Facile Hydrophobic Modification Strategy on Hydrophilic Metal Organic Frameworks to Improve Volatile Organic Compounds Removal from Air and Aqueous Environments

Clean air quality is essential to the wellbeing of all living species on the planet. Chemical emissions including volatile organic compounds (VOCs) and toxic aromatic hydrocarbons contribute strongly to the urban atmospheric air pollution as they pose great harms to the environment and human health. Adsorption technology in the form of commercial air filters has commonly been used for indoor VOCs abatement. These air filtration units are either equipped with activated carbon (AC), zeolites or hybrid materials among many others [1,2] but, these conventional technologies suffer from several limitations such as low adsorption capacity, structural amorphism and high regeneration costs [3]. As the pursuit for effective sorptive technology continues, the potent roles of metal-organic frameworks (MOFs) with their high surface area, chemical and thermal stability, tailorable functionalities for enhanced adsorption and reusability can help resolve the problems [4]. Of our interest is the ability to post-synthetically modify the structures to enhance adsorption or generate novel properties.

To enable efficient VOCs removal from air, the omnipresence of moisture must first be addressed by means of a systematically developed hydrophobic surface modification. Attempted strategies to improve hydrophobic character of MOFs include functionalising the MOF with fluoro-based linkers [5], co-synthesizing them with hydrophobic materials [6] or via an interfacial assembling pathway [7]. However, most reported methods are not suitable for industrial scalability. Therefore, by using a facile modification method, we will demonstrate that rationally designed MOFs have the upper hand for atmospheric VOCs capture over carbon-based adsorbents. Preliminary experiments indicate almost complete porosity retainment after the MOF has been modified.

To assert a realistic assessment, investigations will cover the sorptive behaviour of an environmentally benign MOF alongside its hydrophobically modified version towards a mixture of harmful representative airborne pollutants at ambient conditions (single species and competitive adsorption with co-existing pollutants), relative performance under varying humidity, desorption, breakthrough and dynamic reusability studies. Besides, the resulting water-repellent feature renders the modified MOF suitable for VOCs adsorption from aqueous phase systems too as supported from our ongoing experimental data. The outcomes from this in-depth materials characterization and development will provide excellent MOF protection from moisture and harsh operating conditions while offering a practical solution to many plaguing environmental issues.

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