Well-dispersed Silver Nanoparticles Research Articles

Hydrated alginate polysaccharide fabrics grafted with sliver nanocrystals for wearable thermal and health management

The creation of functional components with precise chemistries on carbohydrate polymers is of great significance for future wearable biomedicine and health management. Among various carbohydrate polymers, marine polysaccharide featured with antimicrobial, biodegradable and biocompatible properties is an ideal platform while the water-swelling nature makes it difficult to form stable interface. Here, well-dispersed silver nanoparticles have been in-situ assembled on hydrated alginate fabric (AF), involving chemical absorption of Ag ions and in-situ reduction of conductive Ag layer. Owing to the stable complex formed between Ag ions and carboxyl groups, the Ag-grafted AF exhibits superior Joule heating capability, including low operating voltage (1–3 V), high saturation temperature (63 °C), rapid response time (25 s) and outstanding durability against harsh conditions. Furthermore, the Ag-grafted AF demonstrates noticeable inhibition against E. coli and S. aureus as compared with the pristine AF. This work provides a rational strategy for the functionalization of hydrated polysaccharide and enables wearable thermotherapy devices for human health management.

Punica granatum: A plant with a high potential for the synthesis of silver nanoparticles

O Objective: To use pomegranate (Punica granatum L.) extracts as a reducing agent for a simple and eco-friendly biosynthesis of silver nanoparticles and to test the latter’s antimicrobial potential against different bacteria. Methodology: The leaves and peel of ripe fruits of pomegranate were used to prepare aqueous and methanolic extracts to synthesize silver nanoparticles (AgNP). Then we evaluated these nanoparticles with techniques that allowed us to define their size, shape, and dispersion quality in aqueous media. To characterize the AgNPs we resorted to UV-Vis spectroscopy and dynamic light scattering (DLS). We determined their antimicrobial activity against Escherichia coli, Pseudomonas aeruginosa, Enterococcus faecalis, and Staphylococcus aureus. Results: UV-Vis spectra were observed with absorption peaks at 425 nm for the nanoparticles synthesized with both aqueous and methanolic extracts. Regarding size, distribution, and dispersion in solution, the zeta potential shows that the surface charge in all cases is negative, with an average value ranging from -28.0 mV to -52.0 mV. Smaller nanoparticles were obtained from the aqueous extracts of the peel and leaves, with values between 1.42 - 2.96 nm, while the methanolic extracts yielded nanoparticles of 10 - 19.04 nm. Inhibition of microorganisms proved to be best against Escherichia coli, with a minimum inhibitory concentration (MIC) of 0.83 µg/mL up to 6.68 µg/mL. Conclusions: This study suggests that pomegranate extracts synthesize small-sized, well-dispersed silver nanoparticles with an almost spherical morphology, and good antimicrobial activity against gram-negative bacteria such as Escherichia coli.

Green carboxylation of CO2 triggered by well-dispersed silver nanoparticles immobilized by melamine-based porous organic polymers

CO2 fixation via directly formation of C-C bonds to obtain carboxylation compound is an essential reaction in industry. Creating efficient, inexpensive and industrially valuable key catalysts have always been a desire, but also an urgent challenge. Here, we synthesized a kind of melamine-based porous organic polymers (POPs) evenly loaded Ag Nanoparticles (Ag NPs/Melamine-based POPs) by the gas bubbling-assisted membrane reduction (GBMR) approach. The melamine-based POPs were used as good nitrogen-rich supports for loading and dispersing Ag nanoparticles. Ag NPs/ melamine-based POPs exhibited good CO2 absorption capacity (2.1 mmol/g, 273 K and 0.1 MPa) and the excellent activity was up to 93% towards the carboxylation of terminal alkynes with CO2 under mild reaction conditions (323 K, 0.1 MPa). And the TOF is 2.23 h−1. Specially, this is very few report of heterogeneously catalyzed directly formation of carboxylation compound only applying terminal alkynes with CO2 under low temperature and atmospheric pressure. The mechanistic study revealed that the well-dispersed Ag active species promoted highly efficient and green conversion of CO2. Moreover, the catalyst was easily recovered and could be reused at least six times with retention of high catalytic activity.

Efficient and continuous chemical conversion in a thin membrane comprising three-dimensional network trapping Ag nanoparticles

In this work, we report a novel and highly efficient catalytic membrane (PES/PNM-Ag) comprising well-dispersed silver nanoparticles (NPs). The membrane can be straightforwardly constructed via dynamic loading expansible hybrid microgels PNM-Ag into a commercially-available poly(ether sulfone) (PES) membrane with asymmetric structure. Characterization results of PNM-Ag and PES/PNM-Ag indicate that a nanoscale three-dimensional network embedded with Ag NPs was developed in membrane pores by swollen microgels. The flat-sheet membrane reactor assembled with PES/PNM-Ag can efficiently and continuously catalyze the reduction of 4-nitrophenol (apparent reaction rate constant reaching 1.12 s−1) and showed good stability. The improved catalytic activity was attributed to fully accessible surface of Ag NPs as well as the unique structure of the membrane, in which the reactant was restricted to flow through immobilized catalyst. Present strategy hints to design other noble metal NPs loaded catalytic membranes for efficient conversion of nitro-aromatic pollutants.

Well-Dispersed Silver Nanoparticles on Cellulose Filter Paper for Bacterial Removal.

In this study, a polydopamine (PDA) and polyethyleneimine (PEI)-assisted approach was developed to generate well-distributed PDA/PEI/silver (PDA/PEI/Ag) nanocomplexes on the surfaces of commercial cellulose filter papers to achieve substantial bacterial reduction under gravity-driven filtration. PDA can bind to cellulose paper and act as a reducer to produce silver nanoparticles (AgNPs), while PEI can react with oxidative dopamine and act as a dispersant to avoid the aggregation of AgNPs. The successful immobilization of PDA/PEI/Ag nanocomplexes was confirmed by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) were used as pathogen models to test the efficacy of the PDA/PEI/Ag nanocomplex-incorporated filter papers. The PDA/PEI/Ag nanocomplex-incorporated filter papers provided a substantial bacterial removal of up to 99% by simple gravity filtration. This work may be useful to develop a feasible industrial production process for the integration of biocidal AgNPs into cellulose filter paper and is recommended as a local-condition water-treatment technology to treat microbial-contaminated drinking water.

How colloidal surface additivation of polyamide 12 powders with well-dispersed silver nanoparticles influences the crystallization already at low 0.01 vol%

As Additive Manufacturing (AM) is fast-growing, properties adaption of feedstock materials for AM is becoming more and more relevant due to high quality standards in industrial applications. Compared to traditional manufacturing techniques like injection molding, laser powder bed fusion (PBF-LB) of polymers has a very limited variety of processable materials, which is a major obstacle for future growth. Nanocomposites are an established material class for addressing the limitations in PBF-LB but often show poor dispersion of the nanomaterial in/on the polymer powder. Especially in the context of plasmonic nanomaterials and composites, where the state of aggregation considerably influences the optical properties, dispersion plays an important role. Our study presents a deeper understanding of the colloidal surface additivation of polyamide 12 (PA12) powders with laser-generated plasmonic silver nanoparticles, leading to high dispersion of the nanoparticles on the micropowder surface with good reproducibility. The additivation is ruled by colloidal stability and control of electrostatic forces between particles and resulted in powders that could successfully be processed on a PBF-LB machine to generate plasmonic-functionalized parts. Finally, we introduce the surface specific nanoparticle dose (surf%) as scaling key parameter complementary to the commonly used mass specific dose (wt%) to appropriately describe nanoparticle load, proving the effect of such surface additivation on the recrystallization behavior of PA12. Via flash calorimetry, already at 0.01 vol% silver load, significant nanoparticle-induced heterogeneous nucleation effects are evident, whereas the thermal properties analyzed by conventional calorimetry remain unaffected.

Sustainable green chemical synthesis of discrete, well-dispersed silver nanoparticles with bacteriostatic properties from carrot extracts aided by polyvinylpyrrolidone

Large amounts of food products are disposed of around the world because they are below market standards. In Australia, low value, non-marketable carrots (Daucus carota) are ploughed into farmlands as green manure or are treated as waste. In recent years significant research interest has focused on developing waste valorisation strategies using new green chemistry-based sustainable processes. More importantly, strategies that also provide solutions for emerging challenges like the rising reports of resistance of bacteria to existing microbes are favourable. This study explored a facile synthesis process to reduce aqueous silver ions in aqueous carrot extracts to form silver nanoparticles that may have antibacterial properties. The synthesis process produced particles with surface plasmon resonance peaks typical of crystalline silver. The silver nanoparticles produced from pure carrot extracts were spherical and pseudo-spherical, 2 to 25 nm wide. However, with polyvinylpyrrolidone, much wider (10-50 nm), well-dispersed silver nanoparticles of various shapes including spherical, polygonal, rod-like and triangular types were produced. Several biomolecules which may act as reducing and capping agents for the process were identified; they included ascorbic, gallic and chlorogenic acids. The Ag nanoparticles produced significant zones of inhibition against the gram-negative E. coli and gram-positive S. epidermidis, indicating they had bacteriostatic properties. The study demonstrates that producing Ag nanoparticles with antibiotic properties from carrots is a good valorisation strategy because other uses for rejected carrot produce such as application as green manure may not be interrupted.

One-pot synthesis of highly stable and concentrated silver nanoparticles with enhanced catalytic activity

Well-dispersed silver nanoparticles (AgNPs) were synthesized using a benign, one-pot process based on a low-cost wet chemistry technique. Monoethanolamine was used as a strong reducing agent and poly(acrylic acid) (PAA) was used as a stabilizing agent. After the addition of these reagents to a reaction system, one-pot synthesis of AgNPs was completed in ∼45 min at 75 °C with a reaction efficiency of 92.4%. The average particle size of the aqueous dispersion of AgNPs was 14.83±5.96 nm, and the dispersion remained stable even after 14 months in an ambient dark environment, which may be due to the electrostatic repulsion of the carboxylate anions of the stabilizing agent. The role of PAA in the stabilization of the AgNPs was analyzed via Fourier transform infrared spectroscopy and energy-dispersive X-ray spectroscopy. The highly stable AgNPs in the aqueous system showed high catalytic activity for the reduction of methylene blue and p-nitrophenol in the presence of sodium borohydride as the reducing agent based on pseudo-first-order kinetics.

Lobar evenness of deposition/retention in rat lungs of inhaled silver nanoparticles: an approach for reducing animal use while maximizing endpoints

BackgroundInformation on particle deposition, retention and clearance are important for the evaluation of the risk of inhaled nanomaterials to human health. Recent revised OECD inhalation toxicity test guidelines require to evaluate the lung burden of nanomaterials after rodent subacute and subchronic inhalation exposure (OECD 412, OECD 413). These revised test guidelines require additional post-exposure observation (PEO) periods that include lung burden measurements that can inform on lung clearance behavior and translocation. The latter being particularly relevant when the testing chemical is a solid poorly soluble nanomaterial. Therefore, in the spirit of 3 R’s, we investigated whether measurement of retained lung burden of inhaled nanoparticles (NPs) in individual lung lobes is sufficient to determine retained lung burden in the total lung. If it is possible to use only one lobe, it will reduce animal use and maximize the number of endpoints evaluated.ResultsTo achieve these goals, rats were exposed nose-only for 1 or 5 days (6 h/day) to an aerosol of 20 nm well-dispersed silver nanoparticles (AgNPs), which is the desired particle diameter resulting in maximum deposition in the pulmonary region when inhaled as singlets. After exposure, the five lung lobes were separated and silver concentration was measured using inductively coupled plasma-mass spectrophotometer (ICP-MS). The results showed that the retention of deposited silver nanoparticle in the different lung lobes did not show any statistically significant difference among lung lobes in terms of silver mass per gram lung lobe. This novel finding of evenness of retention/deposition of inhaled 20 nm NPs in rats for all five lobes in terms of mass per unit tissue weight contrasts with earlier studies reporting greater apical lobe deposition of inhaled micro-particles in rodents. The difference is most likely due to preferred and efficient deposition of inhaled NPs by diffusion vs. additional deposition by sedimentation and impaction for micron-sized particles.ConclusionAgNPs following acute inhalation by rats are evenly retained in each lung lobe in terms of mass per unit lung tissue weight. Accordingly, we suggest sampling any of the rat lung lobes for lung burden analysis can be used to determine deposited or retained total lung burden after short-term inhalation of NPs and using the other lobes for collecting and analyzing bronchoalveolar lavage fluid (BALF) and for histopathological analysis. Therefore, by combining lung burden measurement, histopathological tissue preparation, and BALF assay in the same rat will reduce the number of animals used and maximize the number of endpoints measured.

Preparation of Well-Dispersed Nanosilver in MIL-101(Cr) Using Double-Solvent Radiation Method for Catalysis

In this study, a double-solvent radiation method is proposed to prepare silver nanoparticles in the pores of metal-organic framework MIL-101(Cr). The results reveal that well-dispersed silver nanoparticles with a diameter of about 2[Formula: see text]nm were successfully fabricated in the cages of monodisperse octahedral MIL-101(Cr) with a particle size of about 400[Formula: see text]nm. The structure of MIL-101(Cr) was not destroyed during the chemical treatment and irradiation. The resulting Ag/MIL-101 exhibits excellent catalytic performance for the reduction of 4-nitrophenol. This method can be extended to prepare other single or bimetallic components inside porous materials.

Characterization of silver nanoparticles produced by biosynthesis mediated by Fusarium oxysporum under different processing conditions.

The goal of this study was the biosynthesis of silver nanoparticles (SNPs) mediated by the fungus Fusarium oxysporum, as well as the characterization of these nanoparticles including evaluation of the particles size and stability under different processing conditions. The results showed that the biosynthesis produced silver nanoparticles having a mean size of 34nm and zeta potential values below -30mV at the conditions used, characterizing the nanoparticles as being stable in suspension. Ultraviolet-visible spectroscopy and flame atomic absorption spectroscopy confirmed the formation of silver nanoparticles and Fourier transform infrared spectroscopy detected the bands corresponding to the binding vibration of amide I and II bands of proteins in addition to the presence of cyclic alkanes, cyclohexane, ethers, and aromatic hydrocarbons. Finally, field emission scanning electron microscopy and transmission electron microscopy revealed the formation of spherical and well-dispersed SNPs.

Synthesis of Well-Dispersed Silver Nanoparticles on Polypyrrole/Reduced Graphene Oxide Nanocomposite for Simultaneous Detection of Toxic Hydrazine and Nitrite in Water Sources

The AgNPs@PPy/rGO composites were synthesized by interfacial polymerization method using organic solvent dispersion of pyrrole as a reducing agent for graphene oxide. Aqueous solution of silver nitrate was used as a precursor for Ag nanoparticles and oxidizing agent to initiate polymerization reaction at the interface. The nanocomposite film electrode was employed for the electrochemical oxidation of inorganic pollutants namely hydrazine and nitrite and their oxidation potential was observed at +0.53 and +0.76 V (vs. Ag/AgCl), respectively in phosphate buffer. The kinetic parameters such as diffusion coefficient (1.67 × 10−5 and 3.9 × 10−5 cm2/s) and electron transfer rate constant (3.03 × 106 and 8.36 × 105 M−1s−1) of hydrazine and nitrite were measured by chronoamperometric method. Differential pulse voltametry was employed to determine individual as well as simultaneous detection of both analytes with well-resolved peak potential window (∼470 mV). The linear dynamics range from 0.6 μM to 6.6 μM and the detection limit of 19 and 21 nM for hydrazine and nitrite respectively were observed. In addition, the proposed sensor shows an enhanced stability and found to be incentive to select pollutants and biomolecules.

Enhanced antimicrobial activities of silver-nanoparticle-decorated reduced graphene nanocomposites against oral pathogens

As a means of capitalizing on the synergistic properties between reduced graphene nanosheets (R-GNs) and silver nanoparticles (AgNPs), an efficient and convenient chemical reduction method was used to prepare silver-nanoparticle-decorated reduced graphene nanocomposites (R-GNs/Ag). The products were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and Raman spectroscopy, which confirmed the loading of well-dispersed silver nanoparticles on reduced graphene sheets. Their antimicrobial activities against oral pathogens such as Candida albicans, Lactobacillus acidophilus, Streptococcus mutans, and Aggregatibacter actinomycetemcomitans were investigated by MIC determination, the counting of colony-forming units (CFU), agar diffusion tests, and growth curve observation. Compared with pure R-GNs and AgNPs, R-GNs/Ag composites exhibited enhanced antimicrobial properties owing to highly dispersed AgNPs on R-GNs.

English

We have investigated the green synthesis and antimicrobial activity of silver nanoparticles using Garcinia kola. Aqueous extract of G. kola was used to reduce AgNO3 solution to obtain black nanocrystal of silver nanoparticles. Antimicrobial activity of the silver nanoparticles was tested against Escherichia coli, Klebsiella pneumonia, Bacillus subtilis, Staphylococcus aureus, Aspergillus niger, Rhizopus stolonifer and Candida albican. The synthesized silver nanoparticles was characterized using UV-vis spectroscopy, X-ray diffraction (XRD), Transmission electron microscopy (TEM), and Fourier transform infrared (FTIR) spectroscopy. UV-visible exhibits prominently the characteristic surface plasmon resonance at around 427 nm. A remarkable particle growth onset of 10 min was observed while the reaction ended within 30 min. The XRD analysis shows that the synthesized silver nanoparticles are crystalline in nature and well-dispersed silver nanoparticles with an approximate size of 10.4 nm were observed on TEM. The synthesized silver was found to possess good antimicrobial activity against all the tested microbes. The application of the green synthesized nanoparticles can be used in many fields such as foods, beverages, cosmetics and medicine. Key words: Silver, nanoparticles, green synthesis, Garcinia kola seed extract, transmission electron microscopy, antimicrobial activity.

Plasma Treatment of Silver Impregnated Mesoporous Aluminosilicate Nanoparticles for Adsorptive Desulfurization

We report a regenerable adsorbent for the removal of refractory organosulfur compounds from fossil fuels. The material is composed of well-dispersed silver nanoparticles confined within the mesochannels of aluminum-doped MCM-41 nanoparticles. With an average initial desulfurization capacity of 15 mg S·g–1, 79% desulfurization capacity is retained after six cycles for the removal of dibenzothiophene from n-decane. The addition of intraframework aluminum to form a mesoporous aluminosilicate nanoparticle (MASN) aids in the retention and dispersion of silver ions within the mesochannels (Ag-MASN). The nanoparticles are subsequently reduced by glow discharge plasma treatment in argon (PT-Ag-MASN). The size dispersion, surface area, and structural integrity were characterized by scanning electron microscopy, annular dark-field scanning transmission electron microscopy (ADF-STEM), nitrogen adsorption analysis (BET), and powder X-ray diffraction. Silver nanoparticle formation within the mesochannels of MASN was confirmed by ADF-STEM and diffuse reflectance UV–vis spectroscopy. Model fuel testing revealed that PT-Ag-MASN had the highest regeneration capacity after six cycles compared to non-plasma-treated (Ag-MASN) and aluminum-free materials (Ag-MSN and PT-Ag-MSN). Initial testing of the military jet fuel JP-8 also shows a high desulfurization capacity of 41 mg S·g–1.

Biosynthesis of Ag/MWf-CNT Nanocomposites Using Aspergillus fumigatus as the CO Oxidation Catalyst

In this research, the biosynthesis process of an Ag nanoparticles/multiwalled carbon nanotubes (Ag/MWf-CNT) catalyst system has been investigated by Aspergillus fumigatus fungus. Characteristic peaks of pure silver and FCC crystallization systems were characterized by X-ray diffraction pattern. TEM images show a well-dispersed spherical silver nanoparticles (≤10 nm) on the carbon nanotubes. Based on the results, reduction of silver ions is mainly dependent on the biomass weight applied in the biosynthesis process. Catalytic activity in CO/CO2 conversion process revealed approximately 100% conversion of CO at 220°C.

Preparation and Characterization of Silver Nanoparticles from the Super-Heated Water Degraded Keratin Solutions.

This research demonstrates that silver nanoparticles can be prepared from the chicken feathers keratin solution obtained by superheated water treatment. Feathers are inexpensive and renewable resources but have limited applications. In this study, a facile method was described for synthesis of silver nanoparticles by the super-heated water degradation of chicken feathers keratin without using any additional chemicals. Stable and well-dispersed silver nanoparticles of about 3.24 nm were biosynthesized. The prepared nanoparticles were characterized using UV-Vis spectroscopy, transmission electron microscopy, FTIR-ATR spectroscopy and X-ray diffract. Prepared silver nanoparticles were stable on keeping at room temperature for more than 6 months and also stable in the presence of NaCl. The agglomerates caused by the decrease of pH value can easily be re-dispersed in alkaline aqueous media with no obvious change in their optical properties. The as-prepared silver nanoparticles have excellent antibacterial property reducing the bacterial population with more than 99.99%.

Facile synthesis of magnetically separable reduced graphene oxide/magnetite/silver nanocomposites with enhanced catalytic activity

In this study, the combination of magnetite (Fe3O4) with reduced graphene oxide (RGO) generates a new hybrid substrate for the dispersion of noble metal nanoparticles. Well-dispersed silver (Ag) nanoparticles loaded on the surface of Fe3O4 modified RGO are achieved by an efficient two-step approach. Through reducing Ag+ ions, highly dispersed Ag nanoparticles are in-situ formed on the RGO/Fe3O4 substrate. It is found that the existence of Fe3O4 nanocrystals can significantly improve the dispersity and decrease the particle size of the in-situ formed Ag nanoparticles. Magnetic study reveals that the as-prepared RGO/Fe3O4/Ag ternary nanocomposites display room-temperature superparamagnetic behavior. The catalytic properties of the RGO/Fe3O4/Ag ternary nanocomposites were evaluated with the reduction of 4-nitrophenol into 4-aminophenol as a model reaction. The as-synthesized RGO/Fe3O4/Ag ternary catalysts exhibit excellent catalytic stability and much higher catalytic activity than the corresponding RGO/Ag catalyst. Moreover, the RGO/Fe3O4/Ag catalysts can be easily magnetically separated for reuse. This study further demonstrates that nanoparticles modified graphene can act as an effective hybrid substrate for the synthesis of multi-component and multifunctional graphene-based composites.

Stable and efficient loading of silver nanoparticles in spherical polyelectrolyte brushes and the antibacterial effects

A more efficient and convenient strategy was demonstrated to immobilize silver nanoparticles (NPs) with a crystalline structure into the spherical polyelectrolyte brushes (SPB) as an antibacterial material. The SPB used for surface coating (Ag immobilized PVK–PAA SPB) consists of a poly(N-vinylcarbazole) (PVK) core and poly(acrylic acid) (PAA) chain layers which are anchored onto the surface of PVK core at one end. Well-dispersed silver nanoparticles (diameter∼3.5nm) then formed and were electrostatically confined in the brush layer. Ag content is controlled by a repeated loading process. Thin film coatings were then constructed by layer-by-layer depositions of positive charged poly(diallyldimethylammonium chloride) (PDDA) and SPB. The multilayer composites display excellent stability as well as antibacterial performance but not for simple PVK–PAA coated surface. The results show that almost complete bacteria growth including both dispersed bacterial cells and biofilms was inhibited over a period of 24h. This approach opens a novel strategy for stable and efficient immobilization of Ag NPs in fabrication of antibacterial materials.

In situ loading of well-dispersed silver nanoparticles on nanocrystalline magnesium oxide for real-time monitoring of catalytic reactions by surface enhanced Raman spectroscopy.

The surface-enhanced Raman spectroscopy (SERS) technique is of great importance for insight into the transient reaction intermediates and mechanistic pathways involved in heterogeneously catalyzed chemical reactions under actual reaction conditions, especially in water. Herein, we demonstrate a facile method for in situ synthesis of nanocrystalline magnesium oxide-Ag(0) (nano MgO-Ag(0)) hybrid nanomaterials with dispersed Ag nanoparticles (Ag NPs) on the surface of nanocrystalline magnesium oxide (nano MgO) via Sn(2+) linkage and reduction. As a benefit from the synergy effect of nano MgO and Ag NPs, the nano MgO-Ag(0) exhibited both excellent SERS and catalytic activities for the reduction of 4-nitrothiophenol in the presence of NaBH4. The nano MgO-Ag(0) was used for real-time monitoring of the catalytic reaction process of 4-nitrothiophenol to 4-aminothiophenol in an aqueous medium by observing the SERS signals of the reactant, intermediate and final products. The intrinsic reaction kinetics and reaction mechanism of this reaction were also investigated. This SERS-based synergy technique provides a novel approach for quantitative in situ monitoring of catalytic chemical reaction processes.