Nanomaterials (NMs) are mostly synthesized by chemical and physical methods, but biological synthesis is also receiving great attention. However, the mechanisms for biological producibility of NMs, ...crystalline versus amorphous, are not yet understood. Here we report biosynthesis of 60 different NMs by employing a recombinant Escherichia coli strain coexpressing metallothionein, a metal-binding protein, and phytochelatin synthase that synthesizes a metal-binding peptide phytochelatin. Both an in vivo method employing live cells and an in vitro method employing the cell extract are used to synthesize NMs. The periodic table is scanned to select 35 suitable elements, followed by biosynthesis of their NMs. Nine crystalline single-elements of Mn₃O₄, Fe₃O₄, Cu₂O, Mo, Ag, In(OH)₃, SnO₂, Te, and Au are synthesized, while the other 16 elements result in biosynthesis of amorphous NMs or no NM synthesis. Producibility and crystallinity of the NMs are analyzed using a Pourbaix diagram that predicts the stable chemical species of each element for NM biosynthesis by varying reduction potential and pH. Based on the analyses, the initial pH of reactions is changed from 6.5 to 7.5, resulting in biosynthesis of various crystalline NMs of those previously amorphous or not-synthesized ones. This strategy is extended to biosynthesize multielement NMs including CoFe₂O₄, NiFe₂O₄, ZnMn₂O₄, ZnFe₂O₄, Ag₂S, Ag₂TeO₃, Ag₂WO₄, Hg₃TeO₆, PbMoO₄, PbWO₄, and Pb₅(VO₄)₃OH NMs. The strategy described here allows biosynthesis of NMs with various properties, providing a platform for manufacturing various NMs in an environmentally friendly manner.
Abstract
Many heterogeneous catalytic reactions occur at high temperatures, which may cause large energy costs, poor safety, and thermal degradation of catalysts. Here, we propose a light-assisted ...surface reaction, which catalyze the surface reaction using both light and heat as an energy source. Conventional metal catalysts such as ruthenium, rhodium, platinum, nickel, and copper were tested for CO
2
hydrogenation, and ruthenium showed the most distinct change upon light irradiation. CO
2
was strongly adsorbed onto ruthenium surface, forming hybrid orbitals. The band gap energy was reduced significantly upon hybridization, enhancing CO
2
dissociation. The light-assisted CO
2
hydrogenation used only 37% of the total energy with which the CO
2
hydrogenation occurred using only thermal energy. The CO
2
conversion could be turned on and off completely with a response time of only 3 min, whereas conventional thermal reaction required hours. These unique features can be potentially used for on-demand fuel production with minimal energy input.
Because of the large surface-to-volume ratio of colloidal nanocrystals (NCs), surfactant molecules grafted at the NC surface play an important role in NC growth, interparticle interaction, ...processing, and application. For this reason, much progress has been made in understanding the surface chemistry of NCs along with the organic ligand shell, particularly in terms of grafted polar groups. However, most explanations of aliphatic counterparts are based on spherical NCs that usually have a dilute ligand layer. In anisotropic NCs such as nanorods and nanoplatelets, the linearly extended dimension results in a high-density aliphatic layer on the NC surface. Unlike spherical NCs, the compact organic shell could serve as a permeation membrane, effectively impeding a penetration of foreign molecules toward the NC surface. In this Perspective, we highlight the effects of ligand configuration on the properties of anisotropic NCs by exploring morphologies, assembled superstructures, and surface reaction of anisotropic NCs.
Abstract
The past decade has witnessed remarkable progress in the device efficiency of quantum dot light-emitting diodes based on the framework of organic-inorganic hybrid device structure. The ...striking improvement notwithstanding, the following conundrum remains underexplored: state-of-the-art devices with seemingly unfavorable energy landscape exhibit barrierless hole injection initiated even at sub-band gap voltages. Here, we unravel that the cause of barrierless hole injection stems from the Fermi level alignment derived by the surface states. The reorganized energy landscape provides macroscopic electrostatic potential gain to promote hole injection to quantum dots. The energy level alignment surpasses the Coulombic attraction induced by a charge employed in quantum dots which adjust the local carrier injection barrier of opposite charges by a relatively small margin. Our finding elucidates how quantum dots accommodate barrierless carrier injection and paves the way to a generalized design principle for efficient electroluminescent devices employing nanocrystal emitters.
Successful exploitation of semiconductor nanocrystals (NCs) in commercial products is due to the remarkable progress in the wet-chemical synthesis and controlled assembly of NCs. Central to the ...cadence of this progress is the ability to understand how NC growth and assembly can be controlled kinetically and thermodynamically. The arrested precipitation strategy offers a wide opportunity for materials selection, size uniformity, and morphology control. In this colloidal approach, capping ligands play an instrumental role in determining growth parameters and inter-NC interactions. The impetus for exquisite control over the size and shape of NCs and orientation of NCs in an ensemble has called for the use of two or more types of ligands in the system. In multiple ligand approaches, ligands with different functionalities confer extended tunability, hinting at the possibility of atomic-precision growth and long-range ordering of desired superlattices. Here, we highlight the progress in understanding the roles of ligands in size and shape control and assembly of NCs. We discuss the implication of the advances in the context of optoelectronic applications.
The multiple ligands with different functionalities enable atomic-precision control of NCs morphology and subtle inter-NC interactions, which paves the way for novel optoelectronic applications.
Advances in nanotechnology have enabled precise design of catalytic sites for CO2 photoreduction, pushing product selectivity to near unity. However, activity of most nanostructured photocatalysts ...remains underwhelming due to fast recombination of photogenerated electron–hole pairs and sluggish hole transfer. To address these issues, we construct colloidal CdS nanosheets (NSs) with the large basal planes terminated by S2– atomic layers as intrinsic photocatalysts (CdS–S2– NSs). Experimental investigation reveals that the S2– termination endows ultrathin CdS–S2– NSs with facet-resolved redox-catalytic sites: oxidation occurs on S2–-terminated large basal facets and reduction happens on side facets. Such an allocation of redox sites not only promotes spatial separation of photoinduced electrons and holes but also facilitates balanced extraction of holes and electrons by shortening the hole diffusion distance along the (001) direction of the ultrathin NSs. Consequently, the CdS–S2– NSs exhibit superb performance for photocatalytic CO2-to-CO conversion, which was verified by the isotope-labeled experiments to be a record-breaking performance: a CO selectivity of 99%, a CO formation rate of 2.13 mol g–1 h–1, and an effective apparent quantum efficiency of 42.1% under the irradiation (340 to 450 nm) of a solar simulator (AM 1.5G). The breakthrough performance achieved in this work provides novel insights into the precise design of nanostructures for selective and efficient CO2 photoreduction.
Electronic devices comprised of nanocrystal (NC) thin film are projected to demonstrate enhanced figure of merit if NC building blocks self-assemble into highly uniform, 2-dimensional (2-D) ...superstructures with long-range order. Despite intensive research efforts and remarkable progress, long-range assembly of colloidal anisotropic NCs into thin films with orientational and positional order has remained to be addressed. One of the most promising approaches is to dissolve excess free molecules into NC solution, which has enabled the formation of NC monolayers with exceptional quality at air/solution interface. Nevertheless, the assembly mechanism and the role of free molecules have not been comprehensively elucidated, restricting the use of the approach. Here, we find that the interfacial assembly of CdSe/CdS core/shell nanorods (NRs) results in various ordered structures in the presence of free oleic acid molecules. The structures include a bundle of standing NRs, a belt of multilayered lying NRs, and a monolayer smectic phase, obtained by simple change in density of surface ligands on the NRs. Experimental observation and theoretical calculation reveal that the assembly is initiated at the air/solution interface due to the preferential depletion attraction of NRs to the interface. However, subsequent growth is significantly altered depending on the ligand density that determines the relative magnitude of interface-NR depletion attraction to inter-NR attraction. Highly ordered structures of NRs, especially for the monolayer smectic phase, are promising as a polarized light-emitting layer for thin-film optical devices. In addition, our findings on the depletion-mediated NR assembly provide important and universal design criteria for 2-D structuring of NCs with diverse geometries and compositions.
We present a centrifugal microfluidic device which enables multiplex foodborne pathogen identification by loop-mediated isothermal amplification (LAMP) and colorimetric detection using Eriochrome ...Black T (EBT). Five identical structures were designed in the centrifugal microfluidic system to perform the genetic analysis of 25 pathogen samples in a high-throughput manner. The sequential loading and aliquoting of the LAMP cocktail, the primer mixtures, and the DNA sample solutions were accomplished by the optimized zigzag-shaped microchannels and RPM control. We targeted three kinds of pathogenic bacteria (Escherichia coli O157:H7, Salmonella typhimurium and Vibrio parahaemolyticus) and detected the amplicons of the LAMP reaction by the EBT-mediated colorimetric method. For the limit-of-detection (LOD) test, we carried out the LAMP reaction on a chip with serially diluted DNA templates of E. coli O157:H7, and could observe the color change with 380 copies. The used primer sets in the LAMP reaction were specific only to the genomic DNA of E. coli O157:H7, enabling the on-chip selective, sensitive, and high-throughput pathogen identification with the naked eyes. The entire process was completed in 60min. Since the proposed microsystem does not require any bulky and expensive instrumentation for end-point detection, our microdevice would be adequate for point-of-care (POC) testing with high simplicity and high speed, providing an advanced genetic analysis microsystem for foodborne pathogen detection.
•A centrifugal LAMP microdevice for pathogen detection was developed.•Zigzag-shaped microchannels provide sequential aliquoting of the LAMP components.•Simple and user-friendly EBT-mediated colorimetric detection method was devised.•The proposed system does not require any bulky or expensive instrument for detection.•This microdevice would be adequate for point-of-care pathogen detection.
Functionalization of quantum dots (QDs) via ligand exchange is prone to debase their photoluminescence quantum yield (PL QY) owing to the unavoidable surface damage by excess reactants, and even ...worse in aqueous medium. Herein, the oligomeric zinc thiolate as the multidentate hydrophilic ligand featuring facile synthetic protocol is proposed. A simple reaction between ZnCl2 and 3‐mercaptopropionic acid produces oligomeric ligands containing 3–6 zinc thiolate units, where the terminal moieties provide multidentate anchoring to the surface as well as hydrophilicity. 2D proton nuclear Overhauser effect spectroscopy (2D 1H NOESY) and X‐ray photoelectron spectroscopy (XPS) reveal that the oligomeric zinc thiolate ligands adsorb on the surface via multidentate metal carboxylate bindings without destruction of molecular structure, regardless of partial dissociation of thiolate branches in aqueous phase. Enhanced binding affinity granted by the multidentate nature allows for the effective exchange of original surface ligands without considerable surface deterioration. The zinc thiolate‐capped Cd‐free aqueous QDs exhibit a high photoluminescence quantum yield of ≈90% and extended stability against long‐term storage and photochemical stress.
Highly efficient aqueous Cd‐free quantum dots (QDs) are achieved by the oligomeric zinc thiolate ligand with multidentate carboxylates, enabling nondestructive ligand exchange thanks to enhanced binding affinity. Intact adsorption of aqueous Cd‐free quantum dots, revealed by 1H nuclear Overhauser effect spectroscopy (NOESY), forms a sturdy ligand shell protecting the surface from photochemical stresses.
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