Copper stands at the forefront of materials driving the global transition to renewable energy and is a valued material for various important applications. For the first time, this paper presents an environmentally sustainable approach for recovering metallic copper through photocatalytic processes on a pilot scale, avoiding the energy-intensive conventional techniques. The study is focused on the selective photocatalytic reduction of copper(II) to either copper(I) or zerovalent copper (Cu(0)) based on the reaction conditions. This entire process does not involve strong acids or bases or any hazardous chemicals but needs only light and simple photocatalysts such as zinc oxide (ZnO) and poly(o-phenylenediamine)/zinc oxide (POPD/ZnO). A raceway pond reactor (RPR) was used to scale up the process in deionized water (DW), tap water (TW), and seawater (SW) using ZnO. Thermodynamic considerations were used to predict the reduction of Cu(II) to Cu(I) {Cu(II)/Cu(I) (+0.153 V)} and Cu(0){Cu(II)/Cu(0) (+0.337 V), Cu(I)/Cu(0) (+0.521 V)}. Formic acid served as a sacrificial reagent, while chloride ions modulated the reaction pathways and products at pH 6.5. The copper speciation of Cu(II), Cu(I), and Cu(0) was analyzed using X-ray diffraction (XRD), fluorescence spectroscopy (FS), laser-induced breakdown spectroscopy (LIBS), energy-dispersive X-ray spectroscopy (EDX), and flame atomic absorption spectroscopy (FAAS). The “first copper coin” was produced solely through 100% solar energy-driven photocatalysis. With an 80% recovery rate of Cu(0), our approach demonstrates a proof of concept for efficient copper recovery from wastewater, the mining industry, and e-waste. These findings offer valuable insights for further exploration of solar-driven metal recovery processes, underscoring the potential of solar energy in fostering sustainable industrial practices.

The present study reports the synthesis of Fe₂O₃ nanoparticles on Pinus radiata sawdust (Fe₂O₃@PS) using a Eucalyptus globulus leaf extract. The morphology and structure of Fe₂O₃@PS were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and UV–Vis diffuse reflectance. The adsorption capacity of the system was evaluated by testing its ability to remove the Rhodamine B (RhB) dye. The optimization of the system was carried out using the Plackett–Burman design (PBD) and the response surface methodology (steepest ascent and the Box–Behnken design), which provided information on the main parameters affecting the adsorption process. The PBD results showed that the most important parameters for the removal of RhB using Fe₂O₃@PS were the removal time, the RhB concentration, and the initial pH of the system. The reusability of Fe₂O₃@PS under optimal conditions was tested and it was found to maintain its efficiency after five cycles of use. The efficiency and rate of RhB removal observed at pH values near 7.0 were found to be predominantly influenced by electrostatic interactions. In contrast, the analyses conducted at pH values near 8.3 exhibited reduced influence from electrostatic attractions, with π–π interactions and hydrogen bonds emerging as dominant forces. At pH values exceeding 8.3, all potential interactions between RhB and Fe₂O₃@PS exhibited diminished strength. This research provides valuable information on the formation of eco-friendly nanoparticles immobilized on a forest residue such as sawdust, which can effectively remove organic pollutants like RhB. This contributes to the valorization of resources and the search for solutions to water pollution.

The embryonic developing cerebral cortex is characterized by the presence of distinctive cell types such as progenitor pools, immature projection neurons and interneurons. Each of these cell types is diverse on itself, but they all take part of the developmental process responding to intrinsic and extrinsic cues that can affect their calcium oscillations. Importantly, calcium activity is crucial for controlling cellular events linked to cell cycle progression, cell fate determination, specification, cell positioning, morphological development and maturation. Therefore, in this work we measured calcium activity in control conditions and in response to neurotransmitter inhibition. Different data analysis methods were applied over the experimental measurements including statistical methods entropy and fractal calculations, and spectral and principal component analyses. We found that developing projection neurons are differentially affected by classic inhibitory neurotransmission as a cell type and at different places compared to migrating interneurons, which are also heterogeneous in their response to neurotransmitter inhibition. This reveals important insights into the developmental role of neurotransmitters and calcium oscillations in the forming brain cortex. Moreover, we present an improved analysis proposing a Gini coefficient-based inequality distribution and principal component analysis as mathematical tools for understanding the earliest patterns of brain activity.