Wenjiang Li

Synthesis of tunable ZnS–CuS microspheres and visible-light photoactivity for rhodamine B

Tunable ZnS–CuS microspheres were readily prepared via replacing the Zn2+ ions of solid ZnS microspheres with Cu2+ ions in an aqueous solution under a hydrothermal condition, and were then characterized by XRD, SEM, TEM, UV-Vis, PL and XPS techniques. The thickness of CuS shell on the surface of ZnS core can be controlled by changing the ion-exchange time, which plays an important role in the visible light photodegradation efficiency of rhodamine B in aqueous solution. Degradation rate can rapidly reach ca. 72% under visible light irradiation for 15 min and then ca. 98% after 60 min using the ZnS–CuS microspheres as the photocatalyst.

Preparation of various kinds of copper sulfides in a facile way and the enhanced catalytic activity by visible light

Various kinds of copper sulfides (CuS, a mixture of Cu7S4–CuS and Cu9S5) were synthesized by simply adjusting the amount of copper chloride and sodium sulfide in a solvothermal process. The different molar ratios of copper chloride and sodium sulfide result in the formation of different kinds of copper sulfides with various morphologies, such as tiny particle, hexagonal plate and octahedron. The products were characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. And the optical properties of the products were recorded by means of UV-Vis absorption and photoluminescence spectroscopy. Moreover, due to the presence of visible light, we found that the catalytic activities of the products for oxidation and decomposition of Rhodamine B with the assistance of hydrogen peroxide were enhanced, and the degradation efficiency of RhB was increased from 40% to 98% in 15 minutes at room temperature.

Preparation and adsorption capacity of porous MoS2 nanosheets

Layered porous MoS2 with high adsorption capacity was synthesized directly using molybdenum trioxide and potassium rhodanate as Mo and S sources in a facile hydrothermal method without any surfactant and sacrificial template. The influences of varying the hydrothermal temperature on the morphology and adsorptive properties of MoS2 are discussed. As-prepared MoS2 samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field-emission scanning electron microscopy (SEM), transmission electron microscopy (TEM), ultraviolet-visible spectrophotometry (UV-Vis), room-temperature photoluminescence spectroscopy (RT-PL), thermogravimetric analysis (TGA) and Brunauer–Emmet–Teller (BET) measurements. MoS2 samples exhibited an optimal nanostructure, specific surface area and thermal stability when the hydrothermal temperature was 190 °C, and the layered porous structure is comprised of many thin nanosheets. In addition, the final adsorption capacities of the layered MoS2 toward RhB, MB and MO were studied. The sample exhibited ultrafast adsorption for dye removal and could reach 163.0 mg g−1, 499.0 mg g−1 and 125.1 mg g−1 at 420 min, respectively. The adsorption mechanism was also studied. The results indicate that layered MoS2 structures possess a significant adsorption ability, which may be useful for further research and practical applications of the layered MoS2 adsorbent in wastewater treatment.

Direct writing of stable Cu–Ag-based conductive patterns for flexible electronics

Cu–Ag-based highly conductive patterns were drawn directly on a flexible substrate using a roller pen filled with Cu–Ag NPs ink. The particle packing density is important for the patterns conductivity. First, the addition of smaller Cu NPs (∼6.5 nm) between the larger Ag particles (∼16.5 nm) improves the particle packing density by filling the pores, which can help improve conductivity at lower temperatures. Furthermore, combination of temperature and stress by hot sintering & hot-pressure sintering makes the residual pore space decrease and improves the conductivity of the patterns. Finally, compared to bulk Cu wire (1.72 μΩ cm), the resistivity of the Cu–Ag patterns sintered at 160 °C is reduced to 6.2 ± 0.4 μΩ cm, which is acceptable for conductive patterns. Samples with a decorative logo drawn by the Cu–Ag NPs exhibited excellent conductive performance and mechanical integrity.

Synthesis of stable CucoreAgshell&Ag particles for direct writing flexible paper-based electronics

Highly conductive flexible paper-based patterns were drawn directly using a brush pen dipped in ink consisting of copper–silver core–shell with individual silver (CucoreAgshell&Ag) particles. Using a cost-effective and green method, the formation of these CucoreAgshell&Ag particles is first driven by a transmetalation reaction on the surface of copper nanoparticles between copper atoms and silver ions, and then excessive Ag ions were further reduced by the glucose to form individual Ag nanoparticles. Characterization of these particles by XRD, SEM and TGA confirm the CucoreAgshell&Ag structure and their stability towards oxidation. The conductivity of the bending pattern was experimentally tested with different bending angles, bending cycles and bending storage times. It was found that the silver shell with external excessive Ag NPs not only improves the packing density, but also enhancing the particle purity results in the high conductivity of the bending pattern. Sintered at a low temperature of 160 °C and after 3000 bending cycles and storage for 300 days, the linear resistivity of the pattern increased from ∼5 μΩ cm to ∼20 μΩ cm, 4 times higher than before the pattern was bent, which is acceptable for conductive patterns in practical applications. Thus, this approach represents a promising method for the formation of microelectrodes or electronic devices with good flexibility and conductivity.

Preparation of monodispersed CuS nanocrystals in an oleic acid/paraffin system

Well-dispersed CuS nanocrystals were synthesized through a simple hot injection approach using cupric oxide and elemental sulfur as the precursors in an oleic acid/liquid paraffin system. The structural, morphological and optical properties of the as-prepared nanocrystal CuS samples were characterized by transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, ultraviolet-visible and near-infrared spectrophotometry, and room-temperature photoluminescence (RT-PL). The band gap of the CuS samples were estimated from the ultraviolet-visible spectra. The formation mechanism of monodispersed CuS nanocrystals in an oleic acid/liquid paraffin system was proposed. The cleaning agents have an important influence on the final morphology of the CuS nanocrystals, and pure hexagonal covellite CuS NCs can be obtained by controlling the ratio of Cu2+ : S2− = 1 : 1. The as-prepared CuS nanocrystals with the narrow band gap reveal dramatically broad absorption bands in the visible-light and near-infrared (NIR) region, exhibiting promising applications in photovoltaic cells, electrochemical sensors and photocatalysts.

Preparation and properties of regenerated cellulose hydrogels

The regenerated cellulose (RCE) hydrogels were successfully prepared via an easy and green environmental method in N-methylmorpholine-N-oxide (NMMO) aqueous solution. The effect of cellulose content on the thermostability properties, swelling behavior and retention rate of hydrogels was investigated. The thermostability of RCE hydrogels was slightly enhanced with the addition of 8 wt% cellulose, the highest decomposition temperature rose from 335 °C to 352 °C, and the least heat loss is about 75.60%. The equilibrium swelling ratio increases from 394.12% for 3% cellulose hydrogels to 619.46% for 8% cellulose hydrogels. The retention ratio increases from 1.13% to 28.46%.

SYNTHESIS OF NANOCRYSTALLINE CdS QUANTUM DOTS VIA PARAFFIN LIQUID AS SOLVENT AND OLEIC ACID AS THE REACTING MEDIA

Fluorescent semiconductor nanocrystals have been widely used as fluorescent materials in chemical sensors, biotechnology, medical diagnostics, biological imaging and many other fields. Compared to the conventional organic fluorophores, the inorganic quantum dots (QDs) have many advantages, including broad absorption spectra, narrow emission spectra, good photostability and long fluorescent lifetime after excitation. Here, the high quality CdS QDs were synthesized directly from sulfur and CdO using the paraffin liquid as solvent and the oleic acid as the reacting media. The synthesized CdS QDs with a zinc blende (cubic) crystal structure were proved by X-ray diffraction. HRTEM observation revealed that the CdS QDs were uniform and the average grain size was about 4 nm. The optical properties of the CdS QDs were characterized by using photoluminescence (PL) spectrophotometer and Ultraviolet-visible (UV-Vis) absorption spectrophotometer. The formation mechanism of CdS QDs in the paraffin liquid and oleic acid system was proposed.

Fabrication, characterization and in vitro evaluation of triboelectric nanogenerator based on 317 L stainless steel and polylactic acid

A novel, cost-effective biomedical triboelectric nanogenerator (TENG) has been fabricated based on biocompatible medical 317 L stainless steel (317 L SS) and polylactic acid (PLLA) films as the friction layers, whose surface roughness was designed by simple and low-cost laser etching and hot-embossing template methods, respectively. With the increase of the TENGs tribo-interface roughness and the molecular weight of the PLLA, the power output of TENG was greatly increased owing to more charges being produced and the excellent mechanical properties PLLA possessed. When the 317 L SS plate surface roughness was 66.54% measured by the image J software and the PLLA film with a larger molecular weight at 500 000 was patterned with the 1000 mesh screen template, the maximal short current, open voltage and transferred charge of TENG reached up to 60 μA, 150 V and ∼125 nC, respectively. At the optimum condition, the maximum instantaneous power of the TENG was 5.5 mW at a load resistance of ∼2.5 MΩ and the saturation voltage was 20 V when the load capacitance was 0.1 μF. The evaluation of the TENGs biocompatibility in vitro was performed by using the simulated body fluid (SBF) solution and ultrasonic wave to mimic the body environment with various vibrations, respectively. After 6 h ultrasonic bath for the directly immersed TENG, the pH of the SBF solution just changed slightly from 7.4 to 7.61 with an acceptable degradation of the output power of TENG. The cellular toxicity test also demonstrates that the mouse L929 cells grow excellently with normal morphology even after 5 d. These results indicate that the TENG has a good stability in the body environment and the output performance can still drive many micro-medical devices.

Preparation and Photocatalytic Activity of Ag2S/ZnS Core–Shell Composites

Ag2S/ZnS core–shell composite microspheres were successfully synthesized via a simple two-step hydrothermal process, in which Ag+ ions might replace Zn2+ ions on the surface of ZnS microspheres via an ion exchange, and subsequently form Ag2S nucleus on the surface of the microspheres. The effect of Ag2S content on the structure, morphology and optical properties of the material was studied in detail. We found that the photocatalytic efficiency of Ag2S/ZnS composites for the degradation of Rhodamine B (RhB) aqueous solution is much higher than that of pure ZnS or Ag2S under solar-simulated light irradiation, which is considered that the combination of a narrow band gap with a wide band gap semiconductor can timely transfer photogenerated electron–hole pairs and rapidly separate photogenerated electrons and holes. Moreover, the catalytic activities of the 4%Ag2S/ZnS sample for oxidation and decomposition of RhB with the assistance of hydrogen peroxide are enhanced with an increase of the degradation efficiency from 68.8 to 90.0% at room temperature.