Biomedical Engineering Reference
In-Depth Information
21.4 FiltrationMedia
Particularly. suitable. as. a. base. for. the. application. of. nanomaterials. are. ceramics. having.
interconnected. porosity,. where. nanomaterials. can. be. grown
directly. in. the. material
.
Ceramics.are.ideal.because.they.can.withstand.the.chemical.treatment.for.growing.nano-
materials.and.are.durable..Many.different.shapes.of.nanocrystals.can.be.grown.directly.
on.to.the.pore.wall..These.are.stable.and.not.removed.by.water.passing.into.or.through.the.
porous.material.
MetaMateria.uses.a.novel.process.for.making.porous.ceramics,.which.allows.formation.
of.simple.or.complex.shapes.using.inexpensive.processing.methods..These.can.be.made.
as. aggregates. or. monoliths,. depending. upon. the. requirements. of. the. cleanup. system..
Inorganic.hydrogels.are.used.to.strongly.bond.together.additives.such.as.zeolite.or.iron-
containing. compounds.. This. approach. allows. for. control. of. material. composition,. pore.
structure,.and.pore.size.distribution..Shown.in.Figure.21.3.are.examples.of.different.prod-
uct.shapes.(21.3a),.microscopic.close.up.of.product.surface.(21.3b).internal.interconnected.
pores.of.different.sizes.(21.3c),.and.nanomaterials.grown.on.the.pore.surfaces.(21.3d).
This.porous.ceramic.is.sold.for.aquaculture.and.waste.gas.cleanup.applications.where.
facultative.bacteria.are.used.for.the.removal.of.ammonia,.nitrites,.nitrate,.and.related.con-
taminants,.or.the.removal.of.odorous.gases.(H
2
S.and.VOCs)..These.products.are.used.in.
systems.where.water.is.circulated.and.reused,.such.as.in.aquaculture.and.where.waste-
water.or.waste.gases.require.intensive.and.specialized.treatment..These.same.materials,.
when.prepared.from.iron-containing.materials,.have.been.shown.to.be.effective.ilters.for.
water.remediation,
5
.such.as.removal.of.phosphates.
These.porous.materials.can.be.made.from.nearly.any.ine-grained.(even.waste).materi-
als,.and.lexibility.exists.for.controlling.porosity.without.iring.the.ceramic,.which.lowers.
cost..Pore.sizes.can.be.controlled.from.submicron.to.250.microns.or.larger..An.intercon-
necting.pore.network.is.formed.that.provides.a.large.surface.area.for.the.growth.of.bac-
teria.or.deposition.of.nanomaterials..The.typical.surface.area.of.these.porous.materials.is.
over.650,000.m
2
/m
3
,.compared.with.12,000.m
2
/m
3
.found.in.a.typical.sand.ilter.bed..This.
provides. for. a. signiicant. increase. in. active. surface. area. and. is. also. a. good. platform. for.
making.ilter.materials.tailored.for.a.wide.number.of.applications,.including.remediation.
and.bioiltration.
The. typical. porosity. of. these. ceramics. is. around. 85%,. and. because. of. the. hierarchy.
of. pores,. water. easily. lows. through. the. material. under. a. low. hydrostatic. pressure,. as.
seen.in.Figure.21.4..In.fact,.140.gallons/minute.can.pass.through.these.porous.ceramics.
Different
forms
Nanocrystals
Interconnecting
pores
Surface pores
.
(a).
(b).
(c).
(d)
FIGURE 21.3
Examples. showing. products(a),. product. surface(b),. internal. pore. structure(c). and. nanocrystals. on. pore.
surfaces.(d).
