Escalab 250xi x

The surface morphology of the nanofibers was observed with a desktop scanning electron microscope (SEM, Phenom ProX type Phenom, Eindhoven, The Netherlands, acceleration voltage: 10 kV) and a field–emission electron microscope (FEM, Sigma 300 type, Zeiss, Oberkochen, Germany, acceleration voltage: 5 kV). An automatic specific surface area tester (BET, TriStarII;3020, Micromeritics Instrument Ltd., Norcross, GA, USA) was used to measure the specific surface area and pore size of the spinning film. The degassing temperature of the fiber film was 110 ℃, and the degassing time was 6 h. The surface element and chemical functional group changes of the sample were characterized with an X-ray photoelectron spectrometer (XPS, ESCALAB 250XI+ X, Thermo Fisher Scientific, Waltham, MA, USA) with a spot diameter of 500 μm. The film strain response test was performed with an electrochemical workstation (AUTOLAB PGSTAT302N, Metrohm, Herisau, Switzerland), and the sampling time was 0.1 s. The viscosity of the spinning solution is measured with a micro mixing rheometer (Haake Minilab, Thermo Fisher Scientific, Karlsruhe, Germany), the measurement mode was the frequency sweep mode (25 ℃, shear rate 0~300 S⁻¹), and the measurement was the zero–time shear viscosity.

The crystal structure
of the samples was determined by a Bruker D8 Advance X-ray diffractometer
(XRD) using Cu Kα radiation (λ = 1.5418 Å) at instrument
settings of 40 kV and 40 mA. The elemental and functional group compositions
of the samples were analyzed by Thermo Fisher Scientific ESCALAB 250Xi
X-ray photoelectron spectroscopy (XPS), using Al Kα excitation
radiation (25 W, hν = 1486.5 eV) and 1 eV energy
resolution. Composite morphology was analyzed with a FEI Talos F200X
transmission electron microscope (TEM) operating at an accelerating
voltage of 200 kV, whereas the localized elemental mapping was screened
by high-angle annular dark-field scanning transmission electron microscopy
(HAADF-STEM). FEI model QuantaFEG 650 scanning electron microscopy
(SEM) with 5 kV acceleration voltage and Bruker EDS energy-dispersive
X-ray spectroscopy were also used for morphology study and element
visualization. The ultraviolet–visible (UV–vis) absorbance
spectra were collected using a Jasco V-670 UV–visible spectrophotometer.
The photoluminescence (PL) spectra were investigated by a PL spectrometer
(Horiba, iHR 320, MicOS) with an excitation wavelength of 325 nm.
The concentration of organic carbon in the wastewater was analyzed
using a combustion-type total organic carbon analyzer (Shimadzu, model
TOC-L, Japan).

Elemental analyses of the GO–PDMS sponges before and after the Pb(ii) sorption tests were performed using an ESCALAB 250Xi X-ray photoelectron spectroscopy (XPS) instrument (Thermo Fisher Scientific, Waltham, MA, USA). The solid and liquid in a given mixture after a batch or filtration experiment were separated by centrifuging the mixture at 4000 rpm for 20 min, then the supernatant was transferred to a 15 mL polypropylene centrifuge tube for chemical analysis. The initial and final Pb(ii) concentrations were determined using a Hitachi Z-5000 atomic absorption spectrometer (Hitachi High-Technologies, Tokyo, Japan). Control tests were performed in the absence of GO–PDMS to assess the potential sorption of Pb(ii) onto the centrifuge tubes or other equipment during the test process. The results confirmed that negligible Pb(ii) sorption occurred onto the propylene centrifuge tubes and other equipment.