Synthetic zeolite
Na-X and clinoptilolite (Cp) as well as their
modifications with quaternary ammonium salts were used to remove volatile
organic compounds (VOCs) and polycyclic aromatic hydrocarbons (PAHs)
from aqueous solutions. A novel procedure was developed for the synthesis
of organo-zeolites which consisted of surface modification with hexadecyltrimethylammonium
bromide (HDTMA) in amounts of 1.0 and 2.0 of external cation exchange
capacity (ECEC). Modification of both zeolites with HDTMA improved
sorption properties. p-Xylene and dibenz[a,h]anthracene
were adsorbed in amounts of 6.82 and 0.65 mg/g, respectively. Ethylbenzene
and naphthalene were the lowest-removed hydrocarbons (2.99 and 0.058,
respectively). The removal efficiencies for BTEX followed the order p-xylene > toluene > benzene > ethylbenzene, and
for PAHs
they followed the order dibenz[a,h]anthracene > benzo[a]pyrene
> anthracene
> naphthalene. Efficiency of sorption depends on the chemical properties
of the various organic compounds (dipole moment, molar mass, molecule
structure, and the time of the sorption process) and zeolites properties,
like the Si/Al ratio, texture parameters, particle size, and external
cation exchange capacity. The mechanism of the sorption consists of
dissolving the VOCs and PAHs into the organic layer of the surfactant
as well as on the penetration of organic solution into the mesopores.
Montmorillonite—the most popular mineral of the smectite group—has been recognized as a low-cost, easily available mineral sorbent of heavy metals and other organic and inorganic compounds that pollute water. The aim of this work was to determine the sorption mechanism and to identify the reaction products formed on the surface of montmorillonite and organo-montmorillonite after sorption of molybdates (Mo(VI)) and tungstates (W(VI)). Montmorillonites are often modified to generate a negative charge on the surface. The main objective of the study was to investigate and compare the features of Na-montmorillonite (Na-M), montmorillonite modified with dodecyl trimethyl ammonium bromide (DDTMA-M), and montmorillonite modified with didodecyl dimethyl ammonium bromide (DDDDMA-M) before and after sorption experiments. The material obtained after sorption was studied by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The XRD pattern showed the presence of a new crystallic phase in the sample that was observed under an SEM as an accumulation of crystals. The FTIR spectra showed bands related to Mo–O and W–O vibration (840 and 940 cm−1, respectively). The obtained results suggest that molybdenum(VI) and tungsten(VI) ions sorb onto the organo-montmorillonite in the form of alkylammonium molybdates and tungstates.
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