Biomedical applications of biodegradable polycaprolactone-functionalized magnetic iron oxides nanoparticles and their polymer nanocomposites.

Magnetic nanoparticles (MNPs) have gained significant attention among several nanoscale materials during the last decade due to their unique properties. These properties make them successful nanofillers for drug delivery and a number of new biomedical applications. MNPs are more useful when combined with biodegradable polymers. In this review, we discussed the synthesis of polycaprolactones (PCL) and the various methods of synthesizing magnetic iron oxide nanoparticles. Then, the synthesis of composites that is made of PCL and magnetic materials (with special focus on iron oxide nanoparticles) were highlighted. In addition, we comprehensively reviewed their application in drug delivery, cancer treatment, wound healing, hyperthermia, and bone tissue engineering. Other biomedical applications of the magnetic PCL such as mitochondria targeting are highlighted. Moreover, biomedical applications of magnetic nanoparticles incorporated into other synthetic polymers apart from PCL are also discussed. Thus, great progress and better outcome with functionalized MNPs enhanced with polycaprolactone has been recorded with the biomedical applications of drug delivery and recovery of bone tissues.

Microwave Irradiation-Assisted Synthesis of Zeolites from Coal Fly Ash: An Optimization Study for a Sustainable and Efficient Production Process.

Class F South African coal fly ash was used as a precursor for the synthesis of zeolite A via complete microwave irradiation. To attain optimal conditions for the synthesis of zeolite A with minimum impurities, the microwave synthesis time, irradiation power, and Si/Al ratio were varied. Sodalite with fly ash phases were obtained when the Si/Al ratio in the coal fly ash was not adjusted and when the microwave irradiated coal fly ash slurry was used instead of the extract solution. Increased microwave irradiation time power and time favored the crystallization of zeolite A phase due to sufficient energy needed to ensure the dissolution of Al and Si from coal fly ash. A Brunauer-Emmett-Teller surface area of 29.54 m2/g and a cation exchange capacity of 3.10 mequiv/g were achieved for zeolite A, suggesting its potential application as an adsorbent and cation exchange material for environmental remediation. Complete microwave irradiation offers a greener approach toward zeolite synthesis from coal fly ash compared to conventional hydrothermal and fusion methods that consume a lot of energy and require longer reaction times.

Poly (ether) sulfone electrospun nanofibrous membranes embedded with graphene oxide quantum dots with antimicrobial activity.

This work describes the development of novel electrospun nanofibrous membranes (ENMs) prepared by embedding graphene oxide quantum dots (GOQDs) into poly (ether) sulfone (PES). FTIR and Raman spectroscopy confirmed the successful incorporation of the GOQDs into the PES membranes. The optimal electrospinning polymer concentration that showed no defects or bead formation was at 26 wt% of the PES polymer. Spectroscopy, microscopy and contact angle were some of the techniques used to characterize the ENMs. SEM images showed smooth and unbranched ENMs. The average diameter upon incorporation of the GOQDs was determined to be 2.45 µm. XRD revealed that the GOQDs were structurally close to graphite with an interlaying space of 0.36 nm. The antimicrobial effect of the GOQDs-PES electrospun nanofibrous membranes was assessed against three bacterial strains (Escherichia coli (E. coli), Staphylococcus aureus (S. aureus) and Bacillus cereus (B. cereus)) using the disc diffusion method. The electrospun nanofibres containing 10 wt% of GOQDs showed the most active antimicrobial activity against all three bacterial strains tested. The zones of inhibition ranged from 9 to 40 mm. The minimum inhibitory concentration (MIC) was determined to be 0.5 mg/mL, 0.3 mg/mL and 0.2 mg/mL for E. coli, B. cereus and S. aureus, respectively. The results demonstrated that incorporating GOQDs in the PES nanofibre gives rise to new antimicrobial properties, and as a result, the GOQDs-PES nanofibrous membrane can be used in antimicrobial applications such as water treatment.

Microwave-assisted synthesis of coal fly ash-based zeolites for removal of ammonium from urine.

Zeolites synthesized from biomass waste materials offer a great opportunity in the sustainable utilization of the waste. In this work, energy-efficient processes (i.e. microwave and ultrasound irradiation) were used to synthesize pure phase sodalite (zeolite) from coal fly ash obtained from a power plant in South Africa. The pure-phase sodalite was obtained with a comparatively higher surface area (16 m2 g-1) and cation exchange capacity (2.92 meq. g-1) with 40 min total reaction time. The removal of ammonium from urine was carried out using (i) the coal fly ash-derived sodalite, (ii) raw coal fly ash and (iii) a commercially available natural zeolite (clinoptilolite). The pure phase sodalite exhibited the highest removal efficiency of about 82% and 73% in synthetic and real hydrolyzed urine respectively. The adsorption process followed the pseudo second-order kinetic model and the Freundlich adsorption isotherm, indicating that the adsorption process occurred on a heterogeneous surface.

Mechanistic pathways for the degradation of SMX drug and floatation of degraded products using F-Pt co-doped TiO2 photocatalysts.

This work presents smart pathways to enhance the photocatalytic activity of TiO2 via co-doping with fluorine (F) and platinum (Pt) to form F-Pt co-doped TiO2 photocatalysts and investigates the unique and unusual fluorination of the floated products. Our investigations indicate that the crystalline structure of the photocatalysts was a mixture of anatase and brookite phases and that the nanoparticles of the synthesized nanocomposites had nanometric sizes (4-25 nm). The F-Pt co-doped TiO2 nano-photocatalysts demonstrated degradation of sulfamethoxazole (SMX) drug of >93% within 90 min under direct solar light and 58% degradation within 360 min under a solar simulator. Thus, co-doping TiO2 with F and Pt atoms to form F-Pt co-doped TiO2 nanocomposite is an efficient pathway to achieve high photocatalytic performance escorted with the formation of floating metal-fluoropolymer, unlike pristine TiO2 which has less photocatalytic degradation and no generation of a floating polymer. Our photocatalytic protocol demonstrates that the degradation of SMX started with redox reactions of oxygen and water absorbed on the surface of the prepared nanocomposites to form superoxide anions (O2˙-) and hydroxy radicals (˙OH) which have oxidation superpower. The resultant products were subsequently fluorinated by fluoride radical ions and floated as metal-fluoropolymer.

Facile Synthesis of Nitrogen Doped Graphene Oxide from Graphite Flakes and Powders: A Comparison of Their Surface Chemistry.

Nitrogen-doped graphene oxide (NGO) nanosheets were prepared via a facile one-pot modified Hummer's approach at low temperatures using graphite powder and flakes as starting materials in the presence of a nitrogen precursor. It was found that the morphology, structure, composition and surface chemistry of the NGO nanosheets depended on the nature of the graphite precursor used. GO nanosheets doped with nitrogen atoms exhibited a unique structure with few thin layers and wrinkled sheets, high porosity and structural defects. NGO sheets made from graphite powder (NGOp) exhibited excellent thermal stability and remarkably high surface area (up to 240.53 m2 ·g-1) compared to NGO sheets made from graphite flakes (NGOf) which degraded at low temperatures and had an average surface area of 24.70 m2 ·g-1. NGOf sheets had a size range of 850 to 2200 nm while NGOp sheets demonstrated obviously small sizes (460-1600 nm) even when exposed to different pH conditions. The NGO nanosheets exhibited negatively charged surfaces in a wide pH range (1 to 12) and were found to be stable above pH 6. In addition, graphite flakes were found to be more suitable for the production of NGO as they produced high N-doping levels (0.65 to 1.29 at.%) compared to graphite powders (0.30 to 0.35 at.%). This study further demonstrates that by adjusting the amount of N source in the host GO, one can tailor its thermal stability, surface morphology, surface chemistry and surface area.

Application of gallium nitride nanostructures and nitrogen doped carbon spheres as supports for the hydrogenation of cinnamaldehyde.

This paper reports on the synthesis and use of nanostructures of gallium nitride (GaN NSs) and nitrogen doped carbon spheres (NCSs) as support materials for the hydrogenation of cinnamaldehyde. This study provides the first investigation of GaN as a catalyst support in hydrogenation reactions. The GaN NSs were synthesized via chemical vapour deposition (CVD) in a double stage furnace (750 degrees C) while NCSs were made by CVD in a single stage furnace (950 degrees C) respectively. TEM analysis revealed that the GaN NSs were rod-like with average diameters of 200 nm, while the NCSs were solid with smoother surfaces, and with diameters of 450 nm. Pd nanoparticles (1 and 3% loadings) were uniformly dispersed on acid functionalized GaN NSs and NCS. The Pd nanoparticles had average diameters that were influenced by the type of support material used. The GaN NSs and NCSs were tested for the selective hydrogenation of cinnamaldehyde in isopropanol at 40 and 60 degrees C under atmospheric pressure. A comparative study of the activity of the nanostructured materials revealed that the order of catalyst activity was 3% Pd/GaN > 3% Pd/NCSs > 1% Pd/NCSs > 1% Pd/GaN. However, 100% selectivity to hydrocinnamaldehyde (HCALD) was obtained with 1% Pd/GaN at reasonable conversion rates.

AC-conductance and capacitance measurements for ethanol vapor detection using carbon nanotube-polyvinyl alcohol composite based devices.

We report the preparation of inexpensive ethanol sensor devices using multiwalled carbon nanotube-polyvinyl alcohol composite films deposited onto interdigitated electrodes patterned on phenolite substrates. We investigate the frequency dependent response of the device conductance and capacitance showing that higher sensitivity is obtained at higher frequency if the conductance is used as sensing parameter. In the case of capacitance measurements, higher sensitivity is obtained at low frequency. Ethanol detection at a concentration of 300 ppm in air is demonstrated. More than 80% of the sensor conductance and capacitance variation response occurs in less than 20 s.

Composites of polyvinyl alcohol and carbon (coils, undoped and nitrogen doped multiwalled carbon nanotubes) as ethanol, methanol and toluene vapor sensors.

We investigate the chemical sensing behavior of composites prepared with polyvinyl alcohol and carbon materials (undoped multiwalled carbon nanotubes, nitrogen-doped multiwalled carbon nanotubes and carbon nanocoils). We determine the sensitivity of thin films of these composites for ethanol, methanol and toluene vapor, comparing their conductance and capacitance responses. The composite that exhibits highest sensitivity depends on specific vapor, vapor concentration and measured electrical response, showing that the interactivity of the carbon structure with chemical species depend on structural specificities of the carbon structure and doping.

A facile procedure to shorten multiwalled carbon nanotubes.

Multi-walled carbon nanotubes (MWCNTs) with > 95% purity were synthesized over a Fe-Co/CaCO3 catalyst using chemical vapour deposition (CVD). Both the CNT yield and the outer diameters increased with time on line in the presence of acetylene. More significantly, the tubes were reduced in length and became stub-like with time. TEM analysis revealed that the CNTs commenced shortening after 2 h of reaction time. Reagent residues (e.g., Ca, CaO, OH/COOH groups and Fe-Co oxides) were found not to influence the CNT bond breaking reaction. CNT growth over Fe-Co supported on silica or CaCO3-Ca3(PO4)2 gave similar results. Further, MWCNTs produced by a floating catalyst method, carbon helices produced from Fe-Co-In/A2O3, and N doped CNTs also revealed tube shortening as a function of reaction time under a flow of acetylene. It is thus apparent that MWCNTs can readily be shortened by the facile procedure of depositing carbon from excess C2H2 on the outer walls of CNTs.