Suresh D. Kulkarni

Analytical predictive capabilities of Laser Induced Breakdown Spectroscopy (LIBS) with Principal Component Analysis (PCA) for plastic classification

A Laser Induced Breakdown Spectroscopy (LIBS) technique has been applied for the identification of four widely used plastics, polyethylene terephthalate (PET), high-density polyethylene (PE), polypropylene (PP) and polystyrene (PS), whose recycling is required from commercial and biosafety points of view. The 3rd harmonic (355 nm) nanosecond pulse from an Nd:YAG laser is used to create plasma on the sample surface and identification of the type of the plastic is derived from the plasma emission. Principal Component Analysis (PCA) of the LIBS spectra is employed for the classification of plastics. Distinct methods have been used, apart from principal components of PCA, to further confirm our results. Statistical parameters, viz., Mahalanobis distance (M-distance) and spectral residuals were used for decisive match/no match test which provided successful classification of plastics. Receiver Operating Characteristic (ROC) and Youdens index analyses were carried out to obtain the diagnostic threshold for classification of all four classes of plastics. Sensitivity, specificity, predictive values and discriminative accuracy of the classification tests based on the optimum threshold were calculated. This proves the analytical predictive capabilities of the LIBS technique for plastic identification and classification. The technique of LIBS, in future, can be routinely used in field applications such as plastic waste sorting and recycling.

Controlled inversion and surface disorder in zinc ferrite nanocrystallites and their effects on magnetic properties

A new strategy to control the inversion of zinc ferrite nanocrystallites is demonstrated, while the correlation of process–structure–property is understood with the help of thorough structural and magnetic characterization. It is found that a very high degree of inversion (>0.5) could be induced by rapid microwave-assisted synthesis carried out below 100 °C. Rietveld refinement of high resolution X-ray diffraction patterns of various annealed samples has been employed to investigate the influence of the nature of post-synthesis annealing and the temperature of annealing on the degree of inversion. It is found that magnetization follows the degree of inversion more closely than it does the size of the nanocrystals. Furthermore, slow and prolonged (2 h) annealing results in very different magnetic characteristic than short pulse (2 min) thermal treatment does. Temperature-dependent magnetization (M–T plots) studies confirmed the superparamagnetic nature of all annealed samples which displayed relatively high blocking temperatures (25 K to 56 K) compared to bulk zinc ferrite (10 K). Coercivity follows the trend of blocking temperature closely. Samples subjected to rapid annealing are found to be associated with a degree of surface disorder that influences the coercivity profoundly. Magnetic measurements suggest that rapid annealing can effectively control the surface disorder in zinc ferrite nanocrystallites, which can screen the interparticle dipolar interaction and thus coercivity. Therefore, a combination of microwave-assisted synthesis to induce a high degree of inversion, followed by different annealing protocols to tune the inversion, can deliver magnetic ferrites of desired characteristics to meet futuristic applications.

Quantification and morphology studies of nanoporous alumina membranes: a new algorithm for digital image processing.

A new mathematical algorithm is reported for the accurate and efficient analysis of pore properties of nanoporous anodic alumina (NAA) membranes using scanning electron microscope (SEM) images. NAA membranes of the desired pore size were fabricated using a two-step anodic oxidation process. Surface morphology of the NAA membranes with different pore properties was studied using SEM images along with computerized image processing and analysis. The main objective was to analyze the SEM images of NAA membranes quantitatively, systematically, and quickly. The method uses a regularized shock filter for contrast enhancement, mathematical morphological operators, and a segmentation process for efficient determination of pore properties. The algorithm is executed using MATLAB, which generates a statistical report on the morphology of NAA membrane surfaces and performs accurate quantification of the parameters such as average pore-size distribution, porous area fraction, and average interpore distances. A good comparison between the pore property measurements was obtained using our algorithm and ImageJ software. This algorithm, with little manual intervention, is useful for optimizing the experimental process parameters during the fabrication of such nanostructures. Further, the algorithm is capable of analyzing SEM images of similar or asymmetrically porous nanostructures where sample and background have distinguishable contrast.

Microwave solution route to ceramic ZnAl2O4 nanoparticles in 10 minutes: inversion and photophysical changes with thermal history

Microwave-assisted synthesis of ZnAl2O4 nanoparticles in minutes using metalorganic precursors is reported. Phase-pure ZnAl2O4 with an average crystallite size of ∼5 nm is formed in the solution medium at 185 °C. Annealing in air at temperatures between 500 and 1200 °C increases the crystallite size to ∼32 nm. The as-prepared particles are largely shapeless, whereas polyhedral crystallites with well-defined grain boundaries can be seen in the HR-TEM image of the annealed samples. Diffuse reflectance spectroscopy provides insight into the structural development of the oxide spinel. Rapid synthesis leads to significant crystallographic inversion (∼33%), as observed by X-ray photoelectron spectroscopy. Photoluminescence spectroscopy shows that the different emission bands are due both to anti-site defects in the form of zinc interstitials caused by cationic inversion and to oxygen and zinc vacancies. Optical measurements suggest that inhomogeneity in cationic distribution, probably caused by the rapidity of synthesis, is prevalent even after annealing at temperatures up to 1200 °C, and plays a significant role in controlling the emission properties of the spinel. The microwave-assisted technique using metalorganic precursors is an easy path to the rapid synthesis of doped ZnAl2O4 phosphors.

A hybrid LIBS–Raman system combined with chemometrics: an efficient tool for plastic identification and sorting

AbstractClassification of plastics is of great importance in the recycling industry as the littering of plastic wastes increases day by day as a result of its extensive use. In this paper, we demonstrate the efficacy of a combined laser-induced breakdown spectroscopy (LIBS)–Raman system for the rapid identification and classification of post-consumer plastics. The atomic information and molecular information of polyethylene terephthalate, polyethylene, polypropylene, and polystyrene were studied using plasma emission spectra and scattered signal obtained in the LIBS and Raman technique, respectively. The collected spectral features of the samples were analyzed using statistical tools (principal component analysis, Mahalanobis distance) to categorize the plastics. The analyses of the data clearly show that elemental information and molecular information obtained from these techniques are efficient for classification of plastics. In addition, the molecular information collected via Raman spectroscopy exhibits clearly distinct features for the transparent plastics (100% discrimination), whereas the LIBS technique shows better spectral feature differences for the colored samples. The study shows that the information obtained from these complementary techniques allows the complete classification of the plastic samples, irrespective of the color or additives. This work further throws some light on the fact that the potential limitations of any of these techniques for sample identification can be overcome by the complementarity of these two techniques. Graphical Abstractᅟ

Diffusion-controlled growth of CuAl2O4 Nanoparticles: Effect of Sintering and Photodegradation of Methyl Orange

ABSTRACT Facile synthesis of CuAl2O4 and sintering effects on the phase composition are reported. Annealing at 500 °C showed only CuO phase and the spinel phase started evolving at 700 °C with the concurrent decrease in the CuO phase. Diffusion-mediated growth of spinel phase was also observed at higher temperatures forming CuAl2O4 at 1000 °C. The material was stoichiometric and the average particle size was 55 nm, as evidenced by EDS and FE-SEM studies, respectively. The zeta potential of +30 mV and lower (0.346) value of the poly dispersive index (PDI), confirmed the high dispersability of CuAl2O4 in water. The favourable band gap (2.2 eV) makes it suitable as visible light photocatalyst. Owing to its positive surface charge and conducive pH, material could adsorb anionic methyl orange dye. A total of 74% of the dye could be recovered by a simple methanolic extraction. The visible light photocatalysis of the same dye leads to 67% decolouration and the addition of H2O2 accelerated the photodegradation to completion. The catalyst displayed excellent reusability and stability even after five successive runs.

Adsorptive CuO/CuAl2O4 nanoparticles for the separation of aqueous methyl orange

A simple method for the separation of aqueous methyl orange, an azo dye, is reported, where CuO/CuAl2O4 nanoparticles synthesisedby co-precipitation methodwere used as the adsorbent. The presence of cubic CuAl2O4 (CAO) and monoclinic CuO phase of this composite material was confirmed by X-Ray diffraction and its specific surface area wasdetermined by BET nitrogen adsorption method.To study the nature of surface charge, theisoelectric point of the material was determined using the pH drift methodfollowing which the rate of decolouration was studied forpH 5and pH 7. Theexperiments in the absence oflight show that adsorption of the dye is prevalent even up to 6h leading to 86% decolouration.A methanolic extraction was effectivefor quantitative separation ofadsorbed dye fromCuO/CuAl2O4 nanoparticles regenerating them for reuse. The presence of methyl orange in the extracted solution and on the nanoparticles at various stages was verified byUV-Visible and FT-IR spectroscopic methods.The extent of adsorption was quantified and found tobe as high as 86%. The catalyst aftercomplete extraction ofmethyl orange (MO),could be reused for the decolouration. Stability of the nanoparticles after reuse was verified by the closematch of XRD patterns ofthe pure and reused CAOwhich show no significant changes in itscrystal structure. The separation method shown here can be extended for the removal of other azo dyesfrom textile effluents.