Gemini 2375

The nanoparticles were imaged by SEM using a JEOL JSM-7610F microscope (Japan) at 15 kV without any pretreatment. For TEM imaging, a JEOL JEM-1400 microscope was used at 100 kV by placing a drop of nanoparticles diluted in ethanol on a copper grid and dried at 60 °C. Infrared (IR) spectra were acquired using a Perkin-Elmer Spectrum BX instrument (USA), using KBr pellets at the region of 400–4400 cm⁻¹ with a resolution of 4 cm⁻¹. The surface area, pore volume, and pore size were measured using N₂ physisorption isotherms on a Micrometrics Gemini 2375 volumetric analyzer (USA). Before analysis, samples were degassed at 140 °C for 10 h. Thermogravimetric analysis (TGA) was performed on a Perkin-Elmer Pyris 1 TGA instrument (USA) in a temperature range of 25–600 °C and a heating rate of 20 °C/min. XPS measurements were used (model number JPS-9030) manufactured by JOEL company, Japan. All samples were etched for 20 s by Ar gas to remove surface contamination inside an Ultra High Vacuum Chamber (UHV) of about 10⁻⁹ Torr. Particle size was measured at different pH values using DLS Malvern instruments (Zetasizer Nano ZS, UK) at 25 °C. UV spectra were obtained using a SpectraMax Plus 384 microplate reader (USA).

The as-prepared rGO was characterized by X-ray diffraction (XRD) with a Bruker Inc (Germany) AXS D8 ADVANCE diffractometer (reflection q–q geometry, 40 kV and 30 mA using a Cu Kα (λ = 1.5418 Å) radiation source, 0.2 mm receiving slit, and high-resolution energy-dispersive detector). The morphology of the samples was characterized by high-resolution scanning electron microscopy (HRSEM) with a FEI Megallen 400 L microscope and environmental scanning electron microscopy (ESEM) with an INSPECT-FEI instrument. Images of rGO were measured using a high-resolution transmission electron microscopy (HRTEM) JEOL 2100 microscope at an acceleration voltage of 200 kV. The specific surface area of the rGO powder was measured by the Brunauer–Emmett–Teller (BET) method using a Micrometrics Gemini 2375 analyzer with nitrogen adsorbate at 77 K. Raman spectra were measured in a back scattering configuration using a micro-Raman spectrometer (model HR 800, Jobin Yvon Horiba) with a He–Ne laser (excitation line 632.8 nm) and a microscope objective (50×, Olympus LWD).

Handheld x-ray fluorescence (XRF, S1 titan 600, Bruker, Berlin, Germany) was used to determine the elemental composition, surface chemistry of the adsorbent was determined using Fourier Transform Infra-red spectrum-attenuation total reflectance (FTIR-ATR) (Bruker, Germany) at wavelength range 450 to 4,500 cm⁻¹. The pore size distribution, pore volume and surface area were determined using Barrett Joyner Halenda (BJH) (micrometrics ASAP 2020, Norcross, GA, USA) and Brunauer Emmett Teller (BET) (micrometrics Gemini 2375, Norcross, GA, USA) models, respectively. The morphology was determined using scanning electron microscopy (SEM) (Leo1450 SEM, Voltage 10 kV, working distance 14 mm, Ramsey, NJ, USA).