Post-synthesis Treatment Research Articles

Synthesis of SrTiO3 and Al-doped SrTiO3via the deep eutectic solvent route

SrTiO3 and aluminum-doped SrTiO3 are synthesized by calcination of metal salts dissolved in a deep eutectic solvent (DES) without any post-synthesis treatment.

Red-emissive nanocrystals of Cs4MnxCd1-xSb2Cl12 layered perovskites.

Layered double perovskites are currently being investigated as emerging halide-based materials for optoelectronic applications. Herein, we present the synthesis of Cs4MnxCd1-xSb2Cl12 (0 ≤ x ≤ 1) nanocrystals (NCs). X-ray powder diffraction evidences the retention of the same crystal structure for all the inspected compositions; transmission electron microscopy revealed monodisperse particles with a mean size between 10.7 nm and 12.7 nm. The absorption spectra are mostly determined by transitions related to Sb3+, whereas Mn2+ induced a red emission in the 625-650 nm range. The photoluminescence emission intensity and position vary with the Mn2+ content and reach the maximum for the composition with x = 0.12. Finally, we demonstrate that the photoluminescence quantum yield of the latter NCs was increased from 0.3% to 3.9% through a post-synthesis treatment with ammonium thiocyanate. The present work expands the knowledge of colloidal layered double perovskite nanocrystals, stimulating future investigations of this emerging class of materials.

The synthesis and electrical transport properties of carbon/Cr2GaC MAX phase composite microwires.

While MAX phases offer an exotic combination of ceramic and metallic properties, rendering them a unique class of materials, their applications remain virtually hypothetical. To overcome this shortcoming, a sol-gel based route is introduced that allows access to microwires in the range of tens of micrometers. Thorough structural characterization through XRD, SEM, EDS, and AFM demonstrates a successful synthesis of carbonaceous Cr2GaC wires, and advanced low temperature electronic transport measurements revealed resistivity behavior dominated by amorphous carbon. The tunability of electronic behavior of the obtained microwires is shown by a halide post-synthesis treatment, allowing purposeful engineering of the microwires' electrical conductivity. Raman studies revealed the polyanionic nature of the intercalated halides and a slow decrease in halide concentration was concluded from time-dependent conductivity measurements. Based on these findings, the process is considered a viable candidate for fabricating chemiresistive halogen gas sensors.

Ambient environment induced synergetic improvement in morphology and iodine vacancy passivation by MAI surface engineering in mixed-cation lead mixed-halide (FA0.85MA0.15PbI0.55Br0.45) perovskite solar cells

Perovskite solar cells (PSCs), have made tremendous progress but are still far away from theoretically estimated power conversion efficiencies (PCEs) and commercialization. Defects present in the perovskite materials and at various interfaces (between ETL/HTL and perovskite) in devices are inhibiting the performance to get closer to the theoretical limits, whereas the controlled atmosphere fabrication is creating a bottleneck in large scale production. Therefore, meticulous attention is required to overcome these problems. In this work, we report a very simple, facile and efficient post-synthesis surface treatment with methyl ammonium iodide (MAI) for surface and grain boundary defect passivation in the PSCs processed in fully ambient atmosphere. Ambient atmosphere, MAI surface treatment showed synergetic improvement, firstly it healed the defects (iodine trap states) existing on the surface/interface and grain boundaries and secondly increased the grain size, thereby reducing the defect sites. The improved crystallinity, morphology and decreased defects, reduced the trap density and non-radiative recombination losses leading to fast charge extraction. As a result, planar (n-i-p) PSCs, passivated with optimum MAI concentration, showed significantly higher boost (14%) in the power conversion efficiency (PCE) compared to previous MAI surface treatments, where no morphological changes were observed.

Complete chemical and structural characterization of selenium-incorporated hydroxyapatite

Hydroxyapatite (HAp) has long been used as synthetic bone tissue replacement material. Recent advances in this area have led to development of dual-functional bioceramics exhibiting high biocompability/osteoconductivity together with the therapeutic effect. Selenium, in that respect, is an effective therapeutic agent with promising antioxidant activity and anticancer effects. In this study, selenium-incorporated hydroxyapatite (HAp:Se) particles have been synthesized by modified aqueous precipitation method using calcium (Ca(NO3)2·4H2O) and phosphate ((NH4)2HPO4) salts and sodium selenite (Na2SeO3). The effects of selenium incorporation and post-synthesis calcination treatment (900–1100 °C) on physical, chemical properties and crystal structure of resultant HAp powders have been investigated. Complete chemical identification was performed with spectroscopical analyses including Fourier transform infrared and x-ray photoelectron spectroscopy to elucidate the mechanism and chemical nature of selenium incorporation in HAp. Meanwhile, detailed x-ray diffraction studies by Rietveld refinement have conducted to explain changes in the HAp crystal structure upon selenium incorporation.

Influence of Oxygen Dopants on the HER Catalytic Activity of Electrodeposited MoOxSy Electrocatalysts

Amorphous, polymeric molybdenum sulfide has attracted significant attention as a non-platinum group electrocatalyst for the hydrogen evolution reaction (HER). To elucidate the influence of oxygen incorporation on molybdenum sulfide catalysts, MoOxSy electrocatalysts were synthesized via a potentiostatic electrodeposition method. The presence of oxygen and the associated molybdenum oxidation state were modified by postsynthesis treatments of air exposure, annealing in an inert atmosphere, and annealing in a sulfur flux. The as deposited sample exhibited the best performance, requiring only 171 mV to reach a cathodic current density of 10 mA/cm2. While the modified films exhibited worse HER performance compared to the as deposited sample, by utilizing extensive X-ray photoelectron spectroscopy studies, we highlighted the importance of the Mo5+ oxidation state while identifying a previously unreported state within MoOxSy catalysts between Mo4+ and Mo5+.

Post-synthesis treatment of graphene oxide/silica particles nanocomposite with piranha acid for functionalization

The discovery of 2D materials has led researchers to a broad material platform. Their excellent physical, chemical and electrical properties along with the layered structure have found applications in various fields. However, these materials also have limitations and functionalisation is one of the mechanisms that improves their properties. In our previous work, we observed surface-enhanced Raman spectroscopy (SERS) after covalent attachment of protein to the graphene nanocomposite where piranha acid was used to generate the functional groups. The current work describes the synthesis and characterisation of a graphene oxide-silica particle nanocomposite after piranha acid treatment at different time intervals. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy were performed to indicate structural changes which facilitated the protein attachment. The SEM and TEM results indicated that the sample which was piranha acid activated for 3 min displayed better arrangement of silica particles on the graphene sheets with exposition of the highest net surface area in the graphene sheet, compared to the other samples and determined to be the best functionalised nanocomposite for further applications. Morphological instability of the graphene sheets and clustering of silica particles were observed in the samples treated for more than 3 min. Interestingly, the same degree of graphitisation was observed in all the samples when I D /I G ratios {(≤0.99) ≠ 0} were determined by Raman spectroscopy.

Promoting effect of post-synthesis treatment strategy on NH3-SCR performance and hydrothermal stability of Cu-SAPO-18

The influence of post-synthesis treatment with MnSO4, (NH4)2SO4 and (NH4)2S2O8 blended solution on NH3-SCR activity and hydrothermal stability of Cu-SAPO-18 (Cu-18) was investigated. Via adjusting the mixed solution concentration, the optimal Mn/Cu-18-Ⅲ with higher deNOx activity and hydrothermal stability was acquired. Based on the optimal Mn/Cu-18-Ⅲ, diverse metal cations such as La3+, Ce3+, Sm3+ or Zr4+ were simultaneously doped into Cu-18 during Mn2+ and NH4+ blended solution treatment to further promote its catalytic performance before and after hydrothermal treatment. The doping with Sm could improve the NH3 activity and hydrothermal stability of Mn/Cu-18-Ⅲ to the greatest extent. The elevation of acid sites content and the disappearance of CuO species in Mn/Cu-18-Ⅲ caused the enhancement of its NH3-SCR activity. More Cu2+ and acid sites in SmMn/Cu-18-Ⅲ were responsible for its higher NH3-SCR activity than Mn/Cu-18-Ⅲ. The decline of vulnerable Brønsted acid sites by substituting Mn2+ or Sm3+ for H+ could restrain the hydrolysis of Cu-18 and enhance the hydrothermal stability of Cu-18 during hydrothermal treatment. The mechanism analysis demonstrates that the fresh and aged Cu-18, Mn/Cu-18-Ⅲ and SmMn/Cu-18-Ⅲ follow both Eley–Rideal (E–R) and Langmuir–Hinshelwood (L–H) mechanism in NH3-SCR reaction, with the L–H mechanism being more dominated.

Defect Sites in Zeolites: Origin and Healing.

This paper deals with the synthesis conditions–defect formation relationship in zeolites. Silicalite‐1 (MFI‐type) is used as a model material. Samples synthesized from a system with high basicity (at 100 °C), a system with moderate basicity (at 150 °C), and a fluoride‐containing system in neutral medium (at 170 °C) are compared. Well‐crystallized materials with sizes ≈0.1, 1–10, and 30–40 µm are obtained. The samples are analyzed by complementary methods providing information on the short‐ and long‐range order in the zeolite framework. A strong correlation between the number of point defects in the zeolite framework and preparation conditions is established. Silicalite‐1 synthesized under mild synthesis conditions from a highly basic system exhibits a larger number of framework defects and thus low hydrophobicity. Further, the calcined samples are subjected to aluminum and silicon incorporation by postsynthesis treatment. The Al/Si incorporation in the zeolite framework and its impact on the physicochemical properties is studied by XRD, TEM/SEM, solid‐state NMR, FTIR, and thermogravimetric analyses. The defects healing as a function of the number of point defects in the initial material and zeolite crystal size is evaluated. The results of this study will serve for fine‐tuning zeolite properties by in situ and postsynthesis methods.

A mild post-synthesis oxidative treatment of Pd-In/HOPG bimetallic catalysts as a tool of their surface structure fine tuning

Intermetallic Pd-In particles formation and their deliberate post-synthesis modification by oxidative treatments under carefully controlled conditions have been investigated by the combination of synchrotron radiation-based photoelectron spectroscopy and scanning tunneling microscopy. It is demonstrated that a prolonged contact of Pd-In/HOPG samples with air led to a partial decomposition of intermetallic particles giving rise to the formation of Pd0 species homogeneously distributed over bulk, surface indium hydroxide and subsurface indium oxide. A mild oxidative treatment (0.25 mbar O2, 150 °C) leads to the indium surface segregation and formation of indium oxide homogeneously distributed over the depth and metallic Pd predominantly localized in the interior. The indium oxide component becomes surface localized upon further temperature increase to 200 °C.

Mesoporous onion-like carbon nanostructures from natural oil for high-performance supercapacitor and electrochemical sensing applications: Insights into the post-synthesis sonochemical treatment on the electrochemical performance

Although onion-like carbon nanostructures (OLCs) are attractive materials for energy storage, their commercialization is hampered by the absence of a simple, cost-effective, large-scale synthesis route and binder-free electrode processing. The present study employs a scalable and straightforward technique to fabricate sonochemically tailored OLCs-based high-performance supercapacitor electrode material. An enhanced supercapacitive performance was demonstrated by the OLCs when sonicated in DMF at 60 °C for 15 min, with a specific capacitance of 647 F/g, capacitance retention of 97% for 5000 cycles, and a charge transfer resistance of 3 Ω. Furthermore, the OLCs were employed in the electrochemical quantification of methylene blue, a potential COVID-19 drug. The sensor demonstrated excellent analytical characteristics, including a linear range of 100 pM to 1000 pM, an ultralow sensitivity of 64.23 pM, and a high selectivity. When used to identify and quantify methylene blue in its pharmaceutical formulation, the sensor demonstrated excellent reproducibility, high stability, and satisfactory recovery.

Post-synthesis treatment improves the electrical properties of dry-spun carbon nanotube yarns

Researchers expect carbon nanotube (CNT) yarns as an alternative to metallic wiring. However, the electrical properties of CNT yarns remain relatively low, necessitating further improvement. In this study, we fabricated CNT yarns by dry-spinning and performed several post-synthesis treatments to enhance the electrical properties. Polymer solution impregnation increased the electrical conductivity 1.82 × and the current capacity 1.58 × , attributable to densification of the CNT yarn bundles. Graphitization (GT) increased the electrical conductivity 2.58 × and the current capacity 1.83 × , attributable to purification of the crystalline structure. Iodinemonochloride/dichloromethane (ICl/DCM) doping increased the electrical conductivity 1.79 × and the current capacity 1.31 × , attributable to the increased electron carrier density. We achieved further enhancement by a two-step treatment—GT and ICl/DCM doping—resulting in a 4.88 × increase in conductivity and reaches a maximum of 5.12 × 105 S/m. We observed greater doping effects after GT, which increased the electrical conductivity 1.89 × , whereas doping for pristine CNT yarn only increased the electrical conductivity 1.79 × . The X-ray photoelectron spectra of CNT yarn in each step indicated a positive relationship between the peak area of the π–π∗ transition component and the electrical conductivity. Therefore, we hypothesize that purification of the crystalline structure increases the electron carrier density by doping.

Rapid pore expansion of mesoporous silica-based materials using microwave irradiation and pore swelling agents

In the present work we analyze the use of microwave radiation in the presence of pore swelling agents as a post-synthesis treatment for expanding the pore size of non-calcined SiO2-based mesoporous materials. In comparison with traditional hydrothermal treatments, using microwaves decreases significantly the time required for this process and is compatible with both ionic and non-ionic surfactant pore templates (e.g. cetyltrimethylammonium bromide (CTAB) and polypropyleneglycol-based surfactants). The evolution of the mesostructural parameters has been followed with small angle X-ray scattering (SAXS), X-ray diffraction (XRD), field-emission Scanning electron microscopy (FESEM) and N2 porosimetry. In particular, this strategy allows an easy approach for post-processing non-calcined templated siliceous materials and tailoring their final pore dimensions.

Evolution of Structural and Magnetic Properties of Fe-Co Wire-like Nanochains Caused by Annealing Atmosphere.

Thermal treatment is a post-synthesis treatment that aims to improve the crystallinity and interrelated physical properties of as-prepared materials. This process may also cause some unwanted changes in materials like their oxidation or contamination. In this work, we present the post-synthesis annealing treatments of the amorphous Fe1−xCox (x = 0.25; 0.50; 0.75) Wire-like nanochains performed at 400 °C in two different atmospheres, i.e., a mixture of 80% nitrogen and 20% hydrogen and argon. These processes caused significantly different changes of structural and magnetic properties of the initially-formed Fe-Co nanostructures. All of them crystallized and their cores were composed of body-centered cubic Fe-Co phase, whereas their oxide shells comprised of a mixture of CoFe2O4 and Fe3O4 phases. However, the annealing carried out in hydrogen-containing atmosphere caused a decomposition of the initial oxide shell layer, whereas a similar process in argon led to its slight thickening. Moreover, it was found that the cores of thermally-treated Fe0.25Co0.75 nanochains contained the hexagonal closest packed (hcp) Co phase and were covered by the nanosheet-like shell layer in the case of annealing performed in argon. Considering the evolution of magnetic properties induced by structural changes, it was observed that the coercivities of annealed Fe-Co nanochains increased in comparison with their non-annealed counterparts. The saturation magnetization (MS) of the Fe0.25Co0.75 nanomaterial annealed in both atmospheres was higher than that for the non-annealed sample. In turn, the MS of the Fe0.75Co0.25 and Fe0.50Co0.50 nanochains annealed in argon were lower than those recorded for non-annealed samples due to their partial oxidation during thermal processing.

Microporous vanadosilicate films with tailorable V4+/V5+ ratio to achieve enhanced visible-light photocatalysis

This study investigates the changes induced into the photocatalytic activity under solar light irradiation upon changing the structural film properties and tailor the concentration of defects in microporous vanadosilicate AM-6 films. For this purpose, the preparation of AM-6 films with different V4+/V5+ ratios and their utilization as photocatalysts for the decomposition of MB were carried out. Two approaches were used for obtaining AM-6 films with different V4+/V5+ ratios: altering the seed layer coating technique and altering the molar water content of the secondary growth gel. It was seen that dip coating method resulted in an increase in the thickness of the films and it was presumed that the adsorption of MB by AM-6 films was the predominant factor in photocatalytic activity. The second approach of increasing the molar water content of the secondary growth gel provided an increase in the defect concentration resulting in an enhanced photocatalytic activity under the solar light. In the current study, the defect concentration of the prepared films was determined by using XPS and Raman spectroscopy techniques. Accordingly, it was determined that the samples with lower amount V4+/V5+ ratio showed better photocatalytic activity under the solar light irradiation indicating that V5+ cations are responsible for the photocatalytic activity under visible light irradiation. This work provides methods of production of microporous films showing photocatalytic activity under visible light without the requirement of any post-synthesis treatments.

An in-situ assessment of post-synthesis thermal annealing of platinum nanoparticles supported on graphene

The catalytic activity of as-synthesised nanoparticles is hindered by several factors such as impurities and lattice imperfections. Often, a post-synthesis treatment is mandatory to optimize the performance of these particles but little is known in regards to what this does to them. Here, graphene-supported platinum (Pt) nanoparticles were subjected to thermal annealing in a reductive atmosphere. Surface migration and re-structuring of the particles were observed through in-situ structural and chemical analysis. In addition, residual organic impurities were removed, though the oxide layer coating the Pt surface is not eliminated. Notwithstanding, the interaction of the nanoparticles and the substrate improved with the annealing step, and so did their electrochemically active surface area (ECSA). In these circumstances, better catalytic performance in nano-scaled Pt systems may be a result of the enhancement in ECSA and catalyst-substrate interaction, as opposed to the commonly used argument of surface oxide removal.

Synthesis of nanostructured lanthanum hexaboride via simple borothermal routes at low temperatures

Rare-earth hexaborides, especially lanthanum hexaboride (LaB6) are popular materials as thermionic cathodes. It is a great challenge to synthesise these hexaborides at a low temperature without any post-synthesis purification treatments. In this research work, we demonstrate a simple synthesis technique, namely borothermal method for preparing pure lanthanum hexaboride by reacting lanthanum oxide (La2O3) with boron (B). In this investigation, different pressed pellets were made using the starting powders mixed either by milling mildly for 30 min or high-energy milling (HEM) for 8/16 h. Later, the prepared pellets were put into a low-vacuum furnace at different temperatures. The synthesised products were characterised using X-ray diffraction (XRD), scanning electron microscope (SEM), electron dispersive spectroscopy (EDS) and a Schottky device for their structural, chemical, morphological and thermionic properties. Both synthesis methods are found to produce LaB6 with a purity above 99% at a relatively low temperature of 1250 °C. High-energy ball milling does not result in reducing synthesis temperatures, rather introduces some iron impurities. From XRD and SEM investigations, the average crystallite size of pure LaB6 prepared by borothermal methods is observed to be in the range of 225–250 nm. From thermionic emission data, partially sintered LaB6 pellets prepared from powders via the simple borothermal and the borothermal method with HEM exhibit work functions of 2.86 ± 0.05 eV and 2.64 ± 0.08 eV, respectively. The results suggest that nanostructured LaB6 with a low work function can be easily prepared at lower temperatures for applications in thermionic energy converters, high-power electron devices and photonics.

Transformation of Wurtzite ZnO to a New Triclinic Nanoporous ZnO Phase via Hydrothermal Treatment with Metformin for Designing Proton Conducting Material.

Zinc oxide is one of the most widely studied semiconductor metal oxides, which predominantly crystallizes as hexagonal wurtzite and often cubic zinc-blende phases. Here we report the transformation of the highly stable wurtzite ZnO to a new triclinic phase NZO-2 by using metformin as a template during post-synthesis hydrothermal treatment. This crystalline phase of the material NZO-2 has been identified through the refinement of the powder XRD data. NZO-2 possesses porous rod like particle morphology consisting of the self-assembly of 3-7 nm size spherical nanoparticles and interparticle nanoscopic voids spaces. NZO-2 has been surface phosphorylated and the resulting material displayed good proton conductivity. Further, NZO-2 displayed ultra-low band gap of 1.74 eV, thereby responsible for red emission under high energy laser excitation and this may open new opportunities in optoelectronic application of ZnO.

Manipulation of the Optical Properties of Colloidal 2D CdSe Nanoplatelets

Driven by the unique optoelectronic features arising from the strong quantum confinement along the thickness direction, rapid development of CdSe‐based nanoplatelets (NPL) has accomplished facile bandgap tunability over a broad spectrum via different preparation protocols or various postsynthesis treatments. The anisotropic geometry of NPLs also stimulates the exploitation of self‐assembled CdSe NPL superstructures to enhance light extraction efficiency in display technologies and achieves polarized lasing performance or even electrically pumped laser by adjusting the transition dipole orientation. Although several review articles about the general optical properties of CdSe NPLs have been published, none of them focus on the ability of spectral tunability and precise control of orientations in the solid‐state phase of CdSe NPLs. Herein, the band structure engineering approaches in the CdSe NPL family are systematically summarized and the optical properties and device performance metrics of these deliberately engineered NPLs are compared. Then, the recent advanced studies of the motivation and assembly methods of geometrically anisotropic CdSe NPL superlattices are discussed. Finally, the current challenges and future outlook on the controlled modification of optical features and the influences of the approaches in the aspect of CdSe NPL–based devices’ performance are highlighted.

Improving the thermal stability and n-butanol oxidation activity of Ag-TiO2 catalysts by controlling the catalyst architecture and reaction conditions

We demonstrate a novel methodology of encapsulating and dispersing Ag nanoparticles in a reducible, mesoporous TiO2 nanosphere to enhance thermal stability and catalytic activity for VOC oxidation. Through comparisons with surface-impregnated Ag-TiO2, which suffer from significant sintering and deactivation after aging at 550 °C, we show that encapsulation helps maintain a uniform Ag particle distribution (2−5 nm) and promotes metal-support interactions by maximizing interfacial sites, thereby improving activity and stability. In addition, we discover that subjecting the encapsulated catalyst to a post-synthesis solvothermal treatment step anchors the active metal more strongly to the support, which helps maintain superior activity under repeated aging cycles. Finally, recognizing that industrial flue gas streams inevitably contain water vapor we examine a constructive method of deliberately exposing the catalyst’s surface to water vapor before beginning the reaction. This simple method enhances the rate of VOC oxidation up to six-fold at temperatures as low as 40 °C.