Simultaneous and rapid removal of Safranin O (SO) and Basic blue 41 (BB) dyes by sulfonated 1 polyacrylamide (PAA-SO 3 H) as super-adsorbent, isotherms, and kinetics studies

The goal of this piece of research would be delving into the nature of simultaneous ultrasound removal 7 of SO and BB dyes into solutions by means of sulfonated polyacrylamide as an efficient adsorbent. Sulfonated 8 polyacrylamide has been synthesized and fully described, applying FT-IR technique. The percentage level of dye 9 removal was investigated under several factors such as the time of sonicating, initial concentrations of dye, pH, 10 and adsorbent dosage. Optimization of parameters was conducted using central composite design (CCD) with 11 response surface methodology (RSM). An acceptable degree of consonance between experimental and calculated 12 values was arrived at. High percentage removal (90.0% and 99.9%) of SO and BB in short time (2.16 min) were 13 recorded through the application of an ultrasound-assisted adsorbent (0.008g).


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There is a relatively wide spectrum of differing pollutants affecting life, of which the two main sources are 28 environmental pollution and human pollution. One of the most significant sources of environmental pollution is 29 sewage coming from industries such as textiles, leather, cytology, printing, food etc.; these apply pigments and 30 dyes in the manufacturing of their final products. The rest of the dyes have the capability to interfere with aquatic 31 life and even to contaminate the food chain. Furthermore, the greater part of the harm arises from the fact that 32 some dyes cause allergy, skin disturbance, irritation, cancer, and even mutation in humans (Mullerova et al. 2019).

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Consequently, dyes undoubtedly represent a genuine danger not only to water environment but also human health 34 ). This is because such dyes possess characteristics of persistent, extremely visible, non-35 biodegradable nature; this is over and above the fact that they are mostly stable to oxidizing agent and sunlight

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It has been estimated that something more than 700,000 t of dyestuff produced per year, in addition to the very 39 available dyes are emitted into the environment while no truly proper treatment has been exerted on them (Shariati 40 et al. 2011). As a result, there is real necessity to remove these from industrial effluents for purposes of creating 41 a healthy purified aqueous environment. It ought to be noted that the said dyes have some structural diversity-42 their removal is laborious during the waste water treatment.

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In order to eliminate pollutants from wastewater, adsorbents can be introduced as an efficatious and simple

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The synthesis of sulfonated polyacrylamide was followed by its characterization by means of FT-IR 59 techniques. The SO and BB retrieval from solutions was remarkably accelerated as ultrasonic instrument was 60 brought in to rapidly assist the adsorption method. This was detected by UV-Vis spectrophotometer. Next to the were fitted to conventional kinetic modeling, including pseudo first and second-order besides intra-particle 65 diffusion models, and so the adsorption was assayed. (0.5 g/L) of them were prepared and the needed concentrations daily were produced by their proper dilution.

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The pH measurements were performed by pH meter (Metrohm, model 827, Switzerland) and the BB and SO  The ultrasound can simultaneously remove BB and SO, and can accelerate this. In the ultrasonic device, which 81 contained 2.5 L water, constant temperature during the experiment was hold. The experiment of sono-chemical 82 adsorption was carried out: determined amounts of 400.0 mg/L of BB and SO solution (50 mL) were mixed with 83 0.01g of PAA-SO 3 H under ultrasound radiation over 3 min at room temperature. At the end, the samples were 84 rapidly centrifuged and non-retained BB and SO contents were evaluated according to the calibration curve at the 85 same condition.  The concentrations of dye were measured based on the plots of calibration achieved at the equal conditions.

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The removal values of BB and SO (RE%) were determined using the following Equation. (1): where, C 0 (mg/L) and C t (mg/L) are the target concentrations at initial and next time t, respectively. The 104 adsorbed BB and SO amounts (q e (mg/g)) were calculated as follows (i.e., mass balance relationship):    Table 2.

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The experimental error and the reproducibility of the data were determined using the center points. Using the 155 second order polynomial model, the mathematical relationships between the three independent variables can be 157 Table 1 158 Design matrix for the 2 5 central composite designs where, y is the calculated response (removal percentage) in Equation (3); X i 's are the independent variables (time 165 of sonicating, SO and BB concentrations and amount of adsorbent). The β 0 is the constant in model; β i is the linear 166 coefficient; β ii is the quadratic coefficient and β ij is the cross-product coefficient.

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The complete design was randomly performed to minimize the effects of non-controlled variables. This design

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The tridimensional graph plotting leads to generate the surface response for predicting the best operating 191 conditions based on p-value and F-value.
The linear plots of C e /q e versus C e suggest the applicability of the Langmuir isotherm in Table 4. The

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A useful empirical theory that express the adsorption mechanism with a Gaussian energy distribution onto a 281 heterogeneous surface is D-R isotherm (Dubinin 1960(Dubinin , 1965  where, Q m is the theoretical saturation capacity K DR (mol 2 / (KJ 2 )) is related to free energy of adsorption and ε is 286 the Polanyi potential that can Equation (11): Based on Equation (10), plotting Ln q e versus ε 2 enables to be determine as K (mol 2 /(kJ) 2 ) and adsorption 289 capacity (Q m (mg/g)) through the interception and the slope values, respectively. The estimated values of D-R parameters are given in Table 4 The model saturation adsorption capacity at 294 optimum states by adsorbents in the range of 0.008-0.01 g, respectively has proper agreement with the relative 295 Langmuir value (20000 for SO and 8333.4 mg/g for BB).

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In this study, several Kinetic models and their parameters have been used to describe and predict adsorption 299 data and potential rate controlling steps, which are helpful for the prediction of adsorption rate, describe the kinetic 300 process of adsorption and give important information for designing and modeling the adsorption processes. Here 301 we used four widely-used kinetic models to investigate the processes of the simultaneous adsorption of SO and 302 BB on the PAA-SO 3 H. Therefore, the mentioned models are discussed in the following sections.

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The rate of adsorption in pseudo-first-order model (LAGERGREN and S. 1898) is based on the adsorption 304 capacity and generally expressed as follows Equation (13): where, q e and q t are the amount of the SO and BB on the PAA-SO 3 H surface at equilibrium and at time t (mg/g),

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respectively. k 1 is the pseudo-first order rate constant (L/min). By this equation, the plot of first order model log

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The curve fitting plot of log (q e -q t ) versus t does not show good results for the entire adsorption period. The 316 kinetic data such as k 2 and equilibrium adsorption capacity, q e , for the adsorption of SO and BB onto PAA-SO 3 H 317 surface were calculated based on the intercept and slope of the plot of t/q t versus t, respectively in Table 5. The  Table 5. This shows that the adsorption 320 16 mechanism of PAA-SO 3 H obeys the pseudo-second-order kinetic model for the entire adsorption period. Also, 321 with increasing initial concentration SO and BB, the diffusion rate enhancement and the value of k 2 increased.

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One of the most useful kinetic model to evaluate the adsorption process is the Elovich equation (Aharoni and   323 Ungarish 1977). This equation is expressed as follows according to the adsorption capacity: Important parameters, such as Elovich maximum adsorption capacity and Elovich constant can be calculated 326 from the slope and intercept of the equation of Equation (15) and reported in Table 5.

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Another kinetic model that evaluate the adsorption process is Intra-particle diffusion (Thompson and 328 Doraiswamy 1999; Chakma and Moholkar 2011). In this process, SO and BB may be transported and movement 329 from the bulk of the solution to the adsorbent (PAA-SO 3 H) by intra-particle diffusion. Therefore, the intraparticle 330 diffusion model has been used to study the rate-limiting step for the adsorption of both dyes onto PAA-SO 3 H 331 surface. A general equation indicates the intra-particle diffusion model as follows: The values of k id and C are determined using the slope and intercept of the plot of q t versus t 1/2 , respectively 334 in Table 5. C and k id are constant and intra particle diffusion rate constant, respectively. If the plot of q t versus t 1/2 335 passes through the origin, intra-particle diffusion alone is the rate limiting step (Midathana and Moholkar 2009).

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Based on the obtained data in Table 5, The R 2 value for this kinetic model was far from the unity. This show that 337 the intra-particle diffusion model cannot be appropriate. As a final result and R 2 values obtained, we concluded 338 that pseudo-second-order kinetic model for the SO and BB removal over entire sorption period is understood    shown that the pseudo-second-order model has proper fitting with the adsorption data for both dyes. Several