Rational design of graphitic carbon nitride photocatalysts for efficient visible-light-driven water treatment

Almalki, Mshaal 2026. Rational design of graphitic carbon nitride photocatalysts for efficient visible-light-driven water treatment. PhD Thesis, Cardiff University. Item availability restricted.

	PDF - Accepted Post-Print Version Restricted to Repository staff only until 13 July 2027 due to copyright restrictions. Available under License Creative Commons Attribution Non-commercial No Derivatives. Download (19MB)
	PDF (Cardiff University Electronic Publication Form) - Supplemental Material Restricted to Repository staff only Download (221kB)

Abstract

Photocatalysis offers a sustainable approach for removing organic contaminants from water without additional chemical oxidants or energy-intensive processes. However, metal-free photocatalysts such as graphitic carbon nitride (GCN) remain limited by low surface area, sub-optimal charge separation, and intrinsic structural disorder. This thesis establishes quantitative structure–property–performance relationships for metal-assisted and metal-free GCN modifications through systematic and comparative investigation of metal deposition, chemical exfoliation, thermal exfoliation, and combined post-synthetic treatments under identical experimental conditions, providing design principles linking synthesis methodology to photocatalytic performance. The first research chapter investigates gold-functionalised GCN photocatalysts synthesised using four deposition methods. Mild reduction (WIW and Im) produced highly dispersed Au⁰ with a bimodal size distribution (~2 nm surface nanoparticles and <0.5 nm interlayer-confined species), resulting in a four fold increase in activity (k = 2.05 × 10⁻² min⁻¹) relative to bare GCN (k = 0.5 × 10⁻² min⁻¹). WIW was selected as the preferred preparation method due to its simplicity, as the overnight stirring step employed in Im provided no measurable improvement in performance. Operating parameters can significantly influence performance, and HCl post-treatment regenerated deactivated catalysts and activated bare GCN, prompting exploration of metal-free strategies. The second research chapter optimises intrinsic GCN properties through chemical and thermal exfoliation. Chemical treatment at 0.5 M HCl achieved a 2.75-fold enhancement (k = 1.24 × 10−2 min−1) through protonation and defect engineering, while thermal exfoliation at 620°C under flowing air yielded a 4.5-fold enhancement (k = 2.02 × 10−2 min−1) via improved crystallinity. Chemical treatment enables rapid initial pollutant removal through superoxide radical generation, while thermal treatment achieves more complete MO removal with sustained activity, complementary mechanisms that motivated the combined strategy investigated subsequently. The final research chapter integrates both approaches sequentially. The thermal to chemical route produces uniform flat nanosheets within a narrow optimisation window (620°C and 0.5 M HCl); deviation from these conditions yields curled, porous, or degraded structures. The optimised 620CNs 0.5 catalyst achieved a seven-fold activity enhancement (k = 3.50 × 10−2 min−1) with near-complete methyl orange mineralisation (98.8% COD removal) within 120 min. Activity across structurally diverse pollutants, including colourless phenol and Bisphenol A, confirmed by COD analysis, provides robust evidence of genuine broad-spectrum photocatalytic mineralisation capability, with coloured dye results (Rhodamine B) interpreted in light of potential photosensitisation contributions.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Schools > Chemistry
Funders:	Saudi Arabia University
Date of First Compliant Deposit:	13 July 2026
Last Modified:	13 Jul 2026 11:46
URI:	https://orca.cardiff.ac.uk/id/eprint/188152

Actions (repository staff only)

Edit Item