Modification of MCM-41 by Surface Silylation with Trimethylchlorosilane and Adsorption Study

Abstract

Siliceous MCM-41 samples were modified by silylation using trimethylchlorosilane (TMCS). The surface coverage of functional groups was studied systematically in this work. The role of surface silanol groups during modification was evaluated using techniques of FTIR and 29Si CP/MAS NMR. Adsorption of water and benzene on samples of various hydrophobicities was measured and compared. It was found that the maximum degree of surface attachments of trimethylsilyl (TMS) groups was about 85%, corresponding to the density of TMS groups of 1.9 per nm2. The degree of silylation is found to linearly increase with increasing pre-outgassing temperature prior to silylation. A few types of silanol groups exist on MCM-41 surfaces, among which both free and geminal ones are responsible for active silylation. Results of water adsorption show that aluminosilicate MCM-41 materials are more or less hydrophilic, giving a type IV isotherm, similar to that of nitrogen adsorption, whereas siliceous MCM-41 are hydrophobic, exhibiting a type V adsorption isotherm. The fully silylated Si−MCM-41 samples are more hydrophobic, giving a type III adsorption isotherm. Benzene adsorption on all MCM-41 samples shows type IV isotherms regardless of the surface chemistry. Capillary condensation occurs at a higher relative pressure for the silylated MCM-41 than that for the unsilylated sample, though the pore diameter was found reduced markedly by silylation. This is thought attributed to the diffusion constriction posed by the attached TMS groups. The results show that the surface chemistry plays an important role in water adsorption, whereas benzene adsorption is predominantly determined by the pore geometry of MCM-41.

Enhancement of Gaseous BTEX Adsorption on RH-MCM-41 by Chlorosilanes

“…Its pore diameter is ranged between 20-30 Å and its surface area is about 700-900 m 2 g -1 (Chiarakorn et al 2007). This material has been introduced to be an alternative adsorbent for the adsorption of various air pollutants, supporting material for catalytic reaction, ion exchange media and filter (Appaturiet al 2012;Artklaet al 2009;Beck et al 1992;Chumeeet al 2009;Klankawet al 2012;Tong-On et al 2009;Wantalaet al 2010;Yoshitakeet al 2002;Zhao & Lu 1998). Nevertheless, it was reported that the hydrophilicity of surface caused low adsorbability when MCM-41 is applied for non-polar volatile organic compounds (VOCs) adsorption under high relative humidity condition (Branton et al 1999;Idris et al 2010;Ohashi et al 1999).…”

“…To resolve this drawback, the surface modification via silylation has been introduced. Generally, the silylation is a well-known technique for surface tailoring on several materials containing silanol groups such as MCM-41, MCM-48, SBA-1 and silica gels (Deschner et al 2010;Koyano et al 1997;Lin et al 2008;Yokoi et al 2004;Yuan et al 2006;Zhao & Lu 1998). The common reagents used for the silylation are organosilanes.…”

“…However, there are few studies focusing on the silylating techniques and effects of silane functional group on the improvement of hydrophobic surface. For example, Zhao and Lu (1998) modified by trimethylchlorosilane (TMCS) and claimed that the modified MCM-41 was a promising adsorbent for volatile organic compound removal. The study of Patel et al (2011) also confirmed the enhancement of benzene adsorption in aqueous solution by silylated (Patel et al 2011).…”

Physicochemical Properties of CuO2 (acac)2 Supported on Functionalized MCM41 Containing Thiourea Ligand

“…Zhao and Lu* (1998) was studied the modification of MCM41 by surface silylation with trimethylchlorosilane and adsorption study. They found the surface chemistry of MCM41 can be effectively modified to be more hydrophobic by chemical attachment of organic species and be an effective technique in selective adsorbents for the removal of organic compounds from streams or wastewater [5].…”

Solid state, dry zinc/MCM-41/air cell as relative humidity sensor

“…The MCM-41 surface structure is covered with silanol groups (Si-OH) formed during the synthesis of the material [9,10]. The hydrophilic characteristic of the material is attributed to the existence of these Si-OH groups.…”