TGA: Thermogravimetric Analysis (TGA) was measured using a TGA Star System, Mettler Toledo. All the samples were measured in N2 atmosphere (10 ml min -1 ) from 30 to 600 °C at a heating rate of 10 °C min -1 . All the samples were normalized to weight loss %. The weight change was calculated from the step change on the slope of the curve.