Temporary and permanent changes to the defect equilibrium due to ultraviolet exposure: Surface and bulk effects on ZnO nanostructures

We report on the influence of prolonged exposure of above band gap illumination (UV) on the surface electronic structure (core and valence band) and bulk defect equilibrium of ZnO nanorods. We investigated two samples (ZnO1 and ZnO2) of mutually contrasting surface electronic structure as well as photoluminescence responses. The changes due to the above gap exposure were juxtaposed of as-prepared, UV-treated and healed samples. As prepared samples consist of CC, COC and COOH groups at the surface. The intrinsic surface/defect mediated photocatalytic activity under UV-illumination regenerated the lattice oxygen, oxidized the excess zinc and increased the COC fraction. The surface of ZnO2 was catalytically more active than that of ZnO1 due to zinc interstitials (Zn(i)s) and extended Zn(i)s (ex-Zn(i)s). Also, we identify chemisorbed oxygeneous species, interstitial hydrogen (H, +/- ), multidentate complexes and disassociated O-2 molecule at oxygen vacancies (V-O). As a result of the catalytic activity severe changes occurred to the valance band (VB) edge and deeper-VB structure. After the course of healing, the VB edge for ZnO1 recovered to its pristine condition, unlike ZnO2. Additionally, we note increased fraction of O2s component for both the samples which, after healing did not recover to their as prepared condition. In the context of defect equilibrium the UV-treatment reduced the density of charged oxygen vacancy (V-O(delta)) and the thickness of the depletion layer which we attribute to the desorption of some chemisorbed gases and reconstruction of lattice oxygen. For ZnO1, ex-Zn(i)s are induced after UV-treatment, which subdued to an extent in the course of healing. In sharp contrast, for ZnO2 the UV-treatment subdued the ex-Zn-i related emission, which slightly recovered after healing in addition to a further loss of V-O(delta) related emission. The slow recovery and reorganization of intrinsic defects are attributed to the diffusivity of H-i(+) and the associated lattice distortion, and Zn(i)s in the neighborhood of V(O)s. Furthermore, the non-Coulombic attractive interaction between neutral V(O)s and Zn(i)s mediate the migration of defects and subsequent stabilization on slower timescales. The changes due to UV illumination on the electronic structure and defect equilibrium enhance the applicability and understanding of ZnO nanostructures in optoelectronic applications

Controlling the photoconductivity: Graphene oxide and polyaniline self assembled intercalation

We report on controlling the optoelectronic properties of self-assembled intercalating compound of graphene oxide (GO) and HCl doped polyaniline (PANI). Optical emission and X-ray diffraction studies revealed a secondary doping phenomenon of PANI with -OH and -COOH groups of GO, which essentially arbitrate the intercalation. A control on the polarity and the magnitude of the photoresponse (PR) is harnessed by manipulating the weight ratios of PANI to GO (viz., 1: 1.5 and 1:2.2 are abbreviated as PG1.5 and PG2.2, respectively), where +/-PR=100(R-Dark -RUV-Vis)/ R-Dark and R corresponds to the resistance of the device in dark or UV-Vis illumination. To be precise, the PR from GO, PANI, PG1.5, and PG2.2 are +34%, -111%, -51%, and +58%, respectively. (C) 2015 AIP Publishing LLC

Speciation of Arsenic in Fish by High-Performance Liquid Chromatography-Inductively Coupled Plasma-Mass Spectrometry

Arsenic speciation in fish was performed using isocratic elution with cation exchange column high-performance liquid chromatography and inductively coupled plasma-mass spectrometry detection. The separation of arsenobetaine and dimethylarsinic acid was performed in 12 min. DOLT-4 dogfish liver and NIST RM-50 albacore tuna certified reference materials were used to evaluate the accuracy for the determination of total arsenic in fish. In addition, reference materials were analyzed for arsenobetaine and dimethylarsinic acid, although they were not certified for these analytes. The limits of detection for arsenic in arsenobetaine and dimethylarsinic acid were 0.20 and 0.33 ng/mL, and the limits of quantitation were 0.58 and 1.11 ng/mL, respectively. Total arsenic and arsenic species were determined in fish using the developed method. The predominant arsenic species was arsenobetaine; the measured concentrations were from 0.43 to 12.0 mg/kg arsenic as arsenobetaine. Dimethylarsinic acid concentrations were below the limit of quantitation. The relative standard deviations were between 3.36 and 10.49 for total arsenic and 3.51 and 9.30 for arsenobetaine

Associative behaviour and effect of functional groups on the fluorescence of graphene oxide

We have juxtaposed the structural, vibrational and emission properties of graphene oxide (GO) with various degrees of reduction with and without a model dispersant, unveiling a strong associative behavior between GO sheets and the influence of H-bonds. The interlayer spacings are similar to 0.84 and 0.78 nm for the as prepared and reduced samples. -OH groups are predominantly effected by the photo-thermal reduction. Also we note some regeneration of > C=O and -COOH groups in reduced samples. Clear changes to the phonon density of states indicated the doping effects due to H-bonds via the oxygeneous groups. Importantly, the defect related Raman bands are rather prone to the effect of dispersant, unveiling their intrinsic nature. In the context of fluorescence, internal vibration relaxation mediated by CC stretch vibrations emphasized the localized nature of sp(2) domains of relatively smaller size. Fluorescence consists of 6 components, where the higher energy components are more influenced due to H-bonds than those of the lower energy regime, attributed to their associative behavior and chemical functionality, respectively. Excitation dependent fluorescence measurements indicated a range of optical gaps from similar to 3.5 to 2 eV. The associative behavior of GO and rGO with and without a dispersant provides crucial insights into the fundamental understanding of various molecular processes

Graphene oxide-doped PEDOT:PSS as hole transport layer in inverted bulk heterojunction solar cell

Transparent poly (3,4-ethylenedioxythiophene): poly (styrenesulfonate) (PEDOT:PSS) is widely used hole conducting material in optoelectronic devices. Secondary doping of PEDOT:PSS enables the tunability of its electronic properties. In this work, graphene oxide (GO) was used as a secondary dopant for PEDOT:PSS and the doped materials (composites) were tested for their efficiency as hole transport material in inverted bulk heterojunction (BHJ) solar cell. The composites were studied to unveil the effects of Coulombic interaction between GO and PEDOT:PSS where we note some segregation of PEDOT phase. We found that the GO majorly interacts with PSS through oxygeneous functional groups which promote the detachment of PEDOT from PSS and segregation of PEDOT. Electrochemical properties with and without illumination revealed some photo-induced changes to surface of the samples. Device performances showed about 2.2% efficiency enhancement when GO doping level was 0.25 (v:v) when compared to that of pristine PEDOT:PSS

Evaluation of Serum Fibrinogen, Plasminogen, α2-Anti-Plasmin, and Plasminogen Activator Inhibitor Levels (PAI) and Their Correlation with Presence of Retinopathy in Patients with Type 1 DM

Background. Diabetic retinopathy (DR) is the leading cause of blindness in the world. Retinopathy can still progress despite optimal metabolic control. The aim of the study was to determine whether different degrees of DR (proliferative or nonproliferative) were associated with abnormally modulated hemostatic parameters in patients with T1DM. Method. 52 T1DM patients and 40 healthy controls were enrolled in the study. Patients were subdivided into three categories. Group I was defined as those without retinopathy, group II with NPRP, and group III with PRP. We compared these subgroups with each other and the control group (Group IV) according to the serum fibrinogen, plasminogen, alpha2-anti-plasmin (α2-anti-plasmin), and PAI. Results. We detected that PAI-1, serum fibrinogen, and plasminogen levels were similar between the diabetic and control groups (P=0.209, P=0.224, and P=0.244, resp.), whereas α2-anti-plasmin was higher in Groups I, II, and III compared to the control group (P<0.01, P<0.05, and P<0.001, resp.). There was a positive correlation between serum α2-anti-plasmin and HbA1c levels (r=0,268, P=0.031). Conclusion. To our knowledge there is scarce data in the literature about α2-anti-plasmin levels in type 1 diabetes. A positive correlation between α2-anti-plasmin with HbA1c suggests that fibrinolytic markers may improve with disease regulation and better glycemic control

Hydrophobic Antifouling Electrospun Mats from Zwitterionic Amphiphilic Copolymers

A porous material that is both hydrophobic and fouling-resistant is needed in many applications, such as water purification by membrane distillation. In this work, we take a novel approach to fabricating such membranes. Using the zwitterionic amphiphilic copolymer poly­(trifluoroethyl methacrylate-<i>random</i>-sulfobetaine methacrylate), we electrospin nonwoven, porous membranes that combine high hydrophobicity with resistance to protein adsorption. By changing the electrospinning parameters and the solution composition, membranes can be prepared with a wide range of fiber morphologies including beaded, bead-free, wrinkly, and ribbonlike fibers, with diameters ranging between ∼150 nm and 1.5 μm. The addition of LiCl to the spinning solution not only helps control the fiber morphology but also increases the segregation of zwitterionic groups on the membrane surface. The resultant electrospun membranes are highly porous and very hydrophobic, yet resist the adsorption of proteins and retain a high contact angle (∼140°) even after exposure to a protein solution. This makes these materials promising candidates for the membrane distillation of contaminated wastewater streams and as self-cleaning materials

Evaluation of Microorganisms Causing Ventilator-Associated Pneumonia in a Pediatric Intensive Care Unit

Objective: The aim of this study was to identify microorganisms causing ventilator-associated pneumonia (VAP) and also study the antibiotic resistance/susceptibility