3.8.1 UV-Vis spectrophotometer
The change in phenol concentration in each photodegraded solution was monitored by ultraviolet-visible (UV-Vis) spectrophotometer. The maximum absorbance of phenol was measured at respective λmax of 269 nm in UV-Vis spectrometer (Perkin Elmer Lambda 45) through two Hellma precision cells made of quartz Suprasil. The percentage of degradation of phenol solution was calculated from the following equation [378]
Percentage degradation =
Where C0 the initial concentration of phenol solution ppm is, Ct is the concentration of phenol solution after irradiation and after selected time interval ppm.
3.8.1.1 Sample preparation
The initial concentration of the model pollutant of 100 ppm (phenol) was prepared as follows: exactly 0.1000 g of phenol was weighted and quantitatively transferred into a 1000 mL volumetric flask and brought to the calibration curve with Milli-Q-purified H2O. Different solutions of 50, 25, 10 and 5 ppm were prepared by serial dilution of a 100 ppm initial concentration of phenol. Each of these solutions was separately used to carry out photocatalysis experiments.
3.8.1.2 UV-Vis analysis
The both two cells washed and filled with deionized water and kept in the compartment in the UV instrument for a baseline set up using deionized water as a reference solution.
After setting up the baseline, one of the cells was removed and the other cell stayed in
3.8 Analytical methods 107 the machine as a reference. Washing and filling the removed cell with the sample of interest and putting it back into the UV compartment. The maximum absorbance of phenol was measured at respective λmax of 269 nm in UV-Vis spectrometer λ absorbance and other parameters could be obtained. To measure the concentration of these absorbance values, calibration curve of the standards solutions was prepared from (5-50 ppm) as it mentioned before.
3.8.2 Total organic carbon analyser (TOC)
TOC determines the carbon content present in water solution. To measure the carbon content, it is important to remove the inorganic carbon exits in the solution like carbonante (CO32ˉ), monohydrongencarbonate (HCO3ˉ), bicarbonate and dihydrogencarbonate (H2CO3), some drops of concentrated phosphoric acid (84%) are added to the solution to yield CO2 which degassed by running nitrogen from a cylinder.
The sample of interest is injected in a TOC Analyser (TOC-VCPH Shimadzu) equipped with an auto sampler (ASI-V Shimadzu), in which the organic molecules are totally oxidized at 850 °C in the presence of a Pt catalyst. The amount of CO2 liberated by the reaction is then determined by infrared spectrometry. Prior to injecting the samples into the instruments, the solutions were filtered through a syringe filter of 0.2 µm pore size to remove photocatalysts Nps.
3.8.3 Chemical oxygen demand (COD)
COD measures the quantity of oxygen equivalent used for the total oxidation of organic and mineral substances by excess of strong chemical oxidizing agent potassium dichromate in a mixture. The oxidation is carried out in an acid medium in the presence of the catalyst as silver sulphate; the oxidation could be performed for 2 h at 150 °C. It defines the total quantity of oxygen required for the degradation of organic compound to CO2 and H2O.
3.8.3.1 Colorimetric method for the measurement of COD
To determine the COD in phenol and its byproducts, samples were treated as follows: 2 mL of supernatant in a screw cap tube was amended with 0.05 g of mercury sulphate,
used to avoid the complexes and the interference of the chloride ion. 0.5 mL of 1.0 N potassium dichromate used in excess strong oxidizing agent and 2.5 mL of concentrated sulphuric acid (contained 5.5 mg silver sulphate per gram as a catalyst). The mixture in the tube refluxed for 2 h at 150 °C in a heater model DRB 200. After cooling, COD was determined by absorbance using Hach Lange model DR-2000 spectrophotometer with λof 420 nm which shows directly the COD value. In order to use this method, samples should be diluted to bring them to the range of the standards in the tube.
3.9
High performance liquid chromatography (HPLC)Phenol photodegradation products were analysed by HPLC using a P580 high-precision pump from Dionex (Germering, Germany), which fulfilled the requirement for a measured mobile phase delivery rate. Analysis of HPLC was carried out by:
Injector port: Is a manual injector a Rheodyne (Cotati) 8125 valve fitted with a 20 μL loop. The selection of the loop is important according to the size of the column and the concentration of the pollutants analysed. In addition, it allows a constant injected volume which is very important for the quantitative analysis.
Detector: Dionex UVD 170/340S diode array detector jointed with a recorder to show the chromatogram. The detector measures the absorption of the light by the contaminant at the outlet of the column, when it enters the detector. The detector can be operated by a constant λ which is fixed by the operator through the software. Deuterium lamp is used at λ varying from 190-350 nm.
Pump: Thermo Scientific Dionex Ultimate 3000 Series. The pump includes the isocratic or the gradient system for the solvent (mobile phase) programming. The pump can perform in two ways:
Isocratic run, which means with an elution of constant solvent composition been prepared outside the system during all time of analysis.
Gradient run, the system will prepare and mix with a variation of the solvent mixture, prepared by the operator through the machine.
Columns: The column in HPLC also called stationary phase. The analysis of phenol and its byproducts was carried out and separated using different C18 columns. Supelco:
3.9 High performance liquid chromatography (HPLC) 109 C18 column of (250 m × 4.6 mm), composed of spherical micro-particles (4.6 mm) of silica transplanted with alkyl chains of C18. The second column was Restek C18 column of (150 mm × 3.0 μm), also composed of spherical micro-particles (3.0 μm) of silica transplanted with alkyl chains. Phenomenex: A C18 monolithic column of (50 mm x 4.6 mm) all these columns were maintained at room temperature. The attaining and the conducting of chromatograms are achieved by the software called chromeleon 6.2.
3.9.1 HPLC analysis
At the beginning of the analysis time, the mixture to be separated was injected in the injector port connected to the column. The mixture was diluted in the mobile phase and from the injector port the mixture was continued its way to the column.
3.9.1.1 HPLC mobile phase preparation
The mobile phase for the HPLC separation was prepared by mixing methanol with water at a ratio of 45:55. In a 100 mL measuring cylinder, 45 mL of methanol was mixed with 55 mL of Milli-Q H2O later transferred into a 250 mL beaker with magnetic follower.
The beaker was placed on a stirrer and stirred slowly with a pH electrode inside model (Mettler Toledo). The mobile phase was adjusted to pH 3.0 by adding drops of 0.1 M H2SO4 through 5 mL syringe. The preparation of the acid was explained earlier in section 3.5.4. The mobile phase (solvent) was filtered through 0.2 µm vacuum filter model (Millipore xx1009020) and sonicated by (JAC ultra sonic 2010 (P)[CE] KODO) model technical research Co., Ltd. for 10 min. If the mobile phase is well selected then the components of the mixture are unequally retained during the movement through the column which would give an indication of the consistence of the baseline. If the baseline is not consistent, checking for leakages or adjusting system pressure is necessary. From this point a phenomenon called retention, so the components of the unknown moved slower than the mobile phase. After elution from the column, the eluent passed through a diode array detector jointed with a recorder and showed the chromatogram. The detector was set at 254 nm to determine phenol and its byproducts. The mobile phase passed through the column created a signal as a baseline on the recorder or the integrator without the analyte and without stop. Phenol and its byproducts if separated would also
show the exit of each separated constituent and its peak time (retention time) is recorded on the detector. Photodegraded phenol and control samples were eluted at a flow rate of 1 mL/min or sometimes less depends on the column size. All the solvents were sonicated and filtered through vacuum system as it mentioned before.