Hydrogen and carbon monoxide generation from laser-induced graphitized nanodiamonds in water

Laser-Induced Modification of Hydrogenated Detonation Nanodiamonds in Ethanol

Apart from the frequently used high-temperature annealing of detonation nanodiamonds (DNDs) in an inert environment, laser irradiation of DNDs in a liquid can be effectively used for onion-like carbon (OLC) formation. Here, we used fully de-aggregated hydrogenated DNDs (H-DNDs) dispersed in ethanol, which were irradiated for up to 60 min using a 532 nm NdYAG laser with an energy of 150 mJ in a pulse (5 J/cm²) at a pulse duration of 10 ns and a repetition rate of 10 Hz. We investigated the DND surface chemistry, zeta potential, and structure as a function of laser irradiation time. Infrared spectroscopy revealed a monotonical decrease in the C-H_x band intensities and an increase of the C-O and C=O features. Transmission electron microscopy (TEM) revealed the formation of OLC, as well as a gradual loss of nanoparticle character, with increasing irradiation time. Surprisingly, for samples irradiated up to 40 min, the typical and unchanged DND Raman spectrum was recovered after their annealing in air at 450 °C for 300 min. This finding indicates the inhomogeneous sp³ to sp² carbon transformation during laser irradiation, as well as the insensitivity of DND Raman spectra to surface chemistry, size, and transient structural changes.

Laser-Induced Hydrogen Generation from Methanol with Graphene Aerogel as the Target

The present work demonstrates a new concept of the efficient generation of hydrogen from methanol by the continuous wave laser diode irradiation of an immersed graphene aerogel (GA) scaffold as the target. It was observed that the process occurred very intensively when it was assisted by bright white light emission in the spot of a laser-irradiated GA scaffold. The yield of hydrogen emission increased exponentially with the applied laser power. The light emission was assisted by the intense production of H₂, CH₄, and CO gases. It was found that with increasing excitation laser power, the H₂ generation increased at the expense of CO. It is shown that the volume of CO decreases because of the formation of C₂ molecules and CO₂ gases. The mechanism of the laser-driven dissociation of methanol was discussed in terms of the violent ejection of hot electrons from the GA surface as a result of the laser-induced light emission of the graphene target.