Catalytic reduction of aldehydic and nitro groups of nitro-benzaldehyde derivatives by silver nanoparticle-containing smart alginate-poly(N-isopropylacrylamide-methacrylic acid) microgels

Aromatic compounds containing aldehyde and nitro groups are very toxic to human health. Moreover, complete degradation of these compounds is not possible. Therefore, these compounds are converted into less toxic but more useful hydroxy-methyl aniline (HMA) derivatives. This conversion is performed using a suitable catalyst and a reducing agent. Therefore, alginate-poly(N-isopropylacrylamide-methacrylic acid) (AN-P(NIPAM-MAAc)) (AN-P(NM)) microgels were synthesized via a free radical precipitation polymerization (FRPP) method and were used as a micro-reactor for synthesis of silver (Ag) nanoparticles (NPs) into the polymeric network using in situ reduction methods. The synthesized AN-P(NM) microgels and Ag-AN-P(NM) hybrid microgels were characterized through SEM, FTIR, TEM, XRD, UV-vis spectroscopy, and EDX. Ag-AN-P(NM) exhibited temperature- and pH-responsive behavior as well as long-term stability of Ag nanoparticles in a polymeric network of AP(NM). Catalytic reduction of 4-nitrobenzaldehyde (4NBA) was evaluated under different conditions, such as different contents of Ag-AN-P(NM), 4NBA concentrations, temperatures, and concentrations of NaBH4. The Ag-AP(NM) hybrid microgels catalytically reduced 3-nitrobenzaldehyde (3NBA), 4NBA, and 3,5-dinitrobanzaldehyde (3,5DNBA) into their corresponding HA compounds in a water medium. The apparent rate constant (k ob) values for 3NBA, 4NBA, and 3,5DNBA were found to be 1.73 min-1, 1.48 min-1, and 1.19 min-1, respectively. Ag-AP(NM) exhibited outstanding catalytic efficiency, recyclability, and stability as well as retained its performance across multiple cycles.

Catalytic degradation of various dyes using silver nanoparticles fabricated within chitosan based microgels

Precipitation polymerization method was used to synthesize chitosan based poly[chitosan-N-isopropylmethacrylamide-acrylic acid] [P(CS-NI-AA)] microgel particles. Synthesized P(CS-NI-AA) microgel particles were utilized as micro-reactors for the fabrication of silver nanoparticles (AgNPs) inside the structure of microgels through chemical reduction of Ag+ ions using NaBH4 as reducing agent. P(CS-NI-AA) and Ag-P(CS-NI-AA) systems were analyzed using various characterization techniques like scanning electron microscopy (SEM), ultraviolet-visible (UV-visible) spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. Catalytic activity of Ag-P(CS-NI-AA) for individual and simultaneous degradation of various dyes like methylene blue (MB), Congo red (CR), brilliant blue (Bb), methyl orange (MO) and Rhodamine B (RB) was investigated in aqueous phase using NaBH4 as reductant. The Pseudo 1st order rate constant (k1) for dyes degradation were evaluated. The Ag-P(CS-NI-AA) hybrid system was observed to be efficient, low-cost and stable catalyst for quick degradation of dyes.

Spectroscopic monitoring of polyurethane-based nanocomposite as a potential catalyst for the reduction of dyes

In this study, AgNPs-loaded polyurethane-sodium alginate (PU-S/Alg) composite polymers were prepared by precipitation polymerization and in-situ reduction method. Their catalytic potential was evaluated for the reduction of methyl orange (MO), brilliant blue (BB), Rhodamine B (RhB), 4-nitroaniline (4-NA), and 4-nitrophenol (4-NP). Successful preparation of samples was confirmed by UV-Visible spectrophotometry (UV-Visible), Fourier transform infrared (FTIR), and Scanning electron microscopy (SEM) analysis. During the catalytic study, the value of kapp for the reduction of MO in the presence of NaBH4 and catalyst was found 0.488 min-1 while, in the presence of NaBH4 and catalyst alone, were found as 0.9 × 10-4 and 0.8 × 10-5 min-1, respectively which indicates the role of catalyst in making the reaction speedy. The value of kapp for the reduction of BB, RhB, 4-NA, and 4-NP was found as 0.764, 0.475, 0.212 and 0.757 min-1, respectively. Simultaneous reduction of dyes induced a decreased reaction completion time under the same reaction conditions. A slight increase in the value of kapp for the catalytic reduction of MO was also observed when reactions were performed in the presence of ionic media of different salts such as NaCl, KCl, CaCl2, and MnCl2. The rate of reduction of MO was increased with the increase in ionic strength of the medium. However, the presence of SDS (surfactant) in the reaction mixture induced the decreased activity of the catalyst and increased reaction completion time. The same value of kapp for the reduction of MO was observed in the case of freshly prepared and several days old nanocomposite catalyst. These results illustrate the stability and maintained catalytic potential of metal NPs for a prolonged time. Our reported catalyst also showed good potential for the treatment of dyes-polluted textile industry wastewater.

A review on Ag nanoparticles fabricated in microgels

In recent years, there has been growing interest in the composites of multi-responsive microgels and silver nanoparticles. This innovative hybrid system harnesses the responsive qualities of microgels while capitalizing on the optical and electronic attributes of silver nanoparticles. This combined system demonstrates a rapid response to minor changes in pH, temperature, ionic strength of the medium, and the concentration of specific biological substances. This review article presents an overview of the recent advancements in the synthesis, classification, characterization methods, and properties of microgels loaded with silver nanoparticles. Furthermore, it explores the diverse applications of these responsive microgels containing silver nanoparticles in catalysis, the biomedical field, nanotechnology, and the mitigation of harmful environmental pollutants.

pH-Responsive Super-Porous Hybrid Hydrogels for Gastroretentive Controlled-Release Drug Delivery

Super-porous hydrogels are considered a potential drug delivery network for the sedation of gastric mechanisms with retention windows in the abdomen and upper part of the gastrointestinal tract (GIT). In this study, a novel pH-responsive super-porous hybrid hydrogels (SPHHs) was synthesized from pectin, poly 2-hydroxyethyl methacrylate (2HEMA), and N, N methylene-bis-acrylamide (BIS) via the gas-blowing technique, and then loaded with a selected drug (amoxicillin trihydrate, AT) at pH 5 via an aqueous loading method. The drug-loaded SPHHs-AT carrier demonstrated outstanding (in vitro) gastroretentive drug delivery capability. The study attributed excellent swelling and delayed drug release to acidic conditions at pH 1.2. Moreover, in vitro controlled-release drug delivery systems at different pH values, namely, 1.2 (97.99%) and 7.4 (88%), were studied. These exceptional features of SPHHs—improved elasticity, pH responsivity, and high swelling performance—should be investigated for broader drug delivery applications in the future.

Physicochemical aspects of inorganic nanoparticles stabilized in N-vinyl caprolactam based microgels for various applications

The vinyl caprolactam (VCL) based microgel system has become the center of great attention due to its versatile properties. Copolymerization of VCL with an ionic monomer imparts pH responsive properties into the microgel system in addition to thermo-sensitivity. Stimuli responsive behavior of VCL-based microgels makes them prospective and appealing candidates for practical applications covering the fields of drug delivery, catalysis and optical devices. In the last few years, VCL-based microgels have been used as microreactors and stabilizers for the synthesis and stabilization of inorganic nanoparticles to obtain hybrid microgels. The present review article provides a summary of the present-day progress of fabrication, stabilization, categorization and analysis of VCL-based microgels and their hybrids with different morphologies. The stimuli responsive properties and applications of VCL-based hybrid microgels have been reviewed critically. The remaining problems which need to be addressed have been pointed out for further advancement in this field.