ZnO/NiO heterostructures with enhanced photocatalytic activity obtained by ultrasonic spraying of a NiO shell onto ZnO nanorods

Towards all inorganic antimony sulphide semitransparent solar cells

NiO, a wide band gap hole-transporting material (HTM), is gaining attention in photovoltaics due to its optical transparency, chemical stability, and favourable band alignment with absorber. This study uses NiOx nanoparticle-based HTM in semi-transparent Sb2S3 solar cells via a simple chemical precipitation method. We optimised NiOx layer by varying precursor solution concentration and studied its impact on optical and structural properties, composition of nanoparticles and subsequent effect on the performance of semi-transparent Sb2S3 solar cell. NiOx nanoparticles, deposited from nickel(II)nitrate hexahydrate (precursor solution concentrations of 0.2 M to 1.2 M), were thermally treated by two steps at 90 °C for 6 h and 270 °C for 3 h. Nanoparticles with crystallite sizes of 6-9 nm had band gaps (Eg) of ca. 3.65-3.70 eV. Using 1.2 M concentration yielded the largest crystallites (9 nm), lowest Eg (3.65 eV) while retaining the most precursor residues. The highest power conversion efficiency (2.68%) was achieved with NiOx from a 0.5 M precursor, a 60% improvement over HTM-free cells. The effect of precursor solution concentration on the solar cell parameters (efficiency, fill factor, open circuit voltage and short circuit current) are discussed. Present work paves a path toward stable, efficient, and cost-effective all-inorganic Sb2S3 solar cells using NiOx HTM instead of organic counterparts.

Research advances in ZnO nanomaterials-based UV photode tectors: a review

Ultraviolet photodetectors (UV PDs) have always been the research focus of semiconductor optoelectronic devices due to their wide application fields and diverse compositions. As one of the best-known n-type metal oxides in third-generation semiconductor electronic devices, ZnO nanostructures and their assembly with other materials have received extensive research. In this paper, the research progress of different types of ZnO UV PDs is reviewed, and the effects of different nanostructures on ZnO UV PDs are summarized in detail. In addition, physical effects such as piezoelectric photoelectric effect, pyroelectric effect, and three ways of heterojunction, noble metal local surface plasmon resonance enhancement and formation of ternary metal oxides on the performance of ZnO UV PDs were also investigated. The applications of these PDs in UV sensing, wearable devices, and optical communication are displayed. Finally, the possible opportunities and challenges for the future development of ZnO UV PDs are prospected.

Ultrasound-Assisted Synthesis of a ZnO/BiVO4 S-Scheme Heterojunction Photocatalyst for Degradation of the Reactive Red 141 Dye and Oxytetracycline Antibiotic

The preparation of novel sunlight active photocatalysts for complete removal of pollutants from aqueous solutions is a vital research topic in environmental protection. The present work reports the synthesis of a ZnO/BiVO4 S-scheme heterojunction photocatalyst for degradation of the reactive red dye and oxytetracycline antibiotic in wastewater. ZnO and BiVO4 were first fabricated by a hydrothermal technique, and then, the ZnO/BiVO4 heterostructure was synthesized using an ultrasonic route. An increase of the surface area, compared to that of ZnO, was found in ZnO/BiVO4. The enhancement of charge separation efficiency at the interface was obtained so that a remarkable enhancement of the photocatalytic performance was detected in the prepared heterojunction photocatalyst. Complete detoxification of harmful pollutants was achieved by using the economical solar energy. The removal of the pollutants follows the first-order reaction with the highest rate constant of 0.107 min-1. The stability of the prepared photocatalyst was detected after five cycles of use. The ZnO/BiVO4 S-scheme heterostructure photocatalyst still provides high photoactivity even after five times of use. Hydroxyl radicals play an important role in the removal of the pollutant. This work demonstrates a new route to create the step-scheme heterojunction with high photoactivity for complete removal of the toxic dye and antibiotic in the environment.

Highly operative NiO/ZnO nanocomposites for photocatalytic removal of azo dye

The far-reaching technology of semiconductors in treating water pollutants reduces serious health hazards to humans and other eco-systems. With this interpretation, this work is attempted for the first time to synthesize nanosized pristine NiO and ZnO materials, and NiO/ZnO (70:30, 50:50) composites by co-precipitation method. The synthesized materials were then portrayed for their properties using various instrumental techniques such as X-ray diffraction (XRD), Transmission electron microscope (TEM), Energy dispersive X-ray spectrum (EDXS), Fourier transform Infrared spectrum (FT-IR). The main approach of this work is connected with the ultra violet (UV) photocatalytic degradation of MO (methyl orange) by employing the synthesized nanomaterials as catalysts. In view of results, the photocatalytic degradation of NiO/ZnO (70:30) has reported the greatest efficiency than the other catalysts. This outcome lies with the consideration of higher content of NiO present in the composite than ZnO. Further, there was the existence of higher surface area analysed from the BET result. Also, the NiO/ZnO (50:50) sample showed lower degradation efficiency in terms of formed agglomeration when surveyed through TEM. Besides, the positive mechanism of photocatalysis reaction forms the essential hydroxyl radicals which correspond to MO degradation. Moreover, the highly efficient NiO/ZnO (70:30) sample has been trialled for photocatalytic repetition process to observe the stability of degradation. It has accounted with good efficiency for 5 repeated cycles. Finally for UV degradation, the recognized photocatalytic aspect was due to the surface morphology enhanced surface area, synergistic effects of metal oxides and electron-hole charge separation.