Functional cellulosic porous materials - Structure design, surface engineering, and applications
Due to the COVID-19 crisis the PhD defence of Huan Cheng will take place online.
The PhD defence can be followed by a live stream.
Huan Cheng is a PhD student in the research group Sustainable Polymer Chemistry (SPC). His supervisor is prof.dr. G.J. Vancso from the Faculty of Science and Technology (S&T) and prof. dr. X. Sui (Donghua University).
The application of functional porous materials for tackling challenges in the areas of environment, energy, and healthcare has attracted distinguished interest. Cellulose within this class of materials, which is one of the most abundant and renewable polymers, provides attractive alternatives to synthetic plastics for numerous applications. The inherent properties of hydrophilicity, biodegradability and the rich chemistry enabled by its hydroxyl groups make cellulose easy to modify and functionalize. When cellulosic materials are endowed with controlled (micro)porous structures, a range of applications becomes feasible due to the combined advantages of controlled porosity, high specific surface area, and the intrinsic materials’ properties of cellulose. For example, porous cellulosic materials with precise surface modification and engineered pore structure have been employed in molecular delivery, catalyst support, absorption, separation, and thermal insulation.
Structure design and surface modification are promising ways to improve the application performance of functional cellulosic porous materials. This thesis starts with a general introduction, including the introduction and problem statements of cellulosic porous materials and presents an outline, which briefly describes the recent advances and the research work performed on structure design and surface modification of cellulosic porous materials.
Chapter 2 provides a literature review on cellulosic porous materials. Based on the current state of the art, novel structures and effective modification methods are considered for improving the application performance of cellulosic porous materials in the fields of environment, energy, and healthcare.
Chapter 3 presents a new hemostatic wound dressing construct sponge obtained by the integration of heterogenous, microporous materials with different wettability. Benefitting from the 3D fibrous cellular network that consists of flexible cellulose nanofibers and organosilanes, the sponges showed Janus characteristics, exhibiting excellent underwater flexibility and shape-memory behavior. The comprehensive advantages of the unique Janus structure with different wettability on both sides, supported by the hemostatic property of chitosan, endowed the sponges with a 49% reduction of blood loss compared with only a hydrophilic control sample and common gauze.
In order to further give full play to the advantages of similar Janus structures, in chapter 4, we designed and constructed systems in a cylindrical shape. A robust, nature-inspired and high-performance monolithic integrated cellulose aerogel-based evaporator (MiCAE) for seawater desalination was fabricated from these Janus systems using the facile and scalable heterogeneous mixing and freeze-drying technique. Inspired by woods and mushrooms, the incorporation of the hydrophobic SCA (possessing intrinsic low thermal conductivity) with mushroom-shaped CPA (having vertically aligned channels and porous structures analogous to woods) realized heat localization and effectively suppressed heat dissipation of the system, enhancing the solar-thermal conversion efficiency. The hydrophilic CPA component integrated in the SCA enabled fast water transportation by capillary action and great salt excretion because of the low tortuosity porous structure. By virtue of a synergistic effect of the integrated functional structures, the evaporator can realize the combination of high light absorption, efficient salt-resistance and impressive efficiency. As a result, the MiCAE exhibits a high irradiation absorption of 94%, a great evaporation rate of 1.90 kg m−2 h−1 and an impressive efficiency of 89% under one-sun irradiation. Moreover, the evaporator demonstrates a stable vapor generation with almost no salt deposition when actual East China Sea water is used, and exhibits an obvious salt-resistance performance in highly concentrated brine (17.5 wt.%) under one-sun irradiation for continuous evaporation of 8 hours.
We describe in chapter 5 a wearable heater based on the previous work. This chapter presents an effective strategy for fabricating lightweight, robust, stretchable and multifunctional CP/PU/PFC composite aerogels. These materials exhibit satisfactory Joule heating performance (up to 173 ℃ at 4 V) with low working voltage and rapid heating rate. Excellent waterproof performance could be achieved with CP-48/PU/PFC-6 which has a large WCA of 135°. Despite having highly waterproof surfaces, the CP/PU/PFC composite aerogels showed prominent breathable performance (the WVT rate of 5.8±0.8 kg m−2 d−1) owing to their interconnected porous structure. These results suggest that the mechanically robust and multifunctional CP-48/PU/PFC composite aerogels are highly promising as wearable heaters for applications in harsh environments, such as frigid polar regions, pluvial mountainous areas, and cryogenic workshops.
Combining the unique properties of poly(ferrocenylsilanes) (PFS) with those of cellulose, in chapter 6, a Pd NPs loaded cellulose/PFS-PIL composite sponge was fabricated by co-dissolving, solvent exchange, and subsequent freeze-drying. The PFS-PILs can reduce and immobilize metal NPs in an in-situ process, which required no external reducing agents. The porous cellulose/PFS-PIL sponges were found to be effective supports for Pd NPs. These sponges demonstrated excellent catalytic properties which could be improved to reach a rate constant value of k = 0.51 min−1 for the reduction of 4-nitrophenol to 4-aminophenol. The employed method used to form and immobilize metal NPs on renewable support materials can be applied to create a broad range of metal NP-decorated porous structures.
Overall, we presented different structure designs and surface modification methods of cellulosic porous materials which have great potential for application in the areas of environment, energy, and healthcare. Firstly, we designed cellulosic porous materials with a Janus structure. This unique structure with different wettability provides these materials with novel application opportunities. We explored the application of this Janus structure in hemostatic wound dressing and in evaporators for seawater desalination, and obtained superior results compared with some commercial products and results shown in other published work. Second, based on our previous work and the widely researched polymer PFS, we used a post-modification and physical mixing method to prepare two kinds of porous materials. One is a wearable heater and the other is a catalyst support. In order to further explore the combination of cellulose and PFS, we added some PFS structures in the outlook chapter, hoping to broaden the functionalization options of cellulosic porous materials. Overall, the results presented in this thesis were realized by introducing novel structure and surface modification methods for porous materials with the aim of gaining access to new application areas, and to hopefully give inspiration to researchers in the development of advanced cellulosic porous materials.
