Mesoporous activated carbon prepared from branches of pomegranate trees (BP) using physiochemical activation (potassium hydroxide treatment and carbon dioxide gasification). Based on the central composite design (CCD), two factor interaction (2FI) and quadratic models were respectively employed to correlate the activated carbon preparation variables. The effects of the activation temperature, activation time, and chemical impregnation ratios on the carbon yield, methylene blue (MB) removal were investigated. From the analysis of variance (ANOVA), the most influential factor on each experimental design response was identified. The optimum conditions for preparing activated carbon from branches of pomegranate trees (BP) were found to be activation temperature of
Dyes are widely used by textile industries to color their products. One of the major problems concerning textile wastewaters is colored effluent. This wastewater contains a variety of organic compounds and toxic substances, which are harmful to fish and other aquatic organisms [
Activated carbon is the most widely used adsorbent material for adsorption due to its efficiency and economic feasibility. Utilization of activated carbon can be in the form of powder, granular, and fiber or cloth. Activated carbon-cloth having very high specific surface area coupled with high adsorption capacity and mechanical strength has gained increasing attention in recent years. Activated carbon is used for the removal of many pollutants from waste water by adsorption [
However, commercially available activated carbon is expensive. In the last years, special emphasis on the preparation of activated carbons from several agricultural by-products has been given due to the growing interest in low cost activated carbons from renewable resources, especially for application concerning treatment of wastewater. Researchers have studied the production of activated carbon from palm tree [
The focus of the research is to evaluate the adsorption potential of branches of pomegranate trees-based activated carbon for methylene dye due to the fact that the branches of pomegranate trees are a very abundant and inexpensive material. MB was chosen in this study because of its known strong adsorption onto solids and it often serves as a model compound for removing organic contaminants and colored bodies from aqueous solutions. MB which is the most commonly used material for dying cotton, wood, and silk has a molecular weight of 373.9 g mol−1, which corresponds to methylene blue hydrochloride with three groups of water. The equilibrium data of adsorption studies were processed to understand the adsorption mechanism of the dye molecules onto the activated carbon.
Methylene blue (MB) supplied by Sigma-Aldrich was used as an adsorbate and was not purified prior to use. Distilled water was used to prepare all solutions. Table
Branches of pomegranate trees (BP) are used as precursors for preparation of activated carbon. The precursor was first crushed into pieces of (1-2 cm) then was washed to remove dirt from its surface and was then dried in an oven at 75°C for three days. The dried precursors was crushed and screened to particle size of 1–4 mm and carbonized at 400°C under nitrogen flow for 2 h using stainless steel vertical tubular reactor placed in a tube furnace. The char produced was mixed with KOH pallets with different impregnation ratio (IR), as calculated using (
Scanning electron microscopy (SEM) analysis was carried out on the activated carbon prepared under optimum conditions, to study its surface texture and the development of porosity. Brunaeur, Emmett and Teller (BET) suggested to determine the pore size distributions, the surface area, and pore characteristics of activated carbons using Micromeritics (Model ASAP 2020, USA).
Response surface methodology (RSM) is a collection of mathematical and statistical techniques that are useful for modeling and analysis of problems in which a response of interest is influenced by several variables [
The activated carbons were prepared using physiochemical activation method by varying the preparation variables using the CCD. The activated carbon preparation variables studied were
The experimental sequence was randomized in order to minimize the effects of the uncontrolled factors. Each response (
The activated carbon was derived from these precursors by physiochemical activation method which involved the use of KOH treatment and followed by gasification with CO2. The parameters involved in the preparation were varied using the response surface methodology (RSM). The three variables studied were
The most important characteristic of an activated carbon is its adsorption uptake or its removal capacity which is highly influenced by the preparation conditions. Besides, activated carbon yield during preparation is also a main concern in activated carbon production for economic feasibility. Therefore, the responses considered in this study were
The experimental activated carbon yield was calculated based on the following equation (
Batch adsorption was performed in 20 sets of 250 mL Erlenmeyer flasks. In a typical adsorption run, 100 mL of methylene blue solution with initial concentration of 100 mg/L was placed in a flask. 0.30 g of the prepared activated carbon (BPAC), with particle size of 2 mm, was added to the flask and kept in an isothermal shaker (120 rpm) at 30°C until equilibrium was attained. The concentrations of dye solution before and after adsorption were determined using a double-beam UV-vis spectrophotometer (UV-1700 Shimadzu, Japan). The maximum wavelength of the methylene blue was found to be 668 nm. The percentage removal of dye at equilibrium was calculated by the following equation (
The surface morphology of the prepared activated carbon was examined using scanning electron microscope (Model Leo Supra 50VP Field Emission, UK). The surface of activated carbon prepared contains a well-developed pores where there is a good possibility for dye to be absorbed into the surface of the pores.
The Brunauer-Emmett-Teller (BET) surface area and the average pore diameter were 535 m2/g and 2.96 nm, respectively, using Micromeriticsue (Model ASAP 2020, USA).
The complete design matrix for the yield response of activated carbon prepared from branches of pomegranate trees (BPAC) with the removal of methylene blue solution from the experimental works include 20 runs, five runs from them at the center point were conducted to determine the experimental error and the reproducibility of the data.
The yield of activated carbon and the removal of methylene blue were influenced not only by the preparation variables but also depending on the type and nature of the original precursors as different precursors would have different physical and chemical characteristics.
The experimental data revealed that the activation time have the greatest effect on the BPAC yield response and gave the highest
ANOVA for response surface quadratic model for BPAC yield.
Source | Sum of squares | Degree of freedom | Mean square | Prob > | |
---|---|---|---|---|---|
Model | 16.08 | 9 | 1.79 | 13.5 | 0.0001 |
0.16 | 1 | 0.16 | 1.28 | 0.2839 | |
0.84 | 1 | 0.84 | 6.66 | 0.0274 | |
8.51 | 1 | 8.51 | 67.89 | <0.0001 | |
0.24 | 1 | 0.24 | 1.90 | 0.1979 | |
4.13 | 1 | 4.13 | 32.93 | 0.0002 | |
2.88 | 1 | 2.88 | 22.95 | 0.0007 | |
0.080 | 1 | 0.080 | 0.64 | 0.4430 | |
0.080 | 1 | 0.080 | 0.64 | 0.4430 | |
0.000 | 1 | 0.000 | 0.000 | 1.0000 |
Figures
Three-dimensional response on the yield of BPAC, (a) the variables activation temperature and activation time, (b) the variables activation temperature and IR, and (c) activation time and IR.
In general, the BPAC yield was found to decrease with increasing activation temperature, activation time, and chemical impregnation ratio. The increase in activation temperature would increase the removal of volatiles and impurities from the sample due to thermal decomposition and carbon monoxide emission via C-CO2 reaction, this resulted into a decrease in sample weight [
The experimental values obtained for the removal of methylene blue and its response (Table
ANOVA results for MB removal by BPAC.
Source | Sum of squares | Degree of freedom | Mean square | Prob > | |
---|---|---|---|---|---|
Model | 1843.81 | 9 | 204.87 | 14.77 | 0.0001 |
0.0003 | |||||
0.8119 | |||||
0.0001 | |||||
0.2964 | |||||
0.8448 | |||||
0.0063 | |||||
0.0026 | |||||
0.8532 | |||||
0.1598 |
Some properties of the MB used.
Properties | |
---|---|
Chemical formula | C16H18ClN3S·3H2O |
Molecular weight | 373.9 g/mol |
Type | Basic dye |
Solubility | Soluble in water |
Solution pH | 6.5 |
Wave length | 668 nm |
Figures
Three-dimensional response between the variables activation temperature, time and IR for the removals of methylene blue onto BPAC, (a) the variables activation temperature and activation time, (b) the variables activation temperature and IR, and (c) activation time and IR.
In order optimize the preparation conditions for activated carbon used for methylene blue removal, the targeted criteria was set as maximum values for the two responses of activated carbon yield (
Branch pomegranate tree were used as precursor to prepare mesoporous-activated carbon with high surface area, sufficient yield of carbon, and high dye removal. A central composite design was conducted to study the effects of three activated carbon preparation variables, which were the activation temperature, activation time, and chemical impregnation ratio on the activated carbon yield and the removal of methylene blue. Through analysis of the response surfaces derived from the models, the BPAC yield was found to decrease with increasing activation temperature, activation time, and chemical impregnation ratio. It was found that the removal of methylene blue increases with the increasing of activation temperature and IR. The optimum conditions to prepare BPAC were obtained using 620°C activation temperature, 1.4 h activation time, and 1.5 KOH: char impregnation ratio.