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In this investigation, attempts have been made to study the inhibitive effect of hexamethylenetetramine (HMTA) on carbon steel in 10% HCl (mass%) by weight loss, potentiodynamic polarization, EIS, and AFM. Results indicate that inhibition efficiency (IE) of HMTA increases with the increase in pickling immersion time from 10 to 60 min, and IE also increases with the increase in temperature. At higher temperatures (80°C), the IE values are higher and almost independent of pickling time. HMTA can be adsorbed on the surface of metal and reduce the corrosion rate of metal. HMTA is a kind of mixed inhibitor and can retard both the anodic dissolution and cathodic hydrogen evolution reactions independently. IE increases with the concentration of HMTA. Electrochemistry measurement shows that adsorption follows the Langmuir isotherm and the value of free energies of adsorption (ΔG_ads) is < 0, so the adsorption process can occur automatically. AFM analyses show HMTA can affect the surface roughness and protect metal.

This study reports the third-order nonlinear optical (NLO) properties of hexamethylenetetramine (HMTA) stabilized pure and transition metals (Cu, Co and Mn) doped ZnS nanoparticles (NPs) and their electronic structures. The third-order NLO properties of pure and transition metals (Cu, Co and Mn) doped ZnS NPs were measured by $Z$-scan technique. From these measurements, the pure and doped ZnS samples exhibit negative nonlinearity i.e., self-defocusing. The open aperture $Z$-scan measurement shows saturated absorption within the medium. The prepared pure and doped ZnS samples exhibit nonlinear refractive index of the order of 10${}^{-8}$(cm²/W), nonlinear absorption (NLA) coefficient of the order of 10${}^{-4}$cm/W and nonlinear optical susceptibility of the order of 10${}^{-6}$esu. The electronic structures of these ZnS NPs were investigated using near edge X-ray absorption fine structure (NEXAFS) measurements at the C K-, N K- and Co L${}_{3,2}$-edges. The C K- and N K-edges XANES spectra reveal the appearance of several spectral features in the range 285–290eV and 390–430eV respectively. The Co L${}_{3,2}$-edge NEXAFS spectrum exhibits multiplet absorption lines similar to those of Co${}^{2+}$ ions coordinated in tetrahedral symmetry with four sulfur nearest neighbors. These results clearly demonstrate that divalent Co ions substitute Zn sites. From the Raman spectra, the appearance of multiple resonance Raman peaks indicates that the prepared ZnS samples have good optical quality.

Cadmium sulfide nanoparticles have been synthesized by hydrothermal method using cadmium acetate, thiosemicarbazide, and sodium hydroxide as precursors with hexamethylene tetramine as the surfactant. From the X-ray diffraction analysis, it is observed that synthesized CdS nanoparticles show cubic phase. The presence of HMTA in CdS was confirmed by FT-IR analysis. The bandgap value of CdS nanostructure has been estimated by DRS–UV-Visible spectral analysis. The formation of flower-like nanoclusters was observed using scanning electron microscopy (SEM). The application of CdS nanoparticles in photocatalytic degradation was also studied.

Cerium-doped ZnS nanoparticles have been synthesized through hydrothermal method. The nanoparticles were stabilized using hexamethylenetetramine (HMTA) as surfactant in aqueous solution. The average particle size of the prepared samples is about 2 nm. The structure of the as-prepared ZnS nanoparticles is cubic (zinc blende) as demonstrated by X-ray powder diffraction (XRD) and selected area electron diffraction (SAED) analysis. TEM results showed that the synthesized nanoparticles were uniformly dispersed in the HMTA matrix without aggregation. The UV–Vis absorption spectra of the prepared ZnS nanoparticles show a considerable blueshift in the absorption band edge compared to bulk ZnS indicating a strong quantum confinement effect. Formation of HMTA-capped ZnS nanoparticles was confirmed by FTIR studies. Photoluminescence studies showed that the relative emission intensity of Ce³⁺-doped ZnS nanoparticles is higher than that of undoped ZnS nanoparticles, which is due to the enhancement of radiative recombination in the luminescence process. The PL spectra showed two emission peaks at around 420 nm and 442 nm, which may be attributed to deep-trap emission or defect-related emission of ZnS and presence of various surface states.