It is well known that C60 (buckminsterfullerene) and some of its functionalized derivatives can photochemically produce reactive oxygen species such as singlet oxygen and superoxide. This conversion of light energy to oxidizing power has been extensively studied and applied for photocatalytic organic synthesis and photodynamic therapy. Although fullerene-based photocatalysis is also a promising sustainable approach for water treatment, such aqueous phase applications have been limited by the difficulty to make C60 accessible to target pollutants in water, since pristine C60 is virtually nonwettable. Even if C60 is rendered water soluble (for example, by functional derivatization), it is challenging to prevent C60 release to product water and recycle it for prolonged use. The overarching objective of the proposed research is to overcome the above limitations and develop environmentally benign C60-based photocatalysts for water and wastewater treatment and reuse. They plan to achieve this goal by immobilizing photoactive form of C60 onto easily recoverable support materials via covalent bonding. Specific research objectives include: 1) developing new and enhancing existing methods to immobilize C60 and selected functionalized C60 onto support material surfaces; 2) quantifying their photochemical reactivity, mainly related to 1O2 production, as a function of support substrate and water chemistry; and 3) evaluating these novel photosensitizers for degradation of selected organic contaminants and inactivation of a representative microorganism.
They hypothesize that: 1) chemical attachment of C60 and C60 derivatives to polymeric surface is achievable without any significant loss in photochemical activity for 1O2 production which originates from C60s cage structure; 2) C60 based catalyst will exhibit minimal reduction of photocatalytic activity after prolonged use due to the chemical stability of C60, and 3) immobilization via covalent bonding will minimize catalyst release to environment and enhance recycling. Validity of these hypotheses forms a foundation for developing an innovative C60-based photocatalysis process.
This is a two-institution collaboration that brings together expertise in photoactive nanomaterial synthesis, fundamental photochemistry, and photocatalyst application for oxidative degradation of organic contaminants and inactivation of microorganisms. They will initially employ selected homogenized and immobilized forms of tetrakis- and hexakis-C60 adducts with carboxylic, hydroxyl, and amine moieties. Specific tasks include: 1) syntheses of water-soluble functionalized C60, C60(or derivatized C60)-coated beads, and C60 (or derivatized C60)-incorporated polymer; 2) characterization of photochemical properties of these materials with focus on kinetics and mechanisms of 1O2 production using wet-chemical method, electron spin resonance (ESR) trapping technique, and laser flash photolysis (LFP); and 3) kinetics and mechanistic studies on photocatalytic oxidation of selected organic pollutants and inactivation of representative microorganisms (bacteria and virus). This is one of the first attempts to apply fullerene-based photocatalysis in environmental engineering. They are motivated by the unique properties of C60, including 1) exceptional photocatalytic activity, 2) ability to use visible light for photoexcitation, and 3) chemical stability. Immobilization of C60 is conducive to prevention of secondary contamination and facilitating recycle and reuse, which will encourage further research on applications of fullerene-based photocatalysis. For example, surface immobilized C60 could be applied for antibacterial surface synthesis or air purification. Fundamental understanding gained on how the photocatalytic properties of fullerenes change upon attachment and bactericidal mechanisms will also be important to inform ecotoxicological risk assessment.
Ensuring access to inexpensive and clean sources of water is one of the greatest global challenges of this century. Nanotechnology offers opportunities to leapfrog over traditional infrastructure-intensive technologies to develop more sustainable approaches for water management. This project has a great potential to develop safe, easy to implement, and reusable C60-based photocatalysts that require only sunlight for water remediation and reuse. Results will be broadly disseminated in publications and integrated into undergraduate and graduate courses. They will also train students in an emerging area where qualified professionals are in short supply. These students will gain interdisciplinary and collaborative experience with applications of nanochemistry, photochemistry and environmental engineering.
