Statistical optimization of activated carbon from Thapsia transtagana stems and dyes removal efficiency using central composite design

This study focused on the preparation of activated carbons from Thapsia transtagana stems by boric acid activation and their evaluation for dyes removal. The central composite design and response surface methodology were used to optimize the preparation conditions.

Journal of Science: Advanced Materials and Devices (2019) 544e553 Contents lists available at ScienceDirect Journal of Science: Advanced Materials and Devices journal homepage: www.elsevier.com/locate/jsamd Original Article Statistical optimization of activated carbon from Thapsia transtagana stems and dyes removal efficiency using central composite design A Machrouhi a, H Alilou a, b, M Farnane a, S El Hamidi a, M Sadiq a, M Abdennouri a, H Tounsadi c, *, N Barka a, ** a Sultan Moulay Slimane University of Beni Mellal, Research Group in Environmental Sciences and Applied Materials (SEMA), FP Khouribga, B.P 145, 25000 Khouribga, Morocco b Facult e Polydisciplinaire de Taroudant, Universit e Ibn Zohr, Agadir, Morocco c Laboratoire d'Ing enierie, d'Electrochimie, de Mod elisation et d'Environnement, Universit e Sidi Mohamed Ben Abdellah, Facult e des Sciences Dhar El Mahraz, F es, Morocco a r t i c l e i n f o a b s t r a c t Article history: Received 29 March 2019 Received in revised form 21 August 2019 Accepted September 2019 Available online 13 September 2019 This study focused on the preparation of activated carbons from Thapsia transtagana stems by boric acid activation and their evaluation for dyes removal The central composite design and response surface methodology were used to optimize the preparation conditions The effect of activation temperature, impregnation ratio and activation time on iodine number (IN), methylene blue index (MB index) and removal efficiencies of methyl violet (MV), methyl orange (MO) and indigo carmine (IC) were fully evaluated The activated carbon samples prepared in optimal conditions were characterized by FTIR, XRD, SEM-EDX, Boehm's titration, and point of zero charge (pHPZC) The equilibrium data for dyes sorption onto optimum activated carbons were best fitted with Langmuir isotherm © 2019 Publishing services by Elsevier B.V on behalf of Vietnam National University, Hanoi This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/) Keywords: Thapsia transtagana stems Dyes removal Chemical activation Central composite design Introduction Nowadays, the extensive uses of textile dyes are considered the main sources of water pollution [1] It has been estimated that 10%e15% of the dye used during the manufacturing of textile products are released into the environment worldwide annually [2] Moreover, many of these organic compounds can cause allergies, skin irritation or even cancer and human mutations [3] It is, therefore, essential to remove dyes from wastewater and water reuse to avoid contamination and destruction of natural resources Currently, there are numerous methods employed to remove dye molecules from aqueous solutions including adsorption [4], precipitation [5], ion-exchange [6], coagulation [7], membrane filtration [8], photocatalytic degradation [9], etc Among these processes, the adsorption is more applicable because it is an efficient, simple and economic method for the removal of dyes from aqueous solutions [10,11] For that, various types of low-cost, easily * Corresponding author ** Corresponding author Fax: ỵ212 523 49 03 54 E-mail addresses: hananetounsadi@gmail.com (H Tounsadi), barkanoureddine@ yahoo.fr (N Barka) Peer review under responsibility of Vietnam National University, Hanoi available and highly effective adsorbents are reported such as activated carbon, zeolite, clay, polymer, and nanomaterials [12e16] From economic point of view, the process of adsorption onto activated carbon is advantageous due to the plentiful accessibility of low cost raw material Also, activated carbon is basically referred as carbonaceous materials, with a high physicochemical stability, high porosity, high sorption capacity and with immense surface area Recently, many studies have been carried out to investigate the use of inexpensive biomasses to produce low-cost activated carbons using agricultural solid wastes including coffee ground [17], Carob shell [18], Diplotaxis harra [19], Glebionis coronaria L [20], maize corncob [21], beetroot seeds [22], apricot stones [23], hazelnut shells [24] and loofah sponge [25] Activated carbon can be produced in a two-step process: carbonization and activation Carbonization is usually conducted via pyrolysis at temperatures of 400e850  C in the absence of oxygen [26] The activation process converts carbonized materials to activated carbon via heating Carbon dioxide, air or steam is used as a physical activation method to develop the porosity of the carbonaceous materials The increase of surface area and the pore volume is achieved through the elimination of internal carbon mass https://doi.org/10.1016/j.jsamd.2019.09.002 2468-2179/© 2019 Publishing services by Elsevier B.V on behalf of Vietnam National University, Hanoi This is an open access article under the CC BY license (http:// creativecommons.org/licenses/by/4.0/) A Machrouhi et al / Journal of Science: Advanced Materials and Devices (2019) 544e553 and the removal of volatiles [27] However, in chemical activation, the carbonization temperature is done only between 400 and 600  C This method highlights an impregnation of the precursor or raw material with dehydrating agents such as alkali metal hydroxide or acid This method produces an activated carbon with higher yield and well developed microporosities The objective of this research was to investigate the feasibility of activated carbon produced from Thapsia transtagana stems biomass, by H3BO3 activation and their ability for cationic and anionic dyes removal from aqueous solution Central composite design (CCD) combined with response surface methodology (RSM) was used to optimize the process The factors chosen are impregnation ratio, activation temperature and activation time Five responses including iodine number (IN), methylene blue index (MB index) and removal efficiencies for methyl violet (MV), methyl orange (MO) and indigo carmine (IC) are investigated Material and methods 2.1 Material The independent variables were coded as ỵ1 and which represent the eight factorial points at their low and high levels, respectively The six axial points were located at (±a, 0, 0), (0, ±a, 0), (0, 0, ±a), and the six replicates were at the center (0, 0, 0) were run to examine the experimental error and the reproducibility of the data Where a is the distance of axial point from center which makes the design rotatable; its value was fixed at 1.682 This value of rotatability a, which depends on the number of parameters in the experiment, was obtained from the following equation [30]: a ¼ Np1/4 (3) In this study, the independent variables studied were activation temperature (A), impregnation ratio (B) and activation time (C) These three variables with their respective ranges were selected based on the literature and preliminary studies as given in Table The responses were determined using the optimal quadratic model predictor Eq (4) given as: Y ¼ b0 ỵ All the chemicals/reagents used in this study were of analytical grade H3BO3 (100%), HCl (37%), I2 (99.8e100.5%), Na2S2O35H2O, Na2CO3, NaHCO3 (99.5e100.5%), commercial activated carbon (powder form) (100%), methyl violet, methyl orange and indigo carmine (100%) were purchased from SigmaeAldrich (Germany) (100%) Methylene blue was purchased from Panreac (Spain) (100%) HNO3 (65%) was provided from Sharlau (Spain) NaOH (!99%) from Merck (Germany), potassium iodide (KI) (100%) was obtained from Pharmac (Morocco) 545 Xn !2 Xn bx ỵ iẳ1 i i ỵ b x iẳ1 ii i Xn-1 Xn b xx jẳ1ỵ1 ij i j iẳ1 (4) 0where Y is the predicted response, bo is the offset term, bi the linear effect, bii the squared effect, bij the interaction effect and xi, xj are the coded values of the variables considered The quality of the fit of the polynomial model was expressed by the correlation coefficient (R2) The significance and adequacy of the used model was further explained using F-value (Fisher variation ratio), probability value (Prob > F), and adequate precision (AP) [31] 2.2 Preparation of activated carbons 2.4 Iodine number (IN) The T transtagana plant was collected from the region of Oued zem, Morocco Steams were cut into small pieces and were powdered to a particles of size F” less than 0.05 indicate that model terms are significant Especially larger F-value with the associated P value (smaller than 0.05, confidence interval) means that the experimental systems can be modeled effectively with less error Therefore, interaction effects as adequate model terms can be used for modeling the experimental system 3.2.1 Iodine number According to the ANOVA analysis for the iodine number, the significant terms are the activation temperature (A), impregnation ratio (B), activation time (C), the interaction between activation temperature and impregnation ratio (AB), the interaction between impregnation ratio and activation time (BC), the quadratic term of activation temperature (A2) and the quadratic term of activation time (C2) Eq (6) Y1 ẳ 703.26 ỵ 44.10 A ỵ 56.46 B 0.74 C 1.75 AB ỵ 1.75 BC 28.35 A2 20.94 C2 (6) 3.1 Experimental results The experimental results obtained at the designed experimental conditions according to the central composite design are presented in Table S1 From this table, it could be seen that the activated carbon sample activated at 500  C for 145 with an impregnation ratio of g/g gives the optimum of MB index (188.75 mg/g), MO adsorption (116.84 mg/g) and MV adsorption (140.76 mg/g The greater iodine number of 794.58 mg/g is obtained for the activated carbon prepared at 450  C for 130 with an impregnation ratio of 2.34 g/g Under these same conditions, the optimum for IC adsorption (44.87 mg/g) is also acquired On the other hand, the regression analysis was performed to fit the response functions with the experimental data Table shows the values of the regression coefficients obtained According to this table, the three studied factors present a positive effect on the five responses The table also indicates that the targeted responses are more influenced by activation temperature and impregnation ratio than by activation time 3.2 Analysis of variance (ANOVA) The analysis of variance (ANOVA) was used to determine the significance of the curvature in the responses at a confidence level of 95% After discarding the insignificant terms, the ANOVA data of the coded quadratic models for the five responses are presented in supplements (Tables S2eS6) The effect of a factor is defined as the change in response produced by a change in the level of the factor This is frequently called a main effect because it refers to the primary factors of interest in the experiment The ANOVA results showed that the equations adequately represent the actual The activation temperature, the impregnation ratio and the interaction between impregnation ratio and activation time showed a positive effect on the iodine number Although, the activation time, the interaction between activation temperature and impregnation ratio, the quadratic term of activation temperature and the quadratic term of activation time showed a negative effect on the iodine number Besides, the impregnation ratio has the largest significant effect on the iodine number due to the high Fvalue (99.05) followed by the activation temperature, the quadratic term of activation temperature and the quadratic term of activation with an F-value of 60.43, 26.61, and 14.52, respectively (Table S2) Hence, it could be seen that the number of micropores are higher with the impregnation ratio of 2.34 g/g in the studied domain In fact, at the high level of the significant model terms, the activation reaction may take place rapidly producing a development of porosity of the obtained activated carbons and an increase in the microporosity 3.2.2 Methylene blue index The most significant effects for the methylene blue index are activation temperature (A), impregnation ratio (B), activation time (C), interaction between activation temperature and impregnation ratio (AB) and the quadratic term of impregnation ratio (B2) Eq (7) Y2 ẳ 133.98 ỵ 13.17 A ỵ 29.11 B ỵ 4.97 C ỵ 10.04 AB 9.90 B2 (7) The activation temperature, impregnation ratio, activation time and interaction between activation temperature and impregnation ratio showed a positive effect on the methylene blue index response Although, the quadratic term of the impregnation ratio A Machrouhi et al / Journal of Science: Advanced Materials and Devices (2019) 544e553 presented a negative effect on the development of mesopores According to Table S3, the impregnation ratio has the most significant effect on the methylene blue index due to the higher F-value (43.55) After that, follow the activation temperature, the quadratic term of impregnation ratio and the interaction between activation temperature and impregnation ratio with F-values of 8.92, 5.41 and 3.03, respectively 3.2.3 Methyl orange and methyl violet removal Based on the ANOVA data for methyl orange and methyl violet removal responses, the most significant factors are activation temperature (A), impregnation ratio (B) activation time (C), interaction between activation temperature and impregnation ratio (AB), interaction between impregnation ratio and activation time (BC) and quadratic term of impregnation ratio (B2) Eqs (8) and (9) Y3 ¼ 93.97 ỵ 9.69 A ỵ 16.57 B ỵ 2.18 C þ 0.63 AB À 0.16 BC À 5.38 B2 (8) Y4 ẳ 113.21 ỵ 9.89 A ỵ 14.66 B ỵ 4.46 C ỵ 4.71 AB 2.27 BC 5.09 B2 (9) The activation temperature, impregnation ratio, activation time and interaction between activation temperature and impregnation ratio showed a positive effect on the methyl orange and methyl violet removal response Although, the interaction between impregnation ratio and activation time and the quadratic term of impregnation ratio presented a negative effect From Tables S4 and S5, it could be seen that the impregnation ratio has the largest effect on the methyl orange and methyl violet removal with an Fvalue of 53.15 and 26.10, respectively, followed by the activation temperature and quadratic term of impregnation ratio for the MO and MV removal 3.2.4 Indigo carmine removal The significant model terms for indigo carmine removal are the activation temperature (A), impregnation ratio (B), activation time (C), the interaction between activation temperature and impregnation ratio (AB), the interaction between activation temperature and activation time (AC) and the quadratic term of activation temperature (A2) Eq (10) Y5 ẳ 27.67 ỵ 3.76 A ỵ 10.63 B þ 1.83 C þ 2.95 AB À 0.39 AC À 3.22 A2 (10) The activation temperature, impregnation ratio, activation time and interaction between activation temperature and impregnation ratio showed a positive effect on the indigo carmine removal response However, the interaction between activation temperature and activation time and the quadratic term of activation temperature presented a negative effect on the indigo carmine removal According to Table S6, it could be seen that the impregnation ratio has the most pronounced effect on the indigo carmine removal based on the highest F-value of 60.03 In contrast, the activation temperature, quadratic term of activation temperature and interaction between activation temperature and impregnation ratio have an F-value of 7.52, 5.94, and 2.72, respectively 3.3 Response surface analysis The mathematical models for the iodine number, MB index and dyes removal were used to build response surfaces as well as to determine the optimal conditions of the process Fig present the 3D response surfaces plots for the significant interactions 547 For the iodine number, the most significant interactions were the impregnation ratio/activation temperature and the activation time/impregnation ratio The Fig 1(a) indicates that the iodine number increased with the increase of activation temperature and impregnation ratio Fig 1(b) shows that the iodine number increased with increase of the impregnation ratio and decrease of activation time when the activation temperature is fixed at 500  C For the MB index, the most significant interaction was the impregnation ratio/activation temperature From Fig 1(c), it can be observed that the MB index increased with the increase of the activation temperature and the impregnation ratio The maximal MB index response was obtained at an activation time of 145 In the removal of MV and MO dyes, the same significant interactions are found, including the impregnation ratio/activation temperature and the activation time/impregnation ratio From Fig 1(d)e(f), it can be observed that the MV and MO removal increased with increase of the activation temperature and impregnation ratio The maximal MV and MO removal responses were obtained at an activation time of 145 Fig 1(e)e(g), shows that the MO and MV removal increased with increasing impregnation ratio and decreasing activation time in case the activation temperature is fixed at 500  C For the removal of IC, the most significant interactions were the impregnation ratio/activation temperature and the activation time/ activation temperature From the 3D response surface plot as shown in Fig 1(h), it was observed that the indigo carmine removal increases with increase of the impregnation ratio and activation temperature in case the activation time is fixed at 130 Fig 1(i) shows that for a decrease of the activation time and an increase of the activation temperature, the IC removal response increased In general, the impregnation of the precursor allows the development of the internal structure of the activated carbon by the creation of new pores and the enlargement of existing pores In this context, several parameters including the activation time, the activation temperature and the impregnation ratio play an important role in the development of the porosity of activated carbons and, consequently, the evolution of the adsorption performance In fact, during activation, the boric acid catalyzes the dehydration and promotes the formation of aromatic structures during pyrolysis [36] In addition, the formation of an impenetrable glassy coating on the solid surface from boric acid decomposition products inhibits the release of volatile substances, which also promotes the formation of carbon [37,38] Then, this vitreous coating prevents the diffusion of oxygen and prevents the propagation of exothermic combustion reactions [39] 3.4 Diagnostic model Table S7 summarizes the information of the proposed models of statistic the actual and predict values for testing the significant effects of the regression coefficients Predicted values obtained were compared with experimental values These values for the models nearly coincide, which indicates a correspondence between the mathematical model and the experimental data The correlations between the theoretical and experimental responses, calculated by the model, are satisfactory Therefore, the R2 values are in reasonable agreement with those of the Radj2 In addition, the model F-value of the iodine number, methylene blue index, methyl orange, methyl violet and indigo carmine removal read as 28.21, 12.44, 13.06, 6.60 and 13.00 respectively These values implicate that models are significant 3.5 Normal probability plot of residuals The normal probability plot of the residuals is presented in Fig The normality of the data can be checked by plotting a 548 A Machrouhi et al / Journal of Science: Advanced Materials and Devices (2019) 544e553 Fig Surface response plots for the iodine number (aeb), MB index (c), MV removal (dee), MO removal (feg) and IC removal (hei) normal probability plot of the residuals If the data points on the plot fall fairly close to the straight line, the data are normally distributed [40] It appears that for the iodine number, methylene blue index and dyes responses, the data points were fairly close to the straight line, indicating that the experiments come from a normally distributed population 3.6 Optimization analysis The optimum conditions for the three variables, activation temperature, impregnation ratio and activation time were obtained using numerical optimization features of Design-Expert 10.0.0 The software searches for a combination of factors that simultaneously satisfy the requirements placed on each of the response factors The goal was to find the optimum process parameters that will produce activated carbons with high iodine number, high dyes removal, as well as high methylene blue index From the experimental results, the optimized activated carbon sample activated at 500  C for 145 with an impregnation ratio of g/g, under which a maximum MB index of 188.75 mg/g, a MO and MV removal of 116.84 mg/g and 140.76 mg/g could be achieved, respectively For the maximum IN and removal of IC the optimal preparation conditions were determined as: activation temperature of 450  C, impregnation ratio of 2.34 g/g and activation time of 130 Under this condition the maximum values of IN and the adsorption capacity for IC were 794.58 mg/g and 44.87 mg/g, respectively In addition, it was observed that experimental values obtained were in good agreement with the values predicted from the models, with relatively small errors between the predicted and the experimental values, which were only 0.01% for iodine number and MO removal responses, 0.04% for IC removal, 0.15% for the MB index and 0.22% for the MV removal responses 3.7 Structural and textural properties of activated carbons 3.7.1 Morphology of ACs SEM images of raw and activated TTS surfaces are illustrated in Fig Only a very limited number of pores were found on the smooth and irregular surface of TTS (Fig 3(a)) The activated carbon prepared with an impregnation ratio of g/g at an activation temperature of 500  C for 145 and which exhibits the high adsorption performance of dyes has an heterogeneous A Machrouhi et al / Journal of Science: Advanced Materials and Devices (2019) 544e553 549 Fig Normal probability plots of residuals for the five responses: (a) Iodine number, (b) MB, index, (c) MV, (d) MO and (e) IC removal capacities texture with irregular cavities distributed on the surface Fig 3(b) Fig 3(c) presents a smooth and featureless surface with very little pores available on activated carbon prepared at 450  C for 130 with an impregnation ratio of 2.34 g/g The activated carbon prepared at 500  C for 115 with an impregnation ratio of g/g shown in Fig 3(d) indicates a rough and heterogeneous surface and contains a limited number of pores These observations indicate that the activation with boric acid at different conditions produces an increase in surface area and pore volume in the inner surface of the ACs 550 A Machrouhi et al / Journal of Science: Advanced Materials and Devices (2019) 544e553 Fig SEM micrographs of: (a) precursor (TTS), (b) 500  C/145 min/2 g/g, (c) 450  C/130 min/2.34 g/g and (d) 500  C/115 min/2 g/g 3.7.2 Energy dispersive X-ray (EDX) analysis The proximate analysis indicates that T transtagana stems is a good alternative for producing activated carbon due to its high content of fixed carbon (27.85%) and volatile matter (39.45%) and low ash (7.25%) Moreover, the energy dispersive X-ray analysis (Table 3) showed that TTS contains 63.27% of carbon and 31.45% of oxygen associated with some minerals such as potassium, nitrogen, and calcium After the impregnation of TTS with H3BO3, an increase in the carbon content by 13.26% and a decrease in the oxygen content by 13.72 for activated carbon prepared at 500  C for 145 with an impregnation ratio of g/g can be seen For activated carbon prepared at 450  C in 130 with an impregnation ratio of 2.34 g/g, there is an increase in the carbon content by 11.92% and a decrease of the oxygen content by 12.63% For activated carbon prepared at 500  C in 115 with an impregnation ratio of g/g, there is an increase in the carbon content by 8.42% and a decrease in the oxygen content by 6.89% This may be ascribed to the oxygen removal and carbon enrichment, resulting from loosened oxygen attached to the carbonaceous material during chemical activation The presence of carbon in significant quantity provided the active surface for the attachments of the organic pollutants to the surface of the activated carbons 3.7.3 X ray diffraction In order to determine the crystal structure of optimized activated carbons, X-ray diffraction analyzes were performed Fig presents the XRD patterns of the studied activated carbons This Table Percent atomic of: (a) precursor (TTS), (b) 500  C/145 min/2 g/g, (c) 450  C/130 min/ 2.34 g/g and (d) 500  C/115 min/2 g/g Element Atomic % a b c d C O Al Na Cl K Ca 63.27 31.45 4.62 0.2 0.14 0.12 0.12 76.53 17.73 e e e e e 75.19 18.82 e e e e 0.08 71.69 22.56 e 0.03 e 0.02 0.02 figure shows generally an amorphous structure of all activated carbons with similar profiles and broad band at 23 The simple band at 23 may be due to the disordered stacks of graphite layers [41] Activated carbons have interplanar distances of d002, higher than those of graphite These activated carbons are considered to be in disorder and out of graphitization 3.7.4 Boehm titration and pH of zero charge Table presents the estimated chemical groups on the surface of ACs and pHPZC The pHPZC values were 6.62, 5.86 and 6.28, which assign an acid character to the samples While, acid groups are greater than basic groups (1.4179, 1.4481 and 1.4432 meq/g compared to 0.3665, 0.3549 and 0.3575 meq/g, respectively) This acidity gave them greater exchange properties with the cationic dyes than with the anionic dyes Although, studied activated carbons have an important quantity of phenolic and lactonic groups in comparison of the amount of carboxylic groups Hence, the greater adsorption performance of cationic and anionic dyes of these three activated carbons optimized can be related to the availability of this type of functional groups 3.7.5 Infrared spectroscopy The functional groups of activated carbons and precursor material are presented in Fig According to this figure, the surface groups of the activated carbons were different from those of the biomass Some peaks have a low intensity or even disappeared in the prepared ACs relative to the raw T transtagana stems, as many of the functional groups disappeared after the activation processes This result is due to the thermal degradation effect during the activation processes which resulted in the destruction of some intermolecular bondings Concerning the FT-IR spectra of the precursor material (TTS), there are large band at 3700 and 3200 cmÀ1 attributed to the stretching vibration of hydrogen bonds of the hydroxyl group linked in cellulose, lignin, adsorbed water and to NeH Stretching, respectively [42] The bands at 3000e2800 cmÀ1 are attributed to aliphatic CeH stretching vibrations of an aromatic methoxyl group in methyl and methylene groups of side chains The small band at 1676 cmÀ1 is assigned to OeH bending The spectra also indicate a band at 1615.95 cmÀ1 which is characteristic of C]O stretching vibrations of ketones, aldehydes, lactones or A Machrouhi et al / Journal of Science: Advanced Materials and Devices (2019) 544e553 551 Fig XRD patterns of ACs-: (a) 500  C/145 min/2 g/g, (b) 450  C/130 min/2.34 g/g and (c) 500  C/115 min/2 g/g Table Chemical groups on the surface of the ACs and pHpzc Activated carbon AC-500  C/145 min/2 g/g AC-450  C/130 min/2.34 g/g AC-500  C/115 min/2 g/g Surface group (meq/g) pHPZC Carboxylic Lactonic Phenolic Total acid Total basic 0.4324 0.4310 0.4231 0.4962 0.5049 0.5013 0.4893 0.5122 0.5188 1.4179 1.4481 1.4432 0.3665 0.3549 0.3575 6.62 5.86 6.28 Fig FT-IR spectra of: (a) precursor (TTS), (b) AC-500  C/145 min/2 g/g, (c) AC-450  C/130 min/2.34 g/g and (d) AC-500  C/115 min/2 g/g carboxyl groups The activated carbons present similar profiles with different bands intensities The band between 3200 and 3700 cmÀ1 that correspond to OeH stretching vibrations of the hydroxyl functional groups including hydrogen bonding, was of low intensity in ACs This reduction in the peak intensity corresponds to a reduction in the hydrogen bonding which may be due to the reaction between H3BO3 and precursor [43] The band appearing in the spectrum between 1500 and 1700 cmÀ1 is attributed to vibrations of the C]C bonds in the aromatic rings or of the groups C]O of carboxylic acids, acetate groups (COOe), ketones, aldehydes or lactones The shoulder at 900e970 cmÀ1 is attributed to a chemical ionized bonding PỵeO or to symmetric vibrations in the PeOeP chains (polyphosphate) This band is an indication of the presence of phosphorus-oxygen compounds in the samples It appears that activation of the samples impregnated with H3BO3 leads to decomposition of phosphoric compounds Also, the shoulder at 600e640 cmÀ1 could correspond to vibration elongation of PeOeC (aliphatic), asymmetric elongation of PeOeC (aromatic), PeO stretching in >P]OOH, strain PeOH asymmetric stretching PeOeP in polyphosphates in complex phosphate-carbon 552 A Machrouhi et al / Journal of Science: Advanced Materials and Devices (2019) 544e553 Fig Experimentals points and nonlinear fitted curves isotherms of AC-500  C/145 min/2 g/g: removal of (a) MB, (b) MO, (c) MV and (d) IC 3.7.6 Adsorption isotherm The use of an experimental design allowed us to optimize the preparation conditions and to evaluate the cationic and anionic dyes removal onto prepared activated carbons In fact, the sample activated at 500  C during 145 with an impregnation ratio of g/g was considered as optimized activated carbon for studying the isotherm models of methylene blue, methyl violet, methyl orange and indigo carmine adsorption It was observed from Fig that the adsorption efficiency increases with the increase of the initial concentration, indicating that the adsorption process is more favorable at increasing concentration of dyes The equilibrium characteristics of this adsorption study were described using Langmuir [44] and Freundlich [45] isotherm models Based on the result tabulated in supplements (Table S8), the correlation coefficients of the Freundlich model are lower than the values of the Langmuir model While, the experimental equilibrium data can be best fitted with the Langmuir isotherm model In fact, r2 values of 0.996, 0.993, 0.990 and 0.997 are found for MB, MO, MV and IC adsorption, respectively The results from the Freundlich isotherm model show that the value for n is greater than unity, which further supports the favorable adsorption of MB, MV, MO and IC onto the activated carbon Moreover, the maximum adsorption capacities obtained with the application of the Langmuir isotherm model are 219.70, 118.10, 137.80 and 44.70 mg/g for MB, MO, MV and IC adsorption, respectively These capacities assume monolayer adsorption processes for MB, MV, MO and IC that are close to the observed adsorption capacities at equilibrium The maximum Langmuir adsorption capacities mentioned above were compared to previous studies on various activated carbons with different preparation conditions (Table S9) It could be seen that the experimental data in the present study are higher than those of the most often prepared activated carbons used in cationic and anionic dyes adsorption in the literature Conclusion This work has shown that T transtagana stems is a new good alternative precursor for the preparation of activated carbons for the elimination of cationic and anionic dyes The optimization of preparation conditions was investigated using the central composite design with response surface methodology Results indicate that the activation temperature and the impregnation ratio are the most important factors in the activation process The iodine number increases as the activation temperature and the impregnation ratio increase It was also clear that the influence of the activation time is more pronounced at higher temperature and impregnation ratio The adsorption of the dyes increases when the impregnation ratio increases from 0.66 to g/g However, with an impregnation ratio of 2.34 there is a slight decrease in the adsorption of MV and MO In addition, with an activation temperature of 366  C, the activated carbon indicates minor adsorption capacities of the dyes also the iodine number and the methylene blue index The maximum adsorption capacities obtained with the application of the Langmuir isotherm model are 219.70, 118.10, 137.80 and 44.70 mg/g for MB, MO, MV and IC, respectively, for AC activated at 500  C during 145 with an impregnation ratio of g/g Conflict of interest We have no conflict of interest to declare Appendix A Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.jsamd.2019.09.002 A Machrouhi et al / Journal of Science: Advanced Materials and Devices (2019) 544e553 References [1] J.N Halder, M.N Islam, Water pollution and its impact on the human health, J Environ Human (2015) 36e46, https://doi.org/10.15764/EH.2015.01005 [2] M.L Parisi, E Fatarella, D Spinelli, R Pogni, R Basosi, Environmental impact assessment of an eco-efficient production for coloured textiles, J Clean Prod 108 (2015) 514e524, https://doi.org/10.1016/j.jclepro.2015.06.032 [3] D.S Brookstein, Factors associated with textile pattern dermatitis caused by contact allergy to dyes, finishes, foams, and preservatives, Dermatol Clin 27 (2009) 309e322, https://doi.org/10.1016/j.det.2009.05.001 [4] M El Ouardi, S Qourzal, A Assabbane, J Douch, Adsorption studies of cationic and anionic dyes on synthetic ball clay, J Appl Surf Interface (2017) 28e34 [5] P.K Sane, S Tambat, S Sontakke, P Nemade, Visible light removal of reactive dyes using CeO2 synthesized by precipitation, J Environ Chem Eng (2018) 4476e4489, https://doi.org/10.1016/j.jece.2018.06.046 [6] M.M Hassan, C.M Carr, A critical review on recent advancements of the removal of reactive dyes from dyehouse effluent by ion-exchange adsorbents, Chemosphere 209 (2018) 201e219, https://doi.org/10.1016/ j.chemosphere.2018.06.043 [7] R Li, B Gao, K Guo, Q Yue, H Zheng, Y Wang, Effects of papermaking sludgebased polymer on coagulation behavior in the disperse and reactive dyes wastewater treatment, Bioresour Technol 240 (2017) 59e67, https://doi.org/ 10.1016/j.biortech.2017.02.088 [8] S Ren, D Liu, Y Chen, S An, Y Zhao, Y Zhang, Anionic channel membrane encircled by SO3H-polyamide particles for removal of anionic dyes, J Membr Sci 570e571 (2019) 34e43 [9] A Tiya-Djowe, P.N Lemougna, A Emadak, M Pitap-Mbowou, S Laminsi, U Chinje-Melo, Taking advantage of iron contained in natural volcanic ash for catalytic degradation of Rhodamine 6G, J Appl Surf Interface (2018) 10e16 [10] A.R Bagheri, M Ghaedi, S Hajati, A.M Ghaedi, A Goudarzi, A Asfaram, Random forest model for the ultrasonic-assisted removal of chrysoidine G by copper sulfide nanoparticles loaded on activated carbon; response surface methodology approach, RSC Adv (2015) 59335e59343, https://doi.org/ 10.1039/C5RA08399K [11] M Dastkhoon, M Ghaedi, A Asfaram, M.H Ahmadi Azqhandi, M.K Purkait, Simultaneous removal of dyes onto nanowires adsorbent use of ultrasound assisted adsorption to clean waste water: chemometrics for modeling and optimization, multicomponent adsorption and kinetic study, Chem Eng Res Des 124 (2017) 222e237, https://doi.org/10.1016/j.cherd.2017.06.011 [12] E Sharifpour, H.Z Khafri, M Ghaedi, A Asfaram, R Jannesar, Isotherms and kinetic study of ultrasound-assisted adsorption of malachite green and Pb2ỵ ions from aqueous samples by copper sulfide nanorods loaded on activated carbon: experimental design optimization, Ultrason Sonochem 40 (2018) 373e382, https://doi.org/10.1016/j.ultsonch.2017.07.030 [13] E.A Abdelrahman, Synthesis of zeolite nanostructures from waste aluminum cans for efficient removal of malachite green dye from aqueous media, J Mol Liq 253 (2018) 72e82, https://doi.org/10.1016/j.molliq.2018.01.038 [14] A Kausar, M Iqbal, A Javed, K Aftab, Z.H Nazli, H.N Bhatti, S Nouren, Dyes adsorption using clay and modified clay: a review, J Mol Liq 256 (2018) 395e407 [15] A Gouthaman, R.S Azarudeen, A Gnanaprakasam, V.M Sivakumar, M Thirumarimurugan, Polymeric nanocomposites for the removal of Acid red 52 dye from aqueous solutions: synthesis, characterization, kinetic and isotherm studies, Ecotoxicol Environ Saf 160 (2018) 42e51, https://doi.org/ 10.1016/j.ecoenv.2018.05.011 [16] A Asfaram, M Ghaedi, S Agarwal, I Tyagi, V.K Gupta, Removal of basic dye Auramine-O by ZnS: Cu nanoparticles loaded on activated carbon: optimization of parameters using response surface methodology with central composite design, RSC Adv (2015) 18438e18450 [17] S Rattanapan, J Srikram, P Kongsune, Adsorption of methyl orange on coffee grounds activated carbon, Energy Procedia 138 (2017) 949e954, https:// doi.org/10.1016/j.egypro.2017.10.064 [18] M Farnane, A Machrouhi, A Elhalil, H Tounsadi, M Abdennouri, S Qourzal, N Barka, Process optimization of potassium hydroxide activated carbon from carob shell biomass and heavy metals removal ability using BoxeBehnken design, Desalin Water Treat 133 (2018) 153e166, https://doi.org/10.5004/ dwt.2018.22977 [19] H Tounsadi, A Khalidi, M Abdennouri, N Barka, Activated carbon from Diplotaxis Harra biomass: optimization of preparation conditions and heavy metal removal, J Tai Ins Chem Eng 000 (2015) 1e11, https://doi.org/ 10.1016/j.jtice.2015.08.014 [20] H Tounsadi, A Khalidi, A Machrouhi, M Farnane, R Elmoubarki, A Elhalil, M.Sadiq, N Barka, Highly efficient activated carbon from Glebionis coronaria L biomass: optimization of preparation conditions and heavy metals removal using experimental design approach, J Environ Chem Eng S2213-3437 (16) 30380-30383 https://doi.org/10.1016/j.jece.2016.10.020 [21] M Farnane, H Tounsadi, A Machrouhi, A Elhalil, F.Z Mahjoubi, M Sadiq, M Abdennouri, S Qourzal, N Barka, Dye removal from aqueous solution by [22] [23] [24] [25] [26] [27] [28] [29] [30] [31] [32] [33] [34] [35] [36] [37] [38] [39] [40] [41] [42] [43] [44] [45] 553 raw maize corncob and H3PO4 activated maize corncob, J Water Reuse Desal (2017) 214e224, https://doi.org/10.2166/wrd.2017.179 A Machrouhi, M Farnane, A Elhalil, R Elmoubarki, M Abdennouri, S Qourzal, H Tounsadi, N Barka, Effectiveness of beetroot seeds and H3PO4 activated beetroot seeds for the removal of dyes from aqueous solutions, J Water Reuse Desal (2017) 522e531, https://doi.org/10.2166/wrd.2017.034 C Djilani, R Zaghdoudi, F Djazi, B Bouchekima, A Lallam, Ali Modarressi, M Rogalski, Adsorption of dyes on activated carbon prepared from apricot stones and commercial activated carbon, J Taiwan Inst Chem Eng 000 (2015) 1e10, https://doi.org/10.1016/j.jtice.2015.02.025 M Kwiatkowski, E Broniek, An analysis of the porous structure of activated carbons obtained from hazelnut shells by various physical and chemical methods of activation, Colloids Surf A 529 (2017) 443e453, https://doi.org/ 10.1016/j.colsurfa.2017.06.028 X.L Su, J.R Chen, G.P Zheng, J.H Yang, X.X Guan, P Liu, X.C Zheng, Threedimensional porous activated carbon derived from loofah sponge biomass for supercapacitor applications, Appl Surf Sci 436 (2018) 327e336, https:// doi.org/10.1016/j.apsusc.2017.11.249 A.M Abioye, F.N Ani, Recent development in the production of activated carbon electrodes from agricultural waste biomass for supercapacitors: a review, Renew Sustain Energy Rev 52 (2015) 1282e1293, https://doi.org/ 10.1016/j.rser.2015.07.129 V Subramanian, C Luo, A.M Stephan, K.S Nahm, T Sabu, B Wei, Supercapacitors from activated carbon derived from banana fibers, J Phys Chem C 111 (2007) 7527e7531, https://doi.org/10.1021/jp067009t R Azargohar, A.K Dalai, Production of activated carbon from Luscar char: experimental and modelling studies, Micropor Mesopor Mater 85 (2005) 219e225, https://doi.org/10.1016/j.micromeso.2005.06.018 J.M Salman, Optimization of preparation conditions for activated carbon from palm oil fronds using response surface methodology on removal of pesticides from aqueous solution, Arabian J Chem (2014) 101e108, https://doi.org/ 10.1016/j.arabjc.2013.05.033 M.A Ahmad, R Alrozi, Optimization of preparation conditions for mangosteen peel-based activated carbons for removal of brilliant blue R using response surface methodology, Chem Eng J 165 (2010) 883e890, https://doi.org/ 10.1016/j.cej.2010.10.049 R Kumar, R Singh, N Kumar, K Bishnoi, N.R Bishnoi, Response surface methodology approach for optimization of biosorption process for removal of Cr(VI) Ni(II) and Zn(II) ions by immobilized bacterial biomass sp Bacillus brevis, Chem Eng J 146 (2009) 401e407, https://doi.org/10.1016/ j.cej.2008.06.020 C Elliott, T Colby, H Iticks, Activated carbon obliterans alter aspiration of activated charcoal, Chest 96 (1989) 672e674 C.A Nunes, M.C Guerreiro, Estimation of surface area and pore volume of activated carbons by methylene blue and iodine numbers, Quim Nova 34 (2011) 472e476, https://doi.org/10.1590/S0100-40422011000300020 H.P Boehm, E Diehl, W Heck, R Sappok, Surface oxides of carbon, Angew Chem Int Ed (1964) 669e677, https://doi.org/10.1002/anie.196406691 J.S Noh, J.A Schwarz, Estimation of the point of zero charge of simple oxides by mass titration, J Colloid Interface Sci 130 (1989) 157e164, https://doi.org/ 10.1016/0021-9797(89)90086-6 Q.W Wang, J Li, J.E Winandy, Chemical mechanism of fire retardance of boric acid on wood, Wood Sci Technol 38 (2004) 375e389 B.K Kandola, A.R Horrocks, D Price, G.V Coleman, Flame-retardant treatments of cellulose and their influence on the mechanism of cellulose pyrolysis, J Macromol Sci Polym Rev 36 (1996) 721e794, https://doi.org/ 10.1080/15321799608014859 C Di Blasi, C Branca, A Galgano, Flame retarding of wood by impregnation with boric acid-Pyrolysis products and char oxidation rates, Polym Degrad Stab 92 (2007) 752e764, https://doi.org/10.1016/j.polymdegradstab.2007.02.007 B.K Kandola, A.R Horrocks, D Price, G.V Coleman, J Macromol Sci Rev Macromol Chem Phys 36 (1996) 1967e1982 M.K.B Gratuito, T Panyathanmaporn, R.A Chumnanklang, N.B Sirinuntawittaya, A Dutta, Production of activated carbon from coconut shell: optimization using response surface methodology, Bioresour Technol 99 (2008) 4887e4895, https://doi.org/10.1016/j.biortech.2007.09.042 K Kinoshita, Carbon, Electrochemical and Physicochemical Properties, Wiley, New York, 1988 M.R.H Mas Haris, K Sathasivam, The removal of methyl red from aqueous solutions using banana pseudostem fibers, Am J Appl Sci (2009) 1690e1700, https://doi.org/10.3844/ajassp.2009.1690.1700 F Suarez-Garcia, A Martinez-Alonso, J.M.D Tascon, Pyrolysis of apple pulp: chemical activation with phosphoric acid, J Anal Appl Pyrol 63 (2002) 283e301, https://doi.org/10.1016/S0165-2370(01)00160-7 I Langmuir, The constitution and fundamental properties of solids and liquids Part I Solids, J Am Chem Soc 38 (1916) 2221e2295 H Freundlich, W Heller, The adsorption of cis- and trans-azobenzene, J Am Chem Soc 61 (1939) 2228e2230  ... wavelength of maximum absorbance of 665 nm [33] 2.3 Design of experiments using central composite design 2.6 Dyes removal Central composite design (CCD) was used to study the individual and synergetic... objective of this research was to investigate the feasibility of activated carbon produced from Thapsia transtagana stems biomass, by H3BO3 activation and their ability for cationic and anionic dyes removal. .. the preparation of activated carbons for the elimination of cationic and anionic dyes The optimization of preparation conditions was investigated using the central composite design with response