Surface Properties of Synthesized Nanoporous Carbon and Silica Matrices

Summary

Here we report the synthesis and characterization of ordered nanoporous carbon (with a 4.6 nm pore size) and SBA-15 (with a 5.3 nm pore size). The work describes the surface and textural properties of nanoporous molecular sieves, their wettability, and the melting behavior of D₂O confined in the materials.

Abstract

In this work, we report the synthesis and characterization of ordered nanoporous carbon material (also called ordered mesoporous carbon material [OMC]) with a 4.6 nm pore size, and ordered silica porous matrix, SBA-15, with a 5.3 nm pore size. This work describes the surface properties of nanoporous molecular sieves, their wettability, and the melting behavior of D₂O confined in the differently ordered porous materials with similar pore sizes. For this purpose, OMC and SBA-15 with highly ordered nanoporous structures are synthesized via impregnation of the silica matrix by applying a carbon precursor and by the sol-gel method, respectively. The porous structure of investigated systems is characterized by an N₂ adsorption-desorption analysis at 77 K. To determine the electrochemical character of the surface of synthesized materials, potentiometric titration measurements are conducted; the obtained results for OMC shows a significant pH_pzc shift toward the higher values of pH, relative to SBA-15. This suggests that investigated OMC has surface properties related to oxygen-based functional groups. To describe the surface properties of the materials, the contact angles of liquids penetrating the studied porous beds are also determined. The capillary rise method has confirmed the increased wettability of the silica walls relative to the carbon walls and an influence of the pore roughness on the fluid/wall interactions, which is much more pronounced for silica than for carbon mesopores. We have also studied the melting behavior of D₂O confined in OMC and SBA-15 by applying the dielectric method. The results show that the depression of the melting temperature of D₂O in the pores of OMC is about 15 K higher relative to the depression of the melting temperature in SBA-15 pores with a comparable 5 nm size. This is caused by the influence of adsorbate/adsorbent interactions of the studied matrices.

Introduction

In 1992, ordered nanoporous silica materials were obtained for the first time, using an organic template; since then, a large number of publications related to different aspects of these structures, synthetic methods, the investigation of their properties, their modifications, and different applications have appeared in the literature^1,2,3. The interest in SBA-15 nanoporous silica matrix⁴ is due to their unique quality: a high surface area, wide pores with a uniform pore size distribution, and good chemical and mechanical properties. Nanoporous silica ....

Protocol

1. Preparation of the OMC Materials

1. Synthesis of a silica matrix as OMC precursor
   1. Prepare 360 mL of 1.6 M HCl by adding 50 mL of HCl (36% - 38%) in a 500 mL round-bottom flask and, then, adding 310 mL of ultrapure water (resistivity of 18.2 MΩ·cm).
   2. To that, add 10 g of PE 10500 polymer (6.500 g/mol).
   3. Place the flask in an ultrasonic bath. Heat the solution to 35 °C and stir it until the solid polymer is completely dissolved, making a homogeneous mixture.
   4. Add 10 g of 1,3,5-trimethylbenzene to the flask and stir the content (at a stirring rate of 220 rpm) by maintaining it at 35 °C in the water ba....

Results

To characterize the porous structure of the investigated samples of OMC and SBA-15, the N₂ adsorption-desorption isotherms were recorded at 77 K. The experimental N₂ gas adsorption-desorption isotherms characterizing the investigated systems, as well as the pore size distributions (PSD) obtained from the adsorption and desorption data, are presented in Figure 1A-D. The position of the inflection points on the sorption is.......

Discussion

The critical steps during the preparation of the ordered mesoporous carbon material include the preparation of the ordered mesoporous silica materials as the template with well-defined structural properties that affect the properties of the final materials and a tempering/carbonization step under a nitrogen atmosphere. The modification of the typical method of preparation of the mesoporous ordered silicates with cylindrical pores²⁸ concerns the application of an untypical structure-directing agent.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
1,3,5-trimethylbenzene	Sigma-Aldrich, Poland	M7200 Sigma-Aldrich	Mesitylene, also known as 1,3,5-trimethylbenzene, reagent grade, assay: 98%.
anhydrous ethanol	POCH, Avantor Performance Materials Poland S.A.	396480111	Assay, min. 99.8 %, analysis-pur (a.p.)
ASAP 2020. Accelerated Surface Area and Porosimetry System	Micromeritics Instrument Corporation, Norcross, GA, USA		Samples were outgassed before analysis at 120 oC for 24 hours in degas port of analyzer. The dead space volume was measured for calibration on experimental measurement using helium as a adsorbate.
Automatic burette Dosimat 665	Metrohm, Switzerland		The surface charge properties were experimentally determined by potentiometric titration of the suspension at constant temperature 20°C maintained by the thermostatic device. Prior to potentiometric titration measurements, the solid samples were dried by 24 hours at 120 oC. The initial pH was established by addition of 0.3 cm3 of 0.2 mol/L HCl. T The 0.1 mol/L NaOH solution was used as a titrant, added gradually by using automatic burette.
Digital pH-meter pHm-240	Radiometer, Copenhagen		Device coupled with automatic burette
ethyl alcohol	POCH, Avantor Performance Materials Poland S.A.	396420420	Assay, min. 96 %.analysis-pur (a.p.)
glucose	POCH, Avantor Performance Materials Poland S.A.	459560448	assay 99.5%
Hydrochloric acid	POCH, Avantor Performance Materials Poland S.A.	575283115	Hydrochloric acid, 35 - 38% analysis-pur (a.p.)
HOPG graphite substrate	Spi Supplies	LOT#1170906	HOPG SPI-2 Grade, 20x20x1 mm
Impedance analyzer Solartron 1260	Solartron
Pluronic PE 6400 polymer	BASF (Polska)		(EO13PO70EO13)
Pluronic PE10500	BASF Canada Inc.		Molar mass 6500 g/mol
potassium hydroxide	Sigma-Aldrich, Poland	P5958 Sigma-Aldrich	BioXtra, ≥85% KOH basis
SEM microscope	JEOL JSM-7001F		Scanning Electron Microscope with EDS detector
Sigma Force Tensiometer 701	KSV, Sigma701, Biolin Scientific		force tensiometer
Sulfuric acid (VI)	POCH, Avantor Performance Materials Poland S.A.	575000115
surface glass type KS 324 Kavalier	Megan Poland		80 % of SiO2 , 11% of Na2O and 9% of CaO
Tecnai G2 T20 X-TWIN	FEI, USA		Transmission Electron Microscope with EDX detector.
TEM microscope	JEOL JEM-1400
temperature controller ITC503	Oxford Instruments
Tetraethylorthosilicate	Sigma-Aldrich, Poland	131903	Tetraethyl silicate, TEOS, reagent grade, assay 98%
Ultrapure water	Millipore, Merck KGaA, Darmstadt, Germany	SIMSV0001	Simplicity Water Purification SystemUltrapure Water: 18.2 MegOhm·cm, TOC: <5 ppb