Weiwei Zhao

Nanoporous Single‐Crystal‐Like CdxZn1−xS Nanosheets Fabricated by the Cation‐Exchange Reaction of Inorganic–Organic Hybrid ZnS–Amine with Cadmium Ions

Porous nanostructures have received considerable attention because of their improved chemical and physical performance over solid materials as well as their intriguing applications in nanoreactors, actuators, energy storage, solar cells, ultrafiltration and separation, CO2 capture, catalysis, cell imaging, and drug delivery. Among materials with various shapes, nanosheets have attracted intensive interests as sheetlike materials with predominantly exposed crystal facets may exhibit improved catalytic performance over their wirelike or spherical structures. But, the efficient synthesis of porous single-crystalline sheets still remains a challenge. Thus, their improved properties and promising applications are driving researchers to develop facile strategies to synthesize porous sheetlike materials, especially with adjustable composition and pore size. Since the discovery by Alivisato and co-workers of the cation-exchange reaction in nanocrystals, much attention has been paid to the transformation of one crystalline material to another through cation exchange in aqueous solution. At present, research efforts mainly focus on the modulation of the composition, structure, and properties of solid inorganic nanocrystals and nanowires. In these cases, some hollow regions are produced because of the Kirkendall effect. Recently, metal–organic frameworks and coordinating compounds have been found to exhibit unique cationexchange properties. Our previous study demonstrated that vapor-phase cation-exchange reactions of CdS with organic zinc could generate 1D nanostructures with adjustable composition and morphology. Although these advances have been achieved, the development of solution-phase cation-exchange reactions for the synthesis of nanoporous 1D and 2D nanostructures, especially sheetlike materials with predominantly exposed crystal facets, is still in its infancy. The inorganic–organic hybrid nanomaterials can be used as a template for the preparation of functional materials. For example, Yu and co-workers found that hybrid nanowires could be transformed into inorganic nanotubes by removing the organic components in selected solvents. The thermal decomposition of hybrid materials in air can lead to the formation of porous oxides. However, to the best of our knowledge, there are few reports on using hybrid semiconductors as starting materials for ion-exchange reactions to produce porous materials with modulated pore size and composition. Here we adopt the inorganic–organic hybrid semiconductor sheets as the starting materials and describe a facile cation-exchange strategy to fabricate single-crystal-like porous nanosheets. We show that nanoporous inorganic CdxZn1 xS nanosheets with controlled pore size and adjustable composition are accessible by this approach. The asprepared single-crystal-like porous Cd0.5Zn0.5S nanosheets are highly active for photocatalytic H2 evolution from water splitting. In addition, the cation-exchange strategy of inorganic–organic hybrid materials is suitable for fabricating other porous nanostructures. To demonstrate the cation-exchange method of hybrid materials for producing porous nanostructures, transforming inorganic–organic hybrid ZnS–diethylenetriamine (DETA) into porous CdxZn1 xS nanosheets is selected as the model system. As shown in Figure 1 a, the ZnS–DETA nanosheets are first prepared using a modified amine-assisted hydrothermal method, and then react with different concentrations of Cd cations to obtain nanoporous CdxZn1 xS and CdS (see the Supporting Information). The ZnS–DETA nanosheets are firstly examined using scanning electron microscopy (SEM). The SEM images (the inset in Figure 1 b and Figure S1-1a in the Supporting Information) clearly show that ZnS–DETA nanosheets were successfully fabricated in high yields. Typical X-ray diffraction (XRD) pattern of the asprepared hybrid precursors indentify them as the ZnS(DETA)0.5 (see Figure S1e in the Supporting Information). When the ZnS–DETA nanosheets exchange with Cd cations, solid sheets become nanoporous (see Figure 1e). After the hybrid precursors have reacted with excessive Cd cations, the completely exchanged products are nanoporous CdS nanosheets with a pore size of 10–50 nm (see Figure 1 g,h and Figure S1-1c,d in the Supporting Information) and a thickness of around 20 nm (see Figure S1-2 in the Supporting Information). FTIR spectra shown in Figure S1-1f in the [*] Dr. Y. Yu, J. Zhang, X. Wu, W. Zhao, Prof. Dr. B. Zhang Department of Chemistry, School of Science Tianjin University, Tianjin 300072(P.R. China) E-mail: bzhang@tju.edu.cn [] Both authors contributed equally to this work.

Synthesis of ultrathin CdS nanosheets as efficient visible-light-driven water splitting photocatalysts for hydrogen evolution

Ultrathin CdS nanosheets with a thickness of ~4 nm have been synthesized through an ultrasonic-induced aqueous exfoliation method involving lamellar CdS-DETA hybrid nanosheets as starting materials and L-cysteine as a stabilizing agent. The as-obtained CdS ultrathin nanosheets exhibit efficient photocatalytic activity and good stability for hydrogen production.

Nanoporous Hollow Transition Metal Chalcogenide Nanosheets Synthesized via the Anion-Exchange Reaction of Metal Hydroxides with Chalcogenide Ions

Nanoporous hollow transition metal chalcogenides are of special interest for a variety of promising applications. Although some advanced synthetic methods have been reported, the development of a facile and general strategy to fabricate porous hollow nanostructures of transition metal chalcogenides, especially with enhanced electrocatalytic performance, still remains highly challenged. Herein, we report a facile chemical transformation strategy to prepare nanoporous hollow Co3S4 nanosheets via the anion exchange reaction of Co(OH)2 with sulfide ions. The chemical transformation mechanism involves the as-formed layer of nanoporous cobalt sulfide on Co(OH)2 driven by the anion-exchange-reaction and lattice mismatch induced quick strain release, a following diffusion-effect-dominated core-shell hollow intermediate with hollow interiors, and subsequent Ostwald ripening growth of hollow nanosheets at elevated temperatures. This anion-exchange strategy of transition metal hydroxides with chalcogenide ions is also suitable for fabricating nanoporous hollow nanosheets of other metal chalcogenides (e.g., CoSe2, CoTe2, CdS, and NiS). The as-prepared nanoporous hollow Co3S4 nanosheets are found to be highly active and stable for electrocatalytic oxygen evolution reaction.

Porous single-crystalline CdS nanosheets as efficient visible light catalysts for aerobic oxidative coupling of amines to imines

Porous single-crystal-like CdS nanosheets fabricated through a facile cation-exchange strategy exhibit a noticeable photocatalytic activity for aerobic oxidative coupling of amines to imines with 1 atm O2 under visible-light irradiation (λ > 420 nm) at room temperature.

A Heterogeneous Photocatalytic Hydrogen Evolution Dyad: [(tpy

The development of an artificial heterogeneous dyad by covalently anchoring a hydrogen-evolving molecule catalyst to a semiconductor photosensitizer through a bridging ligand is highly challenging. Herein, we adopt the inorganic-organic hybrid CdS-DETA NSs (DETA=diethylenetriamine, NSs=nanosheets) as initial matrix to successfully construct an imine bond (-CH=N-) linked heterogeneous dyad [CdS-N=CH-Ni] through the condensation reaction between the amino groups of CdS-DETA and the aldehyde group of the water reduction molecular catalyst, [(tpy-CHO)2 Ni]Cl2 (tpy=terpyridine). The [CdS-N=CH-Ni] enables a turnover number (TON) of about 43 815 versus Ni catalysts and an initial turnover frequency (TOF) of approximately 0.47 s-1 in 26 h under visible-light irradiation (λ>420 nm). The apparent quantum yield (AQY) reaches (9.9±0.8) % at 420 nm. Under optical conditions, the [CdS-N=CH-Ni] can achieve a considerable amount of hydrogen production, 507.1±27 μmol H2 for 6 h, which is 1.27 times that generated from the mechanically mixed system of CdS-DETA NSs and [(tpy-CH=NR)2 Ni]Cl2 (III) under otherwise identical conditions. Furthermore, its TON value based on Ni species is also higher than that of the mixed system of CdS-DETA and III.

Shape-controlled self-assembly of colloidal nanoparticles

In this paper, we have successfully directed self-assembly of colloidal nanoparticles (NPs) of Au and CdTe into perfect hexagonal microflakes or ultralong microwires, via stepwise reducing the electrostatic repulsion potential of neighboring NPs in their dispersions with the help of L-cysteine. The hexagonal microflakes were formed via slow self-assembly of short NP chains, while the ultralong microwires were formed via the fast self-assembly of long NP chains. The microwires were kinetically stable and gradually transformed to flakes during incubation in water. This underlines a pronounced correlation of the shape of the resulting supracrystals with the length of the starting NP chains and their self-assembly kinetics. This correlation should provide a fundamental basis not only for better interpretation and even prediction of shape-controlled crystallization but also for organization of nanoscale building blocks to mesoscopic and macroscopic artificial solids.