Modified multi-walled carbon nanotubes including multi-walled carbon nanotubes and carboxylate moieties and related methods

1 . A modified multi-walled carbon nanotube (MWCNT) comprising:

a MWCNT comprising an outer surface; and

a plurality of C 8-26 carboxylate moieties covalently bonded to the multi-walled carbon nanotube.

2 . The modified MWCNT of claim 1 , wherein the MWCNT comprises an outer surface, and the plurality of C 8-26 carboxylate moieties are covalently bonded to the outer surface.

3 . The modified MWCNT of claim 1 , wherein the modified MWCNT has a water contact angle of 135° to 150°.

4 . The modified MWCNT of claim 1 , wherein at least one of the following holds:

the modified MWCNT has an absorption capacity of at least 25 g/g for hexadecane;

the modified MWCNT has an absorption capacity of at least 20 g/g for dodecane;

the modified MWCNT has an absorption capacity of at least 20 g/g for decane; or

the modified MWCNT has an absorption capacity of at least 15 g/g for hexane.

5 . The modified MWCNT of claim 1 , wherein at least one of the following holds:

the modified MWCNT has a separation efficiency of at least 90% for hexadecane in water;

the modified MWCNT has a separation efficiency of at least 90% for dodecane in water;

the modified MWCNT has a separation efficiency of at least 90% for decane in water; or

the modified MWCNT has a separation efficiency of at least 90% for hexane in water.

6 . The modified MWCNT of claim 1 , wherein at least one of the following holds:

the modified MWCNT has an absorption capacity of at least 25 g/g for hexadecane after 5 cycles of oil water separation;

the modified MWCNT has an absorption capacity of at least 20 g/g for dodecane after 5 cycles of oil water separation;

the modified MWCNT has an absorption capacity of at least 20 g/g for decane after 5 cycles of oil water separation; or

the modified MWCNT has an absorption capacity of at least 15 g/g for hexane after 5 cycles of oil water separation.

7 . The modified MWCNT of claim 1 , wherein at least one of the following holds:

an absorption capacity after five absorption-desorption cycles in hexadecane is at least 90% relative to an absorption capacity after the first absorption;

an absorption capacity after five absorption-desorption cycles in dodecane is at least 90% relative to an absorption capacity after the first absorption;

an absorption capacity after five absorption-desorption cycles in decane is at least 90% relative to an absorption capacity after the first absorption; or

an absorption capacity after five absorption-desorption cycles in hexane is at least 90% relative to an absorption capacity after the first absorption.

8 . The modified MWCNT of claim 1 , wherein at least one of the following holds:

the modified MWCNT has a length of 0.5 μm to 100 μm; or

the modified MWCNT has an outer diameter of 15 nm to 150 nm.

9 . The modified MWCNT of claim 1 , wherein the C 8-26 carboxylate moieties comprise laurate moieties.

10 . The modified MWCNT of claim 1 , wherein at least one of the following holds:

the MWCNT has an outer diameter of 10 nm to 100 nm;

the MWCNT has a maximum linear dimension of 0.5 μm to 100 μm; or

the MWCNT comprises 3 to 9 walls.

11 . A method comprising:

contacting multi-walled carbon nanotubes (MWCNTs) comprising an outer surface functionalized with hydroxyl groups with C 8-26 carboxylic acid to form a plurality of functionalized MWNCTs, each functionalized MWCNT comprising a MWCNT having C 8-26 carboxylate moieties covalently bonded thereto.

12 . The method of claim 11 , wherein, in the contacting, a ratio of the multi-walled carbon nanotubes to C 8-26 carboxylic acid is 1:5 to 1:20 by weight.

13 . The method of claim 11 , wherein, in the contacting, a ratio of the multi-walled carbon nanotubes to C 8-26 carboxylic acid is 1:10 by weight.

14 . The method of claim 11 , wherein the contacting forms a first mixture and the method further comprises:

sonicating the first mixture;

adding an acid to the multi-walled carbon nanotubes and C 8-26 carboxylic acid to form a second mixture; and

heating the second mixture.

15 . A method comprising:

i) contacting modified MWCNTs comprising MWCNTs with C 8-26 carboxylate moieties covalently attached with an aqueous solution comprising an organic contaminant so that the modified MWCNTs absorbs at least a portion of the organic contaminant.

16 . The method of claim 15 , further comprising:

ii) removing the modified MWCNTs with organic contaminant absorbed thereto from the aqueous solution; and

iii) separating the absorbed organic contaminant from the modified MWCNTs.

17 . The method of claim 16 , wherein i)-iii) are repeated.

18 . The method of claim 15 , wherein the aqueous solution is produced water.

19 . A system comprising:

a hydrocarbon producing well; and

a plurality of the modified MWCNT of claim 1 ,

wherein the system is configured such that produced water comprising a hydrocarbon produced from the hydrocarbon producing well is contacted with the plurality of modified MWCNTs, thereby reducing a concentration of the hydrocarbon in the produced water.

20 . A system, comprising:

a gas-oil separation plant (GOSP); and

a plurality of the modified MWCNTs of claim 1 ,

wherein:

the system is configured such that a first stream in the GOSP is contacted with the plurality of modified MWCNTs, thereby forming a second stream; and

a concentration of a hydrocarbon in the second stream is lower than a concentration of the hydrocarbon in the first stream.