Using Corn Cob Derived Biomaterials to Remove Heavy Metals and Kill Bacteria in Contaminated Water.
Last edited Sun Oct 4, 2020, 04:32 PM - Edit history (1)
The paper I'll discuss in this post is this one: Polyethylenimine-Grafted-Corncob as a Multifunctional Biomaterial for Removing Heavy Metal Ions and Killing Bacteria from Water (Qin Meng, Shengdong Wu, and Chong Shen Industrial & Engineering Chemistry Research 2020 59 (39), 17476-17482).
With a little bit of googling, it appears to me that the world produces about 1.1 billion tons of corn each year, presumably measured as grain. According to the introduction of the above cited paper, which I will excerpt, corn cobs, which are generally discarded, account for a mass 1/4 as large as the grain itself, somewhere around 250 million tons. From a table in the paper, that I'll reproduce from the paper, it appears that corncobs are about 43% carbon, meaning that somewhere around 100 to 110 million tons of carbon can be obtained from corncobs.
While we are engaged in Godotian waiting for the grand so called "renewable energy" nirvana that has not come, is not here, and won't come, we are currently dumping about 35 billion tons of the dangerous fossil fuel waste carbon dioxide into the planetary atmosphere.
The interesting product discussed in this paper will not sequester all that much carbon in use, even if - as surely will not happen - all the corn cobs in the world were utilized to make the biomaterial discussed herein. Nevertheless this is carbon captured from the air, and every little bit counts. In theory, at least, carbon captured from corn cobs and sequestered as value added products might remove a billion tons every decade, not all that much, but nothing at which to sneeze. Thus this is an interesting little paper.
The corn cobs in this paper are functionalized, as noted in the title, with polyethylenimine, which is a polymer synthesized by chain ring opening of aziridine, the simplest nitrogen organic heterocycle, a cyclic molecule having two carbons, five hydrogens and one nitrogen. Aziridine is generally made via various routes from ethylene. All, or almost all, of the world's ethylene is obtained from dangerous fossil fuels. However many other starting materials are certainly possible on an industrial scale. Syngas is a mixture of hydrogen and carbon oxides - generally the monoxide - which can be made from pretty much any carbon containing material and water, including carbon dioxide with the agency of heat, nuclear heat if one is seeking a carbon free route. There are many routes to ethylene from syngas. My personal favorite proceeds via the intermediate dimethyl ether, which I personally believe should be the core chemical portable energy medium in a sustainable world. It is described here: Direct Conversion of Syngas into Methyl Acetate, Ethanol, and Ethylene by Relay Catalysis via the Intermediate Dimethyl Ether (Zhou et al., Angew. Chem. Int. Ed. 2018, 57, 12012 –12016)
Ethylene can also be made via the partial hydrogenation of acetylene, and acetylene can be made from multiple carbon sources by many means, notably heating a carbon source with calcium metal, albeit with varying degrees of efficiency. The calcium hydroxides produced in such a process can be useful for carbon dioxide capture from either air or from combustion gases or reformer gases.
Thus it is theoretically possible to derive the corn cob derived product described here entirely from carbon dioxide in the air, although any polyethylenimine used for these purposes would merely sequester dangerous fossil fuel derived carbon.
Here is the cartoon accompanying the abstract of the paper:
From the paper's introduction:
By now, corncob-based biochars, corncob mixtures, and even corncob itself have been developed into biosorbents for removal of heavy metal ions from aqueous solution. For example, calcined corncob biochars showed maximum adsorption capabilities of less than 40 mg/g for Cu2+,(7) Pb2+,(8) and Cd2+,(8) while the acrylonitrile modification on the biochars improved the Cd2+ adsorption capacity to 85.6 mg/g.(2) In addition, a mixture of tea waste, corncob, and sawdust had adsorptive capacities of 39.5, 94.0, and 41.5 mg/g for Cu2+, Pb2+, and Cd2+.(9) Interestingly, Garg et al. reported that corncob itself could remove 105.6 mg/g of Cd2+ from aqueous solution,(10) even more potent than the biochars and mixtures. Nevertheless, the adsorptive capabilities of these biosorbents are not high because the mechanism was dominated by physisorption via the weak van der Waals force between the metal ions and corncob surface(8) due to the lack of functional groups on the sorbents.
Polyethylenimine (PEI), a polymer that contains a large amount of primary and secondary amine side groups, can bind to heavy metal ions via chelating forces.(11) The strong binding forces of chelation attributed to the high adsorptive capability (>100 mg/g) of PEI modified materials such as bacterial cellulose,(12) P84 nanofiltration membrane,(13) chitin,(14) and magnetic nanoparticles(15) to heavy metal ions. In addition, PEI also displayed wide-spectrum antimicrobial effects(16) due to its cation property, so that the PEI-grafted materials (e.g., polyurethane ureteral stents) showed potent antibacterial ability in medical applications.(17,18) Economically, PEI is a bulk chemical that is much cheaper than other materials such as silver nanoparticles.
Because of these properties of PEI, this paper aims to develop a multifunctional material via grafting PEI on corncob. The PEI-modified corncob is expected to perform functions like removing heavy metal ions and killing bacteria. As the two aspects are critical and usually coexist in treatment of polluted water, multifunctional PEI-g-OC should be a useful biomaterial in the application of water treatment, e.g., portable devices for water purification. The PEI-g-OC performs significant advantages on cheapness, lightweight and environmental-friendliness over chemical synthetic materials.
A cartoon about the route to the product, a photograph of the starting materials, intermediate and product, and some spectra:
The caption:
A table of the elemental composition of the final product and the intermediates, giving a feel, as mentioned above, for the carbon sequestration capability of these materials:
Copper, for which toxicity is concentration dependent, is pretty much found in all potable water from piping, cadmium and lead to varying degrees from historic solders and or leachate from landfills, cadmium from discarded nickel cadmium batteries, and - increasingly in the future - from discarded CIGS type photovoltaic devices, both portable (as in old calculators and toys) and/or solar cells.
An idea of the capacity of these materials for heavy metals, in this case cadmium, copper and lead:
The caption:
Langmuir and Freundlich isotherms, which are technical measurements of evaluating surface chemistry:
The caption:
The antibacterial properties of the PEI impregnated corn cob material was determined against E. coli, P. aeruginosa, and S. aureus:
The caption:
The caption:
The authors determined that the product was reusable:
The caption:
The paper's conclusion:
It is notable that products like these that capture metals can be utilized to create low grade ores. The inexhaustibility of uranium resources is tied to precisely such an approach.
It's an interesting little paper.
I wish you a safe, healthy and enjoyable Sunday afternoon.
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