Formation Of Degradation By-products Research Articles

Photothermal Mediated Chemical Recycling to Monomers via Carbon Quantum Dots.

Plastic recycling strategies to combat rapidly increasing waste buildup are of utmost environmental importance. Chemical recycling to monomers has emerged as a powerful strategy that enables infinite recyclability through depolymerization. However, methods for chemical recycling to monomers typically rely on bulk heating of polymers, which leads to unselective depolymerization in complex polymer mixtures and the formation of degradation byproducts. Here, we report a selective chemical recycling strategy facilitated by photothermal carbon quantum dots under visible light irradiation. Upon photoexcitation, we found that carbon quantum dots generate thermal gradients that induce depolymerization of various polymer classes, including commodity and postconsumer waste plastics, in a solvent-free system. This method also provides selective depolymerization in a mixture of polymers, not possible by bulk heating alone, enabled by localized photothermal heat gradients and the subsequent spatial control imparted over radical generation. Photothermal conversion by metal-free nanomaterials facilitates chemical recycling to monomers, an important approach in addressing the plastic waste crisis. More broadly, photothermal catalysis enables challenging C-C bond cleavages with the generality of heating but without indiscriminate side reactions typical of bulk thermolysis processes.

Environmental Fate of Organic Sunscreens during Water Disinfection Processes: The Formation of Degradation By-Products and Their Toxicological Profiles.

The development of any commercial product should also be aimed at reducing the risk associated with it, according to the safe-by-design concept; that is, risk assessment should always be at the center of the design, and the impact on human and environmental health should be assessed and eliminated during the product development phase and not afterwards. Unfortunately, even today, most operators in any production sector implement the philosophy of “risk management” or rather of managing the problem when it occurs, using spot interventions instead of changing the approach. This argument is also valid in the production of solar filters, which have reached a satisfactory degree of efficiency in the face of a substantial underestimation of the risks associated with their possible environmental fate. In fact, solar filters have been found in bathing waters and their environmental fate may depend on various factors such as the pH of the water, the presence of organic material, metal ions and light, and, above all, the chemical agents used in the disinfection of the water itself. Thus, during disinfection processes, the generation of dozens of products with a lower molecular weight and generally of an aromatic nature has been tested, where some of them did not receive an exact structural definition and a precise evaluation of their precise toxicological profile. Therefore, it is interesting to draw a complete picture of organic sunscreens and of the byproducts obtained under different conditions and their related ecotoxicological profile.

Secondary Effects of Hypochlorite Treatment on the Emerging Pollutant Candesartan: The Formation of Degradation Byproducts and Their Toxicological Profiles.

In recent years, many studies have reported the frequent detection of antihypertensive agents such as sartans (olmesartan, valsartan, irbesartan and candesartan) in the influents and effluents of wastewater treatment plants (WWTPs) and in the superficial waters of rivers and lakes in both Europe and North America. In this paper, the degradation pathway for candesartan (CAN) was investigated by simulating the chlorination process that is normally used to reduce microbial contamination in a WWTP. Twelve isolated degradation byproducts (DPs), four of which were isolated for the first time, were separated on a C-18 column by employing a gradient HPLC method, and their structures were identified by combining nuclear magnetic resonance and mass spectrometry and comparing the results with commercial standards. On the basis of these results, a mechanism of formation starting from the parent drug is proposed. The ecotoxicity of CAN and its DPs was studied by conducting a battery of ecotoxicity tests; bioassays were performed using Aliivibrio fischeri (bacterium), Daphnia magna (planktonic crustacean) and Raphidocelis subcapitata (alga). The ecotoxicity results shed new light on the increased toxicity of DPs compared with the parent compound.

On the importance of mechanisms analysis in the degradation of micropollutants by laccases: The case of Remazol Brilliant Blue R

Abstract The efficiency of methods to reduce the pollution induced by dyes is often evaluated using a color change measurement. This approach might hide complex mechanisms, that, if neglected, can lead to inadequate design of treatment units. This paper highlights this complexity on the case of Remazol Brilliant Blue R (RBBR), an industrial anthraquinone dye, degraded using Trametes versicolor laccases. A kinetic model describing the degradation of RBBR and the formation of degradation byproducts, one of which was found to have an orange color, is proposed. The complex links between RBBR degradation and the decolorization of the medium are highlighted, allowing to identify limits to the degradation achievable by the laccases in this case.

Improving the Oxidative Stability of Shape Memory Polyurethanes Containing Tertiary Amines by the Presence of Isocyanurate Triols

Shape memory polymers (SMPs) have been proposed for a wide variety of biomedical applications, such as cerebrovascular aneurysm occlusion; however, risks associated with degradation byproduct formation have raised the need for more biostable formulations. In this study, the use of cyclized isocyanates, in the form of isocyanurate-containing alcohols, was examined in aliphatic SMPs as a method of improving biostability. The materials were investigated for thermomechanical behavior, shape memory response, biostability, and cytocompatibility. In vitro experiments indicated that the isocyanurate-containing porous SMPs possess similar mechanical properties, albeit with improved toughness and no impact to strain recovery shape memory behavior, although atmospheric water uptake increased. Importantly, SMP life span was greatly increased, as control materials were demonstrated to fully degrade in accelerated testing by 25 days, while the modified materials retain more than 90% of their original mass. These modifi...

Toxicological Profile of 1,4-Benzoquinone and Its Degradation By-Products during Electro-Fenton, Electrocoagulation, and Electrosynthesized Fe(VI) Oxidation

AbstractThis paper reports on the degradation of 1,4-benzoquinone (1,4-BQ) and its toxic behaviors in association with the formation of degradation by-products during electro-Fenton (EF), electroco...

Degradation of an Azo Dye by Fenton Type Processes Assisted with UV Irradiation

Organic synthetic dyes are widely produced and used today. Significant losses of organic and inorganic content occurs during the manufacturing and application of dyes and its discharge in the effluent presents a threat to the eco-systems due to general toxicity and resistance to destruction by biological treatment methods. Particularly azo dyes are of special environmental concern due to their degradation products such as aromatic amines, which are considered highly carcinogenic. So, dyes have to be removed from coloured wastewater before discharge. However, traditional treatment methods (adsorption, coagulation/flocculation) mainly transfer the contaminants from wastewater to secondary waste. Therefore, advanced oxidation processes seem to be sustainable and clean technology to decolorize and minimize organic dyes content from wastewater. In this paper, degradation of an azo dye C.I. Direct Orange 39 (DO39) using Fenton type processes (Fe2+/H2O2, Fe3+/H2O2and Fe0/H2O2) has been performed. The molar ratio of Fenton’s type reagents has been varied in the range of 1 : 5 up to 1 : 50 at 0.5 and 1.0 mM concentrations of iron salts and iron powder. Experiments have been conducted for two hours in a batch reactor with magnetic stirring, ambient conditions and pH 3. The process efficiency and formation of degradation by-products have been determined on the basis of results obtained by UV/VIS spectrophotometric, total organic carbon (TOC) and high performance liquid chromatography (HPLC) analyses. The optimal Fenton and Fenton ``like" processes parameters have been applied in the photo reactor, too. It has been observed that simultaneous utilization of UV irradiation with Fenton's and Fenton ``like" reagents increases the degradation of DO39 dye. Degradation of the dye in dilute aqueous solution follows pseudo-first order kinetics. The maximal decolourization of 20 mg L-1 DO39 in water of 93.2% and TOC degradation of 76.9% were obtained using Fe3+/H2O2= 1 : 5 molar ratio. The results indicate that the treatment of DO39 dye wastewater with UV/Fe3 +/H2O2 system was found to be the most efficient.

Present and Future of PLA Polymers

Abstract Lactic acid-based aliphatic polyesters (PLAs) are well known biocompatible bioresorbable polymers which are being increasingly used as biomaterials for temporary therapeutic applications. Because of their sensitivity to water and the formation of degradation by-products which can be easily metabolized by microorganisms, this type of polymers also has potential to replace commodity polymers in packagings or as mulch films. From an overview of synthesis routes, structural characteristics, and performances, an attempt is made to evaluate the future of PLA polymers insofar as industrial development is concerned.