Research on dye wastewater decoloration by pulsedischarge plasma combined with charcoal derived from spent tea leaves

Tiecheng Wang1,2,*,Guangzhou Qu1,2, Shuzhao Pei1,2, Dongli Liang1,2, Shibin Hu1,2

1College of Natural Resources and Environment, Northwest A&F University, Yangling, Shaanxi Province 712100, PR China

2Key Laboratory of Plant Nutrition and the Agri-environment in Northwest China, Ministry of Agriculture, Yangling, Shaanxi 712100, PR China

*Corresponding author: Tiecheng Wang

E-mail:

5Pages

Text S1-S2

4Figures

2 Tables

S1 Charcoal preparation and adsorption experiment

Waste tea leaves were boiled in deionized water for several times till the supernatant water became colorless, and the boiled tea leaves were dried in an oven at 60 0C. The dried tea leaves were grinded and sieved, and then the carbon precursor was obtained.

The carbon precursor was impregnated with 50% ZnCl2 solutions for 16 h, and then placed in a furnace at 300 0C for 90 min; after that, it was heated to 500 0C with 60 min holding time. The resulting carbon was boiled in 1% HCl solutions for 20 min, and washed with deionized water until the washing water was neutral. This resulting carbon was dried, and finally the charcoal was obtained.

For charcoal adsorption experiment, 50 mL solutions containing varying concentrations of MO dye was added to 250 mL flasks, and several amounts of charcoal was added to the solutions, and the solution wasagitated at 150 rpm on a shaker at 25 0C. Samples were collected at suitable time intervals and then analyzed for residual dye concentration. The amount of adsorbed MO per g of solid in the equilibrium (qe, mg g-1) was calculated using the following equation:

(1)

where C0 was the initial concentration of MO (mg L-1), Ce was the equilibrium concentration of MO in solution (mg L-1), V was the volume of the solution, and m was the mass of charcoal.

S2 Methods and analyses

The discharge voltage and current were measured using a Tektronix TDS2012 digital oscilloscope equipped with a Tektronix P6021 high voltage probe and a Tektronix A6021 current probe. The typical discharge voltage and current waveforms were shown in Fig. S1.

The decoloration of MOwas measured using a UV-Vis spectrophotometer (UV-1901). MO degradation intermediates were analyzed by GC-MS (6890-5973). Helium was used as carrier gas at flow rate of 1.2 mL/min. The temperature programfor GC oven with initial temperature 500C was held for 3 min, and increased to 2600C with the rate of 15 0C/min and held for 5 min. The massspectrum condition was: electron impact ionization 70 eV, electron multiplier voltage 420 V, ion source temperature 2200C, interface temperature 2500C, scan range 0-500 m/z, and selected ion monitoring mode. Aqueous ozone equivalent concentration (CO3) was detected using 50 mL KI solutions absorption as described by Suarasan et al (2002). H2O2 concentration was determined by a UV-Vis spectrophotometry at wavelength of 400 nm as described by Sellers (1980).FTIR (Nicolet NEXUS 470) and SEM (S-4800, Hitachi) were applied to characterize the morphology and structure of charcoal. MO adsorption process was modeled using adsorption kinetic models (pseudo-firstorder kinetic model,pseudo-secondorder kinetic model and intra-particle diffusion model) and isotherm models (Langmuir,Freundlich, and Temkin) (Goswami et al., 2014). Variouschemical functional groups oncharcoal surface were determined usingthe titration method of Boehm (Boehm, 2002).

Fig. S1Typical pulsed discharge voltage and current waveforms obtained in the experiment

Fig. S2 Changes of MO concentration with time at different charcoal concentrations

Fig. S3 Adsorption kinetics of MO on charcoal surface

Fig. S4 Total ion chromatogram of MO degradation intermediates by GC-MS

Table S1Values of kinetic parameters of various models for MO adsorption by charcoal

Model / Pseudo-firstorder kinetic model / Pseudo-secondorder kinetic model / Intra-particle diffusion model
Equation / ln(qe-qt)= lnqe- kt / t/qt=1/(kqe2)+ (1/qe)t / qt=kt1/2 +C
Parameter / R2= 0.9764
k = 0.21 min-1
qe= 60.3 mg g-1 / R2= 0.9994
k = 0.00355 min g mg-1
qe= 64.0 mg g-1 / R2= 0.8030
k = 3.59 mg g-1 min-0.5
C = 27.4 mg g-1
Fitted equation / qt= 60.3 (1-e-0.21t) / t/qt = 0.069 + 0.016 t / qt=3.59t1/2 +27.4

Table S2Values of isotherm parameters of various models for MO adsorption by charcoal

Model / Langmuir model / Freundlich model / Temkin model
Equation / ce/qe=1/(KLqm)+(1/qm)ce / logqe= logKf + 1/nlogCe / qe=BlnA + Blnce
Parameter / qm = 143.3 mg g-1
KL = 1.736 L mg-1
R2 = 0.9919 / Kf = 78.5 mg g-1
n= 3.96
R2 = 0.9989 / B = 20.53
A= 68.93
R2 =0.9908
Fitted equation / ce/qe= 0.007ce + 0.004 / logqe= 0.253logCe + 4.36 / qe=20.53lnce + 86.9

Reference

BoehmHP (2002)Surface oxides on carbon and their analysis: a critical assessment. Carbon 40: 145-149.

Goswami M, Borah L, Mahanta D, Phukan P (2014)Equilibrium modeling, kinetic and thermodynamic studies on the adsorption of Cr(VI) using activated carbon derived from matured tea leaves. JPorous Mater 21:1025-1034.

Sellers RM (1980)Spectrophotometric determination of hydrogen-peroxide using potassium titanium (IV) oxalate.Analyst 105:950-954.

Suarasan I, Ghizdavu L, Ghizdavu I, Budu S, Dascalescu L (2002) Experimental characterization of multi-point corona discharge devices for direct ozonization of liquids. J Electrostat 54:207-214.

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