Watermelon peel residues were used to produce a new biochar by dehydration method. The new biochar has undergone two methods of chemical modification and the effect of this chemical modification on its ability to adsorb Cr(VI) ions from aqueous solution has been investigated. Three biochars

Melon-B

Melon-BO-NH

2

and Melon-BO-TETA

were made from watermelon peel

via

dehydration with 50% sulfuric acid to give Melon-B followed by oxidation with ozone and amination using ammonium hydroxide to give Melon-BO-NH

2

or Triethylenetetramine (TETA) to give Melon-BO-TETA. The prepared biochars were characterized by BET

BJH

SEM

FT-IR

TGA

DSC and EDAX analyses. The highest removal percentage of Cr(VI) ions was 69% for Melon-B

98% for Melon-BO-NH

2

and 99% for Melon-BO-TETA biochars of 100 mg·L

-1

Cr(VI) ions initial concentration and 1.0 g·L

-1

adsorbents dose. The unmodified biochar (Melon-B) and modified biochars (Melon-BO-NH

2

and Melon-BO-TETA) had maximum adsorption capacities (

Q

m

) of 72.46

123.46

and 333.33 mg·g

-1

respectively. The amination of biochar reduced the pore size of modified biochar

whereas the surface area was enhanced. The obtained data of isotherm models were tested using different error function equations. The Freundlich

Tempkin and Langmuir isotherm models were best fitted to the experimental data of Melon-B

Melon-BO-NH

2

and Melon-BO-TETA

respectively. The adsorption rate was primarily controlled by pseudo-second-order rate model. Conclusively

the functional groups interactions are important for adsorption mechanisms and expected to control the adsorption process. The adsorption for the Melon-B

Melon-BO-NH

2

and Melon-BO-TETA could be explained for acid-base interaction and hydrogen bonding interaction.