Adsorbent Preparation And Characterization
2.2 Characterization of adsorbents
which is an iron oxide hydroxide adsorbent, was generated by homogenous hydrolysis ofFe2
SO4
3.nH2O using urea as a neutral agent. After dissolving about 12.5 g ofFe2
SO4
3.5H2O in 250 mL of distilled water, the solution was preheated at about 70°C and slowly stirred for 10 min. 5 mL of the slurry containing the fresh nanomagnetite particles was added to the solution and 250 mL of 5M urea solution was added drop-wise for about 2–4 hrs into the solution. When precipitating of crystals begun, the color of the solution was changed from red to brownish yellow and the reaction was continued until half of the initial solution was vaporized. After solid–liquid separation, solid part was rinsed for removal of impurities. Then the yielded material was dried below 40°C. The dried material is now ready for fluoride adsorption.and Langmuir surface area, BJH adsorption and desorption, pore size distribution, t- plot, total pore volume and more were obtained from the adsorption isotherm.
X-ray powder diffraction (XRD)
X-ray powder diffraction (XRD) is a rapid analytical technique primarily used for phase identification of a crystalline material and can provide information on unit cell dimensions. The structural analysis of adsorbents was recorded using XRD(D8 ADVANCE, Bruker Axs). Powder X-ray diffraction of the adsorbents were recorded by a diffractometer operating with a Cu Kα radiation source and nano bragg mode. The XRD analysis result is recorded from 5° to 90° with a step increase rate of 0.05o per second.
The spectrum of the analyzed adsorbents showed broad and diffuse peaks. Therefore, the identification of peaks with such broad humps is a well known confirmed characteristic of phases which are amorphous or poorly crystalline in nature.
Scanning electron microscopy (SEM) and energy dispersive X-Ray (EDX) The morphology of the adsorbents were analyzed by SEM, whereas elemental information of the adsorbents were recorded using EDX. Furthermore, it is mention worthy that before SEM analysis the sample was finely grinded and coated with the Au inside a plasma chamber operated under vacuum for 135 seconds with a leakage current of 4 mA. This was done to ensure the less possibility of charging during the analysis.
Sample was analyzed under the application of the probe current of 94 pA and at different magnifications with the primary electron hitting the sample with energy of 10 kV – 15 kV. EDX is an integrated part of the scanning electron microscopy where energy
dispersion according to the element was calibrated with a standard Co (cobalt) sample before the analysis.
Fourier transform infrared spectroscopy (FTIR)
Fourier transform infrared spectroscopy (FTIR, Make: Perkin Elmer, USA, Model: LR 64912C) was used to analyze the organic functional groups of the adsorbent.
The adsorbent was mixed with potassium bromide properly and pressed under 5 Ton weight for 10 seconds to prepare the pellet necessary for analysis. Furthermore, the pellet was subjected to the Infrared spectra and scans were recorded with wave numbers ranging from 4000 to 450 cm-1. Different peaks at different wave numbers were leveled and matched with the standard data available for certain identified bond stretching. Some peaks were not been identified due to the lack of standard data related to our work.
Nonetheless, the available data well matched with the experimental results which are presented in this chapter.
Laser particle size analyzer (LPSA)
The particle size distribution of adsorbents was evaluated using a laser particle size analyzer (Malvern, Mastersizer 2000, UK). Laser-diffraction-size analysis is based on the principle that particles of a given size diffract light through a given angle, the angle increasing with decreasing size. A narrow beam of monochromatic light from a He- Ne laser, λ = 633 nm, is passed through a suspension and the diffracted light is focused onto a detector. This senses the angular distribution of scattered light energy. A lens placed between the illuminated sample with the detector at its focal point focuses the undiffracted light to a point at the center and leaves only the surrounding diffraction
pattern, which does not vary with particle movement. Thus, a stream of particles was passed through the beam to generate a stable diffraction pattern and the optimized particle size distribution plot was obtained and stored in an online computer.
Vibrating sample magnetometer (VSM)
The magnetic behaviour of the adsorbent was detected by VSM (Lakeshore 7410).
A vibrating sample magnetometer or VSM is a scientific instrument that measures magnetic properties of a sample. A sample is placed inside a uniform magnetic field to magnetize the sample. The sample is then physically vibrated sinusoidally, typically through the use of a piezoelectric material. The induced voltage in the pickup coil is proportional to the sample's magnetic moment, but does not depend on the strength of the applied magnetic field. In a typical setup, the induced voltage is measured through the use of a lock-in amplifier using the piezoelectric signal as its reference signal. By measuring in the field of an external electromagnet, the hysteresis curve of the adsorbent material is obtained.
Zero point charge (pHZPC)
The zero point charge (pHZPC) of adsorbent describes the pH value at which the surface charge of the adsorbent is zero. This is an important property of adsorbents. The pHZPC used for adsorption experiment was determined for all the four adsorbents by using solid to liquid ratio of 1:1000. For this, 0.1 g of adsorbent was added to 100 mL of 0.01M NaCl solution with varying pH from 2 to 12 and stirred for 48 hrs. The suspensions were filtered through whatmann filter paper and the final pH values were measured again. The
final pH of the solution was plotted against initial pH and the value of pHZPC was determined separately for all the adsorbents considered in this study.