Urea Hydrolysis Method Research Articles

Fabrication of hierarchical Zn-Al structures onto cellulose through urea hydrolysis methodology: Design and study of physical properties

The paper concerns the production of a hybrid material based on the precipitation of Zn/Al hierarchical structures onto cellulose surface through urea hydrolysis method. The assessment of the morphological, spectroscopic and sorption properties is carried out. Morphological and spectroscopic analyses proved the deposition of inorganic structures onto cellulose. The improvement of thermal stability of hybrid material was even evaluated by TGA analysis. Besides, band gap energy of 3.71 eV was evaluated through Kubelka-Munk theory. Water sorption isotherms are investigated demonstrating the reduction of sorption coefficient after the surface modification of cellulose (4.60 and 8.23 g/g*1/atm for Cellulose and Zn/Al Cellulose). Oil adsorption tests were finally carried out by using different oils while the potential antioxidant activity (15.3% for Zn/Al Cellulose and 0.15% for Cellulose) was demonstrated by performing DPPH antioxidant assay.

Zirconium copper oxide microflowers based non-enzymatic screen-printed electrochemical sensor for the detection of glucose in saliva, urine, and blood serum.

Zirconium copper oxide microflowers (Zr/CuO MF) based non-enzymatic sensor was developed for glucose detection in saliva, urine, and blood. An easy urea hydrolysis method was employed for the synthesis of the metal oxide and further calcined to improve the catalytic property. The flower-like morphology of the Zr/CuO was confirmed by SEM analysis and the presence of copper and zirconium was examined using energy dispersive X-ray analysis (EDAX). The Zr/CuO MF modified screen-printed electrodes exhibited excellent glucose sensing performance in 0.15M NaOH medium and could quantify glucose in the range from 10µM to 27mM. A high sensitivity of 1.815 ± 0.003mAmM-1cm-2 was obtained for lower glucose concentration from 15µM to 3mM and 1.250 ± 0.006mAmM-1cm-2 for higher concentration glucose from 3 to 27mM. The limit of detection of the fabricated sensor was found to be 0.8µM. The sensor displayed high selectivity and stability towards glucose in different body fluids like saliva, urine, and blood serum at a working potential of 0.6V (vs. Ag/AgCl). In saliva, urine, and serum samples, the sensor exhibited excellent recovery of 95-108, 92-108, and 93-101% in saliva, urine, and serum, respectively, with a relative standard deviation of less than 10%, demonstrating high accuracy and reliability of the sensor. The developed sensor is promising for developing an invasive and non-invasive point-of-care testing device for glucose detection.

Anti-coking Cu-Ni bimetallic catalyst for hydrogen production: Thermodynamic and experimental study of methanol autothermal reforming

Autothermal reforming has emerged as a promising route for hydrogen production from bio-methanol, offering a balance between hydrogen production and the energy demand of the process. To address the low catalytic performance of non-precious metal catalysts, one of the approaches is to introduce a second metal. In this work, a series of Cu-Ni bimetallic catalysts derived from Ca-Al hydrotalcite-like compounds were prepared by the urea hydrolysis method combined with hydrothermal treatment, featuring well-dispersion with a size of 3-5 nm. The electron redistribution triggered by the incorporation of Cu enhances the absorption of methanol at the electron-poor surface, leading to maintained catalytic activity at 450°C for 96 hours with few carbon-deposition observed for methanol autothermal reforming. The boundary conditions of the thermal-neutrality system are analyzed by thermodynamic calculations and similar trends to the simulation results were also obtained from experiments.

Polypropylene (PP) nanocomposites with transition metal (MgCoAl, MgNiAl, MgCuAl, MgZnAl) layered double hydroxides (t-LDHs): Flammability, thermal and mechanical analysis

Over the last few years, transition metal based LDHs are drawing more and more attention. This is especially true for tri-metal LDHs due to their wide range of applications. This research work highlights four types of tri-metal layered double hydroxide (t-LDH) that were synthesized and used in polypropylene (PP) nanocomposites. The effect and interaction of cobalt (Co), nickel (Ni), copper (Cu) and zinc (Zn) containing MgAl LDHs in PP nanocomposite were prepared and tested. These t-LDHs (MgCoAl, MgNiAl, MgCuAl, MgZnAl) were synthesized using the urea hydrolysis method. The t-LDH/PP nanocomposites were prepared using melt mixing in a small-scale compounder. Structural and morphological analysis of t-LDH and their PP nanocomposites were done using XRD spectroscopy and SEM. The thermal behaviour of the nanocomposites was studied using DSC and TGA. Rheological analysis was done using a rheometer, flammability was analysed using limiting oxygen index (LOI) and UL94 testing. Mechanical properties were compared by a UTM and Charpy impact test. The thermal stability, flame retardancy and mechanical strength are increased with the addition of these t-LDHs. MgCuAl/PP nanocomposites showed superior thermal and mechanical properties as compared to MgAl/PP, MgCoAl/PP, MgNiAl/PP, MgZnAl/PP nanocomposites. In comparison to pure PP with the addition of only 5 wt.% of MgCuAl-LDH the degradation temperature was 43 °C higher.

Resistive switching of two-dimensional NiAl-layered double hydroxides and memory logical functions

Two-dimensional NiAl layered double hydroxides (LDHs) were synthesized by urea hydrolysis method. Considering its unique layered structure and high-speed carrier transfer channel, NiAl-LDHs were applied to the active layer of memristor through spin coating process. It is found that the Al/NiAl-LDHs/Al memristor exhibits unipolar resistance switching characteristics, which resistive switching mechanism is attributed to formation and fusing of conductive filaments controlled by oxygen vacancies. Based on this Al/NiAl-LDHs/Al memristor, a D-type latch was constructed. A memtransistor with Si/SiO2/graphene oxide (GO)/Al/NiAl-LDHs/Al structure was built by connecting Al/NiAl-LDHs/Al memristor in series on the drain electrode of GO transistor. The memtransistor exhibits excellent gate controllability and resistive switching characteristics. Combined with its characteristics, we used the memtransistor to build a D-trigger and verify its memory logical function. The result shows the great potential of layered bimetallic hydroxide materials in the field of resistance switching memory and memory computing.

Studies on fabrication of high-performance flexible printed supercapacitor using cobalt hydroxide nanowires

We report the successful fabrication and testing of a printed symmetric flexible supercapacitor based on cobalt hydroxide nanowire-carbon ink composite. The urea hydrolysis method provides a controlled way of cobalt hydroxide nanowire formation. The microscopic studies reveal nanowires with an average diameter of approximately 70 nm. Moreover, the material exhibited a high specific surface area of 13.08 m2g−1 and a pore volume of 0.060 cc g−1. Electrochemical studies with the nanocomposite revealed a very high areal capacitance. The cobalt hydroxide nanowire was used for fabricating a printed supercapacitor prototype using PVA/KOH gel as the electrolyte. It exhibited a high areal capacitance of 6.27 mF cm−2 with 0.7101 μWh cm−2 areal energy density and 32.7 μW cm−2 areal power density. Excellent capacitance retention was observed even after 8500 charge-discharge cycles. Series combination of printed capacitors yields summation of individual potentials, and its application was demonstrated using different LEDs and electronic devices. Furthermore, excellent capacitance retention at various bending angles and the performance remains the same even after 1500 bending cycles show high mechanical stability. Hence, it finds potential applications in flexible and wearable electronics.

Silver-manganese nanocomposite modified screen-printed carbon electrode in the fabrication of an electrochemical, disposable biosensor strip for cystic fibrosis.

A silver-manganese nanocomposite was successfully prepared by the urea hydrolysis method and used to detect chloride ions in sweat electrochemically. The synthesis involves the reaction of manganese sulphate, silver nitrate, and urea at 100°C for 24h. The crystalline nature of the particle was studied by diffraction analysis and found to be mixed-phase oxides of manganese alongside the oxides of silver. Morphological studies revealed the presence of quasi-prism-like structures, which is characteristic of β-MnO2. A disposable sensor was fabricated by screen-printing the catalyst and used for the electrochemical detection of chloride ions in sweat. The sensor exhibited good selectivity, a sensitivity of 22.93 ± 0.64µAmM-1cm-2 in solution and 3010 ± 60µA(log mM) -1cm-2for the fabricated sensor strip with a detection range from 5mM up to 200mM. The detection limit is 207 ± 7µM (S/N = 3) in solution and 17 ± 6µM for the fabricated sensor strip. The relative standard deviation (RSD) of sensor response is 2.38%. A prototype of the biosensor strip was fabricated and validated using real samples. This brings the possibility of developing a real-time biosensor strip for cystic fibrosis in point-of-care testing applications.

Effect of the annealing temperature of multi-elemental oxides (FeCoNiCuZn)yOx on the electrocatalytic hydrogenation of nitrobenzene at room temperature

Nitrobenzene (NB) in effluent waters is a serious and complicated environmental problem due to its environmental toxicity and health hazard. In this study, the selective electrocatalytic hydrogenation of NB to aniline (AN) was studied using multi-elemental oxides (Fe0.3Co0.05Ni0.05Cu0.3Zn0.2)O, synthesized via urea hydrolysis method and heat-treated at different temperatures (300–1000 °C). The synthetic route chosen allowed the obtention of multi-phase materials and high entropy oxide (HEO) conditions, to be used as electrocatalysts, and to evaluate the effect of the crystal structure on the catalytic performance. The catalysts were characterized using physical methods scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and X-ray diffraction. The electrochemical properties were evaluated using cyclic voltammetry, linear sweep voltammetry, electrochemical impedance spectroscopy, and chronoamperometry. The polycrystalline structure obtained at 500 °C (HEO500) showed the highest selectivity (above 45%), while the more crystalline catalyst (HEO800) exhibited the highest conversion (30%) and kinetic constant (k = 9.4 × 10−3 s−1). The catalytic performance of the materials demonstrated a strong correlation with the microstructure and surface properties, like crystallite size, initial crystal phase, oxygen vacancies concentration, and redox properties. All the HEO materials exhibited a better catalytic performance than the commercial benchmark, Pt/C 5% wt catalyst, which showed no selectivity towards aniline and low conversion in 1.0 M KOH solution at -1.4 V vs Ag/AgCl. This improvement was attributed to the increase in the surface concentration of hydrogen found on the HEOs. These results highlight the importance of the surface defects on the activity and selectivity of multi-step surface-dependent catalytic hydrogenation reactions; and provide fundamental information on the importance of carefully choosing the synthesis and calcination conditions.

Noticeable improvement in adsorption capacity of glycine-modified MgAl-LDH in the removal of Methyl Orange dye compared to urea standard method

ABSTRACT In this paper, a simple chemical method in the presence of glycine is described to fabricate the hierarchical structure of MgAl-based Layered Double Hydroxides (Gly-LDH), served as high-performance adsorbent for Methyl orange (MO) . To elucidate the effect of glycine on the adsorption capacity, the MgAl-LDH intercalated with CO3 2- anions was also prepared by urea hydrolysis method (Ur-LDH). The as-synthesised nanostructures were characterised by X-ray diffraction (XRD), Thermogravimetry/Differential Scanning Calorimetry (TG–DSC), Fourier transform infrared spectroscopy (FTIR), and Scanning Electron Microscopy (SEM), . The results demonstrated that the glycine intercalated LDH exhibited high adsorption capacity for MO dye compared with MgAl-LDH obtained by urea hydrolysis method. Adsorption isotherm data for MO adsorption on Gly-LDH at 300 K and acidic pH fitted well to the Langmuir isotherm model with a maximum adsorption capacity of 800 mg/g. l. The sorption mechanism indicates that MO molecules could be sorbed onto Gly-LDH via electrostatic attraction, and ion exchange.

Synthesis of ZrO2/MgAl-LDH composites and evaluation of its isotherm, kinetics and thermodynamic properties in the adsorption of congo red dye

Recently, the treatment of waste water by Zr-based adsorbents had significantly attracted wide interest among researchers owing to its distinct features. The unique properties of Zr such as thermal stability, large size, high positive charge, greater mechanical rigidity and acid-base nature are mainly responsible for its diverse application. In this work, designing of the new adsorbent material containing tetravalent Zr metal oxide layered double hydroxide (LDH) composite for the removal of anionic dye was studied. The modification of LDH was conducted via the urea hydrolysis method by using zirconium salts as a precursor material. The adsorption efficiency of the as-synthesized material represented as ZrO2/MgAl-LDH was investigated for the decontamination of congo red (CR) dye from an aqueous medium. The adsorbent ZrO2/MgAl-LDH composite was characterized by several instrumental techniques including powder X-ray diffraction (P-XRD), Brunauer-Emmett-Teller (BET), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy(FT-Ir), scanning emission microscopy(SEM), energy dispersive X-ray(EDX), transmission emission microscopy(TEM) and thermogravimetric analysis(TGA). The influence of several experimental factors on the adsorption equilibrium studies such as pH, temperature, initial dye concentration, contact time, adsorbent dosages, and interfering ions are examined under optimized conditions. The thermodynamic study manifests the spontaneous and endothermic nature of the sorption process. Additionally, based on fitting the experimental data with different models the isotherm and kinetics mechanism are found to be more appropriate with Langmuir isotherm, Redlich-Peterson isotherm, and pseudo-second-order kinetics. The spectral analysis further indicates the oxidizing nature of the material, therefore favoring the adsorption of anionic dye. The maximum dye removal efficiency of ZrO2/MgAl-LDH reached up to 97.19% under the optimum reaction condition (initial dye concentration = 50 mg/L, contact dosages = 0.02 g, temperature = 303 K). In addition, the maximum monolayer adsorption capacity (qmax= 169.42 mg) for CR adsorption also reveals its superiority in adsorption test. Moreover, the adsorbent can be easily retrieved and reused up to fifth cycle. Therefore, the characterization and experimental results of ZrO2/MgAl-LDH affirms its potential application for effective decontamination of waste water.

Impact of Synthesis Method and Metal Salt Precursors on the CO2 Adsorption Performance of Layered Double Hydroxides Derived Mixed Metal Oxides

Since the 1990s, Mg-Al layered double hydroxide- (LDH-) based mixed metal oxides (MMOs) have emerged as promising CO2capture sorbents. Despite the numerous attempts to improve these materials, the impact of the synthesis method and employed metal salt precursors on the properties of LDHs and MMOs remains unknown. In order to address this gap, the present study investigated how two common synthesis methods (i.e., co-precipitation and urea hydrolysis) and two different salt precursors (i.e., metal chlorides and metal nitrates) affected the physical properties of LDHs and CO2capture performance of derived MMOs at intermediate temperature (200°C). The true chemical composition of the LDH phase was confirmed by the lattice parameter “a”, which reveals the Mg/Al ratios at the octahedral layers. The impact of synthesis methods and metal salt precursors was evaluated in terms of synthesis efficiency metrics (e.g., synthesis yield, purity, and percentage of unreacted reactants), and their relationship was studied with the CO2adsorption behavior of MMOs in different aspects (e.g., adsorption capacities, kinetics, and cyclic stability). Pure MgO was used as a reference to assess the cyclic stability of MMOs sorbents. It was found that the LDHs synthesized by the co-precipitation method are superior in terms of high synthesis yields (∼100%), good LDH purity, high adsorption capacities, and kinetics. In contrast, the LDHs synthesized with the urea hydrolysis method are better in terms of cyclic stability but tend to have low synthesis yields (54%–81%) and LDH purity (containing many amorphous impurities of Al-based hydroxides).

In situ one‐step fabrication of layered double hydroxide deposited on cellulose: Effect of modified cellulose on physical properties of polyurethane composites

AbstractThe article reports the fabrication of cellulose‐layered double hydroxide (LDH) obtained by urea hydrolysis method. A wide characterization was carried out to assess the morphological, spectroscopic and barrier properties of LDH modified cellulose. The cellulose‐LDH was then used as hybrid reinforcement in polyurethane (PU) composites. A slight improvement in thermal stability of PU was achieved and a better hydrophilicity was obtained, due to the intrinsic polarity of LDH. Elastic modulus of PU composites increased up to 48 MPa for a filler loading of 10% wt. Finally, UV barrier properties were studied in the range 280–700 nm. The produced composite showed a noticeable decrease in light transmission as the reinforcement content increase, displaying high light‐blocking properties with a quasi‐total resistance to transmission in UV range.

Fabrication of Hydrotalcite-like Copper Hydroxyl Salts as a Photocatalyst and Adsorbent for Hexavalent Chromium Removal

Cu-HyS-urea and Cu-HyS-NaOH, which are hydrotalcite-like copper hydroxyl salts, were prepared by two different methods, urea hydrolysis and precipitation, respectively. Both synthesis methods provided the successful formation of a copper hydroxyl salt, Cu2(OH)3NO3. From XRD and UV-DRS results, the product from the urea hydrolysis methods (Cu-HyS-urea) displayed higher crystallinity, small bandgap energy (Eg), and high light absorption ability because of some intercalated carbonate anions. For the Cr(VI) removal test, the Cu-HyS-NaOH showed superior adsorption of Cr(VI) than Cu-HyS-urea due to a higher specific surface area, confirmed by BET analysis. However, the Cu-HyS-urea presented higher photocatalytic Cr(VI) reduction under light irradiation than Cu-HyS-NaOH, owing to narrow Eg, less recombination, and a high transfer of the photogenerated charge carriers, proven by the results from photoluminescence, photocurrent density, and electrochemical impedance spectroscopy. Thus, this work provides a new function of the hydrotalcite-like copper hydroxyl salts (Cu-HyS-urea and Cu-HyS-NaOH) that can be utilized not only for adsorption of Cr(VI) but also as photocatalysts for Cr(VI) reduction under light irradiation.

CO2 hydrogenation to methanol over Cu/ZnO/ZrO2 catalysts: Effects of ZnO morphology and oxygen vacancy

Cu/ZnO/ZrO2 catalysts with flower, plate, and rod-like ZnO morphologies were prepared by urea hydrolysis method and used for CO2 hydrogenation to methanol. Among these catalysts, Cu/ZnO/ZrO2 with flower-like ZnO (CZZ-flower) exhibits the best catalytic performance (10.7 % yield of methanol and 4.3 mmolMeOH/(gcat·h) STYMeOH). The characterization results show that the CCZ-flower possesses the largest amount of oxygen vacancies. The experimental results reveal that the yield of methanol increases linearly with the increment of oxygen vacancy concentration, suggesting that oxygen vacancy plays an important role in CO2 hydrogenation to methanol. Additionally, the amount of oxygen vacancy can be modulated by changing reduction temperature, reduction time, and reducing gas concentration. It can be seen from DFT (density functional theory) calculations that oxygen vacancy is able to promote CO2 and active hydrogen (H*) adsorption, activate reaction intermediate and reduce the whole energy barriers.

Layered Double Hydroxide (MgFeAl-LDH)-Based Polypropylene (PP) Nanocomposite: Mechanical Properties and Thermal Degradation.

This work analyzes the thermal degradation and mechanical properties of iron (Fe)-containing MgAl layered double hydroxide (LDH)-based polypropylene (PP) nanocomposite. Ternary metal (MgFeAl) LDHs were prepared using the urea hydrolysis method, and Fe was used in two different concentrations (5 and 10 mol%). Nanocomposites containing MgFeAl-LDH and PP were prepared using the melt mixing method by a small-scale compounder. Three different loadings of LDHs were used in PP (2.5, 5, and 7.5 wt%). Rheological properties were determined by rheometer, and flammability was studied using the limiting oxygen index (LOI) and UL94 (V and HB). Color parameters (L*, a*, b*) and opacity of PP nanocomposites were measured with a spectrophotometer. Mechanical properties were analyzed with a universal testing machine (UTM) and Charpy impact test. The thermal behavior of MgFeAl-LDH/PP nanocomposites was studied using differential scanning calorimeter (DSC) and thermogravimetric analysis (TGA). The morphology of LDH/PP nanocomposites was analyzed with a scanning electron microscope (SEM). A decrease in melt viscosity and increase in burning rate were observed in the case of iron (Fe)-based PP nanocomposites. A decrease in mechanical properties interpreted as increased catalytic degradation was also observed in iron (Fe)-containing PP nanocomposites. Such types of LDH/PP nanocomposites can be useful where faster degradation or faster recycling of polymer nanocomposites is required because of environmental issues.

Complete fabrication of a nonenzymatic glucose sensor with a wide linear range for the direct testing of blood samples

A scalable method for the fabrication of a nonenzymatic disposable blood glucose sensor was made possible by preparing large quantities of catalytic materials and using screen-printing technology. The copper-aluminium double hydroxide microspheres were synthesized by urea hydrolysis method using sulfate salts of aluminium and copper at 100 °C for 24 h. Morphological studies revealed the presence of novel coral-like copper-aluminium microspheres. The prepared compound was used for the fabrication of an electrochemical glucose sensor by screen-printing. The sensor tested in 0.15 M NaOH medium showed a sensitivity of 1111.15 ± 7.96 µA mM-1 cm-2, linear response up to 27 mM glucose concentrations and a limit of detection of 17.60 ± 0.13 µM (S/N = 3). In the presence of exogenous and endogenous interfering species, the fabricated sensor was found to be selective towards glucose. A laboratory prototype of the sensor strip was fabricated using a cellulose membrane, hydrophilic membrane, and customized adhesive layers. The prototype was calibrated and tested with whole blood samples and obtained results are highly correlative with the commercial glucose sensor strips. The sensitivity of the prototype was found to be 0.3057 ± 0.02 µA mM−1 cm−2 with a linear range upto 24.44 mM (440 mg dL−1) and a calculated LOD of 0.9873 ± 0.06 mM (17.77 ± 1.11 mg dL−1). The ease of fabrication method and the reliability of the results with real blood samples show the potential of the nonenzymatic blood glucose sensor prototype for industrial fabrication.

Calcined ZnAl-LDH trapping performance in alginate beads for adsorption of Congo Red dye

ABSTRACT In this study, we report the adsorption process of Congo Red (CR) dye by calcined Layered Double Hydroxide (ZAC) at 550°C. The urea hydrolysis method was applied to produce highly crystalline Zn2Al-LDH. Samples characterisation was carried out by X-ray diffraction (XRD), Thermogravimetric/differential thermal analysis (TG/DTA), and Fourier transform infrared spectroscopy (FTIR). The results show that the adsorption of CR on calcined ZnAl-LDH was accompanied by the reconstruction of the layered structure. The ZAC showed higher adsorption efficiency versus other adsorbent under investigation and optimum conditions of contact time, adsorbent dose, pH and temperature were found to be 50 min, 0.02 g, 7 and 318 K, respectively. Isotherm studies show that the Langmuir isotherm model was appropriate to describe the CR adsorption data compared with Freundlich and Temkin isotherm models, with a higher correlation coefficient (R2 > 0.99) and maximum adsorption capacity of 406.5 mg/g. The thermodynamic parameters revealed that the adsorption process was spontaneous, endothermic, and governed by chemisorption. To further facilitate the recovery process in CR adsorption, we test the feasibility of applying ZnAl-LDH and its calcined product at 550°C entrapped in alginate beads. Experimental results indicate that alginate-coated ZAC beads, which exhibited remarkable adsorption performance, were more stable and require less effort to pull and separate than the alginate/ZnAl-LDH composite beads.

Study of Different Morphology of Zinc Hydroxide Salt as Adsorbent of Azo Dyes

AbstractIn this study, zinc layered hydroxide salts (Zn‐LHS) intercalated with dodecyl sulfate (DDS) anion in nanocone morphology (LHS‐NC) and conventional stone‐like co‐precipitation LHS phases (LHS‐CO) were investigated as adsorbent of Orange G (OG) and Sunset Yellow (SY) dye. LHS‐NC was prepared by urea hydrolysis method, while LHS‐DDS was prepared by co‐precipitation method. XRDP, FTIR, and SEM were used to characterize their structure and showed the formation of layered compounds with very well layered stacking with nanocone and conventional layer stone morphology. After OG and SY adsorption, the results (XRDP, FTIR, UV‐Vis, Zetametry) showed that the Freundlich adsorption isotherms had been well fitted, and both OG and SY dyes were intercalated in interlayer space of LHS, where LHS‐CO and LHS‐NC present high uptake capability of SY dye remotion equal a 227.79 and 442.48 (mg g−1) while OG adsorption capability were 2.52 and 6.39 (mg g−1), respectively. For the kinetics study, the best fit was obtained by the pseudo‐second‐order model, whereas the results of intraparticle diffusion show a one‐step adsorption process. Hence, this study demonstrated Zn‐LHS in nanocone morphology, and conventional stone‐like co‐precipitation phase makes them potentially attractive adsorbents in water purification.

Dry reforming of methane over Ni–ZrOx catalysts doped by manganese: On the effect of the stability of the structure during time on stream

Ni–Mn–ZrOx catalyst prepared by a one-step urea hydrolysis method was tested in the dry reforming of methane (DRM) reaction at medium temperature. The catalyst was characterized by H2-TPR, CO2-TPD, XRD, XPS, TGA, Raman, and TEM. On Ni–Mn–ZrOx catalyst, the catalytic activity increased with time on stream, while a decrease was observed on Ni–ZrOx catalyst. In order to understand this phenomenon, the catalysts were characterized at pre-reaction and during reaction for different time on stream such as 100 min, 300 min, and 480 min. According to the XPS results, it was shown that the Zr species on Ni–ZrOx were reduced during the reaction, whereas the Zr species was almost in equilibrium on Ni–Mn–ZrOx catalyst. In combining the results of XRD and activity in DRM, we can conclude that a stable ZrO2 structure on Ni–Mn–ZrOx catalyst might promote the redox of nickel species during the reaction, and further promote the redistribution of nickel species. However, on the Ni-ZrOx catalyst, the unstable ZrO2 support might result in a decrease of surface nickel content while an increase of Ni particle size, thus led to a decrease of activity for DRM.

RETRACTED ARTICLE: Kinetic, isotherm, thermodynamic and mechanism investigations of dihydrogen phosphate removal by MgAl-LDH

In this study, Mg–Al layered double hydroxide (MgAl-LDH) was synthesized by the urea hydrolysis method and used as sorbent to remove phosphate from aqueous solutions. Structural and morphological studies show that MgAl-LDH was prepared successfully with good crystallinity. The influences of sorbent dosage, time, initial concentrations, solution pH, temperature and competitive ions on the phosphate uptake have been investigated. It has been found that the uptake of phosphate onto MgAl-LDH was rapid and reached equilibrium within 60 min. The kinetic data were studied in terms of the pseudo-first-order, pseudo-second-order, elovich and intraparticle diffusion kinetic models. The pseudo-second-order model best described the sorption process. The isothermal data are best fitted by Freundlich, suggesting that multiple processes may control the adsorption of phosphate on the MgAl-LDH. The maximum adsorption capacity at 25 °C was found to be 346.4 mg/g. The sorption mechanism of phosphate onto LDHs could be via electrostatic attraction, ligand exchange and ion exchange. Phosphates ion uptake in the presence of other ions decreases in the order NO3− > Cl− > SO42−. Thermodynamic experiments suggested that the phosphate adsorption was spontaneous (− ΔG°) and endothermic (+ ΔH°) and increased the randomness (+ ΔS°) in the system. Thus, MgAl-LDH prepared by urea hydrolysis method is an effective sorbent for the removal of phosphate from aqueous solutions.