Evaluation of Kinetic and Equilibrium studies for Phytoremediation of Methylene Blue Dye (Triarylmethane) and Congo Red (Diazo) using Trachyspermum Ammi L.

Phytoremediation developed as a green-clean, solar-driven and innovative technique for the eradication of 12 contaminants from the environment from last two decades. In the present research work, phytoremediation 13 potential of an ornamental plant Trachyspermum ammi L. ( T. ammi ) was examined for the removal of a 14 triarylmethane-Methylene blue (MB) and di-azo-Congo red (CR) dye. The various parameters such as initial dye 15 concentration, contact time, and pH were focused to explore the dye removal capability of T. ammi. The increase 16 in initial dye concentration affects the decolorization potential of the T. ammi . The decolorization potential of T. 17 ammi found to be reduced with enhancing the initial dye concentration of both the dyes. The plant achieved 18 condition of equilibrium after the 40 h of contact time with both MB and CR dye. The favorable pH for T. ammi 19 for the MB dye was observed as 5 while for CR dye was 6. The kinetics of phytoremediation reaction with both 20 MB and CR dyes were studied with help of pseudo-first order, pseudo-second order, and Elovich models and the 21 results were well appropriated to pseudo-first order with the correlation value R 2 ≥ 0.95 for MB and R 2 ≥ 0.97 for 22 CR. The Langmuir and Freundlich isotherms studies of phytoremediation reaction found in favor of Freundlich equilibrium isotherm with correlation R 2 ≥ 0.99 for both MB and CR dyes. The mechanism of T. ammi for removal of dyes was supported with the help of analytical techniques such as Fourier Transform-Infrared Spectroscopy and Scanning Electron Microscope (SEM). examine the phytoremediation ability of T. plant a dye (CR) a triaryl methane dye Methylene the phytoremediation the of initial dye and studied. The mechanism of dye removal by plant in living analysed observed at pH while 95% decolorization at pH for The maximum decolorization T. ammi explored its utilization for removal of the contaminants from the especially can be grown in the dye contaminated area. The adsorption isotherms of Langmuir and Freundlich models investigate the adsorption pattern of MB and CR dyes on the T. ammi surface and Freundlich model found to be 293 a little bit better fit for adsorption of both dyes MB (R 2 ≥ 0.990) and CR (R 2 ≥ 0.990) dye molecules on T. ammi root surface. The kinetic studies results supported the pseudo-first order kinetic model with the maximum correlation value R 2 ≥ 0.95 and 0.97 for MB and CR respectively for phytoremediation by T. ammi. FTIR and studies confirmed that dye molecules get phytoadsorbed by plant roots through the functional group After phytoadsortion, dye get finally assimilated inside the root cells where it gets detoxified. Future work will plan to explore detoxification mechanism inside the plant cells. Hence, the observed outcomes that T. ammi ornamental plant for phytoremediation of noxious dyes from and can be utilized as an effective phytoremediator which provide sustainable solution for present of environmental


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The quantity of dye removed by the T. ammi at any time is 'qt' (mg g -1 ) and 'qe' (mg g -1 ) at equilibrium 97 determined from equations 2 and 3 respectively (Mahajan and Kaushal 2020): The kinetics of T. ammi for the removal of the MB and CR dyes was interpreted by using the pseudo-first order, 105 pseudo-second order and Elovich models as demonstrated by equations 4, 5 and 6 respectively (Ahmed et al. where 'K1' and 'K2' are the rate constants for pseudo-first order and pseudo-second order, respectively. In eq. 111 6 ′ ′ determine the chemisorption, and ′ ′ find out that how much adsorption takes place at adsorbent surface.

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The application and importance of suitability of the kinetic models to experiment data are predicted with the 113 regression value (R 2 ) and standard deviation of normalized value (Δ qt%). The normalized standard deviation

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The equilibrium studies of phytoremediation reactions were determined with the help of Langmuir and 121 Freundlich models represented by equations (8) and (9)

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T. ammi has shown the efficient removal of the MB and CR dyes up to 40 h and found to active after eliminating 141 the maximum percentage of the dyes. The equilibrium stage of experiment was achieved after 40 h and both MB phytoremediation of both MB and CR dyes. The FTIR spectra T. ammi roots before and after dye adsorption was 147 shown in Fig. 3 and comparative interpretation of results of FTIR spectra was presented in Table 1.

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The FTIR spectra depicts the presence of functional groups such as phenolic and carboxyl group which is indicated 149 in roots of T. ammi and these results agree with the previous spectra reported for  Mahajan 2021). Therefore, the phytoremediation kinetics study of MB and CR dyes with the help of T. ammi was 177 studied with pseudo-first order, pseudo-second order, and Elovich models. The kinetic graphs of various models 178 at different concentrations of MB and CR dyes are shown in Fig. 5-7. The constants of kinetics and other used 179 parameters determined from kinetic plots for MB and CR dye are presented in Table 2 and 3 respectively. Fig 5a-180 b depicts the pseudo-first order straight-line graph with negative value of slope when log (qe-qt) against time (t) 181 had plotted at various concentrations for T. ammi. Figure 6a-b depicted a linearized plot with the positive slop 182 when t/qt plotted versus "t" for pseudo-second order kinetic model and k2 and qe (theor) values are predicted with 183 the help of intercept and slope respectively for different concentration for both the dyes. The Elovich constants α 184 and β has been determined by the slope and intercept, of the plot between qt vs ln t depicted in Fig. 7a

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The equilibrium studies on phytoremediation were also work out by using the Langmuir and Freundlich

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Therefore, the optimum value of pH for removal of MB and CR by T. ammi is at pH value 8 and 5 respectively.

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Based on these result and discussions, a hypothetical mechanism is also proposed for phytoremediation of dyes 257 by T. ammi plant (Fig. 11). The roots of T. ammi plant plays an important role in removal of dyes from solution.

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The phytoabsorption of MB and CR dye by plant root has been confirmed through SEM studies of roots of T.
259 ammi (Fig. 4). It has been clearly inferred the presence of phenolic and carboxyl functional groups in roots of T.

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Competing interests: The authors declare that there is no competing interests.

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Ethics approval and consent to participate: "Not applicable", as research does not report on or involve the 305 use of any animal or human data or tissue.