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Using N-acetyl-L-cysteine (NAC) as capping agent and different amounts of hydrazine hydrate as growth promoter, in this paper, we report a simple way for preparation of aqueous-based ZnS nanocrystals (NCs). The small-sized and well-dispersed NCs with cubic zinc blende structure and size-dependent optical behavior have been characterized by XRD, TEM, FT-IR, UV-Vis, and photoluminescence (PL) measurements. Disappearance of the thiol-related peak in the FT-IR spectrum of NAC-capped ZnS NCs demonstrated the well-passivation of ZnS NCs by deprotonated NAC molecules. Variation of optical properties of ZnS NCs has been studied at different hydrazine amounts and refluxing times. The growth-assisting characteristic of hydrazine hydrate was demonstrated by redshift in absorption edge as the hydrazine amount increased from 5 to 20 mmol, and ensuing decrease in band gap energy of ZnS NCs from 4.47 eV to 4.0 eV. On the other hand, increasing the refluxing time duration up to 20 h, resulted in obvious redshift in absorption edge and subsequent decrease in the band gap energy from 4.56 eV to 3.85 eV. The optical estimation on the size of the as-prepared ZnS NCs was obtained through effective mass approximation. Results indicated that all the NCs are small enough near the excitonic Bohr radius of ZnS which revealed the presence of strong quantum confinement effects. Effect of these parameters on PL emission intensity of ZnS NCs was studied and it was observed that the best emission result is at the presence of 12.5 mmol hydrazine hydrate and during 16 h heating. Finally, analyzing chemical stability of the as-prepared ZnS NCs against H₂O₂ corrosion demonstrated a well-accepting stability of emission intensity even after 108 min.

II–VI Semiconductor nanocrystals (NCs) with tunable visible emission, such as CdS, CdSe and CdTe, were synthesized in aqueous solution using thiols as capping molecules. Hydrazine was found to promote the growth of NCs through a special mechanism. In only a few hours, the synthesis process was completed at room temperature. Under moderate conditions, the capping molecules not only changed the growth rate of NCs simply by varying the concentration, but also altered the spectral properties of NCs. The capping molecules with amino groups were propitious to the growth of CdS NCs, whereas the kinetic growth of CdS NCs was more affected by the surface passivation efficiency of NCs than by steric hindrance in the system. The fastest growth of the CdS NCs was achieved when glutathione was used as a capping molecule, while the emission of CdS and CdSe NCs were shown to remain steady and tunable using the same capping molecule. The growth rate of 3-mercaptopropionic acid-capped CdS and CdSe NCs slowed down significantly, while CdTe NCs were obtained with excellent emission properties when capped with the same molecule. Furthermore, our approach will also be useful for the study of the kinetic growth of NCs in aqueous solution.

Halloysite nanotubes@polydopamine (HNTs@PDA) nanocomposites were successfully synthesized, and Au nanoparticles (Au NPs) were loaded on HNTs@PDA by electrostatic adsorption. The electrochemical sensor based on HNTs@PDA–Au nanocomposites was constructed. The effect of the composition, structure and property of HNTs@PDA–Au on the response performance of the sensor was explored. The morphology and composition of the nanocomposites were characterized by field emission scanning electron microscopy, transmission electron microscopic, X-ray diffraction, energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. Electrochemical results revealed HNTs@PDA–Au as the sensing interface with good effect on electrocatalytic oxidation of N₂H₄. This sensor detected N₂H₄ in the range from 0.75$\mu$mol$\cdot$L${}^{-1}$ to 2.8mmol$\cdot$L${}^{-1}$, with a sensitivity of 171.7$\mu$A (mmol$\cdot$L${}^{-1}{)}^{-1}$cm${}^{-2}$ and a detection limit of 0.25$\mu$mol$\cdot$L${}^{-1}$ (S/N $=$ 3).

The composite oxide additive containing Mn, Ni, Cr and Co elements for the ZnO varistor was successfully synthesized through the low-temperature combustion synthesis approach. The combustion reaction was carried out using nitrate mixtures of Mn, Ni, Cr and Co as oxidants and hydrazine as fuel. Herein, hydrazine acts as a bidentate bridge ligand, and it forms a complex with metal nitrate. Controlling the pH value of reactant solution by adding the hydrazine had a considerable effect on the combustion characteristics of the precursor and the final synthesized powder properties. The results of the XRD, FT-IR, SEM and TEM analysis indicated that the suitable pH value for synthesizing the composite additive powder with fine grain size and good crystallinity was 7. The precursor prepared at $\mathrm{\text{pH}}=7$ exhibited steady and slow combustion characteristics, and its yield rate achieved ca. 100%. With this method, the composite additive fine powder suitable for improvement of the electrical characteristics of ZnO varistor can be synthesized simultaneously on a large scale.

A selective and sensitive method was proposed for the determination of hydrazine by electrochemical deposition of Au nanodendrites (AuNDs) on the electropolymerized-2-(3,4-dihydroxybenzaldehyde) malononitrile (AuNDs/HBM/GCE). Deposition of AuNDs on the surface of HBM modified electrode effectively increased the electron transfer and active surface area. The surface analysis techniques substantiated the deposition of AuNDs and HBM molecules at the electrode surface. As-prepared modified electrode produced a sharp peak for hydrazine oxidation at $+0.08$ versus Ag/AgCl, with a significant negative potential shift (about 0.43V) compared with unmodified glassy carbon electrode (GCE). The proposed electrode showed a linear response over 0.2$\mu$M–2.4mM with the detection limit of 0.08$\mu$M ($Y_{\mathrm{\text{LOD}}}=Y_B+3\sigma )$. Moreover, AuNDs/HBM/GCE exhibited appropriate stability, selectivity and reproducibility. One of the brilliant advantages of the proposed method is the determination of hydrazine in the presence of hydroxylamine. The peaks of these two compounds are completely separate at $+0.08$ and $+0.20$V. Therefore, the fabricated electrode is capable of hydrazine quantification in real samples without apparent hydroxylamine interference.

DFT calculations of ground-state hydrazine and benzohydrazide derivatives were performed by using hybrid functional B3LYP and CAMB3LYP with 6–31G (d, p) as basis set. The electric dipole moment ($\mu )$, polarizability ($\alpha )$ and molecular first hyperpolarizability ($\beta )$ were characterized in these compounds. The HOMO–LUMO energy gaps and the global chemical reactivity descriptors were computed by B3LYP and CAMB3LYP using 6–31G (d,p), while the excitation energies have determined by time dependent DFT (TDDFT). Besides, the stability and charge delocalization were studied by natural bond orbital analysis. Topological analyses such as atom in molecule (AIM), natural bonding orbital (NBO) and molecular electrostatic potential (MEP) have used to compute intermolecular interactions and in particular hydrogen bonds. The obtained first-order hyperpolarizabilities in the range of 1.5 × ${10}^{-30}$ to 30.2 × ${10}^{-30}$ esu revealed that the hydrazine and benzohydrazide derivatives have better NLO properties. The low-energy gap of 3.53 eV generates an intramolecular charge transfer, leading to the enhancement of the NLO activity in these compounds.