The crystallization problem is an outstanding challenge in the chemistry of porous covalent organic frameworks (COFs). Their structural characterization has been limited to modeling and solutions based on powder x-ray or electron diffraction data. Single crystals of COFs amenable to x-ray diffraction characterization have not been reported. Here, we developed a general procedure to grow large single crystals of three-dimensional imine-based COFs (COF-300, hydrated form of COF-300, COF-303, LZU-79, and LZU-111). The high quality of the crystals allowed collection of single-crystal x-ray diffraction data of up to 0.83-angstrom resolution, leading to unambiguous solution and precise anisotropic refinement. Characteristics such as degree of interpenetration, arrangement of water guests, the reversed imine connectivity, linker disorder, and uncommon topology were deciphered with atomic precision-aspects impossible to determine without single crystals.

Soft pneumatic actuators and motor-based mechanisms being concomitant with the cumbersome appendages have many challenges to making the independent robotic system with compact and lightweight configuration. Meanwhile, shape memory actuators have shown a promising alternative solution in many engineering applications ranging from artificial muscle to aerospace industry. However, one of the main limitations of such systems is their inherent softness resulting in a small actuation force, which prevents them from more effective applications. This issue can be solved by combining shape memory actuators and the mechanism of stiffness modulation. As a first, this study describes a shape memory alloy-based soft gripper composed of three identical fingers with variable stiffness for adaptive grasping in low stiffness state and effective holding in high stiffness state. Each finger with two hinges is fabricated through integrating soft composite actuator with stiffness changeable material where each hinge can approximately achieve a 55-fold changeable stiffness independently. Besides, each finger with two hinges can actively achieve multiple postures by both selectively changing the stiffness of hinges and actuating the relevant SMA wire. Based on these principles, the gripper is applicable for grasping objects with deformable shapes and varying shapes with a large range of weight where its maximum grasping force is increased to ∼10 times through integrating with the stiffness changeable mechanism. The final demonstration shows that the finger with desired shape-retained configurations enables the gripper to successfully pick up a frustum-shaped object.

A soft-bodied robot made of smart soft composite with inchworm-inspired locomotion capable of both two-way linear and turning movement has been proposed, developed, and tested. The robot was divided into three functional parts based on the different functions of the inchworm: the body, the back foot, and the front foot. Shape memory alloy wires were embedded longitudinally in a soft polymer to imitate the longitudinal muscle fibers that control the abdominal contractions of the inchworm during locomotion. Each foot of the robot has three segments with different friction coefficients to implement the anchor and sliding movement. Then, utilizing actuation patterns between the body and feet based on the looping gait, the robot achieves a biomimetic inchworm gait. Experiments were conducted to evaluate the robot's locomotive performance for both linear locomotion and turning movement. Results show that the proposed robot's stride length was nearly one third of its body length, with a maximum linear speed of 3.6 mm s(-1), a linear locomotion efficiency of 96.4%, a maximum turning capability of 4.3 degrees per stride, and a turning locomotion efficiency of 39.7%.

No abstract

Methane and carbon dioxide are known greenhouse gases, and the conversion of these two C1-building blocks into useful fuels and chemicals is a subject of great importance. By solid-state NMR spectroscopy, we found that methane and carbon dioxide can be co-converted on a zinc-modified H-ZSM-5 zeolite (denoted as Zn/H-ZSM-5) to form acetic acid at a low temperature range of 523-773 K. Solid-state (13)C and (1)H MAS NMR investigation indicates that the unique nature of the bifunctional Zn/H-ZSM-5 catalyst is responsible for this highly selective transformation. The zinc sites efficiently activate CH4 to form zinc methyl species (-Zn-CH3), the Zn-C bond of which is further subject to the CO2 insertion to produce surface acetate species (-Zn-OOCCH3). Moreover, the Brønsted acid sites play an important role for the final formation of acetic acid by the proton transfer to the surface acetate species. The results disclosed herein may offer the new possibility for the efficient activation and selective transformation of methane at low temperatures through the co-conversion strategy. Also, the mechanistic understanding of this process will help to the rational design of robust catalytic systems for the practical conversion of greenhouse gases into useful chemicals.