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Nanomaterials have attracted much interest in cement-based materials during the past 9 decade. In this study, the effects of different nano-CaCO 3 and nano-SiO 2 contents on flowability, heat 10 of hydration, mechanical properties, phase change, and pore structure of ultra-high strength concrete 11 (UHSC) were investigated. The dosages of nano-CaCO 3 were 0, 1.6%, 3.2%, 4.8%, and 6.4%, by the 12 mass of cementitious materials, while the dosages of nano-SiO 2 were 0, 0.5%, 1.0%, 1.5%, and 2%. 13 The results indicated that both nano-CaCO 3 and nano-SiO 2 decreased the flowability and increased 14 the heat of hydration with the increase of their contents. The optimal dosages to enhance 15 compressive and flexural strengths were 1.6% to 4.8% for the nano-CaCO 3 and 0.5% to 1.5% for the 16 nano-SiO 2 . Although compressive and flexural strengths were comparable for the two nanomaterials 17 after 28 d, their strength development tendencies with age were different. UHSC mixtures with 18 nano-SiO 2 showed continuous and sharp increase in strength with age up to 7 d, while those with 19 nano-CaCO 3 showed almost constant strength between 3 and 7 d, but sharp increase thereafter. 20 Thermal gravimetry (TG) analysis demonstrated that the calcium hydroxide (CH) content in UHSC 21 samples decreased significantly with the increase of nano-SiO 2 content, but remained almost 22 constant for those with nano-CaCO 3 . Mercury intrusion porosimetry (MIP) results showed that both 23 porosity and critical pore size decreased with the increase of hydration time as well as the increase of 24 nanoparticles content to an optimal threshold, beyond which porosity decreased. The difference 25 between them was that nano-CaCO 3 mainly reacted with C 3 A to form carboaluminates, while 26 *Corresponding author. Tel./2 nano-SiO 2 reacted with Ca(OH) 2 to form C-S-H. Both nano-CaCO 3 and nano-SiO 2 demonstrated 27 nucleation and filling effects and resulted in less porous and more homogeneous structure. 28 29

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In this work, we introduce a synthesis method for a nanofiber membrane made of polyacrylonitrile and verify its filtration ability with micron-size particles. The polyacrylonitrile nanofiber membrane was produced by electro-spun technique with a thickness less than 0.2 mm. The filtration experimental result from micron-size particle penetration proved that after 60-min deposition, the polyacrylonitrile nanofiber membrane successfully filtrated ~99% micron-size particles in solution. We found that uniform morphology, consistent nanofiber diameter without disordered beads will lead to a better filtration performance. This finding will provide a low-cost, environmental-friendly and straightforward filtration approach for future PM2.5 elimination in an aqueous and harsh environment.