New achievements by Chinese scientists! Can this material really cope with the crisis of fresh water shortage?

Water is the source of life and the basis for the survival of all things in the world. Although the coverage of water on the earth we live in exceeds 70%, the fresh water resources are less than 3%. The distribution of these fresh waters is extremely uneven. They exist in lakes, rivers, underground, and Antarctic ice sheets. There is less than 1% of fresh water available for human consumption.

Image source: unsplash.com Photographer: David Becker

In addition, affected by a series of problems such as environmental pollution and population growth, the global shortage of fresh water resources will become more serious in the future. Therefore, solving the problem of fresh water shortage is a top priority.

On September 13, 2023, Chinese scientists published an article on new photothermal conversion materials in the journal Nature. The advent of this material is expected to bring a steady supply of fresh water resources to mankind and ensure a safe and sufficient supply of fresh water!

Image source: Nature magazine.

Preparation and principle of new materials

Solar energy is a renewable energy source that is widely used for heating and energy storage. Solar-driven interfacial water evaporation technology has been proposed for nearly a decade, that is, solar energy is absorbed and converted into heat energy, promoting the evaporation of water molecules into water vapor, and the water vapor is collected for subsequent treatment. This technology has broad application prospects in the field of seawater desalination to produce clean fresh water. The use of solar energy can alleviate the consumption of fossil energy and a series of environmental pollution problems caused by it.

The core of this technology is how to improve the conversion efficiency of solar thermal energy. The high-efficiency new photothermal conversion material newly developed by Chinese scientists has brought hope for the widespread use of this technology!

Starting from the nature of the interaction between sunlight and matter to generate heat, scientists have used relevant experiments such as chemistry, physics, and calculation to discover that the Ti-Ti dimer structure present in titanium dioxide (TinO2n-1) will limit the distribution range of the 3d-layer electron movement of the electronic structure outside the Ti nucleus, causing real-space localization of the electrons, and can introduce flat-band electronic states near the Fermi level, thereby leading to an enhancement in the joint state density of electron transitions.

Based on the above principles, further experiments have shown that as a titanium oxide substance, the absorption rate of λ-Ti3O5 to sunlight can exceed 95%.

Reflection spectrum and electronic structure. Image source: Reference [1]

Scientists further used λ-Ti3O5 and polyvinyl alcohol materials to make evaporators. In order to improve the efficiency of water evaporation, the evaporator was designed into a three-dimensional porous interconnected structure. Experiments have found that under the conditions of sunlight (1 kW m-2), the amount of water evaporated per hour through this device can reach 6.09 kg m-2, which is the fastest level of water evaporation by solar-driven interfacial water evaporation technology. Scientists further used this device in seawater desalination experiments, and the amount of fresh water collected per day can reach 23 L m-2.

It can be seen that if this equipment is put into the field of seawater desalination, large-scale fresh water preparation can be achieved, which will greatly solve the problem of shortage of fresh water resources and bring new ideas for the purification and treatment of sewage and wastewater.

Schematic diagram of the operation of a three-dimensional porous interconnected structure evaporator (a. Outdoor seawater desalination device; b. Changes of solar energy, freshwater collection rate and total amount of freshwater collected over time; c. Changes of temperature and humidity over time; d. Daily average light flux and freshwater collection rate). Image source: Reference [1]

What can we do about freshwater conservation?

The discovery of new materials has made us no longer fear having no water to drink in the future, but we must also save water and raise awareness of protecting freshwater resources.

First, the government has successively issued laws and regulations to improve the protection of freshwater resources, and through legal constraints, remind everyone of the importance of protecting freshwater. It has also increased the publicity of policies related to freshwater protection to enhance everyone's awareness of water conservation. At the same time, it has optimized the use of freshwater in agriculture and industry and increased the utilization rate of freshwater.

In life, each of us should pay attention to saving water. At the same time, be careful not to discard waste, chemicals, medicines, etc. into the sewers, which can easily cause fresh water pollution.

Let us work together to protect freshwater resources, use water rationally, and not let the last drop of water on the earth become our tears!

References

[1] Yang, B., Zhang, Z., Liu, P. et al. Flatband λ-Ti3O5 towards extraordinary solar steam generation. Nature (2023).

[2] Li Xueqin. New solar collector and its application in seawater desalination[J]. General Machinery, 2012. DOI:CNKI:SUN:TYJS.0.2012-03-037.

[3] Xie Lixin, Li Pingli, Wang Shichang. Current status of seawater desalination technology and review of various desalination methods [J]. Chemical Industry Progress, 2003, 22(10):4. DOI:10.3321/j.issn:1000-6613.2003.10.011.

[4] Lu Zhu. Prospects of water conservation and water resource recycling technology[J]. Water Purification Technology, 2002(S1):5.DOI:CNKI:SUN:ZSJS.0.2002-S1-013.

Planning and production

Produced by | Science Popularization China

Producer｜China Science Expo

Author: Shi Wuyao, PhD in Biology

Editor: Yinuo