Nanomaterials

Cadmium sulphide (CdS) semiconductor nanocrystals are of interest because of their optical properties and potential in photocatalysis. Here, we examine their structural, optical, photocatalytic, electrochemical, antimicrobial, and theoretical characteristics for possible environmental and energy-related applications. CdS nanocrystals were prepared by aqueous co-precipitation. X-ray diffraction (XRD) confirmed the formation of hexagonal wurtzite CdS, while FESEM, HRTEM, and EDAX were used to examine morphology, crystallinity, and elemental composition. UV–visible spectroscopy and Tauc analysis gave an optical band gap of 2.15 eV. Under visible-light irradiation, the material degraded 89.93% of methylene blue within 120 min. Antibacterial activity was also observed against the Gram-positive bacterium Staphylococcus aureus and the Gram-negative bacterium Pseudomonas aeruginosa. Cyclic voltammetry yielded a specific capacitance of 17.75 F g⁻¹, indicating the potential of the material for further investigation in energy storage applications. Density functional theory (DFT) calculations were used to examine the electronic structure, charge distribution, and related features of the CdS nanoclusters. Taken together, the experimental and theoretical results provide an initial assessment of the multifunctional behaviour of the prepared CdS nanocrystals. Further work is needed to establish their performance and safety under application-specific conditions.

This study experimentally investigated CO₂ absorption in APTES-modified Fe₃O₄/water nanofluids under continuous bubbling at nanoparticle concentrations of 0–0.1 wt% and temperatures of 10, 20, and 30 °C. Performance was evaluated using effective CO₂ uptake and the apparent absorption rate constant, with enhancements calculated relative to deionized (DI) water at the same temperature. Effective uptake decreased with increasing temperature and exhibited a nonmonotonic concentration dependence, whereas normalized uptake profiles generally indicated a more rapid approach to the final uptake at higher temperatures. The highest uptake was 2.084 g L⁻¹ at 10 °C and 0.01 wt%. The largest uptake enhancement was approximately 13.2% at 30 °C and 0.05 wt%, although the apparent rate constant decreased by approximately 4.1% under this condition. The greatest kinetic enhancement occurred at 10 °C and 0.1 wt%. Enhancement ranges across concentrations widened with increasing temperature for both metrics, while the largest ranges across temperatures occurred at different concentrations for uptake and kinetics. Normalized performance maps showed that conditions favoring uptake did not necessarily maximize the kinetic benefit of nanoparticle addition. These results support selecting nanoparticle concentration in relation to operating temperature and the relative importance of uptake and absorption rate.

Substrate orientation offers a route to tailoring the dielectric and energy-storage properties of lead-free oxide thin films. In this work, 1.0 mol.% Mn-doped 0.96NaNbO₃–0.04CaZrO₃ (NNCZ–Mn) thin films were fabricated via a sol–gel method on (100)-, (110)-, and (111)-oriented Nb-doped SrTiO₃ substrates and exhibited corresponding preferential out-of-plane orientations. The (111) film combined higher permittivity and lower leakage current with a larger recoverable polarization, yielding the best energy-storage performance among the three orientations. It achieved a recoverable energy density of approximately 23 J/cm³ with an efficiency of 65% at an electric field of 666.67 kV/cm and reached approximately 35 J/cm³ at 970 kV/cm with an efficiency of 48%. Its recoverable energy density also exhibited moderate thermal stability over 23–160 °C, good frequency stability over 400–2000 Hz, and good fatigue resistance after 10⁶ cycles. This study demonstrates the potential of substrate orientation control for improving solution-processed NaNbO₃-based thin-film capacitors.