MATERIALS AND METHODS
This chapter includes the materials and general methods implemented to carry out this work and which are not completely described through the research articles content.
3.1 Materials and Equipments
All the reagents used for this current investigation were of analytical grade (AR) obtained from different manufacturer: NaOH and HCl (Merck India Ltd.), 2,6-Dichlorophenol (Kem-Light Laboratories PVT. Ltd. Mumbai, India).
B. Apparatus and Equipments:
Standard test sieve (1.68 mm), glass bottles, pestle and mortar, weighing machine, pH/conductivity meter (Jenway 430 pH/cond.), petri dish, beakers, conical flasks, volumetric flasks (1000 ml, 100 ml capacity), 50 ml pycnometer, funnel, 1000 ml round and flat bottom flasks, measuring cylinders (10 ml, 100 ml, 1000 ml capacity), porcelain dish, electric oven, dessicator, stirrer, electric burner, water bath, electric muffle furnace, glass stoppered 250 ml erlenmenyer flasks, rubber stopper, mechanical shaker, centrifuge machine, filter papers, FT-IR spectrophotometer (Perkin-Elmer infrared spectrometer ASCII PEDS 1.60), UV spectrophotometer, IR-grade KBr in an agate mortar.
3.2 Collection and Preparation of Adsorbent Sample (Almond Nut Shells)
The common reagents used for the preparation and treatment of adsorbents are hydrochloric acid, phosphoric acid, sodium hydroxide and zinc chloride. But in this present study, the adsorbent was subjected to acid treatment using hydrochloric acid since it is an inexpensive and non-volatile agent compared to phosphoric acid, while sodium hydroxide was utilized for the alkali treatment preferred to zinc chloride which constitute problems of additional environmental contamination by zinc.
3.2.1 Collection of Almond Nut Shells Sample
In this work, the corky fibrous endocarp (nut) shells of the fruit (Almond) were collected from the premise of News Agency of Nigeria (NAN) National Headquarters, Central Business District Abuja-FCT (Plate 2).
Plate 2: Raw and Processed Almond (Terminalia catappa) nut shells
3.2.2 Preparation and Modification of Almond Nut Shells
Fruit seed shells of Almond (Terminalia catappa) were crushed using wooden mallet and thoroughly washed with double distilled water for several times to remove all the foreign matters, and sun dried for some days. Then the dried seed shells was homogenized to a fine powder using pestle and mortar, and the powdered particles were sieved to obtain a desired average particle size of 1.68 mm using standard test sieve (Plate 2). The modification process was carried out using 150 g of the powdered, sieved adsorbent which was pre-treated with chemical solvent to increase the 2, 6-dichlorophenol uptake efficiency. For this purpose, adsorbent was first treated by boiling in 0.1 N HCl for three hours. After decanting the solution, the residue was boiled again with 0.1 N NaOH for three hours. The treated sorbent was washed well several times with double distilled water. Later, it was soaked in water for sufficient time interval, to ensure swelling, as it would make more sorption sites available; and finally, the sorbent material was dried in the oven, after which it was stored in an air tight plastic container prior to use as an adsorbent. The chemically treated Terminalia catappa nut shell powder was used for further experiments and henceforth shall be denoted as MTCNS in the forthcoming discussions.
3.3 Preparation of Adsorbate (2,6-Dichlorophenol)
A stock solution was prepared by dissolving 1.0 g of 2,6- Dichlorophenol (DCP) in 1litre of sterilized de-ionized water. From this original stock solution, five test working solutions with various concentrations (100, 200, 300, 400, and 500 mg/l) were obtained by successive dilution with de-ionized distilled water (DDW). Before mixing the adsorbent, the pH of each 2,6-Dichlorophenol (DCP) solution was adjusted to the required value by 0.1 M NaOH or 0.1 M HCl solution (Agarry & Ogunleye, 2014).
3.4 Characterization of Modified Adsorbent
The procedures for physicochemical and surface characteristics of the modified adsorbent are compiled as follows:
3.4.1 pH and Conductivity
Approximately 1.0 gram of MTCNS (adsorbent) was weighed and transferred to 250 ml beaker. 30 ml of freshly boiled and cooled double distilled water (adjusted to pH 7.0) was added and heated to boiling. After 10 minutes, the solution was filtered and the first 15 ml of the hot filtrate was discarded. The remaining filtrate solution was cooled to room temperature. The pH and conductivity was determined using Jenway 430 pH/cond. Meter (Ademiluyi et al., 2008).
3.4.2 Moisture Content
Approximately 0.25 g of MTCNS (adsorbent) was weighed in petri dish and placed in an electric oven maintained at 383±5 K for about 2 hours. The dish was covered and cooled in desiccators and then weighed. Heating, cooling and weighing were repeated at 30 minutes intervals until the difference between two consecutives weighing was less than 5 mg (Abdul Halim et al., 2001).
Moisture Content (%)=((W-X))/W ×100 …3.1
where, W= Weight of the material (g)
X = Weight of the material after drying (g)
3.4.3 Bulk Density
The MTCNS (adsorbent) was placed in a 10 ml graduated measuring cylinder, tapped several times until constant volume obtained and then weighed. The bulk density was calculated as the ratio of the weight of MTCNS (adsorbent) to its volume and expressed in g/ml (Mudoga et al., 2007).
3.4.4 Specific Gravity
Approximately 2.5 g of MTCNS (adsorbent) was weighed and placed in a small porcelain dish, 25 ml of double distilled water was added and the content was heated to boil gently for 3 minutes to expel the air. After cooling in a water bath to 288 K, the sorbent suspension was transferred to 50 ml pycnometer and weighed (Wc). Later, the pycnometer was filled with double distilled water and weighed (Wb) (Agarry & Ogunleye, 2014).
Specific gravity= (Weight of MTCNS (adsorbent) (W_a))/(Volume of displaced water (V)) … 3.2
where,V= (W_a +W_b +W_c)/(Density of water)
Wa = Weight of MTCNS (adsorbent)
Wb = Weight of pycnometer with water
Wc = Weight of pycnometer with MTCNS (adsorbent) residue
3.4.5 Pore Volume
Approximately 2.0 g of MTCNS (adsorbent) was weighed and transferred completely into a 10 ml graduated measuring cylinder and its height in the cylinder was recorded. This was poured into a beaker containing 20 ml of deionized water and boiled for 5 minutes. The content in the beaker was filtered and measured. The pore volume of MTCNS was determined by dividing the increase in weight of the adsorbent by the density of water (Aneke & Okafor, 2005).
Porosity was determined by dividing the pore volume (Vp) of the MTCNS by its total volume (Vt) (Aneke & Okafor, 2005).s
Porosity (P_t)= (Pore Volume (V_p))/(Total Volume (V_t)) ×100 … 3.3
where, Vt = Vs + Vp and Vs = solid volume (ml)
3.4.7 Ash Content
Approximately 2.0 g of MTCNS (adsorbent) was weighed (Ws) and placed in a pre-weighed porcelain crucible (We). The crucible and it content was placed in an electric oven at 383±5 K for about 5 hours. The crucible was removed from the oven and the content was ignited in an electric muffle furnace at a temperature of 800 K for about 2 hours. The crucible was removed and cooled in a desiccators and then weighed (Wc). Heating, cooling and weighing was repeated at 30 minutes intervals until the difference between two consecutives weighing was less than 5.0 mg (Shetty & Rajkumar, 2009). The ash content was calculated as percentage by weight using the relation:
Ash Content (%)=(W_c-W_e)/W_s ×100 …3.4
3.4.8 FT-IR Spectra Analysis
Fourier transform infrared spectra analysis of MTCNS (adsorbent) sample was performed by using a Perkin-Elmer infrared spectrometer ASCII PEDS 1.60. This was carried out as a preliminary and qualitative analysis to determine the type of functional groups present in the sorbent that might have involved in the 2,6-dichlorophenol uptake. The MTCNS (adsorbent) was blended with IR-grade KBr in an agate mortar and pressed into pellets. The spectrum of MTCNS (adsorbent) was recorded within the range of 400 – 4000 cm-1.
3.5 Batch Mode Adsorption Studies
Adsorption experiments were carried out in batch mode at ambient temperature. The influence of various experimental parameters such as initial adsorbate concentration, pH, MTCNS (adsorbent) dosage and contact or exposure time on the adsorption efficiency of 2,6-DCP were conducted under optimized conditions. Only one of the parameters was changed at a time while others were maintained constant.
3.5.1 Adsorption Experiments
Adsorption equilibrium experiments were conducted in a set of glass-stoppered 250 ml Erlenmenyer flasks, where 100 ml of working volume with different initial concentrations (100, 200. 300, 400 and 500 mg l-1) of 2,6-DCP having a solution pH of 7 were added in these flasks. A weighed amount (2.0 g) of adsorbent (MTCNS) was added to the solution. The flasks were agitated at a constant speed of 150 rpm for 150 minutes in a temperature controlled water-bath shaker at 30 oC. Samples were collected from the flasks at predetermined time intervals of 30 minutes for analyzing the residual 2,6-DCP concentration in the solution. Prior to analysis, samples were centrifuged to separate adsorbent from the adsorbate and minimize interferences. At time t = 0 and equilibrium, the 2,6-DCP concentrations were determined using UV-spectrophotometer at an absorbance wavelength of 340 nm. Three replicate per sample were done and the average results are presented. The amount of adsorption at equilibrium, qe (mg/g) was calculated according to the expression (Crisafully et al., 2008):
q_e=(C_o-C_e )V/W ….3.5
where Co and Ce (mg/l) are the initial and final (equilibrium) concentrations of 2,6-DCP in aqueous solution. V (ml) is the volume of the aqueous solution and W (g) is the mass of dry adsorbent used.
3.5.2 Batch Adsorption Kinetic Studies
The procedures of kinetic studies were basically identical to those of batch equilibrium studies. The amount of 2,6-DCP sorbed at time t , qt was calculated according to Eq. (3.6) (Xun et al., 2007):
q_t=(C_o-C_t )V/W ….3.6
where Ct is the concentration of 2,6-DCP in aqueous solution at time t.
The percentage of 2,6-DCP removal was calculated using Eq. (3.7) (Hamad et al., 2011):
Removal Efficiency (%)= ((C_o-C_t ) 100)/C_o ….3.7
3.5.3 Effect of pH
The effect of pH on the amount of 2,6-DCP removal was analysed over the pH range from 2 to 10. In this study, 100 ml of 2,6-DCP solution 100 mg l-1 was taken in stoppered conical flask and agitated with 2.0 g of MTCNS (adsorbent) using a temperature controlled water-bath shaker at a constant speed of 150 rpm for 30 minutes at 30 oC. The samples were centrifuged, and the left out concentration in the supernatant solution were analysed using a UV spectrophotometer at an absorbance wavelength of 340 nm (Moyo et al., 2012).
3.5.4 Effect of Adsorbent Dosage
The effect of MTCNS (adsorbent) mass on the amount of removal of 2,6-DCP solution was obtained by contacting 100 ml of 2,6-DCP solution of initial concentration of 100 mg l-1 at the optimal pH of 7, with different weighed amount ranging from 2.0 g to 10 g. Each sample was then agitated in a temperature controlled water-bath shaker at a constant speed of 150 rpm for 30 minutes at 30 oC. The samples were then centrifuged and the concentrations were then analysed as before (Moyo et al., 2012).
3.5.5 Effect of Contact Time
The effect of contact time on the removal of 2,6-DCP was carried out at different intervals ranging from 30 – 150 minutes. In each case 100 ml of 2,6-DCP solution of initial concentration 100 mg l-1 was added to each of the conical flasks. Corresponding masses of approximately 2.0 g of MTCNS (adsorbent) were added to each of the flasks and the mixture agitated in a temperature controlled water-bath shaker at a constant speed of 150 rpm at 30 oC. After the stated time the samples were removed from the rotary shaker and centrifuged. The supernatant solution was then analysed using the UV spectrophotometer at an absorbance wavelength of 340 nm (Moyo et al., 2012).