In this article we present the first comparative study of the transient decay dynamics of photo-generated charges for the three polymorphs of TiO2. To our knowledge, this is the first such study of the brookite phase of TiO2 over timescales relevant to the kinetics of water splitting. We find that the behavior of brookite, both in the dynamics of relaxation of photo-generated charges and in energetic distribution, is similar to the anatase phase of TiO2. Moreover, links between the rate of recombination of charge carriers, their energetic distribution and the mode of transport are made in light of our findings and used to account for the differences in water splitting efficiency observed across the three polymorphs.
In this work, the emission efficiency of InxGa1-xN based light emitting diodes (LEDs) had been numerically investigated with the variation of the number of quantum well. From our calculation, we found that non-uniformity of carriers distribution (especially electron) in the wells leads to serious inhomogeneity of radiative recombination distribution that would degrade the efficiency of the LED with more wells. However, the problem was minimized when the selected quantum barriers were doped with a reasonable doping level. Comparison with other reported experimental works were also included. At the end of this work, we proposed several types of preferable LEDs designs with optimum structural parameters.
Human bocavirus (HBoV) is a single-stranded DNA virus in Parvoviridae family, causing respiratory diseases in human. The recent identifications of genomic recombination among the four human bocavirus genotypes and related non-human primate bocaviruses have shed lights into the evolutionary processes underpinning the diversity of primate bocavirus. Among these reports, however, we found inconsistency and possible alternative interpretations of the recombination events. In this study, these recombination events were reviewed, and the related genome sequences were re-analysed, aiming to inform the research community of bocavirus with more consistent knowledge and comprehensive interpretations on the recombination history of primate bocavirus.
A high recombination rate and low charge collection are the main limiting factors of copper oxides (cupric and cuprous oxide) for the photocatalytic degradation of organic pollutants. In this paper, a high performance copper oxide photocatalyst was developed by integrating cupric oxide (CuO) and cuprous oxide (Cu2O) thin films, which showed superior performance for the photocatalytic degradation of methylene blue (MB) compared to the control CuO and Cu2O photocatalyst. Our results show that a heterojunction photocatalyst of CuO-Cu2O thin films could significantly increase the charge collection, reduce the recombination rate, and improve the photocatalytic activity.
The existence of surface organic capping ligands on quantum dots (QDs) has limited the potential in QDs emission properties and energy band gap structure alteration as well as the carrier localization. This drawback can be addressed via depositing a thin layer of a semiconductor material on the surface of QDs. Herein, we report on the comparative study for photoluminescent (PL) properties of PbS and PbS/MnS QDs. The carrier localization effect due to the alteration of energy band gap structure and carrier recombination mechanism in the QDs were investigated via PL measurements in a temperature range of 10-300 K with the variation of the excitation power from 10 to 200 mW. For PbS QDs, the gradient of integrated PL intensity (IPL) as a function of excitation power density graph was less than unity. When the MnS shell layer was deposited onto the PbS core, the PL emission exhibited a blue shift, showing dominant carrier recombination. It was also found that the full width half-maximum showed a gradual broadening with the increasing temperature, affirming the electron-phonon interaction.
A facile one-pot impregnation-thermal reduction strategy was employed to fabricate sandwich-like graphene-g-C3N4 (GCN) nanocomposites using urea and graphene oxide as precursors. The GCN sample exhibited a slight red shift of the absorption band edge attributed to the formation of a C-O-C bond as a covalent cross linker between graphene and g-C3N4. The GCN sample demonstrated high visible-light photoactivity towards CO2 reduction under ambient conditions, exhibiting a 2.3-fold enhancement over pure g-C3N4. This was ascribed to the inhibition of electron-hole pair recombination by graphene, which increased the charge transfer.
A complex HIV-1 unique recombinant form involving subtypes CRF01_AE, B, and B' was recently identified from an injecting drug user in Malaysia. A total of 13 recombination breakpoints were mapped across the near-full-length genome of isolate 10MYPR226, indicating the increasingly diverse molecular epidemiology and frequent linkage among various high-risk groups.
Three strains of HIV-1 unique recombinant forms (URFs) descended from subtypes B, B', and CRF01_AE were identified among people who inject drugs in Kuala Lumpur, Malaysia. These three URFs shared a common recombination breakpoint in the reverse transcriptase region, indicating frequent linkage within the drug-injecting networks in Malaysia.
A silver nanoparticle-decorated N,S-co-doped TiO2 nanocomposite was successfully prepared and used as an efficient photoanode in high-performance dye-sensitized solar cells (DSSCs) with N719 dye. The DSSCs assembled with the N,S-TiO2@Ag-modified photoanode demonstrated an enhanced solar-to-electrical energy conversion efficiency of 8.22%, which was better than that of a DSSC photoanode composed of unmodified TiO2 (2.57%) under full sunlight illumination (100 mWcm(-2), AM 1.5 G). This enhanced efficiency was mainly attributed to the reduced band gap energy, improved interfacial charge transfer, and retarded charge recombination process. The influence of the Ag content on the overall efficiency was also investigated, and the optimum Ag content with N,S-TiO2 was found to be 20 wt%. Because of the enhanced solar energy conversion efficiency of the N,S-TiO2@Ag nanocomposite, it should be considered as a potential photoanode for high-performance DSSCs.
This paper reports the synthesis of two-dimensional, hierarchical, porous, and (001)-faceted metal (Ag, Zn, and Al)-doped TiO2 nanostructures (TNSs) and the study of their photocatalytic activity. Two-dimensional metal-doped TNSs were synthesized using the hydrolysis of ammonium hexafluorotitanate in the presence of hexamethylenetetramine and metal precursors. Typical morphology of metal-doped TNSs is a hierarchical nanosheet that is composed of randomly stacked nanocubes (dimensions of up to 5 μm and 200 nm in edge length and thickness, respectively) and has dominant (001) facets exposed. Raman analysis and X-ray photoelectron spectroscopy results indicated that the Ag doping, compared to Zn and Al, much improves the crystallinity degree and at the same time dramatically lowers the valence state binding energy of the TNS and provides an additional dopant oxidation state into the system for an enhanced electron-transfer process and surface reaction. These are assumed to enhance the photocatalytic of the TNS. In a model of photocatalytic reaction, that is, rhodamine B degradation, the AgTNS demonstrates a high photocatalytic activity by converting approximately 91% of rhodamine B within only 120 min, equivalent to a rate constant of 0.018 m-1 and ToN and ToF of 94 and 1.57 min-1, respectively, or 91.1 mmol mg-1 W-1 degradation when normalized to used light source intensity, which is approximately 2 times higher than the pristine TNS and several order higher when compared to Zn- and Al-doped TNSs. Improvement of the crystallinity degree, decrease in the defect density and the photogenerated electron and hole recombination, and increase of the oxygen vacancy in the AgTNS are found to be the key factors for the enhancement of the photocatalytic properties. This work provides a straightforward strategy for the preparation of high-energy (001) faceted, two-dimensional, hierarchical, and porous Ag-doped TNSs for potential use in photocatalysis and photoelectrochemical application.
The development of semiconductor heterojunctions is a promising and yet challenging strategy to boost the performance in photoelectrochemical (PEC) water splitting. This paper describes the fabrication of a heterojunction photoanode by coupling α-Fe2O3 and g-C3N4via aerosol-assisted chemical vapour deposition (AACVD) followed by spin coating and air annealing. Enhanced PEC performance and stability are observed for the α-Fe2O3/g-C3N4 heterojunction photoanode in comparison to pristine α-Fe2O3 and the reason is systematically discussed in this paper. Most importantly, the fabricated α-Fe2O3/g-C3N4 film shows impressive stability, retaining more than 90% of the initial current over 12 h operating time. The excellent stability of the heterojunction photoanode is achieved due to the unique nanoflake structure of α-Fe2O3 induced by AACVD. This nanostructure promotes good adhesion with the g-C3N4 particles, as the particles tend to be trapped within the α-Fe2O3 valleys and eventually create strong and large interfacial contacts. This leads to improved separation of charge carriers at the α-Fe2O3/g-C3N4 interface and suppression of charge recombination in the photoanode, which are confirmed by the transient decay time, charge transfer efficiency and electrochemical impedance analysis. Our findings demonstrate the importance of nanostructure engineering for developing heterojunction structures with efficient charge transfer dynamics.
The ability of band offsets at multiferroic/metal and multiferroic/electrolyte interfaces in controlling charge transfer and thus altering the photoactivity performance has sparked significant attention in solar energy conversion applications. Here, we demonstrate that the band offsets of the two interfaces play the key role in determining charge transport direction in a downward self-polarized BFO film. Electrons tend to move to BFO/electrolyte interface for water reduction. Our experimental and first-principle calculations reveal that the presence of neodymium (Nd) dopants in BFO enhances the photoelectrochemical performance by reduction of the local electron-hole pair recombination sites and modulation of the band gap to improve the visible light absorption. This opens a promising route to the heterostructure design by modulating the band gap to promote efficient charge transfer.
Well aligned TiO2 nanotubes were successfully synthesized by anodization of Ti foil at 60 V in a fluorinated bath comprised of ethylene glycol with 5 wt% of NH4F and 5 wt% of H2O2. In order to enhance the visible light absorption and photoelectrochemical response of pure TiO2 nanotube arrays, a mixed oxide system (W-TiO2) was investigated. W-TiO2 nanotube arrays were prepared using radio-frequency (RF) sputtering to incorporate the W into the lattice of TiO2 nanotube arrays. The W atoms occupy the substitutional position within the vacancies of TiO2 nanotube arrays. The as-anodized TiO2 is amorphous in nature while the annealed TiO2 is anatase phase. The mixed oxide (W-TiO2) system in suitable TiO2 phase plays important roles in efficient electron transfers due to the reduction in electron-hole recombination. In this article, the effect of the sputtered W into the as-anodized/annealed TiO2 nanotube arrays on the photoelectrochemical response was presented.
This study investigated the different thicknesses of TiO2 photoanode films and the effect of surface plasmon resonance (SPR) of Ag-TiO2 nanocomposites on the current-voltage (I-V) performance of dye-sensitized solar cells (DSSC). The TiO2 layer was deposited using the doctor blade technique and the thickness of the TiO2 films was controlled by using a different number of Scotch tape layers. The silver nanoparticles (AgNP) were synthesised using a chemical reduction method and the concentration of sodium citrate as a reducing agent was varied from 4 to 12 mM to study the effect of citrate ion on the size of the nanoparticles. Ag-TiO2 nanopowder was prepared by adding pure anatase TiO2 powder into AgNP colloidal solution. The mixture was left to dry for 24 h to obtain Ag-TiO2 powder for paste preparation. The three-layer Scotch tape, with thickness of 14.38 µm, achieved a high efficiency of 4.14%. This results showed that three layers was the optimal thickness to improve dye loading and to reduce the charge recombination rate. As for the Ag-TiO2 nanocomposites, 10 mM of AgNP, with a mean diameter of 65.23 nm and high efficiency of 6.92%, proved that SPR can enhance the absorption capability of dye and improve the photon-to-electron generation.
AgCl/BiYO3
composite was successfully synthesized via the aqueous precipitation method followed by calcination. The
varied amount of AgCl (10, 20 and 30%) was mixed into BiYO3
via sonochemical-assisted method. The structures and
morphologies of the as-prepared AgCl/BiYO3
composite were characterized by x-ray diffraction (XRD), scanning electron
microscopy (SEM) and UV-vis diffused reflectance spectroscopy (UV-vis DRS). The optical absorption spectrum of AgCl/
BiYO3
composite showed strong absorption in visible region. The photocatalytic activity of AgCl/BiYO3
composite was
evaluated by the photodegradation of reactive orange16 (RO16), which was selected to represent the dye pollutants,
under UV and visible light irradiation. The results indicated that 20% AgCl/BiYO3 photocatalyst was the most capable
photocatalyst in this series in the degradation of RO16 under both UV and visible light illumination within 1 h. Moreover,
the mechanism of photocatalytic degradation of AgCl/BiYO3
was elucidated using three types of free radical scavengers.
The significant enhancement was attributed to the formation of AgCl/BiYO3
heterojunction resulting in the low electronhole
pair recombination rate.
Vanadia (V2O5)-incorporated fibrous silica-titania (V/FST) catalysts, which were successfully synthesized using a hydrothermal method followed by the impregnation of V2O5. The catalysts were then characterized using numerous techniques, including X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, nitrogen adsorption-desorption analyses, ultraviolet-visible diffuse reflectance spectroscopy, Fourier-transform infrared, X-ray photoelectron spectroscopy, and photoluminescence (PL) analyses. The study found that varying the amount of V2O5 (1-10 wt%) had a significant impact on the physicochemical properties of the FST, which in turn improved the photodegradation efficiency of two organic compounds, ciprofloxacin (CIP) and congo red (CR). 5V/FST demonstrated the best performance in degrading 10 mg L-1 of CIP (83%) and CR (100%) at pH 3 using 0.375 g L-1 catalyst under visible light irradiation within 180 min. The highest photoactivity of 5V/FST is mainly due to higher crystallinity and the highest number of V2O5-FST interactions. Furthermore, as demonstrated by PL analysis, the 5V/FST catalyst has the most significant impact on interfacial charge transfer and reduces electron-hole recombination. The photodegradation of both contaminants follows the Langmuir-Hinshelwood pseudo-first-order model, according to the kinetic study. The scavenger investigation demonstrated that hydroxyl radicals and holes dominated species in the system, indicating that the catalyst effectively generated reactive species for pollutant degradation. A possible mechanism was also identified for FST and 5V/FST. Interestingly, V2O5 acts as an electron-hole recombination inhibitor on FST for selective hole oxidation of ciprofloxacin and congo red photodegradation. Finally, the degradation efficiency of the catalyst remained relatively stable even after five cyclic experiments, indicating its potential for long-term use in environmental remediation.
Streptococcus dysgalactiae is an emerging pathogen of fish. Clinically, infection is characterized by the development of necrotic lesions at the caudal peduncle of infected fishes. The pathogen has been recently isolated from different fish species in many countries. Twenty S. dysgalactiae isolates collected from Japan, Taiwan, Malaysia and Indonesia were molecularly characterized by biased sinusoidal field gel electrophoresis (BSFGE) using SmaI enzyme, and tuf gene sequencing analysis. DNA sequencing of ten S. dysgalactiae revealed no genetic variation in the tuf amplicons, except for three strains. The restriction patterns of chromosomal DNA measured by BSFGE were differentiated into six distinct types and one subtype among collected strains. To our knowledge, this report gives the first snapshot of S. dysgalactiae isolates collected from different countries that are localized geographically and differed on a multinational level. This genetic unrelatedness among different isolates might suggest a high recombination rate and low genetic stability.
A growing number of emerging HIV-1 recombinants classified as circulating recombinant forms (CRFs) have been identified in Southeast Asia in recent years, establishing a molecular diversity of increasing complexity in the region. Here, we constructed a replication-competent HIV-1 clone for CRF33_01B (designated p05MYKL045.1), a newly identified recombinant comprised of CRF01_AE and subtype B. p05MYKL045.1 was reconstituted by cloning of the near full-length HIV-1 sequence from a newly-diagnosed individual presumably infected heterosexually in Kuala Lumpur, Malaysia. The chimeric clone, which contains the 5' LTR (long terminal repeat) region of p93JP-NH1 (a previously isolated CRF01_AE infectious clone), showed robust viral replication in the human peripheral blood mononuclear cells. This clone demonstrated robust viral propagation and profound syncytium formation in CD4+, CXCR4-expressing human glioma NP-2 cells, indicating that p05MYKL045.1 is a CXCR4-using virus. Viral propagation, however, was not detected in various human T cell lines including MT-2, M8166, Sup-T1, H9, Jurkat, Molt-4 and PM1. p05MYKL045.1 appears to proliferate only in restricted host range, suggesting that unknown viral and/or cellular host factors may play a role in viral infectivity and replication in human T cell lines. Availability of a CRF33_01B molecular clone will be useful in facilitating the development of vaccine candidates that match the HIV-1 strains circulating in Southeast Asia.
In many parts of Southeast Asia, the HIV-1 epidemic has been driven by the sharing of needles and equipment among intravenous drug users (IDUs). Over the last few decades, many studies have proven time and again that the diversity of HIV-1 epidemics can often be linked to the route of infection transmission. That said, the diversity and complexity of HIV-1 molecular epidemics in the region have been increasing at an alarming rate, due in part to the high tendency of the viral RNA to recombine. This scenario was exemplified by the discovery of numerous circulating recombinant forms (CRFs), especially in Thailand and Malaysia. In this study, we characterized a novel CRF designated CRF74_01B, which was identified in six epidemiologically unlinked IDUs in Kuala Lumpur, Malaysia. The near-full length genomes were composed of CRF01_AE and subtype B', with eight breakpoints dispersed in the gag-pol and nef regions. Remarkably, this CRF shared four and two recombination hotspots with the previously described CRF33_01B and the less prevalent CRF53_01B, respectively. Genealogy-based Bayesian phylogenetic analysis of CRF74_01B genomic regions showed that it is closely related to both CRF33_01B and CRF53_01B. This observation suggests that CRF74_01B was probably a direct descendent from specific lineages of CRF33_01B, CRF53_01B and subtype B' that could have emerged in the mid-1990s. Additionally, it illustrated the active recombination processes between prevalent HIV-1 subtypes and recombinants in Malaysia. In summary, we report a novel HIV-1 genotype designated CRF74_01B among IDUs in Kuala Lumpur, Malaysia. The characterization of the novel CRF74_01B is of considerable significance towards the understanding of the genetic diversity and population dynamics of HIV-1 circulating in the region.