Browsing by Author "Fang, Qiyi"

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    Selective membranes in water and wastewater treatment: Role of advanced materials
    (Elsevier, 2021) Zuo, Kuichang; Wang, Kunpeng; DuChanois, Ryan M.; Fang, Qiyi; Deemer, Eva M.; Huang, Xiaochuan; Xin, Ruikun; Said, Ibrahim A.; He, Ze; Feng, Yuren; Walker, W. Shane; Lou, Jun; Elimelech, Menachem; Huang, Xia; Li, Qilin; NSF Nanosystems Engineering Research Center for Nanotechnology-Enabled Water Treatment
    Membrane separation has enjoyed tremendous advances in relevant material and engineering sciences, making it the fastest growing technology in water treatment. Although membranes as a broad-spectrum physical barrier have great advantages over conventional treatment processes in a myriad of applications, the need for higher selectivity and specificity in membrane separation is rising as we move to target contaminants at trace concentrations and to recover valuable chemicals from wastewater with low energy consumption. In this review, we discuss the drivers, fundamental science, and potential enabling materials for high selectivity membranes, as well as their applications in different water treatment processes. Membrane materials and processes that show promise to achieve high selectivity for water, ions, and small molecules—as well as the mechanisms involved—are highlighted. We further identify practical needs, knowledge gaps, and technological barriers in both material development and process design for high selectivity membrane processes. Finally, we discuss research priorities in the context of existing and future water supply paradigms.
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    Superior mechanical properties of multilayer covalent-organic frameworks enabled by rationally tuning molecular interlayer interactions
    (PNAS, 2023) Fang, Qiyi; Pang, Zhengqian; Ai, Qing; Liu, Yifeng; Zhai, Tianshu; Steinbach, Doug; Gao, Guanhui; Zhu, Yifan; Li, Teng; Lou, Jun
    Two-dimensional (2D) covalent-organic frameworks (COFs) with a well-defined and tunable periodic porous skeleton are emerging candidates for lightweight and strong 2D polymeric materials. It remains challenging, however, to retain the superior mechanical properties of monolayer COFs in a multilayer stack. Here, we successfully demonstrated a precise layer control in synthesizing atomically thin COFs, enabling a systematic study of layer-dependent mechanical properties of 2D COFs with two different interlayer interactions. It was shown that the methoxy groups in COFTAPB-DMTP provided enhanced interlayer interactions, leading to layer-independent mechanical properties. In sharp contrast, mechanical properties of COFTAPB-PDA decreased significantly as the layer number increased. We attributed these results to higher energy barriers against interlayer sliding due to the presence of interlayer hydrogen bonds and possible mechanical interlocking in COFTAPB-DMTP, as revealed by density functional theory calculations.
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    Synthesis, Characterization and Application of 2D Covalent-organic-frameworks
    (2023-04-19) Fang, Qiyi; Lou, Jun
    Covalent-organic-frameworks (COFs) are crystalline porous polymers with periodic skeleton that assembled from diverse building blocks that attracted increasing interest due to their high designability and porosity, which show potential applications in many areas, such as gas separation, organic opto/electronics, membrane filtration and energy storage/conversion. However, much attention was only focusing on structural designs and preparation methods towards their functional utilizations, and very limited work had been reported on their mechanical properties which play critical roles in practical applications. Considering its two-dimensional nature and covalently bonded skeleton, 2D COFs are envisioned to process outstanding mechanical properties, and distinct from inorganic 2D materials such as graphene and MoS2, which are strong yet brittle as they lack sufficient interlayer interaction, COFs can be designed and synthesized with molecular level control, By rational design monomers, we can control the skeleton of 2D COFs, such as the pore size and pore shape, as well as the surface chemistry that can form strong interactions between layers, which provide an exciting platform to control the membrane mechanical properties at diverse dimensional. The objection of this thesis is to develop a systematic study of the mechanical properties of COF membranes. Specific Aim 1 is to perform in-situ tensile test under SEM and investigate the crack propagation in porous 2D COF membranes (Chapter 2). Specific Aim 2 is to rationally design the monomer to enhance the interlayer interaction between COF adjacent layers, and further study how hydrogen bonds affect the mechanical properties of multilayer COF membranes (Chapter 3). Specific aim 3 is to prepare 2D COF by a vapor phase method and study its mechanical and electronic properties, and its heterostructure with transition metal dichalcogenides are also studied(Chapter 4). This thesis provided systemic investigation on the synthesis, characterization of 2D COFs and the potential application of 2D COFs in nanoelectronics.