Fangxiao Wang

Enhanced photocatalytic activity over the Ag2O–g-C3N4 composite under visible light

The Ag2O–g-C3N4 composite was prepared by the coprecipitation method and was well characterized by X-ray diffraction, transmission electron microscopy with energy dispersion X-ray spectroscopy, UV-vis diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy, photoluminescence spectroscopy and surface photovoltage spectroscopy. The photocatalytic activities were evaluated in the degradation of Rhodamine B aqueous solution. The results showed that Ag2O sized 5–10 nm was highly anchored on the surface of the pure g-C3N4 support, causing the Ag2O–g-C3N4 composite to show stronger absorption in the visible light region and higher photocatalytic activities than pure g-C3N4 and Ag2O. The enhanced photocatalytic activities were attributed to combined effects, including highly dispersed smaller Ag2O particles, stronger visible absorption and higher charge separation efficiency. The possible mechanism for the photocatalytic activity of Ag2O–g-C3N4 was tentatively proposed.

Polycondensation of guanidine hydrochloride into a graphitic carbon nitride semiconductor with a large surface area as a visible light photocatalyst

A low-cost, widely available and environmentally benign compound guanidine hydrochloride was applied to prepare g-C3N4 by thermal-induced polymerization at different temperatures. The as-prepared g-C3N4 was thoroughly characterized by X-ray diffraction, Fourier transform infrared spectroscopy, elemental analyses, N2 adsorption–desorption isotherms, thermal gravimetric analysis and differential scanning calorimetry, transmission electron microscopy, UV-vis diffuse reflectance spectra and photoluminescence spectra. It was noticeable that g-C3N4 prepared from guanidine hydrochloride possessed a much larger surface area than that prepared from melamine. And its photocatalytic activity was evaluated for degrading Rhodamine B dye which demonstrated that the g-C3N4 synthesized from guanidine hydrochloride exhibited a much higher activity than that prepared from melamine. Moreover, the activity can be further enhanced by increasing the condensation temperature of g-C3N4. In addition, the as-prepared g-C3N4 was also stable as demonstrated in the recycling experiments.

Periodic Mesoporous Organosilica with a Basic Urea‐Derived Framework for Enhanced Carbon Dioxide Capture and Conversion Under Mild Conditions

A periodic mesoporous organosilica with a basic urea-derived framework (PMO-UDF) was prepared and characterized thoroughly. The PMO-UDF showed an enhanced CO2 capture capacity at low pressure (≤1 atm) and an exceptional catalytic activity in CO2 coupling reactions with various epoxides to yield the corresponding cyclic carbonates under mild conditions because of the presence of a high surface area, basic pyridine units, and multiple hydrogen-bond donors. The highly stable catalyst could be reused at least six successive times without a significant decrease of the catalytic efficiency or structural deterioration, thus the PMO-UDF composite is considered as a promising material for CO2 capture and conversion.

Zn-based ionic liquids as highly efficient catalysts for chemical fixation of carbon dioxide to epoxides

The novel Zn-based task-specific ionic liquids (Zn-TSILs) catalysts were developed for the coupling of carbon dioxide and epoxides to form cyclic carbonates under mild reaction conditions without using additional organic solvents and cocatalysts. Due to the synergistic effects of the cation and anion in this catalytic system, excellent yields and selectivities to cyclic carbonates were achieved with high TOF values up to 794 h−1. Among the catalysts investigated, OH-containing Zn-TSILs showed better activity than COOH-containing Zn-TSILs, and [(CH2CH2OH)Bim]ZnBr3 was found to be the best. Additionally, the influences of CO2 pressure and catalyst concentration were also investigated over [(CH2CH2OH)Bim]ZnBr3. In addition, the rate constants as well as the activation energies for the cycloaddition reaction catalyzed by Zn-TSIL and TSIL were comparatively determined. The activation energy was calculated to be 34.1 kJ mol−1 for bare TSIL catalyst, whereas the Zn-TSIL reduced the activation energy value by 14.7 kJ mol−1. Moreover, the Zn-TSIL was easily recyclable without significant loss of activity, representing the exceptionally promising candidate for the effective fixation of CO2 to epoxides.

In situ bubble template promoted facile preparation of porous g-C3N4 with excellent visible-light photocatalytic performance

Porous graphitic carbon nitride (pg-C3N4) was facilely and economically prepared through in situ bubble templates such as (NH4)2S2O8, and the surface area of the resultant pg-C3N4 was controlled from 6.4 to 55.0 m2 g−1 by adjusting the mass ratio of (NH4)2S2O8/melamine. Moreover, pg-C3N4 was also obtained by other gas-generating porogens of ammonium salts, displaying the generality of the preparation method. The as-prepared g-C3N4 presented a porous structure with a higher surface area and displayed an improved separation efficiency for photogenerated electron–hole pairs. These integrative positive factors contributed to pg-C3N4 possessing more excellent photocatalytic activity for degrading Rhodamine B and phenol pollutants, and splitting water to H2 than bulk g-C3N4 under visible-light. Moreover, the as-prepared pg-C3N4 exhibited unexceptionable stability and reusability even after four photocatalytic runs. The simple, economical and general fabrication strategy with bubble-generated porogen agents for porous graphitic carbon nitride with superior visible-light photocatalytic performance is attractive for environmental and energy application fields.

Melamine–ZnI2 as heterogeneous catalysts for efficient chemical fixation of carbon dioxide to cyclic carbonates

In this contribution, the combination of melamine with Lewis acid ZnI2 was developed as heterogeneous dual catalysts for the cycloaddition of carbon dioxide with epoxides yielding the corresponding cyclic carbonates. With molar ratio of 1 : 3.3 of ZnI2 to melamine, high yield (96%) and selectivity (99%) of propylene carbonate was obtained at 150 °C and 3.0 MPa for 4.0 h. The binary catalysts were also effectively versatile for CO2 cycloaddition to other epoxides, especially the less active epoxides such as styrene oxide and cyclohexene oxide. Additionally, the catalysts could be separated easily from the products after reaction and then reused efficiently. Furthermore, a possible synergistic catalytic mechanism was proposed, wherein, melamine played the dual roles to activate CO2 and epoxide simultaneously, ZnI2 activated epoxide and subsequently attacked the activated epoxide, the synergetic effects from melamine and ZnI2 promoted the reaction smoothly. The binary catalysts showed the advantages of simple preparation, low cost, abundant availability and high catalytic activity for CO2 chemical fixation into valuable chemicals.

Facile synthesis of a g-C3N4 isotype composite with enhanced visible-light photocatalytic activity

A highly active g-C3N4 isotype composite was prepared with a precursor mixture of melamine and thiourea by a one-step thermal treatment. The differences in the electronic band structure of the as-prepared isotype g-C3N4 made the band levels match with each other. This novel metal-free isotype composite was demonstrated to promote the separation of photoinduced charges, leading to a significant enhancement in the photocatalytic activity for degrading rhodamine B under visible-light irradiation. Moreover, the resultant g-C3N4 isotype composite possessed excellent stability after three recycles. Finally, the relevant mechanism for the photodegradation process was also proposed.

A Simple Method for the Preparation of TiO2 /Ag-AgCl@Polypyrrole Composite and Its Enhanced Visible-Light Photocatalytic Activity.

A novel and facile method was developed to prepare a visible-light driven TiO2 /Ag-AgCl@polypyrrole (PPy) photocatalyst with Ag-AgCl nanoparticles supported on TiO2 nanofibers and covered by a thin PPy shell. During the synthesis, the PPy shell and Ag-AgCl nanoparticles were prepared simultaneously onto TiO2 nanofibers, which simplified the preparation procedure. In addition, because Ag-AgCl aggregates were fabricated via partly etching the Ag nanoparticles, their size was well controlled at the nanoscale, which was beneficial for improvement of the contact surface area. Compared with reference photocatalysts, the TiO2 /Ag-AgCl@PPy composite exhibited an enhanced photodegradation activity towards rhodamine B under visible-light irradiation. The superior photocatalytic property originated from synergistic effects between TiO2 nanofibers, Ag-AgCl nanoparticles and the PPy shell. Furthermore, the TiO2 /Ag-AgCl@PPy composite could be easily separated and recycled without obvious reduction in activity.

The crystal phase transformation of Ag2WO4 through loading onto g-C3N4 sheets with enhanced visible-light photocatalytic activity

A g-C3N4/Ag2WO4 composite photocatalyst was synthesized via a simple co-precipitation method at room temperature and was thoroughly characterized by X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, UV-visible diffuse reflectance spectroscopy and photoluminescence spectroscopy. The characterization results indicated that upon depositing Ag2WO4 onto the surface of g-C3N4 its morphology changed from primary rod-like particles to globular nanoparticles and its phase changed from α-type to β-type Ag2WO4. When the composite was used as the catalyst in the photodegradation of Rhodamine B, 40%-g-C3N4/Ag2WO4 exhibited the highest photocatalytic activity with its rate constant was about 10.8 times larger than that of pure g-C3N4 and 3.12 times larger than that of bare Ag2WO4. The enhanced photocatalytic activity can be attributed to the complementary potentials of the conduction bands and valence bands of g-C3N4 and Ag2WO4, which could not only realize the effective separation of photoinduced electron and hole pairs, but also retained the catalysts high stability and photocatalytic performance even after five recycles. Furthermore, a possible photocatalytic mechanism for the degradation of RhB over the g-C3N4/Ag2WO4 composite was proposed according to the results of active species quenching experiments.