CAS: Nanocellulose-Enabled Nanocomposites for Sustainable Water Remediation

纳米纤维素可以从所有木质纤维素植物（木质和非木质）中提取，这是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的优秀构建块材料，如阴离子生物吸附剂和膜屏障层。在纳米纤维素支架中掺入功能性金属氧化物纳米颗粒，可以为水净化创造新型的可持续阳离子生物吸附剂和光催化剂，同时也消除了使用纳米颗粒进行环境修复的典型不利影响。然而，在创建能够在水环境中保持稳定性和有效性的分层结构纳米纤维素-金属氧化物纳米复合材料的过程中，在充分理解结构-性能-过程/合成关系方面存在一些基本的知识空白。该项目旨在研究该学科的几个基本问题，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被认识到，在气候变化增加了清洁水短缺的频率和严重程度的情况下，它显示出特别的重要性。除研究外，还将开展一系列教育活动，吸引博士后、研究生、本科生（特别是少数民族和女科学家）和高中生，重点关注作为全球可持续性问题的安全饮用水的获取，同时学习可持续性和水净化的基本概念。本研究的总体目标是了解和控制模型阳离子金属氧化物纳米颗粒与不同电荷密度和纤维化程度的阴离子纤维素纳米纤维支架的结合，旨在从可再生和可持续的来源创造新的功能纳米复合材料，用于水净化。这个项目的具体目的有两个。(1)了解纳米纤维素的结构和功能对金属氧化物纳米颗粒在混合和原位合成过程中的传递和相互作用的影响。选择了两种模型纳米粒子（NP）系统：(i)尺寸在纳米纤维素支架孔径范围内的氧化铝（Al2O3） NPs，通过混合方法探索有效和异常的扩散过程，形成稳定和均匀的复合材料框架；（ii）通过原位合成和成核/生长过程形成的“白色”和“黑色”（低带隙）氧化钛（TiO2） NPs，了解控制纳米复合材料结构和性能的关键因素。NP的转运和形成机制，以及由此产生的动力学行为将根据纳米纤维素支架的形态、纤颤程度和静电性能进行评估。(2)发展先进的表征和建模技术，揭示纳米复合材料形成过程中的结构-性能-加工关系。主要的工艺结构表征方法将包括无剪切混合结合原位扫描小角度x射线散射（SAXS）， x射线光子相关光谱（XPCS）和其他使用同步辐射的光谱技术，而性能评估将集中在阴离子污染物的吸附上(例如，该奖项反映了美国国家科学基金会的法定使命，并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，被认为值得支持。

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.