Optofluidic Photonic Crystal Fiber Microreactors for In Situ Studies of Carbon Nanodot-Driven Photoreduction

Abstract

Performing quantitative in situ spectroscopic analysis on minuscule sample volumes is a common difficulty in photochemistry. To address this challenge, we use a hollow-core photonic crystal fiber (HC-PCF) that guides light at the center of a microscale liquid channel and acts as an optofluidic microreactor with a reaction volume of less than 35 nL. The system was used to demonstrate in situ optical detection of photoreduction processes that are key components of many photocatalytic reaction schemes. The photoreduction of viologens (XV 2+ ) to the radical XV •+ in a homogeneous mixture with carbon nanodot (CND) light absorbers is studied for a range of different carbon dots and viologens. Time-resolved absorption spectra, measured over several UV irradiation cycles, are interpreted with a quantitative kinetic model to determine photoreduction and photobleaching rate constants. The powerful combination of time-resolved, low-volume absorption spectroscopy and kinetic modeling highlights the potential of optofluidic microreactors as a highly sensitive, quantitative, and rapid screening platform for novel photocatalysts and flow chemistry in general.

In situ Detection of Cobaloxime Intermediates During Photocatalysis Using Hollow‐Core Photonic Crystal Fiber Microreactors

“…Cobaloximes were synthesized and characterized via protocols outlined in previous work, [28, 46] and [Ru(bpy) 3 ]Cl 2 was purchased from a commercial supplier. These were spectroscopically characterized within kagomé‐style HC‐PCFs with two excitation sources ( λ ex =365 nm, 450 nm, see Supporting Information, Figure S1) in the same manner as reported in previous work [37] . Kagomé‐style HC‐PCFs (Figure 2a), a PCF type first used by Benabid et al., [47] were employed as their guidance mechanism permits broadband transmission extending from the ultraviolet (UV) to the near‐infrared in water and hence, are the preferred choice of HC‐PCF for broadband UV/Vis spectral measurements [36] .…”

Stern–Volmer analysis of photocatalyst fluorescence quenching within hollow-core photonic crystal fibre microreactors

“…, five orders of magnitude less than in conventional sample cells) and well-defined light-matter interactions: all key for the quantitative analysis of photochemistry. 14–21 As such, they provide an ideal way to gain insight into the energy dispersal mechanisms of PCs under reaction conditions.…”

“…12,13 By infiltrating chemicals and monitoring their spectra (fluorescence, absorption, infrared, and/ or Raman), reaction dynamics and steady-state concentrations can be probed in situ. [14][15][16][17][18][19][20][21] Major advantages of these new 'optofluidic microreactors' over conventional sample cells are the enhanced detection sensitivity (from meter-scale optical-paths), tiny sample volumes of a few nL per cm fibre length (i.e., five orders of magnitude less than in conventional sample cells) and well-defined light-matter interactions: all key for the quantitative analysis of photochemistry. [14][15][16][17][18][19][20][21] As such, they provide an ideal way to gain insight into the energy dispersal mechanisms of PCs under reaction conditions.…”

Photothermal Waveguide-Directed Microreactor for Enhanced Copper Ion Detection from Quantum Dots

“…Miniaturized optofluidic platforms offer potentials for more functional and more compact devices. , The integrated systems exhibit superior characteristics such as low reagent consumption, handy operation process, as well as improvement of heat and mass transfer. − Due to requirements of inexpensive instruments and low reagent consumption, Cu 2+ detection still needs to be improved in the micro level. A wide variety of optofluidic devices, serving as microreactors, can accelerate reaction efficiency and enable safe handling of even hazardous or highly exothermic reactions. , Due to a relatively large ratio of surface area to volume, the microreactor provides an ideal environment for heterogeneous processes, like sensing, , polymerization, , and nanoparticle synthesis …”

“…A wide variety of optofluidic devices, serving as microreactors, can accelerate reaction efficiency and enable safe handling of even hazardous or highly exothermic reactions. 16,17 Due to a relatively large ratio of surface area to volume, the microreactor provides an ideal environment for heterogeneous processes, like sensing, 18,19 polymerization, 20,21 and nanoparticle synthesis. 22 As one of the primary forms of lab on a chip, droplet-based microreactors are important for the miniaturization of synthesis/analysis systems.…”