Interfacial solar vapor generation (ISVG) is an emerging approach that directly uses sunlight to desalinate water while achieving zero liquid discharge. However, the vast majority of materials that have been studied for this process maintain a two-dimensional (2D) structure that floats at the air-water interface. In this process, water is wicked through a porous substrate that functions as both a water supplier using capillary action to wick water to the evaporative interface and an insulator that retains photothermally generated heat at that same evaporative interface. While optimization of material properties, heat localization, and water transport capabilities have led to extremely high solar-vapor conversion efficiencies, the evaporative flux rates of 2D evaporators remain low (typically between 1.5 and 3.0 kg m-2 h-1) resulting in a relatively large spatial footprint. This work describes recent advancements in the development of three-dimensional (3D) solar evaporators, and uses a graphene oxide (GO) stalk that operates near the capillary wicking limit to achieve a normalized flux rate as high as 34.7 kg m-2 h-1 under 1-sun condition (1 kW/m2). Through this investigation, we found that the evaporation area index (EAI)—or the total surface area of evaporation relative to its projected ground area—to be the primary driver for these high evaporative flux values. By conducting a rigorous energy balance, it was found that the additional surface available for evaporation achieves sub-ambient temperatures when it is not in indirect sunlight, allowing the 3D GO stalk to derive additional energy for evaporation from the ambient environment. Through a systematic investigation, the 3D GO stalk demonstrated a variety of advantages over its 2D counterpart, including omni-direction sunlight utilization, enhanced response to external convection, and resilience to salt accumulation. The normalized evaporative flux achieved by the 3D GO stalk represents a nearly 100x enhancement over conventional solar evaporation ponds and more than 10x enhancement over 2D solar evaporating materials. This performance makes the 3D GO stalk well-suited for the development of a zero liquid discharge technology that is able to balance both low operating costs and low spatial footprint for brine management applications.

Adapting interfacial solar vapor generation by 3D graphene oxide stalks for brine treatment

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.