Rational design of solar absorption, heat conversion and water supply for efficient solar steam generation.

Using abundant solar energy to generate steam offers unique solution overcoming the lack of freshwater resources. Despite extensive explorations, low-cost devices with high efficiency are still critically wanting. In this work, the extremely cheap carbonized kelp with good stability, high solar absorption (∼93%), porous microstructure, and hydrophilic surface is found to be efficient for solar steam generation (SSG) and seawater desalination for the first time. A SSG device meeting the requirements of the “most stable triangle” is thus designed. The carbonized kelp is utilized as the solar absorber, with thermal insulation by an expanded polystyrene foam and water supply by a fiber cotton wick via the capillary force. A high solar to steam conversion efficiency of 84.8% and evaporation rate of 1.351 kg·m^-2·h^-1 are attained under 1 sun irradiation. This work develops a promising and bioinspired device with long-term stability for SSG that can be produced economically (∼3.8 $/m²).

Photonic synapses combining photosensitivity and synaptic function can efficiently perceive and memorize visual information, making them crucial for the development of artificial vision systems. However, the development of high-performance photonic synapses with low power consumption and rapid optical erasing ability remains challenging. Here, we propose a photon-modulated charging/discharging mechanism for self-powered photonic synapses. The current hysteresis enables the devices based on CsPbBr ₃ /solvent/carbon nitride multilayer architecture to emulate synaptic behaviors, such as excitatory postsynaptic currents, paired-pulse facilitation, and long/short-term memory. Intriguingly, the unique radiation direction-dependent photocurrent endows the photonic synapses with the capability of optical writing and rapid optical erasing. Moreover, the photonic synapses exhibit exceptional performance in contrast enhancement and noise reduction owing to the notable synaptic plasticity. In simulations based on artificial neural network (ANN) algorithms, the pre-processing by our photonic synapses improves the recognition rate of handwritten digit from 11.4% (200 training epochs) to 85% (~60 training epochs). Furthermore, due to the excellent feature extraction and memory capability, an array based on the photonic synapses can imitate facial recognition of human retina without the assistance of ANN.

To develop solar steam generation (SGG) for water treatment, light absorbers have been widely synthesized by carbonization of plants at high temperature. However, the thermal treatment has high energy‐consumption and is environmentally unfriendly. Thus, it is urgent to explore new green approaches to convert biomasses to carbon materials for SSG. Herein, a concentrated acid‐induced dehydration method is developed to convert fallen leaves to carbon powders, fallen‐leaf photothermal film prepared by dehydration (FLPD). The resultant FLPD exhibits a strong absorption covering a wide spectrum. It also contains sufficient oxygen‐containing groups on the surface, leading to low water evaporation enthalpy. To meet the demands of practical applications, the FLPD membrane is modified with polyvinyl alcohol (PVA) to improve the mechanical stabilities and the surface wettability is further enhanced by an oxygen plasma treatment. An SSG device based on the modified membrane attains a competitive evaporation rate of 1.355 kg m⁻² h⁻¹ under 1 sun irradiation. The evaporation rate remains approximately constant when evaporating the seawater. Moreover, the salt deposited on the surface could be self‐cleaned due to the high wettability. Therefore, herein, it is demonstrated that concentrated acid‐induced dehydration is an effective and green approach to convert cheap biomasses to carbon materials for SSG applications.