Polyacrylamide-Grafted Actinidia deliciosa peels powder (PGADP) for the sequestration of crystal violet dye: isotherms, kinetics and thermodynamic studies

Herein, a novel and eco-friendly low-cost adsorbent polyacrylamide-grafted Actinidia deliciosa (Kiwi fruit) peels powder (PGADP) was synthesized and utilized as a potential adsorbent for the sequestration of crystal violet (CV) dye from aqueous solution. The material was characterized by various analytical techniques such as Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), X-ray diffractometer (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The adsorption process was carried out in a batch process with different concentrations, adsorbent doses, pH, contact time and temperatures. The maximum adsorption of CV dye from aqueous solution was observed at pH 7.3, contact time 180 min and initial dye concentration 20 mgL−1. The equilibrium data were tested by applying various isotherms models such as Langmuir, Freundlich, Temkin and Dubinin–Radushkevich (D-R), and the results showed that Langmuir was found to be the best fitted model based on the highest correlation coefficient (R2). Kinetic data showed that pseudo-second order model was best obeyed over wide range of concentrations. In thermodynamic study, positive value of ∆Ho and negative value of ΔG° confirm endothermic and spontaneous nature of adsorption process with increased randomness at solid-solution interface. Desorption of CV dye was performed successfully using 1 M acetic acid with excellent regenerating capacity that lasts up to fourth cycle. Therefore, PGADP can be used effectively and economically for removal of CV dye from aqueous solution and industrial waste water.


Introduction
Numerous studies have demonstrated that azo dyes are a series of synthetic organic compounds that are widely used and applied in different industrial sectors like textile dyeing, paper making, printing and cell biology (Osma et al. 2007; Gupta and Suhas 2009;Konicki et al. 2013). During dye production and textile manufacturing process, a large quantity of wastewater containing dye stuffs with intensive color and toxicity are introduced into the aquatic systems (Ibhadon et al. 2008). The discharge of industrial dye effluent into the water systems and environment has become a serious pollution problem and human health risk because of its high visibility and toxicity (Gupta and Suhas 2009;Konicki et al. 2013;Zhang et al. 2014). Due to increasingly drastic restrictions on the organic content of industrial effluents, it is essential to remove dyes from wastewater before it is discharged to the normal water bodies (Ahmad 2009). Many of these dyes are also toxic specifically, the crystal violet (CV) is an organic cationic dye and widely used as textile colorant and biological stain. Several studies indicated that accumulation of CV has been suspected to cause harmful effects such as cancer on human beings . Therefore, considerable efforts have been devoted for the treatment of dye effluents using different techniques such as coagulation, flocculation, reverse-osmosis, photo-degradation processes and ion-exchange. Among the various techniques, adsorption process is the most preferred method to remove the dyes from aqueous solution due to its simplicity, efficiency, convenience, ease of operation and inexpensive nature (Martins et al. 2017).
Activated carbon as an adsorbent has been widely used for the removal of dyes, heavy metals and other organic pollutants from aqueous solution, but its high cost limits its commercial application. In recent years, extensive research has been undertaken to develop alternative and low-cost adsorbents (Ahmad 2009). Adsorbents utilized for dye removal should be characterized by an excellent adsorption capacity derived fundamentally from the combination of pore structure and surface chemistry (Pang et al. 2019). Recent literature survey revealed that various adsorbents have been employed in the treatment of dye-polluted waters includes clay minerals (Kausar et al. 2018), zeolites (Sivalingam and Sen 2019), polymer composite (Jayasantha Kumari et al. 2017), fly ash (Gao et al. 2015) and reduced the cost of adsorption process various biomasses have been suggested as dye adsorbents: rice husks (Franco et al. 2015), grape wastes (Vanni et al. 2017), ouricuri fibers (Meili et al. 2017) and para chestnut husk (Georgin et al. 2018).
Recently, intense research is going on to search for new conventional and low-cost green adsorbent for waste water treatment. Moreover, to further increase mechanical strength and sorption capacity of the conventional adsorbent, the lignocellulosic part was modified by various organic and inorganic compounds, acid and bases and also blended with several synthetic polymers reported elsewhere (Wang et al. 2015), biopolymer (Zhang et al. 2013), metal oxide nanoparticles (Gopalakannan and Viswanathan 2015), nano-clay materials (Hassani et al. 2015) and poly (methyl metha acrylate)-grafted alginate @Cys-bentonite copolymer hybrid nanocomposite (Hasan and Ahmad 2019). Moreover, phosphate-treated sawdust (lignocellulosic material) shows a remarkable increase in sorption capacity of Cr(VI) as compared to untreated sawdust (Ajmal et al. 1996). Therefore, to further enhance the capacity of the adsorbent we introduced a suitable procedure for surface modification which involved the grafting of polyacrylamide onto Actinidia deliciosa peels powder using N,N'-methylenebisacrylamide as a cross-linking agent and subsequent functionalization of the polymer network with desired reagent for treating dyes wastewater (Unnithan and Anirudhan 2001). After modification, it was found that the adsorption capacity and stability of the adsorbent materials have increased, which is an important aspect of commercial development of biosorbent materials. In this quest, author has attempted to explore a novel low-cost and abundantly available material Actinidia deliciosa peels powder (ADP) to remove hazardous crystal violet dye (CV) from aqueous solution and waste water.
Herein, we report the preparation of a novel and ecofriendly adsorbent, polyacrylamide-grafted Actinidia deliciosa peels powder (PGADP) and its application for the sequestration of crystal violet (CV) dye from aqueous solution. The experiments were carried out to see the effects of various parameters such as pH, contact time, initial dye concentration and temperature on the adsorption of dye onto (PGADP). The obtained experimental adsorption data were applied to validate the Langmuir, Freundlich, Temkin and Dubinin-Radushkevich (D-R) isotherm models. The equilibrium data were further tested by using pseudo-first, pseudosecond order, intra-particle diffusion and elovich kinetic models. In order to make the process more economical and feasible, the exhausted material was further desorbed and regenerated. To see the morphology of the prepared adsorbent, PGADP was characterized by FTIR, XRD, SEM, EDX, TEM and TGA techniques.
The main novelty of present material PGADP is its high monolayer adsorption capacity of (75.19 mgg −1 ) as compared to other adsorbents in the literature ( Table 5). The PGADP also exhibits very good regenerative capability, and it can be used up to fourth cycle successfully without much loss in efficiency for the removal of CV dye. Therefore, PGADP can be used very effectively and economically for the removal of CV dye from the developing countries.

Materials and reagents
Actinidia deliciosa peels (Kiwi fruit) ADP were procured from local market (Aligarh), India. All analytical grade reagents were purchased from commercial sources. N, N'methylenebisacrylamide was purchased from Sigma-Aldrich (USA). Ethylene diamine was provided by Fisher Scientific. Peroxydisulfate and toluene were supplied by Merck, India. Crystal violet dye (C 25 N 3 H 30 Cl) was purchased by CDH, New Delhi. Hydrochloric acid (HCl) and sodium hydroxide (NaOH) used were of analytical grade.

Preparation of adsorbent
Actinidia deliciosa peels (ADP) were collected from the local market of Aligarh. The peels were washed several times with tap water then double distilled water to remove the adhering dirt and dried in an oven at 80 °C. The dried materials of ADP were crushed to make fine powder. The material was grafted with polyacrylamide using the method reported elsewhere (Unnithan et al. 2004). Firstly, 20 g of ADP powder was soaked with 300 mL of solution containing 5 g of N, N′-methylenebisacrylamide and 2 g potassium peroxydisulfate for 15 min before graft copolymerization was started. Then, 7.5 g of acrylamide was added to the mixture gradually and stirred vigorously at 70 °C for 3 h. The polyacrylamide-grafted ADP (PGADP) was then washed with double distilled water and dried at 80 °C. To convert material into an anion exchanger, PGADP was refluxed with 25 mL of ethylenediamine for 8 h. The product was then washed with toluene and dried. It was further shaken with 0.1 M HCl for 4 h and washed well to remove excess chloride ions and finally dried at 80 °C. The yield percentage of functionalized PGADP (PGADP-NH 3+ Cl − ) material was found to be (76.81%), and the material was stored in an air tight container for further studies.

Characterization
The elemental analysis and surface morphology of the raw ADP and PGADP before and after adsorption were examined by scanning electron microscope (SEM) equipped with energy-dispersive x-ray spectrometer (EDX) (model JSM 6510LV, JEOL, Japan) after gold coating. The particle size of (PGADP) was examined by high-resolution transmission electron microscope (TEM, JEM 2100, JEOL, Japan). FTIR measurements were recorded in the range of 400-4000 cm −1 with (PerkinElmer 1600 infrared spectrometer) from samples in KBr pellets. XRD pattern was carried out using (Rigaku, Smart Lab) X-ray diffractometer with Cu α radiation (λ = 1.542 A o ). The absorbance of the CV dye sample was measured by (T70 UV/VIS Spectrometer, PG Instruments Ltd, U.K.) UV-Vis spectrophotometer at λ max of 588 nm.

Adsorption studies
The stock solution of 1000 mgL −1 of crystal violet dye (CV) was prepared by dissolving requisite amount in double distilled water. The batch adsorption studies were conducted using 0.025 g of adsorbent, 20 mL of initial CV (20-100 mgL −1 ), contact time (5-360 min), adsorbent dose (0.01-0.05 g), pH (2-11) and temperature at 30 to 50 °C by shaking in a series of conical flask. Supernatant was separated by filtration using Whatman paper No.1 and determined for remaining dye content. The concentration of dye samples was determined using UV-Vis spectrophotometerfor crystal violet at (λ max 588 nm).
The percent removal of CV dye from aqueous solution at equilibrium was calculated by the using Eq. (1) where C i is the initial concentration of dye and C e is the final concentration of dye.
The amount of adsorbate per unit mass of the adsorbent was evaluated by using Eq. (2).
where q e (mgg −1 ) was the adsorption capacity of the adsorbent, C i and C e were the initial concentration and concentration at equilibrium (mgL −1 ), W was the mass of the adsorbent (g) and V was the initial volume of the adsorbate solution in liter (L), respectively (Ahmad and Mirza 2017).

Point of zero charge (pHpzc)
Point of zero charge was examined by solid addition method using 0.1 M KCl solution (Rao et al. 2016). Take 20 mL of 0.1 M KCl solution in a series of conical flask with 0.025 g adsorbent and pH value adjust between 1-12 using 0.5 M HCl and 0.5 M NaOH and the solution was left for 24 h. After 24 h, the solutions were filtered and final pH (pH f ) of the solution was measured. The difference between pH i and pH f was obtained by plotting against pHi.

Breakthrough studies
Breakthrough studies were carried out by column process. 0.05 g of PGADP adsorbent was taken in a glass wool supported column (0.6 cm i.d.). 250 mL solution of 20 mgL −1 CV dye was taken in a column and passed with flow rate of 1 mL min −1 . The effluent was collected in 10 mL fraction and examined by UV/VIS spectrophotometer. The breakthrough capacity was calculated by plot between C e /C o versus volume of effluent.

Results and discussions
Characterization SEM micrograph of raw ADP before grafting Fig. 1a, after grafting with polyacrylamide PGADP Fig. 1b and after adsorption of CV dye onto the surface of PGADP is shown in Fig. 1c. The image of the ADP shows rough and patchy surface morphology which seems to be less porous. After grafting, the SEM micrograph of PGADP showed highly cross-linked and porous structure that provide sites for adsorption of crystal violet dye. The SEM image of CV dye loaded PGADP showed highly smooth and cloudy type of surface that confirms the successful binding and adsorption of dye molecule onto the surface of PGADP. The average size of PGADP was found to be 42.1 nm as shown in TEM image (Fig. 2). The EDX and elemental analysis of raw ADP and PGADP before and after adsorption of CV dyes are reported in Table 1. The major elements present in the spectra of ADP, PGADP and after adsorption of CV dye onto the surface of PGADP, respectively, with percent are shown in Fig. 3a-c. The EDX of ADP showed the presence of C, O while after grafting represents the spectra of PGADP showed the presence of C, O, N and K these elements confirmed that grafting onto the ADP was successful. The CV dye-treated PGADP   (Fig. 4). The XRD pattern of PGADP revealed semi-crystalline nature of the material with a strong characteristic peak due to grafting with polyacrylamide.
FTIR spectra of raw ADP, PGADP and PGADP after the adsorption of CV dye on the surface of material are shown in Fig. 5a-c. FTIR spectra of raw ADP Fig. 5a show a broad peak at 3408 cm −1 due to -OH stretching vibration (Ali Khan Rao and Khatoon 2017). The band at 2924 cm −1 and 2857 cm −1 was aroused due to the presence of -CH 2 group asymmetric and symmetric stretching (Li et al. 2007). A short and weak peak at 1750 cm −1 was assigned due to C=O group (Abdolali et al. 2015). The peak at 1640 cm −1 and 1444 cm −1 attributed due to the carboxylate ions (-COO − ) and N-H stretching vibrations of amine group, respectively Ali Khan Rao and Khatoon 2017). A strong absorption peak at 1066 cm −1 was aroused due to C-N stretching vibration of  (Hossain et al. 2014). A short and broad band at 594 cm −1 corresponds to metal oxide bond . FTIR spectra of PGADP in Fig. 5b showed the absorption peak at 1750 cm −1 was disappeared while absorption peak at 3408, 2924, 2857, 1640, 1444, 1023 and 594 cm −1 was shifted to 3389, 2949, 2832, 1646, 1450, 1016 and 613 cm −1 , respectively. All these changes noticed that the grafting of polyacrylamide onto raw material (Actinidia deliciosa) peels fetch some change in the functional groups of ADP, specifically in C=O groups, whereas the crystal violet-loaded adsorbent showed peaks at 3401, 2930, 284, 1658, 1450, 1025 and 619 and 448 cm −1 , respectively (Bizani et al. 2006;Sobana et al. 2006). There are shifting of peaks in PGADP after being treated with CV dye that showed successful adsorption of dye onto the surface of PGADP.
The TGA thermogram of PGADP in Fig. 6 showed that the degradation occurs in two steps. Due to loss of physically adsorbed water, the initial weight loss occurs at 97.51 °C. The weight loss at 388.01 °C is accredited due to dehydration process, segmentation of cross-links and decarboxylation of anion. The thermogram clearly signifying greater thermal stability of the prepared adsorbent PGADP by decomposition at higher temperature.

Effect of pH and pH pzc
The solution pH greatly affects the adsorption process by influencing the surface charge of the adsorbent and also the degree of ionization of adsorbate species present in the solution. The test for the effect of pH (ranging 2-11) on adsorption process was carried out at experimental conditions by taking dye concentration 20 mgL −1 and 0.025 g of adsorbent for 24 h at room temperature. The adsorption capacity (q e ) of CV dye increases (9.126 to 15.337 mgg −1 ) with increase in pH and reaches maximum at pH 7.3 (15.337 mgg −1 ) as shown in Fig. 7a. After pH 7.3, there is decrease in adsorption capacity. This fact could be explained as-at higher pH, there is electrostatic attraction between the negatively charged sites of the adsorbent and positively charged dye molecules till pH (7.3). With further increase in pH, the dye molecule starts deprotonating and competes with increased OH ions at higher pH which results in further decrease in adsorption capacity. Therefore, for further experimental studies, pH 7.3 was selected as optimum pH and similar results were also reported by (Sahoo et al. 2005). The point of zero charge of PGADP was found at 2.4. If the pH ˃ pH pzc , then the surface of adsorbent is negatively charged. Figure 7b showed that the surface of PGADP is negatively charged and the adsorption increased onto the surface by the attraction of positive charge CV dye and also reported by elsewhere (Martins et al. 2017).

Effect of adsorbent dose
One of the parameters that strongly affects the sorption capacity is the amount of the adsorbent. With fixed dye concentration (20 mgL −1 ), contact time (24 h), pH (7.3), it can be easily inferred that the percent removal of dye increases while the adsorption capacity decreases with increasing amount of the adsorbents (0.01-0.05 g). Figure 8. Showed that the percent adsorption increases from 87.81 to 97.36% and adsorption capacity decreases from 35.13 to 7.79 mgg −1 with increasing adsorbent dose. This is due to greater availability of the exchangeable sites or surface area at higher concentration of the adsorbent (Mirza and Ahmad 2020).

Effect of contact time and kinetic study
The test for the effect of contact time (ranging 5-720 min) on adsorption process was carried out at experimental conditions taking 0.025 g dose of adsorbent with varied CV dye concentration 20, 50 and 100 mgL −1 at room temperature and pH (7.3), respectively. As seen from Fig. 9, the adsorption capacity increases with increase in contact time (till 180 min) and after the equilibrium time, no significant changes were observed in the adsorption capacity. This could be explained as the increase in adsorption capacity in initial stages is due to the high availability of adsorption sites (till 180 min) and after that, dye molecules have to compete for available adsorption sites (Song et al. 2008). Therefore, for further experimental studies contact time of 180 min was selected.
To examine the rate, mechanism and rate controlling step of adsorption behavior of adsorbate onto PGADP, various kinetic models were tested namely pseudo-first order pseudo-second order, intra-particle diffusion and elovich kinetic models. Eqs. (3-6) for these models, respectively, are as follows: where q t (mgg −1 ) and q e (mgg −1 ) are the adsorption capacity at contact time (t) and at equilibrium, k 1 (min −1 ) and k 2 (g mg −1 min −1 ) are the constants of pseudo-first order and pseudo-second order equation, respectively. K id (mg g −1 min −1/2 ) is the intra-particle diffusion rate constant and C is the intercept. A (mg g −1 min −1 ) and B (g mg −1 ) are elovich constants.
The experimental data of kinetic parameters are summarized in Table 2. The highest correlation coefficient, R 2 , was found in pseudo-second order (0.998) as compared to pseudo-first order. The calculated adsorption capacity q e cal (mgg −1 ) from pseudo-second-order model represents a good agreement with the experimental adsorption capacity q e exp as shown in Fig. 10a-d. This indicated that pseudo-secondorder model was the best fitted kinetic model for the adsorption of CV dye onto PGADP and the rate limiting step may be chemisorption. The adsorption rate of dye onto the surface of PGADP might be controlled by complexation and coordination because the large number of functional groups present in the material of PGADP (Niu et al. 2017). From kinetic model of intra-particle diffusion, indicated increased boundary layer effect by increase in the value of C (constant) with increasing concentration of CV dye (Kratochvil 1998;Ghodbane and Hamdaoui 2008). The plots of q t against t 1/2 for different concentration of CV dye showed deviation from origin indicated that intra-particle diffusion not the only the rate controlling step but some other mechanism for example surface adsorption, film diffusion and pore diffusion might also be involved in the adsorption process (Zhang et al. 2016).

Effect of initial dye concentration and adsorption isotherm
The effect of the initial dye concentration (20-100 mgL −1 ) was examined by treating 0.025 g (dose), 7.3 (pH), 180 min (contact time) and temperature (303-323 K), respectively. As shown in Fig. 11, the adsorption capacity increases with increase in initial concentration at all temperature that might be due to increased concentration gradient between the bulk solution and the adsorbent surface (Tünay et al. 1996). The adsorption isotherm model gives the information about the optimization of the adsorption reactions (Hasan and Ahamd 2019). The equilibrium data were elucidated using four isotherm models namely, Langmuir, Freundlich, Temkin and Dubinin-Radushkevich (D-R) isotherm models. Eqs. (7-10) for these models are represented as: where q e and q m are the adsorption capacity (mgg −1 ) at equilibrium and monolayer adsorption capacity (mgg −1 ).
10) ln q e = ln q m − 2 C e is the adsorbate equilibrium concentration (mg L −1 ) and b is the constant related to adsorption energy (Lmg −1 ). K F ((mgg −1 ) (Lmg −1 ) 1/n ) is the Freundlich isotherm constant, n is the indication of adsorption intensity. A (mgL −1 ) and B (J mol −1 ) are Temkin constants related to the equilibrium binding constant and the heat of adsorption, respectively. β (mol K −2 J −2 ) is the isotherm constant related to parameter E (mean free energy per molecule of adsorbate) (kJ mol −1 ), and ε is the polanyi potential related to C e , respectively, determined in Eqs. (11-12) where R (8.314 J mol −1 K −1 ) and T (K) are the gas constant and absolute temperature, respectively, (Foo and Hameed 2010).
The results of various isotherm models are tabulated in Table 3. Based on high correlation coefficient value (R 2 ) as can be observed from Fig. 12a-d, the Langmuir isotherm model fitted best with the equilibrium adsorption data refers to monolayer coverage of CV dye on the specific homogenous sites of PGADP. The plot of log q e versus log C e in Freundlich gives straight line at different temperatures. Freundlich isotherm model is used for the identification of the surface heterogeneity of adsorbent and gives the details of interaction between adsorbate and the active sites of the adsorbent with the large range of adsorbate concentrations (Sharifnia et al. 2016). The obtained value of n greater than 1, at all temperature indicates that the adsorption of CV dye onto the surface of PGADP was favorable by positive binding because if n ˃ 1, then adsorption indicates favorable condition. Temkin model describe that heat of adsorption is assumed to be decreased linearly with coverage. The values of constant A and B were obtained from the plot of q e versus lnC e which represents binding energy and enthalpy of adsorption, respectively. Increasing the value of constant A with increased in temperature signifies strong binding of adsorbate and adsorbent at a higher temperature. Dubinin-Radushkevich isotherm is generally used to described the mechanism of adsorption with respect to Gaussian energy distribution onto a heterogeneous surface and determine the nature of adsorption as physical or chemical based on the free mean sorption energy (Dabrowski 2001;Rao and Rehman 2010). The value of free mean energy, E, was obtained less than 8 (kJ mol −1 ) at all temperature suggesting physical adsorption occurs of CV dye at the surface of the PGADP (Anayurt et al. 2009).

Thermodynamic study
The thermodynamic parameters like free energy change (ΔG°), enthalpy change (ΔH°) and entropy change (ΔS°) for the adsorption of CV dye onto the surface of PGADP were calculated from the following Eqs. (13-15): where C i and C e were the initial concentration and concentration at equilibrium time (mgL −1 ). T is the temperature (K), K c is the distribution coefficient, and R (JK −1 mol −1 ) is the universal gas constant, respectively. The thermodynamic parameters like ΔH° and ΔS° were evaluated using the plot of log K c versus 1/T, and values are summarized in Table 4 and shown in Fig. 13. The negative values of ΔG° for adsorption of CV dye onto the surface of PGADP indicate the feasibility and spontaneous nature of adsorption and the negative ΔG° values obtained lower than − 20 (kJ mol −1 ) at all temperature signifying physical adsorption (Huang et al. 2014). The positive values of ∆H° and ∆S° confirm the endothermic nature of adsorption and reflect the affinity of PGADP for CV and also show the increased randomness at the solid-solution interface.

Adsorption mechanism
To comprehend the mechanism of the interaction between functionalized PGADP and molecules of CV dye, a number of different spectroscopic techniques such as FTIR and EDX were used. The interaction between adsorbate-adsorbent depends on the chemistry of adsorbate, solution pH, chemical and physical nature of adsorbent. At lower   . 13 Adsorption thermodynamics for the adsorption of CV onto PGADP pH, the -NH 2 and -OH functional groups of negatively charged adsorbent PGADP have a strong coordinative affinity toward CV dye by surface complexation through electrostatic interaction, while this affinity decreases at higher pH as due to repulsive force between positively charged cationic dye ions and lone pairs of the -NH 2 and -OH groups of PGADP. The Dubinin-Radushkevich isotherm results show that the mechanism of adsorption with respect to Gaussian energy distribution onto a heterogeneous surface and determined based on the free mean sorption energy physical adsorption occurs on the surface of PGADP. After the adsorption of CV dye, some changes in the absorption wave numbers and also the intensities of absorption bands of the adsorbent were observed. Indeed, slight shifts in the peak positions were observed in the regions 2832-2844 and 1646-1658 cm −1 which are probably due to the removal of CV over PGADP via a strong hydrogen bonds and electrostatic interactions between ions of the dye molecules with the -NH 2 and -OH groups of PGADP.

Breakthrough studies
Breakthrough capacity can be used to determine the concentration gradient between the solute adsorbed by the adsorbent and remaining in the solution (Rao et al. 2016).
Breakthrough studies were carried out by column process. 0.05 g of adsorbent was accurately weighed and transfer in a glass wool supported column (0.6 cm i.d.). 250 mL solution of CV dye with initial concentration 20 mgL −1 was taken in a column and passed with flow rate of 1 mLmin −1 .
The effluent was collected in 10 mL fraction and examined by UV/VIS spectrophotometer. The breakthrough curve plotted between the (C e /C o ) versus volume of effluent (mL) is shown in Fig. 14. As seen from breakthrough curve, 40 mL solution of CV dye could flow down the column without being detected in the effluent. From the breakthrough experiment by using column process, the breakthrough capacity was found to be 16 (mgg −1 ) while exhaustive capacity was determined as 68 (mgg −1 ).

Desorption and regeneration
The desorption study of CV dye was carried out by batch adsorption process using several reagents. After the attainment of equilibrium time, adsorbent was filtered and subsequently washed several times with double distilled water. The washed adsorbent was transferred into a conical flask containing 1 M acetic acid (CH 3 COOH) solution, and the mixture was left for 24 hat room temperature. The result showed that the maximum desorption of CV dye was 89% in 1 M CH 3 COOH solution (Fig. 15). The % desorption decreases up to 45% in fourth cycle as the number of cycles increased. Therefore, the adsorbent can be reused up to fourth cycle successfully.

Comparison of monolayer adsorption capacity (q m )
The monolayer adsorption capacity of PGADP onto CV dye was compared by other adsorbents from the literature, and the results are reported in Table 5. It is clearly evident from Table that the present PGADP adsorbents have better adsorption capacity as compared to the other adsorbents for the removal of CV dye. This suggests that the PGADP material has great prospective in practical applications for the enhanced removal of CV dye from aqueous solution and industrial waste water.

Conclusion
In this wok, a novel and eco-friendly low-cost adsorbent polyacrylamide-grafted Actinidia deliciosa peels powder (PGADP) has been successfully synthesized and further explored as a potential adsorbent for the sequestration of crystal violet dye (CV) from aqueous solution. The maximum adsorption of CV dye from aqueous solution was observed at pH 7.3, contact time 180 min, initial dye concentration 20 mgL −1 . The kinetic data showed that pseudosecond order model was best obeyed over a wide range of concentrations. The equilibrium data were best fitted to Langmuir isotherm with maximum coefficient of (R 2 , 0.998) at 30 °C. In thermodynamic study, positive value of ∆H o and negative value of ΔG° confirms endothermic and spontaneous nature of adsorption process with increased randomness at solid-solution interface with increase in temperature. Desorption study showed that 89% of adsorbed CV dye could be desorbed successfully by using 1 M Acetic acid. To make the process more economical, the exhausted adsorbent was further regenerated and it was observed that it can be regenerated up to fourth cycle without significant loss in capacity. Therefore, the present material can be utilized to treat the waste water economically in developing countries at large scale.
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75.19
This study