RESUMO
This study investigates the growth time effect on the structural, morphological, optical, and photoelectrochemical characteristics of highly oriented ZnO nanorod arrays (ZNRAs). The nanorod arrays were grown on ITO substrates using the unified sol-gel spin coating and hydrothermal techniques. ZnO nanoparticles (ZNPs) were synthesized using the sol-gel spin coating method. In contrast, the hydrothermal method was used to grow the ZnO nanorods. The hydrothermal growth time investigated was between 4 and 12 h. The synthesized ZNRAs were used as the photoanode electrodes to investigate their photoelectrochemical (PEC) electrode potency. The as-prepared ZNRAs were characterized using various analytical tools to determine their structures, morphologies, optical, and photoelectrochemical traits. EDX spectra showed the presence of uncontaminated ZnO chemical composition, and FTIR spectra displayed the various functional groups in the samples. A rod-shaped ZnO nanocrystallite with mean lengths and diameters of 300-500 nm and 40-90 nm, respectively, is depicted. HRTEM images indicated the nucleation and growth of ZNRAs with a lattice fringe spacing of 0.26 nm and a growth lattice planer orientation of [002]. The optimum ZNRAs (grown at 8 h) as photoelectrode achieved a photoconversion efficiency of 0.46% and photocurrent density of 0.63 mA/cm2, that was 17 times higher than the one shown by ZNPs with Ag/AgCl as the reference electrode. Both values were higher than those reported in the literature, indicating the prospect of these ZNRAs for photoelectrode applications.
RESUMO
This paper reports the structures, morphologies, optical properties, and photoconversion efficiency (η%) of the In2S3/ZnO core-shell heterostructures nanorod arrays (IZCSHNRAs) produced via the controlled successive ionic layer absorption and reaction (SILAR) cycles. As-produced samples were characterized using XRD, FESEM, TEM, UV-Vis, PL, XPS and FTIR techniques. The proposed IZCSHNRAs revealed nearly double photocurrent density and η% values compared to the pure ZnO nanorod arrays (ZNRAs). In addition, the light absorption, crystallinity and microstructures of the specimens were appreciably improved with the increase of the SILAR cycles. The deposited nanoparticles of In2S3 (ISNPs) on the ZNRAs surface was responsible for the improvement in the heterostructures, light absorption and photogenerated electron-hole pairs separation, thus enhancing the photoconversion performance. It is established that a simple SILAR approach can be very useful to produce good quality IZCSHNRAs-based photoelectrodes required for the future development of high performance photoelectrochemical cells (PECs).
RESUMO
Ga2O3/ITO/glass photoelectrodes prepared by the CVD method has rarely been tested in the electrochemical cell for water splitting. In this study, we investigate the photoelectrolytic performance of Ga2O3/ITO-glass photocatalysts produced by the high-temperature CVD route. The changing of N2 carrier gas flow rate from 0 to 1800 seem induces change in the materials properties. XRD signal strength of the produced bi-phase Ga2O3 is observed to deteriorate, while diffraction line width broadens with increasing N2 supply. Films show a combination of nanoclumps and nanostrips morphology. Ga/O ratio decreases, while the optical bandgap gradually increases from 4.37 to 4.42 eV with increasing O content and crystallite size. Photoluminescence measurements show UV, blue, green and red emissions, respectively. Linear sweep voltammetry of the electrodes in 0.1 M KOH electrolyte shows improvement in photocurrent density from 160 to 257 µA/cm² versus Ag/AgCl at 1 V bias, and a maximum photon-to-current conversion efficiency 0.06%.
RESUMO
Superior sensitivity towards H2 gas was successfully achieved with Pt-decorated GaN nanowires (NWs) gas sensor. GaN NWs were fabricated via chemical vapor deposition (CVD) route. Morphology (field emission scanning electron microscopy and transmission electron microscopy) and crystal structure (high resolution X-ray diffraction) characterizations of the as-synthesized nanostructures demonstrated the formation of GaN NWs having a wurtzite structure, zigzaged shape and an average diameter of 30-166nm. The Pt-decorated GaN NWs sensor shows a high response of 250-2650% upon exposure to H2 gas concentration from 7 to 1000ppm respectively at room temperature (RT), and then increases to about 650-4100% when increasing the operating temperature up to 75°C. The gas-sensing measurements indicated that the Pt-decorated GaN NWs based sensor exhibited efficient detection of H2 at low concentration with excellent sensitivity, repeatability, and free hysteresis phenomena over a period of time of 100min. The large surface-to-volume ratio of GaN NWs and the catalytic activity of Pt metal are the most influential factors leading to the enhancement of H2 gas-sensing performances through the improvement of the interaction between the target molecules (H2) and the sensing NWs surface. The attractive low-cost, low power consumption and high-performance of the resultant decorated GaN NWs gas sensor assure their uppermost potential for H2 gas sensor working at low operating temperature.
RESUMO
The Burstein-Moss shift and band gap narrowing of sputtered indium-doped zinc oxide (IZO) thin films are investigated as a function of carrier concentrations. The optical band gap shifts below the carrier concentration of 5.61 × 1019 cm-3 are well-described by the Burstein-Moss model. For carrier concentrations higher than 8.71 × 1019 cm-3 the shift decreases, indicating that band gap narrowing mechanisms are increasingly significant and are competing with the Burstein-Moss effect. The incorporation of In causes the resistivity to decrease three orders of magnitude. As the mean-free path of carriers is less than the crystallite size, the resistivity is probably affected by ionized impurities as well as defect scattering mechanisms, but not grain boundary scattering. The c lattice constant as well as film stress is observed to increase in stages with increasing carrier concentration. The asymmetric XPS Zn 2p3/2 peak in the film with the highest carrier concentration of 7.02 × 1020 cm-3 suggests the presence of stacking defects in the ZnO lattice. The Raman peak at 274 cm-1 is attributed to lattice defects introduced by In dopants.