No abstract

We report here a new phenomenon of dynamic enhancement of chemical reactions by nanomaterials under hard X-ray irradiation. The nanomaterials were gold and platinum nanoparticles, and the chemical reaction employed was the hydroxylation of coumarin carboxylic acid. The reaction yield was enhanced 2000 times over that predicted on the basis of the absorption of X-rays only by the nanoparticles, and the enhancement was found for the first time to depend on the X-ray dose rate. The maximum turnover frequency was measured at 1 × 10(-4) s(-1) Gy(-1). We call this process chemical enhancement, which is defined as the increased yield of a chemical reaction due to the chemical properties of the added materials. The chemical enhancement described here is believed to be ubiquitous and may significantly alter the outcome of chemical reactions under X-ray irradiation with the assistance of nanomaterials.

No abstract

A theorem is established to show that nanoscale energy deposition in water by X-rays can be greatly enhanced via the geometry of nanostructures. The calculated results show that enhancement over background water can reach over 60 times for a single nanoshell made of gold. Other geometries and nanostructures are investigated, and it is found that a shell of gold nanoparticles can generate similar enhancement. The concepts of composition, matrix, and satellite effects are established and studied, all of which can further increase the enhancement of the effect of X-rays.

We for the first time used highly water soluble silica-covered gold nanoparticles (AuNP@SiO 2 ) in water to successfully isolate average physical enhancement from other enhancements such as nanoscale physical enhancement, chemical enhancement and antienhancement, and obtained the highest enhancement slope of 1.03 per weight percent (wp -1 ) and the highest experimental enhancement factor of 4.5 fold (ߝ ௫௧ =4.5; and ߝ ௫௧ = 0 for no enhancement) at 7.5 wp of gold in water. The slope and ߝ ௫௧ agree with the theoretically predicted values obtained from simulation of enhancement of X-rays by gold nanoparticles in water, and the experimental enhancement coefficient (ߛ = ߝ ௫௧ /ߝ ௧ , 0 ≤ ߛ ≤ 1) is approximately 0.90. The enhancement dependency on X-ray energy, silica layer thickness and sample thickness are studied experimentally and theoretically. The results presented here elucidate the mechanism of the average physical enhancement by nanomaterials under X-ray irradiation.KEYWORDS X-ray nanochemistry, enhancement of X-ray effect, nanomaterials, nanoscale energy deposition, physical enhancement.