In recent years, due to the fast development of industrialization and modern agricultural technology, toxic chemicals are released or used. Because of these toxic materials, human health and the environment are at a greater risk. Environmental security is a major concern of our mankind. Environmental pollutants at different levels exist all over the world, and it has to be reduced effectively to safeguard our well beings. Nanomaterials in nanotechnology are the greatest boon to mankind which can resolve these problems in different ways and can improve the quality of human life. Using effective nanomaterials, various analytical tools are available to detect pollutants. But surface-enhanced Raman spectroscopy (SERS)-based analytical sensors can be a low-cost, selective, and sensitive tool to detect low-concentration pollutants among other sensing methods. This chapter discusses the various types of nanomaterials as a SERS substrate to detect environmental pollutants like dyes, pesticides, toxins, pathogens, heavy metals, and phenols.

In early years, SERS-active substrates were generally noble metals. However, their practical applications were limited due to their poor biocompatibility, low uniformity and high cost. Recently, the utilization of semiconductor SERS-active substrates has greatly expanded the applications of SERS in many fields. However, metal-free SERS-active substrates have a low enhancement factor (EF), which can be overcome by adjusting their oxygen deficiency or through the effective preparation of non-stoichiometric semiconducting oxide materials. This is the key strategy and may work as an efficient and simple way to achieve high sensitivity and obtain an enhancement factor (G-factor) comparable to that of noble metals. Here, we report the preparation of flower-like rGO-Bi2O3/Bi2O2.75 and rGO-Ag-Bi2O3/Bi2O2.75 hybrid thin film nanocomposites using a liquid/liquid interface method (LLI) for the first time. In addition to the synergic effect of different enhancement mechanisms, the 3-D flower-like morphology of the substrate shows more favourable properties to improve the G-factor due to the existence of more hotspots. The rGO-Ag-Bi2O3/Bi2O2.75 hybrid thin-film nanocomposites show an EF of 1.8 × 109 with a detection ability of up to 1 nM towards Rhodamine 6G (R6G), which is highly toxic to humans and the aquatic environment.

Sea urchin MoO3 with low loading of silver (Ag/SUMoO3) forming hierarchical micro-nano structures are explored as surface-enhanced Raman scattering (SERS) substrates. Owing to the high concentration of oxygen defects and consequently, Mo+5 states, possessing unique morphology of sea urchins, SUMoO3 are beneficial for achieving superior SERS properties. Silver nanoparticles are decorated on SUMoO3 by photoreduction, achieving an excellent Ag-MoO3 interface without the use of any coupling agents and the underlying scaffold prevents the silver from aggregation and oxidation. Ag/SUMoO3 substrate shows a high enhancement factor of 9.2 x 109 and a detection limit of 1 nM for 4-mercaptobenzoic acid. The synergetic effect of charge transfer enhancement from defect-rich SUMoO3 coupled with electromagnetic enhancement from silver nanoparticles is responsible for the high enhancement factor. Further, the detection of an environmental pollutant and a potent carcinogenic, N-nitrosodiphenylamine (NDPhA) up to 10- 5 M is demonstrated using Ag/SUMoO3 as a SERS substrate for the first time. Antibacterial testing reveals the higher zone of inhibition achieved for Ag/SUMoO3 against E. coli than for bulk MoO3-Ag revealing the superior role of the unique morphology and composition of Ag/SUMoO3.

Graphene oxide/reduced Graphene oxide based hybrid nano composites have been a hot topic of research in the past few decades. Their Remarkable optical, electrical, mechanical and thermal properties brought them fore front among other 2-D materials. Graphene is a single 2-D sheet of graphite. So it is known to be mother of other carbon materials like carbon nanotube, fullerene, and their derivatives graphene oxide (GO), reduced Graphene Oxide (rGO). Graphene derivatives (GO, rGO) and their hybrids with metals (M) and Metal Oxides (MO) have proven to be an effective materials for sensors, solar cells, water purification and so on. This review article comprises the low cost synthesis techniques most commonly used to produce these graphene derivatives, discuss how synthesis affects their key material properties and highlight some examples of hybrid metal/metal oxide Nano composites with unique and impressive properties and its applications. Specifically, this review highlights their performance in spectroscopy based optical sensors, energy storage and water purifications. Finally, this review discusses the outlook and remaining challenges in the field of practical industrial-scale production.

For the first time, a detailed study was conducted on the impact of temperature for the transformation of biowaste to sustainable, porous carbon nanostructures. In this work, we performed green conversion of onion peel waste to carbon nanospheres. The biowaste was pyrolyzed at different consecutive temperatures from 200 to 1000 °C. The shape, size, elemental composition, particle arrangement, surface area and porosity of carbonized material at each temperature were elaborately studied by using FESEM, TEM, EDS, FTIR, XRD, Raman spectroscopy, and BET. The spherical shaped carbon nanostructures started to form from 500 °C; and their size reduced with increase in temperature, i.e., 115 nm (500 °C) to 63 nm (1000 °C). The physical–chemical properties were optimized with the temperature; thus, the nanospheres produced at 1000 °C exhibited superior qualities such as the highest carbon content (~ 91%), largest surface area (2961.90 m2 g−1) and pore volume (2.1 cm3 g−1) in comparison with the nanospheres obtained at lower temperatures. The mesoporous carbon nanospheres formed were crystalline and graphitic in nature as confirmed by XRD and Raman spectroscopy, respectively. Thus, the carbon nanospheres obtained from onion peels by pyrolysis, provide a platform for the conversion of waste to environment friendly spherical nanocarbons.

A low cost reduced graphene oxide-copper hybrid nano thin-film modified Pencil Graphite Electrode has been employed to detect the l-tyrosine enantiomer. The free-standing rGO-Cu hybrid nano-thin film was prepared by a simple one-step liquid-liquid interface method. Electrochemical Cyclic Voltammetry, Differential Pulse Voltammetry, pH-dependent and scan rate dependent studies on bare PGE, Cu, rGO, and rGO-Cu for l-tyrosine have been explained in detail. The rGO-Cu modified PGE based biosensor exhibits good detection of l-tyrosine. The linear range detection limit was estimated to be 1 × 10-7 M. The calculated sensitivity is 0.4 μA ppm-1 mm2. This electroactive biosensor is easily fabricated and controlled and is cost-effective. The surface orientation of l-tyrosine on the Ag electrode at a particular potential and its comparison with vibrational DFT calculations have been studied for the first time.

Functional materials based on reduced graphene oxide (rGO) and metal oxide nanoparticles possess superior properties arising from the synergy of the individual properties. Obtaining these materials in the form of large area films are advantageous for most applications involving sensing, photovoltaics, supercapacitors, etc. We have synthesized free standing, thin films of rGO with semiconductor nanostructures such as ZnO, CuO, SnO2, and magnetic nanoparticles such as Fe2O3 at a liquid/liquid interface employing a simple interfacial reaction of the precursors. The method can be adopted as a general route to prepare rGO-based metal oxide films. rGO-ZnO films consist of hexagonal cylinders of ZnO, and rGO-Fe2O3 films exhibit particle or rod-like morphologies of iron oxide interspersed with rGO layers. The applications of these hybrid films as renewable surface-enhanced Raman substrates (SERS) and supercapacitors are demonstrated. The higher photodegradation rates provided by the metal oxide-rGO hybrids enable regeneration of the used SERS substrate while the contribution from electric double layer capacitance of rGO and pseudocapacitance due to metal oxide enhances the charge storage in hybrids.

Graphene oxide/reduced Graphene oxide hybrid nanomaterials have been widely used as substrates for surface enhanced Raman spectroscopy. This is mainly due to that they have unique structures and inherent properties including highest specific surface area, chemical and electrochemical inertness and easy surface modification etc. It is the parent of all graphite form and is an interesting topic of research in the last three to four years. It can be stacked to form 3D graphite, rolled to form ID nanotubes and wrapped to form 0D fullerenes. The long-range π-conjugation in graphene shows extraordinary thermal, mechanical and electrical properties. The carbon nanomaterial-based spectroscopy detection of chemical and biological molecules has gained much attention with its extensive applications to genomic, proteomic and environmental analysis as well as for clinical diagnosis.Surface enhanced Raman (SERS) spectroscopyhas proven to be an effective technique for analyzing the innovative nanomaterials, graphene. This technique has also helped in identifying some unique properties ofgrapheneas a Raman substrate for the suppression of fluorescence. The requirement for a substrate that is biocompatible, chemically inert, and capable of Raman enhancement is a major technological objective and grapheneserves as a suitable material.

Hybrid films of reduced graphene oxide-osmium nanoparticles (rGO-Os NPs) synthesized at a liquid/liquid interface are explored for their electrocatalytic activity towards the oxidation of rhodamine B (RhB), a popular colourant found in textile industry effluents and a non-permitted food colour. The free-standing nature of the films enables them to be lifted directly on to electrodes without the aid of any binders. The films consist of aggregates of ultra-small Os NPs interspersed with rGO layers. The hybrid film exhibits enhanced RhB oxidation when compared to its constituents arising from the synergic effect between rGO and Os NPs, Os contributing to electrocatalysis and rGO contributing to high surface area and conductance as well as stabilization of Os nanoparticles. The electrochemical sensor based on rGO-Os NP hybrid film on pencil graphite electrode shows a remarkable performance for the quantitative detection of RhB with a linear variation in a wide range of concentrations, 4–1300 ppb (8.3 nM–2.71 μM). The modified electrode presents good stability over more than 6 months, reproducibility and anti-interference capability. The use of developed sensor for adequate detection of RhB in real samples such as food samples and pen markers is also demonstrated.

Amongst soft chemical synthetic routes, the ionothermal synthesis method (using an ionic liquid) has attracted research tremendously due to their remarkable features especially in the case of TiO2 nanoparticles synthesis. On the other hand, the significant role of TiO2 nanoparticles in the fields of photocatalysis, photovoltaics, batteries etc. is noteworthy. Here, by considering these two remarkable aspects, TiO2 has been prepared by using an ionic liquid. The band gap of 3.2 eV has been determined through UV-Vis absorption spectra. The crystallite size was found to be 62 nm by PXRD. Additionally, TEM images have confirmed that the size of the particles is in the nanoscale. Furthermore, the significant properties of TiO2 nanoparticles have been studied and utilized for photocatalytic water splitting, as well as for the development of antibacterial activities. (C) 2018 The Authors. Publishing services by Elsevier B.V. on behalf of Vietnam National University, Hanoi.

Reduced graphene oxide–osmium (rGO-Os) hybrid nano dendtrites have been prepared by simple liquid/liquid interface method for the first time. The method involves the introduction of phase-transfered metal organic precursor in toluene phase and GO dispersion in the aqueous phase along with hydrazine hydrate as the reducing agent. Dendritic networks of Os nanoparticles and their aggregates decorating rGO layers are obtained. The substrate shows improved catalytic and surface-enhanced activities comparable with previous reports. The catalytic activity was tested for the reduction of p-nitroaniline into p-phenyldiamine with an excess amount of NaBH4. The catalytic activity factors of these hybrid films are 2.3 s−1 g−1 (Os film) and 4.4 s−1 g−1 (rGO-Os hybrid film), which are comparable with other noble metal nanoparticles such as Au, Ag, but lower than Pd-based catalysts. Surface-enhanced Raman spectroscopy (SERS) measurements have been done on rhodamine 6G (R6G) and methylene blue dyes. The enhancement factor for the R6G adsorbed on rGO-Os thin film is 1.0 × 105 and for Os thin film is 7 × 103. There is a 14-fold enhancement observed for Os hybrids with rGO. The enhanced catalytic and SERS activities of rGO-Os hybrid thin film prepared by simple liquid/liquid interface method open up new challenges in electrocatalytic application and SERS-based detection of biomolecules.

Free standing, thin films of reduced graphene oxide (rGO) with ZnO, CuO and SnO(2) nanostructures are prepared at a water/toluene interface utilizing simple interfacial reaction and self-assembly. rGO-ZnO, rGO-CuO and rGO-SnO(2) films exhibit unique morphologies such as hexagonal cylinders, elongated splinters, and balls, respectively, wrapped by rGO layers. The hybrid films exhibit surface enhanced Raman scattering (SERS) of rhodamine 6G dye with enhancement factors one order higher than bare metal oxide caused by a synergic effect of charge transfer between the dye, metal oxide and rGO. Doping with Ag+ ions improves SERS enhancement in rGO-Ag–ZnO hybrid films, exploiting the electromagnetic effect of metal surface plasmons. Detection sensitivity up to 10 μM dye with an enhancement factor of 104 is shown. The enhanced photodegradation rate by the hybrid films is utilized for UV induced regeneration of the used SERS substrate and is demonstrated for successive use of different analytes.

We have successfully synthesized CeO2 nanoparticles (Nps) via the solution combustion method using sugarcane juice as a novel combustible fuel. The structural features, optical properties and morphology of the nanoparticles were characterized using XRD, FTIR, and Raman spectroscopy, UV-Vis, SEM and TEM. Structural characterization of the product shows cubic phase CeO2 . FTIR and Raman spectrum show characteristic peaks due to the presence of Ce-O vibration. SEM images show a porous structure and, from TEM images, the size of the nanoparticles were found to be ∼ 50 nm. The photocatalytic degradation of the methylene blue (MB) dye was examined using CeO2 Nps under solar irradiation as well as UV light irradiation and we studied the effect of p H, catalytic load and concentration on the degradation of the MB dye. Furthermore, the antibacterial properties of CeO2 Nps were investigated against Gram+ve and Gram- ve pathogenic bacterial strains using the agar well diffusion method.

Ceria ( CeO2 is a technologically important rare-earth material because of its unique properties and various engineering/biological applications. In the present work, cerium oxide nanoparticles have been prepared by a simple solution combustion method using watermelon juice as a novel combustible fuel. The structure and morphology of the synthesized CeO2 nanoparticles were analyzed using various analytical tools such as PXRD, FTIR, Raman, UV-Visible and SEM. PXRD pattern confirms that the prepared material is composed of cubic-phase cerium oxide nanoparticles. Photocatalytic degradation of Methylene blue dye using CeO2 nanoparticles shows 98% of degradation in UV irradiations. Furthermore the antibacterial properties of CeO2 nanoparticles were investigated by their bacterial activity against two bacterial strains using the agar well diffusion method.

In the present work, Zinc Oxide nanoparticles (ZnO Nps) have been prepared by a simple and low temperature solution combustion method using Zinc nitrate as a precursor and solid water melon juice as a novel fuel for the first time. The structure and morphology of the synthesized ZnO NPs have been analyzed using various analytical techniques such as Powder X-ray diffraction, FTIR spectroscopy, Raman spectroscopy, UV-Visible spectroscopy, photoluminescence spectroscopy, scanning electron microscope and transmission electron microscope. ZnO NPs show good photo catalytic activity for the degradation of methylene blue (MB) dye. It also shows significant antibacterial activities against three bacterial strains.

In this paper, we have successfully synthesized ZnO nanoparticles (Nps) via solution combustion method using sugarcane juice as the novel fuel. The structure and morphology of the synthesized ZnO Nps have been analyzed using various analytical tools. The synthesized ZnO Nps exhibit excellent photocatalytic activity for the degradation of methylene blue dye, indicating that the ZnO Nps are potential photocatalytic semiconductor materials. The synthesized ZnO Nps also show good electrochemical sensing of dopamine. ZnO Nps exhibit significant bactericidal activity against Klebsiella aerogenes, Pseudomonas aeruginosa, Eschesichia coli and Staphylococcus aureus using agar well diffusion method. Furthermore, the ZnO Nps show good antioxidant activity by potentially scavenging 1-diphenyl-2-picrylhydrazyl (DPPH) radicals. The above studies clearly demonstrate versatile applications of ZnO synthesized by simple eco-friendly route.

We have employed low cost-thin films of reduced graphene oxide (rGO) with Ag nanoparticle hybrids as surface enhanced Raman scattering (SERS) substrates. The hybrids are prepared by a simple one step liquid/liquid interface method. These hybrid films offer SERS hotspots to detect Rhodamine 6G (R6G) molecules till 1nM concentration with 1second accumulation time. The enhancement factor is of the order 108. This excellent SERS enhancement is due to coupled mechanism of surface plasmon, charge transfer and molecular resonances of Ag and R6G along with the synergic effect contributed by rGO and Ag nanoparticles in the hybrid thin film.

High pressure Raman spectroscopic studies on perfluorohexane and perfluoroheptane have performed up to 12 GPa. Perfluorohexane under goes two pressure induced transitions: (1) liquid-solid transition at 1.6 GPa and (2) solid-solid transition at 8.2 GPa. On the contrary, perfluoroheptane under goes three phase transitions, they are as follows: (1) liquid-solid transition at 1.3 GPa, (2) intermediate solid I transition at 3 GPa, (3) solid II transition at 7 GPa. The change in slope (d omega/dP) shows that the solid I transition at 3.0 GPa could be the conversion of mid-gauche defect into trans conformers for perfluoroheptane. The pressure induced Raman spectra and the behavior of individual band with pressure shows that the solid phase comprises more than one conformer beyond crystallization. The intensity ratio for both the compounds shows that the high pressure phase beyond 8.2 and 7.0 GPa tends to have close packing with distorted all-trans conformers. (C) 2015 Elsevier B.V. All rights reserved.

Temperature dependent acoustic phonon behavior of PbWO4 and BaWO4 using Brillouin spectroscopy has been explained for the first time. Low temperature Brillouin studies on PbWO4 and BaWO4 have been carried out from 320–20K. In PbWO4, we observe a change in acoustic phonon mode behavior around 180K. But in the case of BaWO4, we have observed two types of change in acoustic phonon mode behavior at 240K and 130K. The change in Brillouin shift ω and the slope dω/dT are the order parameter for all kinds of phase transitions. Since we do not see hysteresis on acoustic phonon mode behavior in the reverse temperature experiments, these second order phase transitions are not related to structural phase change and could be related to acoustic phonon coupled electronic transitions. In PbWO4, the temperature driven phase transition at 180K could be due to changes in the environment around the lead vacancy (VPb2−) changes the electronic states. In the case of BaWO4, the phase transition at 240K shows the decrease in penetration depth of WO3 impurity. So it becomes more metallic. The transition at 130K could be the same electronic transitions as that of PbWO4 as function of temperature. The sound velocity and elastic moduli of BaWO4 shows that it could be the prominent material for acousto-optic device applications.

Low-temperature Brillouin scattering studies on Chalcopyrite AgGaS2 have been carried out between the temperatures ranges 20300 K. We observe the Brillouin modes for AgGaS2 as follows: for crossed polarization (VH) the two modes are around 5.4 and 18 GHz, labelled as RSW1 (Rayleigh surface mode), LA (longitudinal) modes and for parallel polarization (HH), we see the modes are around 4.5 and 11 GHz, labelled as RSW2, TA (transverse acoustic). According to this acoustic phonon mode behaviour with temperature, we do see phase transition at 80 K for AgGaS2. The phase change observed at 80 K is attributed to a strong electronphonon coupling between the acoustic modes, which modulates the acoustic mode frequency 1015%. The strong electronphonon coupling between acoustic modes (LA and TA), which is seen from the anomalous behaviour below 80 K, shows the electronic transition to be of the type direct to indirect band gap. The sound velocity and elastic constants have been calculated using Brillouin modes, which are in good agreement with previous reports.