Novel spindle-shaped nanoporous TiO2 coupled graphitic g-C3N4 nanosheets with enhanced visible-light photocatalytic activity

Highly efficient visible-light-driven heterojunction photocatalysts, spindle-shaped nanoporous TiO₂ coupled with graphitic g-C₃N₄ nanosheets have been synthesized by a facile one-step solvothermal method. The as-prepared photocatalysts were characterized by X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N₂ adsorption-desorption analysis and UV–vis diffuse reflectance spectrometry (DRS), proving a successful modification of TiO₂ with g-C₃N₄. The results showed spindle-shaped nanoporous TiO₂ microspheres with a uniform diameter of about 200 nm dispersed uniformly on the surface of graphitic g-C₃N₄ nanosheets. The g-C₃N₄/TiO₂ hybrid materials exhibited higher photocatalytic activity than either pure g-C₃N₄ or nanoporous TiO₂ towards degradation of typical rhodamine B (RhB), methyl blue (MB) and methyl orange (MO) dyes under visible light (>420 nm), which can be largely ascribed to the increased light absorption, larger BET surface area and higher efficient separation of photogenerated electron–hole pairs due to the formation of heterostructure. In addition, the possible transferred and separated behavior of electron–hole pairs and photocatalytic mechanisms on basis of the experimental results are also proposed in detail.     

Novel visible light-induced g-C3N4–Sb2S3/Sb4O5Cl2 composite photocatalysts for efficient degradation of methyl orange

A series of g-C₃N₄–Sb₂S₃/Sb₄O₅Cl₂ (SCL-CX) composite photocatalysts were successfully prepared via a hydrothermal method. The as-prepared materials were characterized by TM3000, powder X-ray diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS) and UV–vis diffuse reflectance spectra (UV–vis DRS). The obtained photocatalyst showed higher photocatalytic activity than pure g-C₃N₄, Sb₄O₅Cl₂ and Sb₂S₃/Sb₄O₅Cl₂ (SCL). The optimum photocatalytic of the composite with the mass of 170 mg g-C₃N₄ and a degradation efficiency up to 95% for methyl orange (MO) under visible light was achieved within 60 min. The enhanced photocatalytic performance could be attributed to the stronger absorption in the visible region and the more efficient electron–hole separation.     

Synthesis and properties of nanocomposites of WO3 and exfoliated g-C3N4

The nanocomposites of WO₃ nanoparticles and exfoliated graphitized C₃N₄ (g-C₃N₄) particles were prepared and their properties were studied. For this purpose, common methods used for characterization of solid samples were completed with dynamic light scattering (DLS) method and photocatalysis, which are suitable for study of aqueous dispersions.The WO₃ nanoparticles of monoclinic structures were prepared by a hydrothermal method from sodium tungstate and g-C₃N₄ particles were prepared by calcination of melamine forming bulk g-C₃N₄, which was further thermally exfoliated. Its specific surface area (SSA) was 115 m² g⁻¹.The nanocomposites were prepared by mixing of WO₃ nanoparticles and g-C₃N₄ structures in aqueous dispersions acidified by hydrochloric acid at pH = 2 followed by their separation and calcination at 450 °C. The real content of WO₃ was determined at 19 wt%, 52 wt% and 63 wt%. It was found by the DLS analysis that the g-C₃N₄ particles were covered by the WO₃ nanoparticles or their agglomerates creating the nanocomposites that were stable in aqueous dispersions even under intensive ultrasonic field. Using transmission electron microscopy (TEM) the average size of the pure WO₃ nanoparticles and those in the nanocomposites was 73 nm and 72 nm, respectively.The formation of heterojunction between both components was investigated by UV–Vis diffuse reflectance (DRS) and photoluminescence (PL) spectroscopy, high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), photocatalysis and photocurrent measurements. The photocatalytic decomposition of phenol under the LED source of 416 nm identified the formation of Z-scheme heterojunction, which was confirmed by the photocurrents measurements. The photocatalytic activity of the nanocomposites decreased with the increasing content of WO₃, which was explained by shielding of the g-C₃N₄ surface by bigger WO₃ agglomerates. This study also demonstrates a unique combination of various characterization techniques working in solid and liquid phase.     

Enhanced visible-light photocatalytic properties of g-C3N4 by coupling with ZnAl2O4

A series of g-C₃N₄/ZnAl₂O₄ composites were prepared using a conventional calcination method and the heterostructures were systematically characterized. It was found that the combination of g-C₃N₄ with ZnAl₂O₄ significantly improve their photocatalytic activities. The optimum photocatalyst of composite is at 5% (wt%) of ZnAl₂O₄, whose degradation efficiency for methyl orange (MO) was 96% within 120 min under visible-light irradiation. The formation of heterojunction between g-C₃N₄ and ZnAl₂O₄ can facilitate efficient charge separation of photogenerated electron-hole pairs, which were confirmed by electrochemical impedance spectroscopy (EIS). As a result, the photocatalytic properties of composites were enhanced.     

Onion-like carbon modified porous graphitic carbon nitride with excellent photocatalytic activities under visible light

A series of onion-like carbon modified porous g-C₃N₄ (OLC/pg-C₃N₄) composites have been fabricated by a simple ultrasonic adsorption approach. The resultant OLC/pg-C₃N₄ composites exhibit excellent photocatalytic activity and stability towards the degradation of the dyes and phenol in aqueous solution under visible-light irradiation. The composite with 2.0 wt% OLC content shows the optimal photocatalytic activity for degrading rhodamine B (RhB), its rate constant is about three times that of pure pg-C₃N₄. The improved photocatalytic activity is mainly attributed to the synergetic effect of pg-C₃N₄ and OLC, including larger surface area, stronger visible light adsorption and efficient separation of photogenerated electrons and holes. Moreover, a possible mechanism of photocatalytic reaction over OLC/pg-C₃N₄ composite is proposed.     

C60/graphene/g-C3N4 composite photocatalyst and mutually- reinforcing synergy to improve hydrogen production in splitting water under visible light radiation

g-C₃N₄ as a new metal-free photocatalytic material for water splitting has attracted much attention in recent years, but its photocatalytic efficiency needs further improvement. Here we synthesized novel C₆₀/graphene/g-C₃N₄ composite photocatalytic materials with high hydrogen generation ability for water splitting under visible light radiation (λ>420 nm). These materials take full advantage of the electron conduction expressing of graphene and the superior-strong electron-attracting ability of C₆₀. The mutually-reinforcing synergy between graphene and C₆₀ improves the migration and utilization efficiency of photo-generated electrons and accelerates the separation of photo-generated charges, thus significantly enhancing the hydrogen generation capacity of g-C₃N₄. The hydrogen production amount and rate of C₆₀/graphene/g-C₃N₄ (10 mg/L C₆₀ and graphene) after 10 h are 5449.5 µmol/g and 545 µmol/g/h, which is 539.6 times of pure g-C₃N₄ under the same condition. The values are 50.8 and 4.24 times of graphene/g-C₃N₄ (10 mg/L graphene) and C₆₀/g-C₃N₄ (10 mg/L C₆₀), respectively. The apparent quantum yield of C₆₀/graphene/g-C₃N₄ (10 mg/L C₆₀ and graphene) in 97 h is about 7.2%. The improvement of hydrogen generation activity in 97 h suggests the high long-time stability of C₆₀/graphene/g-C₃N₄ in photocatalytic water spitting. The photocatalytic ability of C₆₀/graphene/g-C₃N₄ can be controlled by regulating the addition of graphene and C₆₀. The mutually-reinforcing synergy between graphene and C₆₀ was proved by X-ray photoelectron spectroscopy, photoluminescence spectrum and organic electron acceptors of MV²⁺. Thus, the joint action of C₆₀ and graphene promotes the migration, separation and utilization of photo-generated electrons, which is responsible for the significant enhancement of photocatalytic performance.     

In-situ synthesis of visible-light-driven plasmonic Ag/AgCl-CdWO4 photocatalyst

Novel plasmonic photocatalyst of Ag/AgCl-CdWO₄ was successfully synthesized via an in situ loading and photoreduction process. The as-obtained Ag/AgCl-CdWO₄ samples were characterized by various analytical techniques. The Ag/AgCl-CdWO₄ nanocomposites present a remarkable visible-light photocatalytic activity. The optimal Ag/AgCl-CdWO₄ can completely degrade RhB, MB and MO within 30 min. Moreover, 95% of phenol can also be degraded within 90 min. The enhanced photocatalytic activity was mainly attributed to two factors: the strong SPR of Ag NPs would improve the visible-light absorbance effectively. Simultaneously, the photo-generated electron–hole pairs can transfer and separate among the Ag/AgCl-CdWO₄ hybrid effectively.     

Synthesis of MoS2/g-C3N4 as a solar light-responsive photocatalyst for organic degradation

A novel molybdenum disulfide (MoS₂) and graphitic carbon nitride (g-C₃N₄) composite photocatalyst was synthesized using a low temperature hydrothermal method. MoS₂ nanoparticles formed on g-C₃N₄ nanosheets greatly enhanced the photocatalytic activity of g-C₃N₄. The photocatalyst was tested for the degradation of methyl orange (MO) under simulated solar light. Composite 3.0 wt.% MoS₂/g-C₃N₄ showed the highest photocatalytic activity for MO decomposition. MoS₂ nanoparticles can increase the interfacial charge transfer and thus prevent the recombination of photo-generated electron–hole pairs. The novel MoS₂/g-C₃N₄ composite is therefore shown as a promising catalyst for photocatalytic degradation of organic pollutants using solar energy.     

Carbon nitride nanowires/nanofibers: A novel template-free synthesis from a cyanuric chloride–melamine precursor towards enhanced adsorption and visible-light photocatalytic performance

The development of a graphitic carbon nitride (g-C₃N₄) photocatalyst is of great importance to a variety of visible utilization application fields. The desired high efficiency can be achieved by employing well-controlled g-C₃N₄ nanostructures. In this study, we successfully synthesized high surface area g-C₃N₄ nanowires and nanofibers using a cyanuric chloride and melamine precursor dispersed in a solvothermal reaction and with a subsequent calcination step. The obtained novel nanowire product had a diameter of 10–20 nm and a length of several hundreds of nanometers, while the nanofibers revealed fibrous nanostructures of randomly dispersed fibers with an average diameter of ~15 nm. The adsorption and photocatalytic experimental results indicated that the as-prepared nanowires and nanofibers showed enhanced activities compared with bulk g-C₃N₄. Based on our experimental results, a possible photocatalytic mechanism with hydroxyl and superoxide radical species as the main active species in photocatalysis was proposed. Moreover, our strategy may provide progress toward the design and practical application of 1D g-C₃N₄ nanostructures in the adsorption and photocatalytic degradation of pollutants.     

Synthesis of Mo-doped graphitic carbon nitride catalysts and their photocatalytic activity in the reduction of CO2 with H2O

Molybdenum doped graphitic carbon nitride (g-C₃N₄) catalysts were prepared by a simple pyrolysis method using melamine and ammonium molybdate as precursors. The characterization results indicated that the obtained Mo-doped g-C₃N₄ catalysts had worm-like mesostructures with higher surface area. Introduction of Mo species can effectively extend the spectral response property and reduce the recombination rate of photogenerated electrons and holes. CO₂ photocatalytic reduction tests showed that the Mo-doped g-C₃N₄ catalysts exhibited considerably higher activity (the highest CO and CH₄ yields of 887 and 123 μmol g^− 1-cat., respectively, after 8 h of UV irradiation.) compared with pure g-C₃N₄ from melamine.     

Inorganic–organic photocatalyst BiPO4/g-C3N4 for efficient removal of gaseous toluene under visible light irradiation

BiPO₄/g-C₃N₄ with different amounts of BiPO₄ was prepared through wet impregnation with calcination method. The BiPO₄/g-C₃N₄ showed large surface area (172.9 m² g^− 1) and the incorporation of BiPO₄ caused a red-shift of g-C₃N₄ in visible light. The photocatalytic degradation of toluene over the samples was investigated. The degradation of toluene could get 82% in BiPO₄/g-C₃N₄ photocatalysts under optimum reaction conditions. The BiPO₄/g-C₃N₄ exhibited a higher photocatalytic activity than pure g-C₃N₄ or BiPO₄. The improved photoactivity of BiPO₄/g-C₃N₄ could be attributed to strong absorption in visible light and effective separation of photo-induced hole-electron pairs between BiPO₄ and g-C₃N₄.     

Nanocomposites of SnO2 and g-C3N4: Preparation,characterization and photocatalysis under visible LED irradiation

Tin dioxide nanoparticles were prepared in the presence of graphitized carbon nitride (g-C₃N₄) forming nanocomposites with different contents of SnO₂ up to 40 %. G-C₃N₄ was synthetized by heating of melamine at 550 °C in the open air and Sn²⁺ ions were precipitated by sodium hydroxide in g-C₃N₄ aqueous dispersions. Resulting mixtures were dried by freezing at ?20 °C and calcined at 450 °C to obtain SnO₂/g-C₃N₄ nanocomposites.The nanocomposites were characterized by common characterization methods in solid state and in their aqueous dispersions using dynamic light scattering (DLS) analysis and photocatalysis. SnO₂ nanoparticles in the nanocomposites were found to have an average size of 4 nm, however, those precipitated without g-C₃N₄ had an average size of 14 nm. Separation of photoinduced electron and holes via heterojunction between SnO₂ and g-C₃N₄ was demonstrated by photocatalytic decomposition of Rhodamine B (RhB) under LED visible irradiation (416 nm) and photocurrent measurements. The most photocatalytically active nanocomposite contained 10 % of SnO₂. Graphitized carbon nitride was assumed to serve as a template structure for the preparation of SnO₂ nanoparticles with a narrow size distribution without using any stabilizing additives.     

Novel 3D flowerlike BiOCl0.7Br0.3 microspheres coupled with graphene sheets with enhanced visible-light photocatalytic activity for the degradation of rhodamine B

Highly efficient visible-light-driven 3D flowerlike BiOCl_0.7Br_0.3 microspheres coupled with graphene sheets with different graphene contents have been synthesized by a facile solvothermal process. The as-prepared samples were characterized by power X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), N₂ adsorption–desorption analysis and UV–vis diffuse reflectance spectra (DRS). Characterization results showed BiOCl_0.7Br_0.3 microspheres were composed of numerous nanoplates with a thickness of about 20 nm and dispersed uniformly on the surface of graphene. Moreover, the photocatalytic activities of these BiOCl_0.7Br_0.3/graphene composites under visible-light irradiation (λ>420 nm) were evaluated by the degradation of rhodamine B (RhB). The results indicate all BiOCl_0.7Br_0.3/graphene composites exhibited much higher photocatalytic activities than pristine BiOCl_0.7Br_0.3, pure BiOBr and BiOCl, and the highest activity was reached by the BiOCl_0.7Br_0.3/graphene composite photocatalyst with 10 wt% of graphene. The enhanced photocatalytic activity could be largely ascribed to more effective charge transportations and separations, larger BET surface areas and the increased light absorption. In addition, a possible photocatalytic mechanism of the BiOCl_0.7Br_0.3/graphene composites on basis of the experimental results was also proposed.     

Synthesis and characterization of graphitic carbon nitride sub-microspheres using microwave method under mild condition

Graphitic carbon nitride(g-C₃N₄) sub-microspheres was first prepared via a facile microwave synthesis through polymerization reaction between cyanuric chloride(C₃N₃Cl₃) and sodium azide (NaN₃) using acetonitrile (ACN) as solvent, and the prepared samples were investigated by XRD, FTIR, XPS, SEM, TEM, UV–Vis, PL, TGA and BET, respectively. The results show that g-C₃N₄ are insoluble to conventional solvents except DMSO, and it exhibits a good chemical stability, thermal stability(< 650 °C), particle size with 0.076–0.137 μm in diameter, surface area of 89.1 m²/g and a band gap of 2.41 eV. Additionally, g-C₃N₄ prepared by microwave method also displays higher thermal stability, smaller particle radius, larger surface area, lower band gap and stronger emission intensity than traditional solvothermal method. Finally, the effect of microwave on the behavior of C₃N₄ sub-microsphere is proposed as well.     

Preparation and its photocatalysis of Cd1−xZnxS nano-sized solid solution with PAMAM as a template

Cd_1−xZn_xS solid solution was prepared by coprecipitation method with PAMAM as a template, calcined at 573 K under N₂ atmosphere and characterized by BET, XRD, UV–vis, HRTEM and XRF. The size of Cd_1−xZn_xS solid solution particles was about 5 nm and the bandgap was estimated to be 2.09–3.12 eV. The photocatalytic activities of Cd_1−xZn_xS solid solutions on degradation of rhodamine B were evaluated under visible-light irradiation. The results indicated that Cd_0.59Zn_0.22S solid solution exhibited the highest photocatalytic activity among all the as-prepared samples. The mechanism of photocatalysis under visible-light irradiation was also discussed.     

Enhanced photoluminescence and photocatalytic activity of ZnO-ZnWO4 nanocomposites synthesized by a precipitation method

Zinc oxide (ZnO)-zinc tungstate (ZnWO₄) nanocomposites ((ZnO)_1−x(ZnWO₄)_x, x=0, 0.1, 0.2, 0.3, 0.5, 0.7, 0.9, 1) were prepared using a convenient precipitation method. The structural, morphological and optical properties of the samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), Ultraviolet-visible (UV–vis) absorbance measurements and photoluminescence (PL) spectroscopy. The photocatalytic performance of the samples was evaluated utilizing methyl orange (MO) under UV light irradiation. The SEM and HR-TEM analyses revealed that an intimate contact was possibly formed at the ZnO-ZnWO₄ interface. The PL spectra of the composites of ZnO and ZnWO₄ exhibited a stronger blue-green emission band in the range of 400–540 nm under 272 nm radiations compared with that of single phase ZnWO₄. And their photocatalytic performances were also elevated significantly when the value of the x was 0.1, 0.2, 0.3 and 0.5, almost twice as much to that of ZnO. The superior fluorescent and photocatalytic performances might be ascribed to the suitable energy levels related to the intimate contact between two different semiconductors, which are beneficial to the interfacial charge transfer between the conduction and valence bands.     

A novel TiO2 − xNx/BN composite photocatalyst: Synthesis,characterization and enhanced photocatalytic activity for Rhodamine B degradation under visible light

A novel TiO_2 − xN_x/BN composite photocatalyst was prepared via a facile method using melamine–boron acid adducts (M·2B) and tetrabutyl titanate as reactants. The morphological results confirmed that nitrogen-doped TiO₂ nanoparticles were uniformly coated on the surface of porous BN fibers. A red shift of absorption edge from 400 nm (pure TiO₂) to 520 nm (TiO_2 − xN_x/BN composites) was observed in their UV–Vis light absorption spectra. The TiO_2 − xN_x/BN photocatalysts exhibited enhanced photocatalytic activity for the degradation of Rhodamine B (RhB) and the highest photocatalytic degradation efficiency reached 97.8% under visible light irradiation for 40 min. The mechanism of enhanced photocatalytic activity was finally proposed.     

Synthesis of Ag3PO4–ZnO nanorod composites with high visible-light photocatalytic activity

Ag₃PO₄ nanoparticles with 50–100 nm in size distributed on the surface of ZnO nanorods with ca. 20 nm in diameter and 1–2 μm in length have been synthesized by a facile method. The Ag₃PO₄–ZnO nanorod composites had much higher photocatalytic activity toward degradation of Rhodamine B (RhB) under visible light irradiation than pure ZnO nanorods, and had better recyclability and stability than pure Ag₃PO₄ nanoparticles. The Ag₃PO₄–ZnO nanorod composite with the molar ratio of Ag₃PO₄:ZnO = 1:40 exhibited the highest photodegradation efficiency of RhB (93%), which was 1.5 times of pure ZnO nanorods.     

Growth mechanism and photocatalytic activity of chrysanthemum-like anatase TiO2 nanostructures

Chrysanthemum-like hierarchical anatase TiO₂ nanostructures self-assembled by nanorods have been successfully fabricated by a simple solvothermal route without using template materials or structure-directing additives. The products were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), Raman spectrometer system (Raman), UV–vis absorption spectroscopy (UV–vis) and N₂ adsorption–desorption measurement. The results indicate that synthesized chrysanthemum-like hierarchical anatase TiO₂ nanostructures have a spherical shape with an average diameter of 1.5 μm and they are composed of nanorods with a width of about 30 nm and a length of about 300 nm. The pore distribution of the sample exhibits two kinds of pores. Such mesoporous structure of the sample might be extremely useful in photocatalysis because they possess efficient transport pathways to the interior and supplies higher specific area for more pollutant molecules to be absorbed. In addition, the synthesized TiO₂ nanostructures show enhanced photocatalytic activity compared with commercial P25 for the degradation of RhB under UV light irradiation, which can be attributed to their special hierarchical structure and high light-harvesting capacity.     

Tailoring the bandgap of N-rich graphitic carbon nitride for enhanced photocatalytic activity

Nitrogen - rich graphitic carbon nitride (Ng-C₃N₄) with improved photocatalytic activity was engineered using a facile post-annealing treatment of pristine g-C₃N₄ in N₂ atmosphere. The thermal annealing did not modify the crystal structure, vibrational modes, or morphology of the N-rich g-C₃N₄ (Ng-C₃N₄). However, it decreased the crystallinity by broadening the dominant X-ray diffraction (XRD) peak and increased the surface area and mesoporous nature because of the formation of carbon vacancies. Diffuse reflectance spectroscopy indicated that the bandgap of the annealed Ng-C₃N₄ decreased from 2.82 to 2.77 eV compared to pristine g-C₃N₄. The increase of nitrogen content in the annealed Ng-C₃N₄ was quantified by X-ray photoelectron spectroscopy (XPS), which was also used to examine the formation of carbon vacancies. Photocurrent and electrochemical impedance spectroscopy measurements showed that the annealed Ng-C₃N₄ had higher light absorption capacity than the pristine g-C₃N₄. The photocatalytic performance of the samples was investigated for the degradation of crystal violet (CV) under ultra-violet light irradiation. The annealed Ng-C₃N₄ sample exhibited superior photodegradation of CV over pristine g-C₃N₄.