Wenjun Fa

Ag3PO4/Ag2CO3 p–n heterojunction composites with enhanced photocatalytic activity under visible light

Abstract Formation of a p–n heterojunction rather than p-type or n-type semiconductors can enhance the separation of photogenerated electrons and holes and increase the quantum efficiency of photocatalytic reactions owing to the difference of the electric potential in the inner electric field near the junction, pointing from n toward p. n-Ag3PO4/p-Ag2CO3 p–n heterojunction composites are prepared through a facile coprecipitation process. The obtained Ag3PO4/Ag2CO3 p–n heterojunctions exhibit excellent photocatalytic performance in the removal of rhodamine B (RhB) compared with Ag3PO4 and Ag2CO3. The 40%-Ag3PO4/Ag2CO3 composite photocatalyst (40 mol% Ag3PO4 and 60 mol% Ag2CO3) exhibits the best photocatalytic activity under visible light, demonstrating the ability to completely degrade RhB within 15 min. Transient photovoltage characterization and an active species trapping experiment further indicate that the formation of a p–n heterojunction structure can greatly enhance the separation efficiency of photogenerated carriers and produce more free h+ active species, which is the predominant contributor for RhB removal.

Preparation and characterisation of Ag3PO4/BiOBr composites with enhanced visible light driven photocatalytic performance

Abstract Ag3PO4/BiOBr composites were prepared by a facile room temperature liquid phase method. The samples were characterised by X-ray diffraction, SEM, energy dispersive X-ray spectroscopy, ultraviolet–visible and photoluminescence (PL) techniques. The photocatalytic activity was evaluated by photodegrading methylene blue under visible light irradiation. The results show that Ag3PO4/BiOBr composites were successfully formed and the Ag3PO4 nanoparticles were randomly distributed on the surface of BiOBr nanosheets. The composites exhibit better visible light absorption ability, and the PL results show that the composites have enhanced photogenerated carrier separation efficiency. The best photocatalytic performance is obtained for the sample with Ag/Bi ratio of 0·5, the photocatalytic efficiency of which is six times that of BiOBr. The improvement of the photocatalytic activity is associated with the coupling effects of the two semiconductors.

Design and synthesis of ternary semiconductor Cu7.2(SexS1−x)4 nanocrystallites for efficient visible light photocatalysis

A new series of ternary semiconductor compounds, Cu7.2(SexS1−x)4 (0.2 ≤ x ≤ 0.8) nanocrystallites, that exhibited good photocatalytic activity under visible-light irradiation, were facilely synthesized under mild conditions. The Cu7.2(SexS1−x)4 nanocrystallites were characterized by powder X-ray diffraction, transmission electron microscopy, energy dispersive X-ray spectroscopy and UV-Vis absorption spectra. From X-ray data it is found that the cell constant a of different samples varies linearly with the composition x as: a (A) = 5.5959 + 0.1586x. UV-Vis absorption spectra indicate that the apparent band gap energies can be tuned by adjusting the composition x so as to better match to the whole solar spectrum. Unlike the most studied TiO2 that only responds to the UV-light irradiation, the present Cu7.2(SexS1−x)4 nanocrystallites exhibited much better photocatalytic activity under visible light on degradation of RhB. It is believed that the photocatalytic superiority of the Cu7.2(SexS1−x)4 nanocrystallites is mainly due to the compositional gradient arisen from uneven distribution of Se/S compositions in the compounds, which may induce a more efficient charge separation/transport in the Cu7.2(SexS1−x)4 photocatalysts.

Heavy doping of S2 in Cu7.2S4 lattice into chemically homogeneous superlattice Cu7.2Sx nanowires: strong photoelectric response

This is the first time a series of chemically homogeneous superlattice Cu7.2Sx (x = 4.07, 4.52, 6.01, 6.20, 6.45) nanowires have been successfully synthesized by heavy doping of S2 species in Cu7.2S4 lattice through a simple wet-chemical route. This superlattice structure is a polytypoid structure tuned by adjusting the atom ratio of S2 to S in lattice configuration. The perfect superlattice Cu7.2S6.20 structure interestingly consists of two alternating lattice fringes corresponding to the atom layers of Cu–S and Cu–S2 in an even spacing of 5.70 A. The article describes the formation, morphology, composition and structure of the Cu7.2Sx superlattice nanowires. Photoluminescence (PL) spectra and transient photovoltage (TPV) measurements reveal that the generation and separation efficiency of the photogenerated charges of Cu7.2Sx nanowires could be greatly improved by adjusting the S2/S ratio in the lattice configuration, and thus enhance the luminescence quantum efficiency. This study reveals that the S2 species in Cu7.2Sx nanowires play a very important role in determining the dynamic properties of photogenerated charge carriers.

Construction of cross-linked polymer films covalently attached on silicon substrate via a self-assembled monolayer

A new synthetic approach was developed to fabricate cross-linked polymer films covalently attached on a silicon substrate via a self-assembled monolayer (SAM) using a low energy proton beam as the initiator. The widely used silane coupling reagent 3-(mercaptopropyl) trimethoxysilane [HS(CH2)3Si(OCH3)3] was employed as an intermediate SAM to chemically bond the cross-linked polymer film to the silicon substrate. Dotriacontane was selected as a precursor that was spin-coated on the SAM-terminated silicon wafers. The film thickness can be easily controlled by spin-coating precursor solutions of different concentrations. X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and contact angle measurements confirmed the formation of SAM on the silicon substrate and the subsequent cross-linkage between the SAM and the upper polymer film formed. The resulting cross-linked polymer films are relatively stable, with all layers covalently attached together so that the whole film could not be removed by rinsing in both organic solvent and even more reactive HF solutions. In particular, the resistance of the cross-linked polymer film towards HF etching can be useful for lithography and device fabrication for polymer based electronics. The capability of using different SAMs to attach various polymer films was also demonstrated.

From BiOCl to Bi2WO6 in Bi–W–Cl–O solvothermal system: phase-morphology evolution and photocatalytic performance

Abstract The phase and morphology evolution in the Bi–W–Cl–O solvothermal system was investigated. The products were characterised by X-ray diffraction, SEM and high resolution TEM. The optical properties and photocatalytic performance of the samples were evaluated. The results show that the composite Bi2WO6/BiOCl sample was obtained for the reaction time of 15 h. The light absorption ability and the photodegradation efficiency were enhanced obviously for Bi2WO6/BiOCl. The mechanisms for the formation of the composite and the optimisation of the photocatalytic activity were also discussed.

Thermal physical properties of Al-coated diamond/Cu composites

To acquire a well bonded interface between the copper and the diamond particles in diamond-copper matrix composites, an available process to apply a vapor deposited aluminum (Al) coating onto diamond particles was used to solve this interfacial problem. The diamond-copper matrix composites were prepared by spark plasma sintering (SPS) process and the effect of Al-coated diamond particles was demonstrated. The experimental results showed that the densification, interfacial bonding and thermal conductivity of Al-coated composites were evidently improved compared to those of the uncoated composites. A maximum thermal conductivity (TC) of 565 W/(m·K) was obtained in the coated composite containing 50vol% diamond particles sintered at 1 163 K. Additionally, the experimental data of thermal conductivity and coefficient of thermal expansion (CTE) were compared with the predictions from several theoretical models.

Insight into the reactivity difference of two iron phthalocyanine catalysts in chromogenic reaction: DFT theoretical study

ABSTRACT Chromogenic reaction catalyzed by metal phthalocyanine (MPc) complexes is a novel and practical method for the facile identification of phenolic pollutants. Exploring the catalytic reaction mechanism is the current concern in the investigation. In this work, tetranitro iron (II) phthalocyanine (TNFe(II)Pc) and iron (II) phthalocyanine (Fe(II)Pc) catalyzed chromogenic reactions were studied at the B3LYP level on the basis of the density functional theory (DFT) calculation. The molecular structure, atomic charge, and frontier molecular orbital of these two kinds of iron phthalocyanine complex were investigated. The calculation results demonstrate that no obvious difference for geometry structures of Fe(II)Pc and TNFe(II)Pc macrocycle can be found, while the atomic charge of Fe atom increases obviously with the four nitro groups substituted on the peripheral of macrocycle. By applying the descriptor of donor–acceptor molecular hardness, the difference of electron transfer from chlorophenol substrates to TNFe(II)Pc/Fe(II)Pc was well explained. Our investigations could provide a new strategy in designing various MPc catalysts for chromogenic identification of chlorophenol pollutants.