Water Purification/Harvesting: Harnessing Solar‐Driven Photothermal Effect toward the Water–Energy Nexus (Adv. Sci. 18/2019)

Adaptation of solar energy in the Global South: Prospects, challenges and opportunities

The Global South comprising economically disadvantaged regions of the world face various challenges such as limited access to electricity, clean water, industrialization, and food security. Solar energy, as a sustainable and abundant resource, holds great potential to address these challenges. Despite its immense potential, the Global South encounters hurdles related to technology adoption, infrastructure, and financial constraints. This review examines the history, classifications, global statistics, merits, and demerits of solar technology in the Global South. Furthermore, it delves into various applications of solar energy, including extreme environments, residential electricity generation, transportation, and industrial usage in this region. This study concludes by providing new insighths and highlighting the significant role solar energy can play in shaping the future of the Global South if challenges are adequately addressed, and opportunities are embraced.

Boosting Water Evaporation by Construction of Photothermal Materials with a Biomimetic Black Soil Aggregate Structure

Solar-driven interfacial evaporation is considered an efficient way to get fresh water from seawater. However, the low evaporation rate, surface salt crystallization, and low energy collection of the photothermal evaporation layer limit its further application in an outdoor freshwater field. And the aggregate structure design of the material itself is often ignored in solar-driven water evaporation. Black soil (BS), with a unique soil aggregate structure, is rich in tubular pores, which can be used for multilevel sunlight utilization and good capillary water transport. Based on the extraordinary photothermal properties and pumping capacity of BS, a reasonable unidirectional salt-collecting device is designed, which can realize long-term collection of mineral salts and continuous evaporation of seawater and generate electric energy in the continuous evaporation. Inspired by the unique aggregate structure, the photothermal material doping of halloysite and nigrosin will simulate the generation of this aggregate structure and retain a good water transport effect while obtaining multistage utilization of sunlight. The solar-driven evaporation rate of a nigrosin-halloysite solar steam generator is 1.75 kg m-2 h-1 under 1 kW m-2 mimic solar radiation; it can achieve stable salt leaching-induced voltage generation of 240 mV. This work demonstrates not only a solar evaporator that can continuously achieve desalination but also the design strategy of BS-like aggregate photothermal materials, which promotes the development of low-cost resource recovery and energy generation for practical outdoor seawater desalination.

Waste sawdust-based composite as an interfacial evaporator for efficient solar steam generation

Interfacial evaporation is the technology of localizing heat energy at the air-water interface and is used for getting potable water from salty or seawater effectively. In this work, we introduce a novel interfacial evaporator by blending different weight ratios of waste sawdust (1 g, 2 g, 3 g and 4 g) with bisphenol-A epoxy resin (LY556) and triethyltetramine hardener (HY951). The fabricated epoxy hardener sawdust (EHS) composite material was subjected to various characterizations for the possibility of using it in solar steam generation. Consequently, EHS displayed high light absorption, amorphous structure, functional groups, and large number of pores. The main objective of the study was to investigate interfacial solar steam generation with and without interfacial evaporators (EHS-1g, EHS-2g, EHS-3g, and EHS-4g) under indoor conditions. The maximum mass loss of water, evaporation rate and evaporation efficiency were found to be 4.5 g, 1.398 kg m^-2 h^-1, and 92.99%, respectively, for the EHS-4g evaporator. The salinity of the distilled condensed water was measured and was below the WHO standards. The results are due to (i) the large number of cross-linked porous structures used to permeate water at the evaporative surface by capillary action, (ii) low thermal conductivity of the composite that offers an efficient broad and strong light absorption, and (iii) existence of a larger hydraulic diameter and small tortuosity of pores, which reduces the salt ion penetration distance and dispatch back to bulk water.

Latest development in salt removal from solar-driven interfacial saline water evaporators: Advanced strategies and challenges

Solar-driven interfacial water evaporation, which gets rid of the limitation of saline waters, enables to supply potable water in the worldwide, especially in remote areas where only solar energy and water are available. This technique has also exhibited great potential applications in fields such as seawater desalination, steam sterilization, and fuel production. However, the evaporation efficiency decreases during continuous operation in saline water due to the blockage of the solar absorber resulting from crystalline salt deposition. Therefore, it is still a great challenge to design a stable and efficient solar-driven interfacial saline water evaporator. Herein, a variety of structural designs and engineering strategies for salt removal of evaporators in the latest years were reviewed. We classified these strategies as remaining unsaturated evaporation of saline water, preventing salt ions from contacting the solar absorber, dissolving and/or migrating back of crystalline salts, and keeping salt crystallization away from evaporation area. Finally, the current challenges and future research opportunities were discussed. The purpose of this review was: (1) to provide ideas to solve the problem of the reduced efficiency causing by salt deposition during saline water evaporation and (2) to promote the application of solar-driven interfacial saline water evaporation technology by providing the latest achievements in structural designs for salt removal.