Synthesis of novel mesoporous materials as high-performance adsorbents

Abstract

The rapid growth of nanotechnology has brought in advanced technologies. One demonstrative case is nanoadsorbents which are defined as nanostructured materials with a high affinity to adsorb substances. Owing to their exclusive features such as adjustable structural properties, tunable surface chemistry, and short diffusion distance, nanoadsorbents have shown great promise in catalysis and water treatment to host various species. However, the effectiveness of typical nanoadsorbents is generally restricted by the inadequate textural properties or functionalities. Therefore, it is essential to develop highly effective nanostructured adsorbents to host various substances.Polycyclic aromatic hydrocarbons (PAHs) are an important family of organic pollutants composed of fused benzene rings. They have been categorized as priority pollutants due to their toxic, mutagenic, and carcinogenic properties. Adsorption has recently found to be a promising technology to remove PAHs in a cost-effective and green manner. Nonetheless, the performance of proposed adsorbents is typically poor because of the inadequate textural and functional properties. Therefore, developing novel adsorbents with tailored features for superior removal of PAHs is crucial.Lipase has found key industrial applications as shows astonishing catalytic performance in a green manner. nHowever, the effectiveness of free lipase is significantly reduced by its limited activity and low stability. Immobilization of lipase on nanomaterials is a promising approach to improve lipase catalytic performance. Nonetheless, lipase shows a severe decrease in catalytic activity after immobilization. Thus, developing an effective approach to improve the catalytic performance of lipase remains an ongoing challenge.This project emphases on the synthesis of innovative mesoporous materials with rationally designed textural properties and functionality as high-performance adsorbents. The advanced nanoadsorbents have shown excellent performances to host various species with significantly improved adsorption performance.nThe main achievements in this thesis are listed below.nIn the first part of this thesis, organic-based nanomaterials were developed for adsorption of PAHs. First, rattle-type magnetic mesoporous hollow carbon (RMMHC) were synthesized through a surfactant-free synthesis approach. It was demonstrated that the textural properties of RMMHC nanoparticles can be adjusted by changing the carbonization temperature. The adsorption capacity of the optimized sample towards di (2-ethylhexyl) phthalate reaches as high as 783.1 mg g-1 while retaining 89% of its initial adsorption capacity after five cycles. In the next part, novel superhydrophobic dendritic mesoporous organosilica nanoparticles (SHDMONs) with an exceptional content of organic moieties and an outstanding mesopore volume were successfully developed for adsorption of pyrene. The optimized SHDMONs display quick adsorption rate (30 min) and an extremely high pyrene adsorption capacity (757.5 mg g-1) which is substantially better than previous studies. Finally, dendritic mesoporous carbon nanoparticles (DMCNs) with open mesopore channels (18.4 nm) and an exceptional mesopore volume (1.484 cm3 g-1) were fabricated through subjecting SHDMONs to carbonization and selective removal of silica. Resultant DMCNs show an extremely high adsorption capacity towards anthracene (751.6 mg g-1), significantly higher than those reported in the literature. Collectively, it is revealed that both high hydrophobic content and large mesopore volume are responsible for the superior PAHs removal.Textural properties and composition of silica-based nanocarriers are two fundamental issues for superior lipase immobilization. In the second part of this project, silica nanoparticles with a high content C18 moieties and a wide range of textural properties were developed. The impacts of pore size, particle size, and surface chemistry of materials on their performance as nanocarriers to host lipase molecules have been investigated. The advantages of designed porous materials are credited to small particle size, a tailor-made pore size, and more importantly the increased hydrophobic content. An exceptional activity (5.23 times higher than that of the free lipase) and an excellent cyclability is achieved which is the top performance described so far. On the basis of obtained knowledge, benzene-bridged dendritic mesoporous organosilica nanoparticles (BDMONs) with highly enriched benzene groups in the pore channel wall were fabricated by a delayed addition method to host lipase molecules. This platform exhibited a specific activity 6.5 times higher than that of the free lipase with an enhanced stability. In addition to textural and compositional properties of desired nanocarriers to accommodate lipase, an ideal carrier should be also cost-effective. In this regard, low-cost functionalized mesoporous silica materials were fabricated through spray-drying technology to accommodate lipase molecules. The optimized biocatalysis system displays high lipase loading (100 mg g-1), enhanced enzymatic activity (1.14 times than that of free enzyme), and excellent stability performance. When applied for continuous production of biodiesel, the developed integrated immobilized lipase-reactor system shows a significant potential with an unprecedented conversion rate (99%) and outstanding stability (retaining 64% of initial conversion after 24 h).In summary, innovative nanoadsorbents have been successfully advanced through tailoring parameters such as synthesis strategy, size, morphology, and composition of materials. The developed nanomaterials have shown great potential to host different species,nwhich is important for the industrial biocatalysis and water treatment.n