Ultrasound assisted fabrication of InVO4/In2S3 heterostructure for enhanced sonophotocatalytic degradation of pesticides

A cost effective and environmentally benign ultrasonic method has been developed for the synthesis of InVO4 (InV), In2S3 (InS) and the InVO4/In2S3 heterostructure (InV/InS). All the designed materials were evaluated for their structural, morphological, spectroscopic, and electrochemical characterizations. Materials were examined for photocatalytic, sonocatalytic, and sonophotocatalytic degradation of carbofuran (CBF) and diazinon (DZN) pesticides under visible light. InV/InS showed enhanced degradation of CBF and DZN when compared to InV and InS. Photocatalytic degradation was accelerated by ultrasonication and found to degrade 97 and 98 % of CBF and DZN in 60 and 70 min, respectively. The reaction conditions, like pH, catalyst dosage, acoustic intensity, and ultrasound power, were carefully optimized. Electron spin resonance (ESR) spectroscopy shows the generation of superoxide radical anion and hydroxyl radicals as reactive species during photoredox reaction. The CBF and DZN degradation intermediates were analyzed using liquid chromatography mass spectroscopy (LC-MS) that shows the mineralization of the CBF and DZN to CO2 and H2O. The effect of Cl-, and PO43- were examined towards degradation of CBF and DZN under optimal conditions in the presence of InV/InS. The degradation of CBF and DZN is decreased in presence of Cl-, CO32- and NO3- but PO43- ions does not show any effect on degradation. The bandgap and Mott-Schottky results suggest the existence of type-II heterostructure between InV and InS through the interface. The synthesis of heterostructure and degradation of pesticides utilizes ultrasonic waves, which prove their multiple applications and attract researchers towards the effective use of sonication.

Unveiling Hierarchical Dendritic Co3O4-SnO2 Heterostructure for Efficient Water Purification

The construction of a desirable, environmentally friendly, and cost-effective nanoheterostructure photoanode to treat refractory organics is critical and challenging. Herein, we unveiled a hierarchical dendritic Co₃O₄-SnO₂ heterostructure via a sequential hydrothermal process. The time of the secondary hydrothermal process can control the size of the ultrathin SnO₂ nanosheets on the basis of the Ostwald solidification mass conservation principle. Ti/Co₃O₄-SnO₂-168h with critical growth size demonstrated a photoelectrocatalysis degradation rate of ∼93.3% for a high dye concentrate of 90 mg/L with acceptable long-term cyclability and durability over reported Co₃O₄-based electrodes because of the large electrochemically active area, low charge transfer resistance, and high photocurrent intensity. To gain insight into the photoelectric synergy, we proposed a type-II heterojunction between Co₃O₄ and SnO₂, which prevents photogenerated carriers' recombination and improves the generation of dominant active species •O₂^-, ¹O₂, and h⁺. This work uncovered the Ti/Co₃O₄-SnO₂-168 as a promising catalyst and provided a simple and inexpensive assembly strategy to obtain binary integrated nanohybrids with targeted functionalities.

Designing a Novel Monolayer β-CSe for High Performance Photovoltaic Device: An Isoelectronic Counterpart of Blue Phosphorene

Using the first-principles method, an unmanufactured structure of blue-phosphorus-like monolayer CSe (β-CSe) was predicted to be stable. Slightly anisotropic mechanical characteristics in β-CSe sheet were discovered: it can endure an ultimate stress of 5.6 N/m at 0.1 along an armchair direction, and 5.9 N/m at 0.14 along a zigzag direction. A strain-sensitive transport direction was found in β-CSe, since β-CSe, as an isoelectronic counterpart of blue phosphorene (β-P), also possesses a wide indirect bandgap that is sensitive to the in-plane strain, and its carrier effective mass is strain-dependent. Its indirect bandgap character is robust, except that armchair-dominant strain can drive the indirect-direct transition. We designed a heterojunction by the β-CSe sheet covering α-CSe sheet. The band alignment of the α-CSe/β-CSe interface is a type-II van der Waals p-n heterojunction. An appreciable built-in electric field across the interface, which is caused by the charges transfering from β-CSe slab to α-CSe, renders energy bands bending, and it makes photo-generated carriers spatially well-separated. Accordingly, as a metal-free photocatalyst, α-CSe/β-CSe heterojunction was endued an enhanced solar-driven redox ability for photocatalytic water splitting via lessening the electron-hole-pair recombination. This study provides a fundamental insight regarding the designing of the novel structural phase for high-performance light-emitting devices, and it bodes well for application in photocatalysis.

Physical Properties and Photovoltaic Application of Semiconducting Pd₂Se₃ Monolayer

Palladium selenides have attracted considerable attention because of their intriguing properties and wide applications. Motivated by the successful synthesis of Pd₂Se₃ monolayer (Lin et al., Phys. Rev. Lett., 2017, 119, 016101), here we systematically study its physical properties and device applications using state-of-the-art first principles calculations. We demonstrate that the Pd₂Se₃ monolayer has a desirable quasi-direct band gap (1.39 eV) for light absorption, a high electron mobility (140.4 cm²V^-1s^-1) and strong optical absorption (~10⁵ cm^-1) in the visible solar spectrum, showing a great potential for absorber material in ultrathin photovoltaic devices. Furthermore, its bandgap can be tuned by applying biaxial strain, changing from indirect to direct. Equally important, replacing Se with S results in a stable Pd₂S₃ monolayer that can form a type-II heterostructure with the Pd₂Se₃ monolayer by vertically stacking them together. The power conversion efficiency (PCE) of the heterostructure-based solar cell reaches 20%, higher than that of MoS₂/MoSe₂ solar cell. Our study would motivate experimental efforts in achieving Pd₂Se₃ monolayer-based heterostructures for new efficient photovoltaic devices.

Phase-Engineered Type-II Multimetal-Selenide Heterostructures toward Low-Power Consumption, Flexible, Transparent, and Wide-Spectrum Photoresponse Photodetectors

Phase-engineered type-II metal-selenide heterostructures are demonstrated by directly selenizing indium-tin oxide to form multimetal selenides in a single step. The utilization of a plasma system to assist the selenization facilitates a low-temperature process, which results in large-area films with high uniformity. Compared to single-metal-selenide-based photodetectors, the multimetal-selenide photodetectors exhibit obviously improved performance, which can be attributed to the Schottky contact at the interface for tuning the carrier transport, as well as the type-II heterostructure that is beneficial for the separation of the electron-hole pairs. The multimetal-selenide photodetectors exhibit a response to light over a broad spectrum from UV to visible light with a high responsivity of 0.8 A W^-1 and an on/off current ratio of up to 10² . Interestingly, all-transparent photodetectors are successfully produced in this work. Moreover, the possibility of fabricating devices on flexible substrates is also demonstrated with sustainable performance, high strain tolerance, and high durability during bending tests.

Low Threshold Multiexciton Optical Gain in Colloidal CdSe/CdTe Core/Crown Type-II Nanoplatelet Heterostructures

Colloidal cadmium chalcogenide core/crown type-II nanoplatelet heterostructures, such as CdSe/CdTe, are promising materials for lasing and light-emitting applications. Their rational design and improvement requires the understanding of the nature of single- and multiexciton states. Using pump fluence and wavelength-dependent ultrafast transient absorption spectroscopy, we have identified three spatially and energetically distinct excitons (in the order of increasing energy): interface-localized charge transfer exciton (X_CT, with electron in the CdSe core bound to the hole in the CdTe crown), and CdTe crown-localized X_CdTe and CdSe core-localized X_CdSe excitons. These exciton levels can be filled sequentially, with each accommodating two excitons (due to electron spin degeneracy) to generate one to six exciton states (with lifetimes of ≫1000, 209, 43.5, 11.8, 5.8, and 4.5 ps, respectively). The spatial separation of these excitons prolongs the lifetime of multiexciton states. Optical gain was observed in tri- (XX_CTX_CdTe) and four (XX_CTXX_CdTe) exciton states. Because of the large absorption cross section of nanoplatelets, an optical gain threshold as low as ∼43 μJ/cm² can be achieved at 550 nm excitation for a colloidal solution sample. This low gain threshold and the long triexciton (gain) lifetime suggest potential applications of these 2D type-II heterostructures as low threshold lasing materials.