Discarded-leaves derived biochar for highly efficient solar water evaporation and clean water production: The crucial roles of graphitized carbon

Abstract

Solar-driven interfacial evaporation is an effective technique to alleviate the current freshwater crisis. Carbon-based materials as one of the photothermal materials have attracted attention due to their excellent light absorption in a broad spectrum, height-adjustable structure, low cost, and abundant resources. Herein, this article uses discarded leaves as a precursor to prepare leaf biochar (BC). The relative content of sp2 hybridization in the leaf biochar is adjusted by controlling different pyrolysis temperatures so that electrons can more easily undergo transitions and inhibit electron recombination to enhance the photothermal conversion performance of BC. BC with high graphitized carbon content can inhibit electronic recombination and has better optical properties in the near-infrared spectrum. Leaf biochar with a calcination temperature of 800 ℃ (BC-800) achieves solar evaporation efficiency up to 65.64% under 1.37 sun illumination, and it has an evaporation rate of 1.32 kg·m−2·h−1. Furthermore, BC-800 shows a removal rate of about 99.00% in the purification of metal ions, which can effectively reduce the ion concentration in seawater for desalination. Simultaneously, using BC-800 to produce clean water from wastewater, it was discovered that the content of Chemical Oxygen Demand (COD), Ammonia Nitrogen (NH3-N), and Total Nitrogen (TN) in the distilled water dropped considerably.