Functionalization of synthesized NaP zeolite with silver nanoparticles capped with alkyl dimethyl hydroxyethyl ammonium for sorption and reduction of chromate (VI) oxoanions

NaP zeolite crystals were synthesized and used as templating support species for the purpose of hosting and the confinement of silver nanoparticles. This was being adapted primarily by introducing trace amounts of alkyl dimethyl hydroxyethyl ammonium chloride (ADHA) ranging from 50 to 200 ppm into the zeolite (Ag/ADH-NaP50–200). For comparison purposes, ADHA/NaP and Ag/NaP were also prepared under the same conditions. These solids have been examined by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FE-SEM), Raman spectroscopy (LRS), X-ray photoelectron spectroscopy (XPS), diffuse reflectance UV–Vis spectroscopy as well as surface texture measurements. By increasing the concentration of ADHA and under the effect of UV radiation, the XRD analysis of Ag/ADHA-NaP has shown increase in unit cell parameters of the zeolite along with new peaks attributed to silver nanoparticles (AgNPs) were observed at d values of 2.370 and 2.047 Å. This was confirmed by XPS peaks corresponding to Ag 3d at 368.7 and 374.7 eV. Upon addition of aqueous Cr(VI) to the Ag/ADHA-NaP200 sample, adsorbed species on the silver surface such as CrO4 2− and Cr(OH)3 produced Raman scattering at 853 and 664 cm−1, respectively. The latter sample was able to adsorb the Cr(VI) completely, but unlike the other samples, at an initial concentration of 20 ppm. The high effective surface area of AgNPs shows enhanced adsorption and photreduction of Cr(VI) to Cr(III), in compatible with the evaluation of optical band gaps. The adsorption process of Cr(VI) was thought to result from a surface uptake and intra-particle diffusion which operate simultaneously through the interaction between Cr(VI)ions and Ag/ADHA-NaP200.