2.2.1. Physical and physicochemical characterization The particle size distribution of the Ch-zeolite was determined using a laser diffraction equipment (CILASk 1064) and standard wet sieving (Mesh Tylerk series). Scanning electron mic... 2.2.1. Physical and physicochemical characterization
The particle size distribution of the Ch-zeolite was
determined using a laser diffraction equipment (CILASk
1064) and standard wet sieving (Mesh Tylerk
series).
Scanning electron microscopy (SEM-PHILIPSk
XL20) was used for photomicrographs as well as to
analyse the Ch-zeolite composition (Energy Dispersion
X-ray， EDX). The sample was initially placed in
a vacuum chamber for coating with a thin layer (few
nanometers) of gold (Au).
The specific surface area of the material was
measured by the methylene blue technique and by
nitrogen gas adsorption methods， with the latter also
providing information about particle porosity.
In the methylene blue adsorption method， aqueous
solutions (50 ml) of methylene blue (100 mg l 1) were
agitated using an orbital shaker (Marconik) for an
hour at room temperature in the presence of different
quantities of the Ch-zeolite (0.05–0.3 g). The suspensions
were then allowed to settle for 23 h and the
resulting supernatants were centrifuged at 5000 rpm
before the analysis of the residual methylene blue
concentration. Results obtained correspond to averaged
values of three different experiments. The specific
surface area was evaluated by the Langmuir
model， assuming the formation， at high concentrations，
of a dye monolayer and 1.08 nm2 molecule 1， for the
cross-sectional area (Van den Hul and Lyklema， 1968).
The Ch-zeolite specific surface area was evaluated
by the nitrogen gas adsorption method， using automated
equipment (Autosorb 1-Quantachrome
Instrumentsk)， employing multipoint BET isotherm
adsorption data fitting. Also from these data， the
porosity of the material was evaluated through parameters
such as volume of total pores (d < 206 nm)，
surface area and volume of micropores (d < 2 nm;
Micropore Analysis Method).
Zeta potential measurements for the natural and
ammonia loaded zeolite， as a function of medium
pH， were determined using a Zeta Plusk equipment
(Brookhaven Instruments). Suspensions (0.01% v/v)
of the Ch-zeolite， previously sieved below 37 Am
(400 Mesh Tylerk)， in a 10 3 mol l 1 solution of
KNO3 were used and the medium pH was controlled
with the addition of HNO3 (pH< 7) and
KOH (pH>7)， separately. For the Ch-zeolite saturated
with ammonia， suspensions of the material were
prepared by the same procedure， except that the
sample was loaded with 100 mg NH3–N l 1 of
ammonia. 展开
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