Synthesis Of Chitosan Derived Materials And Their Adsorption Mechanisms For Pb(â…¡) And Acid Orange 7 From Aqueous Solutions

Chitosan, which is usually obtained by alkaline deacetylation of chitin, has been used for its high content of amino groups and hydroxyl groups. Chitosan canbe used in eliminating wastewate containing metal ions, dye, radioactive materials and phenol. However, chitosan cannot be directly used in acidic solutions for its bad mechanical stability. Chitosan also has the disadvantages of harder solide-liquid separation after the adsosrption process. These drawbacks limited the use of chitosan materials. In this study, we focused on the Pb(II) adsorption using chitosan-based materials. Chitosan-based materials with advantages of easy solide-liquid separation and high adsorption capacity were synthesized by crosslinking, grafting and hybrid. It is well known that the wastewater is likely to contain more than one pollutant in real-life applications. Heavy metal ions often coexist with dyes in the effluents, which may generate different chemical and physical properties. Therefore, it is necessary to investigate the adsorptino behavior in binary systerm. Three adsorbents were synthesized and were used as adsorbents for removing Pb(II) ions from aqueous solution. The best adsorbent was selectied by taking production cost, preparation technology, adorption ability and solid-liquid separation into account. The selected adsorbent was used for simultaneous adsorption of acid orange 7 dye and heavy metal Pb(II). The specific research work and results can be summarized in the following five sections:(1) Chitosan was used to immobilize yeast cells, then glutaraldehyde was added as crosslink agent to improve the mechanical strength and the stability of chitosan. Fe3SO4 nanoparticles serve as supporting materials in order to get easy solide-liquid separation. In order to increase the number of available reactive groups on the material surface, ethylenediamine was grafted onto the materials. Then a new adsorbent named ethylenediamine-modified yeast biomass coated with magnetic chitosan microparticles(EYMC) was synthesized. The adsorption of Pb(II) ions from aqueous solution with EYMC was studied in batch adsorption system. The experiment data was well matched by Langmuir model and Freundlich model, while Langmuir model showed the best description. The maximum adsorption capacities obtained by Langmuir model were 121.26, 127.37 and 134.90 mg/g at 20, 30 and 40 oC, respectively. Kinetic studies indicated that the pseudo-second-order model was appropriate to describe the adsorption process and film diffusion maybe governed the rate of the adsorption. Thermodynamic studies revealed that a spontaneous and endothermic adsorption process. The adsorbents can be well recovered by 0.1 M EDTA.(2) A novel adsorbent named magnetic humic acid/chitosan composites(M-HA/Cs) was synthesized by decorating humic acid/chitosan composites with Fe3O4 nanoparticles. M-HA/Cs composites were then used for Pb(II) removal. The adsorption capacity of M-HA/Cs was 1.5 times of MCs. The effects of solution p H, initial concentration of Pb(II) ions and adsorption temperature on Pb(II) removal were examined in a batch system and further optimized using Box-Behnken analysis. The recommended optimum conditions were: initial Pb(II) concentration of 139.90 mg/L, initial p H of 4.98, and temperature of 43.97 oC. The adsorption processes could be well described by pseudo-second-order model and Elovich model. Isotherm studies revealed that the adsorption process followed Sips and Temkin models. The results of Temkin model indicated that chemisorption and physisorption may be co-existent during the adsorption process. Both homogeneous and heterogeneous adsorption were involved during the whole adsorption process, but dominated by the homogeneous adsorption. The thermodynamic study indicated that the adsorption process was spontaneous and exothermic. The potential mechanism of Pb(II) on M-HA/Cs at p H 5 may be surface electrostatic attraction, coordination and hydrogen bonding. The Pb-loaded M-HA/Cs can be well recovered by EDTA..(3) An effective and low-cost adsorbent named amine shield-introduced-released porous chitosan hydrogel beads(APCB) was synthesized and characterized by SEM, EDX, FTIR, XPS and Zeta potential. FTIR analysis indicated that the amine-shield-release process and amine-introduce process both increased the amount of amine groups. XPS analysis confirmed the chemical compositions of the APCB. Zeta potential analysis indicated that the p Hpzc of APCB was 5.4. SEM images showed the porous structure of APCB. The surface and interior structures were obviously changed after Pb(II) absorbed. EDX results provided a directly evidence of the existence of Pb(II) after adosrption. The adsorption process was strongly influenced by solution p H. The adsorption capacity of APCB was increased with the increasing of solution p H, ionic strength, pore-foaming agent dosages and reaction temperautre. Experimental data were well fitted by pseudo-second-order kinetic model and Langmuir isotherm model, indicating that monolayer coverage of APCB. These results proved that a homogeneous adsorption happened between APCB and Pb(II). The rate limiting step during the whole process was chemical adsorption. The adsorption process was spontaneous and endothermic with the maxmum adsorption capacity 312.31 mg/g. APCB shows well Pb(II) adsorption capacity after 4 times of adsorption-desorptin cycles.(4) The selected adsorbent was APCB because its high adsorptin capacity, low cost and easy prepartion procedure. APCB was used for removing acid orange 7 from aqueous solution. A great change canbe clearly observed by comparing the SEM imges before and after adsorption. The poriferous structure of APCB became rough due to the accumulation of the large amount of acid orange 7. The EDX analysis proved the adsorption behavior of acid orange 7 onto APCB. almost all the characteristic peaks of APCB are weakened and even disappeared, demonstrating that NH2 groups and OH groups were involved during the acid orange 7 adsorption. The maximum adsorption was observed at p H 2.0 with the adsorption capacity of 2803.77 mg/g, the APCB can be well recovered by Na OH.. APCB showed low adsorption capacity in high p H values and exhibited better acid orange 7 adsorption capacity in low ionic strength solutions. Experimental data were well fitted by pseudo-second-order kinetic model and Langmuir isotherm model. It needed 8 h to reach equilibrium. Thermodynamic analysis indicated that the adsorption process was spontaneous and endothermic. The hypothetical mode of acid orange 7 adsorption on APCB may involved both electrostatic interaction and hydrogen bonding. The aromatic rings, hydroxyl, the nitrogen atoms and the sulfonate from acid orange 7 may form hydrogen bonds with oxygen containing groups on the APCB surface.(5) The effect of both dye and heavy metals in the removal behavior of the APCB was determined by using ratio of adsorption capacities(Rq) in the binary solutions. The Rq,OR ?1 while Rq,Pb > 1 indicated that the presence of acid orange 7 significantly favors the removal of Pb(II), while the adsorption capacities of acid orange 7 are not affected by the presence of Pb(II). Isotherm studies showed that the adsorption of acid orange 7 onto APCB in binary solutions canbe best described by the Extended Langmuir model, while the adsorption of Pb(II) fitted Extended Freundlich model. The adsorption of acid orange 7 was homogeneous adsorption in both single and binary systerm. However, the adsorption of Pb(II) was homogeneous adsorption in single systerm but heterogeneous adsorption in binary systerm. There are two different ways for Pb(II) removal, one is directly adsorbed by APCB; the other is adsorbed by negatively charged acid orange 7 after dye bonded on the APCB. A response surface methodology model(RSM model) has been successfully used for fitting binary-component adsorption data.