Enhancing the rates of chemical reactions through the photothermal heating of nanoparticles
Open Access
- Author:
- Ginder, Nathaniel
- Graduate Program:
- Chemistry
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- May 02, 2023
- Committee Members:
- Benjamin Lear, Chair & Dissertation Advisor
Elizabeth Elacqua, Major Field Member
Lauren Zarzar, Major Field Member
Adri van Duin, Outside Unit & Field Member
Philip Bevilacqua, Program Head/Chair - Keywords:
- photothermal
nanoparticle
gold nanoparticle
carbon black
AuNP
heat
polyurethane
urethane
polycaprolactone
laser
light to heat
light
extreme temperature
kinetics
dynamics
reaction kinetics
rate enhancement - Abstract:
- Nanoparticles are very efficient at absorbing light and converting that energy into heat. They reach extreme temperatures in excess of 700 K near the surface of the nanoparticle. This heating method is aptly called photothermal heating, and it’s highly desirable as a nanoscale heat source for driving physical and chemical transformations. Photothermal heating has successfully been used for photothermal cancer therapy, solar energy harvesting, solar distillation, recycling polymers, drug delivery, and chemical synthesis. The really interesting scientific questions about photothermal heating concern the behavior of chemical reactions under extreme temperatures (>700 K), which often is well beyond the boiling point of the reaction mixture. In this work we start by investigating potential factors affecting photothermal heating, which include viscosity and the type of irradiation (pulsed vs CW). We determine the photothermal reaction rate enhancement of three analogous urethane reactions with increasing starting viscosity using two types of light sources. Surprisingly, the results didn’t indicate a dependence on either viscosity or the type of light source. Next, we consider the photothermally driving the unblocking of blocked isocyanate, which traditionally requires bulk heating to volatilize the blocking group. We show photothermal heating effectively unblocks a blocked isocyanate in seconds, which takes hours in an oven at 160℃ to achieve the same degree of unblocking. Even an oven temperature of 400℃ could not match the rate of the photothermal reaction. Because photothermal heating is hottest at the nanoparticle surface, directly tethering a catalyst to the surface of a nanoparticle should result in dramatic reaction rate increases. This hypothesis is tested using a polycaprolactone ring opening polymerization on the surface of a carbon black nanoparticle with a tin catalyst directly attached to the surface. We found that the photothermal polymerization of polycaprolactone is much faster than the the bulk heated polymerization, even at similar bulk temperatures.