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Constructing van der Waals (vdW) heterostructures provides an effective and feasible method for 2D materials to improve their properties and extend their possible applications. Using first-principles calculations, we explored the atomic and electronic structures of Janus In2SeX (X = S or Te) and revealed the existence of a vertical internal intrinsic electric field in these Janus monolayers. Then, we stacked the pristine InSe and Janus In2SeX (X = S or Te) with black phosphorus (BP) vertically to construct vdW heterostructures with a mismatch of less than 5% and systematically investigated their interface atomic structures and possible applications in photovoltaics. The calculation results reveal that the constructed vdW heterostructures can be synthesized experimentally, and the type-II band alignment can be found in all vdW heterostructures, which is independent of the internal electric field of Janus monolayers, the built-in dipole at the interface between two domains, and the number of layers. In addition, the vdW heterostructures show stronger light absorption compared to monolayer individuals, and the type-II band alignment can help the photo-excited carriers to separate and achieve an excellent photovoltaic power conversion efficiency of up to about 21% in these heterostructures. These extraordinary results suggest that these vdW heterostructures have great potential for more efficient solar photovoltaic applications. [ABSTRACT FROM AUTHOR]

Electrostatic control and van der Waals integration are useful methods for 2D materials to help modulate their properties. Here, we constructed nine types of monolayer and multilayer Janus structures based on group-III monochalcogenides and investigated their atomic and electronic structures from first-principles calculations. We found the existence of an intrinsic electric field at Janus structures by comparing their average vacuum electron potentials at two surfaces. Careful charge analyses reveal that the electric field at monolayer Janus structures is mainly due to the dipole of the bond that connects group-III elements of weaker negativity and group-VI elements of stronger negativity. The E-filed at multilayer Janus structures maintains owing to the superposition of dipole at each layer when layer numbers (LN) are not very large, and the electric field starts to reduce when LN is large enough and obvious charge transfer happens between two surfaces of Janus multilayers. Electronic structure calculations at Janus structures demonstrate that the electric field can hardly modulate the charge density population in the monolayer case, while the electric field will significantly bend the bands in multilayer cases and make the charge density of the valence band maximum and the conduction band minimum always located at two separating surfaces, which promotes electron–hole to separate. Furthermore, we investigated the band alignment of isolated monolayer pristine group-III monochalcogenides and isolated Janus group-III monochalcogenides of monolayer, bilayer, and trilayer, and constructed van der Waals (vdW) heterostructures with one pristine monolayer and one Janus monolayer. The results show that the surface termination of Janus structures at the interface can significantly influence the band offset and electronic structures of vdW heterostructures. These results can not only provide a new understanding of the intrinsic electric field of monolayer and multilayer 2D Janus structures but also give a guide that uses electrostatic to modulate the properties of group-III monochalcogenides and other 2D materials. [ABSTRACT FROM AUTHOR]

A highly reliable high-performance liquid chromatography method was developed and validated for determining quality of extracts from the leaves ofDipsacus sativus(Linn.) Honck. Under optimum conditions, the chromatography profile of eight compounds was collected, with compound saponarin as marker. The analysis results indicated that saponarin and isovitexin were the main active components. Pharmacological experiments proved that extracts from the leaves showed significant antioxidant activity. This work could serve to validate the usefulness of high-performance liquid chromatography analyses in traditional Chinese medicine. [ABSTRACT FROM PUBLISHER]

Chitosan (CH), partially N-deacetylatedchitin, is a biodegradable and biocompatible polymer that has showngreat potential in drug delivery and tissue engineering applications.Although bioadhesive, CH has limited mucoadhesion in wet conditionsdue to weak interactions with biological surfaces. DOPA (3,4-dihydroxy-l-phenylalanine), a catechol-containing molecule naturally presentin marine mussel foot proteins, has been shown to increase the mucoadhesionof several polymers. We report here a simple and bioinspired approachto enhance CH mucoadhesion in wet conditions by preparing mixed hydrogelsincluding CH and different catechol-containing compounds, namely DOPA,hydrocaffeic acid (HCA), and dopamine (DA). We characterized the hydrogelsfor their swelling, release kinetics of the catechol compounds, andmucoadhesive strength to rabbit small intestine. The swelling of thehydrogels was pH dependent with maximum swelling at pH 1. The hydrogelswelling was higher in the presence of the DOPA and DA but lower inthe presence of HCA. HCA/CH hydrogel also showed the slowest catecholrelease, most likely due to electrostatic interactions between CHand HCA. Lower hydrogel swelling and slower HCA release resulted inincreased mucoadhesion: HCA/CH showed more than 2-fold enhancementof mucoadhesion to rabbit small intestine compared to CH alone. Sinceit is known that catechol compounds can be oxidized, we analyzed theoxidation of DOPA, HCA, and DA at different pH values and its effecton mucoadhesion. We found that oxidation occurring before contactwith the intestinal mucosa did not improve mucoadhesion, while oxidationoccurring during the contact further increased the mucoadhesion ofHCA/CH hydrogels. These results show that mucoadhesion of CH hydrogelscan be increased with a simple bioinspired approach, which has thepotential to be applied to other polymers since it does not requireany chemical modification. [ABSTRACT FROM AUTHOR]

Constructing van der Waals (vdW) heterostructures provides an effective and feasible method for 2D materials to improve their properties and extend their possible applications. Using first-principles calculations, we explored the atomic and electronic structures of Janus In 2 SeX (X = S or Te) and revealed the existence of a vertical internal intrinsic electric field in these Janus monolayers. Then, we stacked the pristine InSe and Janus In 2 SeX (X = S or Te) with black phosphorus (BP) vertically to construct vdW heterostructures with a mismatch of less than 5% and systematically investigated their interface atomic structures and possible applications in photovoltaics. The calculation results reveal that the constructed vdW heterostructures can be synthesized experimentally, and the type-II band alignment can be found in all vdW heterostructures, which is independent of the internal electric field of Janus monolayers, the built-in dipole at the interface between two domains, and the number of layers. In addition, the vdW heterostructures show stronger light absorption compared to monolayer individuals, and the type-II band alignment can help the photo-excited carriers to separate and achieve an excellent photovoltaic power conversion efficiency of up to about 21% in these heterostructures. These extraordinary results suggest that these vdW heterostructures have great potential for more efficient solar photovoltaic applications.

Two-dimensional materials with excellent surface-volume ratios and massive reaction sites recently have been receiving attention for gas sensing. With first-principles calculations, we explored the performance of monolayer Sc 2 CF 2 as a gas sensor. We investigated how molecule adsorption affects its electronic structure and optical properties. It is found that a large charge transfer quantity happens between Sc 2 CF 2 and NO 2 , which results from the fact that the lowest unoccupied molecular orbital (LUMO) of NO 2 is below the valence band maximum (VBM) of Sc 2 CF 2 . Moreover, the MD simulation shows that NO 2 can adsorb on the Sc 2 CF 2 surface stably at room temperature. We explored the effect of biaxial strain on the adsorption energy and charge transfer quantity of each system, and the results show that the biaxial strain can enhance both the adsorption energy and charge transfer quantity of the NO 2 system and thus can improve the sensitivity of Sc 2 CF 2 in detecting the NO 2 molecule. Furthermore, we investigated the adsorption behavior and charge transfer of polar polyatomic molecules at the Sc 2 CF 2 surface with h -BN as a substrate, and the results demonstrate that the h -BN substrate can hardly modify the main results. Our result predicts that Sc 2 CF 2 can be a promising selective and sensitive sensor to detect the NO 2 molecule, and could also give a theoretical guide for other terminated MXenes used for gas sensors or detectors., Competing Interests: The authors declare no competing financial interest., (© 2022 The Authors. Published by American Chemical Society.)