Study On Electrosorption Of Phenol In Aqueous Solution Using A Plasma-Actived CNT/TiO₂ Electrode

In this research, The CNT/TiO₂ composite electrode was prepared by coating method, and then activated with radio frequency inductively coupled air-plasma. It was marked P-CNT/TiO₂ after modification. The preparation of the two electrodes was optimized, and it was found that the best ratio of TiO₂ in the process for preparing CNT/TiO₂ composite electrode was 10%; the suitable time of plasma modification for the composite electrode was 3min.The surface morphology of electrodes was observed by scanning electron microscopy?SEM?. Surface composition was analyzed by X-ray photoelectron spectroscopy?XPS?. The hydrophilic properties of the electrodes were characterized by contact angle measurements. And electrochemical properties of the electrodes were measured by cyclic voltammetry?CV?. Then the electrosorption experiment was conducted to assay the electrical removal capacity of phenol. The results showed that: Compared to CNT electrode, the pore ratio on the surface of the composite electrode increased after adding TiO₂. The carbon nanotubes was evenly attached by a great deal of white particle TiO₂. The contact angle decreased from 90±0.6° to 50±0.8°, hydrophilic of the electrode was enhanced. The specific capacitance increase by 38%, its electrochemical performance was improved. And the adsorption amount of phenol increased by 32%. Further studies showed:the plasma-modified P-CNT/TiO₂ electrode had a more massive hole structure, the surface contents of TiO₂ and oxygen containing functional groups on the surface of the electrode increases after activation. Its hydrophilic and electrochemical properties were also improved. The contact angle decreased from 50±0.6° to 20±0.8°, its capacitance values increased by 54%. And the adsorption amount of phenol decreased by 45%.The operation parameters of electrosorption apparatus were optimized. The effect of voltage, electrode distance, velocity of flow, number of electrodes on the removal of phenol were studied. It was found that the adsorption capacity of phenol increased with the increase of the voltage. It had the maximum adsorbances when the distance between electrodes and velocity of flow were 3mm and 4mL/min, respectively. With the increase number of electrode, the removal efficiency of phenol increased while the adsorption capacity decreased.The effect of water condition on the electrosorption of phenol was investigated. The results showed that:the adsorption capacity of phenol increased with the increase of influent concentration of phenol solution.The low content of salt can promote the electrosorption of phenol while the high concentration had a inhibitory function. The optimal concentration of Na2SO4 is 0.05mol/L for this research. The adsorbance of phenol increased when the temperature increased.The adsorption mechanism of CNT/TiO₂ and P-CNT/TiO₂ electrodes on the removal of phenol was investigated with adsorption kinetics and isotherm models. It was found that the adsorption process of phenol removal by the two kinds of electrodes well fitted the pseudo-second-order kinetic and Langmuir isotherm models. The adsorption process was dominated by electrosorption and accompanied by physical adsorption. The adsorption type is single molecule layer adsorption.The regeneration effect of CNT/TiO₂ and P-CNT/TiO₂ electrodes was studied by using electrochemical desorption. After the first time of regeneration, its regeneration of the two electrodes were 72.68% and 75.81%. And it remained stable after 6 circulation of adsorption/desorption which indicated that they had good recycling properties. On one hand, it is beneficial to the reuse of phenol and utilization of wastewater. On the other hand, it is conductive to the recovery of electrode materials and the reduction of the cost of water treatment. So the prepared CNT/TiO₂ composite electrode and the use of plasma activation to modify electrode material have a broad application prospect in the field of water treatment.