The present work utilizes Raman and infrared (IR) spectroscopy, supported by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) to re-examine the fine structural details of Ni(OH) 2 , which is a key material in many energy-related applications. This work also unifies the large body of literature on the topic. Samples were prepared by the galvanostatic basification of nickel salts and by aging the deposits in hot KOH solutions. A simplified model is presented consisting of two fundamental phases (α and β)o fN i ( O H ) 2 and a range of possible structural disorder arising from factors such as impurities, hydration, and crystal defects. For the first time, all of the lattice modes of β-Ni(OH) 2 have been identified and assigned using factor group analysis. Ni(OH) 2 films can be rapidly identified in pure and mixed samples using Raman or IR spectroscopy by measuring their strong O−H stretching modes, which act as fingerprints. Thus, this work establishes methods to measure the phase, or phases, and disorder at a Ni(OH) 2 sample surface and to correlate desired chemical properties to their structural origins.

The applications of in situ vibrational spectroscopy for identifying bulk and surface Ni(OH)2 are discussed. Raman spectra from α- and β-Ni(OH)2 samples immersed in water are generally similar to those collected from comparable dry samples. However, the Raman scattering intensities vary, and dry β-Ni(OH)2 additionally exhibits a surface O-H stretching mode at 3690 cm(-1). Using in situ Raman spectroscopy, the spontaneous transformation of α-Ni(OH)2 to β-Ni(OH)2 in room-temperature water was monitored. Such transformations are conventionally performed in high-temperature alkaline media. An intralayer OH-diffusion model is proposed. Internal stresses at the α/β-phase boundary caused shifted peaks, higher order vibrational modes, and a new water peak at 3520 cm(-1). We conclude that Raman spectroscopy may be applied to observe Ni(OH)2 materials in situ during chemical and electrochemical treatments. Such measurements provide information on the proportions of α- and β-Ni(OH)2 and their fine structural details with high sensitivity.

Self-assembled multi-layered vertically aligned gold nanorod (AuNR) arrays have been fabricated by a simple preparation process that requires a balance between the particle concentration and the ionic strength of the solvent. An experimentally determined critical AuNR concentration of 2.0nM and 50mM NaCl produces well-ordered vertically aligned hexagonally close-packed AuNR arrays. We demonstrate surface treatment via UV Ozone cleaning of such samples to allow introduction of analyte molecules (benzenethiol and cannabinol) for effective surface enhanced Raman scattering detection. This is the first demonstration of the SERS analysis of cannabinol. This approach demonstrates a cost-effective, high-yield and simple fabrication route to SERS sensors with application in the screening for the cannabinoids.

Paper‐based surface‐enhanced Raman spectroscopy (SERS) sensors can be fabricated easily by dropcasting or inkjet printing colloidal Au nanoparticles onto cellulose‐based filter papers. They are flexible, economical, and sensitive and provide the crucial advantage of point‐of‐need sampling for application in the field. In this study, paper‐based SERS sensors are fabricated through inkjet printing of a colloidal Au sol onto a filter paper substrate. We have characterized their SERS performances with benzenethiol and pyridine molecules using a handheld Raman analyzer. Due to the heterogeneous loading of the Au nanoclusters on the paper substrate, we introduce the concept of receiver operating characteristic as an alternate measurand to quantify the performance of these sensors. With their inherent filtration sampling capability, we demonstrate the use of paper SERS sensors for the detection of chemical aerosols. Lastly, we present the use of a precision materials printer to deposit quantifiable amounts of analyte (fentanyl) uniformly across the active sensing area of a paper SERS sensor. This will allow for analyte‐loaded certified references to be prepared and used in the field as standards for comparison.

An inkjet-printed paper-based Surface-enhanced Raman scattering (SERS) sensor is a robust and versatile device that provides trace sensing capabilities for the detection and analysis of narcotics and drugs. Such sensors generally work well for analytes with good binding affinity towards the Au or Ag plasmonic nanoparticles (NPs) resident in the sensors. In this report, we show that iodide functionalization of the printed sensors helps to remove adsorbed contaminants from AuNP surfaces enabling superior performance with improved detection of narcotics such as fentanyl, heroin and cocaine by SERS. SERS signals are easily doubled with the iodide-functionalized sensors which also showed orders of magnitude improvement in detection limit. In this report, we show that a short (90 s) iodide treatment of the sensors significantly improved the detection of heroin. We propose that iodide functionalization be integrated into field detection kits through the solvent that wets paper-based sensor prior to swabbing for narcotics. Alternatively, we have also demonstrated that iodide functionalized sensors can be stored in ambient for up to 1 week and retain the improved performance towards heroin detection. This report will help to significantly improve the performance of paper-based sensors for field detection of narcotic drugs.