CAS: Nanocellulose-Enabled Nanocomposites for Sustainable Water Remediation

第1部分：非技术合成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，木质和非木质植物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、高效率的水净化介质的优良的积木材料，如阴离子生物吸附剂和膜阻隔层。将功能性金属氧化物纳米颗粒引入到纳米纤维素支架中，可以创建新型的阳离子生物吸附剂和光催化剂，用于水的净化，同时还可以消除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层次化结构的纳米纤维素-金属氧化物纳米复合材料的过程中，在充分理解结构-性质-工艺/合成关系方面存在一些基本的知识空白。该项目旨在调查这一主题的几个基本问题并提供新的见解，并填补这些知识空白。使用这种纳米复合材料用于净水的好处才刚刚开始实现，在气候变化增加了清洁水短缺的频率和严重性的情况下，这一点显示出特别重要的意义。除了这项研究之外，还将开展一系列教育活动，以吸引博士后、研究生、本科生(特别是少数族裔和女科学家)和高中生，将获得安全饮用水作为全球可持续发展的一个问题，同时学习可持续发展和水净化的基本概念。第2部分：技术总结本研究的总体目标是了解和控制将模型阳离子金属氧化物纳米颗粒加入不同电荷密度和原纤化程度的阴离子纤维素纳米纤维支架中，旨在利用可再生和可持续来源创造新的功能纳米复合材料用于净水。这个项目的具体目标有两个。(1)了解纳米纤维的结构和功能对金属氧化物纳米颗粒在纳米复合材料形成过程中的混合和原位合成过程中的传输和相互作用的影响。选择了两个纳米粒子(NP)模型系统：(I)纳米纤维支架孔径范围内的氧化铝(Al_2O_3)纳米粒子，通过混合方法探索有效和反常的扩散过程，以形成稳定而均匀的复合框架；(Ii)将通过原位合成形成的“白色”和“黑色”(低禁带)二氧化钛(TiO2NPs)纳米粒子，以及成核/生长过程，以了解控制纳米复合材料结构和性能的关键因素。将根据纳米纤维素支架的形态、原纤化程度和静电特性来评估NP的传输和形成机制，以及由此产生的动力学行为。(2)发展先进的表征和建模技术，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和原位扫描小角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(例如氟化物和硝酸盐)的吸附和光催化降解太阳辐射。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，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.