Preconcentration and selective extraction of trace Hg(ii) by polymeric g-C3N4 nanosheet-packed SPE column.

In this study, we successfully synthesized polymeric graphitic carbon nitride (g-C3N4) nanosheets through thermal means and proposed their application in solid-phase extraction (SPE) for the enrichment of trace Hg(ii). The nanosheets underwent characterization using scanning electron microscopy, tunnelling electron microscopy, and energy-dispersive X-ray spectroscopy. The column packed with polymeric carbon nitride nanosheets demonstrated effective extraction of trace Hg(ii) ions from complex samples. The g-C3N4 nanosheets possess a zeta potential value of -20 mV, enabling strong interaction with positively charged divalent Hg(ii) ions. This interaction leads to the formation of stable chelates with the nitrogen atoms present in the polytriazine and heptazine units of the material. The proposed method exhibited a high preconcentration limit of 0.33 µg L-1, making it suitable for analysing trace amounts of Hg(ii) ions. Moreover, the method's applicability was confirmed through successful analysis of real samples, achieving an impressive preconcentration factor of 200. The detection limit for trace Hg(ii) ions was determined to be 0.6 µg L-1. To assess the accuracy of the method, we evaluated its performance by recovering spiked amounts of Hg(ii) and by analysing certified reference materials. The results indicated excellent precision, with RSD consistently below 5% for all the analyses conducted. In conclusion, the thermally synthesized polymeric carbon nitride nanosheets present a promising approach for solid-phase extraction and preconcentration of trace Hg(ii) from real samples. The method showcases high efficiency, sensitivity, and accuracy, making it a valuable tool for environmental and analytical applications.

In Situ Fabrication and Characterization of g-C3N4 onto Cellulose Nanofibers and Selective Separation of Heavy Metal Ions.

Graphitic carbon nitride nanosheets were synthesized onto cellulose nanofiber surfaces utilizing an eco-friendly salt melt approach. The fabricated material CNF@C3N4 selectively removes Ni(II) and Cu(II) from electroplating wastewater samples. The immobilization of g-C3N4 on solid substrates eases handling of nanomaterial in a flow-through approach and mitigates sorbent loss during column operations. Characterization techniques such as scanning electron microscopy, tunneling electron microscopy, and X-ray photoelectron microscopy were employed to analyze the surface morphology and chemical bonding within the synthesized material. Selective Cu(II) and Ni(II) sorption predominantly arises from the soft-soft interaction between metal ions and associated nitrogen groups. An inner-sphere surface complexation mechanism effectively elucidated the interaction dynamics between the metal and CNF@C3N4. Experimental findings demonstrated satisfactory separation of Ni(II) and Cu(II) ions, with the extraction of 340.0 and 385.0 mg g-1 of material, respectively. Additionally, the devised technique was executed for the preconcentration and quantification of trace metals ions in water samples with a detection limit and limit of quantification of 0.06 and 0.20 µg L-1, respectively.

Cellulose nanocrystals doped silver nanoparticles immobilized agar gum for efficient photocatalytic degradation of malachite green.

The present study involves the synthesis of green functional material based on the silver nanoparticle (Ag NPs) doped cellulose nanocrystals (CNC) immobilized agar gum (AA) biopolymer using chemical coprecipitation method. The stabilization of Ag NPs in cellulose matrix and functionalization of the synthesized material through agar gum was analyzed using various spectroscopic techniques such as Fourier Transform Infrared (FTIR), Scanning electron microscope (SEM), Energy X-Ray diffraction (EDX), Photoelectron X-ray (XPS), Transmission electron microscope (TEM), Selected area energy diffraction (SAED) and ultraviolet visible (UV-Vis) spectroscopy. The XRD results suggested that the synthesized AA-CNC@Ag BNC material is composed of 47 % crystalline and 53 % amorphous nature having distorted hexagonal structure due to capping of Ag NPs by amorphous biopolymer matrix. The Debye-Scherer crystallite sized was calculated as 18 nm which is found in close agreement with TEM analysis (19 nm). The SAED yellow fringes simulates the miller indices values with XRD patterns and supported the surface functionalization of Ag NPs by biopolymer blend of AA-CNC. The XPS data supported the presence of Ag0 as indexed by Ag3d orbital corresponding to Ag3d3/2 at 372.6 eV and Ag3d5/2 at 366.6 eV. The surface morphological results revealed a flaky surface of the resultant material having well distributed Ag NPs in the matrix. The EDX and atomic concentration results given by XPS supported the presence if C, O and Ag in the bionanocomposite material. The UV-Vis results suggested that the material is both UV and visible light active having multiple SPR effects with anisotropy. The material was explored as a photocatalyst for remediation of wastewater contaminated by malachite green (MG) using advance oxidation process (AOP). Photocatalytic experiments were performed in order to optimize various reaction parameters such as irradiation time, pH, catalyst dose and MG concentration. The obtained results showed that almost 98.85 % of MG was degraded by using 20 mg of catalyst at pH 9 for 60 min of irradiation. The trapping experiments revealed that •O2- radicals played primary role in MG degradation. This study will provide new possible strategies for the remediation of wastewater contaminated by MG.

Electronic structure and defect-induced luminescence study of phase-stabilized t-ZrO2 nanocrystals.

Luminescent tetragonal-ZrO2 (t-ZrO2 ) nanocrystals were synthesized using an optimized combustion method without post-synthesis annealing and characterized using X-ray diffraction, electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, UV-Vis. spectroscopy, photoluminescence spectroscopy, thermoluminescence (TL), and vibrating sample magnetometry. The as-synthesized t-ZrO2 nanocrystals have a bandgap of 4.65 eV and exhibit defect-assisted blue emission (Commission Internationale de I'Elcairage coordinates 0.2294, 0.1984) when excited at 270 nm. The defect states were qualitatively and quantitatively analyzed using TL after irradiating nanocrystals with γ- and UV radiations at various doses. The TL glow curves show intense emission in the high-temperature region from 523 to 673 K for both UV- and γ-irradiated samples; however, another less-intense TL peak was also observed in the low-temperature region from 333 to 453 K with γ irradiation at higher doses, indicating the formation of shallow trapping states. The activation energies, frequency factor, and order of kinetics were estimated using the computerized glow curve deconvolution method for the shallow and deep traps for γ- and UV-irradiated samples. The present study shows that phase-stabilized t-ZrO2 nanocrystals are potential candidates for luminescence-based applications.

N-Containing Hybrid Composites Coatings for Enhanced Fire-Retardant Properties of Cotton Fabric Using One-Pot Sol-Gel Process.

In this report, a unique methodology/process steps were followed using Sol-gel-based concept to deposit thin flame-retardant coatings on cotton fabric. Surface microstructure and compositional analysis of the coated cotton were carried out using scanning electronic microscope (SEM), which explored significant coverage of the fabric. The obtained samples were further analyzed through rupturing mechanism test and color check. Compositional investigation of the coated samples was carried through Attenuated total reflection Fourier transform infrared (ATR-FTIR) and energy-dispersive X-rays spectroscopy (EDS) analysis. Thermal analyses were carried out through Thermogravimetric analysis (TGA) and Vertical flame tests (VFT), which suggested higher resistance of the coatings obtained for 5 h and zero heat-treatment time on the cotton fabric. A 28.86% char residue was obtained for the same sample (ET-5h-RT) coupled with higher degradation temperature and excellent combustion properties.

Systematic study of physicochemical and electrochemical properties of carbon nanomaterials.

Carbon nanomaterials exhibit exceptional properties and broad horizon applications, where graphene is one of the most popular allotropes of this family due to its astounding performance in every stratum vis-à-vis other classical materials. The large surface area of 2630 m2 g-1, high electrical conductivity, and electron mobility of non-toxic graphene nanomaterials serve as the building blocks for supercapacitor studies. In this article, comparative studies are carried out between electrochemically exfoliated graphene sheets (GSs), solvothermally synthesized graphene quantum dots (GQDs) and acid refluxed carbon nanotubes (CNTs) as an energy storage electrode nanomaterial through cyclic voltammetry (CV). The electrochemical properties of the materials are well correlated with the physicochemical characteristics obtained from Raman, Fourier-transform infrared, and absorption spectroscopy. Thin GSs (0.8-1 nm) and small size (6-10 nm) GQDs fabricated by using laboratory-grade 99% purity graphite rods resulted in promising low-cost materials at mass scale as compared to conducting CNTs. The 0D graphene quantum dots proved to be an excellent energy electrode material in an alkaline electrolyte solution compared to other carbon nanomaterials. The distinct characteristic features of GQDs, like superior electrical properties, large surface area, and abundant active sites make them an ideal candidate for utilization in supercapacitors. The GQDs exhibited an enhanced specific capacitance of 113 F g-1 in 6 mol L-1 KOH through cyclic voltammetry.

Selective Extraction of Trace Arsenite Ions Using a Highly Porous Aluminum Oxide Membrane with Ordered Nanopores.

Metal ion extraction and determination at trace level concentration are challenging due to sample complexity or spectral interferences. Herein, we prepared a through-hole aluminum oxide membrane (AOM) by electrochemical anodization of aluminum substrates. The prepared AOM was characterized by scanning electron microscopy, surface area analysis, porosity measurements, and X-ray photoelectron spectroscopy. The AOM with ordered nanopores was highly porous and possess inherent binding sites for selective arsenite sorption. The AOM was used as a novel sorbent for solid-phase microextraction and preconcentration of arsenite ions in water samples. The AOM's sub-micrometer thickness allows water molecules to flow freely across the pores. Before instrumental determination, the suggested microextraction approach removes spectral interferents and improves the analyte ion concentration, with a detection limit of 0.02 µg L-1. Analyzing a standard reference material was used to validate the procedure. Student's t-test value was less than critical Student's t-value of 4.303 at a 95% confidence level. With coefficients of variation of 3.25%, good precision was achieved.

LBL generated fire retardant nanocomposites on cotton fabric using cationized starch-clay-nanoparticles matrix.

In this work, starch-clay-TiO2-based nanocomposites were deposited on cotton fabric through layer-by-layer (LBL) process and their effect on the flame retardancy, inhibition of pyrolysis and combustion processes were discussed in details. Polyelectrolyte solutions/suspensions of cationized starch and VMT (vermiculite)/TiO2 nanoparticles were used to deposit these nanocomposites in the form of multi-layered coatings (5, 7, 10 and 15 bilayers). Uniform fabric coverage and presence of electrolytes was imaged by scanning electron microcopy (LV-SEM), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and EDX characterizations. The greatest pyrolysis reduction was found for the StVT-7 sample (7 bilayers); ~30% and 21%, based on microscale combustion calorimetry (MCC) and thermogravimetric analysis (TGA). When using MCC, the improved values of the PHRR ~ 193 W/g, THR ~ 10.7 kJ/g), HRC ~ 390 J/g∙K and LOI ~ 22.2% were found for the StVT-7 sample which was strongly supported by the UL-94 test.

Excellent Fire Retardant Properties of CNF/VMT Based LBL Coatings Deposited on Polypropylene and Wood-Ply.

In this report, layer by layer (LBL) fire retardant coatings were produced on wood ply and Polypropylene Homopolymer/Flax fiber composites. FE-SEM and EDAX analysis was carried out to analyze the surface morphology, thickness, growth rate and elemental composition of the samples. Coatings with a high degree of uniformity were formed on Polypropylene composite (PP/flax), while coatings with highest thickness were obtained on wood ply (wood). FTIR and Raman spectroscopy were further used for the molecular identifications of the coatings, which confirmed the maximum deposition of the solution components on the wood substrate. A physiochemical analysis and model was proposed to explain the forces of adhesion between the substrate and solution molecules. Fire protection and thermal properties were studied using TGA and UL-94 tests. It was explored, that the degradation of the coated substrates was highly protected by the coatings as follows: wood > PP/flax > PP. From the UL-94 test, it was further discovered that more than 83% of the coated wood substrate was protected from burning, compared to the 0% of the uncoated substrate. The flammability resistance of the samples was ranked as wood > PP/flax > PP.

Preconcentration and determination of trace Hg(ii) using ultrasound-assisted dispersive solid phase microextraction.

Defect rich molybdenum disulfide (MoS2) nanosheets were hydrothermally synthesized and their potential for ultrasound assisted dispersive solid phase microextraction of trace Hg(ii) ions was assessed. Ultrasonic dispersion allows the MoS2 nanosheets to chelate rapidly and evenly with Hg(ii) ions and results in improving the precision and minimizing the extraction time. The multiple defect rich surface was characterized by X-ray diffraction and high-resolution transmission electron microscopy. The surface charge of intrinsically sulfur rich MoS2 nanosheets and their elemental composition was characterized by zeta potential measurements, energy dispersive spectroscopy, and X-ray photoelectron spectroscopy. The cracks and holes on the basal planes of MoS2 led to diffusion of the Hg(ii) ions into the interior channels. Inner-sphere chelation along with outer-sphere electrostatic interaction were the proposed mechanism for the Hg(ii) adsorption onto the MoS2 surface. The experimental data showed good selectivity of MoS2 nanosheets towards Hg(ii) adsorption. The systematic and constant errors of the proposed method were ruled out by the analysis of the Standard Reference Material (>95% recovery with <5% RSD). The Student's t-test values for the analyzed Standard Reference Material were found to be less than the critical Student's t value at 95% confidence level. The limit of detection (3S) was found to be 0.01 ng mL-1. The MoS2 nanosheets were successfully employed for the analysis of Hg(ii) in environmental water samples.

Flower-Like α-Fe2O3 for Removal of Heavy Metals from Wastewater.

In the present work flower-like, α-Fe2O3 were synthesized by ethylene-glycol mediated polyol method. The synthesized flower-like, α-Fe2O3 were separated cadmium (Cd2+) chromium (Cr6+) and lead ions (Pb2+) from wastewater. XRD pattern and FESEM images show the obtained sample is pure hematite and flower-like nanostructures average particle sizes 4.0 µm. The BET specific surface area was 47.55 m²g-1. Adsorption experiments were investigated the adsorbent dose, influence pH of the metal ions, sorption times and initial concentrations of heavy metal ions. High efficiency of Cd2+, Cr6+ and Pb2+ removal occurred at pH 7.0, 3.0 and 5.5, respectively. The adsorption equilibrium study showed that the heavy metal ions adsorption of flowers like α-Fe2O3 followed a Langmuir and Freundlich isotherm model. The heavy metal ions adsorption equilibrium data were followed to the Langmuir model. The maximum adsorption capacities were 16.95, 22.22 and 25.64 mg g-1 for Cd2+, Cr6+ and Pb2+ ions respectively. This work determines that the synthesized flower-like α-Fe2O3 is proposed as an efficient nano-adsorbent for wastewater treatment.

Fabrication of TiO2-Nanotube-Array-Based Supercapacitors.

In this work, a simple and cost-effective electrochemical anodization technique was adopted to rapidly grow TiO2 nanotube arrays on a Ti current collector and to utilize the synthesized materials as potential electrodes for supercapacitors. To accelerate the growth of the TiO2 nanotube arrays, lactic acid was used as an electrolyte additive. The as-prepared TiO2 nanotube arrays with a high aspect ratio were strongly adhered to the Ti substrate. X-ray diffraction (XRD) and transmission electron microscopy (TEM) results confirmed that the TiO2 nanotube arrays were crystallized in the anatase phase. TEM images confirmed the nanotublar-like morphology of the TiO2 nanotubes, which had a tube length and a diameter of ~16 and ~80 nm, respectively. The electrochemical performance of the TiO2 nanotube array electrodes was evaluated using the cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge/discharge (GCD) measurements. Excellent electrochemical response was observed for the electrodes based on the TiO2 nanotube arrays, as the cells delivered a high specific capacitance of 5.12 mF/cm2 at a scan rate of 100 mV/s and a current density of 100 µA/cm2. The initial capacity was maintained for more than 250 cycles. Further, a remarkable rate capability response was observed, as the cell retained 88% of the initial areal capacitance when the scan rate was increased from 10 to 500 mV/s. The results suggest the suitability of TiO2 nanotube arrays as electrode materials for commercial supercapacitor applications.

Morphological, Magnetic and Optical Properties of α-Fe2O3 Nanoflowers.

We report the morphological, structural and magnetic properties of the flower like iron oxide α-Fe2O3 samples prepared by the polyol method. The α-Fe2O3 samples were prepared by using different amount of the iron chloride in the starting materials and the impact of the different iron chloride amount on the morphology of the precursor and after heat treatment of the samples was investigated. The X-ray diffraction (XRD) analysis confirmed the formation of the α-Fe2O3 phase without detecting any impurity phase. The transmission electron microscopy (TEM) and the field emission scanning electron microscopy (FESEM) results showed that the flower like structures are composed of nanopetals with an average thickness and width of 60 nm and 735 nm respectively. A strong impact on the formation of the flower like iron oxide and the morphologies of these samples was observed with the variation of iron chloride concentration during synthesis process. The magnetic hysteresis measurements demonstrated that as prepared samples displayed ferromagnetic behavior and magnetic properties were found to be depending on the morphologies of as-prepared samples. The band gap energy was measured by using Tauc's method, and values for all the samples were found to be in the range 1.94-2.27 eV. The results obtained in the present work show that the α-Fe2O3 can be used as potential candidate material for use in gas sensors, photocatalysis and energy storage devices.

Low temperature growth of ZnO nanotubes for fluorescence quenching detection of DNA.

In this work, large-scale and single-crystalline ZnO nanotubes were fabricated by a simple technique from an aqueous solution at a low temperature of 65 °C. According to detailed morphology, structural and compositional analyses showed that the ZnO nanotubes [diameter ~200 nm (wall thickness ~50 nm); length ~1 µm] have single-crystallite with wurtzite structure. As-prepared ZnO nanotubes showed an effective fluorescence quenching for the detection of calf thymus DNA. In particular, increasing DNA concentrations (5-50 µM) into the fixed concentration of ZnO nanotubes (50 µM) progressively quenched the intrinsic fluorescence of nanotubes, which showed that the nanotubes fluorescence was efficiently quenched upon binding to DNA. At the highest ZnO-DNA molar ratios of 1:1.8, around 50.1 % of fluorescence quenching of DNA was observed. Significance of this study provides simple, cost-effective, and low temperature synthesis of ZnO nanotubes revealed better fluorescence property toward a platform of DNA sensor. ZnO nanotubes with diameter of ~200 nm (wall thickness ~50 nm) and length of about 1 µm prepared at low temperature (65 °C) showed fluorescence was efficiently quenched upon binding to DNA. In particular, around 50.1 % of DNA fluorescence quenching at the highest ZnO-DNA molar ratios of 1:1.8 was observed.

Effect of Zinc Nitrate Concentration on the Optical and Morphological Properties of ZnO Nanorods for Photovoltaic Applications.

We report the effect of zinc nitrate (ZN) concentration on the growth of zinc oxide (ZnO) nanorods and their optical and morphological properties. As prepared ZnO nanorods on glass substrate were characterized using field emission scanning electron microscopy (FE-SEM), ultra violet-visible (UV-Vis), Raman and Photo-luminescence (PL) spectroscopy. FE-SEM results show that the nanorods were obtained for the 0.033 and 0.053 M concentration of ZN. As the ZN concentration increased from 0.033 M to 0.053 M, the diameter of the nanorods was increased. It indicated that the diameter of the nanorods was affected by the ZN concentration. The Raman spectra of nanorods show only one peak at 438 cm(-1) corresponding to E2(high) high mode, which means that ZnO nanorods grown perpendicularly on the glass substrate, i.e., the ZnO nanorod arrays are highly c-axis oriented. Room-temperature PL spectrum of the as-grown ZnO nanorods reveals a near-band-edge (NBE) emission peak and defect induced green light emission. The green light emission band at -579 nm might be attributed to surface oxygen vacancies or defects. The UV-visible measurements reflect that the total transmittance for the as grown ZnO nanorods is over 80%. The simple technique presented in this study to grow ZnO nanorods on a glass substrate can be helpful for making the cost effective photovoltaic devices.

Vertically Aligned ZnO Nanorods: Effect of Synthesis Parameters.

This report is devoted to the synthesis of high quality nanorods using spin coating technique for seed layer growth. Effect of different parameter i.e., spins coating counts, spin coating speed, and the effect of temperature during the drying process was analyzed. Hot plate and furnace technique was used for heating purpose and the difference in the morphology was carefully observed. It is worthy to mention here that there is a substantial effect of all the above mentioned parameters on the growth and morphology of the ZnO nanostructure. The ZnO nanorods were finally synthesized using wet chemical method. The morphological properties of the obtained nanostructures were analyzed by using FESEM technique.

Magnetization and Magnetocaloric Effect in Sol-Gel Derived Nanocrystalline Copper-Zinc Ferrite.

We report the sol-gel synthesis and magnetocaloric effect in nanocrystalline copper-zinc ferrite (Cu0.5Zn0.5Fe2O4). The synthesized powder was characterized by using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDX) and magnetization measurements. The XRD results confirm the formation of single phase spinel structure. The average particle size was found to be ~58 nm. FE-SEM results suggested that the nanoparticles are agglomerated and spherical in shape. Magnetization measurement reveals that Cu0.5Zn0.5Fe2O4 nanoparticles exhibit transition temperature (Tc) above room temperature. The maximum magnetic entropy change (ΔSM)max shows interesting behaviour and was found to vary with the applied magnetic field. This nanopowder can be considered as potential material for magnetic refrigeration above room temperature.

Relationship Between Structural, Morphological, Optical and Magnetic Properties of Transition Metal (TM)-Doped ZnO Nanostructures Prepared by Microwave-Hydrothermal.

In this work, pure and 3% TM (Co, Ni, and Cu)-doped ZnO nanostructures were prepared by microwave-hydrothermal method. The striking similarities between changes in the lattice volume, bandgap energy, morphology and saturation magnetization indicated a strong correlation between these properties. XRD, SAED and HRTEM analyses revealed that all the TM-doped ZnO nano-structures have wurtzite structure and no secondary phase was detected. FESEM and TEM results confirmed a higher aspect ratio and highly crystalline nature of nanostructures. Raman spectra revealed that no defect related mode was observed which indicated that the nanostructures have high quality and negligible defects. The value of bandgap was found to decrease with the increase in atomic number of TM dopants. RTFM was observed in all the TM-doped ZnO nanostructures and the value of Ms and Mr were decreased with TM dopants.

Synthesis and Characterization of Nanocrystalline Doped-ZnO Powder for Advanced Varistor Application.

The nanocrystalline doped ZnO powder has been synthesized by solution combustion method using sucrose as fuel and zinc acetate as oxidant. The as-prepared nanopowders were characterized by XRD, showing particle size approximately 39 and 48 nm for fuel to oxidant ratio of 1:1 (stoichiometric) and 2:1 (fuel rich). The powders were compacted and sintered for 9 hours. The sintered samples were characterized by SEM and XRD, showing the presence of spinel (Zn7Sb2Ol2) and pyroclore (Zn2Bi3Sb3Ol4) phases at intergranular spacing. The phase distribution [spinel (Zn7Sb2Ol2), pyroclore (Zn2Bi3Sb3O14), ß-Bi2O3, and δ-Bi203] was found to be more homogeneous in case of samples obtained by adding the stoichiometric amount of fuel. The current-voltage (J-E) characterization shows the high non-linearity coefficient (α) ~22 and break-down voltage (VB) of ~0.41 kV/mm for the fuel rich sample.

Study of Magnetic and Magnetocaloric Behaviour of (1 - Y)La0.7Ca0.3MnO3/(Y)MnFe2O4, (1 - Y)La0.7Ca0.3MnO3/(Y)Ni0.9Zn0.1Fe2O4 Composites.

We report the structural, magnetic and magnetocaloric properties of (1 - Y)La0.7Ca0.3MnO3/ (Y)MnFe2O4 (LCMO/MFO) and (1 - Y)La0.7Ca0.3MnO3/(Y)Ni0.9Zn0.1Fe2O4 (LCMO/NZFO) composites. Polycrystalline LCMO/MFO samples were prepared using the conventional solid-state reaction technique. The results of X-ray diffraction indicates mainly LCMO phase without characteristic lines of the MFO and NZFO phase. The magnetic study has revealed that the Curie temperature was influenced by the concentration of MFO and NZFO phases. A large magnetic entropy change has been observed for La0.7Ca0.3MnO3 compound. The value of the maximum magnetic entropy change was found to decrease in the composites samples with increasing the concentration of the MFO and NZFO phases. This investigation suggests that LCMO/MFO and LCMO/NZFO types of composites can give a new kind of refrigeration candidates, which can easily provide the tunable magnetocaloric effect.