Template-free Synthesis Research Articles

Template-free synthesis of hollow spherical carbons: Curvature-dependent electrocatalytic performance for oxygen reduction reaction

Developing high-efficiency and economical non-PGM catalysts for oxygen reduction reaction (ORR) is of great significance for energy conversion and storage devices. In this work, a template-free strategy has been developed to prepare Fe, N co-doped hollow spherical carbon (FeNHSC) with a certain curvature, through a simple hydrothermal method and then NH3 activation. The obtained FeNHSC exhibits remarkably improved ORR activity, good long-term stability, and outstanding resistance to methanol crossover, which are much higher than the commercial Pt/C in alkaline medium. The enhancement of the above electrocatalytic performances can be attributed to the curved shell of the synthesized hollow spherical carbon, which contributes to exposure active Fe in form of the Fe–N4 moieties anchored on the carbon. Density functional theory (DFT) calculation results further reveal that the FeNHSC with a curved structure can efficiently boost the ORR rate, compared with the non-curved carbon. For the curved carbon, the positively shifted d-band center (εd) and increased positive surface charges of the Fe sites in form of Fe–N4 structure should be responsible for the curvature-dependent ORR activity. This finding may open a way to fabrication next-generation transition metal-nitrogen-carbon catalysts for clean energies.

Intra-Crystalline Mesoporous Zeolite [Al,Zr]-Y for Catalytic Cracking

A facile, direct, and template-free synthesis of intra-crystalline mesoporous zeolite Y involving the introduction of Zr atoms under hydrothermal conditions is proposed for the first time. The pres...

High photoactivity of Bi2O2(CO3)/Zn5(CO3)2(OH)6 prepared by a facile one-pot synthesis for the efficient degradation of phenol under UV light

The synthesis of Bi2O2(CO3)/Zn5(CO3)2(OH)6 heterojunction at low-temperature and template-free synthesis was carried out promoting the growth of sheet-like structures. The novel material has shown a high photocatalytic performance in the phenol removal under UV light when is compared to the Zn5(CO3)2(OH)6 and Bi2O2(CO3) bare photocatalysts. It is worth mentioning that, the material composed by a molar ratio of Bi/Zn = 0.08 showed the highest percentage of phenol mineralization. All the synthesized materials were characterized by X-ray diffraction, infrared spectroscopy with Fourier transform, diffuse reflectance spectroscopy, adsorption-desorption isotherms of N2, X-ray photoelectron spectroscopy, scanning electron microscopy and high-resolution transmission electron microscopy. The addition of Bi2O2(CO3) to the Zn5(CO3)2(OH)6 structure promotes the oxygen vacancies (OV) increment which make slower the recombination process between the e− and h+ species. This is because the OV sites act like a trap of the photogenerated holes. Thus, the photocatalytic activity is enhanced when Zn5(CO3)2(OH)6 is modified by the addition of Bi2O2(CO3) propitiate an increase on the production of hydroxyl and superoxide radicals as oxidant species for the phenol removal. As a novel material, Bi2O2(CO3)/Zn5(CO3)2(OH)6 could potentially be applied as an efficient material for phenol removal in photocatalysis due to the high performance, facile preparation and the synergetic effect achieved by the heterojunction presence.

Secondary template-free synthesis of hierarchical beta zeolite nanocrystals with tunable porosity and size

Abstract Mesoporous Beta zeolite nanocrystals with tunable porosity and size have been facilely prepared without additional mesoporous template or post-synthetic procedure. This synthetic strategy for mesoporosity could be realized by simply adjusting the reaction conditions without any special raw material. The as-prepared mesoporous Beta zeolite exhibits much higher adsorption efficiency compared with the bulk phase. The shorten crystallization time (8 h) and high yield (99%) allow this strategy suitable for the large-scale synthesis of mesoporous Beta zeolite with low cost.

Facile and green template-free synthesis of morphology-controllable Co3O4 catalysts for CO oxidation

A facile and green template-free hydrothermal method was conducted to controllably synthesize spinel type cobalt oxides (Co3O4) with cube, truncated octahedron and octahedron morphologies. The catalytic performance over various shapes of catalysts was investigated towards CO oxidation. Among of them, the Co3O4 cube performs the best catalytic activity, which can even be comparable to those of certain noble metal catalysts. The phenomenon might be ascribed to the synergistic effects of exposed Co3+ active sites and surface oxygen distribution on the surface of the catalyst. The results may provide significant insights for the fabrication of metal oxide catalysts for CO oxidation.

Perovskite Granular Wire Photodetectors with Ultrahigh Photodetectivity.

Control over the morphology and crystallinity of metal halide perovskite materials is of key importance to enable high-performance optoelectronics. Here, a simple yet effective template-free self-assembly synthesis of perovskite granular wires with ultrahigh photodetectivity (3.17 × 1015 Jones) is reported. The 1D self-assembly of perovskite grains is driven by differences in the surface interaction energies of the granular facets. The superb photodetecting performance originates from extremely low dark current engendered by energetic barriers featuring unique band-edge modulation along the long axis of wire. Flexible photodetector arrays, fabricated by selectively placing perovskite granular wires onto pre-patterned electrode arrays on a transparent polymer substrate, show independently addressable photonic signal mapping with remarkably high detectivity, photoconductive gain, and responsivity. The "self-assembled nanograin engineering" strategy developed in this study provides a viable method for the development of high-performance perovskite photodetectors and can be extended to other integrated optoelectronic systems.

Direct Conversion of Rice Husks to Nanostructured SiC/C for CO2 Photoreduction.

A one-step and template-free synthesis of a SiC nanowires/C (SiC-NW/C) composite from rice husks (RHs) is realized via a molten-salt-assisted electrochemical method. The process integrates simultaneously carbonization, electrodeoxidation, nanostructuring, and self-purification for converting RHs to a SiC-NW/C hybrid that is assembled from SiC NWs embedded in porous N-doped graphitic carbon with strong coupling. The SiC-NW/C nanostructure enables efficient CO2 adsorption and fast separation and transfer of charge carriers. Benefiting from the structural and compositional merits, the SiC-NW/C composite shows superior activity for photoreduction of CO2 to CO, in the absence of any additional cocatalysts or sacrificial agents. The process proposed herein might help to bridge a closed-loop carbon cycle in the whole production-utilization of biomass.

Scalable one-step template-free synthesis of ultralight edge-functionalized g-C3N4 nanosheets with enhanced visible light photocatalytic performance

Herein, we report a scalable, green and “bottom-up” approach for the synthesis of ultralight g-C3N4 nanosheets. The ultralight g-C3N4 nanosheets (9.6 mg cm−3) have been entirely synthesized in a wet atmosphere in one step without pretreatment or any other additives. The as-prepared material (UMCN-wet) appears as a foam-like exterior with ultrathin nanosheets (3.5 nm), short-order polymerization and sharp edges. The X-ray diffraction (XRD), Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses confirm the formation of melon units with edge-enriched active sites. UMCN-wet exhibits a higher specific surface area (137.44 m2 g−1) and pore volume (0.2076 cm3 g−1), compared with that of the as-synthesized materials in the air (MCN-air) and nitrogen (MCN-N2) atmospheres. The optical and electrochemical analyses reveal that UMCN-wet manifests fast photogenerated charge separation and transfer with slow decay kinetics. As a result, UMCN-wet nanosheets exhibit superb photocatalytic degradation of rhodamine B (RhB), methylene blue (MB) and methyl orange (MO) under visible light irradiation with photodegradation rate constant (k) of 0.17687, 0.02409 and 0.00537 min−1, respectively. Moreover, UMCN-wet exhibits excellent stability and reusability performance. Such a sustainable approach does not only overcome the prolonged time processing, extra energy consumption and utilization of hazardous chemicals for synthesis ultrathin g-C3N4 nanosheets, but also paves a new pathway for industrial upscale production with numerous expected environmental applications.

An efficient chemical sensor based on CeO2 nanoparticles for the detection of acetylacetone chemical

Facile, economic, template free and low-temperature hydrothermal synthesis of CeO2 nanoparticles was carried out in this research article. As-synthesized CeO2 nanoparticles were characterized through different techniques including FESEM, TEM, XRD, FTIR, UV–visible spectroscopy, Raman spectroscopy, and XPS analysis. XRD diffraction peaks confirmed the cubic fluorite structure for CeO2 nanoparticle. Highly agglomerated nanostructures with an average particle diameter of 15 ± 2 nm were observed from FESEM and TEM analyses. A single defined absorbance at 302 nm corresponding to the bandgap energy of 4.11 eV was recorded from the UV–visible spectrum. Vibrational and scattering properties as analyzed from FTIR and Raman spectra confirmed the formation of CeO2 nanoparticle. The CeO2 nanoparticles were immobilized on a glassy carbon electrode which showed excellent electrocatalytic activity in 0.1 M PBS with pH 7.4 for acetylacetone. The sensitivity, LOD and regression coefficient (R2) were respectively, 262 mA·mM−1 cm−1, 11.6 mM and 0.87339 for the fabricated chemical sensor. The study conducted herein confirms that CeO2 nanoparticles are promising candidates for electro-analytical sensing applications.

Cu-Exchanged CHA-Type Zeolite from Organic Template-Free Synthesis: An Effective Catalyst for NH3-SCR

A Cu-containing CHA-type zeolite was prepared via aqueous ion exchange of the CHA zeolite from organic template-free synthesis. The thus-obtained template-free Cu-CHA showed the best catalytic perf...

Template-free Synthesis of Mesoporous and Crystalline Transition Metal Oxide Nanoplates with Abundant Surface Defects

Summary Mesoporous transition metal oxides with crystalline walls show promising applications in catalysis and energy storage. Syntheses of those crystalline mesoporous oxides, however, currently remain as an unmet challenge because of the large volume shrinkage during crystallization in a sol-gel process. Here, we demonstrate a facile and general template-free method to prepare six mesoporous transition metal oxides, e.g., CuO, CoO, and spinel MCo2O4 (M = Co, Cu, Mn, Zn), with highly crystalline walls and continuous mesopores in the forms of two-dimensional nanoplates or nanosheets. The method is based on the thermal crystalline transformation from basic carbonates to mesoporous metal oxides. The crystal interconversion not only endows the crystallinity and mesoporosity of oxides but also generates abundant surface-step defects that show remarkable enhancement of the catalytic activity of porous oxides. Our method likely provides an alternative paradigm for cost-effective and universal synthesis of crystalline mesoporous oxides beyond the traditional templating methods.

Template-free microwave-assisted hydrothermal synthesis of manganese zinc ferrite as a nanofertilizer for squash plant (Cucurbita pepo L)

Manganese, zinc, and iron are the most essential micronutrients required for plant growth and applied as foliar fertilizers. Herein, a simple template-free microwave-assisted hydrothermal green synthesis technique was adapted to produce manganese zinc ferrite nanoparticles (Mn0.5Zn0.5Fe2O4 NPs) at different temperatures (100, 120, 140, 160 and 180 °C). The prepared nanomaterials were employed at different concentrations (0, 10, 20, and 30 ppm) as foliar nanofertilizers during the squash (Cucurbita pepo L) planting process. X-ray diffraction patterns of the prepared nanomaterials confirmed successful production of the nanoferrite material. The prepared nanofertilizers showed type IV adsorption isotherm characteristic for mesoporous materials. FE-SEM and HR-TEM imaging showed that the nanoparticles were cubic shaped and increased in particle size with the increase in microwave temperature during production. The impact of application of the synthesized ferrite nanoparticles on vegetative growth, proximate analysis, minerals content and the yield of squash plant was investigated for two consecutive successful planting seasons. The nanoferrite synthesized at 160 °C and applied to the growing plants at a concentration of 10 ppm gave the highest increase in % yield (49.3 and 52.9%) compared to the untreated squash for the two consecutive seasons, whereas the maximum organic matter content (73.0 and 72.5%) and total energy (260 and 258.3 kcal/g) in squash leaves were obtained in plants treated with 30 ppm ferrite nanoparticles synthesized at 180 °C. On the other hand, the maximum organic matter content (76.6 and 76.3%) and total energy (253.6 and 250.3 kcal/g) in squash fruits were attained with plants supplied by 20 ppm ferrite nanoparticles synthesized at 160 °C. These results indicate that the simple template-free microwave-assisted hydrothermal green synthesis technique for the production of manganese zinc ferrite nanoparticles yields nanoparticles appropriate for use as fertilizer for Cucurbita pepo L.

Template-free one-step synthesis of micro-mesoporous CeO2–ZrO2 mixed oxides with a high surface area for selective hydrogenation

Ceria-zirconia oxide materials with a specific surface area ranging from 160 to 240 m2/g and different meso- and micropores ratio were obtained by a simple deposition-precipitation method with urea (DPU), which allows preparation of ceria-zirconia oxides directly in one-step while avoiding the formation of oxo-hydroxo species and further thermal treatment to obtain oxide phases. Moreover, a microwave-assisted DPU method allowed the decrease of the synthesis time from 24 to 3.5 h. The prepared samples were studied by TG-DTA, BET, N2 adsorption, XRD, SEM, and TEM methods. Pt-containing catalysts based on synthesized oxides have shown a high catalytic activity in selective hydrogenation of benzaldehyde, citral, and cinnamaldehyde at room temperature and atmospheric pressure.

Template-free one-step synthesis of the multi-layer carbon or stacked graphene sheets coessentially coating N-doped graphene tubes and their field emission and photoluminescence properties

Graphene nanotubes (GNTs), as a rising member among the carbon nanomaterials family, has drawn significant research interest. The fabrication of the GNTs-based coessential composites could be a more facile and effective strategy to promote GNTs performances. Herein, based on the self-prepared N-doped graphene tubes (N-GNTs), multi-layer carbon wrapped N-doped GNTs (MLC@N-GNTs) and numerous stacked wrinkled graphene sheets encapsulated N-doped GNTs (GS@N-GNTs) are constructed via a facile free-template, one-step CVD method. The growth mechanism of the two types of coessential carbon composites was investigated in detail. The products, especially GS@N-GNTs display the most excellent field emission properties with a very low Eto of 0.33 V/mm, Ethr of 0.96 V/mm and a high field enhancement factor of 50237. The excellent field emission properties is attributed to the synergistic effect of the improved electronic conductivity, the high density of structure defects, the abundance of effective electron emission sites along with the high field enhancement factor and the electronic properties changes induced by the winkled graphene. In addition, MLC@N-GNTs and GS@N-GNTs show the more intense photoluminescence emission than that of pristine N-GNTs, because the coessential coatings induces the interfaces and large amounts of structure defects, which can act as trapping sites for the excitation energy.

Spin-crossover in iron(II)-phenylene ethynylene-2,6-di(pyrazol-1-yl) pyridine hybrids: toward switchable molecular wire-like architectures

Luminescent oligo(p-phenylene ethynylene) (OPE) and spin-crossover (SCO) active Fe(II)-2,6-di(pyrazol-1-yl) pyridine (BPP) systems are prominent examples proposed to develop functional materials such as molecular wires/memories. A marriage between OPE and Fe(II)-BPP systems is a strategy to obtain supramolecular luminescent ligands capable of metal coordination useful to produce novel spin-switchable hybrids with synergistic coupling between spin-state of Fe(II) and a physical property associated with the OPE skeleton, for example, electronic conductivity or luminescence. To begin in this direction, two novel ditopic ligands, namely L1 and L2, featuring OPE-type backbone end-capped with metal coordinating BPP were designed and synthetized. The ligand L2 tailored with 2-ethylhexyloxy chains at the 2 and 5 positions of the OPE skeleton shows modulated optical properties and improved solubility in common organic solvents relative to the parent ligand L1. Solution phase complexation of L1 and L2 with Fe(BF4)2·6H2O resulted in the formation of insoluble materials of the composition [Fe(L1)]n(BF4)2n and [Fe(L2)]n(BF4)2n as inferred from elemental analyses. Complex [Fe(L1)]n(BF4)2n underwent thermal SCO centred at T1/2 = 275 K as well as photoinduced low-spin to high-spin transition with the existence of the metastable high-spin state up to 52 K. On the other hand, complex [Fe(L2)]n(BF4)2n, tethered with 2-ethylhexyloxy groups, showed gradual and half-complete SCO with 50% of the Fe(II)-centres permanently blocked in the high-spin state due to intermolecular steric interactions. The small angle x-ray scattering (SAXS) pattern of the as-prepared solid complex [Fe(L1)]n(BF4)2n revealed the presence of nm-sized crystallites implying a possible methodology towards the template-free synthesis of functional-SCO nanostructures.

Uniform Spheres of α-NaYF4:RE3+ (RE=Eu, Tb, Ce, Er, and Tm): Template-Free Synthesis, Multi-Color Photoluminescence, and Their Application in Cellular Imaging

Uniformly dispersed luminescent probes with a high brightness and high resolution are desired in bio imaging fields. Here, ~100 nm sized and well-dispersed spheres of RE3+ doped α-NaYF4 (rare earth (RE) = Eu, Tb, Ce, Er, and Tm) have been facile synthesized through hydrothermal processing in the absence of a template, followed by a proper annealing. The processing window of the cubic structured spheres is wide, because the hydrothermal products are independent of the processing conditions, including reaction time and temperature. The original morphology and crystal structure can be well retained with a calcination temperature up to 600 °C. However, calcination gives rise to a reduction of particle sizes, as a result of the crystallite growth and densification. Under ultraviolet radiation, α-NaYF4:RE3+ spheres show characteristic f-f emissions of RE3+ (RE = Eu, Tb, Ce, Er, and Tm), and exhibit orange red, green, ultraviolet (UV), blue green, and blue emissions, respectively. Mainly because of the near-infrared emission at ~697 nm (5D0→7F4 transitions of Eu3+), the successful imaging of macrophages was achieved by NH2-NaYF4:Eu3+ probes, indicating their excellent imaging capacity for cells in vitro.

Template-free synthesis of platinum hollow-opened structures in deep-eutectic solvents and their enhanced performance for methanol electrooxidation

As a novel non-aqueous green solvent that can deem to be the optimal substitution of conventional solvents and ionic liquids, deep-eutectic solvents (DESs) have attracted significant attention from academia and industry in terms of chemical synthesis in recent years. Herein, we report the highly effective preparation of Pt nanoparticles with hollow-opened structures (Pt HOSs) as an efficient electrocatalyst for methanol oxidation reaction (MOR) via a facile template-free solvothermal synthesis in DESs. The as-obtained Pt HOSs are consisted of well assembled secondary and tertiary branches, which can remarkably improve the utilization efficiency and electrocatalytic activity of Pt via promoting the access of electroactive species to the full-extent Pt surface. In this regard, the as-prepared Pt HOSs possess higher electrochemically active surface areas (ECSAs) and show improved electrochemical properties for MOR. Furthermore, the Pt HOSs retain a higher reactivity after the long-term testing compared with commercial Pt black, suggesting that they have enhanced electrocatalytic durability. In specific, the rational design of Pt HOSs in DESs may enrich the synthetic strategies for producing more electrocatalysts with impressive activity and stability.

Rectifying resistance switching behaviors of SnO2 microsphere films modulated by top electrodes

Based on the bipolar resistive switching (RS) characteristics of SnO2 films, we have fabricated a new prototypical device with sandwiched structure of Metal/SnO2/fluorine-doped tin oxide (FTO). The SnO2 microspheres film was grown on FTO glass by template-free hydrothermal synthesis, which was evaporated with various commonly used electrodes such as aluminium (Al), silver (Ag), and gold (Au), respectively. Typical self-rectifying resistance switching behaviors were observed for the RS devices with Al and Au electrodes. However, no obvious rectifying resistance switching behavior was observed for the RS device with Ag electrode. Above results were interpreted by considering the different interface barriers between SnO2 and top metal electrodes. Our current studies pave the ways for modulating the self-rectifying resistance switching properties of resistive memory devices by choosing suitable metal electrodes.

Template-free synthesis and lithium-ion storage performance of multiple ZnO nanoparticles encapsulated in hollow amorphous carbon shells.

Due to the limited utilization of electrode materials, the rational design and facile synthesis of composite structures are still challenging issues for lithium-ion batteries (LIBs). Herein, a simple approach has been developed to prepare multiple core–shell structures of ZnO nanoparticles (NPs) encapsulated in hollow amorphous carbon (AC) shells. The as-synthesized ZnO@AC composites showed a uniform dispersion of ZnO NPs, compliant buffer AC shells, and nanoscale void spaces between the ZnO NP cores and AC shells. As a result of their structural merits, the ZnO@AC composites were evaluated as anode materials for LIBs and delivered enhanced coulombic efficiency, high reversible capacity, high rate capability, and improved cycling stability.

The design of zinc-substituted cobalt (pyro)phosphates as efficient bifunctional electrocatalysts for zinc-air batteries.

In an effort to rationally design economic electrocatalysts, zinc-substituted cobalt phosphate and pyrophosphate were prepared using facile template-free combustion synthesis. They act as efficient stable bifunctional electrocatalysts due to the tuning of oxygen affinity by zinc substitution and catalytically active cobalt sites. Exploiting their bifunctional activity, these cobalt (pyro)phosphates were incorporated into a zinc-air battery in an alkaline electrolyte.