Photo-reforming and degradation of waste plastics under UV and visible light for H2 production using nanocomposite photocatalysts

Plastics are recalcitrant and difficult to be removed from a natural environment. As a result, plastics have accumulated in the environment and food chain, causing adverse effects on living organisms and human health. Photo-reforming, a process of generating H2 from an organic substrate in aqueous solutions using catalysts, is promising to address the challenge of treating plastics and recovering energy from these large-volume waste products. TiO2 nanoparticles doped with Au and Pt and ZnO doped with Pt were studied to enhance the light utilization efficiency and catalytic activity. The preliminary photodegradation screening experiments revealed that 5 % Au-doped TiO2 (Au/TiO2) was the most photoactive catalyst among the developed catalysts. However, Pt/TiO2, Au/TiO2, and Pt/ZnO performed differently in H2 evolution experiments. The change of the Au/TiO2 properties was characterized using a transmission electron microscope (TEM), powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FTIR) spectroscopy. Computational simulation using Quantum ESPRESSO was performed to predict the narrowed bandgap of TiO2 when the surface of nano-TiO2 particles was modified with nano-Au particles. Polyethylene terephthalate (PET) was selected as representative plastic for photo-reforming, which was demonstrated effective for degrading and converting common plastic wastes to H2. The effectiveness of pre-treatment using different KOH concentrations and temperatures was studied to achieve efficient PET hydrolysis. H2 production under the different pretreatment conditions showed that higher temperature and KOH concentration increased hydrogen yield. Further, Pt/TiO2 performed better than Au/TiO2 in H2 production while Pt/ZnO was the lowest hydrogen producer. Microscopic examination and FTIR analysis were conducted to identify the morphology and functionality change during the photo-reforming of PET. The variation of carbonyl index, vinyl index, and band area ratios respective to the C-H band area confirmed the plastic degradability. This study demonstrates that photo-reforming is an attractive, low-cost, easy-to-use clean H2 technology, which improves environmental sustainability by reducing greenhouse gas emissions and removing plastic waste using solar energy.