Yihe Zhang

Fabrication of Multiple Heterojunctions with Tunable Visible- Light-Active Photocatalytic Reactivity in BiOBr−BiOI Full-Range Composites Based on Microstructure Modulation and Band Structures

The fabrication of multiple heterojunctions with tunable photocatalytic reactivity in full-range BiOBr-BiOI composites based on microstructure modulation and band structures is demonstrated. The multiple heterojunctions are constructed by precipitation at room temperature and characterized systematically. Photocatalytic experiments indicate that there are two types of heterostructures with distinct photocatalytic mechanisms, both of which can greatly enhance the visible-light photocatalytic performance for the decomposition of organic pollutants and generation of photocurrent. The large separation and inhibited recombination of electron-hole pairs rendered by the heterostructures are confirmed by electrochemical impedance spectra (EIS) and photoluminescence (PL). Reactive species trapping, nitroblue tetrazolium (NBT, detection agent of (•)O2(-)) transformation, and terephthalic acid photoluminescence (TA-PL) experiments verify the charge-transfer mechanism derived from the two types of heterostructures, as well as different enhancements of the photocatalytic activity. This article provides insights into heterostructure photocatalysis and describes a novel way to design and fabricate high-performance semiconductor composites.

Preparation of aligned porous gelatin scaffolds by unidirectional freeze-drying method

Porous gelatin scaffolds with microtubule orientation structure were manufactured by unidirectional freeze-drying technology, and their porous structure was characterized by scanning electron microscopy. Scaffolds with tunable pore size and high porosity up to 98% were obtained by adjusting the concentration of the gelatin solution and crosslinking agent during the preparation process. All the porous gelatin scaffolds exhibited oriented microtubule pores, with width and length from 50 to 100 microm and 100 to 500 microm, respectively. Meanwhile, the properties of the scaffolds, such as porosity, water adsorption ability and compressive strength, were studied. In vitro enzymatic degradation results showed that the absolute weight loss of the gelatin scaffolds exhibited an increasing trend from low to high gelatin concentration used to prepare gelatin scaffolds; in vitro cell culture results indicated that the porous gelatin scaffolds were non-toxic to cartilage cells, since the cells spread and grew well.

Deep-Ultraviolet Nonlinear Optical Materials: Na2Be4B4O11 and LiNa5Be12B12O33

Deep-UV coherent light generated by nonlinear optical (NLO) materials possesses highly important applications in photonic technologies. Beryllium borates comprising anionic planar layers have been shown to be the most promising deep UV NLO materials. Here, two novel NLO beryllium borates Na2Be4B4O11 and LiNa5Be12B12O33 have been developed through cationic structural engineering. The most closely arranged [Be2BO5]∞ planar layers, connected by the flexible [B2O5] groups, have been found in their structures. This structural regulation strategy successfully resulted in the largest second harmonic generation (SHG) effects in the layered beryllium borates, which is ~1.3 and 1.4 times that of KDP for Na2Be4B4O11 and LiNa5Be12B12O33, respectively. The deep-UV optical transmittance spectra based on single crystals indicated their short-wavelength cut-offs are down to ~170 nm. These results demonstrated that Na2Be4B4O11 and LiNa5Be12B12O33 possess very promising application as deep-UV NLO crystals.

Bi2O2(OH)(NO3) as a desirable [Bi2O2]2+ layered photocatalyst: strong intrinsic polarity, rational band structure and {001} active facets co-beneficial for robust photooxidation capability

Developing high-performance photocatalytic materials is of huge significance and highly desirable for fulfilling the pressing need in environmental remediation. In this work, we demonstrate the use of bismuth nitrate Bi2O2(OH)(NO3) as an absorbing photocatalyst, which integrates multiple superiorities, like a [Bi2O2]2+ layered configuration, a non-centrosymmetric (NCS) polar structure and highly reactive {001} facets. Bi2O2(OH)(NO3) nanosheets are obtained by a facile one-pot hydrothermal route using Bi(NO3)3·5H2O as the sole raw material. Photocatalysis assessment revealed that Bi2O2(OH)(NO3) holds an unprecedented photooxidation ability in contaminant decomposition, far out-performing the well-known photocatalysts BiPO4, Bi2O2CO3, BiOCl and P25 (commercial TiO2). Particularly, it displays a universally powerful catalytic activity against various stubborn industrial contaminants and pharmaceuticals, including phenol, bisphenol A, 2,4-dichlorophenol and tetracycline hydrochloride. In-depth experimental and density functional theory (DFT) investigations co-uncovered that the manifold advantages, such as large polarizability and rational band structure, as well as exposed {001} active facets, induced robust generation of strong oxidating superoxide radicals (˙O2−) in the conduction band and hydroxyl radicals (˙OH) in the valence band, thus enabling Bi2O2(OH)(NO3) to have a powerful and durable photooxidation capability. Bi2O2(OH)(NO3) also presents high photochemical stability. This work not only rendered a highly active and stable photocatalyst for practical applications, but also laid a solid foundation for future initiatives aimed at designing new photoelectronic materials by manipulating multiple advantageous factors.

Macroscopic Polarization Enhancement Promoting Photo- and Piezoelectric-Induced Charge Separation and Molecular Oxygen Activation

Efficient photo- and piezoelectric-induced molecular oxygen activation are both achieved by macroscopic polarization enhancement on a noncentrosymmetric piezoelectric semiconductor BiOIO3 . The replacement of V5+ ions for I5+ in IO3 polyhedra gives rise to strengthened macroscopic polarization of BiOIO3 , which facilitates the charge separation in the photocatalytic and piezoelectric catalytic process, and renders largely promoted photo- and piezoelectric induced reactive oxygen species (ROS) evolution, such as superoxide radicals (. O2- ) and hydroxyl radicals (. OH). This work advances piezoelectricity as a new route to efficient ROS generation, and also discloses macroscopic polarization engineering on improvement of multi-responsive catalysis.

Dielectric behavior and dependence of percolation threshold on the conductivity of fillers in polymer-semiconductor composites

Polymer-semiconductor PVDF∕LNO (polyvinylidene fluoride∕Li doped NiO) composites were fabricated via simple blending and hot-molding technique. The dielectric behavior of such composites was studied over broad frequency. The results revealed the dependence of percolation threshold on the conductivity of LNO filler in the composites. And the conductivity of the LNO fillers played an important role on the dielectric properties and critical exponents of the PVDF∕LNO composites. High dielectric constants and low conductivities of the composites were observed near the percolation threshold. Finally, critical exponents were also used to explain the experimental results, and provided useful information for understanding the resultant dielectric properties.

In situ co-pyrolysis fabrication of CeO2/g-C3N4 n–n type heterojunction for synchronously promoting photo-induced oxidation and reduction properties

Development of efficient photocatalysts with both photoinduced oxidation and reduction properties is of great importance for environmental and energy applications. Herein, we report the fabrication of CeO2/g-C3N4 hybrid materials by a simple in situ co-pyrolysis method using Ce(IO3)3 and melamine as precursors. The CeO2/g-C3N4 composite catalysts possess outstanding photocatalytic activity for phenol degradation and NO removal under visible light irradiation. The degradation efficiency reaches up to 68.5 and 17.3 times higher than that of pure CeO2 and g-C3N4, respectively. Significantly, it simultaneously exhibits an enhanced hydrogen production rate, which is 1.5 times that of the pure g-C3N4. The highly enhanced photo-induced oxidation and reduction activity could be attributed to the construction of a CeO2/g-C3N4 n–n type heterojunction established by our in situ co-pyrolysis route, which enables intimate interaction across the phase interfaces; this facilitates separation and transfer of photoexcited charge carriers. This study could not only provide a facile and general approach to the fabrication of high-performance carbon-nitride-based photocatalytic materials, but also increase our understanding further on designing new hybrid composite photocatalysts for multi-functional applications.

Sulfur Embedded in a Mesoporous Carbon Nanotube Network as a Binder-Free Electrode for High-Performance Lithium–Sulfur Batteries

Sulfur-porous carbon nanotube (S-PCNT) composites are proposed as cathode materials for advanced lithium-sulfur (Li-S) batteries. Abundant mesopores are introduced to superaligned carbon nanotubes (SACNTs) through controlled oxidation in air to obtain porous carbon nanotubes (PCNTs). Compared to original SACNTs, improved dispersive behavior, enhanced conductivity, and higher mechanical strength are demonstrated in PCNTs. Meanwhile, high flexibility and sufficient intertube interaction are preserved in PCNTs to support binder-free and flexible electrodes. Additionally, several attractive features, including high surface area and abundant adsorption points on tubes, are introduced, which allow high sulfur loading, provide dual protection to sulfur cathode materials, and consequently alleviate the capacity fade especially during slow charge/discharge processes. When used as cathodes for Li-S batteries, a high sulfur loading of 60 wt % is achieved, with excellent reversible capacities of 866 and 526 mAh g(-1) based on the weights of sulfur and electrode, respectively, after 100 cycles at a slow charge/discharge rate of 0.1C, revealing efficient suppression of polysulfide dissolution. Even with a high sulfur loading of 70 wt %, the S-PCNT composite maintains capacities of 760 and 528 mAh g(-1) based on the weights of sulfur and electrode, respectively, after 100 cycles at 0.1C, outperforming the current state-of-the-art sulfur cathodes. Improved high-rate capability is also delivered by the S-PCNT composites, revealing their potentials as high-performance carbon-sulfur composite cathodes for Li-S batteries.

Fabrication and enhanced dielectric properties of graphene–polyvinylidene fluoride functional hybrid films with a polyaniline interlayer

Graphene–polyvinylidene fluoride hybrid films (GPNs–PVDF) with a polyaniline (PANI) interlayer are fabricated by a facile and effective process. The morphology of the graphene–polyaniline nanoflakes (GPNs) is examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) and the interaction between graphene and PANI is investigated by Fourier transform infrared spectroscopy (FTIR), UV-visible spectroscopy, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The GPNs have a layered structure resembling a cake with the graphene sheets sandwiched between the PANI layers. The GPNs have a uniform morphology which can be controlled by adjusting the ratio of PANI to graphene. The PANI inter-layer plays an active role in the dielectric properties of the GPNs–PVDF composites which have low dielectric loss, high breakdown field, and large energy density. The enhanced dielectric performance originates from the insulating PANI layer which not only ensures good dispersion of graphene sheets in the PVDF but also acts as an inter-particle barrier to prevent direct contact with the graphene sheets.

Biocompatibility and bioactivity of plasma-treated biodegradable poly(butylene succinate).

Poly(butylene succinate) (PBSu), a novel biodegradable aliphatic polyester with excellent processability and mechanical properties, is a promising substance for bone and cartilage repair. However, it typically suffers from insufficient biocompatibility and bioactivity after implantation into the human body. In this work, H(2)O or NH(3) plasma immersion ion implantation (PIII) is conducted for the first time to modify the PBSu surface. Both the treated and control specimens are characterized by X-ray photoelectron spectroscopy, contact angle measurements and atomic force microscopy. The plasma treatments improve the hydrophilicity and roughness of PBSu significantly and the different PIII processes result in similar hydrophilicity and topography. C-OH and C-NH(2) functional groups emerge on the PBSu surface after H(2)O and NH(3) PIII, respectively. The biological results demonstrate that both osteoblast compatibility and apatite formability are enhanced after H(2)O and NH(3) PIII. Furthermore, our results suggest that H(2)O PIII is more effective in rendering PBSu suitable for bone-replacement implants compared to NH(3) PIII.