A multivariate study of the rGO/g-C3N4 composite for the photocatalytic degradation of bisphenol A: Characterization, degradation kinetics, products identification, and ecotoxicity

Bisphenol A (BPA), a common polymer plasticizer, is a contaminant of emerging concern with endocrine disrupting activity. Among existing abatement methods, photodegradation demands easily fabricated, inexpensive, high photoactive catalysts, leading to non-toxic byproducts after degradation. It is proposed an optimized (surface response methodology) catalyst for those goals: graphitic carbon nitride impregnated with reduced graphene oxide. The method was based on the sonication of preformed particles followed by reduction with hydrazine in reflux, a methodology that allows for better reproducibility and larger specific surface areas. The catalyst removed 90% of BPA (100 mL, 100 µg L− 1) in 90 min under UV irradiation (365 nm, 26 W) compared to 50% with pure g-C3N4 (pseudo-first-order kinetics). Tests with radicals scavengers revealed that superoxide radical was the main oxidation agent in the system. By mass spectrometry, two major degradation products were identified, which were less ecotoxic than BPA towards a series of organisms, according to in silico estimations performed with the ECOSAR 2.0 software.

Recycled calcium carbonate is an efficient oxidation agent under deep upper mantle conditions

Observations of high ferric iron content in diamond garnet inclusions and mantle plume melts suggest a highly heterogeneous distribution of ferric iron in the mantle. Recycling of oxidized materials such as carbonates from Earth’s surface by subduction could explain the observed variations. Here we present high-pressure high-temperature multi-anvil experiments to determine the redox reactions between calcium-, magnesium-, or iron-carbonate and ferrous iron-bearing silicate mineral (garnet or fayalite) at conditions representative of subduction zones with intermediate thermal structures. We show that both garnet and fayalite can be oxidized to ferric iron-rich garnets accompanied by reduction of calcium carbonate to form graphite. The ferric iron content in the synthetic garnets increases with increasing pressure, and is correlated with the Ca content in the garnets. We suggest that recycled sedimentary calcium carbonate could influence the evolution of the mantle oxidation state by efficiently increasing the ferric iron content in the deep upper mantle.

Combination of Persulfate /Peroxymonosulfate Activated By Ion (II) with Hydrogen Peroxide for Mineralization and Valorization of Vinasse

Recently, there is an increasing demand for water due to rapid industrialization and a growing human population. There is a too shortage of available water sources; thus, one option for increasing existing resources is the treatment and reuse of wastewaters. Vinasse poses a long-term risk to public health because of its toxic nature and a huge amount. This study investigates a new prospect of a combination of persulfate (PS)/ peroxymonosulfate (PMS) (activated by Ion (II)) and hydrogen peroxide (H2O2) for reducing total organic carbon (TOC) from vinasse and reuse of treated vinasse as well. Behaviors of PS/Fe(II)/ H2O2 and PMS/ Fe(II)/ H2O2 on total organic carbon (TOC) removal are explored by evaluating various effects, including H2O2 dosage, Fe (II) dosage, pH and reaction time. Hydrogen peroxide was used as an oxidation agent to improve the degradation of the organic matter of vinasse. The addition of H2O2 to PS/ Fe (II) or PMS/ Fe (II) generates highly oxidizing radicals, which enhanced, significantly, the removal of TOC. Both of PS/ Fe (II)/ H2O2 and PMS/ Fe (II)/ H2O2 systems favored neutral pH in removing the organic matter, and they were very active in the first 5 minutes. At the optimum conditions, about 86 % and 83% of TOC removal were achieved by PS/ Fe (II)/ H2O2 and PMS/ Fe (II)/ H2O2, respectively. Therefore, a combination of PS/PMS activated by Fe (II) with H2O2 can be considered as a capable technique for sugarcane vinasse treatment and allowing to reuse the effluents in many applications.

Kinetics of Zinc Corrosion in Concrete as a Function of Water and Oxygen Availability

This paper studies the effect of water as an oxidation agent and also of oxygen on zinc corrosion kinetics in active state in concrete, using high-sensitivity electrical resistance sensors. It was proven that zinc corrosion in active state is strongly affected by the presence of water at its surface. Zinc corrosion in real concrete in the absence of water can be misinterpreted as salt passivity. The presence of oxygen results in an increase of zinc corrosion rate, however at pH 12.6, passivity can occur. It was verified that corrosion products consisting primarily of Ca[Zn(OH)3]2·2H2O cannot effectively passivate zinc surface in concrete, even after 1800 h of exposure and zinc, or hot-dip galvanized steel can corrode at an unacceptable corrosion rate (more than 4 µm·a−1).

Promoting Effect of H+ and Other Factors on NO Removal by Using Acidic NaClO2 Solution

In this study, NaClO2 was selected as a denitration oxidant. In order to clarify the mechanism of NaClO2 as an oxidation agent for NO removal efficiency, the effects of H+ and other factors (NaClO2 concentration, temperature, and the other gas) on the NO removal efficiency were investigated. NaClO2 showed a promotional ability on NO removal, whose efficiency increased with the increase of NaClO2 concentration. One hundred percent removal efficiency of NO could be achieved when the NaClO2 concentration was 0.014 mol/L. Furthermore, raising the reaction temperature benefited the removal of NO. The lower the pH, the better the NO removal efficiency. The promoting effect of H+ on the NO removal was studied by the Nernst equation, ionic polarization, and the generation of ClO2. Under the optimal conditions, the best removal efficiency of NO was 100%. Based on the experimental results, the reaction mechanism was finally speculated.

Effect of Oxidation Agents on Photo-Decolorization of Vitamin B12 in the Presence of ZnO/UV-A System

The aim of this work was to apply the many various oxidation agents namely H2O2, K2S2O8 and Fe2+ on the aqueous solution of vitamin B12 with the presence of ZnO. The results indicated that the use of the mixture of H2O2 and K2S2O8 in suspension of vitamin B12 and ZnO gave a maximum efficiency percentage about 95.85% in 12 min; it was higher than that without the addition of oxidation reagent 79.33% in the same time. The obtained results demonstrated that the activation energy for this photoreaction without the addition of oxidation agent was more than that the apparent activation energy value with the used mixture of H2O2 and K2S2O8. The thermodynamic study showed that both reactions were endothermic, less-random and non-spontaneous. The ΔH# with the oxidant agents (31.43 kJ mol-1) is less than that without using oxidant agents (35.81 kJ mol-1). Moreover, the addition of series of oxidant agent solution to vitamin B12 solution led to change the photocatalytic activity for decolorization of vitamin B12 in suspension solution of ZnO, and was found the activity sequence as follows: (H2O2 + K2S2O8) > (H2O2 + Fe(II)) (Fenton reaction) > (H2O2) > (K2S2O8) > (without the oxidation agents) > (K2S2O8 + Fe(II)) > Fe(II).

Indium-based metal–organic frameworks as catalysts: synthesis of 2-nitro-3-arylimidazo[1,2-a]pyridines via oxidative amination under air using MIL-68(In) as an effective heterogeneous catalyst

The metal–organic framework MIL-68(In) has emerged as a productive heterogeneous catalyst for the synthesis of 2-nitro-3-arylimidazo[1,2-a]pyridines via oxidative amination between 2-aminopyridines and nitroalkenes using air as an oxidation agent.