Herein we show that the Ti3SiC2 MAX phase can be used as a support for deposition of different amounts of metal oxides (MOx, M = Cu or V) (5, 10 and 20 wt%) for the direct oxidation of methane to formaldehyde using molecular oxygen, at relatively low temperatures and atmospheric pressure. The oxides were deposited using a hydrothermal method at 180 degrees C without affecting the bulk MAX phase structure. However, during the hydrothermal treatment (HT) a thin oxide layer - found to play an important role in the reaction's selectivity- was evidenced by X-ray photoelectron spectroscopy. We thus conclude that the MOx species are responsible for the CH4 activation, while the Ti3SiC2 surface is responsible for the high selectivity to formaldehyde indicating that, Ti3SiC2 has great potential for designing innovative catalysts for direct oxidation of methane using molecular oxygen and at atmospheric pressure.

Plastics are indispensable materials for packaging and many products from our daily life, and their recycling is essential to ensure a circular economy. In this study, -SO3H-modified, Ti3C2-MXene was used as a recoverable solid acid catalyst for upcycling of polyethylene terephthalate (PET) to terephthalic acid (TPA) and ethylene glycol by hydrolysis. For the grafting of -SO3H groups to the Ti3C2Tx surface (where T-x represents the surface moieties, such as -OH or -O), sulfonation with an aryl diazonium salt obtained from sulfanilic acid was employed. X-ray photoelectron and Fourier transform infrared spectroscopy analyses provided a direct indication that sulfonation of the Ti3C2Tx was successfully performed, while X-ray diffraction and transmission electron microscopy analyses evidence the presence of -SO3H groups between the Ti3C2Tx layers due to the increases of the interlayer spacing through the intercalation of functional groups. The higher the concentration of acid groups, the higher the interlayer spacing. The depolymerization of PET in water occurred with a very good isolated yield in TPA (99%) for the MXene with the highest amount of sulfonic acid groups. We conclude that the acidity is mandatory to perform the hydrolysis reaction, in agreement with the acidity measurements, which show that the MXenes modified with the highest amount of derived sulfonic acids are the most active. Nevertheless, the accessibility to the acidic sites is a key factor that promotes the 2D acid-modified MXene materials as important catalysts for PET upcycling to TPA.

Plastics are indispensable materials for packaging and many products from our daily life, and their recycling is essential to ensure a circular economy. In this study, -SO3H-modified, Ti3C2-MXene was used as a recoverable solid acid catalyst for upcycling of polyethylene terephthalate (PET) to terephthalic acid (TPA) and ethylene glycol by hydrolysis. For the grafting of -SO3H groups to the Ti3C2Tx surface (where T-x represents the surface moieties, such as -OH or -O), sulfonation with an aryl diazonium salt obtained from sulfanilic acid was employed. X-ray photoelectron and Fourier transform infrared spectroscopy analyses provided a direct indication that sulfonation of the Ti3C2Tx was successfully performed, while X-ray diffraction and transmission electron microscopy analyses evidence the presence of -SO3H groups between the Ti3C2Tx layers due to the increases of the interlayer spacing through the intercalation of functional groups. The higher the concentration of acid groups, the higher the interlayer spacing. The depolymerization of PET in water occurred with a very good isolated yield in TPA (99%) for the MXene with the highest amount of sulfonic acid groups. We conclude that the acidity is mandatory to perform the hydrolysis reaction, in agreement with the acidity measurements, which show that the MXenes modified with the highest amount of derived sulfonic acids are the most active. Nevertheless, the accessibility to the acidic sites is a key factor that promotes the 2D acid-modified MXene materials as important catalysts for PET upcycling to TPA.

The incorporation of therapeutic-capable ions into bioactive glasses (BGs), either based on silica (SBGs) or phosphate (PBGs), is currently envisaged as a proficient path for facilitating bone regeneration. In conjunction with this view, the single and complementary structural and bio-functional roles of CuO and Ga2O3 (in the 2-5 mol% range) were assessed, by deriving a series of SBG and PBG formulations starting from the parent glass systems, FastOs (R) BG -38.5SiO2-36.1CaO-5.6P2O5-19.2MgO-0.6CaF2, and 50.0P2O5-35.0CaO-10.0Na2O-5.0 Fe2O3 (mol%), respectively, using the process of melt-quenching. The inter-linked physico-chemistry -biological response of BGs was assessed in search of bio-functional triggers. Further light was shed on the structural role -as network former or modifier -of Cu and Ga, immersed in SBG and PBG matrices. The preliminary biological performance was surveyed in vitro by quantification of Cu and Ga ion release under homeostatic conditions, cytocompatibility assays (in fibroblast cell cultures) and antibacterial tests (against Staphylococcus aureus). The similar (Cu) and dissimilar (Ga) structural roles in the SBG and PBG vitreous networks governed their release. Namely, Cu ions were leached in similar concentrations (ranging from 10-35 ppm and 50-110 ppm at BG doses of 5 and 50 mg/mL, respectively) for both type of BGs, while the release of Ga ions was 1-2 orders of magnitude lower in the case of SBGs (i.e., 0.2-6 ppm) compared to PBGs (i.e., 9-135 ppm). This was attributed to the network modifier role of Cu in both types of BGs, and conversely, to the network former (SBGs) and network modifier (PBGs) roles of Ga. All glasses were cytocompatible at a dose of 5 mg/mL, while at the same concentration the antimicrobial efficiency was found to be accentuated by the coupled release of Cu and Ga ions from SBG. By collective assessment, the most prominent candidate material for the further development of implant coatings and bone graft substitutes was delineated as the 38.5SiO2-34.1CaO-5.6P2O5-16.2MgO-0.6CaF2-2.0CuO-3.0Ga2O3 (mol%) SBG system, which yiel-ded moderate Cu and Ga ion release, excellent cytocompatibility and marked antibacterial efficacy. (c) 2021 The Chinese Ceramic Society. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Currently, there is a considerable time-lag in the industrialisation of innovative technological solutions for the functionalization of osseous implants, with ever-demanding healthcare requirements (e.g., controlled release of therapeutic ions, match of biomaterial degradation - bone growth rates, antimicrobial efficiency). As third-generation biomaterials, phosphate bio-glasses (PBGs) have demonstrated an ability to stimulate specific biological responses from tissue to molecular level, by successfully coupling bioactive and resorbable material properties. Here, radio-frequency magnetron sputtered (RF-MS) PBGs were explored as sacrificial resorbable layers for prospective biomedical implant designs. A PBG powder with a 50-P2O5, 35-CaO, 10-Na2O and 5-Fe2O3 composition (mol%) was used as source (target) material. The influence of the argon working pressure (0.2-1 Pa) - one of the most prominent RF-MS variables - on the morphology, structure, uniformity, composition, degradation rate and cytocompatibility of PBG films was investigated. The engineered modification of physical-chemical and biological features of the PBG sputtered films was multi-parametrically surveyed by AFM, EDXS, spectroscopic ellipsometry, GIXRD, FTIR spectroscopy measurements and in vitro assays. Results suggested that the film thickness, composition, density and structure were preserved over a uniformity region having a diameter of similar to 30 mm, irrespective of sputtering pressure. The network connectivity and the surface porosity of the films were found to have antagonistic roles with respect to the in vitro degradation performance. The possibility of fine tuning the composition, structure and thereby biological interaction of the PBG films by conveniently modifying the sputtering pressure was shown (i.e., permitting their complete controlled degradation, without cytotoxic effects). This work is the first to show in vitro cytocompatibility outcomes of sputtered PBG films and their cross-area uniformity, and thus, it could prove to be an important technological step in their future biomedical application and suggest implications for future industrial scale-up.

In this work, the structural, thermal, vibrational, morphological, magnetic and optical properties of LaPO4:Ce/RE/Me (RE=Nd3+, Tb3+; Me-Cr3+, Mn2+) and LaPO4:Yb3+/Er3+ phosphors prepared by the co-precipitation method are presented. The obtained materials crystallized in monoclinic structure with the P2(1)/n space group and the particles were of nanorod shape with about 200 nm in length and the diameter approximately 19 nm. The presence of dopant ions was confirmed by both electron paramagnetic resonance (EPR) and UV-visible spectroscopies. In addition, the down-conversion (DC) and up-conversion (UC) of the LaPO4 nanophosphors via the 275 and 980 nm excitations, respectively, were considered, and a wide range of electronic transitions was observed. Based on the photoluminescence (PL) spectra, there is an efficient energy transfer (ET) process from Ce3+ donors to Nd3+ and Tb3+ acceptors, and the computed ET efficiency was 70% and 88%, respectively. The Ce3+/Cr3+ and Ce3+/Mn2+ doped LaPO4 showed weak far-red and green luminescence with much smaller ET efficiency of about 3.7 and 0.4%, respectively. LaPO4:Yb3+/Er3+ showed UC luminescence under the 980 nm laser radiation, and the resulted red and green light was attributed to the Er3+ transitions.

Fuel cells are devices that transform efficiently the chemical energy of hydrogen or another fuel into clean electricity. The fuel cell technology is attractive for its high-energy efficiency and expanded fuel flexibility and it became very relevant in the last decade. Moreover, the utilization of fuel cells for portable electronic devices has seen remarkable increase in the last few years. Performances of fuel cells, among others, strongly depend on the types of electrocatalysts and membrane, anion exchange or cation exchange, used in the system. Therefore, a status report about the latest advances in electrocatalysts and electrodes for portable fuel cells is the objective of this review paper. Herein, the recent progress in designing electrocatalysts for producing high performance fuel cells with truly potential applicability to be used in portable devices is highlighted.

Cation-substituted hydroxyapatite (HA), standalone or as a composite (blended with polymers or metals), is currently regarded as a noteworthy candidate material for bone repair/regeneration either in the form of powders, porous scaffolds or coatings for endo-osseous dental and orthopaedic implants. As a response to the numerous contradictions reported in literature, this work presents, in one study, the physico-chemical properties and the cytocompatibility response of single cation-doped (Ce, Mg, Sr or Zn) HA nanopowders in a wide concentration range (0.5-5 at.%). The modification of composition, morphology, and structure was multiparametrically monitored via energy dispersive X-ray, X-ray photoelectron, Fourier-transform infrared and micro-Raman spectroscopy methods, as well as by transmission electron microscopy and X-ray diffraction. From a compositional point of view, Ce and Sr were well-incorporated in HA, while slight and pronounced deviations were observed for Mg and Zn, respectively. The change of the lattice parameters, crystallite size, and substituting cation occupation factors either in the Ca(I) or Ca(II) sites were further determined. Sr produced the most important HA structural changes. The in vitro biological performance was evaluated by the (i) determination of leached therapeutic cations (by inductively coupled plasma mass spectrometry) and (ii) assessment of cell behaviour by both conventional assays (e.g., proliferation-3-(4,5-dimethyl thiazol-2-yl) 5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium assay; cytotoxicity-lactate dehydrogenase release assay) and, for the first time, real-time cell analysis (RTCA). Three cell lines were employed: fibroblast, osteoblast, and endothelial. When monophasic, the substituted HA supported the cells' viability and proliferation without signs of toxicity. The RTCA results indicate the excellent adherence of cells. The study strived to offer a perspective on the behaviour of Ce-, Mg-, Sr-, or Zn-substituted HAs and to deliver a well-encompassing viewpoint on their effects. This can be highly important for the future development of such bioceramics, paving the road toward the identification of candidates with highly promising therapeutic effects.

MAX phases and MXenes are important materials that have recently gained great popularity due to their special properties, which render them particularly useful in many applications, including catalytic ones. This can be seen in the large number of publications that appear annually on these materials and their applications. This review aims to evaluate MAX phases and MXenes as materials for heterogeneous, non-electrocatalytic, catalytic applications. The review begins with a brief introduction to the MAX phase and MXene properties that recommend them as potential materials for heterogeneous catalytic applications, followed by four sections grouped according to the processes in which they have already proven effective. These include supports to activate the C-H or C-O bonds in applications such as dehydrogenation of light or aromatic alkanes, methanol formation from CH4, dry reforming, and CO oxidation or the water gas shift reaction (Section 2), and their use in fine chemical reactions (Section 3) and in chemical degradation (Section 4). The last section deals with photocatalytic applications (Section 5). The review ends by highlighting the huge potential of these materials for a wide range of heterogeneous catalytic applications as well as the challenges ahead.

Palladium is one of the most efficient metals for the hydrogenation of organic compounds. However, when molecules, such as nitroaromatics, with several reducible functionalities, are hydrogenated, Pd, like any other very active metal, such as nickel or platinum, often behaves unselectively. One strategy to render Pd more selective is to choose the proper support. Herein, we show that MAX phase powders of Ti3SiC2, Ti2AlC, or Ti3AlC2 can chemoselectively hydrogenate 4-nitrostyrene to 4-aminostyrene, with 100% selectivity, at around 3-4% conversion. To boost the latter, we loaded Ti3SiC2 with 0.0005 wt % Pd and increased the conversion to 100% while maintaining the 4-AS selectivity at >90%. By optimizing the Pd loading, we were also able to increase the turnover frequency 100-fold relative to previous literature results. The identification of this highly efficient and chemoselective system has broad implications for the design of cost-effective, earth-abundant, nontoxic, metal catalysts, with ultralow noble metal loadings.

Silica-based bioactive glasses (SBG) hold great promise as bio-functional coatings of metallic endo-osseous implants, due to their osteoproductive potential, and, in the case of designed formulations, suitable mechanical properties and antibacterial efficacy. In the framework of this study, the FastOs(R)BG alkali-free SBG system (mol%: SiO2-38.49, CaO-36.07, P2O5-5.61, MgO-19.24, CaF2-0.59), with CuO (2 mol%) and Ga2O3 (3 mol%) antimicrobial agents, partially substituting in the parent system CaO and MgO, respectively, was used as source material for the fabrication of intentionally silica-enriched implant-type thin coatings (similar to 600 nm) onto titanium (Ti) substrates by radio-frequency magnetron sputtering. The physico-chemical and mechanical characteristics, as well as the in vitro preliminary cytocompatibility and antibacterial performance of an alkali-free silica-rich bio-active glass coating designs was further explored. The films were smooth (R-RMS < 1 nm) and hydrophilic (water contact angle of similar to 65 degrees). The SBG coatings deposited from alkali-free copper-gallium co-doped FastOs(R)BG-derived exhibited improved wear performance, with the coatings eliciting a bonding strength value of similar to 53 MPa, Lc3 critical load value of similar to 4.9 N, hardness of similar to 6.1 GPa and an elastic modulus of similar to 127 GPa. The Cu and Ga co-doped SBG layers had excellent cytocompatibility, while reducing after 24 h the Staphylococcus aureus bacterial development with 4 orders of magnitude with respect to the control situations (i.e., nutritive broth and Ti substrate). Thereby, such SBG constructs could pave the road towards high-performance bio-functional coatings with excellent mechanical properties and enhanced biological features (e.g., by coupling cytocompatibility with antimicrobial properties), which are in great demand nowadays.