Photoelectrochemical study on photosynthetic pigments-sensitized nanocrystalline ZnO films

Sensitive photoelectrochemical detection of colitoxin DNA based on NCDs@CuO/ZnO heterostructured nanocomposites with efficient separation capacity of photo-induced carriers

A metal-organic framework (MOF) of Cu-TPA (terephthalic acid) microsphere was prepared, followed by calcinating the MOF precursor of Cu-TPA/ZIF-8 mixture to obtain the CuO/ZnO. N-doped carbon dots (NCDs) were employed to combine the CuO/ZnO composite to form a tripartite heterostructured architecture of NCDs@CuO/ZnO, which led to a fierce enlargement of the photocurrent response. This  was ascribed to the thinner-shell structure of the CuO microsphere and the fact that hollow ZnO particles could sharply promote the incidence intensity of visible light. The more porous defectiveness exposed on CuO/ZnO surface was in favor of rapidly infiltrating electrolyte ions. The p-n type CuO/ZnO composite with more contact interface could abridge the transfer distance of photo-induced electron (e^-1)/hole (h⁺) pairs and repress their recombination availably. NCDs not only could boost electron transfer rate on the electrode interface but also successfully sensitized the CuO/ZnO composite, which resulted in high conversion efficiency of photon-to-electron. The probe DNA (S1) was firmly assembled on the modified ITO electrode surface (S1/NCDs@CuO/ZnO) through an amidation reaction. Under optimal conditions, the prepared DNA biosensor displayed a wide linear range of 1.0 × 10^-6 ~ 7.5 × 10^-1 nM and a low limit of detection (LOD) of 1.81 × 10^-7 nM for colitoxin DNA (S2) measure, which exhibited a better photoelectrochemistry (PEC) analysis performance than that obtained by differential pulse voltammetry techniques. The relative standard deviation (RSD) of the sensing platform for target DNA detection of 5.0 × 10^-2 nM was 6.3%. This proposed DNA biosensor also showed good selectivity, stability, and reproducibility, demonstrating that the well-designed and synthesized photoactive materials of NCDs@CuO/ZnO are promising candidates for PEC analysis.

Methyl Orange Photo-Degradation by TiO2 in a Pilot Unit under Different Chemical, Physical, and Hydraulic Conditions

The photo-catalytic degradation of a textile azo-dye as Methyl Orange was studied in an innovative unit constituted by a channel over which a layer of titanium dioxide (TiO2) catalyst in anatase form was deposited and activated by UVB irradiation. The degradation kinetics were followed after variation of the chemical, physical, and hydraulic/hydrodynamic parameters of the system. For this purpose, the influence of the TiO2 dosage (g/cm3), dye concentration (mg/L), pH of the solution, flow-rate (L/s), hydraulic load (cm), and irradiation power (W) were evaluated on the degradation rates. It was observed that the maximum dosage of TiO2 was 0.79 g/cm3 while for higher dosage a reduction of homogeneity of the cement conglomerate occurred. The Langmuir–Hinshelwood (LH) kinetic model was followed up to a dye concentration around 1 mg/L. It was observed that with the increase of the flow rate, an increase of the degradation kinetics was obtained, while the further increase of the flow-rate associated with the modification of the hydraulic load determined a decrease of the kinetic rates. The results also evidenced an increase of the kinetic rates with the increase of the UVB intensity. A final comparison with other dyes such as Methyl Red and Methylene Blue was carried out in consideration of the pH of the solution, which sensibly affected the removal efficiencies.

Solid state synthesis of tin-doped ZnO at room temperature: characterization and its enhanced gas sensing and photocatalytic properties

A room temperature solid-state reaction has been used to prepare crystalline tin-doped ZnO. Zinc nitrate hexahydrate, cetyltrimethyl ammonium bromide, stannic chloride pentahydrate and sodium hydroxide with proper ratios were ground together. As-synthesized samples were characterized by inductively coupled plasma analysis (ICP), scanning electron microscopy (SEM) and X-ray powder diffraction (XRD); The products were of different morphologies, well dispersed and exhibited good crystallinity, it is also found that the growth direction and morphology of ZnO depend on the amount of Sn doped, which is mainly caused by the difference in sizes between Zn and Sn atoms as well as the change of pH value. Moreover, gas sensing and photocatalytic properties of the obtained products were studied. The materials showed a high gas response to ethanol vapor, and the gas response can reach a maximum of R(a)/R(g) = 124. In addition, tin-doped ZnO materials exhibited improved photocatalytic performance toward methyl orange (MO) solution under a current density of 0.03 mg L(-1) comparison with undoped ZnO.

Fabrication and characterization of Meldola's blue/zinc oxide hybrid electrodes for efficient detection of the reduced form of nicotinamide adenine dinucleotide at low potential

We report the synthesis and the electrochemical properties of hybrid films made of zinc oxide (ZnO) and Meldola's blue dye (MB) using cyclic voltammetry (CV). MB/ZnO hybrid films were electrochemically deposited onto glassy carbon, gold and indium tin oxide-coated glass (ITO) electrodes at room temperature (25+/-2 degrees C) from the bath solution containing 0.1 M Zn(NO3)2, 0.1 M KNO3 and 1x10(-4) MMB. The surface morphology and deposition kinetics of MB/ZnO hybrid films were studied by means of scanning electron microscopy (SEM), atomic force microscopy (AFM) and electrochemical quartz crystal microbalance (EQCM) techniques, respectively. SEM and AFM images of MB/ZnO hybrid films have revealed that the surfaces are well crystallized, porous and micro structured. MB molecules were immobilized and strongly fixed in a transparent inorganic matrix. MB/ZnO hybrid films modified glassy carbon electrode (MB/ZnO/GC) showed one reversible redox couple centered at formal potential (E0') -0.12 V (pH 6.9). The surface coverage (gamma) of the MB immobilized on ZnO/GC was about 9.86x10(-12) mol cm(-2) and the electron transfer rate constant (ks) was determined to be 38.9 s(-1). The MB/ZnO/GC electrode acted as a sensor and displayed an excellent specific electrocatalytic response to the oxidation of nicotinamide adenine dinucleotide (NADH). The linear response range between 50 and 300 microM NADH concentration at pH 6.9 was observed with a detection limit of 10 microM (S/N=3). The electrode was stable during the time it was used for the full study (about 1 month) without a notable decrease in current. Indeed, dopamine (DA), ascorbic acid (AA), acetaminophen (AP) and uric acid (UA) did not show any interference during the detection of NADH at this modified electrode.

The electrochemical preparation of FAD/ZnO with hemoglobin film-modified electrodes and their electroanalytical properties

Flavin adenine dinucleotide (FAD)-modified zinc oxide self-assembly films were prepared using repeated cyclic voltammetry. The electrochemical reaction of the hemoglobin with the FAD/ZnO self-assembly film-modified electrodes and their electrocatalytic properties were investigated. This paper describes the successful loading of the electrochemically active molecules of hemoglobin and FAD along with ZnO by electrochemical method. In addition to the cyclic voltammetry, an electrochemical quartz crystal microbalance was used to study the growth mechanism and the properties of the films. The FAD/zinc oxide films exhibited a single redox couple, which corresponded to the FAD redox couple. The electrocatalytic properties of the O2, H2O2, trichloroacetic acid and SO(3)2- were studied by the FAD/zinc oxide films in the absence or in the presence of hemoglobin. The electrocatalytic reduction current had been developed from the cathodic peak of the FAD/zinc oxide redox couple. The electrocatalytic process involved an interaction of hemoglobin and FAD/GC film-modified electrode to increase the electrocatalytic reduction current. The electrocatalytic reduction of O2 using the FAD/zinc oxide films was investigated by cyclic voltammetry and rotating ring-disk electrode methods.