简介概要

Visible light response ZnO-C₃N₄ thin film photocatalyst

来源期刊：Rare Metals2021年第1期

论文作者：Yue Zhang Shu-Man Zhao Qi-Wen Su Jun-Li Xu

文章页码：96 - 104

摘要：Nanoflower-like ZnO-C₃ N₄ thin film with a porous net structure was successfully synthesized by a simple chemical corrosion method.The prepared ZnOC₃ N₄ thin films presented remarkable photocatalytic activities for the degradation of methyl orange under visible light irradiation,and more than 90% methyl orange was removed from water by ZnO-C3 N4 composite.Meanwhile,the ZnO-C₃ N₄ composite presented an enhanced photocatalytic stability.The loading content of C3 N4 had a great effect on the photocatalytic performance.Moreover,the photocatalytic activities were higher in acidic media than those in alkaline conditions.The adsorption of methyl orange was enhanced,and the recombination of photogenerated electrons and holes was suppressed with a suitable content of C3 N4.However,too much loading content of C3 N4 resulted in a poor dispersion of C3 N4 as the aggregated C3 N4 can behave as recombination centers.In addition,the prepared ZnO-C₃ N₄ thin film can be used for the water splitting in water-methanol system under simulated solar light irradiation.

稀有金属(英文版) 2021,40(01),96-104

Visible light response ZnO-C₃N₄ thin film photocatalyst

Yue Zhang Shu-Man Zhao Qi-Wen Su Jun-Li Xu

School of Science,Northeastern University

作者简介：Jun-Li Xu e-mail:jlxu@mail.neu.edu.cn;

收稿日期：12 March 2018

基金：financially supported by the National Natural Science Foundation of China (No.51574071);

Visible light response ZnO-C₃N₄ thin film photocatalyst

Yue Zhang Shu-Man Zhao Qi-Wen Su Jun-Li Xu

School of Science,Northeastern University

Abstract：

Nanoflower-like ZnO-C₃ N₄ thin film with a porous net structure was successfully synthesized by a simple chemical corrosion method.The prepared ZnOC₃ N₄ thin films presented remarkable photocatalytic activities for the degradation of methyl orange under visible light irradiation,and more than 90% methyl orange was removed from water by ZnO-C3 N4 composite.Meanwhile,the ZnO-C₃ N₄ composite presented an enhanced photocatalytic stability.The loading content of C3 N4 had a great effect on the photocatalytic performance.Moreover,the photocatalytic activities were higher in acidic media than those in alkaline conditions.The adsorption of methyl orange was enhanced,and the recombination of photogenerated electrons and holes was suppressed with a suitable content of C3 N4.However,too much loading content of C3 N4 resulted in a poor dispersion of C3 N4 as the aggregated C3 N4 can behave as recombination centers.In addition,the prepared ZnO-C₃ N₄ thin film can be used for the water splitting in water-methanol system under simulated solar light irradiation.

Keyword：

ZnO-C₃N₄ thin film; Photodegradation; Water splitting; Visible light irradiation; Photocatalytic stability;

Received： 12 March 2018

1 Introduction

Rapid developments of various industries result in the increased release of organic pollutants into water [ 1] .It can threaten public health as well as the environment,especially if they are left untreated or are improperly treated.Photocatalysis is one of the most effective treatment processes,and a variety of photocatalysts have been explored now.One of the most popular photocatalysts is ZnO due to its low toxicity,high catalytic efficiency,stability,low cost and harmlessness to the environment [ 2, 3] .However,pristine ZnO has the wide band gap (Eg=3.2eV),and it can just absorb the ultraviolet region of solar right.

The photocatalytic activity of the catalyst is severely dependent on its crystal morphology and structure [ 4, 5, 6, 7] .It has been proved that the flower-like nanostructures of ZnO and two-dimensional (2D) porous ZnO nanostructures show significantly enhanced photocatalytic properties [ 8, 9, 10, 11, 12, 13, 14] .Recently,nanonet-structure ZnO and ZnO-graphene composites which present excellent visible light photocatalytic performance on the degradation of methyl orange were obtained through a simple chemical corrosion method [ 15] .However,this material still exhibited low cycle property mainly because of the photoinduced corrosion of ZnO.How to improve the photostability of ZnO remains a challenge.

Graphitic carbon nitride (g-C₃N₄) with band energy of2.4-2.8 eV attracts wide concern because of its high chemical stability,electrical and optical properties,low cost and non-toxicity.It has attracted great interest in water splitting and organic pollutant degradation [ 16] .Owing to its narrow band gap,the large specific surface area and high photostability,g-C₃N₄ was considered as a promising doped material for ZnO [ 17] .Although much work has been done on the photocatalytic property of ZnO-C₃N₄ in late years,most reported ZnO-C₃N₄ photocatalysts can only work under ultraviolet (UV) or simulated solar light irradiations.Moreover,researches mainly focus on the photocatalytic property of ZnO-C₃N₄ powder.The reports on ZnO-C₃N₄ thin-film catalyst are very scarce yet.Here,we developed ZnO-C₃N₄ thin film by a chemical corrosion method,and the photocatalytic activities of pristine ZnO and ZnO-C₃N₄ composites were evaluated by the degradation of methyl orange (MO) under visible light irradiation and water splitting under simulated sunlight irradiation,respectively.Compared to the reported preparation methods for ZnO/g-C₃N₄ thin film,the used chemical corrosion method is simpler and quicker.Besides,the prepared ZnO/g-C₃N₄ thin film shows good catalytic activity and photostability,which are very attractive for the real photocatalytic applications.

2 Experimental

2.1 Synthesis of g-C3N4 and ZnO-C3N4

g-C₃N₄ was synthesized as per the report of Dong et al. [ 18] .Typically,10 g urea (CH₄N₂0,99.0%) was placed in a crucible with a lid,and the crucible was heated to 550℃from room temperature in 60 min (8.75℃·min^-1) and kept at 550℃for 2 h.Light yellow bulk g-C₃N₄ was collected when the temperature was cooled to the room temperature.Then,it was crushed into powder with an agate mortar.For the preparation of ZnO-C₃N₄ thin film,the prepared g-C₃N₄ was first dispersed into 6 ml concentrated H₂SO₄ (18.4 mol·L^-1),and the mixture was ultrasonicated for 30 min.Then,60 ml deionized water was added slowly into the g-C₃N₄/H₂SO₄ mixture.It was observed that all g-C₃N₄ was dissolved into H₂SO₄ solution during the diluting process and a colorless g-C₃N₄/H₂SO₄solution was formed.After that,zinc plate (geometric area of 3 cm²) was immersed into g-C₃N₄/H₂SO₄ solution for4 min and then taken out for thorough rinse with deionized water.In this case,the weight of added g-C₃N₄ was controlled to be 0,0.02,0.04,0.06 g,and the corresponding samples were labeled as ZnO,ZCN-1,ZCN-2,ZCN-3,respectively.The principle of preparing ZnO-C₃N₄ is similar to that of ZnO-graphene which was reported in Ref. [ 15] .

2.2 Characterization

The crystal structure of the obtained ZnO and ZnO-C₃N₄thin film was characterized by a PANalytical B.V.’MPDDY2094 X-ray diffractometer (XRD) with Cu Kαradiation (λ=0.15406 nm).A Zeiss ultra plus field emission scanning electron microscopy (FESEM) instrument attached with an energy-dispersive spectrometer (EDS)was used to study the surface microstructure of the obtained samples.The presence of chemical bonding was detected by using a Fourier transform infrared spectroscopy(FTIR,Thermo scientific Nicolet IS 10) from 400 to4000 cm^-1.X-ray photoelectron spectroscopy (XPS)spectra were obtained by a Thermo ESCALAB 250Xi (Al Ka,150 W) apparatus.The binding energies were calibrated against the C 1s carbon contamination signal(284.8 eV).Ultraviolet-visible diffuse reflectance spectra(UV-Vis DRS) were performed on a Perkin Elmer,Lambda 35 UV-Vis spectrometer with a scan range of200-800 nm.Mott-Schottky and photocurrent measurements were measured in a 0.5 mol·L^-1 Na₂SO₄ solution using a three-electrode electrochemical work station (CHI660,China).The obtained ZnO or ZnO/g-C₃N₄ thin film was used as the working electrode.The counter electrode and reference electrode were a Pt plate and a saturated Ag/AgCl,respectively.The experiments were performed at room temperature.For the tests of photocurrents,the photosource was a 300 W Xe lamp with a power of80 mW.cm^-2.

2.3 Photocatalytic activity tests

The photocatalytic experiments for the prepared pristine ZnO and ZnO-C₃N₄ thin films were evaluated by measuring the decomposition of MO solution under visible light irradiation and hydrogen content for water splitting under simulated sunlight irradiation.For the degradation of MO tests,a piece of prepared thin film was used as catalysts.The used volume of MO solution is 100 ml with a concentration of 5.0×10^-5 mo1·L^-1,and it was contained in a quartz cylindrical reactor.The initial pH value of the MO solution was adjusted with either HCl or NH₃·H₂O.The reactor temperature was controlled by a circulating water jacket surrounding the quartz reactor,and the light irradiation was provided by a 300 W xenon lamp(80 mW·cm^-2,Beijing Science and Technology Co,Ltd.Park Philae) from the top of reactor with a glass filter of420 nm to block UV light.After every 30-min illumination,2-3 ml MO solution was taken out and centrifuged.Then,it was analyzed by a UV-Vis spectrophotometer(TU-1900,Beijing Purkinje General Instrument Co,Ltd.).For the water splitting tests,10 ml methanol (served as hole scavenger) and 90-ml deionized water mixture was put into a quartz reactor with a surrounding circulating water jacket.A 300 W xenon lamp with a power of97.6 mW·cm^-2 (Beijing Science and Technology Co.,Ltd.Park Philae,emitting in the 200-1100 nm wavelength range) was used as the light source.The content of hydrogen evolution was determined every 1 h by a gas chromatograph with a thermal conductivity detector (TCD,GC7900,TECHCOMP Ltd Co,China).

3 Results and discussion

3.1 Structure and morphology

Figure 1 shows SEM images of the obtained pristine ZnO and ZCN-2 samples.As shown in Fig.la,a porous network structure is gown with high uniformity on the surface of Zn substrate,and the porous network is constructed by nanosheets as shown in Fig.lb.Compared with that of pristine ZnO,the nanosheets are smaller for ZCN-2,which indicates that it may have better adsorption capacity.From the cross-sectional micrograph of ZCN-2 (Fig.1d),the film is about 50μm in size.Figure le-h shows selected-area elemental mapping of Zn and O.Zn is uniformly diffusive,while O is mainly diffusive on the surface.EDX analysis of the free draw 1 in Fig.1g shows that O/Zn ratio is about1.55,indicating the existence of zinc vacancy in ZCN-2.

Figure 2 shows XRD patterns of zinc sheets etched by C₃N_4-H₂SO₄ solution.Compared with the standard PDF card,it could be found that 36.35⁰ corresponds to the diffraction peak of (101) of ZnO (JCPDS No.00021-1486),and the peaks at 39.08°,43.22°and 54.50⁰ correspond to(311),(202) and (040) crystalline planes of ZnSO₄ (JCPDS No.00001-1086).The diffraction peaks at 36.35°,39.08°,43.22°,54.50°,70.66°,82.10°and 86.54°correspond to(002),(100),(101),(102),(110),(112) and (201) crystalline planes of Zn (JCPDS No.03065-3358).As can be seen from Fig.1b,the prepared pristine C₃N₄ shows diffraction peaks at 13.00°and 27.40°,which correspond to(100) and (002) planes of C₃N₄ [ 19] ,respectively.Moreover,the diffraction peak of ZnO-C₃N₄ composite is similar to that of ZnO,indicating that the existence of C₃N₄does not lead to the new crystal's curvature or change the original ZnO crystal orientation.No typical diffraction peaks of g-C₃N₄ are observed for ZnO-C₃N₄ thin film.This is because of the low content or the relatively low diffraction intensity of C₃N₄ in the patterns [ 20] .

Fig.2 XRD patterns of C₃N₄,ZnO and ZnO-C₃N₄ composites

Figure 3a shows a wide-scan XPS pattern of ZCN-2 thin film to investigate the chemical states of elements in the composite.It can be seen that the surface of ZCN-2 contains C,Zn and O.Figure 3b shows the binding energy of Zn 2p.The peaks at 1022.7 and 1045.7 eV are attributed to Zn 2p3/2 and Zn 2pm of Zn0 [ 21] .The binding energy of1022.7 eV is higher than that of metallic Zn (1021.0 eV) or Zn0 (1021.4 eV),which reveals that palent Zn is associated with Zn-N bonds which connect Zn with conjugated tri-s-triazine rings [ 22, 23, 24] .The standard binding energy difference between Zn 2p3/2 and Zn 2p1/2 peaks is 23 eV(±0.05 eV) [ 25, 26] ,which is the same as the detected value (23 eV).Figure 3c shows the binding energy of Zn LMM Auger.The peak at 496.4 eV can be attributed to interstitial zinc bond [ 27] ,and the Zn LMM Auger peak at499.5 eV supports the existence of Zn-N bond [ 22, 23] .As shown in Fig.3d,the O 1s peak can be deconvoluted into two inpidual peaks at the binding energies of 530.3 and531.7 eV,which correspond to the lattice oxygen of Zn0and hydroxide (OH^-),respectively [ 21] .Figure 3e shows that N 1s peak can be deconvoluted into two peaks.The peak at 398.6 eV is related to C=N-C bond,and the peak at400.0 eV can be assigned to C≡N bonds [ 22] .Figure 3f shows that C 1s peaks can be deconvoluted into three peaks,indicating that there are three existing forms of C in Z1nO-C₃N₄ composite.The peaks at 284.7,285.7 and289.6 eV are assigned to the adventitious carbon (C-C) [ 28] ,sp3 C-N bond [ 22] and OH-C=O bonds [ 29] ,respectively.

Fig.1 SEM images of obtained ZnO and ZCN-2 samples:a,b pristine ZnO;c,d ZCN-2;e cross-sectional images of ZCN-2;f SEM image of ZCN-2 and corresponding EDX mappings of g Zn and h O

Fig.3 XPS survey spectra of ZCN-2:a typical wide-scan XPS spectrum,b Zn 2p,c Zn LMM Auger,d O 1s,e N 1s and f C 1s

The FTIR spectra of pristine ZnO and ZnO-C₃N₄samples are shown in Fig.4.The peak at around 495 cm^-1is considered to the stretching of Zn-O bond [ 30] ,and the peak at 812 cm^-1 belongs to the bending modes of s-triazine repeating units of g-C₃N₄ [ 31] .The peaks at 1240and 1325 cm^-1 are assigned to the aromatic C-N stretching vibration modes [ 32] ,and the peak at 1632 cm^-1corresponds to the-C-N heterocyclic stretching vibration modes [ 33] .The broad peak at 3296 cm^-1 corresponds to the stretching vibration modes of N-H [ 31] .All the characteristic peaks of g-C₃N₄ and ZnO are found clearly in the spectra of composites ZCN-2 and ZCN-3.However,the characteristic peaks of g-C₃N₄ cannot be seen completely from the spectra of ZCN-1 because the content of g-C₃N₄in this composite is too low to be detected.Moreover,compared with pristine g-C₃N₄,the bending modes of s-triazine repeating units of g-C₃N₄ shift to higher frequency region slightly.It can be deduced that there are strong interactions between C₃N₄ and ZnO.

Fig.4 FTIR spectra of ZnO,C₃N₄ and ZnO-C₃N₄ samples

3.2 Optical properties

Figure 5 a shows UV-Vis diffused reflectance spectra of pristine ZnO and ZnO-C₃N₄ samples.As shown in Fig.5b,the band gap energy can be obtained from the curves of(αhv)² versus hv,whereα,h and v are absorption coefficient,Planck constant and light frequency,respectively.The band gap energy of the pristine ZnO is 2.66 eV,while it is 2.60 eV (ZCN-1),2.46 eV (ZCN-2) and 2.48 eV(ZCN-3),respectively.The band gap energy decreases with the loading of g-C₃N_4.This phenomenon indicates that the electronic energy level of ZnO is affected by the loading content of g-C₃N₄ [ 34] .ZCN-2 possesses the narrowest band gap,which indicates that it can absorb more visible light and presents better photo-response under visible light irradiation.

Fig.5 a UV-Vis diffused reflectance spectra of pristine ZnO and ZnO-C₃N₄ samples;b plots of transformed Kubelka-Munk function versus energy of light

Mott-Schottky (MS) measurement can be used to investigate the electronic properties of semiconductor.The type of semiconductor can be deduced from the slope of the linear plot of l/ (C_sc is the space charge capacitance)versus potential (E),and the flat band potential is obtained by the intercept of the linear plot at 1/ =0.The MS plots of the prepared pristine ZnO and ZnO-C₃N₄ samples are shown in Fig.6.Positive slopes were obtained from the MS plots for all the samples,which indicate that all the prepared samples are n-type semiconductors.ZnO,ZCN-1,ZCN-2 and ZCN-3 samples exhibit the electrochemical flat band (EFB) of about-1.31,-1.49,-1.52 and-1.47 V(vs.Ag/AgCl),which are equal to-3.39,-3.21,-3.18and-3.23 eV,respectively.Combined with the band gap energy and the potential of conduction band,the potential of the valence bands for all samples can be obtained,and the results are shown in Table 1.

Fig.6 Mott-Schottky curves of ZnO,and ZnO-C₃N₄ samples in0.5 mo1·L^-1 Na₂SO₄ aqueous solution at fixed frequency of 1000 Hz

3.3 Photocatalytic properties

Figure 7a shows the MO photodegradation curves of ZnO and ZnO-C₃N₄ thin films under visible light irradiation.About 80%and 14%MO were degraded in 2.5 h by pristine ZnO and g-C₃N₄,respectively.All ZnO-C₃N4composites have better photocatalytic activity than pure ZnO and g-C₃N_4.ZCN-2 sample shows the best photocatalytic activity,and 92%MO was degraded in 2.5 h.The improved photocatalytic activity for ZnO-C₃N₄ thin films may be caused by the heterojunction structure between g-C₃N₄ and ZnO.The degradation reaction kinetics of MO can be expressed quantitatively using the pseudo-first-order model-ln(C/C₀)=kt,where C₀ is the original dye concentration,C is the MO concentration,k is the pseudo-firstorder rate constant and t is the irradiation time.According to this equation,k can be obtained from a linear plot of—In(C/C₀) against t.The kinetic plots for photocatalytic degradation of MO over composites with different C₃N₄loadings are presented in Fig.7b,and the calculated k values are displayed in Fig.7c.The k is 0.01248,0.01635,0.01392,0.01095 and 0.00106 min^-1 for ZCN-1,ZCN-2,ZCN-3,ZnO and g-C₃N₄ by calculation,respectively.The value of k of ZCN-2 is about 1.49 times and 15.4 times as large as that of pristine ZnO and g-C₃N₄,respectively.

The point of zero charge of ZnO is about 9.3 [ 35] .Thus,the ZnO surface is positively charged when pH is less than9.3.Since MO is a cationic dye,lower pH will be favorable for the photodegradation of MO.Moreover,the isoelectric point (IEPs) of g-C₃N₄ is 5.1 [ 36] .The g-C₃N₄ particles surface is negatively charged when pH value is below 5.1,while it is positively charged when pH is above 5.1.Therefore,the loading of C₃N₄ on ZnO can improve the adsorption of cationic dye MO,which is advantage for improving photcatalytic activities.Moreover,the photocatalytic activities are higher in acidic media than those in alkaline conditions,as proved by Fig.7d.The highest photocatalytic activity is obtained at pH 4.45 for ZCN-2.

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Table 1 Potential of conduction band,potential of valence band and band gap energy of ZnO and ZnO-C₃N₄ samples

Fig.7 a Relationship between degradation efficiency of MO and irradiation time at pH 6.45;b Pseudo-first-order rate constants of MO photocatalytic degradation;c degradation rate constant values of ZnO and ZnO-C₃N₄ samples;d photocatalytic degradation of MO on ZCN-2 at different pH values;e photocurrent density curves of ZnO and ZnO-C_aN₄ samples;and f reuse of ZnO and ZCN-2 for photocatalytic degradation of MO

Moreover,as shown in Table 1,the potential position of conduction band (CB) and valance band (VB) is-3.39 and-6.05 eV for the prepared ZnO,while it is-2.97 and-5.59 eV for g-C₃N₄ as reported [ 37] .Since both the bottom of CB and the top of VB of ZnO are higher than those of g-C₃N₄,the photoholes like to transfer from the VB of C₃N₄ to that of ZnO,while photoelectrons like to transfer to the CB of C₃N₄ from that of ZnO.Therefore,the recombination of the photogenerated carriers of ZnO can be suppressed by the coupling of C₃N_4.

The photocurrent response of ZnO and ZnO-C₃N₄samples under the irradiation of visible light is shown in Fig.7e.The photocurrent density generated by ZCN-1 and ZCN-2 samples is much higher than that by ZnO,indicating that the efficiency separation rate of photogenerated carriers can be highly improved with the loading of C₃N_4·However,with the further increase in loading content of C₃N₄,the photocurrent density of ZCN-3 sample is lower than that of ZnO.This may be caused by the poor dispersion of C₃N₄ in ZCN-3,and the aggregated g-C₃N₄ can behave as recombination centers which leads to a decrease in photocatalytic activity.Moreover,as shown in Fig.7a,pristine C₃N₄ presents almost no photocatalytic activity for the degradation of MO,so higher C₃N₄ loading content in ZnO may result in a lower photocatalytic activity because of the reduction in active photocatalyst mass and active site.

Stability is an important factor for the application of photocatalysts.Herein,the cycling stabilities of the prepared ZnO and ZCN-2 samples were evaluated.In Fig.7f,the photocatalytic performance of ZnO gradually decreases to 66%in the fifth cycle,while it decreases to87%after two cycles and then it keeps 73%in the remaining time for ZCN-2.The photocatalytic stability of ZnO could be improved by the loading of C₃N_4.

Fig.8 a Scavenger effects on degradation of MO solution under visible light irradiation;b schematic diagram illustrating principle of photoinduced charge transfer in ZnO-C₃N₄ semiconductor

Active species trapping experiments were conducted to determine the contribution of active species in photodegradation process.Isopropanol,ammonium oxalate and benzoquinone were added into MO solution,serving as·OH scavengers,h⁺scavengers and· scavengers,respectively.The photodegradation efficiency decreases obviously with the addition of ammonium oxalate or benzoquinone.However,the photodegradation efficiency with the addition of isopropanol is almost the same as that without scavengers,as shown in Fig.8a.It is reasonable to deduce that h⁺and· are the primary reactants for the photodegradation of MO.The main role of h⁺and· for the photodegradation of MO can be explained as follows.

Photoelectrons and holes are generated on the CB and VB of ZnO and C₃N₄,respectively,when catalysts are irradiated by visible light.O₂ is reduced to· by the photogenerated electrons on the CB of ZnO and C₃N₄because both the CB potentials of ZnO (-1.55 V vs.NHE)and g-C₃N₄ (-1.09 V vs.NHE) are more negative than the redox potential of O₂/· which is about-0.3 V (vs.NHE) as reported [ 38, 39] .Then,the reduced product reacts with MO and degrades it.However,OH^-cannot be oxidized to OH by the photogenerated holes on the VB of ZnO (1.11 V vs.NHE) and C₃N₄ (1.53 V vs.NHE) due to the higher redox potential of OH^-/·OH (1.99 V vs.NHE) [ 40] ,while MO is oxidized by the photogenerated holes on the CB of C₃N₄ directly as the redox potential of MO is1.48 V (vs.NHE) [ 41] ,changing MO into CO₂ and H₂O,as shown in Fig.8b.

In addition,as the conduction band potentials of the ZnO and ZnO-C₃N₄ thin films are higher than the reduction potential of H⁺/H₂,the photocatalytic activities of water splitting under simulated solar light irradiation in H₂O-CH₃OH solution were studied.The produced hydrogen content at different irradiation times for the prepared ZnO and ZnO-C₃N₄ thin films is shown in Fig.9.ZnO-C₃N₄ samples show improved activities for water splitting than pristine ZnO.The best photocatalytic performance is obtained by ZCN-2,reaching 1.86μmol·cm^-2·h^-1,which is about two times as that of pristine ZnO.

Fig.9 Activities of H₂ evolution for splitting of water using ZnO and ZnO-C₃N₄ as photocatalysts

4 Conclusion

In summary,flower-like ZnO and ZnO-C₃N₄ net nanostructures thin film on zinc substrate was manufactured by adopting a straightforward chemical corrosion method in a very short time at room temperature.The prepared ZnO-C₃N₄ composite shows high photocatalytic activity not only for the degradation of MO,but also for the water splitting.With the increase in C₃N₄ loading content,the photocatalytic activity of ZnO-C₃N₄ thin film increases first and then decreases.Efficiency of 92%for the degradation of methyl orange is achieved in 150 min under visible light irradiation for ZnO-C₃N₄ sample.Moreover,the photocatalytic activities are higher in acidic media than those in alkaline conditions.The enhanced photocatalytic activities are attributed to the improved adsorption of MO and the separation efficiency of photogenerated charge carriers.Holes (h⁺) and O^2-are the major reactive species for the degradation of methyl orange with the presence of ZnO-C₃N₄ photocatalyst.