Chemical Composition Gradient Research Articles

Differential associations of five riverine organism groups with multiple stressors

The decline of river and stream biodiversity results from multiple simultaneous occuring stressors, yet few studies explore responses explore responses across various taxonomic groups at the same locations. In this study, we address this shortcoming by using a coherent data set to study the association of nine commonly occurring stressors (five chemical, one morphological and three hydraulic) with five taxonomic groups (bacteria, fungi, diatoms, macro-invertebrates and fish). According to studies on single taxonomic groups, we hypothesise that gradients of chemical stressors structure community composition of all taxonomic groups, while gradients of hydraulic and morphological stressors are mainly related to larger organisms such as benthic macro-invertebrates and fish.Organisms were sampled over two years at 20 sites in two catchments: a recently restored urban lowland catchment (Boye) and a moderately disturbed rural mountainous catchment (Kinzig). Dissimilarity matrices were computed for each taxonomic group within a catchment. Taxonomic dissimilarities between sites were linked to stressor dissimilarities using multivariable Generalized Linear Mixed Models.Stressor gradients were longer in the Boye, but did in contrast to the Kinzig not cover low stress intensities. Accordingly, responses of the taxonomic groups were stronger in the Kinzig catchment than in the recently restored Boye catchment. The discrepancy between catchments underlines that associations to stressors strongly depend on which part of the stressor gradient is covered in a catchment. All taxonomic groups were related to conductivity. Bacteria, fungi and macro-invertebrates change with dissolved oxygen, and bacteria and fungi with total nitrogen. Morphological and hydraulic stressors had minor correlations with bacteria, fungi and diatoms, while macro-invertebrates were strongly related to fine sediment and discharge, and fish to high flow peaks. The results partly support our hypotheses about the differential associations of the different taxonomic groups with the stressors.

Сравнительный анализ химического состава и механических свойств различных участков сварного соединения дюралюмина, полученного сваркой трением с перемешиванием

Friction stir welding is an advanced method of joining various metals and alloys in the aircraft and mechanical engineering industries. This type of welding is used to join materials that are difficult to weld or not weldable by conventional methods. The high-strength D16 aluminum alloy is difficult to weld by fusion, which is associated with the formation of a dendritic structure in the fusion zone leading to a decrease in the mechanical strength of the joint. In the work, the microstructure and microhardness of a welded seam of the D16 aluminum alloy produced by friction stir welding was studied. Using scanning electron microscopy and optical metallography, the authors identified the presence of three zones: the weld core, the thermomechanical impact zone, and the heat effected zone. In the central part of the welded joint (in the core), a laminated onion ring structure was discovered. A change in the chemical composition of the aluminum solid solution was identified in different areas of the weld zones, as well as the presence of a concentration gradient within each zone. In the upper part of the welded seam, the solid solution is silicon-enriched and depleted in copper. Due to the solid solution depletion in alloying elements, the aluminum content in the solid solution in the zone of the welded joint is higher compared to the initial state. The microhardness values in different areas of the welded joint correlate with changes in the chemical composition. In the welded joint zone, a significant decrease in microhardness was found compared to the initial state, and a change in microhardness associated with the chemical composition gradient within each zone was also observed.

Effect of Thermal Aging on the Microstructure and Mechanical Properties of ER308L/Z2CND18.12N2 Dissimilar Welds.

A multi-analytical approach was used to investigate the effect of thermal aging on the microstructure and mechanical properties of ER308L/Z2CND18.12N2. The results demonstrated that fractures occurred preferentially on the ER308L side. Z2CND18.12N2 exhibited superior fracture toughness compared to ER308L regardless of thermal aging time. The ultimate tensile strength significantly increased from 564.5 MPa in the unaged condition to 592.7 MPa to MPa after thermal aging and the fracture mode changed from ductile fracture into a ductile + quasi-cleavage fracture. The fusion zone (FZ) with the chemical composition gradient was about 40 μm from the Z2CND18.12N2 to ER308L. After thermal aging, spinodal decomposition and G-phase precipitation were observed for the first time in the ferrite phase of the FZ. Moreover, the hardness presented the following trend: FZ > ER308L > Z2CND18.12N2. The hardness of the ferrite phase dramatically increased from 6.13 GPa in an unaged condition to 8.46 GPa in a 10,000 h aged condition.

Microstructure Evolution at Ni/Fe Interface in Dissimilar Metal Weld between Ferritic Steel and Austenitic Stainless Steel.

The formation and evolution of microstructures at the Ni/Fe interface in dissimilar metal weld (DMW) between ferritic steel and austenitic stainless steel were investigated. Layered martensitic structures were noted at the nickel-based weld metal/12Cr2MoWVTiB steel interface after welding and post-weld heat treatment (PWHT). The formation of the interfacial martensite layer during welding was clarified and its evolution during PWHT was discussed by means of scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), electron probe microanalysis (EPMA), focused ion beam (FIB), transmission electron microscopy (TEM), energy dispersive X-ray (EDX), transmission kikuchi diffraction (TKD), phase diagrams, and theoretical analysis. In as-welded DMW, the Ni/Fe interface structures consisted of the BCC quenched martensite layer and the FCC partially mixed zone (PMZ), which was the result of inhomogeneous solid phase transformation due to the chemical composition gradient. During the PWHT process, the BCC interfacial microstructure further evolved to a double-layered structure of tempered martensite and quenched martensite newly formed by local re-austenitization and austenite-martensite transformation. These types of martensitic structures induced inhomogeneous hardness distribution near the Ni/Fe interface, aggravating the mismatch of interfacial mechanical properties, which was a potential factor contributing to the degradation and failure of DMW.

Long-term trends in inorganic aerosol chemical composition and chemistry at an urban and rural site in the northeastern US

Atmospheric nitrate and sulfate are major inorganic particulate matter components that impact human and ecosystem health and air quality. Over the last several decades, emissions of the precursor gases, nitrogen oxides (NOx = NO + NO2) and sulfur dioxide (SO2), have dramatically decreased in the US in response to federal regulations. However, the response in concentrations of particulate nitrate (pNO3) and sulfate (pSO4) have not followed predictions due to complex non-linear chemistry feedbacks that may differ amongst environments (i.e., urban vs. rural). In this study, we explored the long-term response of particle chemistry for urban and rural environments in southern New England, a region historically impacted by NOx and SO2 emissions. Particulate matter (PM10) samples collected via the same method from 2005 to 2015 at urban and rural locations in Rhode Island were analyzed for their major inorganic components, and air mass trajectories and statistical analysis were used to identify source regions over time. Our results indicated a significant urban-rural aerosol chemical composition gradient for sampling locations within 40 km. Over time, as anthropogenic influences have decreased, the relative contribution of marine and crustal sources has increased greatly, impacting fine and coarse particle chemistry in recent years. Total mass concentrations of chemical species, particularly anthropogenic pSO4 and particulate ammonium (pNH4), have shown dramatic decreases over the ten years at both the urban and rural sites; however, pNO3 concentration increased by 95 % and 57 % in the urban and rural sites, respectively, despite significant NOx emission reductions. Our results demonstrate that changes in chemical mechanisms due to the decrease in SO2 emissions contributed to decreases in pNH4, along with enhanced pNO3 concentration. Furthermore, the change in SO2 emissions has significantly impacted the atmospheric lifetime and transport distance of pNH4, favoring more localized contributions in recent years.

Evolution mechanism of interfacial microstructure and its effect on failure in dissimilar metal welds containing ferritic heat resistant steels

This study investigated the behaviour and mechanism of interfacial microstructure evolution during long term high temperature exposure and the effect of interface structure on creep failure in the dissimilar metal welds (DMWs) involving ferritic heat resistant steels with nickel-based filler metal. The welding of nickel-based and ferritic materials led to the formation of interfacial martensite layer in the ferritic steel side of DMW. During long term high temperature exposure, interfacial martensite transformed to ferrite due to C diffusion and migration in the micro-region near the BCC/FCC interface between the martensite layer and the weld metal. The martensite-ferrite transformation was attributed to the large C chemical potential gradient caused by chemical composition gradient. Under creep condition, the failure of DMW was prone to occur along the weld metal/ferritic steel interface, which was related to strain concentration around the interfacial ferrite formed during service. Hence, the relationships between interface structures before and after service and interfacial failure in the DMWs were clarified.

Influence of interface orientation and surface quality on structural and mechanical properties of SS316L/IN718 block produced using directed energy deposition

Functionally graded materials manufactured by additive manufacturing technologies reached high interest in additive manufacturing community over the last decades. High potential of additively manufactured multi-materials was demonstrated by many studies over the last 10 years. Most of the studies dealing with functionally graded materials had one common sign, which is the chemical composition gradient being controlled in the building direction of the final product. Hence, the multi-material interface is mostly situated in horizontal plane (XY) of the product. However, due to a complex geometry of the product, it is not always possible or desirable to achieve certain interface orientation and multi-material interface might incline from the ideal horizontal plane. Typically, corner zones, where interface orientation changes suddenly from horizontal to vertical orientation, are the most critical locations. Therefore, investigation of the interface orientation is important in order to establish the additive manufacturing limitation for certain applications. The current study revealed that the interface inclination has significant influence on the amount and distribution of formed defects at the materials interfaces. Furthermore, it was shown that the interface surface quality in terms of as-deposited surface or machined surface can significantly affects the defects formation. The effect of defects on the tensile specimen's elongation was significant, which based on the interface angle dropped over more than 70%.

Neutronographic Residual Stress Analysis for Materials With Depth Gradients of the Strain Free Lattice Parameter $${{\varvec{d}}}_{0}$$ for the Example of a Case-Hardened Steel 20MnCr5

AbstractIn the present work, ring-shaped samples made from steel 20MnCr5 were low-pressure carburized (LPC) and subsequently hardened by gas quenching (case-hardened). This results in a near-surface gradient in chemical composition, microstructure- and hardness distribution, as well as a three-dimensional residual stress (RS) distribution, which was investigated by neutron diffraction. Near-surface RSs in the ferrite-/martensite- and austenite phase are additionally determined by X-ray diffraction. It is shown that the chemical gradient has an influence on the chosen $${d}_{0}$$ d 0 strategy and how such a reference sample should be extracted. If near-surface RS values are to be determined by neutron diffraction, the pseudo-strain effect must be taken into account. For this purpose, a suitable approach using the “open source” software SIMRES and STRESSFIT is also presented. By combining neutron and X-ray diffraction data, a complete RS distribution over the whole sample can be obtained.

Effect of composition gradient design on microstructure and mechanical properties of dual-wire plasma arc additively manufactured 316L/IN625 functionally graded materials

Wire and arc additive manufacturing (WAAM) is a promising technology for the preparation of refractory metal functional gradient materials (FGMs) due to its high material utilization, high deposition efficiency and ability to create large-sized parts. In the present work, 316L/IN625 FGM with chemical composition gradients of 25 wt% and 100 wt% were fabricated using dual-wire plasma arc additive manufacturing (DW-PAAM) by changing the wire feeding speeds (WFSs) layer by layer. The phase evolution, microstructure, chemical composition and mechanical properties of the FGM were analyzed. The results demonstrated that the microstructure in all regions was predominantly the austenite phase, and no cracks or defects were observed. The microstructure of the 100 wt% 316L zone was composed of the austenite phase (face-centered cubic, FCC) and a small amount of ferrite phase (body-centered cubic, BCC), whereas mainly FCC structure was observed in the other chemical composition regions. There was a certain error between the actual composition gradient and the designed gradient. The microhardness transition of S1 was smoother and wider, while the tensile test results of S2 were better. In addition, the position of the tensile fracture was different for S1 and S2. In conclusion, the DW-PAAM process shows great potential for manufacturing FGM with desirable properties for various industrial applications. Further studies are warranted to optimize process parameters and develop new design strategies to enhance the performance of FGM in various industrial applications.

Nontarget Chemical Composition of Surface Waters May Reflect Ecosystem Processes More than Discrete Source Contributions.

We investigated environmental, landscape, and microbial factors that could structure the spatiotemporal variability in the nontarget chemical composition of four riverine systems in the Oregon Coast Range, USA. We hypothesized that the nontarget chemical composition in river water would be structured by broad-scale landscape gradients in each watershed. Instead, only a weak relationship existed between the nontarget chemical composition and land cover gradients. Overall, the effects of microbial communities and environmental variables on chemical composition were nearly twice as large as those of the landscape, and much of the influence of environmental variables on the chemical composition was mediated through the microbial community (i.e., environment affects microbes, which affect chemicals). Therefore, we found little evidence to support our hypothesis that chemical spatiotemporal variability was related to broad-scale landscape gradients. Instead, we found qualitative and quantitative evidence to suggest that chemical spatiotemporal variability of these rivers is controlled by changes in microbial and seasonal hydrologic processes. While the contributions of discrete chemical sources are undeniable, water chemistry is undoubtedly impacted by broad-scale continuous sources. Our results suggest that diagnostic chemical signatures can be developed to monitor ecosystem processes, which are otherwise challenging or impossible to study with existing off-the-shelf sensors.

Powder Production via Atomisation and Subsequent Laser Powder Bed Fusion Processing of Fe+316L Steel Hybrid Alloy

The current investigation shows the feasibility of 316L steel powder production via three different argon gas atomisation routes (closed coupled atomisation, free fall atomisation with and without hot gas), along with subsequent sample production by laser powder bed fusion (PBF-LB). Here, a mixture of pure Fe and atomised 316L steel powder is used for PBF-LB to induce a chemical composition gradient in the microstructure. Optical microscopy and μ-CT investigations proved that the samples processed by PBF-LB exhibit very little porosity. Combined EBSD-EDS measurements show the chemical composition gradient leading to the formation of a local fcc-structure. Upon heat treatment (1100 °C, 14 h), the chemical composition is homogeneous throughout the microstructure. A moderate decrease (1060 to 985 MPa) in the sample’s ultimate tensile strength (UTS) is observed after heat treatment. However, the total elongation of the as-built and heat-treated samples remains the same (≈22%). Similarly, a slight decrease in the hardness from 341 to 307 HV1 is observed upon heat treatment.

Anomalous hysteresis loops of ferrimagnetic Gd-Co films of different thickness near the magnetic compensation temperature

Triple hysteresis loops were observed for amorphous ferrimagnetic Gd-Co films near the magnetic compensation temperature, which can be a consequence of both the spin-flop transition and the chemical composition gradient. In the work, an assessment of the possible chemical inhomogeneity of the films based on magnetic measurements was carried out and its relationship with the thickness of the samples was observed. Keywords: amorphous magnetic films, perpendicular magnetic anisotropy, ferrimagnetism, magnetic domain structure, magnetic hysteresis.

Аномальные петли гистерезиса ферримагнитных пленок Gd-Co различной толщины вблизи температуры магнитной компенсации

Triple hysteresis loops were observed for amorphous ferrimagnetic Gd-Co films near the magnetic compensation temperature, which can be a consequence of both the spin-flop transition and the chemical composition gradient. In the work, an assessment of the possible chemical inhomogeneity of the films based on magnetic measurements was carried out and its relationship with the thickness of the samples was observed.

Improvement of thin-film Ni-rich ALD cathode for microbatteries

Thin-film Li-ion batteries produced by precise thickness control atomic layer deposition (ALD) method are promising, safe, and high-energy density sources for miniature devices. The paper presents a detailed analysis of the multilayer thin film cathode for microbatteries. Structures were obtained by combining several technological parameters to increase capacity, uniformity, and lifetime. The protective function of a nano-sized coating was demonstrated. The influence of coating application on cathode capacity was explained. The studied structure consists of Ni-rich cathode layer modified with an amorphous Li-Ta-O functional layer on a steel substrate with a Cr coating. The cathode and the functional layer were obtained by the ALD multilayer approach followed by heat treatment at 800 °C for a minute. According to XPS and TEM data, the composition of the cathode after annealing was LiNi0.7Co0.3O2 well-defined structure without separation into Ni-rich and Co-rich layers, with texturing of crystallite pillars and with the absence of Fe. The Li-Ta-O films have a slight chemical composition gradient from Li3Ta1.2O4 on the surface to Ta1.7O5 in bulk. The electrochemical characterization showed that combining the functional layer and cathode heat treatment preserves the electrochemical capacity (32 µAh·µm−1·cm−2) and increases Coulomb efficiency.

Bioinspired superwettability: From interfacial materials to chemistry

<p indent="0mm">Interfacial wettability is one of the fundamental problems in material science. The research on wettability regulation is of great significance in exploring new knowledge and creating new applications. Learning from nature, Prof. Jiang has summarized three basic principles of superwettability: (1) The static wetting is determined by the cooperative effect of nanostructure and surface energy; (2) the transition point of the superlyophilicity and superlyophobicity on the nanostructure is the lyophilicity-lyophobicity limitation; (3) the direction of liquid transport is regulated by chemical composition gradient, rough gradient, curvature gradient, etc. Based on these principles, he further extended the superwettability interfacial material systems to interfacial chemistry. He established a superwetting interfacial material system including 64 combinations, and expanded to various liquid systems with different pressure and temperature ranges, leading and promoting the global development of this field. In this paper, we will introduce the design of superwetting interface and the new law of liquid/gas/solid three-phase interfacial wettability. Based upon the new law of three-phase interfacial wettability, we state the application of water-oil separation, pesticide spraying, electrochemical sensors, and photoelectric material patterning. And the recent research and application prospect in the field of quantum-confined superfluid are discussed. In the part of water-oil separation, focusing on the key issue of constructing membrane materials with both fine pore structure and super-wetting properties, without changing the traditional separation membrane preparation process, the micro-nano multi-level structure of the membrane surface is constructed through structure-induced tuning, and the surface is chemically modified. Synergistic action is used to realize the regulation of membrane transport behavior of water droplets or oil droplets, and a series of novel structural membrane separation materials have been successfully prepared, realizing high-precision and high-throughput separation of oil-water emulsions under low driving pressure. In-depth research on the relationship between the molecular structure of surfactants and the kinetic behavior and thermodynamic state of droplets on specially wetted surfaces has led to the discovery of a very cheap anionic surfactant (sulfosuccinic acid) capable of forming vesicles. Sodium dioctyl ester (AOT) can inhibit the ejection and sputtering of pesticide droplets on the surface of superhydrophobic plants at a very low concentration (3/1000 mass concentration). Aiming at the historical problem of “deficient oxygen” during the use of electrochemical enzyme sensors, we proposed and constructed an oxygen-enriched enzyme electrode with solid/liquid/gas three-phase coexistence. The three-phase electrode will greatly improve the detection performance of existing sensors, has extremely broad application prospects in future disease monitoring, and provides a new design idea for the development of high-efficiency enzyme sensors. We exploit the principle of “liquid bridge confinement assembly” by inducing site-specific condensation and crystallization of small organic molecules by exploiting asymmetric wettability interfaces, fabricating one-dimensional arrays of organic polymer semiconductors by exploiting highly adhesive three-phase interfaces, and exploiting superwetting The micro-nano interface controls the three-dimensional dewetting process and realizes the preparation of highly oriented one-dimensional single-crystal nanowires. These three methods are the key issues to realize one-dimensional micro-nano materials from material preparation to device application. Since 2008, we have successfully achieved the fabrication of smart nanopores that mimic ion channels in biomembranes. This channel has properties similar to biological ion channel switching, selection and rectification. Furthermore, by imitating the mechanism of energy conversion in living systems, the design of energy conversion systems driven by chemical potential gradients based on biomimetic nanopores and the design of nanopore-based sensing devices are realized. Since 2018, we focused on dynamic superwetting. The concept of ionic/molecular superfluid is proposed, which promotes the understanding of the realization of ultra-low energy conversion and information transmission in biological systems and provides new ideas for the study of ultra-low energy chemical synthesis in biological systems. It is believed that future research on ionic/molecular superfluidity will promote the development of neuroscience and brain science, develop quantum ion technology, develop future chemical and chemical reactors with high flux, high selectivity and low energy consumption, and will produce a series of disruptive technologies.

A Review on Additive Manufacturing of Functional Gradient Piezoceramic.

Functionally graded piezoceramics are a new generation of engineering materials whose final properties are determined by a chemical composition gradient (volume distribution), material microstructure, or design characteristics. This review analyzes possible ways to create a functionally graded piezoceramic material (gradient chemical composition, gradient porosity—controlled and disordered porosity) by additive manufacturing methods, to control such materials’ functional characteristics. An analysis of the creation of gradient piezoceramics using binder jetting technology is presented in more detail. The review shows that today, the creation of functional gradient piezoceramics by additive manufacturing is a poorly-studied but promising research area, due to the rapid development of the additive manufacturing market and their unique features in shaping parts.

Graded Inconel 625 coatings with in-situ processing of Ni3Al

Ni superalloys have been widely used to process coatings due to a bouquet of attractive properties in a wide range of temperature. However, higher performance Ni alloys are typically those that offer larger processing challenges. Materials systems have been studied to mitigate this challenge. In hardfacing coatings multilayers have been processed both to reduce the detrimental effects of dilution with the substrate and to enhance the resistance to crack propagation, the latter of particularly relevance when depositing alloys reinforced with hard particles with a reduced weldability but that offer enhanced performance at the surface. The present study addressed the effects of customizing a commercial Inconel 625 atomized alloy, with increasing additions of Ni and Al elemental powder mixtures, to obtain multilayered coatings with a composition and property gradient. The gradual additions of Ni + Al powder mixture to the IN 625 atomized alloy allow for the in-situ synthesis of aluminides while maintaining good weldability, increasing mechanical properties and oxidation resistance. Results show a continuous solidification microstructure, crack-free multilayer coatings with smooth chemical composition profiles and property gradient. A gradual change on the strengthening mechanisms is identified, from solid solution on the first layer of IN 625 to a mixture of solid solution and Ni3Al precipitate dispersion on the top layer processed with the feedstock richer in the Ni + Al powder mixture. These changes induced increasing elastic modulus, hardness and oxidation resistance at 1300 °C following the chemical composition gradient in coatings.

Influence of solidification conditions on chemical heterogeneities and dislocations patterning in additively manufactured 316L stainless steel

The dendritic substructure of 316L stainless steel processed by Laser Powder Bed Fusion (L-PBF) is experimentally investigated on three specimens built with significantly different scanning speeds and solidification cooling rates. Microstructural features of interest are misorientations between dendrites, gradients of chemical composition and dislocations structures. Similar amplitudes of chemical heterogeneities are found for all three samples, possibly related to the conjunction of relatively low variations of solidification rates and large partition coefficients for the considered solute elements. No crystalline misorientations between neighboring dendrites are observed, implying that interdendritic dislocations are not geometrically necessary dislocations stemming from solidification but arise from thermomechanical straining during post-solidification cooling. Dislocations patterning appear to be closely correlated to the periodicity of microsegregations, hinting at an effect of the local chemistry. No simple Hall-Petch-like effect of the dendrite size is observed on compression tests, possibly due to different strengthening mechanisms depending on the dislocations structures.

Asteroseismology of the dip structure in period-spacings of rapidly rotating γ Doradus stars caused by the coupling between core and envelope oscillations

ABSTRACT Recent asteroseismic observations by the Kepler space mission have revealed the dip fine structure in the period-spacing versus period diagram of rapidly rotating γ Doradus stars. Following the successful reproduction of the dip structure by numerical calculations in previous studies, we present in this paper the physical mechanism of how the dip is formed as a result of the interaction between the gravito-inertial waves in the radiative envelope and the pure inertial waves in the convective core. We analytically describe the wave solutions in both of the radiative envelope and the convective core, and match them at the interface to construct an eigenmode. We have found from the analysis the following points: the dip structure is mainly controlled by a parameter that has an inverse correlation with Brunt–Väisälä frequency at the interface; the depth and the width of the dip is shallower and larger, respectively, as the parameter gets large; the shape of the dip can be approximated by the Lorentzian function; the period at the central position of the dip is equal to or slightly smaller than that of the involved pure inertial mode in the convective core. We have also understood based on the evolutionary models of main-sequence stars that the parameter is inversely correlated with the chemical composition gradient at the convective-core boundary. The dip structure thus would provide information about the poorly-understood physical processes, such as diffusion, convective overshooting and rotational mixing, around the boundary between the convective core and the radiative envelope.

Facile synthesis of Cd1-xZnxSe1-ySy/CdSe/Cd1-xZnxSe1-ySy nanoplatelets with precisely controlled emission wavelength

A facile synthetic strategy toward passivating Cd1-xZnxSe1-ySy shell on CdSe core nanoplatelets (NPLs) with a graded chemical composition gradient was introduced via a one-pot synthesis approach by capitalizing on the difference of chemical reactivity between cadmium oleate and zinc oleate precursors. Plain CdSe NPLs were first synthesized and then followed by precise passivation with the graded Cd1-xZnxSe1-ySy shell. The effect of precursor solubility on the morphology of NPLs was corroborated by transmission electron microscopy characterization. The photophysical properties of NPLs were explored using a UV–vis spectrometer and a spectrofluorometer.