An Analysis Of TGA Analysis: Thermal Gravimetric Analysis

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3.1.3. TGA analysis
Thermal gravimetric analyses (TGA) were recorded under N2 atmosphere over the temperature range of 25- 800 oC at a heating rate of 15 oC/min, to evaluate both the composition and the thermal stability of f-silica and AgNPs/f-silica. As shown in Fig. 1D the mass loss noticed between 25 oC and 180 oC represents the physically adsorbed water. Adsorbed water accounted 7.4%, 6.43% and 2.2% for f-silica, AgNPs/f-silica sample using [Ag+] = 0.005 M, and AgNPs/f-silica sample using [Ag+] = 0.05 M, respectively. The decrease in the amount of physically adsorbed water can be attributed to the increasing amount of AgNPs anchoring on the functionalized silica surface, which due to the increase of the precursor [Ag+]. The second weight
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The effects of contact time, IC concentration, and temperature on adsorption were investigated. The adsorption kinetic was determined by analyzing adsorption capacity of the aqueous solution at different time intervals.

4. 1. Variation of AgNPs/functionalized silica composition
The proficiency of AgNPs/ f-silica samples for the adsorptive elimination of IC from aqueous solutions has been assessed with respect to several synthesis factors. These factors are [Ag], [Nigella seed], and the reflux time. The synthesis conditions, the abbreviation symbol and the IC removal efficiency of each sample are listed in Table 1.

4. 1. 1. Effect of [Ag]
The effect of AgNPs/f-silica samples prepared at various AgNO3 concentrations on the adsorption rate of the IC was examined (Fig. 4A and Table 1). The adsorption efficiency reached a maximum at ca 0.03 M (sample S3) and after that, it decreases. This was probably as a result of the increase in the formation of larger particles of AgNPs as the [Ag] increased (Sinha et al., 2015; Venkatesham et al., 2014). Our findings appear to be well supported by the increase in the [Ag], results in an increase in the density of nuclei that leads to high collision possibility between nuclei. Hence, the growth rate of AgNPs is enhanced and therefore an increase of particle size is obtained. It is reasonable to state that the binding of the dye molecules to the AgNPs/f-silica depends on the surface area available for interaction. Smaller particles having the larger surface area accessible for interaction will give more adsorption productivity than the larger particles and

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