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Critical process parameters for optimum yield of Co3O4 catalyst for application in textile effluent treatment
Author(s)
Theart, Jorika
Date Issued
2023
Type
Thesis
Publisher
Cape Peninsula University of Technology
Abstract
The interest in nanostructured materials has increased due to the electrical, catalytic, optimal
and magnetic properties of the nanoscale particles that are uniquely different from those of
their corresponding bulk counterparts. The technological applications of Co3O4 nanostructures
such as solid-state sensors, anode materials in lithium-ion rechargeable batteries,
electrochromic sensors, heterogeneous catalyst, energy storage and magnetic materials have
drawn attention to the controlled synthesis of these nanomaterials. There is a lack in the
understanding of the effect of synthesis operating conditions (such as reaction temperature,
residence time, type of precursor anion and precursor concentration) and their interactions on
the produced Co3O4 nanoparticles. During this study the produced Co3O4 nanostructures were
applied as a catalyst for the degradation of methyl orange (MO) solution to establish if there
is a relationship between the product yield, crystallite size and the degradation percentage.
The chemicals that are used during the dying process as well as the structure of the dyestuff
makes the generated effluent highly polluted and difficult to treat. Advantaged oxidation
processes (AOP) have gained considerable interest due to the low selectivity to organic
pollutants in wastewater. AOPs involve the generation of hydroxyl free radicals by using
different oxidants that ultimately destroy components that are not removed under conventional
oxidation processes.
During this study, a Co3O4 nanocatalyst was produced through the hydrothermal synthesis
using three precursor salts with different counter anions (cobalt acetate tetrahydrate, cobalt
chloride and cobalt nitrate). A factorial design (face-centred central composite design) was
applied to create a design that would produce a prediction model to evaluate the effect of the
operating parameters (reaction temperature, precursor concentration and residence time) on
the product yield and crystallite size. X-ray diffraction (XRD) analysis showed that after
calcination Co3O4 nanostructures were produced.
Comparing the maximum yield obtained for each precursor the order was as follows:
Co(NO3)2
.6H2O (100%) > CoCl12
.6H6O (82%) > Co(C2H3O2)2 (66%). The product yields
obtained for Co(NO3)2
.6H2O–derived Co3O4 ranged from 56% to 100%.The product yields
obtained for CoC12
.6H2O–derived Co3O4 ranged from 1% to 82%. The product yields obtained
for Co(C2H3O2)2–derived Co3O4 ranged from 12% to 66%.
The crystallite size of Co(NO3)2
.6H2O– and Co(C2H3O2)2–precursor derived Co3O4 presented
the same trends and ranged between 4.15 nm and 21.22 nm. For CoC12
.6H6O–derived Co3O4
nanoparticles, the crystallite sizes ranged between 3.06 nm and 17.97 nm. Methyl orange (MO) was treated using peroxymonosulfate that was activated by the
synthesised heterogeneous Co3O4 nanocatalyst for 30 minutes. Comparing the efficiency of
the Co3O4 nanocatalyst that was produced by three different precursor salts; it was found that
Co(NO3)2
.6H2O –derived Co3O4 nanocatalyst performed the best, removing 96% of the MO
solution while Co(C2H3O2)2–precursor derived Co3O4 nanocatalyst performed the worst, only
removing 67.93%.
A cost comparative analysis on the synthesis cost of Co3O4 via various cobalt precursors and
treatment cost of MO solution was used to evaluate the viability of a full-scale treatment
process. It was found that Co(NO3)2
.6H2O-derived Co3O4 nanocatalyst is the most cost efficient
and had the best performance in the treatment of MO solution. The production process
involves low reaction temperature and residence time to achieve the maximum yield whereas
CoC12
.6H6O and Co(C2H3O2)2 precursor salts have the higher requirements for the process
conditions.
and magnetic properties of the nanoscale particles that are uniquely different from those of
their corresponding bulk counterparts. The technological applications of Co3O4 nanostructures
such as solid-state sensors, anode materials in lithium-ion rechargeable batteries,
electrochromic sensors, heterogeneous catalyst, energy storage and magnetic materials have
drawn attention to the controlled synthesis of these nanomaterials. There is a lack in the
understanding of the effect of synthesis operating conditions (such as reaction temperature,
residence time, type of precursor anion and precursor concentration) and their interactions on
the produced Co3O4 nanoparticles. During this study the produced Co3O4 nanostructures were
applied as a catalyst for the degradation of methyl orange (MO) solution to establish if there
is a relationship between the product yield, crystallite size and the degradation percentage.
The chemicals that are used during the dying process as well as the structure of the dyestuff
makes the generated effluent highly polluted and difficult to treat. Advantaged oxidation
processes (AOP) have gained considerable interest due to the low selectivity to organic
pollutants in wastewater. AOPs involve the generation of hydroxyl free radicals by using
different oxidants that ultimately destroy components that are not removed under conventional
oxidation processes.
During this study, a Co3O4 nanocatalyst was produced through the hydrothermal synthesis
using three precursor salts with different counter anions (cobalt acetate tetrahydrate, cobalt
chloride and cobalt nitrate). A factorial design (face-centred central composite design) was
applied to create a design that would produce a prediction model to evaluate the effect of the
operating parameters (reaction temperature, precursor concentration and residence time) on
the product yield and crystallite size. X-ray diffraction (XRD) analysis showed that after
calcination Co3O4 nanostructures were produced.
Comparing the maximum yield obtained for each precursor the order was as follows:
Co(NO3)2
.6H2O (100%) > CoCl12
.6H6O (82%) > Co(C2H3O2)2 (66%). The product yields
obtained for Co(NO3)2
.6H2O–derived Co3O4 ranged from 56% to 100%.The product yields
obtained for CoC12
.6H2O–derived Co3O4 ranged from 1% to 82%. The product yields obtained
for Co(C2H3O2)2–derived Co3O4 ranged from 12% to 66%.
The crystallite size of Co(NO3)2
.6H2O– and Co(C2H3O2)2–precursor derived Co3O4 presented
the same trends and ranged between 4.15 nm and 21.22 nm. For CoC12
.6H6O–derived Co3O4
nanoparticles, the crystallite sizes ranged between 3.06 nm and 17.97 nm. Methyl orange (MO) was treated using peroxymonosulfate that was activated by the
synthesised heterogeneous Co3O4 nanocatalyst for 30 minutes. Comparing the efficiency of
the Co3O4 nanocatalyst that was produced by three different precursor salts; it was found that
Co(NO3)2
.6H2O –derived Co3O4 nanocatalyst performed the best, removing 96% of the MO
solution while Co(C2H3O2)2–precursor derived Co3O4 nanocatalyst performed the worst, only
removing 67.93%.
A cost comparative analysis on the synthesis cost of Co3O4 via various cobalt precursors and
treatment cost of MO solution was used to evaluate the viability of a full-scale treatment
process. It was found that Co(NO3)2
.6H2O-derived Co3O4 nanocatalyst is the most cost efficient
and had the best performance in the treatment of MO solution. The production process
involves low reaction temperature and residence time to achieve the maximum yield whereas
CoC12
.6H6O and Co(C2H3O2)2 precursor salts have the higher requirements for the process
conditions.
Additional information
Thesis (MEng (Chemical Engineering))--Cape Peninsula University of Technology, 2023
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