Heteroatom Sr doped MCM-41 molecular sieve for VOC adsorption: Study of the surface functionalization and adsorption performance

Abstract

Volatile organic compounds (VOCs) are recognized as greater adverse effects on both environment and human health, and adsorption is a simple and effective method. Ordered mesoporous MCM-41 molecular sieve were functionalized with heteroatom Sr to change the pore size and surface property by one-step hydrothermal method and adsorption performance for toluene (C7H8) and formaldehyde (CH2O) were investigated. It is found that Sr doped MCM-41 achieves high static adsorption capacities of 534 mg/g for C7H8 and 388 mg/g for CH2O. The dynamic adsorption of C7H8 follows the Langmuir model over Sr doped and undoped MCM-41 under different process conditions, but the dynamic adsorption capacity is only 21 ∼ 99 mg/g. Sr doped MCM-41 maintains a typical pore structure of MCM-41, with some Sr entering the skeleton to form Sr-O-Si bonds. Sr-M−130 has 857 m2/g of SBET and 0.86 cm3/g of Vtotal, but high hydrothermal temperature (150 °C) causes the sintering of MCM-41 structure. Sr doping decreases surface acidity of MCM-41 and increases surface hydroxyl groups (Si-OH). The kinetic diameter and polarity of the adsorbate cause differences in adsorption performance of Sr doped or undoped MCM-41, meaning that the adsorption behavior of non-polar C7H8 mainly depends on surface area and micropore volume while that of polar CH2O is related to the number of ultra-micropore (<1 nm) and forms chemical adsorption of C = O with Si-OH by hydrogen bonds.