Sensitive photoelectrochemical sensing of glucose using hematite decorated with NiAl-layered double hydroxides.

Hematite (α-Fe2O3) is a promising photoelectrode material for photoelectrochemical (PEC) sensors. However, it still suffers from serious surface charge recombination and slow interfacial charge transfer kinetics. In this work, NiAl-layered double hydroxides decorated on α-Fe2O3 (NiAl-LDH/α-Fe2O3) was successfully fabricated via a facile hydrothermal method. The NiAl-LDH/α-Fe2O3 exhibits excellent PEC response toward glucose, with a good linear range from 0.01 to 2 mM, a high sensitivity of 274.7 µA·mM-1·cm-2 and a low detection limit of 0.005 mM. NiAl-LDH/α-Fe2O3 PEC sensor could be used for glucose determination in various food samples, such as bread, toast and glucose oral solution, which achieved comparable results with that of HPLC. PEC and electrochemical characterizations indicate NiAl-LDH could act as and/or provide active sites for glucose detection, enlarge the band bending and decrease the charge transfer resistance, thus significantly improve the PEC response of α-Fe2O3 toward glucose.

Insights into the multirole CoAl layered double hydroxide on boosting photoelectrochemical activity of hematite: Application to hydrogen peroxide sensing.

As an important compound in many industrial and biological processes, hydrogen peroxide (H2O2) would cause harmfulness to human health at high concentration level. It thus is urgent to develop highly sensitive and selective sensors for practical H2O2 detection in the fields of water monitoring, food quality control, and so on. In this work, CoAl layered double hydroxide ultrathin nanosheets decorated hematite (CoAl-LDH/α-Fe2O3) photoelectrode was successfully fabricated by a facile hydrothermal process. CoAl-LDH/α-Fe2O3 displays the relatively wide linear range from 1 to 2000 µM with a high sensitivity of 132.0 µA mM-1 cm-2 and a low detection limit of 0.04 µM (S/N ≥ 3) for PEC detection of H2O2, which is superior to other similar α-Fe2O3-based sensors in literatures. The (photo)electrochemical characterizations, such as electrochemical impedance spectroscopy, Mott-Schottky plot, cyclic voltammetry, open circuit potential and intensity modulated photocurrent spectroscopy, were used to investigate the roles of CoAl-LDH on the improved PEC response of α-Fe2O3 toward H2O2. It revealed that, CoAl-LDH could not only passivate the surface states and enlarge the band bending of α-Fe2O3, but also could act as trapping centers for holes and followed by as active sites for H2O2 oxidation, thus facilitated the charge separation and transfer. The strategy for boosting PEC response would be help for the further development of semiconductor-based PEC sensors.

High Efficiency CIGS Solar Cells by Bulk Defect Passivation through Ag Substituting Strategy.

Cu(In,Ga)Se2 (CIGS) is considered a promising photovoltaics material due to its excellent properties and high efficiency. However, the complicated deep defects (such as InCu or GaCu) in the CIGS layer hamper the development of polycrystalline CIGS solar cells. Numerous efforts have been employed to passivate these defects which distributed in the grain boundary and the CIGS/CdS interface. In this work, we implemented an effective Ag substituting approach to passivate bulk defects in CIGS absorber. The composition and phase characterizations revealed that Ag was successfully incorporated in the CIGS lattice. The substituting of Ag could boost the crystallization without obviously changing the band gap. The C-V and EIS results demonstrated that the device showed enlarged Wd and beneficial carrier transport dynamics after Ag incorporation. The DLTS result revealed that the deep InCu defect density was dramatically decreased after Ag substituting for Cu. A champion Ag-substituted CIGS device exhibited a remarkable efficiency of 15.82%, with improved VOC of 630 mV, JSC of 34.44 mA/cm2, and FF of 72.90%. Comparing with the efficiency of an unsubstituted CIGS device (12.18%), a Ag-substituted CIGS device exhibited 30% enhancement.

Oscillation of absorption bands of Zn(1-x)Mn(x)S clusters: an experimental and theoretical study.

Electroporation of synthetic vesicles is utilized for the preparation of molecular size uncapped Zn(1-x)Mn(x)S clusters. The absence of caps permits (i) continued growth of the Zn(1-x)Mn(x)S clusters formed, (ii) the assessment of their true absorption spectra unaltered by stabilizing ligands, and (iii) the previously inaccessible live observation of the growth of the clusters in the molecular size regime. Upon cluster growth, the UV spectra exhibit novel, time-dependent, oscillation of red and blue shifts of the characteristic absorption band. The structure and electronic properties of Zn(N-1)MnS(N) clusters with N = 1-9 are calculated using the first-principles DMol(3) package. On the basis of similarities between the oscillating trend of the experimentally observed absorption spectra and that of the calculated highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gap of Zn(N-1)MnS(N) clusters with N = 1-9, the wavelengths of the sequential spectral peaks can be assigned to Zn(2)MnS(3), Zn(3)MnS(4), Zn(4)MnS(5), Zn(6)MnS(7), and Zn(8)MnS(9), respectively. Our results demonstrate that both the cluster size and the composition can be used to tune the optical properties.

Synthesis and bandgap oscillation of uncapped, ZnO clusters by electroporation of vesicles.

A convenient preparation is reported for subnanometre size uncapped ZnO quantum dots, which permits the previously inaccessible live observation of the growth of the clusters in the molecular size regime. The preparation method utilizes electric field-induced transient pore formation (electroporation) in synthetic unilamellar vesicles. This condition allows for facile monitoring of the time-dependent UV spectra associated with the growth of the clusters which are found to initially exhibit novel, oscillating red and blue shifts of the characteristic absorption band, ultimately followed by a monotonic red shift-the latter reflecting cluster growth beyond a size of ∼10 Å. Through a comparison of the observed oscillating transition energies with the corresponding trends found theoretically by others, the wavelengths of the sequential spectral peaks can be assigned to the (ZnO)(1) monomer (5.66 eV), dimer (ZnO)(2) (5.19 eV), (ZnO)(5) (6.21 eV), (ZnO)(12) (5.76 eV), and (ZnO)(15) (6.01 eV). Growth beyond (ZnO)(15) is associated with the customary monotonic red shift of the absorption band (5.59 and 4.95 eV). The reason for oscillation of red and blue shift of the HOMO-LUMO gaps was explained by the structural differences of Zn(i)O(i) (i = 1-15). Under the experimental conditions used, a stable system is reached after 12 days. This solution is estimated to contain 1.4 × 10(17) (ZnO)(15) particles, each with a greatest dimension of ∼10 Å.