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.     

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.     

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.     

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.     

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.     

Direct microwave synthesis of graphitic C3N4 with improved visible-light photocatalytic activity

The graphitic carbon nitride (g-C₃N₄) was rapidly synthesized via direct high-energy microwave heating approach. During the preparation process, only low-cost melamine and artificial graphite powders were used, without any metal catalysts or inert protective gas. The microstructure was investigated by using X-ray diffraction (XRD), Flourier transformed infrared (FT-IR), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM). The spectra of XRD and HRTEM indicated that the obtained g-C₃N₄ had a high crystallinity. The optical spectra covering Photoluminescence (PL) and Ultraviolet-visible (UV–vis) were also measured at room temperature. PL peak and UV–vis absorption edge of the g-C₃N₄ were shown at 455 nm and 469 nm, respectively, indicating visible-light photocatalytic property. Finally, the photocatalytic activity of g-C₃N₄ was investigated and evaluated as photocatalyst for the photo-degradation of Rhodamine B (RhB) and Methyl Orange (MO) in aqueous solution under visible-light (λ>420 nm) irradiation, respectively. Results indicated that the g-C₃N₄ sample displayed an excellent performance of removing of RhB and MO due to the improved crystallinity and large surface area of 126 m²/g. After the visible-light photocatalytic reaction for 40 min, the decolorization ratios of RhB and MO reached up to 100% and 94.2%, respectively.     

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.     

Extraordinary toughening enhancement and flexural strength in Si3N4 composites using graphene sheets

Two types of Si₃N₄ composites containing graphene nanostructures using two different graphene sources, pristine graphene nanoplatelets and graphene oxide layers were produced by Spark Plasma Sintering. The maximum toughness of 10.4 MPa m^1/2, measured by flexure testing of pre-cracked bars, was achieved for a composite (∼60β/40α-Si₃N₄, ∼300 nm grain size) with 4 vol.% of reduced graphene oxide, indicating a toughening enhancement of 135% when compared to a similar Si₃N₄. This was also accompanied by a 10% increase in flexure strength (1040 MPa). For the composites with thicker graphene nanoplateletes only a 40% of toughness increase (6.6 MPa m^1/2) without strength improvement was observed for the same filler content. The large difference in the maximum toughness values accomplished for both types of composites was attributed to variations in the graphene/Si₃N₄ interface characteristics and the extent of monolayer graphene exfoliation.     

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.     

Calix[4]arene–carbazole-containing polymers: Synthesis and properties

New highly fluorescent calix[4]arene-containing phenylene-alt-ethynylene-3,6- and 2,7-carbazolylene polymers (CALIX-PPE-CBZs) have been synthesized for the first time and their photophysical properties evaluated. Both polymers were obtained in good isolated yields (70–84%), having M_w ranging from 7660–26,700 g mol⁻¹. It was found that the diethynyl substitution (3,6- or 2,7-) pattern on the carbazole monomers markedly influences the degree of polymerization. The amorphous yellow polymers are freely soluble in several nonprotic organic solvents and have excellent film forming abilities. TG/DSC analysis evidences similar thermal behaviors for both polymers despite their quite different molecular weight distributions and main-chain connectivities (T_g in the range 83–95 °C and decomposition onsets around 270 °C).The different conjugation lengths attained by the two polymers dictates much of their photophysical properties. Thus, whereas the fully conjugated CALIX-PPE-2,7-CBZ has its emission maximum at 430 nm (E_g = 2.84 eV; Φ_F = 0.62, CHCl₃), the 3,6-linked counterpart (CALIX-PPE-3,6-CBZ) fluoresces at 403 nm with a significant lower quantum yield (E_g = 3.06 eV; Φ_F = 0.31, CHCl₃). The optical properties of both polymers are predominantly governed by the intrachain electronic properties of the conjugated backbones owing to the presence of calix[4]arenes along the polymer chain which disfavor significant interchain interactions, either in fluid- or solid-state.     

Highly active and selective ethylene oligomerization catalysts: Asymmetric 2,6-bis(imino)pyridyl iron (II) complexes with alkyl and halogen substitutients

A series of asymmetric 2,6-bis(arylimino)pyridines with alkyl and halogen substitutients on different iminoaryl rings and corresponding iron (II) complexes ([2-(Ar₁N = CCH₃)-6-(Ar₂N = CCH₃)C₅H₃N]FeCl₂, 3a–3j) are synthesized and characterized. These Fe(II) complexes are highly active for ethylene oligomerization with high selectivity for linear α-olefins. The oligomer distributions can be tuned by the synergism of alkyl-steric effect and halogen electronic effect, and the production of C₆–C₁₆ can reach more than 80% with the highest selectivity being 87.5% for 3 g (Ar₁ = 2-ethylphenyl, Ar₂ = 2-fluorophenyl), which is 15–30% higher than that catalyzed by their methyl or fluoro-substituted symmetric counterparts.     

Graphitic carbon nitride nanosheet-assisted preparation of N-enriched mesoporous carbon nanofibers with improved capacitive performance

N-enriched mesoporous carbon nanofibers (NMCNFs) were prepared by an electrospinning technique using graphitic carbon nitride (g-C₃N₄) nanosheets both as sacrificial template and N-doping source. The resultant NMCNF film has a high N-doping level of 8.6 wt% and a high specific surface area of 554 m² g⁻¹. When directly used as the electrode material for supercapacitor, the free-standing NMPCNF film shows a significantly improved capacitive performance including a higher specific capacitance (220 F g⁻¹ at 0.2 A g⁻¹) and a better rate capability (∼70% retention at 20 A g⁻¹) than those of microporous carbon nanofiber film prepared using the same process without using g-C₃N₄ nanosheets (145 F g⁻¹ at 0.2 A g⁻¹ and ∼45% retention at 20 A g⁻¹). Moreover, the NMCNFs show superior stability with only a ∼3% decrease of its initial capacitance after 1000 cycles at a high current density of 10 A g⁻¹. More significantly, the energy density of a symmetrical supercapacitor (SC) based on the NMPCNF film can reach 12.5 Wh kg⁻¹ at a power density of 72 W kg⁻¹.     

Solvothermal in situ synthesis of (Schiff-base)-containing dinuclear cobalt compound

A new dinuclear cobalt compound, namely Co₂(L)(H₂O)Cl₂ (1, H₂L = N,N′-o-phenylenebis(salicylide-neimine) was obtained by one-pot solvothermal self-assembly of CoCl₂, 1,2-phenylenediamine, and salicylaldehyde in C₂H₅OH. The magnetic studies suggest weak antiferromagnetic behavior and the magnetic data were interpreted by means of a dinuclear cobalt model with the parameters of g = 2.12, J = ?1.25 cm^?1, θ = ?3.12 K.     

Alkylated graphene nanosheets for supercapacitor electrodes: High performance and chain length effect

Single electrode materials capable of both electric double-layer and Faradic redox-based pseudo capacitance can be used for fabrication of high performance supercapacitors in an easy way and thus are highly desirable in the energy storage field. This contribution reports a new kind of such materials based on alkylated graphene materials (C_nrGO, n is the carbon number of their alkyl side chains) having different alkyl side chains (n = 4, 8, and 16). These materials were prepared via esterification of KOH-treated GO with the corresponding alkyl bromides in the presence of a phase transfer catalyst. More importantly, water was used as the reaction medium, and thus endowing the preparation method an eco-friend feature. The so-prepared graphene materials displayed chain length-dependent specific surface area and the population of residue CO functionalities, and thus affording vast differences in their supercapacitor behaviors. C₄rGO, the product having butyl side chains, showed the best supercapacitor performance with a capacitance up to 242.2 F g⁻¹ at a scan rate of 100 mV s⁻¹ and a good cycling stability.     

Experimental study on the stability of graphitic C3N4 under high pressure and high temperature

The stability and decomposition of graphitic C₃N₄ (g-C₃N₄) were studied in the pressure and temperature range of 10–25 GPa and up to 2000 °C by multi-anvil experiments and phase characterization of the quenched products. g-C₃N₄ was found to remain stable at relatively mild temperatures, but decomposes to graphite and nitrogen at temperatures above 600–700 °C and up to 15 GPa, while it decomposes directly to diamond (plus nitrogen) above 800–900 °C and between 22 and 25 GPa. The estimated decomposition curve for g-C₃N₄ has a positive slope (~ 0.05 GPa/K) up to ~ 22 GPa, but becomes inverted (negative) above this pressure. The diamond formed through decomposition is characterized by euhedral crystals which are not sintered to each other, but loosely aggregated, suggesting the crystallization in a liquid (nitrogen) medium. The nitrogen release from the graphitic CN framework may also play an important role in lowering the activation energy required for diamond formation and enhancing the grain growth rate. No phase transition of g-C₃N₄ was found in the studied P–T range.     

Hydrazine hydrate-induced hydrothermal synthesis of MnFe2O4 nanoparticles dispersed on graphene as high-performance anode material for lithium ion batteries

Herein, a MnFe₂O₄/graphene (MnFe₂O₄/G) nanocomposite has been synthesized via a facile N₂H₄·H₂O-induced hydrothermal method. During the synthesis, N₂H₄·H₂O is employed to not only reduce graphene oxide to graphene, but also prevent the oxidation of Mn²⁺ in alkaline aqueous solution, thus ensuring the formation of MnFe₂O₄/G. Moreover, MnFe₂O₄ nanoparticles (5–20 nm) are uniformly anchored on graphene. MnFe₂O₄/G electrode delivers a large reversible capacity of 768 mA h g⁻¹ at 1 A g⁻¹ after 200 cycles and high rate capability of 517 mA h g⁻¹ at 5 A g⁻¹. MnFe₂O₄/G holds great promise as anode material in practical applications due to the outstanding electrochemical performance combined with the facile synthesis strategy.     

1-D networks formed by metal⋯sulfur van der Walls contacts: Novel tetrazole–thiolato Pd(II) and Pt(II) complexes

Pd(II)– and Pt(II)–azido complexes, [M(N₃)(PMe₃)₂(C–L)] {LH = 2-(2′)-thienyl pyridine; M = Pd (1), Pt(2)}, which contain σ-bonded heterocycles (L), were treated with aryl isothiocyanate (Me₂C₆H₃–NCS) to afford the corresponding Pd(II) and Pt(II) tetrazole–thiolato complexes, trans-{M[SCN₄(2,6-Me₂C₆H₃)](PMe₃)₂(C–L)} {M = Pd (3), Pt (4)}. Complexes 3 and 4 have a 1-D helical network formed by the intermolecular M?S van der Waals contacts.     

Micro/nano-structured graphitic carbon nitride–Ag nanoparticle hybrids as surface-enhanced Raman scattering substrates with much improved long-term stability

Surface-enhanced Raman scattering (SERS) substrates with high SERS activity and stability are important for SERS sensors. A facile method was developed to fabricate efficient and stable SERS substrates by combining Ag nanoparticles (NPs) and micro-scale sheeted graphitic carbon nitride (g-C₃N₄). The g-C₃N₄/Ag NPs hybrid could provide a great number of hot spots and concentrated the analyte by the π–π stacking interaction between analyte molecules and g-C₃N₄, making a dramatic Raman enhancement. Moreover, the g-C₃N₄/Ag NPs hybrid uniformly immobilized Ag NPs on the surface and edges of g-C₃N₄ sheets by an interaction between Ag NPs and g-C₃N₄, leading to much improved long-term stability. This could be explained in terms of the electron–donor effect of g-C₃N₄, which was further confirmed by density functional theory calculations. The inherent Raman enhancing effect of g-C₃N₄ itself also contributed to the total SERS responses. Due to multiple enhancement contributions, the g-C₃N₄/Ag NPs hybrid exhibited a strong Raman enhancement effect for with an enhancement factor of 4.6 × 10⁸ (evaluated by using crystal violet as a probe), and possessed wide adaptability from dyes, pesticides to bio-molecules.     

A highly efficient and noble metal-free photocatalytic system using NixB/CdS as photocatalyst for visible light H2 production from aqueous solution

Photocatalytic H₂ production from water is one of the most attractive issues for the conversion of solar energy into chemical energy. In this study, the Ni_xB/CdS photocatalyst was firstly used for photocatalytic H₂-evolution reaction and showed efficient visible-light photocatalytic activity and good stability for H₂-evolution from aqueous solution. The optimal Ni_xB loading content was determined to be 0.8 wt.%, and the corresponding H₂-production rate reached up to 4.8 mmol·h^− 1·g^− 1 after a 10 h visible light irradiation. It is proposed that the loading of Ni_xB on the surface of CdS could effectively increase the separation of photo-generated electrons and holes and greatly enhance the photocatalytic activity.     

Amine-directed structural studies of four zinc metal-organic frameworks based on a novel phosphonocarboxylate ligand

A novel phosphonocarboxylic ligand, 4′-phosphonobiphenyl-3,5-dicarboxylic acid (H₄pbpdc), was synthesized to construct 4 zinc compounds, namely, {[Zn₃(pbpdc)₂·2R}_n (R = C₅H₁₂N for 1, C₄H₁₀N for 2 and C₆H₁₆N for 3) and {[Zn₂pbpdc]·C₆H₁₈N₃}_n(4), which were characterized by X-ray crystallography, elemental analysis, FTIR and TG. Structures 1 ~ 3 have the same 3-dimensional (3-D) frameworks with point symbol of {4.6.7³.8}₂{4².6.7².8}₂{4².6².7.8}₂{4².6².7²}. Structure 4 is constructed from a 6-connected metallic cluster and 3-connected phosphonocarboxylic building units resulting in a topology of flu-3,6-C2/c. The luminescent properties of compounds 1 ~ 4 and organic ligand were studied.