This study investigated the adsorption of Methylene Blue (MB) present in wastewater onto the activated carbon produce from Lantana camara stem. The agricultural material ( Lantana camara stem) was carbonized at 300° C for 2 h, ground and steam-activated. The Steam-Activated Lantana camara (SALC) stem carbon was characterized using Scanning Electron Microscope (SEM) and Fourier Transform Infrared (FTIR) Spectrophotometry before and after adsorption. Batch model experiments were conducted at 20° C to study the effects of pH, agitation time, adsorbent dosage and initial concentration of methylene blue. The equilibrium adsorption isotherms and kinetics were investigated. The FTIR bands at 3500, 2500, 2196 and 1682 cm-1 were shifted to 3646.3, 3030, 2822, 1709.05 cm-1 after MB adsorption. Similarly, the Scanning Electron Microscopy (SEM) analysis showed that the average pore size on the activated carbon was 20 μm. The Methylene Blue (MB) uptake increased with the increase in pH. Similarly, the dye adsorption increased as contact time increased, and reached equilibrium at 60 minutes. The removal of the dye increased when the dosage was increased from 0.5 - 2.0 g · L-1, at different dye concentrations (50 - 200 mg · L-1). The percentage removal decreased with increasing initial dye concentration for SALC. The adsorption isotherm data fitted well to the Freundlich isotherm (R2 = 0.989) while the experimental data fitted very well to the pseudo-second-order kinetic model (R2 = 0.99). This study suggests that adsorbent prepared from Lantana camara stem can be used effectively for the adsorption of methylene blue in wastewater.
Dyes are important hazardous substances found in textile industry, food industry, pharmaceutical industry, paper industry and plastics industry. Their presence in water bodies reduces light penetration and this consequently thwarts the photosynthesis of aqueous flora [
Various treatment methods for the remove dyes from wastewater have been investigated and these methods can be classified as chemical coagulation/flocculation, ozonation, oxidation processes, chemical precipitation, ion exchange, reverse osmosis, and ultra-filtration [
Adsorption is rapidly gaining prominence among the treatment technologies and [
The purpose of this work is to investigate convenient and economic method for basic dye (methylene blue) removal from wastewater by adsorption on an abundantly available adsorbent, but in this case, adsorption of methylene blue dye onto steam activated carbon from Lantana camara stem (SALC). Batch studies involving process parameters such as the effect adsorbent dosage, initial dye concentration, pH of solution, and contact time, were carried out. Equilibrium and kinetic analysis were conducted to determine the factors controlling the rate of adsorption, the optimization of various parameters in dye recovery and to find out the possibility of using this material as low-cost adsorbent for dye removal. The experimental data obtained were analysed using isotherm models such as Langmuir and Freundlich isotherm models.
The natural low cost material, Lantana camara, was obtained from Stadium Area, Ogbomosho, and OyoState, Nigeria. The stems were separated from the seed and flower and were extensively washed with tap water to remove soil and dust particles. It was then sundried, and further crushed into smaller size. The Lantana camara was carbonized using an electric furnace at 300˚C for 2 h. The carbonized sample was ground into granular form and the carbon was activated using steam activating reactor. The resultant activated carbon was oven-dried at 105˚C for 2 h and cooled to room temperature in a desiccator. It was then ground with mortar and pestle and sieved to 2 mm mesh size. It was later stored inside a desiccator to avoid moisture absorption. The Infrared spectroscopic analysis was conducted on the Steam-Activated Lantana camara Stem (SALCS) to investigate the functional groups present on its surface using Fourier Transform Infrared Spectrometer (Perkin-Elmer Spectrum GX, Kuala Lumpur, Malaysia). The morphologies of the steam activated carbon were characterized using a scanning electron microscope (SEM, JEOL JSM-6480 LV).
The adsorb ate was prepared by dissolving 1 g of methylene blue powder in small quantity of distilled water in 1000 ml volumetric flask. More distilled water was added to make up to the mark. It was then shaken vigorously for five minutes to ensure complete dissolution and homogeneity; this makes the stock solution of concentration 1000 mg/L. Different concentrations were prepared by serial dilution [
100 ml of (50 mg/L) dye solution was poured into a conical flask with adsorbent dosage 0.5 g and place inside a shaker (environmental orbital shaker, Deneb Instruments). The samples were withdrawn from the shaker at predetermined time intervals and the dye solution was separated from the adsorbent by the help of a micropipette.
The absorbance of the solution was then measured. The dye concentration was measured after 50, 100, 150, and 200, until the equilibrium was reached. To study the effects of initial pH of the solution on the adsorption process, 100 ml of 50 mg/L dye solution was poured into a conical flask with adsorbent dosage of 1 g. The pH of the dye solutions was adjusted with dilute HCl (0.05 N) or KOH (0.05 N) solution by using a pH meter (EUTECH Instrument, pH 510). 10 ml of dye solution was prepared taking dye and the pH of solution was changed from 3 to 10.
The adsorbent dosage was varied as 0.5, 1.0, 1.5, and 2.0 g/150ml. Effect of concentration 100 ml of dye solution was prepared in conical flask with dye concentration 50 mg/L and adsorbent dose (1 g/L) and place the shaker. The temperature was maintained at 20˚C. The final dye concentration readings were taken at 50, 100, 150, and 200. Dye concentration was estimated, spectrophotometrically, at the wavelength corresponding to maximum absorbance, λ max using a spectrophotometer (JASCO UV/Vis-550). The samples were withdrawn from the shaker at predetermined time intervals (30, 45, 60 and 120 min) and the dye solution was separated from the adsorbent by the help of a micropipette. The absorbance of the solution was then measured. The dye concentration was measured after 50, 100, 150 and 200, until the equilibrium was reached. The qe is expressed as
where, qe = amount of dye adsorbed per unit mass of adsorbent (mg/g), Co = initial dye concentration (mg/L), Ce = final dye concentration (mg/L), V = volume of dye solution and M = mass of adsorbent (g/L).
The FTIR spectra of SALC were taken before and after the adsorption of MB to ascertain the possible involvement of the functional groups on the surface of SALC in the adsorption of MB (
Plates 1(a) and (b) shows the SEM micrographs of SALC samples before and after dye adsorption. The SALC exhibits a caves-like, uneven and rough surface morphology. The surface of dye-loaded adsorbent, however, shows that the surface of SALC is covered with dye molecules: (a) fresh SALC and (b) dye adsorbed SALC.
The pH of the dye solution plays an important role in the whole adsorption process and particularly on the adsorption capacity [
MB dye was studied at different initial dye concentrations (50 - 200 mg∙L−1) at room temperature. The dye uptake was found to increase with an increase in pH (
thus making (H+) ions compete effectively with cationic dyes causing a decrease in the amount of dye adsorbed [
The adsorption of MB dye at initial concentration of 50 mg∙L−1was studied at different contact time (30 - 120 min). The dye adsorption uptake was increased as contact time increased, and reaches equilibrium at 60 minutes (
The solid/solution ratio is an important factor determining the capacity of adsorbent in a batch adsorption. The effect of adsorbent dosages on the percentage removal of MB dye has been shown in
It can be clearly seen that the removal of MB dye increased with increasing the amount of SALC. However the amounts of adsorbed dye per unit weight (Qe) of the SALC decreased with increasing the solid/solution ratio (
The effect of the initial dye concentration on the dye adsorption capacity was investigated in the concentration range of 50 - 200 mg/L−1 at room temperature without changing the initial pH of the medium. The results represented in
ions competing for the available sites on the surface of SALC was high, hence, resulting in higher MB adsorption capacity [
The adsorption isotherm indicates how the adsorption molecules distribute between the liquid phase and the solid phase when the adsorption process reaches an equilibrium state. The analysis of equilibrium adsorption data, by fitting them to different isotherm models, is an important step to find the suitable model that can be used for design purpose [
The linear form of Langmuir’s isotherm model plotted is given by the following equation.
where: Ce is the equilibrium concentration of the adsorbate (MB) (mg/L), Qo is the amount of adsorbate adsorbed by unit mass of adsorbate (mg/g), Qob are Langmuir constant related to monolayer adsorption capacity and affinity of adsorbent towards adsorbate respectively [
When Ce/Qo was plotted against Ce straight line with slope 1/Qo was obtained (
where: Qob is the Langmuir constants and Ce is the highest dye concentration (mg/L).
The value of RL indicates the type of the isotherm to be either unfavourable (RL > 1), linear (RL = 1), favourable (0 < RL < 1) or irreversible (RL = 0) (
The well-known logarithmic form of Freundlich model used in this is given by the following equation.
where: qe is the amount adsorbed at equilibrium (mg/g), Ce is the equilibrium concentration of the adsorbate (MB) and Kf and n are Freundlich constants; n given an indication of how favourable is the adsorption capacity of the adsorbent [
Kf can be defined as the adsorption or distribution coefficient and represents the quantity of methylene blue onto SALCS for a unit equilibrium concentration. The slope 1/n ranging between 0 and 1 is a measure of absorption intensity or surface heterogeneity, becoming more heterogeneous as its, value gets closer to zero [
The adsorption capacities of SALC were compared to previously reported works on the adsorption capacities
Langmuir isotherm constants | Freundlich isotherm constants | ||||
---|---|---|---|---|---|
Qo [(mg/g) (L/mg)] | b | R2 | 1/n | Kf [(mg/g) (L/mg)] | R2 |
19.84 | 0.548 | 0.986 | 0.751 | 1.111 | 0.989 |
Values of KR | Type of isotherm |
---|---|
KR > 1 | Unfavourable |
KR = 1 | Linear |
0< KR < 1 | Favourable |
KR = 0 | Irreversible |
Source: [
of various low-cost adsorbent. The experimental data of the present study was found to be higher than those of walnut bark (15.1 mg/g) and yellow passion fruit (16 mg/g) and lower than those of rice husk (4.59 mg/g), cherry saw dust (39 mg/g), sugarcane bagasse (34.2 mg/g) and banana peel (20.8 mg/g) (
It is important to be able to predict the rate at which contaminants is removed from aqueous solution in order to design adsorption treatment plant. In order to investigate the mechanism of adsorption and potential rate controlling steps such as mass transfer and chemical reaction, the kinetics of MB sorption onto SALC was investigated using two different models: the pseudo-first-order kinetic [
The rate constant of adsorption was determined from the pseudo-first-order equation given by
where: qe and qt are the amounts of methylene blue adsorbed (mg/g) at equilibrium and at time (min), respectively and K1 the rate constant of adsorption (2 h). Values of K1 were calculated from plots of
Sum of square of errors is a test of kinetic models. Beside the value of R2, the applicability of both kinetics models were verified through the sum of error squares (SSE, %). The adsorption kinetics of MB on adsorbent prepared from Lantana camara stem (SALC) was tested at different initial concentration. The validity of each
Adsorbents | Adsorption capacities (mg/g) | References |
---|---|---|
Banana peel | 20.80 | [ |
Cherry saw dust | 39.00 | [ |
Rice husk | 40.59 | [ |
Sugarcane bagasse | 34.20 | [ |
Walnut bark | 15.10 | [ |
Yellow passion fruit | 16.00 | [ |
Lantana camera stem | 19.84 | This work |
model was determined by the sum of error squares (SSE, %) given by;
where: N is the number of data points:
The higher the value of R2 and the lower the value of SSE, the better the goodness of the fit.
Lantana camara stem like other agricultural waste can be used in the treatment process of dyes in wastewater.
Initial conc. (mg/L) | Qe (mg/g) | First order kinetics model | SSE (%) | Second order kinetics model | SSE (%) | ||||
---|---|---|---|---|---|---|---|---|---|
K1 (min−1) | qecal (mg/g) | R2 | K2 (g/mg/mm) | qecal (mg/g) | R2 | ||||
50 | 12.34 | 0.077 | 13.52 | 0.98 | 0.60 | 0.0053 | 13.83 | 0.99 | 0.48 |
100 | 24.77 | 0.082 | 26.00 | 0.91 | 0.57 | 0.0026 | 27.49 | 0.99 | 0.95 |
150 | 37.00 | 0.061 | 37.12 | 0.98 | 0.04 | 0.0018 | 42.49 | 0.99 | 1.45 |
200 | 47.00 | 0.058 | 46.82 | 0.98 | 0.69 | 0.0012 | 55.25 | 0.99 | 1.98 |
The adsorption capacity is dependent on pH solution, contact time, adsorbent dosage and adsorbate concentra- tion. Maximum percentage MB removal (85%) was attained at 60 minutes. The adsorption capacity of SALC increased with the increase in pH and initial MB concentration. The Langmuir maximum adsorption capacity showed a slight increase. The Freundlich constant (n) revealed that the adsorption process was favourable and that the adsorption of MB into SALC was dominated by chemisorption. The kinetic modelling of adsorption of MB onto SALC followed the pseudo-second-order kinetic model. The value of the maximum adsorption capacity, Qo (19.84 mg/g) was comparable with the values observed for other adsorbents reported in the earlier studies. These preliminary studies suggest that adsorbent prepared from Lantana camara stem can be used effectively for the adsorbent of MB in wastewater.
The authors acknowledge the financial support received from Ladoke Akintola University of Technology, Ogbomoso, Nigeria, through Senate Research Grant, LAU/SRG/13/007.