D max 2400

A scanning electron microscopy (SEM, JSM-7000F, JEOL Inc., Japan) with energy dispersive spectrometer (EDS) was used for the observation of the morphology and structure. The samples were characterized by a D/max-2400 X-ray diffraction spectrometer (Rigaku, D/max-2400, Japan) and a UV-vis spectrometry (Ultrospec 2100 pro) was also used. To evaluate the photocatalytic activity of the as-synthesized Cu₂O-TiO₂ NTA heterojunction, we took methyl orange (MO), a typical organic indicator, as the degraded object. The Cu₂O-TiO₂ NTA films (3.0 × 1.5 cm²) were immersed in 5 × 10⁻⁵ mol/L of MO aqueous solution and irradiated with seven 4 W visible bulbs (Toshiba, Cool white, FL4W, Japan). Then, the solution was magnetically stirred in the dark for 30 min to ensure adsorption-desorption equilibrium prior to photocatalytic degradation. Photodegradation experiments lasted 180 min with 1.5 mL samples withdrawn periodically. The concentration of the residual MO was measured by a spectrophotometer at about 460 nm on the basis of the Beer-Lambert law. The degradation efficiency of the MO could be defined as follows: $$C_t/C_0=\left(A_t/A_0\right)\times 100\%$$
And the varying of A_t/A₀ referred to the changing in C_t, which represented the photocatalytic activity of the tested samples.

The morphologies were examined by scanning electron microscopy (SEM, JSM-6701) and transmission electron microscopy (TEM, TECNAI TF20). The crystal structures and compositions of the as-prepared samples were characterized by using X-ray diffraction (XRD, D/max-2400, Rigaku, Cu Kα, 0.154056 nm). X-ray photoelectron spectra (XPS) were recorded on a Perkin-Elmer PHI ESCA system. Specific surface areas were measured by Brunauer-Emmett-Teller (BET) nitrogen adsorption–desorption (Micromeritics ASAP 2020 Instrument, USA) and pore-size distributions were calculated by the Barrett-Joyner-Halenda (BJH) method using the desorption branch of the isotherm.

SEM images and EDX spectroscopy elemental mapping analyses were obtained with a FEI model Quanta microscope at accelerating voltages of 15–30 kV. TEM images were obtained with a FEI Tecnai G2 microscope. XRD patterns were obtained with a Rigaku D/MAX 2400 instrument with a Cu source. XPS analyses were conducted with an Al Kα X-ray source (1486.6 eV) and a hemispherical concentric analyzer (CLAM2–VG Microtech). Fourier Transform Infrared Spectrometer (FTIR) (Brook Vertex 70) was used to identify the related functional groups in the catalyst.