Z-scheme WOx/Cu-g-C3N4 heterojunction nanoarchitectonics with promoted charge separation and transfer towards efficient full solar-spectrum photocatalysis.

Construction of Z-scheme heterojunctions has been considered one superb method in promoting solar-assisted charge carrier separation of carbon-based materials to achieve efficient utilization of solar energy in hydrogen production and CO2 reduction. One interesting concept in nanofabrication that has become trend recent years is nanoarchitectonics. A heterostructure photocatalyst constructed based on the idea of nanoarchitectonics using the combination of g-C3N4, metal and an additional semiconducting nanocomposite is investigated in this paper. Z-scheme tungsten oxide incorporated copper modified graphitic carbon nitride (WOx/Cu-g-C3N4) heterostructures are fabricated via immobilization of WOx on Cu nanoparticles modified superior thin g-C3N4 nanosheets. Mechano-chemical pre-reaction and a two-step high-temperature thermal polymerization process are the keys in attaining homogeneous distribution of Cu nanoparticles in g-C3N4 nanosheets. The horizontal growth of homogeneously distributed WOx nanobelts on Cu modified g-C3N4 (Cu-g-C3N4) base via solvothermal synthesis is achieved. The photocatalytic performances of the heterostructures are evaluated through water splitting and CO2 photoreduction measurements in full solar spectrum irradiation condition. The presence of Cu nanoparticles in the composite system improves charge transport between g-C3N4 and WOx and thus enhances the photocatalytic performances (H2 generation and CO2 photoreduction) of the composite material, while the presence of WOx nanocomposites enhances light absorption of the composite material in the near infrared range. The synthesized heterostructure with optimized WOx to Cu-g-C3N4 ratio and in case of no co-catalyst addition exhibits enhanced photocatalytic H2 evolution (4560 µmolg-1h-1) as well as excellent CO2 reduction rate (5.89 µmolg-1h-1 for CO generation).

Photodegradation Process of Organic Dyes in the Presence of a Manganese-Doped Zinc Sulfide Nanowire Photocatalyst.

Zinc sulfide (ZnS) nanowires represent a promising candidate in many fields, including optoelectronics and photocatalysis because of their advantages such as excellent optical properties, chemical stability and an easy-scalable simple synthesis method. In this study, an energy-friendly microwave radiation process was used to develop the single-step, solvothermal process for the growth of manganese-doped zinc sulfide (ZnS) and undoped nanocrystals (NCs) in the forms of nanowires using two short amines as a stabilizer, e.g. ethylenediamine and hydrazine, respectively. ZnS nanowires doped with Mn atoms show absorbance in UV and in the visible region of the spectrum. The photocatalytic degradation of rhodamine B in the presence of Mn-doped and undoped ZnS nanocrystals illuminated with only a 6-W UV lamp has been comprehensively studied. The effect of Mn doping and the presence of a nanocrystal stabilizer on the degradation process was determined. It was found that the efficiency of a photocatalytic degradation process was strongly affected by both factors: the doping process of nanowires with Mn2+ atoms and the attachment of ligands to the nanocrystal surface.

Construction of 2D/2D MoS2/g-C3N4 Heterostructures for Photoreduction of Cr (VI).

2D/2D MoS2/g-C3N4 (MCN) surface heterostructures were created by second thermal polymerization of bulk g-C3N4 and the reaction of thiourea and MoO3 at 670 °C. MoS2 networks grew vertically along the (002) facet on superior thin g-C3N4 nanosheets. The layered heterostructures drastically improved the Cr(VI) removal ability. In the dark case, 27% of Cr(VI) was removed within 45 min. The result indicates that the adsorption of Cr(VI) was a chemical adsorption process involving the sharing and transfer of electrons. The equilibrium data indicate that the adsorbent was covered with a monolayer adsorbate, which conformed to the Langmuir isotherm model (R2 = 0.9618). In addition, MCN nanocomposites could convert Cr(VI) into non-toxic Cr(III) by photoreduction under visible light irradiation. With an optimized composition, 100% of Cr(VI) was removed within 30 min, which was ∼10 times quicker compared with Cr(VI) removal under dark conditions. Because g-C3N4 nanosheets (sample CN670) with higher photocurrent density revealed the lowest photoreduction Cr(VI) ability, adsorption plays an important role in Cr(VI) removal. For MoS2/g-C3N4 nanocomposites used in Cr(VI) removal, adsorption and photoreduction were incorporated together to get excellent performance.

Modification of Higher Alkanes by Nanoparticles to Control Light Propagation in Tapered Fibers.

This study presents the doping of higher alkanes, namely, pentadecane (C15) and hexadecane (C16), with ZnS:Mn nanoparticles to create new types of in-line optical fiber sensors with unique optical properties. In this research, the phenomenon of light beam leakage out of the taper and its interaction with the surrounding materials is described. The fabricated new materials are used as cladding in a tapered optical fiber to make it possible to control the optical light beam. The manufactured sensor shows high sensitivity and fast response to the change in the applied materials. Results are presented for a wide optical range of 1200-1700 nm with the use of a supercontinuum source and an optical spectrum analyzer, as well as for a single wavelength of 800 nm, corresponding to the highest transmitted power. The results present a change in the optical property dependence on the temperature in the cooling and heating process. For all materials, the measurements in a climatic chamber are provided between 0 and 40 °C, corresponding to the phase change of the alkanes from solid to liquid. The addition of nanoparticles to the volume of alkanes is equal to 1 wt%. To avoid a conglomeration of nanoparticles, the anti-agglomeration material, Brij 78 P, is used.

Thermo-Optical Switching Effect Based on a Tapered Optical Fiber and Higher Alkanes Doped with ZnS:Mn.

The paper investigates the effect of thermo-optic switching resulting from the hybrid combination of a tapered optical fiber (TOF) with alkanes doped with nanoparticles of zinc sulfide doped with manganese (ZnS:Mn NP). Presented measurements focused on controlling losses in an optical fiber by modification of a TOF cladding by the alkanes used, characterized by phase change. Temperature changes cause power transmission changes creating a switcher or a sensor working in an ON-OFF mode. Phase change temperatures and changes in the refractive index of the alkane used directly affected power switching. Alkanes were doped with ZnS:Mn NPs to change the hysteresis observed between ON-OFF modes in pure alkanes. The addition of nanoparticles (NPs) reduces the difference between phase changes due to improved thermal conductivity and introduces extra nucleating agents. Results are presented in the wide optical range of 550-1200 nm. In this investigation, hexadecane and heptadecane were a new cladding for TOF. The higher alkanes were doped with ZnS: Mn NPs in an alkane volume of 1 wt.% and 5 wt.%. The thermo-optic effect can be applied to manufacture a thermo-optic switcher or a temperature threshold sensor.

Formation and stability of manganese-doped ZnS quantum dot monolayers determined by QCM-D and streaming potential measurements.

Manganese-doped ZnS quantum dots (QDs) stabilized by cysteamine hydrochloride were successfully synthesized. Their thorough physicochemical characteristics were acquired using UV-Vis absorption and photoluminescence spectroscopy, X-ray diffraction, dynamic light scattering (DLS), transmission electron microscopy (HR-TEM), energy dispersive spectroscopy (EDS) and Fourier transform infrared (FT-IR) spectroscopy. The average particle size, derived from HR-TEM, was 3.1nm, which agrees with the hydrodynamic diameter acquired by DLS, that was equal to 3-4nm, depending on ionic strength. The quantum dots also exhibited a large positive zeta potential varying between 75 and 36mV for ionic strength of 10-4 and 10-2M, respectively (at pH 6.2) and an intense luminescent emission at 590nm. The quantum yield was equal to 31% and the optical band gap energy was equal to 4.26eV. The kinetics of QD monolayer formation on silica substrates (silica sensors and oxidized silicon wafers) under convection-controlled transport was quantitatively evaluated by the quartz crystal microbalance (QCM) and the streaming potential measurements. A high stability of the monolayer for ionic strength 10-4 and 10-2M was confirmed in these measurements. The experimental data were adequately reflected by the extended random sequential adsorption model (eRSA). Additionally, thorough electrokinetic characteristics of the QD monolayers and their stability for various ionic strengths and pH were acquired by streaming potential measurements carried out under in situ conditions. These results were quantitatively interpreted in terms of the three-dimensional (3D) electrokinetic model that furnished bulk zeta potential of particles for high ionic strengths that is impractical by other experimental techniques. It is concluded that these results can be used for designing of biosensors of controlled monolayer structure capable to bind various ligands via covalent as well as electrostatic interactions.

Au Catalyst Decorated Silica Spheres: Synthesis and High-Performance in 4-Nitrophenol Reduction.

A three-step synthesis has been developed to fabricate Au nanoparticle-decorated silica spheres as a catalyst (Au/SiO2). The Au/SiO2 catalyst was created by depositing uniformly Au nanoparticles with an average diameter of 5 nm on the SiO2 spheres by using optimal preparation conditions. Furthermore, the ratio of SiO2 and gold plays an important role for creating highly monodispersed Au nanoparticles. Compared with pure gold nanoparticles, the catalyst revealed admirable catalytic performance for the reduction reaction of 4-nitrophenol. The catalytic activities of Au/SiO2 samples were evaluated by the catalytic reduction of 4-nitrophenol under the liquid phase hydrogenation. Au/SiO2 catalysts with enough stability and activity can be recycled five times continuously for the reduction of 4-nitrophenol. The reduction mechanism of 4-nitrophenol and the catalytic action of the Au/SiO2 catalyst which has high reaction race constant k were discussed.

ZnO nanoflowers with single crystal structure towards enhanced gas sensing and photocatalysis.

In this paper, ZnO nanoflowers (NFs) were fabricated by thermal decomposition in an organic solvent and their application in gas sensors and photocatalysis was investigated. These single crystal ZnO NFs, which were observed for the first time, with an average size of ∼60 nm and were grown along the {100} facet. It was suggested that oleylamine used in the synthesis inhibited the growth and agglomeration of ZnO through the coordination of the oleylamine N atoms. The NFs exhibited excellent selectivity to acetone with a concentration of 25 ppm at 300 °C because they had a high specific surface area that provided more active sites and the surface adsorbed oxygen species for interaction with acetone. In addition, the ZnO NFs showed enhanced gas sensing response which was also ascribed to abundant oxygen vacancies at the junctions between petals of the NFs. Furthermore, ZnO-reduced graphene oxide (RGO) composites were fabricated by loading the ZnO NFs on the surface of the stratiform RGO sheet. In the photodegradation of rhodamine B tests, the composite revealed an enhanced photocatalytic performance compared with ZnO NFs under UV light irradiation.

Synthesis and Composition-Dependent Visible Photocatalysis of Ag/AgBr Necklace-Like Heterostructures.

A two-step synthesis was developed to fabricate Ag/AgBr necklace-like nano-heterostructures at room temperature. Multiple crystalline Ag nanowires were used as templates following an oxidation route in situ from CuBr2 to create Ag/AgBr heterostructures. Polyvinylpyrrolidone can govern the formation of one-dimensional Ag/AgBr necklace-like nano-heterostructures. The composition of the heterostructures was adjusted by changing the amount of CuBr2 . Experimental conditions were optimized. In particular, the concentration and injection rate of copper bromide solution play an important role in controlling the oxidation of the Ag nanowires for the purpose of adjusting the morphology of the Ag/AgBr heterostructures. As a result, the heterostructures with 40 mol % AgBr displayed a regular necklace-like morphology. Under visible-light irradiation, Ag/AgBr necklace-like heterostructures with AgBr molar ratios of 10 to 50 % exhibited enhanced plasmonic photocatalytic performance for the degradation of organic pollutants (methyl orange, methylene blue, and rhodamine B).