Detection Of Active Species Research Articles

Solvothermal engineering of bismuth molybdate with C3N4 nanosheets, and enhanced photocatalytic activity

Microsphere Bi2MoO6 was fabricated and surface engineered by coupling with C3N4 nanosheets in a one-pot solvothermal reaction. The composites obtained have enhanced visible light absorption, improved separation of photogenerated charge carriers, and enriched photo-production of radicals. The photocatalytic activity of as-prepared Bi2MoO6/C3N4 composites (BC) in the degradation of RhB under visible light irradiation was clearly correlated with the proportion of the components. When the Bi2MoO6 content was 70 wt%, photocatalytic degradation by the composite (BC7) was 3.3, 4.49, and 6.03 times that by the photocatalysts N–TiO2, C3N4, and Bi2MoO6, respectively. A possible mechanism of the photocatalysis is proposed on the basis of detection of active species by use of different scavengers and results from physicochemical characterization by use of XRD, FTIR, UV–visible/DRS, TEM, FL, and transient photocurrent response. Bi2MoO6/C3N4 composites might have potential applications in protection of the environment.

Construction of ZnO/TiO2 photonic crystal heterostructures for enhanced photocatalytic properties

A highly ordered ZnO/TiO2 photonic crystal (ZnO/TiO2-PC) was obtained by a simply pyrolysis strategy. Combined with a series of characterizations, including scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and transmittance spectra, it was found that the in situ formed ZnO phases were uniformly grafted to TiO2-PC framework forming hybrid nanostructure. Additionally, the formation of heterojunction between ZnO and TiO2-PC enhanced the separation efficiency of photogenerated electron–hole pairs, which significantly improved the photocatalytic performances. Based on the results of photoelectrochemical measurement and the detection of active species in photocatalytic degradation process, the photocatalytic degradation mechanism of ZnO/TiO2-PC nanocomposite was proposed. It is hoped that our work could provide a good insight into the preparation of photonic crystal heterostructures for the environmental purification.

Comparison of atmospheric air plasmas excited by high-voltage nanosecond pulsed discharge and sinusoidal alternating current discharge

In this paper, atmospheric pressure air discharge plasma in quartz tube is excited by 15 ns high-voltage nanosecond pulsed discharge (HVNPD) and sinusoidal alternating current discharge (SACD), respectively, and a comparison study of these two kinds of discharges is made through visual imaging, electrical characterization, optical detection of active species, and plasma gas temperature. The peak voltage of the power supplies is kept at 16 kV while the pulse repetition rate of nanosecond pulse power supply is 100 Hz, and the frequency of sinusoidal power supply is 10 kHz. Results show that the HVNPD is uniform while the SACD presents filamentary mode. For exciting the same cycles of discharge, the average energy consumption in HVNPD is about 1/13 of the SACD. However, the chemical active species generated by the HVNPD is about 2–9 times than that excited by the SACD. Meanwhile, the rotational and vibrational temperatures have been obtained via fitting the simulated spectrum of N2 (C3Πu → B3Πg, 0-2) with the measured one, and the results show that the plasma gas temperature in the HVNPD remains close to room temperature whereas the plasma gas temperature in the SACD is about 200 K higher than that in HVNPD in the initial phase and continually increases as discharge exposure time goes on.

High photocatalytic activity of C-ZnSn(OH)6 catalysts prepared by hydrothermal method

Carbon-doped nano-ZnSn(OH)6 (C-ZnSn(OH)6) photocatalysts with different weight percents of carbon were successfully synthesized by a facile and economical hydrothermal process at 433K, and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) spectroscopy, UV–vis diffuse reflection spectroscopy (UV–vis DRS) and nitrogen physisorption studies. The photocatalytic activity was evaluated on the degradation of organic pollutants under ultraviolet (UV) light illumination. The results showed that compared to commercial P25 and pure ZnSn(OH)6, the photocatalytic performance of 0.58% C-ZnSn(OH)6 was remarkably improved. The photocatalytic conversion ratio of benzene and cyclohexane by 0.58% C-ZnSn(OH)6 was up to 77% and 50.5%, which is about 16.0 and 1.39, 12.3 and 6.39 times higher than that of P25 and pure ZnSn(OH)6, respectively. The 0.58% C-ZnSn(OH)6 catalyst also exhibited high photocatalytic activity toward methyl orange (MO) and phenol in suspended solution. Based on the characterization results and the detection of active species, the enhanced photocatalytic activities of C-ZnSn(OH)6 catalysts were discussed.

A high efficient photocatalyst Ag3VO4/TiO2/graphene nanocomposite with wide spectral response

Great efforts have been made to develop efficient visible light activated photocatalysts in recent years. In this work, Ag3VO4/TiO2/graphene nanocomposite as a wide spectrum responsive photocatalyst was prepared first by a two-step process, which exhibited obviously increased visible light absorption and photocatalytic activity in degradation of organic pollutants including methyl orange and Rhodamine B, compared with Ag3VO4/TiO2 and TiO2/GR nanocomposites. For Ag3VO4/TiO2/graphene nanocomposite, the introduction of graphene contributed to the uniform dispersion of Ag3VO4 and TiO2 nanoparticles on graphene sheets. The capacity of graphene in storing and shuttling electrons and the formation of heterojunction between Ag3VO4 and TiO2 facilitated together the enhancement of efficiency in the separation of photogenerated electron–hole pairs. Based on the results of photoelectrochemical measurement and the detection of active species in photocatalytic degradation process, the transfer of photogenerated carriers and photocatalytic degradation mechanism on Ag3VO4/TiO2/graphene nanocomposite were proposed and discussed in detail.

Spectroscopic Detection of Active Species on Catalytic Surfaces: Steady-State versus Transient Method

Discrimination between active and spectator species is an important and demanding task in catalysis research. A comparative study of the Pd-catalyzed CO hydrogenation using in situ diffuse reflectance IR Fourier transform spectroscopy (DRIFTS) in steady-state and dynamic (transient) experiments shows that the information on surface species differs significantly depending on the type of experiment. In order to discriminate between active species and spectator species not involved in the surface reactions, DRIFTS was combined with a transient technique, modulation excitation spectroscopy (MES). This approach allows the detection of surface species responding to a specific periodic external stimulus, i.e.achieved by concentration modulation, and thereby offers excellent potential to unveil features of the surface processes, which are not accessible by steady-state experiments. However, the example of CO hydrogenation shows that the perturbation imposed to the system has to be chosen properly to benefit from the transient technique. Modulation of the CO concentration did not provide deeper insight into the reaction mechanism, whereas periodic changes of the hydrogen concentration provided valuable information concerning the active surface species and the reaction pathway. The study revealed that only a small fraction (about 4%) of CO molecules adsorbed on specific Pd sites reacted with hydrogen, while the majority of adsorbed CO was inactive. The inactive CO molecules overwhelmingly contributed to the spectra measured under steady-state conditions.

Identifying active foraminifera in the Sea of Japan using metatranscriptomic approach

Metagenetics represents an efficient and rapid tool to describe environmental diversity patterns of microbial eukaryotes based on ribosomal DNA sequences. However, the results of metagenetic studies are often biased by the presence of extracellular DNA molecules that are persistent in the environment, especially in deep-sea sediment. As an alternative, short-lived RNA molecules constitute a good proxy for the detection of active species. Here, we used a metatranscriptomic approach based on RNA-derived (cDNA) sequences to study the diversity of the deep-sea benthic foraminifera and compared it to the metagenetic approach. We analyzed 257 ribosomal DNA and cDNA sequences obtained from seven sediments samples collected in the Sea of Japan at depths ranging from 486 to 3665m. The DNA and RNA-based approaches gave a similar view of the taxonomic composition of foraminiferal assemblage, but differed in some important points. First, the cDNA dataset was dominated by sequences of rotaliids and robertiniids, suggesting that these calcareous species, some of which have been observed in Rose Bengal stained samples, are the most active component of foraminiferal community. Second, the richness of monothalamous (single-chambered) foraminifera was particularly high in DNA extracts from the deepest samples, confirming that this group of foraminifera is abundant but not necessarily very active in the deep-sea sediments. Finally, the high divergence of undetermined sequences in cDNA dataset indicate the limits of our database and lack of knowledge about some active but possibly rare species. Our study demonstrates the capability of the metatranscriptomic approach to detect active foraminiferal species and prompt its use in future high-throughput sequencing-based environmental surveys.

High photocatalytic performance of zinc hydroxystannate toward benzene and methyl orange

Two facile and green methods without any templates, catalysts, surfactants or organic solvents were applied to synthesize ZnSn(OH)6 nanoparticles, i.e. homogeneous precipitation (HP) and hydrothermal (HT). The photocatalytic activities were evaluated on the degradation of organic pollutants under ultraviolet light illumination. Compared to commercial P25, the photoactivity of ZnSn(OH)6 was remarkably improved. The conversion and mineralization ratio of the photocatalytic degradation of benzene by the ZnSn(OH)6-HP were up to 75% and 68%, which is about 20 and 2 times higher than that of P25. The ZnSn(OH)6 has also exhibited high performance toward other persistent organic compounds as well as methyl orange in suspended solution. The order of photodegradation efficiencies of different catalysts was ZnSn(OH)6-HP>P25>ZnSn(OH)6-HT. Based on the characterization results and the detection of active species, the possible mechanism of the high photocatalytic activity of ZnSn(OH)6-HP was discussed. The simplified synthesis of zinc hydroxystannate with outstanding activity could be promisingly used in the future photocatalytic application.

Fabrication of Titanium Dioxide and Tungstophosphate Nanocomposite Films and Their Photocatalytic Degradation for Methyl Orange

Photocatalytic multilayer films with different numbers of bilayers were prepared via an electrostatic layer-by-layer (LbL) self-assembly method. These LbL films were characterized by UV-vis spectroscopy, atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). Our results indicate that TiO(2) and tungstophosphate (H(3)PW(12)O(40), abbreviated as PW(12)) are successfully incorporated into the thin films. The as-prepared (TiO(2)/PW(12))(n) films show good photocatalytic performance toward methyl orange (MO) solution at pH 2.0, which is attributed to the synergistic effect between TiO(2) and PW(12). The effect of experimental parameters including number of bilayers, initial concentration, and pH value of dye solution were also studied. The multilayer films can be easily recovered and reused several times with little change of degradation, indicating that they are stable under the ultraviolet (UV) irradiation. The detection of active species displays that active holes (h(+)) play a dominant role for MO photodegradation in the TiO(2)/PW(12) system. Taking advantage of immobilization of catalysts on glass slides, the problem of recovery is solved. It is expected that photocatalytic multilayer films have substantial applications in industry.

Detection of active soil fungi by RT-PCR amplification of precursor rRNA molecules

Microbial ecologists have used direct RT-PCR amplification of 16S rRNA molecules for the detection of active species of bacteria and archaea, and 18S rRNA molecules for the detection of active fungi. The drawback to this approach for fungi is that 18S rRNA sequences often do not provide sufficient taxonomic resolution to allow identification of taxa in mixed communities to genus or species level. Internal transcribed spacer (ITS) sequences are known to be more taxonomically informative than 18S rRNA sequences and are the common target in DNA based studies but are thought to be absent from RNA pools as they are cleaved after transcription of the large rRNA precursor molecule to leave the mature rRNA's for ribosome synthesis. Here we show, however, that fungal ITS regions can be detected in RNA pools by RT-PCR amplification of fungal precursor rRNA molecules. This suggests that precursor rRNA molecules reside in the cells of active fungi for sufficient time to allow RT-PCR amplification of ITS regions prior to their removal by post-transcriptional cleavage. The RT-PCR conditions for this approach were initially optimised using a range of fungi grown in pure culture prior to applying the approach to complex fungal communities in two contrasting soil types.

Electron attachment mass spectrometry as a diagnostics for electronegative gases and plasmas

Electron attachment mass spectrometry (EAMS) has been developed to study mixtures of electronegative gases and plasmas. A quadrupole mass spectrometer (QMS) has been used to detect negative ions, formed from sampled species by attachment of low energy electrons. Varying the electron energy allows to collect the attachment cross section of the considered species. EAMS appears to be a very powerful technique to study the chemistry of electronegative gases. Unlike ionization mass spectrometry, where cross sections are low at the threshold and rather flat over a broad range of electron energies, attachment resonances are sharp and distinct. Also very limited fragmentation of the parent negative ion occurs, so a given molecule yields only a few different negative ions. This facilitates identification of components in a gas mixture. It is particularly advantageous for detection of large, fragile molecules, which break up after ionization, but can be easily transformed into large negative ions. Moreover, sensitive detection of active species is possible due to their relatively high attachment cross sections. A particularly important application of EAMS is the determination of an effective attachment cross section in a plasma. Recording this cross section allows to decide on the actual negative ion formation mechanism in the plasma environment, where active products of plasma conversion can significantly alter the negative ion production channels and consequently the whole balance of charged particles. Examples of EAMS applications to fluorocarbon gases and low-pressure radio-frequency plasmas are discussed. In a CF4 discharge conversion of the parent gas into species like C2F6 and C3F8 is easily visualized. The dominant mechanism of negative ion formation in the plasma is electron attachment to these minority species and not to the parent gas. Also larger polymers are readily formed in fluorocarbon plasmas. In a C2F6 discharge molecules with up to ten carbon atoms (the mass limit of our apparatus) have been detected using EAMS.