Solid-State Reaction Synthesis of Nanoscale Materials: Strategies and Applications

Nanomaterials (NMs) with unique structures and compositions can give rise to exotic physicochemical properties and applications. Despite the advancement in solution-based methods, scalable access to a wide range of crystal phases and intricate compositions is still challenging. Solid-state reaction (SSR) syntheses have high potential owing to their flexibility toward multielemental phases under feasibly high temperatures and solvent-free conditions as well as their scalability and simplicity. Controlling the nanoscale features through SSRs demands a strategic nanospace-confinement approach due to the risk of heat-induced reshaping and sintering. Here, we describe advanced SSR strategies for NM synthesis, focusing on mechanistic insights, novel nanoscale phenomena, and underlying principles using a series of examples under different categories. After introducing the history of classical SSRs, key theories, and definitions central to the topic, we categorize various modern SSR strategies based on the surrounding solid-state media used for nanostructure growth, conversion, and migration under nanospace or dimensional confinement. This comprehensive review will advance the quest for new materials design, synthesis, and applications.

Dendritic Mesoporous Silica Hollow Spheres for Nano-Bioreactor Application

Mesoporous silica materials have attracted great research interest for various applications ranging from (bio)catalysis and sensing to drug delivery. It remains challenging to prepare hollow mesoporous silica nanoparticles (HMSN) with large center-radial mesopores that could provide a more efficient transport channel through the cell for guest molecules. Here, we propose a novel strategy for the preparation of HMSN with large dendritic mesopores to achieve higher enzyme loading capacity and more efficient bioreactors. The materials were prepared by combining barium sulfate nanoparticles (BaSO4 NP) as a hard template and the in situ-formed 3-aminophenol/formaldehyde resin as a porogen for directing the dendritic mesopores’ formation. HMSNs with different particle sizes, shell thicknesses, and pore structures have been prepared by choosing BaSO4 NP of various sizes and adjusting the amount of tetraethyl orthosilicate added in synthesis. The obtained HMSN-1.1 possesses a high pore volume (1.07 cm3 g−1), a large average pore size (10.9 nm), and dendritic mesopores that penetrated through the shell. The advantages of HMSNs are also demonstrated for enzyme (catalase) immobilization and subsequent use of catalase-loaded HMSNs as bioreactors for catalyzing the H2O2 degradation reaction. The hollow and dendritic mesoporous shell features of HMSNs provide abundant tunnels for molecular transport and more accessible surfaces for molecular adsorption, showing great promise in developing efficient nanoreactors and drug delivery vehicles.

Borane-Catalyzed, Chemoselective Reduction and Hydrofunctionalization of Enones Enabled by B-O Transborylation

The use of stoichiometric organoborane reductants in organic synthesis is well established. Here these reagents have been rendered catalytic through an isodesmic B-O/B-H transborylation applied in the borane-catalyzed, chemoselective alkene reduction and formal hydrofunctionalization of enones. The reaction was found to proceed by a 1,4-hydroboration of the enone and B-O/B-H transborylation with HBpin, enabling catalyst turnover. Single-turnover and isotopic labeling experiments supported the proposed mechanism of catalysis with 1,4-hydroboration and B-O/B-H transborylation as key steps.

Biomedical applications of dendritic fibrous nanosilica (DFNS): recent progress and challenges

Dendritic fibrous nanosilica (DFNS), with multi-component and hierarchically complex structures, has recently been receiving significant attention in various fields of nano-biomedicine. DFNS is an emerging class of mesoporous nanoparticles that has attracted great interest due to unique structures such as open three-dimensional dendritic superstructures with large pore channels and highly accessible internal surface areas. This overview aims to study the application of DFNS towards biomedical investigations. This review is divided into four main sections. Sections 1–3 are related to the synthesis and characterization of DFNS. The biomedical potential of DFNS, such as cell therapy, gene therapy, immune therapy, drug delivery, imaging, photothermal therapy, bioanalysis, biocatalysis, and tissue engineering, is discussed based on advantages and limitations. Finally, the perspectives and challenges in terms of controlled synthesis and potential nano-biomedical applications towards future studies are discussed.

Dendritic fibrous nanosilica (DFNS) , with multi-component and hierarchically complex structures, has recently been receiving significant attention in various fields of nano-biomedicine.

Comprehensive understanding of the synthesis and formation mechanism of dendritic mesoporous silica nanospheres

The interest in the design and controlled fabrication of dendritic mesoporous silica nanospheres (DMSNs) emanates from their widespread application in drug-delivery carriers, catalysis and nanodevices owing to their unique open three-dimensional dendritic superstructures with large pore channels and highly accessible internal surface areas. A variety of synthesis strategies have been reported, but there is no basic consensus on the elucidation of the pore structure and the underlying formation mechanism of DMSNs. Although all the DMSNs show a certain degree of similarity in structure, do they follow the same synthesis mechanism? What are the exact pore structures of DMSNs? How did the bimodal pore size distributions kinetically evolve in the self-assembly? Can the relative fractions of small mesopores and dendritic large pores be precisely adjusted? In this review, by carefully analysing the structures and deeply understanding the formation mechanism of each reported DMSN and coupling this with our research results on this topic, we conclude that all the DMSNs indeed have the same mesostructures and follow the same dynamic self-assembly mechanism using microemulsion droplets as super templates in the early reaction stage, even without the oil phase.

Synthesis of dendritic fibrous nanosilica over a cubic core (cSiO2@DFNS) with catalytically efficient silver nanoparticles for reduction of nitroarenes and degradation of organic dyes

In this study, dendritic fibrous core–shell silica particles having cubic morphology with uniform and vertical nanochannels have been successfully synthesised. The synthesized dendritic fibrous nanosilica over a cubic core (cSiO₂@DFNS) have been characterized by using various techniques, such as powder X-ray diffraction, TEM, FE-SEM, TGA EDS, FT-IR and N₂ adsorption–desorption experiments. The prepared DFNS particles demonstrated a very high surface area and pore diameter. Amine groups were functionalized on the fibres of cSiO₂@DFNS and after that silver nanoparticles could be successfully immobilized on amine functionalized cubic silica particles. Due to the presence of a high surface area and a uniform pore diameter, the silver nanoparticle loaded cSiO₂@DFNS could be successfully employed as an efficient and recoverable catalyst for reduction of toxic aromatic nitro compounds and degradation of organic dyes. Higher catalytic activity of the prepared material could be attributed to its fibrous morphology which could facilitate proper interactions of the reactants molecules with the silver nanoparticles.

Graphical abstract showing the reduction of nitroarenes and degradation of organic dyes using cSiO₂@DFNS@Ag.

Colloidal Palladium Nanoparticles for Selective Hydrogenation of Styrene Derivatives with Reactive Functional Groups

This article presents the catalysis investigation of octanethiolate-capped palladium nanoparticles (C8 PdNP) and phenylethanethiolate-capped palladium nanoparticles (PhC2 PdNP) for chemoselective catalytic hydrogenation reactions of styrene derivatives in the presence of other reducible functionalities. The results show that the C8 PdNP is highly active under mild reaction conditions (room temperature and atmospheric pressure) and selective for hydrogenating monosubstituted alkene groups without reducing other reactive functional groups such as nitro, halo, carbonyls, and so forth. In comparison, the noncovalent interactions between surface phenyl ligands and aromatic substrates are found to hinder the hydrogenation activity of PhC2 PdNP.

Molecular reactors for synthesis of polymeric nanocomposites with noble metal nanoparticles for catalytic decomposition of 4-nitrophenol

HYPOTHESIS

A new, facile in-situ method for synthesis of polymeric nanocomposites (NCs) with nanoparticles (NPs) of Au, Pt and Pd is proposed. The method involves reduction-coupled sorption of Au(III), Pt(VI), and Pd(II), which avoids diffusion limitations, allowing the precipitation and stabilization of the NPs directly in the polymeric matrix.

EXPERIMENTS

The obtained nanomaterials were characterized by transmission electron microscopy (TEM), and Fourier-transformation infrared spectroscopy (FT-IR). NPs loaded into polymers were also investigated using X-ray diffraction (XRD).

FINDINGS

Based on the results, it was concluded that the amino functionalities simultaneously reduced noble metals ions and capped the NPs. The average diameter of the obtained AuNPs ranged from 25 to 109 nm, while reduction-coupled sorption was carried out in 1 and 3 mol L^-1 HCl solutions, respectively. Applying a 0.1 mol L^-1 HCl solution containing Au(III), Pd(II) and Pt(VI), a NC with AuNPs and cubic-like PdNPs was fabricated, while using a solution of the same composition, but in 3 mol L^-1 HCl, resulted in formation of a NC with flower-like PtNPs. Ultimately, the selected NC based on a resin with functionalities derived from 1-(2-aminoethyl)piperazine and with bi-metallic active sites, i.e. AuNPs and PdNPs, revealed catalytic activity in the reduction of 4-nitrophenol.

Selectivity control of Pd(PMe3)4-catalyzed hydrogenation of internal alkynes to E-alkenes by reaction time and water content in formic acid

The modulation of selectivity of transfer hydrogenation of alkynes to E-alkenes using formic acid is achieved through the control of water content and reaction time.

Improving the size uniformity of dendritic fibrous nano-silica by a facile one-pot rotating hydrothermal approach

This article provides a facile, low-cost, and reproducible one-pot rotating hydrothermal approach to synthesize dendritic fibrous nano-silica with outstanding uniformity.

Dendritic fibrous nano-silica & titania (DFNST) spheres as novel cataluminescence sensing materials for the detection of diethyl ether

Selective and controllable cataluminescence (CTL) sensors for volatile organic compounds (VOCs) are significant for chemical safety, environmental monitoring, health effects on human beings, and so forth. Most of the exploited CTL-based sensors suffer relatively low response and poor selectivity because of their high sensitivities to interferential substances. In this investigation, dendritic fibrous nano-silica & titania (DFNST) spheres have been synthesized as novel sensing materials and the corresponding DFNST-based CTL sensor has been fabricated to detect diethyl ether with high selectivity via a method of utilizing one 440 nm bandpass filter. The as-prepared DFNST hybrids not only keep the excellent dendritic fibrous morphology but also bear ca. 21 wt% catalytic titanium oxide of anatase crystalline structure. The DFNST-based sensor exhibits extremely strong CTL emission at 440 nm toward diethyl ether against other VOCs like acetone, ethyl acetate, butanol, and so forth. The high response can be attributed to the unique architectural texture of DFNST. Under the optimum parameters, ether could be easily detected in a wide range from 2.0 to 40.0 mM with a fine detection limit of 1.55 mM (S/N = 3). Furthermore, the working life of this CTL sensor is satisfactory with outstanding stability and durability, far from damaging the morphology and activity of the DFNST sensing material. In conclusion, it is expected that this novel sensing material, the relevant CTL sensor, and the approach of employing the bandpass filter will be significant for the detection of diethyl ether in actual applications.

Dendritic fibrous nano-silica & titania (DFNST) nanospheres have been successfully prepared as the sensing materials for the detection of diethyl ether via a DFNST-based cataluminescence (CTL) sensor.

Facile synthesis of palladium nanoparticles on hierarchical hollow silica spheres and its catalytic properties in Suzuki-reaction

A novel well-dispersed Pd@HHSS catalyst was synthesized by reduction of Pd(OAc)2 immobilized on HHSS we reported. When the ratios of Pd/SiO2 were 5 : 100 and 10 : 100, the Pd nanoparticles size was about 5-10 nm. The Pd@HHSS catalyst (Pd/SiO2 = 10 : 100) showed high catalytic activity in Suzuki-reaction with yields of 91-99% and the catalyst is reusable after four successive cycles without obvious loss of catalytic activity.

Pd anchored on C3N4 nanosheets/reduced graphene oxide: an efficient catalyst for the transfer hydrogenation of alkenes

Pd nanoparticles anchored on g-C₃N₄ NS/rGO were prepared by means of a cost-effective and facile co-assembly approach. The hybrid composite showed high catalytic activity and stability for the hydrogenation of alkenes with FA and HCOONH₄ as hydrogen donors.

Nitrogen-enriched porous carbon supported Pd-nanoparticles as an efficient catalyst for the transfer hydrogenation of alkenes

Well-dispersed Pd nanoparticles supported on nitrogen-enriched porous carbon were prepared and this material displayed excellent catalytic activity for the transfer hydrogenation of alkenes. The Pd@NPC catalyst exhibited high catalytic activity and stability for the hydrogenation of alkenes.

Catalytic dehydrogenative aromatization of cyclohexanones and cyclohexenones

Prompted by the scant attention paid by published literature reviews to the comprehensive catalytic dehydrogenative aromatization of cyclohexa(e)nones, this review describes recent methods developed to-date involving transition-metal-catalyzed oxidative aromatization and metal-free strategies for the transformation of cyclohexa(e)nones to substituted phenols.

Microwave assisted hydrogenation of olefins by Pd NPs@polystyrene resin using a gas addition kit: a robust and sustainable protocol

Polystyrene (PS) resin bead supported palladium nanoparticles (Pd NPs@PS resin) were prepared and their catalytic activity for the hydrogenation of olefins was investigated under microwave heating.

Dendritic Fibrous Nanosilica for Catalysis, Energy Harvesting, Carbon Dioxide Mitigation, Drug Delivery, and Sensing

Morphology-controlled nanomaterials such as silica play a crucial role in the development of technologies for addressing challenges in the fields of energy, environment, and health. After the discovery of Stöber silica, followed by that of mesoporous silica materials, such as MCM-41 and SBA-15, a significant surge in the design and synthesis of nanosilica with various sizes, shapes, morphologies, and textural properties has been observed in recent years. One notable invention is dendritic fibrous nanosilica, also known as KCC-1. This material possesses a unique fibrous morphology, unlike the tubular porous structure of various conventional silica materials. It has a high surface area with improved accessibility to the internal surface, tunable pore size and pore volume, controllable particle size, and, importantly, improved stability. Since its discovery, a large number of studies have been reported concerning its use in applications such as catalysis, solar-energy harvesting, energy storage, self-cleaning antireflective coatings, surface plasmon resonance-based ultrasensitive sensors, CO2 capture, and biomedical applications. These reports indicate that dendritic fibrous nanosilica has excellent potential as an alternative to popular silica materials such as MCM-41, SBA-15, Stöber silica, and mesoporous silica nanoparticles. This Review provides a critical survey of the dendritic fibrous nanosilica family of materials, and the discussion includes the synthesis and formation mechanism, applications in catalysis and photocatalysis, applications in energy harvesting and storage, applications in magnetic and composite materials, applications in CO2 mitigation, biomedical applications, and analytical applications.

C–C coupling reactions using a gold(iii) phosphorus complex confined within metal–organic framework fibers in aqueous solution

HPG@KCC-1/PPh₂/Au NPs were used for the first time as a catalyst for the C–C cross-coupling between allylarenes or methyl acrylate and benzoxazole, and they showed excellent catalytic activities under green conditions.

Synthesis of manganese incorporated hierarchical mesoporous silica nanosphere with fibrous morphology by facile one-pot approach for efficient catalytic ozonation

Manganese incorporated fibrous silica nanosphere (MnOx-0.013/KCC-1) was synthesized by one step hydrothermal method for the first time and its catalytic activity for ozonation of oxalic acid was studied. For comparison, manganese loaded MCM-41 (MnOx-0.013/MCM-41) was prepared by impregnation method. Various characterizations showed that the morphological, structural and textural properties of MnOx-0.013/KCC-1 were well preserved. Ozonation and catalytic ozonation by MnOx-0.013/KCC-1 and MnOx-0.013/MCM-41 led to 4, 85 and 60% reduction in TOC respectively. Furthermore, 0.05 and 1.2mgL(-1) leaching of Mn was detected from MnOx-0.013/KCC-1 and MnOx-0.013/MCM-41, which are approximately 2.0 and 42.0% of the total Mn present in MnOx-0.013/KCC-1 and MnOx-0.013/MCM-41 respectively. The high catalytic activity was attributed to the generation of hydroxyl radical. Surface hydroxyl groups investigated by using phosphates and ATR-FTIR were believed to be the active sites. Our proposed method of synthesis can be generalized for the synthesis of other metal oxides incorporated fibrous silica for environmental catalysis and other catalytic reactions.

Size-Dependent Catalytic Activity of Palladium Nanoparticles Fabricated in Porous Organic Polymers for Alkene Hydrogenation at Room Temperature

Ultrafine palladium nanoparticles (Pd NPs) with 8 and 3 nm sizes were effectively fabricated in triazine functionalized porous organic polymer (POP) TRIA that was developed by nonaqueous polymerization of 2,4,6-triallyoxy-1,3,5-triazine. The Pd NPs encapsulated POP (Pd-POP) was fully characterized using several techniques. Further studies revealed an excellent capability of Pd-POP for catalytic transfer hydrogenation of alkenes at room temperature with superior catalytic performance and high selectivity of desired products. Highly flammable H2 gas balloon at high pressure and temperature used in conventional hydrogenation reactions was not needed in the present synthetic system. Catalytic activity is strongly dependent on the size of encapsulated Pd NPs in the POP. The Pd-POP catalyst with Pd NPs of 8 nm in diameter exhibited higher catalytic activity for alkene hydrogenation as compared with the Pd-POP catalyst encapsulating 3 nm Pd NPs. Computational studies were undertaken to gain insights into different catalytic activities of these two Pd-POP catalysts. High reusability and stability as well as no Pd leaching of these Pd-POP catalysts make them highly applicable for hydrogenation reactions at room temperature.

Size and Fiber Density Controlled Synthesis of Fibrous Nanosilica Spheres (KCC-1)

We report a facile protocol for the synthesis of fibrous nano-silica (KCC-1) with controllable size and fiber density. In this work, we have shown that the particle size, fiber density, surface area and pore volume of KCC-1 can be effectively controlled and tuned by changing various reaction parameters, such as the concentrations of urea, CTAB, 1-pentanol, reaction time, temperature, solvent ratio, and even outside stirring time. For the first time, we were able to control the particle size ranging from as small as 170 nm to as large as 1120 nm. We were also able to control the fiber density from low to medium to very dense, which consequently allowed the tuning of the pore volume. We were able to achieve a pore volume of 2.18 cm(3)/g, which is the highest reported for such a fibrous material. Notably we were even able to increase the surface area up to 1244 m(2)/g, nearly double the previously reported surface area of KCC-1. Thus, one can now synthesize KCC-1 with various degrees of size, surface area, pore volume, and fiber density.

Preparation and characterization of a highly dispersed and stable Ni catalyst with a microporous nanosilica support

Microporous Stöber silica was synthesized by controlling the post-drying conditions. Using the silica as support, a highly dispersed Ni catalyst was successfully prepared by a simple impregnation method.

Immobilized ruthenium metal-containing ionic liquid-catalyzed dehydrogenation of dimethylamine borane complex for the reduction of olefins and nitroarenes

An efficient immobilized ruthenium metal containing ionic liquid (ImmRu-IL) catalyst has been developed for the transfer hydrogenation of olefins and nitroarenes. This methodology uses eco-friendly dimethylamine borane as a reducing agent.

Bis(4-pyridylamino)triazine-stabilized magnetite KCC-1: a chemoselective, efficient, green and reusable nanocatalyst for the synthesis of N-substituted 1,4-dihydropyridines

Fe₃O₄/KCC-1/BPAT as a novel nanostructured compound catalyzed the synthesis of N-substituted 1,4-dihydropyridines.

Three dimensional Ag/KCC-1 catalyst with a hierarchical fibrous framework for the hydrogenation of dimethyl oxalate

A novel fibrous nano-silica (KCC-1) based silver nanocatalyst exhibits excellent catalytic activity with a high TOF value in the hydrogenation of DMO to MG.