Colloidal chemical approaches to inorganic micro- and nanostructures with controlled morphologies and patterns

Solution-Phase Synthesis of KCl Nanocrystals Templated by PEO-PPO-PEO Triblock Copolymers Micelles

The current work introduces the synthesis of inorganic salt nano/micro-crystals during the reduction of hydrogen tetrachloroaurate(III) by Pluronic triblock copolymers (P123, PEO20-PPO70-PEO20). The morphologies and component were confirmed using an electron microscope with an electronic differential system (EDS), and the crystal structures were determined with X-ray diffraction (XRD). The morphologies highly depend on the concentrations of Pluronic and pH values. The mean size of the nanocrystal and hollow micro-crystal were controlled typically in the range of 32-150 nm (side length) and 1.4 μm, respectively. Different from the electrospray-ionization (EI) method, a model in which KCl forms a supersaturated solution in the micellar core of Pluronic is used to explain the formation process. This work provides the new insight that inorganic salt nanocrystals could be synthesized with the template of micelles in pure aqueous solutions.

γ-CuI from ionic liquid/poly(ionic liquid)s precursors with controllable morphologies and improved photocatalytic performance

γ-phase copper(I) iodide (abbreviated to CuI hereafter) with different morphologies is realized through a one-step redox process from I-containing ionic liquid (IL) or poly(ionic liquid)s (PILs) precursors at room temperature. The phase composition, morphology, and electronic states of the synthesized CuI samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The resulting CuI products exhibit three different types of morphologies, namely nanocrystals, with an average size of 0.8 ± 0.2 μm, nanoplates, with a thickness of 35.8 ± 0.9 nm, and nanoflowers, with petals with a thickness of 12.2 ± 0.8 nm. Moreover, the as-synthesized CuI samples exhibit gradually diminishing bandgaps and improved photocatalysis performance for the photodegradation of rhodamine B (RhB) under visible light irradiation as the thickness decreases. XPS measurements confirm that IL/PILs coupled to the CuI surface, resulting in a further charge transfer between Cu and I. These results conclusively prove that IL/PILs serve as both the reducing agents and assemble as orientation templates in the formation of the CuI nanostructures, and also successfully mediate the functional properties of the samples by changing the surface electronic structures.

Unconventional-Phase Crystalline Materials Constructed from Multiscale Building Blocks

Crystal phase, an intrinsic characteristic of crystalline materials, is one of the key parameters to determine their physicochemical properties. Recently, great progress has been made in the synthesis of nanomaterials with unconventional phases that are different from their thermodynamically stable bulk counterparts via various synthetic methods. A nanocrystalline material can also be viewed as an assembly of atoms with long-range order. When larger entities, such as nanoclusters, nanoparticles, and microparticles, are used as building blocks, supercrystalline materials with rich phases are obtained, some of which even have no analogues in the atomic and molecular crystals. The unconventional phases of nanocrystalline and supercrystalline materials endow them with distinctive properties as compared to their conventional counterparts. This Review highlights the state-of-the-art progress of nanocrystalline and supercrystalline materials with unconventional phases constructed from multiscale building blocks, including atoms, nanoclusters, spherical and anisotropic nanoparticles, and microparticles. Emerging strategies for engineering their crystal phases are introduced, with highlights on the governing parameters that are essential for the formation of unconventional phases. Phase-dependent properties and applications of nanocrystalline and supercrystalline materials are summarized. Finally, major challenges and opportunities in future research directions are proposed.

High-performance natural-sunlight-driven Ag/AgCl photocatalysts with a cube-like morphology and blunt edges via a bola-type surfactant-assisted synthesis

Ag/AgCl-based structures have recently been receiving considerable attention as visible-light-driven plasmonic photocatalysts, wherein the fabrication of Ag/AgCl species shaped with an anisotropic morphology is considered to be an efficient way to enhance their performances. While the past decade has witnessed great progress in this direction, it is still strongly desired to initiate a green and low-cost protocol for the synthesis of Ag/AgCl based structures with high catalytic activity. Using a surfactant-assisted synthesis protocol, wherein a cationic bola-type surfactant of chloride counteranions serves both as a reactant (namely, source of chlorine) for the generation of AgCl structures and as a directing template to assist the formation of anisotropic structures, we herein report that cube-like Ag/AgCl with blunt edges could be fabricated simply by dropping an aqueous solution of silver nitrate into an ethanol solution of the hexane-1,6-bis(trimethylammonium chloride) surfactant. Importantly, compared to the sphere-like counterparts manufactured using a conventional tadpole surfactant, the as-fabricated cube-like structures exhibit substantially improved catalytic performances under visible-light or natural-sunlight irradiation. It has been revealed that photogenerated holes might serve as the main active species during the catalytic process. Meanwhile, our results have disclosed that in contrast to the sphere-like Ag/AgCl structures, the as-constructed cube-like structures are relatively enriched with high-index AgCl facets of smaller hole effective mass, which promote a faster carrier transfer, facilitate the migration of the photogenerated holes to the surface to be involved in photocatalytic reactions, and suppress carrier recombination, leading to their enhanced photocatalytic performances. Considering the tremendous diversity of surfactants (bola-, gemini-, polymeric surfactants etc.) with various halide counteranions and their sophisticated template effects, our new strategy might open up new opportunities for silver/silver halide (Ag/AgX, X = Cl, Br, and I)-based plasmonic structures with various morphologies and with superior light-to-chemical energy conversion capability.

Spontaneous precipitation pattern formation by crystallites of Mn-Fe-based Prussian blue analogues in agarose gel

Precipitation patterns spontaneously formed by Mn-Fe-based Prussian blue analogues (Mn-Fe PBAs) in agarose gel were investigated over wide concentration ranges for the outer (0.10 ≤ [Mn2+] ≤ 0.70 M) and inner electrolytes (0.01 ≤ [[Fe(CN)6]3-] ≤ 0.35 M). The precipitation patterns were classified into five types: continuous in the inner electrolyte gel, continuous in the outer electrolyte gel, a very short band close to the gel boundary, periodic bands in the inner electrolyte gel, and filament-like patterns in the inner electrolyte gel. The concentrations found to be suitable for applications as pulsatile 137Cs adsorbent delivery materials, for which the periodic patterns were most distinct and frequently occurring, were [Mn2+] ≈ 0.55 M and [[Fe(CN)6]3-] ≈ 0.10 M. The filament-like pattern, reported here for the first time, was generated near the cylindrical gel surface in a local, stochastic, and two-dimensional manner. Scanning electron microscopy (SEM) images of the periodic band patterns indicate that the Mn-Fe PBA precipitates in periodic patterns consist of cubic crystallites (3-10 μm, each side), suggesting significant contributions from Ostwald ripening to the precipitation process. In contrast, precipitates in the filament-like pattern consist of relatively smaller cubic crystallites (≲1 μm, each side), implying an important role of rapid nucleation in the formation of this structure. SEM observations also suggest that, overall, agarose gels support crystallite ripening more effectively, and hence also better suppress the formation of definite periodic bands, than water-glass gels. These findings provide useful information for future applications of self-assembled Mn-Fe PBA patterns in gels.

Facile synthesis and electrochemical Mg-storage performance of Sb2Se3 nanowires and Bi2Se3 nanosheets

Sb₂Se₃ nanowires and Bi₂Se₃ nanosheets are investigated as conversion-type cathodes for rechargeable Mg batteries.

Synthesis-Structure-Activity Relationships in Co3O4 Catalyzed CO Oxidation

In this work, a statistical design and analysis platform was used to develop cobalt oxide based oxidation catalysts prepared via one pot metal salt reduction. An emphasis was placed upon understanding the effects of synthesis conditions, such as heating regimen and Co²⁺ concentration on the metal salt reduction mechanism, the resultant nanomaterial properties (i.e., size, crystal structure, and crystal faceting), and the catalytic activity in CO oxidation. This was accomplished by carrying out XRD, TEM, and FTIR studies on synthesis intermediates and products. Additionally, high-throughput experimentation was employed to study the performance of Co₃O₄ oxidation catalysts over a wide range of reaction conditions using a 16-channel fixed bed reactor equipped with a parallel infrared imaging system. Specifically, Co₃O₄ nanomaterials of varying properties were evaluated for their performance as CO oxidation catalysts. Figure-of-merits including light-off temperatures and activation energies were measured and mapped back to the catalyst properties and synthesis conditions. Statistical analysis methods were used to elucidate significant property-activity relationships as well as the design rules relevant in the synthesis of active catalysts. It was found that the degree of grain boundary consolidation and anisotropic growth in fcc and hcp CoO intermediates significantly influenced the catalytic activity. By utilizing the discovered synthesis-structure-activity relationships, CO oxidation light off temperatures were decreased to <90°C.

High Performance Shape-Stabilized Phase Change Material with Nanoflower-Like Wrinkled Mesoporous Silica Encapsulating Polyethylene Glycol: Preparation and Thermal Properties

Nanoflower-like wrinkled mesoporous silica (NFMS) was prepared for further application as the carrier of polyethylene glycol (PEG) to fabricate the new, shape-stabilized phase change composites (PEG/NFMS); NFMS could improve the loading content of PEG in the PEG/NFMS. To investigate the properties of PEG/NFMS, characterization approaches, such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), thermal gravimetric analysis (TGA), Brunauer-Emmett-Teller (BET) analysis, and differential scanning calorimetry (DSC), were carried out. The characterization results illustrated that the PEG was completely adsorbed in the NFMS by physical adsorption, and the nanoflower-like wrinkled silica did not affect the crystal structure of PEG. As reported by the DSC test, although NFMS had a restriction influence on the activity of the PEG molecules, the melting and binding enthalpies of the PEG/NFMS could reach 136.6 J/g and 132.6 J/g, respectively. In addition, the TGA curves demonstrated that no evident weight loss was observed from 20 °C to 190 °C for the PEG/NFMS, and the results revealed that the PEG/NFMS had remarkable thermal stability. These results indicated that the NFMS is a potential carrier of organic phase change material for the preparation of shape-stabilized phase change composites.

Impacts of ionic liquid capping on the morphology and photocatalytic performance of SbPO4 crystals

A novel hydrothermal route to prepare SbPO₄ with [BMIM][PO₄] or Na₂HPO₄·12H₂O as the phosphorus source has been developed. The morphology transition of SbPO₄ photocatalysts from microparticles to microspheres was shown by changing the reaction temperature.

Encapsulating Proteins in Nanoparticles: Batch by Batch or One by One

Encapsulation of proteins in nanoparticles (NPs) can greatly improve the properties of proteins such as their stability against denaturation and degradation by proteases, and branches out the applications of natural proteins from their intrinsic localizations and functions in living organisms for biomedical and industrial applications. We recently developed several methods to armor proteins in NPs with sizes from nanometers up to >100nm, batch by batch or one by one, covalently or noncovalently, for a wide range of applications from biocatalysis to bioimaging and drug delivery. In this chapter, we provide detailed protocols on these methods. Key steps of specific protocols are explained with particular examples to help other laboratories to adopt and modify these methods for their own purposes. The advantages and disadvantages of each method are summarized, and guidelines for choosing the right method for a given application, as well as the current challenges and future directions of this field, are discussed.

Sheetlike gold nanostructures/graphene oxide composites via a one-pot green fabrication protocol and their interesting two-stage catalytic behaviors

Au nanoplate/GO composites are facilely synthesized via a one-pot green protocol. The composites display a fascinating two-stage catalytic behavior, where the catalytic reactivity of the latter stage increases substantially by a factor of 9 times.

Enhanced thermal properties of novel shape-stabilized PEG composite phase change materials with radial mesoporous silica sphere for thermal energy storage

Radial mesoporous silica (RMS) sphere was tailor-made for further applications in producing shape-stabilized composite phase change materials (ss-CPCMs) through a facile self-assembly process using CTAB as the main template and TEOS as SiO₂ precursor. Novel ss-CPCMs composed of polyethylene glycol (PEG) and RMS were prepared through vacuum impregnating method. Various techniques were employed to characterize the structural and thermal properties of the ss-CPCMs. The DSC results indicated that the PEG/RMS ss-CPCM was a promising candidate for building thermal energy storage applications due to its large latent heat, suitable phase change temperature, good thermal reliability, as well as the excellent chemical compatibility and thermal stability. Importantly, the possible formation mechanisms of both RMS sphere and PEG/RMS composite have also been proposed. The results also indicated that the properties of the PEG/RMS ss-CPCMs are influenced by the adsorption limitation of the PEG molecule from RMS sphere with mesoporous structure and the effect of RMS, as the impurities, on the perfect crystallization of PEG.

Visible-light-driven Ag/AgCl plasmonic photocatalysts via a surfactant-assisted protocol: enhanced catalytic performance by morphology evolution from near-spherical to 1D structures

Fibrous Ag/AgCl structures with boosted photocatalytic performances have been fabricatedviaa one-pot surfactant-assisted morphology evolution from near-spherical to 1D architectures.

Branched Au nanostructures enriched with a uniform facet: facile synthesis and catalytic performances

Well–defined noble metal nanocrystals (NMNCs) of a unique morphology yet a uniform facet have attracted broad interests. In this regard, those with a highly branched architecture have gained particular attention. Most of the currently existing branched NMNCs, however, are enclosed by mixed facets. We now report that branched Au nanoarchitectures could be facilely fabricated by mixing an aqueous solution of KAuCl₄, an aqueous dispersion of graphene oxide, and ethanol under ambient conditions. Interestingly, unilike the conventional branched NMNCs, our unique Au nanostructures are predominately enriched with a uniform facet of {111}. Compared to the spherical Au nanostructures exposed with mixed facets, our branched nanospecies of a uniform facet display superior catalytic performances both for the catalytic reduction of 4–nitrophenol and the electrocatalytic oxidation of methanol. Our investigation represents the first example that Au nanostructures simultaneously featured with a highly branched architecture and a uniform crystal facet could be formulated. Our unique Au nanostructures provide a fundamental yet new scientific forum to disclose the correlation between the surface atomic arrangement and the catalytic performances of branched NMNCs.

Synthesis and Characterization of Highly Efficient Nickel Nanocatalysts and Their Use in Degradation of Organic Dyes

The present study describes the synthesis of highly active and ordered structures of nickel nanocatalysts by a facile, green, and economically viable approach. The study reveals efficient catalytic activity for the degradation of a number of toxic organic dyes, such as eosin-B (EB), rose bengal (RB), eriochrome black-T (ECBT), and methylene blue (MB). The stable ordered nickel nanostructure (Ni NSs) arrays were prepared via a modified hydrazine reduction route with unique and controlled morphologies in a lyotropic liquid crystalline medium using a nonionic surfactant (Triton X-100). Characterization and optimization studies for the fabricated Ni NSs involving their surface binding interactions, size, and morphologies were carried out using UV-Vis spectroscopy, Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), and scanning electron microscopy (SEM).

Surfactant-assisted porphyrin based hierarchical nano/micro assemblies and their efficient photocatalytic behavior

In this report, we have demonstrated the synthesis of surfactant-assisted different morphologies of meso-tetra(4-carboxyphenyl)porphyrin assemblies (spherical to flower shaped). These nano/micro assemblies are well characterized by scanning electron microscopy and X-ray diffraction. The formation of assemblies is driven by noncovalent interactions such as hydrophobic-hydrophobic and aromatic π-π stacking between the molecules. The steady state and time-resolved spectroscopic investigation reveal that different assemblies are formed by virtue of special supramolecular organizations. The photocatalytic activities of different assemblies have been demonstrated with an organic pollutant Rhodamine B dye under the visible light irradiation. Such porphyrin based assemblies could pave the way for designing new optical based materials for the applications in photocatalytic, photovoltaic, and light harvesting system.

Supramolecular templating of hierarchically porous metal–organic frameworks

This tutorial review summarises recent advances in the soft templating of metal–organic frameworks with hierarchical porosity across the micro- and mesoporous regimes.

One-dimensional porphyrin nanoassemblies assisted via graphene oxide: sheetlike functional surfactant and enhanced photocatalytic behaviors

Surfactant-assisted self-assembly (SAS) has received much attention for supramolecular nanoassemblies, due to its simplicity and easiness in realizing a controllable assembly. However, in most of the existing SAS protocols, the employed surfactants work only as a regulator for a controllable assembly but not as active species for function improvement. In this paper, we report that a porphyrin, zinc 5,10,15,20-tetra(4-pyridyl)-21H,23H-porphine (ZnTPyP), could be assembled to form one-dimensional (1D) supramolecular nanostructures via a SAS method, wherein graphene oxide (GO) plays a fascinating role of sheetlike surfactant. We show that, when a chloroform or tetrahydrofuran solution of ZnTPyP is injected into an aqueous dispersion of GO, 1D supramolecular nanoassemblies of ZnTPyP with well-defined internal structures could be easily formulated in a controllable manner. Our experimental facts disclose that the complexation of ZnTPyP with the two-dimensional GO nanosheets plays an important role in this new type of SAS. More interestingly, compared with the 1D ZnTPyP nanoassemblies formulated via a conventional SAS, wherein cetyltrimethylammonium bromide is used as surfactant, those constructed via our GO-assisted SAS display distinctly enhanced photocatalytic activity for the photodegradation of rhodamine B under visible-light irradiation. Our new findings suggest that GO could work not only as an emergent sheetlike surfactant for SAS in terms of supramolecular nanoassembly but also as functional components during the performance of the assembled nanostructures.

One-pot synthesis of spheres-on-sphere silica particles from a single precursor for fast HPLC with low back pressure

Spheres-on-sphere (SOS) silica particles are prepared in a one-pot scalable synthesis from mercaptopropyltrimethoxysilane with hydrophilic polymer and cationic surfactant under alkaline conditions. The SOS particles exhibit solid-core porous-shell properties. The fast separation of small molecules and proteins with low back pressure are demonstrated by high-performance liquid chromatography (HPLC) for the columns packed with SOS-particles.

High-throughput preparation of complex multi-scale patterns from block copolymer/homopolymer blend films

A simple, straightforward process for fabricating multi-scale micro- and nanostructured patterns from polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP)/poly(methyl methacrylate) (PMMA) homopolymer in a preferential solvent for PS and PMMA is demonstrated. When the PS-b-P2VP/PMMA blend films were spin-coated onto a silicon wafer, PS-b-P2VP micellar arrays consisting of a PS corona and a P2VP core were formed, while the PMMA macrodomains were isolated, due to the macrophase separation caused by the incompatibility between block copolymer micelles and PMMA homopolymer during the spin-coating process. With an increase of PMMA composition, the size of PMMA macrodomains increased. Moreover, the P2VP blocks have a strong interaction with a native oxide of the surface of the silicon wafer, so that the P2VP wetting layer was first formed during spin-coating, and PS nanoclusters were observed on the PMMA macrodomains beneath. Whereas when a silicon surface was modified with a PS brush layer, the PS nanoclusters underlying PMMA domains were not formed. The multi-scale patterns prepared from copolymer micelle/homopolymer blend films are used as templates for the fabrication of gold nanoparticle arrays by incorporating the gold precursor into the P2VP chains. The combination of nanostructures prepared from block copolymer micellar arrays and macrostructures induced by incompatibility between the copolymer and the homopolymer leads to the formation of complex, multi-scale surface patterns by a simple casting process.

Novel tunable hierarchical Ni-Co hydroxide and oxide assembled from two-wheeled units

A novel hierarchical Ni-Co hydroxide assembled from two-wheeled units was successfully synthesized via a simple, hydrothermal method through the reaction of nickel salt, cobalt salt and sodium hydroxide, and with a chelating agent (EDA) to control the precipitation rate. The as-synthesized materials were characterized by x-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), Fourier transform infrared spectroscopy (FTIR), atomic absorption spectrophotometer (AAS) and thermogravimetric analysis (TG). The Ni(2+)/Co(2+) molar ratio R in the initial solution plays an important role to control the morphology of the hierarchical Ni-Co hydroxide. The influence of the EDA concentration, reaction temperature and NaOH concentration on the formation of the hierarchical Ni-Co hydroxide was also investigated. The formation mechanism of the hierarchical Ni-Co hydroxide assembled by two-wheeled units was proposed. A Ni-Co oxide with a similar structure was obtained by calcination of the as-prepared Ni-Co hydroxide.

Untraditional approach to complex hierarchical periodic arrays with trinary stepwise architectures of micro-, submicro-, and nanosized structures based on binary colloidal crystals and their fine structure enhanced properties

A unique approach for fabricating complex hierarchical periodic arrays with trinary stepwise architectures of micro- and submicro- as well as nanosized structures by combining a novel double-layered binary colloidal crystal with pulsed laser deposition techniques is developed. The present strategy is universal and nanostructures with different materials can be easily prepared in the complex hierarchical periodic arrays. This approach offers the advantage of low costs compared to conventional lithographic techniques. These as-prepared unique structures cannot be directly fabricated by conventional lithography. These special hierarchically structured arrays demonstrate fine structure-enhanced performances, including superhydrophilicity without UV irradiation and surface enhanced Raman scattering (SERS), which is highly valuable for designing micro/nanodevices, such as biosensors or microfluidic devices.

Mimicking natural fibrous structures of opals by means of a microemulsion-mediated hydrothermal method

Silica-based nanomaterials are of great interest because of their potential applications in constructing electronic and optoelectronic nanodevices. Especially significant are those that combine the properties of photonic crystal with a fibrous semiconductor structure. Here we report the use of microemulsion droplet systems as a simple and controllable route for the synthesis of 3D opals materials with an unusual fibrous microstructure similar to those that exist in nature. By this method, we demonstrate the creation of very long fibrils of 30-50 nm diameter and more than 20 μm length showing simultaneous short and long wavelength light emissions and band gap values (5.50 and 4.41 eV) comparable to those obtained for silicon-based metal oxide semiconductors.

Hierarchical superstructure of alkylamine-coated ZnS nanoparticle assemblies

We describe methodology for producing highly uniform, ordered and reproducible superstructures of surfactant-coated ZnS nanorod and nanowire assemblies, and propose a predictive multiscale "packing model" for superstructure formation based on electron microscopy and powder X-ray diffraction data on the superstructure, as well as on individual components of the nanostructured system. The studied nanoparticles showed a hierarchical structure starting from the individual faceted ZnS inorganic cores, onto which the crystalline surfactant molecules are adsorbed, to the superstructure of the nanoparticle arrays. Our results point out the critical role of the surfactant headgroup and polarity in nanoparticle assembly, and demonstrate the relationship between the molecular structure of the surfactant and the resulting superstructure of the nanoparticle assemblies.

Controlled synthesis of PbS-Au nanostar-nanoparticle heterodimers and cap-like Au nanoparticles

Uniform PbS-Au nanostar-nanoparticle heterodimers consisting of one Au nanoparticle grown on one horn of a well-defined six-horn PbS nanostar were prepared using the PbS nanostars as growth substrates for the selective deposition of Au nanoparticles. The size of the Au nanoparticles on the horns of the PbS nanostars could be readily adjusted by changing the PbS concentration for the deposition of Au nanoparticles. An optimum cetyltrimethylammonium bromide concentration and temperature were essential for the selective deposition of uniform Au nanoparticles on single horns of the PbS nanostars. Unusual PbS-Au nanoframe-nanoparticle heterodimers were obtained by etching the PbS-Au nanostar-nanoparticle heterodimers with oxalic acid while novel cap-like Au nanoparticles were obtained by etching with hydrochloric acid. The obtained heterodimeric nanostructures and cap-like nanoparticles are promising candidates for anisotropic nanoscale building blocks for the controllable assembly of useful, complex architectures.