Adsorptions by Carbons

735 Pages·2008·60.85 MB·english

by  Bottani E.J.

DEDICATION
The genesis of this book can be traced back to July 2003, the date of the
Carbon2003 Conference. ThispresentedEduardoJ. Bottaniandmyselfwithan
excellentopportunitytointroduceourprojectto lainCraig, theCommissioning
Editor with whom we discussed the scope and contents of the book. Soon
afterwards, the publication ofthe book was approved by Elsevier Science and
we established initial contacts with some prospective authors. However, the
unexpected death ofEduardoJ. Bottani on October24,2003, meant that Inow
had a dual responsibility, not only to the publisher and the authors who had
already agreed to contribute chapters, but also to the memory ofEduardo, to
whom I wish to dedicate this book. Needless to say, I accept full responsibility
for any faults in the editing as Eduardo passed away before we began the work
in earnest.
Prof. EduardoJorge Bottani was born in BahiaBlanca, Argentina, onJuly 2,
1955. After completing his studies in Chemistry (speciality: Physical Chemistry)
at the Universidad Nacional de La Plata (UNLP), he went on to gain a PhD
in the same university and speciality in 1982. His thesis, carried out under
the supervision of Prof. Lydia E. Cascarini de Torre, was entitled "Study of
interactions in physically adsorbed molecules."
Exceptforseveralperiodsofstudyabroad,firstatLouvain-Ia-Neuve,Belgium,
andlateratState College, PA, USA (withProf. W.A. Steele),EduardoJ. Bottani
spent most ofhis life in La Plata and his entire professional career at INIFTA, a
renowned research institute devoted to Basic and Applied Physical Chemistry.
It was here while a member ofthe Physical Adsorption Laboratory that he held
several positions as a research scientist for CIC. Towards the end ofhis life he
also collaborated with Profs A.J. Arvia and E.A. Castro, successive directors of
the Institute, in organizational tasks. While carrying out his scientific research,
he taught General, Inorganic and Physical Chemistry at UNLP (his Alma Mater
which, I regret to say, returned him much less than he had given her). Later
on, he was given the post ofVisiting Professor at the Universidad Nacional del
Litoral (UNL) in the city ofSanta Fe, where, together with Prof. H.S. Odetti,
he formed a flourishing research team.
I first met Eduardo on October 12, 1992, when Lydia Cascarini and he
welcomed me at Ezeiza Airport in Buenos Aires (the date is easy to remember
as it was exactly 500 years to the day after a famous discovery known to
all mankind). This was the beginning of a period of collaboration that has
culminatedin theproductionofthis book. Since 1999, EduardoJ. Bottanispent
onemonthayearinOviedo, wherewe combinedoureffortsininvestigatinggas
physisorptionon different materials such as carbonblacks, fullerenes, and carbon
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vi Dedication
nanotubes. Moreover, he and I shared an interest in art (especially architecture)
and made many weekend visits to different monuments ofour Spanish cultural
heritage.
At the time he passed away, Prof Bottani was Deputy Director ofINIFTA
and General Secretary of the Argentine Chemical Society (Asociaci6n Qu£mica
Argentina, AQA). Shortly before, he had been appointed Editor-in-Chief of
theJournal ofthe Atgentine Chemical Society, where he took up the challenge of
convertingthe traditionalAnalesde laAQAinto atrulyinternationaljournal. He
was also responsible for the organization ofanumber ofArgentine Conferences
on Chemistry. All ofthese facts about his life show that EduardoJ. Bottani was
at the summitofhis careeratthe time ofhis death, sadlyyetanotherunfortunate
case ofa gifted person with a promising future brought to a premature end.
EduardoissurvivedbyhiswifeJovitaMontonideBottani, daughterEstefania,
and sons Eduardo and Ezequiel, to whom, together with his mother, Dona
Elvira Gar6foli de Bottani and rest ofthe family, friends, and colleagues I offer
this book as a token ofmy esteem.
Juan M.D. Tasc6n
FOREWORD
It has been a great pleasure for me to write a foreword for this very interesting
book on Adsorption by Carbons in response to an invitation I first received
from the editors in August 2003 when the book was still only a project. This
invitation has afforded me the opportunity and the privilege of uniting the
efforts ofan outstanding group ofrenowned scientists as authors ofthe different
chapters, some ofwhom have been either my colleagues or disciples.
Part 1 ofthe book is ofan introductory nature. Thus, Chapter 1 provides
an updated overview of adsorption by carbons, differentiates the features of
adsorption on nonporous and porous carbons, and identifies the main obstacles
still hindering the study of gas adsorption by porous carbons. Recent major
developments and research needs in this field are also mentioned. Chapter 2
presents a survey ofcarbons in the context ofadsorption and classifies them on
the basis ofstructural criteria. This chapter might help nonspecialists in carbon
to find materials that they can use for adsorption purposes.
Part2 ofthebookaddresses the fundamental aspects ofadsorptionbycarbons.
The first few chapters deal with the energy aspects of gas adsorption. Thus,
Chapter 3 focuses on thermodynamic quantities, with particularattention being
paid to their significance and relation to experimental results. Cursory descrip
tions ofthe classical and statistical thermodynamic approaches are presented in
the form ofessential equations. Chapter4presents two types ofsimulation tech
niques (Monte Carlo and Molecular Dynamics) that help us to understand the
behavior ofmolecules on surfaces ofcarbons and other materials. It is pointed
out that the former method is more useful for studying transport properties,
whereas the latter provides information about the thermodynamic properties at
the adsorbent/adsorbate interface. New areas under development in this field
are outlined. Chapter 5 focuses on models of porous carbons that are useful
for predicting and explaining the behavior ofadsorbed phases. The discussion
encompasses both classical single-pore models (e.g., the well-known slit-shaped
pore) as well as more realistic models that include factors such as connectivity or
tortuosity. The connection between models and experimental techniques and
the needfor improvingmethods ofobtainingexperimental data are emphasized.
Chapter6 dealswithadsorptionhysteresis or, to bemoreprecise, the originof
adsorption hysteresis. It addresses the peculiar characteristics ofhysteresis in the
case ofcarbon adsorbents, namely, structurallability and the presence ofsurface
chemical structures (principally, oxygenated groups) that modify the energetics
and wettability behavior ofcarbon surfaces. The surface heterogeneity ofcar
bons is analyzed in Chapter 7 on the basis that practically all real adsorbents
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xviii Foreword
are heterogeneous. The big differences within the ensemble ofcarbon mate
rials (ranging from higWy homogeneous graphites to extremely heterogeneous
activated carbons) are discussed and the factors that cause heterogeneity are ana
lyzed. The wetting ofsolid surfaces by liquids is addressed next in Chapter 8.
To analyze the wetting ofcarbon, the study was extended from graphite (by
far the most widely studied carbon surface) to include other materials such as
carbon nanotubes, the geometry ofwhich greatly affects the wetting properties.
The theory and simulation ofgas adsorption on carbon nanotube bundles is
addressed in Chapter 9, which focuses on the structural, dynamic, and thermal
properties ofgases adsorbed at sites such as grooves between pairs ofnanotubes,
interstitial channels, or inner spaces inside the individual tubes. This chapter
serves as a background for Chapter 15, which belongs to Part 3 ofthe book.
The section on fundamentals ends with Chapter 10, which follows two general
approaches (the generalized Gaussian model and the bivariate model) to charac
terize the energy topography ofcarbon surfaces. The former model is attractive
due to its simplicityandworks wellwith substrateswith arough-surface adsorp
tive energy. The bivariate model is applicable to heterogeneous surfaces with
two kinds ofsites.
The series of 10 chapters that constitute Part 3 of the book deals mainly
with the use ofadsorption as a means ofcharacterizing carbons. Thus, the first
three chapters in this section complement each other in the use of gas-solid
or liquid-solid adsorption to characterize the porous texture and/or the surface
chemistry ofcarbons. Porous texture characterization based on gas adsorption
is addressed in Chapter 11 in a very comprehensive manner and includes a
description ofa number ofclassical and advanced tools (e.g., density functional
theory and Monte Carlo simulations) for the characterization of porosity in
carbons. Chapter 12 illustrates the use ofadsorption at the liquid-solid interface
as ameans to characterize both pore texture and surface chemistry. The authors
propose these methods (calorimetry, adsorption from solution) to characterize
carbons for use in such processes as liquid purification or liquid-solid hetero
geneous catalysis, for example. Next, the surface chemical characterization of
carbons is comprehensively treated in Chapter 13, which discusses topics such
as hydrophilicity and functional groups in carbon as well as the amphoteric
characteristics and electrokinetic phenomena on carbon surfaces.
The next block (Chapters 14-18) is principally devoted to the characteriza
tion ofseveral types ofcarbon that deserve attention for their novelty. Thus,
fullerenes, which are dealt with in Chapter 14, are studied as adsorbents with
various objectives in mind: for the fundamental investigation of their surface
energetics; as tools for the preconcentration and analysis ofspecies in solution;
or even as possible substrates for hydrogen storage. This last topic is still a "hot"
one in the case of carbon nanotubes, which explains why two whole chap
ters (besides Chapter 9) have been dedicated to this type ofmaterial. One of
them (Chapter 15) addresses hydrogen adsorption from amore theoreticalpoint
of view, while the other (Chapter 16) takes a look at the actual knowledge
obtained from the experimental results published in the literature and therefore
Foreword xix
offers the reader a complementary, more practical view. Chapter 15 identifies
two problems that continue to obstruct progress in research, namely, the vari
ability ofthe materials being studied by different teams and the lack ofreliable
computational methods for determining adsorption potentials or chemisorption
interactions. Chapter 16 discusses the nature ofdifferent types ofadsorption sites
onnanotube surfaces and concludes thatfurther research is neededto make such
sites more easily identifiable, particularly high energy binding sites.
The next two chapters deal mainly with the use ofadsorption to character
ize porous solids. In the case ofactivated carbon fibers (Chapter 17), methods
to characterize microporosity, and particularly ultramicroporosity, by physi
cal adsorption are of particular relevance for understanding the behavior of
these adsorbents and extending the range of their applications. Moreover, in
Chapter 18 the pore structure of ordered mesoporous carbons is shown to
differ greatly from that of conventional activated carbons for which most of
the available data treatment methods have been developed. Therefore, suitable
procedures for correctly analyzing the pore structure ofthese novel carbons are
proposed in this chapter.
Two chapters related with the solid-liquid interface conclude Part 3. The
electrochemical behavior of carbons is the subject of Chapter 19, which dis
cussesthe characteristicsofcarbon electrodematerialswith reference to concepts
such as roughness or fractality, and also the electrochemical kinetics on carbon
electrodes. Chapter 20 deals with the application ofscanningprobe microscopy
to the study ofinorganic and organic adsorbates deposited on highly oriented
pyrolytic graphite (HOPG) at the submonolayerandmonolayerlevel. The basal
plane surface ofHOPG is taken as a model system, thanks to its atomic-scale
smoothness and low chemical reactivity.
Part 4 ofthe book deals with the applications ofadsorption in different fields
oftechnologywith explanations as to why carbons exhibit aparticularbehavior.
First ofall, gas-phase applications are addressed, eitherfor the removal ofpollu
tants (both volatile organic compounds and inorganic gases, Chapter 21) or for
gas separationandstorage (Chapter22). Thesetwo chapterspresent comprehen
sive summaries ofthe surface science involved in these important processes and
provide clues for selecting the right carbons to be used as adsorbents. Another
application ofcarbons in the field ofenergy is that ofelectrochemical energy
storage. Chapter 23 discusses the two most important current lines ofinvestiga
tion, namely, lithiumbatteriesandsupercapacitors, andrelates theirperformance
to carbon characteristics and identifies present research needs.
Finally, Chapters 24-27 deal with the environmental applications ofcarbons
as adsorbents for the removal ofpollutants from aqueous solutions. These four
chapters are highly complementary. Thus, Chapter 24, which addresses the
problems associated with the removal ofinorganic species, finds its "alter ego"
in Chapter 25, which deals with the adsorption oforganic solutes from dilute
aqueous solutions. Both chapters provide insights into the fundamental reasons
for the performance exhibitedby acarbonaceous adsorbent. The global topic of
waterpurification using carbons as adsorbents is addressedin Chapter 26, which
xx Foreword
deals with the science and technology involved in the removal ofa surprising
variety of pollutants from water employing activated carbon, either in pow
dered or in granular form. Finally, Chapter 27 is somewhat complementary to
Chapter 25 as it discusses the sorption ofviscous organics (as opposed to dilute
organic solutes). However, there is a significant difference in the type ofadsor
bent. Indeed, the removal ofviscous organics (e.g., heavy oils and biomedical
molecules) requires a macroporous adsorbent (e.g., exfoliated graphite) rather
than a microporous one.
From the preceding overview it is easy to imagine the enormous effort
required ofthe editors and the authors ofthe different chapters to bring this
important piece of work to a satisfactory conclusion. I believe that this will
become a reference book for any person interested in the subject ofadsorption
andcarbons. Itwillbe usefulnotonlyto thosebeginningtheirstudyofactivated
carbons and related materials, but also to specialists wishing to further explore
this interesting field ofresearch. New discoveries are constantly being made in
this area, leading to the solution ofnumerous problems, both ofa theoretical
natureandintheappliedfieldofmodernscienceandtechnology. Letmeconvey
again my congratulations to the editors and my esteem for Prof Bottani of
whom I have a fond memory. Finally, may I wish Prof Tascon further success
in this interesting field ofresearch.
Prof Dr.Juan de Dios Lopez-Gonzalez
Granada and Madrid, Spain
PREFACE
The essential aim ofthis work is to fill the gap that exists between the fields of
adsorption and carbon materials, an area that, to our knowledge, has not been
encompassed so far in one single book. Several books address the phenomenon
ofadsorption from both a fundamental and an applied perspective, while pub
lications on the structure, properties, and applications ofcarbons, either general
or restricted to specific types ofmaterials, are increasingly common. There are,
also, a number ofworks devoted to porosity in carbons or other solids. How
ever, adsorption is involved in many areas other than porosity characterization.
In short, the interplay between adsorption and carbon materials has not been
addressed yet in one volume. There is a vacuum ofknowledge between both
fields that, iffilled, could give birth to new concepts and ideas.
Adsorption cannot occur without the active and mutual participation ofthe
adsorbent and adsorbate. Indeed, the book is purposely entitled "Adsorption by
Carbons" (ratherthan, forinstance, "Adsorptionon Carbons") to emphasize the
dynamic characterofadsorptionandthe active participationofthe carbonaceous
adsorbent, which not only provides adsorption sites but also attracts adsorbates
to its surface.
The book consists offour parts. Part 1 which is the shortest (two chapters),
introduces the reader to the field ofadsorption by carbons and to the realm of
carbon materials. The following eight chapters address the fundamental aspects
ofadsorptionby carbons through such topics as adsorption energetics, computer
simulations, modeling, surfaceheterogeneity, andso on. Indeed, thissecondpart
ofthebookdevelopsaseriesofconceptsthatcontributetoabetterunderstanding
ofwhat follows in the third section, in which adsorption is mainly envisaged as
a tool to characterize carbon surfaces. The third part, consisting of10 chapters,
begins with a look at the adsorption methods used to study the porous texture
and surface chemistry of carbons, and then follows with chapters devoted to
several novel types ofmaterials to conclude with a discussion on certain aspects
ofthe electrochemistry ofadsorption by carbons. Finally, the fourth part (seven
chapters) deals with the most significant technological applications ofadsorption
by carbons, either at the gas-solid or at the liquid-solid interface, which have
direct implications especially for the fields ofenvironment and energy. Overall,
the ensemble of27 chapters tries to cover the subject ofadsorption by carbons
as comprehensively as possible.
In my view, the main strength ofthe book derives from the stature ofthe
contributing authors. I have always thought that Eduardo Bottani and I were
beingalittle overambitious (perhaps even daring?) in inviting the best specialists
in the various areas to contribute chapters. Some were our friends, others were
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xxii Preface
just acquaintances we had met at conferences, and there are still a few whom I
still do not know personally. But all ofthem share one thing in common, and
that is that they are leaders in their respective fields. The important thing is that
we succeeded in our invitation, and I am very happy with the result of this
collective effort. The book has an undeniably international flavor, as it includes
authors from 13 different countries. Apart from a possibly slight imbalance in
favor ofthe New World (USA and Argentina), the geographical distribution
ofthe authors is fairly representative ofthe places where adsorption by carbons
is being investigated. I will purposely avoid citing authors' names here, as this
would make the preface outstandinglylong. Let me simply thank all the authors
collectively for having accepted the invitation to produce their chapters, for the
care they have taken in preparing them, and for their continued willingness
to help me. My thanks are extended to the staffofElsevier, particularly lain
Craig, Commissioning Editor, Kristi Green, Administrative Editor, and Sunita
Sundararajan, Project Manager, for their very professional assistance at many
stages ofbook's preparation.
Last but not least, my warmest thanks go to Prof DrJuan de Dios Lopez
Gonzalezfor havingacceptedtowrite aforeword to thisbook. NeitherEduardo
Bottani nor Iare direct descendants ofthe scientific school that originallyspread
from Granada University under his guidance. The international reputation that
the Spanish-speaking scientific community enjoys in the field ofadsorption by
carbons owes much to the efforts ofthat school. Interestingly, the first papers
that came to the attention of Eduardo and myself at the beginning of our
research careers in the late 1970s were those ofProfessor Lopez-Gonzalez and
coworkers. Thus we shared the same introductory academic experience in two
such distant places as far apart as La Plata and Madrid! I refer, of course, to
physical distance, since few countries are so close to each other emotionally as are
Argentina and Spain.
Juan M.D. Tascon
LIST OF CONTRIBUTORS
AlejandroJ. Arvia
Instituto de Investigaciones Fisicoquimicas Te6ricas y Aplicadas (INIFTA)
Universidad Nacional de La Plata-Consejo Nacional de Investigaciones
Cientificas y Tecnicas
La Plata, Argentina
[email protected]
TeresaJ. Bandosz
Department ofChemistry
City College ofNew York
New York, NY, USA
[email protected]
Fran~oisBeguin
Centre de Recherche sur la Matiere Divisee
CNRS-Universite
Orleans Cedex, France
[email protected]
Henry Bock
Department ofChemical and Biomolecular Engineering
North Carolina State University
Raleigh, NC, USA
[email protected]
Hans-Peter Boehm
Department ofChemistry and Biochemistry
University ofMunich, Germany
[email protected]
MaryJ. Bojan
Department ofChemistry
The Pennsylvania State University
University Park, PA, USA
[email protected]
Agustin E. Bolzan
Instituto de Investigaciones Fisicoquimicas Te6ricas y Aplicadas (INIFTA)
UNLP-CIC-CONICET
La Plata, Argentina
[email protected] (or) [email protected]
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