Surface-Enhanced Raman Spectroscopy Facilitates the Detection of Microplastics <1 µm in the Environment.

Micro- and nanoplastics are considered one of the top pollutants that threaten the environment, aquatic life, and mammalian (including human) health. Unfortunately, the development of uncomplicated but reliable analytical methods that are sensitive to individual microplastic particles, with sizes smaller than 1 µm, remains incomplete. Here, we demonstrate the detection and identification of (single) micro- and nanoplastics by using surface-enhanced Raman spectroscopy (SERS) with Klarite substrates. Klarite is an exceptional SERS substrate; it is shaped as a dense grid of inverted pyramidal cavities made of gold. Numerical simulations demonstrate that these cavities (or pits) strongly focus incident light into intense hotspots. We show that Klarite has the potential to facilitate the detection and identification of synthesized and atmospheric/aquatic microplastic (single) particles, with sizes down to 360 nm. We find enhancement factors of up to 2 orders of magnitude for polystyrene analytes. In addition, we detect and identify microplastics with sizes down to 450 nm on Klarite, with samples extracted from ambient, airborne particles. Moreover, we demonstrate Raman mapping as a fast detection technique for submicron microplastic particles. The results show that SERS with Klarite is a facile technique that has the potential to detect and systematically measure nanoplastics in the environment. This research is an important step toward detecting nanoscale plastic particles that may cause toxic effects to mammalian and aquatic life when present in high concentrations.

Heterogeneous Formation of Sulfur Species on Manganese Oxides: Effects of Particle Type and Moisture Condition.

The heterogeneous reaction of SO2 on manganese oxides is poorly understood. By means of in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), this study investigated the reaction kinetics and product fractions on four types of manganese oxides. Due to the positive and negative moisture impacts, 68% RH (relative humidity) becomes the most favorable condition for the uptake of SO2. Mn3O4 shows the greatest uptake capacity of SO2, followed by MnO2 and Mn2O3, with that of MnO being the weakest. Curve-fitting procedures were undertaken to further dissect the product spectra. Increased RH facilitates the physical adsorption of SO2 and generally weakens the oxidation capacity of manganese oxides. The oxidation ability is greatest for MnO, followed by MnO2 and Mn3O4, with that of Mn2O3 being the weakest. Additionally, the particle acidity (pH) was estimated by the ionization equilibrium of sulfurous acid and the relative contributions of S(IV) species. MnO and Mn3O4 become more acidic as RH increases while Mn2O3 and MnO2 are the most acidic at 50% RH, which can be attributed to the different uptake capacities of SO2 and H2O on each sample. Overall, for the heterogeneous reaction of SO2 on manganese oxides, both particle type and moisture condition influence the reaction kinetics and product fractions. This work improves the understanding of the heterogeneous process on atmospheric manganese-rich particles.

Boosting photocatalytic chlorophenols remediation with addition of sulfite and mechanism investigation by in-situ DRIFTs.

Sulfite is recently found to be promising in enhancing photocatalytic pollutants degradation, which is a byproduct from flue gas desulfuration process. Herein, 4-chlorophenol (4-CP) photodegradation was systematically investigated in a sulfite mediated system with g-C3N4 as photocatalyst. The degradation efficacy was improved by about 3 times with addition of 25 mM Na2SO3. The dominant responsible reactive oxygen species for chlorophenols remediation in the presence of sulfite included O2·-, SO3·-, and SO4·- as confirmed by radical quenching experiments and electron spin resonances technology. In-situ DRIFTs results indicated the improved cleavage of CCl and CH bonds with the simultaneous formation of CO and CC bonds when bisulfite was added. Degradation intermediates such as 4-chlorocatechol, hydroquinone, and muconic acid were detected by HPLC-MS. Furthermore, the photodegradation mechanisms of 4-CP were tentatively discussed . Other chlorophenols (phenol, 2-CP, 2,4-DCP, and their mixture) were also efficiently removed in the system, suggesting that sulfite could be universally applied in photocatalytic wastewater purification.

Brown carbon: An underlying driving force for rapid atmospheric sulfate formation and haze event.

The rapid sulfate formation is a crucial factor determining the explosive growth of fine particles and the frequent occurrence of severe haze events in China. Recent field observations also show that brown carbon is one of the most critical components in aerosol particles sampled during haze episodes. To this day, there is limited knowledge that accesses the role of brown carbon in atmospheric chemistry. In fact, these carbonaceous particulate matters, mainly derived from forest fires, biomass burning, and biogenic release, can act as photosensitizers and produce varieties of active intermediates to alter oxidation capacity. Experimental results in this work provide evidence that hydroxyl radical (∙OH) stems from brown carbon proxies fulvic acid /humic acid (FA/HA) upon irradiation, leading to rapid SO2 oxidation on brown carbon particles in the atmosphere. Further correlation analyses for sulfate formation and chromophore properties of 12 model compounds demonstrate that brown carbon particles with higher aromaticity and E2/E3 (the ratio of absorbance at 254 nm to that at 365 nm) would facilitate ∙OH production and SO2 photo-oxidation. Uptake coefficient measurements and sulfate production rate estimation indicate that brown carbon could gain importance in atmospheric SO2 oxidation. A better understanding of SO2 uptake kinetics on brown carbon surfaces favors in defining new regulations to improve air quality and reduce the harmful effects of haze events on resident health and the environment.