Presence Of Hexamethylenetetramine Research Articles

ZnO nanostructures with controlled morphological and optical properties for applications as efficient photocatalyst for malachite green degradation

This study aims to comparatively investigate the morphological and optical characteristics of zinc oxide nanoparticles as a function of the preparation conditions. A series of ZnO nanoparticles were synthesized by facile precipitation method at constant temperature, by varying the zinc sources (zinc acetate, zinc nitrate and zinc chloride) or the precipitant nature (hexamethylenetetramine, urea). The structural, morphological and optical attributes of the prepared ZnO samples were assessed by SEM, XRD, FTIR, UV–Vis and photoluminescence analyses. The morphology of the achieved samples varies from spiky sticks to hexagons or foils with irregular shapes, observing that urea favour the development of two- or three-dimensional ZnO nanostructures, while hexamethylenetetramine predominantly triggered the formation of highly organized one-dimensional structures. The XRD patterns of all ZnO samples matches zincite crystalline hexagonal phase and the evaluation of crystallite size revealed higher values for the samples prepared in the presence of hexamethylenetetramine (HMTA). The optical band gap of ZnO NPs, as estimated from the UV–Vis absorption spectra, varied slightly from 3.13 to 3.21 eV, while fluorescence investigation proves that samples prepared with urea precipitant have a lower rate of charge recombination. Tests on the photocatalytic degradation of malachite green dye under UV light irradiation demonstrated that the dynamics of photogenerated charge carriers play a significant role in the photocatalytic performance of ZnO samples.

Ag-Doped Free-Standing 2D TiO2 Sheets: Electronic, Optical, Magnetic, and Self-Healing Behaviour.

Beyond a critical doping level, Ag - 2D TiO2 sheets (ATO) are deemed to be a flexible transparent conductor, useful for visible-range functional photonic/optoelectronic devices/sensors, sunlight-sensitive catalysis, and light-activated resistive switching. Due to the lack of control of surface energy which often leads to the formation of structural defects and even dimensionality crossover (2D to 0D) of materials during doping reaction, it is challenging to obtain ATO with a controlled doping level. Gauging the urgency, therefore we report the surface energy-controlled synthesis of ATO employing liquid phase exfoliation of TiO2 and subsequent hydrothermal Ag-doping in the presence of Hexamethylenetetramine (HMTA). Electron microscopy and atomic force microscopy reveal ATO sheets with large lateral dimensions. 6-fold, 4-fold, and strain-mediated crystallographic phases of 2D ATO have been revealed by high-resolution electron imaging. Successful tuning of the band gap down to ~ 2 eV with Ag doping up to ~ 10% is obtained. Synthesized 2D ATO have been investigated for their electrical, optical, optoelectronic, photoluminescence, and ferromagnetic behaviour. Visible light-sensitive thermally/structurally robust semiconductor/conductor via tuneable doping will pave the way for their flexible as well as wearable device applications. Self-healing effect of AFM tip-generated mechanical stress has also been demonstrated.

Facile one-pot hydrothermal synthesis of a zinc oxide/curcumin nanocomposite with enhanced toxic activity against breast cancer cells.

Zinc oxide/Curcumin (Zn(CUR)O) nanocomposites were prepared via hydrothermal treatment of Zn(NO3)2 in the presence of hexamethylenetetramine as a stabilizing agent and CUR as a bioactive element. Three ZnO : CUR ratios were investigated, namely 57 : 43 (Zn(CUR)O-A), 60 : 40 (Zn(CUR)O-B) and 81 : 19 (Zn(CUR)O-C), as assessed by thermogravimetric analyses, with an average hydrodynamic diameter of nanoaggregates in the range of 223 to 361 nm. The interaction of CUR with ZnO via hydroxyl and ketoenol groups (as proved by X-ray photoelectron spectroscopy analyses) was found to significantly modify the key properties of ZnO nanoparticles with the obtainment of a bilobed shape (as shown by scanning electron microscopy), and influenced the growth process of the composite nanoparticles as indicated by the varying particle sizes determined by powder X-ray diffraction. The efficacy of Zn(CUR)O as anticancer agents was evaluated on MCF-7 and MDA-MB-231 cancer cells, obtaining a synergistic activity with a cell viability depending on the CUR amount within the nanocomposite. Finally, the determination of reactive oxygen species production in the presence of Zn(CUR)O was used as a preliminary evaluation of the mechanism of action of the nanocomposites.

Formation of Ultimate Thin 2D Crystal of Pt in the Presence of Hexamethylenetetramine.

Platinum naturally crystalizes into a three-dimensional crystal due to its highly symmetrical fcc lattice, with a metallic bond which is non-directional and highly isotropic. This inherently means ultimately that 2D crystals of a few atoms thick growth are hardly available in this material. Here, we discovered that a combinative effect of formic acid reductant and hexamethylenetetramine surfactant during the reduction of their metal ions precursor can realize an ultimate thin 2D crystal growth in platinum. High-resolution transmission electron microscopy and filed-emission electron microscopy analysis have also discovered that the 2D crystal of Pt has 111 facets with a lateral dimension that can be up to more than 5 μm × 2 μm. The thickness of the 2D crystal of Pt is 1.55 nm. A mechanism for obtaining ultimate thin 2D crystal of Pt using the present approach is proposed.

Influence of Co-Precipitation Agent on the Structure, Texture and Catalytic Activity of Au-CeO2 Catalysts in Low-Temperature Oxidation of Benzyl Alcohol

The aim of the study was to establish the influence of a co-precipitation agent (i.e., NaOH–immediate precipitation; hexamethylenetetramine/urea–gradual precipitation and growth of nanostructures) on the properties and catalytic activity of as-synthesized Au-CeO2 nanocomposites. All catalysts were fully characterized with the use of XRD, nitrogen physisorption, ICP-OES, SEM, HR-TEM, UV-vis, XPS, and tested in low-temperature oxidation of benzyl alcohol as a model oxidation reaction. The results obtained in this study indicated that the type of co-precipitation agent has a significant impact on the growth of gold species. Immediate co-precipitation of Au-CeO2 nanostructures with the use of NaOH allowed obtainment of considerably smaller and more homogeneous in size gold nanoparticles than those formed by gradual co-precipitation and growth of Au-CeO2 nanostructures in the presence of hexamethylenetetramine or urea. In the catalytic tests, it was established that the key factor promoting high activity in low-temperature oxidation of benzyl alcohol was size of gold nanoparticles. The highest conversion of the alcohol was observed for the catalyst containing the smallest Au particle size (i.e., Au-CeO2 nanocomposite prepared with the use of NaOH as a co-precipitation agent).

Synthesis of nanocrystalline eskolaite via grimaldiite

Grimaldiite (α-CrOOH) was precipitated hydrothermally from the CrCl3 aqueous solution in the presence of hexamethylenetetramine (HMTA). The crystallite size of grimaldiite samples was estimated to be ~ 2 nm. Eskolaite (α-Cr2O3) was produced by the calcination of grimaldiite at 500 and 700 °C. FE-SEM images showed amorphous-like aggregates of grimaldiite due to very fine particles (crystallites), whereas eskolaite was in the form of sphere-like nanoparticles. Synthesized grimaldiite and eskolaite were used in the investigation of rhodamine B (RhB) degradation. The significant degradation percentage of RhB obtained by grimaldiite was explained as catalytic effect (in dark) and photocatalytic contribution (with illumination).

Retraction statement: Effective and green one‐pot multicomponent synthesis of novel derivatives of 4H‐pyrans in the presence of hexamethylenetetramine as catalyst in water medium

Retraction statement: Effective and green one‐pot multicomponent synthesis of novel derivatives of 4<i>H</i>‐pyrans in the presence of hexamethylenetetramine as catalyst in water medium

Effects of hexamethylenetetramine (HMTA) on the aqueous solution structure, dynamics and ion solvation scenario: A concentration and temperature dependent study with potential HMTA models

The local hydrogen bonding structure of water and its dynamics in hexamethylenetetramine (HMTA) solution is investigated by using classical molecular dynamics simulations. In this study, we have compared two potential HMTA models with different Lennard-Jones (L-J) combination rules. We have considered five different concentrations of HMTA, ranging from pure water to 6.181 m HMTA at 298 K, whereas to calculate the temperature dependence from 298 K to 353 K, we have used 4.187 m concentration of HMTA. From the radial distribution function, it is observed that the addition of HMTA facilitates structural making of water, whereas our calculated values of the tetrahedral order parameter and asphericity of water suggests disordered structure with increasing HMTA concentration. Also there is a significant development of self-aggregation among water and HMTA molecules at higher concentration of HMTA. The self-diffusion coefficient values of water and HMTA is found to be decreased with increasing HMTA concentration in the solution, whereas at concentrations below 1.0 m, it matches well with the experimental observations. Our calculated activation energy of diffusion for HMTA (4.10 ± 0.2 kcal/g mol for Model-II), is very close to the experimental observation (4.34–4.44 kcal/g mol). The structure of the hydration shell of ions of different charges and sizes is also investigated in the presence of HMTA. For all the models, it is observed that the structural and dynamical properties of water and the hydration shell of ion shows negligible difference with varying concentration and temperature. In contrast, the ion−HMTA correlations are model dependent. It is suggested that the HMTA model-I (AM) is the suitable model for representing ion-solvation structure and dynamics particularly at lower concentrations of aqueous-HMTA solution.

Cu5Pt Dodecahedra with Low-Pt Content: Facile Synthesis and Outstanding Formic Acid Electrooxidation.

Tailoring composition and structure are significantly important to improve the utilization and optimize the performance of the precious Pt catalyst toward various reactions, which greatly relies on the feasible synthesis approach. Herein, we demonstrate that Cu-rich Cu5Pt alloys with unique excavated dodecahedral frame-like structure (Cu5Pt nanoframes) can be synthesized via simply adjusting the amounts of salt precursors and surfactants under hydrothermal conditions. It is established that the presence of hexamethylenetetramine and cetyltrimethylammonium bromide, as well as the selection of a proper Pt/Cu ratio are key for the acquisition of the target product. The immediate appeal of this material stems from frame-like architecture and ultralow Pt content involved, which can be used to greatly improve the utilization efficiency of Pt atoms. When benchmarked against commercial catalysts, the developed Cu5Pt nanostructures display superior electrocatalytic performance toward formic acid oxidation, owing to unique electronic effect and ensemble effect. This work elucidates a promising methodology for the synthesis of Pt-based nanostructures while highlights the significance of composition and structure in electrocatalysis.

Preparation of transparent amorphous ZnSnO3 cubic nanoparticles and light-induced homostructures: Application in UV sensor and room-temperature gas sensor

ZnSn(OH)6 polycrystalline cubic particles with perovskite structure were synthesized by hydrothermal method with the presence of hexamethylene tetramine (HMTA) as organic functional reagent. Experiments reveal that HMTA can adjust the nucleation rate and growth rate of ZnSn(OH)6 in the synthesizing system. When the content of HMTA is 4.6 wt%, the nucleation rate of ZnSn(OH)6 is more than its growth rate. As a result, the particle size of ZnSn(OH)6 cube obtained at this condition is smallest whereas its average crystalline size is biggest compared with other samples. After dehydration of ZnSn(OH)6 precursor at high temperature, the above particle and crystalline size characteristics make the resulting amorphous ZnSnO3 display an excellent UV sensitivity and gas-sensing property at room temperature comparable to other UV photo- and gas-sensitive materials. Possible reason of its comprehensive properties were discussed. Moreover, if Zn in the ZnSnO3 molecule is partly replaced by Mg with the formation of Zn0.9Mg0.1SnO3, its UV photoelectric properties can be further enhanced. The ratio of Ilight/Idark of the Zn0.9Mg0.1SnO3 sample is >104, and its response and recovery time are about 4 s and 9 s, respectively.

Flow-Accelerated Corrosion Inhibition of Steel in Hydrochloric Acid by Hexamethylenetetramine: Gravimetric, Density Functional Theory and Multiphysical Studies

In the present study, the flow-accelerated corrosion (FAC) behaviour of API 5L X65 steel was examined in hydrochloric acid environment in the presence of hexamethylenetetramine (HMT) as the organic inhibitor. Traditional experimentation was done through gravimetric method; density functional theory (DFT) was employed to explain the inhibitive tendency and reactive sites of the HMT as a corrosion inhibitor and computational fluid dynamics (CFD) simulation was used to study the hydrodynamics. The experimental results revealed that the optimum inhibition efficiency was achieved at 600 ppm inhibitor concentration with possible antagonism between the hydrodynamics and the inhibition process. The DFT study showed that HMT is a good organic inhibitor with the HOMO and HOMO-1 participating in the adsorption process while the CFD results revealed different flow fields around the surface of the specimen which are directly connected to the mass transfer rate.

Effect of hexamethylenetetramine on the properties of electrodeposited ZnO thin films for dye sensitized solar cell applications

Zinc oxide (ZnO) thin films were obtained on fluorine doped tin oxide substrates by pyrolyzing the electrodeposited zinc hydroxide chloride thin films. The effect of hexamethylenetetramine (HMTA) concentrations on the structural, morphological, vibrational and optical properties was investigated. The ZnO growth orientation is changed from (101) to (002) plane as the HMTA concentrations get increased from 0 to 9 mM. The well-defined hexagonal nanorods and nanowires structures are observed for ZnO thin films deposited in the absence and presence of HMTA. The increase in intensity of E2 (high) vibrational mode, near band edge emission and UV absorbance confirms the ZnO nanowires synthesized in the solution containing 9 mM HMTA having better crystallinity, lesser atomic defects and higher dye loading, respectively. The efficiency of dye sensitized solar cells (DSSCs) based on nanorods and nanowires synthesized in the solutions containing 0 and 9 mM HMTA is 0.36 and 1.02%, respectively. The DSSC based on nanowires photoanode has a higher Rrec, τn, σn and Ln than another DSSC.

Two-Dimensional, Hierarchical Ag-Doped TiO2 Nanocatalysts: Effect of the Metal Oxidation State on the Photocatalytic Properties

This paper reports the synthesis of two-dimensional, hierarchical, porous, and (001)-faceted metal (Ag, Zn, and Al)-doped TiO2 nanostructures (TNSs) and the study of their photocatalytic activity. Two-dimensional metal-doped TNSs were synthesized using the hydrolysis of ammonium hexafluorotitanate in the presence of hexamethylenetetramine and metal precursors. Typical morphology of metal-doped TNSs is a hierarchical nanosheet that is composed of randomly stacked nanocubes (dimensions of up to 5 μm and 200 nm in edge length and thickness, respectively) and has dominant (001) facets exposed. Raman analysis and X-ray photoelectron spectroscopy results indicated that the Ag doping, compared to Zn and Al, much improves the crystallinity degree and at the same time dramatically lowers the valence state binding energy of the TNS and provides an additional dopant oxidation state into the system for an enhanced electron-transfer process and surface reaction. These are assumed to enhance the photocatalytic of the TNS. In a model of photocatalytic reaction, that is, rhodamine B degradation, the AgTNS demonstrates a high photocatalytic activity by converting approximately 91% of rhodamine B within only 120 min, equivalent to a rate constant of 0.018 m–1 and ToN and ToF of 94 and 1.57 min–1, respectively, or 91.1 mmol mg–1 W–1 degradation when normalized to used light source intensity, which is approximately 2 times higher than the pristine TNS and several order higher when compared to Zn- and Al-doped TNSs. Improvement of the crystallinity degree, decrease in the defect density and the photogenerated electron and hole recombination, and increase of the oxygen vacancy in the AgTNS are found to be the key factors for the enhancement of the photocatalytic properties. This work provides a straightforward strategy for the preparation of high-energy (001) faceted, two-dimensional, hierarchical, and porous Ag-doped TNSs for potential use in photocatalysis and photoelectrochemical application.

Formation of Zinc-Oxide Nanorods by the Precipitation Method

Zinc oxide (ZnO) rod-shaped nanoparticles are produced by the precipitation method upon the hydrolysis of zinc-nitrate hexahydrate (Zn(NO3)2 · 6H2O) in the presence of hexamethylenetetramine (C6H12N4). The effect of various parameters on the ZnO-nanorod size and shape is shown. The ZnO nanopowders produced are studied by scanning electron microscopy and X-ray diffraction analysis. The adhesive and mechanical properties of samples containing ZnO nanoparticles and microparticles as additions are studied.

Comparative hydrothermal synthesis of hydroxyapatite by using cetyltrimethylammonium bromide and hexamethylenetetramine as additives

Comparative synthesis ways for preparing HA (Ca10(PO4)6(OH)2) nanoparticles in presence of hexamethylenetetramine (HMTA) and cetyltrimethylammonium bromide (CTAB) were carried out. The reactions were performed in a Teflon-lined stainless-steel reactor at 120°C during 12h. The effects of the additive concentration and the cooling mode (fast and slow) were analyzed. The obtained powders were characterized by X-ray Diffraction (XRD), Raman Spectroscopy, Dynamic Light Scattering (DLS) and Scanning Electron Microscopy (SEM). The two hydrothermal ways carried out for preparing HA nano powders produced a pure crystalline phase of HA. When the fast cooling mode was used, the obtained particles exhibited smaller mean particle sizes. The highest concentrations of used additives (HTMA or CTAB) resulted in opposite effect on the obtained mean particle size of HA particles. These observations were associated to the different behavior of these additives in the HA formation processes.

Synthesis of MnO2/N-doped ultramicroporous carbon nanospheres for high-performance supercapacitor electrodes

We demonstrate a simple and highly efficient strategy to synthesize MnO2/nitrogen-doped ultramicroporous carbon nanospheres (MnO2/N-UCNs) for supercapacitor application. MnO2/N-UCNs were fabricated via a template-free polymerization of resorcinol/formaldehyde on the surface of phloroglucinol/terephthalaldehyde colloids in the presence of hexamethylenetetramine, followed by carbonization and then a redox reaction between carbons and KMnO4. As-prepared MnO2/N-UCNs exhibits regular ultramicropores, high surface area, nitrogen heteroatom, and high content of MnO2. A typical MnO2/N-UCNs with 57wt.% MnO2 doping content (denoted as MnO2(57%)/N-UCNs) makes the most use of the synergistic effect between carbons and metal oxides. MnO2(57%)/N-UCNs as a supercapacitor electrode exhibits excellent electrochemical performance such as a high specific capacitance (401F/g at 1.0A/g) and excellent charge/discharge stability (86.3% of the initial capacitance after 10,000 cycles at 2.0A/g) in 1.0mol/L Na2SO4 electrolyte. The well-designed and high-performance MnO2/N-UCNs highlight the great potential for advanced supercapacitor applications.

Structural, optical and electrical properties of well-ordered ZnO nanowires grown on (1 1 1) oriented Si, GaAs and InP substrates by electrochemical deposition method

ZnO semiconductors, especially in form of nanomaterials, possess many excellent properties and have been employed in many applications. In this article, we reported the selective area growth of ZnO nanowires on different (1 1 1) oriented Si, GaAs, and first time on InP substrates by electrochemical deposition method without any seed layers, using zinc nitrate hexahydrate precursor in the presence of hexamethylenetetramine. The position, density and orientation of such ZnO nanowires were controlled by the substrate patterning technique using electron-beam lithography. As-synthesized ZnO nanowires grown on patterned substrates show smaller diameter, higher density and better orientation, compared to the one grown on unpatterned substrates. In particular, the ZnO nanowires grown on GaAs patterned substrate indicate the best morphological property, with the average diameter, length and density of about 100 nm, 2.4 µm and 35 µm−2, respectively. The x-ray diffraction and Raman scattering also demonstrate high crystalline quality of our ZnO nanowires. Moreover, as-reported ZnO nanowires are also conductive, which would allow their use in field-effect transistor and other potential nanoscale device applications.

Controlled synthesis of microsheets of ZnAl layered double hydroxides hexagonal nanoplates for efficient removal of Cr(VI) ions and anionic dye from water

The removal of effluents from water is necessary for environmental concerns. The common approach to the development of methodologies for water purification is to search for excellent materials with optimised chemical compositions and unique structural dimension. Here a facile chemical approach has been developed for the synthesis of microsheets of chlorine interlayer ZnAl layered double hydroxides (Cl-ZnAl LDHs) hexagonal nanoplates by simply varying the molar ratio of salts precursors in the presence of hexamethylenetetramine (HMTA). The possible formation mechanism of microsheets of Cl-ZnAl LDHs hexagonal nanoplates has been described on the basis of different characterization. The prepared unique structural microsheets exhibited ultrafast adsorption rates and high adsorption capacities in the removal of anionic methyl orange (MO) dye and Cr(VI) ions from aqueous solution. The adsorption isotherms, kinetics models and mechanisms for Cr(VI) ions and MO onto Cl-ZnAl LDHs were also investigated in detail. The high uptake capability, reusability and ultrafast kinetics make Cl-ZnAl LDHs unique structural microsheets a potentially attractive low-cost adsorbent for the efficient removal of metal ions and toxic dye from contaminated water. Furthermore, the simple synthesis strategy might be envisaged for another type of LDHs, and consequently, a variety of applications can target due to their specific structural dimensions.

Retracted: Effective and Green One‐Pot Multicomponent Synthesis of Novel Derivatives of 4H‐Pyrans in the Presence of Hexamethylenetetramine as Catalyst in Water Medium

Hexamethylenetetramine (HMTA) catalyzes synthesis of new polyfunctionalized 4H‐pyrans by reaction of aromatic aldehyde, malononitrile, and β‐keto esters via one‐pot three‐component procedure in water medium. Addition of reactants was performed by two methods led to achieve similar results. Using HMTA in catalytic amount not only represents the economic face of the reaction, but also due to the use of water, a green and safe reaction condition is organized. Thus, the current strategy provides the benefits of high productivity, convenient operation, and environmental friendliness. Structure of all products was proved by elemental analysis, IR, 1H‐NMR, and 13C‐NMR spectroscopy.

Effective and Green One‐Pot Multicomponent Synthesis of Novel Derivatives of 4H‐Pyrans in the Presence of Hexamethylenetetramine as Catalyst in Water Medium

Hexamethylenetetramine catalyzes synthesis of new polyfunctionalized 4H‐pyrans by the reaction of aromatic aldehyde, malononitrile, and β‐keto esters via one‐pot three‐component procedure in water medium. Addition of reactants was performed by two methods led to achieve similar results. Using hexamethylenetetramine in catalytic amount not only represents the economic face of the reaction but also due to the use of water, a green and safe reaction condition is organized. Thus, the current strategy provides the benefits of high productivity, convenient operation, and environmental friendliness. The structure of all products were proved by elemental analysis, IR, 1H NMR, and 13C NMR spectroscopy.