Clay-Based Porous Adsorption/Catalysis Materials For Purification Performance Of Typical Volatile Organic Compounds

With increasing aggravation of indoor air pollution, the removal of volatile organic compounds (VOCs) is a key issue in the field of Environmental Science & Engineering. Clay-based materials have been developed to remove VOCs due to their excellent properties of adsorbents and/or catalysts. In this work, porous clay heterostructures (PCHs) and clay-based anatase titanium dioxide (TiO2) catalyst were synthesized from organic bentonites or disused organic bentonites. The removal performances and the underlying mechanisms of VOCs by adsorption on PCHs or by photocatalystic degradation with clay-based TiO2 were examined and related with the physicochemical properties of VOCs and adsorbents/catalysts. Several conclusions are as follows:1. The multivariate linear model of the adsorption of VOCs on typical PCHs was employed to establish the relationships between the adsorption capacities of VOCs on PCHs and the physicochemical properties of VOCs (e.g., molecular cross-sectional area, polarizability, evaporation enthalpy and the critical volume, etc.). The removal performances and the underlying mechanisms of VOCs by adsorption on PCHs were examined. The adsorption capacity of the carbonyl VOCs (e.g., acetone) on PCHs was higher than that of aromatic VOCs (e.g., toluene, ethylbenzene, O-xylene, m-xylene and p-xylene).2. As the air humidity increased, the equilibrium adsorption capacities of PCHs or AC for toluene decreased and the breakthrough time was shortened. The effect of the water vapor of adsorptive properties of toluene on AC was more obvious than that of PCHs. It showed that the descending tendency of equilibrium adsorption capacities on AC for toluene were more obvious than that of PCHs at relatively higher humidity. The adsorption-desorption isotherms indicated the water vapor adsorption capacities of AC was higher than that of PCHs. The similarities and differences of hydrophobic properties of PCHs and AC were compared. Meanwhile, the adsorption-desorption circulation mechanism of water moleculars was also proved.3. Clay-based anatase titanium dioxide (TiO2) catalyst with large surface area, pore volume and uniform pore size distribution was synthesized, which had strong absorbance in the ultraviolet light wavelength range of about 250-400 nm. The high photocatalytic degradation rate of toluene by clay-based TiO2 depended on the specific surface area of catalysts. The addition of the small co-surfactant (DDA) or p-Nitrophenol (PNP) contributed to the increasing of specific surface area and pore volume, while the decreasing of average diameters. Besides, the degradation efficiency of toluene can also be enhanced by adding DDA or PNP to the surface of catalyst. The degradation rates of toluene by photocatalytic materials increased from 17.90% to 74.60% and 76.50% with the addition of DDA or PNP, respectively, when humidity was 80%.