Uv 3600 plus spectrophotometer

Photoluminescence spectra were measured via using OmniFluo fluorescence spectrometer (Zolix, Beijing, China). Ultraviolet-visible (UV-vis) absorption spectra were taken on a UV-3600 Plus spectrophotometer (SHIMADZU CO., Ltd., Hong Kong, China). X-ray diffraction (XRD) measurements were measured on a Bruker/D8 FOCUS X-ray diffractometer (Billerica, MA, USA) with a Cu Kα radiation source (wavelength at 1.5405 Å). Transmission electron microscope (TEM) and high-resolution TEM (HRTEM) images were recorded with a Technai F20 transmission electron microscope (FEI, Hillsboro, OR, USA). Scanning electron microscopy (SEM) images were taken on a S-4800 SEM microscope (Hitachi, Ltd., Tokyo, Japan).

To prepare the DCS/Fe₃O₄-Cu, a certain amount of the DCS/Fe₃O₄ was added into 30 mL of CuSO₄·5H₂O solution. The solution pH (2–6, adjusted using 0.1 M H₂SO₄ or 0.1 M NaOH), adsorbent dosage (1–8 g L⁻¹), initial Cu ions concentration (50–300 mg L⁻¹), and contact time (0–700 min) were investigated. Using a thermostatic shaker (SHZ-C, Suzhou, China) at 25 °C/150 rpm during the whole adsorption process, the concentration of Cu ions was determined by the inductively coupled plasma optical emission spectrometer (ICP-OES, Avio 500, PerkinElmer, Waltham, MA, USA).
Similarly, for the batch adsorption experiments of MO, 0.015 g of CS/Fe₃O₄, DCS/Fe₃O₄ or DCS/Fe₃O₄-Cu adsorbent was added into 30 mL of MO aqueous solution (MO initial concentration of 10–100 mg L⁻¹) at 25 °C. The MO concentration in solution was determined by an UV-3600 PLUS spectrophotometer (Shimadzu, Kyoto, Japan) at a wavelength of 460 nm. The removal efficiency (R, %) and adsorption capacity (Q_e, mg g⁻¹) can be calculated by the following Equation 8 and Equation 9, respectively.
$$R=\frac{C_0-C_{\mathrm{e}}}{C_0}\times 100\%$$
$$Q_e=\frac{\left(C_0-C_e\right)·V}{m}$$
where C₀ (mg L⁻¹) is the initial concentration of Cu²⁺ or MO, C_e (mg L⁻¹) is the equilibrium concentration, V (L) is the volume of solution, and m (g) is the mass of adsorbent.

The morphology of PbS CQDs film was measured by scanning electron microscope (SEM, FEI NovaNanoSEM450) and atomic force microscope (AFM, SPM-9700 Shimadzu Co.,Japan). Transmission electron microscopy (TEM) images were obtained using FEI Tecnai G2 20 microscope with a LaB₆ filament operated at 200 KV. The absorption spectra were measured by Shimadzu UV-3600 plus spectrophotometer. The crystal structure of PbS CQDs film was identified by X-ray diffraction (XRD, Philips, X pert pro MRD, Cu Kα radiation) with a step of 0.013°. The Fourier transform infrared (FTIR) spectra of PbS CQDs film were investigated using VERTEX 70 ATR-FTIR spectroscope (Bruker Co., Germany). The X-ray photoelectron spectroscopy (XPS) measurements were performed on AXIS-ULTRA DLD-600W Ultra spectrometer (Kratos Co. Japan).