Role of Seawater Ions in Forming an Effective Interface between Photocatalyst/Cocatalyst.

Photocatalytic (PC) hydrogen production from water splitting is a promising route to fulfill the current energy demand in a sustainable manner. For photocatalysis to become industrially viable, seawater should be used as an ideal solvent. Until now, a variety of semiconductor photocatalysts have been exploited for seawater splitting; however, there has been a lack of a well-established catalytic system for seawater splitting, as seawater ions have an uncertain effect on water splitting. Recently, ionized carbon nitride PC has been shown to substantially enhance water splitting in the presence of ions; however, the underlying manner by which the ions promote PC has still not been fully understood. Presented here is a systematic evaluation of an ionized low-cost carbon nitride-based semiconductor for seawater splitting. A detailed study has been done using this salt-type semiconductor in the presence of a variety of ions (Na+, K+, Mg2+, Ca2+, Cl-, SO42-), and their role has been probed in modulating the photocatalytic activity. Multiple measurements have provided insight as to how the presence of cations aid advantageously in forming an effective in situ interface between catalyst/cocatalyst for improved electron transfer. Previously, these ions were purported to change the hole quenching ability only of the photocatalyst, whereas here it has been shown that the change in the electron transfer ability of the photocatalyst to cocatalyst appears to be the cause for augmented PC. This improved interfacial electron transfer has been used to rationalize the 8-fold enhancement in the photocatalytic rate in the presence of simulated seawater compared to deionized water and provides the impetus for the use of ionized carbon nitride structures for sustainable PC splitting of seawater.

Biomimetic Hydroxyapatite a Potential Universal Nanocarrier for Cellular Internalization & Drug Delivery.

PURPOSE: Functional biomaterials can be used as drug loading devices, components for tissue engineering or as biological probes. As such, the design, synthesis and evaluation of a variety of local-drug delivery structures has been undertaken over the past few decades with the ultimate aim of providing materials that can encapsulate a diverse array of drugs (in terms of their sizes, chemical compositions and chemical natures (i.e. hydrophilic/hydrophobic). METHODS: Presented here is the evaluation of specifically hollow 1D structures consisting of nanotubes (NTs) of HAp and their efficacy for cellular internalization using two distinguished anti-cancer model drugs: Paclitaxel (hydrophobic) and Doxorubicin hydrochloride (hydrophilic). RESULTS: Importantly, it has been observed through this work that HAp NTs consistently showed not only higher drug loading capacity as compared to HAp nanospheres (NSs) but also had better efficacy with respect to cell internalization/encapsulation. The highly porous structure, with large surface area of nanotube morphology, gave the advantage of targeted delivery due to its high drug loading and retention capacity. This was done using the very simple techniques of physical adsorption to load the drug/dye molecules and therefore this can be universally applied to a diverse array of molecules. CONCLUSIONS: Our synthesized nanocarrier can be widely employed in biomedical applications due to its bio-compatible, bio-active and biodegradable properties and as such can be considered to be a universal carrier. Graphical Abstract Schematic representation for a comparative study of hydroxyapatite (hollow nanotubes vs solid nanospheres) with variety of drug/ dye molecules.

Insight into the Excitation-Dependent Fluorescence of Carbon Dots.

High quantum yield, photoluminescence tunability, and sensitivity to the environment are a few distinct trademarks that make carbon nanodots (CDs) interesting for fundamental research, with potential to replace the prevalent inorganic semiconductor quantum dots. Currently, application and fundamental understanding of CDs are constrained because it is difficult to make a quantitative comparison among different types of CDs simply because their photoluminescence properties are directly linked to their size distribution, the surface functionalization, the carbon core structures (graphitic or amorphous) and the number of defects. Herein, we report a facile one-step synthesis of mono-dispersed and highly fluorescent nanometre size CDs from a 'family' of glucose-based sugars. These CDs are stable in aqueous solutions with photoluminescence in the visible range. Our results show several common features in the family of CDs synthesized in that the fluorescence, in the visible region, is due to a weak absorption in the 300-400 nm from a heterogeneous population of fluorophores. Fluorescence quenching experiments suggest the existence of not only surface-exposed fluorophores but more importantly solvent inaccessible fluorophores present within the core of CDs. Interestingly, time-resolved fluorescence anisotropy experiments directly suggest that a fast exchange of excitation energy occurs that results in a homo-FRET based depolarization within 150 ps of excitation.

Crafting Inorganic Materials for Use in Energy Capture and Storage.

Harnessing solar energy effectively by the judicious use of photoactive inorganic/hybrid structures has become a pivotal requirement in the pursuit of environmentally benign technologies. The synthesis of new inorganic materials whose stoichiometry, structure, and activity can be tuned while maintaining a high level of architectural homogeneity and the successful evaluation of each material as a viable component in specific energy-capture- and storage-based applications are being presented here. Two of our current projects are detailed, involving (i) new 1D-structured hybrid perovskite that is a more temporally and thermally stable analogue of the oft-cited methylammonium lead iodide and (ii) a new electroactive material that can function not only as a conventional electrode in a battery but also, because of the material's inherent photoactivity, as a component in solar batteries. Hence, the concept that energy capture and energy storage can be coupled in a single device is also being detailed.

Coupling Energy Capture and Storage - Endeavoring to make a solar battery.

Storage of solar radiation is currently accomplished by coupling two separate devices, one that captures and converts the energy into an electrical impulse (a photovoltaic cell) and another that stores this electrical output (a battery or a supercapacitor electrochemical cell). This configuration however has several challenges that stem from a complex coupled-device architecture and multiple interfaces through which charge transfer has to occur. As such presented here is a scheme whereby solar energy capture and storage have been coupled using a single bi-functional material. Two electroactive semiconductors BiVO4 (n-type) and Co3O4 (p-type) have been separately evaluated for their energy storage capability in the presence and absence of visible radiation. Each of these have the capability to function as a light harvester and also they have faradaic capability. An unprecedented aspect has been observed in that upon photo-illumination of either of these semiconductors, in situ charge carriers being generated play a pivotal role in perturbing the electroactivity of the redox species such that the majority charge carriers, viz. electrons in BiVO4 and holes in Co3O4, influence the redox response in a disproportionate manner. More importantly, there is an enhancement of ca. 30% in the discharge capacity of BiVO4 in the presence of light and this directly provides a unique route to augment charge storage during illumination.

Nanostructured MoS2/BiVO4 Composites for Energy Storage Applications.

We report the optimized synthesis and electrochemical characterization of a composite of few-layered nanostructured MoS2 along with an electroactive metal oxide BiVO4. In comparison to pristine BiVO4, and a composite of graphene/BiVO4, the MoS2/BiVO4 nanocomposite provides impressive values of charge storage with longer discharge times and improved cycling stability. Specific capacitance values of 610 Fg-1 (170 mAhg-1) at 1 Ag-1 and 166 Fg-1 (46 mAhg-1) at 10 Ag-1 were obtained for just 2.5 wt% MoS2 loaded BiVO4. The results suggest that the explicitly synthesized small lateral-dimensioned MoS2 particles provide a notable capacitive component that helps augment the specific capacitance. We discuss the optimized synthesis of monoclinic BiVO4, and few-layered nanostructured MoS2. We report the discharge capacities and cycling performance of the MoS2/BiVO4 nanocomposite using an aqueous electrolyte. The data obtained shows the MoS2/BiVO4 nanocomposite to be a promising candidate for supercapacitor energy storage applications.

Enhancement in Rate of Photocatalysis Upon Catalyst Recycling.

Recyclability is an important aspect for heterogeneous photo-catalysts. Ease of recovery and stability of the photo-catalyst in terms of efficiency over the number of cycles are highly desired and in fact it is ideal if the efficiency is constant and it should not decrease marginally with each cycle. Presented here is a seminal observation in which the photocatalytic activity is shown to improve with increasing number of catalytic cycles (it is 1.7 times better after the 1st cycle and 3.1 times better after the 2nd cycle). Specifically, nanorods of pure TiO2 and TiO2 doped with controlled amount of tungsten have been used to degrade two model pollutants: Phenol and Rhodamine B under exclusive visible light illumination. It was found that, in case of 1 mol.% W incorporation, rate of photocatalysis and also the range of visible light absorption of the photocatalyst increased after the photocatalysis as compared to before photocatalysis. This aspect is unique for doped TiO2 and hence provides an intriguing way to mitigate low photoactivity.

Electrocatalyst on insulating support?: Hollow silica spheres loaded with Pt nanoparticles for methanol oxidation.

Electrocatalytic oxidation of methanol on silica hollow spheres, loaded with platinum nanoparticles (Pt-SiO2-HS), is reported. The functionalized hollow silica spheres were prepared by the surfactant (lauryl ester of tyrosine) template-assisted synthesis. These spheres were loaded with platinum nanoparticles by γ-radiolysis. Energy-dispersive X-ray analysis (EDAX) and X-ray photoelectron spectroscopy (XPS) analyses confirmed presence of Si and Pt in the composite. High-resolution transmission electron microscopy showed the formation of uniformly deposited Pt nanoparticles over the hollow spheres with a predominant Pt(111) lattice plane on the surface. In spite of the poor conducting nature of the silica support, the oxidation potential and current density per unit mass for methanol oxidation were noted to be ca. 0.72 V vs NHE and 270 mA mg(-1), respectively, which are among the best values reported in its class. The composite did not show any sign of a degradation even after repeated use. In fact, the anodic current was found to increase under constant polarization, which is attributed to a facile reaction between adsorbed CO with a surface hydroxyl group present on the silica support. These results are in favor of Pt-SiO2-HS as a promising electrocatalyst material in the direct methanol fuel cell (DMFC) applications.

Synthesis of hydroxyapatite nanotubes for biomedical applications.

Single phase, stoichiometrically pure, hollow nanotubes of hydroxyapatite have been synthesized and single-particle analysis has been performed to successfully prove the sole formation of Ca10(PO4)6(OH)2 phase. The facile synthesis involves a sol-gel process under neutral conditions in the presence of a sacrifical anodic alumina template. The structures formed are hollow nanotubes that have been characterized by XRD, SEM, TEM, SAED, EELS, EDS and BET measurements. The diameter of the resulting tubes is in the range of 140-350 nm, length is on the order of a few microns and the wall thickness of the tubes was found to be ca. 30 nm. Moreover these tubes had a large BET surface area of 115 m(2)/g and were found to be biocompatible. They displayed inertness in the presence of NIH 3T3 mouse fibroblast cells as dictated by an MTT assay.

A facile methodology for the design of functionalized hollow silica spheres.

A new amino acid derived amphiphile, lauryl ester of tyrosine (LET) is shown to provide a facile methodology for the preparation of hollow silica spheres. In a previous study on the interface adsorption, it was shown that phenolic OH group in LET plays a key role in the formation and stabilization of close packed structures, typically at the oil/water interface. Drawing an analogy between the air/water and the oil/water interface, we detail here a procedure where air droplets are capped with LET aggregated structures, and in turn they are utilized as viable templates in the production of hollow silica spheres. We demonstrate that hollow silica spheres are formed at pH 4.0 specifically under conditions of vortexing within a short period of time (ca. 15 min). The dimensions of the structures are 0.43±0.15 µm in diameter and they have then subsequently been used as templates for directing the synthesis of silica-silver and silica-polyanthranilic composite hollow spheres.

Zinc glycolate: a precursor to ZnO.

A simple and versatile solvent-growth process using ethylene glycol has been demonstrated for the synthesis of novel faceted bipyramidal zinc glycolate. Upon thermal treatment in air, this structure can be converted into a ZnO hexagonal phase with wurtzite structure via solid-state transformation. The morphology, microstructure, and crystallinity of the products before and after thermal treatment have been characterized by scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, and solid-state (13)C NMR measurements. In addition, the room-temperature photoluminescence of the resulting ZnO has also been investigated.