Nature Water – 20 July 2023
Biomimetic surface engineering for sustainable water harvesting systems
Yi Wang, Weinan Zhao, Mei Han, Jiaxin Xu, and Kam Chiu Tam
This review article addresses the worldwide challenge of freshwater scarcity, due to many factors but increasingly becoming more prevalent because of climate change. WIN member and Professor in the Department of Chemical Engineering at the University of Waterloo, Michael Tam and his PhD students (Yi Wang and Weinan) report on nanotechnology-based methods to harvest water from the atmosphere, using techniques inspired from nature.
In this paper, Tam and his team investigated surfaces, structures and compositions used by various plants and insects to gather water needed for their survival. Using surface engineering and nanotechnology, smart surfaces with the desired properties were developed and fabricated that enable droplet nucleation, growth and removal, vapour sorption and desorption, and evaporation for atmospheric water generation.
With these innovations, we can harvest water from the atmosphere by three distinct processes: fog harvesting – suitable in mountainous regions that are often foggy/cloudy (rel. humidity >80%); dew harvesting may be feasible in regions with an associated dew point and ambient temperature; and moisture harvesting, based on solar energy to extract water vapour from arid climates (rel. humidity <40%). The ultimate goal is to provide clean and fresh water to remote community or locales with limited access to traditional water sources (rivers, lakes, aquifers) that is cost effective, energy efficient, portability and possesses minimal environmental footprint.
Nature has long been a source of inspiration for scientists and engineers, and researchers have looked to the unique topographies and compositions found on many biological surfaces that collect water vapour, convert to liquid and channel and store for consumption. One example is the Namib beetles, with a wax-coated hydrophobic area and non-waxy hydrophilic area on its wings, or elytra. Here, water droplets land on the hydrophilic sections and grow rapidly. Once reaching a critical size, the water droplet is transported via the waxy regions on the wings for consumption. Taking this cue, smart surfaces can be engineered with similar hydrophilic/hydrophobic and bumpy features to enhance nucleation in areas with ample dew or fog to collect water. The publications cites several other examples of species with unique water-management capabilities, including cacti, spider webs and wheat awns.
The article delves into the importance of sustainability when designing these smart systems, which minimize the use of hazardous materials and solvents, reduce waste and conserve energy and resources. Techniques such as 3D printing, replica moulding, microfluidics, photolithography and plasma etching can be used to fabricate the structures for water-harvesting, and methods such as CVD, spray and spin coating can be used to generate desired surface properties to collect, move and store the collected water.
The paper states that there still is much more work to be done to bring the technologies to market and the remote or harsh environments for consumers. Many research opportunities remain to bridge the gaps between these harvesting systems and practical use to achieve self-autonomous and sustainable systems in the future.
“Waterloo can become a center of excellence in the development of sustainable solutions to meet the UN Sustainable Development Goals. This can be accomplished by integrating nanotechnology, chemistry, and chemical engineering in the design of systems and processes using natural resources, such as the abundant forest and agriculture biomass.” – Professor Michael Tam