The values of iodine number (I2 No) of OB, COB, and OOBAR were evaluated using back titration with 0.05 mol/L I2 and Na2S2O3 solutions. The I2 No of OB, COB, and OOBAR were 406.1, 320.1 and 291.9 mg/g (3.2, 2.5 and 2.3 mmol/g). The I2 No of OOBAR were decreased than OB and COB due to the coupling the biosorbent with phthalic acid. Methylene blue value (MB) of OB, COB and OOBAR were 176.97, 216.32 and 220.7 mg/g (0.59, 0.68 and 0.69 mmol/g). The increasing of MB value of OOBAR due to additional of functional groups. The results obtained indicated that the I2 No depends on the adsorption process while the MB value depends on the cation exchange process (the amount surface of total acidic sites is greater than basic sites in OB and COB). The I2 No of OOBAR was 291.9 mg/g (2.3 mmol/g) and methylene blue was 220.7 mg/g (0.69 mmol/L), these values are greater than those reported for other biosorbents 43-55.
The zero-point charge is the pH value that the charge of a biosorbent surface is equal to zero 56. The pHPZC values of OB, COB and OOBAR were7.0, 3.2 and 3.6. Maximum values of ?pH was 1.5, -1.9 at pH= 5.2, 9.1 for OB, -6.7 at pH= 11 for COB and -4.4 at pH= 9.4 for OOBAR. The surface would be negatively charged due to the deprotonation of the surface functional groups for OB, COB and OOBAR at pH values above 7.0, 3.2 and 3.6 while the surface became positively charged below pH 7.0, 3.2 and 3.6. The shifted of pHPZC value OB from pH 7 to pHs 3.2 and 3.6 for COB and OOBAR due to the increasing of functional groups in the matrix of COB and OOBAR. The OB, COB, and OOBAR sorbents have surface buffering (non-effect with acidic and basic medium) at pHs (5.4-9), (4.2-10.8), and (6.9-9.3).
The higher percentages (98%) for the sorption of molybdenum (V) from aqueous solution were in strongly acidic medium H2SO4 (0.6 – 3.6 mol/L). This was happened because of ion association complex between cationic OOBAR+ in acidic medium (pH < 3.6) and anionic ammonium thiocyanate Mo(SCN)6– complex.
Electrical conductivity measurements were obtained by the method of Ahmenda using an EDT instrument BA380 57. Bulk electrical DC conductivity (?) was recorded at room temperature in the solid state, pressing the samples at 10 tons in the form of a circular disk and potential equal to 2 volts. The values of electrical conductivity were 0.12×10-7 and 4.1×10-6 ?-1 cm-1 for OB and COB. The value of COB was greater than OB due to increasing of active sites (functional groups) with the oxidation process. While the lower value of OOBAR than COB (0.001 ?-1 cm-1) indicates that due to converting from matrix of COB to polymer chain in OOBAR.