Photothermal Membrane Water Treatment for Two Worlds

Abstract

Conspectus In meeting the increasing need for clean water in both developing and developed countries and in rural and urban communities, photothermal membrane water treatment technologies provide outstanding advantages: For developing countries and rural communities, by utilizing sunlight, photothermal membrane water treatment provides inexpensive, convenient, modular, decentralized, and accessible ways to clean water, which can reduce the consumption of conventional energy (e.g., electricity, natural gas) and the cost of clean water production. In developed countries and urban communities, photothermal membrane water treatment can improve the energy efficiency during water purification. In these water purification processes, the light absorption and light-to-heat conversion of photothermal materials are important factors in determining the membrane efficacy. Nanomaterials with well-controlled structure and optical properties can increase the light absorption and photothermal conversion of newly developed membranes. This Account introduces our recent work on developing scalable, cost-effective, and highly efficient photothermal membranes for four water purification applications: reverse osmosis (RO), ultrafiltration (UF), solar steam generation (SSG), and photothermal membrane distillation (PMD). By utilizing photothermal materials, first, we have demonstrated how sunlight can be used to improve the membrane’s resistance to biofouling in RO and UF processes by photothermally induced inactivation of microorganisms. Second, we have developed novel SSG membranes (i.e., interfacial evaporators) that can harvest solar energy, convert it to localized heat, and generate clean water by evaporation. This desalination approach is particularly useful and promising for treatment of highly saline water. These new interfacial evaporators utilized graphene oxide (GO), reduced graphene oxide (RGO), molybdenum disulfide (MoS2), and polydopamine (PDA). The solar conversion efficiency and environmental sustainability of the interfacial evaporators were optimized via (i) novel and versatile bottom-up biofabrication (e.g., incorporation of photothermal materials during bacterial nanocellulose (BNC) growth) and (ii) easy and cost-effective top-down preparation (e.g., modification of natural wood with photothermal materials). Third, we have developed membranes for PMD that incorporate photothermal materials to generate heat under solar irradiation, thus providing a higher transmembrane temperature difference and higher driving force for effective vapor transport, making the membrane distillation process more energy-efficient. Lastly, this Account compares the photothermal membrane applications, summarizes current challenges for photothermal membrane applications, and offers future directions to facilitate the translation of photothermal membranes from the laboratory to large engineered systems by improving their scalability, stability, and sustainability.

Intensifying Heat Using MOF‐Isolated Graphene for Solar‐Driven Seawater Desalination at 98% Solar‐to‐Thermal Efficiency

“…Solar-driven steam generation is an important process that relies on the high-performance solar light-harvesting materials to generate heat for diversified applications such as seawater desalination and contaminated water purification. [36,37] Notably, our G@ZIF can be easily and reproducibly applied as a standalone film on any solid or water surface in a scalable manner (Figures S20 and S21, Supporting Information). Briefly, we form a uniform G@ZIF film by depositing G@ZIF nanosheets on an anodic aluminum oxide membrane (AAO) (Figure S22A, Supporting Information).…”

Sandwich Photothermal Membrane with Confined Hierarchical Carbon Cells Enabling High‐Efficiency Solar Steam Generation

“…Water and energy are scarce resources in modern society, both of which are closely linked to the economic and social development of nations. [ 1 ] In many areas, the energy–water nexus is exacerbated by the shortage of both fresh water resources and energy generation infrastructures. [ 2 ] Solar‐driven vaporization using photothermal materials is a green and viable solution to address both the issues by utilizing the abundant source of solar energy.…”

IPT: An Index to Rank Molecular Photothermal Agents

“…In the last two decades, the photothermal effect has aroused strong interest to develop light‐responsive materials such as actuators, [1] drug delivery system for chemo‐photothermal combination cancer therapy [2] as well as smart materials for water purification [3] or contrast agents for bioimaging [4,5] . Many photothermal agents have been used spanning from inorganic nanoparticles to conducting polymers and molecular entities [6–9] .…”