Enhanced Photocatalytic Degradation of Environmental Pollutants Using a Triphenylamine-Based Polymer: Synthesis, Characterization, and Mechanistic Insights.

Abstract

Conjugated porous organic polymers have sparked growing research attention as photocatalysts owing to their high surface area, tunable pores, and capacity to collect and transfer light energy via their delocalized backbone. However, the synthesis methods for preparing these polymers require difficult experimental setups, such as high polymerization temperature, inert atmosphere, and use of transition metal catalysts. In the present work, a triphenylamine-based conjugated porous polymer (TPA-BPA) has been synthesized employing tris(4-aminophenyl)amine (TPA) and biphenyldicarboxaldehyde (BPA) as precursors via a one-pot Schiff base reaction in ambient conditions in the absence of the metal catalyst. The synthesized TPA-BPA polymer has been characterized using Fourier transform infrared spectroscopy, ¹³C cross-polarization magic angle spinning nuclear magnetic resonance, Brunauer-Emmett-Teller (BET), thermogravimetric analysis, field emission scanning electron microscopy, high-resolution transmission electron microscopy, valence band X-ray photoelectron spectroscopy, X-ray photoelectron spectroscopy, cyclic voltammetry, powder X-ray diffraction, electron paramagnetic resonance (EPR), and diffuse reflectance spectroscopy (DRS) techniques. The DRS analysis revealed that TPA-BPA has an optical band gap of 2.1 eV, demonstrating its semiconductive nature. The EPR study has shown that the synthesized polymer exhibits an intense radical signal at g = 2.00, confirming free radical generation upon photoexcitation and facilitating the breakdown of organic contaminants by photocatalysis. TPA-BPA possesses an exceptional porous structure with a surface area of 36 m²/g, as confirmed by BET studies, and high thermal stability up to 420 °C. It has been confirmed by photocatalytic studies that TPA-BPA shows effective degradation of methyl orange (92%), Congo red (91.5%), tobramycin (96%), and hydroquinone (85%) under visible light irradiation in 60 min. Owing to these observations, TPA-BPA can be an excellent candidate as a photocatalyst for environmental remediation. These findings pave the way for large-scale manufacturing of metal-free conjugated porous polymers as photocatalysts with variable photoelectrical characteristics.