Deep eutectic solvents (DESs) enable many processes to be environmentally friendly. This Tutorial Review aims to showcase the roles of DESs in the synthesis of functional materials from a green chemistry perspective.

The development of high-performance, portable and miniaturized gas sensors has aroused increasing interest in the fields of environmental monitoring, security, medical diagnosis, and agriculture. Among different detection tools, metal oxide semiconductor (MOS)-based chemiresistive gas sensors are the most popular choice in commercial applications and have the advantages of high stability, low cost, and high sensitivity. One of the most important ways to further enhance the sensor performance is to construct MOS-based nanoscale heterojunctions (heteronanostructural MOSs) from MOS nanomaterials. However, the sensing mechanism of heteronanostructural MOS-based sensors is different from that of single MOS-based gas sensors in that it is fairly complex. The performance of the sensors is influenced by various parameters, including the physical and chemical properties of the sensing materials (e.g., grain size, density of defects, and oxygen vacancies of materials), working temperatures, and device structures. This review introduces several concepts in the design of high-performance gas sensors by analyzing the sensing mechanism of heteronanostructural MOS-based sensors. In addition, the influence of the geometric device structure determined by the interconnection between the sensing materials and the working electrodes is discussed. To systematically investigate the sensing behavior of the sensor, the general sensing mechanism of three typical types of geometric device structures based on different heteronanostructural materials are introduced and discussed in this review. This review will provide guidelines for readers studying the sensing mechanism of gas sensors and designing high-performance gas sensors in the future.

A tactile sensor system enables natural interaction between humans and machines; this interaction is crucial for dexterous robotic hands, interactive entertainment, and other smart scenarios. However, the lack of sliding friction detection significantly limits the accuracy and scope of interactions due to the absence of sophisticated information, such as slippage, material and roughness of held objects. Here, inspired by the stick-slip phenomena in the sliding process, we have developed a multifunctional biomimetic tactile system based on the stick-slip sensing strategy, which is a universal method to detect slippage and estimate the surface properties of objects by sliding. This system consists of a flexible fingertip-inspired tactile sensor, a read-out circuit and a machine-learning module. Based on the stick-slip sensing strategy, our system was endowed with high recognition rates for slippage detection (100.0%), material classification (93.3%) and roughness discrimination (92.8%). Moreover, robotic hand manipulation, interactive games and object classification are demonstrated with this multifunctional system for comprehensive and promising human–machine interactions.

Nowadays, there are challenges facing high-performance electrode materials that are still obstructing their practical application in a new class of all-solid-state asymmetric supercapacitors (AASs) for the development of future portable energy-storage devices. Among various methods, the development of an effective synthesis methodology that could give a high-quality outcome using special synergetic construction and enhancement of adhesion between the collector substrate and active material is a feasible strategy to solving the above bottleneck problem. Hence, in this paper we reported a universal, facile and low cost self-assembly strategy to fabricate binder-free Ni/Co-LDH array materials in situ on different substrates (typically: Ni foam, Cu foil, fabric, and CNT/rGO film) using a hypothermal chemical coprecipitation strategy under low temperature (55 °C) and normal pressure reaction conditions. The resulting Ni/Co-LDH array materials’ growth on each substrate displayed a special three-dimensional hierarchical structure with a well-defined nanosheet interconnected network configuration, which provides a generality and versatility to this synthetic method that is applicable to large-scale production. Significantly, electrochemical characterization reveals that the binder-free Ni/Co-LDH array electrode materials all exhibit a high specific capacitance over 2380 F g⁻¹ (1 A g⁻¹) regardless of the in situ substrate material, and excellent cycling stability (105.7% remained after 2700 cycles). The design and fabrication of AASs are also demonstrated by exploiting this binder-free LDH array as the positive electrode material, which has a high energy density (141.03 W h kg⁻¹) and power density (1.17 kW kg⁻¹). These results have greatly exceeded that of previously reported nickel or cobalt oxide/hydroxide based AASs and other typical AASs, such as those based on NiCo₂O₄, Mn₃O₄, and CoMoO₄. Remarkably, with cycling up to 1000 times under a high scan rate of 100 mV s⁻¹, the AASs still retain over 89.6% of their initial capacitance values.