Carbon is the stuff of life! A vital element in nature, it is also one of the most abundant elements and present in every life form. Indeed, we, humans, have been classified as "carbon units" by V'Ger in Star Trek: The Motion Picture. It is a sort of friendly element, easily reacting with other elements, resulting in a library of millions of compounds. While carbon has been used since prehistoric times, it took thousands of years to discover the various forms or allotropes known to us today. Carbon's ubiquitous nature also gives rise to the so-called carbon cycle, a biogeochemical process involving the cycling of carbon atoms between earth and its atmosphere. Recognition as an element came in the eighteenth century and a carbon isotope forms the basis of the carbon dating (Nobel Prize in 1960) technology so critical to archeology.
Carbon's allotropic nature can be traced to its electronic structure. The process is referred to as carbon hybridization and involves the creation of hybrid orbitals for bond formation. Carbon with sp3 hybridization will form tetrahedral lattices yielding diamond while carbon with sp2 hybridization will form hexagonal sheets yielding graphite. What a difference this makes! Diamond is hard and electrically insulating while graphite is slippery and electrically conducting. Graphite in turn can be separated into individual sheets to form graphene and rolled into tubes to fabricate carbon nanotubes.
From commodity to advanced materials, graphite, amorphous carbon, diamond, carbon nanotubes, fullerenes, graphene are elemental carbon in different structural arrangements. Related carbon forms include soot, carbon black, pyrolytic/glassy carbon, coal, activated carbon, and carbon fibers. We barbeque with charcoal, clean air and water with activated carbon, impress with glittering diamonds, drive around on tires loaded with carbon black, write with pencils containing graphite, make use of polymer composites with various carbon forms, operate metallurgical operations with carbon electrodes and looking to carbon nanotubes and graphene for the next generation electronics while coal remains a major global energy source. The carbon march has been impressive and I believe that there is more to come. Applications derived from these carbon allotropes will surely continue to expand.
Egyptians and Sumerians used charcoal in their metallurgical processing of metals way back in 3750 BC. Medicinal usage was noted around 1500BC! First purification applications were done in 450BC. After a lull in applications, gas adsorption behavior was exploited in the eighteen century. Early 19th century saw the onset of decolorization for sugars while activated carbon was introduced in the early 20th century. Fullerenes were introduced in 1985 (Nobel Prize in 1996) followed by carbon nanotubes in 1991. Graphene is the latest carbon kid on the block, with recognition for graphene discovery going to Geim and Nuvoselov (Nobel Prize in 2010). Then there are diamonds! Diamonds were found thousands of years ago and we all know the economics and attachment associated with these carbon stones. Imagine finding a planet of diamonds! Well, in 2012, astronomers reported that the planet, 55 Cancri e, twice the size of Earth, possibly holds at least three times earth's mass in diamonds!
But it's not all good news! While the significant benefits of carbon are clear, the carbon link to climate change is inescapable. There are serious environmental problems linked to increased greenhouse gas emissions and many public policy initiatives, such as, carbon tax and cap and trade, are being put in place to address the issue. Innovative technologies to capture, store, and recycle greenhouse gases are being explored. But progress is slow and more action is needed.
In the meanwhile, advanced carbon materials continue to facilitate deployment of clean technologies by enabling next generation energy storage systems, lightweight materials for energy efficient transportation and energy generation, innovative pollution control systems, sustainable manufacturing processes and advanced electronics.