A laser-based technique developed by a Japanese research team could make it easier to degrade the plant product cellulose, which is used to produce biofuel. The new technique is based on a type of laser called the infrared-free electron laser (IR-FEL), whose wavelength is tunable in the range of 3 to 20 μm. Owing to its dense, rigid structure, cellulose is challenging to break down without use of extreme processes such as microwave radiation, hydrolysis, and ultrasonication. The researchers knew that IR-FELs had been used to perform dissociation reactions on various biomolecules. “So far, this technology has been used in the basic fields of physics, chemistry, and medicine, but we wanted to use [it] to spur advances in environmental technology,” researcher Takayasu Kawasaki at the Tokyo University of Science said. “One of the unique features of the IR-FEL is that it can induce a multiphoton absorption for a molecule and can modify the structure of a substance.” A novel laser-based strategy for the effective degradation of cellulose into useful products. Courtesy of Tokyo University of Science. Cellulose is a biopolymer composed of molecules that form covalent bonds. The polymer has three IR bands, at the 9.1-, 7.2-, and 3.5-μm wavelengths, that correspond to three different bonds. The researchers irradiated powdered cellulose by tuning the wavelength of the IR-FEL to these three wavelengths. When they analyzed the resulting cellulose products using mass spectrometry and synchrotron radiation IR microscopy, they found that the cellulose molecules had decomposed into glucose and cellobiose — precursor molecules for bioethanol production. The cellulose products were obtained at high yields, indicating that this could be an efficient way to degrade cellulose. The laser irradiation technique used by the researchers is based on the vibration-mode selective multiphoton absorption reaction and requires no co-solvents and no high temperatures or pressures to exert the irradiation effect. One day of operation can process several hundred milligrams of the solid cellulose sample at the current laboratory scale. “This was the first method in the world to efficiently obtain glucose from cellulose by using an IR-FEL,” Kawasaki said. “Because this method does not require harsh reaction conditions such as harmful organic solvents, high temperature, and high pressure, it is superior to other conventional methods.” In addition to generating biofuels, cellulose can be used as a functional biomaterial in biocompatible cell membranes, antibacterial sheets, and hybrid paper materials, making this method for degrading cellulose potentially useful for health care, technology, and engineering, in addition to green energy. Kawasaki is optimistic that the team’s method can be used to process other wood constituents and provide a way to recycle forest biomass. Scientists from Tokyo University of Science, Kyoto University, Nihon University, and Ritsumeikan University participated in the research. The research was published in Energy & Fuels (www.doi.org/10.1021/acs.energyfuels.0c01069).
