Abstract
Aluminum-free zeolite silicalite-1 and the ordered mesoporous silicates Mobile Crystalline Material No. 48 (MCM-48) were prepared and functionalized with 3-aminopropyltriethoxysilane (APTES) and 3-mercaptopropyltrimethoxysilane (MPTMS) for the enhancement of adsorption capacity. Functionalization via post synthesis grafting method was adopted and the functionalized silicate systems were denoted as silicalite-1-NH2, silcalite-1-SH, MCM-48-NH2and MCM-48-SH. Functionalization, that was confirmed by XRD, FT-IR and surface area measurements, indicated no structural changes on the silicate materials. The adsorption of Pb(II) ions into these modified silicates was investigated in aqueous solutions with optimized pH at 5.5 where adsorption influencing factors including contact time, adsorbent dose and metal ion initial concentration were studied. Adsorption experimental data for silicalite-1-NH2, MCM-48-NH2and MCM-48-SH showed satisfactory correlation with Langmuir and Freundlich models. According to Langmuir isotherm, the maximum capacities for the above three modified silicate systems, for 100 ppm Pb(II) dose, are 43.5, 75.2 and 31.2 mg/g and with Kfconstant values of 16.9, 44.4 and 12.0 L/mg from Freundlich isotherm, respectively. The three modified silicate systems exhibited complete sequestration of Pb(II) ion concentrations in the range 0.48–1.7 ppm from samples collected from Zarqa River in four seasons of the year 2013.
Highlights
Persistent, toxic and non-biodegradable heavy metals are discharged from anthropogenic sources into the environment (Bradl, 2005; Das et al, 2011), the aquatic and ecosystems (Das et al, 2011; Schipper et al, 2008), causing them to be accumulated where different life species including humans are exposed to these metals by different routes including water and the food chain (Smith et al, 1999)
The silicate systems and their functionalized derivatives were characterized by XRD, FT-IR, surface area measurements and Thermal gravimetric analysis (TGA) analysis
The X-ray diffraction pattern of the prepared silicalite-1 (Figure 1) showed the characteristic peaks of the ZSM-5 structure which is in agreement with its diffractograms according to International Zeolite Association (IZA-SC)
Summary
Persistent, toxic and non-biodegradable heavy metals are discharged from anthropogenic sources into the environment (Bradl, 2005; Das et al, 2011), the aquatic and ecosystems (Das et al, 2011; Schipper et al, 2008), causing them to be accumulated where different life species including humans are exposed to these metals by different routes including water and the food chain (Smith et al, 1999). The silicate materials with modified surfaces were used to study the adsorption of Pb(II) ions in aqueous solutions, where after that representative samples from polluted Zarqa river near Jerash (48 km north of Amman) were tested for Pb(II) ion contamination.
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