Synthesis of hollow Cd(x)Zn(1-x) Se nanoframes through the selective cation exchange of inorganic-organic hybrid ZnSe-amine nanoflakes with cadmium ions

Porous Zn1-xCdxSe/ZnO Nanorod Photoanode Fabricated from ZnO Building Blocks Grown on Zn Foil for Photoelectrochemical Solar Hydrogen Production

Solar energy is the most promising, efficient, environmentally friendly energy source with the potential to meet global demand due to its non-polluting nature. Herein, a porous Zn1-xCdxSe/ZnO nanorod (NR) heterojunction was synthesized by hydrothermal and low-temperature solvothermal methods. First, the ZnO NR was grown on a Zinc foil, and an inorganic-organic hybrid ZnSe(en)0.5 material was developed by the low-temperature solvothermal method. In this work, the ZnO NR acted as a base material and a building block for the growth of ZnSe(en)0.5. Moreover, after the solvothermal process, the reduced Se2- reacts with the ZnO NR and forms inorganic-organic hybrid ZnSe(en)0.5. After the selenization process, the obtained material shows a red brick color due to the absorbance of excessive Se metal particles during the solvothermal process. Furthermore, in order to enhance the photoelectrochemical properties, the Cd2+ ion exchange method was applied at various temperatures (140, 160, and 180 °C for 3 h) to produce a precursor material to a porous Zn1-xCdxSe/ZnO NR nanostructure. The optimum Zn1-xCdxSe/ZnO NR-160 photoanode showed a high photocurrent density of 7.8 mA·cm-2 at -0.5 V vs. Ag/AgCl with a hydrogen evolution rate of 199 μmol·cm-2/3 h. The improved photocurrent performance was attributed to effective light absorption and prolonged recombination lifetime.

Understanding systematic growth mechanism of porous Zn1-xCdxSe/TiO2 nanorod heterojunction from ZnSe(en)0.5/TiO2 photoanodes for bias-free solar hydrogen evolution

Herein, a porous Zn_1-xCd_xSe structure was developed on TiO₂ nanorod (NR) array for photoelectrochemical (PEC) application. Firstly, TiO₂ NR and ZnO/TiO₂ NR photoanode were synthesized via a series of hydrothermal methods on FTO. Next, the solvothermal synthesis method was adopted to develop inorganic-organic hybrid ZnSe(en)_0.5 on ZnO /TiO₂ NR-based electrode using different concentrations of the selenium (Se). We found that the ZnO NR acts as a mother material for the formation of inorganic-organic hybrid ZnSe(en)_0.5, whereas TiO₂ NR acts as a building block. In order to further improve the PEC charge transfer performance, inorganic-organic hybrid ZnSe(en)_0.5/TiO₂ NR electrode was transferred into a porous Zn_1-xCd_xSe/TiO₂ NR photoanode using the Cd²⁺ ion-exchange method. The optimized porous Zn_1-xCd_xSe/TiO₂ NR -(2) photoanode converted from ZnSe(en)_0.5 -(2) electrode (optimized Se concentration) showed a higher photocurrent density of 6.6 mA·cm^-2 at applied potential 0 V vs. Ag/AgCl. The enhanced photocurrent density was owing to the effective light absorption, enhanced charge separation, delay the charge recombination, and porous structure of Zn_1-xCd_xSe. This work highlights the promising strategy for the synthesis of porous Zn_1-xCd_xSe/TiO₂ NR from inorganic-organic ZnSe(en)_0.5/TiO₂ NR for effective charge separation and prolonging the lifetime during the photoelectrochemical reaction.

Recent Progress of Metal Sulfide Photocatalysts for Solar Energy Conversion

Artificial photosynthetic solar-to-chemical cycles enable an entire environment to operate in a more complex, yet effective, way to perform natural photosynthesis. However, such artificial systems suffer from a lack of well-established photocatalysts with the ability to harvest the solar spectrum and rich catalytic active-site density. Benefiting from extensive experimental and theoretical investigations, this bottleneck may be overcome by devising a photocatalytic platform based on metal sulfides with predominant electronic, physical, and chemical properties. These tunable properties can endow them with abundant active sites, favorable light utilization, and expedited charge transportation for solar-to-chemical conversion. Here, it is described how some vital lessons extracted from previous investigations are employed to promote the further development of metal sulfides for artificial photosynthesis, including water splitting, CO₂ reduction, N₂ reduction, and pollutant removal. Their functions, properties, synthetic strategies, emerging issues, design principles, and intrinsic functional mechanisms for photocatalytic redox reactions are discussed in detail. Finally, the associated challenges and prospects for the utilization of metal sulfides are highlighted and future development trends in photocatalysis are envisioned.

Transformations of Magic-Size Clusters via Precursor Compound Cation Exchange at Room Temperature

The transformation of colloidal semiconductor magic-size clusters (MSCs) from zinc to cadmium chalcogenide (ZnE to CdE) at low temperatures has received scant attention. Here, we report the first room-temperature evolution of CdE MSCs from ZnE samples and our interpretation of the transformation pathway. We show that when prenucleation stage samples of ZnE are mixed with cadmium oleate (Cd(OA)₂), CdE MSCs evolve; without this mixing, ZnE MSCs develop. When ZnE MSCs and Cd(OA)₂ are mixed, CdE MSCs also form. We propose that Cd(OA)₂ reacts with the precursor compounds (PCs) of the ZnE MSCs but not directly with the ZnE MSCs. The cation exchange reaction transforms the ZnE PCs into CdE PCs, from which CdE MSCs develop. Our findings suggest that in reactions that lead to the production of binary ME quantum dots, the E precursor dominates the formation of binary ME PCs (M = Zn or Cd) to have similar stoichiometry. The present study provides a much more profound view of the formation and transformation mechanisms of the ME PCs.

Composition-dependent activity of ZnxCd1-xSe solid solution coupled with Ni2P nanosheets for visible-light-driven photocatalytic H2 generation

Metal selenide semiconductors have been rarely used for photocatalytic water splitting because of their poor stability and severe photocorrosion properties. Hence, designing stable metal selenides with suitable bandgap energies has considerable practical significance in photocatalytic H₂ evolution. In this work, a novel series of Zn_xCd_1-xSe (x = 0 ∼ 1) with tunable band structure were fabricated through a simple solvothermal method. Impressively, the ZnSe exhibited a maximum H₂ production rate of 1056 µmol g^-1h^-1, which was higher than that of CdSe and Zn_xCd_1-xSe solid solutions. Such visible-light photoactivity for water reduction to H₂ was attained even after 6 cycling photocatalytic experiments. Moreover, the two-dimensional (2D) Ni₂P nanosheets act as a high-efficiency cocatalyst integrated with Zn_xCd_1-xSe semiconductor to boost photocatalytic H₂ generation performance. The optimal 8% Ni₂P/ZnSe composites displayed excellent cycling stability and superior photocatalytic H₂ evolution performance (4336 µmol g^-1h^-1), which was about 4.1 times that of pure ZnSe under visible light irradiation. Photoelectrochemical (PEC), photoluminescence (PL), and time-resolved photoluminescence (TRPL) measurements reveal that the improved photoactivity Ni₂P/ZnSe photocatalysts were ascribed to the effective separation and migration of photoinduced carriers. The present work paves a pathway to explore the fabrication of Zn_xCd_1-xSe solid solutions and the hybridization of 2D transition metal phosphides nanosheets toward photocatalytic applications.

Topotactic and Self-Templated Fabrication of Zn1-xCdxSe Porous Nanobelt-ZnO Nanorod for Photoelectrochemical Hydrogen Production

Herein, we propose the topotactic and self-templated fabrication of Zn1-xCdxSe porous nanobelt-ZnO nanorod (termed as ZnCdSe/ZnO) photoelectrode via the cadmium (Cd2+) ion-exchange process on zinc (Zn) foil. Inorganic-organic hybrid ZnSe(en)0.5 nanobelt (NB) was synthesized on Zn foil by a facial solvothermal method at different temperatures of 140, 160, and 180 °C for 12 h. The interfacial properties and photoelectrochemical (PEC) performance of inorganic-organic ZnSe(en)0.5 NB fabricated through the Cd2+ ion-exchange method at different time durations of 6, 12, 18, and 24 h at 140 °C were investigated. The TEM analysis results indicate that the inorganic-organic ZnSe(en)0.5 NB transformed into ZnCdSe and a self-assembled ZnO formed on the Zn foil. In particular Cd2+ ion temperature (140 °C/18 h), the optimized ZnCdSe/ZnO-(F) photoelectrode shows an excellent photocurrent density of 14 mA·cm-2 at 0 V vs Ag/AgCl with 219 μmol·cm-2 hydrogen gas evolution for 3 h under 1 sun illumination. The higher photocurrent value resulted from the optimum growth of ZnO, the formation of porous ZnCdSe, and the effective electrolyte penetration for electron-hole pair separation. The photoluminescence spectroscopy shows that the photoexcited charged carriers promoted a longer lifetime. Furthermore, we provide a full account of the possible charge-transfer mechanism during PEC hydrogen production.

Cation-exchange construction of ZnSe/Sb2Se3 hollow microspheres coated by nitrogen-doped carbon with enhanced sodium ion storage capability

Recently, anode materials with synergistic sodium storage mechanisms of conversion combined with alloying reactions for sodium ion batteries (SIBs) have received widespread attention due to their high theoretical capacities. In this work, through reacting with an appropriate concentration of Sb³⁺ ions and a simple carbonization process, hollow ZnSe/Sb₂Se₃ microspheres encapsulated in nitrogen-doped carbon (ZnSe/Sb₂Se₃@NC) are progressively synthesized based on a cation-exchange reaction, using polydopamine-coated ZnSe (ZnSe@PDA) microspheres as the precursor. Benefiting from the synergistic effects between the unique structure and composition characteristics, when serving as an anode material for SIBs, they result in higher sodium diffusion coefficients (8.7 × 10^-13-3.98 × 10^-9 cm² s^-1) and ultrafast pseudocapacitive sodium storage capability. Compared with ZnSe@NC and Sb₂Se₃@NCs exhibit, ZnSe/Sb₂Se₃@NC exhibits more stable capacity (438 mA h g^-1 at a current of 0.5 A g^-1 after 120 cycles) and superior rate performance (316 mA h g^-1 at 10.0 A g^-1). Our work provides a convenient method to construct high performance anodes with tunable composition and structure for energy storage.

Two-dimensional (2D) MnIn2Se4 nanosheets with porous structure: a novel photocatalyst for water splitting without sacrificial agents

Novel 2D porous MnIn₂Se₄ nanosheet photocatalysts have been synthesized for the first time via a simple hydrothermal method, which exhibit promising activity for photocatalytic water splitting without any sacrificial agent due to their large specific surface area, 2D layered morphology, porous structure and suitable energy gap.

Atomically thin two-dimensional ZnSe/ZnSe(ea)x van der Waals nanojunctions for synergistically enhanced visible light photocatalytic H2 evolution

Two-dimensional (2D) photocatalysts have been widely studied due to their short charge carrier migration pathways and tunable electronic structures. Herein, a facile one-pot solvothermal process with ethylamine (ea) constructs a novel 2D nanojunction based on ZnSe. The ea molecules coordinate with Zn2+ to form 2D ZnSe(ea)x, where the consequent 2D ZnSe grows in an epitaxial way resulting in the self-assembled 2D/2D ZnSe/ZnSe(ea)x nanojunctions driven by van der Waals (VDW) force, which largely extend the absorption range. The atomic thickness of the 2D structure offers a short charge migration pathway, low electric resistance and rich active sites for the surface reaction of photocatalysis. All the above favorable factors work synergistically to reach a superior hydrogen evolution of 2875 μmol g-1 h-1 under visible light irradiation (≥420 nm) and a notable quantum yield of 64.5% at 450 nm, which are among the highest recorded values of non-noble metal photocatalysts.

Ultrathin Visible-Light-Driven Mo Incorporating In2 O3 -ZnIn2 Se4 Z-Scheme Nanosheet Photocatalysts

Inspired by natural photosynthesis, the design of new Z-scheme photocatalytic systems is very promising for boosting the photocatalytic performance of H₂ production and CO₂ reduction; however, until now, the direct synthesis of efficient Z-scheme photocatalysts remains a grand challenge. Herein, it is demonstrated that an interesting Z-scheme photocatalyst can be constructed by coupling In₂ O₃ and ZnIn₂ Se₄ semiconductors based on theoretical calculations. Experimentally, a class of ultrathin In₂ O₃ -ZnIn₂ Se₄ (denoted as In₂ O₃ -ZISe) spontaneous Z-scheme nanosheet photocatalysts for greatly enhancing photocatalytic H₂ production is made. Furthermore, Mo atoms are incorporated in the Z-scheme In₂ O₃ -ZISe nanosheet photocatalyst by forming the MoSe bond, confirmed by X-ray photoelectron spectroscopy, in which the formed MoSe₂ works as cocatalyst of the Z-scheme photocatalyst. As a consequence, such a unique structure of In₂ O₃ -ZISe-Mo makes it exhibit 21.7 and 232.6 times higher photocatalytic H₂ evolution activity than those of In₂ O₃ -ZnIn₂ Se₄ and In₂ O₃ nanosheets, respectively. Moreover, In₂ O₃ -ZISe-Mo is also very stable for photocatalytic H₂ production by showing almost no activity decay for 16 h test. Ultraviolet-visible diffuse reflectance spectra, photoluminescence spectroscopy, transient photocurrent spectra, and electrochemical impedance spectroscopy reveal that the enhanced photocatalytic performance of In₂ O₃ -ZISe-Mo is mainly attributed to its widened photoresponse range and effective carrier separation because of its special structure.

Trifunctional metal–organic platform for environmental remediation: structural features with peripheral hydroxyl groups facilitate adsorption, degradation and reduction processes

A Cd(ii)-based metal–organic framework (MOF) has been demonstrated to have trifunctional properties, namely as an efficient and selective adsorbent for dyes, a visible-light-active photocatalyst for the degradation of dyes and a photocatalyst for Cr(vi) reduction.

CoSe2/CdS-diethylenetriamine coupled with P clusters for efficient photocatalytic hydrogen evolution

A novel binary solution (DETA/H₂O) reaction for preparing composite catalyst composed of CdS nanoparticles grown on CoSe₂ nanobelts, which exhibits excellent catalytic activity for a hydrogen evolution reaction.

Synergetic Transformation of Solid Inorganic-Organic Hybrids into Advanced Nanomaterials for Catalytic Water Splitting

The rational synthesis of advanced nanomaterials with well-defined structures has been intensively studied due to the remarkable properties and intriguing applications of the formed materials. Recently, inorganic-organic hybrids have been widely adopted as precursors for chemical transformations toward the preparation of diverse nanomaterials. Specifically, inorganic and organic species with nano/molecule/atom-scale distribution serve as self-templates and sacrificial agents, respectively, endowing the products with controlled morphologies, band gaps, defects, and spatial architectures. However, previous works have focused mostly on the transformation of porous coordination polymers, such as metal-organic frameworks (MOFs), which would produce daughter nanomaterials with the inherited structure of their parental hybrids. Moreover, conventional transformation strategies often encounter difficulties in simultaneously manipulating multiple structural parameters of the target materials. Therefore, a synergetic transformation strategy involving the simultaneous removal of organic components and the reconstruction of inorganic components to transform solid inorganic-organic hybrids into functional nanomaterials is developed. In this Account, we review recent advances in the utilization of solid inorganic-organic hybrids as precursors and their transformation into inorganic functional nanomaterials through a synergetic transformation strategy with an emphasis on understanding the conversion mechanism. The synergetic transformation strategy we discussed is categorized by organic component removal coupled with different methods for the reconstruction of inorganic components, including ion exchange, interfacial reaction, redox reaction and self-assembly. The key to a synergetic transformation strategy lies in the cooperation and/or competition among different transformation tools through dynamics and/or thermodynamics. By controlling the rate and position of the ion exchange reaction coupled with the removal of organics, a series of nanomaterials with designed band gaps and spatial architectures are produced from the solid inorganic-organic hybrid nanosheet-based precursors. The dissimilarity of organics removal between the inner and outer regions of hybrids induced by interfacial reaction is capable of producing controlled porous/hollow structures. For the coupling of a redox reaction with organics removal, the products of the decomposition of organics induce the in situ oxidation/reduction of inorganic components to generate defects and a porous structure. Along with organics removal, the self-assembly of inorganic components can be achieved to yield novel nanomaterials with hierarchical structures. Based on the understanding of the conversion mechanism, diverse advanced nanomaterials with elaborately designed structures are prepared by adopting appropriate precursors and synergetic transformation strategies. We then summarize the applications of the conversion products for photo(electro)/electrocatalytic water splitting. The precisely modulated structure can specifically improve photon adsorption, electron transport, catalytic activity and durability. Thus, the conversion products can be directly used as photo(electro)/electrocatalysts with high activities and cycling stabilities. Finally, we provide an outlook on the current challenges and promising opportunities in this research area. We believe that the advanced synergetic transformation strategy of solid inorganic-organic hybrids will open up a new avenue for the preparation of nanomaterials with fascinating performance.

Co3O4 nanowire@NiO nanosheet arrays for high performance asymmetric supercapacitors

Herein, we report a simple and facile sequential hydrothermal process for the synthesis of Co₃O₄ nanowire@NiO nanosheet arrays (CNAs).

Heterovalent Doping in Colloidal Semiconductor Nanocrystals: Cation-Exchange-Enabled New Accesses to Tuning Dopant Luminescence and Electronic Impurities

Heterovalent doping in colloidal semiconductor nanocrystals (CSNCs), with provisions of extra electrons (n-type doping) or extra holes (p-type doping), could enhance their performance of optical and electronical properties. In view of the challenges imposed by the intrinsic self-purification, self-quenching, and self-compensation effects of CSNCs, we outline the progress on heterovalent doping in CSNCs, with particular focus on the cation-exchange-enabled tuning of dopant luminescence and electronic impurities. Thus, the well-defined substitutional or interstitial heterovalent doping in a deep position of an isolated nanocrystal has been fulfilled. We also envision that new coordination ligand-initiated cation exchange would bring about more choices of heterovalent dopants. With the aid of high-resolution characterization methods, the accurate atom-specific dopant location and distribution could be confirmed clearly. Finally, new applications, some of the remaining unanswered questions, and future directions of this field are presented.

Recent Progress in Energy-Driven Water Splitting

Hydrogen is readily obtained from renewable and non-renewable resources via water splitting by using thermal, electrical, photonic and biochemical energy. The major hydrogen production is generated from thermal energy through steam reforming/gasification of fossil fuel. As the commonly used non-renewable resources will be depleted in the long run, there is great demand to utilize renewable energy resources for hydrogen production. Most of the renewable resources may be used to produce electricity for driving water splitting while challenges remain to improve cost-effectiveness. As the most abundant energy resource, the direct conversion of solar energy to hydrogen is considered the most sustainable energy production method without causing pollutions to the environment. In overall, this review briefly summarizes thermolytic, electrolytic, photolytic and biolytic water splitting. It highlights photonic and electrical driven water splitting together with photovoltaic-integrated solar-driven water electrolysis.

Formation of Onion-Like NiCo2 S4 Particles via Sequential Ion-Exchange for Hybrid Supercapacitors

Onion-like NiCo₂ S₄ particles with unique hollow structured shells are synthesized by a sequential ion-exchange strategy. With the structural and compositional advantages, these unique onion-like NiCo₂ S₄ particles exhibit enhanced electrochemical performance as an electrode material for hybrid supercapacitors.

A robust and efficient catalyst of CdxZn1−xSe motivated by CoP for photocatalytic hydrogen evolution under sunlight irradiation

Cd_xZn_1−xSe/CoP composites have a high efficiency of 45.1 mmol h⁻¹ g⁻¹ and a high quantum yield of 11.8% at ∼520 nm.

Consecutive Reaction to Construct Hierarchical Nanocrystalline CuS "Branch" with Tunable Catalysis Properties

New CuS nanocrystals with a 3D hierarchical branched structure are successfully synthesized through in situ consecutive reaction method with copper foam as template. The formation mechanism of the 3D hierarchical branched structure obtained from the secondary reaction is investigated by adjusting the reaction time. The morphology of CuS nanosheet arrays with the 3D hierarchical branched structure is changed through Cu(2+) exchange. In this method, the copper foam reacted completely, and the as-synthesized CuS@Cu9S5 nanocrystals are firmly grown on the surface of the 3D framework. This tunable morphology significantly influence the physical and chemical properties, particularly catalytic performance, of the materials. The as-obtained material of Cu@CuS-2 with the 3D hierarchical branched structure as catalyst for methylene blue degradation exhibits good catalytic performance than that of the material of Cu@CuS with 2D nanosheets in dark environment. Furthermore, the cation exchange between Cu and Cu(2+) indicates that Cu(2+) in wastewater could be absorbed by Cu@CuS-2 with the 3D hierarchical branched structure. The exchanged resultant of CuS@Cu9S5 retains its capability to degrade organic dyes. This in situ consecutive reaction method may have a significant impact on controlling the crystal growth direction of inorganic material.

Ambient Aqueous Growth of Cu2Te Nanostructures with Excellent Electrocatalytic Activity toward Sulfide Redox Shuttles

A new aqueous and scalable strategy to synthesize surfactant-free Cu2Te nanotubes and nanosheets at room temperature has been developed. In aqueous solution, Cu2E (E = O, S, Se) nanoparticles can be easily transformed into Cu2Te nanosheets and nanotubes via a simple anion exchange reaction under ambient conditions. The formation of Cu2Te nanosheets is ascribed to a novel exchange-peeling growth mechanism instead of simple Kirkendall effect; and the resultant nanosheets can be further rolled into nanotubes with assistance of stirring. The morphologies of Cu2Te nanosheets and nanotubes can be easily controlled by changing the synthesis parameters, such as the concentration of precursors, the size of nanoparticle precursor, and the amount of NaBH4, as well as the stirring speed. Thus-formed Cu2Te nanostructures exhibit excellent catalytic activity toward sulfide redox shuttles and are exploited as counter electrodes catalysts for quantum dot sensitized solar cells. The performance of Cu2Te nanostructures strongly depends on their morphology, and the solar cells made with counter electrodes from Cu2Te nanosheets show the maximum power conversion efficiency of 5.35%.

2D Transition-Metal-Dichalcogenide-Nanosheet-Based Composites for Photocatalytic and Electrocatalytic Hydrogen Evolution Reactions

Hydrogen (H2) is one of the most important clean and renewable energy sources for future energy sustainability. Nowadays, photocatalytic and electrocatalytic hydrogen evolution reactions (HERs) from water splitting are considered as two of the most efficient methods to convert sustainable energy to the clean energy carrier, H2. Catalysts based on transition metal dichalcogenides (TMDs) are recognized as greatly promising substitutes for noble-metal-based catalysts for HER. The photocatalytic and electrocatalytic activities of TMD nanosheets for the HER can be further improved after hybridization with many kinds of nanomaterials, such as metals, oxides, sulfides, and carbon materials, through different methods including the in situ reduction method, the hot-injection method, the heating-up method, the hydro(solvo)thermal method, chemical vapor deposition (CVD), and thermal annealing. Here, recent progress in photocatalytic and electrocatalytic HERs using 2D TMD-based composites as catalysts is discussed.

A general chemical transformation route to two-dimensional mesoporous metal selenide nanomaterials by acidification of a ZnSe-amine lamellar hybrid at room temperature

A family of mesoporous nanosheets of metal selenides can be synthesized using an intermediate precursor so-called “red Se remaining Zn” (RSRZ), which is generated by acidification of inorganic–organic hybrid ZnSe(DETA)_0.5 nanosheets.

Two-dimensional inorganic nanomaterials have drawn much attention due to their excellent properties and wide applications associated with unique 2D structures. However, an efficient and versatile chemical synthesis method using ambient conditions for 2D nanomaterials, especially with secondary structures (e.g. mesopores), has still not been reported. Herein, we report a versatile method to synthesize a family of ultrathin and mesoporous nanosheets of metal selenides based on a precursor so-called “red Se remaining Zn” (RSRZ). The principle of our synthesis is based on a template-assisted chemical transformation process via acidification of inorganic–organic hybrid ZnSe(DETA)_0.5 nanosheets (DETA: diethylenetriamine). An appropriate amount of acid was added into an aqueous dispersion of ZnSe(DETA)_0.5 nanosheets under air for activation. The acidification induced chemical transformation mechanism was studied by tracking the acidification process. This acid controlled reactivity of lamellar hybrids allows it to be possible to capture the highly reactive intermediates, which will provide a new platform for the synthesis of various mesoporous metal selenides.

Engineering the Morphology and Configuration of Ternary Heterostructures for Improving Their Photocatalytic Activity

Heteronanomaterials composed of suitable semiconductors enable the direct conversion from solar power into clean and renewable energy. Ternary heterostructures with appropriate configuration and morphology possess rich and varied properties, especially for improving the photocatalytic activity and stability synchronously. However, suitable ternary heterostructure prototypes and facile while effective strategy for modulating their morphology and configuration are still scarce. Herein, various ternary ZnS-CdS-Zn(1-x)Cd(x)S heterostructures with tunable morphology (0 to 2 D) and semiconductor configurations (randomly distributed, interface mediated, and quantum dots sensitized core@shell heterostructures) were facilely synthesized via one-pot hydrothermal method resulting from the different molecular structures of the amine solvents. Semiconductor morphology, especially configuration of the ternary heterostructure, shows dramatic effect on their photocatalytic activity. The CdS sensitized porous Zn(1-x)CdxS@ZnS core@shell takes full advantage of ZnS, Zn(1-x)Cd(x)S and CdS and shows the maximal photocatalytic H2-production rate of 100.2 mmol/h/g and excellent stability over 30 h. This study provides some guidelines for the design and synthesis of high-performance ternary heterostructure via modulation of semiconductor configuration and morphology using one-pot method.

Rational design of semiconductor-based photocatalysts for advanced photocatalytic hydrogen production: the case of cadmium chalcogenides

This review summarizes the recent advances in developing CdX (X = S, Se, Te)-based photocatalyst systems for photocatalytic hydrogen production from water.

Formation of Co3O4 microframes from MOFs with enhanced electrochemical performance for lithium storage and water oxidation

MOF-derived Co₃O₄ microframes synthesized via a facile chemical etching and subsequent annealing strategy exhibit enhanced electrochemical performance for LIBs/OER.

Cation Exchange Synthesis and Unusual Resistive Switching Behaviors of Ag2Se Nanobelts

Ag2Se nanobelts are prepared through employing ZnSe nanobelts as templates via a facile cation exchange approach. The templates are derived from precursor ZnSe·0.5N2 H4 nanobelts, which are synthesized by a simple hydrothermal method. As-synthesized precursor nanobelts are with 200 nm in width and several hundreds of micrometers in length. Annealed in N2 , they are transformed into ZnSe nanobelts with preserving their initial morphology. Following with a complete replacement of Zn(2+) by Ag(+), Ag2Se nanobelts with single crystalline are obtained via a cation-exchange reaction. Combined with the Langmuir-Blodgett assembly technique, regular films of ZnSe nanobelts can be achieved on transparent glass substrates and Si wafers with interdigital Au electrode arrays. Further, the optical and electrical evolutions are investigated from ZnSe nanobelts to Ag2 Se nanobelts. Finally, the resistive switching characteristic are carefully explored for Ag2Se nanobelts regularly arranged on interdigital Au microelectrodes. The results indicate that it is analogous to complementary resistive switching behaviors, which is different from that of traditional two terminal devices about previously reported Ag2Se. In order to clarify this phenomenon, a possible mechanism has been proposed and indirectly demonstrated through in situ SEM (scanning electron microscropy) observation.

Assembly of multicomponent nanoframes via the synergistic actions of graphene oxide space confinement effect and oriented cation exchange

Multicomponent nanoframes (NFs) with a hollow structural character have shown the potential to be applied in many fields. Here we report a novel strategy to synthesize Zn x Cd1-x S NFs via the synergistic actions of the graphene oxide (GO) confinement effect and oriented cation exchange. The obtained samples have been systematically characterized by x-ray diffractometry (XRD), field-emission scanning electron microscopy (SEM), transmission electron microscopy (TEM), x-ray photospectroscopy (XPS) and Raman spectrometry. The results show that the two dimensional space confinement effect induced by GO and the oriented cation exchange reaction are responsible for the formation of the multicomponent NFs. The high photoelectrochemical activity and the low cost of the starting materials will make the multicomponent NFs applicable in photoelectronic and photoelectrocatalytic fields.

Face the Edges: Catalytic Active Sites of Nanomaterials

Edges are special sites in nanomaterials. The atoms residing on the edges have different environments compared to those in other parts of a nanomaterial and, therefore, they may have different properties. Here, recent progress in nanomaterial fields is summarized from the viewpoint of the edges. Typically, edge sites in MoS2 or metals, other than surface atoms, can perform as active centers for catalytic reactions, so the method to enhance performance lies in the optimization of the edge structures. The edges of multicomponent interfaces present even more possibilities to enhance the activities of nanomaterials. Nanoframes and ultrathin nanowires have similarities to conventional edges of nanoparticles, the application of which as catalysts can help to reduce the use of costly materials. Looking beyond this, the edge structures of graphene are also essential for their properties. In short, the edge structure can influence many properties of materials.

Self-assembly of a mesoporous ZnS/mediating interface/CdS heterostructure with enhanced visible-light hydrogen-production activity and excellent stability

We designed and successfully fabricated a ZnS/CdS 3D mesoporous heterostructure with a mediating Zn_1-x Cd _x S interface that serves as a charge carrier transport channel for the first time. The H₂-production rate and the stability of the heterostructure involving two sulfides were dramatically and simultaneously improved by the careful modification of the interface state via a simple post-annealing method. The sample prepared with the optimal parameters exhibited an excellent H₂-production rate of 106.5 mmol h^-1 g^-1 under visible light, which was 152 and 966 times higher than CdS prepared using ethylenediamine and deionized water as the solvent, respectively. This excellent H₂-production rate corresponded to the highest value among the CdS-based photocatalysts. Moreover, this heterostructure showed excellent photocatalytic stability over 60 h.

Converting 2D inorganic-organic ZnSe-DETA hybrid nanosheets into 3D hierarchical nanosheet-based ZnSe microspheres with enhanced visible-light-driven photocatalytic performances

Engineering two-dimensional (2D) nanosheets into three-dimensional (3D) hierarchical structures is one of the great challenges in nanochemistry and materials science. We report a facile and simple chemical conversion route to fabricate 3D hierarchical nanosheet-based ZnSe microspheres by using 2D inorganic-organic hybrid ZnSe-DETA (DETA = diethylenetriamine) nanosheets as the starting precursors. The conversion mechanism involves the controlled depletion of the organic-component (DETA) from the hybrid precursors and the subsequent self-assembly of the remnant inorganic-component (ZnSe). The transformation reaction of ZnSe-DETA nanosheets is mainly influenced by the concentration of DETA in the reaction solution. We demonstrated that this organic-component depletion method could be extended to the synthesis of other hierarchical structures of metal sulfides. In addition, the obtained hierarchical nanosheet-based ZnSe microspheres exhibited outstanding performance in visible light photocatalytic degradation of methyl orange and were highly active for photocatalytic H2 production.

A General Strategy toward Carbon Cloth-Based Hierarchical Films Constructed by Porous Nanosheets for Superior Photocatalytic Activity

Herein, the controlled synthesis of 3D hierarchical films on carbon cloth (CC) in a high yield through a hydrothermal process and their high photocatalytic properties are reported. As representative examples, the obtained ZnIn2 S4 /CdIn2 S4 composites are composed of porous nanosheets. During the hydrothermal process, l-cysteine plays an important dual role as a coordinating agent and sulfur source, which is in favor of adjusting stoichiometry of the final product and forming the nanoporous structure. This facile method can be extended to synthesize other sulfides and oxides on CC substrates, such as CoIn2 S4 , MnIn2 S4 , FeIn2 S4 , SnS2 , and Bi2 WO6 . When evaluated the photocatalytic activity, the optimized ZnIn2 S4 /CdIn2 S4 (20%)-CC with an easily recycling feature shows higher photocatalytic degradation activity for methylene blue (MB) than ZnIn2 S4 -CC, CdIn2 S4 -CC, and ZnIn2 S4 /CdIn2 S4 (20%) powder. More importantly, ZnIn2 S4 /CdIn2 S4 (20%)-CC also exhibits superior H2 production activity. The enhanced photocatalytic activity is attributed to the unique porous sheet-like structure and the formation of heterojunction. Our results could provide a promising way to develop high-performance photocatalytic films, which makes it possible to be used in real devices.

Space-confined creation of nanoframes in situ on reduced graphene oxide

Nanoframes (NFs) are created in situ on reduced graphene oxide (rGO) through confining the evolutions of precursor nanosheets, such as ZnS(EN)0.5 (EN = ethylenediamine), and nanoparticles within quasi-two-dimensional spaces generated from graphene oxide. The resultant composites of ZnS-NF@rGO exhibit excellent photocurrent responses. This work provides a new strategy to synthesize and modulate nanostructures and nanomaterials for rGO composites.