Adsorption of Methylene Blue and Safranine Using Activated Carbon of Cinnamon Plant Surface.

Cinnamon plant Activated Carbon (C/AC) was prepared by chemical and thermal activation. The adsorption behaviour of (C/AC) in aqueous Methylene blue (MB) and Safranine (S) dyes was investigated and characterized by XRD, TEM and FESEM. The possible mechanism of the adsorption of (MB) and (S) dyes on the (C/AC) surface was studied. The influence of various adsorption control parameters like the initial dye concentration, pH, contact time, and temperature was studied. The data confirmed a high removal of (MB) and (S) at pH=11. The experimental data were fitted to Langmuir and Freundlich isotherms to examine the adsorption mechanism. The adsorption data reveal (MB) with the maximum capacity of (294.11) mg/g and (S) with the capacity of (285.714) mg/g. The kinetic data for different initial dye concentration were computed using pseudo-first order, pseudo-second order, and intraparticle diffusion model. Thermodynamic parameters includes enthalpy (∆H), entropy (∆S), free energy (∆G), and activation energy (E a ) of the adsorption process were calculated and used to interpret the results, and revealed that the adsorption systems were a spontaneous and endothermic process for adsorption of MB and S dyes onto the adsorbent surface. Also, low activation energy values (E a <40 kJ/mol) were characteristics of the physisorption mechanism

In general, the dye is toxic and hazardous chemicals in the environment, particularly in the water bodies and biosphere. In addition the dye can cause dysfunction of the kidneys, reproductive system, liver, brain, and nervous system of human beings [9]. Approximately, 100,000 different types of dyestuffs are available on the global market but the annual production rate is about 7 10 5 t [10]. Methylene blue is cationic dye with heterocyclic aromatic chemical compound (C 16 H 18 N 3 SC) which is commonly used for dyeing of cotton, wool and silk. About 40% 0f the synthetic dyes like methylene blue and Safranine are toxic, mutagenic, and carcinogenic compounds that remained in industrial effluent and can cause sever public and environmental health problems [11].
Generally, conventional wastewater treatment plants are not effective for the removal of dyes from textile industrial wastewater. However, advanced wastewater treatment for dyes removal from textile industrial wastewater are very effective and efficient. The most applicable advanced wastewater treatments are chemical precipitation, nanofiltration, advanced oxidation process, ion exchange, reverse osmosis, membrane separation, electro-coagulation, and electrodialysis. However, these technologies are a very expensive and not sustainable mechanism for wastewater treatment in every sector, especially in developing countries [12]. In addition these methods required high energy, chemical, operational and capital inputs, and advanced technologies. Among advanced treatment methods, adsorption has been found to be good treatment technology for dye removal [13,14], and the researchers have relied on many ideas and new materials used as adsorbent surfaces [15,16].
Fundamentally, adsorption treatment technology is flexible, simple for design, relative ease of operation, cost-effective, high efficiency, recyclability, and environmentally friendly [12]. The technical and economical disadvantages have resulted in using bio-sorption methods that has been found to be efficient and costeffective. The use of activated carbon biosorbent not only serves to control pollution but also reduces agricultural waste generation. Various agricultural waste biomaterials were used for adsorption process such as rambutan seed, Rambutan seeds activated carbon (RSAC) was prepared using potassium hydroxide (KOH) activation and carbon dioxide (CO 2 ) gasification methods, RSAC used for the removal of MG dye [17], spent tea leaves [18], pomelo peel [19], sugar beet pulp [20] sugar beet pulp based activated carbon was prepared by using phosphoric acid as activating agent for adsorption of methylene blue, and rice husk [21] concluded from this study that porous bio-char and activated carbon could be prepared in normal environmental conditions instead of inert media. This study shows a method and possibility of activated carbon from agro-waste, and it could be scaled up for commercial production. The remarkable adsorption characteristics of activated carbon are that it contains small, low-volume pores that increase the surface area available for adsorption or chemical reaction [22].
Cinnamon is a spice obtained from the inner bark of several tree species from the genus Cinnamomum. Cinnamon is used mainly as an aromatic condiment and flavouring additive in a wide variety of cuisines, sweet and savoury dishes, tea and traditional foods. The aroma and flavour of Cinnamon derive from its essential oil and principal component, cinnamaldehyde, as well as numerous other constituents including eugenol. Cinnamon is the name for several species of trees and the commercial spices products that some of them produce. All are members of the genus Cinnamomum in the family Lauraceae. Only a few Cinnamomum species are grown commercially for spice [23].

Material and Methods
Preparation of Adsorbent and Adsorbate. The dried ground Cinnamon was subjected to chemical activation with 20.4 ml of 1N H 3 PO 4 were measured into a crucible containing 5g from laboratory ground Cinnamon carefully measured and stirring for 30 minutes at room temperature. The sample was oven dried for 24 hours at 105 0 C and then allowed to cool.
After cooling the sample was activated in the furnace for 1 hour at 700 0 C. This was followed by soaking the activated carbon in 0.1N HCl, and stirred for 30 minutes then allowed to stand for 24 hours and washing with distilled water until the pH is in the range of 6-7, all of that to remove the residual acid from its pores.
After that the sample was oven dried for 24 hours at 105 0 C and cooled, crushed, and sieved (by using 75-micron sieve). Methylene blue and Safranine were purchased from (Sigma-Aldrich) and used to prepare adsorbate solution. The stock solution of the dyes of 1000 ppm was prepared using de-ionized distilled water.

Experimental
A series of dye solutions were prepared by adjusting the pH over a range of (3-5-7-9-11) by using 0.1N HCl and 0.1N NaOH solution to evaluate the role of pH on adsorption of Methylene blue and Safranine dyes onto (Cinnamon/Active Carbon) or (C/AC). The experiment was carried out using 100ml of the aqueous MB and S dyes at concentrations 200ppm. It was treated with 0.25g of (C/AC) and shaken in bench top incubator cum orbital shaker at a constant speed of 200rpm for a time period of 3hours.
Residual dye concentration was recorded using a double beam UV/vis spectrophotometer (Model: T80 (EMC-LAB) / PG instruments, England) at 668nm for MB and 525nm for S for which the molecular structure is shown in Fig.1 and 2. The equilibrium amount of dye adsorbed on (C/AC) was calculated by equation 1, and the removal efficiency of the dye in percentage was calculated by equation 2 as listed in Table1.

Adsorption Isotherms.
The adsorbate-adsorbent interaction at equilibrium was found by fitting the experimental data in Langmuir, and Freundlich 3, and 5 respectively, as summarized in Table 1. 2.3 Kinetic Studies. The equation 6, 7, and 8 shown in Table 1 were used to examine the reaction kinetics for a specific contact time, t (5, 15, 30, 45, 60, 80, 120, and 180 min.) using 0.25g of (C/AC) with 200 ppm MB and S dye solutions, at room temperature.

Thermodynamic Studies.
The thermodynamic nature of adsorption of MB and S onto (C/AC) was studied using Gibbs and Van't Hoof equations 9, and 10 as given in Table 1. 1.
Removal efficiency , % Where is the initial dye concentration, is the final dye concentration at equilibrium, V is the operating volume of the solution, and M is the mass of adsorbent.

Freundlich isotherm ⁄
Where is the amount of dye adsorbed per g, is the monolayer adsorption capacity, is Langmuir adsorption constant, n is Freundlich constant.

7.
Pseudo-second order equation Where is the amount of dye adsorbed at equilibrium, is the amount of dye adsorbed at any time t, is the pseudofirst order rate constant in , is the pseudosecond order rate constant, is the intraparticle diffusion rate constant, and C is the intercept. Thermodynamic studies.
Van't Hoff equation Where is the equilibrium constant, is Gibbs free energy change, is the change in enthalpy of adsorption, is entropy change, and T is the operating temperature. _________________________________________________________________________ 4.3 Characterization of (C/AC). The physical characteristics of (C/AC) such as the surface morphology of (C/AC) was characterized by Field Emission Scanning Electron Microscopy (FESEM) using the (FEI NOVA Nano SEM 450) model. Figure (3) the (SEM) image of the (C/AC) sample obviously shows the surface morphology with an irregular texture and high surface roughness and different levels of porosity, which provides possible sites for adsorption of the dyes. The surface roughness and the macropores which are important factors for the dye adsorption were responsible for the high surface area making the (C/AC) a good adsorbent [24].
(C/AC) also characterized by X-Ray Diffraction using (Rigaku X-Ray Powder Diffraction Diffractometer). Figure (4) shows the XRD pattern of (C/AC), the broad peaks at round 25 0 and 43 0 due to the hexagonal graphite structures (002) and (100). The d 002 value of (C/AC) calculated using Bragg's equation ( ⁄ ) by assumed n=1, and nm, the result was (0.371 nm) which is higher than that in graphite (d 002 = 0.335 nm). Indicating that (C/AC) had more randomly oriented graphitic carbon layers [25,26].
Transmission Electron Microscopy (TEM) analysis was also performed by using (CM 120, 100Kv, Philips) model. As shown in Figure (5) which revealed a complete porous carbon architecture. The existence of these pores is attributed to the H 3 PO 4 activation process adopted in synthesizing of (C/AC) [27,28].  [29]. From the experimental data, it is found that the removal efficiency of MB and S dyes increased with increasing of pH from (3 to 11) as shown in Figure (6) and Figure (7) respectively. Maximum adsorption for MB and S was observed at pH=11 and it was (221.850 mg/g) for MB and (177.203 mg/g) for S. The increase in the adsorption efficiency in the alkaline medium is due to the strong hydrostatic interactions between the adsorbent molecules and the dyes. On the other hand, the increase in the adsorption efficiency depend on the competition between hydrogen ions H + and the dye ions to be adsorbed from their aqueous solution on the active sites of the adsorbent surfaces, in the lower value of pH (2-6) (acidic medium) the hydrogen ions H + concentration is increase and the competition between them and the dye ions to be adsorbed on the active side of the adsorbent surface increase that leads to decrease in the adsorption efficiency. The increasing of pH values (alkaline medium), the hydrogen ion H + concentration decreases and thus the competition between hydrogen ion H + and the dye ions to be adsorbed on the active site located on the surface of the adsorbent is decrease, which leads to an increase in the adsorption efficiency directly until reaching for the optimum pH value [30,31].

Effect of Contact Time and Temperatures on dyes adsorption.
The effect of contact time between the adsorbate and adsorbent is one of the most important parameters in the adsorption process since it is important to estimate the equilibrium contact time to foretell the performance and feasibility of an adsorption for a process [32].
The effect of contact time on the adsorption of MB and S onto (C/AC) were presented in Figures (8) and (9), at the initial concentration of adsorbent and optimum pH=11 in three different temperatures (25, 40, 60) 0 C. As shown in both Figures (8) and (9) the adsorption had increased rapidly from 5-180 min for MB. While the adsorption of S had increased rapidly from 5-120 min and then the equilibrium was achieved within 180min for MB and 120min for S.
Generally, the trend was observed for dyes adsorption onto (C/AC) was the same, it is clear that the extent of adsorption was rapid in the initial stages, because of the availability of a wide number of adsorption active sites on the adsorbent surface and becomes slow in later stages due to a reduction in the number of adsorption active sites on the surface of the adsorbent until equilibrium was achieved. Also, the Figures showed that the adsorption capacity of prepared adsorbent surface (C/AC) for MB and S dyes increased with temperature from 25 0 C to 60 0 C. This may be ascribed that with an increase in temperature there was an increase in the mobility of the large dye ion. An increasing number of molecules also acquire sufficient energy to undergo an interaction with active sites at the surface [33].
Besides that, the equilibrium capacity of the adsorbent for a specific adsorbate can be affected by temperature change [34].

Isotherm Studies.
The study on adsorption isotherm is very important in describing the adsorption characteristics for a solid-liquid adsorption system [35]. Figure (10) and Figure (11) gives the Langmuir plot ( vs. /q e ) for MB and S dye adsorption and isotherm constant and are from the slope and intercept, respectively.
Langmuir isotherm assumes adsorption at homogeneous sites on the adsorbent thus forming a saturated monolayer of the dye inside the pores [36].
The dimensionless separation factor if (0 < < 1 favourable, > 1 unfavourable, = 0 irreversible) for the adsorption of MB was (R L = 0.045) and for S was (R L= 0.079) were assumed the adsorption was favourable.

Kinetic Studies.
Kinetic models such as pseudo-first order, pseudo-second order, and intraparticle diffusion models were used to interpret the experimented data [38]. The plot (ln (q eq t ) vs. t) for linearized Lagergren pseudo-first order equation for MB and S is given by Figures (14) and (15). The values of (-K 1 ) and q 1 were calculated from the slope and intercept respectively, and R 2 is listed in Table (4). The straight lines in the pseudo-first order plot for MB and S dyes imply the feasibility of pseudo-first order kinetics. Further, the values of coefficient of determination, R 2 > 0.9, for MB and S dyes, adsorption confirm the best fit [39]. However, pseudo-second order plot (t/q t vs. t) shown in Figures (16) and (17), did not indicate a good compliance for MB and S dyes adsorption and thus proves the no proximity of the model against the examined data. The intraparticle diffusion mechanism ascribes to the travelling of dye molecules from the bulk of the solution to the solid adsorbent. This mechanism can be understood from the plot (q t vs. t 1/2 ) for MB and S dyes adsorption as displayed in Figures (18) and (19). The plot indicates a linear regression for MB and S dyes and skips away from the origin. This infers that intraparticle diffusion mechanism onto (C/AC) was not the rate-determining step and not the overall step controlling adsorption process [40].      Table (7). ΔH and ΔS were obtained from the slope and intercept of the linear plot of Van ' t Hoff of (ln K eq vs. (20) and (21). These parameters allow for the determination of whether the process is favorable from thermodynamic standpoint, the system ' s spontaneity, and whether the adsorption process occurs with adsorption or release of energy [41].

1/T) as shown in Figures
The positive values of ΔH for adsorption of MB and S onto (C/AC) also prove the endothermic nature of the process [42,43]. The positive values of ΔS indicate increase in randomness at the carbon-dye interface during the adsorption of dyes onto (C/AC), this could be possible due to the increase in mobility of adsorbate molecules present in the solution with an increase in temperature [44], and the adsorption systems were spontaneous revealed that from negative values of ΔG.
Also, the E a was calculated from the plots of (ln K vs. 1/T) as shown in Figures (22) and (23) and the slope of the straight line gives the E a values, the activation energy E a gives indicates whether the adsorption mechanism is primarily physical or chemical [45]. Generally low activation energy (less than 40 KJ mol -1 ) for adsorption of MB and S dyes onto (C/AC) are characteristic for physisorption [46].

Conclusion
It is possible to prepare activated carbon derived from natural materials available at cheap prices and use it as adsorbent surfaces to remove hazardous dyes from the aqueous solutions. The adsorption capacity in terms pH of the solution, agitation time and temperature was examined. The control parameters were optimized and fixed. The isotherm investigation on adsorption of Methylene blue and Safranine onto activated carbon derived from cinnamon (C/AC) revealed best fit of Freundlich isotherm that indicated multilayer adsorption for MB and S onto the adsorbent surfaces. The kinetic studies confirmed pseudo-first order mechanism for adsorption system of MB and S. The thermodynamic studies indicate that the adsorption was spontaneous, endothermic and from E a values indicate that the kind of adsorption was (physisorption). From all that we indicate that the prepared activated carbon surfaces could be used as adsorbents with high efficiency for removing contaminating dyes MB and S, and the adsorption efficiency depends on pH, time and temperature.