Severe coral bleaching of Siderastrea stellata at the only atoll in the South Atlantic driven by sequential Marine Heatwaves

Threatened by global warming and extreme climatic events, such as El Niño Southern Oscillation (ENSO) and Marine Heatwaves (MHW), coral reefs worldwide faced the worst bleaching and mortality event between 2014 and 2017, induced by the 2015/2016 ENSO. We evaluated the impacts of ENSO and MHW episodes on bleaching and mortality frequencies of Siderastrea stellata at Rocas Atoll, Southwestern Atlantic, using visual censuses conducted in 2016, 2017 and 2019. Bleaching rate varied significantly along the sampling period (11.71% in 2016, 1.52% in 2017, and 88% in 2019), but mortality was always less than 4%. Bleaching events in Atlantic reefs have been constantly associated with ENSO, until these recent events of the last two years. We suggest that MHW were probably the primary driver of the observed bleaching, especially in 2019, when much higher bleaching rates were observed than in ENSO periods. Although Southwestern Atlantic massive corals are considered more resistant to thermal stress than reefs corals worldwide, the strong events registered since 2019 highlight the need for continuous monitoring to better understand coral bleaching dynamics and improve predictions on the effects of global change in the region.

Ag/Ag2O as a Co-Catalyst in TiO2 Photocatalysis: Effect of the Co-Catalyst/Photocatalyst Mass Ratio

Mixtures and composites of Ag/Ag2O and TiO2 (P25) with varying mass ratios of Ag/Ag2O were prepared, employing two methods. Mechanical mixtures (TM) were obtained by the sonication of a suspension containing TiO2 and Ag/Ag2O. Composites (TC) were prepared by a precipitation method employing TiO2 and AgNO3. Powder X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) confirmed the presence of Ag(0) and Ag2O. The activity of the materials was determined employing methylene blue (MB) as the probe compound. Bleaching of MB was observed in the presence of all materials. The bleaching rate was found to increase with increasing amounts of TiO2 under UV/vis light. In contrast, the MB bleaching rate decreased with increasing TiO2 content upon visible light illumination. XRD and XPS data indicate that Ag2O acts as an electron acceptor in the light-induced reaction of MB and is transformed by reduction of Ag+, yielding Ag(0). As a second light-induced reaction, the evolution of molecular hydrogen from aqueous methanol was investigated. Significant H2 evolution rates were only determined in the presence of materials containing more than 50 mass% of TiO2. The experimental results suggest that Ag/Ag2O is not stable under the experimental conditions. Therefore, to address Ag/Ag2O as a (photo)catalytically active material does not seem appropriate.

Synthesis and Photochromic Properties of Conjugated Naphthopyran Derivatives

Three novel types of naphthopyran derivatives containing alkoxyl and phenyl moieties, 13-butyl −6,11-dimethyl-3,3-diphenyl-3,13-dihydrobenzo[h]indeno[2,1-f]chromen-13-ol (NP), 13-butyl-3,3-bis(6-methoxy-[1,1′-biphenyl]-3-yl)-6,6-dimethyl-3,13-dihydrobenzo[h] indeno[2,1-f]chromen-13-ol (NP1) and 13-butyl-3,3-bis(6-methoxy-4′-naphthalenyl-[1,1′-biphenyl]-3-yl)-6,11-dimenthyl-3,13-dihydrobenz[h]indeno[2,1-f]chromen-13-ol (NP2), were synthesised and characterised. Measurements indicated that they possessed an excellent photochromic response, a rapid thermal bleaching rate and good fatigue resistance. Meanwhile, the UV maximum absorption wavelengths of NP1 (562 nm) and NP2 (597 nm) appeared bathochromically shifted compared with NP (536 nm). The bleaching rate of NP1 was found to be approximately twice that of NP. The results indicated that the UV maximum absorption wavelength and bleaching rate increase with increasing length of the phenyl side chain moieties. In PMMA film, the compounds showed almost the same photochromic properties in the solid state as in dichloromethane solution. The UV absorbance with high-contrast switching in solid film could be beneficial for practical applications.

Kinetics and mechanism of destruction of cobalt phthalocyanine derivatives in aqueous solutions

The kinetics of the oxidative destruction of cobalt phthalocyanine derivatives in aqueous solutions has been investigated in the concentration interval 10−4–10−5 M as a function of the concentration of alkali and the partial pressure of oxygen in the system. The kinetic equation for the initial solution bleaching rate is obtained. A mechanism of cobalt phthalocyanine destruction involving an intermediate Co (II) → Co (III) oxidation step is suggested.