Superior Photosensitivity Research Articles

Construction of Z-scheme and p-n heterostructure: Three-dimensional porous g-C3N4/graphene oxide-Ag/AgBr composite for high-efficient hydrogen evolution

Hydrogen is known as an alternative new energy for its advantages of non-pollution and high calorific value, and photocatalysis technology is regarded as one of the most effective means to produce hydrogen in recent years. In this topic, aiming at the poor photoresponse, fast combination of photo-induced carriers and unstable structure of traditional photocatalysts, the three-dimensional porous g-C3N4/graphene oxide framework was constructed by compounding two-dimensional graphene oxide and two-dimensional g-C3N4 via hard template (SiO2 nanoparticles) method and selective chemical etching. Then, silver bromide nanoparticles, a superior photosensitizer, were immobilized on the three-dimensional porous framework to construct the three-dimensional porous g-C3N4/graphene oxide-AgBr photocatalyst with Ag plasmas by solvothermal method. Research showed that this novel photocatalyst based on Z-scheme heterostructure (GO-AgBr), p-n heterostructure (g-C3N4-AgBr) and Ag plasmas presented high-efficient visible-light driven hydrogen evolution (3.69 mmol/g/h) at the absence of Pt co-catalyst, which is higher than the majority of existing catalysts, and it also possessed strong stability on its activity and structure. Accordingly, the enhanced hydrogen evolution and photostability were attributed to the highly ordered structure and fast interfacial electron conduction of three-dimensional porous framework, superior photosensitivity of AgBr and synergistic effect of Ag plasmas. Therefore, this study provided a potential method for exploitation of hydrogen energy.

Evidence of oxygen defects mediated enhanced photocatalytic and antibacterial performance of ZnO nanorods

Defect engineered one-dimensional (1D) ZnO nanostructures have found great interest in diverse fields, including water detoxification and environmental remediation. In this article, we report a facile, low-temperature hydrothermal synthesis of defect enriched ZnO nanorods at different pH conditions. The dimension of all the synthesized ZnO nanostructures was restricted to 1D with changes only in their aspect ratios, unlike previous reports where change in morphology accompanies the effect of pH. With an increment in the pH value of the reaction mixture, oxygen defect concentration was controlled and confirmed using XPS and Raman spectroscopy. Considerable increase in optical light absorption and reduction in the bandgap, as inferred from the UV–vis study, corroborating the pH-dependent enrichment of defect states in 1D ZnO. Superior photosensitivity of oxygen defect rich ZnO nanorods was utilized to study their sunlight-induced photocatalytic and bactericidal activity towards its application in wastewater treatment. Within 4 h and 30 min of sunlight exposure (900 W/cm2), a 100% bacterial population (S.aureus, 106 cells/m) killing and complete degradation of methylene blue dye (10μM) were achieved. Enhanced reactive oxidative species (ROS) formation due to the presence of additional oxygen defect states is ascribed to be the prime factor facilitating improved degradation efficiency. Additionally, during the optimization study, ZnO nanorods were found to be active against bacterial cells even in the absence of light opening avenues in antimicrobial food packaging and protective surface coatings.

Microwave-Polyol Synthesis of Sub-10-nm PbS Nanocrystals for Metal Oxide/Nanocrystal Heterojunction Photodetectors

A rapid microwave-polyol technique is developed to grow bare-surface sub-10-nm lead sulfide (PbS) colloidal nanocrystals (NCs) of uniform size. Growth involves three distinct dynamical stages. PbS NCs homogeneously nucleate and undergo a fast growth process that spontaneously aggregates them into a continuous microstructure of PbS. Next, the interaction of low-power microwave irradiation with the NCs’ dipole moments along different crystallographic axes leads to the development of strain at the NCs’ grain boundaries, which ultimately causes dissociation of the aggregated microstructures into individual uniform-sized PbS NCs. The most distinctive feature of this growth technique is the bare nature and uniform size of the NCs produced. This gives the freedom to fabricate a highly packed NC thin film, which is essential for enhanced charge-transport properties. It simultaneously also precludes the need of undergoing a detrimental solid-state ligand-exchange process, which is indispensably required for casting thin films from conventional counterpart long-aliphatic-ligand-capped NCs. To realize the photosensitivity and charge-transport nature of these microwave-synthesized NCs, we fabricated a lateral heterojunction photoconductor and a phototransistor that work on the principal of electron transfer to the metal oxide layer. The photoconductor exhibits prominent multispectral photosensitivity in the visible region, demonstrating high external quantum efficiency and detectivity of 7.42 × 102% and 1.07 × 1011 jones, respectively. Further, it also shows superior photocurrent generation with respect to the conventional hot-injection-method-synthesized PbS NC-based photoconductor, indicating more efficient inter-NC charge transport in its NC thin film. The unencapsulated photoconductor exhibits a long air-storage lifetime, which reflects air stability of the device and PbS NCs. In addition to the photoconductor, the metal oxide/PbS heterojunction phototransistor also shows superior photosensitivity with a responsivity and a response time of 3 × 10–2A/W and 2.2 s, respectively.

Highly Repeatable and Recoverable Phototransistors Based on Multifunctional Channels of Photoactive CdS, Fast Charge Transporting ZnO, and Chemically Durable Al2O3 Layers.

Highly repeatable and recoverable phototransistors were explored using a "multifunctional channels" structure with multistacked chalcogenide and oxide semiconductors. These devices were made of (i) photoactive CdS (with a visible band gap), (ii) fast charge transporting ZnO (with a high field-effect mobility), and (iii) a protection layer of Al2O3 (with high chemical durability). The CdS TFT without the Al2O3 protection layer did not show a transfer curve due to the chemical damage that occurred on the ZnO layer during the chemical bath deposition (CBD) process used for CdS deposition. Alternatively, compared to CdS phototransistors with long recovery time and high hysteresis (ΔVth = 19.5 V), our "multi-functional channels" phototransistors showed an extremely low hysteresis loop (ΔVth = 0.5V) and superior photosensitivity with repeatable high photoresponsivity (52.9 A/W at 400 nm). These improvements are likely caused by the physical isolation of the sensing region and charge transport region by the insertion of the ultrathin Al2O3 layer. This approach successfully addresses some of the existing problems in CdS phototransistors, such as the high gate-interface trap site density and high absorption of molecular oxygen, which originate from the polycrystalline CdS.

Synthesis dibromo substituted BOPHY dye for the singlet oxygen generation

Abstract A dibromo substituted BOPHY derivative ( 2 ) was prepared and found to exhibit photo-sensitization capability. Rapid oxidation of 80% DPBF at the first 6 min was observed suggesting that 2 is a superior photo-sensitizer than methylene blue. The HOMO–LUMO band gap for the lowest energy absorption bands of the BOPHY 1 is smaller than that of PS 2 , which is in good agreement with the red shift in the absorption observed between 1 and 2 .

Piezoelectricity in two-dimensional group-III monochalcogenides

We find that several layer-phase group-III monochalcogenides, including GaS, GaSe and InSe, are piezoelectric in the monolayer form. First-principles calculations reveal that the piezoelectric coefficients of monolayer GaS, GaSe and InSe are on the same order of magnitude as the earlier discovered two-dimensional piezoelectric materials, such as BN and MoS2 monolayers. Our study expands the family of two dimensional piezoelectric materials, suggesting that strong piezoelectric response can occur in a wide range of two dimensional materials with broken inversion symmetry. The co-existence of piezoelectricity and superior photo-sensitivity in these two-dimensional semiconductors enables the integration of electromechanical and optical sensors on the same material platform.

Synthesis and properties of a novel UV-curable waterborne hyperbranched polyurethane

A series of ultraviolet (UV)-curable waterborne hyperbranched polyurethane dispersions (WHPUDs) have been successfully synthesized by modifying the hyperbranched polyester H10, which was prepared using pentaerythritol as a core molecule and dimethylolpropionic acid as monomers, with succinic anhydride, toluene diisocyanate (TDI), and hydroxypropyl acrylate (HPA). The H10 was characterized by 1H nuclear magnetic resonance spectroscopy and matrix-assisted laser desorption/ionization time of flight mass spectrometry. The properties of the WHPUDs with different content of succinic anhydride and TDI–HPA have been investigated by measuring the stability, the particle size, and the rheological behavior. The effects of the content of succinic anhydride and TDI–HPA were studied in terms of UV-curing rate, water resistance, and thermogravimetric behaviors of WHPUD coatings. The WHPUDs showed good appearance, particle size, viscosity, and storage stability. The WHPUD films showed superior photosensitivity and the percent conversion of C=C bonds reached about 80% when the radiation time was 50 s. Moreover, the UV-cured films had good water resistance and thermostability, which can benefit a waterborne polyurethane resin for waterborne coatings.

Research on the Interaction between Pheophorbide and Bovine Serum Albumin

The interaction between natural pheophorbide (a superior photosensitizer) and bovine serum albumin (BSA) in physiological condition is investigated by means of UV-Vis, fluorescence and synchronous fluorescence spectra so as to provide the basis for clinical use. Natural pheophorbide was isolated from silkworm excrement. BSA in pH 7.4 Tris buffer mixed with different concentration of pheophorbide was kept at certain temperature for 3 h or under illumination by laser at 630 nm for 20 min. UV-Vis absorption of BSA was enhanced and its fluorescence was quenched by pheophorbide. Illumination of laser at 630 nm intensified the quenching. The mechanism is deemed as mainly static quenching. The binding constants Ka at 300, 310, 320 K are separately 6.93×1012,7.40×1012,6.82×1012 L/mol/s respectively. Number of binding sites n is 1; the binding distance R is 3.70 nm, and that suggests non-radiation energy transfer from BSA to pheophorbide. The thermodynamic parameters of the binding reaction are H=36.7 kJ/mol, S=213 J/mol/K, and G negative value, and indicates that hydrophobic force plays a predominant role in the process, and it is a spontaneous interaction. Synchronous fluorescence spectra show that pheophorbide mainly interacts with tryptophan residue of BSA and leads to the promotion of hydrophobic force. Pheophorbide can bind to serum protein and be transported in vivo, makes no destruction to molecular structure of serum protein, but causes its conformational alteration.

Preparation and characterization of UV-curable hyperbranched polyurethane acrylate

A series of UV-curable hyperbranched polyurethane acrylate (HBPUA) oligomers were synthesized with isophorone diisocyanate (IPDI), hyperbranched polyester Boltorn H20 (HBP) and hydroxy-ethyl acrylate (HEA). The structure of HBPUA oligomers was characterized by Fourier transform infrared (FTIR) spectroscopy, 1H nuclear magnetic resonance (1H-NMR) spectroscopy, and gel permeation chromatography (GPC). The UV-curing kinetics of HBPUA films with Darocur 1173 were investigated, and their heat resistance and mechanical properties (including hardness, adhesion force, flexibility, and impact strength) were measured. The results show that the HBPUA oligomers have superior photosensitivity and the percent conversion of C=C reaches 81% when radiation time is 43 s. The heat resistance of the cured films decreased slightly with the increase in the content of the urethane-acrylate terminal group. Moreover, the mechanical properties of the cured films were influenced by the content of the OH group in HBP that reacted with the first NCO group of IPDI. When the content was 60%, the cured film had excellent overall properties. The hardness, flexibility, adhesion force, and impact strength were 4 H, 2 mm, 0 grade, and 47 kg cm, respectively.

Involvement of reactive oxygen species and calcium in photo-induced membrane damage in HeLa cells by a bis-methanophosphonate fullerene

Photo-excited bioactivities of fullerene derivatives are attracting much attention. In this report, a bis-methanophosphonate fullerene (BMPF) and the other two fullerene derivatives, a bis-malonic acid fullerene (BMAF) and a fullerol were incubated with HeLa cells and irradiated with a green light emitted from a mercury lamp on a fluorescent microscopy. By using DNA fluorescent probe propidium iodide staining method, damage towards cell membrane could be detected when cells were treated by irradiation altogether with BMPF or BMAF at a low concentration (4 μM), and the damage was dose-dependent. The activity of BMPF was much higher than that of BMAF, while fullerol had no effects under the same condition. It was also revealed that different kinds of reactive oxygen species (ROS) correlated to BMPF and BMAF. Additionally, presence of extracellular calcium could promote the activities of both derivatives, while removal of extracellular calcium could not abort their membrane-damaged activities. These results indicated that ROS and calcium were involved in the photosensitization of fullerene derivatives, and BMPF was a superior photosensitizer which would find potential application in biomedical field.

Synthesis and evaluation as a visible‐light polymerization photoinitiator of a new dye‐linked bis(trichloromethyl)‐1,3,5‐triazine

AbstractA dye‐linked initiator consisting of a merocyanine dye, which has an absorption maximum at 460 nm, and a substituted bis(trichloromethyl)‐1,3,5‐triazine initiator was prepared in order to achieve an efficient photopolymerization in a visible‐light region. The spectroscopic studies clearly showed that the dye‐linked initiator exhibit a marked increase in the efficiency of fluorescence quenching than a simple mixture of the dye/initiator. These results are reasonably explained in terms of the efficiency of electron transfer between the dye and the initiator. The relative photoinitiating efficiency of dye‐linked initiators in photopolymerization of acrylate monomers was evaluated and the results clearly indicated that the dye‐linked photoinitiator exhibited a marked increase in the photoinitiating efficiency of photopolymerization of acrylates compared to a simple mixture of the dye/initiator in photopolymer coatings particularly at a lower concentration of the initiator. This was explained in terms of the active quenching sphere of the dye/initiator system. Superior photosensitivity in the linked compound at a lower concentration indicates that this would be particularly useful as a visible‐light photoinitiator in holographic‐recording photopolymers. Copyright © 2004 John Wiley & Sons, Ltd.

Study on the Optoelectronic Properties of Al/a-Si:H/a-As2Se3 Photoreceptor for Electrophotography

Due to its superior photosensitivity in visible light, amorphous selenium-based photoreceptors are widely used on photoreceptor drums in copying machines. Hydrogenated amorphous silicon (a-Si:H), which has special homogeniety making it easily deposited on the substrate as well as excellent photosensitivity in visible light, is first applied as a blocking layer on photoreceptors. Because intrinsic a-Si:H film is an n-type semiconductor, this configuration generates Schottky contact and an np junction at the interfaces which could be regarded as an ideal photodiode. Therefore, we attempted to adopt a-Si:H thin film as a blocking layer, and combine it with amorphous arsenic selenide (a-As2Se3) to prepare two structures of Al/Al2O3/a-As2Se3 and Al/a-Si:H/a-As2Se3 photoreceptors. Using an electrostatic paper analyzer (model: EPA-8100) to measure the photoinduced discharge curve (PIDC), we discovered that the Al/a-Si:H/a-As2Se3 structure has a high initial surface potential (Vso∼214 V; 41.63 V/µm), excellent photosensitivity (E1/2∼2.19 lx·s), a low residual potential (Vr∼4 V), and a high contrast voltage ratio (214 V/4 V\\cong53.5). For a better understanding of photoreceptors, we investigated the photosensitivity at different incident wavelengths, the movement of carriers in the photoreceptors and the characteristics of photoreceptors during isothermal annealing.

Study on the optoelectronic properties of amorphous selenium-based photoreceptors

Due to its superior photosensitivity in the visible wavelength region, amorphous selenium-based material is widely used as the basic photoreceptor material in xerography. The optoelectronic properties of the samples were measured and calculated with photoinduced discharge curve (PIDC) by using Electrostatic Paper Analyzer, and the initial surface potential (V so), dark decay time (t d), photosensitivity (E 1/2) and residual potential (V r) could be obtained. It is found that the contrast voltage which affects directly the resolution of image can be improved by the blocking layer between the bulk (such as a-Se, a-As2Se3) and substrate (Al). Furthermore, the relations between thickness and optoelectronic properties of photoreceptor could be identified, and compared with different blocking layers and isothermal annealing effect for the photoreceptors.

Nicotine sensitized DDT formulations.

Nicotine has been found an effective photosensitizer for DDT. At DDT: nicotine (1:5), DDT along with its formed degradation products DDD, DDE and DBP disappeared within 18 and 60 days under UV and sunlight respectively. Because of persistence, nicotine proved a superior photosensitizer to N, N'-diethylaniline. In DDT emulsifiable concen-trates it led to high alkalinity but no DDT degradation up to 60 days at 20_??_25°C. 0.1 and 0.5% DDT emulsions from these formulations showed no adverse effect on Daucus carrota, Vicia faba, Brassica oleracea var. botrytis, and Dahlia sp., but showed mild to severe phyto-toxicity against Pisum sativum and Cicer arietinum; caused by high concentration of nicotine. On Clerodendrum sp. in sunlight, these formulations showed over 20% faster DDT loss be-tween 3_??_15 days of application. DDT-nicotine mixtures showed no synergism against Tribolium castaneum Herbst.