Editing Carbon nanotube (section)

== Functionalization ==
{{Main|Carbon nanotube chemistry|Selective chemistry of single-walled nanotubes}}
Carbon nanotubes can be [[functionalized]] to attain desired properties that can be used in a wide variety of applications.<ref>{{cite journal| last1 = Bekyarova| first1 = E.| last2 = Davis | first2 = M.| last3 = Burch | first3 = T.| last4 = Itkis | first4 = M. E.| last5 = Zhao | first5 = B.| last6 = Sunshine | first6 = S.| last7 = Haddon | first7 = R. C.| title = Chemically Functionalized Single-Walled Carbon Nanotubes as Ammonia Sensors| journal = J. Phys. Chem. B| volume = 108| issue = 51| pages = 19717–19720| publisher = ACS Publications| location = Washington, D.C.| date = October 9, 2004| url = https://www.sensigent.com/img/pdf/2004%20Bekyarova%20et%20al%20J.%20JPhys%20Chem%20Chemically%20Functionalized%20Single-Walled%20Carbon%20Nanotubes%20as%20Ammonia%20Sensors.pdf| issn = 1520-5207| doi = 10.1021/jp0471857 | s2cid = 96173424}}</ref> The two main methods of carbon nanotube functionalization are covalent and non-covalent modifications. Because of their apparent hydrophobic nature,<ref>{{cite journal | vauthors = Stando G, Łukawski D, Lisiecki F, Janas D |date=January 2019 |title=Intrinsic hydrophilic character of carbon nanotube networks|journal=Applied Surface Science |volume=463 |pages=227–233 |doi=10.1016/j.apsusc.2018.08.206 |bibcode=2019ApSS..463..227S|s2cid=105024629 |url=https://depot.ceon.pl/handle/123456789/19888 }}</ref> carbon nanotubes tend to agglomerate hindering their dispersion in solvents or viscous polymer melts. The resulting nanotube bundles or aggregates reduce the mechanical performance of the final composite. The surface of the carbon nanotubes can be modified to reduce the [[Hydrophobe|hydrophobicity]] and improve interfacial [[adhesion]] to a bulk [[polymer]] through chemical attachment.<ref name="Karousis-2010">{{cite journal | vauthors = Karousis N, Tagmatarchis N, Tasis D | title = Current progress on the chemical modification of carbon nanotubes | journal = Chemical Reviews | volume = 110 | issue = 9 | pages = 5366–5397 | date = September 2010 | pmid = 20545303 | doi = 10.1021/cr100018g }}</ref>

Chemical routes such as covalent functionalization have been studied extensively, which involves the oxidation of CNTs via strong acids (e.g. [[sulfuric acid]], nitric acid, or a mixture of both) in order to set the carboxylic groups onto the surface of the CNTs as the final product or for further modification by esterification or amination. Free radical grafting is a promising technique among covalent functionalization methods, in which alkyl or aryl peroxides, substituted anilines, and diazonium salts are used as the starting agents.

Functionalization can improve CNTs characteristically weak dispersibility in many solvents, such as water - a consequence of their strong intermolecular p–p interactions. This can enhance the processing and manipulation of insoluble CNTs, rendering them useful for synthesizing innovative CNT [[nanofluid]]s with impressive properties that are tunable for a wide range of applications.

Free radical grafting of macromolecules (as the functional group) onto the surface of CNTs can improve the solubility of CNTs compared to common acid treatments which involve the attachment of small molecules such as hydroxyl onto the surface of CNTs. The solubility of CNTs can be improved significantly by free-radical grafting because the large functional molecules facilitate the dispersion of CNTs in a variety of solvents even at a low degree of functionalization. Recently an innovative environmentally friendly approach has been developed for the covalent functionalization of multi-walled carbon nanotubes (MWCNTs) using clove buds. This approach is innovative and green because it does not use toxic and hazardous acids which are typically used in common carbon nanomaterial functionalization procedures. The MWCNTs are functionalized in one pot using a free radical grafting reaction. The clove-functionalized MWCNTs are then dispersed in water producing a highly stable multi-walled carbon nanotube aqueous suspension (nanofluids).<ref>{{cite journal | vauthors = Sadri R, Hosseini M, Kazi SN, Bagheri S, Zubir N, Solangi KH, Zaharinie T, Badarudin A | title = A bio-based, facile approach for the preparation of covalently functionalized carbon nanotubes aqueous suspensions and their potential as heat transfer fluids | journal = Journal of Colloid and Interface Science | volume = 504 | pages = 115–123 | date = October 2017 | pmid = 28531649 | doi = 10.1016/j.jcis.2017.03.051 | bibcode = 2017JCIS..504..115S }}</ref>

The surface of carbon nanotubes can be chemically modified by coating spinel [[nanoparticle]]s by hydrothermal synthesis<ref>{{cite journal | vauthors = Sahoo P, Shrestha RG, Shrestha LK, Hill JP, Takei T, Ariga K |title=Surface Oxidized Carbon Nanotubes Uniformly Coated with Nickel Ferrite Nanoparticles |journal=Journal of Inorganic and Organometallic Polymers and Materials |date=November 2016 |volume=26 |issue=6 |pages=1301–1308 |doi=10.1007/s10904-016-0365-z |s2cid=101287773 }}</ref> and can be used for water oxidation purposes.<ref>{{cite journal | vauthors = Sahoo P, Tan JB, Zhang ZM, Singh SK, Lu TB |title=Engineering the Surface Structure of Binary/Ternary Ferrite Nanoparticles as High-Performance Electrocatalysts for the Oxygen Evolution Reaction |journal=ChemCatChem |date=7 March 2018 |volume=10 |issue=5 |pages=1075–1083 |doi=10.1002/cctc.201701790 |s2cid=104164617 }}</ref>

In addition, the surface of carbon nanotubes can be [[Halogenation|fluorinated]] or halofluorinated by heating while in contact with a fluoroorganic substance, thereby forming partially fluorinated carbons (so-called Fluocar materials) with grafted (halo)fluoroalkyl functionality.<ref>{{cite patent|country=US|number=10000382|title=Method for carbon materials surface modification by the fluorocarbons and derivatives|url=http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=/netahtml/PTO/srchnum.htm&r=1&f=G&l=50&s1=10000382.PN.&OS=PN/10000382&RS=PN/10000382|issue-date=June 19, 2018|inventor=Zaderko A, Vasyl UA}} {{Webarchive|url=https://web.archive.org/web/20180917143354/http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=10000382.PN.&OS=PN/10000382&RS=PN/10000382 |date=17 September 2018 }}</ref><ref>{{cite web|url=https://patentscope.wipo.int/search/en/detail.jsf?docId=WO16072959|title=WO16072959 Method for Carbon Materials Surface Modification by the Fluorocarbons and Derivatives|website=patentscope.wipo.int|access-date=2018-09-17}}</ref>