Chemically Modified Carbon Paste Electrodes - Electroanalysis with Carbon Paste Electrodes - page 101

organofunctional. groups. covalently. bonded. to. the. inorganic. component.. Here,. only. hybrids. of.
class.II.are.considered.as.those.of.class.I.usually.overlap.with.inorganic.materials.bearing.organic.
or. organometallic. species. adsorbed. on—or. ion. exchanged. in—the. solid. phase. (see. examples. in.
Sections.4.3.1.1.through.4.3.1.3.for.organic.moieties.entrapped.in.polyoxo-metallates,.natural.clays,.
and.zeolites.or.adsorbed.on.metal.oxides.and.phosphates).
Actually.more.durable.immobilization.organofunctional.groups.onto.the.inorganic.matrix.can.
be.achieved.by.covalent.bonding..This.has.been.especially.developed.with.silica-based.materi-
als. in. electrochemistry. [89,831,1808].. Chemical. modiication. of. the. silica. surface. can. be. per-
formed.by.postsynthesis.grafting.or.by.the.direct.(one-pot).sol-gel.synthesis.involving.the.use.of.
organosilane.reagents..The.irst.examples.of.CPEs.incorporating.organically.functionalized.sili-
cas.dealt.with.long-chain.alkyl-grafted.silica.gels.(C 18 .[646,1809-1813].or.C 8 .[1814,1815]),.which.
were.applied.to.the.detection.of.drugs.and.pharmaceuticals..Then,.silica.samples.functionalized.
with.more.reactive.groups.have.appeared.as.CPE.modiiers,.with.organofunctional.groups.such.as.
propylamine.(for.metal.ions.accumulation.and.detection.[701,702,1816],.as.support.for.electrocat-
alysts.such.as.PMo 12 .[1817-1819],.or.to.immobilize.enzymes.[1167]),.propylpyridinium.(to.immo-
bilize. negatively. charged. redox. mediators. [1820-1824]),. a. wide. range. of. functions. exhibiting.
high. afinity. for. Hg(II). species. (i.e.,. mercaptopropyl. [106,702,1825],. benzothiazolethiol. [1826],.
3-(2-thiobenzimidazoyl)propyl. [1827],. 2,5-dimercapto-1,3,4-thiadiazole. [1828],. or. 2-amino-
thiazole.[1829]),.several.groups.binding.preferably.Cu(II).species.(i.e.,.aminopropyl.[701,1816],.
2-aminothiazole.[1830],.the.carnosine.dipeptide.[1831,1832],.propylsulfonate.[1833],.salicylidine.
[1834],.or.dipyridyl.groups.[1835]),.some.functions.leading.to.Pb(II).detection.(mercaptopropyl.
[106]. or. 2-aminopyridine. [1836),. as. well. as. some. others. likely. to. recognize. other. metal. ions,.
alone.or.in.mixture.[107,771,1837,1838].
Toluidine. blue. [1476]. and. a. salicylaldehyde-based. Schiff. base. ligand. [1211]. have. also. been.
grafted.onto.metal.oxide.particles.before.incorporation.into.CPEs..Besides,.organoclays.started.to.
become.attractive.CPE.modiiers.for.electroanalytical.purposes;.they.can.be.obtained.by.grafting.
(e.g.,.amino-.or.mercaptopropyl.groups.[1088,1089]).or.via.incorporation.of.long-chain.amphiphilic.
ligands.into.the.clay.interlayer.region.[1102,1103]..Finally,.self-assembled.organic-inorganic.hybrid.
materials.belonging.to.the.polyoxometalate.family.have.been.prepared.and.incorporated.in.CPEs.
to.be.exploited.for.the.electrocatalytic.detection.of.hydrogen.peroxide.or.nitrite.[1051,1839-1842].
4.3.3.2 Nanomaterials
Nanotechnology.is.extraordinarily.a.wide.ield.involving.contributions.from.the.physical.sciences,.
life.sciences,.engineering,.and.medicine..It.is.thereby.not.so.surprising.to.ind.some.traces.of.the.
“nanoworld”.also.in.electroanalytical.chemistry.with.CPEs..At.present,.this.has.essentially.appeared.
through.the.incorporation.of.porous.materials.ordered.at.the.nanoscale.or.NPs.in.CPEs.
4.3.3.2.1 Ordered Mesoporous Materials
Substances.of.this.kind.are.highly.porous.solids.(pore.volume.>.0.7.mL.g −1 ).exhibiting.high.spe-
ciic. surface. areas. (500-1500.m 2 . g −1 ). due. to. a. periodic. and. regular. arrangement. of. well-deined.
mesopores.deined.by.amorphous.inorganic.walls..Such.regular.framework.structures.are.usually.
prepared.by.the.sol-gel.process,.involving.the.hydrolysis.and.condensation.of.a.tetraalkoxysilane.
(Si(OR) 4 ),.in.the.presence.of.a.supramolecular.template.(surfactant.or.water-soluble.polymer)..The.
most.widely.used.are.ordered.mesoporous.silica-based.materials.prepared.by.the.surfactant.tem-
plate.route.(see.illustration.for.a.hexagonal.mesostructure.in.Figure.4.16A).
These. materials. have. attracted. the. attention. of. electroanalysts. as. their. regular. channels,. high.
speciic.surface.areas,.and.consequently.high.number.of.easily.accessible.active.sites.have.enabled.
improving.the.performance.of.silica-modiied.electrodes.[89,816,1843],.as.reported.for.the.detec-
tion. of. several. organic. species. (mainly. drugs). [999,1844-1852]. and. some. metal. ions. [1853,1854].
at.mesoporous.silica-modiied.CPEs..Al-doped.mesoporous.silica.in.CPEs.was.also.exploited.for.
its. catalytic. properties. in. epinephrine. and. catechol. sensing. [1855,1856].. Even. more. interesting. is.