Deriving the colloidal synthesis of crystalline nanosheets to create self-assembly monolayers of nanoclusters

Two-dimensional (2D) nanomaterials with the thickness at atomic level are promising candidates for a wide range of applications, and now reach the point to create diversified 2D architectures. The colloidal synthesis route is powerful to produce crystalline nanosheets, nanoribbons and nanoplatelets, and the self-assembly strategy is robust to integrate the functionalities of different nano-objects. In this review, we bridge the colloidal synthesis of nanosheets and the 2D self-assembly of nanoclusters (NCs) with the aim to further optimize the physical and chemical properties of 2D nanomaterials. Ultrasmall NCs, the intermediate for synthesizing nanosheets, are highlighted to show the similarity of 2D crystallization and 2D self-assembly. The modification of conventional 2D colloidal synthesis route greatly permits the controlled self-assembly of NCs into free-standing monolayers in colloidal solutions.     

Structural and Morphological Modulation of BiOCl Visible-light Photocatalyst Prepared via an In situ Oxidation Synthesis

The evolution of morphology and heterostructure of BiOCl was investigated during an in situ oxidation reaction. Morphology and structure transformation of regular 2D nanoflake, 0D nanosphere or 3D nanoflower was achieved by adjusting the ratio of reagent concentration or reaction temperature, respectively. The enhanced photocatalytic degradation ability and the photocurrent intensity of BiOCl nanomaterials may be attributed to the improved degree of crystallinity and the formation of Bi/BiOCl heterostructure. The photocurrent density of Schottky battery was increased due to enhancing the optical pathway and assisting during charge separation. Crystallinity also contributed to the improvement of the photoelectric conversion efficiency and reduction of the recombination rate of photogenerated electron-hole pairs.     

不同制备方法对BiOCl材料的形貌、结构与光催化性能的影响研究

对比采用溶剂热合成、传统固相合成与溶胶-凝胶合成技术,制备了四方相BiOC1和Nd3+掺杂BiOCl光催化材料.运用X射线粉末衍射(XRD)、扫描电子显微镜(SEM)及紫外-可见吸收光谱(UV-Vis),研究了不同合成方法所制备BiOCl材料的相结构、形貌和紫外-可见光吸收性能;并以甲基橙溶液为模拟废水,研究了不同方法所制备的BiOCl材料的光催化性能.结果表明:溶剂热合成的BiOCl是由纳米片组装成粒径小于1μm微球,紫外-可见吸收边为335 nm;固相合成所得BiOCl结晶度较高,其片状颗粒粒径约为6μm,紫外-可见吸收边为430n m;溶胶-凝胶合成法制得BiOCl片状颗粒粒径约为3～4 μm,紫外-可见吸收边为430 nm.进一步地对比研究了稀土离子Nd3+掺杂前后BiOCl样品的结构、紫外-可见光吸收特性,可以发现,Nd3+掺杂后样品的相结构及形貌均无变化,但吸收边均发生不同程度的红移,以溶胶-凝胶法制得的样品效果最为明显,并具有最优的光催化性能.     

Gold and silver nanoparticles as tools to combat multidrug-resistant pathogens

The sudden emergence and rapid spreading of viral, bacterial, and fungal infections and the usual development of resistance against traditional molecular drugs prompt the urgent need for alternative approaches to kill or inactivate pathogenic agents. This motivation has inspired a vast number of research works devoted to the design, synthesis, and application of nanomaterials, specifically inorganic plasmonic nanoparticles, as antimicrobial agents. We will pay special attention to articles from 2019 to 2023 where control of the colloidal properties, i.e., size, morphology, and colloidal stability, are properly considered. Here we will discuss the latest advancement in synthesis, colloidal characterization, and antimicrobial activity of Au and Ag nanoparticles, as well as hybrid systems based on combining metallic NPs with inorganic and organic materials. We will also consider contributions focusing on the green synthesis of plasmonic particles, highlighting the opportunities and the need for better control and predictivity of colloidal and functional properties.     

Immobilization of bismuth oxychloride on cellulose nanocrystal for photocatalytic sulfonylation of arylacetylenic acids with sodium arylsulfinates under visible light

As a promising semiconductor photocatalyst, BiOCl has been widely used in the field of environmental protection. However, due to its weak ability to absorb visible light, the application of BiOCl in other important photocatalytic fields has been significantly limited, such as organic synthesis. In this work, a facile method was used to prepare a highly efficient heterogeneous nano-photocatalyst BiOCl/cellulose nanocrystal (CNC). Subsequently, the BiOCl/CNC was verified by XPS, ESR, BET and other characterization methods. The results show that not only the strong interaction between BiOCl and CNC increases the visible light absorption intensity of the composite, but also the combination of BiOCl and CNC makes the specific area of the catalyst more than twofold. In addition, a large number of hydroxyl groups contained in CNC can be combined with the BO bond in BiOCl through hydrogen bonds, forming abundant oxygen vacancies on BiOCl/CNC. Excitedly, these changes enable BiOCl/CNC to exhibit excellent photocatalytic performance and regeneration performance in the sulfonation reaction of arylacetylene acid and sodium arylsulfinate, with a yield of up to 96%. This work represents a step towards a low-cost, environmentally friendly composite of cellulose and BiOCl, which will provide useful enlightenment for future exploration in related fields.     

Fabrication of FeOOH/BiOCl Nanocomposites with Enhanced Visible Light Photocatalytic Activity

BiOCl as a two‐dimensional layer ternary oxide semiconductor, has been widely used in energy and environmental area due to its non‐toxicity, price and the good photocatalytic performance. However, BiOCl has a wide bandgap and can only absorb ultraviolet light, which limits its solar energy conversion efficiency for practical application. Herein, we report a facile synthesis of FeOOH/BiOCl nanocomposites by hydrothermal method. The results of XPS and FT‐IR indicated that FeOOH has been loaded on the nanocomposites. The chemical and optical properties of the nanocomposite are well‐characterized. The nanocomposite showed much more excellent photocatalytic performance compared with the individual FeOOH and BiOCl single component. Reactive specie trapping experiment indicated that · O^2– and h⁺ were the two main active species during the photocatalytic process of FeOOH/BiOCl nanocomposites.     

Enhancement of the stability and reaction rate by thenoyl and CF3 groups in the formation of gold nanocrystals using β-diketones

We describe a synthetic route for the high yield production of Au nanomaterials via a simple one step reduction process. Thenoyltrifluoroacetone was used as a reducing and stabilizing agent as well for the synthesis of gold nanoparticles. The reaction rate for the formation of Au nanoparticles using thenoyltrifluoroacetone was much faster than that of any other β-diketones such as acetylacetone. By simply varying the reaction temperature and the concentration, the shape and size of the resulting Au nanocrystals were easily controlled. The colloidal state of the Au nanocrystals in water lasts several weeks without any spectral changes.     

A macrocycle-assisted nanoparticlization process for bulk Ag2S

We report herein a new nanoparticlization process for the bulk-to-nano transformation of Ag₂S by incorporating both top-down and bottom-up approaches. Bulk Ag₂S was dissolved in solution with the assistance of a macrocyclic ligand, hexamethylazacalix[6]pyridine (Py[6]), to produce polynuclear silver sulfide cluster aggregates. All Ag–S cluster aggregates obtained in three crystalline complexes were protected by Py[6] macrocycles. Removing the protective Py[6] macrocycles by protonation led to the generation of unconventional Ag–S nanoparticles with a large energy gap. Theoretical calculations by a hybrid DFT method demonstrated that the silver sulfide clusters with high Ag/S ratio exhibited more localized HOMO–LUMO orbitals, which consequently enlarged their band gap energies. These experimental and theoretical studies broaden our understanding of the fabrication of nanomaterials by virtue of the advantages of both bottom-up and top-down methods and meanwhile provide a viable means of adjusting the band gap of binary nanomaterials independent of their size.     

WO3/BiOCl, a novel heterojunction as visible light photocatalyst

A bismuth oxychloride (BiOCl) nanostructure is prepared by a new low temperature route using sodium dodecyl sulfate as template and urea as hydrolytic agent. A novel heterojunction is developed between BiOCl and tungsten oxide (WO(3)) to make it an efficient visible light photocatalyst. The catalysts were characterized by X-ray diffraction analysis, Raman spectroscopy, thermogravimetric analysis, energy-dispersive X-ray spectroscopy, scanning electron microscopy, transmission electron microscopy, and N(2) sorption isotherms. The WO(3)/BiOCl heterojunction system extends the absorption edge to the visible region efficiently. BiOCl works as a main photocatalyst while WO(3) acts as the photosensitizer absorbing visible light in the WO(3)/BiOCl composite. The individual BiOCl and WO(3) show very low photocatalytic efficiency under visible light irradiation but their heterojunction provides unexpectedly high efficiency in decomposing rhodamine B as compared to Degussa P25, pure BiOCl, and WO(3).     

Photochemical Synthesis of Gold and Silver Nanoparticles—A Review

Nanomaterials have supported important technological advances due to their unique properties and their applicability in various fields, such as biomedicine, catalysis, environment, energy, and electronics. This has triggered a tremendous increase in their demand. In turn, materials scientists have sought facile methods to produce nanomaterials of desired features, i.e., morphology, composition, colloidal stability, and surface chemistry, as these determine the targeted application. The advent of photoprocesses has enabled the easy, fast, scalable, and cost- and energy-effective production of metallic nanoparticles of controlled properties without the use of harmful reagents or sophisticated equipment. Herein, we overview the synthesis of gold and silver nanoparticles via photochemical routes. We extensively discuss the effect of varying the experimental parameters, such as the pH, exposure time, and source of irradiation, the use or not of reductants and surfactants, reagents’ nature and concentration, on the outcomes of these noble nanoparticles, namely, their size, shape, and colloidal stability. The hypothetical mechanisms that govern these green processes are discussed whenever available. Finally, we mention their applications and insights for future developments.     

A Facile Controllable Synthesis, Growth Mechanism, and Photocatalytic Properties of Nanoscale BiOCl

Nanoscale tetragonal BiOCl samples have been synthesized using Bi[SC12H25]3 and CHCl3 as bismuth and chlorine sources by solvothermal reactions. The structure, morphology, and formation process have been investigated by SEM, TEM, HRTEM, XRD, and EDX analyses. The layered crystal structure feature of BiOCl may induce the growth of nano plates, which can subsequently aggregate into 3D spherical or flower-like microstructures under the presence of ethanol. The reaction temperature and the identity of secondary solvent influence the morphology. The yield of BiOCl depends on the completeness of the reaction and the degree of a competition reduction of BiOCl to Bi by ethanol. The as-synthesized 3D quasi-spherical BiOCl sample has an optical band gap of 3.15 eV, and shows much better photocatalytic performance on the degradation of methyl orange than that of commercial P25.     

Electronic Structure and Optical-absorption Properties of C-, N-, and S-doped BiOCl: the First-principles Calculations

Impurity formation energy, electronic structure, and photocatalytic properties of C-, N-, or S-doped BiOCl are investigated by density-functional theory plus U calculations(DFT + U). Results show that the doping effect of S is better than that of C or N on the tunable photocatalytic activities of BiOCl. At low concentration, S-doped BiOCl systems are the most stable under Bi-rich growth conditions because of their lower impurity-formation energy. Compared with the electronic structures of S-doped BiOCl, C-or N-doped BiOCl have relatively deeper impurity energy levels appearing in their band gap(except Bi_(36)O_(35)NCl_(36)), which may act as photogenerated carrier-recombination centers and reduce photocatalytic activity. At high concentration, S is substituted on the O lattice site system, whereas some S 3p states mix with the valence band; this mixture leads to an obvious band-gap decrease and continuum-state formation above the valence-band edge of BiOCl. Such activity is advantageous to photochemical catalysis response. Compared with pure Bi OCl and a low-concentration S-doped system, a high-concentration S-doped system shows an obvious redshift on the absorption edge and has better photocatalytic O_2 evolution performance.     

Solar‐Light‐Driven Pure Water Splitting with Ultrathin BiOCl Nanosheets

A suitable photocatalyst for overall water splitting has been produced by overcoming the disadvantage of the band structure in bulk BiOCl by reducing the thickness to the quantum scale. The ultrathin BiOCl nanosheets with surface/subsurface defects realized the solar‐driven pure water splitting in the absence of any co‐catalysts or sacrificial agent. These surface defects cannot only shift both the valence band and conduction band upwards for band‐gap narrowing but also promote charge‐carrier separation. The amount of defects in the outer layer surface of BiOCl results in an enhancement of carrier density and faster charge transport. First‐principles calculations provide clear evidence that the formation of surface oxygen vacancies is easier for the ultrathin BiOCl nanosheets than for its thicker counterpart. These defects can serve as active sites to effectively adsorb and dissociate H₂O molecules, resulting in a significantly improved water‐splitting performance.     

Synthesis and assembly of rare earth nanostructures directed by the principle of coordination chemistry in solution-based process

In this review, several typical nanomaterials are selected to demonstrate the coordination effect on the control of structure/microstructure/texture, surface/interface, particle size and morphology. Based on the principle of coordination chemistry, with some solution-based methods including solvothermal treatment and the thermolysis of metal complex precursors, a series of novel nanostructured rare earth compounds, such as ultra-small colloidal ceria nanoparticles, highly homogenous and stable ceria–zirconia solid solutions, and high-quality rare earth oxide and fluoride nanocrystals, etc., have been prepared by elaborately controlling the synthetic parameters and reaction kinetics. In order to reveal the mechanisms of synthesis, assembly, and properties, the phase, microstructure, texture, and surface state have been characterized systematically. The main applications of coordination chemistry principle in the synthesis and assembly of rare earth nanocrystals have been summarized, which also can be extended to direct the fabrication of other nanomaterials.     

Quantitative Evaluation of the Total Magnetic Moments of Colloidal Magnetic Nanoparticles: A Kinetics‐based Method

A kinetics‐based method is proposed to quantitatively characterize the collective magnetization of colloidal magnetic nanoparticles. The method is based on the relationship between the magnetic force on a colloidal droplet and the movement of the droplet under a gradient magnetic field. Through computational analysis of the kinetic parameters, such as displacement, velocity, and acceleration, the magnetization of colloidal magnetic nanoparticles can be calculated. In our experiments, the values measured by using our method exhibited a better linear correlation with magnetothermal heating, than those obtained by using a vibrating sample magnetometer and magnetic balance. This finding indicates that this method may be more suitable to evaluate the collective magnetism of colloidal magnetic nanoparticles under low magnetic fields than the commonly used methods. Accurate evaluation of the magnetic properties of colloidal nanoparticles is of great importance for the standardization of magnetic nanomaterials and for their practical application in biomedicine.     

Synthesis and Assembly of Dipolar Heterostructured Tetrapods: Colloidal Polymers with “Giant tert‐butyl” Groups

We report on the first synthesis of a heterostructured semiconductor tetrapod from CdSe@CdS that carries a single dipolar nanoparticle tip from a core–shell colloid of Au@Co. A four‐step colloidal total synthesis was developed, where the key step in the synthesis was the selective deposition of a single AuNP tip onto a CdSe@CdS tetrapod under UV‐irradiation. Synthetic accessibility to this dipolar heterostructured tetrapod enabled the use of these as colloidal monomers to form colloidal polymers that carry the semiconductor tetrapod as a side chain group attached to the CoNP colloidal polymer main chain. The current report details a number of novel discoveries on the selective synthesis of an asymmetric heterostructured tetrapod that is capable of 1D dipolar assembly into colloidal polymers that carry tetrapods as side chain groups that mimic “giant tert‐butyl groups”.     

Unprecedented Eighteen‐Faceted BiOCl with a Ternary Facet Junction Boosting Cascade Charge Flow and Photo‐redox

Exposure of anisotropic crystal facets allows the directional transfer of photoexcited electrons (e^?) and holes (h⁺), for spatial charge separation. High‐index facets with a high density of low‐coordinated atoms always serve as reactive catalytic sites. However, preparation of multi‐facets or high‐index facets is highly challenging for layered bismuth‐based photocatalysts. Herein, we report the preparation of unprecedented eighteen‐faceted BiOCl with {001} top facets and {102} and {112} oblique facets via a hydrothermal process. Compared to the conventional BiOCl square plates with {001} top facets and {110} lateral facets, the eighteen‐faceted BiOCl has highly enhanced photocatalytic activity for H₂ evolution and hydroxyl radicals (^.OH) production. Theoretical calculations and photodeposition results disclose that the of eighteen‐faceted BiOCl has a well‐matched {001}/{102}/{112} ternary facet junction, which provides a cascade path for more efficient charge flow than the binary facet junction in BiOCl square plates.     

The Microwave‐Assisted Ionic‐Liquid Method: A Promising Methodology in Nanomaterials

In recent years, the microwave‐assisted ionic‐liquid method has been accepted as a promising methodology for the preparation of nanomaterials and cellulose‐based nanocomposites. Applications of this method in the preparation of cellulose‐based nanocomposites comply with the major principles of green chemistry, that is, they use an environmentally friendly method in environmentally preferable solvents to make use of renewable materials. This minireview focuses on the recent development of the synthesis of nanomaterials and cellulose‐based nanocomposites by means of the microwave‐assisted ionic‐liquid method. We first discuss the preparation of nanomaterials including noble metals, metal oxides, complex metal oxides, metal sulfides, and other nanomaterials by means of this method. Then we provide an overview of the synthesis of cellulose‐based nanocomposites by using this method. The emphasis is on the synthesis, microstructure, and properties of nanostructured materials obtained through this methodology. Our recent research on nanomaterials and cellulose‐based nanocomposites by this rapid method is summarized. In addition, the formation mechanisms involved in the microwave‐assisted ionic‐liquid synthesis of nanostructured materials are discussed briefly. Finally, the future perspectives of this methodology in the synthesis of nanostructured materials are proposed.     

BiOCl/UiO‐66 composite with enhanced performance for photo‐assisted degradation of dye from water

Semiconductor‐based photocatalysis is an environmental friendly and cost‐effective technique for water treatment. Due to their unique properties, metal–organic frameworks (MOFs) are considered as ideal platform to develop composite photocatalyst. In this study, Bismuth oxychloride (BiOCl) was first attempt to be incorporated with highly stable MOFs, UiO‐66(Zr) by hydrothermal reaction. Different characterization methods including X‐ray diffraction, Scanning electron microscopy, Fourier transform infrared spectroscope, X‐ray photoelectron spectroscopy had been used to prove the successful synthesis of composite photocatalyst. The resultant BiOCl/UiO‐66 composite showed higher photodegradation performance of Rhodamine B (RhB) under ultraviolet and visible light irradiation than that of pristine materials and their mechanically mixed sample. In addition, the composite exhibited good structural stability and reusability. The photocatalytic mechanism of RhB degradation over the composite under visible light proceeded via a photosensitization process. A better adsorptivity of RhB and effective electron transfer within the hybrid material might be responsible for the enhanced photocatalytic performance.     

Chemically bonded graphene/BiOCl nanocomposites as high-performance photocatalysts

After the successful solvothermal synthesis of graphene (GR) from ethanol and sodium, we obtained chemically bonded graphene/BiOCl (GR/BiOCl) nanocomposite photocatalysts via a facile chemical-bath method. A significant enhancement was observed in the photodegradation of methylbenzene, which was largely ascribed to the chemical coupling effects between Bi and C, as shown by X-ray photoelectron spectroscopy. Raman spectroscopy also indicated an increased size of the sp(2) ring clusters and decreased disorder in the graphitic structure, as substitutions of defects like vacancies as well as oxygen containing carbonaceous groups with C-Bi attachment take place. Overall, information about chemical coupling effects between GR and BiOCl might take us a step further in GR-based hybrid materials, providing a very good reference to the fabrication of chemically bonded GR/semiconductor compounds and facilitating their applications in environmental protection, photo-electrochemical conversion and photocatalytic decomposition of water.