Cost-effective graphene-based 2D solar evaporator for high-efficiency water purification and desalination

Abstract

This study presents the design and optimization of a two-dimensional solar evaporator utilizing nonwoven cotton material modified with graphene flakes. The system demonstrates high energy efficiency and cost-effectiveness (∼1.4 $·m⁻²), making it a promising candidate for water purification and desalination. An optimal graphene flake concentration within the evaporation zone was identified, directly correlating with maximal evaporation rates and photothermal conversion efficiency. Experiments with distilled water showed a peak evaporation rate of ∼ 1.9 kg/(m²·h) and an efficiency reaching 97 %. Notably, under solar radiation densities up to 2000 W/m², the evaporator exhibited negligible optical losses, confirming effective photothermal conversion. A mathematical model characterizing mass transfer from the evaporator surface was developed, enabling evaluation of factors influencing vaporization and guiding system design. Continuous 8-hour desalination testing with a 3.5 wt% NaCl solution yielded an average vapor generation rate of 1.4 kg/(m²·h) with 70 % efficiency. Performance reduction was attributed to salt crystallization obstructing active zones and increasing optical losses. This highlights the need for strategies to mitigate salt accumulation and sustain high efficiency. Additionally, a model of salt ion transport was developed, accurately predicting accumulation patterns within the vaporization zone. The experimental methodologies and numerical models presented offer a refined approach to assessing photothermal conversion efficiency in interfacial solar vapor generation and provide valuable insights for optimizing future devices.