Thermo- and Photoresponsive Actuators with Freestanding Carbon Nitride Films

Enable Multi-Stimuli-Responsive Biomimetic Actuation with Asymmetric Design of Graphene-Conjugated Conductive Polymer Gradient Film

In this paper, multiresponsive actuators based on asymmetric design of graphene-conjugated poly(3,4-ethylene dioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) gradient films have been developed by a simple drop casting method. The biomimetic actuation is attributed to the hygroscopic expansion property of PEDOT:PSS and the gradient distribution of graphene sheets within the film, which resembles the hierarchical swelling tissues of some plants in nature. Graphene-conjugated PEDOT:PSS (GCP) actuators exhibit reversible bending behavior under multistimuli such as moisture, organic vapor, electrothermal, and photothermal heating. Noticeably, the bending curvature reaches 2.15 cm-1 under applied voltage as low as 1.5 V owing to the high electrical conductivity of GCP actuator. To mimic the motions of nyctinastic plants, a GCP artificial flower that spreads its petals under sunlight illumination has been fabricated. GCP actuators have been also demonstrated as intelligent light-controlled switches for light-emitting diodes and smart curtains for thermal management. Not only do the GCP gradient films exhibit potential applications in flexible electronics and energy harvesting/storage devices but also the facile fabrication of multiresponsive GCP actuators may shed light on the development of soft robotics, artificial muscles, wearable electronics, and smart sensors.

Recent advances and perspectives of g-C3N4-based materials for photocatalytic dyes degradation

Photocatalytic degradation technology is regarded as a promising technology for dye-contained wastewater treatment due to its superior efficiency and recycling. The key to the implementation of photocatalytic degradation technology is the selection of sunlight-active photocatalyst. Graphitic carbon nitride (g-C₃N₄) photocatalyst has been put into a lot of research in the field of organic pollutant degradation because of its low cost, suitable electronic structure and high chemical stability. In this perspective review, we comprehensively discuss the recent advance of photocatalytic dyes degradation over g-C₃N₄-based materials. The properties, structure and preparation methods of g-C₃N₄ are briefly introduced. Furthermore, the progress in improving the degradation efficiency of g-C₃N₄-based photocatalyst is highlighted in the article. The possible pathways and different active species for dyes decomposition are also summarized. We expect this review can provide instructive application of g-C₃N₄-based catalysts for environmental remediation.

3D Printing Ultraflexible Magnetic Actuators via Screw Extrusion Method

Soft magnetic actuators with programmable structure design and controllable deformation ability based on 3D printing technology have attracted extensive attention. In this paper, a novel 3D printing strategy is developed to manufacture the ultraflexible magnetic actuator, in which the printed material is composed of magnetic particles and thermoplastic rubber materials. Different from the traditional fused deposition printing, this printing strategy introduces screw extrusion technology to the heating components of the printer to overcome the problem of filament buckling in the flexible material. Thus, the tensile modulus of the printed products can be reduced to as low as ≈2 MPa. Based on the above method, biomimetic magnetic actuators of the sucker and the pump are constructed for adhering and releasing object and pumping liquid. The contraction performance of the magnetic actuator is studied via a series of experiments and the magnetic field-induced deformation is analyzed by the multiphysics-based finite element model. This work proves that ultraflexible magnetic actuators fabricated by this 3D printing strategy show broad prospects in the fields of soft robotics and bionics.

Light-Responsive Soft Actuators: Mechanism, Materials, Fabrication, and Applications

Soft robots are those that can move like living organisms and adapt to the surrounding environment. Compared with traditional rigid robots, the advantages of soft robots, in terms of material flexibility, human–computer interaction, and biological adaptability, have received extensive attention. Flexible actuators based on light response are one of the most promising ways to promote the field of cordless soft robots, and they have attracted the attention of scientists in bionic design, actuation implementation, and application. First, the three working principles and the commonly used light-responsive materials for light-responsive actuators are introduced. Then, the characteristics of light-responsive soft actuators are sequentially presented, emphasizing the structure strategy, actuation performance, and emerging applications. Finally, this review is concluded with a perspective on the existing challenges and future opportunities in this nascent research frontier.

Facile synthesis of nitrogen-defective g-C3N4 for superior photocatalytic degradation of rhodamine B

Developing a new photocatalyst for fast and highly efficient organic dye degradation plays an essential role in wastewater treatment. In this study, a photocatalyst graphite phase carbon nitride (g-C₃N₄) containing nitrogen defects (CN) is reported for the degradation of rhodamine B (RhB). The porous g-C₃N₄ photocatalyst is facilely synthesized through a polycondensation method and then characterized by X-ray diffraction (XRD), infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), N₂ isotherm adsorption line, and X-ray photoelectron spectroscopy (XPS). The photocatalytic activity of the g-C₃N₄ is evaluated through the degradation of RhB under visible light irradiation. The results show that photocatalytic activity of the nitrogen-defective g-C₃N₄ can be improved by optimizating washing conditions, including washing temperature, washing dosage, drying time, and drying temperature. With the prepared nitrogen-defective g-C₃N₄, decolourization of RhB is able to be completed within 20 minutes, in which the degradation rate is 1.7 times higher than that of bulk g-C₃N₄. Moreover, the nitrogen-defective g-C₃N₄ has high stability and reusability in the degradation of RhB. Photocatalytic degradation mechanism investigations by ultraviolet-visible absorption spectroscopy, radical trapping experiments and high-performance liquid chromatography (HPLC) reveal that RhB achieved complete mineralization through the photocatalytic degradation reaction mediated by superoxide radicals (˙O₂⁻). This work thus provides a new approach for the preparation of photocatalysts for organic pollutants treatment in wastewater samples.

Nitrogen-defective g-C₃N₄ is synthesized and characterized as the photocatalyst for degradation of organic dyes, such as rhodamine B, in wastewater.

Highly fluorescent g-C3N4 nanobelts derived from bulk g-C3N4 for NO2 gas sensing

The fluorescent emission wavelengths of nanostructures derived from bulk graphitic carbon nitride were commonly lower than those of their bulk due to the quantum confinement effect, which are disadvantageous for bioimaging and sensing applications. Herein, a new strategy to engineer graphitic carbon nitride nanomaterials with tunable fluorescent wavelength and intensity was proposed via thermal treatment of bulk graphitic carbon nitride at high temperature and then hydrolysis in alkali solution. Highly fluorescent g-C₃N₄ nanobelts with emission peak at 494 nm, 19 nm higher than that of bulk graphitic carbon nitride and 23.6% quantum yield were successfully obtained by controlling the heating temperature at 750 °C for 2 h and the hydrolysis in 4 mol L^-1 NaOH solution for 8 h. Finally, a home-made portable gas sensor for reversibly sensing of toxic NO₂ gas at room temperature was designed by utilizing graphitic carbon nitride nanobelts as the fluorescent nanoprobe, which can overcome the disadvantages of high operation temperature or the interference of humidity resulting from the common chemiresistive sensors.

3D Printing Magnetic Actuators for Biomimetic Applications

Biomimetic actuators with stimuli-responsiveness, adaptivity, and designability have attracted extensive attention. Recently, soft intelligent actuators based on stimuli-responsive materials have been gradually developed, but it is still challenging to achieve various shape manipulations of actuators through a simple 3D printing technology. In this paper, a 3D printing strategy based on magneto-active materials is developed to manufacture various biomimetic magnetic actuators, in which the new printable magnetic filament is composed of a thermoplastic rubber material and magnetic particles. The continuous shape transformation of magnetic actuators is further demonstrated to imitate the motion characteristic of creatures, including the predation behavior of octopus tentacles, the flying behavior of the butterfly, and the flower blooming behavior of the plant. Furthermore, the magnetic field-induced deformation of the biomimetic structure can be simulated by the finite element method, which can further guide the structural design of the actuators. This work proves that the biomimetic actuator based on soft magneto-active materials has the advantages of programmable integrated structure, rapid prototyping, remote noncontact actuation, and rapid magnetic response. As a result, this 3D printing method possesses broad application prospects in soft robotics and other fields.

Graphitic Carbon Nitride Films: Emerging Paradigm for Versatile Applications

Graphitic carbon nitride (g-C₃N₄) is a well-known two-dimensional conjugated polymer semiconductor that has been broadly applied in photocatalysis-related fields. However, further developments of g-C₃N₄, especially in device applications, have been constrained by the inherent limitations of its insoluble nature and particulate properties. Recent breakthroughs in fabrication methods of g-C₃N₄ films have led to innovative and inspiring applications in many fields. In this review, we first summarize the fabrication of continuous and thin films, either supported on substrates or as free-standing membranes. Then, the novel properties and application of g-C₃N₄ films are the focus of the current review. Finally, some underlying challenges and the future developments of g-C₃N₄ films are tentatively discussed. This review is expected to provide a comprehensive and timely summary of g-C₃N₄ film research to the wide audience in the field of conjugated polymer semiconductor-based materials.

Deterministic Role of Carbon Nanotube-Substrate Coupling for Ultrahigh Actuation in Bilayer Electrothermal Actuators

Here, the actuation response of an architectured electrothermal actuator comprising a single layer of carbon nanotube (CNT) film and a relatively thicker film of silk, cellulose, or polydimethylsiloxane is studied. An electric current is passed through the CNT film, which generates heat responsible for electrothermal actuation, in all samples, affixed as per doubly clamped beam configuration. All samples, including pure CNT film, show remarkable actuation such that actuation monotonically increases with the applied voltage. Cyclic pulsed electrical loading shows a lag in the electric current stimulus and the actuation. Remarkably, an ultrahigh actuation of ∼2.8%, which was 72 times more than that shown by pure CNT film, is measured in the CNT-cellulose film, that is, the architectured actuator with the natural polymer having the functional property of hygroexpansion and the structural hierarchy of the CNT film, however, at a significantly larger length scale. Overall, the synergetic contribution of the individual layers in these bilayered actuators enabled achieving ultrahigh electrothermal actuation compared to the homogeneous, synthetic polymer-based devices. A detailed discussion, which also includes examination of the role of the hierarchical substructure and the functional properties of the substrate and numerical analysis using the finite element method, is presented to highlight the actuation mechanism in the fabricated actuators.

Polymer actuators based on covalent adaptable networks

Advances in polymer actuators containing covalent adaptable networks (CANs) are summarized and discussed in this review.

A Focus on Soft Actuation

The present editorial paper analyzes the hundred recent research works on soft actuation to understand the current main research focus in the light of the grand challenges in the field. Two characteristic paper types were obtained: one focuses on soft actuator design, manufacturing and demonstration, while another includes in addition the development of functional materials. Although vast majority of the works showcased soft actuation, evaluation of its robustness by multi-cyclic actuation was reported in less than 50% of the works, while only 10% described successful actuation for more than 1000 cycles. It is suggested that broadening the research focus to include investigation of mechanisms underlying the degradation of soft functional material performance in real cyclic actuation conditions, along with application of artificial intelligence methods for prediction of muscle behavior, may allow overcoming the reliability issues and developing robust soft-material actuators. The outcomes of the present work might be applicable to the entire soft robotics domain.