Dissertation Defence: Development of Carbon Nitride (CNx) Systems with Improved Surface Properties for Enhanced Energy and Environmental Applications

Peter Osei Ohemeng, supervised by Dr. Robert Godin, will defend their dissertation titled “Development of Carbon Nitride (CNx) Systems with Improved Surface Properties for Enhanced Energy and Environmental Applications” in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Chemistry.

An abstract for Peter Osei Ohemeng’s thesis is included below.

Examinations are open to all members of the campus community as well as the general public. Registration is not required for in person exams.

---

ABSTRACT

The use of carbon nitride (CNx) as a benchmark organic photocatalyst for various solar energy conversion reactions has recently garnered significant attention within the catalysis community. This interest is driven by the facile synthesis of CNx coupled with its visible light photocatalytic performance and good stability. However, fully exploring the potential of this class of material in photocatalytic systems remains challenging. This is primarily due to the poor dispersibility of CNx particles, limited detailed information on its surface and interfacial properties, and the lack of comprehensive structure-property-activity relationships. This thesis first reviews the surface properties and reactivity of CNx and then presents new experimental findings on optimizing its synthesis and interfacial properties for enhanced photocatalytic applications. By using a copolymerization approach involving pristine melamine and its methylated form, modified CNx samples with high water dispersibility leading to improvement in photocatalytic activity compared to pristine CNx were made. The improved water dispersibility is traced to the inclusion of methylated melamine (Melmeth) in the synthesis of the modified CNx materials. The best performing modified sample showed three times improvement in sacrificial H2 photoproduction and rhodamine B (RhB) dye degradation. Given the activity enhancement associated with the modified samples, a series of these samples with varying preparation conditions were made. This was done to unravel the influence of preparation conditions on the intrinsic and extrinsic properties of the synthesized samples. The photoactivity as well as the structural and opto-electronic information of the materials were obtained to create a comprehensive dataset analyzed with machine learning (ML) models aimed at identifying underlying relationships. The findings from both the ML models and visual graphical assessments revealed that structure-activity-relationships in CNx is challenging to parse. However, post-synthetic measured parameters show a stronger correlation with activity compared to the synthesis conditions.Moreover, motivated by the adverse effects derived from human exposure to arsenic (As) contamination, the optimized sample was studied for As remediation. Combined with the photoactive nature of CNx, the introduction of positive charges on its surface through the incorporation of methyl groups from Melmeth enhances its potential as a promising As-remediating agent. The results from this study point to the fact that CNx is an efficient As-remediating agent as it serves as both adsorbent and photocatalyst. It’s revealed that the binding of As species onto CNx is likely driven by electrostatic attraction or hydrogen bonding depending on the polarity of the material’s surface groups. Overall, the modified CNx sample, labelled as CNx50, demonstrated high photocatalytic conversion of As(III) to As(V) and exhibited a greater affinity for As(V) species compared to the benchmark CNx prepared from melamine, CNx0. This study offers valuable insights into the potential of CNx as a promising material for clean energy production (exemplified by H2 photoproduction) and environmental remediation (exemplified by As removal).