CAS: Nanocellulose-Enabled Nanocomposites for Sustainable Water Remediation

第一部分：纳米纤维素可以从所有木质纤维素植物（木本和非木本）中提取-地球上最大的天然聚合物来源。纳米纤维素已被证明是形成低成本和有效的水净化介质（例如阴离子生物吸附剂和膜屏障层）的优异的结构单元材料。在纳米纤维素支架中掺入功能性金属氧化物纳米颗粒可以产生用于水净化的新型可持续阳离子生物吸附剂和光催化剂，同时还消除了在环境修复中使用纳米颗粒的典型不利影响。然而，有一些基本的知识差距，在充分理解的结构-性能-过程/合成的关系，在创建分层结构的纳米纤维素-金属氧化物纳米复合材料，可以保持稳定性和有效性，在水环境中。该项目旨在研究该主题的几个基本问题，并提供新的见解，填补这些知识空白。使用这种纳米复合材料进行水净化的好处才刚刚开始实现，随着气候变化增加了清洁水短缺的频率和严重性，这一点尤为重要。除了研究之外，还将开展一系列教育活动，吸引博士后、研究生、本科生（特别是少数群体科学家和女科学家）和高中生，重点关注获得安全饮用水这一全球可持续性问题，同时了解可持续性和水净化的基本概念。技术概述本研究的总体目标是理解和控制模型阳离子金属氧化物纳米颗粒掺入不同电荷密度和原纤化程度的阴离子纤维素纤维素支架中，旨在从可再生和可持续的来源中创造新的功能性纳米复合材料，用于水净化。该项目的具体目标有两个。(1)了解纳米纤维素结构和功能对纳米复合材料形成过程中混合和原位合成过程中金属氧化物纳米颗粒的传输和相互作用的影响。选择两种模型纳米颗粒（NP）系统：（i）尺寸在纳米纤维素支架孔径范围内的氧化铝（Al 2 O3）NP，以通过混合方法探索有效和异常的扩散过程，从而形成稳定和均匀的复合框架，和（ii）“白色”和“黑色”（低带隙）二氧化钛（TiO 2）纳米颗粒将通过合成和成核/生长过程原位形成，以了解可以控制纳米复合材料结构和性能的关键因素。NP运输和形成机制，以及由此产生的动力学行为将针对纳米纤维素支架的形态、原纤化程度和静电性质进行评价。(2)开发先进的表征和建模技术，可以揭示纳米复合材料形成过程中的结构-性能-加工关系。主要的加工结构表征方法将包括无剪切混合结合原位扫描小角X射线散射（SAXS）、X射线光子相关光谱（XPCS）和使用同步辐射的其他光谱技术，而性能评估将集中在阴离子污染物（例如，氟化物和硝酸盐）和通过太阳辐射的光催化降解。该奖项反映了NSF的法定使命，并被认为是值得通过使用基金会的知识价值和更广泛的影响审查标准进行评估的支持。

PART 1: NON-TECHNICAL SUMMARYNanocellulose can be extracted from all lignocellulose plants (woody and non-woody) - the largest natural polymer sources on Earth. Nanocelluloses have been shown to be excellent building block materials to form low-cost and effective water purification media, such as anionic bio-adsorbents and membrane barrier layers. The incorporation of functional metal oxide nanoparticles in the nanocellulose scaffold can create new types of sustainable cationic bioadsorbents and photocatalysts for water purification while also eliminating typical adverse effects of using nanoparticles in environmental remediation. However, there are some fundamental knowledge gaps in fully understanding the structure-property-process/synthesis relationships during the creation of hierarchically structured nanocellulose-metal oxide nanocomposites that can maintain stability and effectiveness in the aqueous environment. This project aims to investigate several fundamental issues of and provide new insights into the subject and fill those knowledge gaps. The benefits of using such nanocomposites for water purification have only begun to be realized, demonstrating particular importance as climate change has increased the frequency and severity of clean-water shortage. In additiopn to the research, a range of educational activities will be developed to engage post-doc, graduate, undergraduate (especially minority and women scientists) and high school students, in focusing on access to safe drinking water as an issue of global sustainability while learning about the fundamental concepts of sustainability and water purification.PART 2: TECHNICAL SUMMARYThe overall objective of this research is to understand and control the incorporation of model cationic metal oxide nanoparticles into anionic cellulose nanofiber scaffolds of different charge density and degree of fibrillation, aiming to create new functional nanocomposites from renewable and sustainable sources for water purification. The specific aims of this project are two. (1) Understand the effects of nanocellulose structure and functionality on the transport and interactions of metal oxide nanoparticles during mixing and in-situ synthesis processes in the formation of nanocomposites. Two model nanoparticle (NP) systems are chosen: (i) aluminium oxide (Al2O3) NPs with sizes in the range of nanocellulose scaffold pore sizes to explore effective and anomalous diffusion processes through the mixing approach to form stable and homogeneous composite frameworks, and (ii) “white” and “black” (low-band gap) titanium oxide (TiO2) NPs that will be formed in-situ through synthesis, and nucleation/growth processes to understand critical factors that can control the structure and properties of nanocomposites. The NP transport and formation mechanisms, as well as the resulting dynamics behavior will be evaluated against the morphology, degree of fibrillation, and electrostatic properties of the nanocellulose scaffolds. (2) Develop advanced characterization and modeling techniques that can reveal the structure-property-processing relationships during nanocomposite formation. The primary processing-structure characterization methods will include shear-free mixing combined with in-situ scanning small-angle X-ray scattering (SAXS), X-ray photon correlation spectroscopy (XPCS), and other spectroscopic techniques using synchrotron radiations, while the performance evaluation will be focused on adsorption of anionic contaminants (e.g., fluorides and nitrates) and photocatalytic degradation by solar radiation..This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.