Crystal structures of two new high-pressure oxynitrides with composition SnGe4N4O4, from single-crystal electron diffraction.

SnGe4N4O4 was synthesized at high pressure (16 and 20 GPa) and high temperature (1200 and 1500°C) in a large-volume press. Powder X-ray diffraction experiments using synchrotron radiation indicate that the derived samples are mixtures of known and unknown phases. However, the powder X-ray diffraction patterns are not sufficient for structural characterization. Transmission electron microscopy studies reveal crystals of several hundreds of nanometres in size with different chemical composition. Among them, crystals of a previously unknown phase with stoichiometry SnGe4N4O4 were detected and investigated using automated diffraction tomography (ADT), a three-dimensional electron diffraction method. Via ADT, the crystal structure could be determined from single nanocrystals in space group P63mc, exhibiting a nolanite-type structure. This was confirmed by density functional theory calculations and atomic resolution scanning transmission electron microscopy images. In one of the syntheses runs a rhombohedral 6R polytype of SnGe4N4O4 could be found together with the nolanite-type SnGe4N4O4. The structure of this polymorph was solved as well using ADT.

Recycling and Reusing of Graphite from Retired Lithium-ion Batteries: A Review.

The proliferation of rechargeable lithium-ion batteries (LIBs) over the past decade has led to a significant increase in the number of electric vehicles (EVs) powered by these batteries reaching the end of their lifespan. With retired EVs becoming more prevalent, recycling and reusing their components, particularly graphite, has become imperative as the world transitions toward electric mobility. Graphite constitutes ≈20% of LIBs by weight, making it a valuable resource to be conserved. This review presents an in-depth analysis of the current global graphite mining landscape and explores potential opportunities for the "second life" of graphitefrom depleted LIBs. Various recycling and reactivation technologies in both industry and academia are discussed, along with potential applications for recycled graphite forming a vital aspect of the waste management hierarchy. Furthermore, this review addresses the future challenges faced by the recycling industry in dealing with expired LIBs, encompassing environmental, economic, legal, and regulatory considerations. In conclusion, this review provides a comprehensive overview of the developments in recycling and reusing graphite from retired LIBs, offering valuable insights for forthcoming large-scale recycling efforts.

Robust Ti3C2Tx MXene foam modified with natural antioxidants for long-term effective electromagnetic interference shielding.

MXenes have been proven to be outstanding lossy phase of advanced electromagnetic interference (EMI) shielding materials. However, their poor tolerance to oxygen and water results in fast degradation of the pristine two-dimensional (2D) nanostructure and fading of the functional performance. Herein, in this research, natural antioxidants (e.g., melatonin, tea polyphenols, and phytic acid) were employed to protect the Ti3C2Tx MXene from its degradation in order to achieve a long-term stability of the EMI shielding performance. The results showed that the synthesized composites comprised of antioxidants and Ti3C2Tx exhibited a decelerating degradation rate resulting in an improved EMI shielding effective (SE) stability. The antioxidation mechanism of the applied antioxidants is discussed with respect to the nanostructure evolution of the Ti3C2Tx MXene. This work contributes to the basic foundations for the further development of advanced MXenes for stable applications in the EM field.

Molybdenum Phosphide Quantum Dots Encapsulated by P/N-Doped Carbon for Hydrogen Evolution Reaction in Acid and Alkaline Electrolytes.

A facile and eco-friendly strategy is presented for synthesizing novel nanocomposites, with MoP quantum dots (QDs) as cores and graphitic carbon as shells, these nanoparticles are dispersed in a nitrogen and phosphorus-doped porous carbon and carbon nanotubes (CNTs) substrates (MoP@NPC/CNT). The synthesis involves self-assembling reactions to form single-source precursors (SSPs), followed by pyrolysis at 900 °C in an inert atmosphere to obtain MoP@NPC/CNT-900. The presence of carbon layers on the MoP QDs effectively prevents particle aggregation, enhancing the utilization of active MoP species. The optimized sample, MoP@NPC/CNT-900, exhibits remarkable electrocatalytic activity and durability for the hydrogen evolution reaction (HER). It demonstrates a low overpotential of 155 mV at 10 mA cm-2 , a small Tafel slope of 76 mV dec-1 , and sustained performance over 20 hours in 0.5 M H2 SO4 . Furthermore, the catalyst shows excellent activity in 1 M KOH, with a relatively low overpotential of 131 mV and long-term durability under constant current input. The exceptional HER activity can be attributed to several factors: the superior performance of MoP QDs, the large surface area and good conductivity of the carbon substrates, and the synergistic effect between MoP and carbon species.

A facile strategy for reclaiming discarded graphite and harnessing the rate capabilities of graphite anodes.

Graphite negative electrodes are unbeaten hitherto in lithium-ion batteries (LiBs) due to their unique chemical and physical properties. Thus, the increasing scarcity of graphite resources makes smart recycling or repurposing of discarded graphite particularly imperative. However, the current recycling techniques still need to be improved upon with urgency. Herein a facile and efficient hydrometallurgical process is reported to effectively regenerate aged (39.5 %, 75 % state-of-health, SOH) scrapped graphite (SG) from end-of-life lithium-ion batteries. Ultimately, the first cycle reversible capacity of SG1 (SOH = 39.5 %) improved from 266 mAh/g to 337 mAh/g while 330 mAh/g (98 %) remain after 100 cycles at 0.5 C. The reversible capacity for the first cycle of SG2 (SOH = 75 %) boosted from 335 mAh/g to 366 mAh/g with the capacity retention of 99.3 % after 100 cycles at 0.5 C, which is comparable with the benchmark commercial graphite. The regenerated graphites RG1 and RG2 exhibit excellent output characteristics even increasing the rate up to 4 C. This is the best rate level reported in the literature to date. Finally, the diffusion coefficient of Li ions during deintercalation and intercalation in the regenerated graphites have been measured by galvanostatic intermittent titration technique (GITT), determining values 2 orders-of-magnitude higher than that of the spent counterparts. Taking advantage of the synergistic effect of acid leaching and heat treatment, this strategy provides a simple and up-scalable method to recycle graphitic anodes.

Structural Electromagnetic Absorber Based on MoS2 /PyC-Al2 O3 Ceramic Metamaterials.

Limited by the types of suitable absorbents as well as the challenges in engineering the nanostructures (e.g., defects, dipoles, and hetero-interface) using state-of-the-art additive manufacturing (AM) techniques, the electromagnetic (EM) wave absorption performance of the current ceramic-based materials is still not satisfying. Moreover, because of the high residual porosity and the possible formation of cracks during sintering or pyrolysis, AM-formed ceramic components may in many cases exhibit low mechanical strength. In this work, semiconductive MoS2 and conductive PyC modified Al2 O3 (MoS2 /PyC-Al2 O3 ) ceramic-based structural EM metamaterials are developed by innovatively harnessing AM, precursor infiltration and pyrolysis (PIP), and hydrothermal methods. Three different meta-structures are successfully created, and the ceramic-based nanocomposite benefit from its optimization of EM parameters. Ultra-broad effective absorption bandwidth (EAB) of 35 GHz is achieved by establishment of multi-loss mechanism via nanostructure engineering and fabrication of meta-structures via AM. Due to the strengthening by the PyC phase, the bending strength of the resulting ceramics can reach ≈327 MPa, which is the highest value measured on 3D-printed ceramics of this type that has been reported so far. For the first time, the positive effect deriving from the engineering of the microscopic nano/microstructure and of the macroscopic meta-structure of the absorber on the permittivity and EM absorption performance is proposed. Integration of outstanding mechanical strength and ultra-broad EAB is innovatively realized through a multi-scale design route. This work provides new insights for the design of advanced ceramic-based metamaterials with outstanding performance under extreme environment.

SiCO Ceramics as Storage Materials for Alkali Metals/Ions: Insights on Structure Moieties from Solid-State NMR and DFT Calculations.

Polymer-derived silicon oxycarbide ceramics (SiCO) have been considered as potential anode materials for lithium- and sodium-ion batteries. To understand their electrochemical storage behavior, detailed insights into structural sites present in SiCO are required. In this work, the study of local structures in SiCO ceramics containing different amounts of carbon is presented. 13 C and 29 Si solid-state MAS NMR spectroscopy combined with DFT calculations, atomistic modeling, and EPR investigations, suggest significant changes in the local structures of SiCO ceramics even by small changes in the material composition. The provided findings on SiCO structures will contribute to the research field of polymer-derived ceramics, especially to understand electrochemical storage processes of alkali metal/ions such as Na/Na+ inside such networks in the future.

Single-Source-Precursor Derived Transition Metal Alloys Embedded in Nitrogen-Doped Porous Carbons as Efficient Oxygen Evolution Electrocatalysts.

Carbon supported metallic nanomaterials are of great interest due to their low-cost, high durability and promising functional performance. Herein, a highly active oxygen evolution reaction (OER) electrocatalyst comprised of defective carbon shell encapsulated metal (Fe, Co, Ni) nanoparticles and their alloys supported on in-situ formed N-doped graphene/carbon nanotube hybrid is synthesized from novel single-source-precursors (SSP). The precursors are synthesized by a facile one-pot reaction of tannic acid with polyethylenimine and different metal ions and subsequent pyrolysis of the SSP. Benefiting from the heteroatom doping of carbon and formation of well-encapsulated metal/alloy nanoparticles, the obtained FeNi@NC-900 catalyst possesses lowest overpotentials of 310 mV to achieve a current density of 10 mA cm-2 for OER with a small Tafel slope value of 45 mV dec-1 , indicating excellent catalytic performance due to the following features: (1) A synergistic electronic effect among metal alloy nanoparticles, nitrogen-doped carbon, and entangled carbon nanotubes; (2) penetration of electrolyte is promoted towards the active sites through the porous structure of the formed mesoporous carbon clusters; (3) the unique core-shell nanostructure of the hybrid material effectively curbs the degradation of electrocatalyst by protecting the alloy nanoparticles from harsh electrolyte. This work advances an inexpensive and facile method towards the development of transition metal-based hybrid material for potential energy storage and conversion.

Electrochemical Performance of Carbon-Rich Silicon Carbonitride Ceramic as Support for Sulfur Cathode in Lithium Sulfur Battery.

As a promising matrix material for anchoring sulfur in the cathode for lithium-sulfur (Li-S) batteries, porous conducting supports have gained much attention. In this work, sulfur-containing C-rich SiCN composites are processed from silicon carbonitride (SiCN) ceramics, synthesized at temperatures from 800 to 1100 °C. To embed sulfur in the porous SiCN matrix, an easy and scalable procedure, denoted as melting-diffusion method, is applied. Accordingly, sulfur is infiltrated under solvothermal conditions at 155 °C into pores of carbon-rich silicon carbonitride (C-rich SiCN). The impact of the initial porosity and microstructure of the SiCN ceramics on the electrochemical performance of the synthesized SiCN-sulfur (SiCN-S) composites is analysed and discussed. A combination of the mesoporous character of SiCN and presence of a disordered free carbon phase makes the electrochemical performance of the SiCN matrix obtained at 900 °C superior to that of SiCN synthesized at lower and higher temperatures. A capacity value of more than 195 mAh/g over 50 cycles at a high sulfur content of 66 wt.% is achieved.

Natural wood templated hierarchically cellular NbC/Pyrolytic carbon foams as Stiff, lightweight and High-Performance electromagnetic shielding materials.

Hierarchically cellular, stiff, and lightweight niobium carbide (NbC)-pyrolytic carbon (PyC) monolithic foam composites possessing excellent electromagnetic interference shielding effectiveness (EMI SE) were developed via a natural wood template-based method. Pyrolytic carbon derived from the decomposed cellulose in the wood worked as the carbon source for the growth of NbC phase, and the NbC-PyC heterogeneous nano-interface formed between the residual PyC and the freshly formed NbC. Multi-loss mechanisms (e.g. conductive loss, dipole polarization loss, and especially interface polarization loss) were established by controlling the NbC content and residual PyC phase in the NbC-PyC foams, which significantly improved the absorption capability. Compared to 28.0 dB of PyC monolith, the EMI SE of NbC-PyC foam can reach 54.8 dB when the thickness is 0.5 mm, which outperforms the other porous-based shielding materials. Due to the highly porous structure of pristine wood, the resulting NbC-PyC foam exhibited a low density of 0.48 g/cm3, which is ~ 1/16 of dense NbC (7.78 g/cm3). Generally, this work introduces innovative ideas for designing novel and advanced transition metal carbide-carbon composite materials.

Polymer-Derived Lightweight SiBCN Ceramic Nanofibers with High Microwave Absorption Performance.

Lightweight SiBCN ceramic nanofibers were prepared by a combination of electrostatic spinning and high-temperature annealing techniques, showing tunable electromagnetic wave absorption. By controlling the annealing temperature, the nanoscale architectures and atomic bonding structures of as-prepared nanofibers could be well regulated. The resulting SiBCN nanofibers ∼300 nm in diameter, which were composed of an amorphous matrix, ß-SiC, and free carbon nanocrystals, were defect-free after annealing at 1600 °C. SiBCN nanofibers annealed at 1600 °C exhibited good microwave absorption, obtaining a minimum reflection coefficient of -56.9 dB at 10.56 GHz, a sample thickness of 2.6 mm with a maximum effective absorption bandwidth of 3.45 GHz, and a maximum dielectric constant of 0.44. Owing to the optimized A + B + C microstructure, SiBCN ceramic nanofibers with satisfying microwave absorption properties endowed the nanofibers with the potential to be used as lightweight, ultrastrong radar wave absorbers applied in military and the commercial market.

Towards a Greener and Scalable Synthesis of Na2Ti6O13 Nanorods and Their Application as Anodes in Batteries for Grid-Level Energy Storage.

Grid applications require high power density (for frequency regulation, load leveling, and renewable energy integration), achievable by combining multiple batteries in a system without strict high capacity requirements. For these applications however, safety, cost efficiency, and the lifespan of electrode materials are crucial. Titanates, safe and longevous anode materials providing much lower energy density than graphite, are excellent candidates for this application. The innovative molten salt synthesis approach proposed in this work provides exceptionally pure Na2Ti6O13 nanorods generated at 900-1100 °C in a yield ≥80 wt%. It is fast, cost-efficient, and suitable for industrial upscaling. Electrochemical tests reveal stable performance providing capacities of ≈100 mA h g-1 (Li) and 40 mA h g-1 (Na). Increasing the synthesis temperature to 1100 °C leads to a capacity decrease, most likely resulting from 1) the morphology/volume change with the synthesis temperature and 2) distortion of the Na2Ti6O13 tunnel structure indicated by electron energy-loss and Raman spectroscopy. The suitability of pristine Na2Ti6O13 as the anode for grid-level energy storage systems has been proven a priori, without any performance-boosting treatment, indicating considerable application potential especially due to the high yield and low cost of the synthesis route.

Effect of the Content and Ordering of the sp2 Free Carbon Phase on the Charge Carrier Transport in Polymer-Derived Silicon Oxycarbides.

The present work elaborates on the correlation between the amount and ordering of the free carbon phase in silicon oxycarbides and their charge carrier transport behavior. Thus, silicon oxycarbides possessing free carbon contents from 0 to ca. 58 vol.% (SiOC/C) were synthesized and exposed to temperatures from 1100 to 1800 °C. The prepared samples were extensively analyzed concerning the thermal evolution of the sp2 carbon phase by means of Raman spectroscopy. Additionally, electrical conductivity and Hall measurements were performed and correlated with the structural information obtained from the Raman spectroscopic investigation. It is shown that the percolation threshold in SiOC/C samples depends on the temperature of their thermal treatment, varying from ca. 20 vol.% in the samples prepared at 1100 °C to ca. 6 vol.% for the samples annealed at 1600 °C. Moreover, three different conduction regimes are identified in SiOC/C, depending on its sp2 carbon content: (i) at low carbon contents (i.e., <1 vol.%), the silicon oxycarbide glassy matrix dominates the charge carrier transport, which exhibits an activation energy of ca. 1 eV and occurs within localized states, presumably dangling bonds; (ii) near the percolation threshold, tunneling or hopping of charge carriers between spatially separated sp2 carbon precipitates appear to be responsible for the electrical conductivity; (iii) whereas above the percolation threshold, the charge carrier transport is only weakly activated (Ea = 0.03 eV) and is realized through the (continuous) carbon phase. Hall measurements on SiOC/C samples above the percolation threshold indicate p-type carriers mainly contributing to conduction. Their density is shown to vary with the sp2 carbon content in the range from 1014 to 1019 cm-3; whereas their mobility (ca. 3 cm2/V) seems to not depend on the sp2 carbon content.

Synthesis of Silver Modified Bioactive Glassy Materials with Antibacterial Properties via Facile and Low-Temperature Route.

There is an increasing clinical need to develop novel biomaterials that combine regenerative and biocidal properties. In this work, we present the preparation of silver/silica-based glassy bioactive (ABG) compositions via a facile, fast (20 h), and low temperature (80 °C) approach and their characterization. The fabrication process included the synthesis of the bioactive glass (BG) particles followed by the surface modification of the bioactive glass with silver nanoparticles. The microstructural features of ABG samples before and after exposure to simulated body fluid (SBF), as well as their ion release behavior during SBF test were evaluated using infrared spectrometry (FTIR), ultraviolet-visible (UV-Vis) spectroscopy, X-ray diffraction (XRD), electron microscopies (TEM and SEM) and optical emission spectroscopy (OES). The antibacterial properties of the experimental compositions were tested against Escherichia coli (E. coli). The results indicated that the prepared ABG materials possess antibacterial activity against E. coli, which is directly correlated with the glass surface modification.

Hydrogen Selective SiCH Inorganic-Organic Hybrid/γ-Al2O3 Composite Membranes.

Solar hydrogen production via the photoelectrochemical water-splitting reaction is attractive as one of the environmental-friendly approaches for producing H2. Since the reaction simultaneously generates H2 and O2, this method requires immediate H2 recovery from the syngas including O2 under high-humidity conditions around 50 °C. In this study, a supported mesoporous γ-Al2O3 membrane was modified with allyl-hydrido-polycarbosilane as a preceramic polymer and subsequently heat-treated in Ar to deliver a ternary SiCH organic-inorganic hybrid/γ-Al2O3 composite membrane. Relations between the polymer/hybrid conversion temperature, hydrophobicity, and H2 affinity of the polymer-derived SiCH hybrids were studied to functionalize the composite membranes as H2-selective under saturated water vapor partial pressure at 50 °C. As a result, the composite membranes synthesized at temperatures as low as 300-500 °C showed a H2 permeance of 1.0-4.3 × 10-7 mol m-2 s-1 Pa-1 with a H2/N2 selectivity of 6.0-11.3 under a mixed H2-N2 (2:1) feed gas flow. Further modification by the 120 °C-melt impregnation of low molecular weight polycarbosilane successfully improved the H2-permselectivity of the 500 °C-synthesized composite membrane by maintaining the H2 permeance combined with improved H2/N2 selectivity as 3.5 × 10-7 mol m-2 s-1 Pa-1 with 36. These results revealed a great potential of the polymer-derived SiCH hybrids as novel hydrophobic membranes for purification of solar hydrogen.

Discovery of Ternary Silicon Titanium Nitride with Spinel-Type Structure.

Here we report on the discovery of a ternary silicon titanium nitride with the general composition (Si1-x,Tix)3N4 with x = 0 < x < 1 and spinel-type crystal structure. The novel nitride is formed from an amorphous silicon titanium nitride (SiTiN) precursor under high-pressure/high-temperature conditions in a large volume high-pressure device. Under the conditions of 15-20 GPa and 1800-2000 °C, spinel-type γ-Si3N4 and rock salt-type c-TiN are formed. In addition, crystals of the discovered nano-sized ternary phase (Si1-x,Tix)3N4 embedded in γ-Si3N4 are identified. The ternary compound is formed due to kinetically-controlled synthesis conditions and is analyzed to exhibit the spinel-type structure with ca. 8 atom% of Ti. The Ti atoms occur in both Ti3+ and Ti4+ oxidation states and are located on the Si sites. The ternary nano-crystals have to be described as (Si,Ti)3N4 with N-vacancies resulting in the general composition (Si4+1-x Ti4+x-δTi3+δ)3N4-δ.

Dielectric Properties and Electromagnetic Wave Absorbing Performance of Single-Source-Precursor Synthesized Mo4.8Si3C0.6/SiC/Cfree Nanocomposites with an In Situ Formed Nowotny Phase.

For the first time, dielectric properties and electromagnetic wave (EMW) absorbing performance of single-source-precursor derived Mo4.8Si3C0.6/SiC/Cfree ceramic nanocomposites with a highly electrically conductive intermetallic Nowotny phase (NP, i.e., Mo4.8Si3C0.6) are reported. High-temperature phase evolution of the nanocomposites reveals that free carbon (Cfree) plays a crucial role in the in situ formation of the NP, indicating that the microstructure of the nanocomposites can be tailored via molecular design of the single-source precursors. Compared with SiC/Cfree and MoSi2/SiC/Cfree nanocomposites obtained under the same conditions, the Mo4.8Si3C0.6/SiC/Cfree nanocomposites exhibit significantly enhanced EMW absorbing performance. A minimum reflection loss (RL) of -59 dB was achieved at 8 GHz for the thickness of 2.46 mm, proving the superiority of the Mo4.8Si3C0.6/SiC/Cfree nanocomposite as an outstanding EMW absorbing material. On the basis of our previous discovery that the Mo4.8Si3C0.6 embedded in a SiC-based matrix with high specific surface area exhibits excellent electrocatalytic properties suitable for the electrochemical hydrogen evolution reaction, the present results prove that Mo4.8Si3C0.6/SiC/Cfree nanocomposites have to be considered as novel multifunctional materials with tailorable microstructure and excellent performance in two different fields including electrochemical water splitting and EMW absorption.

A Novel High-Pressure Tin Oxynitride Sn2 N2 O.

We report the first oxynitride of tin, Sn2 N2 O (SNO), exhibiting a Rh2 S3 -type crystal structure with space group Pbcn. All Sn atoms are in six-fold coordination, in contrast to Si in silicon oxynitride (Si2 N2 O) and Ge in the isostructural germanium oxynitride (Ge2 N2 O), which appear in four-fold coordination. SNO was synthesized at 20 GPa and 1200-1500 °C in a large volume press. The recovered samples were characterized by synchrotron powder X-ray diffraction and single-crystal electron diffraction in the TEM using the automated diffraction tomography (ADT) technique. The isothermal bulk modulus was determined as Bo =193(5) GPa by using in-situ synchrotron X-ray diffraction in a diamond anvil cell. The structure model is supported by DFT calculations. The enthalpy of formation, the bulk modulus, and the band structure have been calculated.

Facile Preparative Access to Bioactive Silicon Oxycarbides with Tunable Porosity.

In the present work, Ca-containing silicon oxycarbides (SiCaOC) with varying Ca content have been synthesized via sol-gel processing and thermal treatment in inert gas atmosphere (pyrolysis). It has been shown that the as-prepared SiCaOC materials with low Ca loadings (Ca/Si molar ratios = 0.05 or 0.12) were X-ray amorphous; their glassy network contains Q3 sites, indicating the presence of Ca2+ at non-bridging-oxygen sites. SiCaOC with high Ca content (i.e., Ca/Si molar ratio = 0.50) exhibits the presence of crystalline calcium silicate (mainly pseudowollastonite). Furthermore, it has been shown that the incorporation of Ca into the SiOC glassy network has a significant effect on its porosity and specific surface area. Thus, the as-prepared Ca-free SiOC material is shown to be non-porous and having a specific surface area (SSA) of 22.5 m2/g; whereas SiCaOC with Ca/Si molar ratio of 0.05 exhibits mesoporosity and a SSA value of 123.4 m2/g. The further increase of Ca content leads to a decrease of the SSA and the generation of macroporosity in SiCaOC; thus, SiCaOC with Ca/Si molar ratio of 0.12 is macroporous and exhibits a SSA value of 39.5 m2/g. Bioactivity assessment in simulated body fluid (SBF) confirms the hydroxyapatite formation on all SiCaOC samples after seven days soaking, unlike the relatively inert ternary silicon oxycarbide reference. In particular, SiCaOC with a Ca/Si molar ratio of 0.05 shows an increased apatite forming ability compared to that of SiCaOC with Ca/Si molar ratio of 0.12; this difference is considered to be a direct consequence of the significantly higher SSA of the sample with the Ca/Si ratio of 0.05. The present work indicates two effects of Ca incorporation into the silicon oxycarbide glassy network on its bioactivity: Firstly, Ca2+ is shown to contribute to the slight depolymerization of the network, which clearly triggers the hydroxyapatite formation (compare the bioactive behavior of SiOC to that of SiCaOC with Ca/Si molar ratio 0.12 upon SBF exposure); secondly, the Ca2+ incorporation seems to strongly affect the porosity and SSA in the prepared SiCaOC materials. There is an optimum of Ca loading into the silicon oxycarbide glassy network (at a Ca/Si molar ration of 0.05), which provides mesoporosity and reaches maximum SSA, both highly beneficial for the bioactive behavior of the materials. An increase of the Ca loading leads, in addition to the crystallization of calcium silicates, to a coarsening of the pores (i.e., macroporosity) and a significant decrease of the SSA, both negatively affecting the bioactivity.