Recent Development of Gas Sensing Platforms Based on 2D Atomic Crystals

Sensors,capable of detecting trace amounts of gas molecules or volatile organic compounds(VOCs),are in great demand for environmental monitoring,food safety,health diagnostics,and national defense.In the era of the Internet of Things(IoT)and big data,the requirements on gas sensors,in addition to sensitivity and selectivity,have been increasingly placed on sensor simplicity,room temperature operation,ease for integration,and flexibility.The key to meet these requirements is the development of high-performance gas sensing materials.Two-dimensional(2D)atomic crystals,emerged after graphene,have demonstrated a number of attractive properties that are beneficial to gas sensing,such as the versatile and tunable electronic/optoelectronic properties of metal chalcogenides(MCs),the rich surface chemistry and good conductivity of MXenes,and the anisotropic structural and electronic properties of black phosphorus(BP).While most gas sensors based on 2D atomic crystals have been incorporated in the setup of a chemiresistor,field-effect transistor(FET),quartz crystal microbalance(QCM),or optical fiber,their working principles that involve gas adsorption,charge transfer,surface reaction,mass loading,and/or change of the refractive index vary from material to material.Understanding the gas-solid interaction and the subsequent signal transduction pathways is essential not only for improving the performance of existing sensing materials but also for searching new and advanced ones.In this review,we aim to provide an overview of the recent development of gas sensors based on various 2D atomic crystals from both the experimental and theoretical investigations.We will particularly focus on the sensing mechanisms and working principles of the related sensors,as well as approaches to enhance their sensing performances.Finally,we summarize the whole article and provide future perspectives for the development of gas sensors with 2D materials.

An Optical Waveguiding Organic Crystal with Phase-Dependent Elasticity and Thermoplasticity over Wide Temperature Ranges

Elastic or plastic bendable organic crystals have attracted increasing attention in the field of crystal engineering.For the application of flexible materials,the applicable temperature range can not be ignored.However,studies on the flexible organic crystals reported so far have not involved the effect of temperature on the mechanical properties of these materials.Here,organic crystals of 9,10-bis(phenylethynyl)anthracene with phase-dependent mechanical properties over wide temperature ranges are reported.