Search

Temporary consolidation technique becomes more and more popular in archaeological excavation. Cyclododecane and menthol are the mostly studied and used temporary consolidants. However, their best applying temperatures are about 20-40 °C higher than their melting points, which can be a problem for temperature-sensitive artifacts or excavation in cold environment. In this work, we take advantage of the concept of eutectic mixtures. Menthyl lactate, a menthol derivative, which can also sublime at ambient conditions, is introduced into menthol to form binary eutectic mixtures. Their potentials as temporary consolidants are carefully and systematically examined. The results indicate the eutectic mixtures are good temporary consolidants and their performances at very low temperatures are much better than the parent compounds. Through this work, a list of temporary consolidants whose melting points range from below 0 to 45 °C are built up for conservators to choose based on their needs.

Menthol, a natural organic compound from plant extract, due to its unique aromatic smell and cooling effect, has wide applications in food, cosmetic and pharmaceutical industries. By taking advantage of its volatile ability at room temperature, this compound has the potential to be used as a temporary consolidant in the field of art conservation. In order to evaluate the effectiveness of menthol as a temporary consolidant for urgent conservation in archaeological field, in this paper, laboratory investigations, such as menthol's penetration, consolidation efficacy and morphological changes during sublimation, are carried out on two kinds of organic and inorganic materials respectively, representing four types of fragile archaeological artifacts. In particular, the morphological changes of consolidated substrates during menthol sublimation process are systematically observed. The result shows that menthol's consolidation efficacy is strongly affected by the inherent nature of substrate to be treated. Menthol whisker growth on these substrates surfaces is observed, and a weak intermolecular hydrogen bond is formed between menthol and substrate, which is confirmed by the shift of hydroxyl group stretching bond in the IR spectrum.

The photoactivity of semiconductor nanostructures makes them potentially useful for environmental remediation and antibacterial applications. Understanding the mechanism underlying the photochemical and photobiological activities of photoexcited semiconductors is of great importance for developing applications and assessing associated risks. In the current work, using electron spin resonance spectroscopy coupled with spin trapping and spin labeling techniques, we comparatively and systematically investigate the abilities of ZnO and ZnS to generate hydroxyl radical, superoxide, singlet oxygen, photoinduced electrons, and oxygen consumption during irradiation. It was found that although ZnO and ZnS, when photoexcited, can produce hydroxyl radical, superoxide, and singlet oxygen, ZnO is more effective than ZnS in producing hydroxyl radical and singlet oxygen while ZnS is more effective than ZnO in generating superoxide. The characterization with ESR spin labeling and oximetry indicates ZnS is about 4 times m...

Nanostructured enzyme mimics are of great interest as promising alternatives to artificial enzymes for biomedical and catalytic applications. Studying the chemical interactions between antioxidants and nano-enzymes may result in a better understanding of the antioxidant capability of antioxidants and may help improve the function of artificial enzymes to better mimic natural enzymes. In this study, using Co3O4 nanoparticles (NPs) as peroxidase mimics to catalyze the oxidation of chromophoric substrates by H2O2, we developed a platform that acts as a biosensor for hydrogen peroxide and glucose and that can study the inhibitory effects of natural antioxidants on peroxidase mimics. This method can be applied specifically to glucose detection in real samples. Three natural antioxidants, gallic acid (GA), tannic acid (TA), and ascorbic acid (AA), were compared for their antioxidant capabilities. We found that these three antioxidants efficiently inhibit peroxidase-like activity with concentration dependence. The antioxidants showed different efficiencies, in the following order: tannic acid > gallic acid > ascorbic acid. They also showed distinct modes of inhibition based on different interaction mechanisms. This study serves as a proof-of-concept that nano-enzyme mimics can be used to evaluate antioxidant capabilities and to screen enzyme inhibitors.

Identifying the dominantly active species and their reactive behaviors in semiconductor photocatalysis is important for developing a full understanding of their photochemical and photophysical properties. Here we report an effective method for studying the reactive oxygen species (ROS) and charge carriers generated by irradiating single crystalline CdS and Ag2S micro-nano structures (MNS). Our method, based on electron spin resonance spectroscopy (ESR) combined with spin trapping and spin labeling techniques, confirmed the generation of superoxide and charge carriers and their contribution to photocatalytic degradation of rhodamine B elicited by CdS and Ag2S MNS. The electronic band structures determined the reactivity of photogenerated holes/electrons and the generation of reactive oxygen species. Our comparison of CdS and Ag2S MNS showed that, because of the large difference between their band edge positions, these two sulfides differ greatly in ROS production and in the reactivity of photoinduced elect...

Temporary consolidation is widely used to protect delicate artefacts or other fragile relics in art conservation. Although cyclododecane is extensively accepted, the safety-related issues have become an increasing concern and its short working time is always annoying. Inspired by its low melting point, polar structure, well-established safety profile, easy local availability and low cost, we propose menthol as a new temporary consolidant on the new excavation site of Qin Shihuang's Terracotta Army. In this paper, we offer a preliminarily exploration of the kinetics of menthol sublimation on two different matrices, its residue after volatilization, its penetrability and distribution in simulated terracotta samples, as well as other important properties in the laboratory. The results obtained from these tests reveal that the sublimation of menthol can be a zero- or a first-order process, depending on the porosity of the matrices, and its best operational temperature resides in the range of 60–80°C. Finally, two field cases at the archaeological site of Qin Shihuang's Terracotta Army are presented to show that menthol is a very effective temporary consolidant.

Tetraethoxysilane (TEOS) is the most commonly used silicon-based stone consolidant in art conservation. However, it is known that the resulting silica gel phase tends to develop cracks inside the stone as the gel shrinks during aging and drying. Such phenomenon may lead to severe damage to the protected objects. By introducing silica nanoparticles into TEOS, a so-called particle modified consolidant (PMC), may minimize such shrinkage by reducing the volume loss and forming mesoporous structure to weaken the capillary forces. But many previous results show significant color changes on the surface of PMC-treated stones which can not be tolerated in the conservation treatments of cultural heritage. In this work, we designed a three-component composite consolidant which consists of 15 nm silica particles, α,ω-hydroxyl-terminated polydimethylsilane (PDMS-OH) and TEOS. Among the three components, TEOS provides the consolidation function, silica nanoparticles prevent the cracking and increase the salt resistance and PDMS-OH further reduces cracking, decreases the color alteration and increases the resistance to wetting of the stone. Experimental results show that the three components have significant synergistic effect, which makes the material exhibiting best overall performance in terms of cultural heritage protection.

Tuning the enzyme-like activity and studying the interaction between biologically relevant species and nano-enzymes may facilitate the applications of nanostructures in mimicking natural enzymes. In this work, AuPt alloy nanoparticles (NPs) with varying compositions were prepared through a facile method by co-reduction of Au3+ and Pt2+ in aqueous solutions. The composition could be tuned easily by adjusting the molar ratios of added Pt2+ to Au3+. It was found that both peroxidase-like and oxidase-like activity of AuPt alloy NPs were highly dependent on the alloy compositions, which thus suggesting an effective way to tailor their catalytic properties. By investigating the inhibitory effects of HS− on the enzyme-like activity of AuPt alloy NPs and natural enzyme, we have developed a method for colorimetric detection of HS− and evaluation of the inhibiting effects of inhibitors on natural and artificial enzymes. In addition, the responsive ability of this method was influenced largely by the composition: AuPt alloy NPs show much lower limit of detection for HS− than Pt NPs while Pt NPs show wider linear range than AuPt alloy NPs. This study suggests the facile way not only for synthesis of alloy nanostructures, but also for tuning their catalytic activities and for use in bioanalysis.

During excavation, archaeologists always discover very fragile materials which require immediate in situ consolidation before removal to laboratories for conservation treatment. Cyclododecane is on...