Research Of Removal Of Triclosan In Aqueous Solution By The Synchronal Action Of Dielectric Barrier Discharge Plasma And Active Carbon Fibers

As a kind of pharmaceuticals and personal care products(PPCPs),triclosan(TCS)is a broad-spectrum antimicrobial agent in many household and personal care products,including soaps,deodorants,toothpastes and various plastic products.As an emerging environmental contaminant,TCS has raised a great concern because it can affect microorganisms in environmental systems as a biologically active compound that specifically targets bacteria.TCS is also a typical endocrine disruptor that can cause adverse effects in animals,such as inducing oxidative stress and decreasing cellular thiol content in rat thymocytes through increasing intracellular Zn2+concentrations.Furthermore,when discharged into surface waters via wastewater,TCS and chlorinated TCS derivatives(CTDs,forming during disinfection with chlorine)will react photochemically to form polychlorinated dioxins,which threaten human health and survival of other organisms.But TCS is ineffectively removed by most commonly used water treatment technologies and the ecosystem of natural environment.Thus,an effective technology attempted for TCS removal has been on the agenda.The removal of triclosan(TCS)in aqueous solution by dielectric barrier discharge plasma with activated carbon fibers(ACFs)was investigated in this paper and the relevant experimental studies were carried out.Dielectric barrier discharge plasma and ACFs coexisted in a planar dielectric barrier discharge plasma reactor,which could synchronously achieve degradation and adsorption of TCS,modification and in situ regeneration of ACFs,enhancing the effect of recycling of ACFs.The properties variation of ACFs under the condition of water medium before and after modification by dielectric barrier discharge plasma were characterized by SEM,BET,XPS and Boehm analysis.Various processing parameters affecting the synergetic removal effect of TCS in this integrative device were also investigated,such as discharge power,initial solution concentration,liquid circulation velocity and thickness of ACFs,and the recycling of ACFs was investigated carefully.The changes of UV-Vis absorption spectra,pH and TOC were analyzed.Furthermore,the degradation intermediates of TCS were identified using liquid chromatography-hybrid quadrupole time-of-flight mass spectrometry(LC-QTOF-MS)API5600 Triple TOFTM combined with theoretical calculation of Gaussian 09 software,and the degradation mechanism and pathway were got accordingly.The results indicated that there existed excellent synchronous collaborative removal effects for TCS between dielectric barrier discharge plasma and ACFs in this device.In the presence of water medium,ACFs could be modified by dielectric barrier discharge plasma,causing the increase of surface oxygen-containing functional groups,enhancing the adsorption and catalytic capacity.And ACFs could realize in situ regeneration and had a very good effect of recycling.The removal efficiency of 120 mL TCS with initial concentration of 10 mg/L could reach 93.2%with 1 mm thick ACFs in 18 min under flow rate of 45mL/min at input power of 80 W,compared with 85.1%by single dielectric barrier discharge plasma.Meanwhile,the removal rate of TOC increased from 12.1%at pH 6.26 to 24.5%at pH 3.50.Furthermore,the action that ACFs were added into this dielectric barrier discharge plasma device,could ameliorate the effect of dielectric barrier discharge and improve the TCS removal efficiency and the energy efficiency by dielectric barrier discharge plasma,especially when dielectric barrier discharge plasma treating TCS solution at high flow rates or at low initial concentrations.The possible degradation pathway of TCS by dielectric barrier discharge plasma was inferred based on 10 intermediates detected by LC-QTOF-MS combined with theoretical calculation of Gaussian 09 software.The changes of concentration of TCS and the 10 intermediates were observed by the mass spectrum analysis.Meanwhile some isomerides were found and distinguished by Octanol-water partition coefficient(Kow)and molecular polarity.The main degradation mechanism of TCS by dielectric barrier discharge plasma involved a series of processes,such as bond breaking,dechlorination-hydroxylation,hydroxylation and oxidative opening of the aromatic ring;ultimately,carboxylic acid and inorganic species were also formed.