Environmental Engineering Reference
In-Depth Information
solvents,.arsenic,.and.other.contaminants.
in situ
..Granular.ZVI.has.been.used.since.
the.mid-1990s.in.groundwater.remediation..Practitioners.realized.early.in.the.use.of.
granular.ZVI.that.the.rate.of.reductive.dechlorination.of.chlorinated.hydrocarbons.
depended.strongly.on.the.surface.area.of.the.ZVI.particles..This.realization.led.to.the.
development.of.nZVI..Particles.of.nZVI.generally.range.between.40.and.300.nm.in.
diameter..This.particle.size,.because.of.the.increased.surface.area,.provides.greater.
reactivity.than.the.granular.ZVI.initially.in.use..The.direct.injection.of.nZVI,.how-
ever,.can.be.limited.in.the.ield.by.the.tendency.of.the.nanoparticles.to.agglomerate,.
and. as. discussed. in. Chapter. 10,. alternative. methods. to. alleviate. this. tendency. are.
being.developed.
2.4.3 s
ilver
Some.95%.of.silver.is.used.in.photography,.jewelry.and.silverware,.and.in.various.
industrial.applications..The.latter.includes.electrical.components,.brazing.alloys.and.
solders,.bearings,.catalysts,.miniature.batteries,.photovoltaic.cells,.and.other.prod-
ucts.[17,.18].
Silver.has.long.been.recognized.as.an.antibacterial.agent..Cyrus.the.Great,.King.
of.Persia,.reportedly.kept.water.fresh.in.the.sixth.century.B.C..by.boiling.the.water.
and.then.storing.it.in.silver.lagons.[19]..Pliny.the.Elder,.writing.in.78.A.D.,.said.that.
silver.slag.“….has.healing.properties.as.an.ingredient.in.plasters,.being.extremely.
effective. in. causing. wounds. to. close. up.”. In. modern. time,. silver. has. been. used. to.
purify.drinking.water,.sanitize.swimming.pools,.and.prevent.sepsis.in.wounds.[17,.
18]..Silver's.antibacterial.function.results.from.its.ability.to.disturb.the.multiplication.
function.of.bacteria.[17].
Thousands.of.years.after.the.irst.apparent.use.of.silver.as.a.bactericide,.nanoscale.
particles.of.silver.lend.antibacterial.qualities.to.new.commercial.products..Approxi-
mately.20%.of.the.available.nanotechnology.consumer.products.are.those.containing.
nano-scale.silver..Most.incorporate.silver.due.to.its.antibacterial.properties..These.
products.include,.as.described.above,.clothing,.food.storage.containers,.and.appli-
ances..They.also.include.wound.care.products.[1].
Nano-scale.silver.may.ind.more.uses.in.the.future..In.one.type.of.application,.
nano-scale. silver. is. used. in. an. extraordinary. analytical. technique.. Two. types. of.
nanoprobes.have.been.developed.under.the.sponsorship.of.the.U.S..Department.of.
Energy.[20,.21]..Each.probe.consists.of.a.silica.optical.iber.between.20.and.100.nm.
in. diameter. coated. with. a. thin. layer. of. silver.. The. “nanobiosensor”. probe. allows.
scientists.to.physically.probe.inside.a.living.cell.without.destroying.it..In.one.appli-
cation,.a.bioreceptor.molecule,.such.as.an.antibody,.DNA,.or.enzyme.that.will.bind.
to. a. speciic. target. molecule. of. interest. inside. the. cell,. is. immobilized. on. the. sil-
ver. surface. at. the. nanoprobe. tip.. Only. the. target. molecules. that. become. bound. to.
the.bioreceptor.are.exposed.to.and.excited.by.an.evanescent.laser.signal,.giving.off.
detectable.luorescent.light..The.team.leader,.Tuan.Vo-Dinh,.has.stated.that:
“[T}he.nanobiosensor.has.important.implications.ranging.from.drug.therapy.to.national.
security,.environmental.protection,.and.a.better.understanding.of.molecular.biology.at.
a.systems.level..This.area.of.research.is.truly.at.the.nexus.of.nanotechnology,.biology,.
and.information.technology.”
