Capturing nitrosamines in aqueous solution by composited super-hydrophobic silicic xerogel

Abstract

Super-hydrophobic silicic xerogel (SG) was prepared from methyltrimethoxysilane (MTMS) and dimethyldimethoxysilane (DMDMS), and the optimized MTMS to DMDMS molar ratio was determined to be 3/2. To fabricate new effective nitrosamines sorbent in tobacco extract solution, SG was modified by epitaxial growth of mesoporous silica to form the coated composite named as MSGx with a large surface area (152-208 m 2 g -1 ) and pore volume (0.133-0.162 mLg -1 ), and the new sorbent could capture 54~59% of nitrosamines in tobacco solution, superior to zeolite and mesoporous silica. 1 IntroductionNitrosamines are deemed to be the widespread carcinogens characterized with N-nitroso group, including volatile nitrosamines (VNA), non-volatile nitrosamines and tobacco specific nitrosamines (TSNA). TSNA are a group of carcinogens found only in tobacco products. They can cause various cancers or tumors in laboratorial animals and possess the potential carcinogenicity to human though their content in tobacco and tobacco products is in the range of μg g -1 (ppm) or ng g -1 (ppb). Among various efforts controlling the pollution of nitrosamines in environment, one strategy is to adsorb TSNA in tobacco extract solution in order to reduce the injurant at source [1][2][3][4], and effective sorbent is the key. TSNA are oily molecules and their adsorption in tobacco extract solution is inevitably interfered by water [1], so the favorable separation performance between water and oil is vital. Nowadays, many porous hydrophobic materials have been extensively studied [5], including carbon based materials [6], metal oxide nanowires [7,8], biological nanometer fiber [9,10], organic polymer [11,12] and macroporous aerogel [13][14][15], etc. However, complex synthesis and high cost hinders their actual application.Recently, hydrophobic polymethylsilsesquioxane (PMSQ) materials have been synthesized by crosslinking polymerization of methyltrimethoxysilane (MTMS), in which mesopores and macropore could be produced through phase separation [16,17].Also, flexible marshmallow-like silicic aerogel/xerogel was synthesized from MTMS and dimethyldimethoxysilane (DMDMS) co-precursor [18]. This aerogel is expected to

Fabricating hydrophobic nanoparticles within mesoporous channel of silica for efficient TSNA removal

“…Compared with the SG modified with epitaxial grew mesoporous silica [16], the mesoporous silica coated with hydrophobic nanoparticles has some advantages for liquid adsorption of TSNA.…”

“…And their weight increment was carefully measured ( Table 2). The residual solution was also heated at 353 K for 24 h to give the solid sample named as SG' [16].…”

“…Two solutions were mixed and enriched in rotary evaporator at 293 K with the rate of 90 r min -1 to reach the density of 1.2-1.22 g cm -3 . The obtained tobacco extract solution was stored at 277 K. 50 mg granular adsorbent was added into 10 mL tobacco extract solution in test tube and performed under dynamic and dark condition at 303 K for 1 h. Thereafter it was centrifuged at 3000 rpm for 10 min to separate solid and solution [8,16].…”

“…6). Suitable hydrophobicity enables sorbent to suppress the competitive adsorption of water [9,16], but makes the sorbent immersed in rather than floated on tobacco extract solution so that it can contact fully with TSNA.…”

“…Micron-sized super hydrophobic silicic xerogel (SG) has been simply synthesized with 3 methyltrimethoxysilane (MTMS) and dimethyldimethoxysilane (DMDMS) [15], and the SG was modified by epitaxial growth of mesoporous silica to prepare a new capturer of N-nitrosamines in tobacco solution [16]. However, SG has a very small specific surface area (4 m 2 g -1 ) though it owns an outstanding liquid adsorption performance in aqueous solution.…”