Achieving tunable chemical reactivity through photo-initiation of energetic materials at metal oxide surfaces

Control of Explosive Chemical Reactions by Optical Excitations: Defect-Induced Decomposition of Trinitrotoluene at Metal Oxide Surfaces

Interfaces formed by high energy density materials and metal oxides present intriguing new opportunities for a large set of novel applications that depend on the control of the energy release and initiation of explosive chemical reactions. We studied the role of structural defects at a MgO surface in the modification of electronic and optical properties of the energetic material TNT (2-methyl-1,3,5-trinitrobenzene, also known as trinitrotoluene, C₇H₅N₃O₆) deposited at the surface. Using density functional theory (DFT)-based solid-state periodic calculations with hybrid density functionals, we show how the control of chemical explosive reactions can be achieved by tuning the electronic structure of energetic compound at an interface with oxides. The presence of defects at the oxide surface, such as steps, kinks, corners, and oxygen vacancies, significantly affects interfacial properties and modifies electronic spectra and charge transfer dynamics between the oxide surface and adsorbed energetic material. As a result, the electronic and optical properties of trinitrotoluene, mixed with an inorganic material (thus forming a composite), can be manipulated with high precision by interactions between TNT and the inorganic material at composite interfaces, namely, by charge transfer and band alignment. Also, the electron charge transfer between TNT and MgO surface reduces the decomposition barriers of the energetic material. In particular, it is shown that surface structural defects are critically important in the photodecomposition processes. These results open new possibilities for the rather precise control over the decomposition initiation mechanisms in energetic materials by optical excitations.

Iron and Copper Doped Zinc Oxide Nanopowders as a Sensitizer of Industrial Energetic Materials to Visible Laser Radiation

The development of methods ensuring reliable control over explosive chemical reactions is a critical task for the safe and efficient application of energetic materials. Triggering the explosion by laser radiation is one of the promising methods. In this work, we demonstrate a technique of applying the common industrial high explosive pentaerythritol tetranitrate (PETN) as a photosensitive energetic material by adding zinc oxide nanopowders doped with copper and iron. Nanopowders of ZnO:Fe and ZnO:Cu able to absorb visible light were synthesized. The addition of one mass percent nanopowders in PETN decreased the threshold energy density of its initiation through Nd:YAG laser second harmonic (2.33 eV) by more than five times. The obtained energetic composites can be reliably initiated by a CW blue laser diode with a wavelength of 450 nm and power of 21 W. The low threshold initiation energy and short irradiation exposure of the PETN-ZnO:Cu composite makes it applicable in laser initiation devices. PETN-ZnO:Cu also can be initiated by an infrared laser diode with a wavelength of 808 nm. The proposed photochemical mechanism of the laser-induced triggering of the explosion reaction in the studied energetic composites was formulated. The results demonstrate the high promise of using nanomaterials based on zinc oxide as a sensitizer of industrial energetic materials to visible laser radiation.