Amitava Pramanik

Concomitant synthesis of highly crystalline Zn–Al layered double hydroxide and ZnO: Phase interconversion and enhanced photocatalytic activity

Metal oxide/hydroxide with hierarchical nanostructures has emerged as one of the most promising materials for their unique, attractive properties and feasibility of applications in various fields. In this report, a concomitant synthesis of crystalline zinc aluminum layered double hydroxide (ZnAl-LDH) nanostructure and ZnO is presented using Al substrate as template. Studies on interconversion of ZnO to LDH phase in bulk solution under hydrothermal conditions produced Al-doped ZnO (AZO) in one case, and in other, it improves the crystallinity of LDH film templated on Al substrate. In presence of Al salt, the self-limiting growth nature of plate LDH turned to non-self-limiting. Materials obtained during phase transition, AZO in bulk solution and crystalline porous ZnAl-LDH on substrate, have been demonstrated as effective photocatalysts for decomposition of congo red in aqueous medium.

Morphology control of ZnO with citrate: a time and concentration dependent mechanistic insight

The effect of citrate as a crystal habit modifier on the morphology of zinc oxide has been explored in a wide range of citrate/Zn ratio from 0 to 0.67. With an increase in concentration of citrate at the lower range of the ratio, the aspect ratio of the hexagonal prismatic crystals of ZnO decreases, forming flatter disks with a progressive increase of roughness on the hexagonal face. At intermediate ratios, the otherwise smooth rectangular faces also become rough, with progressive formation of porous spherical aggregates. At a high concentration of citrate, solid spherical particles form with very low crystallinity, eventually forming plate-like zinc citrate. Thermal and spectroscopic studies confirm a progressive increase in the adsorbed citrate concentration in the particles. Evidence in support of citrate being adsorbed first on the hexagonal face, followed by the other rectangular faces is presented, and a scheme has been proposed. This adsorbed citrate can be removed by calcination and the morphology remains intact, and so this procedure can be used to make pure ZnO with various morphologies. It was found that the ZnO morphologies synthesized in the presence of citrate show novel photoluminescent and enhanced photocatalytic activities compared with ZnO synthesized in the absence of citrate.

Zinc oxide functionalized human hair: A potential water decontaminating agent.

HYPOTHESIS Nano-ZnO is an efficient photocatalyst that can be employed for water purification but its separation from water is difficult. Immobilization of nano-ZnO on a fibrous material is expected to add practicality to its application. EXPERIMENTS We synthesized ZnO nanostructures on a natural waste, human hair, via a cost-effective process, characterized the system and tested the efficacy of the composite for photo-decomposition of a few toxic materials in water. FINDINGS Layers of well crystalline ZnO nanostructures grew homogeneously on hair strands, initially as thin plates that slowly turned with time into nanorods (length 400-600nm, width 28-30nm), converting the mildly hydrophobic hair (water contact angle 104°) surface into superhydrophobic (water contact angle 149°). The composite was found to effectively photodecompose toxic dyes like methylene blue, direct red, alizarin red S and aromatics (toluene), for multiple cycles without losing much efficacy.

Photon Harvesting in Sunscreen-Based Functional Nanoparticles.

The ultraviolet light component in the solar spectrum is known to cause several harmful effects, such as allergy, skin ageing, and skin cancer. Thus, current research attention has been paid to the design and fundamental understanding of sunscreen-based materials. One of the most abundantly used sunscreen molecules is Avobenzone (AB), which exhibits two tautomers. Here, we highlight the preparation of spherically shaped nanoparticles from the sunscreen molecule AB as well as from sunscreen-molecule-encapsulated polymer nanoparticles in aqueous media and study their fundamental photophysical properties by steady-state and time-resolved spectroscopy. Steady-state studies confirm that the AB molecule is in the keto and enol forms in tetrahydrofuran, whereas the enol form is stable in the case of both AB nanoparticles and AB-encapsulated poly(methyl methacrylate) (PMMA) nanoparticles. Thus, the keto-enol transformation of AB molecules is restricted to a nanoenvironment. An enhancement of photostability in both the nanoparticle and PMMA-encapsulated forms under UV light irradiation is observed. The efficient excited energy transfer (60 %) from AB to porphyrin molecules opens up further prospects in potential applications as light-harvesting systems.

A solution spectroscopy study of tea polyphenol and cellulose: effect of surfactants

Catechin, a bioflavonoid, found in green tea leaves has various applications in the food and pharmaceutical industries. However, little has been studied about its behavior with fabric-type materials especially in the presence of surfactants. Studying this lays the footstone for understanding the cause of tea stains on fabrics, which is a nuisance as they do not wash off easily or completely even after washing with a detergent, especially if the stain is aged. The intriguing question that needs to be addressed is what are the possible molecular interactions occurring between the polyphenols and the cellulosic materials, especially in the presence of a surfactant. To find answers, we studied a model system representing a cotton fabric and investigated the effect of a specific tea polyphenol on it under various conditions like pH, time and the presence of surfactants. Experiments were performed using fluorimetry, UV-Visible spectroscopy, FTIR and 1H-NMR spectroscopic techniques to decipher the molecular interactions. The results showed enhanced oxidation of the polyphenol at elevated pH aggravated by surfactants in the presence of a cellulosic substrate. Furthermore, we showed that adding reducing agents in the medium hinders polyphenol oxidation and prevents staining to considerable extent.

Antibacterial and Photocatalytic Properties of ZnO–9-Aminoacridine Hydrochloride Hydrate Drug Nanoconjugates

The development of nanomaterial-based hybrid systems for healthcare and energy-related materials has attracted significant attention nowadays. Here, we have designed a nanocomposite of ZnO nanoparticles (NPs) with anticancer therapeutic drug 9-aminoacridine hydrochloride hydrate (9AA-HCl) for antibacterial and photocatalytic activities. Spectroscopic studies reveal that the photoinduced electron transfer from photoexcited 9AA-HCl to the conduction band of ZnO NP causes the generation of the reactive oxygen species (ROS), which is responsible for antibacterial activity and photocatalytic properties. It is seen that the efficiency of photodegradation of dye molecules increases in ZnO–9AA-HCl nanoconjugated systems than pure ZnO nanoparticles because of efficient charge separation. In addition, the antibacterial efficacy of the nanoconjugate is investigated using a strain of Gram-negative bacteria where the cell-killing activities are observed 99.99 and 100% for 20 and 21 μL/mL nanoconjugate, respectively, and very little cell-killing activity is observed for free ZnO NPs and free drug. Moreover, it is also observed that the nanoconjugate generates sufficient intracellular ROS that can hydrolyze 2′,7′-dichlorodihydrofluoresceindiacetate (DCFH-DA) to highly fluorescent 2′,7′-dichlorofluorescein (DCF). The outcome of the study will provide valuable information for designing new-edge nanoconjugate materials for potential applications in photocatalytic and antibacterial activities.