Solid-state Synthesis Method Research Articles

Remarkable upgrade of hydrogen evolution activity up to 40.8 folds and mechanistic investigation of expediting charge transfer achieved by Bi2O3-modified TiO2 photocatalyst

Targeting on significantly promoting the hydrogen generation activity of titanium dioxide-based photocatalysts without the modification of noble metals by a straightforward synthetic strategy, simultaneously unveiling the photocatalytic mechanism of expedited charge transfer in photocatalyst are necessary but remains challenging. In this work, Bi2O3-modified TiO2 nanocomposite materials were directly synthesized via employing a solid-state synthesis method at mild conditions. The Bi2O3–modified TiO2 photocatalyst enable to achieve a remarkable hydrogen generation rate, dramatically outperforming commercial titanium oxide by 40.8 times. Photoelectric measurements were well matched with the broaden light absorption range and expedited charge transfer in photocatalyst, which are primarily responsible for the high-performance photocatalytic hydrogen evolution. The partially formed metallic Bi serves as a mediator between Bi2O3 and commercial TiO2 to facilitate photoexcited carriers’ separation and migration. The density functional theory simulations were further executed to calculate the differential charge distribution. It successfully unveils the electron transferring property (0.97 e−) in photocatalysts during photocatalytic process, which is well-matched with experiments derived from photoelectric measurements and uncovers the underlying photocatalytic mechanism. This work offers an efficient strategy for modifying the TiO2-based photocatalysts and dramatically achieving high-performance photocatalytic hydrogen evolution activity.

On the role of vanadium in the structure and properties of calcium-bismuth-sodium oxyapatite

This study explores the possibility of obtaining solid solutions with the composition Ca8BiNa(PO4)6-x(VO4)xO (0 < x ≤ 6) and investigating their physicochemical and medicobiological properties. Using solid-state synthesis method, only the composition Ca8BiNa(PO4)5·5(VO4)0·5O was obtained, while for other values of x, mixtures of apatite and secondary phases or mixtures of various vanadates and phosphates without the target apatite structure were obtained. The study considers the dimensional crystal chemical factors influencing the possibility of forming solid solutions in a wide range of compositions. The crystal structure of Ca8BiNa(PO4)5·5(VO4)0·5O was refined by the Rietveld method (a = 9.45154(37) Å, c = 6.93659(28) Å, V = 536.638(47) Å3, R-Bragg = 3.718 %) and confirmed by group analysis of the IR spectrum. Standard MTT test showed that this substance is not cytotoxic at dilutions of 1:2 and higher. No bactericidal activity against S. aureus and E. coli cultures was observed.

Synthesis and Characterization of Vanadium Doped Hexagonal Rubidium Tungsten Bronze

Attempts have been made to synthesize vanadium doped rubidium hexagonal tungsten bronzes with the nominal composition RbxVyW1-yO3 (x = 0.30, 0.25, and 0.0 ≤ y ≤ x). The samples were synthesized using the solid state synthesis method in a silica glass tube under vacuum at (10-2 Torr) 700°C. The X-ray diffraction measurements reveal that a pure hexagonal tungsten bronze (HTB) phase can be formed with a 60% replacement of W5+ by V5+. The systematic incorporation of vanadium into the HTB lattice, as well as the reduction of V/W-O bond lengths in the xy plane and the lengthening of these bonds in the crystallographic c direction, are also revealed by Rietveld structure refinement of XRD data. The XRD results are supported by FTIR absorption spectra of the oxidized phases. Furthermore, an absorption signature develops as a function of y and exhibits a considerable increase in intensity with the eventual replacement of W5+ by V5+, showing a large decrease in the metallic like contribution and revealing the compounds' nonmetallic nature. Elemental analysis indicates good agreement with nominal values, demonstrating that vanadium was systematically incorporated into the RbxVyW1-yO3 system. Dhaka Univ. J. Sci. 72(1): 77-84, 2024 (January)

Screening Peptide Drug Candidates To Neutralize Whole Viral Agents: A Case Study with Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2).

The COVID-19 pandemic revealed the need for therapeutic and pharmaceutical molecule development in a short time with different approaches. Although boosting immunological memory by vaccination was the quickest and robust strategy, still medication is required for the immediate treatment of a patient. A popular approach is the mining of new therapeutic molecules. Peptide-based drug candidates are also becoming a popular avenue. To target whole pathogenic viral agents, peptide libraries can be employed. With this motivation, we have used the 12mer M13 phage display library for selecting SARS-CoV-2 targeting peptides as potential neutralizing molecules to prevent viral infections. Panning was applied with four iterative cycles to select SARS-CoV-2 targeting phage particles displaying 12-amino acid-long peptides. Randomly selected peptide sequences were synthesized by a solid-state peptide synthesis method. Later, selected peptides were analyzed by the quartz crystal microbalance method to characterize their molecular interaction with SARS-CoV-2's S protein. Finally, the neutralization activity of the selected peptides was probed with an in-house enzyme-linked immunosorbent assay. The results showed that scpep3, scpep8, and scpep10 peptides have both binding and neutralizing capacity for S1 protein as a candidate for therapeutic molecule. The results of this study have a translational potential with future in vivo and human studies.

Effects of Sodium Vacancies and Concentrations in Na3SO4F Solid Electrolyte.

The sodium-rich solid electrolyte, Na3SO4F (NSOF), holds promise for eco-friendly and resource-abundant energy storage. While the introduction of heterovalent dopants has the potential to enhance its suitability for battery applications by creating Na vacancies, the effect of vacancies and sodium concentrations on sodium conduction remains unclear. In this work, Mg2+ was introduced into Na+ sites in Na3SO4F, generating sodium vacancies with different contents by using solid-state synthesis method. Among the resulting materials, Na2.96Mg0.02SO4F exhibited an ionic conductivity that is two-order-of-magnitude higher than NSOF at 298 K. Notably, as the sodium concentration decreased, the ionic conductivity also declined, revealing an equilibrium between Na vacancies and concentrations. To further investigate the influence of sodium concentration, excess Na+ was introduced into NaMgSO4F, which inherently possesses a lower sodium content by using solid-state synthesis method. However, this adjustment only led to an approximately one-order-of-magnitude enhancement in optimal ionic conductivity at 298 K. Combined with an in situ X-ray diffraction analysis, our findings underscore the greater sensitivity of sodium conduction to variations in sodium vacancies. This study paves the way for the development of ultrafast sodium ion conductors, offering exciting prospects for advanced energy storage solutions.

Tolerance Factor and Phase Stability of the KCoO2-Type AMN2 Nitrides.

In order to help understand the structural stability of KCoO2-type ternary nitrides AMN2, referring to perovskite structure, a tolerance factor t is proposed to describe the size effect on the phase/symmetry options of the experimentally accessible AMN2 nitrides. This leads to a range of t values above 0.946 for structurally stable KCoO2-type AMN2 nitrides with t values around 0.970 for the orthorhombic and tetragonal phase boundary. In contrast, most of AMN2 nitrides exhibit α-NaFeO2-type structure with t ∼ 0.898-0.946 and cations ordered or disordered rocksalt structure while t below 0.898. Employing the proposed criterion, the structure formation for other ternary AMN2 compositions with lanthanum and alkaline earth cations for the A sites were predicted, which was testified through the synthesis attempts and complemented by formation energy evaluations. The efforts to synthesize the ternary Lanthanide and alkaline earth-based AMN2 nitrides were unsuccessful, which could associate the structural instability with the large formation energies of lanthanide nitrides LaMN2 and the greater tolerance factor of 1.048 for BaTiN2. The experimentally already synthesized AMN2 nitrides could be categorized into three types with different tolerance factors, and scarce AMN2 nitrides with lower formation energies would be accessible using different synthetic routes beyond the traditional solid-state synthesis method.

Graphene oxide-induced CuO reduction in TiO2/CaTiO3/Cu2O/Cu composites for photocatalytic degradation of drugs via peroxymonosulfate activation

Contamination of water bodies is a global environmental and human health issue. Conventional water treatment systems cannot efficiently eliminate organic contaminants, particularly drugs. Photocatalysis is a promising, environmentally friendly oxidation process for the removal of such compounds. A key point is the choice of material to be used as photocatalyst. Here, TiO2/CaTiO3/Cu2O/Cu composites were fabricated by adding different amounts (x) of graphene oxide (GO) (x wt% = 1, 3, and 5 %) to CaCu3Ti4O12 powder using the solid-state synthesis method. The produced pellets were sintered under inert nitrogen atmosphere at 1100 °C for 3 h. X-ray diffraction analysis showed that the Cu metal amount was increased upon GO addition, and the UV–Vis diffuse reflectance spectroscopy showed that the spectral response was extended to the visible range. Then, high performance liquid chromatography assessment of paracetamol degradation by a photocatalytic cell using TiO2/CaTiO3/Cu2O/Cu composites with different GO amounts showed that the removal efficiency was increased upon introduction of 0.5 mM peroxymonosulfate (PMS) as active component to generate SO4‾ radicals. After 3 h under visible light, 96 % of 10 ppm paracetamol was degraded by the composite with 3 % of GO (1 cm2 surface photocatalyst) compared with 50 % by the composite without GO in the same experimental conditions (PMS in 210 mL of aqueous solution). Free radical trapping and the acute toxicity of potential degradation by-products were also investigated. Our results indicate that TiO2/CaTiO3/Cu2O/Cu with 3 % GO displays long-term stability and durability for the photocatalytic removal of pharmaceutical pollutants from wastewater.

Formation, Stability, and Crystallinity of Various Tricalcium Aluminate Polymorphs.

Tricalcium aluminate is an important phase of Portland clinker. In this paper, three polymorphs of C3A were prepared by means of the solid-state synthesis method using intensive milling of the raw material mixture which was doped with various amounts of Na2O and sintered at a temperature of 1300 °C for 2 h. The final products were evaluated through X-ray diffraction using Rietveld analysis. The effect of the Na dopant content on the change in the crystalline structure of tricalcium aluminate was studied. It was proven that the given preparation procedure, which differed from other studies, was close to the real conditions of the formation of Portland clinker, and it was possible to prepare a mixture of different polymorphs of calcium aluminate. Fundamental changes in the crystal structure occurred in the range of 3-4% Na, when the cubic structure changes to orthorhombic. At a dosage of Na dopant above 4%, the orthorhombic structure changes to a monoclinic structure. There are no clearly defined boundaries for the existence of individual C3A phases; these phases arise at the same time and overlap each other in the areas of their formation at different Na doses.

Eco-friendly solid-state synthesis of Na-promoted Mn-Fe/ZrO2 catalyst for Fischer-Tropsch synthesis

The advancement of large-scale and environmentally-friendly solid-state synthesis methods is of paramount importance for the production of precipitated catalysts, notably Fe-based catalysts utilized in Fischer-Tropsch synthesis (FTS). In this study, we present an innovative solvent-independent, wastewater-free solid-state approach for the synthesis of highly efficient Fe/ZrO2 catalysts, elucidating the mechanisms of promotion within this specific methodology. The prepared catalysts underwent rigorous evaluation under industrially-relevant FTS conditions (230–270 °C, 20 bar, and WHSV = 5400 mL/(gcat⋅h)). A comprehensive suite of characterization techniques was employed to establish the intricate interplay between catalytic activity and structural attributes. We meticulously examined the impact of Na as an alkali promoter and the role of transition metals (Cu and Mn) in enhancing FTS catalytic performance. The catalytic outcomes obtained clearly demonstrate the pivotal role of the synergistic interaction between Mn and Na within the Na-Mn-Fe/ZrO2 catalyst system in driving the FTS reaction. This synergism significantly enhances FTS performance, yielding an impressive CO conversion rate (89.91 %) while maintaining low selectivity to CH4 (7.75 %). The incorporation of Mn and Na into the catalyst matrix enhances the dispersion of Fe2O3, thereby improving the reducibility of Mn/Fe oxides and elevating the electron density on the catalyst surface. These factors facilitate the formation of active Hägg iron carbide (χ-Fe5C2), stimulating chain propagation and ultimately leading to the generation of valuable C5+ hydrocarbon products, which underscores its potential as an optimal candidate for future industrial applications in Fe-based Fischer-Tropsch synthesis.

Influence of the La0.2Sr0.7Ti0.95Ni0.05O3 (LSTN) Synthesis Method on SOFC Anode Performance

Solid oxide fuel cells are characterized by a high efficiency for converting chemical energy into electricity and fuel flexibility. This research work focuses on developing durable and efficient anodes for solid oxide fuel cells (SOFCs) based on exsolving nickel from the perovskite structure. A-site-deficient La- and Ni-doped strontium titanates (La0.2Sr0.7Ti0.95Ni0.05O3−δ, LSTN) were synthesized using four different techniques and mixed with Ce0.8Gd0.2O2−δ (GDC) to form the SOFC anode. The synthesis routes of interest for comparison included solid-state, sol-gel, hydrothermal, and co-precipitation methods. LSTN powders were characterized via XRD, SEM, TPR, BET and XPS. In situ XRD during reduction was measured and the reduced powders were analyzed using TEM. The impact of synthesis route on SOFC performance was investigated. All samples were highly durable when kept at 0.5 V for 48 h at 800 °C with H2 fuel. Interestingly, the best performance was observed for the cell with the LSTN anode prepared via co-precipitation, while the conventional solid-state synthesis method only achieved the second-best results.

Effect of Cu2+ doping on fluorescence of Cs2ZnCl4 powder prepared by solid-state synthesis

Recently Cu-doped all-inorganic zero-dimensional (0D) metal halides Cs2ZnX4 (X = Cl, Br) have attracted many researchers due to their excellent fluorescence (FL) performance and low toxicity compared to lead-based perovskites. Although these 0D metal halides nanocrystals or small-sized single crystals are prepared via solution methods in most of the reports, we used the solid-state synthesis method to get Cu-doped Cs2ZnCl4 powders and characterized their FL properties. The results and analysis indicate that Cu2+ can be doped in Cs2ZnCl4 up to 12 at.%, which enhances the FL of Cs2ZnCl4 powder. The photoluminescence quantum yield (PLQY) at 480 nm rises from 1.11 % (undoped) to 20.06 % (6 at.% Cu doping). A modified triplet self-trapped excitons mechanism is presented to explain the enhanced Cu−doped Cs2ZnCl4 powder.

Controlling the europium oxidation state in diopside through flux concentration.

This paper explores the connection between the H3BO3 flux concentration and the co-existence of Eu2+ and Eu3+ dopants within CaMgSi2O6 crystals (diopside). The samples were synthesised using a solid-state synthesis method under varying atmospheric conditions, including oxidative (air), neutral (N2), and reductive (H2/N2 mixture) environments. Additionally, some materials underwent chemical modification by partially substituting Si4+ with Al3+ ions acting as charge compensation defects stabilizing Eu3+ luminescence. Depending on the specific synthesis conditions, the materials predominantly displayed either the orange-red luminescence of Eu3+ (under oxidising conditions) or the blue luminescence of Eu2+; however, the comprehensive results confirmed the co-existence of Eu3+/Eu2+ luminescence in both cases. This work shows that varying flux concentrations added during synthesis significantly affect the relative strength of Eu2+ and Eu3+ emissions in a manner dependent on the synthesis atmosphere. The emission of Eu2+ increases with a higher flux concentration in materials synthesised under oxidative and neutral atmospheres independent of the chemical modification. In contrast, for materials obtained under a reductive atmosphere, the changes in the Eu3+ emission intensity depended on the presence or absence of Al3+ ions namely the increase of flux increased the Eu3+ intensity in the case of unmodified materials and decreased in the Al-modified ones. All observed effects were qualitatively explained considering the double role of the flux in the studied system, which besides facilitating the diffusion of chemical species during synthesis acts as a charge compensating agent by creating B'Si centres stabilizing Eu3+ emission.

Rapid and efficient mechanosynthesis of alkali and alkaline earth molybdates

Mechanochemistry provides a convenient and efficient route for synthesizing high purity alkali and alkaline earth heptamolybdates and trimolybdates in high yields.

Phase relations between Na3Nd(BO3)2, Na3Nd2(BO3)3, NdBO3 and their luminescence properties

The Na3Nd(BO3)2-NdBO3 phase diagram was investigated by the solid-state synthesis and DSC methods. Na3Nd(BO3)2, Na3Nd2(BO3)3 and NdBO3 were grown by spontaneous crystallization from the Na2O- B2O3-NaF flux. Typical Nd3+ luminescence of 4F3/2  4I9/2 and 4F3/24I11/2 electron transitions at 875 nm and 1054 nm were registered. Maximum integral intensity of the luminescence was observed for Na3Nd2(BO3)3 crystals, more than twice that of NdBO3, Na3Nd(BO3)2.

Scalable solid-state synthesis of 2D transition metal oxide/graphene hybrid materials and their utilization for microsupercapacitors.

Two-dimensional metal oxide (MO) nanostructures have unique properties compared with their bulk or 0D and 1D (nanoparticle and nanowire) counterparts. Their abundant surface area and atomically thin 2D structure are advantageous for their applications in catalysis and energy, as well as integration with 2D layered materials such as graphene and reduced graphene oxide (rGO). However, fast and scalable synthesis of 2D MOs and their nanocomposites remains challenging. Here, we developed a microwave-assisted solid-state synthesis method for the scalable generation of 2D MOs and 2D MO/rGO nanocomposites with tunable structure and composition. The structures and properties of 2D Fe2O3 and 2D ZnO as well as their nanocomposites with rGO were systematically investigated. The excellent electrochemical properties of such 2D MO/rGO nanocomposites also enable us to use them as electrode materials to fabricate microsupercapacitors. This work provides new insights into the scalable and solid-state synthesis of 2D nanocomposites and their potential applications in catalysis, energy conversion and storage.

Understanding the Thermal Stability of Li-Rich Disordered Rock-Salt Oxyfluorides

Li-rich disordered rock-salt oxyfluorides (DRS) are a new class of cathode material with unprecedented electrochemical properties. [1,2] DRS materials have already gained popularity by showing high reversible discharge capacity by substituting oxygen (O) with fluorine (F). They are a possible candidate of cathode materials for future high-energy Li-ion batteries with high capacity. Although DRS materials are explored widely for their structure and electrochemical performance, very little is known about their thermal stability. DRS oxyfluorides can be synthesized via solid state and mechanochemical ball milling. [3-5] The solid-state synthesis method is limited because of less fluorine solubility than the mechanochemical ball milling method; however, mechanochemical ball milling produces metastable materials. Few reports utilized thermal treatment on DRS to obtain structural stability and better capacity retention than the pristine DRS. [5,6] The in-depth understanding of the inherent stability of the DRS materials on thermal treatment remains poorly understood. [7] To address this gap, we investigated the thermal stabilities of Li2MO2F stoichiometries with a variety of M (M= Mn, Ni, and Co) and defined the structural transformations at different temperatures, from changes in the local structure of the oxyfluoride to decomposition into other phases, using X-ray diffraction, NMR and X-ray absorption spectroscopy. In this presentation, we will show how thermal treatments affect chemical and structural features by utilizing unique spectral characteristics. Additionally, we will discuss a complete understanding of these thermally treated F-rich phases' better electrochemical performance and capacity retention as battery cathode materials.

Impact of Short Chain Polymer in Ionic Conductivity for Polymer Solid-State Electrolyte Towards Inter-/Intramolecular O-H Bond

Poly(ethylene oxide) (PEO) was first developed as a conducting polymer over a half-century ago and is still the most fascinating electrolyte matrix to use in solid-state batteries. Although thousands of articles have been published on the conductivity of various PEO-based solid-state electrolytes, none of the studies involved a higher EO-to-salt ratio up to 85 to 1. In this study, solid polymer electrolytes (SPE) based on the PEO-PEG complex with Sodium(I) Bis(trifluoromethanesulfonyl)imide (NATFSI) were prepared using the solid-state synthesis methods. The measurement using the Electrochemical Impedance Spectroscopy (EIS) technique demonstrated that EO70Na - 9PEO:3PEG has the most optimum PEO-PEG-NATFSI electrolyte system with conductivities of 0.01 mS/cm and 0.13 mS/cm at 25 °C and 50 °C, respectively. As reported in published articles, the conductivity of the EO to Na ratio started to decline from 15:1 to 25:1 with the dropped in NATFSI concentration. Further decline of Na concentration with the addition of EO from 40 to 70 ratio indicates a new increasing trend for the conductivity series, which result in a bimodal graph distribution. Fourier transform infrared (FTIR) spectral studies for PEO-PEG-based SPE revealed that vibrational changes of intramolecular -OH change as the concentration of short-chain polymer backbone and salt varies. The Raman spectral studies for PEO-PEG-based SPE proposed that the percentage of bis(trifluoromethane)sulfonimide anion (TFSI- anions) increases with the increase in ratio from 15 to 70 of EO to Na. It is proposed that a higher percentage of both intramolecular -OH and TFSI- anions are crucial in providing high conductivity value. The structure of complexed PEO-PEG-based SPE from XRD suggested that the crystalline domain of SPE decreased with the smaller amount of NATFSI.

Fabrication and characterization of highly responsive hydrogen sensor based on Fe2O3:ZnO nanostructured thin film

This work aimed to manufacture a highly sensitive hydrogen gas sensor based on Fe2O3:ZnO thin film. The Fe2O3:ZnO based sputtering target was synthesized by a solid-state synthesis method. Gas-sensitive thin films were deposited onto the alumina substrate by the high-frequency (RF) magnetron sputtering method. The thickness of the sensing film was measured and the morphology of the sensing layers was studied. The Fe2O3:ZnO sensor showed the highest hydrogen gas response at 100 ᵒC and the operating temperature of 150 ᵒC was selected as the optimum working temperature. The sensor showed sensitivity even to extremely low concentrations of hydrogen (100 ppm), where the response was 4.6. The sensing parameters of the fabricated sensor confirm that the Fe2O3:ZnO material may become an excellent nanostructure for the detection of low concentrations of hydrogen.

Investigation of crystal structural and magnetic properties of titanium doped Pr0.67Ba0.33MnO3 perovskite manganites

Pr0.67Ba0.33Mn1-xTixO3 (x = 0 and 0.02) were synthesized using a conventional solid-state synthesis method to investigate the effect of Ti substitution on their magnetic and electrical transport properties. All the samples were structurally evaluated by XRD diffraction Rietveld refinement method which showed an increase in unit cell volume with increasing Ni content, indicating that Ti is partially substituted at Mn. Scanning electron microscopy (SEM) and energy dispersive X-tray (EDX) are used to examine the surface morphology and identified elements in the samples' compounds. Fourier transform infrared spectroscopy (FTIR) reveals that all the samples exhibit a transmission band in the range of 590 cm-1 - 610 cm-1 . For x = 0, magnetization measurements showed paramagnetic (PM) to ferromagnetic (FM) transition at the transition temperature, TC ∼ 213 K. For Ti-substituted samples, ferromagnetic (FM) to PM transition was reduced with Curie temperature (TC), decreasing from 213 K (x = 0) to 205 K (x = 0.02). On the other hand, the M(H) showed the presence of a linear graph for x = 0 and x = 0.02 which may be related to the presence of paramagnetic at room temperature.

Features of Structures and Ionic Conductivity of Na3Fe2(PO4)3 Polycrystals Obtained by Solid Phase and Melt Methods

This article investigates the structures and conductive properties of polycrystals of Na3Fe2(PO4)3 obtained by solid-state and melt synthesis methods using concentrated optical radiation. It has been established that in the melt synthesis method, the material is synthesized under significantly non-equilibrium thermodynamic conditions, leading to the creation of deformations in the sample, which contribute to the enhancement of ionic conductivity. Additionally, the synthesis duration is reduced by half. Through a comparative assessment of the structural parameters and conductive properties of these materials, it is demonstrated that polycrystals obtained by the melt method exhibit better texture and higher ionic conductivity. The occurrence of deformations during the synthesis of α-Na3Fe2(PO4)3 under high temperature-gradient conditions indicates the elasticity of the crystalline framework {[Fe2(PO4)]3−}3∞. It is concluded that the non-equilibrium thermodynamic conditions of α-Na3Fe2(PO4)3 synthesis promote the formation of deformations in the crystalline structure of polycrystals, leading to a partial increase in symmetry and ionic conductivity.