Controlled synthesis of semiconductor nanostructures in the liquid phase

Polytypic metal chalcogenide nanocrystals

By engineering chemically identical but structurally distinct materials into intricate and sophisticated polytypic nanostructures, which often surpass their pure phase objects and even produce novel physical and chemical properties, exciting applications in the fields of photovoltaics, electronics and photocatalysis can be achieved. In recent decades, various methods have been developed for synthesizing a library of polytypic nanocrystals encompassing IV, III-V and II-VI polytypic semiconductors. The exceptional performances of polytypic metal chalcogenide nanocrystals have been observed, making them highly promising candidates for applications in photonics and electronics. However, achieving high-precision control over the morphology, composition, crystal structure, size, homojunctions, and periodicity of polytypic metal chalcogenide nanostructures remains a significant synthetic challenge. This review article offers a comprehensive overview of recent progress in the synthesis and control of polytypic metal chalcogenide nanocrystals using colloidal synthetic strategies. Starting from a concise introduction on the crystal structures of metal chalcogenides, the subsequent discussion delves into the colloidal synthesis of polytypic metal chalcogenide nanocrystals, followed by an in-depth exploration of the key factors governing polytypic structure construction. Subsequently, we provide comprehensive insights into the physical properties of polytypic metal chalcogenide nanocrystals, which exhibit strong correlations with their applications. Thereafter, we emphasize the significance of polytypic nanostructures in various applications, such as photovoltaics, photocatalysis, transistors, thermoelectrics, stress sensors, and the electrocatalytic hydrogen evolution. Finally, we present a summary of the recent advancements in this research field and provide insightful perspectives on the forthcoming challenges, opportunities, and future research directions.

Research progress of out-of-plane GeSn nanowires

With the increasing integration density of silicon-based circuits, traditional electrical interconnections have shown their technological limitations. In recent years, GeSn materials have attracted great interest due to their potential direct bandgap transition and compatibility with silicon-based technologies. GeSn materials, including GeSn films, GeSn alloys, and GeSn nanowires, are adjustable, scalable, and compatible with silicon. GeSn nanowires, as one-dimensional (1D) nanomaterials, including out-of-plane GeSn nanowires and in-plane GeSn nanowires, have different properties from those of bulk materials due to their distinctive structures. However, the synthesis and potential applications of out of plane GeSn nanowires are rarely compared to highlighting their current development status and research trends in relevant review papers. In this article, we present the preparation of out-of-plane GeSn nanowires using top-down (etching and lithography) and bottom-up (vapor-liquid-solid) growth mechanism in the vapor-phase method and supercritical fluid-liquid-solid, solution-liquid-solid, and solvent vapor growth mechanisms in the liquid-phase method) methods. Specifically, the research progress on typical out of plane GeSn nanowires are discussed, while some current development bottlenecks are also been identified. Finally, it is also provided a brief description of the applications of out-of-plane GeSn nanowires with various Sn contents and morphologies.

Recent advances of modification effect in Co3O4-based catalyst towards highly efficient photocatalysis

Tricobalt tetroxide (Co3O4) has been developed as a promising photocatalyst material for various applications. Several reports have been published on the self-modification of Co3O4 to achieve optimal photocatalytic performance. The pristine Co3O4 alone is inadequate for photocatalysis due to the rapid recombination process of photogenerated (PG) charge carriers. The modification of Co3O4 can be extended through the introduction of doping elements, incorporation of supporting materials, surface functionalization, metal loading, and combination with other photocatalysts. The addition of doping elements and support materials may enhance the photocatalysis process, although these modifications have a slight effect on decreasing the recombination process of PG charge carriers. On the other hand, combining Co3O4 with other semiconductors results in a different PG charge carrier mechanism, leading to a decrease in the recombination process and an increase in photocatalytic activity. Therefore, this work discusses recent modifications of Co3O4 and their effects on its photocatalytic performance. Additionally, the modification effects, such as enhanced surface area, generation of oxygen vacancies, tuning the band gap, and formation of heterojunctions, are reviewed to demonstrate the feasibility of separating PG charge carriers. Finally, the formation and mechanism of these modification effects are also reviewed based on theoretical and experimental approaches to validate their formation and the transfer process of charge carriers.

Emerging 2D pnictogens: a novel multifunctional photonic nanoplatform for cutting-edge precision treatment

The elements of the pnictogen group, known as the 15th (VA) family in the periodic table, including phosphorus (P), arsenic (As), antimony (Sb) and bismuth (Bi), have been widely used by alchemists to treat various diseases since ancient times and hold a pivotal position in the history of medicine, owing to their diverse pharmacological activities. Recently, with the development of modern nanotechnology, pnictogen group elements appear in a more innovative form, namely two-dimensional (2D) pnictogens (i.e. phosphorene, arsenene, and bismuthene) with a unique layered crystal structure and extraordinary optoelectronic characteristics, which endow them with significant superiority as a novel multifunctional photonic nanoplatform for cutting-edge precision treatment of various diseases. The puckered layer structure with ultralarge surface area make them ideal drug and gene delivery vectors that can avoid degradation and reduce target effects. The anisotropic morphology allows their easier internalization by cells and may improve gene transfection efficiency. Tunable optoelectronic characteristics endow them with excellent phototherapy performance as well as the ability to act as an optical switch to initiate subsequent therapeutic events. This review provides a brief overview of the properties, preparation and surface modifications of 2D pnictogens, and then focuses on its applications in cutting-edge precision treatment as a novel multifunctional photonic nanoplatform, such as phototherapy, photonic medicine, photo-adjuvant immunotherapy and photo-assisted gene therapy. Finally, the challenges and future development trends for 2D pnictogens are provided. With a focus on 2D pnictogen-based multifunctional photonic nanoplatforms, this review may also provide profound insights for the next generation innovative precision therapy.

2D Zinc Oxide - Synthesis, Methodologies, Reaction Mechanism, and Applications

Zinc oxide (ZnO) is a thermally stable n-type semiconducting material. ZnO 2D nanosheets have mainly gained substantial attention due to their unique properties, such as direct bandgap and strong excitonic binding energy at room temperature. These are widely utilized in piezotronics, energy storage, photodetectors, light-emitting diodes, solar cells, gas sensors, and photocatalysis. Notably, the chemical properties and performances of ZnO nanosheets largely depend on the nano-structuring that can be regulated and controlled through modulating synthetic strategies. Two synthetic approaches, top-down and bottom-up, are mainly employed for preparing ZnO 2D nanomaterials. However, owing to better results in producing defect-free nanostructures, homogenous chemical composition, etc., the bottom-up approach is extensively used compared to the top-down method for preparing ZnO 2D nanosheets. This review presents a comprehensive study on designing and developing 2D ZnO nanomaterials, followed by accenting its potential applications. To begin with, various synthetic strategies and attributes of ZnO 2D nanosheets are discussed, followed by focusing on methodologies and reaction mechanisms. Then, their deliberation toward batteries, supercapacitors, electronics/optoelectronics, photocatalysis, sensing, and piezoelectronic platforms are further discussed. Finally, the challenges and future opportunities are featured based on its current development.

Synthesis of unconventional Pd-Se nanoparticles for phase-dependent ethanol electrooxidation

By tuning the amount of the Se precursors during the synthesis, orthorhombic PdSe₂, cubic Pd₁₇Se₁₅, and monoclinic Pd₇Se₂ nanoparticles are synthesized, which show phase-dependent electrocatalysis for the ethanol oxidation reaction. This work advances the controllable synthesis of transition metal selenides and inspires their applications in electrocatalysis.

Heterogeneous Iridium Single-Atom Molecular-like Catalysis for Epoxidation of Ethylene

Developing efficient and simple catalysts to reveal the key scientific issues in the epoxidation of ethylene has been a long-standing goal for chemists, whereas a heterogenized molecular-like catalyst is desirable which combines the best aspects of homogeneous and heterogeneous catalysts. Single-atom catalysts can effectively mimic molecular catalysts on account of their well-defined atomic structures and coordination environments. Herein, we report a strategy for selective epoxidation of ethylene, which exploits a heterogeneous catalyst comprising iridium single atoms to interact with the reactant molecules that act analogously to ligands, resulting in molecular-like catalysis. This catalytic protocol features a near-unity selectivity (99%) to produce value-added ethylene oxide. We investigated the origin of the improvement of selectivity for ethylene oxide for this iridium single-atom catalyst and attributed the improvement to the π-coordination between the iridium metal center with a higher oxidation state and ethylene or molecular oxygen. The molecular oxygen adsorbed on the iridium single-atom site not only helps to strengthen the adsorption of ethylene molecule by iridium but also alters its electronic structure, allowing iridium to donate electrons into the double bond π* orbitals of ethylene. This catalytic strategy facilitates the formation of five-membered oxametallacycle intermediates, leading to the exceptionally high selectivity for ethylene oxide. Our model of single-atom catalysts featuring remarkable molecular-like catalysis can be utilized as an effective strategy for inhibiting the overoxidation of the desired product. Implementing the concepts of homogeneous catalysis into heterogeneous catalysis would provide new perspectives for the design of new advanced catalysts.

Electric, magnetic, and shear field-directed assembly of inorganic nanoparticles

Ordered assemblies of inorganic nanoparticles (NPs) have shown tremendous potential for wide applications due to their unique collective properties, which differ from those of individual NPs. Various assembly methods, such as external field-directed assembly, interfacial assembly, template assembly, biomolecular recognition-mediated assembly, confined assembly, and others, have been employed to generate ordered inorganic NP assemblies with hierarchical structures. Among them, the external field-directed assembly method is particularly fascinating, as it can remotely assemble NPs into well-ordered superstructures. Moreover, external fields (e.g., electric, magnetic, and shear fields) can introduce a local and/or global field intensity gradient, resulting in an additional force on NPs to drive their rotation and/or translation. Therefore, the external field-directed assembly of NPs becomes a robust method to fabricate well-defined functional materials with the desired optical, electronic, and magnetic properties, which have various applications in catalysis, sensing, disease diagnosis, energy conversion/storage, photonics, nano-floating-gate memory, and others. In this review, the effects of an electric field, magnetic field, and shear field on the organization of inorganic NPs are highlighted. The methods for controlling the well-ordered organization of inorganic NPs at different scales and their advantages are reviewed. Finally, future challenges and perspectives in this field are discussed.

Emerging 2D Copper-Based Materials for Energy Storage and Conversion: A Review and Perspective

2D materials have shown great potential as electrode materials that determine the performance of a range of electrochemical energy technologies. Among these, 2D copper-based materials, such as Cu-O, Cu-S, Cu-Se, Cu-N, and Cu-P, have attracted tremendous research interest, because of the combination of remarkable properties, such as low cost, excellent chemical stability, facile fabrication, and significant electrochemical properties. Herein, the recent advances in the emerging 2D copper-based materials are summarized. A brief summary of the crystal structures and synthetic methods is started, and innovative strategies for improving electrochemical performances of 2D copper-based materials are described in detail through defect engineering, heterostructure construction, and surface functionalization. Furthermore, their state-of-the-art applications in electrochemical energy storage including supercapacitors (SCs), alkali (Li, Na, and K)-ion batteries, multivalent metal (Mg and Al)-ion batteries, and hybrid Mg/Li-ion batteries are described. In addition, the electrocatalysis applications of 2D copper-based materials in metal-air batteries, water-splitting, and CO₂ reduction reaction (CO₂ RR) are also discussed. This review also discusses the charge storage mechanisms of 2D copper-based materials by various advanced characterization techniques. The review with a perspective of the current challenges and research outlook of such 2D copper-based materials for high-performance energy storage and conversion applications is concluded.

Photocatalytic Degradation of Tetracycline in Aqueous Solution Using Copper Sulfide Nanoparticles

In this paper, spherical-shaped pure phase djurleite (Cu31S16) and roxbyite (Cu7S4) nanoparticles were prepared by a solvothermal decomposition of copper(II) dithiocarbamate complex in dodecanthiol (DDT). The reaction temperature was used to control the phases of the samples, which were represented as Cu31S16 (120 °C), Cu31S16 (150 °C), Cu7S4 (220 °C), and Cu7S4 (250 °C) and were characterized by using X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM), and absorption spectroscopy. The samples were used as photocatalysts for the degradation of tetracycline (TC) under visible light irradiation. The results of the study showed that Cu7S4 (250 °C) exhibited the best activity in the reaction system with the TC degradation rate of up to 99% within 120 min of light exposure, while the Cu31S16 (120 °C) system was only 46.5% at the same reaction condition. In general, roxbyite Cu7S4 (250 °C) could be considered as a potential catalyst for the degradation of TC in solution.

A review on bismuth oxyhalide based materials for photocatalysis

Photocatalytic solar energy transformation is the most encouraging solution to alleviate the environmental crisis and energy scarcity. Bismuth oxyhalide (BiOX) is an emerging class of materials that exhibits photocatalytic properties, such as resilient response to light, which causes enhanced energy conversion (solar energy) owing to their exceptional layered structure and attractive band structure. The present review presents a summary of results from the recent developments on the tuning and design of BiOX-based materials to improve the energy conversion. In particular, the preparation and tuning approaches that have the potential to enhance the photocatalytic behavior of BiOX and some other techniques, such as elemental doping, are addressed, which prevent the rapid recombination of charges, and formation of oxygen vacancies, facilitating an improvement in the photocatalytic reaction. Various frameworks are also presented, displaying the significance of BiOX-based nanocomposites. Finally, the main challenges and opportunities associated with the future progress of BiOX-based materials are presented. This review will provide an extended understanding and offer a preferred direction for the innovative design of BiOX-based materials for environmental and especially energy-based applications.

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.

Cost-effective synthesis and characterization of CuO NPs as a nanosize adsorbent for As (III) remediation in synthetic arsenic-contaminated water

The lower concentration of arsenic in the groundwater is serious health concerns of the people who are continuously taking from their drinking water. In this study, synthetic arsenic-contaminated water was prepared in the laboratory with varying concentrations of arsenic (100 to 1000 μg/L) and treated by nanosize adsorbent (copper oxide nanoparticles (CuO NPs)). The colloidal and powder form of CuO NPs were synthesized in the laboratory by the hydrothermal technique on a large scale and their shape and size were confirmed by XRD, FTIR, FESEM, and HRTEM analysis. It was found 30 ± 2 nm as size and spherical shape. The equilibrium adsorption of As (III) occurred at 90 min of contact time, pH 7.5, and 4 g/L adsorbent dosage. The maximum percent removal of As (III) was reached to 97.8, 94.6, 91.5, and 88.4% at an initial arsenic concentration of 100, 200, 500, and 1000 μg/L, respectively. The adsorption of As (III) followed pseudo-second-order kinetic and Freundlich isotherm model. Moreover, the overall cost of the synthesized CuO NPs (including material, operational, manpower, and transport cost with other overhead charges) was Rs. 281.832 g^-1, which is lesser than the market price (Rs. 500.018 g^-1). Hence, the optimized adsorption design would help for the efficient removal of As (III) from aqueous medium.

Optimized Metal Chalcogenides for Boosting Water Splitting

Electrocatalytic water splitting (2H2O → 2H2 + O2) is a very promising avenue to effectively and environmentally friendly produce highly pure hydrogen (H2) and oxygen (O2) at a large scale. Different materials have been developed to enhance the efficiency for water splitting. Among them, chalcogenides with unique atomic arrangement and high electronic transport show interesting catalytic properties in various electrochemical reactions, such as the hydrogen evolution reaction, oxygen evolution reaction, and overall water splitting, while the control of their morphology and structure is of vital importance to their catalytic performance. Herein, the general synthetic methods are summarized to prepare metal chalcogenides and different strategies are designed to improve their catalytic performance for water splitting. The remaining challenges in the research and development of metal chalcogenides and possible directions for future research are also summarized.

Facile synthesis of boronic acid-decorated carbon nanodots as optical nanoprobes for glycoprotein sensing

In this article, we proposed new nitrogen-doped boronic acid-decorated carbon nanodots (CNDs) for the recognition and detection of glycoproteins. These doped, decorated CNDs were obtained by a one-step hydrothermal carbonization method using phenylboronic acid and ethylenediamine as precursors. Compared to traditional synthesized and then functionalized nanoscale sensing systems, this method is more facile and efficient. The as-prepared nitrogen-doped CNDs possessed a quasi-spherical morphology and a high quantum yield of approximately 14.5%. The added glycoproteins (taking horseradish peroxidase as a model protein) can selectively induce the assembly and fluorescence quenching of CNDs through the formation of cyclic boronate esters, because the boronic acid groups on the CND surfaces can covalently interact with cis-diol-containing glycoproteins. These fluorescence responses can be used to properly quantify horseradish peroxidase in the range of 3.3-333.3 μg mL-1 with a detection limit of 0.52 μg mL-1, and the selectivity assay with functionalized CNDs was further investigated using various proteins with different quantities of glycosylation sites as well as using smaller molecules. The results show that the nanosensing system possesses favorable selectivity. Due to its simplicity and effectiveness, the system has great application prospects as a practical platform for glycoprotein sensing.

Small Surface, Big Effects, and Big Challenges: Toward Understanding Enzymatic Activity at the Inorganic Nanoparticle-Substrate Interface

Enzymes are important biomarkers for molecular diagnostics and targets for the action of drugs. In turn, inorganic nanoparticles (NPs) are of interest as materials for biological assays, biosensors, cellular and in vivo imaging probes, and vectors for drug delivery and theranostics. So how does an enzyme interact with a NP, and what are the outcomes of multivalent conjugation of its substrate to a NP? This invited feature article addresses the current state of the art in answering this question. Using gold nanoparticles (Au NPs) and semiconductor quantum dots (QDs) as illustrative materials, we discuss aspects of enzyme structure-function and the properties of NP interfaces and surface chemistry that determine enzyme-NP interactions. These aspects render the substrate-on-NP configurations far more complex and heterogeneous than the conventional turnover of discrete substrate molecules in bulk solution. Special attention is also given to the limitations of a standard kinetic analysis of the enzymatic turnover of these configurations, the need for a well-defined model of turnover, and whether a "hopping" model can account for behaviors such as the apparent acceleration of enzyme activity. A detailed and predictive understanding of how enzymes turn over multivalent NP-substrate conjugates will require a convergence of many concepts and tools from biochemistry, materials, and interface science. In turn, this understanding will help to enable rational, optimized, and value-added designs of NP bioconjugates for biomedical and clinical applications.

Phase Control in Inorganic Nanocrystals through Finely Tuned Growth at an Ultrathin Scale

Crystalline polymorphs have been considered a prevailing phenomenon in inorganic nanocrystals and provide approaches to modulate fundamental properties and innovative advanced applications. As a basic demand for phase engineering, accessible and controllable synthetic methodologies are indispensable for acquisition of high-quality products in expected phases. Phase stability is also a non-negligible issue that determines continuous gains of functionality and long-term sustainability of characteristic features. Maintaining structural stability of metastable phases provides challenges and opportunities for investigations on fascinating properties and intriguing applications of inorganic nanocrystals. Phase engineering is of great significance to acquire metallic (1T) and semiconducting (2H) Mo- and W-based dichalcogenides for hydrogen evolution reaction (HER) and CO₂ reduction reaction (CO₂RR), respectively. The catalysts in 1T phase have superior electron transfer kinetics and abundant active sites on both basal planes and edges for HER, while ones in 2H phase are preferentially deployed for CO₂RR to utilize edge sites for catalysis and restrain competitive HER activity. In addition, the photocatalytic performance for HER has been enhanced by combining anatase and rutile phases because electron transfer between the two phases during photocatalysis facilitates the separation of charge carriers and thus impedes the recombination of electron-hole pairs. Although ample effort has been devoted to developing phase engineering, principle understanding at an ultrathin scale remains obscure. In this Account, we provide comprehensive insight into work from our group regarding controllable synthesis of inorganic nanocrystals with phase engineering, critical effects on phase stability, and noteworthy studies on phase-related properties and applications. For bulk materials, phase control and transition have a large energy barrier, so they can only be achieved under rigorous conditions. However, at the initial stage of synthesis, especially for nucleation, there are a small quantity of chemical bonds that contribute to regulate phase and structure with ease. In our work, we mainly modulate nucleation and growth at an ultrathin scale to demonstrate facile approaches for phase engineering. This unique perspective makes for a distinct guidance of controllable synthesis and deliberate stabilization of inorganic nanomaterials with phase engineering. We have developed a series of synthetic strategies for phase engineering to fabricate inorganic nanocrystals in a specific phase with controlled size and composition and adjustable morphologies and surface features. Four sorts of models (MoS₂, ZrO₂, In₂O₃, and TiO₂) are used for demonstrating finely tuned growth at an ultrathin scale. However, phase engineering has been regarded as immature because only one phase in polymorphs is thermodynamically stable generally. Phase stability of metastable nanocrystals has attracted much interest. Our substantial investigations illustrate several crucial factors on phase stability, leading to inspiration for facilitating persistent emergence of characteristics and functionalities. By full use of the features of a specific phase, we spotlight ligand-induced surface interactions on coverage-dependent electronic structures and chemisorption effects at one-unit thickness of TiO₂(B) nanomaterials with phase engineering. Meanwhile, an energy conversion system for overall water splitting (OWS) drives forward steps in function-oriented synthesis of MoS₂-based nanomaterials with phase engineering. In the last section, we summarize this theme and highlight several promising directions for future development.

Synthetic Techniques and Functionalization Approaches of 2D Transition Metal Dichalcogenides

As typical graphene analogues, two-dimensional (2D) transition-metal dichalcogenides (TMDs), including MoS2, WS2, etc., have attracted increasing research interest due to their semiconducting characteristics, sizable bandgap, large surface area, and outstanding performance in various applications such as electronics/optoelectronics, sensing, catalysis, and energy storage. For the widespread exploration of TMD nanosheets in fundamental studies and promising applications, a rapid pace of progress has recently been achieved in developing methodologies for reliable and scale-up production of atomically thin TMD nanosheets. In this chapter, we will present a comprehensive overview of different synthetic techniques of 2D TMDs and evaluate their relative merits and demerits. Particularly, the design principle, fabrication mechanism, typical process and special conditions will be emphasized to understand or follow the effective methods for obtaining required TMD nanosheets in single and few layers. Based on these synthetic techniques, further functionalization of TMD nanosheets with ligands and other nanocomponents are also discussed for gaining some specific properties. Based on our knowledge, we finally propose some possible challenges and potential opportunities in the exploitation of TMD nanosheets for novel applications.

Nanocluster-Mediated Synthesis of Diverse ZnTe Nanostructures: from Nanocrystals to 1D Nanobelts

Liquid phase one-pot synthesis of semiconductor nanocrystals, by direct nucleation-growth crystallization, is unsuccessful for synthesis of some kinds of semiconductors. Using ZnTe as an example here, highly disperse ZnTe nanoclusters with diameters of 2-3 nm were first synthesized by a facile solvothermal method. Then the ZnTe nanoclusters were chosen as starting crystallization seeds to mediate the synthesis of flexible semiconductor nanostructures. Three-dimensional (3D) oriented assembly of ZnTe nanoclusters to monodisperse dendrimer-like nanocrystals (DLNCs), and one-dimensional (1D) ZnTe nanobelts with cubic phase, have been achieved successfully. Supported by TEM characterization of time-dependent morphology evolution, the oriented attachment assisted seed growth, based on ZnTe nanoclusters, enabled the 1D flexible ZnTe nanobelts formation, which could reach to ≈10 micrometers length.

Self-Assembled Core-Shell CdTe/Poly(3-hexylthiophene) Nanoensembles as Novel Donor-Acceptor Light-Harvesting Systems

The self-assembly of novel core-shell nanoensembles consisting of regioregular poly(3-hexylthiophene) nanoparticles (P3HT_NPs) of 100 nm as core and semiconducting CdTe quantum dots (CdTe_QDs) as shell with a thickness of a few tens of nanometers was accomplished by employing a reprecipitation approach. The structure, morphology, and composition of CdTe_QDs/P3HT_NPs nanoensembles were confirmed by high-resolution scanning transmission microscopy and dynamic light-scattering studies. Intimate interface contact between the CdTe_QDs shell and the P3HT_NPs core leads to the stabilization of the CdTe_QDs/P3HT_NPs nanoensemble as probed by the steady-state absorption spectroscopy. Effective quenching of the characteristic photoluminescence of CdTe_QDs at 555 nm, accompanied by simultaneous increase in emission of P3HT_NPs at 660 and 720 nm, reveals photoinduced charge-transfer processes. Probing the redox properties of films of CdTe_QDs/P3HT_NPs further proves the formation of a stabilized core-shell system in the solid state. Photoelectrochemical assays on CdTe_QDs/P3HT_NPs films show a reversible on-off photoresponse at a bias voltage of +0.8 V with a 3 times increased photocurrent compared to CdTe_QDs. The improved charge separation is directly related to the unique core-shell configuration, in which the outer CdTe_QDs shell forces the P3HT_NPs core to effectively act as electron acceptor. The creation of novel donor-acceptor core-shell hybrid materials via self-assembly is transferable to other types of conjugated polymers and semiconducting nanoparticles. This work, therefore, opens new pathways for the design of improved optoelectronic devices.

Optical determination of crystal phase in semiconductor nanocrystals

Optical, electronic and structural properties of nanocrystals fundamentally derive from crystal phase. This is especially important for polymorphic II-VI, III-V and I-III-VI₂ semiconductor materials such as cadmium selenide, which exist as two stable phases, cubic and hexagonal, each with distinct properties. However, standard crystallographic characterization through diffraction yields ambiguous phase signatures when nanocrystals are small or polytypic. Moreover, diffraction methods are low-throughput, incompatible with solution samples and require large sample quantities. Here we report the identification of unambiguous optical signatures of cubic and hexagonal phases in II-VI nanocrystals using absorption spectroscopy and first-principles electronic-structure theory. High-energy spectral features allow rapid identification of phase, even in small nanocrystals (∼2 nm), and may help predict polytypic nanocrystals from differential phase contributions. These theoretical and experimental insights provide simple and accurate optical crystallographic analysis for liquid-dispersed nanomaterials, to improve the precision of nanocrystal engineering and improve our understanding of nanocrystal reactions.

Recent Advances in Ultrathin Two-Dimensional Nanomaterials

Since the discovery of mechanically exfoliated graphene in 2004, research on ultrathin two-dimensional (2D) nanomaterials has grown exponentially in the fields of condensed matter physics, material science, chemistry, and nanotechnology. Highlighting their compelling physical, chemical, electronic, and optical properties, as well as their various potential applications, in this Review, we summarize the state-of-art progress on the ultrathin 2D nanomaterials with a particular emphasis on their recent advances. First, we introduce the unique advances on ultrathin 2D nanomaterials, followed by the description of their composition and crystal structures. The assortments of their synthetic methods are then summarized, including insights on their advantages and limitations, alongside some recommendations on suitable characterization techniques. We also discuss in detail the utilization of these ultrathin 2D nanomaterials for wide ranges of potential applications among the electronics/optoelectronics, electrocatalysis, batteries, supercapacitors, solar cells, photocatalysis, and sensing platforms. Finally, the challenges and outlooks in this promising field are featured on the basis of its current development.

Influence of the precursor anion on the photoluminescence properties of ZnO

ZnO nanorod arrays were synthesized by hydrothermal method with two different zinc salts as precursors: zinc acetate and zinc nitrate. Different anions in solution distinctly influence the intrinsic defects in ZnO nanostructures, resulting in different photoluminescence properties. The defects induced by precursors were systematically studied by photoluminescence spectroscopy, X-ray photoelectron spectrometer and electron paramagnetic resonance. The results show that zinc acetate precursor mainly introduces zinc vacancy to the lattice while ZnO nanorods obtained from zinc nitrate contain more interstitial oxygen.

Quantum Dot Surface Engineering: Toward Inert Fluorophores with Compact Size and Bright, Stable Emission

The surfaces of colloidal nanocrystals are complex interfaces between solid crystals, coordinating ligands, and liquid solutions. For fluorescent quantum dots, the properties of the surface vastly influence the efficiency of light emission, stability, and physical interactions, and thus determine their sensitivity and specificity when they are used to detect and image biological molecules. But after more than 30 years of study, the surfaces of quantum dots remain poorly understood and continue to be an important subject of both experimental and theoretical research. In this article, we review the physics and chemistry of quantum dot surfaces and describe approaches to engineer optimal fluorescent probes for applications in biomolecular imaging and sensing. We describe the structure and electronic properties of crystalline facets, the chemistry of ligand coordination, and the impact of ligands on optical properties. We further describe recent advances in compact coatings that have significantly improved their properties by providing small hydrodynamic size, high stability and fluorescence efficiency, and minimal nonspecific interactions with cells and biological molecules. While major progress has been made in both basic and applied research, many questions remain in the chemistry and physics of quantum dot surfaces that have hindered key breakthroughs to fully optimize their properties.

Rapid, controllable growth of silver nanostructured surface-enhanced Raman scattering substrates for red blood cell detection

Silver nanostructured films suitable for use as surface-enhanced Raman scattering (SERS) substrates are prepared in just 2 hours by the solid-state ionics method. By changing the intensity of the external direct current, we can readily control the surface morphology and growth rate of the silver nanostructured films. A detailed investigation of the surface enhancement of the silver nanostructured films using Rhodamine 6G (R6G) as a molecular probe revealed that the enhancement factor of the films was up to 10¹¹. We used the silver nanostructured films as substrates in SERS detection of human red blood cells (RBCs). The SERS spectra of RBCs on the silver nanostructured film could be clearly detected at a laser power of just 0.05 mW. Comparison of the SERS spectra of RBCs obtained from younger and older donors showed that the SERS spectra depended on donor age. A greater proportion of the haemoglobin in the RBCs of older donors was in the deoxygenated state than that of the younger donors. This implies that haemoglobin of older people has lower oxygen-carrying capacity than that of younger people. Overall, the fabricated silver substrates show promise in biomedical SERS spectral detection.

Design, synthesis and applications of core-shell, hollow core, and nanorattle multifunctional nanostructures

With the evolution of nanoscience and nanotechnology, studies have been focused on manipulating nanoparticle properties through the control of their size, composition, and morphology. As nanomaterial research has progressed, the foremost focus has gradually shifted from synthesis, morphology control, and characterization of properties to the investigation of function and the utility of integrating these materials and chemical sciences with the physical, biological, and medical fields, which therefore necessitates the development of novel materials that are capable of performing multiple tasks and functions. The construction of multifunctional nanomaterials that integrate two or more functions into a single geometry has been achieved through the surface-coating technique, which created a new class of substances designated as core-shell nanoparticles. Core-shell materials have growing and expanding applications due to the multifunctionality that is achieved through the formation of multiple shells as well as the manipulation of core/shell materials. Moreover, core removal from core-shell-based structures offers excellent opportunities to construct multifunctional hollow core architectures that possess huge storage capacities, low densities, and tunable optical properties. Furthermore, the fabrication of nanomaterials that have the combined properties of a core-shell structure with that of a hollow one has resulted in the creation of a new and important class of substances, known as the rattle core-shell nanoparticles, or nanorattles. The design strategies of these new multifunctional nanostructures (core-shell, hollow core, and nanorattle) are discussed in the first part of this review. In the second part, different synthesis and fabrication approaches for multifunctional core-shell, hollow core-shell and rattle core-shell architectures are highlighted. Finally, in the last part of the article, the versatile and diverse applications of these nanoarchitectures in catalysis, energy storage, sensing, and biomedicine are presented.

Three-dimensional controlled growth of monodisperse sub-50 nm heterogeneous nanocrystals

The ultimate frontier in nanomaterials engineering is to realize their composition control with atomic scale precision to enable fabrication of nanoparticles with desirable size, shape and surface properties. Such control becomes even more useful when growing hybrid nanocrystals designed to integrate multiple functionalities. Here we report achieving such degree of control in a family of rare-earth-doped nanomaterials. We experimentally verify the co-existence and different roles of oleate anions (OA⁻) and molecules (OAH) in the crystal formation. We identify that the control over the ratio of OA⁻ to OAH can be used to directionally inhibit, promote or etch the crystallographic facets of the nanoparticles. This control enables selective grafting of shells with complex morphologies grown over nanocrystal cores, thus allowing the fabrication of a diverse library of monodisperse sub-50 nm nanoparticles. With such programmable additive and subtractive engineering a variety of three-dimensional shapes can be implemented using a bottom–up scalable approach.

Atomic-level control over size, shape and surface composition of nanoparticles is vital for developing materials with integrated multiple functionalities. Here, the authors probe the different roles of oleate ions and oleic acid molecules and their effects on growth mechanisms for sub-50 nm nanoparticles.

Dislocation-driven growth of porous CdSe nanorods from CdSe·(ethylenediamine)(0.5) nanorods

Porous CdSe nanorods having a novel flute-like morphology have been prepared facilely via the hydrothermal treatment of CdSe·(en)0.5 (en = ethylenediamine) nanorods as sacrificial templates. During the hydrothermal process, various crystalline imperfections such as stacking faults and twinning planes appear due to lattice mismatches between orthorhombic CdSe·(en)0.5 and hexagonal wurtzite porous CdSe nanorods and subsequently disappear to release mismatched strains. In the self-healing process of defects, due to the imbalance of in-and-out atomic diffusion, point defects of atomic vacancies are heavily generated in CdSe nanorods to produce volume defects of voids eventually. The photoluminescence of CdSe nanorods shifts to the red region and decreases in intensity with the increase of the hydrolysis time as surface states and selenium vacancies increase. The mean lifetime of photoluminescence increases with the increase of the hydrothermal-treatment time as the fractional amplitude of the surface-state-related component increases.

Fabrication of an olive-like BiVO4 hierarchical architecture with enhanced visible-light photocatalytic activity

The olive-like BiVO₄ hierarchical architecture can be synthesized by a facile, template-free hydrothermal method, which shows high visible-light photocatalytic activity for degradation of methylene blue molecules.

A two-step synthetic route to GdOF:Ln3+ nanocrystals with multicolor luminescence properties

GdOF:Ln³⁺ (Ln = Eu, Tb, Eu/Tb, Ce/Tb, Yb/Er, and Yb/Tm) nanocrystals with multicolor emissions have been synthesized by a novel topotactic transformation route.

Co-doping of Ag into Mn:ZnSe Quantum Dots: Giving Optical Filtering effect with Improved Monochromaticity

In optics, when polychromatic light is filtered by an optical filter, the monochromaticity of the light can be improved. In this work, we reported that Ag dopant atoms could be used as an optical filter for nanosized Mn:ZnSe quantum dots (QDs). If no Ag doping, aqueous Mn:ZnSe QDs have low monochromaticity due to coexisting of strong ZnSe band gap emission, ZnSe trap emission, and Mn dopant emission. After doping of Ag into QDs, ZnSe band gap and ZnSe trap emissions can be filtered, leaving only Mn dopant emission with improved monochromaticity. The mechanism for the optical filtering effect of Ag was investigated. The results indicate that the doping of Ag will introduce a new faster deactivation process from ZnSe conduction band to Ag energy level, leading to less electrons deactived via ZnSe band gap emission and ZnSe trap emission. As a result, only Mn dopant emission is left.