Sunita

We present a derivation of the screening length for a solution containing a charge-regulated macroion, e.g. protein, with its counterions. We show that it can be obtained directly from the second derivatives of the total free energy by taking recourse to the “uncertainty relation” of the Legendre transform, which connects the Hessians or the local curvatures of the free energy as a function of density and its Legendre transform, i.e., osmotic pressure, as a function of chemical potentials. Based on the Fowler-Guggenheim-Frumkin model of charge regulation, we then analyze the “screening resonance” and the “overscreening” of the screening properties of the charge-regulated macroion solution.

In recent years, the demand for selective and accurate sensing techniques for detecting ammonia gas has increased significantly due to its widespread industrial use. The highly toxic and corrosive nature of ammonia poses a threat to both human health and the environment. In this study, WO? nanocrystals were synthesized via a hydrothermal method and surface-modified with Ce-Cu (a rare earth element-transition metal pair) to enable selective ammonia detection over a range of frequencies. Structural analysis was performed using XRD and FESEM, while optical properties were investigated via UV–visible spectroscopy, FTIR, and PL. For chemical composition analysis XPS was performed, these results indicates that after Ce-Cu co-doping active oxygen sites increases with balanced chemisorbed oxygen species, which are beneficial for gas sensing application. The optimum operating temperature for Ce-Cu-doped WO? was determined to be 250°C, at which the sensor exhibited high response and selectivity across the frequency range. The Ce-Cu co-doped WO3 sensor showed long term stability over 100 days and fast ammonia sensing with approximately 8 s response and recovery times. © 2025 Elsevier B.V.