J. Nig. Soc. Phys. Sci. 4 (2022) 183–192 Journal of the Nigerian Society of Physical Sciences Optimization by Box Behnken Design for Eosin Yellow Dye Removal from Aqueous Medium using Date Palm Seeds-Porous Carbon@TiO2 Blend Samsudeen Olanrewaju Azeeza,∗, Akeem Adebayo Jimoha, Ismaila Olalekan Saheeda, Kabir Opeyemi Otuna, Aliru Olajide Mustaphaa, Folahan Amoo Adekolab aDepartment of Chemistry and Industrial Chemistry, Faculty of Pure and Applied Sciences, Kwara State University, 241103, Malete, Nigeria bDepartment of Industrial Chemistry, Faculty of Physical Sciences, University of Ilorin, 240003, Ilorin, Nigeria Abstract Biological stains are potentially harmful compounds present in the environment, in which Eosin yellow dye (EYD) is one of the most commonly applied stains. In this research, date palm seeds-porous carbon (DPSC) and its TiO2 blend (TiO2-DPSC) were prepared and their efficiency on the removal of EYD from an aqueous medium was investigated. Characterization by SEM, EDX, FTIR and BET surface area was performed on the materials. The BET surface area (542.63 m2/g) and pore diameter (2.02 nm) of TiO2-DPSC were found to be higher than that of DPSC (332.74 m2/g and 1.85 nm) indicating that TiO2-DPSC is mesoporous while DPSC is microporous. The major and interactive impacts of the adsorption parameters: initial EYD concentration, pH, adsorbent dose, and time of contact were examined by Box Behnken design in response surface methodology. The high R2 values 0.9658 and 0.9597 for DPSC and TiO2-DPSC agreed with the adjusted R2 values suggesting the quadratic model sufficiently interprets the adsorption data. The optimum removal efficiency of EYD onto DPSC and TiO2-DPSC was 34.63 mg/g and 55.34 mg/g which are in agreement with the predicted removal of 34.75 mg/g and 50.11 mg/g respectively at the center point values of Co=300 mg/L, pH 2, 362.5 min and 0.1 g adsorbent dose. The results also showed the acceptability of the Box Behnken design in response surface methodology for the optimization of EYD removal from aqueous media using DPSC and TiO2-DPSC blends. Hence, better EYD removal reported in TiO2-DPSC compared to DPSC was due to its improved adsorptive features. DOI:10.46481/jnsps.2022.533 Keywords: Porous carbon, TiO2, Adsorption, Eosin yellow dye, Box Behnken design Article History : Received: 21 December 2021 Received in revised form: 17 February 2022 Accepted for publication: 25 February 2022 Published: 29 May 2022 c©2022 Journal of the Nigerian Society of Physical Sciences. All rights reserved. Communicated by: E. Etim 1. Introduction In recent years, industrial evolution has left an indelible mark on the environment. Several industrial, domestic, and labora- tory activities employ dyes for coloring [1,2]. And most of ∗Corresponding author tel. no: Email address: samsudeen.azeez@kwasu.edu.ng (Samsudeen Olanrewaju Azeez ) these dyes are non-biodegradable, highly hazardous, toxic, and carcinogenic which poses a great risk to health [3,4]. Also, the discharge of wastewaters containing dyes into the environment aids the pollution of rivers and greatly affects both human and aquatic lives negatively [1,3,5]. Biological stains are organic dyes commonly applied for the de- termination of biological tissues. These stain substances have been reported as potentially carcinogenic and mutagenic com- 183 Azeez et al. / J. Nig. Soc. Phys. Sci. 4 (2022) 183–192 184 Figure 1. Structure of EYD pounds, therefore their presence in the wastewaters being dis- charged into the environment is a threat to human and aquatic lives [2,4,6]. Eosin yellow dye (EYD) is a reactive, anionic water-soluble acid dye commonly used as a stain. It is hetero- cyclic with the molecular formula of C20H6Br4Na2O5 and IU- PAC name, 2-(2,4,5,6-Tetrabromo-6-oxido-3-oxido-3H xanthenes- 9-yl) benzoate disodium salt as shown in Fig. 1. EYD is pink in color and belongs to the fluorescein class of dye with a λmax of 517 nm. It is commonly used in gram staining [4,6]. Ex- posure to EYD may result in severe eye and skin irritation and adversely affects vital organs such as kidney, liver, etc. It also reduces the pulmonary gas exchangeability of the lungs if in- haled [6,7]. The treatment of wastewater containing dyes before release into the environment becomes germane as a small quantity of dye in water even at part per billion level can be toxic [8]. And gov- ernment policy requires that wastewater containing dye must be treated before discharge, consequently, a need to establish an effective technique that can efficiently remove these dyes from aqueous media has been the concern of the researcher. Before now, various techniques have been used to treat and re- move organic pollutants in wastewater [9] which include chem- ical precipitation, membrane filtration, catalytic, photocatalytic oxidation methods, ion exchange, electrochemical methods, ad- sorption technology, etc [1,4,7,10]. The adsorption technique is widely used now for wastewater treatment due to its efficiency, cheapness, ease to handle, and simplicity of its regeneration procedure [1,10]. The search for a low-cost and effective adsor- bent prepared from agricultural waste to adsorb dyes and other organics from wastewater is of interest to researchers [7,11–14]. Lately, in an attempt to fabricate an adsorbent with improved adsorptive characteristics for better removal of contaminants, research towards the development of composite materials that are more effective and of low cost to treat wastewater pollutants is increasing, Viz; date palm seeds, goethite, and their com- posite was used to remove acid dye from wastewater [4], novel magnetic/activated charcoal/β- cyclodextrin/alginate polymer nanocomposite was utilized in the removal of cationic [10], adsorption of organic dye by nanoporous composites of acti- vated carbon-metal organic frameworks [8], activated carbon prepared from wild date stones was employed in the adsorp- tion of acid dye [1], the adsorption of methyl orange by Fe- grafting sugar beet bagasse was investigated [12] and a new type of porous Zn (II) metal-organic gel was designed for ef- fective adsorption of methyl orange [9]. TiO2 is a non-toxic cheap and biocompatible semiconductor. It is the most com- monly used photocatalyst, due to its high stability and potential in the decomposition of many organic pollutants from aqueous media [15,16]. Loading TiO2 onto activated carbon as support has been reported [17,18]. The date palm (Phoenix dactylifera) is one of man’s earliest plants. It originated from North Africa and the Middle East and was brought to Nigeria. It is a palm tree from the Palmae ( Arecaceae ) family that grows in the tropics [16]. Experimentally, date palm seeds were known to contain about 55-65% carbohydrate, which makes it a suitable agricultural waste precursor for the preparation of high-grade activated carbon [19]. Previously, in adsorption studies, the optimization of process variables was usually investigated individually while keeping the other parameters constant. However, this method does not give the simultaneous effect of all parameters [20]. This ap- proach is time-wasting, requires a lot of experiments, and con- sumes large reagents and chemicals. These setbacks can be prevented by optimizing the independent variables concurrently employing a statistical experimental design like the Box Behnken design (BBD) under response surface methodology (RSM) [1,13]. Therefore, this research is concerned with investigating the op- timization by Box Behnken design for EYD removal from aque- ous medium using date palm seeds-porous carbon and TiO2- composite. 2. Experimental 2.1. Reagents and chemicals All the reagents used in this investigation are of analytical grade and were used with no additional purification. These include Eosin yellow dye (EYD), titanium(IV)oxide (TiO2), phosphoric acid (H3PO4), ethanol (C2H5OH), sodium hydroxide (NaOH), and hydrochloric acid (HCl) which were purchased from Sigma Aldrich, USA. Deionized water was used to prepare all the so- lutions. 2.2. Sample collection and preparation of date palm seeds-porous carbon (DPSC) The date palm fruits were gotten from Kaduna, Nigeria. The seeds were removed from the fruits, washed thoroughly with deionized water, and sundried for 2 days. The seeds were then carbonized in the furnace at 500 ◦C for 120 min. After which it was activated with phosphoric acid. The activation involved 184 Azeez et al. / J. Nig. Soc. Phys. Sci. 4 (2022) 183–192 185 immersing 100 g of the carbonized date palm seeds in 500 mL of 1 M H3PO4 for 48 h. It was then filtered, washed to neutral pH with hot and cold deionized water, and oven-dried at 105 ◦C for 2 h. Subsequently, it was reactivated for 2 h at a temperature of 300 ◦C then cooled, ground, and sieved with < 63 µm mesh. This product was then labeled date palm seeds-porous carbon (DPSC) [19,21]. 2.3. Preparation of TiO2-DPSC blend The titanium (IV) oxide-date palm seeds-porous carbon (TiO2- DPSC) was prepared by the impregnation method as follows: 10 g of DPSC was added to 100 mL of deionized water andtreat- ment in an autoclave at 120 ◦C for 2 h. The stirred for 1 h. 5 g of commercial nanoparticle TiO2 was then added and stirred for another 2 h at 40 ◦C. Subsequently, a 1:1 ratio of ethanol and water was added to the resulting TiO2-DPSC mixture and then subjected to hydrothermal treatment in an autoclave at 120 ◦C for 2 h. The resultant mixture was centrifuged at 4000 rpm for 15 min and the blend solid particles obtained were oven-dried at 110 ◦C for 1 h. It was then calcined at 400 ◦C for 3 h. After cooling it was ground to fine particles and stored for further use [18,22,23]. 2.4. Characterization of DPSC and TiO2-DPSC The adsorbents were characterized using an FTIR spectropho- tometer (Perkin-Elmer Spectrum GX, UK) to ascertain the func- tional groups present on the adsorbents. The surface morphol- ogy and elemental composition of the material were obtained with a scanning electron microscope coupled with energy dis- persive spectroscopy (JEOL JSM-6510LV, Japan). The surface area of both adsorbents was determined by BET analysis via N2 adsorption-desorption at 77 K using Micromeritics ASAP 2020 V3.02H model. 2.5. Preparation of EYD solution A 1000 mg/L of EYD solution was prepared by dissolving 1 g of EYD in 1 L of deionized water and lower concentrations of EYD were then prepared by serial dilution [7]. 2.6. Adsorption experiments The removal of EYD by DPSC and TiO2-DPSC blends were determined in batch mode. The initial EYD concentration, pH, contact time, and adsorbent dosage were investigated. The ad- sorption study involves adding 0.1 g of the adsorbents (DPSC or TiO2-DPSC blend) to 20 mL of different initial concentra- tions (50 to 300) mg/L of EYD solution in a 100 mL conical flask. The flasks containing the solutions were then placed in a temperature-controlled water bath shaker and were agitated for 120 min at 30±2 ◦C and 200 rpm. The pH of the solutions was controlled using 0.1 M NaOH and 0.1 M HCl solutions. The samples were then centrifuged for 10 min at 4000 rpm and filtered. After which, the filtrate was analyzed for change in concentration of EYD using UV/Visible spectrophotometer (Microprocessor UV-VIS Double Beam AVI-2802) at a λmax Table 1. Process parameters and their coded levels for BBD in RSM Range of coded values Parameters Units Factors -1 0 +1 Initial conc mg/L A 50 175 300 pH B 2 7 12 Adsorbent dose g C 0.1 0.3 0.5 Time min D 5 326.5 720 of 517 nm. The quantity of EYD removal was calculated with Eq. (1) [1,4,24,25]: qe = (C0 − Ce) V W (1) where, qe is the quantity of EYD removed, Co is the initial EYD concentration (mg/L), Ce is the equilibrium EYD concentra- tion (mg/L), V is the volume of EYD solution (L) and W is the weight of adsorbent (g). 2.7. Box Behnken experimental design and statistical analysis Optimization of the process parameters was achieved with Box Behnken design (BBD) under RSM. This was employed to de- termine the best interaction between the process parameters in the removal of EYD from aqueous media by DSPC and TiO2- DPSC. The design was used to obtain sets of designed experi- ments by Design Expert 11.1.2.0 with four factors; initial con- centration, pH, adsorbent dose, and time. To study the influence of operating variables on the quantity of EYD removal, the four variables: concentration (A), pH (B), adsorbent dose (C), and time (D) each at three levels were selected as presented in Table 2. The number of experimental runs could as well be calculated using Eq. (2): N = k2 + k + C p (2) where N is the number of experimental runs, k is the number of factors and Cp is the replicate number of central points. Conse- quently, a total of 29 experimental runs was gotten as a function of the four factors on a three-level design, that is (-1. 0, +1) as presented in Table 1 [13,20,26]. The responses were presented as the quantity of EYD re- moved (mg/g) as in Table 3. The experimental data were stud- ied and fitted well with the quadratic polynomial equation model which describes the nature of the process as expressed by Eq. (3): Y = β0 + k∑ i=1 βi xi + k∑ i=1 βii x 2 i + k∑ 1≤i≤ j βi j xi x j + � (3) Where, Y is the response (quantity of EYD removed); xi = variables; k = number of variables; β0 = constant term; βi = coefficients of linear parameters, βi j = coefficient of the inter- action parameters; βii =coefficient of the quadratic parameter; ε = residual associated to the experiments. 185 Azeez et al. / J. Nig. Soc. Phys. Sci. 4 (2022) 183–192 186 Table 2. Characteristics of the Adsorbents DPSC TiO2-DPSC BET Surface area (m2g−1) 332.744 542.634 Average pore volume (cm3g−1) 0.188 0.271 Average pore diameter (nm) 1.853 2.015 %C 70.70 26.71 %O 29.17 44.42 %Ti - 28.87 %Ca 0.13 - 3. Results and Discussion 3.1. Adsorbents Characterization 3.1.1. BET surface area analysis and elemental composition The Brunauer, Emmett and Teller (BET) analysis results of both DPSC and TiO2-DPSC are given in Table 2. The BET surface area of both adsorbents is large which are attributed to carbon materials used as a precursor and the preparation procedure uti- lized, but the surface area of TiO2-DPSC is higher than DPSC. The enhancement of TiO2-DPSC surface area is due to TiO2 incorporated with the carbon. The result also showed that the pore volume and pore diameter of TiO2-DPSC is greater than DPSC. According to IUPAC classification, it is perceived that TiO2-DPSC is mesoporous and DPSC microporous [27]. This result suggests that both adsorbents are materials with a good potential for the removal of EYD. Although, TiO2-DPSC would be a better adsorbent for removal EYD than DPSC owing to its higher surface area and mesoporous surface [21,28]. The EDX results give the elemental composition of the adsor- bents. The major constituents of DPSC are carbon and oxygen with calcium as a minor element while TiO2-DPSC exhibited a high percentage of titanium with lower percentages of car- bon and oxygen as compared to DPSC (Table 2 & Fig. 2.). The relatively high weight percentage of Ti in TiO2-DPSC indi- cates successful incorporation of TiO2 into the date palm seeds- porous carbon. 3.1.2. Scanning electron microscopy (SEM) The SEM micrograph (Fig. 3a) of DPSA showed an irregular coarse surface morphology with many micropores which ex- hibited a high probability for EYD to be adsorbed. Also, the SEM image of TiO2-DPSA (Fig. 3b) revealed an improvement on the surface of the adsorbent due to agglomeration of TiO2 particles on the surface of DSAC indicating its porous nature and supported by the increase in the BET surface area and pore diameter of TiO2-DPSA. 3.1.3. FTIR analysis of the adsorbents The FTIR spectra of DPSC and TiO2-DPSC are given in Fig. 4a. The absorption bands at ∼ 3400 cm−1 observed for both adsorbents are characteristics of O-H stretching vibrations of alcohol [5]. The band at ∼ 1600 cm−1 shows the presence of the C=C aromatic functional group, while the peak at ∼ 1233 cm−1 is related to the C-OH band. A band at 495.88 cm−1 on the TiO2-DPSC spectrum is attributed to Ti-O-Ti bending vi- brations that do not exist on DPSC. All these functional groups Figure 2. EDX spectra of (a) DPSC, (b)TiO2-DPSC Figure 3. SEM micrograph of (a) DPSA and (b) TiO2-DPSA Figure 4. FTIR spectra of DSPC and TiO2-DPSC (a) before adsorption (b) after adsorption will take part in the adsorption process [1,4,19]. Following ad- sorption of EYD (Fig. 4b.), there were differences in intensities of the absorption peak indicating the involvement of the func- tional groups in the adsorption process as a similar observation was reported by [21]. 186 Azeez et al. / J. Nig. Soc. Phys. Sci. 4 (2022) 183–192 187 3.2. Optimization of EYD onto DPSC and DPSC-TiO2 by BBD The optimum conditions for EYD removal onto DPSC and DPSC- TiO2 were established by BBD under RSM. The matrix of ex- perimental design of the four process variables each at three lev- els with their equivalent actual and predicted responses (quan- tity adsorbed in mg/g) are given in Table 3. Design expert 11.1.2.0 was used to obtain the second-order polynomial equa- tions that describe the adsorption responses (quantity adsorbed) with the four operating variables where the insignificant terms (p?0.05) are not included as given by Eq. (4) and Eq. (5) for DPSC and DPSC-TiO2 respectively: YDPS C = +2.90 + 8.38A − 5.02B− 9.41C + 1.84D − 9.21AC − 5.43BD + 4.34B2 + 5.48C2 + 7.77D2 (4) YT iO2−DPS C = +9.82 + 10.14A − 4.49B − 14.13C + 1.63D − 4.15AB − 8.64AC − 4.79BD + 7.90C2 (5) Equations (4) and (5) depict how the interactive model terms impacted the removal of EYD from an aqueous solution by both adsorbents. The synergistic effect of the parameters is indicated by a positive sign while a negative sign represents an antagonis- tic effect [1,29]. 3.2.1. ANOVA Results The adequacy of the proposed model was analyzed using the ANOVA. The results obtained are shown in Table 4. High F-values of the models 28.20 and 23.74 for DPSC and TiO2- DPSC respectively with their p-value less than 0.05 suggested that the quadratic models are significant. The high correlation coefficient (R2) values of 0.965 and 0.960 with adjusted R2 val- ues of 0.932 and 0.919 for DPSC and TiO2-DPSC respectively agreed with their corresponding predicted R2 values of 0.806 and 0.785 implying that the model is adequate to describe the adsorption process. Also, the low values of percentage coef- ficient of variation (%CV) 29.35% and 26.80% for DPSC and TiO2-DPSC respectively signify good reliability and high pre- cision of the experimental values [13]. It is obvious in Table 4 that the linear terms A, B, C, and D, the interaction term AC and BD, and quadratic terms B2, C2, and D2 are statistically signif- icant (p< 0.05) for EYD onto DSPC while for EYD on TiO2- DPSC, the linear term D is not significant (p>0.05), the inter- action terms AB, AC and BD, and quadratic terms C2 are sig- nificant. This infers that the number of experiments performed is acceptable to explain the effects of the process parameters on the amount of EYD removal from aqueous solution by both ad- sorbents [30–32]. Furthermore, Table 4 shows that the lack of fit (F-value = 19.25) with p-value < 0.05 indicates the lack of fit is significant for EYD removal onto DPSC while the lack of fit (F-value = 3.42) and p-value > 0.05 for EYD adsorbed by TiO2- DPSC is not significant compared to the pure error, suggesting that the mathematical model proposed was well explained The graph of actual versus predicted values of EYD removal onto both adsorbents is given in Fig. 5. It can be seen that the Figure 5. The plot of actual versus predicted values for EYD removal by (a) DPSC, (b)TiO2-DPSC points on the plots were well grouped on the straight line; signi- fying a good agreement between the actual and predicted values of the responses for both adsorbents [29]. This indicates that the proposed statistical model is satisfactory for the optimization of EYD removal by both DPSC and TiO2-DPSC [33,34]. DPSC: - Mean = 9.92; C.V.% = 29.35; R2 = 0.9658; Ad- justed. R2 = 0.9315; Predicted. R2 = 0.8057; Adeq. Precision = 19.2583 TiO2-DPSC: - Mean = 14.19; C.V.% = 26.80; R2 = 0.9597; Adjusted. R2 = 0.9192; Predicted. R2 = 0.7850; Adeq. Preci- sion = 18.3713 3.3. Simultaneous effects of process parameters on the removal of EYD The interactions between the process parameters on the quantity of EYD removal from aqueous solution by DPSC and TiO2- DPSC are illustrated by 3D response surface plots (Figs. 6 – 11). These involve the simultaneous effects of any two of the process variables while keeping the other factors at the central level. 3.3.1. Simultaneous effect of initial EYD concentration and pH The simultaneous effect of the initial EYD concentration and pH on the amount of EYD removal by DPSC and TiO2-DPSC is given in Fig. 6. It can be seen (Fig. 6.) that increase in initial EYD concentration at low pH increases the amount of EYD removal per gram for both adsorbents. This dual inter- action is not significant for EYD on DPSC but significant for EYD onto TiO2-DPSC. The increase in the quantity of EYD adsorbed as the adsorbate concentration increases could be as a result of more EYD ions in solution as its concentration in- creases. At low pH, the removal of EYD was at its optimum as a result of more availability of H+ ions in the solution. This may be due to electrostatic attraction between the anionic species of EYD in solution and the protonated surface of the adsorbents. While, at higher pH, the adsorption of EYD by the two ad- sorbents decreased, because more OH− ions exist in the solu- tion and electrostatic repulsion results between the molecules of EYD in solution and the negatively charged surface of the adsorbents. This trend corresponds to the observations reported by Mittal et al. [6], Bello et al. [21] and Abdus-Salam et al. [4]. 187 Azeez et al. / J. Nig. Soc. Phys. Sci. 4 (2022) 183–192 188 Table 3. Box Behnken Experimental Design for EYD Removal onto DPSC & TiO2-DPSC Experimental run Operating variables Responses (mg/g) DPSA Responses (mg/g) TiO2-DPSA Initial conc (mg/L) pH Adsorbent dose (g) Time (min) Actual quantity adsorbed Predicted quantity adsorbed Actual quantity adsorbed Predicted quantity adsorbed 1 50 2 0.3 362.5 2.15 2.01 0.89 0.54 2 175 7 0.5 720 3.86 6.64 3.86 6.21 3 175 12 0.3 720 8.43 6.40 8.43 5.35 4 175 7 0.1 5 24.82 21.77 31.91 31.21 5 175 7 0.1 720 30.4 29.35 34.4 36.78 6 175 12 0.3 5 9.79 13.59 9.15 11.67 7 50 7 0.3 720 1.39 3.17 1.39 2.09 8 175 2 0.3 5 10.64 12.77 11.58 11.08 9 175 7 0.5 5 6.09 6.87 6.00 5.28 10 175 7 0.3 362.5 2.8 2.90 8.50 9.82 11 175 7 0.3 362.5 3.05 2.90 6.54 9.82 12 300 12 0.3 362.5 8.86 8.73 9.82 11.83 13 175 7 0.3 362.5 2.95 2.90 12.03 9.82 14 175 2 0.5 362.5 6.92 6.22 6.87 8.61 15 300 7 0.3 5 17.87 16.26 17.89 19.11 16 50 12 0.3 362.5 -2.39 -5.57 2.12 -0.15 17 175 12 0.5 362.5 -0.26 0.41 -0.02 0.62 18 50 7 0.1 362.5 -4.05 -0.45 10.46 12.55 19 50 7 0.3 5 2.18 0.13 2.39 0.56 20 50 7 0.5 362.5 -0.81 -0.83 -0.08 1.58 21 175 12 0.1 362.5 14.12 14.99 27.70 27.88 22 175 2 0.1 362.5 29.77 29.27 36.58 37.86 23 300 7 0.3 720 18.35 20.57 20.35 24.09 24 300 2 0.3 362.5 18.33 21.24 25.18 29.11 25 175 7 0.3 362.5 3.95 2.90 11.71 9.82 26 300 2 0.1 362.5 34.63 34.75 55.34 50.11 27 300 7 0.5 362.5 1.01 -2.50 10.24 4.57 28 175 2 0.3 720 31.01 27.31 30.01 23.91 29 175 7 0.3 362.5 1.77 2.90 10.31 9.82 Figure 6. 3D response surface plots for the simultaneous effect of initial EYD concentration and pH at constant 0.1 g dosage and 362.5 min contact time on the quantity of EYD adsorbed onto (a) DPSC, (b) TiO2-DPSC 3.3.2. Simultaneous effect of initial EYD concentration and ad- sorbent dose The 3D response surface plots presented in Fig. 7 depict the si- multaneous effects of initial EYD concentration and adsorbent dose on the quantity of EYD removal per gram of the adsor- bents (DPSC and TiO2-DPSC) at a fixed time of 362.5 min and pH 2. These binary interaction terms are significant in achiev- ing the maximum amount of EYD removal by both adsorbents. The increase in initial EYD concentration greatly impacts the removal of EYD onto DPSC and TiO2-DPSC. The uptake of EYD was at the highest at a low adsorbent dose. The vigorous adsorption of EYD observed at a lower dose could be due to many vacant adsorption sites on the adsorbents’ surfaces. How- ever, at a higher dosage, the free adsorption sites reduce because of overlapping of the active adsorption sites [4,11,31] 3.3.3. Simultaneous effect of initial EYD concentration and time Fig. 8 represents the effect of combined interaction between initial EYD concentration and time of contact on the 3D re- sponse surface plots for EYD removal from an aqueous solu- tion at constant pH and adsorbent dose. As seen from the plots, the removal of EYD increases immensely with increasing initial 188 Azeez et al. / J. Nig. Soc. Phys. Sci. 4 (2022) 183–192 189 Table 4. ANOVA analysis using BBD under RSM for EYD removal by DPSC & TiO2- DPSC Source Sum of Squares df Mean Square F-value p-value Remarks %C DPSC TiO2- DPSC DPSC TiO2- DPSC DPSC TiO2- DPSC DPSC TiO2- DPSC DPSC TiO2- DPSC DPSC TiO2- DPSC Model 3345.55 4809.09 14 238.97 343.51 28.2 23.74 < 0.0001 < 0.0001 Significant Significant A- Conc 843.03 1233.23 1 843.03 1233.23 99.5 85.24 < 0.0001 < 0.0001 Significant Significant 25.20 25.64 B-pH 302.71 242.19 1 302.71 242.19 35.73 16.74 < 0.0001 0.0011 Significant Significant 9.05 5.04 C- Dosage 1061.82 2394.75 1 1061.82 2394.75 125.32 165.53 < 0.0001 < 0.0001 Significant Significant 31.74 49.80 D- Time 40.52 31.75 1 40.52 31.75 4.78 2.19 0.0462 0.1606 Significant 1.21 0.66 AB 6.08 68.81 1 6.08 68.81 0.7171 4.76 0.4113 0.0467 Significant 0.18 1.43 AC 339.66 298.6 1 339.66 298.6 40.09 20.64 < 0.0001 0.0005 Significant Significant 10.15 6.21 AD 0.4032 2.99 1 0.4032 2.99 0.0476 0.2069 0.8305 0.6562 0.01 0.06 BC 17.94 0.99 1 17.94 0.99 2.12 0.0684 0.1677 0.7974 0.54 0.02 BD 118.05 91.68 1 118.05 91.68 13.93 6.34 0.0022 0.0246 Significant Significant 3.53 1.91 CD 15.25 5.36 1 15.25 5.36 1.8 0.3704 0.2011 0.5525 0.46 0.11 A2 2.67 1.71 1 2.67 1.71 0.3151 0.1179 0.5834 0.7365 0.08 0.04 B2 122.16 6.84 1 122.16 6.84 14.42 0.4731 0.002 0.5028 Significant 3.65 0.14 C2 194.86 404.41 1 194.86 404.41 23 27.95 0.0003 0.0001 Significant Significant 5.82 8.41 D2 391.83 30.22 1 391.83 30.22 46.24 2.09 < 0.0001 0.1704 Significant 11.71 0.63 Residual 118.62 202.55 14 8.47 14.47 Lack of fit 116.21 181.35 10 11.62 18.13 19.25 3.42 0.0059 0.1235 Significant Not sig- nificant Pure Error 2.41 21.2 4 0.6036 5.3 Cor Total 3464.17 5011.64 28 Std. Dev. 2.91 3.80 Figure 7. 3D response surface plots for the simultaneous effect of initial EYD concentration and adsorbent dose at affixed pH 2 and 362.5 min contact time on the quantity of EYD adsorbed onto (a) DPSC, (b) TiO2-DPSC EYD concentration. This may be due to the low pH of the so- lution and increase in the initial EYD concentration. However, an increase in the time of contact between the adsorbents and initial EYD concentration in solution has a small influence on the amount of EYD adsorbed at the start of the adsorption pro- cess. This low initial EYD removal result may be from several vacant active sites originally available for adsorption. There- fore, EYD molecules quickly filled the active sites. As adsorp- tion advances, the repulsive forces between the EYD molecules on the adsorbents surfaces and in the solution becomes larger needing more time to fill the remaining vacant active sites on the adsorbents surfaces [4,21,31]. This is why there were no considerable differences in the amount of EYD removed over the time investigated. 3.3.4. Simultaneous effect of pH and adsorbent dose The binary effect of interaction between pH and adsorbent dose on the response surface for the removal of EYD from solution at constant initial EYD concentration and time of contact is shown in Fig. 9. The optimum removal of EYD per gram was observed at low pH and low adsorbent doses indicating a synergistic ef- fect between the parameters. The quantity of EYD removal was 189 Azeez et al. / J. Nig. Soc. Phys. Sci. 4 (2022) 183–192 190 Figure 8. 3D response surface plots for the simultaneous effect of initial EYD concentration and time of contact at constant 0.1 g dosage and pH 2 on the quantity of EYD adsorbed onto (a) DPSC, (b) TiO2-DPSC Figure 9. 3D response surface plots for the simultaneous effect of pH and ad- sorbent dosage at affixed 300 mg/L initial EYD concentration and 362.5 min contact time on the quantity of EYD adsorbed onto (a) DPSC, (b) TiO2-DPSC 18.33 mg/g and 25.18 mg/g for DPSC and TiO2-DPSC respec- tively. 3.3.5. Simultaneous effect of time and pH Fig.10 illustrates the simultaneous effect of pH and time of con- tact on the response of EYD removal from aqueous solution at constant initial EYD concentration and adsorbents dose. The binary effect was highly significant for both adsorbents ana- lyzed (Table 4). These dual interaction terms were used in es- tablishing the optimum conditions for this study. According to this figure, the optimum (actual) removal of EYD was found to be 34.63 mg/g and 55.34 mg/g and predicted removal 34.75 mg/g and 50.11 mg/g for DPSC and TiO2-DPSC respectively at the center point values of 300 mg/L initial EYD concentra- tion, pH 2, 362.5 min time of contact and 0.1 g adsorbent dose for the two adsorbents. An additional increase in these two pa- rameters (pH and time) resulted in a decrease in the quantity of EYD adsorbed [31,34,35]. 3.3.6. Simultaneous effect of time and adsorbent dose The simultaneous effect between the time of contact and ad- sorbent dose on the response surface for the amount of EYD uptake per gram by DPSC and DPSC-TiO2 at affixed pH and initial EYD concentration is given in Fig. 11. These binary interaction terms have no significant impact on the quantity of EYD removed by both adsorbents (Table 4). It is seen that the quantity of EYD removal was at the highest at a low dose of 0.1 g for both adsorbents and very rapid at the start of the ad- sorption process. However, an increase in time of contact and Figure 10. 3D response surface plots for the simultaneous effect of pH and contact time at constant 300 mg/L initial EYD concentration and 0.1 g dosage on the quantity of EYD adsorbed onto (a) DPSC, (b) TiO2-DPSC Figure 11. 3D response surface plots for the simultaneous effect of contact time and adsorbent dose at affixed 300 mg/L initial EYD concentration and pH 2 on the quantity of EYD adsorbed onto (a) DPSC, (b) TiO2-DPSC Table 5. Comparison of adsorption efficiencies of DPSC and TiO2-DPSC with other adsorbents for EYD removal Adsorbents Adsorption Efficiency (mg/g) Reference Pineapple peels 11.76 [7] Oil bean acid activated carbon 26.32 [36] Teak leaf litter powder 31.64 [37] Polyaniline saw dust 5.90 [38] Goethite 27.78 [4] Composite of goethite and thermally activated carbon 30.30 [4] Chemically activated carbon 3.13 [4] Thermally activated char-coal 1.98 [4] DPSC 34.63 This investigation TiO2-DPSC 55.34 This investigation adsorbent dose does not influence the quantity of EYD removed as the adsorption progresses. This is due to the availability of various vacant sites ready for adsorption in the early stage of the process. Thus, an increase in adsorbent doses led to a decrease in the quantity of EYD removed while an increase in time do not have a meaningful effect on the removal. 3.4. Interactive effects of the process variables Generally, the perturbation graph is utilized to examine the in- teractive influence of all factors concurrently. The response is designed by changing one of the variables while other parame- 190 Azeez et al. / J. Nig. Soc. Phys. Sci. 4 (2022) 183–192 191 Figure 12. Perturbation graph for EYD Removal onto (a) DPSC, (b) TiO2- DPSC ters are kept constant at the center of the plot. Therefore, a per- turbation plot is employed to determine the factor that greatly impacts the adsorption process. Fig. 12a exhibited that initial EYD concentration, pH, adsorbent dose, and time have a mean- ingful influence on the quantity of EYD removal per gram by DPSC due to their relatively straight line. However, the amount of EYD removal onto TiO2-DPSC was largely influenced by three of the parameters except time due to its curvature (Fig. 12b) and this revealed that EYD removal is less sensitive to this parameter. This is following the report of Rahman &Nasir [35]. 3.5. Contribution of process parameters on the response sur- face plots The contribution (C) of each parameter in percentage on the response model was studied by Eq. 6 [35,39]: %C = S S i S S m × 100 (6) where SSm is the sum of squares for the model and SSi is the sum of squares for the individual parameter. The results are presented in Table 4. The results indicated that the adsorbent dose, initial EYD concentration, and pH of solution immensely contributed to EYD removal by both adsorbents with %C values of 31.74, 25.20, and 9.05 for DPSC and 49.80, 25.64 5.04 for TiO2-DPSC respectively. The percentage contribution of a time of contact is the lowest among the individual parameters for both adsorbents in the response model. The interactive term AC gives a %C value of 10.15 and 6.21 for DPSC and TiO2-DPSC respectively while the other dual terms have lesser contribution in EYD removal from aqueous solution. 4. Conclusion In this research, DPSC and TiO2-DPSC blends were success- fully prepared for the removal of EYD from an aqueous medium. The surface area and pore diameter of TiO2-DPSC is higher than DPSC. The major and interactive impacts of the adsorption parameters which include initial EYD concentration, pH, adsor- bent dose, and time of contact were examined by Box Behnken design based on response surface methodology. The high R2 values of the models are in agreement with the adjusted R2 val- ues. The second-order regression model sufficiently interprets the adsorption data. The adsorbent dose delivered the largest percentage contribution of 49.80% and 31.74% for TiO2-DPSC and DPSC respectively to the response parameters while the dual interaction terms of initial EYD concentration and adsor- bent dose had the highest percentage contribution of 10.15% and 6.21% for DPSC and TiO2-DPSC respectively to EYD re- moval per gram compared to other interaction terms. The op- timum amount of EYD removal onto DPSC and TiO2-DPSC were discovered to be 34.63 mg/g and 55.34 mg/g respectively. The results also showed the reliability of the Box Behnken de- sign in response surface methodology for the optimization of EYD removal from aqueous media. Based on the observed trends, it can be concluded that TiO2-DPSC is a better adsor- bent material in the removal of EYD from an aqueous solution than DPSC. Acknowledgments The authors are highly appreciative of Chemistry and Indus- trial Chemistry Department, Kwara State University, Malete, Nigeria for giving us the laboratory facilities necessary to carry out this research. References [1] L. Brahmi, F. Kaouah, S. Boumaza & M. Trari, “Response surface methodology for the optimization of acid dye adsorption onto activated carbon prepared from wild date stones”, Appl. Water Sci. 9 (2019) 1, https://doi.org/10.1007/s13201-019-1053-2. [2] M. S. M. Amran, D. M. Khalid, W. A. K. W. Azlina & A. Idris, “Cationic and anionic dye adsorption by agricultural solid wastes : A comprehensive review”, Desalination 280 (2011) 1, https://doi.org/10.1016/j.desal.2011.07.019. [3] I. D. Dallabona, L. Mathias, R. Maria & M. Jorge, “A new green float- ing photocatalyst with Brazilian bentonite into TiO 2 / alginate beads for dye removal”, Colloids Surfaces A Physicochem. Eng. Asp. 627 (2021) 127159, https://doi.org/10.1016/j.colsurfa.2021.127159. [4] N. Abdus-salam, A. V Ikudayisi-ugbe & F. A. Ugbe, ”Adsorp- tion studies of acid dye – Eosin yellow on date palm seeds , goethite and their composite”, Chem. Data Collect. 31 (2021) 1, https://doi.org/10.1016/j.cdc.2020.100626. [5] J. P. Lima, G. Alvarenga, A. C. F. Goszczynski, G. R. Rosa & T. J. Lopes, “Batch adsorption of methylene blue dye using En- terolobium contortisiliquum as bioadsorbent: experimental, mathemat- ical modeling and simulation”, J. Ind. Eng. Chem. 91 (2020) 362, https://doi.org/10.1016/j.jiec.2020.08.029. [6] A. Mittal, D. Jhare & J. Mittal, “Adsorption of hazardous dye Eosin yellow from aqueous solution onto waste material de – Oiled S=soya: isotherm, kinetics and bulk removal”, J. Mol. Liq. 179179 (2013) 133, https://doi.org/10.1016/j.molliq.2012.11.032. [7] F. A. Ugbe, P. O. Anebi & V. A. Ikudayisi, ”Biosorption of an anionic dye ,Eosin yellow onto pineapple peels : Isotherm and Thermodynamic Study”, Int. Ann. Sci. 4 (2018) 14, https://doi.org/https://doi.org/10.21467/ias.4.1.14-19 RESEARCH. [8] M. Hasanzadeh, A. Simchi & H. Shahriyari, ”Nanoporous composites of activated carbon-metal organic frameworks for organic dye adsorp- tion : Synthesis, adsorption mechanism and kinetics studies”, J. Ind. Eng. Chem. 81 (2020) 405, https://doi.org/10.1016/j.jiec.2019.09.031. [9] M. Wang, S. Day, Z. Wu, X. Wan, X. Ye & B. Cheng, “A new type of porous Zn ( II ) metal-organic gel designed for effective adsorption to methyl orange dye”, Colloids Surfaces A Physicochem. Eng. Asp. 628 (2021) 127335, https://doi.org/doi.org/10.1016/j.colsurfa.2021.127335. [10] S. Yadav, A. Asthana, R. Chakraborty & B. Jain, “Cationic dye removal using novel magnetic / activated charcoal / β - cyclodex- trin / alginate polymer nanocomposite”, Nanomaterials 10 (2020) 1, https://doi.org/10.3390/nano10010170. 191 Azeez et al. / J. Nig. Soc. Phys. Sci. 4 (2022) 183–192 192 [11] S. Sadaf, H.N. Bhatti, S. Ali & K. Rehman, “Removal of Indosol Turquoise FBL dye from aqueous solution by bagasse , a low cost agri- cultural waste : batch and column study”, Desalin. Water Treat. (2013) 1, https://doi.org/10.1080/19443994.2013.780985. [12] F. Ghorbani & S. Kamari, “Application of response surface methodology for optimization of methyl orange adsorption by Fe- grafting sugar beet bagasse”, Adsorpt. Sci. Technol. 0 (2016) 1, https://doi.org/10.1177/0263617416675625. [13] X. Peng, G. Yang, Y. Shi, Y. Zhou, M. Zhang & S. Li, “Box – Behnken design based statistical modeling for the extraction and physic- ochemical properties of pectin from sunflower heads and the compar- ison with commercial low-methoxyl pectin”, Sci. Rep. 10 (2020) 1, https://doi.org/10.1038/s41598-020-60339-1. [14] M. Azmier, N. Azreen, A. Puad & O. Solomon, “Kinetic, equilibrium and thermodynamic studies of synthetic dye removal using pomegranate peel activated carbon prepared by microwave-induced KOH activation”, Water Resour. Ind. 6 (2014) 18, https://doi.org/10.1016/j.wri.2014.06.002. [15] R. Rajendran, S. Vignesh, A. Sasireka & S. Suganthi, “Designing Ag2O modified g-C3N4 / TiO2 ternary nanocomposites for photocatalytic or- ganic pollutants degradation performance under visible light : synergistic mechanism insight”, Colloids Surfaces A Physicochem. Eng. Asp. 629 (2021) 127472, https://doi.org/10.1016/j.colsurfa.2021.127472. [16] C. Orha, C. Lazau, D. Ursu & F. Manea, “Effect of TiO2 loading on powder-activated carbon in advanced drinking-water treatment”, Water Soc. IV. 216 (2017) 203, https://doi.org/10.2495/WS170191. [17] Z. Azhar, R. M. Ramli & Y. H. Noorfidza, “Photodegradation of 1-Butyl- 3-methylimidazolium chloride [Bmim ] Cl via synergistic effect of ad- sorption – photodegradation of Fe-TiO2/AC”, Technologies 5 (2017) 1, https://doi.org/10.3390/technologies5040082. [18] A. Rezaee, G. H. Pourtaghi, A. Khavanin, R. S. Mamoory, M. T. Ghaneian & H. Godini, “Photocatalytic decomposition of gaseous toluene by TiO2 nanoparticles coated on activated carbon”, Iran. J. Environ. Heal. Sci. Eng. 5 (2008) 305. [19] A. S. Nasir & V. I. Abiola, “Preparation and characterization of synthe- sized goethite and goethite-date palm seeds charcoal composite”, Ife J. Sci. 19 (2017) 99, https://doi.org/https://dx.doi.org/10.4314/ijs.v19i1.10 Ife. [20] Z. Anfar, H. Ait Ahsaine, M. Zbair, A. Amedlous, A. Ait El Fakir, A. Jada & N. El Alem, “Recent trends on numerical investigations of re- sponse surface methodology for pollutants adsorption onto activated car- bon materials: A review”, Crit. Rev. Environ. Sci. Technol. 50 (2020) 1043, https://doi.org/10.1080/10643389.2019.1642835. [21] O. S. Bello, T. A. Fatona, F. S. Falaye, O. M. Osuolale & V. O. Njoku, “Adsorption of Eosin dye from aqueous solution us- ing groundnut hull-based activated carbon: kinetic, equilibrium, and thermodynamic studies”, Environ. Eng. Sci. 29 (2012) 186, https://doi.org/10.1089/ees.2010.0385. [22] D. Kibanova, M. Trejo, H. Destaillats & J. Cervini-silva, “Ap- plied clay science synthesis of hectorite – TiO2 and kaolinite – TiO2 nanocomposites with photocatalytic activity for the degrada- tion of model air pollutants”, Appl. Clay Sci. 42 (2009) 563, https://doi.org/10.1016/j.clay.2008.03.009. [23] A. Zawawi, R. M. Ramli & N. Y. Harunl, “Synergistic effect of adsorption-photodegradation of composite TiO2/AC for degradation of 1- butyl-3-methylimidazolium chloride”, Malaysian J. Anal. Sci. 22 (2018) 648, https://doi.org/https://doi.org/10.17576/mjas-2018-2204-11. [24] S. A. Adesokan, A. A. Giwa & I. A. Bello, “Removal of trimethoprim from water using carbonized wood waste as adsorbents”, J. Niger. Soc. Phys. Sci. 3 (2021) 344, https://doi.org/10.46481/jnsps.2021.320. [25] K. O. Sodeinde, S. O. Olusanya, D. U. Momodu, V. F. Enogheghase & O. S. Lawal, “Waste glass: an excellent adsorbent for crys- tal violet dye, Pb2+ and Cd2+ heavy metal ions decontamina- tion from wastewater”, J. Niger. Soc. Phys. Sci. 3 (2021) 414, https://doi.org/10.46481/jnsps.2021.261. [26] R. Elmoubarki, M. Taoufik, A. Moufti, H. Tounsadi & F. Z. Mahjoubi, “Box-Behnken experimental design for the optimization of methylene blue adsorption onto aleppo pine cones”, J. Mater. Environ. Sci. 8 (2017) 2184, http://www.jmaterenvironsci.com/%0ABox-Behnken. [27] S. O. Azeez & F. A. Adekola, “Sorption of 4-nitroaniline on activated kaolinitic clay and jatropha curcas activated carbon in aqueous solution”, Jordan J. Chem. 11 (2016) 128. [28] S. O. Azeez & F. A. Adekola, “Kinetics and thermodynamics of sorption of 4-nitrophenol on activated kaolinitic clay and jatropha curcas activated carbon from queous solution”, Pak. J. Anal. Environ. Chem. 17 (2016) 93, https://doi.org/10.21743/pjaec/2016.06.014. [29] S. O. Azeez, I. O. Saheed, F. A. Adekola, A. A. Jimoh, D. M. Aransiola & Z. A. Abdulsalam, “Box behnken design in the optimization of rho- damine B adsorption onto activated carbon pprepared from delonix regia seeds and pods”, J. Turkish Chem. Soc. Sect. A Chem. 9 (2022) 205, https://doi.org/10.18596/jotcsa.893472. [30] E. Ben Khalifa, B. Rzig, R. Chakroun, H. Nouagui & B. Hamrouni, “Ap- plication of response surface methodology for chromium removal by ad- sorption on low-cost biosorbent”, Chemom. Intell. Lab. Syst. 189 (2019) 18, https://doi.org/10.1016/j.chemolab.2019.03.014. [31] K. M. Oghenejoboh, “Biosorption of nickel (II) ion from synthetic wastewater on watermelon rind activated carbon using reponse sur- face methodology (RSM) optimization approach”, Niger. J. Technol. 37 (2018) 647, https://doi.org/10.4314/njt.v37i3.13. [32] Z. S. Alman-Abad, H. Pirkharrati & F. Asadzadeh, M. Maleki-Kakelar, “Application of response surface methodology for optimization of zinc elimination from a polluted soil using tartaric acid”, Adsorpt. Sci. Tech- nol. 38 (2020) 79, https://doi.org/10.1177/0263617420916592. [33] F. Ghorbani & S. Kamari, “Application of response surface methodology for optimization of methyl orange adsorption by Fe- grafting sugar beet bagasse”, Adsorpt. Sci. Technol. 35 (2017) 317, https://doi.org/10.1177/0263617416675625. [34] D. Allouss, Y. Essamlali, O. Amadine, A. Chakir & M. Zahouily, “Re- sponse surface methodology for optimization of methylene blue adsorp- tion onto carboxymethyl cellulose-based hydrogel beads: Adsorption ki- netics, isotherm, thermodynamics and reusability studies”, RSC Adv. 9 (2019) 3785, https://doi.org/10.1039/c9ra06450h. [35] N. Rahman & M. Nasir, “Application of Box–Behnken design and de- sirability function in the optimization of Cd(II) removal from aqueous solution using poly(o-phenylenediamine)/hydrous zirconium oxide com- posite: equilibrium modeling, kinetic and thermodynamic studies”, En- viron. Sci. Pollut. Res. 25 (2018) 26114, https://doi.org/10.1007/s11356- 018-2566-1. [36] C. Okoye & D. Chime, “Removal of Eosin yellow dye from aqueous so- lution using oil bean seed shells based activated carbons: Equilibrium, Kinetics and thermodynamics studies”, Int. J. Sci. Eng. Res. 9 (2018) 140, http://www.ijser.org. [37] E. O. Oyelude, J. A. M. Awudza & S. K. Twumasi, “Equilibrium, kinetic and thermodynamic study of removal of Eosin yellow from aqueous solution using teak leaf litter powder”, Sci. Rep. 7 (2017) 1, https://doi.org/10.1038/s41598-017-12424-1. [38] R. Ansari & Z. Mosayebzadeh, “Removal of Eosin Y, an Anionic dye, from aqueous solutions using conducting electroactive polymers”, Iran. Polym. Journa. 19 (2010) 541,. http://journal.ippi.ac.ir. [39] F. Bandari, F. Safa & S. Shariati, “Application of response surface method for optimization of adsorptive removal of eriochrome black T using mag- netic multi-wall carbon nanotube nanocomposite”, Arab J Sci Eng. 40 (2015) 3363, https://doi.org/10.1007/s13369-015-1785-8. 192