Wood as a renewable naturally occurring resource has been the focus of much research and commercial interests in applications ranging from building construction to chemicals production. Here, a ...facile approach is reported to transform wood into hierarchical porous graphene using CO2 laser scribing. Studies reveal that the crosslinked lignocellulose structure inherent in wood with higher lignin content is more favorable for the generation of high‐quality graphene than wood with lower lignin content. Because of its high electrical conductivity (≈10 Ω per square), graphene patterned on wood surfaces can be readily fabricated into various high‐performance devices, such as hydrogen evolution and oxygen evolution electrodes for overall water splitting with high reaction rates at low overpotentials, and supercapacitors for energy storage with high capacitance. The versatility of this technique in formation of multifunctional wood hybrids can inspire both research and industrial interest in the development of wood‐derived graphene materials and their nanodevices.
Laser‐induced porous graphene (LIG) is formed on wood by laser irradiation. This LIG is engineered into energy‐storage devices and electrocatalysis electrodes. The LIG from pine (P‐LIG) is coated with polyaniline to form supercapacitors and with metals Co, Ni, and Fe to form electrocatalysts. The electrocatalysis of water using metal‐coated P‐LIG produces H2 and O2.
The molecular crystals of acridonyl‐tetraphenylethene (AD‐TPE) exhibit an intriguing turn‐on and color‐tuned luminescence in response to mechanical grinding and hydrostatic compression. On the basis ...of in‐depth experimental and computational studies, it is hypothesized that the origin of the piezochromic behavior from the D‐phase to the B‐phase is the change of the intramolecular geometrical conformation, especially for the torsion angle between the TPE and AD moiety. The different molecular conformation in the two distinctive solid phases causes the substantial switching of the intramolecular charge transfer (ICT) process, which can be directly correlated with the subsequent fluorescence from locally excited (LE) state and ICT state in both phases. The AD‐TPE molecular system presents a very rare example of high‐contrast reversible fluorescence tuning driven by a switching of the excited state in the solid state under the mechanical stimuli, and thus provides a novel mechanism of the piezochromic behavior.
Tuning the solid state luminescence of organic materials under mechanical stimuli is an attractive subject for both the fundamental research and practical application in the optical recording and sensing. Herein, a structurally well‐defined molecule, acridonyl‐tetraphenylethene is reported, whose molecular crystals exhibit an intriguing turn‐on and color‐tuned luminescence with high contrast in response to the mechanical stimuli such as grinding and hydrostatic pressure.
The cathodic oxygen reduction reaction (ORR) is essential in the electrochemical energy conversion of fuel cells. Here, through the NH3 atmosphere annealing of a graphene oxide (GO) precursor ...containing trace amounts of Ru, we have synthesized atomically dispersed Ru on nitrogen-doped graphene that performs as an electrocatalyst for the ORR in acidic medium. The Ru/nitrogen-doped GO catalyst exhibits excellent four-electron ORR activity, offering onset and half-wave potentials of 0.89 and 0.75 V, respectively, vs a reversible hydrogen electrode (RHE) in 0.1 M HClO4, together with better durability and tolerance toward methanol and carbon monoxide poisoning than seen in commercial Pt/C catalysts. X-ray adsorption fine structure analysis and aberration-corrected high-angle annular dark-field scanning transmission electron microscopy are performed and indicate that the chemical structure of Ru is predominantly composed of isolated Ru atoms coordinated with nitrogen atoms on the graphene substrate. Furthermore, a density function theory study of the ORR mechanism suggests that a Ru-oxo-N4 structure appears to be responsible for the ORR catalytic activity in the acidic medium. These findings provide a route for the design of efficient ORR single-atom catalysts.
All‐solid‐state, flexible, symmetric, and asymmetric microsupercapacitors are fabricated by a simple method in a scalable fashion from laser‐induced graphene on commercial polyimide films, followed ...by electrodeposition of pseudocapacitive materials on the interdigitated in‐plane architectures. These microsupercapacitors demonstrate comparable energy density to commercial lithium thin‐film batteries, yet exhibit more than two orders of magnitude higher power density with good mechanical flexibility.
The photoluminescence properties of organic fluorescent materials in the solid state are closely related to their aggregation structures. Herein, we present an organic fluorescent molecule ...9,10-bis(2,2-di(4-fluorophenyl)vinyl)anthracene (BDFVA) with two crystal polymorphisms to provide an ideal molecular model for understanding the nature of luminescence from the J- and X-aggregates. Detailed structural and photophysical studies reveal that both J- and X-aggregate crystals exhibit enhanced emission in comparison with the corresponding dilute solution because of crystallization-induced emission enhancement (CIEE). Additionally, the X-aggregate (B-phase) crystal with crossed molecular packing exhibits a higher fluorescence efficiency (ΦF = 0.60), giving a 1.4-fold promotion of ΦF compared to the J-aggregate crystal (G-phase) with staggered molecular packing because the split excited states are all optically allowed in the X-aggregate. Optical waveguide experiments show that the two crystals exhibit excellent amplified spontaneous emission (ASE), demonstrating a promising potential application in organic solid-state lasers.
The modification of graphene‐based materials is an important topic in the field of materials research. This study aims to expand the range of properties for laser‐induced graphene (LIG), specifically ...to tune the hydrophobicity and hydrophilicity of the LIG surfaces. While LIG is normally prepared in the air, here, using selected gas atmospheres, a large change in the water contact angle on the as‐prepared LIG surfaces has been observed, from 0° (superhydrophilic) when using O2 or air, to >150° (superhydrophobic) when using Ar or H2. Characterization of the newly derived surfaces shows that the different wetting properties are due to the surface morphology and chemical composition of the LIG. Applications of the superhydrophobic LIG are shown in oil/water separation as well as anti‐icing surfaces, while the versatility of the controlled atmosphere chamber fabrication method is demonstrated through the improved microsupercapacitor performance generated from LIG films prepared in an O2 atmosphere.
The modification of graphene‐based materials has been an important topic, and this study aims to expand the properties of laser‐induced graphene (LIG). With a controlled atmosphere chamber, both superhydrophobic and superhydrophilic LIG surfaces can be obtained. Characterizations show that the different wetting properties result from surface morphology and chemical composition. Applications are demonstrated in oil/water separation, anti‐icing, as well as micro‐supercapacitors.
An efficient metal‐free catalyst is presented for oxygen evolution and reduction based on oxidized laser‐induced graphene (LIG‐O). The oxidation of LIG by O2 plasma to form LIG‐O boosts its ...performance in the oxygen evolution reaction (OER), exhibiting a low onset potential of 260 mV with a low Tafel slope of 49 mV dec−1, as well as an increased activity for the oxygen reduction reaction. Additionally, LIG‐O shows unexpectedly high activity in catalyzing Li2O2 decomposition in Li‐O2 batteries. The overpotential upon charging is decreased from 1.01 V in LIG to 0.63 V in LIG‐O. The oxygen‐containing groups make essential contributions, not only by providing the active sites, but also by facilitating the adsorption of OER intermediates and lowering the activation energy.
The oxidation of laser‐induced graphene (LIG) by O2 plasma to form oxidized LIG boosts its performance in both the oxygen evolution reaction (OER) and the oxygen reduction reaction. The oxygen‐containing groups make essential contributions, not only by providing the active sites, but also by facilitating the adsorption of oxygen evolution reaction (OER) intermediates and lowering the activation energy.
A chameleon under pressure: The observed piezochromic behavior of the title compound (BP2VA) was found to depend on its molecular aggregation state and specifically on the strength of the π–π ...interaction between the anthracene rings of adjacent molecules. When BP2VA is ground or placed under pressure, its molecular aggregation state changes, and a red shift in the fluorescence emission from green via orange to red occurs (see picture).
Nowadays, the evaluation of students’ learning effect in colleges and universities mainly rely on manual management and supervision, which is inefficient and inaccurate. What’s worse, it completely ...depends on the subjective judgment of the supervisors, many potential teaching quality data could be ignored. Using an unsupervised classroom monitoring system based on deep learning can master the learner’s learning result. This paper mainly researched a learner’s behavior evaluation method based on deep learning. Firstly, MTCNN is being used to detected learner’s facial feature in order to confirm their identification. Then, collected the data set in learning environment and a Mosaic data enhancement had been done. Later, an improved method, is proposed. Identifying the students’ actions of playing the mobile phone, moving to classroom, eating, reading, writing, this method has more advantages on classroom behavior detecting. In addition, by building a quantitative evaluation method–CFIndex (class focus index), the time of students' behaviors in classroom has been calculated. Therefore, CFIndex evaluation method can well reflect the real performance of students in the classroom. In this paper, compared with Fast R-CNN and classical algorithm on the same data set, the proposed method has better performance in classroom behavior detection, and it can better reflect the students’ real actions in the classroom, it has certain meaning of theoretical guidance.
The mechanochromic property of tetrakis(4-(dimethylamino)phenyl)ethylene (TDMAPE) with natural propeller shape and nearly centrosymmetric structure was investigated. The destruction of the ...crystalline structure leads to the planarization of molecular conformation, which is considered as a possible reason for the red-shift of absorption and fluorescence spectra after grinding. And the polymorphism-dependent emissions of the two polymorphs of TDMAPE are mainly determined by the intramolecular conformation, which show the increased coplanarity or conjugation degree, ultimately leading to the bathochromic shift of the emissions.
PDF
