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Crystalline BQDs are synthesized through a bottom-up strategy and used to fabricate a BQD–PVP memory device with nonvolatile rewritable memory effects.

Interfacial solar driven water evaporation is an attractive and green method to alleviate the scarcity of clean and fresh water, and tremendous efforts have been devoted to prepare efficient photothermal materials. However, the practical condition for interfacial solar driven water evaporation is complex, increasing contamination by pollutants and bacterial can inactive the photothermal materials. Herein, to address this problem, Ti-Ag-O nanoporous powders, which possess photothermal, photocatalytic and anti-bacterial properties, were prepared by TiAg alloy anodization and subsequent laser irradiation method. It was found that metallic Ag nanoparticles, which were mainly formed by TiAg alloy anodization, will be oxidized into Ag2O nanoparticles after laser irradiation. Through this laser induced transformation, the surface wettability of Ti-Ag-O powders can be improved for the hydrophilicity nature of Ag2O, and the Ti-Ag-O powders with Ti90Ag10 alloy anodization and subsequent laser irradiation for 10 min showed the highest water evaporation rate (2.27 kg m−2 h−1). Meanwhile, this Ti-Ag-O powders also showed the highest photocatalytic property due to the junction between TiO2 and Ag2O. Moreover, the diffusion inhibition test indicated that antibacterial property of this Ti-Ag-O powders was excellent for the incorporation of Ag/Ag2O nanoparticles. The as-prepared trifunctional Ti-Ag-O nanoporous powders holds potential for the practical application of interfacial solar driven water evaporation technology, the TiAg alloy anodization and subsequent laser irradiation method could be extended to prepare other multifunctional photothermal materials.

Defect states in the TiO2 nanoparticles can cause severe charge recombination and poor electron-transport efficiency when used as a photoanode in dye-sensitized solar cells (DSSCs). Herein, we report a simple and practical way to passivate the surface defects of TiO2 through hydrothermal treating with acetic acid and H2SO4, introducing a high percentage of 101 facets and sulfonic acid functional groups on the TiO2 surface. A high efficiency of 8.12% has been achieved, which is 14% higher than that of untreated TiO2 under the same condition. EIS results prove that the multiacid-treated TiO2 can promote electron transport and reduce charge recombination at the interface of the TiO2 and electrolyte. This work provides an efficient approach to engineer the electron-transport pathway in DSSCs.

The development of self-chargeable lithium-ion batteries is of great significance for expanding the usable range of the lithium-ion battery and it has received intensive attention from numerous researchers. Solar cells can generate electricity from the sunlight and ensure sustainable access to electrical power for charging lithium-ion batteries. Herein, a photo-charging integrated device is constructed by combining four conventional dye-sensitized solar cells and a three-electrode hybrid lithium-ion battery, including a dye-sensitized TiO2 photo-anode, LiFePO4 electrode and metal lithium electrode. When the device is operated under solar illumination, DSSCs can match the charging voltage for the hybrid lithium-ion battery. The LiFePO4 electrode in the three-electrode device plays two roles, serving as a reversible redox agent for the regeneration of dye and as the cathode for lithium-ion batteries. The integrated device can effectively harvest solar energy and store it in situ within the hybrid lithium-ion battery through the photo-charging process. The proposed strategy is in favor of exploiting the small-sized, light-weight, self-chargeable battery and may have the potential to be employed as the power supply for miniaturized sensors and mobile devices.

Excellent electrocatalytic properties and low cost are main requirements for the suitable counter electrodes of dye sensitized solar cells (DSSCs). In this work, serials of electrocatalytic films were facilely fabricated by blending the PEDOT polymers and transition metal phosphides nanoparticles (Ni2P or Co2P). All yielded films as counter electrodes were assembled into intact cells and their electrocatalytic performances were carefully investigated. Compared to the PEDOT-only electrode or phosphide-only electrode, the achieved composite electrodes display the superior electrocatalytic performances. The continuous PEDOT polymers can significantly alleviate phosphides nanoparticles aggregations and thereby generate more active area for redox couple. DSSCs with the optimal PEDOT-Ni2P-3 electrode and PEDOT-Co2P-3 electrode show the power conversion efficiency (PCE) of 7.14% and PCE of 6.85%, respectively. And PCE value of the optimal PEDOT-Ni2P-3 is comparable to that (7.09%) of Pt electrode on the same test condition. Moreover, electrochemical measurements reveal the type of composite electrode holding decent dissolution-resistant ability. Considering the outstanding and available electrocatalytic activities, the potential application of PEDOT-phosphides electrodes as the substitute of Pt electrode is worth to be expected.

There are numerous defect states in the anatase TiO2 nanoparticles, which are most frequently used as the electron transporting layers in perovskite solar cells (PSCs), resulting in severe charge recombination and poor electron extracted efficiency. Herein, we report a simple and practical way to passivate the surface defects of TiO2 by hydrothermal treating with acetic acid and H2SO4. Modified TiO2 with a high percentage of {101} facets and sulfonic acid functional group is proved to be beneficial for the growth and crystallization of FAMA perovskite film. Furthermore, it can facilitate the electron extraction and inhibit the charge recombination at the perovskite-TiO2 interface. A high PCE of 20.27% has been achieved in our modified TiO2-based PSCs, which is 30% higher than that of control devices under the same condition. Simultaneously, the solar cells display negligible hysteresis, improved device reproducibility and stability. This work provides an efficient approach to engineer the electron transport pathway at perovskite-TiO2 interface.

The photocatalytic performance of carbon dots is strongly related to surface modifications and graphitization. Herein, we show that carbon dots without metal loaded can serve as an efficient photocatalyst for reducing CO2. The conjugate carbon great π could stabilize the photogenerated electrons, which turned out to improve the separation of the photogenerated electron-hole pairs and can kinetically promote interfacial reaction. Besides, the strong chemisorption of the nitrogen-containing groups on the carbon dots to the CO would help to further conversion of the intermediate in the demonstrated CO2 photo-reduction systems. As a result of these merits, the highly graphitized carbon dots prepared from graphene oxide with plenty of nitrogen-containing groups exhibit 74.8% electronic selectivity of methane. This strategy provides an important requirement for designing of CO2 photocatalysts.

TiO2 with exposed (001) facets were composited with CdS nanorods to construct 2D/1D heterojunction. As comparison, P25 with mainly exposed (101) facets were employed to combine with CdS nanorods. The 2D/1D heterojunction of TiO2 nanosheets and CdS nanorod displayed 3.7 times higher hydrogen generation than that of P25/CdS composites. The results indicated that TiO2 with exposed (001) facets were favorable for enhancing the photocatalytic activity of CdS via optimizing the heterojunction between TiO2 and CdS. Photoluminescence and photoelectrochemical characteristics results demonstrated that the 2D-TiO2/1D-CdS heterojunction exhibits higher separation efficiency of photoinduced carriers and superior electron transfer ability. This work exemplifies that heterojunction modification is an effective strategy to improve the efficiency of the photocatalyst composites.

Nitrogen-doped graphene frameworks (N-GFs) with a large specific surface area (1149 m2 g−1) are successfully synthesized from fumaric acid in the presence of sodium carbonate with urea added as nitrogen precursor through a facile one-step fast pyrolysis. The N-GFs can be utilized as an excellent counter electrode in hole transport material (HTM)-free perovskite solar cells (PSCs), achieving the power conversion efficiency of 10.32%, higher than the PSCs using undoped graphene frameworks. The enhanced performance of N-GF-based PSCs is probably due to the superiority of N-GFs in enabling increased charge extraction efficiency and transportation to substantially reduce charge recombination losses. This work indicates the great potential of N-GFs to replace expensive organic HTM and noble-metal electrodes in developing low-cost and efficient HTM-free PSCs.

Selective oxidation of alcohols to highly valued chemicals in a clean manner (e.g., with water as a solvent and O2 or H2O2 as the primary oxidant) is the subject of considerable research attention. This paper presents a simple and environmentally friendly approach for the selective oxidation of isopropanol to pinacol C6 (2,3-dimethyl-2,3-butanediol) in water with hydrogen peroxide (H2O2) through UV irradiation under mild conditions. A selectivity of 82–95% is achieved at H2O2 feeding rates below 4 mL h−1. The introduction of TiO2 nanotubes can further accelerate isopropanol conversion and enhance pinacol C6 formation. The highest formation rate of pinacol C6 and the highest conversion rate of isopropanol are 29.4 and 71.4 mmol h−1, respectively. The proposed strategy provides a green solution for the synthesis of aliphatic pinacol and offers a new design for the construction of C–C bonds with alphatic alcohol.

Water oxidation and reduction over semiconductor-based photocatalysts intrinsically occur at different spatial sites. Modulation of the reaction sites and charge transfer between them are logically important in speeding up the reaction. Here, we demonstrate that divorcing a CdSe–CdS–Pt donor–acceptor system on different surface sites of TiO2 can significantly increase the H2 generation rate. The increase is derived from an effective reset of water oxidation and reduction sites. Widening of the site distance by employing a TiO2 membraniform acceptor effectively decreases the electron–hole recombination especially for a membrane of TiO2 nanotube arrays. The oriented charge transfer characteristic of TiO2 nanotube arrays benefits long-range electron transport, thereby increasing the electron lifetime and reaction rate. When more conductive carbon nanotube arrays serve as an electron acceptor to replace TiO2, the electron transport is greatly improved, resulting in an ultrahigh H2 generation rate of 1270 mmol g−1 h−1. This work provides a basis for the design and construction of highly efficient photocatalysts through rational modulation of reaction sites and charge transport.

The morphological characteristics of a photocatalyst is central to its photocatalytic activity for solar energy conversion. Herein, Pt–ZnS/CdS composites comprising ZnS nanosheets, embedded via the geometry and size modulation and tuning of band gap of CdS with 0D, 1D or 2D structure, were investigated for solar hydrogen production. The photoactivity results indicate that the shape and morphology of CdS in the Pt–ZnS/CdS heterojunction play a pivotal role in affecting the photocatalytic performance. CdS with a 1D structure deposited on porous Pt–ZnS nanosheets endow the heterojunction with increased efficiency for the separation and transport of photoinduced electron–hole pairs. The proposed mechanism for the boosted suppression of charge recombination was further confirmed by the transient photocurrent response and photoluminescence.

Three-dimensional (3D) graphene frameworks (GFs) loading CuS nanocrystals composite (GFs–CuS) are prepared by an in-situ hydrothermal process. We find that 3D graphene frameworks exhibit an excellent supporter for even growth and good distribution of CuS nanocrystals. Such 3D architecture composite could provide multi-direction channels that greatly facilitate electron transport and ion diffusion as well as offer more accessible catalytic active sites. These intrinsic factors are essential for an efficient counter electrode (CE) of quantum dot-sensitized solar cells (QDSSCs). As expected, the CdS/CdSe QDSSCs based on GFs-CuS CE achieves a high power conversion efficiency of 5.04%, which is higher than those of the traditional Pt CE (3.18%), GFs CE (3.60%) and CuS CE (3.75%), even better than 2D graphene–CuS composite CE (4.17%). The electrochemical impedance spectra and Tafel polarization curve analysis reveal that the 3D GFs–CuS composite counter electrode exhibits the lower charge-transfer resistance, faster ion diffusion ability and the higher electrocatalytic activity in comparison with the Pt, GFs, CuS and 2D graphene–CuS electrodes. Furthermore, the GFs–CuS CE exhibits excellent stability, demonstrating its promising potential application as effective counter electrode material in QDSSCs.

Due to the limited electronic conductivity, the application of many metal oxides that may have attractive (photo)-electrochemical properties has been limited. Regarding these issues, incorporating low-dimensional conducting scaffolds into the electrodes or supporting the metal oxides onto the conducting networks are common approaches. However, some key electronic processes like interfacial charge transfer are far from being consciously concerned. Here we use a carbon-TiO2 contact as a model system to demonstrate the electronic processes occurring at the metal-semiconductor interface. To minimize the energy dissipation for fast transfer of electrons from semiconductor to carbon scaffolds, facilitating electron tunneling while avoiding high energy-consuming thermionic emission is desired, according to our theoretical simulation of the voltammetric behaviors. To validate this, we manage to sandwich ultrathin TiO2 interlayers with heavy electronic doping between the carbon conductors and dopant-free TiO2. The radially graded distribution of the electronic doping along the cross-sectional direction of carbon conductor realized by immobilizing the dopant species on the carbon surface can minimize the energy consumption for contacts to both the carbon and the dopant-free TiO2. Our strategy provides an important requirement for metal oxide electrode design.

Tartronic acid (TA) is a high value-added chemical widely used as a pharmaceutical product and a preservative; however, its synthesis technology is complicated and high cost. In this study, aqueous solutions of lactic acid were photochemically converted into TA via green oxidation by using hydrogen peroxide (H2O2).

Back reactions were suppressed effectively by double blocking barrier, organic molecules and ZnS on the photoanode of quantum dot (QDs) sensitized solar cells (QDSSCs), thereby achieving higher conversion efficiency. In this work, four different organic molecules were applied in QDSSCs, the efficiency increased two-fold from 2.21% to 4.25% when co-modifications with 4-tert-butyl pyridine (TBP) and ZnS were sequentially applied. The incident photon-to-current efficiency (IPCE) and parameters obtained from impedance spectroscopy (IS) such as recombination resistance (Rrec), chemical capacitance (Cμ), and electron lifetimes were consistent with the measured photovoltaic performance. We speculated that organic molecules mainly inhibit the charge recombination of the injected electrons in TiO2 with electrolyte, because of its steric factor and the electron-donating property of the tert-butyl group. The selective site of modification has been tested for assessing the dominant mechanism underlying the improvement of solar cell characteristics.

Theoretically, selective C–H manipulation in ethanol can result in a direct C–C coupling synthesis of 2,3-butanediol (2,3-BDO). However, this process is typically extremely difficult to achieve because of the high complexity of the involved chemical bonds. In this work, we determine that hydroxide radicals generated from the photolysis of H2O2 can selectively attack the α-hydrogen atom in ethanol aqueous solutions and crack the C–H bond to produce hydroxyethyl radicals, which subsequently undergo C–C coupling to form 2,3-BDO. This selective C–H breakage is determined by the reaction rate, which is primarily controlled by the local H2O2 concentration at a given irradiation intensity. At a moderate reaction rate of ethanol (37 mmol h−1), the 2,3-BDO selectivity reaching as high as 91% can be obtained. The introduction of a catalyst can further increase ethanol conversion and enhance the 2,3-BDO formation rate by controlling the reaction rate. This result provides an environment-friendly approach to convert bio-ethanol directly to 2,3-BDO and to manipulate a single bond selectively in complex bonding situations.

Substrates are normally required in the chemical synthesis of graphene to enhance its formation. However, removing substrates in the post purification stage is difficult, during which harsh reagents are used and the substrates are usually consumed undesirably. In this paper, we report that universal sodium carbonate (Na 2 CO 3 ) particles can effectively promote the construction of well-structured graphene frameworks based on a quick thermal decomposition of fumaric acids. Notably, the Na 2 CO 3 particles are easily separated from graphene through a simple and green method, namely, washing with water at room temperature. Together with the reused characteristic of the recovered Na 2 CO 3 particles, this approach is undoubtedly beneficial to the low-cost and clean synthesis of graphene. Benefiting from the framework structure, the as-synthesized graphene exhibits excellent performance in the supercapacitor. The specific capacitance of the GFs-modified electrode was calculated to be 242 F g −1 at 0.5 A g −1 , which was almost twice that of the RGO-modified electrode (134 F g −1 ). More importantly, the GFs-modified electrode maintained 92.6% retention of its initial specific capacitance (from current density of 0.5 to 16 A g −1 ), which was much higher than that of 2D graphene-modified electrode.

Graphene with a cellular framework structure (GFs) exhibits unique advantages that facilitate quasi-isotropic electron conduction, promote ion diffusion, and induce transport. GFs can act as an ideal support to uniformly disperse platinum (Pt) nanoparticles to better catalyze molecular or ionic reactions, which are intrinsically important for an effective counter electrode (CE) in dye-sensitized solar cells (DSSCs) systems. The power conversion efficiency of optimized DSSCs with GFs CE is 6.15%, which is comparable to that of the conventional Pt CEs (6.71%) and markedly than that of 2D graphene sheets CE (3.60%). More importantly, the GFs-Pt composite CEs could achieve an efficiency of 7.26%. The dynamic discipline behind the improved performance of GFs-based CEs in DSSCs is systematic investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and Tafel polarization analysis, revealing that the better diffusion coefficient of the I3− ion and lower charge transfer resistance at CE interface result in the higher efficiency of GFs based solar cells.

The scale-up application of dye-sensitized solar cells (DSSCs) will desire the efficient and low-cost electrocatalytic counter electrodes. Carbon materials derived from the natural materials have been extensively used in the new energy fields owing to numerously distinct advantages. In this work, a new-style carbon matrix incorporated with Ni species is manufactured through pyrolyzing the humic acid-Ni complex compounds under an inert atmosphere. Systematic electrochemical measurements reveal that the Ni-incorporated carbon holds an elevated triiodide reducing properties in contrast to the single carbonized humic acid. The improvement of electrocatalytic ability may be ascribed to Ni incorporated in carbon matrix that offer more electroactive sites. As a result, when the prepared Ni-incorporated material serves as electrocatalyst in iodide-mediated DSSC, the corresponding device yields a PCE of 7.01%, which increases by 14% in contrast to the single carbonized humic acid (6.14%) and is close to that (7.1%) of as-reference Pt electrode. This study indicates that the proposed carbonaceous material may be in favour of large-scale production of low cost and high efficiency DSSCs.

In this work, we report the construction of three-dimensional (3D) CdS nanosphere/graphene networks by a one-step hydrothermal self-assembly route. The 3D graphene networks not only enhance the light scattering, thanks to the interconnected 3D architecture, but also improve the crystallinity of deposited CdS nanospheres, and at the same time provide a direct electron pathway to quickly separate the photogenerated electron-hole pairs from CdS, which thus dramatically improve the photocatalytic activity. The optimized 3D CdS nanosphere/graphene networks with 2 wt% of graphene could produce molecular hydrogen at a rate of 2310 µmol gcatalyst−1 h−1 under visible-light illumination (λ > 400 nm). ASTAR (Agency for Sci., Tech. and Research, S’pore) MOE (Min. of Education, S’pore)

Doping nitrogen in TiO2 crystals is a simple and effective approach to extend the absorption spectrum of TiO2 to visible light range, but it leads to a serious decline in charge transfer and total loss of the catalytic ability for overall water splitting. Here, TiO2 was co-doped with phosphorus and nitrogen by high temperature method and found the sample of P–N–TiO2-I could realize overall water splitting under visible light while the samples of P–N–TiO2-II, P–N–TiO2-III and N–TiO2 cannot do it. The structures of the photocatalysts were described by various analytical techniques. Through XRD and HRTEM, lots of long-range defect such as twins and dislocations could be clearly observed for P–N–TiO2-II, P–N–TiO2-III and N–TiO2. But for P–N–TiO2-I, the long-range defect was decreased drastically. We proposed that because of various sizes and bonding modes of N, O, P and Ti, proper mole ratios of P to N replace Ti and O respectively can reduce the long-range defect, as that of P–N–TiO2-I. Furthermore, this co-doping effect results in a significant improvement in the separation of photo-excited electrons and holes and enables the nitrogen-doping TiO2 to catalyze the overall splitting of water into molecular hydrogen and oxygen under visible light irradiation, in the absence of sacrificial agents. These observations might arouse new strategies to mend the hybrid-atom-doping-induced structural damage in semiconductor crystals and to modulate their functional properties.

Graphene frameworks (GFs) were incorporated into TiO2 photoanode as electron transport medium to improve the photovoltaic performance of quantum dot-sensitized solar cells (QDSSCs) for their excellent conductivity and isotropic framework structure that could permit rapid charge transport. Intensity modulated photocurrent/photovoltage spectroscopy and electrochemical impedance spectroscopy results show that the electron transport time (τ(d)) of 1.5 wt % GFs/TiO2 electrode is one-fifth of that of the TiO2 electrode, and electron lifetime (τ(n)) and diffusion path length (Ln) are thrice those of the TiO2 electrode. Results also revealed that the GFs/TiO2 electrode has a shorter electron transport time (τ(d)), as well as longer electron lifetime (τ(n)) and diffusion path length (Ln), than conventional 2D graphene sheets/TiO2 electrode, thus indicating that GFs could promote rapid electron transfer in TiO2 photoanodes. Photocurrent-voltage curves demonstrated that when incorporating 1.5 wt % GFs into TiO2 photoanode, a maximum power conversion efficiency of 4.2% for QDSSCs could be achieved. This value was higher than that of TiO2 photoanode and 2D graphene sheets/TiO2 electrode. In addition, the reasons behind the sensitivity of photoelectric conversion efficiency to the graphene concentration in the TiO2 were also systematically investigated. Our results provide a basic understanding of how GFs can efficiently promote electron transport in TiO2-based solar cells.

Modulation of the TiO2 structure to achieve efficient photocatalytic usage of solar light is still a challenging issue. Here we report that simple bombardment of anatase TiO2 nanocrystals by hot molecules can alter its phase transformation kinetics and lead to the reconstruction of the resulting rutile surfaces into a metastable TiO2 crystalline structure. Moreover, the metastable surface crystalline phase is able to harvest visible light up to 480 nm, and exhibits good properties for photocurrent generation. Photocatalysis tests show that upon irradiation by visible light (λ > 420 nm), the surface-reconstructed TiO2 crystals display excellent and stable photocatalytic activity for hydrogen production from aqueous ethanol solution, with a hydrogen production rate of 302 μmol g−1 h−1. This finding might bring a new approach to kinetically tune the structure of TiO2 or other semiconductor crystals in order to modulate their properties.

Three-dimensional (3D) graphene frameworks are usually limited by a complicated preparation process and a low specific surface area. This paper presents a facile suitable approach to effectively synthesize 3D graphene frameworks (GFs) with large specific surface area (up to 1018 m(2) g(-1)) through quick thermal decomposition from sodium chloroacetate, which are considerably larger than those of sodium acetate reported in our recent study. The chlorine element in sodium chloroacetate may possess a strong capability to induce in situ activation and regulate graphene formation during pyrolysis in one step. These GFs can be applied as excellent electrode materials for supercapacitors and can achieve an enhanced supercapacitor performance with a specific capacitance of 266 F g(-1) at a current density of 0.5 A g(-1).

Many chemicals have been found to induce DNA damages which may lead to gene mutation and tumor generation. In this report, a microplate-based photoelectrochemical DNA sensor array was developed for the rapid and high throughput screening of DNA damaging chemicals. A 96-well plate with built-in electrodes was fabricated on a plastic substrate by the standard electronics industry processes. The working electrode in each well was deposited with SnO2 nanoparticles, and the resulting film was sintered at low temperatures tolerable for the plastic substrate. The film was characterized by scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. On the plates sintered at 150 degrees C, a significant amount of photocurrent was obtained in a Ru(bpy)(3)(2+) (bpy = 2,2'-bipyridine) solution. To construct a DNA sensor, poly-(diallydimethyl ammonium chloride) and double-stranded DNA were sequentially assembled on the SnO2 electrode by electrostatic interaction, and a DNA intercalator, Ru(bpy)(2)(dppz)(2+) (dppz = dipyrido[3,2-a:2',3'-c]phenazine) was used as the photoelectrochemical signal indicator. After the DNA film was exposed to tetrafluoro-1,4-benzoquinone (TFBQ) or TFBQ/H2O2, the photocurrent dropped by 38% and 73% respectively. The photocurrent reduction can be attributed to less binding of Ru(bpy)(2)(dppz)(2+) to the electrode after DNA damage. Photocurrent measurement of the entire 96-well plate was completed within 22 min automatically. (C) 2011 Elsevier B.V. All rights reserved.

To propel the commercialization of fuel cells, the development of efficient nonprecious metal catalysts, specifically cathodic oxygen reduction catalysts, is turning into reality because the great advancements have been made on nitrogen-doped carbon materials recently. In this study, we demonstrated that nitrogen-doped hollow carbon nanoparticles (N-HCNPs) exhibit excellent electrocatalytic performance for oxygen reduction reaction (ORR) in alkaline fuel cells. Cyclic voltammetry and rotating ring-disk electrode voltammetry showed that the ORR activity of N-HCNPs approaches that of commercial Pt–C catalyst and is much better compared with nitrogen-free counterparts due to the incorporation of nitrogen atoms into graphitic structures. Kinetic studies indicated that the involvement of nitrogen induces a totally different oxygen adsorption mechanism and a four-electron dominated reaction pathway for N-HCNPs in comparison with nitrogen-free HCNPs, very similar to the observations in Pt–C. Moreover, N-HCNPs ex...

Nanomaterials have been used increasingly in a wide variety of applications, and some of them have shown toxic effects on experimental animals and cells. In this study, a previously established photoelectrochemical DNA sensor was employed to rapidly detect DNA damage induced by polystyrene nanosphere (PSNS) suspensions. In the sensor, a double-stranded DNA film was assembled on a semiconductor electrode, and a DNA intercalator, Ru(bpy)2(dppz)2+ (bpy = 2,2′-bipyridine, dppz = dipyrido[3,2-a:2′,3′-c]phenazine) was used as the photoelectrochemical signal indicator. After the DNA-modified electrode was exposed to 2.0 mg/mL PSNS suspension, photocurrent of DNA-bound Ru(bpy)2(dppz)2+ decreased by about 20%. The decrease is attributed to the chemical damage of DNA and consequently less binding of Ru(bpy)2(dppz)2+ molecules to the electrode. Gel electrophoresis of DNA samples incubated with PSNS suspension confirmed DNA damage after the chemical exposure. However, in both photoelectrochemical and gel electrophoresis experiments, extensively washed PSNS did not induce any DNA damage, and the supernatant of PSNS suspension exhibited comparable DNA damage as the unwashed PSNS suspension. Furthermore, UV-visible absorption spectrum of the supernatant displayed a pattern very similar to that of styrene oxide (SO), a compound which has been shown to induce DNA damage by forming covalent DNA adducts. It is therefore suggested that styrene oxide and other residual chemicals in the PSNS may be responsible for the observed DNA damage. The results highlight the importance of full characterization of nanomaterials before their toxicity study, and demonstrate the utility of photoelectrochemical DNA sensors in the rapid assessment of DNA damage induced by chemicals and nanomaterials.

In dye-sensitized solar cells, there is a competition between transport of electrons through the porous semiconductor electrode toward the conducting substrate and back-reaction of electrons to recombination with I-3(-) ions on the semiconductor electrolyte interface, which determines the charge collection efficiency and is strongly influenced by the electronic site distribution in intraband and geometrical structure of the semiconductors. Herein, we systematically analyze the electrochemical parameters of TiO2 nanoribbon- and nanoparticle-based electrodes by electrochemical impedance spectroscopy. The results show that the intrinsic one-dimensional crystalline structure of TiO2 nanoribbons can promote formation of a space charge layer on the surface of the semiconductor, which effectively blocks the recombination of electrons with I-3(-) ions in the semiconductor electrolyte interface, resulting in an increase of electron lifetime and a higher cell voltage. Furthermore, the boundaryless structure of the TiO2 nanoribbons provides efficient channels for electron transport and therefore increases electron diffusion length. The combination of TiO2 nanoparticle-based electrode with TiO2 nanoribbons can significantly improve energy conversion efficiency of similar to 60%. These data provide a basic understanding of the role of TiO2 geometrical structure in solar energy conversion.

Halogenated phenols are widely used as biocides and are considered to be possibly carcinogenic to humans. In this report, a previously developed photoelectrochemical DNA sensor was employed to investigate DNA damage induced by tetra-halogenated quinones, the in vivo metabolites of halogenated phenols. The sensor surface was composed of a double-stranded DNA film assembled on a SnO(2) semiconductor electrode. A DNA intercalator, Ru(bpy)(2)(dppz)(2+), was allowed to bind to the DNA film and produce photocurrent upon light irradiation. After the DNA film was exposed to 300 microM tetrafluoro-1,4-benzoquinone (TFBQ), the photocurrent dropped by 20%. In a mixture of 300 microM TFBQ and 2 mM H(2)O(2), the signal dropped by 40%. The signal reduction indicates less binding of Ru(bpy)(2)(dppz)(2+) due to structural damage of ds-DNA in the film. Similar results were obtained with tetra-1,4-chlorobenzoquinone (TCBQ), although the signal was not reduced as much as TFBQ. Fluorescence measurement showed that TFBQ/H(2)O(2) generated more hydroxyl radicals than TCBQ/H(2)O(2). Gel electrophoresis proved that the two benzoquinones produced DNA strand breaks together with H(2)O(2), but not by themselves. Using the photoelectrochemical sensor, it was also found that TCBQ covalently bound with DNA did not produce additional oxidative damage in the presence of H(2)O(2). The combined photoelectrochemistry, gel electrophoresis, and fluorescence data revealed distinctive differences between TFBQ and TCBQ in terms of DNA adduct formation and hydroxyl radical generation.

The metal ion dependent decomposition of hydrogen peroxide, the so-called Fenton Reaction, yields hydroxyl radicals that can cause oxidative DNA damage both in vitro and in vivo. We have previously reported a photoelectrochemical sensor for the detection of oxidative DNA damage induced by an Fe(2+)-mediated Fenton Reaction, using a DNA intercalator as a photoelectrochemical signal reporter (Liang, M.; Guo, L.-H. Environ. Sci. Technol. 2007, 41, 658). The intercalator binds less to the damaged DNA in the sensor film than the native form, resulting in a reduction in the measured photocurrent. In this report, some mechanistic aspects of the sensor were investigated. It was found that Fe(2+) alone (without the coexistence of H(2)O(2)) suppressed the photocurrent of the intercalator bound to the DNA film in a pH-dependent manner. Similar pH dependence was observed for the zeta potential of the tin oxide nanoparticle colloid used in the preparation of the semiconductor electrode, leading to the hypothesis that the metal ion binds to the surface oxide groups on the electrode and quenches the photoelectrochemical response. At pH 3, the quenching effect was reduced substantially to permit the detection of DNA damage by as low as 10 muM Fe(2+) and 40 microM H(2)O(2), a concentration that is within the physiologically relevant range. It was also found that Fe2+ ions associated with the DNA in the sensor film and participated in the DNA damage reaction, a mechanism that has been implicated in previous studies on metal carcinogenesis.

Photoelectrochemical sensors were developed for the rapid detection of oxidative DNA damage induced by Fe2+ and H2O2 generated in situ by the enzyme glucose oxidase. The sensor is a multilayer film prepared on a tin oxide nanoparticle electrode by layer-by-layer self-assembly and is composed of separate layers of a photoelectrochemical indicator, DNA, and glucose oxidase. The enzyme catalyzes the formation of H2O2 in the presence of glucose, which then reacts with Fe2+ and generates hydroxyl radicals by the Fenton reaction. The radicals attack DNA in the sensor film, mimicking metal toxicity pathways in vivo. The DNA damage is detected by monitoring the change of photocurrent of the indicator. In one sensor configuration, a DNA intercalator, Ru(bpy)2(dppz)2+ (bpy = 2,2'-bipyridine, dppz = dipyrido[3,2-a:2',3'-c]phenazine), was employed as the photoelectrochemical indicator. The damaged DNA on the sensor bound less Ru(bpy)2(dppz)2+ than the intact DNA, resulting in a drop in photocurrent. In another configuration, ruthenium tris(bipyridine) was used as the indicator and was immobilized on the electrode underneath the DNA layer. After oxidative damage, the DNA bases became more accessible to photoelectrochemical oxidation than the intact DNA, producing a rise in photocurrent. Both sensors displayed substantial photocurrent change after incubation in Fe2+/glucose in a time-dependent manner. And the detection limit of the first sensor was less than 50 microM. The results were verified independently by fluorescence and gel electrophoresis experiments. When fully integrated with cell-mimicking components, the photoelectrochemical DNA sensor has the potential to become a rapid, high-throughput, and inexpensive screening tool for chemical genotoxicity.

A common framework, which can be used to analyze the two-party security protocols, is proposed in this paper. With the common framework, a common program is developed in order that any two-party security protocol can be automatically analyzed through SMV with slight modification of the common program. Finally, we illustrate the feasibility and efficiency of the common program analysis with the SSL 3.0 protocol as a case study.

Nitrogen-doped carbons with highly ordered macroporous structures are fabricated via the assembly and carbonization of polymethylmethacrylate (PMMA)–polyacrylonitrile (PAN) core–shell nanoparticles. During the carbonization, PMMA (acting as a template) is completely removed, and the resulting hollow PAN particles are fused to form ordered macroporous structures. Micropores are present on the macropore walls, providing desirable inter-macropore channels. The nitrogen atoms partially remain in the resulting carbon structures and exhibit mainly pyridinic and quaternary configurations under relatively high carbonization temperatures. The careful control of the pre-stabilization and carbonization conditions is crucially important for the formation of the ordered macroporous structures. As a demonstration, the obtained nitrogen-doped macroporous carbons exhibit excellent electrochemical catalytic activities both for the reduction of Sn2− electrolyte ions in QDSSCs and the reduction of oxygen in fuel cells.

The functions of nitrogen-doped hollow carbon nanoparticles (N-HCNPs) as counter electrodes in quantum dot sensitized solar cells (QDSSCs) have been studied in this paper. Electrochemical impedance spectroscopy (EIS) and Tafel-polarization tests reveal a low charge transfer resistance and a high exchange current density between polysulfide electrolyte and the N-HCNPs electrode. Cyclic voltammetry results indicate that the N-HCNPs electrode shows high electrocatalytic activity and excellent tolerance toward the S 2� /Sn 2� electrolyte. A power conversion efficiency of 2.67% is achieved for the QDSSCs based on N-HCNPs counter electrodes, which is clearly higher than those of the QDSSCs based on HCNPs, carbon nanotubes and Pt counter electrodes. The results reveal that the N-HCNPs electrode is a promising counter electrode candidate for QDSSCs.