Khalida Naseem

Catalytic Reduction of 2-Nitroaniline in Aqueous Medium Using Silver Nanoparticles Functionalized Polymer Microgels

Poly(N-isopropylacrylamide-co-methacrylic acid) [P(NIPAM-co-MAA)] microgels were prepared by free radical precipitation polymerization in aqueous medium. Silver nanoparticles were fabricated inside the microgel network by in situ reduction of silver ions. The pure and hybrid microgels were characterized by FTIR and UV–Vis spectroscopy. Dynamic light scattering was performed to investigate the pH sensitivity of the microgels. The TEM and XRD analysis was used to determine the size of silver nanoparticles. The value of λSPR was found to be red shifted with increase of pH of the medium due to change of refractive index around Ag nanoparticles as a result of swelling of microgels. The hybrid microgels were used as catalyst for reduction of 2-nitroaniline (2-NA) in aqueous medium. The progress of the reaction was monitored by UV–Vis spectrophotometry in the presence of various concentrations of NaBH4, 2-NA and hybrid microgel dose. The data was used to explore the inside mechanism of catalytic reduction of 2-NA in aqueous medium.

A review of responsive hybrid microgels fabricated with silver nanoparticles: synthesis, classification, characterization and applications

Abstract Multi-responsive microgels loaded with silver nanoparticles have gained much attention in the recent years. Such hybrid system combines responsive behavior of microgels with optical and electronic properties of silver nanoparticles. This composite system shows quick response to slight variation of temperature, pH and ionic strength of medium and concentration of certain biological substances. This review article describes the recent research progress of synthesis, classification, methods of characterization and properties of silver nanoparticles containing microgels. It also covers applications of silver nanoparticles-loaded responsive microgels in catalysis, biomedical field, nanotechnology and degradation of toxic environmental moieties.Graphical Abstract

Engineering of silver nanoparticle fabricated poly (N-isopropylacrylamide-co-acrylic acid) microgels for rapid catalytic reduction of nitrobenzene

Abstract Three different poly(N-isopropylacrylamide-co-acrylic acid) [p(NIPAM-AA)] microgel samples were prepared using a precipitation polymerization method by varying the concentration of NIPAM and AA in aqueous medium. The microgels were used as microreactors to fabricate Ag nanoparticles (NPs) by in situ a reduction method. Fourier transform infrared (FTIR) and UV-visible spectroscopy were used to characterize the pure and hybrid microgels. The hybrid microgels with different AA content were used as catalysts for reduction of nitrobenzene (NB) into aniline. The progress of the reaction was monitored by a UV-visible spectrophotometer. The results show that the value of the apparent rate constant for catalytic reduction of NB decreases from 0.431 min-1 to 0.227 min-1 by increasing AA content from 3 mol% to 7 mol%, respectively. Decrease in apparent rate constant with increase of AA content can be attributed to an increase in hydrophilicity with increase of AA contents of the microgels. The increase in induction period with increase of AA contents indicates that diffusion of NB towards the catalytic surface becomes difficult due to an increase of hydrophilicity.

Catalytic reduction of 2-nitroaniline: a review

Abstract2-nitroaniline (2-NA) is highly toxic and environmental contaminant. It is reduced to less toxic and environmental benign product o-phenylenediamine by using different reducing agents like sodium borohydride, potassium borohydride, or hydrazine hydrate in the presence of various catalytic systems. These catalytic systems have various advantages and drawbacks. Silica-supported gold nanoparticles are frequently reported catalyst for the reduction of 2-nitroaniline in aqueous medium. In this review article, different catalytic systems reported for reduction of o-nitroaniline under various reaction conditions have been discussed. The critical review of the recent research progress for development of novel catalysts used for the reduction of 2-nitroaniline has been provided here.

Fabrication of silver nanoparticles in pH responsive polymer microgel dispersion for catalytic reduction of nitrobenzene in aqueous medium

Copolymer microgels based on N-isopropylacrylamide (NIPAM) and methacrylic acid (MAA) have been synthesized by free radical emulsion polymerization using N,N-methylenebisacrylamide (BIS) as a cross-linker. Synthesized microgels were characterized by Fourier transform infrared spectroscopy (FTIR). Then silver nanoparticles were fabricated in the synthesized microgels by in-situ reduction of AgNO3 with NaBH4. The formation of silver nanoparticles was confirmed by UV–Vis spectroscopy. The pH sensitivity of the copolymer microgels was investigated using dynamic light scattering technique (DLS). Hydrodynamic radius of P (NIPAM–MAA) microgels increases with increase in pH of the medium at 25°C. Surface plasmon resonance wavelength (λSPR) of silver nanoparticles increases with increase in hydrodynamic radius due to change in pH of the medium. The catalytic activity for the reduction of nitrobenzene (NB), an environmental pollutant, into aniline was investigated by UV–Vis spectroscopy in excess of NaBH4 using hybrid microgels as catalyst. The value of apparent rate constant (kapp) of the reaction was calculated using pseudo first order kinetic model and it was found to be linearly related to the amount of catalyst. The results were compared with literature data. The system was found to be an effective catalyst for conversion of NB into aniline.

Advancement in Multi-Functional Poly(styrene)-Poly(N-isopropylacrylamide) Based Core–Shell Microgels and their Applications

GRAPHICAL ABSTRACT ABSTRACT Core–shell microgels made of non-responsive polystyrene core and responsive poly(N-isopropylacrylamide) shell show exceptional properties as compared to homogenous microgels prepared by conventional methods. Due to the presence of solid polystyrene core, such type of microgels can be easily recycled from reaction mixture. Different methodologies adopted to prepare polystyrene-poly(N-isopropylacrylamide) based core–shell microgels have been described in this review article. Extraordinary properties of core–shell microgels induced due to the presence of solid polystyrene core have also been elaborated. Temperature responsive, feed contents tuned as well as charged-based characteristics of these core–shell microgels have also been discussed in detail. Various analytical techniques used to characterize these core–shell microgels have also been enlightened. Application of polystyrene-poly(N-isopropylacrylamide) based core–shell microgels as micro-reactor, efficient adsorbent for various type of proteins, source for synthesis of hollow microspheres for various applications, and catalysts in oxidation/reduction reactions have also been discussed critically in detail in this review article. Future directions of polystyrene-poly(N-isopropylacrylamide) based core–shell microgels have also been described to help researchers working in this field.

Facile synthesis of silver nanoparticles in a crosslinked polymeric system by in situ reduction method for catalytic reduction of 4-nitroaniline

ABSTRACT In this study, poly(N-isopropylmethacrylamide-co-methacrylic acid) microgels prepared by free radical precipitation polymerization were used as micro-reactors for the synthesis and stabilization of silver nanoparticles. UV-Visible spectroscopy, Transmission Electron Microscopy and Fourier-transform infrared spectroscopy were used to characterize both pure and hybrid microgels. The catalytic reduction of 4-nitroaniline was carried out in the presence of hybrid microgels to test their catalytic activity, and the catalysis mechanism was explored by varying the concentrations of reacting species like 4-nitroaniline and NaBH4, as well as the dose of the catalyst. The kinetic data indicates that this reaction follows pseudo-first order. The variation in apparent rate constant (kapp) with respect to NaBH4 concentration also discloses it to be the following Langmuir–Hinshelwood mechanism. The relationship between catalyst concentration and apparent rate constant was found to be increasing in a linear manner. The data obtained also confirmed that silver nanoparticles loaded microgels have the potential to be used as an excellent micro-reactor for selective reduction of 4-nitroaniline to p-phenylenediamine.

A systematic study for removal of heavy metals from aqueous media using Sorghum bicolor: an efficient biosorbent

This review is based on the adsorption characteristics of sorghum (Sorghum bicolor) for removal of heavy metals from aqueous media. Different parameters like pH, temperature of the medium, sorghum concentration, sorghum particle size, contact time, stirring speed and heavy metal concentration control the adsorption efficiency of sorghum biomass for heavy metal ions. Sorghum biomass showed maximum efficiency for removal of heavy metal ions in the pH range of 5 to 6. It is an agricultural waste and is regarded as the cheapest biosorbent, having high adsorption capacity for heavy metals as compared to other reported adsorbents, for the treatment of heavy metal polluted wastewater. Adsorption of heavy metal ions onto sorghum biomass follows pseudo second order kinetics. Best fitted adsorption isotherm models for removal of heavy metal ions on sorghum biomass are Langmuir and Freundlich adsorption isotherm models. Thermodynamic aspects of heavy metal ions adsorption onto sorghum biomass have also been elaborated in this review article. How adsorption efficiency of sorghum biomass can be improved by different physical and chemical treatments in future has also been elaborated. This review article will be highly useful for researchers working in the field of water treatment via biosorption processing. The quantitative demonstrated efficiency of sorghum biomass for various heavy metal ions has also been highlighted in different sections of this review article.

Designed synthesis of silver nanoparticles in responsive polymeric system for their thermally tailored catalytic activity towards hydrogenation reaction

Poly(N-isopropylacrylamide-acrylamide-methacrylic acid) [p(NIPa-AAm-Ma)] polymer microgels were prepared by free radical precipitation polymerization method. AgNPs were fabricated in the sieves of polymer network by chemical reduction using AgNO3 salt as a precursor of silver ions. Various techniques like dynamic light scattering (DLS), transmission electron microscopy (TEM), Fourier transform infrared microscopy (FTIR), and UV-Visible spectroscopy were used for characterization of pure and composite microgels. The diameter of AgNPs fabricated in polymeric network was found to be in the range of 10-15 nm. Stimuli responsive behavior of hybrid microgels was same as that of pure microgels. Catalytic efficiency of the hybrid microgels was investigated by reducing 4-Nitroaniline (4-NA) into 4-Aminoaniline (4-AA) using NaBH4 as reducing agent under different conditions of temperature of the medium, concentration of reducing agent, 4-Nitroaniline and hybrid microgels to explore the catalysis process. Kinetic and thermodynamic aspects of reduction of 4-Nitroaniline in the presence of catalyst were also discussed on the basis of values of Arrhenius and Eyring parameters like pre-exponential factor, activation energy, enthalpy of activation and entropy of activation. Catalytic activity of the hybrid microgels was found to be thermally tunable in the temperature range of 25-70 oC. The value of rate constant (kapp) for reduction of 4-NA was minimum at 55 °C, which can be attributed to volume phase transition of the hybrid microgels.

Microgels as efficient adsorbents for the removal of pollutants from aqueous medium

Abstract Due to their responsive behavior, high stability, and reusability, microgels have gained importance as adsorbents for the removal of aqueous pollutants such as heavy metals, nitroarenes, organic matter, and toxic dyes. However, there are few challenges that need to be addressed to make microgels as potential adsorbents for the removal of aqueous pollutants. This review article encircles the recent developments in the field of microgel usage as adsorbents for the extraction of aqueous pollutants. Many factors that influence the adsorption of pollutants such as pH, temperature of the medium, agitation time, pollutant concentration, microgel dose, and feed contents of microgels have been discussed in detail. Different adsorption isotherms as well as the kinetic and thermodynamic aspects of the adsorption process have also been enlightened to interpret the insight of the adsorption process. Microgel recovery from the reaction mixture as well as reusability is discussed from the financial point of view. The biodegradability of microgels induced due to the incorporation of specific biomacromolecules is also discussed.