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In this research, the effects of chitosan on the corrosion behavior of mild steel in 0.1 M hydrochloric acid was investigated by different approaches. According to weight loss measurements, increasing the concentration of chitosan from 0.3 to 1.8 mM, significantly reduced the corrosion rate of mild steel, for example, from 95.5 ± 5 to 7.5 ± 5 mpy at 298 K. The thermodynamic calculations indicate an increase in the corrosion activation energy and the enthalpy of activation when 1.8 mM chitosan was added to the aggressive solution. The electrochemical polarization technique revealed a decrease in corrosion current density which is compatible with the observed increase in the charge transfer resistance measured by electrochemical impedance spectroscopy. The EDS spectra confirmed the adsorption of chitosan on mild steel. Analyzing the surface topography of the coupons by atomic force microscopy showed a remarkable decrease in the corrosion rate of the specimens in the presence of chitosan.

As a revolutionary material, hybrid halide perovskites can greatly improve the solar conversion efficiency of solar cells. In this work, a first-principles theoretical study is performed to investigate the role of methylammonium (MA) rotation in the MAPbX3 (X = I, Br, and Cl) perovskites. To provide a full understanding of the MA rotation, we report electronic and optical properties in different rotational angles and modes. Our results evidence that rotation of MA with R z and R x modes causes substantial changes in band structure, density of states, partial density of states, electron density, dielectric function, and absorption spectra. We also showed that these changes are deeply affected by cation–cation (MA–Pb) and cation–anion (MA–X) interactions. Furthermore, the halogens of MAPbX3 were changed to iodide, bromide, and chloride anions to study the inorganic–organic interactions inside the MAPbX3 in detail. Interestingly, we conclude that the rotational modes, location, and orientation of organic cation can be used as an efficient tool to control the band gap, static dielectric constant, and absorption edge of the optical spectra. Our results providing useful and accurate insight into the behavior of MA embedded in inorganic octahedra are in good agreement with experimental data being used in photovoltaic applications.