[Show abstract][Hide abstract] ABSTRACT: Recently, a flow photoelectrochemical cell has been first developed and applied to assay global antioxidant capacity in our group. Yet, shortcomings of liquid reference electrode such as sample contaminations from the leaking of the reference solution, mechanically fragile, temperature and light sensitivity, etc. are significant restrictions for integration and miniaturization of photoelectrochemical sensing instruments, which have greatly limited their practical applications. Bearing these problems, in this work a novel two electrode flow photoelectron-chemical system (two-EPCS) has been developed for detection of antioxidant capacity. It is noteworthy that the electrochemical modulation-free mode (detection at the potential of 0.0V) is performed, which has greatly simplified the analysis process and will result in significant simplifications of the instrument integrations. During the sample analysis, both standard antioxidants and commercial beverages were detected. Results evaluated from the two-EPCS are well agreed with those of the traditional three-EPCS at low potentials. By unloading of the reference electrode, it is of great convenience to design a novel photoelectrochemical microfluidic chip based on the two-EPCS, which has also been successfully applied for antioxidant capacity assay. It is satisfactory that comparable detection concentration range and sensitivity were accomplished by applying the microfluidic chip technique. Moreover, the two-EPCS is verified to be a universal platform which does not depend on selected optoelectronic materials but pervasive for general photocatalysts. Such a two-EPCS should be considered as a feasible alternative to the three-EPCS, which will become a promising candidate for industrial and commercial photoelectrochemical sensing instrument integrations in the future.
[Show abstract][Hide abstract] ABSTRACT: Herein, a novel photoelectrochemical platform with WS2/TiO2 composites as optoelectronic materials was designed for selective detection of o-diphenol and its derivatives without any biomolecule auxiliary. Firstly, catechol was chosen as a model compound for the discrimination from resorcinol and hydroquinone; then several o-diphenol derivatives such as dopamine, caffeic acid and catechin were also detected by employing this proposed photoelectrochemical sensor; Finally, the mechanism of such a selective detection has been elaborately explored. The excellent selectivity and high sensitivity should be attributed to two aspects: i) chelate effect of adjacent double oxygen atoms in the o-diphenol with Ti (IV) surface site to form a five/six-atom ring structure, which is considered as the key point for distinction and selective detection. ii) This selected WS2/TiO2 composites with proper band level between WS2 and TiO2, which could make photo-generated electron and hole easily separated, and results in great improvement of sensitivity. By employing such photoelectrochemical platform, practical samples including commercial clinic drugs and human urine samples have been successfully performed for dopamine detection. This biomolecule-free WS2/TiO2 based photoelectrochemical platform demonstrates excellent stability, reproducibility, remarkably convenient and cost effective advantages, as well as low detection limit (e.g. 0.32 ?mol?L-1 for dopamine). It holds great promise to be applied for detection of o-diphenol kind species in environment and food fields.
[Show abstract][Hide abstract] ABSTRACT: The antioxidants in biological organisms can scavenge excess free radicals and effectively reduce oxidative stress, which protects DNA, protein and lipids in the human body from damage, thus preventing diseases from being induced. Therefore, it is particularly significant to assay the antioxidant capacities of our habitual foods during dietary evaluation. Herein, ultrathin graphitic carbon nitride (utg-C3N4)/TiO2 composites have been introduced as sensing elements into a photoelectrochemical platform with a thin layer structured flow-cell, for the real-time assay of the global antioxidant capacity in practical samples. In this system, the two-dimensional utg-C3N4 nanosheet/TiO2 nanoparticle composite material provided a much better optoelectronic function than the individual materials. In comparison with previous reports, this photoelectrochemical strategy shows considerable advantages, including excellent anti-interference properties, a high level of stability and reproducibility, and it is also proved to be the most prompt, convenient and cost-effective method for antioxidant capacity detection up to now. Moreover, utilizing theoretical and experimental examinations, we revealed its photoelectrochemical sensing mechanism in depth. It is proposed that the developed method will pave the way for the development of excellent antioxidant assays with the advantages of photoelectrochemistry and fluidic cells . It is expected to be further applied in food quality inspections and health guides, as well as in other fields.
[Show abstract][Hide abstract] ABSTRACT: TiO2 is an abundant and environmentally benign material, but has a wide band gap, which greatly confines its applications in photocatalysis. Doping and modifying the material composition are both generally used to change and control the photocatalytic activity of semiconductors. Herein, we describe a method and resulting activity of depositing Ce-/S-codoped TiO2 nanoparticles (NPs) on water-soluble sulfonated graphene (SGE) sheets, which guarantees a direct contact and satisfactory electron transfer between the semiconductor and graphene. The Ce/S–TiO2 NPs are homogeneously fixed on the surface of SGE sheets with an average particle size of 7 nm. The resulting composite showed noticeable activity in photodegrading methyl orange (κ = 0.425 h−1). This improved performance can be attributed to the synergistic effects of Ce- and S-codoping toward TiO2 and the composite action between TiO2 NPs and SGE. This type of novel composite is expected to stimulate the development of doped and graphene-involved photocatalysts for addressing environmental problems.
[Show abstract][Hide abstract] ABSTRACT: The usage of coplanar π-conjugated segments represents a feasible strategy on reducing the energy gap of organic push–pull dyes for mesoscopic titania solar cells. In this paper, we report two new dyes coded as C254 and C255 with the respective 1,4-di(thiophen-2-yl)benzene and indacenodithiophene π-linkers, in combination with the electron-releasing triphenylamine and electron-withdrawing cyanoacrylic acid units. The energy-gap reduction stemming from the rigidity of the π-linker is accompanied by a negative shift of the ground-state redox potential, which however does not affect the yield of hole injection from the oxidized state of dye molecules to a cobalt redox electrolyte. On the other side, we have identified from femtosecond transient absorption measurements a diminished rate of electron injection from the relaxed, low-energy excited state of C255 to titania, albeit a comparable rate of electron injection from the high-energy excited states of these two dyes. The bulkier C255 dye with four hexyl side chains tethered on the two sp3 carbons of the fused indacenodithiophene unit can form a more compact self-assembling monolayer on titania, considerably attenuating the charge recombination of photoinjected electrons in titania with the cobalt electrolyte and thus enhancing the cell photovoltage and efficiency.
Full-text · Article · Feb 2014 · The Journal of Physical Chemistry C
[Show abstract][Hide abstract] ABSTRACT: Correlation between current–voltage curves and recombination kinetics of dye-sensitized solar cells was a key subject for understanding the operation mechanisms and improving the device performance. A galvanostatic constant intensity light perturbation (GCILP) technique carried out on the current–voltage curve was developed to discover the correlation. The technique focused on synchronously deriving recombination kinetics and energetic distribution of trap state from the photovoltage responses and reconstructing the current–voltage curve by these derived kinetic parameters. In this technique, the photovoltage response amplitude was analyzed to obtain recombination kinetic parameters such as equilibrium dark recombination current density (or exchange current density) and recombination reaction order; the photovoltage response time trace was used to determine energetic distribution of trap states. Based on these analysis results, not only the effects of conduction band shifts and changes in the recombination rate on the open-circuit voltage could be analyzed but also the current–voltage curves could be successfully reconstructed. So this technique provided a new more convenient approach for efficiently evaluating and deeply understanding the important characteristics of solar cells.
No preview · Article · Jul 2013 · The Journal of Physical Chemistry C
[Show abstract][Hide abstract] ABSTRACT: A novel photoelectrochemical sensor has been designed with polyaniline-reduced graphene oxide-titanium dioxide, which was further applied to sense gallic acid and exhibited extraordinary rapid response, high sensitivity and excellent anti-inference. Meanwhile, the mechanism has been elaborately explored.
Full-text · Article · Jul 2013 · Chemical Communications
[Show abstract][Hide abstract] ABSTRACT: A numerical model for interpretation of the light-intensity-dependent nonlinear characteristics of the short-circuit current in dye-sensitized solar cells is suggested. The model is based on the continuity equation and includes the influences of the nongeminate recombination between electrons and electron acceptors in the electrolyte and the geminate recombination between electrons and oxidized dye molecules. The influences of the order and rate constant of the nongeminate recombination reaction, the light-absorption coefficient of the dye, the film thickness, the rate constant of geminate recombination, and the regeneration rate constant on the nonlinear characteristics of the short-circuit current are simulated and analyzed. It is proposed that superlinear and sublinear characteristics of the short-circuit current should be attributed to low electron-collection efficiency and low dye-regeneration efficiency, respectively. These results allow a deep understanding of the origin of the nonlinear characteristics of the short-circuit current in solar cells.
[Show abstract][Hide abstract] ABSTRACT: We report two triarylamine-cyanoacrylic acid based push–pull dyes C252 and C253 featuring the π-conjugated linkers of 2,6-di(thiophen-2-yl)-4H-dithieno[3,2-b:2′,3′-d]pyrrole and 4H,4′H-2,2′-bidithieno[3,2-b:2′,3′-d]pyrrole, respectively. Benefitting from an improved coplanarity of the conjugated units, the C253 dye displays a red-shifted absorption peak and an enhanced maximum molar absorption coefficient in comparison with C252. However, this pattern of conjugated linker alternation is associated with an 80 mV negative shift of the ground-state oxidation potential, which dominates an almost 5 times reduced rate of hole injection from the oxidized state of C253 to the divalent tris(2,2′-bipyridine)cobalt (Co-bpy) cation in the redox electrolyte, resulting in a considerably poor net charge separation yield. On the other side, a dye-sensitized solar cell employing the C252 photosensitizer and the Co-bpy electrolyte exhibits a good power conversion efficiency of 9.5% measured under the 100 mW cm−2 simulated AM1.5 sunlight. The dissimilarity of cell photovoltage is scrutinized by evaluating the shift of the titania conduction band edge and the variation of interfacial charge recombination kinetics, the latter of which presents a clear correlation with dye coating thickness on titania derived from X-ray photoelectron spectroscopy measurements. Our work has underlined the important energetic and kinetic interplays which should be seriously considered in the further optimization of active components in dye-sensitized solar cells.
[Show abstract][Hide abstract] ABSTRACT: OH radicals as reactive oxygen species in an organism were applied to assay antioxidant capacity since the obtained results present high biological relevance. As a proper photocatalyst, titanium dioxide was employed to generate OH radicals under ultraviolet light irradiation. However, ultraviolet light can damage molecular probe (DNA or protein) during the detection of antioxidant capacity, which interferes with the results. In this article, a novel composite graphene oxide-titanium dioxide (GO-TiO2) nanostructure was synthesized, which can generate numerous OH radicals just under visible light irradiation. In addition, a novel electrochemical antioxidant capacity sensor was designed with GO-TiO2 composites as source of OH radicals and DNA as a molecular probe. Antioxidants were measured by using the suppression of the decline of reduction current of methylene blue used as an intercalating agent for DNA after irradiation and ˙OH-mediated DNA damage. Using gallic acid (GA) as a mode antioxidant species, the detection of GA at levels as low as 0.85 mg L-1 was possible. The antioxidant capacity of other antioxidants was also assayed. Finally, the novel sensor was applied to the determination of antioxidant capacity in tea.
[Show abstract][Hide abstract] ABSTRACT: Decorating graphene with high destiny and uniform size of noble metal nanoparticles is very important for a number of applications including sensing and electrocatalysis. Herein, a novel approach based on in situ diazonium chemistry was reported to design gold nanoparticles/graphene hybrid materials (Au-NPs/G). Graphene oxide was firstly electro-reduced on the glassy carbon electrode, and then this modified electrode was grafted by aminophenyl diazonium cations, generated in situ from p-phenylenediamine. Subsequently, gold nanoparticles (Au-NPs) were deposited on the p-phenylenediamine grafted electrode by a potentiostatic method. X-ray photoelectron spectroscopy, scanning electron microscopy, cyclic voltammetry and electrochemical impedance spectroscopy were used to characterize the Au-NPs/G. The results demonstrated that the Au-NPs with high destiny and uniform size were dispersed on the electro-reduced graphene oxide. In addition, the obtained Au-NPs/G was utilized in electrocatalysis toward the oxidation of methanol showing excellent catalytic activity.
Full-text · Article · Feb 2013 · Journal of electroanalytical chemistry
[Show abstract][Hide abstract] ABSTRACT: A new research strategy for determining the conduction band movement of TiO(2) films and charge recombination between electrons in the TiO(2) film and electron acceptors in the electrolyte was proposed. Steady-state short-circuit current density versus open-circuit voltage was employed to attain the exchange current density and recombination reaction order. Transient photovoltage decay and open-circuit voltage decay measurements were carried out to obtain the energetic distribution of trapped electrons. Reduced voltage-dependent trapped electron concentration and trapped electron concentration-dependent recombination current density were used to analyze influence factors of open-circuit voltage, including contributions from conduction band movement and charge recombination. The simulated and measured electron concentration were in agreement and confirmed the validity of this method for extracting conduction band movement and recombination parameters. This new approach provides a physical insight which could help us to more conveniently and efficiently understand the operation of DSCs.
Preview · Article · Nov 2012 · Physical Chemistry Chemical Physics