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

Journal Pre-proof Statistical optimization of activated carbon from Thapsia transtagana stems and dyes removal efficiency using central composite design A Machrouhi, H Alilou, M Farnane, S El Hamidi, M Sadiq, M Abdennouri, H Tounsadi, N Barka PII: S2468-2179(19)30220-5 DOI: https://doi.org/10.1016/j.jsamd.2019.09.002 Reference: JSAMD 251 To appear in: Journal of Science: Advanced Materials and Devices Received Date: 29 March 2019 Revised Date: 21 August 2019 Accepted Date: September 2019 Please cite this article as: A Machrouhi, H Alilou, M Farnane, S El Hamidi, M Sadiq, M Abdennouri, H Tounsadi, N Barka, Statistical optimization of activated carbon from Thapsia transtagana stems and dyes removal efficiency using central composite design, Journal of Science: Advanced Materials and Devices, https://doi.org/10.1016/j.jsamd.2019.09.002 This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain © 2019 Publishing services by Elsevier B.V on behalf of Vietnam National University, Hanoi Statistical optimization of activated carbon from Thapsia transtagana stems and dyes removal efficiency using central composite design A Machrouhi 1, H Alilou 1,2, M Farnane 1, S El Hamidi 1, M Sadiq 1, M Abdennouri 1, H Tounsadi 3,*, N Barka 1,** Sultan Moulay Slimane University of Beni Mellal, Research Group in Environmental Sciences and Applied Materials (SEMA), FP Khouribga, B.P 145, 25000 Khouribga, Morocco Faculté Polydisciplinaire de Taroudant, Université Ibn Zohr, Agadir, Morocco Laboratoire d’Ingénierie, d’Electrochimie, de Modélisation et d’Environnement, Université Sidi Mohamed Ben Abdellah, Faculté des Sciences Dhar El Mahraz, Fès, Morocco * Corresponding author: Tel.: +212 645 20 85 64; E-mail: hananetounsadi@gmail.com ** Corresponding author: Tel.: +212 661 66 66 22; fax: +212 523 49 03 54; E-mail: barkanoureddine@yahoo.fr Aicha Machrouhi ; E-mail: machrouhi.aicha90@gmail.com Hakim Alilou ; E-mail : alilouhakim@gmail.com Meryem Farnane; E-mail: farnane.meryem@gmail.com Sanaa El Hamidi ; E-mail : sanaa.elhamidi@gmail.com M’hamed Sadiq ; E-mail : sadiqmhamed@hotmail.com Mohammed Abdennouri: E-mail: abdennourimohamed@yahoo.fr Hanane Tounsadi : E-mail : hananetounsadi@gmail.com Noureddine Barka: E-mail: barkanoureddine@yahoo.fr Statistical optimization of activated carbon from Thapsia transtagana stems and dyes removal efficiency using central composite design A Machrouhi 1, H Alilou 1,2, M Farnane 1, S El Hamidi 1, M Sadiq 1, M Abdennouri 1, H Tounsadi 3,*, N Barka 1,** Sultan Moulay Slimane University of Beni Mellal, Research Group in Environmental Sciences and Applied Materials (SEMA), FP Khouribga, B.P 145, 25000 Khouribga, Morocco Faculté Polydisciplinaire de Taroudant, Université Ibn Zohr, Agadir, Morocco Laboratoire d’Ingénierie, d’Electrochimie, de Modélisation et d’Environnement, Université Sidi Mohamed Ben Abdellah, Faculté des Sciences Dhar El Mahraz, Fès, Morocco * Corresponding author: Tel.: +212 645 20 85 64; E-mail: hananetounsadi@gmail.com ** Corresponding author: Tel.: +212 661 66 66 22; fax: +212 523 49 03 54; E-mail: barkanoureddine@yahoo.fr Abstract This study focused on the preparation of activated carbons from Thapsia transtagana stems by boric acid activation and their evaluation for dyes removal 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 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 Keywords: Thapsia transtagana stems; Dyes removal; Chemical activation; Central composite design 1 Introduction Nowadays, the extensive uses of textile dyes are considered the main sources of water pollution [1] It has been estimated that 10 % to 15 % 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] and photocatalytic degradation [9] etc Among these processes, the adsorption is more applicable because it is an efficient, simplest and economic method for the removal of dyes from aqueous solutions [10-11] For that, various types of low-cost, easily available and highly effective adsorbents are reported such as activated carbon, zeolite, clay, polymer, and nanomaterials [12-16] 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 two-step process: carbonization and activation Carbonization is usually conducted via pyrolysis at the temperature of 400-850°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 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 All the chemicals/reagents used in this study were of analytical grade H3BO3 (100%), HCl (37%), I2 (99.8-100.5%), Na2S2O35H2O, Na2CO3, NaHCO3 (99.5-100.5%), commercial activated carbon (powder form) (100%), methyl violet, methyl orange and indigo carmine (100%) were purchased from Sigma-Aldrich (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) 2.2 Preparation of activated carbons The Thapsia 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 < 125 µm using a domestic mixer 15 g of the biomass were impregnated with H3BO3 as the activating agent at desired mass ratio Later, the sample was loaded in a stainless steel vertical tubular reactor placed into a furnace under purified nitrogen atmosphere The obtained activated carbons were washed with distilled water and dried at 105 °C for 24 h The powder was sieved in particles of size lower than 125 µm using a normalized sieve and kept in a hermetic bottle for a further use The impregnation ratio of the activating agent with the precursor was computed using Eq (1): Impregnation ratio = (dried weight of H3BO3 / precursor of TTS) (1) 2.3 Design of experiments using central composite design Central composite design (CCD) was used to study the individual and synergetic effect of the three factors towards defined responses This method can reduce the number of experimental trials required to evaluate main effect of each parameter and their interactions [28] It is characterized by three operations namely: 2n factorial runs, 2n axial runs and six center runs [29] For this case, it’s translated into eight factorial points, six axial points and six replicates at the center which gives a total of 20 experiments as calculated from Eq (2): Total number of experiments (N) = 2n +2n+nc (2) where n is the number of factors, nc is the number of center points (six replicates) The independent variables were coded as +1 and -1 which represent the eight factorial points at their low and high levels respectively The six axial points were located at (±α, 0, 0), (0, ±α, 0), (0, 0, ±α), 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 α is the distance of axial point from center which makes the design rotatable and had value fixed at 1.682 This value of rotatability α, which depends on the number of parameters in the experiment, was obtained from the following equation [30]: α = 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 Table 1: Process factors and their levels Variables Code Unit Coded variable levels -α -1 +α Activation temperature A °C 366 400 450 500 534 Impregnation ratio B g/g 0.66 1.5 2.34 Activation time C mins 105 115 130 145 155 The responses were determined using the optimal quadratic model predictor Eq (4) given as: Y = b0 + + + (4) where Y is the predicted response, bo is the constant coefficients, bii the quadratic coefficients, bij the interaction coefficients and xi, xj are the coded values of the activated carbon preparation variables considered The quality of the fit of 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] 2.4 Iodine number (IN) Iodine number is a measure of micropore content (0–2 nm) by adsorption of iodine from solution The iodine number is defined as the milligrams of iodine adsorbed by 1.0 g of carbon when the iodine concentration of the filtrate is 0.02 N It was determined according to the ASTM D4607-94 method [32] 2.5 Methylene blue index (MB index) The methylene blue index is a measure of mesoporosity (2–50 nm) present in activated carbon Sorption equilibrium was established for different methylene blue initial concentration between 20 and 500 mg/L for 12 h at room temperature Residual concentrations were determined by spectrophotometric method at the wavelength of maximum absorbance of 665 nm [33] 2.6 Dyes removal Stock solutions of methyl orange, methyl violet and indigo carmine at 500 mg/L were prepared by dissolving 0.5 g of each dye in L of distilled water Sorption experiments were investigated in a series of beakers containing 50 mL of dyes solutions at 500 mg/L and 50 mg of each activated carbon The mixtures were stirred for h without any pH adjustment After each sorption experiment, samples were centrifuged at 3400 rpm for 10 and the dyes concentration was determined using UV–vis spectrophotometer The adsorption capacities of the dyes at equilibrium were defined as the amount of adsorbate per gram of adsorbent (in mg/g) and were calculated using following equation: q= (5) where q is the adsorbed quantity (mg/g), Co is the initial dye concentration (mg/L), C is the residual dye concentration (mg/L), and R is the mass of activated carbon per liter of aqueous solution (g/L) 2.7 Surface and chemical characterization Textural properties of optimized activated carbon were observed by scanning electron microscopy (SEM) using TESCAN VEGA3-EDAX equipped with an Energy-Dispersive XRay detector (EDX) The functional groups present on the surface of the starting material and AC was determined by Fourier Transform Infrared (FTIR) spectroscope (FTIR-2000, Perkin Elmer) in a range of 4000-400 cm-1 Crystallographic characterization was examined by XRD measurements in 2θ range from 10 to 70° using a Bruker-axs D2-phaser advance diffractometer operating at 30 kV and 10 mA with CuKα The acidic and basic functional groups on the surface of ACs were determined quantitatively by the Boehm’s titration method [34] The pH of point of zero charge (pHpzc) was determined according to the method described by Noh and Schwarz [35] Results and discussion 3.1 Experimental results The experimental results obtained at designed experimental conditions according to the central composite design are presented in Table S1 From this table, it could be seen that 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 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 Table 2: Values of model coefficients of the five responses Main coefficients Y1 Y2 Y3 Y4 Y5 b0 710.80 143.79 100.28 120.79 29.97 b1 46.15 13.17 9.69 6.89 4.01 b2 55.08 29.11 16.57 14.66 10.46 b3 1.30 4.97 2.19 4.46 2.08 b12 1.75 10.04 0.63 4.71 3.40 b13 5.24 -1.84 -1.81 0.61 0.03 b23 5.24 2.93 -0.16 -2.27 0.30 b11 -27.52 -7.78 -3.93 -5.15 -3.29 b22 -12.71 -11.09 -6.15 -6.01 -2.98 b33 -20.11 -5.40 -4.54 -5.04 -0.32 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 S2-S6) 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 relationship between each response and the significant variables The F value implies that the models are significant and the values of “Prob > F” less than 0.05 indicate that models 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 = 703.26 + 44.10 A + 56.46 B - 0.74 C - 1.75 AB + 1.75 BC - 28.35 A2 -20.94 C2 (6) The activation temperature, the impregnation ratio and the interaction between impregnation ratio and activation time showed a positive effect on the iodine number Fig.3 SEM micrographs of: (a) precursor (TTS), (b) 500°C/145min/ 2g/g, (c) 450°C/130min/ 2.34g/g and (d) 500°C/115min/ 2g/g 3.7.2 Energy dispersive X-ray (EDX) analysis Proximate analysis indicates that Thapsia 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, it can be seen 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 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 17 during chemical activation The presence of carbon in significant quantity provided active surface for the attachments of the organic pollutants to the surface of the activated carbons Table 3: Percent atomic of: (a) precursor (TTS), (b) 500°C/145min/ 2g/g, (c) 450°C/130min/ 2.34g/g and (d) 500°C/115min/ 2g/g Atomic % Element a b c d C 63.27 76.53 75.19 71.69 O 31.45 17.73 18.82 22.56 Al 4.62 - - - Na 0.2 - - 0.03 Cl 0.14 - - - K 0.12 - - 0.02 Ca 0.12 - 0.08 0.02 3.7.3 X ray diffraction In order to determine the crystal structure of optimized activated carbons, X-ray diffraction analyzes were performed The Fig.4 presents the XRD patterns of the studied activated carbons This 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 d002, higher than those of graphite These activated carbons are considered in disorder and out of graphitization 18 Fig.4 XRD patterns of ACs-: (a) 500°C/145min/ 2g/g, (b) 450°C/130min/ 2.34g/g and (c) 500°C/115min/ 2g/g 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 Table 4: Chemical groups on the surface of the ACs and pHpzc Surface group (meq/g) Activated carbon Carboxylic Lactonic Phenolic Total acid Total basic pHPZC AC- 500°C/145min/2 g/g 0.4324 0.4962 0.4893 1.4179 0.3665 6.62 AC- 450°C/130min/2.34 g/g 0.4310 0.5049 0.5122 1.4481 0.3549 5.86 AC- 500°C/115min/2 g/g 0.4231 0.5013 0.5188 1.4432 0.3575 6.28 19 3.7.5 Infrared spectroscopy The functional groups of activated carbons and the precursor material are presented in Fig.5 According to this figure, the surface groups of the activated carbons were different from the biomass Some peaks have a low intensity or even disappeared in the prepared ACs relative to the raw Thapsia transtagana stems, as many of the functional groups disappeared after the activation processes This result due to the thermal degradation effect during the activation processes which resulted in the destruction of some intermolecular bonding Concerning the FT-IR spectra of the precursor material (TTS), there is a large band at 3700 and 3200 cm-1 attributed to the stretching vibration of hydrogen-bended of the hydroxyl group linked in cellulose, lignin, adsorbed water and N─H Stretching [42] The bands at 3000–2800 cm-1 are attributed to aliphatic C-H stretching vibrations in an aromatic methoxyl group, in methyl and methylene groups of side chains The small band at 1676 cm-1 is assigned to O-H bending The spectra also indicate the bands at 1615.95 cm-1 are characteristic of C=O stretching vibrations of ketones, aldehydes, lactones or carboxyl groups The activated carbons present similar profiles with different bands intensities The band between 3200 and 3700 cm-1 correspond to O‒H stretching vibrations of the hydroxyl functional groups including hydrogen bonding, was of low intensity in ACs This reduction in the peak intensity corresponds to the reduction in hydrogen bonding which may be due to the reaction between H3BO3 and precursor [43] The band appearing on the spectrum between 1500 and 1700 cm-1 is attributed to vibrations of the C=C bonds in the aromatic rings or the groups C=O of carboxylic acids, acetate groups (COO─), ketones, aldehydes or lactones The shoulder 900970 cm-1 is attributed to chemical ionized bonding P+─O or the symmetric vibration in the P─O─P chains (polyphosphate) This band is an indication of the presence of phosphorusoxygen compounds in the samples It appears that activation of the samples impregnated with H3BO3 leads to decomposition of phosphoric compounds Also, the shoulder at 600-640 cm-1 could correspond to vibration elongation of P─O─C (aliphatic), asymmetric elongation of 20 P─O─C (aromatic), P─O stretching in >P=OOH, strain P─OH asymmetric stretching P─O─P in polyphosphates in complex phosphate-carbon Fig.5 FT-IR spectra of : (a) precursor (TTS), (b) AC-500°C/145min/2 g/g, (c) AC450°C/130min/2.34 g/g and (d) AC-500°C/115min/2 g/g 3.7.6 Adsorption isotherm The use of experimental design allowed us the optimization of the preparation conditions and the evaluation of 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 studding the isotherm models of methylene blue, methyl violet, methyl orange and indigo carmine adsorption It was observed from Fig.6 that the adsorption efficiency increases with increasing of 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 Freundlich model are lower than the values of Langmuir model While, the experimental equilibrium data can be best fitted with Langmuir isotherm model In fact, the r2 values (0.996, 0.993, 0.990 and 0.997) for MB, MO, MV and IC adsorption respectively The results 21 from the Freundlich isotherm model show that the n is greater than unity, which further support 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 those 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 the most prepared activated carbons using in cationic and anionic dyes adsorption in the literature Fig Experimentals points and nonlinear fited curves isotherms of AC-500°C/145min/2 g/g: removal of (a) MB, (b) MO, (c) MV and (d) IC 22 Conclusion This work aims that Thapsia transtagana stems was a new good alternative precursor for de preparation of activated carbon for the elimination of cationic and anionic dyes The optimization of preparation conditions was investigated using 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 but 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, onto AC activated at 500 °C during 145 with an impregnation ratio of g/g References [1] J.N Halder, M.N Islam, Water pollution and its impact on the human health J 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studies of methyl orange and methyl violet adsorption on activated carbon derived from Phragmites australis, Desalination 252 (2010) 149-156 DOI: 10.1016/j.desal.2009.10.010 29 Highlights Thapsia transtagana is a new precursor to produce activated carbon Preparation conditions and dyes removal were optimized by central composite design High adsorption capacities of textile dyes from aqueous solution were investigated Optimal AC-H3BO3 was efficient than many adsorbents reported in the literature Conflict of interest Title: Statistical optimization of activated carbon from Thapsia transtagana stems and dyes removal efficiency using central composite design Authors: A Machrouhi, H Alilou, M Farnane, S El Hamidi, M Sadiq, M Abdennouri, H Tounsadi, N Barka We wish to draw the attention of the Editor to the following facts which may be considered as potential conflicts of interest We wish to confirm that there are no known conflicts of interest associated with this publication and there has been no significant financial support for this work that could have influenced its outcome We confirm that we have given due consideration to the protection of intellectual property associated with this work and that there are no impediments to publication, including the timing of publication, with respect to intellectual property In so doing we confirm that we have followed the regulations of our institutions concerning intellectual property We further confirm that the manuscript has been read and approved by all named authors and that there are no other persons who satisfied the criteria for authorship but are not listed We confirm that we have provided a current, correct email address which is accessible by the Corresponding Author and which has been configured to accept email from Signed by corresponding author: Friday, Mars 29, 2019 .. .Statistical optimization of activated carbon from Thapsia transtagana stems and dyes removal efficiency using central composite design A Machrouhi 1, H Alilou 1,2,... E-mail: barkanoureddine@yahoo.fr Statistical optimization of activated carbon from Thapsia transtagana stems and dyes removal efficiency using central composite design A Machrouhi 1, H Alilou 1,2,... focused on the preparation of activated carbons from Thapsia transtagana stems by boric acid activation and their evaluation for dyes removal Central composite design and response surface methodology