توصيفگر ها :
هيدروكسيدهاي لايه اي دوگانه , كيتوسان , تانيك اسيد , نانوكامپوزيت زيستي , رنگزاي راكتيو
چكيده انگليسي :
Recently, layered double hydroxides (LDH) are of great interest as strong adsorbents for the removal of dyes. Due to high specific surface area and good chemical stability, LDH adsorbents have excellent adsorption performance. In the present study, ZnFe LDH was synthesized in a two-step process including co-precipitation and oxidation. Next, in order to increase the interlayer space of the prepared LDH and facilitate its distribution in chitosan (Cs) polymer matrix, ZnFe LDH was treated with tannic acid (TA). The XRD analysis results showed the exfoliation of LDH layers due to the penetration of the large anions of TA in the interlayer spaces. In the following, bionanocomposite films containing Cs, TA and ZnFe LDH were made using solution casting method. Various characterization techniques including XRD, FTIR, FESEM, EDS and BET were used to determine the physical and chemical properties of the prepared adsorbent. Also, the effect of LDH% and TA% in the bionanocomposite films on their moisture content, water solubility and swelling degree were determined using gravimetric method. All the prepared films had very low water solubility (less than 1%) which was favorable for their application as adsorbents. The moisture content of the films were in the range of 10.1-12.1% and they did not change significantly with the changes of LDH% and TA%. However, the swelling degree of the films, which were in the range of 115-268%, significantly decreased with the increase of LDH% and TA%. The prepared films were applied to remove reactive blue 4 (RB4) from aqueous solution. The response surface methodology with Box-Benken design was used to optimize the TA% and LDH% in the bionanocomposite film, as well as the application conditions in the adsorption process (pH, adsorbent dosage, and time). Each of the five considered independent variables were changed at three levels as follows: LDH%: 0, 10, and 20%, TA%: 0, 10, and 20%, pH: 5, 7, and 9, absorbent dosage: 0.5, 1, and 1.5 g L-1, and time: 30, 60, and 90 minutes. After conducting the experiments and interpreting the results using ANOVA, the relationship between the considered independent variables and the response variable [percentage of RB4 removal (DR%)] was determined using a quadratic equation (R2=0.96). The results showed that the increase in LDH%, decrease in pH, increase in the contact time, and increase in the adsorbent dosage significantly increased the DR%. The estimated optimal conditions for the removal of RB4 were as follows: LDH%: 20, TA%: 10, pH=5, time: 71 min, and adsorbent dosage: 1.5 g L-1. Applying these conditions led to the removal of 98.2% of the RB4 from water. The maximum adsorption capacity of the optimized bionanocomposite film was 406 mg g-1 for RB4. Further, considering that in many purification systems, polymer beads are applied to fill the purification columns, and also considering the promising absorption properties of mixed metal oxides (MMO) derived from LDH, bionanocomposite beads containing Cs and LDH modified with TA, and Cs and MMO modified with TA were prepared and their absorption performance were investigated for the simultaneous removal of three reactive dyes. The experiments were designed based on a full factorial design. The results showed that in the comparison between the film and beads prepared with the identical composite composition, the maximum absorption capacity for RB4 dye for beads (483 mg g-1) was higher than that of bionanocomposite film (406 mg g-1). Also, MMO-containing bionanocomposite beads compared to LDH-containing beads showed lower maximum absorption capacities (>332 mg g-1) for all three studied dyes.
