题型:阅读理解 题类:常考题 难易度:普通
江苏省常州“教学研究合作联盟”2018-2019高二下学期英语期中考试试卷
Metal-organic frameworks(MOFs) are compounds that are set to solve some tough challenges: producing water in the desert, removing greenhouse gases from the air and storing dangerous gases more safely.
The Arizona desert is really dry. Anyone stuck in it without water would die from dehydration (脱水) within three days. Unless, that is, they had one of Omar Yaghi's next-generation water harvesters. Although daytime humidity(湿度)is only about 10 per cent, this rises to 40 per cent at night, which means there's enough water in the atmosphere to support life — if it can be transformed into liquid form.
That's exactly what Yaghi's device does. It's a box about the size of a small microwave oven designed to suck the humidity from the air at night and turn it into drinking water the next day using only the heat of the sun as its power source. What makes it work is a special material called a metal-organic framework (MOF), which at normal temperatures attracts water molecules (分子) onto its surface of its internal pores(细孔). Warm it up and the water is released, each harvest producing one-third of a cup of pure drinking water.
"With further improvements, a device, the size of a washing machine, could produce enough water for the basic needs of a household," says Yaghi, a chemist at the University of California. One-third of the world's population lacks safe drinking water; for them such a device could be a lifesaver.
These crystalline cluster(结晶群)of metals, such as aluminum or magnesium, linked by organic molecules can be made into materials with an extremely high absorption ability, attracting specific molecules to their surface. In this way, MOFs cling to a variety of liquids and gases.
MOFs work thanks to their unique structure—large quantities of nanometer-sized internal spaces. In fact one MOF has so many pores that they would cover an area as large as six football fields. MOFs are also extremely stable light and have many different uses: their molecular structure can be varied to attract specific molecules, such as water, and their pores can be designed to best store them. Adding a small amount of heat or pressure causes the MOF to release what it is holding. More than 70,000 different MOFs have been produced to date for various applications.
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