Rhodamine B in dissolved and nano-bound forms: Indicators for light-based advanced oxidation processes.

Area of Science:

• Environmental Chemistry
• Photocatalysis
• Advanced Oxidation Processes (AOPs)

Background:

• Rhodamine B (RhB) is a fluorescent dye utilized in environmental and biotechnological flux studies.
• Evaluating RhB's degradation efficiency requires understanding its behavior in different forms (free vs. nano-bound) under various environmental processes.

Purpose of the Study:

• To assess the degradation efficiency of free and nano-bound RhB using direct UV photolysis, UV/H2O2 AOP, and solar light-induced photocatalysis.
• To compare the performance of titanium dioxide and bismuth photocatalysts.
• To determine the suitability of free and nano-bound RhB as indicators in environmental remediation.

Main Methods:

• Degradation experiments were conducted using a collimated beam apparatus with a medium-pressure mercury vapor lamp for UV treatments.
• Solar light-induced photocatalysis was performed in a solar simulator utilizing titanium dioxide and bismuth catalysts.
• Adsorption of RhB onto catalysts was analyzed to understand degradation mechanisms.

Main Results:

• Direct UV photolysis and solar light showed negligible RhB degradation.
• UV/H2O2 and photocatalysis/photosensitization demonstrated nearly linear RhB degradation in the presence of catalysts.
• Free RhB adsorbed onto the bismuth catalyst, while nano-bound RhB and both forms on titanium dioxide did not, impacting degradation rates.

Conclusions:

• Close proximity between catalyst active sites and the target molecule significantly enhances degradation.
• Nano-bound RhB is a more promising indicator for AOPs due to its non-adsorption and potential for easy separation.
• The soluble form of RhB may not be optimal for use as an environmental indicator.