Researchers have recently paid a lot of attention to semiconductor photocatalysts, especially ZnO-based heterostructures. Due to its availability, robustness, and biocompatibility, ZnO is a widely researched material in the fields of photocatalysis and energy storage. It is also environmentally beneficial. However, the wide bandgap energy and quick recombination of the photoinduced electron–hole pairs of ZnO limit its practical utility. To address these issues, many techniques have been used, such as the doping of metal ions and the creation of binary or ternary composites. Recent studies showed that ZnO/CdS heterostructures outperformed bare ZnO and CdS nanostructures in terms of photocatalytic performance when exposed to visible light. This review largely concentrated on the ZnO/CdS heterostructure production process and its possible applications including the degradation of organic pollutants and hydrogen evaluation. The importance of synthesis techniques such as bandgap engineering and controlled morphology was highlighted. In addition, the prospective uses of ZnO/CdS heterostructures in the realm of photocatalysis and the conceivable photodegradation mechanism were examined. Lastly, ZnO/CdS heterostructures’ challenges and prospects for the future have been discussed.

A simple chemical precipitation route was utilized for the synthesis of ZnO nanoparticles (NPs), CdS NPs and ZnO–CdS nanocomposites (NCs). The synthesized nanostructures were examined for the crystal structure, morphology, optical properties and photodegradation activity of rhodamine B (RhB) dye. The ZnO–CdS NCs showed a mixed phase of hexagonal wurtzite structure for both ZnO NPs and CdS NPs. Pure ZnO NPs and CdS NPs possessed bandgaps of 3.2617 and 2.5261 eV, respectively. On the other hand, the composite nanostructures displayed a more narrow bandgap of 2.9796 eV than pure ZnO NPs. When compared to bare ZnO NPs, the PL intensity of near-band-edge emission at 381 nm was practically suppressed, suggesting a lower rate of photogenerated electron–hole (e⁻/h⁺) pairs recombination, resulting in enhanced photocatalytic activity. Under solar light, the composite nanostructures displayed a photodegradation efficiency of 98.16% towards of RhB dye. After four trials, the structural stability of ZnO–CdS NCs was verified.

Nanomaterials with collective optical and magnetic properties are called smart or functional materials and have promising applications in many fields of science and technology. Undoped and Co-doped ZnAl₂O₄ were prepared using a co-precipitation-assisted hydrothermal method. A systematic investigation was carried out to understand the effects of the Co concentration on the crystalline phase, morphology, and optical and magnetic properties of Co-doped ZnAl₂O₄. X-ray diffraction confirmed the cubic spinel structure with the Fd3m space group, and there was no impurity phase. X-ray photoelectron spectroscopy of Co-doped ZnAl₂O₄ confirmed the existence of Zn, Al and O, and the Co in the optimized sample of ZAO-Co-3 confirmed the oxidation state of cobalt as Co²⁺. Transmission electron microscopy of pure and Co-doped ZnAl₂O₄ revealed micro-hexagons and nanosheets, respectively. The optical absorption results showed that the bandgap of ZnAl₂O₄ decreased with increasing Co concentration. The hysteresis loop of Co-doped ZnAl₂O₄ revealed clear ferromagnetic behavior at room temperature. The as-prepared materials are suitable for energy storage applications, such as in supercapacitors and fuel cells. This work aims to focus on the effect of cobalt ions in different concentrations on structural, optical and magnetic properties.

This review article provides current developments in SnO₂ quantum dots (QDs) as effective catalysts over the last five years. SnO₂ QDs are exceptional prospects for catalytic applications because of their high surface area, compact size, and tunable optical features. SnO₂ QDs have recently made strides in their production and functionalization, which has enabled successful use of them as photocatalytic catalysts. The basic concepts of SnO₂ QDs, including their electrical and optical characteristics, are described in this review paper, along with the most current findings on their production and functionalization. Additionally, it covers the fundamental mechanisms that support SnO₂ QDs’ catalytic activity and emphasizes the difficulties involved in using them as catalysts. Lastly, it offers a forecast for the direction of research in this quickly evolving topic. Overall, our analysis demonstrates SnO₂ QDs’ potential as a successful and cutting-edge catalytic system in recent years.