Photothermal catalytic properties of layered titanium chalcogenide nanomaterials.

The search for novel photocatalysts that make use of almost the entire solar spectrum remains an ongoing task to achieve high efficiency in energy conversion. While titanium chalcogenides offer a variety of phase compositions with different photophysical properties, their photocatalytic performance in pollutant degradation has not been investigated to date. In contrast to the model photocatalyst titanium dioxide, titanium chalcogenides possess small band gaps which make them eligible to absorb light in the visible range up to the near-infrared region, thus making them interesting candidates for photocatalysis. Herein titanium chalcogenide-based photocatalysts are synthesized by the chemical vapor transport (CVT) method and studied for their photocatalytic activity towards pollutant degradation. A series of titanium chalcogenides TiXn (X = S, n = 1-3; X = Se, n = 2; X = Te, n = 1) have been characterized by a variety of physico-chemical methods. Due to the expected non-stoichiometry of some titanium sulfides, they offer a large number of defect states which make them interesting candidates for photocatalysis. Thus, these titanium-chalcogenides were systematically studied for the photocatalytic degradation of pollutants using methyl orange dye as the test pollutant under simulated sunlight. Particularly TiS and TiS3 show high photocatalytic and thermocatalytic activity, outperforming the activity of titanium dioxide (pure anatase). By controlling the ratios of titanium and chalcogen elements and the specific reaction conditions, a variety of titanium chalcogenides with different compositions and phases showing a high photocatalytic activity can be accessed. Furthermore, it is found that the formation of a titanium dioxide passivation layer during photocatalysis results in a titanium oxide/titanium sulfide heterostructure. This allows further enhancement of the photocatalytic and thermocatalytic activity compared to the bare Ti-chalcogenides.

Controlling surface morphology and sensitivity of granular and porous silver films for surface-enhanced Raman scattering, SERS.

The design of efficient substrates for surface-enhanced Raman spectroscopy (SERS) for large-scale fabrication at low cost is an important issue in further enhancing the use of SERS for routine chemical analysis. Here, we systematically investigate the effect of different radio frequency (rf) plasmas (argon, hydrogen, nitrogen, air and oxygen plasma) as well as combinations of these plasmas on the surface morphology of thin silver films. It was found that different surface structures and different degrees of surface roughness could be obtained by a systematic variation of the plasma type and condition as well as plasma power and treatment time. The differently roughened silver surfaces act as efficient SERS substrates showing greater enhancement factors compared to as prepared, sputtered, but untreated silver films when using rhodamine B as Raman probe molecule. The obtained roughened silver films were fully characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron (XPS and Auger) and ultraviolet-visible spectroscopy (UV-vis) as well as contact angle measurements. It was found that different morphologies of the roughened Ag films could be obtained under controlled conditions. These silver films show a broad range of tunable SERS enhancement factors ranging from 1.93 × 102 to 2.35 × 105 using rhodamine B as probe molecule. The main factors that control the enhancement are the plasma gas used and the plasma conditions, i.e., pressure, power and treatment time. Altogether this work shows for the first time the effectiveness of a plasma treatment for surface roughening of silver thin films and its profound influence on the interface-controlled SERS enhancement effect. The method can be used for low-cost, large-scale production of SERS substrates.

SO2 gas adsorption on carbon nanomaterials: a comparative study.

Owing to their high stability against corrosive gases, carbon-based adsorbents are preferentially used for the adsorptive removal of SO2. In the present study, SO2 adsorption on different carbon nanomaterials namely carbon nanohorns (CNHs), multiwalled carbon nanotubes (MWNTs), single-walled carbon nanotubes (SWNTs) and vertically aligned carbon nanotubes (VACNTs) are investigated and compared against the adsorption characteristics of activated carbon and graphene oxide (GO). A comprehensive overview of the adsorption behavior of this family of carbon adsorbents is given for the first time. The relative influence of surface area and functional groups on the SO2 adsorption characteristics is discussed. The isosteric heat of adsorption values are calculated to quantify the nature of the interaction between the SO2 molecule and the adsorbent. Most importantly, while chemisorption is found to dominate the adsorption behavior in activated carbon, SO2 adsorption on carbon nanomaterials occurs by a physisorption mechanism.

Gas adsorption capacity in an all carbon nanomaterial composed of carbon nanohorns and vertically aligned carbon nanotubes.

Whereas vertically aligned carbon nanotubes (VACNTs) typically show a promising adsorption behavior at high pressures, carbon nanohorns (CNHs) exhibit superior gas adsorption properties in the low pressure regime due to their inherent microporosity. These adsorption characteristics are further enhanced when both materials are opened at their tips. The so prepared composite material allows one to investigate the effect of physical entrapment of CO2 molecules within the specific adsorption sites of VACNTs composed of opened double walled carbon nanotubes (CNTs) and in specific adsorption sites created by spherically aggregated opened single walled carbon nanohorns. Combining 50 wt% of tip opened CNTs with tip opened CNHs increases the CO2 adsorption capacity of this material by ∼24% at 30 bar and 298 K compared to opened CNHs alone.

ZnS/ZnO@CNT and ZnS@CNT nanocomposites by gas phase conversion of ZnO@CNT. A systematic study of their photocatalytic properties.

ZnS nanoparticles have been synthesized on vertically aligned carbon nanotubes by gas-phase conversion of ZnO nanoparticles which have been tethered on vertically aligned carbon nanotubes using atomic layer deposition (ALD). The resulting ZnO@CNT nanocomposite has been converted to ZnS@CNT by reacting it with hydrogen sulfide using thioacetamide as a precursor. The composition of the resulting nanocomposite could be tuned from a mixed ternary ZnS/ZnO@CNT nanocomposite to a pure ZnS@CNT nanocomposite. At the same time, the amount of wurtzite and sphalerite phases varies in the ZnS@CNT nanocomposite. The resulting nanocomposites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), selected area electron diffraction (SAED), ultraviolet-visible diffuse reflectance spectroscopy (UV-VIS DRS) and photoluminescence spectroscopy (PL). Finally, the different nanocomposites were tested for their photocatalytic activity by the photocatalytic decomposition under visible light using methyl orange (MO). Herein a systematic study of the photocatalytic activity of different compositions of ZnS in the ZnS@CNT nanocomposite was performed for the first time.

Synchronous spectrofluorimetric determination of naphthalene in water samples using mixed micellar medium.

A mixed micellar medium of sodium dodecyl sulfate and Pluronic F-127 was used to enhance the fluorescence of naphthalene and to obtain lower LODs. The method was based upon measuring the first-derivative synchronous fluorescence spectrum of naphthalene by using a mixed micellar medium at a constant wavelength difference delta lambda = 60 nm, where a greater fluorescence enhancement was observed if compared to using a single surfactant separately. A linear fluorimetric calibration curve was obtained for naphthalene in a concentration range of 10-200 ng/mL. The LOD was 7.13 ng/mL, which is well below the health advisory limit for naphthalene in drinking water as suggested by the U.S. Environmental Protection Agency. The method can be easily adopted for determination of naphthalene in aqueous media including tap water and river water. The recoveries obtained were 95.979-115.645%. The proposed method was validated according to International Conference on Harmonization guidelines and successfully applied to determine naphthalene in real life water samples from different sources.

Novel method for determination of anthracene by coupling dispersive liquid-liquid extraction to first-derivative synchronous spectrofluorimetry.

A novel method could be adopted successfully for determination of anthracene in environmental samples, utilizing dispersive liquid-liquid extraction followed by first-derivative synchronous fluorimetry at a constant wavelength difference Δλ = 165 nm, where a linear calibration curve was obtained in a concentration range of 0.5-100 ng mL(-1) at 244 nm. The detection limit was 0.1 ng mL(-1). The method can be easily adopted for determination of anthracene in aqueous media including tap water and river water. The recoveries obtained were 85.40-108.02%. The proposed method was validated according to International Conference of Harmonization (ICH) guide lines and successfully applied to determine anthracene in pure form and in water samples including real life water samples from different sources. All the results obtained were compared with those of published method, where no a significant difference was observed.