Graphitic carbon nitride (g-C₃N₄) was produced on a large scale by the pyrolysis of urea under ambient pressure without additive assistance. The retainable pyrolysis-generated self-supporting atmosphere and the reaction temperature are two necessary conditions. This g-C₃N₄ as photocatalyst shows recyclable adsorption and photocatalytic activity under visible light.

Energy captured directly from sunlight provides an attractive approach towards fulfilling the need for green energy resources on the terawatt scale with minimal environmental impact. Collecting and storing solar energy into fuel through photocatalyzed water splitting to generate hydrogen in a cost-effective way is desirable. To achieve this goal, low cost and environmentally benign urea was used to synthesize the metal-free photocatalyst graphitic carbon nitride (g-C₃N₄). A porous structure is achieved via one-step polymerization of the single precursor. The porous structure with increased BET surface area and pore volume shows a much higher hydrogen production rate under simulated sunlight irradiation than thiourea-derived and dicyanamide-derived g-C₃N₄. The presence of an oxygen atom is presumed to play a key role in adjusting the textural properties. Further improvement of the photocatalytic function can be expected with after-treatment due to its rich chemistry in functionalization.

Highly ordered ${\mathrm{TiO}}_{\mathrm{2}}$ nanowire (TN) arrays were prepared in anodic alumina membranes (AAMs) by a sol-gel method. The TNs are single crystalline anatase phase with uniform diameters around 60 nm. At room temperature, photoluminescence (PL) measurements of the TN arrays show a visible broadband with three peaks, which are located at about 425, 465, and 525 nm that are attributed to self-trapped excitons, F, and $F^{+}$ centers, respectively. A model is also presented to explain the PL intensity drop-down of the TN arrays embedded in AAMs: the blue PL band of AAMs arises from the $F^{+}$ centers on the pore walls, and the TNs first form in the center area of the pores and then extend to the pore walls.

Capable of converting stimuli into electrical signals, hydrogel-based ionic devices are of great significance in soft robots, wearable devices, and artificial sensors. However, profound challenges remain in developing ionic devices that retain their properties in extreme environmental conditions, such as subzero temperatures. Based on a zwitterionic poly(ionic liquid) (PIL), an anti-freezing hydrogel was designed and synthesized for use in a multimodal artificial skin. This zwitterionic PIL hydrogel exhibited super-stretchability (approximately 900%), self-healing ability, and high conductivity (−1.1 S m⁻¹), even at low temperature (−20 °C). Based on this zwitterionic PIL hydrogel, three sensing modes, capacitive, resistive, and triboelectric modes, can be achieved in one device, which is stable under a wide temperature range (−20 °C to 60 °C). Further applications of these multimodal sensors with a soft robotic gripper suggested a new approach for developing sophisticated stimuli-responsive skin with multifunctionality and adaptability to varied environmental conditions.