Supporting Information

Supporting Information

Multifunctional Gas-spinning Hierarchical

Architecture: A Robust and Efficient

Nanofiber Membrane for Simultaneous Air

and Water Contaminant Remediation

Dan Lv^a‡, Guosheng Tang^a‡, Long Chen^a, Mengjie Zhang^a, Jiaxin Cui^a, Ranhua Xiong^b*, Chaobo Huang^ac*

aJoint Laboratory of Advanced Biomedical Technology (NFU-UGent), College of Chemical Engineering, Nanjing Forestry University (NFU), Nanjing 210037, P. R. China

bLab General Biochemistry & Physical Pharmacy, Department of Pharmaceutics, Ghent University, Gent 9000, Belgium

cLaboratory of Biopolymer based Functional Materials, Nanjing Forestry University, Nanjing, 210037, P. R. China

‡These authors contributed equally to this work.

Email: [email protected]

Air filtration

The air filtration performance, including filtration efficiency and pressure drop of the Fe3O4@PAN/CS composite nanofiber membranes for oily (Di-Ethyl-Hexyl-Sebacat, DEHS) particulates and non-oily (NaCl) particulates with different sizes (0.3, 0.5, 1, 3, 5, 10 μm) were tested. The air flow in our experiment was set as 85 L min^-1 according to the United States standards stated in the National Institute for Occupational Safety and Health (NIOSH) as a particulate filtering facepiece respirator (FFR) (NIOSH 42CFR-84) and the Chinese standards stated in GB 19083-2010, each membrane was tested three times. The resulting fiber membrane was subjected to a cycle test of 50 cycles to evaluate the durability and reusability of the Fe3O4@PAN/CS composite nanofiber membrane. DEHS and NaCl aqueous solution (2 wt%) was respectively employed to generate the DEHS and NaCl aerosol particles with diameters ranging from 0.3 to10 µm using the atomizer. The particle counts and size distributions can be measured by the laser condensation particle counter. The pressure drop over the upstream and downstream sides of the membrane was measured by a flow gauge and two electronic pressure transmitters, as shown in Figure S2, Electronic Supplementary Information. The removal efficiency can be calculated by detecting the airborne particles in the upstream and downstream of the air flow, which could be calculated from the Eq (1)

^{= 1 ―ε1}

ε₂ (1)

where η is the removal efficiency of the membrane, ε1 and ε2 represent the quantities of aerosol particles in the downstream and upstream of the filter, respectively. The quality factor (QF), a widely used parameter to synthetic evaluate the filtration performance of the filters, was calculated by the Eq (2)

𝑄𝐹 = ―^{𝑙𝑛(1 ―)}

^𝑃 (2) where η is the removal efficiency of the membrane and Δp is the pressure drop over the filtration membrane.

Antibiotic adsorption

The TC solution with a concentration of 25-250 mg L^-1 at 100 mL and a composite fiber membrane with a mass of about 500 mg were added to the brown bottle and shaken at 150 rpm and 25 °C until the equilibrium was established. After the adsorption is completed, TC solution was filtered by a 0.45 μm membrane filters and the TC concentration was further analyzed according to the standard curve.

To investigate the effect of pH on the adsorption of TC, the tetracycline solution pH was adjusted and maintained at 2−11 by 0.1 M HCl and 0.1 M NaOH solution. The initial concentration of TC was kept at 25 mg L^-1. The experiments were conducted in duplicate to ensure the reliability of the results. To investigate the adsorption capacity of the Fe3O4@PAN/CS adsorbent, Fe3O4@PAN/CS composite NFs were added to the TC solutions with initial concentration varying from 10 to 250 mg L^-1. Solution pH was

initially adjusted to 6.00 ± 0.05 and maintained during the isotherm experiment. The equilibrium adsorption amounts of TC were calculated by Eq (3),

𝑞_𝑒=^{(𝐶0― 𝐶𝑒)𝑉}

𝑚 (3) where qe (mg g^-1) is the amount of TC adsorbed at equilibrium, C0 (mg L^-1) is the initial concentration of tetracycline hydrochloride solution, Ce (mg L^-1) is the equilibrium concentration of tetracycline solution after reaching adsorption equilibrium, V (L) is the volume of TC solution, m (g) is the mass quality of the Fe3O4@PAN/CS composite membrane. In order to obtain more accurate test data, each test was repeated three times.

The operation procedure in the adsorption kinetics experiment was the same as that of the equilibrium adsorption test. A 500 mg of the composite Fe3O4@PAN/CS nanofiber membrane was added to 100 mL of TC solution with an initial concentration of 25 mg L^-1, and the initial pH was designed at 6.00 ± 0.05. The tetracycline solution of about 1.5 mL was extracted at predetermined time intervals and filtered, and the absorbance of TC was tested to determine the TC concertation. The amount of tetracycline adsorbed at each specific time was calculated according to Eq (4)

𝑞_𝑡=^{(𝐶0― 𝐶𝑡)𝑉}

𝑚 (4) Where Ct (mg L^-1) and qt (mg g⁻¹) represents the tetracycline concentration and adsorption capacity of tetracycline at time t, respectively.

The TC adsorption kinetics were investigated by the commonly used pseudo-first- order and pseudo-second-order kinetics models The detailed formulas are respectively given by Eq (5) and Eq (6)

𝑞_𝑡= 𝑞_𝑒×

(

)

𝑞_𝑡= ^𝑞

2𝑒^𝐾2^𝑡

1 + 𝑞_𝑒𝐾₂𝑡 (6) Where k1 and k2 (g mg⁻¹ h⁻¹) are the equilibrium rate constant associated of pseudo- first-order and pseudo-second-order sorption, respectively, qt and qe (mg g⁻¹) are the amount of TC adsorbed at time t and equilibrium, respectively.

Both Langmuir isotherm model and Freundlich isotherm model was applied to analyse the adsorption process, detailed formulas are presented in Eq (7) and Eq (8).

𝑞_𝑒=^{𝐾𝐿𝑞𝑚𝑎𝑥𝐶𝑒}

1 + 𝐾_𝐿𝐶_𝑒 (7) 𝑞_𝑒= 𝐾_𝑓𝐶^1/𝑛_𝑒 (8) Where Ce (mg L⁻¹) and qe (mg g⁻¹) is the concentration and adsorption capacity of TC at equilibrium, respectively. qmax (mg g⁻¹) is the maximum adsorption capacity of the monolayer adsorbent surface according to Langmuir isotherm, n is the Freundlich linearity index, KL and Kf is the adsorption constant of Langmuir and Freundlich isotherm, respectively.

Oil water separation

To evaluate the oil-water separation performance of the composite nanofibrous membrane, a mixture of oil (n-hexane) and water was selected and further separated by

the designed composite membrane to characterize the oil-water separation performance of the Fe3O4@PAN/CS fibrous membrane, including the separation flow rate and separation efficiency. The oil and water were respectively dyed with Oil Red O and Methyl blue in advance, and then 20 mL of oil-water mixture of the dyed oil and water mixed in equal volume (1/1, v/v) was obtained by ultrasonic vibration. Since the interface of the composite nanofiber membrane was superhydrophilic, the oil was trapped in the upper glass tube, while the water easily penetrated the composite fiber membrane under gravity, and further collected by the beaker through the glass tube below, thus, realized the separation for oil-water mixture under gravity. The separation flux was calculated based on the complete oil-water separated time for multiple times, which could be calculated from Eq (9)

𝐹 = ^𝑉

𝐴∆𝑡 (9) Where V is the volume of the permeate phase, here it refers to the blue water as shown in Figure 10c. A is the effective contact area of the membrane and the mixture, and ∆t is the time required for the completion of the separation process. The oil-water separation efficiency of the composite membrane was calculated by detecting the weight of the original water in oil-water mixture and the separated water, which was calculated from Eq (10)

§ = ^𝑀

𝑀₀× 100% (10) where § is the separation efficiency, M and M0 is the weight of the water after the separation and the initial weight prior to the separation.

Figure S1. Illustration of the gas-spinning setup. (a) schematic presentation of the preparation of the membranes gas-spinning. (b) construction of the core-shell needle. Figure was created by Guosheng Tang.

Filtration measurement of the fibrous membrane

The filtration performance of the composite membranes was evaluated by the automated LZC-K1 filter tester (Huada Filter Technology Co., Ltd., China) under ambient temperature of 25 ℃ and humidity of 50%, the optical photograph of the tester was presented in Figure S1 (a) and the work mechanism are illustrated in Figure S1 (b). NaCl and Di-Ethyl-Hexyl-Sebacat (DEHS) aqueous solution (2 wt%) was employed to respectively generate the NaCl and DEHS aerosol particles with diameters ranging from 0.3 µm to10 µm using the QRJ-1 NaCl atomizer.¹ The particle counts and size distributions can be measured by the BCJ-1K laser condensation particle counter based on the light scattering method. During the filtration test, the composite membrane (10

× 10 cm² effective area) was clamped by the holder, then 300,000-500,000 NaCl or DEHS particles were charge neutralized by electrostatic neutralization device and delivered through the membrane steadily and uniformly. The pressure drop in the upstream and downstream of the filter could be tested by two electronic pressure transducers. The removal efficiency can be calculated by detecting the number of airborne particles in the upstream and downstream of the airflow, which could be calculated from the equation η = 1−ε1/ε2, where ε1 and ε2 represented the quantities of aerosol in the downstream and upstream of the filter, respectively. The test equipment for the evaluation of filtration efficiency could accurately determine the values up to three decimal places.²

Figure S2. (a) Optical photograph and (b) schematic diagram of the tester for evaluating the filtration performance of air filters.

Leaching test

Considering the final promising application may focus on wastewater treatment, the stability of the Fe3O4 NPs loaded composite membrane and possible secondary pollution in aqueous solution was evaluated, leaching tests were carried out. A sample of composite membrane (1 and 2 wt% Fe3O4, 0.2 g) was immersed in 20 ml of distilled water and gently shook in a water-bath shaker (25 °C, 200 rpm) for various time periods. After shaking, the suspensions were filtered. The filtrate was analyzed by inductively coupled plasma atomic emission spectroscopy (ICP-AES) in order to study the leached quantity of the Fe3O4 nanoparticles into the water. The vigorous agitation condition adopted for leaching test represented a more adverse condition that may not necessarily be experienced but is important to ensure the material is stable under any circumstance. The accepted concentrations of Fe3O4 (as Fe) in drinking water approved by World Health Organization (WHO) are 2 mg/l. As shown in Table S1, the concentrations of Fe were <0.005 to 32.180 μg/L between 0 and 48 h. The obtained results indicate that the Fe3O4 loaded materials do not pose any danger for drinking water treatment since the leached metals were below the maximum allowable concentrations. The obtained ICP measurement results indicate that the concentrations of leached metals were relatively low after continuously shaking which can be attributed to the good attachment of both Fe3O4 nanoparticles and the nanofibers.

Table S1. Leaching test results of Fe3O4 nanoparticles. (μg/L)

N.D. stands for Not Detectable.

Samples 0 min 1 h 12 h 24 h 48 h

PAN N.D. N.D. N.D. N.D. N.D.

Fe3O4@PAN <0.005 8.305 19.110 33.675 34.625

Fe3O4@PAN/CS <0.005 6.215 15.410 30.335 32.180

Figure S3. SEM image and diameter distribution of the gas-spinning fibers. (a) PAN fibers, (b) Fe3O4@PAN fibers and (c) Fe3O4@PAN/CS fibers.

Figure S4. EDS spectrum of the Fe3O4@PAN/CS composite membrane.

Figure S5. Filtration efficiency of the Fe3O4@PAN/CS composite membrane varying in Fe3O4 dosage ratios. Experimental conditions: air flow = 85 L/min, basic weight = 53 g/m², T = 25℃.

Figure S6. Filtration performance of the Fe3O4@PAN/CS composite membrane varying in (a) basic weight and (b) air flow. The air flow was set as 85 L/min in (a) and the membrane basic weight was 53 g/m² in (b).

Table S2. Filtration performance comparison of this work and previous works

No. adsorbent Filtration

efficiency

Pressure drop

Particle types / sizes

Face velocity ref

1 PAN/SiO2 NPs filter 63.145 43.1 NaCl / 0.3-0.5 μm 85 L/min ³

2 PAN/SiO2 NPs filter 73.64 64.5 NaCl / 0.3-0.5 μm 85 L/min ³

3 cellulose acetate- nylon 80 40 NaCl / 0.6 μm 5.3 cm/s ⁴

4 cellulose–PVP membrane 86.4 17 Dusts / 0.3-0.5 μm NM ⁵

5 PA6–PTT membrane 95.825 55 DOP / 0.-0.4 μm 14.2 cm/s ⁶

6 three-layer PI membrane 94.83 136 NaCl / 0.3-1.0 μm 10 cm/s ⁷

7 PLA membrane 99.997 165.3 NaCl / 0.26 μm 14.1 cm/s ⁸

8 PTFE–nylon fabrics 96 >200 Cigarette smoke NM ⁹

9 wool keratin–PEO nanofiber 88 200 keratin powder 85L/min ¹⁰

10 PAN nanofiber 91 220 NaCl / 0.3μm 5.3cm/s; 32 L/min ¹¹

11 PAN nanofiber 95 250 NaCl / 0.3μm 5.3cm/s; 32 L/min ¹¹

12 PLA/PHB membrane 97 320 NaCl / 0.02-0.6 μm 5.3 cm/s ¹²

13 γ-alumina fibrous membrane 99.987 464.5 DOP / 0.3μm 85 L/min ¹³

14 PES/PA66 filtration media 99.999 510 NM /0.3μm 42 cm / s ¹⁴

15 Fe3O4@PAN/CS membrane >99.99% 48 NaCl&DEHS /

0.3μm ^{85 L/min}

This work The air flow in this work was set as 85 L/min, larger than most of the related

literatures.

OH NH₂

O O O

OH OH

CH₃

HO ^N

HO

H₃C CH₃

HCl H

H

Scheme S1. Chemical structure of tetracycline hydrochloride (TC).

Figure S7. TC adsorption capacities on the Fe3O4@PAN/CS composite membrane varying in Fe3O4 dosage ratios. Experimental conditions: initial TC concentration = 25 mg L^-1, pH = 6.00 ± 0.05, T = 25 ℃.

Figure S8. EDS spectra and EDS elemental mappings of the Fe3O4@PAN/CS composite membrane after TC adsorption.

Table S3. Parameters of adsorption kinetics

Pseudo-first order kinetic mode Pseudo-second order kinetic mode qe,exp

(mg g^-1) ^qe,c (mg g^-1)

K₁×10^-4 (h^-1)

R² q_e,c (mg g^-1)

K₂×10^-4 (g mg^-1 h^-1)

R²

30.09 28.13 927 0.9932 32.95 31.2 0.9969

Table S4. Adsorption parameters of the Langmuir and Freundlich isotherm

Langmuir Isotherm Freundlich Isotherm

qmax

(mg g^-1)

KL

(L mg^-1)

R² Kf

(mg g^-1) (L mg^-1)^1/n

n R²

468.33 0.00435 0.9978 5.308 1.43 0.9747

Table S5. Maximum TC adsorption capacities of previously reported adsorbents

No. adsorbent ^C0

(mg L^-1) ^pH

T (℃)

qmax

(mg g^-1) ^ref

1 Fe3O4 magnetite NPs N.M. 6.5 25 500 ¹⁵

2 NaOH-activated carbon 250 3 25 455.83 ¹⁶

3 chitosan 222.2 6.7 N.M. 441.35 ¹⁷

4 functionalized magnetic GO 50 4 25 356 ¹⁸

5 graphene oxide 333.3 3.6 25 313.48 ¹⁹

6 multi-walled carbon nanotubes 50 4.8 20 269.54 ²⁰

7 Fe3O4-rGO 75 N.M. 25 95 ²¹

8 GO functionalized particles 50 N.M. 25 39.1 ²²

9 bamboo charcoal 100 7 30 22.7 ²³

10 BiOI microsphere 80 N.M. 25 28.35 ²⁴

11 nitrifying granules 50 N.M. 25 9.51 ²⁵

12 Fe3O4@PAN/CS membrane 25 6.0 25 468.33 This work

N.M. stands for Not Mentioned.

Figure S9. The surface wetting properties of Fe3O4@PAN/CS composite membrane. Photographs of dynamic measurements of (a) oil-adhesion and (b) water spreading on the surface of Fe3O4@PAN/CS composite membrane. (c) setup of the oil-water separation experiment.

Figure S10. Underwater oil contact angles of the Fe3O4@PAN/CS composite membrane varying in Fe3O4 dosage ratios.

Table S6. Oil-water separation performance of previously reported separation media

N.M. stands for Not Mentioned.

No. separation media ^Flux

(L m^-2 h^-1)

Separation efficiency

Reuse

cycles ^ref

1 Au@ZIF-8@PAN-TD membrane 650 97.80% 16 ²⁶

2 nitrocellulose membrane 188 >99.5% 11 ²⁷

3 PVDF-g-PAA membrane 9600 >99.58% 10 ²⁸

4 nylon -POSS -PDMS 200 ≥99.9% N.M. ²⁹

5 cellulose sponge 91 >99.94% 6 ³⁰

6 PAN@ZIF-8 membrane 900 >99.98% 20 ³¹

7 Nonwoven/PVDF/SiO2/DOPA/mPEG-SH 2000 99.99% 50 h ³²

8 SWCNT-based bilayer membrane 25820 ± 4000 >99.95% 9 ³³

9 SNP/PBZ/PI membrane 4798 >99% 20 ³⁴

10 Fe3+–PA/OTMS/PI membrane 8424 ± 105 >99% 20 ³⁵

11 PDMS/SNPs-PI membrane 4400 >99.55 20 ³⁶

12 Fe3O4@PAN/CS membrane 28996 >99.99% 50 ^This

work

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