การเตรียมวัสดุเชิงประกอบชีวภาพฐานพอลิแลกไทด์เพื่อประยุกต์ใช้ในการบำบัดน้ำเสีย

Abstract

Powder adsorbents are widely used due to their high adsorption efficiency, but they are inconvenient for practical use. In this work, polylactide (PLA) - based biocomposte adsorbents were developed for easy use, and environmental friendliness. Biocomposite adsorbents were prepared in membrane and bead forms using phase inversion method for cationic dye removal from water. To prepare biocomposite adsorbent, the cellulose fiber from agricultural waste such as oil palm empty fruit bunch (EFB) and lemongrass leaf (LGL) were firstly modified using maleic anhydride (MAH). The presence of carboxyl groups in MAH-modified EFB (MEFB) and LGL (MLGL) provided an excellent binding tocationic methylene blue (MB).The second step is the combination of modified fiber with biopolymers to produce adsorbents in membrane and bead forms. The biocomposite membrane from the PLA/ Poly(butylene adipate-coterephthalate) (PBAT) polymer blend added with MEFB was prepared by phase inversion method. The PLA/PBAT-MEFB biocomposite membrane could be twisted or bent. Moreover, the biocomposite membrane showed higher porosity and water absorption and more hydrophilicity than the PLA/PBAT blend membrane. Based on these results, by batch adsorption process, the biocomposite membrane showed higher adsorption capacity than the blend membrane. By filtration adsorption test, the pure water flux of biocomposite membrane was much higher than that of blend membrane and the separation efficiency of biocomposite membrane was 97.2% while blend membrane removed only 58.7%. The existence of MEFB in polymer matrix improved the adsorption efficiency of biocomposite due to the electrostatic binding between the carboxyl groups in MEFB and cationic MB. By filtration the mixed dye solution of cationic MB and anionic dye methyl orange (MO) through the PLA/PBAT MEFB membrane, cationic MB was almost completely absorbed by the negatively charged membrane. Whereas the negatively charged MO molecules passed through the membrane due to electrostatic repulsion between similar charged on membrane and MO molecules. In addition, the biocomposite membrane could be reused five times and retained more than 95% MB filtration efficiency. Biocomposite adsorbent bead from PLA added with MLGL (PLA-MLGL beads) could be prepared by two methods: Post modification (PM) and One pot (OP) methods. By scanning electron microscope (SEM) , the result demonstrated that the surface of the OP biosorbent had larger pores than the PM adsorbent. Moreover, the MLGL embedded on the surface of PLA matrix was observed on the surface of OP bead. In addition, the thermal property by thermogravimetric analysis (TGA) demonstrated that the thermal stability of OP bead was higher than that one of PM bead. The effects of adsorption time, pH, and initial dye concentration on the adsorption efficiency of OP bead were studied. The maximum adsorption capacity (qmax) of PLA-MLGL bead by OP method was 86.19 mg g-1 under the equilibrium adsorption time of 24 h at pH 8. In addition, OP bead could be reused over 5 cycles. By batch adsorption study, the kinetics adsorption of membrane and bead composite biosorbent toward MB obeyed the pseudo-second order (PSO) model, indicating that the adsorption between the biosorbent and the MB occurred through the opposite charges. Both membrane and bead adsorbents fitted well with the Langmuir isotherm and the monolayer adsorption with qm values were 35.97 and 90.09 mg g-1, respectively. The biocomposite adsorbents in membrane and bead could be reused several times using the acetic acid solution as the desorbing agent and maintain satisfy adsorption efficiencies. From the results, it was concluded that the proposed biocomposite adsorbents were not only simply fabricated but also were easy to practical use and environmental friendliness.They are useful for application to remove dyes from water.