Molar Ratio Of Precursors Research Articles

Hydrothermally synthesized cobalt vanadate nanoparticles for photocatalytic degradation of Fast Orange Red dye and supercapacitor applications

Herein, Co2V2O7 and Co3V2O8 nanoparticles (NPs) were synthesized by changing only the precursor molar ratio using a simple hydrothermal approach. Numerous analytical approaches were used to characterise the synthesized NPs. The crystal structures of the NPs were found to be monoclinic (Co2V2O7) and orthorhombic (Co3V2O8) with an average crystallite size of 29 nm and 25 nm, respectively. Furthermore, the band gaps for Co2V2O7 and Co3V2O8 were calculated to be 1.8 eV and 2.1 eV, respectively. The supercapacitor properties of both the synthesized NPs were performed. After 1000 cycles, the specific capacitance values were determined to be 628 F·g−1 for Co2V2O7 nanoparticles and 415 F·g−1 for Co3V2O8, indicating an excellent retention rate of almost 90 % for both materials. Furthermore, stability measurements at a current density of 5 A·g−1 demonstrated that even after 3000 cycles, the capacitive retention remained stable at 90 %. The photocatalytic investigations for the degradation of Fast Orange Red dye using Co2V2O7 and Co3V2O8 was performed. Co2V2O7 showed a decolourization rate of 93.8 %, whereas Co3V2O8 had a decolourization rate of 88.95 % within 120 min of UV light irradiation. Overall, the research sheds light on the properties of Co2V2O7 and Co3V2O8 nanoparticles, making them viable candidates for practical energy and environmental applications. The obtained results also motivate the synthesis of comparable NPs with improved characteristics for real-world applications.

Understanding the growth mechanisms of ultrasmall silver selenide quantum dots for short-wave infrared detectors

Colloidal quantum dots (CQDs) allow for wavelength-tunable, economic, and elegant access to the infrared (IR) spectrum by utilizing inter- and intraband excitonic transitions in narrow bandgap semiconductors. With the emergence of new applications for IR detection, developing competitive non-toxic and environmentally benign alternatives to heavy metal-containing semiconductors is of increasing importance. Over the last decade, silver selenide (Ag2Se) has emerged as an alternative to lead- and mercury-based QDs, especially with large, intraband Ag2Se CQDs showing promising performance in the mid-wave IR. Herein we explored the critical nucleation and growth mechanisms of ultrasmall (2.5–3.5 nm) interband absorbing Ag2Se CQDs operating in the near to short-wave IR. Classical nucleation and growth was observed at most reaction conditions, with a growth temperature of 140 °C and a Ag:Se precursor molar ratio of 1:2 providing the most robust control over the IR absorption spectrum. We proceeded to perform an in-depth study of the impact of surface ligand chemistry of CQD thin-films on resulting optoelectronic properties. By tuning the functional groups and optimizing ligand exchange parameters, we obtained IR responsivity values of ∼25 mA/W in photoconductor devices and ∼1.8 mA/W in photodiode devices in the range 800 – 1250 nm.

Comparative life cycle assessment analysis of mono, binary and ternary construction and demolition wastes-based geopolymer binders

The global construction industry is in high demand of sustainable building materials that are cost-effective and simultaneously have a low carbon footprint and energy consumption. As a result, geopolymeric materials primarily derived from construction and demolition wastes (CDWs) have become more attractive sustainable alternatives to ordinary Portland cement (OPC)-based cementitious materials. This paper aims to comparatively analyze the life cycle assessment (LCA) of CDW-based geopolymers comprising recycled brick powder (RBP), recycled ceramic tile powder (RTP) and recycled concrete powder (RCP) at the mono, binary and ternary geopolymer (GP) binder systems. The mono GP binders were synthesized based on pre-targeted design chemical parameters of SiO2/Al2O3 and Na2O/SiO2 molar ratios and liquid-to-solid (L/S) ratio, while the binary and ternary combinations considered different RBP, RTP and RCP precursor contents at the optimized SiO2/Al2O3 and Na2O/SiO2 molar ratios of each constituent CDW precursor in the geopolymer matrices. The LCA analysis was performed through experimental results in terms of embodied energy (E-energy) consumption (Ef), and embodied carbon dioxide (E-CO2) emissions (Cf) as indicators of the global warming potential (GWP) of these GP systems while considering ambient curing. Interesting results were attained in terms of improved sustainable environmental impact of the ternary integration of CDW materials than their mono and binary counterparts when used as precursors in geopolymer binders. The synthesis of the optimal ternary composition of BTC-20:40:40 synthesized at SiO2/Al2O3, Na2O/SiO2 and L/S ratios of 10.2, 0.18 and 0.30, respectively resulted in the lowest embodied CO2 emission of Cf = 5.58 kg/ton/MPa and embodied energy of Ef = 18.61 MJ/ton/MPa, indicating 110.8% and 157.9% reduction in terms of embodied carbon dioxide and embodied energy, respectively, as compared to the reference Portland cement (OPC) binder with equivalent strength at 28 days.

Controlling the Molar Ratios of Cation to Anion of Precursors for High Performance Capacitive Properties of MnO2 Hybridized Carbon-Based Materials Electrode

Controlling the cation to anion (Mn2+/MnO4−) molar ratios of the precursors was used to obtain a highly performance capacitive properties of nanostructural MnO2 hybridized carbon-based materials on nickel foam (NF) through successive ionic layer adsorption and reaction technology. SEM, XRD, BET, and XPS analyses are utilized to investigate the influence of cation/anion molar ratios of precursors on the as-obtained MnO2 electrode materials. At a lower molar ratio of cation/anion of 1, the prepared manganese oxide deposited on the NF with obvious δ-MnO2 phase. The average pore size distribution of BET analysis of the as-obtained δ-MnO2 is about 4.6 nm, the specific surface area is 155.7 m2 g−1, exhibiting a mesoporous structure. However, when the molar ratio of cation/anion is higher than 5, the deposited film produced by the reaction exhibits a γ-MnO2 crystal phase. The capacitance of δ-MnO2/NF electrode is 280 F g−1 at 1 A g−1 in a 1 M Na2SO4 aqueous electrolyte solution. In addition, reduced graphene oxide (rGO) mixed with multi-wall carbon nanotube (MWCNT) was added to synthesize γ-MnO2/rGO-MWCNT/NF electrode, which has a high capacitance of 377.4 F g−1 under the charge/discharge current density at 1 A g−1.

Nearly monodisperse Cu|pd alloyed Nanocrystals: Ultrasound induced stepwise thermoreduction in organic Medium, and catalytic alcoholysis for hydrogen evolution

Active search for efficient and inexpensive catalyst is the basic premise and urgent requirement to promote the practicality of the new hydrogen storage material-ammonia borane. We herein propose an ultrasonic-induced stepwise thermoreduction protocol to fabricate serial bimetal Cu|Pd alloyed nanocrystals with various metal molar ratios, and scientifically evaluate respective catalytic activity for alcoholyzing ammonia borane. Comprehensive characterizations and analysis confirm that the as-fabricated Cu|Pd crystalline grains appear as nearly monodisperse microspheres with mean size of about 10 nm, taking on almost superlattice arrangement. The ultrasound and precursor molar ratio can affect grain size and dispersity to varying degrees. Regardless of the Pd/Cu molar ratio, alloy phase microstructure can be formed. The Pd-rich nanoagent Cu40Pd60 unfold the upmost catalytic ability for alcoholyzing ammonia borane, even exceeding Pd NCs, with the turnover frequency (TOF) value of 66.51 mol (H2)·min−1·(mol Pd)-1 and apparent activation energy of 30.35 kJ·mol−1. Moreover, the Cu40Pd60 nanocrystals possess the exceptional stability with only 10% loss of the original catalytic activity after 5 round cyclic utilization. The catalytic methanolysis at the given conditions is identified as first-order reaction. The current findings can enrich the family of the serial bimetal alloyed nanocatalyst, also offer an optional strategy for fabricating the poly-metal composite catalysts with high activity.

Influence of Humidity and Heating Rate on the Continuous ZIF Coating during Hydrothermal Growth.

Zeolitic imidazolate frameworks (ZIFs) have potential for various gas and ion separations due to their well-defined pore structure and relatively easy fabrication process compared to other metal-organic frameworks and zeolites. As a result, many reports have focused on preparing polycrystalline and continuous ZIF layers on porous supports with good separation performance in various target gases, such as hydrogen extraction and propane/propylene separation. To utilize the separation properties in industry, membrane is required to be prepared in large scale with high reproducibility. In this study, we investigated how humidity and chamber temperature influence the structure of a ZIF-8 layer prepared by the hydrothermal method. Many synthesis conditions can affect the morphology of polycrystalline ZIF membranes, and previous studies have mainly focused on reaction solutions, such as precursor molar ratio, concentration, temperature, and growth time. On the other hand, we found that the humidity of the chamber and the heating rate of the solution also lead to dramatic changes in the morphology of ZIF membranes. To analyze the trend between humidity and chamber temperature, we set up the chamber temperature (ranging from 50 °C to 70 °C) and relative humidity (ranging from 20% to 100%) using a thermo-hygrostat chamber. We found that as the chamber temperature increased, ZIF-8 preferentially grew into particles rather than forming a continuous polycrystalline layer. By measuring the temperature of the reacting solution based on chamber humidity, we discovered that the heating rate of the reacting solution varied with humidity, even at the same chamber temperature. At a higher humidity, the thermal energy transfer was accelerated as the water vapor delivered more energy to the reacting solution. Therefore, a continuous ZIF-8 layer could be formed more easily at low humidity ranges (ranging from 20% to 40%), while micron ZIF-8 particles were synthesized at a high heating rate. Similarly, under higher temperatures (above 50 °C), the thermal energy transfer was increased, leading to sporadic crystal growth. The observed results were obtained with a controlled molar ratio, in which zinc nitrate hexahydrate and 2-MIM were dissolved in DI water at a molar ratio of 1:45. While the results are limited to these specific growth conditions, our study suggests that controlling the heating rate of the reaction solution is critical for preparing a continuous and large-area ZIF-8 layer, particularly for the future scale-up of ZIF-8 membranes. Additionally, humidity is an important factor in forming the ZIF-8 layer, as the heating rate of the reaction solution can vary even at the same chamber temperature. Further research related to humidity will be necessary for the development of large-area ZIF-8 membranes.

Incorporation of Novel Graphene Nanosheet Materials as Cathode Catalysts in Li–O2 Battery

Abstract This study reports the superior performance of graphene nanosheet (GNS) materials over Vulcan XC incorporated as a cathode catalyst in Li–O2 battery. The GNSs employed were synthesized from a novel, eco-friendly, and cost-effective technique involving chamber detonation of oxygen (O2) and acetylene (C2H2) precursors. Two GNS catalysts i.e., GNS-1 and GNS-2 fabricated with 0.3 and 0.5 O2/C2H2 precursor molar ratios, respectively, were utilized in this study. Specific surface area (SSA) analysis revealed significantly higher SSA and total pore volume for GNS-1 (180 m2 g−1, 0.505 cm3 g−1) as compared with GNS-2 (19 m2 g−1, 0.041 cm3 g−1). GNS-1 exhibited the highest discharge capacity (4.37 Ah g-1) and superior cycling stability compared with GNS-2 and Vulcan XC. Moreover, GNS-1 demonstrated promising performance at higher current densities (0.2 and 0.3 mA cm−2) and with various organic electrolytes. The superior performance of GNS-1 can be ascribed to its higher mesopore volume, SSA, and optimum wettability compared to its counterparts.

An in-situ strategy to construct uracil-conjugated covalent organic frameworks with tunable fluorescence/recognition characteristics for sensitive and selective Mercury(II) detection

Previous researches of covalent organic frameworks (COFs) have shown their potential as fluorescent probes, but the regulation of their optical properties and recognition characteristics still remains a challenge, and most of reports required complicated post-decoration to improve the sensing performance. In this context, we propose a novel in-situ strategy to construct uracil-conjugated COFs and modulate their fluorescence properties for sensitive and selective mercury(II) detection. By using 1,3,6,8-tetrakis(4-formylphenyl)pyrene (TFPPy) and 1,3,6,8-tetrakis(4-aminophenyl)pyrene (TAPPy) as fundamental blocks and 5-aminouraci (5-AU) as the functional monomer, a series of COFs (Py-COFs and Py-U-COFs-1 to Py-U-COFs-5) with tunable fluorescence were solvothermally synthesized through an in-situ Schiff base reaction. The π-conjugated framework serves as a signal reporter, the evenly and densely distributed uracil acts as a mercury(II) receptor, and the regular pores (channels) make the rapid and sensitive detection of the mercury(II) possible. In this research, we manage to regulate the crystalline structure, the fluorescence properties, and the sensing performance of COFs by simply changing the molar ratio of precursors. We expect this research to open up a new strategy for effective and controllable construction of functionalized COFs for environmental analysis.

EFFECT OF PHASE TRANSFORMATION ON OPTICAL PROPERTIES OF ZNTIO3 CERAMIC POWDER PREPARED BY SOL-GEL METHOD

ZnTiO3 powders were prepared by sol-gel method using ammonium hydroxide. The effects of calcination temperature (500– 1000∘ C). and the molar ratios ZnO/TiO2. The synthesis of a nano perovskite ZnTiO3 usually results in the formation of one or more of the compounds such as Zn2TiO4, and ZnTiO3 with other secondary impurity phases such as rutileTiO2 or ZnO. To obtain a phase-pure a nano perovskite ZnTiO3 at a low processing temperature is one of the challenges in materials chemistry., pure ZnTiO3 can not be synthesized under normal conditions, because it transforms into Zn2TiO4 and rutile. In the current study, the crystalline and phase transformation behaviors of sol-gel synthesized a nano perovskite ZnTiO3 has systematically been investigated with regard to various Zn:Ti precursor molar ratios. The ZnTiO3 phase can be detected by XRD in the powders calcined above 600 °C. The formation of ZnTiO3 is a slow reaction process, which leads to the development of large ZnTiO3 particles, with dimensions after calcination at 700 °C for 5 h in the range of 68–81 Nm. Calcination temperature increased considerably the crystallite size of the nano perovskite ZnTiO3 from 68 to 81 nm This treatment led also to the creation of holes in the matrix of calcinated solids which increased the mobility of charge carriers (electrons) leading to a significant decrease in the decrease in the optical energy gap reaching to (2.7 to 2 )e.v.

Visible Light‐Driven N–F‐Codoped TiO2 for Photocatalysts as Potential Application to Wastewater Treatment

AbstractN–F‐codoped TiO2 materials were successfully fabricated by a hydrothermal method without any capping agent and further heat treatment. The results indicate interstitial N3− ion doping and the surface‐adsorbed F− ion on the TiO2 surface. By introducing N and F into the TiO2 lattice, the band gap of the obtained material is significantly reduced compared to the undoped TiO2. Moreover, the light absorption ability of the material was demonstrated to extend to visible light regions, contributing to the better photocatalytic activity. Furthermore, the sample with the NH4F/TiCl4 precursor molar ratio of 2:1 displayed the greatest photocatalytic activity with visible radiation. This study provides a new pathway to synthesize a novel photocatalyst having great potential for future applications.

Silver Tungstate Obtained via Successive Seed Crystal Growth: Structural, Morphological, Optical, and Photocatalytic Properties

Synthesis routes and parameters such as synthesis time, precursor molar ratio, pH, and temperature are critical for generating oxides of various sizes and morphological aspects. However, there is no information on how to prepare silver tungstate (Ag2WO4) crystals of different shapes and sizes under laboratory conditions and without using sulfating agents. In this study, we attempted to fill this gap by preparing α-Ag2WO4 crystals of various sizes and morphologies using the coprecipitation method in a 3 h interval at room temperature and without using sulfating agents. The powder X-ray diffraction analysis confirmed that all crystals had an orthorhombic structure, whereas Fourier-transform infrared spectroscopy revealed the degree of structural disorder in the bonds between the atoms in the materials. Scanning electron microscopy revealed that the α-Ag2WO4 crystals had different sizes (5.37-26.83 μm) and morphologies (tetragonal prism, rod, and cypress leave-like rod), whereas ultraviolet-visible diffuse reflectance spectroscopy analysis indicated the optical band gap energy (2.92-3.05 eV), calculated using the method proposed by Kubelka and Munk. Catalytic tests revealed that the synthesized samples with the smallest crystals (AW1) and a tetragonal prism morphology degraded dye more efficiently (apparent rate constant (k) = 5.86 × 10−3 min−1) than other samples.

Mononuclear/Binuclear [VIVO]/[VVO2] Complexes Derived from 1,3-Diaminoguanidine and Their Catalytic Application for the Oxidation of Benzoin via Oxygen Atom Transfer.

Ligands H4sal-dag (I) and H4Brsal-dag (II) derived from 1,3-diaminoguanidine and salicylaldehyde or 5-bromosalicylaldehyde react with one or 2 mol equivalent of vanadium precursor to give two different series of vanadium complexes. Thus, complexes [VIVO(H2sal-dag) (H2O)] (1) and [VIVO(H2Brsal-dag) (H2O)] (2) were isolated by the reaction of an equimolar ratio of these ligands with [VIVO(acac)2] in MeOH. In the presence of K+/Cs+ ion and using aerially oxidized [VIVO(acac)2], the above reaction gave complexes [K(H2O){VVO2(H2sal-dag)}]2 (3), [Cs(H2O){VVO2(H2sal-dag)}]2 (4), [K(H2O){VO2(H2Brsal-dag)}]2 (5), and [Cs(H2O){VVO2(H2Brsal-dag)}]2 (6), which could also be isolated by direct aerial oxidation of complexes 1 and 2 in MeOH in the presence of K+/Cs+ ion. Complexes [(H2O)VIVO(Hsal-dag)VVO2] (7) and [(H2O)VIVO(HBrsal-dag)VVO2] (8) were isolated upon increasing the ligand-to-vanadium precursor molar ratio to 1:2 under an air atmosphere. When I and II were reacted with aerially oxidized [VIVO(acac)2] in a 1:2 molar ratio in MeOH in the presence of K+/Cs+ ion, they formed [K(H2O)5{(VVO2)2(Hsal-dag)}]2 (9), [Cs(H2O)2{(VVO2)2(Hsal-dag)}]2 (10), [K2(H2O)4{(VVO2)2(Brsal-dag)}]2 (11), and [Cs2(H2O)4{(VVO2)2(Brsal-dag)}]2 (12). The structures of complexes 3, 4, 5, and 9 determined by single-crystal X-ray diffraction study confirm the mono-, bi-, tri-, and tetra-anionic behaviors of the ligands. All complexes were found to be an effective catalyst for the oxidation of benzoin to benzil via oxygen atom transfer (OAT) between DMSO and benzoin. Under aerobic condition, this oxidation also proceeds effectively in the absence of DMSO. Electron paramagnetic resonance and 51V NMR studies demonstrated the active role of a stable V(IV) intermediate during OAT between DMSO and benzoin.

Enhanced photocatalytic efficiency of TiO2/CdS nanocomposites by manipulating CdS suspension on TiO2 nanoparticles

• TiO 2 /CdS nanocomposites are synthesized at different concentrations of cadmium and sulphur precursors. • The Cd and S precursors ratios affect the size and morphologies of resulting nanocomposites. • Photocatalytic activities are influenced by the precursor ratio. • Stepwise de-ethylation for RhB is observed during visible light photocatalysis. Titanium Dioxide (TiO 2 ) has long been found to be a promising photocatalyst in the ultraviolet region, although it faces several limitations in the visible range. Various attempts for overcoming these shortcomings have shown that TiO 2 nanocomposites offer excellent results for visible area photocatalysis. In the present work, three different samples of TiO 2 /CdS nanocomposites are synthesized using simple and cost-effective hydrothermal method, based on different concentrations of cadmium and sulphur precursors and a comparison is made among them. Characterization techniques like Scanning Electron Microscopy (SEM), Photoluminescence (PL) spectroscopy, UV-visible spectroscopy, X-Ray Diffraction (XRD), Energy Dispersive X-Ray Analysis (EDX) and Fourier Transform Infrared (FTIR) spectroscopy are employed to study morphological, optical, structural, and elemental properties of the as-synthesized nanocomposites. SEM analysis shows that change in concentration of precursors caused morphological changes in the resulting samples. XRD characterization shows that the crystallite size gets modified at different concentrations ranging from approximately 21 nm to 5 nm. As per the UV-Vis spectroscopy, the band gap of TiO 2 /CdS nanocomposites has substantially decreased, making it highly suitable for photocatalytic application in the visible region in comparison to pure TiO 2 . Photocatalytic degradation processes for as-synthesized TiO 2 /CdS nanocomposites are studied for methylene blue (MB) and rhodamine B (RhB) dyes under visible light exposure. Results demonstrate that degradation results for MB dye are better in comparison to RhB dye for all the three synthesized photocatalysts. Futher, it is concluded that TiO 2 /CdS nanocomposite with a 1:1 molar ratio of cadmium and sulphur precursors has the optimum photocatalytic performance for dye degradation.

Ultra-fast microwave-assisted synthesis of photoluminescent carbon dots with an ultra-high quantum yield for H2O2 detection

The conventional hydrothermal bottom-up synthesis for preparing carbon dots (CDs) usually requires stringent conditions and high energy consumption, whereas the quantum yield (QY) of CDs remains at a relatively low level. Herein, CDs exhibiting strong blue photoluminescence (PL) with an ultra-high QY (up to 94.4%) were prepared via a simple one-step microwave-assisted route using citric acid (CA) and o-phenylenediamine (o-PD) as precursors. The operating conditions, including reaction time, solvent species, amount of solvent, and precursor molar ratio, were optimized. The CDs synthesized within 3.5 min of microwave heating in ethylene glycol (EG) at a CA-to-PD molar ratio of 5:1 exhibited the highest QY (94.4%). A synergistic PL mechanism of the molecule state and carbon core state emissive centers was proposed according to the characterization results of CDs. Moreover, the proof-to-concept H2O2 fluorescent detection performances of the prepared CDs confirmed their great application potential as probe materials. Through directly mixing the CD products and H2O2, a strong PL response could be rapidly detected after merely 1 min, and the detection limit was calculated to be as low as 8.6 nM. Besides, the CDs exhibited high biocompatibility, making them suitable for in-vivo detection of H2O2. Therefore, this work provides a novel and efficient approach for synthesis of ultra-high QY CDs that can be directly applied in biological detection.

Highly efficient removal of ozone by amorphous manganese oxides synthesized with a simple hydrothermal method

Amorphous manganese oxides (MnOx) were synthesized by facile hydrothermal reactions between potassium permanganate and manganese acetate. Synthesis parameters, including hydrothermal time and temperature and molar ratio of precursors, significantly affected the ozone removal performance and structure property of MnOx. Amorphous MnOx-1.5, which was prepared at the Mn2+/Mn7+ molar ratio of 1.5 under hydrothermal conditions of 120°C and 2 hr, showed the highest ozone removal rate of 93% after 480 min at the room temperature, RH (relative humidity) = 80% and WHSV (weight hourly space velocity) = 600 L/(g·hr). The morphology, composition and structure of catalysts were investigated with X-ray diffractometer (XRD), Raman spectra, N2 physisorption, field emission scanning electron microscope (FESEM), X-ray photoelectron spectroscopy (XPS), H2 temperature-programmed reduction (H2-TPR), O2 temperature-programmed desorption (O2-TPD) and in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS). It was confirmed that high catalytic activity of amorphous MnOx for ozone removal was mainly ascribed to its abundant oxygen vacancies, high oxygen mobility and large specific surface area.

Superior CuMgFe mixed oxide catalysts engineered by tuning the redox cycle for enhancing NOx removal performance

In this work, the CuMgFe layered double hydroxides (CuMgFe-LDH) with different Cu/Mg/Fe molar ratios were fabricated, and derived catalysts (CuMgFe-LDO) were tested in the removal of NOx by selective catalytic reduction with NH3 (NH3-SCR). Cu/Mg/Fe molar ratios of LDH precursors were systematically identified to achieve optimal catalytic performance. The results showed that the denitration performances of the as-acquired catalysts were vulnerable to the Cu/Mg/Fe molar ratios. The Cu0.5Mg2.5Fe1-LDO catalyst displayed the superior activity (the NOx conversion was 80% at the range of 180–250 °C) and SO2 resistance (the NOx conversion was decreased by 18% in 8 h when 100 ppm SO2 was introduced at 210 °C). Multiple characterization techniques revealed that superior catalytic performance of Cu0.5Mg2.5Fe1-LDO could be attributed to the well dispersed active ingredients and the electron transfer between copper and iron species (Cu++Fe3+↔Fe2++Cu2+), consequently resulting in higher specific surface area, enhanced acidity, increased redox capacity, and improved cycle reactions of Cu++Fe3+↔Fe2++Cu2+. This work provides a fundamental understanding on Cu++Fe3+↔Fe2++Cu2+ synergistic effect of NH3-SCR and expand the applications of LDH in the field of low-temperature de-NOx.

Precursor concentration effects on crystallite size and enzyme immobilization efficiency of Enzyme@ZIF-8 composite

Composites of zeolitic imidazolate framework-8 (ZIF-8) and biomolecules have garnered much attention because the environmental tolerance of biomolecules is enhanced in the composites with ZIF-8. Those composites are formed easily by dissolving biomolecules with precursors of ZIF-8 in an aqueous solution. However, correlation between the composites’ properties and forming conditions remains unclear. In this study, we specifically examined composites of ZIF-8 and an enzyme (glucose oxidase): a much-researched composite for application purposes. For such composites, the crystallite size dependence of ZIF-8 on prepared molar ratio of precursors (2-methyimidazole / Zn ion, i.e., Hmim/Zn) was assessed and compared to that found in an earlier study for pure ZIF-8 without seeding. Results show that the ZIF-8 crystallite size decreased along with the decrease of the molar ratio of precursors. This correlation is opposite to that in cases of pure ZIF-8. Thus, the formation process of ZIF-8 in presence of enzyme is supposed to be much different from that of pure ZIF-8, and such process was discussed focusing on the pH-dependent coordination state of Zn ion in preformed amorphous phase of composite. Furthermore, the molar ratio of precursors affected the enzyme immobilization efficiency. Along with molar ratio of precursors, variations of counter anion of Zn were also investigated and discussed.

A highly efficient SAPO-34 catalyst for improving light olefins in methanol conversion: Insight into the role of hierarchical porosities and tailoring acid properties based on in situ NH3-poisoning

Hierarchical SAPO-34 zeolites with tunable porosity were hydrothermally synthesized by modulating the Si/Al molar ratios of the gel precursors, and the morphologies of SAPO-34 crystals gradually evolve from well-dispersed ultra-small nanocrystals to compactly polycrystalline aggregates, and to analogous polycrystallinites but adhered with minute amorphous debris by increasing the Si/Al ratio ranging from 0.20 to 0.67. The catalytic tests during methanol-to-olefins (MTO) reaction indicate that the Hier-SAPO-34-0.20 (Si/Al = 0.20) catalyst constructed by loosely nano-sized crystals centered at 50 nm presents prominent catalytic performances with about 2.5 times prolonged catalytic longevity and around 10 % improvement for the selectivity toward light olefins (ethylene and propylene) as compared to a reference catalyst. More interestingly, when Hier-SAPO-34-0.20 catalyst was in situ pretreated with NH3 flowing, the selectivity of light olefins can be greatly increased by 18.1 % at the initial stage and the corresponding even selectivity with time-on-stream can be elevated by 6.9 %. It founds that in situ NH3-poisoned catalysts with improved light olefins selectivity are also suitable for ZSM-5 zeolite. These results reveal that the weakened strong acid sites modified by NH3-poisoning play a pivotal role in suppressing the undesired hydrogen transfer reactions and thus giving a high selectivity for light olefins. This work highlights the importance of acidity fine-tailoring by in-situ NH3-poisoning strategy on hierarchical zeolites for the improvement of light olefin selectivity, which would be valuable guidance for industrial applications.

Effect of solution pH, precursor ratio, agitation and temperature on Ni-Mo and Ni-Mo-O electrodeposits from ammonium citrate baths.

The induced co-electrodeposition of Ni and Mo is a complex process, where metallic Ni-Mo alloys and Ni-Mo-O composites can originate from the complete and partial reduction of Mo respectively. By adjusting electrolyte compositions and electrodeposition parameters, various metallic, metal/oxide composite, and oxide thin films of Ni-Mo and Ni-Mo-O were electrodeposited from ammonium citrate baths. Ni-ammonia complexes, which play a critical role in promoting the deposition of metallic Ni-Mo alloys, were enhanced at alkaline pH (i.e., 8–10) and lower temperature (i.e., 25–45°C). Moreover, the electrochemical reduction of Ni is under mass transfer limitation, so the deposited Mo content decreased with increasing agitation. On the other hand, higher Mo content can be achieved by relatively higher citrate concentration and larger Mo-to-Ni precursor molar ratio. However, a critical molar ratio of metal precursor resulted in transition from alloy to composite due to Ni inducing the reduction of Mo.

Ultrathin single-crystalline perovskites: Toward large area wafers

The growth of large-area ultrathin single-crystalline wafers of methylammonium lead bromide is investigated on a hole transport layer using a diffusion-facilitated inverse temperature crystallization method. It is shown that, in addition to the hydrophobic confining layers, optimized precursor molar ratio and growth temperature are essential for realizing large-area single-crystalline wafers of device-friendly thickness in the range of 20–30 µm. The necessity of the hydrophobic layer for the realization of large-area wafers using the space confined crystal growth method is explained from consideration of the occurrence of heterogeneous nucleation. Space-charge limited current studies of the device fabricated with the synthesized single-crystal wafer show excellent charge transport mobility of 2.12 cm2/vs and a low trap-state density of 1.34 ⋅ 1011 cm−3.