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

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.

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.

Self-supported CdSe nanowire/nanosheet photoanodes on cadmium foil via in situ hydrothermal transformation of CdSe(en)0.5 complex nanostructures

To solve energy crisis, the engineering of highly efficient and cost-effective photoanodes is urgently required for clean fuel generation. Herein, CdSe(en)_0.5 (en = ethylenediamine) hybrid photoanodes were synthesized by a solvothermal approach. It was revealed that a second in situ hydrothermal treatment successfully converts cadmium foil-based inorganic-organic CdSe(en)_0.5 (en = ethylenediamine) hybrid nanosheets to an oriented cadmium hydroxide crowned CdSe nanowire-decorated porous nanosheet (Cd(OH)₂/CdSe NW/NS) heterostructure by dissolution and regrowth mechanisms. The alteration in second hydrothermal reaction conditions could modify the morphology and optical properties of the Cd(OH)₂/CdSe NW/NS heterostructure photoanodes. The possible growth mechanism of the Cd(OH)₂/CdSe NW/NS porous structure is studied at various second hydrothermal times using the control experiments of the synthesis. The optimized 3D porous Cd(OH)₂/CdSe NW/NS photoanodes exhibited an outstanding photocurrent density of 6.1 mA cm^-2 at 0 V vs. Ag/AgCl, which is approximately 7.6 times higher than that of the inorganic-organic CdSe(en)_0.5 hybrid under light irradiation (>420 nm cut off filter). A mechanism is proposed to explain the enhanced charge separation at the Cd(OH)₂/CdSe NW/NS photoanode/electrolyte interface, which is supported by PL and photoelectrochemical analyses. These findings open an avenue of phase and morphology transmutation for efficient formation of other hierarchical structures of metal selenides and sulfides. Additionally, the Al₂O₃ co-catalyst can act as effective hole trapping sites and improves the stability of the photoelectrode through the timely consumption of photogenerated charges, particularly holes.

ZnO nanospheres based simple hydrothermal route for photocatalytic degradation of azo dye

This novel work presents a promising application to use Zinc oxide nanospheres as nanocatalysts in photocatalytic degradation of methyl orange dye. The hydrothermal route was utilized in the synthesis process of ZnO nanospheres. The size of the synthesized ZnO nanoparticles is around 200-250 nm diameter. The synthesized nano-oxides were characterized utilizing several instruments such as X-ray diffraction, Brunauer, Emmett, and Teller (BET), and scanning electron microscope (SEM). The resulting nanoparticles are utilized as an efficient tool for degradation of methyl orange (MO) dye under UV radiation. Essential parameters were studied on degradation process involving the initial concentration of MO, pH, stirring the solution, dose of the ZnO nanospheres, the oxygen content of the solution, calcination of the nanomaterials. All activity experiments under UV radiation provide excellent results for the degradation process of MO. Also, the recovery of ZnO nanomaterials was investigated based on the photocatalytic process efficiency. The results show the high possibility of reuse ZnO nanospheres for several photocatalytic processes. Also, the nanocatalysts were applied for a real environmental sample with providing high photocatalytic performance.

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.

Cascaded photo-potential in a carbon dot-hematite system driving overall water splitting under visible light

Hematite is an earth-abundant and ubiquitous semiconductor with a suitable bandgap of 2.1 eV for solar water splitting. Unfortunately, it suffers from a low conduction band position compared to the H⁺/H₂ potential and typically an external bias has to be applied. Here, we demonstrate carbon dot-hematite (CD-Fe₂O₃) nanocomposites as photocatalysts for visible-light-driven overall water splitting without any external bias or scavenger. Notably, the CD-Fe₂O₃ nanocomposites (carbon dots, 5 wt%) show a hydrogen evolution rate of 0.390 μmol h^-1 and an oxygen evolution rate of 0.225 μmol h^-1 under visible light illumination. In our system, carbon dots have been well coupled with hematite and are detected to generate a photo-induced potential. This photo-potential can be combined with hematite to meet the requirement for overall water splitting. In addition, carbon dots can significantly improve the charge separation efficiency. Our finding may greatly enhance the practical application of hematite for solar water splitting.

Two-Dimensional Transition Metal Oxide and Chalcogenide-Based Photocatalysts

Two-dimensional (2D) transition metal oxide and chalcogenide (TMO&C)-based photocatalysts have recently attracted significant attention for addressing the current worldwide challenges of energy shortage and environmental pollution. The ultrahigh surface area and unconventional physiochemical, electronic and optical properties of 2D TMO&Cs have been demonstrated to facilitate photocatalytic applications. This review provides a concise overview of properties, synthesis methods and applications of 2D TMO&C-based photocatalysts. Particular attention is paid on the emerging strategies to improve the abilities of light harvesting and photoinduced charge separation for enhancing photocatalytic performances, which include elemental doping, surface functionalization as well as heterojunctions with semiconducting and conductive materials. The future opportunities regarding the research pathways of 2D TMO&C-based photocatalysts are also presented.

Recent advances in 2D materials for photocatalysis

Two-dimensional (2D) materials have attracted increasing attention for photocatalytic applications because of their unique thickness dependent physical and chemical properties. This review gives a brief overview of the recent developments concerning the chemical synthesis and structural design of 2D materials at the nanoscale and their applications in photocatalytic areas. In particular, recent progress on the emerging strategies for tailoring 2D material-based photocatalysts to improve their photo-activity including elemental doping, heterostructure design and functional architecture assembly 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.