Hydrophobic Silica Gel Modified by TMCS/PTES: Preparation and Its n‑Pentane/n‑Hexane Adsorption Performance

doi:10.15541/jim20260129

Abstract

Abstract: Competitive adsorption induced by water vapor severely restricts the application of silica gel under high-humidity conditions. In this study, silica gel was hydrophobically modified using trimethylchlorosilane (TMCS) and phenyltriethoxysilane (PTES). Physicochemical properties of the synthesized materials were evaluated by various characterization techniques. Additionally, adsorption performance towards n-pentane and n-hexane was assessed by dynamic adsorption equilibrium experiments coupled with in-situ infrared spectroscopy. Results indicate that the modified silica gels exhibit significantly enhanced moisture resistance. TMCS modification is highly concentration-dependent, and pore structural parameters of the modified silica gel remain constant after reaching the threshold concentration. The optimal sample modified by 17% (in volume) TMCS (SG-17%-TMCS) achieves a contact angle of 130.8° and retains 96.6% of its total pore volume. Conversely, PTES modification depends on multiple interacting factors, with pH and temperature exerting the most significant impacts. The optimal PTES-modified (100%, in volume) sample exhibits a contact angle of 137.4°, but its specific surface area and pore volume decrease markedly to 153 m²/g and 0.061 cm³/g. Adsorption tests reveal that the TMCS-modified silica gel maintains high adsorption selectivity for n‑pentane and n‑hexane even under high-humidity conditions, and its performance advantage expands further as humidity increases. After five adsorption-desorption cycles under high humidity, the capacity retention rates for n-pentane and n-hexane remain at approximately 90% and 92%. In contrast, adsorption capacity of the PTES-modified silica gel decreases due to severe limitations imposed by its altered pore structure and pronounced molecular steric hindrance. This study elucidates how modification conditions affect the hydrophobicity of TMCS- and PTES-modified silica gels, alongside their consequent adsorption behaviors towards n‑pentane and n‑hexane. These findings provide a solid theoretical reference for the efficient removal and recovery of n‑pentane and n‑hexane from high-humidity exhaust gases.

Key words: hydrophobic modification, pore structure regulation, steric hindrance, competitive adsorption

CLC Number:

TQ424

LUO Yuhao, FENG Tingxue, YANG Lihui, DONG Yanchao, LIU Na, HUANG Xueli, HUANG He. Hydrophobic Silica Gel Modified by TMCS/PTES: Preparation and Its n‑Pentane/n‑Hexane Adsorption Performance[J]. Journal of Inorganic Materials, DOI: 10.15541/jim20260129.

References

[1] LI X Q, ZHANG L, YANG Z Q,et al. Adsorption materials for volatile organic compounds (VOCs) and the key factors for VOCs adsorption process: a review. Separation and Purification Technology, 2020, 235: 116213.
[2] HANG W L, SUN J X, ZHAO R H,et al. Selective adsorption of VOCs/water vapor on activated carbon: the role of adsorbent and VOC molecular polarity. Separations, 2025, 12(4): 86.
[3] WU L X, ZHU Y, YUAN J,et al. Advances in adsorption, absorption, and catalytic materials for VOCs generated in typical industries. Energies, 2024, 17(8): 1861.
[4] GAN G Q, FAN S Y, LI X Y,et al. Adsorption and membrane separation for removal and recovery of volatile organic compounds. Journal of Environmental Sciences, 2023, 123: 96.
[5] LI J, CAI J X, LIU X,et al. Design and synthesis of a water-resistant mesoporous silica gel for the VOC adsorption-desorption treatment. Industrial & Engineering Chemistry Research, 2023, 62(48): 20833.
[6] DENG W X, CAI R, YANG H,et al. Hydrophobic organic hybrid silica gels with high adsorption selectivity for fluorocarbon solvents. ACS Omega, 2025, 10(20): 20784.
[7] LU H F, CAO J J, ZHOU Y,et al. Novel hydrophobic PDVB/R-SiO₂ for adsorption of volatile organic compounds from highly humid gas stream. Journal of Hazardous Materials, 2013, 262: 83.
[8] LIU S, PENG Y, CHEN J J,et al. Engineering surface functional groups on mesoporous silica: towards a humidity-resistant hydrophobic adsorbent. Journal of Materials Chemistry A, 2018, 6(28): 13769.
[9] HUANG W Q, XU J X, TANG B,et al. Adsorption performance of hydrophobically modified silica gel for the vapors of n-hexane and water. Adsorption Science & Technology, 2018, 36(3/4): 888.
[10] WANG H N, YANG Q Q, ZHANG Z H,et al. Organosiliceous nanotubes with enhanced hydrophobicity and VOCs adsorption performance under dry and humid conditions. Journal of Porous Materials, 2020, 27(4): 1179.
[11] WANG H N, TANG M, HAN L,et al. Synthesis of hollow organosiliceous spheres for volatile organic compound removal. Journal of Materials Chemistry A, 2014, 2(45): 19298.
[12] WANG H N, WANG T, HAN L,et al. VOC adsorption and desorption behavior of hydrophobic, functionalized SBA-15. Journal of Materials Research, 2016, 31(4): 516.
[13] MAHADIK D B, RAO A V, RAO A P,et al. Effect of concentration of trimethylchlorosilane (TMCS) and hexamethyldisilazane (HMDZ) silylating agents on surface free energy of silica aerogels. Journal of Colloid and Interface Science, 2011, 356(1): 298.
[14] MILLOT Y, HERVIER A, AYARI J,et al. Revisiting alkoxysilane assembly on silica surfaces: grafting versus homo-condensation in solution. Journal of the American Chemical Society, 2023, 145(12): 6671.
[15] KUNIYOSHI M, TAKAHASHI M, TOKUDA Y,et al. Hydrolysis and polycondensation of acid-catalyzed phenyltriethoxysilane (PhTES). Journal of Sol-Gel Science and Technology, 2006, 39(2): 175.
[16] WU X X, ZHANG W, LI Z,et al. Effects of various methylchlorosilanes on physicochemical properties of ambient pressure dried silica aerogels. Journal of Nanoparticle Research, 2019, 21(11): 234.
[17] MALFAIT W J, ZHAO S Y, VEREL R,et al. Surface chemistry of hydrophobic silica aerogels. Chemistry of Materials, 2015, 27(19): 6737.
[18] CROISSANT J G, FATIEIEV Y, KHASHAB N M.Degradability and clearance of silicon, organosilica, silsesquioxane, silica mixed oxide, and mesoporous silica nanoparticles.Advanced Materials, 2017, 29(9): 1604634.
[19] VANSANT E F, VAN DER VOORT P, VRANCKEN K C. Characterization and chemical modification of the silica surface. Amsterdam: Elsevier, 1995.
[20] GONTHIER J, RILLING T, SCOPPOLA E,et al. In operando μCT imaging of silylated silica aerogels during ambient pressure drying and spring-back. Chemistry of Materials, 2023, 35(18): 7683.
[21] CHAKRABORTY S, PISAL A A, KOTHARI V K,et al. Synthesis and characterization of fibre reinforced silica aerogel blankets for thermal protection. Advances in Materials Science and Engineering, 2017, 2017(1): 1.
[22] WU Z, ZHANG L, LI J,et al. Organic—inorganic hybridization for the synthesis of robust in situ hydrophobic polypropylsilsesquioxane aerogels with fast oil absorption properties. RSC Advances, 2018, 8(11): 5695.
[23] TANHEITAFINO S, SHOFIYANI A, SASRI R,et al. Synthesis and characterization of trimethylchlorosilane-modified silica xerogel. Jurnal Kimia Sains dan Aplikasi, 2020, 23(7): 249.
[24] ZEMKE F, GONTHIER J, SCOPPOLA E,et al. Origin of the springback effect in ambient-pressure-dried silica aerogels: the effect of surface silylation. Gels, 2023, 9(2): 160.
[25] BLACHNIO M, ZIENKIEWICZ-STRZALKA M, DERYLO-MARCZEWSKA A,et al. Chitosan-silica composites for adsorption application in the treatment of water and wastewater from anionic dyes. International Journal of Molecular Sciences, 2023, 24(14): 11818.
[26] YANG Q H, YANG J, LIU J,et al. Synthesis and characterization of phosphonic acid functionalized organosilicas with bimodal nanostructure. Chemistry of Materials, 2005, 17(11): 3019.
[27] ÇOK S S, GIZLI N.Hydrophobic silica aerogels synthesized in ambient conditions by preserving the pore structurevia two-step silylation. Ceramics International, 2020, 46(17): 27789.
[28] GOKULAKRISHNAN N, KARBOWIAK T, BELLAT J P,et al. Improved hydrophobicity of inorganic-organic hybrid mesoporous silica with cage-like pores. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2013, 421: 34.
[29] CHEN J H, LIU N S, WANG Y Z,et al. Aminated spherical SiO₂ synthesized from fly ash and its application for Pb²+ and Cu²+ sorption. Water, 2024, 16(8): 1149.
[30] SAKPAL T, KUMAR A, KAMBLE S P,et al. Carbon dioxide capture using amine functionalized silica gel. Indian Journal of Chemistry Section A-Inorganic Bio-Inorganic Physical Theoretical & Analytical Chemistry, 2012, 51(9): 1214.
[31] BAE J Y, JANG S G, CHO J,et al. Amine-functionalized mesoporous silica for efficient CO₂ capture: stability, performance, and industrial feasibility. International Journal of Molecular Sciences, 2025, 26(9): 4313.
[32] CHARMAS B, KUCIO K, SYDORCHUK V,et al. Characterization of multimodal silicas using TG/DTG/DTA, Q-TG, and DSC methods. Colloids and Interfaces, 2019, 3(1): 6.
[33] JITIANU A, LAMMERS K, ARBUCKLE-KIEL G A,et al. Thermal analysis of organically modified siloxane melting gels. Journal of Thermal Analysis and Calorimetry, 2012, 107(3): 1039.
[34] RAHMAT N, SADON N, YUSOF M A.Thermogravimetric analysis (TGA) profile at different calcination conditions for synthesis of PTES-SBA-15.American Journal of Applied Sciences, 2017, 14(10): 938.
[35] CHOMA J, SZCZĘŚNIAK B, KAPUSTA A,et al. A concise review on porous adsorbents for benzene and other volatile organic compounds. Molecules, 2024, 29(23): 5677.
[36] HUNTER-SELLARS E, TEE J J, PARKIN I P,et al. Adsorption of volatile organic compounds by industrial porous materials: impact of relative humidity. Microporous and Mesoporous Materials, 2020, 298: 110090.
[37] GUO J X, HE S L, LIU X X,et al. Hydrophobic modification of walnut shell biomass-derived porous carbon for the adsorption of VOCs at high humidity. Chemical Engineering Journal, 2024, 488: 150792.
[38] LI Z R, JIN Y Q, CHEN T,et al. Trimethylchlorosilane modified activated carbon for the adsorption of VOCs at high humidity. Separation and Purification Technology, 2021, 272: 118659.
[39] FU L P, ZHU J H, HUANG W Q,et al. Preparation of nano-porous carbon-silica composites and its adsorption capacity to volatile organic compounds. Processes, 2020, 8(3): 372.