Heterogeneous singlet oxygen generation: in-operando visible light EPR spectroscopy

Area of Science:

• Photochemistry
• Materials Science
• Environmental Chemistry

Background:

• Photosensitizers immobilized on mesoporous materials enable singlet oxygen (¹O₂) production for synthetic and environmental applications.
• Flow photochemistry and continuous-flow microreactors facilitate ¹O₂-based processes for organic pollutant degradation.
• Covalently attaching photosensitizers to supports allows for their separation from effluents, minimizing environmental impact.

Purpose of the Study:

• To evaluate the singlet oxygen (¹O₂) generation of Rose Bengal (RB) in both homogeneous and heterogeneous systems.
• To compare the efficiency of free RB versus RB immobilized on mesoporous silica nanoparticles (MSNs).
• To assess the potential for using functionalized nanoparticles in flow photochemistry for pollutant degradation.

Main Methods:

• Conjugation of Rose Bengal (RB) with mesoporous SiO₂ nanoparticles (MSNs) to create MSN-RB.
• In-operando evaluation of ¹O₂ generation using electron paramagnetic resonance (EPR) spectroscopy.
• Employing TEMP spin trap to detect ¹O₂ via TEMPO formation and DMPO to exclude other reactive oxygen species (ROS).

Main Results:

• Successful conjugation of RB with MSNs (MSN-RB).
• EPR spectroscopy confirmed ¹O₂ generation from both RB and MSN-RB under visible light.
• Immobilization of RB within MSNs significantly enhanced in situ ¹O₂ generation compared to free RB.

Conclusions:

• Mesoporous silica nanoparticles are effective supports for immobilizing photosensitizers like Rose Bengal.
• Immobilized RB on MSNs demonstrates superior singlet oxygen generation efficiency.
• This approach holds promise for developing efficient and environmentally friendly photosensitized processes in flow chemistry.