Integrating Zeolite-Type Chalcogenide with Titanium Dioxide Nanowires for Enhanced Photoelectrochemical Activity

Assessment of surface and electrical properties of the TiO2@zeolite hybrid materials

Degradation of pollutants in aqueous medium is of high interest due to the impact on environment and human health, therefore, design and study of the physico-chemical properties of photocatalysts for water remediation are of major significance. Among properties of photocatalyst, those related to the surface and electrical mechanism are crucial to the photocatalyst´s performance. Here we report the chemical and morphological characteristics of TiO₂@zeolite photocatalyst by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) respectively, and a coherent electrical conduction mechanism was proposed based on data obtained from assisted laser impedance spectroscopy (ALIS), in which the zeolite was synthesized from recycled coal fly ash. The results obtained by SEM and XPS verified the presence of spherical particles of TiO₂ anatase with presence of Ti³⁺ state. ALIS results showed that impedance of the entire system increases when the amount of TiO₂ increases and the samples with lower capacitive performance allowed a larger transfer of the charges between the solid-liquid interface. All results showed that higher photocatalytic performance of TiO₂ growth over hydroxysodalite with 8.7 wt% and 25 wt% of TiO₂ can be explained in terms of the morphology of TiO₂ and the interactions between substrate-TiO₂ mainly.

Photocatalytic degradation of triclocarban in aqueous solution using a modified zeolite/TiO2 composite: kinetic, mechanism study and toxicity assessment

The current work aimed to investigate the degradation of the triclocarban (TCC) in aqueous solution using a modified zeolite/TiO₂ composite (MZTC) synthesized by applying the electrochemical anodization (ECA). The synthesis process was conducted at different voltages (10, 40, and 60) V in 1 h and using electrophoresis deposition (EPD) in doping zeolite. The MZTC was covered with the array ordered, smooth and optimum elongated nanotubes with 5.1 μm of the length, 120.3 nm of the inner diameter 14.5 nm of the wall thickness with pure titanium and crystalline titania as determined by FESEM/EDS, and XRD. The kinetic study by following Langmuir-Hinshelwood(L-H) model and pseudo first order, the significant constant rate was obtained at pH 11 which was 0.079 ppm/min, 0.75 cm² of MZTC catalyst loading size achieved 0.076 ppm/min and 5 ppm of TCC initial concentration reached 0.162 ppm/min. The high-performance liquid chromatography (HPLC) analysis for mechanism study of TCC photocatalytic degradation revealed eleven intermediate products after the whole process of photocatalysis. In regard of toxicology assessment by the bacteria which is Photobacterium phosphoreum, the obtained concentration of TCC at minute 60 was less satisfied with remained 0.36 ppm of TCC was detected indicates that the concentration was above allowable level. Where the allowable level of TCC in stream is 0.1 ppm.

Modified TiO₂ nanotubes-zeolite composite photocatalyst: Characteristics, microstructure and applicability for degrading triclocarban

The study explored the characteristics and effectiveness of modified TiO₂ nanotubes with zeolite as a composite photocatalyst (MTNZC) for the degradation of triclocarban (TCC) from the aqueous solution. MTNZC samples have been produced via electrochemical anodisation (ECA) followed by electrophoretic deposition (EPD). Three independent factors selected include MTNZC size (0.5-1 cm²), pH (3-10), and irradiation time (10-60 min). The observation revealed that the surface of Ti substrate by the 40 V of anodisation and 3 h of calcination was covered with the array ordered, smooth and optimum elongated nanotubes with average tube length was approximately 5.1 μm. EDS analysis proved the presence of Si, Mg, Al, and Na on MTNZC due to the chemical composition present in the zeolite. The average crystallite size of TiO₂ nanotubes increased from 2.07 to 3.95 nm by increasing anodisation voltage (10, 40, and 60 V) followed by 450 °C of calcination for 1, 3, and 6 h, respectively. The optimisation by RSM shows the F-value (36.12), the p-value of all responses were less than 0.0001, and the 95% confidence level of the model by all the responses indicated the model was significant. The R² in the range of 0.9433-0.9906 showed the suitability of the model to represent the actual relationship among the parameters. The photocatalytic degradation rate of TCC from the first and the fifth cycles were 94.2 and 77.4%, indicating the applicability of MTNZC to be used for several cycles.

Oxygen Vacancy-Enhanced Photoelectrochemical Water Splitting of WO3/NiFe-Layered Double Hydroxide Photoanodes

Photoelectrochemical (PEC) water splitting serves as one of the promising approaches for producing clean and renewable energy, and their solar-hydrogen energy conversion efficiency depends on the interfacial charge separation and carrier mobility. Herein, we report an effective strategy to promote the PEC performance by fabricating a WO₃ photoanode rich in oxygen vacancies (Ov) modified by NiFe-based layered double hydroxide (LDH). When WO₃-Ov/NiFe-LDH is used as a photoanode, the maximum photocurrent density at 1.8 V versus RHE has been significantly enhanced to 2.58 mA·cm^-2, which is 4.3 times higher than that of WO₃. In addition, analogues were studied in controlled experiments without Ov, which further demonstrated that the synergistic effect of NiFe-LDH and Ov resulted in increased carrier concentration and driving force. According to electrical impedance spectroscopy, X-ray photoelectron spectroscopy, and Mott-Schottky analysis, the built-in electronic field in WO₃ homojunction, along with the accelerated hole capture by the NiFe-LDH cocatalyst contributes to the improved charge separation and transport in the WO₃-Ov/NiFe-LDH electrode. This work proposes an efficient and valuable strategy for designing the structure of WO₃-based photoelectrodes.

Heterometallic Actinide-Containing Photoresponsive Metal-Organic Frameworks: Dynamic and Static Tuning of Electronic Properties

Acquiring fundamental knowledge of properties of actinide-based materials is a necessary step to create new possibilities for addressing the current challenges in the nuclear energy and nuclear waste sectors. In this report, we established a photophysics-electronics correlation for actinide-containing metal-organic frameworks (An-MOFs) as a function of excitation wavelength, for the first time. A stepwise approach for dynamically modulating electronic properties was applied for the first time towards actinide-based heterometallic MOFs through integration of photochromic linkers. Optical cycling, modeling of density of states near the Fermi edge, conductivity measurements, and photoisomerization kinetics were employed to shed light on the process of tailoring optoelectronic properties of An-MOFs. Furthermore, the first photochromic MOF-based field-effect transistor, in which the field-effect response could be changed through light exposure, was constructed. As a demonstration, the change in current upon light exposure was sufficient to operate a two-LED fail-safe indicator circuit.

Highly Effective Electrochemical Exfoliation of Ultrathin Tantalum Disulfide Nanosheets for Energy-Efficient Hydrogen Evolution Electrocatalysis

Developing highly efficient transition metal dichalcogenide electrocatalysts would be significantly beneficial for the electrocatalytic hydrogen evolution reaction (HER) from water splitting. Herein, we reported novel ultrathin tantalum disulfide nanosheets (TaS₂ NSs) prepared by electrochemically exfoliating bulk TaS₂ with an alternating voltage in an acidic electrolyte. The obtained TaS₂ NS electrocatalyst possessed an ultrathin structure with a lateral size of 2 μm and a thickness of ∼3 nm. Owing to the unique 2D structure, the achieved TaS₂ NSs displayed remarkable electrocatalytic activity toward the HER by a small overpotential of 197 mV at 10 mA cm^-2 and a small Tafel slope of 100 mV dec^-1 in acidic solution, much lower than those of TaS₂ (>547 mV and 216 mV dec^-1, respectively) and other reported TaS₂-based HER electrocatalysts. Furthermore, highly efficient full water splitting could be realized with two electrodes in which TaS₂ NSs acted as the cathode while Ir/C served as the anode, with help of two AA size batteries or solar cells. By replacing the oxygen evolution reaction with the urea oxidation reaction (UOR), bifunctional TaS₂ NSs enabled an energy-effective HER process in the cathode and UOR process in the anode with decreased applied potential.

Direct observation of charge transfer between molecular heterojunctions based on inorganic semiconductor clusters

A deep understanding of the dynamics of photogenerated charge carriers is extremely important for promoting their germination in semiconductors to enhance the efficiency of solar energy conversion. In contrast to that of organic molecular heterojunctions (which are widely employed in organic solar cells), the charge transfer dynamics of purely inorganic molecular heterojunctions remains unexplored. Herein, we reveal the dynamics of charge transfer between inorganic semiconductor molecular heteroclusters by selecting a group of open-framework metal chalcogenides as unique structure models constructed from supertetrahedral T3-InS ([In₁₀S₂₀]) and T4-MInS ([M₄In₁₆S₃₅], M = Mn or Fe) clusters. The staggered band gap alignment in T3-T4-MInS molecular heterojunctions enables the photogenerated charge carriers to be directionally transferred from T3-InS clusters to adjacent T4-MInS clusters upon irradiation or application of an external electric field. The simultaneous independence of and interactions between such two heteroclusters are investigated by theoretical calculations, steady- and transient-state absorption/photoluminescence spectroscopy, and surface photovoltage analysis. Moreover, the dynamics of cluster-to-cluster-to-dopant photogenerated charge transfer is deliberately elucidated. Thus, this work demonstrates the direct observation of charge transfer between molecular heterojunctions based on purely inorganic semiconductor clusters and is expected to promote the development of cluster-based semiconductors for solar cells.

Charge transfer between inter-clusters is directly observed in inorganic molecular heterojunctions.

Selectively Photocatalytic Activity of an Open-Framework Chalcogenide Built from Corner-Sharing T4 Supertetrahedral Clusters

The photocatalysis process with high selectivity is a very important research forefront for the semiconductor photocatalytic decomposition of organic pollutants. However, the rational design of efficient photocatalysts with high selectivity is still a challenge. Here, we present an open-framework chalcogenide (Heta)₈[In₁₄Sn₂Zn₄Se₃₃] (Heta = ethanolamine-H⁺) (compound 1) constructed from T4 supertetrahedral clusters [In₁₄Sn₂Zn₄Se₃₅]^12- with visible-light-driven selectively photocatalytic degradation activity. Single-crystal XRD analysis shows that compound 1 crystallizes in I4₁/acd (no. 142) space group, with a = b = 24.3462(2) Å, c = 45.0062(9) Å, V = 26676.9(7) ų, and Z = 8. Under visible-light irradiation, the selectively photocatalytic activities of 1 were evaluated by photodegradation of two kinds of cationic dye molecules, i.e., methylene blue (MB) and rhodamine B (RhB), against two anionic dyes, methyl orange (MO) and Kermes red (KR), with different sizes. We show that the adsorption capability and charge-matching between organic dyes and the supertetrahedral cluster together with a suitable band structure make it an excellent and selective photocatalyst. This is the first example of an open-framework chalcogenide based on supertetrahedral T4 for the selectively semiconductor photocatalytic decomposition of organic dyes.

Light-triggered evolution of molecular clusters toward sub-nanoscale heterojunctions with high interface density

Herein, we report a simple, yet highly effective approach for constructing a new type of sub-nanoscale ZnS/ZnO heterojunction (∼2-4 nm) with highly rich interfaces by photoetching hybrid Zn-S-O molecular clusters. The obtained ZnS/ZnO heterojunctions with ZnS spheres decorated with ultrasmall amorphous ZnO dots exhibit superior photocatalytic performance (∼94.0 μmol g^-1 h^-1), compared to nanoscale homologous samples obtained via conventional heat treatment (∼17.0-21.4 μmol g^-1 h^-1). Such a light-triggered molecular-cluster-to-heterojunction strategy provides a synthetic approach to building other sub-nanoscale hetero-structured materials for further promoting the catalytic-related applications.

Brand new 1D branched CuO nanowire arrays for efficient photoelectrochemical water reduction

1D branched CuO nanowire arrays, with large surface area and efficient charge transfer, are reported as photocathodes for photoelectrochemical water reduction.