Environmental Engineering Reference
In-Depth Information
21
NaNomaterials for CarboN DioxiDe aDsorptioN
Luis Ángel Garza Rodríguez
1
and Elsa Nadia Aguilera González
2
1
Facultad de Ingeniería y Arquitectura, Universidad Regiomontana A.C., Monterrey, Mexico
2
Corporación Mexicana de Investigación en Materiales S.A. de C.V., Calle Ciencia y Tecnología No. 790,
Saltillo 400, Saltillo, Coahuila, Mexico
21.1 iNtroDuCtioN
21.1.1 Global Warming
Over millennia, the temperature of the earth has evolved and has experienced warming and cooling cycles. With the passage
of time, the earth has reached a dynamic equilibrium between the amount of heat received from the sun and the amount lost
by the planet. It is estimated that the amount of energy that reaches the top of the atmosphere during the day is 1.360 W m
-2
[1], and 30% is reflected back into space. Two-thirds of these reflections are due to clouds and aerosols. The other third is
due to the light areas on the earth's surface such as ice, deserts, and snow. The remainder of the energy not reflected is
absorbed by the atmosphere and the surface of the earth. Theoretically, the average temperature of the earth should be -18°C
in order to be able to support life in hostile conditions. To maintain the thermal balance, the earth in its natural rotation
cycle exposes a portion of this energy to sunlight (the adsorbed energy), while the dark side begins a cooling process.
During this cooling process, a portion of the energy is radiated from the earth's surface into space (in the form of heat
waves) and absorbed by some constituents in the atmosphere, mainly water vapor, carbon dioxide, ozone, oxide monoxide,
and methane (known as greenhouse gases), by increasing the average temperature of the earth to 15°C, to keep the water in
liquid form and sustain life on the planet. These greenhouse gases naturally regulate the average temperature of the earth
to sustain life.
In the last 100 years, the average global temperature has increased by 0.8°C, of which the 0.6°C increase has occurred in the
last three decades [2]. This change is largely due to the increase in the concentration of water vapor, methane, nitrogen oxides,
ozone, and carbon dioxide, most of which are a result of human activities such as burning fossil fuels, industry, manufacturing
of fertilizers, and deforestation, among others.
The most common among these is carbon dioxide (CO
2
), which is added every day in large quantities due to the burning of
fossil fuels. Global awareness has turned its attention to this gas as the main cause of global warming. This fact can be seen
when analyzing the data collected and published by the Division of National Oceanic and Atmospheric Administration (NOAA)
of the Department of Commerce of the United States, which noted carbon dioxide concentration in the atmosphere of 396.08 ppm
in its report of February 2013 (Fig. 21.1).
The data on CO
2
concentration in the atmosphere obtained by Charles David Keeling at the south pole and in Hawaii since
1958 generated a graph known as the Keeling curve (Fig. 21.2). Obviously, CO
2
concentration has increased by just over 25%
over the past 54 years, reaching a level of 398 ppm in 2013, and growing at a rate of about 1.5 ppm each year.
