Phenol Removal using Corona Discharge Plasma Combined with Porous Polyaniline Nanober

12 A contemporary design for a recirculated flow dual remediation system was successfully developed 13 for phenol remediation. The system involved Corona Discharge Plasma (CDP), accompanied by 14 Polyaniline Nanofiber (PANNFs) as a solid adsorbent. PANNFs was obtained using simple chemical 15 oxidation polymerization at room temperature. Different chemo-physical characterization techniques 16 were employed to examine the produced polyaniline such as Fourier Transform Infrared spectroscopy 17 (FT-IR), X-ray Diffraction (XRD), and Brunauer, Emmett, and Teller (BET) surface area analysis. 18 The primary purpose of the used PANNF powder is to facilitate the phenol degradation using plasma 19 by collecting the phenol molecules on the surface of PANNFs. The phenol removal percentage of 20 99% was attained at a treatment time of 60 min using the developed dual system. Finally, a slight 21 synergetic effect between the used two remediation processes, PANI as adsorbent and CDP treatment, 22 was approved. PANNFs existence in the remediation system also helps to save the consumed power 23 in degradation using CDP.

-3 - The experimental setup is shown in Fig. 1 is composed of two main parts, the electrical power supply 65 system, and non-thermal plasma-based reactor. First, the electrical power supply system consists of 66 three parts; DC battery, Pulsed Wide Modulation (PWM) switching circuit, and an ignition coil 67 (autotransformer). The DC battery is responsible for providing a DC voltage of 12 V to an electronic 68 switching circuit PWM. The output of the PWM circuit is a pulsed voltage directed to the ignition 69 coil, which in turn converts the low voltage to a high voltage of 15 KV. Voltage and current sensors 70 are placed after the ignition coil and connected to an oscilloscope to show the waveforms of the 71 voltage and current. High voltage generated is applied to the electrodes to produce the electrical 72 discharge between the high voltage electrode and the ground one which called Corona Discharge 73 Plasma as a type of Non-thermal Plasma technique for industrial wastewater treatment.  Second, the reactor consists of a high voltage pin electrode (7 pins) fixed over a rectangle vessel (21 79 * 7*10 cm), tube as a ground electrode, recirculating water pump, and circular reservoir placed over 80 a stirrer. The pins electrodes were fixed vertically 15 mm over the wastewater surface. The seven pins 81 have 1 mm in diameter, 30 mm in height, placed in a linear pattern 15 mm apart of each other's, and 82 connected to the high voltage cables. The ground stainless-steel tube was submerged in the liquid and 83 perforated to be used as an air inlet for wastewater agitation. At the reservoir, the contaminated water 84 (aqueous phenol solution) was mixed with PANI powder, stirred at 500 rpm for a certain time, and 85 then recirculated through the system at 150 mL/min using a submerged water pump (without 86 preventing water stirring). Air was pumped into the ground electrode tube using a compressor with a 87 uniform flow rate of 0.1 L/min. The air passed from the tube to the discharge region across the 88 wastewater vessel. Then, the air and the gases resulted from the phenol degradation passed the pipe 89 between the discharge region and the reservoir, before being released from the reservoir.  The APS solution was mixed with the aniline solution at once with continuous stirring at 1000 rpm 99 for 1 hr. The polymerization process was kept for 24 hours at room temperature. The precipitated 100 polymer powder was filtered, collected, and washed with 0.2 M of HCl, ethanol, methanol, and 101 distilled water then separated by centrifugation for 15 min at 5000 rpm. Then, the produced polymer 102 was dried overnight at 60 o C. 103

Characterization techniques 104
The FT-IR spectra and X-ray diffraction analysis of the produced PANI were measured using an IR 105 spectrometer (Vertex 70, Bruker Scientific Instruments, Germany) and LabX XRD-6100 (Shimadzu, 106 Japan), respectively. Scanning Electron Microscopy (SEM, JEOL JSM 6360LA, Japan) was 107 employed to show the produced morphology. Nitrogen adsorption/desorption isotherms at 77 K and 108 Brunauer-Emmett Teller (BET) surface area tests were conducted using a Belsorp Mini II (BEl Japan 109 Inc., Japan). The pore size distribution and the total pore volume were evaluated using the Barrett,110 Joyner, and Halenda (BJH) method. The classification of pores and isotherms standardized by The 111 International Union of Pure and Applied Chemistry (IUPAC) was used in this study. The phenol 112 concentration before and after the treatment process was measured using a UV spectrometer 113 (HITACHI U-3900). 114

Energy Consumption 116
A significant factor in identifying the feasibility of phenol degradation using the newly designed 117 system is the power consumption estimation for a fixed quantity of wastewater and treatment time. 118 The consumed energy consumed per unit volume (Ec) (J/L) is calculated using Eq. (2). 119 120 = * (2) 121 122 Where t is the treatment time (s), P is the power (W), and Vo is the solution volume (L).

129
Where Cf is the final phenol concentration (mg/L). 130

Energy yield for phenol remediation 131
The energy yield (G) (g/kWh) is defined as the amount of pollutant in grams could be decontaminated 132 when 1 kWh of powers is consumed. It could be calculated using the following relation, ( Where D% is the percentage of phenol removal, Co in (mg/L), P in (kW), and t (hour). 137 138 3 RESULTS AND DISCUSSION 139 PANNFs weight of (0, 0.05, 0.1, 0.15, 0.2, and 0.25 g) were mixed with 400 mL of phenol/water 140 solution with phenol initial concentration of (5, 10, 20, 40, 60, 80, and 100 mg/L). The mixtures were 141 stirred at 500 rpm continuously at room temperature. After a while, the mixture was recirculated by 142 a pump with a flow rate of 150 mL/min to the reactor and then exposed to the Corona Discharge 143 Plasma System (CDPS). The reactor was extra agitated with fresh air pumped into the system with a 144 flow rate of 0.1 L/min. Furthermore, a typical experiment was conducted using 0.25 g of PANNFs 145 alone without plasma to measure the proposed synergy effect between the two phenol removal 146 techniques. 1 mL of the solution was drawn After a time interval of 10 min, and the phenol 147 concentration was measured using a UV spectrophotometer (HITACHI U-3900) at a wavelength of 148 265 nm. The remediation efficiency RE of the dual system was calculated by: 149 % RE =(Co-Ct)/Co *100 (1) 150 151 Where Co and Ct are the initial phenol concentration [mg/L] and the concentration at time t, 152 respectively. 153

Morphology of PANI 155
The morphology of the prepared PANI was observed by SEM. Figure 3a showed that nanofibers were 156 obtained with an average diameter of 40 nm. Furthermore, it was noticed that the fibers were directed 157 in one direction with a rough surface. The rough surface may help increase the surface area which 158 plays a crucial role in the adsorption process.  The band at 1379 cm -1 was attributed to the ‫‪N‬ــــ‪C‬‬ stretching vibration of the secondary aromatic 175 amine. The peak at 695 cm -1 is accompanied by the aromatic ‫‪H‬ــــ‪C‬‬ out-of-plane bending vibrations. 176 The band at 1203 cm -1 corresponds to N=Q=N, where Q represents the quinoid unit. The band at 881 177 cm -1 is associated with ‫‪C‬ــــ‪C‬‬ and ‫‪H‬ــــ‪C‬‬ for the benzenoid unit.

Non-thermal plasma system characterization 185
The non-thermal plasma system was characterized by measuring the pulsed high voltage obtained 186 from the ignition coil. The waveform of the high voltage and corona current, from the ignition coil to 187 the remediation system, were measured by using a high voltage probe (Tektronix P6015A) and a 188 current probe (Tektronix A6021), respectively. A digital storage oscilloscope (Tektronix TDS2014) 189 was also used to display the waveforms. As shown in Fig. 4

222
The percentage removal of phenol using both removal techniques was always slightly more than the 223 summation of the PANNFs and plasma alone systems. Accordingly, it could be concluded that there 224 is a slight synergy effect between the two remediation systems. The plasma may affect the PANNFs 225 surface by breaking the bond between the PANI chains and the chlorine atom, which may, in turn, 226 increase the porosity or surface area of PANI.
Energy yield and EE/O for the phenol degradation process were shown in Fig. 6 and 7. polyaniline chains, which may help increase the phenol absorption. Based on Fig. 7, it was observed 239 that the EE/O decreased with the increase of PANNFs dosage. This may be because the system must 240 remove much more phenol when the initial concentration was high. Also, releasing chlorine ions 241 (widely used in water purification) may help purify the water. 242 243

Effect of initial phenol concentration 244 245
To investigate the effect of the initial concentration of phenol on the overall degradation process, the 246 initial concentration of phenol was changed as (5, 10, 20, 40, 60, 80, and 100 mg/L) and a fixed 247 amount (0.2 g) of PANNFs was employed. Figure 8

259
The energy yield for degradation was shown in Fig. 9. It was observed that higher energy yield 260 required with the higher phenol initial concentration. The used corona discharge plasma directly 261 degrades the phenol molecules. As it is known, phenol molecule includes a phenyl ring (−C6H5) 262 linked to a hydroxyl group (−OH), so the direct plasma treatment releases the hydroxyl group. 263 Accordingly, the more phenol concentration leads to more hydroxyl molecules released, i.e. more 264

Phenol initial concentration
Generally, ozone is generated in a two-steps process (Eqs. 5 and 6) when non-thermal plasma is 276 applied to air, as a process gas, at atmospheric pressure and room temperature. These two steps are 277 electrons utilization for O2 molecules dissociation and described as follows (Wang et al. 2008

Degradation mechanism 292
Phenol degradation using plasma may follow several mechanisms. One of the proposed mechanisms 293 for the phenol degradation process is the formation of carbon dioxide and water passing some

301
Furthermore, the redox reaction of hydroquinone produced 1,4-benzoquinone while the unstable 302 catechol transformed into 1,2-benzoquinone. A different mechanism was also proposed to describe 303 the degradation process using the ‫٭‬ OH group. In this second case, aliphatic by-products (formic acid, 304 oxalic acid, and aldehydes, etc.) were produced by the continuous oxidation of the aromatic rings. All 305 the produced by-products were mineralized into carbon dioxide and water at the end of reactions. 306 These two mechanisms are illustrated in Fig. 11. 307 308 4 Conclusion 309 A dual remediation system utilizes two different removal techniques for phenol degradation; non-310 thermal plasma accompanied by adsorption of phenol onto the surface of polyaniline nanofiber 311 PANNFs was designed. Upon the results, the prepared polyaniline showed a nanofibrous structure 312 with fibers of an average diameter of 40 nm and a surface area of 26.42 m 2 /g. The phenol degradation 313 efficiency of 92 % was obtained in 60 min when plasma treatment was used alone, while 98 % phenol 314 was removed when 0.25 g of PANNFs was employed (20 mg/L initial phenol concentration). 315 Furthermore, the dual remediation system lowered the consumed energy by 30 % (according to the 316 EE/O calculations). Generally, a slight synergistic effect between the non-thermal plasma oxidation 317 and PANI adsorption techniques was recorded. PANI surface captured the phenol molecules and may 318 make it easy for plasma to degrade the collected phenol molecules instead of scattered molecules. 319