Corrosion of mild steel in acidic environments is a major industrial challenge, driving the synthesis of efficient and tunable organic inhibitors. Herein, twelve halogenated 4-aminoantipyrine amide derivatives (M1-M12) were synthesized and characterized by FT-IR and NMR (1H-NMR, 13C-NMR, COSY, and HSQC) spectroscopy and HRMS. Their ability for the corrosion inhibition of mild steel in 1 M HCl was evaluated by weight loss, PDP, EIS, and SEM analyses and DFT calculations. At 1 mM, M5, M12 and M7 exhibited inhibition efficiencies (IE) of 96.46 ± 1.9%, 95.58 ± 1.9% and 94.69 ± 1.8%, respectively; M5 also exhibited the highest electrochemical efficiencies at 0.5 mM (PDP 96.51 ± 0.9% and EIS 95.70 ± 1.1%). Efficiency increased with concentration and decreased with temperature. Negative ΔG° values (-15.53 to -10.86 kJ mol-1) and the Langmuir fit indicate spontaneous, predominantly physical adsorption, possibly with specific donor-acceptor contributions. PDP showed mixed-type behaviour, and EIS showed increased charge-transfer resistance. Halogen type, substituent position and alkyl-chain length strongly influenced performance.
This study is based on the removal of methylene blue (MB) from aqueous solution by cost effective and biodegradable adsorbent carboxymethyl starch grafted polyvinyl pyrolidone (Car-St-g-PVP). The Car-St-g-PVP was synthesized by grafting vinyl pyrolidone onto carboxymethyl starch by free radical polymerization reaction. The structure and different properties of Car-St-g-PVP were determined by 1H NMR, FT-IR, XRD, TGA and SEM. A series of batch experiments were conducted for the removal of MB, The adsorption affecting factors such as temperature, contact time, initial concentration of MB dye, dose of Car-St-g-PVP and pH were studied in detail. The other parameters like the thermodynamic study, kinetics and isothermal models were fitted to the experimental data. The results showed that pseudo 2nd order kinetics and Langmuir's adsorption isotherms were best fitted to experimental data with regression coefficient R2 viz. 0.99 and 0.97. The kinetic study showed that the adsorption mechanism favored chemisorption. The Gibbs free energy (ΔG°) for the adsorption process was found to be -7.31 kJ/mol, -8.23 kJ/mol, -9.00 kJ/mol and -10.10 kJ/mol at 25 °C, 35 °C, 45 °C and 55 °C respectively. The negative values of ΔG° suggested the spontaneous nature of the adsorption process. Similarly, the positive values of entropy (ΔS°) and enthalpy (ΔH°) 91.27 J/k.mol and 19.90 kJ/mol showed the increasing randomness and endothermic nature of the adsorption process. The value of separation factor (RL) was found to be less than one (RL