Self-cleaning solar steam generator based on engineered carbonized waste tea photothermal layer

Abstract

In this work, an efficient, eco-friendly, self-cleaning, and low-cost solar steam generator with a reverse conical-shape is fabricated using carbonized waste tea as a photothermal layer. Waste tea is carbonized through three different methods comprising heating in the furnace at high temperature, pyrolysis process, and mild carbonization utilizing aluminophosphate solution. Among the three processes used, thermal treatment in the furnace (CWTF-400) results in the highest performance due to its superior characteristics, which are applicable in this field. Using a conical configuration for the photothermal layer, making device independent of light orientation and self-cleaning. Taking the advantages of the conical configuration, not only the incident photons are absorbed more efficiently, but also salt deposition is localized at the edge. Remarkably, because of the provided self-cleaning property, salt crystals dissolve back into the bulk water in 11 h. Treating CWTF-400 device with sodium alginate, the water supply is improved, leading to roughly no salt crystal formation in artificial seawater experiment and the reduction of time duration of salt crystals dissolving to 5.5 h at 20 wt% saline solution. Additionally, it could considerably improve the overall performance of device in potable water experiments. A remarkable evaporation rate of 2.93 kg.m⁻².h⁻¹ and an efficiency of 97.51 % are achieved for CWTF-400 + SA device. Under real conditions, after 7 h of desalination in 3.5 wt% NaCl solution, no salt crystals are formed. This study advances the principles of sustainable material use by converting biowaste (waste tea) into a functional photothermal layer for water purification, minimizing dependence on synthetic or hazardous substances.