Muhammad Ajmal

Highly versatile p(MAc)–M (M: Cu, Co, Ni) microgel composite catalyst for individual and simultaneous catalytic reduction of nitro compounds and dyes

Poly(methacrylic acid) (p(MAc)) microgels were synthesized by inverse suspension polymerization and used as a template for copper, nickel, and cobalt nanoparticle preparation. Upon absorption of Co(II), Ni(II), and Cu(II) by p(MAc) microgels from related aqueous solutions, the metal ion laden microgels were treated with sodium borohydride (NaBH4) to obtain the corresponding metal nanoparticles within the p(MAc) network as p(MAc)–M (M: Co, Ni, Cu). The microgels and metal nanoparticle containing composites were visualized and analyzed by Optical Microscopy, SEM, and TEM analysis. Thermal properties and the metal nanoparticle content of the prepared composites were investigated by TG analysis. However, the exact amounts of metal nanoparticles entrapped within the microgels was calculated by AAS measurements after dissolution of the metal nanoparticles within p(MAc) the microgel composites by concentrated HCl acid treatment. The prepared p(MAc)–M composites were employed as a catalyst for the degradation of some organic dyes such as Eosin Y (EY), and methyl orange (MO), and reduction of nitro aromatic pollutants such as 2-nitrophenol (2-NP), 4-nitrophenol (4-NP), 4-nitroaniline (4-NA) to their corresponding amino phenols. More importantly, we report the simultaneous degradation of EY and 4-NP reduction catalyzed by p(MAc)–Cu microgel composites. Various parameters effecting the degradation of dyes and nitro compound reduction such as metal types, and their amounts, temperature and amount of reducing agent were investigated.

Silver nanoparticles containing hybrid polymer microgels with tunable surface plasmon resonance and catalytic activity

Multi-responsive poly(N-isoprpylacrlamide-methacrylic acid-acrylamide) [P(NIPAM-MAA-AAm)] copolymer microgel was prepared by free radical emulsion polymerization. Silver nanoparticles were fabricated inside the microgel network by in-situ reduction of silver nitrate. Swelling and deswelling behavior of the pure microgels was studied under various conditions of pH and temperature using dynamic light scattering. A red shift was observed in surface plasmon resonance wavelength of Ag nanoparticles with pH induced swelling of hybrid microgel. The catalytic activity of the hybrid system was investigated by monitoring the reduction of p-nitrophenol under different conditions of temperature and amount of catalysts. For this catalytic reaction a time delay of 8 to 10min was observed at room temperature, which was reduced to 2 min at high temperature due to swelling of microgels, which facilitated diffusion of reactants to catalyst surface and increased rate of reaction.

Synthesis, Characterization, and Silver Nanoparticles Fabrication in N-isopropylacrylamide-Based Polymer Microgels for Rapid Degradation of p-Nitrophenol

Multiresponsive poly(N-isopropylacrylamide-co-methacrylic acid) microgels were synthesized by precipitation polymerization in aqueous medium. Then silver-poly(N-isopropylacrylamide-co-methacrylic acid) hybrid microgels were prepared by in-situ reduction of silver ions. Formation of microgels was confirmed by Fourier transform infrared spectroscopic analysis. pH and temperature sensitivity of microgel was studied by dynamic light scattering. Hydrodynamic radius of microgels decreases with increase in temperature at pH 8.20 and show volume phase transition temperature around 45°C. At pH 2.65, hydrodynamic radius decreases with increase in temperatures upto 35°C but further increase in temperature causes aggregation and microgel becomes unstable due to increase of hydrophobicity. With increase in pH of medium, the hydrodynamic radius of microgels increases sigmoidally. Formation of silver nanoparticles inside microgel and pH dependence of surface plasmon resonance wavelength of the hybrid microgels were investigated by ultraviolet-visible spectroscopy. The value of surface plasmon resonance band and absorbance associated with surface plasmon resonance band increases with increases in pH of the medium. The apparent rate constant of reduction of p-nitrophenol was found to be linearly dependent on volume of hybrid microgels used as catalyst. The system has a potential to be used as effective catalyst for rapid degradation of industrial pollutant.

Magnetic Co–Fe bimetallic nanoparticle containing modifiable microgels for the removal of heavy metal ions, organic dyes and herbicides from aqueous media

Poly(methacrylic-co-acrylonitrile) (p(MAc-co-AN)) microgels were prepared and nitrile groups were converted to amidoxime groups by chemical modification. Amidoximated microgels, amid-p(MAc-co-AN) microgels were used for in situ synthesis of cobalt–iron (Co–Fe) bimetallic magnetic nanoparticles by simultaneous reduction of Co(II) and Fe(II) ions within microgel. The prepared magnetic microgels as amid-mag-p(MAc-co-AN) microgel were found to be very effective adsorbents for the removal of metal ion such as Cd(II), Cr(III), and organic dyes e.g., methylene blue (MB), rhodamine 6G (R6G) and a herbicide, paraquat (PQ). A tremendous increase in the adsorption capacities of amid-p(MAc-co-AN) microgels was found as 88.1, 89.9, 190.0, 334.5 and 166.5 mg g−1 from 40.2, 37.4, 75.3, 57.4, and 56.3 for MB, R6G, PQ, Cd(II), and Cr(III), respectively. Moreover, a further increase in adsorption capacity of amid-mag-p(MAc-co-AN) microgel composites were also accomplished with the existence of magnetic particles. Adsorption of these contaminants from tap, river and seawater was also studied. The effects of different parameters i.e., pH, concentration of adsorbent solution and amount of adsorbate was also studied. Langmuir, Freundlich and Temkin adsorption models were applied, and the adsorption of Cd(II) and Cr(III) was found to obey Langmuir adsorption isotherm better.

Effect of crosslinker feed content on catalaytic activity of silver nanoparticles fabricated in multiresponsive microgels

We investigated the effect of crosslinking density of poly(N-isopropyl acrylamide-co-acrylic acid) microgels on catalytic activity of silver nanoparticles fabricated hybrid microgels. Multiresponsive poly(N-isopropyl acrylamide-co-acrylic acid) microgels with 2, 4, 6 and 8 mole percentage of N,N-methylene-bis-acrylamide were synthesized by emulsion polymerization. These microgels were characterized by dynamic light scattering and were used as microreactors to synthesize silver nanoparticles. Hybrid system was characterized by ultraviolet-visible spectroscopy. The catalytic activity of hybrid microgels with different crosslinker content was compared by studying the reduction of pnitrophenol as a model reaction. Kinetics of reaction was monitored by spectrophotometry. The value of the apparent rate constant decreases from 0.568 to 0.313min−1, when content of crosslinker are increased from 2 to 8 mole percentage respectively. This decreases in value of apparent rate constant is due to increase in diffusional barrier offered by high crosslinking of polymer network at high mole percentages of N,N-methylene-bis-acrylamide.

Simultaneous catalytic degradation/reduction of multiple organic compounds by modifiable p(methacrylic acid-co-acrylonitrile)–M (M: Cu, Co) microgel catalyst composites

We prepared poly(methacrylic acid-co-acrylonitrile) (p(MAc-co-AN)) microgels by inverse suspension polymerization, and converted the nitrile groups into amidoxime groups to obtain more hydrophilic amidoximated poly(methacrylic acid-co-acrylonitrile) (amid-p(MAc-co-AN)) microgels. Amid-microgels were used as microreactors for in situ synthesis of copper and cobalt nanoparticles by loading Cu(II) and Co(II) ions into microgels from their aqueous metal salt solutions and then converted to their corresponding metal nanoparticles (MNPs) by treating the loaded metal ions with sodium borohydride (NaBH4). The characterization of the prepared microgels and microgel metal nanoparticle composites was carried out by SEM, TEM and TG analysis. The amounts of metal nanoparticles within microgels were estimated by AAS measurements by dissolving the MNP entrapped within microgels by concentrated HCl acid treatment. Catalytic performances of the prepared amid-p(MAc-co-AN)–M (M: Cu, Co) microgel composites were investigated by using them as catalysts for the degradation of cationic and anionic organic dyes such as eosin Y (EY), methylene blue (MB) and methyl orange (MO), and for the reduction of nitro aromatic pollutants like 2-nitrophenol (2-NP) and 4-nitrophenol (4-NP) to their corresponding amino phenols. Here, we also report for the first time, the simultaneous degradation/reduction of MB, EY and 4-NP by amid-p(MAc-co-AN)–Cu microgel composites. Different parameters affecting the reduction rates such as metal types, the amount of catalysts, temperature and the amount of reducing agent were investigated.

Introduction of double amidoxime group by double post surface modification on poly(vinylbenzyl chloride) beads for higher amounts of organic dyes, As (V) and Cr (VI) removal

In this study, the synthesis of micron-sized poly(vinylbenzyl chloride) (p(VBC)) beads and subsequent conversion of the reactive chloromethyl groups to double amidoxime group containing moieties by post modification is reported. The prepared beads were characterized by SEM and FT-IR spectroscopy. The amidoximated p(VBC) beads were used as adsorbent for the removal of organic dyes, such as eosin y (EY) and methyl orange (MO), and heavy metals containing complex ions such as dichromate (Cr2O7(2-)) and arsenate (HAsO4(2)(-)) from aqueous media. The effect of the adsorbent dose on the percent removal, the effect of initial concentration of adsorbates on the adsorption rate and their amounts were also investigated. The Langmuir, Freundlich and Temkin adsorption isotherms were applied to the adsorption processes. The results indicated that the adsorption of both dichromate and arsenate ions obeyed the Langmuir adsorption model. Interestingly, it was found that the prepared beads were capable of removing significant amounts of arsenate and dichromate ions from tap and river (Sarıcay, Canakkale-Turkey) water.

Facile synthesis of graphene oxide–silver nanocomposite for decontamination of water from multiple pollutants by adsorption, catalysis and antibacterial activity

Here in, we presented a facile one-step method for the synthesis of Graphene oxide-silver (GO-Ag) nanocomposite and its applications as a sorbent for the elimination of some toxic pollutants from aqueous medium, as an efficient catalyst in the individual as well as simultaneous reduction reactions of multiple compounds, and as an antibacterial agent for the destruction of some harmful microorganisms existent in wastewater. GO was prepared using a modified Hummers method and Ag nanoparticles were integrated on GO sheets by chemical reduction of Ag+ ions on the surfaces of GO sheets. The composition and morphology of the nanocomposite was extensively characterized with elemental dispersive X-ray analysis (EDX), Fourier transform infra-red (FT-IR) spectroscopy, transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), and thermal gravimetric analysis (TGA). The GO-Ag nanocomposite demonstrated remarkable adsorption capacities and recyclability for malachite green (MG) and ethyl violet (EV) dyes. Various experimental parameters affecting adsorptive behavior of nanocomposite like temperature, pH, time of contact between dye and adsorbent, and adsorbent dose were evaluated thoroughly. Experimental data was simulated with different adsorption isotherms and kinetic models to evaluate adsorption behavior of both dyes and results confirmed the adsorption of both the dyes to be followed by pseudo 2nd order kinetic model and Langmuir adsorption model. Moreover, adsorbent was regenerated in suitable media for both dyes without any loss in removal efficiency. The catalytic performance for the 2-nitroaniline (2-NA) reduction was investigated in detail. Most importantly, the prepared nanocomposite was found to have potential to adsorb multiple pollutants all together as well as to catalyze the simultaneous reduction of a mixture of dyes (MG, MO, and EV) and 2-NA. An additional advantage of the GO-Ag nanocomposite was its antibacterial activity acquired to the presence of Ag nanoparticles. Two bacterial strains (Gram-negative bacterium, E. coli and the Gram-positive bacterium, S. aureus) were used to test antibacterial activity of composite and the results confirmed the remarkable performance of the nanocomposite in destroying harmful pathogens.