posted on 2020-06-03, 12:36authored byJoão Restivo, Carla Alexandra Orge, Ana Sofia Guedes Gorito dos Santos, Olívia Salomé
Gonçalves Pinto Soares, Manuel Fernando Ribeiro Pereira
Multiwalled carbon nanotubes (MWCNTs)
are known to have great potential to be used as catalysts in the ozonation
of organic pollutants in water. However, solutions are required toward
their practical application to overcome difficulties with the handling
of nanosized powders. One such alternative is their coating on macrostructured
ceramic supports. The majority of instances of such applications are
based on the in situ formation of a nanocarbon layer by chemical vapor
deposition. With recent advances in the modification of MWCNTs by
mechanical methodologies showing that these can enhance their catalytic
activity, there is an interest in the coating of ceramic macrostructures
with a premodified MWCNTs because mechanical methods are not applicable
to in situ grown materials. The coating of a MWCNTs using a conventional
dip-coating technique would allow for premodification of the carbon
by mechanical means. However, several obstacles in the formation of
the slurry and nanostructured layers exist because of the behavior
of the MWCNTs in suspension. In this work, the textural and morphological
modification of MWCNTs by ball milling and subsequent interaction
with different organic binders and surfactants in slurries was investigated.
The main characteristics influencing the slurry stability and its
use in the dip-coating of cordierite macrostructures were identified.
Different modes of nanostructured layer formation were observed depending
on the particle size distribution of the slurry, which is influenced
by the surface chemistry and morphology of the MWCNTs. A correlation
between the nanostructured layer homogeneity and adhesion and the
slurry particle size distribution was established. This understanding
was applied to form nanostructured layers with a pretreated nitrogen-containing
MWCNTs. The material’s basic character resulted in larger slurry
particle sizes and consequently poorly adhered coatings. An approach
using a premixed MWCNTs with a nitrogen precursor was shown to be
able to produce nanostructured coatings with a nitrogen-doped MWCNTs
and good adherence. The resulting nanostructured layers of MWCNTs
were found to be catalytically active in the ozonation of a model
organic pollutant (oxalic acid).