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Cellulose aerogels have great prospects for noise reduction applications due to their sustainable value and superior 3D interconnected porous structures. The drying principle is a crucial factor in the preparation process for developing high-performance aerogels, particularly with respect to achieving high acoustic absorption properties. In this study, multifunctional cellulose nanocrystal (CNC) aerogels were conveniently prepared using two distinct freeze-drying principles: refrigerator conventional freezing (RCF) and liquid nitrogen unidirectional freezing (LnUF). The results indicate that the rapid RCF process resulted in a denser CNC aerogel structure with disordered larger pores, causing a stronger compressive performance (Young's modulus of 40 kPa). On the contrary, the LnUF process constructed ordered structures of CNC aerogels with a lower bulk density (0.03 g/cm3) and smaller apertures, resulting in better thermal stability, higher diffuse reflection across visible light, and especially increased acoustic absorption performance at low–mid frequencies (600–3000 Hz). Moreover, the dissipation mechanism of sound energy in the fabricated CNC aerogels is predicted by a designed porous media model. This work not only paves the way for optimizing the performance of aerogels through structure control, but also provides a new perspective for developing sustainable and efficient acoustic absorptive materials for a wide range of applications. [ABSTRACT FROM AUTHOR]

Structural color technology has garnered extensive attention in the development of ink-free color technology for applications such as color displays, color reflectors, and colorimetric devices. A Fabryâ€"Perot (Fâ€"P) structure formed by stacking a metal base, an interference cavity, and a phase change material layer (MIP) is of significant interest as a lithography-free and scalable color-reflecting structure. Such a structure can selectively reflect interfered light over a range of visible wavelengths, resulting in bright colors. However, obtaining a wide range of saturation regulation spaces has become a challenge. In this study, an Fâ€"P color reflector based on a phase-change material (PCM) base is proposed, which consists of a PCM base, an interference layer, and a PCM top layer (PIP). The results of the finite element simulation and experimental measurements demonstrated that the PIP reflector had an adjustable saturation range 10.75 times larger than that of the MIP reflector. The effects of the structure size and phase change of the PCM layer on the structural characteristics were further analyzed. In addition, the performance of laser-induced color change and its application in color printing were demonstrated. The present study sheds new light on color reflectors, and the strategy proposed indicates their potential optoelectronic applications based on saturation modulation. [ABSTRACT FROM AUTHOR]

We studied the structural, electronic, and optical characters of SiS2, a new type of group IV–VI two-dimensional semiconductor, in this article. We focused on monolayer SiS2 and its characteristic changes when different strains are applied on it. Results reveal that the monolayer SiS2 is dynamically stable when no strain is applied. In terms of electronic properties, it remains a semiconductor under applied strain within the range from −10% to 10%. Besides, its indirect band-gap is altered regularly after applying a strain, whereas different strains lead to various changing trends. As for its optical properties, it exhibits remarkable transparency for infrared and most visible light. Its main absorption and reflection regions lie in the blue and ultraviolet areas. The applied uniaxial strain causes its different optical properties along the armchair direction and zigzag direction. Moreover, the tensile strain could tune its optical properties more effectively than the compressive strain. When different strains are applied, the major changes are in blue and ultraviolet regions, but only minor changes can be found in infrared and visible regions. So its optical properties reveal good stability in infrared and visible regions. Therefore, SiS2 has a promising prospect in nano-electronic and nano-photoelectric devices. [ABSTRACT FROM AUTHOR]

The inorganic-organic perovskite CH3NH3P bI3 is a hot research material owing to its outstanding performances as one light absorbing layer of solid-state dye-sensitized solar cells. In this study, we focused on the atomic size effect on CH3NH3 BI3 ( B = Sn, Pb), provided the best atomic size with which CH3NH3 BI3 absorbs widest range of different wavelengths of light, by first-principles calculation. We found that the halogen I- p states are mainly composed of the valence band maximum (VBM) of CH3NH3 BI3, and the cation B- p states are primarily composed of the conduction band minimum (CBM). Besides, the bandgap of CH3NH3 BI3 decreases and absorptive capacities of different wavelengths of light expand when we reduced the size of the atom and changed B atom from Pb to Sn during the change of suitable range. From all of the above, it is discovered that when the atomic size is 20% less than the normal size, CH3NH3P bI3 has the best optical properties, and its light-absorption range is the widest among all sizes of CH3NH3 BI3 compounds. All these results reveal that the stress and strain on CH3NH3 BI3 change the atomic size which leads to alteration of bandgap and optical properties in high-efficiency solar cells among all CH3NH3 BI3 compounds, namely we can enhance the efficiency of the inorganic-organic perovskite solar cells by setting up suitable pressure on the material in future. [ABSTRACT FROM AUTHOR]

The transition energies and formation energies of N, C, F, Cl, and S as substitutional dopants in Ag3PO4 are studied using first-principles calculations based on the hybrid Hartree-Fock density functional, which correctly reproduces the band gap and thus provides the accurate defect states. Our results show that NO and CO act as deep acceptors, FO, ClO, and SP act as shallow donors. NO and CO have high formation energies under O-poor condition therefore they are not suitable for p-type doping Ag3PO4. Though FO, ClO, and SP have shallow transition energies, they have high formation energies, thus FO, ClO, and SP may be compensated by the intrinsic defects (such as Ag vacancy) and they are not possible lead to n-type conductivity in Ag3PO4. [ABSTRACT FROM AUTHOR]

Planar bismuthene grown on SiC substrate provides a promising candidate to engineer van der Waals double-layer (DL) made of two dimensional (2D) topological insulators. We perform systematical calculations in DL hydrogenated bismuthene (H-Bi) that can be used to simulate the experimentally grown planar bismuthene to explore realizable 2D topological insulator van der Waals DL. Two possible geometry configurations of AA- and AB-stacked DL H-Bi are investigated. Due to pseudo Jahn-Teller effect, AB-stacked DL H-Bi has a strong interlayer coupling interaction and shows buckled lattice. Particularly, both AA- and AB-stacked DL H-Bi are topologically trivial rather than topologically nontrivial. The physical origin of the trivial topology is clarified by analyzing orbital composition. We discuss how the electronic properties are modified by interlayer coupling, external strain, and metal atom intercalation. It is also found that, for AB-stacked DL H-Bi, metal atom intercalation gives rise to novel multiple Rashba splitting near the valence band top, which is expected to manipulate the same spin in different planar bismuthene layers. Our results present various and tunable electronic properties of van der Waals DL H-Bi and allow for probing into multiple Rashba effect in 2D inversion-asymmetric topological insulators.

The optical properties, structural properties and electronic properties of a new two-dimensional (2D) monolayer C 3 N under different strains are studied in this paper by using first-principles calculations. The applied strain includes in-layer biaxial strain and uniaxial strain. The monolayer C 3 N is composed of a number of hexagonal C rings with N atoms connecting them. It is a stable indirect band gap 2D semiconductor when the strain is 0%. It could maintain indirect semiconductive character under different biaxial and uniaxial strains from ε = -10% to ε = 10%. As for its optical properties, when the uniaxial strain is applied, the absorption and reflectivity along the armchair and zigzag directions exhibit an anisotropic property. However, an isotropic property is presented when the biaxial strain is applied. Most importantly, both uniaxial tensile strain and biaxial tensile strain could cause the high absorption coefficient of monolayer C 3 N to be in the deep ultraviolet region. This study implies that strain engineering is an effective approach to alter the electronic and optical properties of monolayer C 3 N. We suggest that monolayer C 3 N could be suitable for applications in optoelectronics and nanoelectronics., Competing Interests: The authors declare no competing financial interests., (This journal is © The Royal Society of Chemistry.)

As the isoelectronic counterpart of phosphorene, monolayer group IV-VI binary MX (M = Ge, Sn; X = Se, S) compounds have drawn considerable attention in recent years. In this paper, we construct four high-symmetry stacking models for bilayer MX to tune their electronic properties. We systematically explore the dynamical and thermal stabilities of all bilayer MX. It is found that five of them are possible at room temperature. Then, we perform first-principles calculations to study how the bilayer structure affects their electronic properties. The results demonstrate that the electronic properties of MX materials can be modulated by forming bilayer structures. Their bandgap can be tuned over a wide range from 0.789 to 1.617 eV, and an indirect-to-direct transition occurs in three cases. Considering the flexibility of bilayer MX, we utilize in-plane uniaxial tensile strain to adjust their band structures and achieve much more indirect-to-direct bandgap transitions. The realization of direct bandgaps will be helpful for their application in next-generation high-efficiency modern nano-optoelectronic and photovoltaic devices. We also study the responses of different bilayer MX to an external vertical electric field. It is found that their bandgaps decrease rapidly with the increase of the electric field.

Objective: To develop a composite material containing human hair keratin (HHK), collagen sponge (inner layer) and poly 2-hydroxyethyl methacrylate (PHEMA) film that allows sustained release of polydatin and test its effect as a biological dressing in promoting burn wound healing in SD rats., Methods: Three HHK materials with fast, moderate, and low degradation rates were mixed at the ratio of 4:3:3 to prepare a reticular structure, which was processed into a composite material with bovine tendon-derived collagen sponge, and further complexed with HEMA film containing PD prepared by polymerization. Degree II burn wound was induced in SD rats by scalding and within postburn day 2-5, the wounds were cleansed and covered with the composite material or with glutaraldehyde-treated porcine skin (positive control). At week 1, 2, 4, 6 and 8 following wound dressing, 6 full-thickness skin samples were harvested from the wounds for histological observation and immunohistochemical detection of collagen and elastic fibers, and the wound healing time and healing rate were recorded., Results: The prepared collagen sponge film was transparent and porous (50-300 microm in diameter) and allowed sustained PD release into normal saline within 48 h. Compared with the porcine skin, the composite material reduced exudation and maintained ideal moisture of the wound, and significantly shortened the wound healing time (P=0.000). On day 7, 14, and 21 following dressing, the composite material and porcine skin significantly increased the wound healing rate as compared with the negative control group (P=0.000), and on day 14, the composite achieved significantly greater healing rate than the porcine skin (P<0.05)., Conclusion: HHK-collagen sponge-PHEMA/PD composite as a dressing material promotes burn wound healing in rats by allowing in vivo construction of tissue engineered epidermis. PHEMA is feasible for sustained drug delivery in this composite.

Aim: To design and synthesize a novel vector for colon-site specific drug delivery system and investigate the relationship between the biodegradation properties and composition of materials in the simulated colon fluid., Methods: The azocopolymer P (HEMA-MMA-MAA) was synthesized using 2-hydroxyethylmethacrylate (HEMA), methyl methacrylate (MMA) and methacrylic acid (MAA) as comonmer, azobisisobutyronitrilel (AIBN) as initiator, cross-linked with divinylazobezene (DVAB). The chemical structure of the synthesized series of azocopolymer is examined by UV, FTIR spectroscopy and nuclear magnetic resonance data. Their swelling behavior is evaluated by the swelling equilibrium parameter Q, the biodegradation tests of the materials were carried out at physiologically relevant buffer designed to mimic the colon environment. The biodegradation properties were assessed using the differential scanning calorimeters (DSC) and gel permeation chromatography (GPC) and the morphology on the surface of materials before and after degradation was observed by scanning electron microscopy (SEM)., Results: The swelling equilibrium parameter Q increased with increasing the contents of HEMA and MAA in the materials. The degradation behavior was relevant to the ratio of three components in the copolymers., Conclusion: This materials may become a good carrier for the colon-site specific drug delivery system if the contents of commoners HEMA, MMA and MAA are adjusted reasonably.

Objective: To synthesize p, p'-divinylazobenzene (DVAB)., Method: Wittig reagent was initially synthesized using P-nitrobenzyl bromide and triphenylphosphine, followed by reaction with formaldehyde to produce p-nitro styrene, which was then deoxidized by Zn/NaOH for the final product of DVAB., Results: Fourier transform infrared spectroscopy, nuclear magnetic resonance and element analysis were employed to identify the structure of DVAB, and the lambda(max) as determined by ultraviolet spectroscopy occurred at 357 nm., Conclusions: The synthesis procedure of DVAB was therefore optimized with high yield.