Environmental Engineering Reference
In-Depth Information
...
Particle-induced x-Ray emission (Pixe)
PIXE. measurements. can. provide. major,. minor,. and. trace. constituent. analyses. of.
nanoparticles..The.instrument.directs.a.beam.of.protons.from.a.high-energy.particle.
accelerator.that.will.knock.out.core.electrons.from.the.atoms.of.the.sample..X-rays.
are.then.emitted.when.outer.shell.electrons.drop.into.the.orbital.from.which.the.pro-
ton-ejected.electron.came..The.resulting.x-ray.spectrum.of.the.sample.can.be.used.
for.elemental.identiications..The.requirement.for.a.particle.accelerator.to.generate.
the. proton. beam. makes. PIXE. techniques. very. costly. and. available. in. only. a. lim-
ited.number.of.research.laboratories..The.technique.has.been.used.for.trace.element.
analysis.of.background.aerosol.particles.in.the.heavily.polluted.air.of.Mexico.City.
[28],.but.it.is.likely.to.remain.a.research.tool.with.limited.use.
5.1.3 s
urFaCe
a
rea
: p
rOduCt
C
haraCteriZatiOn
and
a
ir
m
OnitOring
Surface.area.is.a.critical.parameter.inluencing.the.properties.and.activity.of.nanopar-
ticles..In.large.part,.this.is.believed.due.to.the.comparatively.high.number.of.atoms.on.
the.surface.of.the.particle.as.opposed.to.larger.particles.where.most.atoms.are.interior..
Surface.areas.for.individual.particles.can.be.estimated.from.the.imaging.techniques.
discussed.above,.but.techniques.for.determining.the.average.surface.area.for.a.bulk.
sample. of. nanoparticles. are. more. commonly. used. to. monitor. production. of. nano-
materials.for.speciic.uses..Some.of.these.methods.also.are.applicable.for.materials.
characterization.before.laboratory.exposure.studies,.and.for.environmental.samples.
...
the brunauer emmett teller (bet) Method
The.BET.method.is.named.for.the.three.scientists.who.recognized.that.particulate.
surface.area.can.be.determined.based.on.the.volume.of.gas.that.will.adsorb.to.the.
surface. of. a. given. mass. of. sample.. The. BET. equation. relates. the. volume. of. gas.
adsorbed. to. form. a. monolayer,. the. size. of. the. gas. molecules,. and. the. mass. of. the.
material.to.derive.surface.area.per.unit.mass..Commercial.analyzers.are.available.
that.perform.this.measurement,.which.may.be.used.during.development.and.produc-
tion..In.a.representative.research.application,.BET.measurements.were.relied.upon.
for.size.characterization.of.nitrogen-doped.titanium.dioxide.prepared.as.a.photocat-
alyst.for.
Escherichia coli
.disinfection.[29]..Because.BET.requires.a.relatively.pure.
bulk.sample.of.a.chemically.homogeneous.material,.it.has.not.found.application.for.
environmental.analyses.
...
epiphaniometer
The.epiphaniometer.is.a.relatively.simple.device.that.measures.the.active.surface.area.
of.aerosol.particles..Particles.entering.the.instrument.are.charged.with.radioactive.
lead.ions.and.then.collected.on.a.collection.ilter..The.measured.total.radioactivity.
is.a.measure.of.the.attachment.rate,.which.then.allows.calculation.of.the.total.active.
surface.area.of.particles.in.the.sample..The.requirement.for.a.radioactive.source.lim-
its.the.wide.use.of.this.instrument,.but.it.has.been.used.in.research.programs.such.as.
mobile.laboratory.studies.of.on-road.air.quality.as.related.to.trafic.emissions.[30].
