Near-infrared Spectrophotometer Research Articles

Promising molybdenum trioxide films for optically detectable gas sensor and solar cell applications

Sub-stoichiometric molybdenum trioxide (MoO3−x) thin films were grown by thermal evaporation techniques on glass, single crystal silicon Si and Fluorine doped Tin Oxide (FTO) glass substrates with different thicknesses. It was found that, Oxygen vacancies play an important role on properties of MoO3−x films. The structural properties of these films were analyzed by means of x-ray diffraction, energy dispersive analysis of x-ray, scanning electron microscopy. The film surface uniformity and smoothness with thickness was tested using the surface roughness measurement for MoO3−x films grown on glass and FTO. The optical properties of all presented films were investigated using UV–vis–near-infrared (NIR) spectrophotometer Optical transmittance and reflection of MoO3−x film were measured in the wavelength range from 200 to 2500 nm. MoO3−x film with 500 nm thick was tested optically for gas sensor applications. The effect of chlorine exposure on the optical transmittance of MoO3−x film with 500 nm thick deposited on glass was studied. Transmittance degradation as increasing the period of exposure was observed, indicating to the high sensitivity of MoO3−x to chlorine gas. The electrical resistivity and Seebeck coefficient of MoO3−x film with 500 nm thick were measured. Low resistivity (∼10−3 Ω.cm) and high transmittance (∼78%) in the visible spectrum of the film of 100 nm thick deposited on FTO coated glass substrate recommended it to be promising as transparent conductive electrode for solar cell.

Near-infrared spectroscopy-based methods for quantitative determination of active pharmaceutical ingredient in transdermal gel formulations

Semi-solid pharmaceutical forms, like topical and transdermal products, are widely used for medical purposes since they provide convenient and pain-free treatment for patients. In this study, two transdermal gel formulations with different active pharmaceutical ingredients were analyzed with near-infrared spectrophotometers with three distinct optical arrangements (dispersive, Fourier transform, and diode-array spectrophotometers) for the measurement of active pharmaceutical ingredient concentration. The reference concentrations were measured with high-performance liquid chromatography methods.The developing of calibration for reference concentrations based on near-infrared spectra was performed using partial least squares regression. The spectra from near-infrared spectrophotometer with diode-array optical arrangement presented the best root mean square error of cross-validation results with 0.045% and 0.144% for the two active pharmaceutical ingredients. The root mean square error of cross-validation using dispersive spectra were 0.125% and 0.193% and using Fourier transform spectra were 0.130% and 0.344% for the active pharmaceutical ingredients. The results of partial least squares regression were confirmed using simulated spectra based on the measured datasets.Near-infrared spectroscopy can be used successfully for the quantitative measurement of active pharmaceutical ingredient concentration in transdermal gel formulations. The type of optical arrangements of spectrophotometers can influence the performance of calibrations and have to be optimized case by case.

Discriminating muscle type of selected game species using near infrared (NIR) spectroscopy

In this study near infrared (NIR) spectroscopy was used to discriminate between different muscle types within each species of selected game animals, and to classify species regardless of the muscle. Muscle steaks from longissimus thoracis et lumborum (LTL) located at the 6th rib of the carcasses, infraspinatus (IS) and supraspinatus (SS) located on the forequarter, and biceps femoris (BF), semitendinosus (ST) and semimembranosus (SM) located on the hindquarter of impala and eland species; and samples from fan fillet (FF), big drum (BD), triangle steak (TS), moon steak (MS) and rump steak (RS) of ostrich species were scanned with a handheld NIR spectrophotometer in the spectral range of 908–1700 nm. Spectra were pre-treated with different pre-processing methods and classification models were developed using partial least squares discriminant analysis (PLS-DA). Classification accuracies were higher when the muscles were grouped according to their anatomical location in the carcass, than attempting to classify them separately. Classification accuracies ranging from 85.0 to 100% were achieved throughout, with forequarter muscles yielding the highest classification accuracy rate for both impala and eland species. Furthermore, when the species were discriminated regardless of muscles, PLS-DA models pre-treated with SNV-Detrend and Savitzky-Golay 1st derivative yielded accuracies of 97, 81 and 92% for eland, impala and ostrich, respectively. These results indicate that NIR spectroscopy can be used for the authentication of game meat, specifically impala, eland and ostrich. Furthermore, it was easier to discriminate species regardless of the muscle used than different muscles within each species.

Structure and optical properties of CrOxNy films with composition modulation

ABSTRACTThe composition and structure properties of the CrOxNy films deposited by RF reactive magnetron sputtering were investigated and correlated with their optical properties. Two kinds of targets Cr2O3 and CrN compounds with variation of N2 and O2 gas flow were used to prepare two series of samples. The phase structure, chemical composition and optical properties of CrOxNy films were characterised by X-ray diffraction, X-ray photoelectron spectroscopy and ultraviolet–visible near-infrared spectrophotometer, respectively. The films mainly consist of Cr2N and CrO3 phases. The Cr/ON ratio derived by XPS varies with the variation of nitrogen with Cr2O3 target. But only lower nitrogen content is detected with variation of oxygen using CrN target. The CrOxNy films with higher nitrogen content possess high absorbance around at 35% in the visible light range no matter the target.

Synthesis and Non-Destructive Characterization of Zinc Selenide Thin Films

Abstract The present work encloses the deposition of three zinc selenide (ZnSe) thin films of thickness 175 nm, 243 nm, and 286 nm using thermal evaporation technique under a vacuum of 5 × 10−5 mbar. The deposited ZnSe thin films are characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), surface profilometer, ultraviolet (UV)-visible (Vis)-near-infrared (NIR) spectrophotometer and Raman spectroscopic measurements. The structure and morphology measurements reveal that the deposited ZnSe material is nanocrystalline having a cubic structure whose crystallinity increases with an increase in film thickness/evaporation rate. The optical band gap estimated from the optical transmission spectra of the films is found to be 2.62 eV, 2.60 eV, and 2.57 eV, respectively, which decreases with an increase in film thickness. The estimation and polynomial curve fit analysis of refractive index, extinction coefficient, and dielectric constant indicates that these physical quantities are fifth-order polynomial function of wavelength. The obtained results are compared and analysed for justification and application of ZnSe thin films.

Superhydrophobic coatings with self-cleaning and antibacterial adhesion properties for denture base

In this paper, coatings with antibacterial adhesion, excellent biocompatibility, good superhydrophobicity and highly transmittance were fabricated by mixing hydroxyl group fluropolymer (PHF), polyurethane oligomer (Pre-PU) with epoxy functionalized SiO2 nanoparticles and thermal-crosslinked. The properties of coatings were investigated by Fourier transform infrared spectroscopy (FT-IR), Scanning electron microscopy (SEM), Atomic force microscopy (AFM), Ultraviolet near-infrared visible spectrophotometer (UV-3600). The morphology results indicated that the roughness scale of micro-nano structure surface can be monitored by changing the contents of functionalized polymers and SiO2. The coating S2 showed outstanding superhydrophobicity with the contact angle of 155.9°, the sliding angle less than 1°, and good transparency. Furthermore, the coating exhibited antibacterial adhesion and favorable biosafety, confirming a potential for application in the oral field.

Evaluation of a low-cost portable near-infrared spectrophotometer for in situ cocaine profiling

The potential of a low-cost (∼US$ 1000) portable near-infrared (NIR) spectrophotometer for in situ characterization of seized cocaine samples was evaluated. A set of 240 samples of cocaine seized in several regions and cities across Brazil by its federal police was employed in this study. These samples were previously analyzed by chromatography at the Forensic Chemistry Laboratory of the National Institute of Criminalistics in Brasília-DF for the contents of several constituents to chemically characterize the samples. A low-cost NanoNIR spectrophotometer (Texas instruments) was used to acquire the NIR spectra of the samples in the range 900–1700 nm. The spectra set was treated by the second derivative to construct and validate multivariate regression (Partial Least Square – PLS) and classification (software independent modeling of class analogy – SIMCA) models aiming to characterize the samples. Consequently, an informative toll for objective decision making could be used by the police agents to produce immediate answers to forensic questions raised at the point of seizing. Among those questions the most relevant are: does the seized sample contain cocaine? what is the cocaine form? what is its content? is the sample adulterated and/or diluted? what is the content of adulterant? is the sample significantly adulterated and/or diluted? what is the degree of oxidation of the cocaine? The results of this work allow to propose a NIR/chemometrics based analytical protocol providing fast answers to these questions with satisfactory confidence level for the purpose of reliably screen the seized samples.

Development and performance test of an in-situ soil total nitrogen-soil moisture detector based on near-infrared spectroscopy

In order to accurately acquire soil total nitrogen (STN) content and soil moisture (SM) content, an in-situ STN-SM content detector was developed, and the stability and accuracy of the detector were tested. The in-situ detector consisted of an optical unit, a control unit and a mechanical unit. The optical unit comprised eight single band Near-infrared (NIR) laser sources at 1260, 1330, 1360, 1430, 1530, 1580, 1660 and 1450 nm, collimator and an InGaAs photoelectric sensor, a laser source holder with “Eight faces” umbrella structure and sapphire glass. The control unit was composed of hardware part and software part. The hardware part included I-U conversion circuit, amplifier and filter circuit, and JN5139 module responsible for A/D conversion and data transmission. The software part of the program was written in the JN5139 microcontroller unit. The mechanical unit comprised a cylindrical detection darkroom, an electrical component mounting tray and a cylindrical shading and dust cover. The stability test results showed that the repeatability error at eight sensitive bands were 0.7758%, 0.8091%, 0.7958%, 0.5189%, 0.6405%, 0.8556%, 0.7391% and 0.5294%, respectively. The correlation coefficients between the absorbance of in-situ detector and MATRIX-I Fourier transform near-infrared spectrophotometer were all above 0.88. A portable LED STN content detector was taken as the reference in the performance test. The results showed that the calibration coefficient Rc2 and the validation coefficient Rv2of in-situ detector model were 0.8322 and 0.7832, respectively. While those of the portable LED STN content detector model were 0.7205 and 0.6851, respectively. Two regression models were established for the SM content by respectively using the portable LED STN content detector and the in-situ detector, and the results showed that both detectors had good detection effects in SM. The experimental results showed that compared with the portable LED STN content detector, in-situ detector greatly improved the STN content detection precision, and could realize STN and SM content field detection in real-time.

Effect of Ni Addition on Catalytic Performance of Fe87Si5B2P3Nb2Cu1 Amorphous Alloys for Degrading Methylene Blue Dyes

Fe-based amorphous alloys have shown great potential in degrading azo dyes and other organic pollutants. It has been widely investigated as a kind of environmentally friendly material for wastewater remediation. In this paper, we studied the effect of Ni addition on the catalytic performance of Fe87Si5B2P3Nb2Cu1 amorphous alloy for degradation of methylene blue dyes and analyzed the reaction mechanism. (Fe87Si5B2P3Nb2Cu1)86Ni14 amorphous powder with desirable performance was produced by specific ball milling durations. Characterization of the Fe87Si5B2P3Nb2Cu1 and (Fe87Si5B2P3Nb2Cu1)86Ni14 amorphous alloys prepared by ball milling was performed by XRD and SEM. Fe87Si5B2P3Nb2Cu1 and (Fe87Si5B2P3Nb2Cu1)86Ni14 amorphous alloys were used as catalysts to catalyze the degradation of methylene blue dyes, which were detected by UV-VIS near-infrared spectrophotometer. By a series of comparative experiments, it was found that a catalyst dosage of 0.2 g and a reaction temperature of 80 °C were conditions that produced the best catalytic effect. The degradation rate of (Fe87Si5B2P3Nb2Cu1)86Ni14 amorphous alloy to methylene blue dyes prepared by ball milling increased from 67.76% to 99.99% compared with the Fe87Si5B2P3Nb2Cu1 amorphous alloy under the same conditions.

Calibration development for nutritional evaluation of Yam (Dioscorea sp.) using Near-Infrared Reflectance Spectrophotometry (NIRS)

The aim of yam breeders is to produce many hybrids, which can form the basis of selecting quality nutritional traits and other characteristics using certain agronomic criteria. Chemical methods are employed to determine the main constituents of yam, which are time-consuming, expensive, and involve sample destruction. However, the constraints of lengthy analysis time and the cost needed to analyze thousands of these genotypes are major constraints to yam breeding in Nigeria. This study was undertaken to develop and validate calibration equations on the Near-Infrared Reflectance Spectrophotometer (NIRS) for determining chemical compositions of selected yam genotypes. Equations developed for moisture, ash, protein, crude fiber, and tannin showed high coefficients of determination (R2) for the calibration curve (0.87, 0.84, 0.83, 0.80, and 0.89, respectively) and high to medium coefficients of determination in cross-validation (0.80, 0.68, 0.69, 0.68, and 0.50). The standard errors of calibration (SEC) and the standard errors in cross-validation (SECV) were low for most constituents. A total of 360 ascensions of yam flour were predicted for selected traits to test the equations, and the results were comparable with data from conventional methods. Results of this study have shown that NIRS could be a very useful tool to help yam breeders screen large sample sets using limited resources with very short time. This will enhance breeders’ rapid selection of genotypes at screening stage where many breeding lines are to be evaluated within the shortest time possible.

Evaluation of a handheld near-infrared spectrophotometer for quantitative determination of two APIs in a solid pharmaceutical preparation

The aim of this study is to evaluate the performance of a handheld NIR spectrophotometer for the quantitative determination of two APIs in a solid pharmaceutical preparation (tablet).

The substratostat - an automated near-infrared spectroscopy-based variable-feed system for the continuous alcoholic fed-batch fermentation of high gravity grape must at static sugar concentrations

Aim: High sugar concentrations in musts cause a hyperosmotic stress response in Saccharomyces cerevisiae increasing the risk of sluggish and stuck alcoholic fermentations and/or causing high acetic acid levels. Applying a fed-batch technique where sugar levels are kept at a constant, low rate throughout fermentations reduces this stress but requires in-situ quantification of sugars and process automation for practicability. The aim of this work was to develop and validate a near-infrared (NIR) spectroscopy method allowing for the continuous in-situ quantification of total fermentable sugars in fully turbid alcoholic fermentations of grape musts. Calibration models for glucose, fructose and the fermentation product ethanol were also established.Methods and results: A research Fourier-transform NIR spectrophotometer equipped with a transflectance probe was used to acquire spectra from 240 natural and semisynthetic standards from fermentations conducted using varying concentrations of yeast and yeast nutrients. Using chemometric software, calibration models for total sugars, glucose, fructose and ethanol demonstrated R2 values >0.93 and prediction error (RMSEP) values of 11.6 g l-1, 12.3 g l-1, 10.2 g l-1, and 0.328 % v/v, respectively. The method was integrated with modern process automation technology and was able to maintain sugar concentrations within 5 g l-1 of the 45 g l-1 setpoint adjusted during alcoholic fermentations.Conclusions: The NIR calibration models generated allow prediction of total sugar levels accurately enough to conduct fully automated fed-batch grape must fermentations at constant substrate concentrations. Application of a transflectance probe measuring a high proportion of back-scattered radiation proved useful and necessary considering the high degree of turbidity during fermentations. Placement of the measurement probe in a recirculation loop decreased interference from biomass sedimentation and adherence of CO2 bubbles.Significance and impact of the study: This study presents a fully automated system to carry out fed-batch fermentations which allow circumventing the hyperosmotic stress response of S. cerevisiae during alcoholic fermentations. Calibrated for other substrates, the system may be used in other food and non-food fermentations, too.

Improving anti-infrared radiation and heat insulation by potassium hexatitanate whisker-doped Al 2 O 3 –SiO 2 composite xerogel

Taking potassium hexatitanate whisker (PTW) modified by silane coupling agent KH550, aluminium nitrate inorganic salt and tetraethyl orthosilicate and deionized water, respectively, as infrared sunscreen, aluminium source and raw materials forming the network structure of a composite xerogel, a series of structurally intact PTW-doped Al2O3–SiO2 composite xerogel thermal-insulating materials were prepared by the sol–gel method and dried under atmospheric pressure. The infrared spectral characteristics, infrared radiation transmittance, microstructures, morphology and thermal conductivity of different composite materials prepared have been determined by a Fourier transform infrared spectrometer, UV–visible–near-infrared spectrophotometer, X-ray diffractometer, scanning electron microscope and thermal conductivity tester. The results exhibit that when the Al to Si molar ratio is 1 : 9, the composite material with 5 wt% modified PTW shows the best infrared radiation blocking performance and the lowest thermal conductivity (0.0604 W m−1 K−1).

Technical note: Comparison of dry matter measurements from handheld near-infrared units with oven drying at 60°C for 48 hours and other on-farm methods

This study compared dry matter (DM) predictions of 3 handheld near-infrared spectrophotometer (NIRS) units (Moisture Tracker, Digi-Star Inc., Fort Atkinson, WI) to conventional oven drying at 60°C using 2 alfalfa and 2 corn silages. In addition, on-farm DM methods [microwave, Koster tester (Koster Moisture Tester Inc., Brunswick, OH), and food dehydrator methods] were also compared. Corn and alfalfa silages (1,600 g) obtained from the University of Wisconsin Dairy Cattle Center (DCC) and the Arlington Research Station (ARS) were analyzed for DM daily for 20 d. Two NIRS calibration methods were also tested within each unit. The DM predicted from the factory-preset calibrations was NIRf. The adjusted DM prediction was NIRa, where the average difference between oven-dried and NIRf determined on duplicate forage samples for 3 d before the experiment was used as a bias adjustment for all subsequent DM determinations. The average predicted DM from the 20 scans was recorded as the forage DM. The process was repeated 3 times with each NIRS unit. Two 100-g subsamples of each forage were also oven-dried for 48 h at 60°C daily in a forced-air oven. Oven DM of ARS and DCC alfalfa silages were 37.3 ± 1.1% and 48.5 ± 1.9%, respectively (mean ± standard deviation). Oven DM of ARS and DCC corn silages were 34.7 ± 1.2% and 37.4 ± 0.5%, respectively (mean ± standard deviation). Dry matter determinations from NIRf were on average 3.5 units higher than the oven DM values. The NIRa DM predictions were on average 1.7 DM units lower than the oven DM values. Additionally, differences among the 3 NIRf probe results were detected (43.1, 40.7, and 41.3% DM, respectively), but all other results were similar between probes. Determinations of DM by the microwave and food dehydrator were also similar with the 60°C, 48-h oven method, whereas the Koster tester was lower than the oven. The handheld NIRS units more accurately predicted DM content of the alfalfa silage but were not as accurate with corn silages when the factory preset calibrations were corrected for bias.

Smartphone near infrared monitoring of plant stress

The most widely used method for monitoring plant stress is the use of near infrared (NIR) spectrophotometry to calculate normalized difference vegetation index (NDVI), as defined by [NIR reflectance − red reflectance]/[NIR reflectance + red reflectance]. NDVI measures the chlorophyll absorption in the red spectrum relative to the scattering by cellular structure in NIR, and has been used to monitor vegetation health and subsequently its stress from aerial or satellite images. Rather than using an NIR spectrophotometer or an NIR camera that is rather expensive, we attempted to use a commercial smartphone, utilizing its (potentially unintended) ability in recognizing near infrared (NIR) color. Some of the most recent versions of smartphones have eliminated the NIR block filters on their cameras, and able to recognize NIR in their red pixels of CMOS array. Through attaching an inexpensive high pass filter at 800 nm to a smartphone camera, we were able to collect the NIR reflectance (with a high pass optical filter) and the red reflectance (without a filter), enabling NDVI assessments. This method was verified by measuring the NDVI values from a series of chlorophyll solutions, and showed a strong linear correlation with R2 = 0.948, corroborating the smartphone’s ability in evaluating NDVI. Using the leaves from three different plant species, the NDVI values were evaluated using the smartphone and compared with the plants’ chlorophyll contents using acetone extraction and subsequent spectrophotometry. A good linear relationship was found with R2 = 0.88–0.92. We further evaluated the NDVI values against the plants’ water contents (measured by oven-drying), showing the non-linear relationship with the NDVI saturation above 50% water content. The assay time was almost instantaneous, requiring only a smartphone and a high pass filter, thus allowing inexpensive, easy-to-use, rapid, and early prediction of plant stress that can be used for field and household applications.

Transparent heat insulation coatings with high selective shielding ability designed with novel superstructures of copper sulfide nanoplates

In the present work, novel CuS superstructures composed of intersectional CuS nanoplates (CuS i-nanoplates) and snowflake-like CuS nanoplates (CuS s-nanoplates) were successfully synthesized at a low temperature (80 °C) by a simple chemical precipitation method. It has been found that the as-synthesized CuS superstructures were formed by the growth of CuS i-nanoplates along the direction perpendicular to the basal nanoplate with a thickness of 29.64 ± 3.16 nm and CuS s-nanoplates were prepared with the snowflake-like morphology with a thickness of 16.82 ± 3.62 nm. Subsequently, a new transparent heat insulation coating with CuS superstructures composed of CuS i-nanoplates as NIR shielding agent (coded as H–X coating) was prepared by mixing with acrylic-amino-alkyd baking varnish and coating to ordinary glass substrates. Simultaneously, another transparent heat insulation coating with s-nanoplates (coded as S–X coating) was also synthesized. Optical properties of those coatings were studied as a function of the CuS content by using ultraviolet–visible–near-infrared spectrophotometer. And the H–X coatings were shown to have a higher selective shielding ability for solar light than S–X coatings since the shielding ability of S–X coatings in the region of 1180–2500 nm rapidly weakened with increasing wavelength. The comparative study on the properties of nanomaterials with different morphologies in this paper may provide some new guidance for material design to improve its performance. Moreover, the CuS superstructure-based transparent heat insulation coatings with excellent NIR shielding property have a potential application in energy-saving windows for architectures and vehicles.

Classification of Chicken Parts Using a Portable Near-Infrared (NIR) Spectrophotometer and Machine Learning.

Identification of different chicken parts using portable equipment could provide useful information for the processing industry and also for authentication purposes. Traditionally, physical-chemical analysis could deal with this task, but some disadvantages arise such as time constraints and requirements of chemicals. Recently, near-infrared (NIR) spectroscopy and machine learning (ML) techniques have been widely used to obtain a rapid, noninvasive, and precise characterization of biological samples. This study aims at classifying chicken parts (breasts, thighs, and drumstick) using portable NIR equipment combined with ML algorithms. Physical and chemical attributes (pH and L*a*b* color features) and chemical composition (protein, fat, moisture, and ash) were determined for each sample. Spectral information was acquired using a portable NIR spectrophotometer within the range 900-1700 nm and principal component analysis was used as screening approach. Support vector machine and random forest algorithms were compared for chicken meat classification. Results confirmed the possibility of differentiating breast samples from thighs and drumstick with 98.8% accuracy. The results showed the potential of using a NIR portable spectrophotometer combined with a ML approach for differentiation of chicken parts in the processing industry.

A prototype measuring system of soil bulk density with combined frequency domain reflectometry and visible and near infrared spectroscopy

A combined-penetrometer sensor prototype (CPSP) for the measurement of topsoil bulk density (BD) was developed and tested under field conditions. The prototype consisted of a standard penetrometer, equipped with a near infrared spectrophotometer (NIRS) (1650–2500 nm) to measure gravimetric moisture content (ω) and a frequency domain reflectometry (FDR) to measure volumetric moisture content (θv), while BD was assessed by the combination of both sensors’ data. The CPSP was tested in situ at five arable and two grassland fields of different soil texture classes in Silsoe, Bedfordshire, UK, during the period from August to December 2013. Artificial neural networks (ANN) were used to predict ω and θv based on data fusion of NIRS diffuse reflectance spectra and FDR output voltage (V), and the predicted values were substituted in a model to predict BD. The CPSP showed more accurate BD assessment in grass fields with root mean square error of prediction (RMSEp) of 0.077 g cm−3, compared to arable fields (RMSEp = 0.104 g cm−3). A collective BD model produced for arable and grass fields provided a moderate accuracy with a RMSEp of 0.102 g cm−3. It can be concluded that the new CPSP can be used successfully to measure BD in the topsoil by combining the NIRS and FDR techniques through ANN-data fusion approach.

Tellurite suboxide based near-infrared reflector and filter

TeO1.4/SiO2 one-dimensional photonic crystals (1D PCs) were prepared using radio frequency (RF) magnetron sputtering to fabricate a reflector and a filter with photonic band gaps (PBGs) in the near infrared (NIR) region. Stoichiometry and phase state of the TeOx thin film were characterized via X-ray photoelectron spectroscopy (XPS) and X-Ray Diffraction (XRD), respectively. The microstructural and optical characteristics of the 1D PCs were evaluated using scanning electron microscopy (SEM), atomic force microscopy (AFM) and ultraviolet visible near-infrared spectrophotometer (UV-VIS-NIR). The experimental reflectance spectra were consistent with the theoretical results simulated using the transfer matrix method (TMM). For the reflector, a PBG of 1273–1676 nm (Δλ = 403 nm) was achieved in the NIR region. For the filter, the introduction of a defect layer in the 1D PC led to a resonant peak at the central wavelength of 1461 nm within the PBG of 1250–1733 nm (Δλ = 483 nm). The effects of the structural parameters, including the incident angle, the state of polarization and the thickness of the defect layer, were also theoretically analyzed.

Coupling Continuous Flow Microreactors to MicroNIR Spectroscopy: Ultracompact Device for Facile In-Line Reaction Monitoring

In this study, we applied a portable near-infrared spectrophotometer (MicroNIR) for in-line monitoring of the synthesis of 5-hydroxymethylfurfural (5-HMF) in a continuous flow microreactor. Under the best reaction conditions using isopropyl alcohol/dimethyl sulfoxide as the reaction solvent and a fixed-bed reactor packed with solid acid catalyst, total conversion of d-fructose was observed, and 5-HMF was obtained in 95% yield with a residence time of just 11.2 min. Principal component analyses and construction of multivariate control charts based on Hotelling’s T2 and Q residuals were also performed and proved the excellent response of the compact MicroNIR device for in-line monitoring of 5-HMF production without variation in the yield over 8 h/day during 5 days. Our results demonstrate the great potential for the application of this compact device in the monitoring of laboratory-scale reactions, which can be extended to industrial scales.