Interfacial Solar Evaporation by a 3D Graphene Oxide Stalk for Highly Concentrated Brine Treatment

Abstract

In this work, we demonstrate a 3-dimensional graphene oxide (3D GO) stalk that operates near the capillary wicking limit to achieve an evaporation flux of 34.7 kg m −2 h −1 under 1 sun conditions (1 kW/m 2 ). This flux represents nearly a 100 times enhancement over a conventional solar evaporation pond. Interfacial solar evaporation traditionally uses 2D evaporators to vaporize water using sunlight, but their low evaporative water flux limits their practical applicability for desalination. Some recent studies using 3D evaporators demonstrate potential for more efficient water transfer, but the flux improvement has been marginal because of a low evaporation area index (EAI), which is defined as the ratio of the total evaporative surface area to the projected ground area. By using a 3D GO stalk with an ultrahigh EAI of 70, we achieved nearly a 20-fold enhancement over a 2D GO evaporator. The 3D GO stalk also exhibited additional advantages including omnidirectional sunlight utilization, a high evaporation flux under dark conditions from more efficient utilization of ambient heating, a dramatic increase of the evaporation rate by introducing wind, and scaling resistance in evaporating brines with a salt content of up to 17.5 wt %. This performance makes the 3D GO stalk well suited for the development of a low-cost, reduced footprint technology for zero liquid discharge in brine management applications.

Achieving over 70 kg m-2 h-1 evaporation rate by a 3D polyacrylamide-based hydrogel

“…Figure 7 shows that our 3D CAH showed an advantage in evaporation rate and cost-effectiveness among current reported 3D hydrogels (Table S2) 12,15,37,38,39,40,41,42,43,44,45,46,47 . Although different 3D structures were applied by others, few studies achieved a high evaporation rate over 30 kg m − 2 h − 1 12 . A recent study achieved a high evaporation rate over 30 kg m − 2 h − 1 but the corresponding costeffectiveness was lower than the two studies.…”

“…A small and polyvalent ion shows a higher interaction than a large but monovalent ion 16,17 . The charge density for Cl − , SO 4 2− and PO 4 3− are 6.44×10 12 C/m 3, 7.38×10 12 C/m 3 , and 9.43×10 12 C/m 3 , respectively.…”

“…3D evaporators increase water evaporation by introducing extra cold evaporation surfaces below the environmental temperature to obtain additional energy from the air 13,14 . And evaporation area index (EAI) values (ratio of the total area available for evaporation relative to the projected ground area) of the 3D evaporator is a key factor affecting its evaporation rate 12 . The evaporation rate of 3D evaporators is higher than most 2D evaporators but still lower than 5 kg m − 2 h − 1 , with only a few 3D evaporators achieving the higher EAI (34.7 kg m − 2 h − 1 , EAI = 70) 12,15 .…”

“…And evaporation area index (EAI) values (ratio of the total area available for evaporation relative to the projected ground area) of the 3D evaporator is a key factor affecting its evaporation rate 12 . The evaporation rate of 3D evaporators is higher than most 2D evaporators but still lower than 5 kg m − 2 h − 1 , with only a few 3D evaporators achieving the higher EAI (34.7 kg m − 2 h − 1 , EAI = 70) 12,15 . Therefore, a 3D evaporator with a high EAI can be designed to obtain a higher water evaporation rate.…”

Exploring the agricultural reutilisation of desalination reject brine from reverse osmosis technology

“…Another problem is that most of these systems are optimised for seawater, not for brine, in which the high evaporation rate needed to maintain water output cannot be maintained [90] due to high salinity. In this regard, new materials used as surface covers can keep or increase evaporation rates [90][91][92][93], which presents an interesting field for optimisation to use brine as water source for agricultural fields.…”