Photocatalytic Properties of Copper Nitride/Molybdenum Disulfide Composite Films Prepared by Magnetron Sputtering

Cu3N/MoS2 composite films were prepared by magnetron sputtering under different preparation parameter, and their photocatalytic properties were investigated. Results showed that the composite films surface was uniform and had no evident cracks. When the sputtering power of MoS2 increased from 2 W to 8 W, the photocatalytic performance of the composite films showed a trend of increasing first and then decreasing. Among these films, the composite films with MoS2 sputtering power of 4 W showed the best photocatalytic degradation performance. The photocatalytic degradation rate of methyl orange at 30 min was 98.3%, because the MoS2 crystal in the films preferentially grew over the Cu3N crystal, thereby affecting the growth of the Cu3N crystal. The crystallinity of the copper nitride also increased. During photocatalytic degradation, the proper amount of MoS2 reduced the band gap of Cu3N, and the photogenerated electron hole pairs were easily separated. Thus, the films produces additional photogenerated electrons and promotes the degradation reaction of the composite films on methyl orange solution.


Introduction
With the rapid development of global industry, the environmental pollution problem caused by industrial processing has become a new challenge. Among these problems, the degradation of pollutants of aromatic and azo structures has attracted attention, and the use of photocatalytic technology to degrade dyes has emerged as a promising technology [1][2][3][4][5][6]. Photocatalysts, on the basis of semiconductor materials, such as TiO 2 [7][8][9], ZnO [10][11][12][13][14], CdS [15][16][17][18][19], and WO 3 [20][21][22][23][24], have caused a new upsurge in the degradation of methyl orange structure pollution due to their simplicity, high efficiency, low energy consumption, and mild reaction conditions [25]. Although these conventional semiconductor photocatalysts substantially affect the degradation of methyl orange, they also have limitations [17,20,26,27]. TiO 2 and ZnO photocatalysts are direct bandgap wide bandgap semiconductor materials with short response bands to light and have high semiconductor carrier recombination rate and low photon efficiency [2,9,28,29]. Although CdS has a narrow band gap and a suitable band structure, the electron-hole pair recombination rate is fast, the photocatalytic activity is low, and the material is unstable, which causes photocorrosion that is harmful to the environment and human body [15,[30][31][32]. WO 3 has a small band gap and thus has a good response in the visible range, but its photocatalytic activity is low [23,24]. Given that Cu 3 N and MoS 2 have an adjustable bandgap structure, the photocatalytic performance can be improved by adjusting the size of the band gap, which is a promising photocatalytic material. Therefore, we conducted research in this area.

Experimental
In this experiment, a Cu 3 N/MoS 2 composite films was prepared on a single crystal (100) substrate and a quartz substrate by RF magnetron sputtering (JGP-450a, Chinese Academy of Sciences Shenyang Scientific Instrument Co., Ltd., Shenyang, China). First, the silicon and quartz wafer substrates were separately sonicated in acetone and ethanol solution for 15 min, rinsed with deionized water, dried, and placed in a substrate holder for further use. The sputtering chamber was evacuated to bring the vacuum to 1 × 10 −4 Pa. The surface of the target was cleaned by pre-sputtering for 10 min in an Ar atmosphere before the experiment. A Cu 3 N/MoS 2 composite films was deposited on the substrate in a gas atmosphere of Ar and N 2 at room temperature using a high degree of MoS 2 target (99.99%) and a Cu target (99.99%). The total gas flow rate was set to 40 Sccm, the N 2 and Ar flow ratio = 4:1, and the vacuum chamber pressure was 1.0 Pa. The sputtering power on the Cu target was fixed at 100 W, and those of the MoS 2 target were 2, 4, 6, and 8 W. Both targets were simultaneously sputtered for 5 min.
Films surface morphology was characterized by a field emission scanning electron microscope (S-4800, Hitachi, Tokyo, Japan). The crystal structure of the films was characterized by an X-ray diffractometer (X'Pert PRO, Panalytical, Almelo, The Netherlands). Its light absorption characteristics were investigated by ultraviolet (UV)-visible (vis) spectrometer (UV-2600/2700, Shimadzu, Tokyo, Japan).
The photocatalytic performance of the composite films was investigated by degrading the methyl orange solution. First, in a dark environment, the sample was immersed in a 10 mg/L methyl orange solution for 1 h to avoid interference of the physical adsorption with the experimental results. With a high-pressure Hg lamp as a light source, the sample was exposed to UV light for 30 min, the power was set to 500 W (voltage of 100 V, current of 5 Å), and the methyl orange solution was collected every 3 min. The absorbance of the solution was measured by an UV-vis spectrophotometer. The absorption spectrum of the methyl orange solution as a function of photocatalytic time was obtained.

Results and Discussion
The XRD test pattern of different MoS 2 sputtering power composite Cu 3 N films is shown in Figure 1. The films had the crystallization peaks of Cu 3 N and MoS 2 , of which the 2θ values of 23.3 • ,

Results and Discussion
The XRD test pattern of different MoS2 sputtering power composite Cu3N films is shown in Figure 1. The films had the crystallization peaks of Cu3N and MoS2, of which the 2θ values of 23.3°, 33.1°, and 47.6° corresponded to Cu3N (100), (110), and (200) crystal faces, respectively [52,53]. The peak of 2θ = 62.02° corresponded to the MoS2 (107) crystal plane. Comparison of the diffraction patterns of different composite films showed that when the emission power of MoS2 was 2 W, the films appeared to be bulging at 23.3°, which was not a sharp peak. No diffraction peak was observed at 47.6°, indicating that sputtering MoS2 under power affects the crystal growth of Cu3N [41]. This phenomenon occurred because the entropy of Cu3N was high, causing it to lag behind the growth of MoS2 crystals. At low power, the nucleation rate of MoS2 was low, and the crystallinity was poor, which resulted in Cu3N to have a small growth probability along the grain boundary of MoS2. The nucleation process is difficult. Thus, the crystallinity of Cu3N is also relatively poor. When the sputtering power of MoS2 increased, the diffraction peak of the MoS2 (107) crystal plane in the films became increasingly sharp, the corresponding Cu3N half-width was gradually reduced, and the diffraction peak was enhanced. When the sputtering power of MoS2 was 8 W, the MoS2 (107) crystal plane had the strongest diffraction peak, its half width was the smallest, and the crystallization was the best. Owing to the influence of MoS2, the diffraction peak of Cu3N crystal was the sharpest, and the crystallinity was also the largest. The crystallization of different phases in the composite membrane had a considerable influence on the photocatalytic degradation effect. The presence of MoS2 crystals adjusts the band gap of the Cu3N matrix and finally changes the photocatalytic degradation performance of the films. The surface and cross-sectional morphologies of the Cu3N/MoS2 composite films are shown in Figure 2. Figure 2a shows that the surface of the films sample was rough overall and consisted of spherical particles of uniform size without evident cracks. The rough surface of the films can provide a large specific surface area, which was favorable for the catalytic degradation reaction. Figure 2b shows that the deposited films has a thickness of approximately 50 nm.  The surface and cross-sectional morphologies of the Cu 3 N/MoS 2 composite films are shown in Figure 2. Figure 2a shows that the surface of the films sample was rough overall and consisted of spherical particles of uniform size without evident cracks. The rough surface of the films can provide a large specific surface area, which was favorable for the catalytic degradation reaction. Figure 2b shows that the deposited films has a thickness of approximately 50 nm.

Results and Discussion
The XRD test pattern of different MoS2 sputtering power composite Cu3N films is shown in Figure 1. The films had the crystallization peaks of Cu3N and MoS2, of which the 2θ values of 23.3°, 33.1°, and 47.6° corresponded to Cu3N (100), (110), and (200) crystal faces, respectively [52,53]. The peak of 2θ = 62.02° corresponded to the MoS2 (107) crystal plane. Comparison of the diffraction patterns of different composite films showed that when the emission power of MoS2 was 2 W, the films appeared to be bulging at 23.3°, which was not a sharp peak. No diffraction peak was observed at 47.6°, indicating that sputtering MoS2 under power affects the crystal growth of Cu3N [41]. This phenomenon occurred because the entropy of Cu3N was high, causing it to lag behind the growth of MoS2 crystals. At low power, the nucleation rate of MoS2 was low, and the crystallinity was poor, which resulted in Cu3N to have a small growth probability along the grain boundary of MoS2. The nucleation process is difficult. Thus, the crystallinity of Cu3N is also relatively poor. When the sputtering power of MoS2 increased, the diffraction peak of the MoS2 (107) crystal plane in the films became increasingly sharp, the corresponding Cu3N half-width was gradually reduced, and the diffraction peak was enhanced. When the sputtering power of MoS2 was 8 W, the MoS2 (107) crystal plane had the strongest diffraction peak, its half width was the smallest, and the crystallization was the best. Owing to the influence of MoS2, the diffraction peak of Cu3N crystal was the sharpest, and the crystallinity was also the largest. The crystallization of different phases in the composite membrane had a considerable influence on the photocatalytic degradation effect. The presence of MoS2 crystals adjusts the band gap of the Cu3N matrix and finally changes the photocatalytic degradation performance of the films. The surface and cross-sectional morphologies of the Cu3N/MoS2 composite films are shown in Figure 2. Figure 2a shows that the surface of the films sample was rough overall and consisted of spherical particles of uniform size without evident cracks. The rough surface of the films can provide a large specific surface area, which was favorable for the catalytic degradation reaction. Figure 2b shows that the deposited films has a thickness of approximately 50 nm.   The chemical composition of the Cu 3 N/MoS 2 composite films with different sputtering powers was characterized by XPS. The test results are shown in Figure 3. The four samples in the XPS total spectrum (Figure 3a) had the same high intensity peaks corresponding to the S 2p, Cu 2p, N 1s, O 1s, and Mo 3d peaks, respectively. Among these peaks, the O 1s peak appeared at a binding energy of 532.2 eV [54] mainly because of the trace amount of air remaining in the vacuum chamber during the sputtering process, and the oxidation and physical adsorption of the surface of the films exposed to the atmosphere during the test. Figure 3b shows the high-intensity peaks of the Cu 2p spectra at 932.4 and 952.3 eV, which corresponded to the Cu 2p3/2 and Cu 2p1/2 orbital peaks, respectively [54,55]. Considering the spin-orbit coupling, the splitting energy spacing was approximately 20 eV. The two peaks were attributed to Cu (I), and the figure shows that no peaks were associated with Cu (II) (933.6 and 953.5 eV). The deposited films was a Cu (I) nitride compound having a high purity. The spectrum of N 1s is shown in Figure 3c. The characteristic peak at approximately 397.5 eV can be attributed to be the Cu-N hybrid bond structure in Cu 3 N, which was consistent with the analysis results in XRD. The weaker characteristic peak at approximately 398.7 eV is due to the physical adsorption of N atoms between grains during deposition [54,55]. Figure 3d shows the XPS spectrum of S 2p in the composite films with the binding energies of the two main peaks of 162.7 and 163.8 eV, thereby corresponding to the S 2p3/2 and S 2p1/2 orbital peaks, respectively [56]. The Mo 3d peak appears at a binding energy of approximately 220 eV, but the Mo content in the films was extremely small, and the peak shape trend was not evident. Combining the results of XRD spectrum analysis, we know that MoS 2 has been successfully composited with Cu 3 N to form a composite film. Cu 3 N as a host in the composite films provided a large number of photoelectrons to participate in the catalytic reaction. The addition of MoS 2 promoted the growth of copper nitride and also changed the photocatalytic effect of the composite films. The chemical composition of the Cu3N/MoS2 composite films with different sputtering powers was characterized by XPS. The test results are shown in Figure 3. The four samples in the XPS total spectrum (Figure 3a) had the same high intensity peaks corresponding to the S 2p, Cu 2p, N 1s, O 1s, and Mo 3d peaks, respectively. Among these peaks, the O 1s peak appeared at a binding energy of 532.2 eV [54] mainly because of the trace amount of air remaining in the vacuum chamber during the sputtering process, and the oxidation and physical adsorption of the surface of the films exposed to the atmosphere during the test. Figure 3b shows the high-intensity peaks of the Cu 2p spectra at 932.4 and 952.3 eV, which corresponded to the Cu 2p3/2 and Cu 2p1/2 orbital peaks, respectively [54,55]. Considering the spin-orbit coupling, the splitting energy spacing was approximately 20 eV. The two peaks were attributed to Cu (I), and the figure shows that no peaks were associated with Cu (II) (933.6 and 953.5 eV). The deposited films was a Cu (I) nitride compound having a high purity. The spectrum of N 1s is shown in Figure 3c. The characteristic peak at approximately 397.5 eV can be attributed to be the Cu-N hybrid bond structure in Cu3N, which was consistent with the analysis results in XRD. The weaker characteristic peak at approximately 398.7 eV is due to the physical adsorption of N atoms between grains during deposition [54,55]. Figure 3d shows the XPS spectrum of S 2p in the composite films with the binding energies of the two main peaks of 162.7 and 163.8 eV, thereby corresponding to the S 2p3/2 and S 2p1/2 orbital peaks, respectively [56]. The Mo 3d peak appears at a binding energy of approximately 220 eV, but the Mo content in the films was extremely small, and the peak shape trend was not evident. Combining the results of XRD spectrum analysis, we know that MoS2 has been successfully composited with Cu3N to form a composite film. Cu3N as a host in the composite films provided a large number of photoelectrons to participate in the catalytic reaction. The addition of MoS2 promoted the growth of copper nitride and also changed the photocatalytic effect of the composite films.     Figure 4 shows the change trend of the absorption spectrum and color of methyl orange dye solution with time. The figure shows that in the first 15 min, the absorbance of methyl orange decreases rapidly because the concentration of highly active electrons generated by UV light irradiation on the films surface was high, and photogenerated electrons had strong redox ability, which can rapidly react with methyl orange and reduce the methyl orange content. As the degradation reaction continued, the content of methyl orange in the solution decreased, and the color of the solution became gradually light. Thus, the rate of the decrease in absorbance also slowed down. When degraded for 30 min, the solution became almost transparent. The illustrations reflected the color change of methyl orange during photocatalytic degradation, and the overall degradation and fading process was consistent with the change in absorbance.
Coatings 2020, 10, 79 5 of 10 which can rapidly react with methyl orange and reduce the methyl orange content. As the degradation reaction continued, the content of methyl orange in the solution decreased, and the color of the solution became gradually light. Thus, the rate of the decrease in absorbance also slowed down. When degraded for 30 min, the solution became almost transparent. The illustrations reflected the color change of methyl orange during photocatalytic degradation, and the overall degradation and fading process was consistent with the change in absorbance.
Among them, T represents transmittance, and d represents film thickness. Using the Tauc Equation (2), the Eg of the film can be calculated: where α, hv, and A represent the absorption coefficient, photon energy, and constant, respectively. From the relationship curve of (αhv) 2 and hv, calculate the band gap Eg by extrapolation, as shown in Figure 5b. The Eg range of Cu3N/MoS2 composite films is between 2.05 and 2.10 eV. As the power increases, the Eg of the composite film decreases first and then increases. When the deposition power is 4 W, the Eg of the film is the smallest, which is 2.05 eV. This may be because after MoS2 is recombined with Cu3N, Mo atoms replace Cu vacancies in the Cu3N lattice to act as donors, thus providing carriers to reduce the optical band gap; It is also possible that the film produced at a lower power has more defects. With the increase of power, the MoS2 content increases, and the optical band gap increases due to the hole filling effect in the valence band or the free carriers occupying the bottom of the conduction band.
Among them, T represents transmittance, and d represents film thickness. Using the Tauc Equation (2), the E g of the film can be calculated: where α, hv, and A represent the absorption coefficient, photon energy, and constant, respectively. From the relationship curve of (αhv) 2 and hv, calculate the band gap E g by extrapolation, as shown in Figure 5b. The E g range of Cu 3 N/MoS 2 composite films is between 2.05 and 2.10 eV. As the power increases, the E g of the composite film decreases first and then increases. When the deposition power is 4 W, the E g of the film is the smallest, which is 2.05 eV. This may be because after MoS 2 is recombined with Cu 3 N, Mo atoms replace Cu vacancies in the Cu 3 N lattice to act as donors, thus providing carriers to reduce the optical band gap; It is also possible that the film produced at a lower power has more defects. With the increase of power, the MoS 2 content increases, and the optical band gap increases due to the hole filling effect in the valence band or the free carriers occupying the bottom of the conduction band. The change in concentration in the catalytic degradation of methyl orange solution by composite films with different sputtering power is shown in Figure 6. The figure shows that the composite films had a catalytic degradation effect on methyl orange. With the increase of MoS2 power in the composite films, the concentration of methyl orange first decreased and then increased. When the deposition power was 4 W, the concentration of methyl orange solution was the smallest. At this time, the photodegradation of methyl orange was the most thorough, and then the degradation was weakened with the increase in MoS2 sputtering power. Within 30 min, the MoS2 sputtering power of 2, 4, and 6 W on the films' samples had improved degradation effect on methyl orange. Among the films samples, the films sample with the MoS2 sputtering power of 4 W had a fast degradation rate and a thorough degradation. A schematic diagram of the experimental process is shown in Figure 7. A Cu3N/MoS2 composite film was prepared on a silicon wafer by sputtering Cu target and MoS2 target simultaneously. Then, under the ultraviolet light irradiation, the composite orange film was used for catalytic degradation of the methyl orange solution. The illustration shows the principle of photocatalytic degradation of methyl orange solution by MoS2/Cu3N composite film. When irradiated by UV light, the electrons of the low energy valence band of Cu3N absorbed enough energy to be excited and entered the high energy conduction band beyond the forbidden band. Negatively charged high activity electrons are produced on the conduction band, thereby leaving positively charged holes on the valence band and resulting in highly active photoelectron-hole pairs. After the electrons and holes are separated, they migrated to the Cu3N surface and combined with O2 and OH − in the solution to form O 2− ions and ·OH with strong oxidizing properties. These highly reactive particles undergo redox reactions with methyl orange, which in turn degrade methyl orange [3]. The change in concentration in the catalytic degradation of methyl orange solution by composite films with different sputtering power is shown in Figure 6. The figure shows that the composite films had a catalytic degradation effect on methyl orange. With the increase of MoS 2 power in the composite films, the concentration of methyl orange first decreased and then increased. When the deposition power was 4 W, the concentration of methyl orange solution was the smallest. At this time, the photodegradation of methyl orange was the most thorough, and then the degradation was weakened with the increase in MoS 2 sputtering power. Within 30 min, the MoS 2 sputtering power of 2, 4, and 6 W on the films' samples had improved degradation effect on methyl orange. Among the films samples, the films sample with the MoS 2 sputtering power of 4 W had a fast degradation rate and a thorough degradation. The change in concentration in the catalytic degradation of methyl orange solution by composite films with different sputtering power is shown in Figure 6. The figure shows that the composite films had a catalytic degradation effect on methyl orange. With the increase of MoS2 power in the composite films, the concentration of methyl orange first decreased and then increased. When the deposition power was 4 W, the concentration of methyl orange solution was the smallest. At this time, the photodegradation of methyl orange was the most thorough, and then the degradation was weakened with the increase in MoS2 sputtering power. Within 30 min, the MoS2 sputtering power of 2, 4, and 6 W on the films' samples had improved degradation effect on methyl orange. Among the films samples, the films sample with the MoS2 sputtering power of 4 W had a fast degradation rate and a thorough degradation. A schematic diagram of the experimental process is shown in Figure 7. A Cu3N/MoS2 composite film was prepared on a silicon wafer by sputtering Cu target and MoS2 target simultaneously. Then, under the ultraviolet light irradiation, the composite orange film was used for catalytic degradation of the methyl orange solution. The illustration shows the principle of photocatalytic degradation of methyl orange solution by MoS2/Cu3N composite film. When irradiated by UV light, the electrons of the low energy valence band of Cu3N absorbed enough energy to be excited and entered the high energy conduction band beyond the forbidden band. Negatively charged high activity electrons are produced on the conduction band, thereby leaving positively charged holes on the valence band and resulting in highly active photoelectron-hole pairs. After the electrons and holes are separated, they migrated to the Cu3N surface and combined with O2 and OH − in the solution to form O 2− ions and ·OH with strong oxidizing properties. These highly reactive particles undergo redox reactions with methyl orange, which in turn degrade methyl orange [3]. A schematic diagram of the experimental process is shown in Figure 7. A Cu 3 N/MoS 2 composite film was prepared on a silicon wafer by sputtering Cu target and MoS 2 target simultaneously. Then, under the ultraviolet light irradiation, the composite orange film was used for catalytic degradation of the methyl orange solution. The illustration shows the principle of photocatalytic degradation of methyl orange solution by MoS 2 /Cu 3 N composite film. When irradiated by UV light, the electrons of the low energy valence band of Cu 3 N absorbed enough energy to be excited and entered the high energy conduction band beyond the forbidden band. Negatively charged high activity electrons are produced on the conduction band, thereby leaving positively charged holes on the valence band and resulting in highly active photoelectron-hole pairs. After the electrons and holes are separated, they migrated to the Cu 3 N surface and combined with O 2 and OH − in the solution to form O 2− ions and ·OH with strong oxidizing properties. These highly reactive particles undergo redox reactions with methyl orange, which in turn degrade methyl orange [3]. After MoS2 was combined with Cu3N, the band gap of Cu3N was adjusted to change the rate of producing photoelectron-hole pair, thereby resulting in a change in degradation effect. When the sputtering power of MoS2 was 2 W, the crystallinity of Cu3N was relatively poor. Thus, the effect of the thin films catalytic degradation of methyl orange was poor. When the power of MoS2 increased to 4 W, the crystallinity of Cu3N was affected by MoS2. After Cu3N was combined with MoS2, the band gap of Cu3N was reduced due to the regulation of a small amount of MoS2, which was beneficial to the separation of photogenerated electron-hole pairs and promoted the catalytic degradation of methyl orange. At the same time, MoS2 can also directly participate in the catalytic degradation reaction. Thus, the sample has a good catalytic degradation effect on methyl orange. With the further increase in MoS2 power, the MoS2 content was also increased. The wide band gap of MoS2 itself caused the band gap of the Cu3N body to change directly, thereby decreasing the amount of photogenerated electrons produced by the films sample under the same conditions. Thus, the degradation effect is poor. Therefore, the composite films sample with the MoS2 power of 4 W is likely to produce photoelectron-hole pairs, its photocatalytic degradation rate is fast, and the degree of degradation is good.

Conclusions
Cu3N/MoS2 composite films with different MoS2 powers were prepared on silicon wafers and quartz wafer substrates by magnetron sputtering. Microstructure studies showed that the crystallinity of Cu3N increased with the increase in MoS2 power, mainly because the crystallized MoS2 affected the crystal growth of Cu3N. The diffraction peak of Cu3N was the sharpest, and the crystallization was the best when the sputtering power of MoS2 was 8 W. The composite films surface was distributed with distinct spherical grains and uniform in size, and the films thickness was approximately 50 nm. The Cu3N/MoS2 composite films had good photocatalytic activity by the UV degradation of methyl orange solution, and the photodegradation effect varied for different MoS2 powers of the composite films. When the sputtering power of MoS2 was 4 W, the catalytic degradation rate of the composite films to methyl orange solution is faster and the degree of degradation was thorough. This phenomenon was due to the effect of MoS2 on the band gap of Cu3N in the films, which caused the films to generate additional photogenerated electrons to promote the catalytic degradation of the films sample to methyl orange solution. In general, the Cu3N/MoS2 composite films with a sputtering power of 4 W have a good photocatalytic degradation effect on methyl orange, and the photocatalyst prepared by magnetron sputtering has the advantages of nontoxicity, high efficiency, and easy recycling, which provides additional options for the photocatalytic degradation of methyl orange. After MoS 2 was combined with Cu 3 N, the band gap of Cu 3 N was adjusted to change the rate of producing photoelectron-hole pair, thereby resulting in a change in degradation effect. When the sputtering power of MoS 2 was 2 W, the crystallinity of Cu 3 N was relatively poor. Thus, the effect of the thin films catalytic degradation of methyl orange was poor. When the power of MoS 2 increased to 4 W, the crystallinity of Cu 3 N was affected by MoS 2 . After Cu 3 N was combined with MoS 2 , the band gap of Cu 3 N was reduced due to the regulation of a small amount of MoS 2 , which was beneficial to the separation of photogenerated electron-hole pairs and promoted the catalytic degradation of methyl orange. At the same time, MoS 2 can also directly participate in the catalytic degradation reaction. Thus, the sample has a good catalytic degradation effect on methyl orange. With the further increase in MoS 2 power, the MoS 2 content was also increased. The wide band gap of MoS 2 itself caused the band gap of the Cu 3 N body to change directly, thereby decreasing the amount of photogenerated electrons produced by the films sample under the same conditions. Thus, the degradation effect is poor. Therefore, the composite films sample with the MoS 2 power of 4 W is likely to produce photoelectron-hole pairs, its photocatalytic degradation rate is fast, and the degree of degradation is good.

Conclusions
Cu 3 N/MoS 2 composite films with different MoS 2 powers were prepared on silicon wafers and quartz wafer substrates by magnetron sputtering. Microstructure studies showed that the crystallinity of Cu 3 N increased with the increase in MoS 2 power, mainly because the crystallized MoS 2 affected the crystal growth of Cu 3 N. The diffraction peak of Cu 3 N was the sharpest, and the crystallization was the best when the sputtering power of MoS 2 was 8 W. The composite films surface was distributed with distinct spherical grains and uniform in size, and the films thickness was approximately 50 nm. The Cu 3 N/MoS 2 composite films had good photocatalytic activity by the UV degradation of methyl orange solution, and the photodegradation effect varied for different MoS 2 powers of the composite films. When the sputtering power of MoS 2 was 4 W, the catalytic degradation rate of the composite films to methyl orange solution is faster and the degree of degradation was thorough. This phenomenon was due to the effect of MoS 2 on the band gap of Cu 3 N in the films, which caused the films to generate additional photogenerated electrons to promote the catalytic degradation of the films sample to methyl orange solution. In general, the Cu 3 N/MoS 2 composite films with a sputtering power of 4 W have a good photocatalytic degradation effect on methyl orange, and the photocatalyst prepared by magnetron