Template-free Synthesis Research Articles

Flexible Polymer-Assisted Mesoscale Self-Assembly of Colloidal CsPbBr3 Perovskite Nanocrystals into Higher Order Superstructures with Strong Inter-Nanocrystal Electronic Coupling.

Surface-passivating ligands, although ubiquitous to colloidal nanocrystal (NC) syntheses, play a role in assembling NCs into higher order structures and hierarchical superstructures, which has not been demonstrated yet for colloidal CsPbX3 (X = Cl, Br, and I) NCs. In this work, we report that functional poly(ethylene glycols) (PEG6-Y, Y = -COOH and -NH2) represent unique surface-passivating ligands enabling the synthesis of near-uniform CsPbBr3 NCs with diameters of 3.0 nm. The synthesized NCs are assembled into individual pearl necklaces, bundled pearl necklaces, lamellar, and nanorice superstructures, in situ. It is believed a variety of forces, including van der Waals attractions between hydrophilic PEG tails in a nonpolar solvent and dipole-dipole attraction between NCs, drive mesoscale assembly to form superstructures. Furthermore, postsynthetic ligand treatment strengthens the argument for polymer-assisted mesoscale assembly as pearl necklace assemblies can be successfully converted into either lamellar or nanorice structures. We observe an ∼240 meV bathochromic shift in the lowest energy absorption peak of CsPbBr3 NCs when they are present in the lamellar and nanorice assemblies, representing strong inter-NC electronic coupling. Moreover, pearl necklace structures are spontaneously assembled into micrometer length scale twisted ribbon hierarchical superstructures during storage of colloidal CsPbBr3 NCs. The results show that the self-assembled superstructures of CsPbBr3 NCs are now feasible to prepare via template-free synthesis, as self-assembled structures emerge in the bulk solvent, a process that mimics biological systems except for the use of nonbiological surface ligands (PEG6-Y). Taken together, emergent optoelectronic properties and higher order superstructures of CsPbBr3 NCs should aid their potential use in solid-state devices and simplify scalable manufacturing.

Template-free mesoporous La0.3Sr0.7Ti1-xFexO3±δ for CH4 and CO oxidation catalysis

The design of perovskite oxides with improved textural properties in combination with tunable composition variations is a forward-looking strategy for the preparation of next generation catalytic converter. In the present work we report the template-free synthesis of mesoporous solid solutions of La0.3Sr0.7Ti1-xFexO3±δ (0 ≤ x ≤ 0.5) and the study of their catalytic performance towards CH4 and CO oxidation. Using an innovative polymer complex route, phase pure perovskite solid solutions with specific surface area of 65 m2 g−1 and average pore size of 15 nm were prepared. The iron concentration increase led to a progressive enhancement of not only both concentration and transport of the charge carriers but also reducibility and oxygen desorption capability on the catalyst. As a result, we observed almost complete conversion of CH4 and CO at 600 °C and 300 °C, respectively. Kinetic studies on methane oxidation showed that competing suprafacial and intrafacial reaction mechanisms coexist, and that the concentration of 30% of Fe maximizes the suprafacial contribution. Under reducing conditions at 600 °C the materials retained their structural and morphological integrity, showing superior stability. Finally, the reaction rate of CH4 and CO conversion evidenced that our systems are by a maximum of 90 times more performing than other bulk and nanoporous Fe-based perovskites in literature (e.g. La0.66Sr0.34Co0.2Fe0.8O3-δ), as a result their large surface area, intimate gas-solid contact and short intragrain oxygen diffusion pathways induced by the mesoporous structure.

Synthesis of phosphate-modified zeolite as a modifier in carbon paste electrode for nitrite electrochemical detection

In this work, template-free synthesis of phosphate mordenite zeolites was carried out. Post synthesis impregnation using phosphoric acid was applied to add phosphate group to zeolite framework, i.e. P-loading. Phosphate modification led to disruption of bridging hydroxyl and silanol groups as confirmed by FT-IR spectra. EDX spectra showed that the Si/Al ratio of the zeolite increases with the amount of P-loading and 27Al NMR revealed the formation of aluminophosphate on mordenite. The modified electrodes of phosphate mordenite zeolite were used for the electrocatalytic oxidation of nitrite, which was investigated by using square wave voltammetry. The effect of different electrolytes and pH values were also investigated and the calibration curve of nitrite oxidation at phosphate mordenite carbon paste electrodes showed a linear dependence.

Template-free synthesis and metalation of hierarchical covalent organic framework spheres for photothermal therapy.

Uniform micron sized hierarchical COF (HCOF) spheres were fabricated by a template-free solution-based aging method at room temperature for the first time. The postsynthetic metalation of HCOF with Fe3+ makes the metalated HCOF an excellent photothermal agent (PTA) for photothermal therapy (PTT).

Template-free hydrothermal synthesis of MgWO4 nanoplates and their application as photocatalysts.

As a semiconductor, MgWO4 has a potential in photocatalytic applications; however, it has been overlooked in previous studies; in this study, it has been demonstrated that MgWO4 exhibits the ability to drive photocatalytic hydrogen evolution. Compared to nanoparticle structures, MgWO4 nanoplates show an increased photocatalytic ability due to their higher specific surface area. Moreover, the formation mechanism of MgWO4 nanoplates has been discussed. An oriented attachment and ripening process is proposed for the formation of the MgWO4 nanoplates. This study demonstrates that MgWO4 can be considered a valuable photocatalytic material, and future studies should be focused on how to promote its photocatalytic conversion efficiency.

Large scale N-doped GNTs@a-SiOx(x=1–2)NPs: template-free one-step synthesis, and field emission and photoluminescence properties

N-doped graphene nanotubes coated by amorphous SiOx(x=1–2) nanoparticles (N-doped GNTs@a-SiOx(x=1–2)NPs) were synthesized by a simple template-free one-step calcination method.

Template free synthesis of lithium doped three-dimensional macroporous graphitic carbon nitride for photocatalytic N2 fixation: the effect of Li-N active sites.

In this work, three-dimensional macroporous lithium doped graphitic carbon nitride was synthesized. XRD, N2 adsorption, SEM, XPS, UV-Vis spectroscopy, N2-TPD and photoluminescence were used to characterize the prepared catalysts. The result shows that lithium exists as a coordinative Li-N bond, which can chemisorb and activate N2 molecules, and promote the electron transfer from the catalyst to the nitrogen molecules. The as-prepared lithium doped g-C3N4 shows a NH4+ production rate of 4.8 mg L-1 h-1 gcat-1, which is 20 times that of bulk g-C3N4. Density functional theory (DFT) simulations show that lithium doping can not only increase the N[triple bond, length as m-dash]N bond length, which activates N2 molecules, but also promote the electron-hole separation efficiency of g-C3N4.

Radical addition polymerization: Enzymatic template-free synthesis of conjugated polymers and their nanostructure fabrication.

Conjugated polymers are attractive for many applications due to their unique properties. Their molecular structure can easily be tuned, making them suitable for an enormous number of specific applications. Conjugated polymers have the potential to achieve electrical properties similar to those of noncrystalline inorganic semiconductors; however, their chemical structure is much more complex and somewhat resembles that of biomacromolecules. The molecular conformation and interactions of conjugated polymers play an important role in their functionality. The use of enzymes has emerged as a highly valuable alternative method to synthesize these polymers and is very useful in the fabrication of their nanostructures. Here, we present established strategies for the synthesis of conjugated polymers in template-free systems that do not interfere with the preparation of their nanostructures. These strategies are based on the use of peroxidases (class III; EC 1.11.1.7, donor: hydrogen peroxide oxidoreductase), which are enzymes that have the ability to catalyze the oxidation of a number of compounds (including aromatics such as aniline, pyrrole, thiophene and some of their derivatives), in the presence of hydrogen peroxide, to obtain conjugated polymers.

Template-free synthesis of carbon hollow spheres and reduced graphene oxide from spent lithium-ion batteries towards efficient gas storage

Herein, we report the facile synthesis of carbon hollow spheres and reduced graphene oxide from separators and graphite recovered from a spent lithium-ion battery, respectively, towards a “Waste-to-Wealth” approach.

Template-free synthesis of nanocage-like g-C3N4 with high surface area and nitrogen defects for enhanced photocatalytic H2 activity

Nanocage-like 3D porous graphitic carbon nitride (g-C3N4) with a high surface area and nitrogen defects was successfully prepared via a novel, template-free, cost-effective and hydrothermal-copolymerization route.

Solution-phase, template-free synthesis of PbI2 and MAPbI3 nano/microtubes for high-sensitivity photodetectors.

Organic-inorganic hybrid perovskite materials with exotic semiconducting properties have become inevitable candidates for next-generation electronic devices. Very recently, a low dimensional nanostructure of the perovskite materials has attracted the scientific community due to its enhanced performance in optoelectronics as compared to its bulk counterparts. Herein, a facile method was developed for the scalable, room-temperature synthesis of CH3NH3PbI3 (MAPbI3) nano/microtubes by direct conversion of lead iodide (PbI2) microtubes through a solution-phase method. At first, the PbI2 microtubes were synthesized by the anti-solvent crystallization process and subsequently converted to CH3NH3PbI3 nano/microtubes by the addition of CH3NH3I (MAI) precursor directly in the solution phase. The corresponding photodetectors (PDs) in the lateral metal-semiconductor-metal (MSM) configuration of the PbI2 microtubes and MAPbI3 nano/microtubes on glass substrates were investigated systematically. Compared to the PbI2 based PDs (557 mA W-1, 3.65 × 1012 Jones, 0.251 s/0.252 s), the MAPbI3 based PDs exhibit higher photoresponsivity, specific detectivity, and faster response time (25 A W-1, 9.9 × 1013 Jones, 49 ms/20 ms) under irradiation with 4.6 μW cm-2 intensity light of the 532 nm laser at a bias of 5 V. The proposed method is a low-temperature process, easy to apply in large scale synthesis, and finds potential applications in optoelectronic devices.

Template-free synthesis of oxygen-containing ultrathin porous carbon quantum dots/g-C3N4 with superior photocatalytic activity for PPCPs remediation

We report, for the first time, the fabrication of an oxygen-containing ultrathin porous carbon quantum dots/polymeric carbon nitrogen metal-free composite with a highly enhanced photoresponse.

Mechanochemically-assisted solvent-free and template-free synthesis of zeolites ZSM-5 and mordenite.

Aluminosilicate-based zeolite materials, such as ZSM-5 and mordenite, are well-studied as catalysts. Typical approaches to synthesize these zeolites require either templates or seeds to direct ordered crystal growth and both of these are expensive and add to the complexity of zeolite synthesis. In this paper, we describe a solvent-free and template-free method to synthesize crystalline ZSM-5 and mordenite zeolites without any added seed crystals. Key to the success of this approach is a mechanochemical precursor pre-reaction step. High-energy ball-milling is used to initiate a solid-state metathesis (exchange) reaction between Na2SiO3 and Al2(SO4)3 reagents, forming crystalline Na2SO4 and well-mixed aluminosilicate precursor. The solid precursor mixture is thermally converted to crystalline ZSM-5 or mordenite at moderate 180 °C temperatures without solvents or an organic amine structure directing template. Variations in Si/Al ratios in the precursor mixture and additions of solid NaOH to the mechanochemical reaction were found to influence the subsequent growth of either crystalline ZSM-5 or mordenite zeolites. The crystalline zeolites from this solvent-free and template free method have high ∼300 m2 g−1 surface areas directly from the synthesis without requiring high-temperature calcination. These materials are also comparably active to their commercial counterparts in cellulose and glucose biomass catalytic conversion to hydroxymethylfurfural.

A facile one-pot synthesis of CaO/CuO hollow microspheres featuring highly porous shells for enhanced CO2 capture in a combined Ca–Cu looping process via a template-free synthesis approach

The preparation of CaO/CuO composites with high performance is essential for combined Ca–Cu looping process, where the exothermic reduction of CuO with methane is used in situ to calcine CaCO3.

An eco-friendly route for template-free synthesis of high specific surface area mesoporous CeO2 powders and their adsorption for acid orange 7.

An eco-friendly route was developed for the synthesis of mesoporous CeO2 powders without any additional template. The original cerium precursors were separated from Ce3+ aqueous solution by (NH4)2CO3 or Na2CO3via a chemical precipitation method, then H2O2 was introduced to induce the phase transformation from original cerium precursors to CeO2 precursors with initial porous structures, finally the crystallinities of CeO2 precursors were improved by a hydrothermal treatment, meanwhile the mesoporous structures of final CeO2 powders were formed. The BET surface areas of mesoporous CeO2 powders synthesized using (NH4)2CO3 and Na2CO3 as precipitants were 106.1 and 76.9 m2 g−1, respectively. Moreover, a mesoporous CeO2 sample with BET surface area of 100.0 m2 g−1 was also synthesized using commercial Ce2(CO3)3·xH2O as an existing cerium precursor under the same conditions as control, which could shorten experimental processes and reduce costs. The oxidation-induced phase transformation from original cerium precursors to CeO2 precursors with initial porous structures was the precondition for further forming of mesoporous structures of final CeO2 powders during the hydrothermal process. These mesoporous CeO2 powders showed the rapid and effective adsorption for acid orange 7 dye from simulated wastewater without pH pre-adjustment at room temperature. Furthermore, the adsorption capacities of these mesoporous CeO2 powders for removal of acid orange 7 dye were determined according to the Langmuir linear fits.

Self-assembly of stimuli-responsive imine-linked calix[4]arene nanocapsules for targeted camptothecin delivery.

Here we report template-free synthesis of imine-linked calix[4]arene hollow nanocapsules and their utility in the effective delivery of a poorly soluble cancer drug into tumor cells. These stimuli-responsive nanocapsules show high drug loading and release which resulted in a 40-fold higher cytotoxicity for breast cancer cell line over normal cells.

Tailoring carbon nitride properties and photoactivity by interfacial engineering of hydrogen-bonded frameworks.

The rational synthesis of carbon nitride materials, ranging from polymeric carbon nitride to nitrogen-doped carbon, by supramolecular preorganization of their monomers is a powerful tool for the design of their morphology and photophysical and catalytic activities. Here we show a new facile and scalable approach for the synthesis of ordered CN materials with excellent photoactivity, which consists of supramolecular interfacial preorganization of CN monomers at the interface of two non-miscible solvents. Molecular dynamic simulations supported by experimental results reveal that an appropriate choice of monomers and solvents leads to the formation of a supramolecular assembly solely at the interface of the solvents. As a proof of concept, we show that the properties of the CN materials after thermal condensation can be tuned by adding an additional monomer to one solvent only. The advantages of the new method are demonstrated here through the tunable morphologies and surface area, the formation of new electronic junctions and high activity as a photocatalyst for hydrogen evolution and pollutant degradation of the CN materials.

Rapid template-free synthesis of nanostructured conducting polymer films by tuning their morphology using hyperbranched polymer additives.

Nanostructures in conducting polymer films can enhance charge carrier and ion transfer, provide porosity with high specific area and confer unique optoelectronic properties for potential applications. A general and facile synthesis has been developed to prepare nanostructured conducting polymer films without the need for using templates. This simple approach employs hyperbranched polymers as additives to tune the morphology of conducting polymer films into a continuous nanofibril network. Nanostructured conducting polymer films with improved crystallinity exhibit good charge carrier transport and stable nanofibril network, without sacrificing either property upon removing residual additives. Polymer field-effect transistor sensors have been used to demonstrate the benefits of the large surface area provided by the nanofibril network. The sensors with porous nanostructures exhibit lower detection limits (two times lower) and faster response times (33% faster) compared to the sensors without nanostructures. This general approach can advance the knowledge and development of nanostructured conducting polymer films for energy harvesting and storage, electronics, catalysts, sensors and biomedical applications.

Template-free synthesis of salmon pink tube-shaped structure carbon nitride with enhanced visible light photocatalytic activity.

Designing a highly active and stable photocatalyst to directly solve environmental pollution is desirable for solar energy conversion. Herein, an effective strategy, hydrothermal-calcination, for synthesizing extremely active carbon nitride (salmon pink) from a low-cost precursor melamine, is reported. The salmon pink carbon nitride with tube-shaped structure significantly enhanced response to visible light, improved efficiency of charge separation and remarkably enhanced efficiency of methyl orange (MO) degradation than bulk g-C3N4 (light orange). The M-10-200-24-600 composite possessed the most wonderful ability towards MO degradation irradiated by visible light, which could achieve a highest degradation efficiency of 84% within 120 min. Our findings may provide a promising and facile approach to highly efficient photocatalysis for solar-energy conversion.

Template-free synthesis of NiO skeleton crystal octahedron and effect of surface depression on electrochemical performance

In this work, we were committed to building a nickel oxide (NiO) octahedron with skeleton crystal structure as a capacitor electrode for supercapacitance through a template-free and efficient one-step process. Initially, nickel nitrate hexahydrate (Ni(NO3)2·6H2O) and anhydrous ethanol mixtures were used as a material. The final samples were prepared by calcining the precursor at different temperatures. The mechanism of crystal recrystallization at different temperatures during calcination was discussed. Generally speaking, in the process of rapid growth with only diffusion mechanism, crystal imperfections such as crystal plane depression and skeleton crystal will be formed. At the lower temperature calcination, small depressions are produced due to the effect of crystal face Ostwald ripening. At higher temperatures, the crystal edge growth rate is faster than the surface growth rate during Ostwald ripening and recrystallization, resulting in the formation of NiO octahedron with a large surface depression skeleton crystal structure. The electrochemical test results of the samples showed that the surface depression NiO octahedron has fine supercapacitive behaviors and specific capacitance values (640 F g−1) at the discharging current of 0.5 A g−1 in the 3 mol L−1 KOH electrolyte and maintain excellent cycling stability, remaining constant after 2000 cycles. Electrochemical impedance measurements confirmed the capacitance performance of NiO electrodes.