Stimuli-Responsive Silica Silanol Conjugates: Strategic Nanoarchitectonics in Targeted Drug Delivery

The design of novel drug delivery systems is exceptionally critical in disease treatments. Among the existing drug delivery systems, mesoporous silica nanoparticles (MSNs) have shown profuse promise owing to their structural stability, tunable morphologies/sizes, and ability to load different payload chemistry. Significantly, the presence of surface silanol groups enables functionalization with relevant drugs, imaging, and targeting agents, promoting their utility and popularity among researchers. Stimuli-responsive silanol conjugates have been developed as a novel, more effective way to conjugate, deliver, and release therapeutic drugs on demand and precisely to the selected location. Therefore, it is urgent to summarize the current understanding and the surface silanols' role in making MSN a versatile drug delivery platform. This review provides an analytical understanding of the surface silanols, chemistry, identification methods, and their property-performance correlation. The chemistry involved in converting surface silanols to a stimuli-responsive silica delivery system by endogenous/exogenous stimuli, including pH, redox potential, temperature, and hypoxia, is discussed in depth. Different chemistries for converting surface silanols to stimuli-responsive bonds are discussed in the context of drug delivery. The critical discussion is culminated by outlining the challenges in identifying silanols' role and overcoming the limitations in synthesizing stimuli-responsive mesoporous silica-based drug delivery systems.

Orange Carotenoid Protein in Mesoporous Silica: A New System towards the Development of Colorimetric and Fluorescent Sensors for pH and Temperature

Orange carotenoid protein (OCP) is a photochromic carotenoprotein involved in the photoprotection of cyanobacteria. It is activated by blue-green light to a red form OCPR capable of dissipating the excess of energy of the cyanobacterial photosynthetic light-harvesting systems. Activation to OCPR can also be achieved in the dark. In the present work, activation by pH changes of two different OCPs-containing echinenone or canthaxanthin as carotenoids-is investigated in different conditions. A particular emphasis is put on OCP encapsulated in SBA-15 mesoporous silica nanoparticles. It is known that in these hybrid systems, under appropriate conditions, OCP remains photoactive. Here, we show that when immobilised in SBA-15, the OCP visible spectrum is sensitive to pH changes, but such a colorimetric response is very different from the one observed for OCP in solution. In both cases (SBA-15 matrices and solutions), pH-induced colour changes are related either by orange-to-red OCP activation, or by carotenoid loss from the denatured protein. Of particular interest is the response of OCP in SBA-15 matrices, where a sudden change in the Vis absorption spectrum and in colour is observed for pH changing from 2 to 3 (in the case of canthaxanthin-binding OCP in SBA-15: λMAX shifts from 454 to 508 nm) and for pH changing from 3 to 4 (in the case of echinenone-binding OCP in SBA-15: λMAX shifts from 445 to 505 nm). The effect of temperature on OCP absorption spectrum and colour (in SBA-15 matrices) has also been investigated and found to be highly dependent on the properties of the used mesoporous silica matrix. Finally, we also show that simultaneous encapsulation in selected surface-functionalised SBA-15 nanoparticles of appropriate fluorophores makes it possible to develop OCP-based pH-sensitive fluorescent systems. This work therefore represents a proof of principle that OCP immobilised in mesoporous silica is a promising system in the development of colorimetric and fluorometric pH and temperature sensors.

Structurally engineered ion-receptor probe immobilized porous polymer platform as reusable solid-state chromogenic sensor for the ultra-trace sensing and recovery of mercury ions

This study reports an efficacious solid-state optical sensor through the synergistic coalescences of an original chromoionophoric probe and a structurally engineered porous polymer monolith for the selective and sensitive colorimetric spotting of ultra-trace toxic mercury ions. The unique properties of the bimodal macro-/meso-pore structured polymer, i.e., poly(AAm-co-EGDMA) monolith, offer voluminous and uniform anchoring of probe molecules, i.e., (Z)-N-phenyl-2-(quinoline-4-yl-methylene)hydrazine-1-carbothioamide (PQMHC). The structure/surface features of the sensory system, i.e., surface area, pore dimensions, monolith framework, elemental mapping, and phase composition, were examined by p-XRD, XPS, FT-IR, HR-TEM-SAED, FE-SEM-EDAX, and BET/BJH analysis. The sensor's ion-capturing ability was established through naked eye color transition and UV-Vis-DRS response. The sensor exhibits a strong binding affinity for Hg²⁺, with a linear signal response in the concentration range of 0-200 μg/L (r² >0.999), with a detection limit of 0.33 μg/L. The analytical parameters were optimized to facilitate pH-dependent visual sensing of ultra-trace Hg²⁺ in ≤ 30 s. The sensor exhibits high chemical/physical stability characteristics, with reliable data reproducibility (RSD ≤1.94 %), while testing with natural/synthetic water and cigarette samples. The proposed work offers a cost-effective and reusable naked-eye sensory system for the selective sensing of ultra-trace Hg²⁺, with potential prospects of commercialization considering their simplicity, viability, and reliability.

Porous titania beads for remediation of arsenic contamination from acid mine drainage

Hierarchically porous titania beads with and without amine functionalisation have been developed and tested as adsorbents for removal of highly toxic As(V) from environments affected by acid mine drainage (AMD). The unique acid stability of the titania framework enables these adsorbents to function in highly acidified environments and their granular form facilitates practical deployment under continuous flow conditions. Herein, both non-functionalised and amine-functionalised titania beads have been demonstrated to selectively remove As(V) from simulated and real AMD solutions at pH 2.6. Novel selectivity for As(V) over Na(I), Mg(II), Al(III), Si(VI), Ca(II), Co(II), Cu(II), Zn(II), Nd(III) and Ho(III) was achieved, with competing element concentrations similar to or up to an order of magnitude greater than that of As(V). Although Fe(III) and some Fe(II) were also adsorbed by the titania beads, Fe adsorption did not inhibit As(V) adsorption, indicating different adsorption mechanisms for these two elements. The As(V) adsorption capacity of the titania beads decreased from ∼20 mg/g from pure As(V) solution to ∼10 mg/g from real AMD solution, demonstrating the importance of adsorbent testing under applied conditions. Amine functionalisation increased the kinetics of adsorption, but the non-functionalised titania beads showed greater selectivity for As(V) over Fe(II) and Fe(III) and hence were considered preferable for As remediation applications. Nevertheless, the functionalisation ability of the porous titania beads makes them a promising, flexible technology for remediation of a wide range of AMD affected environments.

Hybrid Materials Based on Imidazo[4,5-b]porphyrins for Catalytic Oxidation of Sulfides

Heterogenized metalloporphyrin catalysts for oxidation reactions are extensively explored to improve chemical production. In this work, manganese meso-tetraarylporphyrins were immobilized on hydrated mesoporous titanium dioxide (SBET = 705 m2 g−1) through carboxylate or phosphonate anchoring groups separated from the macrocycle by the 2-arylimidazole linker fused across one of the pyrrolic rings of the macrocycle. The element composition of two mesoporous hybrid materials thus obtained were investigated and the integrity of the immobilized complexes was shown by different physicochemical methods. Finally, the catalytic efficiency of the more stable material Mn(TMPIP)/TiO2 with the phosphonate anchor was evaluated in the selective oxidation of sulfides to sulfoxides by molecular oxygen in the presence of isobutyraldehyde (IBA). The heterogenized complex has shown excellent catalytic activity exhibiting a turnover (TON) of ~1100 in a single catalytic run of the sulfoxidation of thioanisole. The catalyst was successfully reused in seven consecutive catalytic cycles.

Hydroxypicolinic acid tethered on magnetite core-silica shell (HPCA@SiO2@Fe3O4) as an effective and reusable adsorbent for practical Co(II) recovery

The soaring demand and future supply risk for cobalt (Co) necessitate more efficient adsorbents for its recycling from electronic wastes, as a cheaper and less hazardous option for its production. Herein, a magnetic adsorbent covalently tethered with 5-hydroxypicolinic acid (HPCA) as Co(II) ligand was developed. The magnetic component (Fe₃O₄) was protected with silica (SiO₂), then silanized with chloroalkyl linker and subsequently functionalized with HPCA via S_N2 nucleophilic substitution (HPCA@SiO₂@Fe₃O₄). Results from FTIR, TGA, EA, and XPS confirm the successful adsorbent preparation with high HPCA loading of 2.62 mmol g^-1. TEM-EDS reveal its imperfect spherical morphology with ligands well-distributed on its surface. HPCA@SiO₂@Fe₃O₄ is hydrophilic, water-dispersible and magnetically retrievable, which is highly convenient for its recovery. The Co(II) capture on HPCA@SiO₂@Fe₃O₄ involves monodentate coordination with carboxylate (COO^-) and lone pair acceptance from pyridine (aromatic -N = ) moiety of HPCA, with minor interaction from acidic silanols (Si-O^-). The binding occurs at 2 HPCA: 1 Co(II) ratio, that follows the Sips isotherm model with competitive Q_max = 92.35 mg g^-1 and pseudo-second order kinetics (k₂ = 0.0042 g mg^-1 min^-1). In a simulated LIB liquid waste, HPCA@SiO₂@Fe₃O₄ preferentially captures Co(II) over Li(I) with α_Li(I)^Co(II)=166 and Mn(II) with α_Mn(II)^Co(II)=55, which highlights the importance of HPCA for Co(II) recovery. Silica protection of Fe₃O₄ rendered the adsorbent chemically stable in acidic thiourea solution for its regeneration by preventing the deterioration of the magnetic component. Covalent functionalization averted ligand loss, which allowed HPCA@SiO₂@Fe₃O₄ to deliver consistent and reversible adsorption/desorption performance. Overall results demonstrate the potential of HPCA@SiO₂@Fe₃O₄ as a competitive and practical adsorbent for Co(II) recovery in liquid waste sources.

Best Practices in the Characterization of MOF@MSN Composites

Research on permanently porous nanomaterials has gripped the attention of materials chemists for decades. Mesoporous silica nanoparticles (MSNs) and metal-organic frameworks (MOFs) are two of the most studied classes of materials in this field. Recently, explorations into embedding MOFs within the mesopores of MSNs have aimed to create composites that are greater than the sum of their parts. While initial progress has been promising, it has become clear that the characterization of these MOF@MSN composite materials represents a significant challenge that is often overlooked, leading to an unfortunate ambiguity in the field. The greatest difficulty lies in determining whether the product of a synthesis is simply a physical mixture of the two materials or truly the targeted composite, with MOF exclusively crystallized in the pores or on the surfaces of the MSN. This challenge is aggravated by the dramatically different porosity and composition of the components, often resulting in ambiguous information from common characterization techniques. This Viewpoint will address this challenge by calling attention to the mentioned issues and proposing a standardized approach to characterizing these materials. In particular, the use of powder X-ray diffraction, gas physisorption, and electron microscopy with systematic control experiments and data analysis is outlined. This approach can provide the information needed to clearly validate the architecture of an apparent MOF@MSN composite.

Designing Sites in Heterogeneous Catalysis: Are We Reaching Selectivities Competitive With Those of Homogeneous Catalysts?

A critical review of different prominent nanotechnologies adapted to catalysis is provided, with focus on how they contribute to the improvement of selectivity in heterogeneous catalysis. Ways to modify catalytic sites range from the use of the reversible or irreversible adsorption of molecular modifiers to the immobilization or tethering of homogeneous catalysts and the development of well-defined catalytic sites on solid surfaces. The latter covers methods for the dispersion of single-atom sites within solid supports as well as the use of complex nanostructures, and it includes the post-modification of materials via processes such as silylation and atomic layer deposition. All these methodologies exhibit both advantages and limitations, but all offer new avenues for the design of catalysts for specific applications. Because of the high cost of most nanotechnologies and the fact that the resulting materials may exhibit limited thermal or chemical stability, they may be best aimed at improving the selective synthesis of high value-added chemicals, to be incorporated in organic synthesis schemes, but other applications are being explored as well to address problems in energy production, for instance, and to design greener chemical processes. The details of each of these approaches are discussed, and representative examples are provided. We conclude with some general remarks on the future of this field.

The Role of Transmission Electron Microscopy in the Early Development of Mesoporous Materials for Tissue Regeneration and Drug Delivery Applications

For the last 20 years, silica-based mesoporous materials have provided a sound platform for the development of biomedical technology applied to tissue engineering and drug delivery. Their unique structural and textural characteristics, chiefly, the ordered distribution of homogeneous and tunable pores with high surface areas and large pore volume, and their excellent biocompatibility provide an excellent starting point for bone tissue regeneration on the mesoporous surface, and also to load species of interest inside the pores. Adequate control of the synthesis conditions and functionalization of the mesoporous surface are critical factors in the design of new systems that are suitable for use in specific medical applications. Simultaneously, the use of appropriate characterization techniques in the several stages of design and manufacture of mesoporous particles allows us to ascertain the textural, structural and compositional modifications induced during the synthesis, functionalization and post-in vitro assays processes. In this scenario, the present paper shows, through several examples, the role of transmission electron microscopy and associated spectroscopic techniques in the search for useful information in the early design stages of mesoporous systems, with application in the fields of tissue regeneration and drug delivery systems.

Phosphate functionalised titania for heavy metal removal from acidic sulfate solutions

Adsorbent materials based on titania and phosphate are ideal for treatment of solutions contaminated with heavy metals under acidic conditions, due to their inherent chemical stability and low pKa. Herein, phosphate functionalised titania has been investigated for the first time for removal of heavy metals (Cr, Fe, Cu, Eu, U) under conditions relevant to acid mine drainage (pH 2-5 sulfuric acid). Successful functionalisation was found to depend on the phase of titania used, with anatase preferred according to computational results from density functional theory. The effect of phosphate ligand structure was explored, revealing that the phosphate ethyl ester maximised heavy metal removal. The presence and concentration of counterions (sulfate, nitrate, ammonium) also impacted the speciation and binding of heavy metal cations, demonstrating the importance of adsorbent testing under realistic conditions. Increasing the porosity of the titania framework enhanced heavy metal removal, while maintaining selectivity for the toxic heavy metals over non-toxic cations Na and K. As such, phosphate functionalised titania shows great promise for heavy metal remediation in acidic sulfate environments.

Sol-gel process: the inorganic approach in protein imprinting

Proteins play a central role in the signal transmission in living systems since they are able to recognize specific biomolecules acting as cellular receptors, antibodies or enzymes, being themselves recognized by other proteins in protein/protein interactions, or displaying epitopes suitable for antibody binding. In this context, the specific recognition of a given protein unlocks a range of interesting applications in diagnosis and in targeted therapies. Obviously, this role is already fulfilled by antibodies with unquestionable success. However, the design of synthetic artificial systems able to endorse this role is still challenging with a special interest to overcome limitations of antibodies, in particular their production and their stability. Molecular Imprinted Polymers (MIPs) are attractive recognition systems which could be an alternative for the specific capture of proteins in complex biological fluids. MIPs can be considered as biomimetic receptors or antibody mimics displaying artificial paratopes. However, MIPs of proteins remains a challenge due to their large size and conformational flexibility, their complex chemical nature with multiple recognition sites and their low solubility in most organic solvents. Classical MIP synthesis conditions result in large polymeric cavities and unspecific binding sites on the surface. In this review, the potential of the sol-gel process as inorganic polymerization strategy to overcome the drawbacks of protein imprinting is highlighted. Thanks to the mild and biocompatible experimental conditions required and the use of water as a solvent, the inorganic polymerization approach better suited to proteins than organic polymerization. Through numerous examples and applications of MIPs, we proposed a critical evaluation of the parameters that must be carefully controlled to achieve sol-gel protein imprinting (SGPI), including the choice of the monomers taking part in the polymerization.

Optimization of Mesoporous Silica Nanoparticles through Statistical Design of Experiment and the Application for the Anticancer Drug

The synthesis process or composition of mesoporous silica nanoparticles (MSNs) affects the physicochemical properties. Using these properties, MSNs were synthesized through the Box–Behnken design (BBD) among statistical experimental methods. The effect of the amounts of synthetic reagents, hexadecyl triethyl ammonium bromide (CTAB), tetraethyl orthosilicate (TEOS), and 2 N sodium hydroxide (NaOH), was studied using the reaction surface design. Surface area, particle size, and zeta potential were set as response values. The physicochemical properties of the optimized MSNs were evaluated, and the effect as a drug delivery system was evaluated by loading doxorubicin hydrochloride (DOX). Nano-sized MSNs were successfully prepared with 0.617 g of CTAB, 8.417 mL of TEOS, and 2.726 mL of 2 N NaOH and showed excellent physicochemical properties. The optimized MSNs showed negligible toxicity in MCF-7 cells. The drug release profile from DOX-loaded MSNs (MSN@DOX) showed an increased rate of release with decreasing pH of the medium, with the release profile sustained for 48 h. In the cytotoxicity test, the sustained drug release mechanism of MSN@DOX was confirmed. This study proposed a new statistical approach to the synthesis of MSNs.

Bis(terpyridine) Iron(II) Functionalized Vertically-Oriented Nanostructured Silica Films: Toward Electrochromic Materials

Recent and potential applications of electrochromic materials include smart windows, optoelectronic devices, and energy conversion. In this study, we have incorporated bis(terpyridine) iron (II) complexes into vertically-oriented silica thin films deposited on indium-tin oxide (ITO) and their electrochromic behavior has been investigated. If 2,2′:6′,2″-terpyridine is commonly used as a ligand for forming metallo-supramolecular assemblies, with the objective to get metal-terpyridine complexes with multiple stable redox states, their simple and reliable arrangement into linear structures enabling effective electronic communication is however more challenging. We propose to overcome this difficulty by generating such complexes within vertical nanochannels on electrode. Terpyridine ligands were firstly immobilized by combining a click chemistry azide/alkyne approach with an electrochemically-assisted self-assembly (EASA) method used to grow an oriented mesoporous silica membrane bearing azide groups which were further derivatized with 4′-ethynyl-terpyridine ligands. The resulting terpyridine-functionalized films were consecutively dipped in an aqueous solution of Fe(BF₄)₂ and then in a solution of terpyridine in acetonitrile to form the bis(terpyridine) iron (II) complexes in situ. The electrochromic properties of the films functionalized at various levels were examined by monitoring the changes in their UV/Vis spectra upon electrochemical oxidation at controlled potential of +1.2 V vs. Ag/AgCl. Due to facile charge delocalization during the Fe²⁺ to Fe³⁺ redox process, the bis(terpyridine) iron (II) functionalized silica films exhibited electrochromic properties by changing from violet to non-colored using TBABF₄ in acetonitrile as an electrolyte. The bis(terpyridine) iron(II) film experienced reversible electrochromic switching by applying +0.5 V in a reverse reduction electrochemical process. The Fe(tpy)₂-functionalized silica thin films displayed a good contrast ratio (ΔT%) of 47% and relatively high coloration efficiency (CE) of about 245 cm²/C with a response time of coloring and bleaching of a few seconds (< 4 s).

Controlling the Release of Hydrogen Peroxide from Catechol-Based Adhesive Using Silica Nanoparticle

Catechol-based bioadhesives generate hydrogen peroxide (H₂O₂) as a byproduct during the curing process. H₂O₂ can have both beneficial and deleterious effects on biological systems depending on its concentration. To control the amount of H₂O₂ released from catechol-containing polyethylene glycol-based adhesive (PEG-DA), adhesive was formulated with silica nanoparticles (SiNP) prepared with increased porosity and acid treatment to increase Si-OH surface content. These SiNP demonstrated increased surface area, which promoted interaction with catechol and resulted in increased cure rate, bulk mechanical properties and adhesive properties of PEG-DA. Most importantly, SiNP demonstrated a 50% reduction in the released H₂O₂ while improving the cell viability and proliferation of three primary cell types, including rat dermal fibroblasts, human epidermal keratinocytes, and human tenocytes. Additionally, SiNP degraded into soluble Si, which also contributed to increased cell proliferation. Incorporation of porous and acid-treated SiNP can be a useful approach to simultaneously modulate the concentration of H₂O₂ while increasing the adhesive performance of catechol-based adhesives.

Synthesis and characterization of mesoporous SBA-15 and SBA-16 as carriers to improve albendazole dissolution rate

Albendazole (ABZ, anti-parasitic active pharmaceutical ingredient) is a crystalline low water-soluble drug, thus the dissolution rate in gastrointestinal fluids is limited. Consequently, the improvement of the water solubility and dissolution rate of ABZ implies a great challenge for a more efficient treatment of hydatidosis. In this context, SBA-15 and SBA-16 ordered mesoporous silica materials were synthetized and loaded with ABZ. X-ray diffraction, FT-IR spectroscopy, nitrogen physisorption manometry, particle size distribution and scanning electronic microscopy were used to characterize unloaded and loaded materials (ABZ/SBA-15 and ABZ/SBA-16). The loaded ABZ amount in the carriers was estimated by elemental analysis. For the loaded materials, the drug solubility and release profile were evaluated. In addition, mathematical models were compared to explain the dissolution kinetics of ABZ from mesoporous solids. ABZ was successfully loaded into the mesopores. The amorphous state of the adsorbed ABZ was confirmed by differential scanning calorimetry that resulted in a notable increment in the dissolution rate compared to crystalline ABZ. Drug release behaviors were well simulated by the Weibull model for ABZ/SBA-15 and by the Gompertz function for pure ABZ and ABZ/SBA-16. The SBA-15 carrier exhibited the highest drug loading and dissolution rate becoming a promising material to improve ABZ bioavailability.

Recent advances in the application of silica nanostructures for highly improved water treatment: a review

The demand for high-quality safe and clean water supply has revolutionized water treatment technologies and become a most focused subject of environmental science. Water contamination generally marks the presence of numerous toxic and harmful substances. These contaminants such as heavy metals, organic and inorganic pollutants, oil wastes, and chemical dyes are discharged from various industrial effluents and domestic wastes. Among several water treatment technologies, the utilization of silica nanostructures has received considerable attention due to their stability, sustainability, and cost-effective properties. As such, this review outlines the latest innovative approaches for synthesis and application of silica nanostructures in water treatment, apart from exploring the gaps that limit their large-scale industrial application. In addition, future challenges for improved water remediation and water quality technologies are keenly discussed.

A Comparative Study of the Use of Mesoporous Carbon and Mesoporous Silica as Drug Carriers for Oral Delivery of the Water-Insoluble Drug Carvedilol

Mesoporous carriers have been extensively applied to improve the dissolution velocity and bioavailability of insoluble drugs. The goal of this work was to compare the drug-loading efficiency (LE) and drug-dissolution properties of mesoporous silica nanoparticles (MSN) and mesoporous carbon nanoparticles (MCN) as drug vectors oral delivery of water-insoluble drugs. For this purpose, MSN and MCN with similar particle size, surface area, and mesoporous diameter were prepared to precisely evaluate the effects of different textures on the drug-loading and dissolution behavior of insoluble drugs. Carvedilol (CAR), a Bio-pharmaceutic Classification System (BCS) class II drug, was loaded in the MSN and MCN by the solvent adsorption method and solvent evaporation method with different carrier–drug ratios. The carboxylated MCN (MCN–COOH) had a higher LE for CAR than MSN for both the two loading methods due to the strong adsorption effect and π–π stacking force with CAR. In vitro drug dissolution study showed that both MSN and MCN-COOH could improve the dissolution rate of CAR compared with the micronized CAR. In comparison to MSN, MCN-COOH displayed a slightly slower dissolution profile, which may be ascribed to the strong interaction between MCN-COOH and CAR. Observation of cell cytotoxicity and gastrointestinal mucosa irritation demonstrated the good biocompatibility of both MSN and MCN–COOH. The present study encourages further research of different carriers to determine their potential application in oral administration.

Nanocomposite functionalized membranes based on silica nanoparticles cross-linked to electrospun nanofibrous support for arsenic(v) adsorption from contaminated underground water

Nanocomposite functionalized membranes were synthesized using surface functionalized mesoporous silica nanoparticles (MCM-NH2 or MCM-PEI) cross-linked to a modified polyacrylonitrile (mPAN) nanofibrous substrate for the removal of 1 mg L-1 of As(v); a concentration much higher than what has been reported for underground water in Argentina. Adsorption studies were carried out in batch mode at pH 8 with nanoparticles in colloidal form, as well as the nanoparticles supported on the modified PAN membranes (mPAN/MCM-NH2 and mPAN/MCM-PEI). Results indicate a twenty-fold improvement in As(v) adsorption with supported nanoparticles (nanocomposite membranes) as opposed to their colloidal form. The adsorption efficiency could be further enhanced by modifying the nanocomposite membrane surface with Fe3+ (mPAN/MCM-NH2-Fe3+ and mPAN/MCM-PEI-Fe3+) which resulted in more than 95% arsenic being removed within the first 15 minutes and a specific arsenic adsorption capacity of 4.61 mg g-1 and 5.89 mg g-1 for mPAN/MCM-NH2-Fe3+ and mPAN/MCM-PEI-Fe3+ nanocomposite membranes, respectively. The adsorption characteristics were observed to follow a pseudo-first order behavior. The results suggest that the synthesized materials are excellent for quick and efficient reduction of As(v) concentrations below the WHO guidelines and show promise for future applications.

Grafting and stabilization of ordered mesoporous silica COK-12 with graphene oxide for enhanced removal of methylene blue

Grafting of environmentally friendly produced ordered mesoporous silica (OMS) COK-12 with graphene oxide yields a superior OMS/GO adsorbent for methylene blue.

Highly efficient triazolone/metal ion/polydopamine/MCM-41 sustained release system with pH sensitivity for pesticide delivery

MCM-41 was prepared through the sol-gel method and encapsulated by polydopamine (PDA) before being coordinated with metal ions to form a highly efficient sustained release system (M-PDA-MCM-41) for triazolone delivery. The characterization results confirmed the existence of the coordination bond between the PDA layer and triazolone through the bridge effect from metal ions, which enhanced the interaction between PDA-MCM-41 and triazolone. The adsorption capacity of Fe-PDA-MCM-41 increased up to 173 mg g-1, which was 160% more than that of MCM-41. The sustained release performance of M-PDA-MCM-41 in different pH values was investigated. Under the conditions of pH ≤7, the release speed of triazolone increased with pH decreasing, whereas its release speed in the weak base condition was slower than in the neutral condition. Therefore, the as-synthesized system showed significant pH-sensitivity in the sustained release process, indicating that the sustained release system can be well stored in the neutral or basic environment and activated in the acid environment. Their sustained release curves described by the Korsmeyer-Peppas equation at pH 7 showed the same behaviour, indicating that PDA decoration or metal ion coordination only increases the steric hindrance and the interaction between carrier and triazolone instead of changing the original structure of the pure MCM material in accordance with X-ray diffraction and Brunauer-Emmett-Teller analysis results.

The Hydrolytic Stability and Degradation Mechanism of a Hierarchically Porous Metal Alkylphosphonate Framework

To aid the design of a hierarchically porous unconventional metal-phosphonate framework (HP-UMPF) for practical radioanalytical separation, a systematic investigation of the hydrolytic stability of bulk phase against acidic corrosion has been carried out for an archetypical HP-UMPF. Bulk dissolution results suggest that aqueous acidity has a more paramount effect on incongruent leaching than the temperature, and the kinetic stability reaches equilibrium by way of an accumulation of a partial leached species on the corrosion conduits. A variation of particle morphology, hierarchical porosity and backbone composition upon corrosion reveals that they are hydrolytically resilient without suffering any great degradation of porous texture, although large aggregates crack into sporadic fractures while the nucleophilic attack of inorganic layers cause the leaching of tin and phosphorus. The remaining selectivity of these HP-UMPFs is dictated by a balance between the elimination of free phosphonate and the exposure of confined phosphonates, thus allowing a real-time tailor of radionuclide sequestration. Moreover, a plausible degradation mechanism has been proposed for the triple progressive dissolution of three-level hierarchical porous structures to elucidate resultant reactivity. These HP-UMPFs are compared with benchmark metal-organic frameworks (MOFs) to obtain a rough grading of hydrolytic stability and two feasible approaches are suggested for enhancing their hydrolytic stability that are intended for real-life separation protocols.

Selective Separation and Preconcentration of Scandium with Mesoporous Silica

Separation and preconcentration of scandium (Sc) were successfully achieved using a mesoporous silica support that showed good selectivity for this element. Unmodified mesoporous silica materials were used as an extracting medium in a solid-liquid extraction (SLE) process. Selectivity, extraction capacity, kinetics of extraction, and reusability under acidic conditions were investigated. The results demonstrate the potential of unmodified mesoporous silica materials for the selective separation and preconcentration of Sc. As no chelating ligand was grafted on the silica surface, which is often the case for most solid-phase extraction media for metal-ion separation, the experimental data allow us to hypothesize that the accessible silanols on the material surface are responsible for the selective Sc extraction. This interesting feature would drastically decrease the cost of solid-liquid extraction systems by using unmodified mesoporous silica materials. Moreover, a leachate solution obtained from a real rare-earth element ore was used to determine the performances of the proposed materials in a packed column configuration. The maximum Sc adsorption on the silica material surfaces is moderate (1 mg/g), but it is balanced by a great concentration factor (more than 100 times). The extraction performances are potentially promising, both in terms of selectivity and preconcentration, under the acidic conditions tested.

Functionalization of Mesoporous Carbon Materials for Selective Separation of Lanthanides under Acidic Conditions

New functional mesoporous carbon sorbents were successfully synthesized to overcome some issues of solid-liquid extraction (e.g., selectivity, extraction capacity, and reusability under acidic conditions) in production of pure lanthanides (Ln). Wet-oxidation technique was performed to increase the surface reactivity of pristine ordered mesoporous carbon (OMC), and, in a second step, a surface modification using diglycolamide-based (DGA-based) selective ligands toward Ln was performed. Two types of ligands were tested: the first contains a long spacer (e.g., between carbon support and chelating function), and the second has a shorter one. These materials have been characterized by X-ray photoelectron spectroscopy (XPS), low-angle X-ray diffraction (XRD), thermogravimetric analysis, nitrogen sorption, transmission electron microscopy (TEM), and scanning electron microscopy (SEM). These analyses confirmed that the carbon mesostructure was maintained after organo-functionalization of the surface and showed the covalent attachment of selective ligands. These new materials, and especially the system with a short spacer between the ligand and the surface, reveal unique Ln selectivity profiles with improved extraction performances for the recovery of lanthanides, in terms of both selectivity and adsorption capacity, and unprecedented stability under acidic conditions.

Organic layer formation and sorption of U(vi) on acetamide diethylphosphonate-functionalized mesoporous silica

Solid-state NMR is used to connect the molecular structure of acetamide phosphonate-functionalized mesoporous silica with its macroscopic U(vi) extraction properties.

Highly efficient alginate sodium encapsulated chlorpyrifos/copper(ii) Schiff base mesoporous silica sustained release system with pH and ion response for pesticide delivery

A highly efficient sustained released system (ALG–CH–Cu–MCM-41) was prepared. The as-synthesized system showed significant pH and ion responsive.

Functionalization of mesoporous materials for lanthanide and actinide extraction

Recent advances in the field of functionalized mesoporous solid-phase sorbents designed for rare earth element and actinide separation/concentration could provide answers to limitations occurring in the industrial separation processes of these critical elements.

Synthesis, characterization and photocatalytic studies of mesoporous silica grafted Ni(ii) and Cu(ii) complexes

Synthesis of mesoporous silica grafted Ni(ii) and Cu(ii) complexes and their catalytic applications.

Improved hydrothermal stability of silica materials prepared from ethyl silicate 40

Hydrothermally stable ES40-derived silica matrices with less than 30% pore volume loss are closely associated with a more open silica microstructure formed from thermal consolidation of larger silica particles.

Influence of porous texture and surface chemistry on the CO₂ adsorption capacity of porous carbons: acidic and basic site interactions

Doped porous carbons exhibiting highly developed porosity and rich surface chemistry have been prepared and subsequently applied to clarify the influence of both factors on carbon dioxide capture. Nanocasting was selected as synthetic route, in which a polyaramide precursor (3-aminobenzoic acid) was thermally polymerized inside the porosity of an SBA-15 template in the presence of different H3PO4 concentrations. The surface chemistry and the porous texture of the carbons could be easily modulated by varying the H3PO4 concentration and carbonization temperature. Porous texture was found to be the determinant factor on carbon dioxide adsorption at 0 °C, while surface chemistry played an important role at higher adsorption temperatures. We proved that nitrogen functionalities acted as basic sites and oxygen and phosphorus groups as acidic ones toward adsorption of CO2 molecules. Among the nitrogen functional groups, pyrrolic groups exhibited the highest influence, while the positive effect of pyridinic and quaternary functionalities was smaller. Finally, some of these N-doped carbons exhibit CO2 heats of adsorption higher than 42 kJ/mol, which make them excellent candidates for CO2 capture.

From phosphate rocks to uranium raw materials: hybrid materials designed for selective separation of uranium from phosphoric acid

Innovative hybrid materials with high capacities to selectively extract uranium ions from phosphoric acid media were developed by grafting phosphorous-based ligands within the pores of mesoporous silica (SBA15) or mesoporous carbon (CMK3).