Synthesis Of Hydrotalcite Research Articles

Synthesis of hydrotalcite and titanium dioxide (HT-TiO2) composite for application in heterogeneous photocatalytics processes

The objective of the study was to synthesize a composite of hydrotalcite and titanium dioxide (HT-TiO2) for application in heterogeneous photocatalytic processes to the degradation of organic pollutants in aqueous media. The composites were characterized by X-ray diffraction and surface area, then an experimental design was carried out to evaluate the influence of pH and temperature on the adsorption capacity of pollutants against the anionic dye indigo carmine using a kinetic study. Photocatalytic tests were carried out in a chamber equipped with a UV lamp and hydrogen peroxide as an auxiliary oxidant in degradation. The adsorption results corroborated with the order of surface areas obtained, where the adsorption capacity followed the order of HT, HT-TiO2 5 %, HT-TiO2 10 %, and TiO2, respectively, obtaining removals up to 96.94 %. For the heterogeneous photocatalytic tests, the best conditions of the experimental design were used for each semiconductor, with a removal of up to 99.96 % being observed in 2 h. The use of hydrogen peroxide as an auxiliary oxidant reduced the reaction time to 45 min, demonstrating how joint effluent treatment techniques can increase the speed and efficiency of the process.

Revisiting hydrotalcite synthesis: Efficient combined mechanochemical/coprecipitation synthesis to design advanced tunable basic catalysts

Abstract Hydrotalcite materials (HTs) were synthesized by a facile and swift combined mechanochemistry/coprecipitation approach, and their catalytic activity was evaluated and compared with conventionally synthesized hydrotalcites (co-precipitation method) in the Knoevenagel condensation between furfural and ethyl cyanoacetate/malononitrile. Characterization and catalytic activity results clearly demonstrate that the proposed combined mechanochemical/coprecipitation approach provides an improvement in crystallinity, morphology, tunable basicity, and textural properties (higher surface area and enhanced surface properties) as compared to HTs obtained via conventional coprecipitation methods. In addition, mechanochemically synthesized HTs largely improve catalytic activities, including conversion and product selectivity to Knoevenagel condensation products under solventless conditions, short reaction times, or reaction at room temperature as compared to conventional counterparts (e.g., 30–40 vs > 99% product yields).

Optimizing Green Synthesis of Hydrotalcite - Silver Nanoparticles using Syzygium Nervosum based Reducing Agent.

Hydrotalcite-silver (HT-Ag) nanoparticles have been involved in various daily crucial applications, such as antibacterial, photocatalytic, adsorption, etc. There are many approaches to synthesizing silver nanoparticles (AgNPs) decorated on hydrotalcite (HT) surface and the most used approach is using a strong reducing agent. Thus, affordable but effective "green" reducing agents - Syzygium nervosum leaf extract, are taken into account in this work to solve several issues related to chemical reducing agents. This work aimed to assess the effect of Syzygium nervosum leaf extract as a reducing agent for green synthesis of AgNPs on HT through an optimizing process using response surface methodology (RSM) and the Box-Benken model. The optimal conditions for the synthesis of AgNPs on HT include a reaction time of 6.15 hours, a reaction temperature of 50 °C, and the ratio of diluted Syzygium nervosum leaf extract to reduce AgNO3 of 50.37 mL/mg. Under the optimal conditions, the yield of the reduction reaction reached 77.54 %, close to the theoretical value of 76.97 %. The optimization model was suitable for the experiment data. Besides, the morphology, density, and characteristics of AgNPs on the surface of HT layers have been determined by using Ultraviolet-visible spectroscopy, Field emission scanning electron microscopy (FESEM), High-resolution transmission electron microscopy (HR-TEM), selected area diffraction, X-ray diffraction, Dynamic light scattering (DLS), Infrared (IR) spectroscopy, Fluorescence emission spectroscopy (FE), Brunauer-Emmett-Teller (BET) methods. The spherical AgNPs were synthesized successfully on the surface of HT with the average particle size of 13.0±1.1 nm. Interestingly, HT-Ag hybrid materials can inhibit strongly the growth of E. coli, S. aureus as well as two antibiotic resistance bacterial strains, P. stutzeri B27, and antibiotic resistance E. coli. Especially, the antibacterial activity quantification and durability of the HT-Ag hybrid materials were also tested. Overall, the HT-Ag hybrid materials are very promising for application in material science and biomedicine fields.

The Effect of Molar Ratio and Precipitation Time of Mg/Al Hydrotalcite Synthesis on the Isomerization of Glucose into Fructose

The substitution of Mg/Al hydrotalcite catalyst over the glucose-isomerase is expected to decrease the space-time and reduce the energy consumption of glucose isomerization into fructose. The quality of the Mg/Al hydrotalcite catalyst is determined during the synthesis process. The synthesis has been carried out in the various Mg/Al molar ratio and precipitation times and observed the catalytic activity in the isomerization. Response Surface Methodology (RSM) is used to analyze statistically the optimum condition of the synthesis process. The Mg/Al molar ratio was 1:1 to 4:1 with a precipitation time of 720-1080 min. The characterization of the Mg/Al hydrotalcite catalyst includes the functional groups of the constituent compounds by FTIR, the crystallinity and particle size by (XRD), and the surface area of the catalyst by BET. The RSM results show the optimum condition of the Mg/Al molar ratio and precipitation time to produce the highest mass catalyst product of Mg/Al hydrotalcite catalyst (3,38 g) is 3.34:1 and 984.85 min. The highest degree of crystallinity obtained is 28.70% with the particle size is 10.19 Å. The highest yield and selectivity of the isomerization process are 56.95% and 91.89%, respectively. By the RSM analytical method, the Mg/Al molar ratio and the precipitation time used in this catalyst synthesis do not give a significant effect on the catalytic activity of the isomerization.

Environmentally benign synthesis of hydrotalcite-like materials for enhanced efficiency of aldol condensation reactions

MgAl hydrotalcites (HTCs) are promising catalysts for biomass valorization applications. However, their production suffers from excessive wastewater generation while their application is limited by insufficient accessibility of active sites. Here, we change the paradigm of hydrotalcite synthesis by replacing the traditional co-precipitation by MgO impregnation with aluminum isopropoxide followed by calcination and (re)hydration. This synthesis affords surface HTC phase ensuring excellent accessibility to Brønsted basic sites. HTC supported on MgO surface (bulk Mg/Al = 20) exhibited same conversion and selectivity in aldol condensation of furfural with acetone as conventional HTC (Mg/Al = 3). Besides maximized efficiency of aluminum use to generate accessible Brønsted basic sites, the catalyst was stable in several consecutive catalytic experiments, if optimal rehydration conditions were applied. Moreover, the use of large quantities of water required for the co-precipitation-based method was avoided. This makes the new method superior also from green synthesis and sustainability point of view.

Synthesis of Hydrotalcite from Phosphate Tailings and Its Effect on the Anti-Ultraviolet Aging Properties of Asphalt Binder

Synthesis of Hydrotalcite from Phosphate Tailings and Its Effect on the Anti-Ultraviolet Aging Properties of Asphalt Binder

CO Methanation over NiO-CeO2 Mixed-Oxide Catalysts Prepared by a Modified Co-Precipitation Method: Effect of the Preparation pH on the Catalytic Performance.

In this study, a series of NiO-CeO2 mixed-oxide catalysts have been prepared by a modified co-precipitation method similar to the one used for the synthesis of hydrotalcites. The syntheses were carried out at different pH values (8, 9 and 10), in order to determine the influence of this synthetic variable on the properties of the obtained materials. These materials were characterized by using different techniques, such as TGA, XRD, ICP, N2 adsorption-desorption isotherms, H2 temperature-programmed reduction (H2-TPR), and electron microscopy, including high-angle annular dark-field transmission electron microscopy (HAADF-TEM) and EDS. The characterization results revealed the influence of the preparation method, in general, and of the pH value, in particular, on the textural properties of the oxides, as well as on the dispersion of the Ni species. The catalyst prepared at a higher pH value (pH = 10) was the one that exhibited better behavior in the CO methanation reaction (almost 100% CO conversion at 235 °C), which is attributed to the achievement, under these synthetic conditions, of a combination of properties (metal dispersion, specific surface area, porosity) more suitable for the reaction.

Optimization of Microwave Process Parameters in Preparation of Ni-Fe Hydrotalcite by Response Surface Methodology and Evaluation of Photocatalytic Degradation of Antibiotic Wastewater

Using the response surface method (RSM), the temperature, time and nickel-iron ratio of the synthesis of NiFe-LDH photocatalyst were used as influencing factors, the removal rate of norfloxacin (NOR) was the response factor, the Sub-mathematical equation was structured. The optimized model predicts that the optimal synthesis temperature, time and nickel-iron ratio are: 127.1 °C, 36 min, 2.854:1, and the removal rate of NOR is 88.25%. The actual removal rate of NOR over NiFe-LDH prepared under the conditions was 89.14%, indicating that the model was successfully established. It provides a reference for the synthesis of hydrotalcite by microwave method.

The effectiveness of precipitation pH and temperature of Mg/Al Hydrotalcite synthesis on the glucose isomerization

Mg/Al Hydrotalcite as the catalyst in isomerization of glucose into fructose was made by coprecipitation of Mg(NO3)2.6H2O and Al(NO3)3.9H2O. Operating condition of precipitation including the temperature and pH was determined by Response Surface Method (RSM). The catalyst synthesis was carried out in the mole ratio of Mg/Al 3:1 for 18 h and the catalyst was activated by calcination for 3 h at 500°C. Catalyst characterization was done by FTIR, BET, and XRD. The highest mass product of Hydrotalcite Mg/Al 4.52 g, reached at the precipitation conditions of pH 9 and temperature of 45ºC. The catalytic activity of hydrotalcite Mg/Al was tested by the isomerization of Glucose into Fructose. The highest yield and selectivity were 20.14%, 62.40%, respectively. It was reached in pH 9 and 45ºC. While the highest conversion, 53.47%, was achieved in the pH 11.12 with a precipitation temperature of 45ºC. By the RSM analysis, neither the mass of catalyst product nor the catalytic activity from the isomerization (yield, conversion, and selectivity) were affected significantly by the pH and temperature precipitation.

The influence of various anions in Mg-Al mixed oxides on presence of sodium ions in transesterification of oil

The paper is focused on the influence of sodium ions in Mg-Al mixed oxides as heterogenous catalyst in the transesterification of non-edible Camelina sativa oil. The Mg-Al mixed oxides with a constant molar ratio Mg:Al (2:1) were synthesized from hydrotalcites by thermal treatment (450 °C, 3 h) and rehydrated. The novelty lays in the synthesis of the hydrotalcites with various types of anions (SO4−2, Cl−, CH3COO−, HCO3−, C2O4−2), which influence the sodium amount in materials and so its properties. The results of various characterisation methods such as ICP-OES, XRD, TPD, N2-physisorption, FTIR were statistically evaluated, including transesterification results. The sodium was bonded predominantly in the form of sodium nitrates (nitrates were used for hydrotalcite synthesis) for all types of anions and the rehydration (i) rapidly decreased the sodium content and (ii) caused more similarity of mixed oxides with each other regardless of anion type. The sodium influenced especially acid-base properties and so the ester yield, because the sodium nitrates blocked the pores and also disturbed the TPD determination, which is also a novelty. The explanation of the influence of sodium ions enables to synthesize more stable catalyst, whose use will be environmentally beneficial.

Effect of the particle size on the reactivity of MgO-Al2O3 hydrating mixtures: A long-term kinetic investigation of hydrotalcite synthesis

Hydrotalcite-like compounds (HTlc) are commonly known anionic clay that may potentially be used as hydraulic binder component for refractory materials, ion exchangers, catalyst or carrier of bioactive molecules. According to current state of knowledge LDH (Layered Double Hydroxides) can be synthesized using various methods including mechanochemical synthesis, hydrothermal precipitation, sol–gel syntheses and coprecipitation method. Research on the synthesis of hydrotalcite in the mixture of oxide powders of Al2O3 and MgO cured under specific conditions is particularly important in case of the determination of the relationship between the type (susceptibility to hydration, grain size and specific surface area) of initial powders and reaction kinetics. As a result, the hydration of an equimolar mixture of magnesium and alumina oxides nano- or micro-powders has been proven to be an effective low temperature method of synthesis well crystallized MgAl LDH with highly ordered structures. This investigations clearly show that the kinetics of hydration is influenced only by properties of aluminium oxide as initial powder. The synthesis of Mg6Al2CO3(OH)16∙4H2O as a result of hydration is associated with composite matrix formation which firstly consist of partly reacted initial powders bonded by hydration products. The synthesis of Mg6Al2CO3(OH)16∙4H2O was discussed in terms of molar Gibbs free energy change of reactions within the MgO-Al2O3-CO2-H2O system. The calculated formation Gibbs energy was negative, when Mg(OH)2 was formed as an intermediate product. The standard Gibbs free energies of hydrotalcite formation was estimated based on the simple mechanical mixture model that treats Mg6Al2CO3(OH)16∙4H2O as mixtures of simple oxides. Thermodynamic calculations were performed assuming an equilibrium state between aqueous solutions and corresponding precipitates after synthesis.

Synthesis of Hydrotalcites from Waste Steel Slag with [Bmim]OH Intercalated for the Transesterification of Glycerol Carbonate.

Ca-Mg-Al hydrotalcites were prepared by coprecipitation from Type S95 steel slag of Shanghai Baosteel Group as supports of ionic liquid in this paper. Five basic ionic liquids [Bmim][CH3COO], [Bmim][HCOO], [Bmim]OH, [Bmim]Br and ChOH were prepared and their catalytic performance on the synthesis of glycerol carbonate by transesterification between dimethyl carbonate and glycerol was investigated. The characterization results indicated that [Bmim]OH is the best ionic liquid (IL) for the transesterification reaction of glycerol carbonate. The hydrotalcites before and after intercalation by ionic liquid were characterized by XRD, FTIR, SEM, EDS and the IL were characterized by FT-IR, 13C-NMR and basicity determination via the Hammett method. The analysis results implied that the dispersion of [Bmim]OH in hydrotalcites reduced the alkali density appropriately and facilitated the generation of glycerol carbonate. The yield of glycerol carbonate and the conversion rate of glycerol reached 95.0% and 96.1%, respectively, when the molar ratio of dimethyl carbonate and glycerol was 3:1, the catalyst dosage was 3 wt%, the reaction temperature was 75 °C and the reaction time was 120 min. The layered structure of hydrotalcites increased the stability of ionic liquid intercalated in carriers, thus the glycerol conversion and the GC yield still remained 91.9% and 90.5% in the fifth reaction cycle.

Sequential hydrotalcite precipitation and biological sulfate reduction for acid mine drainage treatment

Hydrotalcite precipitation is a promising technology for the on-site treatment of acid mine drainage (AMD). This technology is underpinned by the synthesis of hydrotalcite that can effectively remove various contaminants. However, hydrotalcite precipitation has only limited capacity to facilitate sulfate removal from AMD. Therefore, the feasibility of coupling biological sulfate reduction with the hydrotalcite precipitation to maximize sulfate removal was evaluated in this study. AMD emanating from a gold mine (pH 4.3, sulfate 2000 mg L−1, with various metals including Al, Cd, Co, Cu, Fe, Mn, Ni, Zn) was first treated using the hydrotalcite precipitation. Subsequently, biological treatment of the post-hydrotalcite precipitation effluent was conducted in an ethanol-fed fluidized bed reactor (FBR) at a hydraulic retention time (HRT) of 0.8–1.6 day. The hydrotalcite precipitation readily neutralized the acidity of AMD and removed 10% of sulfate and over 99% of Al, Cd, Co, Cu, Fe, Mn, Ni, Zn. The overall sulfate removal increased to 73% with subsequent FBR treatment. Based on 454 pyrosequencing of 16S rRNA genes, the identified genera of sulfate-reducing bacteria (SRB) included Desulfovibrio, Desulfomicrobium and Desulfococcus. This study showed that sulfate-rich AMD can be effectively treated by integrating hydrotalcite precipitation and a biological sulfate reducing FBR.

Microwave-modified hydrotalcites for the transesterification of soybean oil

The effects of hydrothermal treatment (traditional and microwave-assisted) in the catalytic activity of hydrotalcite were studied in the soybean oil methanolysis for a biofuel production. The catalysts were produced by coprecipitation (pH ≥ 10) and then characterized by x-ray diffraction, infrared spectroscopy, scanning electron microscopy, surface chemical composition, N2 physisorption at 77 K and surface basicity. Reactions were carried out at 180 °C for 60, 120 and 180 min, molar ratio methanol:soybean oil of 12:1 and 5 wt% of the catalyst. The microwave treatment reduced the aluminum content of catalyst lamellae and increased the surface basicity. The best yield of methyl esters was 95.6% for the catalyst treated by microwave at 110 °C for 300 min. The high yield of methyl esters shows that the use of microwaves in the synthesis of hydrotalcite can reduce the preparation time and increase the industrial competitiveness of this material as a catalyst in the biofuels industry.

SYNTHESIS OF HYDROTALCITE POWDER AND BEAD TO REMOVE ARSENATE

The affecting factors on the synthesis of hydrotalcite (HT) powder and bead for effective arsenate removal were investigated. HTs with a ratio of Mg:Al = 2:1 (MA) were synthesized by the co-precipitation method at 70 oC with reaction times of 1 and 120 - 300 min. The synthesis of MA with a reaction time of 1 min was done under high supersaturation condition, the others under low supersaturation conditions. The characteristics of MA were examined by X-ray diffraction (XRD), scanning electron microscopy, and nitrogen adsorption/desorption isotherms. According to the XRD patterns, pure HT was obtained for all tested conditions. With increasing reaction time from 1 to 300 min, the crystal size of MA increased from 4.9 to 11.3 μm, the surface area of MA increased from 9.3 to 71.4 m2/g. Batch-mode experiments showed that 1-min reaction time MA had the highest As(V) removal capacity. MA beads were separately synthesized using alginate and poly acrylamide (PAM) as binding agents. For alginate/MA, heat drying (110 oC) and freeze drying were applied to test the effect of these drying methods on the beads. The results showed that As(V) adsorption capacity of PAM/MA was the highest, closely followed by freeze drying/alginate/MA, much higher than that of heat drying/alginate/MA bead.

Ruthenium-hydrotalcite (Ru-HT) as an effective heterogeneous catalyst for the selective hydrogenation of CO2 to formic acid

The reaction containing CO2 and H2 has been investigated for the hydrogenation of CO2 to formic acid using ruthenium hydrotalcite (Ru-HT) catalyst. Ruthenium salt was introduced to the synthesis of hydrotalcite as an active metal center to develop ruthenium based heterogeneous catalyst. Hydrotalcite not only acted as a support for the active metal but also acted as a soft solid base avoiding the use of the liquid base, which is normally required under homogeneous conditions for the formation of formic acid from the hydrogenation of CO2. Reaction temperatures were in the range of 40–100 °C, total pressure 10–100 bar with an ideal 1:1 ratio of pCO2:pH2. The maximum Turnover Number (TON) of 11389 was obtained for the formic acid formation under the optimized conditions at 60 °C temperature and 60 bar total pressure, using a mixture of methanol:water as a solvent (5:1, v/v). Ru-HT catalyst was synthesised and thorougly characterized by FT-IR, PXRD, SEM-EDX and surface area analysis. The catalyst was effectively recycled up to 7 times without any loss in catalytic activity.

A green approach to the synthesis of a nano catalyst and the role of basicity, calcination, catalytic activity and aging in the green synthesis of 2-aryl bezimidazoles, benzothiazoles and benzoxazoles

A green synthesis of hydrotalcite (a double layered catalyst) by a grinding method using Al/Mg molar ratios of 1.0–3.0 at room temperature is described.

Keggin type polyoxometalate H4[αSiW12O40].nH2O as intercalant for hydrotalcite

The synthesis of hydrotalcite and polyoxometalate H4[αSiW12O40].nH2O with the ratio (2:1), (1:1), (1:2) and (1:3) has been done. The product of intercalation was characterized using FT-IR spectrophotometer, XRD, and TG-DTA. Polyoxometalate H4[αSiW12O40].nH2O intercalated layered double hydroxide was optimised to use as adsorbent Congo red dye. Characterization using FT-IR was not showing the optimal insertion process. The result using XRD characterization was showed successful of polyoxometalate H4[αSiW12O40].nH2O inserted layered double hydroxide with a ratio (1:1) which the basal spacing was expanded from 7,8 Ȧ to 9,81 Ȧ. Furthermore, the thermal analysis was performed using TG-DTA. The result show that the decomposition of polyoxometalate H4[αSiW12O40].nH2O intercalatedn hydrotalcite with ratio (1:1) was occured at 80oC to 400oC with a loss of OH in the layer at 150oC to 220oC, and then the decomposition of the compound polyoxometalate H4[αSiW12O40].nH2O at 350oC to 420oC. Keywords: Hydrotalcite, Layered Double Hydroxide, Polyoxometalate, Intercalation

The effect of microwave and hydrothermal treatments on the properties of hydrotalcite

In this work, a comparative study of the application of direct microwave or hydrothermal synthesis for obtaining hydrotalcite from solid initial materials and the effect of these treatments (200 °C, 1–3 h) on the thermal stability of formed compounds were investigated. The molar ratios of primary mixtures Mg/Al were equal to 1 and 2, while the water/solid ratio was maintained to 10.0. It was determined that the microwave treatment was suitable for the direct synthesis of hydrotalcite, although the intensities of diffraction maximums characteristic to this compound were decreased under all experimental conditions. Furthermore, it was examined that, after 3 h of isothermal curing, the highest crystallinity of hydrotalcite was obtained. It should be noted that, in a case of microwave synthesis, the crystallite size of hydrotalcite varied in a 33.89–38.50 nm range, while, in a case of hydrothermal treatment, in a 40.06–52.45 nm region. Moreover, the method used for the synthesis of the latter compound did not influence the formation sequence of compounds during solid sintering (575 and 1000 °C, 1 h). In both cases, at 575 °C temperature, MgO and Al2O3 were formed, while at 1000 °C—magnesium and aluminium spinel-type compounds, which have a similar chemical nature, were obtained. The synthetic and calcined products were characterized by XRD, STA and SEM analyses.

Ultrasound-assisted biodiesel production from waste cooking oil using hydrotalcite prepared by combustion method as catalyst

Ultrasound-assisted biodiesel production from waste cooking oil catalyzed by hydrotalcite (HT) catalyst prepared using combustion method was studied. Two important parameters in the HT synthesis i.e., calcination temperature (550–850°C) and fuel type (saccharose, glucose and fructose) were particularly investigated. The dependence of HT’s characteristics on the synthesis parameters and correlations with their catalytic performance under ultrasound condition were successfully elucidated. The HT catalyst prepared using saccharose and calcined at 650°C was the best catalyst to be used in the transesterification reaction. It showed high biodiesel yield (about 76.45%) in just 60min in the presence of low ultrasound amplitude (∼11kHz). The enhancement effect of ultrasound was successfully demonstrated. The reaction only needed short reaction time (about 1h) to give a biodiesel yield of up to 76.45% compared to conventional stirring method that needed about 5h to achieve the same yield.