The methylene blue number is defined as the maximum amount of dye adsorbed by 1 g of adsorbent (Nunes and Guerreiro, 2011).

Methylene blue can measure mesporsity (2-50 nm) of the sorbent and evaluate its cation exchange (Tounsadi et el., 2016). The surface area of MB is 2.

08 nm2 and can enter in micropores and mesopores (Nunes and Guerreiro, 2011). The methylene blue number for [email protected] is 0.84 mmol/g (270.

25 mg/g). This value indicates that the surface of [email protected] contains mesopores and also has better cation-exchange capacity compared to other sorbents (Table 1)Different concentration of Br.G, To.B and Tr.B dyes (2-12 mg/L) was plotted against capacity of [email protected] The R2 values for the sorption of Br.G, To.B and Tr.

B dyes [email protected] onto were 0.962, 0.990 and 0.994.

Also, the intercept values of these plots were 0.013, 0.019 and 0.011, respectively as shown in table 2.

In addition the estimated capacity (Q) of [email protected] for Br.G, To.B and Tr.B were 0.47, 0.30 and 0.19 mmol/g (227, 91.7 and 182.

5 mg/g), respectively. The results indicate that the [email protected] has a good sorption capacity compared to other sorbents (Table 1, 2).Table 1Table 2Thermal properties of PUF, ZnONPs and [email protected] were investigated by TGA, DTA and DSC measurements. TGA curves of [email protected] showed a smooth stepwise manner containing five steps of thermal decomposition (Fig. 5A), the first step decomposition begins at 229 °C and the weight loss are 1.

6, 31.1, 44.6, 11.1 and 13.

2 % in the ranges 27-229, 230-312, 313-421, 421-824 and >824 °C, respectively. In first step, the weight loss of [email protected] (1.6%) at 27-229 °C is due to evaporation of adsorbed water molecules. The major weight losses (75.7%) occur between 230 and 421°C is due to the decomposition of SVTPUP matrix. The decomposition occurs (11.1%) at 421-824 °C is due to the crystallinity of ZnO. At T > 421 ºC, the remained of [email protected] (24.

3 wt %) represents the percentage of ZnO NPs that content in [email protected] TGA curve of PUF showed that the thermal decomposition begins at 207.1 ?C to 400 ?C and the weight loss are 34.1, 55.7 and 10.0% in the ranges 207–302 and 302–400 ?C, respectively (Moawed and El-Shahat, 2013). That indicates thermal stability of [email protected] The DTA and DSC curves of PUF showed two endothermic peaks at 288.

5 and 356.8 ?C (Moawed and El-Shahat, 2013). DTA curve for ZnONPs has exothermic peak between 370 and 520 °C illustrates the maxima at 435 °C (Mashrai et el.

, 2017). While, the [email protected] has four endothermic peaks at 305, 377, 805 and 880°C and two exothermic peaks one at 62 and 943°C as shown in (Fig.5B), this result support the chemical interaction between SVTPUF and ZnONPs.