Multifunctional Applications and Physicochemical Properties of 1-Hexadecylpyridinium Bromide

1-Hexadecylpyridinium bromide can be applied as organic inhibitors for iron and steel protection against acid corrosion and prevent iron dissolution. The study used potentiodynamic polarization and Tafel extrapolation methods to find the effect of 1-hexadecylpyridinium bromide and hexadecyl trimethyl ammonium bromide on the corrosion behaviour of iron and copper in hydrochloric and sulphuric acid solutions. The results showed that 1-hexadecylpyridinium bromide was more efficient than hexadecyl trimethyl ammonium bromide. This may be attributed to the less positively charged nitrogen in the hexadecyl yrimethyl ammonium bromide compared with the nitroden of pyridinium in 1-hexadecylpyridinium bromide due to the electron releasing character of the three methyl groups attached to the nitrogen atom and thus in the effect on the positive charge disturbance. Also in 1-hexadecylpyridinium bromide, delocalization of π orbitals in the pyridine ring may increase the positive charge on the nitrogen atom of the ring. In the presence of Br⁻, the surface charge is changed to negative by the specific adsorption of the anion, resulting in the co-adsorption of the anion with the cation. [1] [2]

Thermodynamic Analysis of Micellization in Aqueous Solutions

The addition of non-electrolytes to solutions of ionic surfactants is well known to influence their micellar properties by changing the structure of the solvent and the surfactant aggregates. Moreover, the micellar properties of surfactants have been found to be very sensitive to temperature changes and, thus, the thermodynamics of micellizaion processes is important. Recent years, the influence of temperature, methanol, crown ethers and sodium bromide on the micellization of 1-hexadecylpyridinium bromide have been studied by using a membrane electrode selective to the surfactant. From the conductivity data, the critical micelle concentration c.m.c., and the effective degree of counter ion dissociation α, were obtained at various temperatures. In all the cases studied, a linear relationship between log ([c.m.c]/mol · dm⁻³) and the mass fraction of cosolvent in solvent mixtures was observed. The thermodynamic properties ∆H_m and ∆S_m were evaluated from the temperature dependence of the equilibrium constants for micellization of the surfactant. While the micellization process in pure water is both enthalpy and entropy stabilized, it becomes entropy destabilized in all solvent mixtures used; the values of ∆S_m being more negative with increase in the cosolvent content of the solvent mixtures. The resulting ∆H_m against T∆S_m plot showed a fairly good linear correlation, indicating the existence of an enthalpy–entropy compensation in the micellization process. [3]

Heavy Metal Sequestration via Surfactant-Modified Zeolites

Recent studies have shown that zeolites modified with certain surfactants or other cationic sorbents has a strong affinity for heavy metal anions and these surfactant- modified zeolites are effective sorbents for multiple types of contaminants. The results show that Cr(VI) adsorption on 1-hexadecylpyridinium bromide-zeolites have quick initial speed and adsorption kinetics follow pseudo-second order kinetic model within the initial adsorption stage. 1-hexadecylpyridinium bromide-zeolites have higher affinities toward chromate than that to natural zeolites, and particularly, 1-hexadecylpyridinium bromide-Haruna zeolite exhibits the highest adsorption capacity in the all samples studied. Additionally, the adsorption of Cr(VI) on 1-hexadecylpyridinium bromide-Pohang zeolite is almost constant in a wide pH range 3.0–11.0 of solution. In contrast, the Cr(VI)-uptake for 1-hexadecylpyridinium bromide-Haruna zeolite strongly depends on the solution pH. The highest Cr(VI) adsorption on 1-hexadecylpyridinium bromide-Haruna zeolite occurs in acidic solutions (pH 3.0–5.0) and the amount of sorbed Cr(VI) decreases rapidly with increasing pH. High solution ionic strength has a significant effect on chromate adsorption. The chromate adsorptions by 1-hexadecylpyridinium bromide-zeolites are not affected by coexisting chloride, nitrate, sulfate, and calcium as well as magnesium ions but are reduced drastically in the presence of bicarbonate and phosphate ions. Moreover, 1-hexadecylpyridinium bromide-zeolites can achieve high regeneration efficiency after using sodium carbonate extraction and hydrochloric acid. The analyses of XRD, FTIR and SEM reveal that 1-hexadecylpyridinium bromide cations are incorporated into the zeolite’s structure via ion-exchange and Van der Waals forces. It also suggests that anion exchange and electrostatic interaction are probably the main mechanisms that govern the Cr(VI) adsorption. [4]

References:

[1] Saleh, M. M., Mahmoud, M. G., & Abd El-Lateef, H. M. (2019). Comparative study of synergistic inhibition of mild steel and pure iron by 1-hexadecylpyridinium chloride and bromide ions. Corrosion Science, 154, 70-79.

[2] Abd El-Maksoud, S. A. (2004). The effect of hexadecyl pyridinium bromide and hexadecyl trimethyl ammonium bromide on the behaviour of iron and copper in acidic solutions. Journal of Electroanalytical Chemistry, 565(2), 321-328.

[3] Jalali, F., Shamsipur, M., & Alizadeh, N. (2000). Conductance study of the thermodynamics of micellization of 1-hexadecylpyridinium bromide in (water+ cosolvent). The Journal of Chemical Thermodynamics, 32(6), 755-765.

[4] Zeng, Y., Woo, H., Lee, G., & Park, J. (2010). Adsorption of Cr (VI) on hexadecylpyridinium bromide (HDPB) modified natural zeolites. Microporous and Mesoporous Materials, 130(1-3), 83-91.

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