Results Of Surface Photovoltage Spectroscopy Research Articles

The construction of lattice-matched CdS-Ag2S heterojunction photocatalysts: High-intensity built-in electric field effectively boosts bulk-charge separation efficiency

The built-in electric field of heterojunction can effectively promote carrier separation and transfer. While, its interface orientation is often random, leading to lattice mismatch and high resistance, thus limiting the efficiency of interfacial charge transfer. Herein, the lattice-matched heterojunction (CdS-Ag2S) was constructed by ion-exchange epitaxial growth. The results of surface photovoltage spectroscopy (SPV), transient photovoltage spectroscopy (TPV), and time-resolved photoluminescence (TRPL) show that the lattice-matched heterojunction has higher charge separation efficiency and longer photogenerated carrier lifetime than that of lattice-mismatched one. The lattice-matched CdS-Ag2S has a high built-in electric field (BIEF) value of 103.42 and a bulk-charge separation (BCS) efficiency of 68.71%, which is about three times higher than that of the lattice-mismatched heterojunction (CdS-Ag2S-M). In addition, the photodegradation efficiency of CdS-Ag2S towards norfloxacin (NOR) was also 3.4 times higher than that of CdS-Ag2S-M. The above results and density functional theory (DFT) calculations indicate that improving the lattice matching at the heterojunction is beneficial for establishing a high-intensity built-in electric field and effectively promoting bulk-charge separation efficiency, thus achieving excellent photocatalytic performance. This work provides an essential reference for the research of high-performance heterojunction photocatalysts.

Enhanced photocatalytic activity of N134 carbon black modified Bi2WO6 benefited from ample oxygen vacancies and boosted separation of photoexcited carriers

N134 carbon black modified Bi2WO6 (BWO) photocatalysts with enhanced oxygen vacancies (OVs) were fabricated through a hydrothermal strategy. The results of XRD and Raman spectra declare that an intense interaction occurs between N134 and BWO. Modification BWO with N134 can curb the recombination of charge carriers, proven by the results of surface photovoltage spectroscopy (SPS). The electron paramagnetic resonance (EPR) and X-ray photoelectron spectroscopy (XPS) analysis reveal that palpable increased amount of the OVs, causing the production of more O2-. O2- radicals are significant contributors for photocatalytic destruction of rhodamine B (RhB) over the 1.0% photocatalyst by the result of trapping experiment. 1.0% reveals boosted photoactivity for destruction of RhB and tetracycline (TC), which is 2.3 times and 1.2 times higher than that of BWO, respectively. 1.0% possesses an exceptional reusability and stability. This work conduces to comprehend the mechanism of boosted photocatalytic activity for carbon blank modified semiconductor photocatalysts.

Remarkably enhanced photoinduced charge separation rate of Bi2WO6 by Cu2+ doping

In this paper, Cu2+ was successfully doped into Bi2WO6 to further promote the photocatalytic performance of Bi2WO6. The presence of Cu2+ in the lattice of Bi2WO6 can be confirmed by the results of X-ray diffraction (XRD), energy dispersive spectrometer (EDS), high-resolution transmission electron microscopy (HRTEM) and element mapping images. The results of surface photovoltage spectroscopy (SPS) show that doping Cu2+ into the lattice of Bi2WO6 can greatly boost the separation rate of photoinduced electron–hole pairs. The electron spin-resonance (ESR) and trapping investigation exhibit that ·O2− is the main active free radicals. The photocatalytic performance of Cu-doped Bi2WO6 photocatalysts toward decolorization of rhodamine B (RhB) was evaluated under simulated sunlight irradiation using a 500 W Xe lamp as light source. Cu-doped Bi2WO6 photocatalysts display remarkably enhanced photocatalytic performance than the bare Bi2WO6, and when the molar ratio of Cu/Bi is 0.6%, the photocatalyst prepared displays the best photocatalytic activity.

In-situ construction of direct Z-scheme Bi2WO6/g-C3N4 composites with remarkably promoted solar-driven photocatalytic activity

As metal-free visible light-driven semiconductor, graphitic carbon nitride (g-C3N4) has attracted increasing attention owing to its excellent properties. However, the photocatalytic performance of the bare g-C3N4 has been significantly hampered by its inherent drawbacks. Herein, to further boost the photocatalytic performance of g-C3N4, Bi2WO6 was in-situ successfully anchored onto g-C3N4 via a routine hydrothermal method. The as-prepared Bi2WO6/g-C3N4 heterojuctions display highly efficient photocatalytic activity toward decay of rhodamine B (RhB) and phenol aqueous solution under simulated sunlight irradiation. When the molar ratio of Bi:g-C3N4 was 4%, the Bi2WO6/g-C3N4 sample prepared exhibits highest photocatalytic activity. The highest photocatalytic performance of the 4% sample can be definitely attributed to the highest separation rate of the photogenerated electron-hole pairs, supported by the results of surface photovoltage spectroscopy (SPS). The cycling experiments show that Bi2WO6/g-C3N4 composites display excellent stability. The photoinduced electron-hole separation and transfer of the Bi2WO6/g-C3N4 composites obey a direct Z-scheme mechanism based on the matched energy band, the analysis of main active species and the enhanced separation rate of photogenerated electron-hole pairs.

Surface photovoltage spectroscopy of porous silicon

Results of surface photovoltage spectroscopy on free-standing porous silicon films fabricated from boron-doped Si wafers of various resistivities are presented. We find that all the films have bandtails, which are about 0.3 eV wide, and their optical band gap is about 2 eV. The majority carriers in the strongly luminescent and poorly photoconducting films are holes, while in the weakly luminescent but photoconducting films they are electrons. This difference between the films appears to be due to different oxygen coverage of the silicon nanocrystallites. We conclude that the origin of the strong red-light luminescence is in the electron optical transitions from the conduction bandtail to the valence bandtail. {copyright} {ital 1997} {ital The American Physical Society}