Structural and permeability sensitivity of cells to low intensity ultrasound: Infrared and fluorescence evidence in vitro

This work is focused on the in vitro study of the effects induced by medical ultrasound (US) in murine fibroblast cells (NIH-3T3) at a low-intensity of exposure (spatial peak temporal average intensity I_ta < 0.1 W cm⁻²). Conventional 1 MHz and 3 MHz US devices of therapeutic relevance were employed with varying intensity and exposure time parameters. In this framework, upon cells exposure to US, structural changes at the molecular level were evaluated by infrared spectroscopy; alterations in plasma membrane permeability were monitored in terms of uptake efficiency of small cell-impermeable model drug molecules, as measured by fluorescence microscopy and flow cytometry. The results were related to the cell viability and combined with the statistical PCA analysis, confirming that NIH-3T3 cells are sensitive to therapeutic US, mainly at 1 MHz, with time-dependent increases in both efficiency of uptake, recovery of wild-type membrane permeability, and the size of molecules entering 3T3. On the contrary, the exposures from US equipment at 3 MHz show uptakes comparable with untreated samples.     

An experimental study on the motion of water droplets in oil under ultrasonic irradiation

The motion of a single water droplet in oil under ultrasonic irradiation is investigated with high-speed photography in this paper. First, we described the trajectory of water droplet in oil under ultrasonic irradiation. Results indicate that in acoustic field the motion of water droplet subjected to intermittent positive and negative ultrasonic pressure shows obvious quasi-sinusoidal oscillation. Afterwards, the influence of major parameters on the motion characteristics of water droplet was studied, such as acoustic intensity, ultrasonic frequency, continuous phase viscosity, interfacial tension, and droplet diameter, etc. It is found that when the acoustic intensity and frequency are 4.89 W cm⁻² and 20 kHz respectively, which are the critical conditions, the droplet varying from 250 to 300 μm in lower viscous oil has the largest oscillation amplitude and highest oscillation frequency.     

Pretreatment of defatted wheat germ proteins (by-products of flour mill industry) using ultrasonic horn and bath reactors: Effect on structure and preparation of ACE-inhibitory peptides

The ultrasonic horn and bath reactors were compared based on production of angiotensin-converting-enzyme (ACE) inhibitory peptides from defatted wheat germ proteins (DWGP). The DWGP was sonicated before hydrolysis by Alcalase. Degree of hydrolysis, ACE-inhibitory activity, surface hydrophobicity, fluorescence intensity, free sulfhydryl (SH), and disulfide bond (SS) were determined. The highest ACE-inhibitory activity of DWGP hydrolysate was obtained at power intensity of 191.1 W/cm² for 10 min in the ultrasonic horn reactor. The fixed frequency of 33 kHz and the sweep frequency of 40 ± 2 kHz resulted in the maximum ACE-inhibitory activity. The combined irradiation of dual fixed frequency (24/68 kHz) produced significant increase in ACE-inhibitory activity compared with single frequency (33 kHz). The ultrasonic probe resulted in significant higher ACE-inhibitory activity compared with ultrasonic bath operating at single or dual fixed and sweep frequencies. The changes in conformation of the DWGP due to sonication were confirmed by the changes in fluorescence intensity, surface hydrophobicity, SH_f and SS contents and they were found in conformity with the ACE-inhibitory activity in case of the ultrasonic horn reactor but not in bath reactor.     

Synergistic effects of combining ultrasound with the Fenton process in the degradation of Reactive Blue 19

The decoloration of reactive dye C.I. Reactive Blue 19 (RB 19) using combined ultrasound with the Fenton process has been investigated. The effect of varying the concentrations of hydrogen peroxide and iron sulfate, initial pH, ultrasonic power, initial dye concentration and dissolved gas on the decoloration and degradation efficiencies was measured. Calibration of the ultrasound systems was performed using calorimetric measurements and oxidative species monitoring using the Fricke dosimeter and degradations were carried out with a 20 kHz probe type transducer at 2, 4, 6 and 8 W cm⁻² of acoustic intensity at 15, 25, 50 and 75 mg L⁻¹ initial dye concentrations. First order rate kinetics was observed. It was found that while the degradation rate due to ultrasound alone was slow, sonication significantly accelerated the Fenton reaction. While the results were similar to those reported for other dyes, the effects occurred at lower concentrations. The rate and extent of decoloration of RB 19 increased with rising hydrogen peroxide concentration, ultrasonic powers and iron sulfate concentration but decreased with increasing dye concentration. An optimum pH value of pH = 3.5 was found. The rate of decoloration was higher when dissolved oxygen was present as compared with nitrogen and argon confirming the solution phase mechanism of the degradation.     

Ultrasound-enhanced coagulation for Microcystis aeruginosa removal

Source water eutrophication has caused serious problems in drinking water supplies, with enhanced coagulation widely used to remove the resulting algae. This paper investigates the use of sonication to improve the removal by coagulation of Microcystis aeruginosa, a common species of toxic algae. The results show that sonication significantly enhances the reduction of algae cells, solution UV254, and chlorophyll a without increasing the concentration of aqueous microcystins. The main mechanism involved the destruction during ultrasonic irradiation of gas vacuoles inside algae cells that acted as ‘nuclei’ for acoustic cavitation and collapse during the “bubble crush” period, resulting in the settlement of cyanobacteria. Coagulation efficiency depended strongly on the coagulant dose and sonication conditions. When the coagulant dose was 0.5 mg/l, 5 s of ultrasonic irradiation increased algae removal efficiency from 35% to 67%. As further sonication enhanced the coagulation efficiency only slightly due to better mixing, optimal sonication time was 5 s. The most effective sonication intensity was 47.2 W/cm², and the highest removal ratio of M. aeruginosa was 93.5% by the sonication–coagulation method. Experiments with reservoir water showed that this method could be successfully applied to natural water containing multiple species of algae.     

Lipase catalyzed ultrasonic synthesis of poly-4-hydroxybutyrate-co-6-hydroxyhexanoate

Four different lipases were compared for ultrasound-mediated synthesis of the biodegradable copolymer poly-4-hydroxybutyrate-co-6-hydroxyhexanoate. The copolymerization was carried out in chloroform. Of the enzymes tested, Novozym 435 exhibited the highest copolymerization rate, in fact the reaction rate was observed to increase with about 26-fold from 30 to 50 °C (7.9 × 10^?3 M s^?1), sonic power intensity of 2.6 × 10³ W m^?2 and dissipated energy of 130.4 J ml^?1. Copolymerization rates with the Candida antarctica lipase A, Candida rugosa lipase, and Lecitase Ultra? were lower at 2.4 × 10^?4, 1.3 × 10^?4 and 3.5 × 10^?4 M s^?1, respectively. The catalytic efficiency depended on the enzyme. The efficiency ranged from 4.15 × 10^?3 s^?1 M^?1 for Novozym 435–1.48 × 10^?3 s^?1 M^?1 for C. rugosa lipase. Depending on the enzyme and sonication intensity, the monomer conversion ranged from 8.2% to 48.5%. The sonication power, time and temperature were found to affect the rate of copolymerization. Increasing sonication power intensity from 1.9 × 10³ to 4.5 × 10³ W m^?2 resulted in an increased in acoustic pressure (P_a) from 3.7 × 10⁸ to 5.7 × 10⁸ N m^?2 almost 2.4–3.7 times greater than the acoustic pressure (1.5 × 10⁸ N m^?2) that is required to cause cavitation in water. A corresponding acoustic particle acceleration (a) of 9.6 × 10³–1.5 × 10⁴ m s^?2 was calculated i.e. approximately 984–1500 times greater than under the action of gravity.     

Ultrasonic processing of dairy systems in large scale reactors

High intensity low frequency ultrasound was used to process dairy ingredients to improve functional properties. Based on a number of lab-scale experiments, several experimental parameters were optimised for processing large volumes of whey and casein-based dairy systems in pilot scale ultrasonic reactors. A continuous sonication process at 20 kHz capable of delivering up to 4 kW of power with a flow-through reactor design was used to treat dairy ingredients at flow rates ranging from 200 to 6000 mL/min. Dairy ingredients treated by ultrasound included reconstituted whey protein concentrate (WPC), whey protein and milk protein retentates and calcium caseinate. The sonication of solutions with a contact time of less than 1 min and up to 2.4 min led to a significant reduction in the viscosity of materials containing 18% to 54% (w/w) solids. The viscosity of aqueous dairy ingredients treated with ultrasound was reduced by between 6% and 50% depending greatly on the composition, processing history, acoustic power and contact time. A notable improvement in the gel strength of sonicated and heat coagulated dairy systems was also observed. When sonication was combined with a pre-heat treatment of 80 °C for 1 min or 85 °C for 30 s, the heat stability of the dairy ingredients containing whey proteins was significantly improved. The effect of sonication was attributed mainly to physical forces generated through acoustic cavitation as supported by particle size reduction in response to sonication. As a result, the gelling properties and heat stability aspects of sonicated dairy ingredients were maintained after spray drying and reconstitution. Overall, the sonication procedure for processing dairy systems may be used to improve process efficiency, improve throughput and develop value added ingredients with the potential to deliver economical benefits to the dairy industry.     

A miniaturized prototype of resonant banana-shaped photoacoustic cell for gas sensing

A resonant photoacoustic cell intended for laser-spectroscopy gas sensing is represented. This cell is a miniature imitation of a macro-scale banana-shaped cell developed previously. The parameters, which specify the cavity shape, are chosen so as not only to provide optimal cell operation at a selected acoustic resonance but also to reduce substantially the cell sizes. A miniaturized prototype cell (the volume of acoustic cavity of ∼5 mm³) adapted to the narrow diffraction-limited beam of near-infrared laser is produced and examined experimentally. The noise-associated measurement error and laser-initiated signals are studied as functions of modulation frequency. The background signal and the useful response to light absorption by the gas are analyzed in measurements of absorption for ammonia in nitrogen flow with the help of a pigtailed DFB laser diode oscillated near a wavelength of 1.53 μm. The performance of prototype operation at the second longitudinal acoustic resonance (the resonance frequency of ∼32.9 kHz, Q-factor of ∼16.3) is estimated. The noise-limited minimal detectable absorption normalized to laser-beam power and detection bandwidth is ∼8.07 × 10⁻⁸ cm⁻¹ W Hz^−1/2. The amplitude of the background signal is equivalent to an absorption coefficient of ∼2.51 × 10⁻⁵ cm⁻¹. Advantages and drawbacks of the cell prototype are discussed. Despite low absorption-sensing performance, the produced miniaturized cell prototype shows a good capability of gas-leak detection.     

High intensity ultrasound treatment of protein isolate extracted from dephenolized sunflower meal: Effect on physicochemical and functional properties

The influence of high intensity ultrasound (HIUS) on physicochemical and functional properties of sunflower protein isolates was investigated. Protein solutions (10% w/v) were treated with ultrasound probe (20 kHz) and ultrasound bath (40 kHz) for 5, 10, 20 and 30 min. Thermal stability of protein isolates was reduced as indicated by differential scanning calorimetry. Minimum thermal stability was observed at 20 min of sonication and increased further with increase in treatment time indicating aggregation at prolonged sonication. SDS-PAGE profile of proteins showed a significant reduction in molecular weight. Further, surface hydrophobicity and sulfhydryl content increased after HIUS treatment indicating partial unfolding of proteins and reduction in the intermolecular interactions. The particle size analysis showed that HIUS treatment reduced the particle size. Less turbid solution were observed largely due to reduction in particle size. HIUS decreased the available lysine content in protein isolates. Solubility, emulsifying capacity, emulsion stability, foaming capacity, foam stability and oil binding capacity were improved significantly, while as, water binding capacity was decreased. The effect of HIUS on physicochemical and functional properties of sunflower protein isolates was more pronounced in probe sonication rather than bath sonication. Protein isolates with improved functional properties can be obtained using high intensity ultrasound technology.     

Efficient H2O2/CH3COOH oxidative desulfurization/denitrification of liquid fuels in sonochemical flow-reactors

The oxidative desulfurization/denitrification of liquid fuels has been widely investigated as an alternative or complement to common catalytic hydrorefining. In this process, all oxidation reactions occur in the heterogeneous phase (the oil and the polar phase containing the oxidant) and therefore the optimization of mass and heat transfer is of crucial importance to enhancing the oxidation rate. This goal can be achieved by performing the reaction in suitable ultrasound (US) reactors. In fact, flow and loop US reactors stand out above classic batch US reactors thanks to their greater efficiency and flexibility as well as lower energy consumption. This paper describes an efficient sonochemical oxidation with H₂O₂/CH₃COOH at flow rates ranging from 60 to 800 ml/min of both a model compound, dibenzotiophene (DBT), and of a mild hydro-treated diesel feedstock. Four different commercially available US loop reactors (single and multi-probe) were tested, two of which were developed in the authors’ laboratory. Full DBT oxidation and efficient diesel feedstock desulfurization/denitrification were observed after the separation of the polar oxidized S/N-containing compounds (S ⩽ 5 ppmw, N ⩽ 1 ppmw). Our studies confirm that high-throughput US applications benefit greatly from flow-reactors.     

Statistical optimization of cell disruption techniques for releasing intracellular X-prolyl dipeptidyl aminopeptidase from Lactococcus lactis spp. lactis

X-prolyl dipeptidyl aminopeptidase (PepX) is an intracellular enzyme from the Gram-positive bacterium Lactococcus lactis spp. lactis NRRL B-1821, and it has commercial importance. The objective of this study was to compare the effects of several cell disruption methods on the activity of PepX. Statistical optimization methods were performed for two cavitation methods, hydrodynamic (high-pressure homogenization) and acoustic (sonication), to determine the more appropriate disruption method. Two level factorial design (2FI), with the parameters of number of cycles and pressure, and Box–Behnken design (BBD), with the parameters of cycle, sonication time, and power, were used for the optimization of the high-pressure homogenization and sonication methods, respectively. In addition, disruption methods, consisting of lysozyme, bead milling, heat treatment, freeze–thawing, liquid nitrogen, ethylenediaminetetraacetic acid (EDTA), Triton-X, sodium dodecyl sulfate (SDS), chloroform, and antibiotics, were performed and compared with the high-pressure homogenization and sonication methods. The optimized values of high-pressure homogenization were one cycle at 130 MPa providing activity of 114.47 mU ml⁻¹, while sonication afforded an activity of 145.09 mU ml⁻¹ at 28 min with 91% power and three cycles.In conclusion, sonication was the more effective disruption method, and its optimal operation parameters were manifested for the release of intracellular enzyme from a L. lactis spp. lactis strain, which is a Gram-positive bacterium.     

Physicochemical characterization of black seed oil-milk emulsions through ultrasonication

The ultrasonic formation of stable emulsions of a bioactive material, black seed oil, in skim milk was investigated. The incorporation of 7% of black seed oil in pasteurised homogenized skim milk (PHSM) using 20 kHz high intensity ultrasound was successfully achieved. The effect of sonication time and acoustic power on the emulsion stability was studied. A minimum process time of 8 min at an applied acoustic power of 100 W was sufficient to produce emulsion droplets stable for at least 8 days upon storage at 4 ± 2 °C, which was confirmed through creaming stability, particle size, rheology and color analysis. Partially denatured whey proteins may provide stability to the emulsion droplets and in addition to the cavitation effects of ultrasound are responsible for the production of smaller sized emulsion droplets.     

Ultrasonically assisted removal of Congo Red,Phloxine B and Fast green FCF in ternary mixture using novel nanocomposite following their simultaneous analysis by derivative spectrophotometry

In this study dependency of simultaneous adsorption of Congo Red (CR), Phloxine B (BP) and Fast green FCF (FG) onto CuS/ZnS nanocomposites loaded on activated carbon (CuS/ZnS-NCs-AC) to pH, adsorbent mass, sonication time and initial dyes concentration were modeled and optimized, while CuS/ZnS-NCs-AC was identified by XRD, FESEM and EDS analysis. CR, PB and FG concentration determination were undertaken by first and second order derivative spectrophotometry in ternary mixture. According to central composite design (CCD) based on desirability function (DF), the best experimental conditions was set as pH 6.0, 0.02 g CuS/ZnS-NCs-AC, 5 min sonication time, 15 mg L⁻¹ for PB and 10 mg L⁻¹ for other dyes. Conduction of experiments to above conditions lead to highest dyes removal efficiency of 99.72, 98.8 and 98.17 for CR, PB and FG, respectively. The adsorption data efficiently fitted by Langmuir isotherm model, while the order of maximum adsorption capacity (Q_max) for PB (128.21 mg g⁻¹) > CR (88.57 mg g⁻¹) > FG (73.40 mg g⁻¹) is related to their different structure and charges. Kinetics of process was efficiently explained according to pseudo-second-order kinetic in cooperation of Weber and Morris based on intraparticle diffusion.     

Improved adsorption performance of nanostructured composite by ultrasonic wave: Optimization through response surface methodology,isotherm and kinetic studies

In this work, ultrasound-assisted adsorption of an anionic dye, sunset yellow (SY) and cationic dyes, malachite green (MG), methylene blue (MB) and their ternary dye solutions onto Cu@ Mn-ZnS-NPs-AC from water aqueous was optimized by response surface methodology (RSM) using the central composite design (CCD). The adsorbent was characterized using Field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), Energy-dispersive X-ray spectroscopy (EDX) and EDX mapping images. The effects of various parameters such as pH, sonication time, adsorbent mass and initial concentrations of SY, MG and MB were examined. A total 33 experiments were conducted to establish a quadratic model. Cu@ Mn-ZnS-NPs-AC has the maximum adsorption efficiency (>99.5%) when the pH, sonication time, adsorbent mass and initial concentrations of SY, MG and MB were optimally set as 6.0, 5 min, 0.02 g, 9, 12 and 12 mg L⁻¹, respectively. Sonication time has a statistically significant effect on the selected responses. Langmuir isotherm model was found to be best fitted to adsorption and adsorption capacities were 67.5 mg g⁻¹ for SY, 74.6 mg g⁻¹ for MG and 72.9 mg g⁻¹ for MB. Four kinetic models (pseudo-first order, pseudo-second order, Weber–Morris intraparticle diffusion rate and Elovich) were tested to correlate the experimental data and the sorption was fitted well with the pseudo-second order kinetic model.     

Ce0.8Sm0.2O1.9 synthesis for solid oxide fuel cell electrolyte by ultrasound assisted co-precipitation method

In this study, the synthesis of Ce_0.8Sm_0.2O_1.9 (SDC) solid electrolyte by the ultrasound assisted co-precipitation method was accomplished to explore the effects of ultrasound power, ultrasound pulse ratio and probe type upon the ionic conductivity of SDC as well as the lattice parameter, the microstructure and the density. Fine powders of uniform crystallite sizes (average 11.70 ± 0.62 nm) were obtained, needing lower sintering temperature. The SDC powders were successfully sintered to a relative density of over 95% at 1200 °C (5 °C min^?1) for 6 h. The micrograph of SDC pellets showed non-agglomerated and well-developed grains with average size of about 200 nm. X-ray diffraction analysis showed that the lattice parameter increased with increasing acoustic intensity and reached a maximum for the 14.94 W cm^?2. Further, a linear relationship was detected between the lattice parameter and the ionic conductivity, inspiring a dopant like effect of US on the electrolyte properties. The highest ionic conductivity as σ_800°C = 3.07 × 10^?2 S cm^?1 with an activation energy E_a = 0.871 kJ mol^?1 was obtained with pulsed ultrasound for an acoustic intensity of 14.94 W cm^?2, using 19 mm probe and 8:2 pulse ratio.     

Ultrasonically enhanced electrochemical oxidation of ibuprofen

A hybrid advanced oxidation process combining sonochemistry (US) and electrochemistry (EC) for the batch scale degradation of ibuprofen was developed. The performance of this hybrid reactor system was evaluated by quantifying on the degradation of ibuprofen under the variation in electrolytes, frequency, applied voltage, ultrasonic power density and temperature in aqueous solutions with a platinum electrode. Among the methods examined (US, EC and US/EC), the hybrid method US/EC resulted 89.32%, 81.85% and 88.7% degradations while using NaOH, H₂SO₄ and deionized water (DI), respectively, with a constant electrical voltages of 30 V, an ultrasound frequency of 1000 kHz, and a power density of 100 W L⁻¹ at 298 K in 1 h. The degradation was established to follow pseudo first order kinetics. In addition, energy consumption and energy efficiencies were also calculated. The probable mechanism for the anodic oxidation of ibuprofen at a platinum electrode was also postulated.     

Green ultrasound-assisted extraction of carotenoids based on the bio-refinery concept using sunflower oil as an alternative solvent

A green, inexpensive and easy-to-use method for carotenoids extraction from fresh carrots assisted by ultrasound was designed in this work. Sunflower oil was applied as a substitute to organic solvents in this green ultrasound-assisted extraction (UAE): a process which is in line with green extraction and bio-refinery concepts. The processing procedure of this original UAE was first compared with conventional solvent extraction (CSE) using hexane as solvent. Moreover, the UAE optimal conditions for the subsequent comparison were optimized using response surface methodology (RSM) and ultra performance liquid chromatography – diode array detector – mass spectroscopy (UPLC–DAD–MS). The results showed that the UAE using sunflower as solvent has obtained its highest β-carotene yield (334.75 mg/l) in 20 min only, while CSE using hexane as solvent obtained a similar yield (321.35 mg/l) in 60 min. The green UAE performed under optimal extraction conditions (carrot to oil ratio of 2:10, ultrasonic intensity of 22.5 W cm^?2, temperature of 40 °C and sonication time of 20 min) gave the best yield of β-carotene.     

Mechanism and dynamic study of reactive red X-3B dye degradation by ultrasonic-assisted ozone oxidation process

The effectiveness of ozone combined with ultrasound techniques in degrading reactive red X-3B is evaluated. A comparison among ozone (O₃), ultrasonic (US), ozone/ultrasonic (O₃/US) for degradation of reactive red X-3B has been performed. Results show that O₃/US system was the most effective and the optimally synergetic factor reaches to 1.42 in O₃/US system. The cavitation of ultrasound plays an important role during the degradation process. It is found that 99.2% of dye is degraded within 6 min of reaction at the initial concentration of 100 mg·L⁻¹, pH of 6.52, ozone flux of 40 L·h⁻¹ and ultrasonic intensity of 200 W·L⁻¹. Ozonation reactions in conjunction with sonolysis indicate that the decomposition followed pseudo-first-order reaction kinetics but the degradation efficiencies are affected by operating conditions, particularly initial pH and ultrasonic intensity. A kinetic model is established based on the reaction corresponding to operational parameters. In addition, the main reaction intermediates, such as p-benzoquinone, catechol, hydroquinone, phthalic anhydride and phthalic acid, are separated and identified using GC/MS and a possible degradation pathway is proposed during the O₃/US process.     

Application of ZnO nanorods loaded on activated carbon for ultrasonic assisted dyes removal: Experimental design and derivative spectrophotometry method

A method based on application of ZnO nanorods loaded on activated carbon (ZnO-NRs-AC) for adsorption of Bromocresol Green (BCG) and Eosin Y (EY) accelerated by ultrasound was described. The present material was synthesized under ultrasound assisted wet-chemical method and subsequently was characterized by FE-SEM, TEM, BET and XRD analysis. The extent of contribution of conventional variables like pH (2.0–10.0), BCG concentration (4–20 mg L⁻¹), EY concentration (3–23 mg L⁻¹), adsorbent dosage (0.01–0.03 g), sonication time (1–5 min) and centrifuge time (2–6 min) as main and interaction part were investigated by central composite design under response surface methodology. Analysis of variance (ANOVA) was adapted to experimental data and guide the best operational conditions mass by set at 6.0, 9 mg L⁻¹, 10 mg L⁻¹, 0.02 g, 4 and 4 min for pH, BCG concentration, EY concentration, adsorbent dosage, sonication and centrifuge time, respectively. At these specified conditions dye adsorption efficiency was higher than 99.5%. The suitability and well prediction of optimum point was tested by conducting five experiments and respective results revel that RSD% was lower than 3% and high quality of fitting was confirmed by t-test. The experimental data were best fitted in Langmuir isotherm equation and the removal followed pseudo second order kinetics. The experimentally obtained maximum adsorption capacities were estimated as 57.80 and 61.73 mg g⁻¹ of ZnO-NRs-AC for BCG and EY respectively from binary dye solutions. The mechanism of removal was explained by boundary layer diffusion via intraparticle diffusion.     

A Boubaker polynomials expansion scheme (BPES)-related protocol for measuring sprayed thin films thermal characteristics

Measurements of In₂S₃ and ZnIn₂S₄ sprayed thin films thermal characteristics have been carried out using the photodetection technique. The thermal conductivity k and diffusivity D were obtained using a new protocol based on photothermal signal parameters analysis. Measured values of k and D were respectively, (15.2 ± 0.85) W m⁻¹K⁻¹ and (69.8 ± 7.1) × 10⁻⁶ m²s⁻¹ for In₂S₃, (7.2 ± 0.7) W m⁻¹K⁻¹ and (32.7 ± 4.3) × 10⁻⁶ m²s⁻¹ for ZnIn₂S₄. These values are extremely important since similar compounds are more and more proposed as Cd-free alternative materials for solar cells buffer layers.