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Single-atom catalysts (SACs), consisting of metals atomically dispersed on a support, are considered as advanced materials bridging homogeneous and heterogeneous catalysis, representing the catalysis at the limit. The enhanced performance of these catalysts is due to the combination of distinct factors such as well-defined active sites, comprising metal single atoms in different coordination environments also varying its valence state and strongly interacting with the support, in this case porous carbons, maximizing then the metal efficiency in comparison with other metal surfaces consisting of metal clusters and/or metal nanoparticles. The purpose of this review is to summarize the most recent advances in terms of both synthetic strategies of producing porous carbon-derived SACs but also its application to green synthesis of highly valuable compounds, an area in which the homogeneous catalysts are classically used. Porous carbon-derived SACs emerge as a type of new and eco-friendly catalysts with great potential. Different types of carbon forms, such as multi-wall carbon nanotubes (MWCNTs), graphene and graphitic carbon nitride or even others porous carbons derived from Metal–Organic-Frameworks (MOFs) are recognized. Although it represents an area of expansion, experimentally and theoretically, much more future efforts are needed to explore them in green fine chemical synthesis.

Multiwall carbon nanotubes (MWCNTs) were systematically fragmented using high density ultrasonic energy and used as fillers of a poly (methyl methacrylate) matrix (PMMA). MWCNT fragmentation was confirmed by scanning electron microscopy and atomic force microscopy. Dedicated MWCNT length measurements yielded a log-normal statistical distribution, with mean value of 1.33 μm for the as-received MWCNTs and 0.66 μm for the fragmented MWCNTs. Higher electrical percolation threshold and lower electrical conductivity were obtained for MWCNT/PMMA composites (0.01–1 wt.% MWCNT concentration) using the fragmented MWCNTs. Higher electro-mechanical (piezoresistive) sensitivity under tensile tests was measured for PMMA nanocomposites with fragmented MWCNTs, which was explained by a competition of mechanisms related to the MWCNT length.

Magnetic citric acid-modified cellulose was successfully produced and tested for the removal of copper in aqueous solution. Initially, the cellulose material was reacted with citric acid solution. The modified cellulose was then attached to the Fe2O3nanoparticle producing an adsorptive magnetic material. Characterization using scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy indicated successful binding and chemical modification of the cellulose. Its adsorption was also studied to evaluate its potential in removing heavy metals such as copper. Removal of copper was as high as 84.74% in solution containing 25 mg/L copper. The sorption of copper in the magnetic sorbent follows second-order kinetics and best fits Freundlich isotherm model. The developed material has a strong magnetic response, thus its recovery in the aqueous solution could be easily facilitated using a magnetic field. Regeneration study indicated high recovery efficiency maintaining above 95.7% copper removal efficiency after three cycles of use. Thus, a highly efficient magnetic adsorptive material was produced using simple chemical modification aside from its easy recovery in the water.

Polyhydroxybutyrate (PHB) is a biopolymer of natural origin, one of the suitable alternatives for synthetic plastics. However, pure PHB has a high production cost, is relatively brittle, and has poor processability, hence its limited application. Combining PHB with biomass fillers and plasticizers can significantly improve the properties of the polymer, leading to its commercial usage. In this study, PHB was incorporated with starch (S) as a cheap biomass filler and lauric acid (LA) as a potential plasticizer. The PHB/S/LA composites were prepared using a modified solvent casting method with the incremental addition of LA. The PHB/S ratio was maintained at a ratio of 80/20 (w/w). Physicochemical characterization via EDS, XRD, and FTIR proved that the composite components have blended through nucleation and plasticization processes. The morphology of the PHB/S blends was found to be a heterogeneous matrix, with decreased inhomogeneity upon the addition of LA in the composite. Thermal characterization done by TGA and DSC showed that the thermal properties of PHB/S films improved with the addition of LA. Mechanical tests (UTM) proved that the elastic strain of the films also increased with the addition of LA, although the tensile strength decreased slightly compared to pure PHB/S. Overall, the results of this study provide baseline information on the improvement of PHB-based bioplastics.

Locust bean gum (LBG) is a natural polymer that belongs to the increasingly attractive biodegradable polymers derived from natural sources. This polymer possesses a number of appealing features such as non-toxicity that confer it a high potential for the use in fields such as pharmacy and food industries. In this work, three methylimidazolium-based ionic liquids (ILs) were used as alternative media in the preparation of biocompatible LBG gel matrices. The process consists of dissolving the biomaterial in a selected IL followed by a multi-step solvent exchange using a mixture of water and ethanol. The final gel (internal surface areas ranging from 60 to 180 m2 g−1) is then dried using a semi-continuous high pressure CO2 extraction process. To the best of our knowledge this is the first time that LBG mesoporous gel matrices are reported using this efficient sustainable method.

In this work polyelectrolyte multilayers (PEMs) produced through the layer-by-layer (LbL) method were used for the in situ synthesis of Au and Ag metal nanoparticles on the surface of float glass in order to colour it. The samples were characterized by UV–Vis absorption spectroscopy, Scanning Electron Microscopy (SEM), Rutherford Backscattering Spectrometry (RBS) and Particle Induced X-Ray Emission (PIXE). The use of temperatures slightly above the glass transition temperature (Tg) during the thermal treatment allowed the fixing of the nanoparticles, colouring the glass surface. Pink and blue colours were obtained from Au nanoparticles, yellow colour from Ag, and orange from a mixture of both Au nanoparticles and Ag nanoparticles. Variables such as the pH value during film assembly, the number of layers used to form the PEMs, the time duration of thermal treatment, and the presence or absence of Sn in the surfaces of float glass, all influence its colouration. Thermal treatments shorter than 1 h already promote the diffusion of Ag into the glass and therefore fix it, while longer times are necessary to fix the Au metal. The Ag colour intensity in the glass is easily controlled through the number of layers while in the case of Au this variable influences not only the colour intensity but also the tone.

The [bmim][BF4] ionic liquid effect on gold nanoparticles formation in silica sol–gel materials is studied in order to produce gel-derived glasses with optical properties. The characteristic red color from gold nanoparticles is observed for transparent glass monoliths obtained sintering, between 365 and 425 °C, a silica sol–gel precursor containing HAuCl4·3H2O and [bmim][BF4], under normal atmospheric conditions. The effect of sintering the ionogel at different temperatures (Tsint) or times (tsint) on the optical properties, shape, size, and distribution of gold nanoparticles is discussed. Presence of the gold particles is observed using transmission electron microscopy images followed by energy dispersive X-ray spectroscopy analysis. The thermal decomposition of [bmim][BF4] in the ionogel is investigate using calorimetric and spectroscopic techniques, and by analysis of volatile compounds released by the sol–gel material during sintering. With these results a mechanism for the formation of the gold nanoparticles is proposed, where a first ionic liquid degradation step provides the reductive environment that enables the gold nanoparticles production at the range of temperatures between 350 and 425 °C. Upon sintering the synthesized materials the ionic liquid acts as a sacrificial additive and the ionic liquid thermal decomposition products enables the formation of gold nanoparticles in the sol–gel matrix.

In this work, coloured glasses were produced based on the synthesis of gold and silver nanoparticles by the sol–gel process having in mind their application in art works. Gold and silver were used separately or as a mixture by varying the mole fractions in order to get a range of colours from yellow to red. The gold and silver nanoparticles were prepared by the reduction of tetrachloroauric acid and silver nitrate with sodium citrate in aqueous solutions which were further introduced in the sol–gel system. Attention was focused on the thermal treatment of the sol–gel samples. Different temperatures were used in order to determine their influence on the obtained colour. The glasses were characterized by UV–Vis absorption spectroscopy and the size of the nanoparticles was examined by transmission electron microscopy (TEM). The range of colours mentioned above is obtained either by preparing nanoparticles of each metal and mixing them or by preparing nanoparticles from solutions containing initially ions of both metals. In the former case, two surface plasmon resonance (SPR) bands were observed for temperatures below 200 °C while higher temperatures promote the formation of alloys between the Ag and Au nanoparticles. In the latter case, only one SPR band is observed and the nanoparticle size distribution is narrower. The results were explained by nanoparticle aggregation promoted by temperature. Glasses containing only Ag did not present the typical yellow colour above 300 °C but it was shown that the colour could be stabilized if Au was added in small amounts (Au/Ag molar ratio 0.1).

The formation of Eu(III) nanoparticles in borosilicate sol−gels and the glass formation heat treatment effect on those particles were studied using luminescence techniques. The presence of the particles was observed using transmission electron microscopy (TEM) images followed by analysis with energy dispersive X-ray spectroscopy (EDS). These experiments showed the presence of particles with a large quantity of europium and chlorine and only small amounts of oxygen with sizes ranging from 30 to 100 nm. Heat treatment at 400, 600, and 800 °C lead to glass samples in which those particles were no longer observed. Steady-state and time-resolved luminescence techniques allowed a detailed study of Eu(III) photophysics in sol−gel and glass samples. In sol−gel matrices, the 5D0 → 7F0 transition is very weak, hinting at Eu(III) species experiencing a rather symmetric crystal field. The 5D0 → 7F2 transition intensity is not very strong, which according to a Judd−Ofelt analysis indicates low interaction with the ani...

Woven Nomex® ribbon cables made up with superconducting niobium–titanium wire are used at millikelvin temperatures in many large cryogenic instruments. It is important to know how much heat in transmitted down such cables. However, the conductivity of the materials used is not well known. Another problem is that the wires are normally clad with alloys which exhibit some magnetism. This is a potential problem for instruments employing superconducting detectors. A safe non-magnetic alternative to the usual materials is phosphor-bronze clad niobium–titanium wiring. However, there is little experience with such wires. We have therefore measured the conductance of a ribbon cable made up with these wires. The measured values are in good agreement with our predictions, suggesting that the values we have used to model the cable are sufficiently accurate, and could therefore be used to predict the performance of ribbon cables using other cladding materials, so long as the conductivity of the cladding is reasonably well known. As part of our analysis, we consider the likely variation in thermal conductivity values for C51000 phosphor bronze caused by legitimate variations in composition.

Tecamax® SRP (self-reinforced polyphenylene) is a new commercially available amorphous polymer which is suitable for use at cryogenic temperatures. It has a high tensile strength (210 MPa at room temperature), resulting from the molecular structure of the polymer rather than by the addition of reinforcing materials. We have measured the thermal conductivity between 60 mK and 280 K. We find that the conductivity below 10 K is similar to, but lower than, most amorphous materials, and the material offers a good combination of low conductivity at low temperatures and high tensile strength. Our results suggest that the material may in fact have a small crystalline component, which may be a partial explanation for the low conductivity. Above 10 K, the temperature dependence of the conductivity is different from most amorphous materials. We are unaware of previous measurements of the thermal conductivity of this material, even at room temperature.

Pitch-bonded graphites are among the best known thermal insulators at sub-kelvin temperatures, but are very good conductors at higher temperatures. This makes them ideal for mechanical supports which must provide good thermal isolation at an operating temperature below 1 K, but must have good conductance at higher temperatures to aid in initially cooling down an instrument (a “passive heat switch”). One type of graphite, AGOT, has been known as having the lowest thermal conductivity below 1 K not only among graphites, but also compared with any other material. It is, however, no longer available. We have carried out thermal conductivity measurements at temperatures between 60 mK and 4 K on a proposed replacement, POCO AXM-5Q graphite, as well as a sample of AGOT graphite. Our measurements show that both graphites have a difference of about six orders of magnitude in conductivity between room temperature and 100 mK, but that AGOT graphite is not as good an insulator as previously believed. We conclude that AXM-5Q graphite is not only a suitable replacement for AGOT, but in fact is somewhat superior.

At very low temperatures, the tunnelling theory for amorphous solids predicts a thermal conductivity κ α Tm, with m = 2. However, most of the data in the literature in the temperature range 0.1–1 K report an m

The specific heat of Torlon has been measured in the 0.15–4.2 K temperature range. Data below 1 K can be represented by c ( T ) = P 1 T 1+ δ + P 2 T 3 , with P 1 = (5.41 ± 0.08)·10 −6 J K −(2+ δ ) g −1 , P 2 = (2.82 ± 0.03) ·10 −5 JK −4 g −1 and δ = 0.28 ± 0.01, as predicted by the tunnelling theory. Above 1 K, the behaviour of c ( T ) is similar to that of other amorphous materials and can be expressed as: c ( T ) = P · T Ω with P = (2.68 ± 0.07)·10 −5 JK Ω +1 g −1 and Ω = 3.32 ± 0.02.

Neutron Transmutation Doped (NTD) germanium thermistors, cut from metallized wafers, are useful in bolometry. The rise time of a bolometer depends on its heat capacity. We report measurements on the heat capacity of two NTD Ge wafers down to 24 mK temperatures. Both wafers were neutron irradiated and annealed, one of them had in addition undergone a boron implantation and metallization process. For the non-metallized wafer we found a Sommerfeld constant γ = 7.52·10−7 J K−2 cm−3. A comparison between the two wafers showed an excess heat capacity in the metallized wafer. For example, at 24 mK temperature, the specific heat of the metallized afer is more than twice the value of the non-metallized one.

The measurement of thermal and mechanical properties of materials at cryogenic temperatures gains more and more importance in the field of the application of novel high-tech materials to aerospace industry and in developing scientific instrumentation. We present a simple and inexpensive interferometric dilatometer for the measurement of the thermal expansion of materials in the 4–300 K range. The dilatometer consists of a Michelson tilt-compensated interferometer in which the path difference is given by the variation in length of a sample enclosed in a 4 K cryostat. The compensation for misalignment permits a fast and simple operation routine that configures the instrument as a valuable tool for materials engineering.

We report about the measurement of the electric characteristics of some NTD Ge thermistors at temperatures down to 25 mK. The dopant concentration is around 6 × 10 16 cm - 3 , producing a material of characteristics close to the metal-to-insulator transition. Fitting the ρ ( T ) characteristics with a variable exponent p Mott's law, a p around 0.6 was obtained. This result confirms the hypothesis of a dependence of p on the doping level.

Torlon is an organic polymer (polyamide-imide) which exhibits room temperature good mechanical and thermal properties and high chemical resistance. The thermal conductivity of Torlon 4203 was measured in the range of temperature 4.2–300 K. These data complete existing measurement in the temperature range 0.1–5 K. The thermal conductivity shows a linear behavior between 30 K and 250 K and a plateau, typical of many amorphous materials, around 7 K.

We report data of thermal conductivity between 30 and 150 mK of three different types of commercial copper, before and after a thermal treatment of the samples. The measurements show that both purity and thermal treatment strongly influence the value of thermal conductivity. Data show a strict linear dependence on the temperature of the thermal conductivity.

Purpose of this experiment was to select the best material for the construction of thermal links aiming at cooling down sensitive masses of the order of 100–1000 kg for the detection of rare decays and gravitational waves. We report on the technique used to measure the thermal conductivity at very low temperatures (down to 30 mK) of three different types of copper, before and after a thermal treatment of the samples. The most conductive copper was used for the thermal link of the CUORICINO experiment, where a mass of about 60 kg needs to be cooled down to a few mK. The cool down time was reduced by at least one order of magnitude with respect to previous similar experiments. An important contribution to this successful result came also from an improved procedure for controlling the residual heating provided by the conversion from ortho- to para-hydrogen in copper.

At ITN, PM10 and PM2.5 aerosols were collected on Nuclepore® polycarbonate filters of 47 mm diameter, using Gent samplers at 15–17 l/min air flux. Filters were analyzed by INAA and PIXE. The availability of certified filters was very scarce, viz.: (1) fly ash embedded in a methyl cellulose 47 mm foil 10 µm thick, BCR CRM128, (2) particle-size reduced air particulate matter (APM) to simulate PM2.5 aerosol matter deposited on a 47 mm polycarbonate filter membrane, NIST SRM 2783. The high price and scarcity of APM standards did not permit their frequent use for analytical quality control. At ITN, to control the filter results' accuracy, the chemical elements potassium, iron and zinc, determined by both techniques, were systematically compared. After a few improvements introduced in INAA, this technique was now considered at ITN as the reference technique in air particulate measurements. Comparison of INAA to PIXE was discussed. Compared to previously reported situation it was concluded that the results were in better agreement for iron and zinc, and potassium values were still biased to the same extent as before.

We have studied the low temperature thermal properties of a polypropylene copolymer (PP): thermal conductivity (between 0.1 and 4 K), specific heat (between 0.06 and 1 K) and thermal expansion (from 4.2 K to room temperature). Both the thermal conductivity and the specific heat temperature data were interpreted using the tunnelling model for phonon scattering. The measured thermal properties show that PP is suitable for use as thermal insulating support material in cryogenic devices.

The optimization of bolometric detectors, like those that will be developed for the rare event experiment CUORE, requires a complete knowledge of the detector's thermal parameters. Since the CUORE detecting elements will consist of TeO2 crystals, we have measured the specific heat of this material down to 60 mK with the thermal relaxation method. Previous available data were taken at temperatures higher than 0.6 K. Our results are clearly consistent with a lattice dominated specific heat. The Debye temperature, evaluated to be (232±7) K, is in excellent agreement with the elastic constant values measured by other authors. The knowledge of the Debye temperature allows a simple prediction of the pulse amplitude of presently working bolometers.

Permaglas ME771 is a glass–epoxy laminate which is suitable for use at cryogenic temperatures. We have measured the thermal conductivity of a sample of this material between 64 mK and 4.2 K in the direction parallel to the reinforcing fibres, enabling us to make a comparison with the better known material G-10CR. The thermal conductivity follows the form that would be expected for such a material, and is similar to that of G-10CR, which has a similar (room temperature) tensile strength. We comment on some confusion that has arisen over the difference between G-10CR, a material specifically produced for cryogenic use, and G-10, the more common equivalent.

An investigation is presented on the influence of impurity concentration and magnetic field on the superconducting transition of high-purity commercial titanium samples. Run-to-run and sample-to-sample reproducibility is evaluated for the purest titanium specimen. Past work on the superconducting transition of titanium is reviewed, and the suitability of titanium as a thermometric reference point is discussed.

A sensitive diaphragm-type pressure transducer, suitable for use at low temperature is described. This device was optimized for pressure up to 3.5 MPa. The external pressure deflects two CuBe disks, which form the electrodes of a capacitor. The transducer sensitivity at 3.43 MPa is about 25 pF/MPa. No hysteresis was detected within the accuracy of the piezoelectric pressure transducer used in the calibration procedure.

We measured the thermal conductivity of a Kevlar 49 in the 7–290 K temperature range. With a maximum error of 4%, our data are fitted by the simple formula: k = 5.03 - 5.07 e ( - 0.00487 ) W/mK Kevlar 49 is a candidate material for the supports of CUORE experiment.

We used Stycast 1266 in a high-pressure, low-temperature transducer. In order to ascertain the dependence of capacitance and loss on temperature, we measured the temperature behaviour of the dielectric constant and the dissipation factor of Stycast 1266 at 1 KHz between 0.07 and 300 K. We found a smooth decrease of the dielectric constant with decreasing T. The temperature dependence below 1 K is well explained by the tunneling model. The loss tangent showed very low values (always less than 5×10−5), with a peak around 260 K that can be ascribed to dielectric relaxation processes.

The thermal conductivity of an aromatic polyimide sheet (Upilex R) in the 0.1 ÷ 1K range was measured. A conductivity k = α · Tn, with α = (1.50 ± 0.06) · 10−5 W/cmKn+1 and n = 1.00 ± 0.03, which is substantially different from what predicted by the tunneling model, was found. The linear dependence on temperature, which reveals the presence of crystalline units inside the sample, has been explained within the framework of the structure scattering theory, together with the standard tunneling model, and the size of the crystallites has been estimated. Our results are compared with the thermal conductivity of other semicrystalline materials.

The influence of impurity concentration c and applied magnetic field H on the superconducting transition of high-purity commercial titanium samples was investigated. The superconductive transition temperature TC was found to be very sensitive to the impurity concentration ( dT C dc ≈ −0.6 mK/w.ppm) and to the applied magnetic field (( dT C dH ) ≈ −1.1 mK/G) . A linear dependence of TC decrease on impurity concentration, as theoretically predicted by various authors, was observed. In the purest sample, a linear decrease of TC on the applied magnetic field was found. The run-to-run and sample-to-sample reproducibility of the transition of the same sample was evaluated, and its suitability as a thermometric reference point below 1K was discussed.

A new method is presented for measuring the low-temperature thermal conductivity of thin electrically-conducting samples. The proposed two-probe technique is useful mainly in the case of non free-standing samples of medium and high thermal resistivity. The method is simple: a resistance bridge is used both for measuring the temperatures and for heating the sample. The limits of this method are discussed. The thermal conductivities below 0.3 K of a normal alloy (manganin) and a superconducting alloy (Al/Si 1%), both which we obtained using this method, are presented.

The thermal conductivity of the Al/Si 1% alloy was investigated in the 0.05–1.2 K temperature range. Wires (typically ⊘ = 25μm) made of this alloy are widely used in the wedge bonding of cryogenic detectors. These wires contribute to or determine the thermal conductance between the detector and the thermal bath. Measurements in both the normal state and in the superconducting state are presented. A critical temperature, Tc =(1.20 ± 0.02)K, was measured. In the superconducting state, the following results were obtained: i) below Tc, a k α exp ( − β T ) law was determined down to T ⋍ 0.3 K; ii) for T

The accurate measurement of thermal expansion coefficient at low temperatures is fundamental in applications where a high mechanical stability is required over the complete procedure of cooling. Here we report on our measurement of thermal expansion of AISI 420 between 20 and 293 K, measured by an interferometric dilatometer. (C) 2014 Elsevier Ltd. All rights reserved.

The transition temperature from normal to superconducting state and the specific heat of Al 5056 aluminium alloy in the 0.1 – 3.6 K temperature range have been measured. This alloy is largely used in resonant detectors of gravitational waves. A comparison with specific heat data of the same material obtained by different measuring methods is given.

We measured the thermal conductivity of Kapton HN and Upilex R in the lengthwise direction of a single layer of material. The temperature range was investigated 0.1–9 K for Upilex and 0.2–5 K for Kapton. For both conductivities, we found a linear dependence on temperature that can be ascribed to the presence of crystalline units inside the solids.

We measured the thermal conductivity of a Kevlar cord, 0.8 mm in diameter, in the 0.1–2.5 K temperature range. The data were fitted with a power-law: k=(3.9±0.2)×10 −5 T 1.17±0.04 W/cm K . Our results are in good accordance with the existing data at T>2 K .

We report the design, the construction and performance of a dilution refrigerator using a pulse-tube cooler as a first cryogenic stage. Both the pulse tube and the dilution unit are commercial. The absence of a Dewar containing cryogenic fluids makes this new type of refrigerator particularly versatile: it was built to carry out cryogenic tests on CUORE components. The system provides a cooling power of about 0.2 mW at 100 mK, and reaches temperatures as low as 6 mK.

We carried out thermal conductivity measurements of Manganin wire having a composition of Cu 84%, Ni 4%, Mn 12% (sample 1) in the 0.1 ÷ 1K temperature range, and of Manganin wire having a composition of Cu 86%, Ni 2%, Mn 12% (sample 2) in the 0.05 ÷ 0.25K range. The measurements were performed in a low-power dilution refrigerator. For sample 1, the fit on the data gives a dependence on T: k = (0.79 ± 0.01)T1.22±0.02 mW/cmK; for sample 2, the fit leads to k = (0.95 ± 0.04)T1.19±0.02 mW/cmK. The difference in thermal conductivity in the overlapping temperature range depends on the different ratio of the Cu Ni content of the samples. A similar sensitivity to a small difference in the composition has also been found for other Cu alloys.

The CUORE cryogenic system consists of a large cryogen-free cryostat cooled by five pulse tubes and one high-power specially designed dilution refrigerator. About 5 × 10 3 kg of lead shielding are to be cooled to below 1 K and a mass of 1.5 × 10 3 kg must be cooled to 10 mK. Several tie-rods are used to support the different parts of the experiment. We have measured the thermal conductivity below 4 K of two candidate materials for the CUORE suspensions: the Ti6Al4V alloy ( k ( T ) = 0.075 · T exp - 1.636 4.38 K T [ W / m K ] ) and the 316LN stainless steel ( k ( T ) = 0.0556 · T 1.15 [ W / m K ] ) .

The characteristics of a CXY23/MO67 varicap diode were measured at millikelvin temperatures. The diode can be used as a d.c. voltage tunable capacity element at temperatures even below 20 mK. The heat dissipation caused by the applied d.c. polarization voltage is negligible even at the lowest temperature reached by a dilution refrigerator (13 mK). The d.c. polarizing voltage can be used in the 0–24V interval at these temperatures.