S3-EG100), respectively. Porous properties and thermal conductivity of S2-EG500 and S3-EG100 have been measured and compared with that of SGP. Experimental results showed that S2-EG500 has higher effect on enhancing the thermal conductivity of the composites where its thermal conductivity reached about 2.8 times that of SGP whilst thermal conductivity of S3-EGP100 is found to be about 2.3 times that of SGP. Adsorption isotherms of composite samples/water pairs have been measured gravimetrically at 30, 50 and 70 °C. The Toth and Dubinin-Astakhov (D-A) equations have been used to fit adsorption uptake measurements, Toth equation shows a better fitting. Isosteric heat of adsorption of the studied pairs have been extracted from the experimental measurements using Clausius-Clapeyron equation. The Linear Driving Force (LDF) model is found to be able to present adsorption kinetics of the studied pairs through a good agreement with the experimental data.

Desulfurization Kinetics and Regeneration of Silica Gel-Supported TiO2 Extrudates for Reactive Adsorptive Desulfurization of Real Diesel

Abstract: Desulfurization kinetics and regeneration of silica gel-supported TiO2 extrudates were explored for reactive adsorptive desulfurization (RADS) process in this work. RADS using TiO2/SiO2 extrudates ...

Silica Gel as a Selective Adsorbent for Biogas Drying and Upgrading

Abstract: Biogas upgrading (CO2 removal) is an essential step towards the production of bio-methane. Bio-methane can be transported in existing natural gas grids or used directly as a vehicular fuel with pro...

Extraction of Silica from Bengkulu Beach Sand using Alkali Fusion Method

Abstract: Silica is one of the potential minerals to be developed and applied in various industrial fields. High purity of silica can be obtained by utilizing natural materials such as beach sand. In this research the solid-liquid extraction (leaching) method was used in three main steps. Bengkulu beach sand as precursors reacted with NaOH (alkaline fusion) at 95°C to form Na 2 SiO 3 , then addition of HCl to form Si(OH) 4 , and drying the silica gel becomes SiO 2 . Based on the initial content analysis in Bengkulu sand contained 69.87% silica and other compounds with a lower percentage. The extracted silica was characterized using XRF and the purity of silica increase to 97.3%. The XRD characterization results showed that the silica formed was in the amorphous phase. Si-O-Si and Si-O bonds which are characteristics of SiO 2 were identified in the FT-IR spectrum with absorption bands of 798.8 cm -1 and 475.1 cm -1 respectively.

Spherical amine grafted silica aerogels for CO2 capture

Abstract: The objective of this research was to develop a novel spherical amine grafted silica aerogel for CO2 capture. A spherical silica gel was synthesized by dropping a sodium silicate based silica sol into an oil bath. Amine grafting was achieved by bonding 3-aminopropyltriethoxysilane onto the framework of the silica gel. The spherical amine grafted silica gels were dried using vacuum drying to prepare the spherical amine grafted silica aerogels (SASAs). The synthetic mechanism of the SASAs was proposed. The structures and the CO2 adsorption performances of SASAs were researched. The amine loading of the SASAs increased with the grafting time, however, the specific surface area and pore volume sharply decreased owing to the blockage of the pore space. Excess amine loading led to the decrease of the CO2 adsorption capacity. The optimal CO2 adsorption capacity was 1.56 mmol g−1 with dry 1% CO2 and at 35 °C. This work provides a low-cost and environmentally friendly way to design a capable and regenerable adsorbent material.

New prominent lithium bromide-based composites for thermal energy storage

Abstract: Four different LiBr-based composite materials have been synthesized with silica gel or activated carbon as host porous matrix. High salt contents were incorporated in these composites: 37 wt% and 53 wt% for silica gel/LiBr composites; 32 wt% and 42 wt% for activated carbon/LiBr composites. The performance of these materials in conditions representative of the applications of sanitary hot water production and space heating demonstrates the very high potential of the silica gel/LiBr 53 wt% composite. It exhibits an unprecedented energy storage density of 261 kWh/m3 (adsorption temperature: 30 °C, desorption temperature: 80 °C and water vapor pressure of 12.5 mbar) and of 381 kWh/m3 when the desorption temperature reaches 120 °C. This promising material presents a good composition homogeneity, high water uptakes between 10 °C and 80 °C, and no measurable loss of sorption properties upon 10 cycles. This composite was tested in an open type laboratory set-up to complete its analysis for heat storage applications, at the scale of 200 g. The best energy storage density reached during 3 h 26 min was as high as 246 kWh/m³ (adsorption temperature: ~29 °C and water vapor pressure of ~12.5 mbar).