Removal of methyl orange from from aqueous solutions using of PANI and PANI@Activated Carbon: Preparation, characterization, regeneration and comparative study

19 This work investigated the elimination of Methyl Orange (MO) using a new adsorbent 20 prepared from Activated Carbon (AC) with polyaniline reinforced by a simple oxidation 21 chemical method. The prepared materials were characterized using XRD, TGA, FTIR and 22 nitrogen adsorption isotherms. Furthermore, PANI@CA highest specific surface area values 23 (near 332 m 2 .g − 1 ) and total mesoporous volume (near 0.038 cm 3 .g − 1 ) displayed the better MO 24 removal capacity (192.52 mg.g − 1 at 298 K and pH 6.0), which is outstandingly higher than that 25 of PANI (46.82 mg.g − 1 ). Besides, the process's adsorption, kinetics, and isothermal analysis 26 were examined using various variables such as pH, MO concentration and contact time. To 27 pretend the adsorption kinetics, various kinetics models, the pseudo first- and pseudo second- 28 orders, were exercised to the experimental results. The kinetic analysis revealed that the pseudo 29 second order rate law performed better than the pseudo first order rate law in promoting the 30 formation of the chemisorption phase. In the case of isothermal studies, an analysis of 31 measured correlation coefficient ( R 2 ) values showed that the Langmuir model was a better 32 match to experimental results than the Freundlich model. By regeneration experiments after 33 five cycles, acceptable results were observed.


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Various dyes are applied for products in the textile industry and paint, food, paper,   [17,18]. 57 Amongst the CPM, PANI receiving a great deal of attention due to their good environmental 58 stability, simple synthesis, ability to dope with protonic acids, and the being of amine groups in 59 its structure and higher electrical conductivity [19]. 60 The existence of amine-imine groups in PANI is the active species for the dye remove. 61 Accordingly, it is widely reported of PANI used as adsorbent of dye in literature review, e.g.
OrangeG) and Tanzifi et al. [2], eliminated the MO by PANI. Whereas that, Li et al., 64 investigated the removal of Methylene-Blue, Congo-Red and Rhodamine-(B) by PANI as 65 adsorbent [21,22], confirming the big capacity for eliminate the diverse dyes types by PANI. 66 However, employing PANI as nanoadsorbent can offer some defies such as aggregation, 67 problem to separate from aqueous solution and thus complicating the regeneration of this 68 adsorbent [23]. Thereby, it is needful to find a method to protect the PANI, overcome the 69 aforesaid difficulties and enhance the efficiency of the PANI without compromise diffusion of 70 effluent. In this consideration, the use of adsorbents based on conductive polymer with diverse 71 inorganic products has proven to be promising for the high removal of organic and inorganic 72 pollutants. Many works have been made to modify the used of PANI and its PANI@inorganic 73 hybrids for the adsorption of pollutants from water. Further, Activated carbon (AC) was vastly 74 used to water and wastewater processing because of its well-developed porosity, high surface 75 area, high mechanical strength, hydrophobic surface and many precursors [24], which make it 76 become an ideal backing during recent nanoadsorbent elaboration processes.

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The essential objectives of these studies were to develop a new adsorbent PANI@AC was synthetized in similar way mentioned above but in absence of AC.    169 To further characterize micromorphology and molecular structure of the products, XRD, 170 FITR, TGA and BET measurements were carried out. Fig. 2 (100) that PANI@AC had better thermal stability than PANI, mainly due to the introduction of AC.

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With measuring N2 adsorption-desorption isotherms, the pore size distribution, specific 213 surface area and pore volume of AC, PANI and PANI@AC were calculated, and results were showed in Fig. 2-d  PANI, the specific, pore size, and pore volume of PANI@AC were significantly increased. The 217 specific surface PANI@AC area was 332 m 2 .g −1 , which was substantially higher than that of 218 PANI (17.52 m 2 .g −1 ). The pore volume increased from 0.023 cm 3 .g −1 to 0.038 cm 3 .g −1 . These 219 mesoporous structure with large surface area were more favorable to the adsorption of dyes.

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To prepare information about factors affecting reaction rate, it is necessary to determine 248 mechanisms that control the adsorption process such as surface adsorption, chemical reaction, 249 and kinetics assessment infiltration mechanisms. Pseudo first order and pseudo second order 250 models have widely used for investigation of the adsorption process. In Table 2, the parameters 251 related to studied kinetic models are presented. The correlation coefficient R 2 represents how 252 good these kinetic models fit the removal process. The R 2 values obtained from kinetic models Hence, the kinetics of adsorption is best defined by the pseudo second order kinetic model for 258 two adsorbents used in this study.  Table 4. Clearly, the PANI@AC product outperformed most of the 267 adsorbents because it has the highest adsorption capacity value.  269 Regeneration and reusability of an adsorbent is an important factor to assess the 270 feasibility for workable applications. Therefore, this adsorbent product was used for several 271 adsorption-regeneration cycles with removal over 60 min. In this study, washing of employed 272 adsorbent with C2H5OH and distilled H2O was used to regenerate the adsorbent PANI@AC. As 273 shown in Fig. 3