This study assessed the distribution of five heavy metals (Cd, Pb, Cu, Zn, and Fe) across the various stages of treatment in three selected sewage treatment facilities and their receiving waterbodies in the Eastern Cape Province, South Africa. Aqueous and solid (sludge) samples were collected monthly from September 2015 to February 2016. Quantitation was achieved by atomic absorption spectrometry after necessary sample preparations. Concentrations of heavy metal cations in the sludge generally varied from <DL (below detection limit) to 1.17 mg kg⁻¹, <DL to 0.14 mg kg⁻¹, 27.588 to 69.789 mg kg⁻¹, and <DL to 0.099 mg kg⁻¹ for Cu, Cd, Fe and Pb; while Zn was below detection all through. Similarly, the levels of Cu, Cd, and Fe in the influents, effluents, upstream and downstream across the three plants ranged from <DL–6.588 mg L⁻¹, <DL–0.636 mg L⁻¹, <DL–0.878 mg L⁻¹ and <DL–0.711 mg L⁻¹, respectively; Zn and Pb were less than DL in all the matrices and study locations. All the contaminants were below hazardous levels in all the sludge and aqueous samples except Cd which was higher in effluents and surface waters across the board. Wastewater Treatment Plant (WWTP)-A exhibited better removal capacity for Fe (86.6%), compared to WWTP-B (34.7%) and WWTP-C (56.9%). However, the removal of Cu and Zn was very poor in all the treatment facilities studied. Carcinogenic and non-carcinogenic risks evaluated were sufficiently low. This suggests that the levels of contamination, even with respect to Cd, was minimal. Nevertheless, efforts should be made to keep the concentrations of these contaminants at levels safe for humans and aquatic organisms. Furthermore, the use of the effluents from these facilities for irrigation should be discouraged to prevent unnecessary build-up of metals in the soil and plants grown with such, as well as subsequent bioaccumulation and biomagnification in the food chain.

Recently, the recovery of metals extracted from the spent membrane electrode assemblies (MEAs) of fuel cells has attracted significant scientific attention due to its detrimental environmental impacts. Two major approaches, i.e., pyrometallurgical and hydrometallurgical, have been explored to recover platinum group metals (PMGs) from used proton exchange membrane fuel cells (PEMFCs). However, the efficacy of these methods has been limited by the low concentrations of the metals and the high costs involved. Essentially, pyrometallurgical processes result in the evolution of harmful gases. Thus, the hydrometallurgical process is preferred as a suitable alternative. In this review, an overview of the application of pyrometallurgical and hydrometallurgical methods in the recovery of PGMs is presented. The health risks, benefits, and limitations of these processes are highlighted. Finally, the hurdles faced by, opportunities for, and future directions of these approaches are identified. It is envisaged that this review will shed light on the current status of processes for the recovery of spent PGMs and propel their advancement for effective recycling strategies.

Perovskite solar cells (PSCs) are regarded as extremely efficient and have significant potential for upcoming photovoltaic technologies due to their excellent optoelectronic properties. However, a few obstacles, which include the instability and high costs of production of lead-based PSCs, hinder their commercialization. In this study, the performance of a solar cell with a configuration of FTO/CdS/BaZrS₃/HTL/Ir was optimized by varying the thickness of the perovskite layer, the hole transport layer, the temperature, the electron transport layer (ETL)’s defect density, the absorber defect density, the energy band, and the work function for back contact. Various hole transport layers (HTLs), including Cu₂O, CuSCN, P3HT, and PEDOT:PSS, were assessed to select the best materials that would achieve high performance and stability in PSC devices. At optimal levels, PEDOT:PSS reached a maximum power conversion efficiency (PCE) of 18.50%, while P3HT, CuSCN, and Cu₂O exhibited a PCE of 5.81, 10.73, and 9.80%, respectively. The high performance exhibited by PEDOT:PSS was attributed to better band alignment between the absorber and the PEDOT:PSS, and, thus, a low recombination of photogenerated charges. The other photovoltaic parameters for the best device were a short-circuit current density (J_sc) of 23.46 mA cm⁻², an open-circuit voltage (V_oc) of 8.86 (V), and a fill factor (FF) of 8.90%. This study highlights the potential of chalcogenide-based PSCs as an efficient and stable alternative to traditional lead-based solar cells, with successful optimization paving the way for future research on eco-friendly materials and scalable production methods.

Nanoscale FeS and FeS₂ mixed phases were synthesized by one-pot decomposition of (N-anil-N-piperldtc)Fe1 as FeS#1), (N-piperldtc)Fe2 as FeS#2) and (N-anildtc)Fe3 as FeS#3) complexes as precursors, with the help of tri-n-octylphosphine oxide (TOPO) coordinating solvent. Their morphology, stability, size, optical and structural characteristics were observed using various material characterization instruments. In comparison to the FeS#2 nano-flower shape, FeS#1 and FeS#3 have a uniform nano-rod shape. A one-step decomposition pattern was obtained from the thermal gravimetric analysis (TGA) results with 3% final mass residual. The high-resolution transmission electron microscopy (HRTEM) image reveals an aggregation and size diameter of around 14.47–30.25 nm for the three samples. The optical response between 3.8 and 4.2 eV from the three samples shows that they are inconsiderable materials for solar cells application. The diffraction peaks for the three samples matched well with the FeS/FeS₂. These nanoscale materials can be used in a variety of applications, including lithium-ion batteries, biosensors, hydrogen evolution, and multifunctional nanocomposite materials.

To date, extensive studies have been done on solar cells on how to harness the unpleasant climatic condition for the binary benefits of renewable energy sources and potential energy solutions. Photovoltaic (PV) is considered as, not only as the future of humanity’s source of green energy, but also as a reliable solution to the energy crisis due to its sustainability, abundance, easy fabrication, cost-friendly and environmentally hazard-free nature. PV is grouped into first, second and third-generation cells. Dye-sensitized solar cells (DSSCs), classified as third-generation PV, have gained more ground in recent times. This is linked to their transparency, high efficiency, shape, being cost-friendly and flexibility of colour. However, further improvement of DSSCs by quantum dot sensitized solar cells (QDSSCs) has increased their efficiency through the use of semiconducting materials, such as quantum dots (QDs), as sensitizers. This has paved way for the fabrication of semiconducting QDs to replace the ideal DSSCs with quantum dot sensitized solar cells (QDSSCs). Moreover, there are no absolute photosensitizers that can cover all the infrared spectrum, the infusion of QD metal sulphides with better absorption could serve as a breakthrough. Metal sulphides, such as PbS, SnS and CuS QDs could be used as photosensitizers due to their strong near infrared (NIR) absorption properties. A few great dependable and reproducible routes to synthesize better QD size have attained much ground in the past and of late. The injection of these QD materials, which display (NIR) absorption with localized surface plasmon resonances (SPR), due to self-doped p-type carriers and photocatalytic activity could enhance the performance of the solar cell. This review will be focused on QDs in solar cell applications, the recent advances in the synthesis method, their stability, and long term prospects of QDSSCs efficiency.

The necessity to develop renewable energy resources that are highly durable and flexible with superior energy density and capacitance ability has attracted considerable interest in the field of solar cell research. Semiconducting compound materials that are easily available, hazard-free and cost-effective are emerging as potential solutions to tackle this challenge. Herein, we present multiple molecular precursors used to grow manganese sulfide nanoparticles through a proficient one-step heat-up approach. For all of the tested samples, the X-ray diffraction peaks correspond to a γ-MnS hexagonal wurtzite structure. UV-Vis spectroscopy yielded absorption wavelengths of 359–420 nm and band-gap energies of 3.78–4.0 eV. Photoluminescence analysis shows characteristics of red and blue shift from 451–602 nm. High-resolution transmission electron microscopy (HRTEM) and selected-area electron diffraction (SAED) reveal a narrow size distribution with nanosticks and large contact areas, which are critical for improved catalytic performance. The current study provides an improved pathway to a well-grown and uniform nanocrystal structure for applications in energy devices.