High Photocatalytic Properties Research Articles

Design of bifunctional sandwich-like Co@Si/Ox-MXene nanocomposite to increase the supercapacitor properties and removal of pollutants from wastewater

Spent supercapacitor electrodes are considered waste after the end of the cycle. Designing a multifunctional material to increase the specific capacity of supercapacitors and eliminate environmental pollution is one of the existing challenges. In this study, Co3O4 was extracted from waste CMB by several tandem hydrothermal methods. Also, 3-Aminopropyl-triethoxysilane (APTES) was used to exfoliate and surface modification of Ti3C2Tx MXene nanosheets. Then, by assembling Co3O4 on the synthesized Ti3C2Tx nanosheet, a sandwich composite of Co@Si/Ox-Ti3C2Tx was formed through the formation of a complex with active surface functional groups on the oxalic acid modified MXene surface. Co3O4 can increase the number of redox reaction sites and fast charge transfer in the conducting channels of MXene by penetrating interlayers. The Co@Si/Ox-Ti3C2 composite electrode showed an increased specific capacity of 1821 Cg−1 at a current density of 1 Ag−1. The prepared hybrid supercapacitor (HSC) with Co@Si/Ox-Ti3C2 composite as the positive electrode and silanized active nanocarbon (Si69@AC) with bis(triethoxysilylpropyl)tetrasulfide as the negative electrode had a high energy density of 50 Wh kg−1 up to a power density of 8422 W kg−1 along with excellent cyclic life of 90.87% capacitance retention. After 15,000 cycles, XRD and XPS analyses confirmed 62% degradation of the positive electrode and conversion to TiO2 after 30 days in water. To graft the separated and agglomerated elements, they were added to the TEOS solution and subjected to the sol-gel process. High photocatalytic properties, 97% degradation of methylene blue (MB), changing the absorption region from UV to visible due to changing its band gap to 3.3 eV were among the characteristics of the new material. This work is a new approach for the construction of eco-friendly new HSCs.

Unraveling the origin of the high photocatalytic properties of earth-abundant TiO2/FeS2 heterojunctions: insights from first-principles density functional theory.

Herein, first-principles density functional theory calculations have been employed to unravel the interfacial geometries (composition and stability), electronic properties (density of states and differential charge densities), and charge carrier transfers (work function and energy band alignment) of a TiO2(001)/FeS2(100) heterojunction. Analyses of the structure and electronic properties reveal the formation of strong interfacial Fe-O and Ti-S ionic bonds, which stabilize the interface with an adhesion energy of -0.26 eV Å-2. The work function of the TiO2(001)/FeS2(100) heterojunction is predicted to be much smaller than those of the isolated FeS2(100) and TiO2(001) layers, indicating that less energy will be needed for electrons to transfer from the ground state to the surface to promote photochemical reactions. The difference in the work function between the FeS2(100) and TiO2(001) heterojunction components caused an electron density rearrangement at the heterojunction interface, which induces an electric field that separates the photo-generated electrons and holes. Consistently, a staggered band alignment is predicted at the interface with the conduction band edge and the valence-band edge of FeS2 lying 0.37 and 2.62 eV above those of anatase. These results point to efficient charge carrier separation in the TiO2(001)/FeS2(100) heterojunction, wherein photoinduced electrons would transfer from the FeS2 to the TiO2 layer. The atomistic insights into the mechanism of enhanced charge separation and transfer across the interface rationalize the observed high photocatalytic activity of the mixed TiO2(001)/FeS2(100) heterojunction over the individual components.

Preparation and sensitive SERS properties of sapphire-supported plasmonic Ag/Au hybrid coupled nanoarray

The regulation of surface plasmon properties of noble metal nanostructure has been a hot topic in the field of nanomaterials preparation and its applications. Surface-enhanced Raman Scattering (SERS), as a sensitive surface-interface trace molecule detection tool, strongly depends on the localized surface plasmonic characteristics. However, how to prepare highly sensitive and reproducible SERS substrates is still under difficult. Herein, Ag/Au hybrid coupled films were attached to the sapphire array by chemical method and interface assembly. Sapphire-based Ag/Au hybrid coupled nanoarrays (SA-Ag/Au HCNAs) with high SERS activity and plasmonic photocatalytic properties were obtained. By monitoring the catalytic reaction of PNTP on the substrate, we found that the prepared SA-Ag/Au HCNAs had significant plasmonic photocatalytic properties. The results show that the synergistic enhancement effect of Ag/Au hybrid coupling is 26.661 times higher than that of pure Au and 9.522 times higher than that of pure Ag. Furthermore, crystal violet (CV), Rhodamine 6G (R6G) and malachite green (MG) were selected as probe molecules, exhibiting good SERS stability and sensitivity of SA-Ag/Au HCNAs substrates. This work provides a simple, low-cost and scalable method for the preparation of hybrid coupled nanoarrays, showing good prospect in photocatalytic dye degradation, environmental monitoring and biomedical analysis.

Poly ortho-chloroaniline and poly ortho-chloroaniline titanium dioxide quantum dots for photo-degradation of organic hazardous materials

Conjugated polymers have recently been under active investigation as promising alternatives to use in photocatalysis. This is due to their unique advantages of low cost, high chemical stability, and molecularly tunable optoelectronic properties. This work explores the easy way to synthesize efficient poly ortho-chloroaniline (pO-CAN) via the chemical oxidative polymerization of O-CAN. Titanium dioxide quantum dots (TiQD) have been prepared and used in preparation of (pO-CAN)/TiQD. X ray diffraction, FTIR, UV &Visible spectra, TGA, surface area, EDX and TEM measurements were used to characterize all prepared polymers. The photocatalytic activities of all recent polymers were investigated by the photodegradation of methyl orang dye as an organic hazardous chemical in an aqueous medium was assessed using a 100-watt xenon lamp light source and direct sunlight for industrial wastewater samples. The effect of irradiation time on photodegradation performance of the dye in presence of recent polymers. (pO-CAN)/TiQD demonstrated high photocatalytic properties, with 79.9 % efficiency, as opposed to 48.8 % for (pO-CAN) only while it is 92.8 % for TiQD. When (pO-CAN), TiQD, and (pO-CAN)/TiQD are present during the recycling processes in the presence of all created samples up to six times, the photodegradation rate decreases by about 57.18, 9.61 and 9.51 % respectively. Also, the recycling and photodegradation performance of the industrial wastewater samples were evaluated and observed interested results.

In-situ dispersion of nano-TiO2 to highly reinforce cement paste

Regardless of how good pre-dispersion of nano-TiO2 in aqueous solutions, re-aggregation rapidly occurs once it is mixed into fresh cement mixtures, limiting the nano-reinforcing efficiency for cement-based materials. In this study, an in-situ release strategy by pre-encapsulating nano-TiO2 in microscaled ice and post-dispersing into fresh cement matrix during ice-melting process was developed to highly reinforce the microstructure and properties of cement paste. Compared with the conventional dispersion strategy, a much better dispersion of nano-TiO2 (0.6 wt% by cement) was achieved using the in-situ release strategy, which not only improved the 7- and 28-day compressive strength of cement paste by 9.2% and 10.1%, respectively, but also reduced the cement hydration heat and water adsorption by 36.1% and 4.6%, respectively. In addition to this, the NO degradation efficiency of cement paste was also improved by 20% due to the larger exposed surface area of nano-TiO2 with better dispersion. These research outcomes demonstrate that the in-situ release strategy facilitates the dispersion of nano-TiO2 in cement matrix and contributes to highly reinforcing cement paste with lower hydration heat and water adsorption, strong mechanical strength and higher photocatalytic properties.

Polyimide/titanium dioxide self-cleaning nano-hybrid films with high photocatalytic properties

Self-cleaning films are considered an emerging paradigm of environmentally functional materials. Enhancing the photocatalytic activities of self-cleaning film is a viable strategy for improving its antifouling characteristics. In this work, a polyimide/titanium dioxide (TiO2) film (PI/TiO2) film was developed by casting a mixture of polyamic acid solution and TiO2 hydrosol with a subsequent thermal imidization. TiO2 with a concentration of 1, 3, and 5 ​wt% was successfully incorporated into the PI matrix and was equally distributed in nanometer size in the PI/TiO2 nano-hybrid films. The addition of TiO2 into the film significantly improved its catalytic performance as indicated by the photocatalytic degradation of methylene blue and resazurin solution, suggesting a good self-cleaning property for antifouling applications. In addition, the thermal and mechanical stability of the PI film were improved with the addition of TiO2. After eight cycles, the PI-TiO2 films also demonstrated excellent cycling stability. This study introduces a novel self-cleaning film family composed of PI/TiO2 nano-hybrid film and emphasizes the engineering potential of photocatalytic materials in the context of self-cleaning film.

Oxygen-Defective Bi2MoO6/g-C3N4 hollow tubulars S-scheme heterojunctions toward optimized photocatalytic performance

Novel S-scheme heterojunction photocatalysts of bismuth molybdate/hollow tube graphite carbon nitride (Bi2MoO6 SOVs/g-C3N4) containing surface defects (SOVs) were prepared by calcination and hydrothermal methods. The hollow tubular structure of g-C3N4 facilitates the enhancement of multiple reflection and scattering of light, and also have a larger range of specific surface areas and more reactive sites, which promotes carrier separation and thus improves photocatalytic performance. The introduction of SOVs to bismuth molybdate not only reduces the band gap of bismuth molybdate, but also promotes the separation of charges. The optimized Bi2MoO6 SOVs/TCN photocatalyst has a hydrogen production efficiency of 2.29 mmol h−1 g−1. It also shows high photocatalytic degradation property of tetracycline and bisphenol A in water, up to 97.3 % and 98.9 %, respectively. Meanwhile, the transfer mechanism of photogenerated charges in S-scheme heterojunctions can be verified by electron paramagnetic resonance and in situ irradiated x-ray photoelectron spectroscopy electron paramagnetic resonance, which accelerated the separation and transfer of photogenerated charge by energy band bending at the interface and internal electric field. This rational structural design strategy provides a new development idea for building high-performance S-scheme heterojunction photocatalysts.

The toxicological effects of nano titanium dioxide on target organs and mechanisms of toxicity.

Nano-titanium dioxide (TiO2 NPs) is widely used for its extremely high stability, corrosion resistance, and photocatalytic properties and has penetrated into various fields of production and life. Assessing its toxicity to different organs should be a key part of preclinical toxicity assessment of TiO2 NPs, which is relatively incomprehensive yet. Therefore, this review focuses on the toxic effects of TiO2 NPs on various organs in mammals and biological mechanisms from different organs. The commonality of toxic effects on various target organs reflected in tissue structure damage and dysfunction, such as liver damage and dysfunction; pulmonary fibrosis; and renal impairment (including hematuria and nephritis); damage of brain tissue and neurons; alteration of intestinal villi; and weight loss. And effects on the reproductive system are affected by different sexes, including ovarian dysfunction, testicular development damage, and sperm viability reduction. We believe that the toxic mechanisms of TiO2 NPs in target organs have commonalities, such as oxidative stress, inflammatory responses, and organelle damage. However, different target organ toxicities also have their specificities. TiO2 NPs disturb the intestinal flora and cause undesirable changes in feces products. And in spleen are infiltration of neutrophils and lymphadenopathy and eventually immune deficiency. Although the toxic pathways are different, but there may be a close link between the different toxic pathways. In this article, the main manifestations of the toxic effects of titanium dioxide nanoparticles on major mammalian organs are reviewed, in order to provide basic data for their better application from a medical perspective.

Engineering oxygen vacancies in Bi2WO6 by introducing heteroatoms for enhancing photo-oxidation/reduction activities

To improve the light-harvesting capability and electron-hole separation efficiency, a novel heteroatom-introduced Bi2WO6 photocatalyst (OV–Bi2WO6) with oxygen vacancies (OVs) was prepared via the partial substitution of O2− by S2− anions. The OV-Bi2WO6 showed high photocatalytic properties in photo-oxidation/reduction reactions under visible-light. The OVs content could be controlled by adjusting the sulfur source amount, and the optimal OV(0.9)-Bi2WO6 with suitable OVs had a high photocatalytic activity with 97.6% of MO removal and 88.2% of Cr(VI) removal efficiency. Density functional theory (DFT) calculations verified that the OVs in Bi2WO6 could induce a new defect level to decrease the bandgap energy and accelerate the carrier separation/migration. Furthermore, the possible photocatalytic mechanisms for MO degradation and Cr(VI) reduction over the OV-Bi2WO6 were proposed, respectively. The present work helped us to better understand the enhancement mechanism of OVs in Bi-based semiconductors and paved the way to develop high-performance photocatalysts for environmental remediation.

Encapsulation of ZnO nanoparticles in POSS for robust anti-photofading coatings on dyed fabrics

As an excellent UV absorber, zinc oxide nanoparticles (ZnO Nps) are limited applications in anti-photofading coating fields due to the high photocatalytic degradation activity, which can accelerate dyed fabrics fading. Herein, a “core-shell” shaped composite nanoparticles with high UV absorption and low photocatalytic degradation properties were successfully fabricated by encapsulating ZnO Nps in polyhedral oligomeric silsesquioxane (POSS) via the alkaline hydrolysis method, and then the POSS coated ZnO Nps (ZnO@POSS Nps) were applied as UV absorber to improve the photostability of dyed polyester fabrics. Field emission scanning electron microscope, Fourier transform infrared spectroscopy and X-ray diffraction analysis confirmed the strong relevance between the POSS shell thickness and micromorphology and structural interface characteristics of “core-shell” shaped ZnO@POSS Nps. The UV–Vis absorption spectrum of ZnO@POSS Nps and C. I. Red 2 degradation experiments indicated when the mole ratio of ZnO to vinyl trimethoxy silane was 1:0.25, ZnO@POSS Nps maintained high comparative UV absorption performance (65.4 %) and restrained the photocatalytic degradation efficiency from 62.0 % to 8.9 % comparing with ZnO Nps. The photostability of fabrics was significantly improved by the presence of ZnO@POSS Nps in the coatings that the color difference values of all three dyed fabrics exposed to strong UV light for 72 h were decreased from 2.62, 2.29, and 3.04 to 1.17, 1.09, and 1.52, respectively. This work presents an effective and simple way to restrain the photocatalysis activity of ZnO Nps and enhance the anti-photofading property of dyed fabrics.

Chitosan and TiO2 functionalized polypropylene nonwoven fabrics with visible light induced photocatalytic antibacterial performances

Chitosan/TiO2 functionalized polypropylene (CS/TiO2/PP) nonwoven fabrics were fabricated through crosslinking of chitosan with glutaraldehyde followed by loading of TiO2 nanoparticles. The functionalized CS/TiO2/PP has super hydrophilicity and excellent visible light induced photocatalytic antibacterial properties owing to the synergistic effects of CS and TiO2. The photocatalytic degradation performance was determined by assessing the degradation of methyl blue under simulated visible light irradiation and its recyclability was also evaluated. In addition, SEM images demonstrated that TiO2 nanoparticles were distributed evenly on the surface of the 2 g/L CS/TiO2/PP. Meanwhile, the polypropylene surface showed a significant increase in hydrophilicity after being treated with chitosan and TiO2. The photocatalytic degradation results revealed that CS/TiO2/PP had higher photocatalytic properties than those of pure PP under visible light, and the degradation rate of methylene blue reached 96.4 % after 90 min of light exposure. Compared to pure PP, the antibacterial properties of CS/TiO2/PP significantly increased, and the bacterial reduction percentages were increased to 98.7 % and 96.3 %, against E. coli and S. aureus, respectively. The functionalized CS/TiO2/PP composites exhibited promising potential in environmentally friendly antibacterial materials.

Recycling and photodegradation processes of organic hazardous materials on polyaniline-titanium dioxide quantum dots catalyst

A photo-catalyst with conducting polymers doped with titanium dioxide, known as TiO2 quantum dots (TiO2 QDs), has a high efficiency for photocatalytic usage. The organic hue methyl orange was broken down in the current study using polyaniline (PANI) and polyaniline titanium dioxide quantum dots (PANI-TiO2 QDs) polymers. PANI and PANI-TiO2 QDs have been produced by chemical oxidative polymerization in an aqueous solution. By characterization of PANI-TiO2 QDs nanocomposites using ultraviolet–visible (UV–vis), Fourier transform infrared (FTIR), and X-ray powder diffraction (XRD), it was demonstrated that the chemical structure of polymer composites had not changed after being doped with TiO2 QDs. To determine the form, size, surface area, and thermal analyses of the produced PANI-TiO2 QDs samples, EDX, BET, and TGA were used. The photocatalytic activity of the PANI-TiO2 QDs in the photo-degradation of methyl orange dye as an organic hazardous chemical in an aqueous medium was assessed using a 50-watt xenon lamp light source and direct sunlight. PANI-TiO2 QDs demonstrated high photocatalytic properties, with a 93% efficiency, as opposed to 35% and 60.1%, respectively, for PANI and TiO2 QDs. When PANI, titanium dioxide quantum dots, and PANI-TiO2 QDs are present during the recycling processes in the presence of all created samples up to four times, the photo-degradation rate decreases by about 50.2%, 15.4%, and 17.4%, respectively.

Porous Ceramic ZnO Nanopowders: Features of Photoluminescence, Adsorption and Photocatalytic Properties

The grainy and porous ZnO powders were synthesized by thermal decomposition of zinc nitrate and polymer-salt method. The comparative study of the crystal structure, morphology, luminescence, adsorptive and photocatalytic properties of ZnO powders was carried out. The addition of PVP in initial aqueous solutions of zinc nitrate determines the remarkable change of powder morphology and decreases the average size of ZnO nanocrystals. Luminescence spectra in the visible spectral range indicate the significant difference of structural defects types in grainy and porous powders. Porous powders demonstrate high ability for singlet oxygen photogeneration and photocatalytic properties. The kinetics of diazo dye adsorption on both powders is described successfully by the kinetic equation of pseudo-second order. Kinetic dependencies of photocatalytic oxidation of Chicago Sky Blue diazo dye using as grain ZnO powder so as porous ZnO powders are described by the Langmuir–Hinshelwood model but process rates are different. Porous ZnO powder demonstrates strong ability for photogeneration of singlet oxygen under visible irradiation and high photocatalytic properties (rate constant 0.042 min−1).

Simultaneously promoting adsorption and charge separation in Z-scheme ZnO/Cu2O heterojunctions for efficient removal of tetracycline

Exploring novel materials with both high adsorption capacity and photocatalytic properties is urgent in environmental remediation. In this work, a Z-scheme ZnO/Cu2O heterostructure with a large surface area of 45.42 m2/g was constructed by using the liquid phase reduction method. Compared to pure ZnO and pure Cu2O, the as-synthesized ZnO/Cu2O nanocomposites exhibited excellent capacity of adsorption and photodegradation for tetracycline (TC), which was degraded 95.3% of TC within 120 min under simultaneous adsorption and photocatalytic processes. Theory and experimental analysis manifested that the excellent adsorption-photocatalytic activity can be attributed to the large BET specific surface area, the efficient charge carrier separation and the high redox capability. The results of this study identified the potential advantages of ZnO/Cu2O composites for removing antibiotics to purify water resources and protect the environment.

Oxygen vacancy-induced efficient photocatalytic antifouling activities of Bi5O7I microspheres on marine concrete

Bi5O7I photocatalysts are considered potentially excellent marine antifouling materials. However, the photocatalytic properties differ for Bi5O7I photocatalysts with various morphologies, and the photocatalytic mechanisms involved remain unclear. In addition, powdered Bi5O7I photocatalysts are difficult to work with in an exact manner on marine structure surfaces, such as concretes, in actual marine environments. Thus, in this study, Bi5O7I photocatalysts with various morphologies comprising nanosheets, nanorods, nanoflowers, and microspheres (MS) were successfully synthesized. Among these Bi5O7I photocatalysts, the highly regular Bi5O7I MS (Bi5O7I-MS) were found to have the highest photocatalytic properties in both the degradation of Rhodamine B and inactivation of bacteria. This strong photocatalytic ability can be attributed to the high specific surface area and rich oxygen vacancies (OVs) in Bi5O7I-MS. The possible photocatalytic mechanism involves h+ playing the major role, with ∙OH and ∙O2− partially contributing to the photocatalytic process. OVs also promoted the photocatalytic properties of Bi5O7I-MS by trapping photoinduced electrons to accelerate the photocatalytic process. Furthermore, Bi5O7I-MS photocatalysts were successfully grown in situ on cement mortar surfaces, where they showed extremely high antifouling performance, with hardly any living bacteria attached. These findings clarify the morphology-dependent mechanism associated with Bi5O7I photocatalysts, as well as facilitating the growth of photocatalysts in situ on cement mortar for applications in marine antifouling.

Selective Cocatalyst Decoration of Narrow-Bandgap Broken-Gap Heterojunction for Directional Charge Transfer and High Photocatalytic Properties.

Narrow-bandgap semiconductors are promising photocatalysts facing the challenges of low photoredox potentials and high carrier recombination. Here, a broken-gap heterojunction Bi/Bi2 S3 /Bi/MnO2 /MnOx , composed of narrow-bandgap semiconductors, is selectively decorated by Bi, MnOx nanodots (NDs) to achieve robust photoredox ability. The Bi NDs insertion at the Bi2 S3 /MnO2 interface induces a vertical carrier migration to realize sufficient photoredox potentials to produce O2 •- and • OH active species. The surface decoration of Bi2 S3 /Bi/MnO2 by Bi and MnOx cocatalysts drives electrons and holes in opposite directions for optimal photogenerated charge separation. The selective cocatalysts decoration realizes synergistic surface and bulk phase carrier separation. Density functional theory (DFT) calculation suggests that Bi and MnOx NDs act as active sites enhancing the absorption and reactants activation. The decorated broken-gap heterojunction demonstrates excellent performance for full-light driving organic pollution degradation with great commercial application potential.

The microstructure and photocatalytic properties of nitrogen-doped nano titanium dioxide loaded on porous ceramics

Nitrogen-doped nano TiO2 powder was prepared using the solvothermal method. The nano TiO2 powder was loaded on the porous ceramic carriers with a different aperture through the vacuum impregnation method using polyvinyl alcohol as a binder. The effects of deionized water content and carrier pore size on the microstructure and photocatalytic activity of nitrogen-doped nano TiO2 powder and supported TiO2 were investigated. The results show that, when introducing 25% deionized water, the nitrogen-doped nano TiO2 powder obtains a good crystallinity, small grain size, and high photocatalytic properties because of adequate hydrolysis of tetrabutyl titanate. The photocatalytic activity of nitrogen-doped nano TiO2 powder is improved by distorting the lattice and inhibiting grain growth. The nano TiO2 powder can be tightly loaded on the surface of the strut or hole-wall of porous ceramic carriers. The absorption and photocatalytic activity of supported TiO2 are demonstrably improved as the macropore provides the transmission channel, and the micropore realizes a good absorbing effect. The 20 PPI carrier with high porosity and suitable strength is beneficial to promote the photocatalytic property of supported TiO2. Moreover, the supported TiO2is easily recycled and reused.

Structural design, biomimetic synthesis, and environmental sustainability of graphene-supported g-C3N4/TiO2 hetero-aerogels

Graphene-supported C3N4/TiO2 hetero-aerogels with high photocatalytic properties and sustainability are designed and synthesized.

Pd nanoparticle-modified TiO2-x composites as efficient visible-light active photocatalysts for tetracycline degradation and microbial disinfection

In the present work, Ti3+-self-doped TiO2 heterostructure photocatalysts were prepared by coupling with different additions of palladium quantum dots by means of deposition-reduction methodology. The electron paramagnetic resonance (EPR) analysis indicated the existence of Ti3+ in synthesized samples. The transmission electron microscopy (TEM) images presented the modification of TiO2-x nanoparticles by coupling with nano palladium. Photoluminescence (PL) results demonstrated the lowest charge carrier recombination rate in 5% Pd/TiO2-x composites. Photocatalytic performances of photocatalysts were evaluated by degrading Tetracycline (TC) and inactivating Escherichia coli (E. coli) and Fusarium oxysporum f. sp. Vasinfectum (Fov) with the presence of visible light, in which an enhanced photocatalytic degradation and inactivation activity was found in all Pd coupled composites with the highest efficiency in 5% Pd/TiO2-x. The improved photocatalytic activity of Pd/TiO2-x was associated to the generation of more hydroxyl radicals (•OH) and superoxide anions radicals (•O2-) during photocatalytic process which were demonstrated by the electron spin-resonance spectroscopy (ESR) technique. Moreover, 5% Pd/TiO2-x composites were found to remain high photocatalytic properties in a circulating photo-disinfection system.

NiO/g-C3N4 composite for enhanced photocatalytic properties in the wastewater treatment.

The massive discharge of colored wastewater has seriously harmed the environment and people's health. Photocatalysis technology is an effective method to purify colored wastewater and has been widely concerned in colored wastewater treatment. In this study, based on the obtained nickel oxide (NiO) nanospheres by solvothermal method and graphite phase carbon nitride (g-C3N4) nanosheets by thermal polymerization method, the p-n heterojunction composed of NiO nanospheres and g-C3N4 nanosheets was successfully constructed by heat treatment for the photocatalytic degradation of methyl orange (MO). The morphology, crystallinity, surface features, and optical properties of the NiO/g-C3N4 composites were investigated by various characterization methods such as scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffractometer (XRD), Fourier transform infrared spectrometer (FT-IR), X-ray photoelectron spectroscopy (XPS), UV-vis spectrophotometer, and fluorescence spectrometer (PL), which provided the evidence for the formation of the heterojunction between NiO and g-C3N4. Compared with the g-C3N4 nanosheets and NiO nanospheres, the NiO/g-C3N4 composites showed the improved photocatalytic activity for the degradation of MO under visible light irradiation. And the NiO/g-C3N4 composite with the mole ratio of NiO and g-C3N4 of 2:8 displayed the best photocatalytic activity of MO, and more than 90% of MO can be degraded under the illumination of 100min. The high photocatalytic properties over the NiO/g-C3N4 composite may be due to high specific surface area, the perfect band matching, and the formation of the p-n heterojunction, which helps to promote interfacial charge transfer and hinder the recombination of photo-generated electrons and holes. Moreover, the NiO/g-C3N4 composite exhibits the universality and cyclic stability, which is expected to have broad application prospects in the treatment of colored wastewater.