Quantum and experimental investigation of the application of Crassostrea gasar (mangrove oyster) shell-based CaO nanoparticles as adsorbent and photocatalyst for the removal of procaine penicillin from aqueous solution.

The present study was designed to synthesize and characterize calcium oxide nanoparticles (using mangrove oyster shell as a precursor) and apply the synthesized nanoparticles as a photocatalyst to degrade procaine penicillin in an aqueous solution. The photocatalyst exhibited an average band gap of 4.42 eV, showed a maximum wavelength of absorbance in the UV region (i.e., 280 nm), and is a microporous nanoparticle with a particle diameter of 50 nm. The photocatalyzed degradation of the drug was conducted under natural sunlight, and the influence of parameters such as the period of contact, catalyst load, pH, initial drug concentration, and ionic strength was investigated concerning the degradation profile. The results obtained from response surface analysis indicated that an optimum degradation efficiency of about 93% can be obtained at a concentration, pH, and catalyst dosage of 0.125 M, 2, and 0.20 g respectively, at 0.902 desirabilities. The Langmuir-Hinshelwood, modified Freundlich, parabolic diffusion, pseudo-first-/second-order, and zero-, first-, and second-order kinetic parameters were tested to ascertain the best model that best described the experimental data. Consequently, the Langmuir-Hinshelwood, modified Freundlich, and pseudo-second-order models were accepted based on the minimum error and higher R2 values. Based on the Langmuir-Hinshelwood rate constants for adsorption and photodegradation as well as the evaluated valence bond potential, the degradation of the drug first proceeded through the mechanism of adsorption and followed by the oxidation of the drug by superoxide (generated from the interaction of electrons that generated by through the absorption of UV radiation). The quantum chemical calculation gave evidence that pointed towards the establishment of strong agreement with experimental data and also showed that the carboxyl functional group in the drug is the target site for adsorption and subsequent degradation.

Stromatolites on the rise in peat-bound karstic wetlands.

Stromatolites are the oldest evidence for life on Earth, but modern living examples are rare and predominantly occur in shallow marine or (hyper-) saline lacustrine environments, subject to exotic physico-chemical conditions. Here we report the discovery of living freshwater stromatolites in cool-temperate karstic wetlands in the Giblin River catchment of the UNESCO-listed Tasmanian Wilderness World Heritage Area, Australia. These stromatolites colonize the slopes of karstic spring mounds which create mildly alkaline (pH of 7.0-7.9) enclaves within an otherwise uniformly acidic organosol terrain. The freshwater emerging from the springs is Ca-HCO3 dominated and water temperatures show no evidence of geothermal heating. Using 16 S rRNA gene clone library analysis we revealed that the bacterial community is dominated by Cyanobacteria, Alphaproteobacteria and an unusually high proportion of Chloroflexi, followed by Armatimonadetes and Planctomycetes, and is therefore unique compared to other living examples. Macroinvertebrates are sparse and snails in particular are disadvantaged by the development of debilitating accumulations of carbonate on their shells, corroborating evidence that stromatolites flourish under conditions where predation by metazoans is suppressed. Our findings constitute a novel habitat for stromatolites because cool-temperate freshwater wetlands are not a conventional stromatolite niche, suggesting that stromatolites may be more common than previously thought.