Search

Removal of brominated flame retardants (BFRs) is imperative for increasing the recycling rate of hazardous plastic waste. In mechanical recycling, BFRs should be removed without damaging the surrounding polymer matrix, but economically viable processes under mild conditions are still rare. In this study, tetrabromobisphenol A (TBBPA) was solvothermally extracted from a compounded high-impact polystyrene (HIPS, 2500 ppm Br) model sample in an autoclave using mixtures of water, isopropanol (IPA) and NaOH as solvents. Removal of total elemental bromine was analyzed with X-ray fluorescence (XRF), whereas the removal of TBBPA and other plastic additives was evaluated with direct insertion probe mass spectrometry (DIP-MS). IPA/NaOH extraction provided efficient bromine removal, but it also extracted plenty of other plastic additives, including phenolic stabilizers Irganox 1076 and Cyasorb UV-2908. The inclusion of water in the IPA/NaOH mixture shifted the extraction selectivity towards TBBPA, leaving most of the other additives unaffected. Furthermore, H2O/IPA/NaOH was found to be equally effective in removing TBBPA from the samples with bromine concentrations an order of magnitude higher (25,000 ppm). Yet, larger plastic particle size hindered the extraction efficiency. 1H NMR and size exclusion chromatography confirmed that the HIPS matrix was left unaffected after all the studied extractions. Additionally, DIP-MS was found to be a valuable characterization method for assessing the removal and decomposition of various additives from solid plastic samples with minimal sample preparation. Overall, the results presented herein offer a target-selective extraction processes under relatively mild conditions for further advancing the mechanical recycling of plastics.

Silver nanoparticles deposits were produced with liquid flame spray (LFS) on glass and TiO2 substrates to study their optical response and photocatalytic enhancement. The correlation between extinction spectrum of the nanoparticle coating and the LFS process parameters was studied. The spectra consisted of two partly overlapping peaks: one centered in the UV region and the other in the visible light region. The visible light peak redshifted as either the silver mass concentration in the precursor solution or the precursor solution feed rate was increased, which also correlated with growing primary particle size. However, simultaneous correlation with photocatalytic activity of the decorated TiO2 surfaces was not observed, which was attributed to particle sintering on the surface. Instead, the photocatalytic activity was seen to change as the surface coverage of silver nanoparticles was varied. When the surface coverage was raised from ∼10 % to roughly 30 %, the activity, and then decreased as the loading was further raised. The increase was assumed to originate from plasmonic activation, and the decrease was attributed to the excessive amount of silver either blocking reactive area of the TiO2 or absorbing/scattering too much of the incoming light, which hindered the photocatalytic activity.

Multicompound inverse opal (IO) structures from titanium dioxide‑silicon dioxide (TiO2-SiO2, TSIO), titanium dioxide‑zirconium dioxide (TiO2-ZrO2, TZIO), and titanium dioxide (TIO) structures were synthesized using the self-convective method. Gold nanoparticles (AuNPs) were deposited into synthesized multicompound IO structures by simply immersing samples in solution with AuNPs. Our results show that highly ordered IO structures were fabricated. The photocatalytic activity of multicompound IO structures without and with AuNPs was examined under UVA and visible light excitation using an in-house built gas-phase reactor. The highest photocatalytic activity under UVA illumination was observed for TSIO with AuNPs that increased the activity by 206% and 125% compared to the reference TIO structure without and with AuNPs, respectively. Additionally, photocatalytic activity was also observed under visible light excitation with AuNP deposited TZIO and TIO structures.

Multicompound TiO2/SiO2 nanoparticles with a diameter of 50–70 nm were generated using a liquid flame spray (LFS) nanoparticle deposition in a single flame. Here, we study the photocatalytic activity of deposited multicompound nanoparticles in gas-phase via oxidation of acetylene into carbon dioxide that gives new insight about the multicompound nanoparticle morphology. A small addition of SiO2 content of 0.5%, 1.0% and 3.0% significantly suppressed the photocatalytic activity by 33%, 44% and 70%, respectively, whereas 5.0% SiO2 addition completely removed the activity. This may be due to a formation of a thin passivating SiO2 layer on top of the of the TiO2 nanostructures during the LFS nanoparticle deposition. Surface wetting results support this hypothesis with a significant increase in water contact angle as the SiO2 content is increased.