Increase In Synthesis Time Research Articles

Luminescent carbon nanoparticles obtained by microwave assisted hydrolysis from dextrin

Carbon nanoparticles (CNPs) were synthesized by acid hydrolysis from dextrin by the microwave-assisted method. The effect of temperature and synthesis time on morphology, size, UV–Vis absorption, and photoluminescence properties was studied. An increase in temperature from 135 to 180 °C decreases the CNPs diameter from 17.8 to 9.7 nm. Similarly, an increase in synthesis time from 2 to 5 min promotes a decrease in sizes from 13.1 to 6.7 nm. UV–Vis absorption spectroscopy and photoluminescence studies indicated that the nanoparticles have a maximum absorbance around 300 nm and when the CNPs are excited with λ close to 400 nm, λ emission occurs in the range of 500–650 nm. CNPs were synthesized maintaining synthesis conditions of 150 °C, for 5 min, varying the type of acid (H2SO4 and CH3COOH) and pH before subjecting the solution to microwave irradiation. It was observed that, when CH3COOH is used as a hydrolysis agent instead of H2SO4, the intensity of the emission increases. Regarding pH, it was observed that CNPs synthesized at alkaline pH have greater photoluminescence than those synthesized at acid pH.

Effect of cerium oxide nanorods growth time on the electrochromic properties of WO3/CeO2 hybrid films

In this study, the cerium oxide nanorods (CeO2) were grown on fluorine-doped tin oxide (FTO) glass substrates by using a hydrothermal process at growth times of 4hrs, 6hrs and 12hrs and annealed at temperature 3500C. The grown samples were characterized by using Scanning electron spectroscopy (SEM), Energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), Raman spectroscopy, and UV–Vis spectrometer. Tungsten oxide (WO3) film was deposited, on these hydrothermally grown nanorods (NRs), by using the DC sputtering process to develop WO3/CeO2 hybrid films. From the SEM and XRD analysis, CeO2 nanorods were observed at different growth times, and crystalline structures were observed respectively. The optical transmittance decreases with the increase in synthesis time, mainly due to the increase in nanorods' thickness. The diffusion coefficient of 11.24 × 10−11 cm2/s and the cathodic peak current of −10.1 mA was observed for 12-h WO3/CeO2 films and the coloration efficiency of 12 cm2/C was observed for 4-h WO3/CeO2 hybrid film.

INFLUÊNCIA DO TEMPO DE SÍNTESE NAS PROPRIEDADES DE HÍBRIDOS PtRu/CARBONO PREPARADOS PELO MÉTODO DA CARBONIZAÇÃO HIDROTÉRMICA

Background: PtRu/C electrocatalysts present good results in methanol electo-oxidation. The activity of these electrocatalysts is strongly dependent on the synthesis method. Additionally, the use of mesoporous carbons or nanostructured carbons increases the performance of electrocatalysts applied in alcohol electro-oxidation. The hydrothermal carbonization method is an alternative to obtain different nanoarchitectures without involving harsh conditions. Aims: Thus, this work aimed to evaluate the influence of synthesis time on the properties of PtRu/Carbon hybrids prepared by the hydrothermal carbonization method. Methods: PtRu/Carbon hybrids were prepared by hydrothermal carbonization at different times of synthesis (6 h and 12 h). It used cellulose as a carbon source and reducing agent and H2PtCl6.6H2O and RuCl3.xH2O as metal sources and catalysts of the carbonization process. The materials were treated at 900 °C and characterized by energy-dispersive X-ray spectroscopy, thermogravimetric analysis, B.E.T isotherms, X-ray diffraction, transmission electron microscope and cyclic voltammetry. The electro-oxidation of methanol was studied by chronoamperometry. Results: The increase in synthesis time from 6 to 12 hours, apparently, resulted in an increase in mean particle size, reduction of mesoporous volume and increase in superficial area and total pore volume. The chronoamperometry of methanol electro-oxidation on these PtRu/Carbon hybrids indicated a higher electroactivity to the material prepared in 6 hours. Discussion: Probably, the higher electroactivity of material prepared in 6 h is associated with smaller particle size, mesoporous structure and surface oxides content. Conclusions: Therefore, it is possible to affirm that the synthesis time is an important parameter that affects the physical-chemical properties of metal/carbon hybrids obtained by the hydrothermal carbonization method.

Hydrothermal synthesis and formation mechanism of controllable magnesium silicate nanotubes derived from coal fly ash

A novel controllable magnesium silicate nanotube (MSN) material derived from coal fly ash was successfully synthesized via a hydrothermal process for the first time, and the reaction conditions and mechanism of synthesizing MSN materials from magnesium oxide and sodium silicate extracted from the fly ash were studied. The optimal preparation conditions are temperature = 220 °C, pH = 13.5, and Mg: Si molar ratio = 3:2, and the tubular structure gradually appeared and showed controllable and regular growth with the increase of synthesis time. The mechanism revealed that with the gradual dissolution of brucite into the sodium silicate solution, the reaction product begins to crystallize and transform from an initial sheet-like structure to a tubular structure, and finally becomes a uniformly arranged nanotube. The formation process of MSN follows Pauling’s fourth rule, Si–O tetrahedral coordination and Mg–OH octahedral coordination is further condensed to form a two-layer structure by the action of active oxygen, then the sheet is rolled into a tube under its structural stress. The growth of both outer tubular diameter and inner tubular diameter has good linear law and controllable, and the growth rate are 0.289 nm h−1 and 0.071 nm h−1, respectively.

Niobium pentoxide as an adsorbent for methylene blue removal: Synthesis, characterization and thermal stability

This study investigated the synthesis of niobium pentoxide (Nb2O5) by peroxide oxidation with hydrothermal treatment and evaluated its application for adsorption of the organic pollutant methylene blue (MB) in aqueous medium. Hydrothermal treatment was performed at 150 °C for different times (4, 12, and 24 h). The resulting materials were characterized by X-ray diffractometry, Raman spectroscopy, thermogravimetry, differential scanning calorimetry, Fourier-transform infrared spectroscopy (FTIR), N2 adsorption isotherm analysis, zeta-potential analysis, and scanning electron microscopy (SEM). Nb2O5 samples had high surface area (174 m2 g−1) and orthorhombic crystal structure. FTIR revealed that an increase in synthesis time produced an increase in surface hydroxylation. Particles dispersed in water had zeta-potential values lower than −31.3 mV, suggesting colloidal stability in aqueous suspension. SEM analyses showed no significant variation in nanoparticle morphology as a function of synthesis time. MB adsorption studies using the sample treated at 150 °C for 24 h showed that the adsorption was higher at pH 6.0, and the process follows pseudo-second order kinetics, suggesting chemical diffusion as the dominant process. The Freundlich isotherm model provided the best fit to experimental data. Thermal analyses indicated a phase transition at about 600 °C, corroborated by analysis of samples after calcination at 500 and 700 °C. Thus, the obtained materials have high specific surface area, adsorption capacity, suspension stability, and thermal stability.

Rapid in-situ phosphorus injection synthesis of large quantity InP polycrystalline

In this paper, a large quantity rapid in-suit phosphorus injection synthesis technology of InP polycrystalline is presented. 20 Kg high-purity InP melt has been synthesized in 170 min, which is the fastest and largest synthesis of InP polycrystalline reported so far. Melt temperature and phosphorus injection rate are two key parameters affecting the synthesis result. Synthesis experiments were carried out under various melt temperatures, the optimal synthesis temperatures of two synthesis processes were determined. The phosphorus injection rate was controlled by adjusting the injector heating power. The injector heating power curves were optimized through experiments. The synthesized InP polycrystalline were characterized by Hall effect measurement and glow discharge mass spectrometer. The results show that the carrier concentration and mobility of synthesized 20 Kg stoichiometric InP polycrystalline were <2.0E15 cm−3 and> 4600 cm2 V−1 s−1, respectively. The results also show that high melt temperature, increase of synthesis time and deviation from stoichiometry will increase the concentration of impurities and reduce the purity of synthesized polycrystalline. It was found that synthesis rate increases with synthesis quantity. With the increase of synthesis quantity, the carrier mobility of polycrystalline increases, the carrier concentration decreases, and the polycrystalline quality can be improved.

Microwave-assisted synthesis and upconversion luminescence of NaYF4:Yb, Gd, Er and NaYF4:Yb, Gd, Tm nanorods

Anisotropic rare earth ion (RE3+) doped fluoride upconversion particles are emerging as potential candidate in diverse areas, ranging from biomedical imaging to photonics. Here, we develop a facile strategy to synthesize NaYF4: Yb, Gd, Er, and NaYF4: Yb, Gd, Tm upconversion nanorods via microwave synthesis route by controlling the synthesis time and compared the optical properties similar nanorods prepared via solvothermal technique. With the increase in synthesis time, the phase of the particle found to change from mixed phase to purely hexagonal and morphology of the particles change mixed phase of spherical and rod-shaped particles to completely nanorods for a synthesis time of 60 min. Further, the intrinsically hydrophobic particles changed to hydrophilic by removal of oleic capping via acid treatment and the amine functionalized silica coating. The upconversion luminescence as well as laser power dependent emission properties of the surface modified particles elucidate that surface modification route influence the upconversion luminescence as well as solvent dependent emission properties. Moreover, the laser power dependent studies elucidate that the upconversion process in a multi-photon process.

Pristine and cobalt doped copper sulfide microsphere particles for seawater splitting

In this work, copper sulfide particles are synthesized with different Co doping concentrations such as 0, 1 and 5% at 80 °C by optimizing synthesis times from 1 to 3 h. Copper sulfide particles possess two structural phases of covellite CuS and digenite Cu9S5. The increase in synthesis time from 1 to 3 h increases the Cu9S5 phase growth and changes the morphology from flower to microsphere. The CuS synthesized with 0, 1 and 5% Co dopant concentrations demonstrate flower consisting of agglomerated nanosheets, microsphere and flower like microsphere. The elemental investigation substantiates Co ions presence in CuS microspheres. The A1g (LO) mode intensity is decreased with increase in Co dopant concentration confirming Co incorporation into CuS microsphere. The CuS synthesized with 0, 1, 5% Co dopants exhibit 322 mV, 305 mV and 289 mV to attain 100 mA/cm2 in 1 M KOH seawater. The CuS synthesized with 5% Co dopant demonstrates higher double layer capacitance (Cdl) of 173.9 mFcm−2 and lower charge transfer resistance (Rct) of 6.07 Ω with 78.84% retention after 10 h continuous stability than that of the other pristine (118.3 mFcm−2, 13.72 Ω) and 1% Co doped CuS microsphere (165.7 mFcm−2, 8.55 Ω) indicating more surface active site and rapid charge carrier transport, respectively.

Relative humidity sensing properties of doped polyaniline-encased multiwall carbon nanotubes: wearable and flexible human respiration monitoring application

Relative humidity (RH) sensors have been fabricated with polyaniline-encased multiwall carbon nanotube (MWCNT) matrix. MWCNT matrices were grown on oxidized Si substrates by catalytic chemical vapour deposition technique. The MWCNT matrices were made hydrophilic by acid treatment. The sensing properties of MWCNTs were improved by encasing the acid-treated MWCNT matrix with PANI. PANI was synthesized via in situ chemical oxidation technique using three acid dopants, named as 5-sulfosalicylic acid, 4-nitrobenzoic acid and hydrochloric acid (HCl). A growth time variation of the PANI was also performed from 1.5 to 2.5 h. The time-varying sensor resistance was recorded with RH change, and RH sensing properties of the corresponding sensors were investigated with the measured data. Doping variation exhibited that CNT–PANI sensor, fabricated with HCl dopant, showed the highest response (42.6% at 90% RH). Synthesis time variation of PANI from 1.5 to 2.5 h exhibited that with an increase in synthesis time, the sensor responsivities degraded from 42.6 to 19.5% at 90% RH. Excellent repeatability, linear response behaviour (R2 = 0.992), low hysteresis loss (± 2.68%) were exhibited by the fabricated RH sensing devices. A facile transfer technology was developed in order to transfer the MWCNT on PET substrate for fabrication of flexible RH sensor. A practical application on human respiration monitoring was demonstrated with the wearable and flexible RH sensors. The humidity sensing mechanism and electron transfer process were schematically explained with the aid of energy band diagram.

Experimental evidence of the metastability of ferric smectite

The stability of clay minerals, and especially ferric smectites, as a function of time, is of interest for natural environments due to their high capacity to exchange electrons that control a large part of the geochemical cycle of different redox-sensitive organic or inorganic compounds (e.g., elements, nutrients, pollutants). An experimental approach based on hydrothermal synthesis was performed for synthesizing two series of iron-rich smectite (Na-nontronite) at two pH (near 12 and 13) from 1 day to several months at 150 °C. XRD, FTIR, and HRTEM data of the synthetic products confirmed the formation of Na-nontronite for the short time duration experiments. However, the dissolution of Na-nontronite and the concomitant formation of aegirine were observed with the increase of synthesis time. The pH of crystallization fluids clearly influences the rate of the reactions. At highest pH, Na-nontronite disappeared totally after two months and aegirine and hematite were the only crystalline phases observed. The chemical compositions of solutions were over time far from the thermodynamic stability field of nontronite, but very close to that of the aegirine-hematite equilibrium, suggesting that the formation of the nontronite depends on kinetics.The formation of nanoparticular Na-nontronite at the earlier stage of the experiments appears likely due to their specific thermodynamic properties linked to the nanoscale particle size (i.e., high surface energy and high hydration properties). However, Na-nontronites dissolve when they reach a critical size, leading to the formation of the stable assemblage aegirine and hematite.

Comparison of Hydrothermal Method and Ultrasonic Method in Zeolite Synthesis and Investigation of Catalytic Activities of Synthesized Zeolites

In this study, ZSM-5 and beta zeolites, which constitutes the most industrially important artificial zeolite species., were synthesized and the effects of synthesized zeolite in catalytic cracking were investigated. ZSM-5 and beta zeolite were synthesized by varying synthesis time, synthesis method and calcination temperatures. The composition of the synthesis was kept constant and than compared with ultrasonic method and hydrothermal method.ZSM-5 and beta zeolite derivatives were synthesized with changing the synthesis method. Beta zeolite is obtained as a result of the synthesis with low temperature in 20 minutes with using of ultrasonic method. On the other hand, ZSM-5 zeolite is achieved at the end of the synthesis with high temperature in 72 hours with using of hidrotermal method.The X-Ray Powder Diffraction (XRD) patterns and Scanning Electron Microscopy (SEM) images of ZSM-5 zeolites showed that the crystal structure and phase purity of ZSM-5 increased with increase in synthesis time and not affected by the calcination temperature. Otherwise, the crystal structure and phase purity of beta zeolite increased with increase in calcination temperature.To determine the catalytic performances of the products, the catalytic cracking processes were performed. First of all, thermal cracking was realized without catalyst for comparison with the others. Then, catalytic cracking was carried out with CaO, Al2O3, SiO2, natural zeolite, ZSM-5 and beta zeolite.Compairing the results, the catalytic efficiency of the synthesized products were higher than the others. Yield of over 70 % was obtained with synthesized ZSM-5 and zeolite beta.

Facile synthesis of sweet corn like Sm2O3 and their catalytic performance for 2-azidoalcohol synthesis

In this work, we report a systematic studies of synthesis, crystal growth mechanism of Sm2O3 sweet corns and their applications as a catalyst. The results of field emission scanning electron microscopy that the morphology of Sm2O3 composed with sweet corn like structure (pH=9) in borosil glass bottle to sweet corn like particles synthesized in hydrothermal conditions (pH=12). Further, the morphology and crystallinity were also studied by the transmission electron microscopy and high-resolution transmission electron microscopy, and it’s clearly consistent with the field emission scanning electron microscopy observations. X-ray diffraction patterns point out the existence of pure cubic phase in Sm2O3 sweet corn and no other impurity was found. The X-ray diffraction study indicates the presence of Sm2O3 phases. The Brunauer- Emmett-Teller surface area increased and reach around 14.1m2/g when an increase in synthesis time from 8h to 12h while further increase in synthesis time had a negative effect on the surface area. Furthermore, 0.67mmolg−1 the total numbers of acid sites per gram of Sm2O3 sweet corn was determined by simple titration with an n-butylamine solution in the presence of an indicator. To test the potential applications of Sm2O3 sweet corn, they are used as catalysts for epoxide opening reactions. We hope this simple and cost effective approach can extend in the development of novel morphologies for possible applications.

Time and temperature mediated evolution of CDHA from ACP nanoparticles in deep eutectic solvents: Kinetic and thermodynamic considerations

Calcium phosphate (CP) nanoparticles were synthesized in choline chloride-urea deep eutectic solvent (DES). The effect of synthesis time and temperature on crystallinity, particulate properties, and elemental/chemical purity of the CP nanoparticles were investigated by X-ray diffraction, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, and Fourier transform infra-red spectroscopy. The results confirmed the formation of amorphous calcium phosphate (ACP) nanoparticles (at 25°C for 10min) with spherical morphology, mean diameter of 29nm, and high elemental-structural purity. The increase of synthesis time from 10min to 48h at 25°C had no significant influence on the phase transformation of ACP nanoparticle so that the nanoparticles showed high degree of amorphization after 48h. The crystallization of particles rapidly rose upon increase of the synthesis temperature so that the nanoparticles of calcium-deficient hydroxyapatite (CDHA) with percent crystallinity of ~97% were obtained in choline chloride-urea DES at 150°C after 24h. Kinetic and thermodynamic studies revealed that upon increase of temperature from 25 to 150°C, the rate constant and Gibbs free energy for growth of CP crystals in the DES rises from 8.70×10−4 to 1.37×10−3min−1 and 3.22×10+2 to 4.57×10+2KJ·mol−1, respectively.

Effect of reaction time on structural, morphology and optical properties of ZnO nanoflakes prepared by chemical bath deposition method

ZnO nanoflakes have been successfully synthesized by the chemical bath deposition (CBD) method for different reaction times. X-ray diffraction (XRD) results confirm the initial formation of the cubic ZnO structure. However, increasing the reaction time resulted into the emergence of the well-known hexagonal wurtzite structure of ZnO. Scanning electron microscopy images showed the presence of agglomerated nanoflakes. The morphology was found not to depend on synthesis time. UV–vis spectra showed a partially increase in the percentage reflectance and the absorption edges red shifted to the higher wavelength with an increase in synthesis time. The highest band gap energy was obtained for ZnO synthesized for 1min, with its estimated band gap energy of 3.91±0.08eV. The estimated band gap decreased with an increase in the reaction time. The photoluminescent intensity of the emission peak at 473nm decreased with an increase in reaction time.

Organic template-free synthesis of ZSM-5 zeolite particles using rice husk ash as silica source

ZSM-5 zeolite particles were synthesized through in-situ extraction of silica from rice husk ash in the absence of organic template by a simple hydrothermal condition at 150°C/72–96h. The powders were characterized by XRD, TGA, DTA, FTIR, N2 physisorption studies, and field emission scanning electron microscopy (FESEM). Crystallization of ZSM-5 started at 150°C/72h. The vibration bands at around 540 and 1220cm−1 indicated the presence of characteristic double 5-ring of ZSM-5. The BET surface area and pore volume increased with increase in synthesis time from 72 to 96h at 150°C. FESEM images showed coffin-shaped morphology of ZSM-5 particles.

Synthesis of hydrophobic zeolite X@SiO2 core–shell composites

Core–shell structures of zeolite X coated with silicalite as well as mesoporous (MCM-41) have been synthesized. Furthermore, the surfaces of the silicalite and mesoporous silica shells were silylated using organosilanes. The materials were characterized by X-ray diffraction, nitrogen adsorption/desorption, scanning and transmission electron microscopy. The results show that the properties of zeolite 13X@silicalite and zeolite 13X@mesoporous silica core–shells composite structures are well maintained even after the modification. As expected, the shell thickness increased with increase in synthesis time, however, the micropore volume decreased. Silylation with smaller organosilanes (trimethyl chlorosilane) resulted in decrease in surface area as they diffused through the pores; however, bulkier silane reacted with surface hydroxyl groups and maintained the pore structure. Contact angle measurements revealed that hydrophobicity of zeolite 13X was enhanced by the microporous and mesoporous shell coating and was further improved by silylation.

전기영동법을 이용한 고체산화물 연료전지용 Ce0.8Sm0.2OS전해질 박막 제조

본 연구에서는 나노 크기의 세리아를 사마리움으로 일부 도핑(samaria-doped ceria(SDC))한 분말을 urea를 첨가제로 사용하여 수열합성법으로 합성하였으며 그 특성들을 XRD, FESEM, TEM 등을 통해 관찰하였다. 합성 시간 및 합성온도가 증가함에 따라 분말의 결정성 및 입도가 증가함을 확인하였다. 또한 이온전도도의 측정을 통해 합성된 SDC 파우더가 중 저온(600~<TEX>$800^{\circ}C$</TEX>) 부근에서 0.1 S/cm의 이온전도도를 보여 중 저온형 고체산화물 연료전지(IT-SOFC)의 고체 전해질에 적합함을 확인할 수 있었다. 합성된 SDC 분말은 중·저온 고체산화물 연료전지의 음극지지형 전해질로 사용하기 위해 전기영동 증착 방법을 이용하여 다공성 NiO-SDC 기판 위에 SDC 박막 증착을 시도하였다. 증착 용액은 acetone을 용매로 사용하고, 20V의 인가전압으로 10초간 증착한 결과 얇고 치밀하며 기공이 없는 SDC 박막이 형성되었음을 FESEM 분석을 통해 확인할 수 있었다. In this work, a nano-sized samaria-doped ceria(SDC) was prepared by a urea-based hydrothermal method and characterized by XRD, FESEM and TEM. It was observed that the increase in synthesis time and temperature gave rise to crystallity and particles size. Moreover, the synthesised powders had a excellent ion-conductivity(0.1 S/cm at 600~<TEX>$800^{\circ}C$</TEX>) which is suitable for electrolyte of intermediate temperature-solid oxide fuel cell(IT-SOFC). Subsequently for use as electrolyte for anode-supported IT-SOFC, we tried to deposit the SDC powder on a porous NiO-SDC substrate by electrophoretic deposition(EPD) method. From the FESEM observation, a compact

Effect of synthesis time and mode of stirring on physico-chemical and catalytic properties of ZSM-5 zeolite catalysts

The H-ZSM-5 zeolite catalysts were synthesized by varying the synthesis time and mode of stirring. The catalysts were characterized using X-ray powder diffraction, scanning electron microscope, X-ray fluorescency, nitrogen adsorption and FTIR of adsorbed pyridine. It was found that the synthesis time and mode of stirring influenced the morphology, phase purity, surface area, acidic and catalytic properties of H-ZSM-5. The XRD patterns of Na-ZSM-5 zeolite synthesized in 3 and 6 h exhibited the presence of amorphous phase. The crystal size of ZSM-5 increased with increase in synthesis time. The FTIR spectra of adsorbed pyridine on H-ZSM-5 catalysts synthesized in 72, 24 and 12 h showed the presence of Brønsted and Lewis acid sites. The H-ZSM-5 catalyst synthesized in 72 h exhibited highest number of Brønsted acid sites. The reaction of n-butane to iso-butane was used as a test reaction to investigate the catalytic property of the synthesized H-ZSM-5 catalysts. The effect of time on stream, temperature and weight hour space velocity (WHSV) on the conversion of n-butane and yield of iso-butane over the H-ZSM-5 catalysts were studied. The H-ZSM-5 catalyst synthesized in 72 h in the static mode showed the highest conversion of n-butane and yield of iso-butane.