Metal-Organic Nanotube (MONT) as a Photocatalyst for the Visible-Light-Driven Selective Dye Degradation

Water pollution is one of the critical challenges of the 21st century, and dyes are a major contributor to it worldwide. Among the several techniques adopted to address this issue, the advanced oxidation process (AOP) is considered an efficient and sustainable technique because it uses sunlight as an energy source. In this study, a new semiconducting metal-organic nanotube (MONT) (HNBGU-1) was designed by carefully combining a rigid organic linker and a flexible organic linker. This MOF could selectively degrade high concentrations (100 ppm) of Congo red (CR) and crystal violet (CV) among the five different organic dyes tested in water via AOP under sunlight. In-depth optical studies revealed that, at high concentrations, the formation of strong aggregates of certain dye molecules in water is the key factor behind this selectivity. This work established that (i) MONTs can be designed by adopting a bottom-up strategy using a rigid and a flexible syn-oriented linker and (ii) the important roles of the aggregation-disaggregation at high concentration, the structure of dye molecules, and the used solvents in a photocatalytic dye degradation study. Further, this study revealed that pH plays an important role in enhancing the rate of photocatalytic degradation of CR dye.