Zinc oxide (ZnO) is a versatile and inexpensive semiconductor with a wide direct band gap that has applicability in several scientific and technological fields. In this work, we report the synthesis of ZnO thin films via two simple and low-cost synthesis routes, i.e., the molecular precursor method (MPM) and the sol–gel method, which were deposited successfully on microscope glass substrates. The films were characterized for their structural and optical properties. X-ray diffraction (XRD) characterization showed that the ZnO films were highly c-axis (0 0 2) oriented, which is of interest for piezoelectric applications. The surface roughness derived from atomic force microscopy (AFM) analysis indicates that films prepared via MPM were relatively rough with an average roughness (Ra) of 2.73 nm compared to those prepared via the sol–gel method (Ra = 1.55 nm). Thin films prepared via MPM were more transparent than those prepared via the sol–gel method. The optical band gap of ZnO thin films obtained via the sol–gel method was 3.25 eV, which falls within the range found by other authors. However, there was a broadening of the optical band gap (3.75 eV) in thin films derived from MPM.

Metal sulphides, including zinc sulphide (ZnS), are semiconductor photocatalysts that have been investigated for the photocatalytic degradation of organic pollutants as well as their activity during the hydrogen evolution reaction and water splitting. However, devising ZnS photocatalysts with a high overall quantum efficiency has been a challenge due to the rapid recombination rates of charge carriers. Various strategies, including the control of size and morphology of ZnS nanoparticles, have been proposed to overcome these drawbacks. In this work, ZnS samples with different morphologies were prepared from zinc and sulphur powders via a facile hydrothermal method by varying the amount of sodium borohydride used as a reducing agent. The structural properties of the ZnS nanoparticles were analysed by X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) techniques. All-electron hybrid density functional theory calculations were employed to elucidate the effect of sulphur and zinc vacancies occurring in the bulk as well as (220) surface on the overall electronic properties and absorption of ZnS. Considerable differences in the defect level positions were observed between the bulk and surface of ZnS while the adsorption of NaBH4 was found to be highly favourable but without any significant effect on the band gap of ZnS. The photocatalytic activity of ZnS was evaluated for the degradation of rhodamine B dye under UV irradiation and hydrogen generation from water. The ZnS nanoparticles photo-catalytically degraded Rhodamine B dye effectively, with the sample containing 0.01 mol NaBH4 being the most efficient. The samples also showed activity for hydrogen evolution, but with less H2 produced compared to when untreated samples of ZnS were used. These findings suggest that ZnS nanoparticles are effective photocatalysts for the degradation of rhodamine B dyes as well as the hydrogen evolution, but rapid recombination of charge carriers remains a factor that needs future optimization.

The resin of the plant Commiphora wildii Merxm. (omumbiri) is traditionally used by Ovahimba women (Kunene, Namibia) as the main ingredient for their perfume. Although essential oil produced from the resin by steam distillation is sold commercially, its detailed chemical composition and biological properties are not known. Knowledge on the potential antimicrobial and antioxidant activities of C. wildii essential oil is desired by perfume, cosmetics, and detergent manufacturers, in order to add value to their products when using the oil as an ingredient. Furthermore, once the oil has been chemically characterized, the concentrations of the bioactive constituents can be monitored for quality‐control purposes. In this study the chemical characterization of the volatile constituents of the essential oil of C. wildii resin was performed using gas chromatography–mass spectrometry (GC–MS) and GC coupled to a flame ionization detector (GC–FID). Fifty compounds were identified in the oil, most of which were terpenoids. The major compounds were α‐pinene (50.0% w/w), heptane (24.0% w/w), and β‐pinene (11.7% w/w). The antimicrobial activity of the oil was determined against Candida albicans, Escherichia coli, Klebsiella pneumaniaea, and Staphylococcus aureus. The best antimicrobial activity was noted against S. aureus, with a minimum inhibitory concentration (MIC) of 8 mg ml–1. Biofilm reduction was below 40%, but inhibition was between 93% (K. pneumaniaea) and 99% (C. albicans). An 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) radical scavenging assay revealed the antioxidant potential of the oil (with a half‐maximal inhibitory concentration, IC50, of 0.2257 mg ml–1).These results may be used by different industries to guide the formulation of their products and also to assess the safety of this oil when used as an ingredient.

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