keywords: Piliostima reticulatum, modification, sorption, crude oil, sorbent
The need to seek inexpensive, abundant and effective materials as oil spill sorbents in water has focus on natural organic sorbents mainly from agricultural products. This study explored the used of crude Piliostigma reticulatum (CPR), retted Piliostigma reticulatum (RPR), bleached Piliostigma reticulatum (PFPR) fiber as sorbent for crude oil removal from water. Sorption capacity studies was carried and optimization at various condition. The results revealed that the efficiency of sorbent to remove crude oil from water is related to the sorbent weight, contact time, initial oil concentration and temperature of sorption. RPR with the highest sorption capacity of 7.92 g/g at 0.7 g of the sorbent was selected and modified through acetylation, succinoylation in ionic liquid, silanylation and salt treatment. The functional groups involved in oil sorption were identified via the determination of the chemical structure of the sorbents before and after oil sorption. Change in the spectral peaks of the sorbents after absorption of crude oil at wave number 2922. 3 cm-1 corresponding to -CH alkane stretching, can be attributed to addition of crude oil. The SEM images show some wrinkles and roughness on the surface of the pretreated and modified sorbents. The elemental composition of the sorbent before treatment and after treatment reveals a reduction in oxygen availability as evidenced by the decrease in peak height of oxygen signal. The sorption capacity of the modified sorbent was compared to that of the pretreated sorbent RPR, to check the sorption capacity after chemical treatment. 0.3 g of the sorbent was used with contact of 20 min at initial oil concentration of 10 g/mL at temperature of 300C. RPR has the least oil removal capacity of 5.69 g/g, compared to ACT-PR (7.79 g/g), SIL-PR (7.70 g/g), SUC-PR (6.84 g/g) and ZN-PR (9.31 g/g). Surface-modified sorbent has noticeable high oil sorption capacity compared with the retted sorbent. RPR attained its highest sorption capacity of 7.92 g/g at 0.7g of the sorbent weight, while ACT-PR, SIL-PR, SUC-PR, ZN-PR attained the highest sorption capacity of 10.51, 10.12, 8.52 and 11.05 g/g at 0.5 g of the sorbent weight after optimization. The sorbent exhibited good reusability after 8 cycles and RPR, ACT-PR, SIL-PR, SUC-PR and ZN-PR losses 33, 18, 17, 22 and 16%, respectively of the initial adsorb oil showing good retention capacity. Effective replacements of hydrophilic hydroxyl groups of fibers by the hydrophobic groups during modification improves its the affinity toward oil.