Fundamental Degradation Processes Relevant to Solar Irradiation of Cellulose: ESR Studies

Photochemical Stability of a Cotton Fabric Surface Dyed with a Reactive Triphenodioxazine Dye

The paper describes the photochemical stability of a commercial triphenodioxazine dye (Reactive Blue_204) linked onto a cotton fabric. Preliminary studies have shown that as a result of irradiation, the dye and its photodegradation products can pass directly onto the skin under conditions that mimic human perspiration and cause side-effects. The cotton dyed fabric was photo irradiated at different time intervals. Standard methods were employed to evaluate the color strength at various levels of pH, temperature, dyeing contact time, and salt concentration. The influence of UV radiation at different doses (λ > 300 nm) on the structural and color modifications of the dyed cotton fabrics was studied. Structural modifications before and after irradiation were compared by applying FTIR, UV–Vis, and near infrared chemical imaging (NIR–CI) techniques. Color modifications were investigated with the CIELAB system. Color differences significantly increased with the irradiation dose. High irradiation doses caused changes in the dye structure.

Stable Organic Radicals in Lignin: A Review

Lignin and the quest for the origin of stable organic radicals in it have seen numerous developments. Although there have been various speculations over the years on the formation of these stable radicals, researchers have not been able to arrive at a solid, unequivocal hypothesis that applies to all treatments and types of lignin. The extreme complexity of lignin and its highly aromatic, cross-linked, branched, and rigid structure has made such efforts rather cumbersome. Since the early 1950s, researchers in this field have dedicated their efforts to the establishment of methods for the detection and determination of spin content, theoretical simulations, and reactions on model compounds and spin-trapping studies. Although a significant amount of published research is available on lignin or its model compounds and the reactive intermediates involved during various chemical treatments (pulping, bleaching, extractions, chemical modifications, etc.), the literature provides a limited view on the origin, nature, and stability of such radicals. Consequently, this review is focused on examining the origin of such species in lignin, factors affecting their presence, reactions involved in their formation, and methods for their detection.

A survey of photogeochemistry

The participation of sunlight in the natural chemistry of the earth is presented as a unique field of study, from historical observations to prospects for future inquiry. A compilation of known reactions shows the extent of light-driven interactions between naturally occurring components of land, air, and water, and provides the backdrop for an outline of the mechanisms of these phenomena. Catalyzed reactions, uncatalyzed reactions, direct processes, and indirect processes all operate in natural photochemical transformations, many of which are analogous to well-known biological reactions. By overlaying photochemistry and surface geochemistry, complementary approaches can be adopted to identify natural photochemical reactions and discern their significance in the environment.

ESR spectroscopy for monitoring the photochemical and thermal degradation of conjugated polymers used as electron donor materials in organic bulk heterojunction solar cells

ESR spectroscopy was applied for monitoring the degradation of conjugated polymers used in organic solar cells and comparing their stability.