## 3 Results and Discussion  
The stone powder is mainly composed of silicon dioxide, calcium carbonate, and other aluminum silicate containing calcium [17], which is identified by XRD measurement shown in the lower red curve in Figure 1 and EDS element detection presented in Table S1 in the Supplementary Materials. The stone powder was mixed with concrete and sand, and then fabricated into aerated bricks. As displayed in Figure 1, an approximate coincidence of diffraction peaks between the two curves confirms that the composition of aerated brick is nearly the same as that of the waste stone powder. The unchanged composition from waste stone powder to aerated bricks was also verified by comparison of the chemical elements employing EDS, which is shown in Figure S1, Table S1 and Table S2 in the Supplementary Materials. Figure 2 shows the microstructure and morphology of the fabricated aerated brick visualized by using SEM at different magnifications. It is observed that the aerated brick is composed of flakes with a diameter of several micrometers and a thickness of hundreds of nanometers, being cross-linked and  
Figure 1: XRD patterns of the waste stone powder (lower red curve) and the aerated brick (upper blue curve). exhibiting a porous structure with the pore size on the micrometer scale. This porous structure enables the aerated brick to possess outstanding properties such as good thermal shielding, sound insulation, light weight, and large pressure tolerance. However, the pores, in turn, could also easily absorb water from rains, consequently facilitating mold growth, suffering from corrosion, and degrading the performances of the bricks. To address the issue of water invasion of the aerated bricks, creating a water-repellent surface is an effective way, by modifying the surface with micro- and nanostructure and nanomaterials. Learning from the lotus effect, a hierarchical double structure, consisting of a characteristic epidermis equipped with micrometer-sized papilla arrays and the covering waxes [13; 15], significantly reduces the contact area and the adhesion force between water droplets and the surface, thus enables the water repellency of the surface. As shown in the schematic diagram in Figure 3, homemade highly dispersive TiO\({}_{2}\) nanoparticles were employed to coat on the aerated brick surface by dip coating method, creating a rough epidermis of the surface with TiO\({}_{2}\) nanoparticle clusters. On the other hand, the TiO\({}_{2}\) nanoparticles clad with TEOS undergo hydrolysis, forming -OH terminal groups on the surface. At the same time, the -Si-OH groups in the hydrolyzed PFOTS are dehydrated with the -OH group on the TiO\({}_{2}\) surface by means of a self-assembling process and eventually build the hierarchical architecture. According to the Cassie-Baxter wetting model [18], this artificial highly textured surface modified with super-hydrophobic groups is responsible for water repellency, holding great potential for self-cleaning and water-proofing applications [19; 20; 21]. Figure 2: SEM photographs of the aerated brick at different magnifications: (**a**) \(\times\)10000; (**b**) \(\times\)5000; (**c**) \(\times\)2000; (**d**) \(\times\)1000. The highly dispersive TiO\({}_{2}\) nanoparticles in water were prepared, enabling the preparation of environmentally friendly aqueous based suspension. Being a wide gap semiconductor [22; 23] and nontoxic material, TiO\({}_{2}\) has been extensively used in areas of solar cells [23], photocatalysis [1], whitening, and ultraviolet shielding. The crystal phase of the prepared TiO\({}_{2}\) was revealed by XRD (Figure S2 in the Supplementary Materials). The diffraction peaks located at 25.2\({}^{\circ}\), 37.7\({}^{\circ}\), 48.0\({}^{\circ}\), 53.9\({}^{\circ}\), 62.6\({}^{\circ}\) were well indexed to its (101), (004), (200), (105) and (204) reflections respectively (JCPDS Card Number 21-1272), indicating anatase crystal structure of TiO\({}_{2}\)[1].