Graphene-Based Standalone Solar Energy Converter for Water Desalination and Purification

Harvesting solar energy for desalination and sewage treatment has been considered as a promising solution to produce clean water. However, state-of-the-art technologies often require optical concentrators and complicated systems with multiple components, leading to poor efficiency and high cost. Here, we demonstrate an extremely simple and standalone solar energy converter consisting of only an as-prepared 3D cross-linked honeycomb graphene foam material without any other supporting components. This simple all-in-one material can act as an ideal solar thermal converter capable of capturing and converting sunlight into heat, which in turn can distill water from various water sources into steam and produce purified water under ambient conditions and low solar flux with very high efficiency. High specific water production rate of 2.6 kg h^–1 m^–2 g^–1 was achieved with near ∼87% under 1 sun intensity and >80% efficiency even under ambient sunlight (<1 sun). This scalable sheet-like material was used to obtain pure drinkable water from both seawater and sewage water under ambient conditions. Our results demonstrate a competent monolithic material platform providing a paradigm change in water purification by using a simple, point of use, reusable, and low-cost solar thermal water purification system for a variety of environmental conditions

Photoprompted Hot Electrons from Bulk Cross-Linked Graphene Materials and Their Efficient Catalysis for Atmospheric Ammonia Synthesis

Ammonia synthesis is the single most important chemical process in industry and has used the successful heterogeneous Haber–Bosch catalyst for over 100 years and requires processing under both high temperature (300–500 °C) and pressure (200–300 atm); thus, it has huge energy costs accounting for about 1–3% of human’s energy consumption. Therefore, there has been a long and vigorous exploration to find a milder alternative process. Here, we demonstrate that by using an iron- and graphene-based catalyst, Fe@3DGraphene, hot (ejected) electrons from this composite catalyst induced by visible light in a wide range of wavelength up to red could efficiently facilitate the activation of N₂ and generate ammonia with H₂ directly at ambient pressure using light (including simulated sun light) illumination directly. No external voltage or electrochemical or any other agent is needed. The production rate increases with increasing light frequency under the same power and with increasing power under the same frequency. The mechanism is confirmed by the detection of the intermediate N₂H₄ and also with a measured apparent activation energy only ∼1/4 of the iron based Haber–Bosch catalyst. Combined with the morphology control using alumina as the structural promoter, the catalyst retains its activity in a 50 h test