Chemically Modified Carbon Paste Electrodes - Electroanalysis with Carbon Paste Electrodes - page 102

Surfactant
(template) + Si(OR) 4

Template
removal

Mesostructured
hybrid network

Mesoporous
silica (A)

15 μA

1 μA

(b)

(d)

(a) (c)

-0.5 -0.4 -0.3
E (V)

-0.2 -0.1 -0.5 -0.4 -0.3

E (V)

-0.2 -0.1

(B)

FIGURE 4.16 Schematic. pathway. for. preparing. surfactant-templated. mesoporous. silica. from. tetralkoxy-
silane.(A)..Comparison.between.thiol-functionalized.silica.gels.and.ordered.mesoporous.silicas.(MCM-41.and.
SBA-15.types).in.CPEs.applied.to.preconcentration.electroanalysis.of.Hg II .species.(B). Experimental condi-
tions :.Electrochemical.curves.obtained.after.2.min.accumulation.in.1.μM.Hg II ,.with.various.mercaptopropyl-
grafted.silica.samples.incorporated.in.carbon.paste.electrodes:.(a).small.pore.(∼4.nm).silica.gel,.(b).large.pore.
(∼6.nm).silica.gel,.(c).small.pore.(∼3.nm).MCM-41,.and.(d).large.pore.(∼6.nm).SBA-15..After.transfer.to.an.
analyte-free.solution.(0.1.M.HCl.+.5%.TU),.the.curves.were.recorded.in.the.DPASV.mode.

the. possibility. to. functionalize. mesoporous. silica. materials.. The. previous. section. has. underlined.
the. very. rich. silica. chemistry. and. the. interest. of. silica-based. organic-inorganic. hybrids. as. CPE.
modiiers,.and.it.is.therefore.not.so.surprising.that.an.increasing.number.of.studies.are.dealing.with.
the.incorporation.of.organically.functionalized.mesoporous.silica.into.CPEs.for.electroanalytical.
purposes..The.main.interest.of.ordered.mesoporous.organosilica.in.comparison.to.their.nonordered.
homologues.is.the.easier.access.to.binding.sites.and.faster.mass.transfer.processes,.inducing.dra-
matic. increases. in. sensitivity. of. the. resulting. modiied. CPEs. (see. illustrative. example. for. Hg(II).
detection.at.thiol-functionalized.silicas.in.Figure.4.16B.[1857]).
Other. examples. are. available. for. mesoporous. silica. functionalized. with. aminopropyl.
[701,1858,1859],.carbamoylphosphonic.acid.[770,771],.2-benzothiazolethiol.[1860-1862],.5-mercapto-.
1-methyltetrazole.[1863],.propylsulfonic.acid.[1833],.thiomorpholine.[1864],.carnosine.[1832],.acet-
ylacetone.[1865],.2-acetylpyridine.[1866],.thiourea.derivatives.[1867,1868],.or.ferrocene.[878]..The.
vast.majority.of.these.works.used.hexagonal.mesostructures.of.MCM-41.or.SBA-15.types..Attention.
should.be.drawn,.however,.to.the.fact.that.all.claimed.nanoporous.silicas.are.not.obligatory.ordered.
as. those. formed. by. the. surfactant. template. route. (see,. e.g.,. dipyridyl-functionalized. nanoporous.
silica.gels.in.CPEs.[1869-1871])..MCM-41.was.also.used.as.a.host.for.electrochemiluminescence.
reagents.as.reported.for.ionic.liquid-based.CPE.[462]..Finally,.it.is.worth.mentioning.that.the.use.of.
mesoporous.materials.other.than.silica.in.CPEs,.such.as.nanostructured.mixed-valence.manganese.
oxides. [1872-1874],. mesoporous. TiO 2 . [994,1875]. or. ZrO 2 . [1876],. as. well. as. ordered. mesoporous.
carbons.[116].