2.2 Characterization of samples
The morphologies of the samples were measured by field emission scanning electron microscope (SEM: JSM-6701F. JEOL) and transmission electron microscope (TEM: FEI Tecnai TF 20). The crystalline structure was analyzed by X-ray diffraction (XRD: Rigaku RINT-2000) patterns, all samples were scanned from 5° to 80° at a scanning rate of 5°/min under 40 mA and 40 kV. The chemical composition and valence state of the catalyst were detected by X-ray photoelectron (XPS: ESCALAB 250Xi). UV-vis diffuse reflectance spectra (DRS) were performed by Shimadzu UV 2550 spectrophotometer with BaSO4 powder was used as a reference. Photoluminescence (PL) spectra and time resolved photoluminescence (TRPL) spectra were analyzed on a FlUOROMAX-4 spectrophotometer (HORIBA Scientific, France) with the excitation wavelength of 390 nm. Brunauer–Emmett–Teller (BET) surface area and N2 adsorption-desorption isotherms were carried out on an ASAP2020M instrument at 77 K.
The electrochemical tests and photoelectrochemical properties of MCS, NiSe2 and MCNS-10 samples were performed by an electrochemical workstation (VersaSTA4-400, AMETEK). The transparent solution of Na2SO4 (0.2 M) was used as electrolyte. In this test system, a platinum sheet was used as the counter electrode and reference electrode of saturated calomel electrode (SCE) and the work electrode of as-prepared was the fluorine-doped tin oxide (FTO) coated. The FTO working electrodes was prepared as follows: the FTO glass were cut to 2×1 cm2, it was orderly washed with acetone, ethanol and deionized water in ultrasonic devices. 5 mg catalyst was ultrasonically dispersion for 1 h in 100 μL anhydrous ethanol containing 10 μL of 5% Nafion solution. Then the dispersed solutions of catalyst was uniformly coated FTO glass with the areas about 1 cm2 until it dried. The linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) were measured at room temperature with a scan rate of 0.05 V s−1. When the forward bias is 0.2 V, the EIS of samples were measured in a frequency range of 1MHz to 1 Hz at AC amplitude of 10 mV. Mott-Schottky was tested under the frequency of 1000 Hz.