Removal of brilliant green dye from synthetic wastewater under batch mode using chemically activated date pit carbon

In this research, a single-stage batch adsorber was designed for removal of brilliant green dye (BG) from aqueous solutions using activated carbon derived from date pits (ADPC) based on the Freundlich isotherm which was the best-fitted isotherm model. Experimental work was carried out within the range of 10–50 ppm initial dye concentration to determine the optimum operating conditions which were 55 min contact time, 0.06 g adsorbent mass, 25 °C, and pH = 8. Process kinetics was best-fitted with the pseudo-second order model, which revealed that the intra-particle diffusion stage is the rate-controlling stage for the process. The process efficiency was assessed by infrared spectroscopy (FTIR), scanning microscopy (SEM), X-ray spectroscopy (EDXS), and Brunauer–Emmett–Teller (BET) where the latter showed that the specific surface area of the adsorbent is 311.38 m2 g−1, which gives a favorable maximum monolayer adsorption capacity (77.8 mg g−1). The thermodynamic study proved that BG adsorption on ADPC was physiosorptive (ΔG = −5.86 kJ mol−1) and spontaneous at low temperature (ΔH = −17.7 kJ mol−1, ΔS = −0.04 kJ mol−1 K−1).


Introduction
Coloring agents and dyestuffs have become the main feedstock for the production of domestic goods, colorful fabrics, paints, printing inks, and so on. 1,2 For instance, the total textile dye consumption is greater than 10 7 kg per year worldwide with roughly 10 6 kg per year of dyes discharged into water streams killing more than three million people, mainly infants, who get water for drinking and irrigation. 3,4 Several kinds of industrial dyestuffs can be found in wastewater and it is classiable into three major groups: anionic (direct, acid, and reactive dyes), cationic (basic dyes) and non-ionic (disperse and vat dyes) 5 while in general, cationic dyes have the most harmful and toxic effects on the ecosystem of receiving water and the whole environment. 6 Releasing such toxic dyes into the environment has become a worldwide concern because of their chemical stability, 7 and cancer-causing and mutagenic impacts that inuence oceanic biota by preventing light from penetrating through water, which slows down photosynthetic activity and also tends to toxify sh and other organisms due to chelating metal ions. Oxidation and reduction of these dyes in water can also produce hazardous substances that raise the necessity of getting rid of them from wastewater. 8,9 They also cause hyperactivity, low frustration tolerance, impulsivity, and lack of attention when they are used as food additives. 10 For that reason, numerous methods such as chemical oxidation, electrolysis, coagulation, ozonation, reverse osmosis, ultrachemical ltration, ion exchange, precipitation, occulation, biological methods, and many others have been used to eliminate organic pollutants. 11,12 However, their use on a large-scale is restricted due to their long operational time, high production cost, and toxic side products. 13,14 Adsorption has been observed to be better than multiple techniques for treating wastewater contaminated with dissolved substances and drugs 15,16 because it is inexpensive, very exible, modest in design, easy to operate, and capable of handling relatively high ow rates of water without production of residual sludge or pollutants. 17,18 Moreover, successful water pollutant adsorption provides their recovery, which is especially required for water nutrients. 19 Adsorption techniques can be classied into batch which is a simple technique that offers a convenient way to better explain the parameters that control the adsorption mechanism or continuous technique which is useful in evaluating the amount of adsorbent required to extract the wastewater contaminants. 20 Commercial activated carbon is a commonly utilized adsorbent in waste-water treatment processes as it consists of a micro-porous homogenous structure that gives large surface area, high adsorption capacity, and high porosity 21 but its wide utilization was restricted because it is costly and its uptake capacity and yield aer regeneration decreased by 10-15%. 22 Hence, scientic researchers have focused their attention on producing activated carbon from renewable domestic agricultural waste because of its low preparation costs. 23,24 " Table 1" shows the advantages and disadvantages of previously reported biomass utilized in wastewater treatment compared with date pits. Physical and chemical activation are the basic processes for producing activated carbon. The rst technique is composed of raw material carbonization and gasication by steam or carbon dioxide of the resulting char. The second technique consists of impregnation of the precursor material with chemical reagent (KOH, ZnCl 2 , H 2 SO 4 , H 3 PO 4 , HNO 3 , and CO 2 ) then carbonization of the impregnated product. 32 ZnCl 2 and H 3 PO 4 appear to be the most used reagents for activated carbon preparation but H 3 PO 4 is preferred because of its ease removing by washing with warm or cold water aer carbon activation. 33 Moreover, the iodine number of carbon prepared from H 3 PO 4 is greater than the iodine number of carbon prepared from ZnCl 2 . 34 The chemical activation process is superior to the physical activation process because of its high productivity and high surface area of the resulted carbon 9 in addition to its low energy costs. 35 BG is an odorless cationic dye in the form of golden-green crystals. 4 It is known as Diamond green G, Solid green, Ethyl green, and Basic green 1. It can be used as a biological mark, dermatologic agent, antimicrobial treatment, and inhibition of mold propagation in poultry food. 36 It is also widely utilized in the dyeing of textiles and manufacturing of inks for printing papers. Approximately 0.8-1.0 kg of BG is utilized per ton of produced paper sheet. 37 For mankind, BG causes gastrointestinal tract discomfort which leads to nausea, vomiting, and diarrhea. It also induces cough and shortness of breath in the respiratory tract. Moreover, it can cause skin irritation with redness and ache in case of direct contact. 38 Decomposition of BG may produce hazardous gases like CO, CO 2 , NO, NO 2 , and SO 2 . 5 As a result, a lot of researchers studied the adsorption of BG from wastewater by carbonized and non-carbonized as given in " Table 2". Date pits can be considered a waste product aer processing of compressed dates (fresh date fruit has 10-15% seed from its weight). 39 It was used as carbonized and non-carbonized compound for many adsorption kinds of research to remove industrial dyes such as Methylene Blue, 40 Indigo Carmine, 9 Methyl Orange, 35 Disperse blue dye, 41 Maxilon blue, 23 and Congo red. 42 The current survey was aimed to determine the optimum contact time, adsorbent Table 1 Comparative study between previously reported biomass utilized in wastewater treatment and date pits

Adsorbent
Advantages Disadvantages Wood 25 Produced activated carbon has a highly porous structure (S BET ¼ 1884 m 2 g À1 ) and useful functional groups The yield of produced activated carbon is low Produced activated carbon can make a rapid adsorption process with high adsorption capacity Wood can be more useful in production of furniture Bagasse 26 Produced activated carbon is very efficient for the adsorption of gases due to its excellent stability and regenerability Produced activated carbon can't be useful in dyes or heavy metals removal because of its non-sufficient functional groups Produced activated carbon has a large specic surface area (S BET ¼ 1113 m 2 g À1 ) Produced activated carbon has a small micro-pore diameter (less than 1 nm) Orange peel 27 Produced activated carbon gives high adsorption capacities.
The yield of produced activated carbon is low Produced activated carbon has many useful functional groups Produced activated carbon requires several treatment processes to control the ash content Biological sludge 28 Produced activated carbon has a large specic area and high micro-pore diameter The yield of produced activated carbon is low due to high liquid content Produced activated carbon gives high adsorption capacities Produced activated carbon can't be useful in heavy metals removal because of its non-sufficient functional groups Rice husks 29 Pyrolyzed rice husk can be used to remove color and turbidity of wastewater Produced activated carbon has a small specic surface area and small adsorption capacity Raw rice husk has been reported to remove 98.24% of humic acid from aqueous solutions Produced activated carbon requires several pre-treatment processes to control the ash content Waste palm shells 30 The yield of produced activated carbon is very high (97.8 wt%) and the activation time is very small (10 min) Produced activated carbon has a small specic surface area and small adsorption capacity Produced activated carbon doesn't need several treatment processes due to low ash content Produced activated carbon has non-sufficient functional groups Coconut husk 31 Produced activated carbon has a large specic surface area (S BET ¼ 1448 m 2 g À1 ) Raw coconut husk can be more useful when used as a fuel for household purposes Produced activated carbon can be regenerated without any damage (desorption efficiency >95%) Raw coconut husk needs several purication processes to eradicate dirt and other contaminants Date pits (present work) Produced activated carbon has a convenient specic surface area and adsorption capacity Grinding of raw date pits need a special mill for hard rocks The yield of produced activated carbon is high (>70 wt%) The purication processes of raw date pits are very simple. Produced activated carbon can be useful in dyes or heavy metals removal due to its sufficient functional groups mass, temperature, pH, and initial BG concentration. Some adsorption isotherm models were studied to know the maximum adsorption capacity for the activated date pits carbon and the best-tted model for the process. The kinetic and thermodynamic studies were investigated to dene the mechanism and the rate-controlling stage for the process. The experimental data was well tted with Freundlich isotherm which was used in designing a batch adsorber with one stage.

Activated date pits carbon preparation
The raw date pits were collected from a factory that produces compressed dates (Agwa) in Damietta, Egypt. The boiled water was used in washing the pits to remove any date residue. The pits were dried at 110 C in an electric oven to make them free from moisture then ground to a ne powder using (RETSCH lab mill). The raw date pits powder was placed in a glass container and a concentrated phosphoric acid (85%) was poured carefully into the container until 20 g of seeds will be impregnated in 40 mL of H 3 PO 4 at 25 C for 24 hours. At the end of the soaking time, the soaked seeds were dried at 110 C for one hour. The seeds were placed on a ceramic cup and subjected to 400 C for 2 hours in a muffle furnace (Hobersal JB-20). Then, neutralization of the seeds was carried out using hot distilled water and aer that, the produced activated carbon was dried at 110 C for 3 hours to remove any undesired moisture within the particles. Finally, the activated date pits carbon was sieved using (SAMA Sieve Shaker) to obtain an equal particle diameter which was (75 mm).
Preparation of the adsorbate BG (C 27 H 34 N 2 O 4 S) was bought with molecular weight 482.62 and was used by dissolving 1 g of BG powder, weighed by a fourdigit analytical balance (KERN-ABS 220-4, UK), in 1 L of distilled water to prepare the stock solution (1000 ppm). Diluting the stock solution with distilled water was carried out to prepare the desired experimental concentrations. The wavelength was measured to be 625 nm and the nal concentrations were measured using (PG instrument Ltd T80, UK) UV-Visible spectrophotometer.

Experimental studies
The batch adsorption process was carried out to study the effect of the experimental parameters (contact time, adsorbent mass, temperature, pH, and initial BG concentration) on the adsorption of BG by activated date pits carbon (ADPC) and can be summarized in " Fig. 1". Firstly, a 0.02 g of ADPC was contacted with 50 mL of a BG solution at different concentrations (10-50 ppm) at neutral pH in 125 mL glass bottles at a xed temperature (25 AE 2 C) and constant shaking speed (240 rpm) in a shaking water bath (Wisd laboratory instruments, DAHAN Scientic co., Ltd, 30, Korea) for different intervals of time until it reached the equilibrium at   (55 min). Secondly, the solutions were centrifuged using (80-1 Electric Centrifuge) and the concentrations of the ltrated samples were determined by the spectrophotometer. The previous procedures were applied at (0.01-0.08 g) of ADPC and constant time (55 min) until the equilibrium was observed at (0.06 g) which is the optimum adsorbent mass. The temperature effect was studied by applying the above procedures at 55 min contact time, 0.06 g dose, neutral pH, and different temperatures (25-95 C). The initial concentration effect was determined by preparing (10-100 ppm) from the stock of the dye solution and applying the repeated process at the optimized conditions of the previous parameters (55 min time, 0.06 g dose).
The pH parameter was investigated by adjusting the pH of the dye solutions using a pH-meter (Hanna-Instruments 8519, pH 211, Canada), HCl, and NaOH and repeating the process as described above at equilibrium time and dose until it gives the highest removal percent which was at pH ¼ 8. The process efficiency was determined using the following equations: where "C o " is the initial concentration of BG solution in (ppm), "C e " is the nal concentration of BG solution in (ppm), "V" is the volume of BG solution in (L), and "W" is the mass of the adsorbent in (g). "Q e " is the adsorption capacity at equilibrium (mg g À1 ). 47

Results and discussion
Characterization of activated date pits carbon SEM analysis was used to obtain surface morphology of activated date pits carbon (ADPC) before and aer adsorption of BG by (JEOL JSM 6510 lv, Japan). " Fig. 2a" displays a heterogeneous morphology of ADPC before adsorption of BG including many small pores that are distributed randomly on the surface. " Fig. 2b" clearly shows the aggregation of BG particles on the surface of ADPC which makes the pores mostly disappeared and this indicates that BG was successfully adsorbed on the surface of ADPC. 47 EDXS analysis was used to clarify the qualitative elemental composition of activated date pits carbon (ADPC) before and aer adsorption of BG by (JEOL JSM 6510 lv, Japan). According to the X-ray spectroscopy, the chemical composition (in wt%) of ADPC unloaded with BG was 76.73 for carbon, 21.92 for oxygen, 0.19 for sodium, 0.56 for phosphorus, 0.39 for copper, and 0.22 for zinc. Furthermore, the chemical composition (in wt%) of ADPC loaded with BG was 79.38 for carbon, 19.06 for oxygen, zero for sodium, 0.82 for phosphorus, 0.42 for copper, and 0.33 for zinc. Based on the noticeable differences in weight percents between ADPC loaded and unloaded with BG, it can be concluded that the chemical structure of ADPC was changed due to the effective adsorption of BG molecules on the pores of ADPC. 47 FTIR analysis was used to see how far the molecular structure of activated date pits carbon (ADPC) has been changed aer adsorption of BG by (ThermoFisher Nicolete IS10, USA). According to the IR spectrum of ADPC before adsorption of BG, there are some strong, moderately strong, and weak bands at

Operating conditions effect
Process time can be represented by " Fig. 3" for adsorption of different concentrations (10-50 ppm) of BG onto a xed weight (0.02 g) of activated date pits carbon (ADPC) in the range of (5-65 min). It can be observed that the low concentrations (10 and 20 ppm) reach the equilibrium very rapidly at the rst twenty minutes while the high concentrations (30, 40, and 50 ppm) reach the equilibrium at (55 min) aer a gradual increase in the removal percent during the time shown in the gure and this could be interpreted by the theory that in adsorption of dyes, rstly, the dye molecules have to compete against the effect of boundary layer interface. Secondly, the penetrating dye molecules move out from the boundary layer lm to distribute onto the surface of the adsorbent. Finally, the remaining dye molecules diffuse into the porous structure of the adsorbent. Based on this theory we conclude that when the initial concentration of dye solutions increases, the number of dye molecules increases, so the process will take a relatively long contact time to reach the equilibrium state. 6 The adsorbent dose parameter was displayed in " Fig. 4", the removal percent of (10-50 ppm) BG onto activated date pits carbon (ADPC) increases with the increase in adsorbent dose ranged from (0.01-0.06 g) due to the availability of more adsorbent active sites as well as greater availability of specic surface area of the adsorbent. Aer that, there are no signicant changes in removal percent were observed due to aggregation of adsorption sites takes place which makes the total ADPC surface area decrease, leading to a slighter increase in BG removal. 52 So, (0.06 g) can be considered the optimal dose for ADPC loading.
The temperature parameter is commonly used to indicate if the process is endothermic or exothermic. " Fig. 5" displays the temperature inuence in neutral medium (pH ¼ 6-7) for adsorption of BG at (10-50 ppm) on the surface of activated date pits carbon (ADPC) with constant weight (0.06 g). It is clearly shown that as temperature increased in the range (25-95 C), the removal percent of BG decreased from 98% to 77%. This may be due to weakness of physical bonding between the dye molecules and the active sites of the adsorbent with increasing temperature. Also, as temperature increases, the solubility of dye increases, the interaction forces between the solute and the solvent become stronger than solute and adsorbent, so the solute is more difficult to adsorb. Therefore, it can be concluded that the process is exothermic. 8,40 The initial BG concentration parameter was studied within the range (10-100 ppm) at 25 C, 0.06 g adsorbent dose, and 55 min contact time. From " Fig. 6" it was observed that the    removal percent decreased sharply with the increase in initial concentration up to 90 ppm then it noticed that there were no considerable changes in the removal percent and this can be explained by the fact that at low initial dye concentration the number of active sites on the adsorbent's surface is more available compared with high initial dye concentration. So, most of the dye molecules have been adsorbed on the surface of activated date pits carbon (ADPC) leading to higher percentage removal while at high initial BG concentration, molecules have low chances to be adsorbed due to the limited number of binding sites at the adsorbent's surface. Thus, some of the dye molecules remain in the solution and do not get adsorbed. 6 The pH parameter was investigated within the range (3-10) at (10-50 ppm) initial concentration of BG and room temperature (25-30 C) as shown in " Fig. 7". The results indicate that the removal percent of BG increases with the increase in pH up to pH 8 aer which was observed no signicant improvement in the process. This may be explained that at lower pH the surface charge of activated date pits carbon (ADPC) may get positively charged which make H + ions compete effectively with dye cation leading to a decrease in the removal percent of dye adsorbed while at higher pH, the surface of ADPC may get negatively charged which enhances the electrostatic force of attraction between the positively charged dye cation and the adsorbent's surface. 53 Also, at higher or lower pH, as the initial dye concentration increases, the competition between dye molecules to be adsorbed increases, so the removal percent decreases. 40 Isotherm and equilibrium study The isotherm study was carried out by tting the experimental data to four isotherm models and nd a convenient model that can be used for design purposes using the correlation coefficients, R 2 values as shown in " Table 3".
For Langmuir model, C e /Q e versus C e has a linear relationship as shown in " Fig. 8", with a slope equal to 1/Q m and an intercept equal to 1/(Q m K L ). The linear Langmuir equation is given as: where "Q m " is the maximum adsorption capacity (mg g À1 ), and "K L " is the Langmuir affinity constant (L mg À1 ) related to "Q m " and rate of adsorption. The feasibility of the process can be evaluated by a separation factor (dimensionless constant) "R L " which is given in the following equation: The "R L " value lays between zero and one for favorable adsorption, whereas (R L > 1), (R L ¼ 1), and (R L ¼ zero) for unfavourable, linear, and irreversible adsorption respectively. 40 For Freundlich model, ln Q e versus ln C e has a linear relationship as shown in " Fig. 9", with an intercept equal to ln K f and a slope equal to 1/n. The logarithmic form of Freundlich is given by the following equation: where "K f " is the Freundlich constant which represents the adsorption capacity of the adsorbent in (mg g À1 ) and "1/n"indicates the favourability of the adsorption process. If the value of "1/ n" lay between zero and one it means adequate adsorption. 40 Temkin model's equation can be expressed as: where K t and q m are the Temkin constants related to adsorption capacity in (L mg À1 ) and heat of sorption in (J mol À1 ) Fig. 7 Effect of pH on the adsorption of BG dye onto ADPC. respectively. 40 The values of q m and K t can be obtained from the slope and intercept of the linear plot of Q e versus ln C e as displayed in " Fig. 10". Dubinin-Radushkevich model can be represented by the following equations: 3 ¼ RT ln ((C e + 1)/C e ) where 3 is Polanyi potential, R is gas constant (kJ mol À1 K À1 ), T is the absolute temperature in (K), and D, Q m are Dubinin constants which related to the transfer of adsorption energy in (mol 2 J À2 ) and the maximum adsorption capacity of the adsorbent in (mg g À1 ) respectively and they can be calculated from the slope and intercept of the plot between ln Q e and 3 2 in " Fig. 11". 40 Kinetic study Four kinetic models were used to t the experimental data at 50 ppm initial dye concentration using a linear regression analysis method. The parameters of these models are summarized in " Table 4". The pseudo-rst-order rate expression is given as: where Q t is the amount of dye adsorbed on the adsorbent at any time, t in (mg g À1 ), and K 1 is the rst-order rate constant. A " Fig. 12" of log(Q e À Q t ) versus t gives a linear relationship from which the value of K 1 and Q e can be determined from the slope and intercept. 54 The linearized form of the pseudo-second-order model is given as: where K 2 is the rate constant of the pseudo-second-order adsorption. The plot of t/Q t versus t in " Fig. 13" gives a linear relationship from which Q e and K 2 can be determined from the slope and intercept of the plot respectively. 55 The Elovich model is generally expressed as: where a is the initial adsorption rate (mg g À1 min À1 ) and b is related to the extent of surface coverage and the activation energy for chemisorption (g mg À1 ). 55 A plot of Q t vs. ln t in " Fig. 14" gives a linear relationship with a slope of "1/b" and an intercept of 1/b ln(ab).    The intra-particle diffusion model used here refers to the theory proposed by Weber and Morris based on the following equation: where K pi (mg g À1 min À0.5 ) is the intra-particle diffusion rate constant, and C (mg g À1 ) describes the boundary layer thickness. 6 The plot of Q t versus t 0.5 in " Fig. 15" gives a linear relationship of slope (K pi ) and an intercept (C).

Thermodynamic study
The thermodynamic parameters that used to describe the adsorption process are the change of Gibbs free energy (DG, kJ mol À1 ), enthalpy (DH, kJ mol À1 ), and entropy (DS, kJ mol À1 K À1 ). They are calculated depending on the equilibrium experimental data obtained at different temperatures from 298.15 to 368.15 K and 50 ppm initial dye concentration by using the Van't Hoff equations as follow: where R is the ideal gas constant (8.314 J mol À1 K À1 ), T is the absolute temperature in kelvin, and K ¼ Q e /C e . The enthalpy (DH) and entropy (DS) of the process were estimated from the slope and intercept of the plot of ln K versus 1/T as shown in " Fig. 16" which gives À17.7324 kJ mol À1 enthalpy and À0.039729 kJ mol À1 K À1 entropy at 298 K. Gibbs free energy (DG) was calculated using "eqn (13)" which gives negative values at all temperatures so, the adsorption of BG onto activated date pits carbon (ADPC) is physiosorptive because the free energy values fall in the range of (À20 to 0 kJ mol À1 ). 6 Hence, the links between dye molecules and the adsorbent surface can be due to van der Waals or electrostatic attraction forces. The negative values of DH and DS indicate that the adsorption of BG onto ADPC is exothermic and spontaneous at low temperature. 40 Design of single-stage batch adsorber The design of batch adsorber is considered the practicable step for using the equilibrium data resulted from experimental work by calculating the required adsorber volume and the optimum adsorbent weight. 40 " Fig. 17" displays a schematic diagram for the single-stage batch adsorber where the initial concentration of the dye changes from C o to C e and the adsorption capacity of the adsorbent changes from Q o to Q e . The mass balance for the batch adsorber with a solution volume (V) and the amount of adsorbent (M) can be written as follow: By using the Freundlich adsorption isotherm model as it is the best-tted model and by assuming that activated date pits carbon (ADPC) is a fresh adsorbent (Q o ¼ zero) so, "eqn (16)" can be rearranged as follow: Based on the previous equation, a relationship was drawn in " Fig. 18a" between the mass of adsorbent and the volume of dye solution that needs to be treated (100 : 2000 L) at a removal percent equal to 85% and a range of initial dye concentration from 20 to 100 ppm. Otherwise, a relationship was drawn in " Fig. 18b" between the previous variables but at different removal percent (60 : 98%) and constant initial dye concentration (200 ppm).     Proposed mechanism for the process The general methodology for any adsorption process can be summarized in the following stages: (a) The dye molecules have to encounter the boundary layer effect for the adsorbent and diffuse from the boundary layer lm onto the adsorbent surface.
(b) Diffusion of the dye molecules into the porous structure of the adsorbent where intra-particle diffusion of solute takes place in the adsorbed state or the liquid-lled pores of the particle.
According to the kinetic study, the pseudo-second-order is the best-tted model for this process (R 2 > 0.99) and from " Fig. 15" it's observed that the plot doesn't pass through the origin. Therefore, it can be concluded that the second stage is the rate-controlling stage. 6,40 According to the thermodynamic study, it's clearly shown that the negative values of DG fall in the range of (À20 to 0 kJ mol À1 ) so, it can be concluded that the process is physiosorptive. 6 Therefore, the process methodology can be deduced as follows: (1) BG molecules encounter the boundary layer lm and diffused rapidly onto the surface of activated date pits carbon (ADPC) due to the continuous shaking of bottles by the shaking water bath (Wisd laboratory instruments, DAHAN Scientic co., Ltd, 30, Korea).
(2) Intra-particle diffusion of BG molecules takes place in the porous structure of ADPC where hydrogen bonds (van der Waals or electrostatic attraction forces) were formed between BG molecules and the hydroxyl groups on the surface of ADPC until the process reaches the equilibrium state.

Conclusion
This study showed that activated carbon prepared from date pits (ADPC) by chemical activation with phosphoric acid was a favorable adsorbent for the removal of brilliant green dye from aqueous solutions over a wide range of concentrations. The optimum experimental data were 55 min contact time, 0.06 g adsorbent dose, and basic medium pH ¼ 8. Kinetic and Equilibrium studies were best tted with the pseudo-second order kinetic model (R 2 > 0.99) and Freundlich isotherm model (R 2 > 0.99). The specic surface area of ADPC was 311.38 m 2 g À1 which gives a convenient maximum monolayer adsorption capacity of 77.8 mg g À1 . The negative values of DG were demonstrated that the process is physical adsorption and spontaneous at low temperatures concerning the negative values of DH and DS which proved that the reaction is exothermic and as the temperature increase, the solubility of dye molecules increase so removal percent decrease.

Conflicts of interest
There are no conicts to declare.