Calcination Of Precursor Research Articles

Vacuum-dried precursor to combustion synthesis CuO- based oxygen carriers with less NOx pollutant and its cyclic performance in chemical looping combustion

Chemical-looping combustion (CLC) technology is considered a promising combustion method with inherent CO2 capture. In this study, the sol-gel method and combustion synthesis were employed to produce precursor materials (P) of CuO-based oxygen carriers (OCs). The effects of vacuum drying conditions on both NOx emissions from precursor combustion and oxygen carrier cycle reaction characteristics were investigated. Vacuum-dried precursors emitted less NOx during the precursor calcination process. At a heating rate of 1 °C/min, the vacuum-dried precursors exhibited an average reduction of 24.13 % in NOx emissions compared with those prepared through atmospheric pressure drying. An increased amount of Cu2(OH)3NO3 in the precursor results in greater heat release during the self-propagating high-temperature combustion synthesis used to synthesize the oxygen carrier. Furthermore, the complete combustion of the nitrogen-containing precursor leads to a reduction in the emission of NOx. CuO-based OCs exhibited stable redox reactions over 10 cycles. Vacuum drying enhanced CH4 conversion and CO2 yield of OC1 by 14.04 % and 13.21 %, respectively, compared to atmospheric pressure drying. The results indicate that the CuO-based OCs obtained through vacuum-dried significantly enhance redox properties. This study shows that vacuum-dried reduces NOx emissions from nitrogen precursors and enhances the cyclic efficiency of OCs from precursor combustion.

Adenine-originated N-doped C3N4 modified glassy carbon electrode for ultra-sensitive electrochemical quantification of cysteamine drug

Cystinosis is a rare autosomal recessive illness in which cystine accumulates in lysosomes, causing crystallisation in important organs. Cysteamine, the only approved therapy, demands precise concentration control because of its therapeutic importance. Cysteamine detection methods, including fluorescence spectroscopy, chemical etching, and HPLC, need sophisticated sample preparation and expensive equipment. Electrochemical sensing provides a simpler alternative with higher sensitivity and selectivity. However, traditional carbon electrodes have limited sensitivity and detection limits. Nitrogen (N-CN), sulfur (S-CN), and nitrogen/sulfur co-doped (N, S-CN) graphitic carbon nitride materials were produced using a one-pot calcination of adenine and methionine precursors. N-CN-modified glassy carbon electrodes demonstrated higher electrocatalytic activity, quicker electron transfer, and increased selectivity, sensitivity, and stability for cysteamine detection. Structural and morphological characterisation of the synthesised materials was performed using various analytical techniques, including Fourier-transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, Brunauer-Emmett-Teller plots, X-ray diffraction, and X-ray photoelectron spectroscopy. The sensor showed a linear relationship between anodic peak current and cysteamine concentration in the range of 0 µM to 1 mM, with a low detection limit of 82.5 nM (0.0825 µM). Moreover, the modified electrode exhibited good reproducibility and stability with a recovery rate of 95.5 % and a relative standard deviation (RSD < 5 %). Real-sample analysis revealed a good agreement between LSV and HPLC for detecting cysteamine in blood serum. The paper describes a unique metal-free N-CN synthesis utilising adenine, allowing effective electrochemical detection.

In-situ growth of nickel-based catalysts on the surface of macroporous Al2O3 for CO2 methanation

Macroporous catalysts often exhibit excellent mass and heat transfer properties, which can reduce pressure drop and mitigate hot spot formation during the reaction process. Addressing the issues of the active component sintering due to the strong exothermicity of CO2 methanation and the demand for operation at high space velocities, in this work, a nickel-based catalyst with high surface area and large pore size and pore volume was prepared by in-situ growth of NiMgAl layered double hydroxide (NiMgAl-LDH) precursors on the surface of macroporous Al2O3. The effects of calcination temperature, reduction temperature, and space velocity on the catalyst structure and reaction performance were investigated. The results demonstrate that the catalyst phase composition can be controlled by adjusting the calcination temperature, while the reduction degree of Ni is regulated by altering the reduction temperature, which are effective in inhibiting the sintering of Ni, increasing the number of active Ni0 sites, and then enhancing the catalytic activity of Ni-MgO/Al2O3. By conducting the calcination of NiMgAl-LDH precursor at 400 °C and subsequent reduction at 650 °C, the resulted Ni-MgO/Al2O3 catalyst shows the highest active Ni surface area and exhibits the highest CO2 conversion and CH4 selectivity in the CO2 methanation, suggesting that the surface area of metal nickel is a crucial factor for the catalytic performance of Ni-MgO/Al2O3. Furthermore, the Ni-MgO/Al2O3 catalyst performs well at a high space velocity of WHSV = 80000 mL/(g·h) and a good stability at 550 °C, where the CO2 conversion and CH4 selectivity keep at 54% and 79%, respectively.

Electron transfer mechanism mediated MOF-derived nanoflowers catalyst for promoting peroxymonosulfate activation and ciprofloxacin degradation

Three MOF-derived nanoparticles were synthesized by manganese doping and calcination of ZIF-67 precursor. The surface physicochemical properties of these materials were compared using SEM, TEM, XRD, FTIR and BET analyses. Among them, cobalt-manganese oxide nanoflowers (CoMn2O4-NFs) exhibited excellent catalytic performance in the degradation of ciprofloxacin (CIP) by activated peroxymonosulfate (PMS), achieving 100 % removal within 30 minutes with a rate constant (kobs) of 0.2960 min−1. The catalytic mechanism was elucidated by quenching experiments, EPR, electrochemical analysis and X-ray photoelectron spectroscopy (XPS). The results show that the non-radical oxidation process was initiated mainly by direct electron transfer and 1O2 (∼80 %), with a small contribution from the radical SO4·- (∼20 %). The nano-confined structure on the surface of CoMn2O4-NFs makes it easy to combine with PMS to form CoMn2O4-NFs/PMS* complexes, which directly capture electrons from CIP to complete the degradation process. The double redox cycle of cobalt-manganese ions and oxygen vacancies on CoMn2O4-NFs could accelerate the electron transfer process. CoMn2O4-NFs maintained high removal efficiency (>99 %) over a wide pH range (3−11), with minimal interference from most environmental anions, demonstrating strong stability and interference resistance. This study provides insights into using metal-based materials for oxidative degradation of organic pollutants via non-radical pathways.

Oxidation cocatalyst/S-scheme junction cooperatively assists photocatalytic H2 production in ternary hybrid: The case of PdO@TiO2-Cu2O

Solar-driven photocatalytic hydrogen production from water splitting holds significant potential in addressing the energy crisis and environmental pollution. However, rapid recombination of photogenerated carriers and insufficient surface catalytic reaction kinetics hinder the photocatalytic process. Constructing the catalytic systems with multi-channel charge-separation can effectively alleviate those issues. In this work, ternary PdO@TiO2-Cu2O composites have been synthesized through precursor calcination and low-temperature reduction, where PdO and Cu2O nanoparticles couple with the TiO2 nanorods. Comparing to single TiO2, binary PdO@TiO2 and TiO2-Cu2O, the PdO@TiO2-Cu2O hybrid exhibits enhanced photocatalytic hydrogen production performance (5831μmol g-1h−1), with a hydrogen production rate more than three times that of single TiO2. Based on the band structures of TiO2 and Cu2O, along with the photochemical/electrochemical, in-situ EPR, Photoluminescence (PL) tests, and work function calculations, the formation of an S-scheme heterojunction at the TiO2-Cu2O interface under light illumination facilitates the recombination of electrons in the conduction band (CB) of TiO2 with holes in the valence band (VB) of Cu2O. In this regard, the established built-in electric field significantly accelerates the transfer of photogenerated charges while preserving their respective strong oxidation and reduction capabilities. Meanwhile, the introduction of PdO enriches the holes and further enhances the rate of charge separation. This S-scheme heterojunction with directional charge transfer and oxidation cocatalyst collectively form multi-channels of charge separation, optimizing charge migration and enabling efficient hydrogen production, thus improving the photocatalytic capability of pristine TiO2. This study provides a rational approach to construct efficient S-scheme heterojunction/oxidation cocatalyst multi-component catalytic systems for water splitting into hydrogen.

Vermiform Ni@CNT derived from one-pot calcination of Ni-MOF precursor for improving hydrogen storage of MgH2

The Ni-coated carbon nanotubes (Ni@CNT) composite was synthesized by the facile “filtration + calcination” of Ni-based metal−organic framework (MOF) precursor and the obtained composite was used as a catalyst for MgH2. MgH2 was mixed evenly with different amounts of Ni@CNT (2.5, 5.0 and 7.5, wt.%) through ball milling. The MgH2−5wt.%Ni@CNT can absorb 5.2 wt.% H2 at 423 K in 200 s and release about 3.75 wt.% H2 at 573 K in 1000 s. And its dehydrogenation and rehydrogenation activation energies are reduced to 87.63 and 45.28 kJ/mol (H2). The in-situ generated Mg2Ni/Mg2NiH4 exhibits a good catalytic effect due to the provided more diffusion channels that can be used as “hydrogen pump”. And the presence of carbon nanotubes improves the properties of MgH2 to some extent.

Lanthanum‐Nickel‐Based Mixed‐Oxide‐Coated Nickel Electrodes for the OER Electrocatalysis

ABSTRACTThe anodic oxygen evolution reaction (OER) remains a bottleneck for electrocatalytic water splitting due to its sluggish kinetics and, thus, high overpotentials. This limits water electrolysis as a key technology for the generation of hydrogen as a sustainable alternative to fossil fuels. For alkaline water splitting, perovskite phases (ABO3) with earth‐abundant first‐row transition‐metals have emerged as a promising material class for OER electrocatalysts. Among these, LaNiO3 has been found to exhibit high intrinsic OER activity. To increase catalyst utilization, a high surface area of the catalyst is desirable and can be achieved by impregnation of porous templates. In this work, La–Ni‐based oxides were prepared via impregnation of activated carbon and subsequent heating, combining precursor calcination and template removal into one step. The phase structure of the samples is analyzed via powder X‐ray diffractometry, and the morphology is determined by scanning electron microscopy. The synergistic effect of B‐site mixing iron as well as A‐site mixing strontium into LaNiO3 is studied and found to increase its OER activity, confirming the activity‐enhancing effect of Fe in Ni‐based OER electrocatalysts. To allow for facile technical application of the catalysts, the electrodes are prepared by coating a perovskite ink onto Ni‐metal as industrially relevant substrates, followed by calcination.

Synergistic Enhancement of Water-Splitting Performance Using MOF-Derived Ceria-Modified g-C3N4 Nanocomposites: Synthesis, Performance Evaluation, and Stability Prediction with Machine Learning.

Diminishing the charge recombination rate by improving the photoelectrochemical (PEC) performance of graphitic carbon nitride (g-C3N4) is essential for better water oxidation. In this concern, this research explores the competent approach to enhance the PEC performance of g-C3N4 nanosheets (NSs), creating their nanocomposites (NCs) with metal-organic framework (MOF)-derived porous CeO2 nanobars (NBs) along with ZnO nanorods (NRs) and TiO2 nanoparticles (NPs). The synthesis involved preparing CeO2 NBs and g-C3N4 NSs through the calcination of respective precursors, while the sol-gel method is employed for ZnO NRs and TiO2 NPs. Following the subsequent analysis of the physicochemical properties of the materials, the binder-free brush-coating method is deployed to fabricate NC-based photoanodes, followed by an evaluation of the PEC performance through various electrochemical techniques. Remarkably, the binary g-C3N4/CeO2 NCs with 20 wt % CeO2 NBs (gC20 NCs) exhibited a significantly enhanced current density of 0.460 mA/cm2 at 1.23 V vs reversible hydrogen electrode, which is 2.3 times greater than that of bare g-C3N4 NSs (0.195 mA/cm2). Further improvements are observed with ternary gC20/TiO2 (gCT50) and gC20/ZnO (gCZ50) NCs, achieving current densities of 1.810 and 1.440 mA/cm2, respectively. These enhanced current densities are attributed to increased donor densities, reduced charge transfer resistances, and efficient charge transport within the NCs. In addition, higher surface areas with beneficial instinctive defects are perceived for gCT50 and gCZ50 NCs, as revealed by Brunauer-Emmett-Teller and electron spin resonance analysis. Finally, the stability of gCZ50 and gCT50 NC-based photoanodes is predicted and forecasted with the help of the recurrent neural network-based long short-term memory technique. Overall, this study demonstrates the efficacy of organic-inorganic hybrids for efficient photoanodes, facilitating advancements in water-splitting studies.

Active-site engineering of a frustrated-Lewis-pair Au-loaded Zn-Al catalyst for the highly stable synthesis of glycerol carbonate from co-utilisation of CO2 and glycerol

Solid frustrated-Lewis-pair catalysts, based on Zn-Al composite oxide modified loaded with Au (Aux/ZnAl-CHT), were prepared by calcination of hydrotalcite precursors and tested for the direct synthesis of glycerol carbonate using CO2 as the carbon source. An Au5/ZnAl-CHT catalyst shows the highest catalytic performance with the glycerol carbonate yield of 19.5 % and the selectivity of 50.5 % at 170 °C and 4.0 MPa CO2, while maintaining good thermal stability and excellent regeneration ability. A series of characterization results and density functional theory (DFT) calculations indicated the introduction of Au leads to more frustrated-Lewis-pairs in Zn-Al composite oxide (ZnAl-CHT), which improve the adsorption and activation of CO2. Meanwhile, FTIR analysis indicates that glycerol is activated by Zn2+ for the formation of zinc glycerolate intermediates. The above dual synergistic activation processes effectively enhance the catalytic performance. And the reaction pathway is proposed for the synthesis of glycerol carbonate from CO2 and glycerol.

A Study on the Nanostructural Evolution of Bi/C Anode Materials during Their First Charge/Discharge Processes.

As a candidate anode material for Li-ion batteries, Bi-based materials have attracted extensive attention from researchers due to their high specific capacity, environmental friendliness, and simple synthesis methods. However, Bi-based anode materials are prone to causing large volume changes during charging and discharging processes, and the effect of these changes on lithium storage performance is still unclear. This work introduces that Bi/C nanocomposites are prepared by the Bi-based MOF precursor calcination method, and that the Bi/C nanocomposite maintains a high specific capacity (931.6 mAh g-1) with good multiplicative performance after 100 cycles at a current density of 100 mA g-1. The structural evolution of Bi/C anode material during the first cycle of charging and discharging is investigated using in situ synchrotron radiation SAXS. The SAXS results indicate that the multistage scatterers of Bi/C composite, used as an anode material during the first lithiation, can be classified into mesopores, interspaces, and Bi nanoparticles. The different nanostructure evolutions of three types of Bi nanoparticles were observed. It is believed that this result will help to further understand the complex reaction mechanism of Bi-based anode materials in Li-ion batteries.

Hydrogenation of waste PET degraded bis(2-hydroxyethyl)cyclohexane- 1,4-dicarboxylate to 1,4-cyclohexanedimethanol over Cu-based catalysts

Upcycling of waste polyethylene terephthalate derived bis(2-hydroxyethyl) cyclohexane-1,4-dicarboxylate (BHCD) to valuable monomer (1,4-cyclohexanedimethanol, CHDM) can decrease the emission of CO2 and microplastics. In this work, a stable Cu-based catalyst (Cu/MgAl2O4) with strong metal-support interaction was synthesized via calcination and reduction of CuMgAl-LDH precursor. The properties of precursor and final catalyst were characterized using XRD, TG-DTA, N2-adsorption, SEM/TEM, H2-TPR, CO2/NH3-TPD and XPS techniques. It was found that Cu/MgAl2O4 has high surface area, strong metal-support interaction and plenty basic sites. Cu/MgAl2O45 exhibited prominent performance for the hydrogenation of PET-derived BHCD to CHDM among the tested Cu/MgAl2O4, Cu/MnAl2O4 and Cu/ZnAl2O4 catalyst. The yield of CHDM over Cu/MgAl2O4 reached 98 % with a complete conversion of BHCD at 240 °C, 4 MPa and 0.525 g.gcat-1.h−1. Besides, it remains its activity for at least 80 h on stream under optimized condition. The structure-performance of these catalysts for the hydrogenation of BHCD to CHDM was discussed.

Carbon nanodots derived from organo-templated zeolites for femtosecond mode-locked fiber laser

Carbon nanodots (CNDs) have been widely investigated due to their physicochemical and optical properties. However, the nonlinear saturable absorption property and its application in laser technology is rarely reported. Here, we report the CNDs as an ideal saturable absorber (SA) for ultra-stable femtosecond mode-locked fiber laser at a wavelength of 1.5 μm. The mono-sized CNDs of 2 nm are fabricated from a dipropylamine-templated zeolite precursor calcination with a temperature of 380 °C. The nonlinear saturable absorption property of the as-synthesized CNDs is investigated by using a balanced twin-detector measurement system. The modulation depth and saturable intensity are measured to be 33 % and 3.1 MW/cm2, respectively. By inputting the CNDs SA into the erbium-doped fiber laser (EDFL) ring cavity, a highly stable mode-locked EDFL with pulse width of 388 fs and single-to-noise ratio (SNR) of 84.4 dB can be obtained. In addition, stable soliton pairs with single-pulse width of 422 fs and SNR of 84.1 dB can also be achieved. These findings demonstrate that the carbon dots can be used as an ideal SA and has promising applications in ultrafast photonics.

Effect of molybdenum valence in low Mo/Sn ratio catalysts for the oxidation of methanol to dimethoxymethane

A series of Mo/Sn (1:20, molar ratio) catalysts were prepared by two-step hydrothermal synthesis method, and the effect of calcination temperature of tin precursors on the reaction performance of methanol oxidation to dimethoxymethane (DMM) was investigated. The crystal structure, surface properties, redox property and valence change of molybdenum species of the catalyst were characterized by XRD, Raman, FT-IR, XPS, NH3-TPD and H2-TPR. The results showed that Mo1Sn20-600°CSn catalyst exhibited better performance than other catalysts, achieving DMM selectivity of 90% with methanol conversion of 30% at 140 °C. From the characterization results, the surface properties of the tin precursors affected the structure of catalyst, the degree of molybdenum oxide dispersion and valence of molybdenum species, and further influenced the performance of the catalysts. The high temperature calcination of tin precursors is more favorable for the generation of Mo6+ in the Mo1Sn20 catalyst.

(Invited) Deciphering the Interplay between Thermodynamics and Kinetics during Cathode Calcination

Synthesis of the cathode materials used in lithium ion batteries involve the two steps, coprecipitation and calcination, where in the first step cathode precursors are formed, and later in the second step lithium ions are inserted into these cathode particles through chemical routes. During calcination, the cathode precursors obtained from the coprecipitation is mixed with lithium salt (LiOH or Li2CO3) and heated at high temperatures (~ 650°C – 1000°C) where oxidation and lithiation of the cathode particles take place. Calcination is considered to be of major significance in determining the final state of the cathode particles because it not only determines the extent of oxidation and lithiation experienced by the cathodes, but also substantially influences its morphology (for example, primary particle size, internal porosity, etc.). Significant surface modification of the cathode particles is also possible during calcination, which can impact its charge transfer resistance. Before the oxidation and lithiation of the cathode precursors, removal of water or CO2 is observed. All these chemical changes within the cathode precursors lead to change in its lattice volume, which is reflected as variation in the size of the primary particles. Apart from this, sintering induced change in particle size is also observed during the calcination process. In order to decipher the structural and morphological variations that occur during the calcination of cathode precursors, detailed experimental characterization is conducted in the present context using in situ X-ray diffraction (XRD) and thermogravimetric analysis (TGA) techniques. Atomistic simulations are conducted to decipher the feasibility of different chemical reactions that can possibly occur under elevated temperatures. Impact of reaction rate constant and mass transport in determining the extent of the oxidation and lithiation experienced by the cathode particles is analyzed by using a mesoscale level computational technique. Sintering induced grain growth experienced by the cathode primary particles is also investigated at the mesoscale level, which is demonstrated in Figure 1. Overall, a thorough understanding of the various physicochemical phenomena that occur during the calcination of cathode precursors has been developed using a combination of experimental and computational techniques, which will be discussed in detail. Figure 1

Solvent-free direct salt precursor mechanochemical synthesis of La0.5Sr0.5Ti0.5Mn0.5O3-δ oxide perovskite and its electrocatalytic behavior as oxygen electrode for solid oxide cells

In this work, a solvent-free mechanochemical route is proposed as a direct salt precursor solid state synthesis for the mixed ionic-electronic conducting (MIEC) Lanthanum Strontium Titanium Manganese oxide perovskite (La0.5Sr0.5Ti0.5Mn0.5O3-δ, LSTM). The resulting mechanochemically synthesized powder is structurally and morphologically characterized and is comprised of fine spherical nanostructures in the sub-micron scale (≤100 nm), with low polydispersity and homogeneous morphology, while the obtained perovskite structure is pure single-phase without any precursor residuals or metal oxide phases. For comparison, conventional synthetic routes (sol-gel and precursor calcination) are presented which result in inferior samples of mixed metal oxides and micron-sized particles. Symmetrical solid oxide cells with single-phase LSTM and LSTM-YSZ composite electrodes reveal a mixed conduction behavior in the temperature range of 700–850 °C under flowing synthetic air atmosphere. With a developed current density of 172 mA cm−2 at 850 °C and +2 V overpotential, and an electrode polarization resistance of 7.5 Ω cm2, perovskite LSTM synthesized by the presented solvent-free direct salt precursor mechanochemical synthesis is therefore proposed as a potential candidate for MIEC electrodes in symmetrical reversible solid oxide cells (r-SOCs).

Preparation of NASICON Silico Phosphates of Composition Na1 + xZr2SixP3 – xO12 by Pyrolysis of Solution in Melt

A new method for preparing Na1 + xZr2SixP3 – xO12 (0 x 3) based on pyrolysis of solution containing a mixture of organic components in rosin melt has been proposed. Effect of superstoichiometric amounts of sodium and phosphorus on the phase composition of synthesis products has been proved. It has been found that precursor for the sample of maximal purity of phase composition is prepared at molar ratio Na : Zr : Si : P = (1.15 + x) : 2 : x : (y – x), where y = 3 (1.20 + x)/(1 + x). Precursor calcination temperature is 1000°C. Different NASICON compositions without crystalline admixtures have been obtained in the range 1.5 ≤ x ≤ 2.12. The prepared samples have been studied by X-ray powder diffraction and scanning electron microscopy. The disclosed method of synthesis is promising for the preparation of NASICON as both bulk materials and thin layer coatings.

Facile fabrication of monodispersed α- and γ-Al2O3 microspheres through controlled calcination of alumina precursors synthesized by homogeneous precipitation

Monodispersed spherical particles of γ- and α-alumina were synthesized by urea-based homogeneous precipitation, using potassium sulfate and aluminum nitrate as the precursor and urea as a precipitating agent. The influence of various synthesis parameters like concentration of reactants, temperature, and reaction time, on the morphological features of alumina were investigated. Results showed that all the experimental parameters had a considerable effect on the morphology of the synthesized alumina, and control of these parameters resulted in monodispersed spherical particles with good dispensability and filtering performance. Extensive optimization of the experimental parameters led to produced alumina precursors with spherical morphology and an average particle size of 610 nm. The precipitated solids were characterized by various techniques and it was noted that the as-prepared particles were amorphous. Relatively well-dispersed and crystalline γ- and α-Al2O3 with higher sintering activity were obtained by calcining the as-synthesized precursors at 1000 and 1200 °C, respectively. The crystallographic results showed that crystallite size increased with an increase in annealing temperature. It was observed that the crystallite size of γ-Al2O3 was much smaller (5.71 nm ± 7.21%) than α-Al2O3 (35.40 nm) ± 4.58%. The Scanning electron microscopic analysis of the calcined alumina showed that the particle morphology was retained to a greater extent after calcination. The synthesized alumina particles can be used as a reinforcement filler in the Ni/Al2O3 composite coatings to enhance the tribological and mechanical properties of Ni-composite coating on a steel surface. The incorporated alumina particles in the composite may improve the properties of the coatings.

Hydrometallurgical recycling of lithium from waste saggar: Studies on influential role of acid/alkaline additives, leaching kinetics and mechanism

Waste recycling has become crucial with the increasing attention paid to environmental rules and the fast-depleting resources of critical elements. Soaring demands for lithium in cathode materials of rechargeable batteries result in a surge in waste saggar after being used in the calcination of cathode precursor. The recycling of lithium from waste saggar is therefore imperative due to the high supply-risk of lithium. Herein, waste saggar composed of various mineral phases (26.26 % LiAlSi4O10 ≅ 0.6 % Li; 6.34 % Li4SiO4 ≅ 1.47 % Li; 0.79 % LiOH∙H2O ≅ 0.13 % Li; 0.03 % Li2CO3 ≅ 0.01 % Li) was leached in water for lithium extraction; while the effects of NaOH, Ca(OH)2, and H2SO4 as potential additives were examined under a wide temperature range of 5–80 °C. Interestingly, the observed order of leaching efficiency at lower temperature (20 °C) H2SO4 > NaOH > Ca(OH)2 was in variance with that at 80 °C (NaOH > H2SO4 Ca(OH)2). The apparent activation energy for lithium extraction was determined to be 29.8 kJ/mol using NaOH, 33.8 kJ/mol using Ca(OH)2, and 14.1 kJ/mol using H2SO4, indicating that the overall leaching process follows a mixed-controlled mechanism. The maximum efficiency of 94 % Li-extraction was achieved with NaOH which was used for the precipitation recovery of Li2CO3 of purity above 99 %.

Preparation of Monolithic LaFeO3 and Catalytic Oxidation of Toluene.

Porous LaFeO3 powders were produced by high-temperature calcination of LaFeO3 precursors obtained by hydrothermal treatment of corresponding nitrates in the presence of citric acid. Four LaFeO3 powders calcinated at different temperatures were mixed with appropriate amounts of kaolinite, carboxymethyl cellulose, glycerol and active carbon for the preparation of monolithic LaFeO3 by extrusion. Porous LaFeO3 powders were characterized using powder X-ray diffraction, scanning electron microscopy, nitrogen absorption/desorption and X-ray photoelectron spectroscopy. Among the four monolithic LaFeO3 catalysts, the catalyst calcinated at 700 °C showed the best catalytic activity for the catalytic oxidation of toluene at 36,000 mL/(g∙h), and the corresponding T10%, T50% and T90% was 76 °C, 253 °C and 420 °C, respectively. The catalytic performance is attributed to the larger specific surface area (23.41 m2/g), higher surface adsorption of oxygen concentration and larger Fe2+/Fe3+ ratio associated with LaFeO3 calcined at 700 °C.

RGO-Modified ZnWO4/WO3 Nanocomposite for Detection of NH3

The composite of ZnWO4/12WO3-0.5 wt % rGO was successfully synthesized for the first time by one-step precursor calcination of equimolar W and Zn precursors, followed by loading rGO prepared by hydrazine reduction. The structure, composition, and morphology of the as-synthesized composite were characterized by various spectral analyses. Compared with reported metal-oxide-based NH3 sensors, our sensor can detect low concentrations of NH3, and the method used herein is simple, low-cost, and effective. The composite-based sensor exhibits the highest response of 10.1–20 ppm NH3, which is 3.98 times that of WO3, and has better selectivity and stability at an operating temperature of 140 °C. The improvement is attributed to the synergistic effect of p–n heterojunction formation and rGO decoration; the former creates an additional depletion layer to expand the resistance change in air and gas, while the latter provides more surface active sites to increase gas adsorption and accelerates the electron transfer for enhancing gas-sensing performance. The work has reference value to develop novel metal-oxide-based NH3 sensors.