Preparation and characterization of natural and pillared clays for catalytic wet peroxide oxidation of 4-nitrophenol
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This work deals with the evaluation of two natural clays (NCs) extracted from Karatau
(KNC) and Akzhar (ANC) deposits (located in the Zhambyl region of Kazakhstan)
to prepare pillared clays (PILCs) for catalytic wet peroxide oxidation (CWPO) of
4-nitrophenol (4-NP), used as model pollutant. NCs were washed with HCl 1 M and then
pillared using a solution containing Fe, Cu and Zr. NCs and PILCs were characterized
by Electron Microprobe (EMP), X-Ray Diffraction (XRD), Fourier Transform Infrared
Spectroscopy (FTIR) and Transmission Electron Microscopy (TEM), as detailed elsewhere
[1,2]. EMP confirms the cation exchange of the Ca contained in the NCs (Ca > 15%) in the
form of calcite (according to DRX and FTIR), by polycations of the pillaring solution (Ca
< 2% for the PILCs). TEM reveals that the impregnation of polycations on the washed NCs
also take place, coupling with its pillarization. CWPO runs were performed following the
methodology and operational conditions described in previous works [1,2]. All materials
show catalytic activity, since the H2O2 is consumed (Fig. 1A) to oxidize the 4-NP. Both
KPILC and APILC, prepared from KNC and ANC, respectively, allow the complete removal
of 4-NP after 4 h, whereas the conversion of 4-NP was less than 20% with the NCs (Fig. 1B).
TOC conversions higher than 60 % were achieved with PILCs after 8 h. The subtraction
of the theoretical TOC contribution of 4-NP from experimental TOC allowed to observe
the formation of oxidazable intermediate compounds (maximum value of TOCexperimental-
TOC4-NP at 1 h of reaction), which are oxidized to form refractory products (Fig. 1C). Based
on these contributions of the TOC, a kinetic model based on TOC lumping into three
blocks (TOCA à TOCB à TOCC, corresponding to the initial TOC of 4-NP, oxidazable
intermediates and refractory products, respectively) was developed for the NCs and PILCs,
predicting suitably the evolution of 4-NP, H2O2 and TOC in the CWPO of 4-NP (Fig. 1).
This work is a result of project “AIProcMat@N2020 - Advanced Industrial Processes
and Materials for a Sustainable Northern Region of Portugal 2020”, with the reference NORTE-01-0145-
FEDER-000006, supported by NORTE 2020, under the Portugal 2020 Partnership Agreement, through
FEDER and of Project POCI-01-0145-FEDER-006984 – Associate Laboratory LSRE-LCM funded by
FEDER through COMPETE2020 - POCI – and by national funds through FCT.
