### The surface area for SVTPUP@ZnONPs was calculated by N2 adsorption/desorption isotherms using Brunauer/Emmett/Teller

The surface area for SVTPUP@ZnONPs was calculated by N2 adsorption/desorption isotherms using Brunauer/Emmett/Teller (BET). Figure 4A shows that the isotherm for sorption and desorption of N2 onto SVTPUP@ZnONPs is nearly similar to ? type of IUPAC classification (Lowell et el., 2011), proving mesopores dominated property. Amount adsorbed increases gradually as a relative pressure increases. The lower line was the nitrogen adsorption isotherm and the upper line was the nitrogen desorption isotherm. The hysteresis loop is explained as type H3 representing aggregates of plate-like particles giving a slit-shaped pore. The surface area of SVTPUP@ZnONPs (10.6 m2/g) is higher than the surface area of polyurethane foam (2.8 m2/g) (Han et el., 2015). Barrett/Joyner/ Halenda (BJH) methods were used to find pore volume and pore radiuses are 0.017 cm3/g and 4.124 nm (Fig. 4B). The ratio of mesopores to micropores volumes (1.7× 10-2 cm3/g: 1.5×10-3 cm3/g) is 11:1; such a ratio indicates that the SVTPUP@ZnONPs would be a good candidate for the removal of dyes.

Figure 4

Iodine number (IN) is the way to know the micro-pore content of surface. The iodine molecule is relatively small with an area of 0.4 nm2 and can enter in the smaller micro pores (Alaya et el., 2000; Baçaoui et el., 2001). The iodine number can use for approach determination of surface area and microporosity (? 2 nm) of the sorbent (Nunes and Guerreiro, 2011; Saka, 2012). The iodine number of SVTPUP@ZnONPs is 3.62 mmol/g (459.05 mg/g). The specific surface area of SVTPUP@ZnONPs was also estimated using iodine number () (Wu, 2007; Mianowski, 2007) where S is the area occupied by adsorbed iodine molecules at the maximum mono-layer surface coverage (m2/g), N is the Avogadro number (6.02 ×1023), A is the iodine surface area (0.2096 ×10?18 m2) and M is the iodine molar mass (126.92 g/mol). So, the specific surface area obtained is 456.4 m2/g. The BET surface area of SVTPUP@ZnONPs is very small compared with calculated surface area by iodine number method. It indicates that the iodine number method is incorrect for determination of SVTPUP@ZnONPs surface area (Tran, 2017). Thus it can be concluded that the adsorption process of iodine molecules occurred not only by the pores of the surface of SVTPUP@ZnONPs but also through its functional groups e.g. ether groups.