Nishith Verma

Removal of volatile organic compounds by cryogenic condensation followed by adsorption

Abstract Removal of volatile organic compounds (VOCs) from gaseous effluents by cryogenic condensation and adsorption has been studied. Mathematical models have been developed to predict the extent of removal of a binary mixture of VOCs in air by these two methods under a wide range of operating conditions. The model results are verified with the published work. A model parametric study carried out in this work suggests that if the concentrations of VOCs in the effluent stream vary over a wide range, condensation followed by adsorption is an effective technique to control the emissions. Condensation is found to be suitable if the VOCs emission levels are high (>1%). On the other hand, if the emission levels are low i.e. parts per millions (ppm) or sub ppm, adsorption is a preferred technique for removing the VOCs from the effluent stream. The model results in this work have significance from the perspective of understanding the mechanism of removal of VOCs by these two methods, determining the key operating parameters that control the removal process and also, defining an effective VOC control strategy.

Flux and retention analysis during micellar enhanced ultrafiltration for the removal of phenol and aniline

Studies were done for the removal of organic solutes under aqueous medium through micellar enhanced ultrafiltration (MEUF). The organic solutes selected for experiments consisted of an ionic compound (phenol) and a non-ionic compound (aniline); whereas cetyl pyridinium chloride (CPC), a counter-ionic surfactant was used for the formation of micelles under aqueous medium. UF was carried out under both stirred and unstirred conditions using batch cells. The effect of important operating parameters (applied pressure, solutes and surfactant bulk concentrations) on the extent of separation of the organic solutes were observed and studied. Solubilization of these solutes in CPC micelles were also experimentally ascertained. A mathematical model developed in this study was used to describe the separation of organic solutes by MEUF and predict permeate solute concentrations under varying operating conditions. The effect of pressure and feed CPC concentration on the behaviour of permeate flux was explained as a consequence of the formation of concentration polarized layer of CPC, upstream of the membrane surface. The removal of organic solutes (phenol and aniline) were observed to increase with increase in feed CPC concentration; however, upto about 150 mM, beyond which it was more or less constant. Solubilization equilibrium constant of phenol in CPC micelles was estimated to be around four times that of aniline.

Adsorbents based on carbon microfibers and carbon nanofibers for the removal of phenol and lead from water

This paper describes the production, characteristics, and efficacy of carbon microfibers and carbon nanofibers for the removal of phenol and Pb(2+) from water by adsorption. The first adsorbent produced in the current investigation contained the ammonia (NH(3)) functionalized micron-sized activated carbon fibers (ACF). Alternatively, the second adsorbent consisted of a multiscale web of ACF/CNF, which was prepared by growing carbon nanofibers (CNFs) on activated ACFs via catalytic chemical vapor deposition (CVD) and sonication, which was conducted to remove catalytic particles from the CNF tips and open the pores of the CNFs. The two adsorbents prepared in the present study, ACF and ACF/CNF, were characterized by several analytical techniques, including SEM-EDX and FT-IR. Moreover, the chemical composition, BET surface area, and pore-size distribution of the materials were determined. The hierarchal web of carbon microfibers and nanofibers displayed a greater adsorption capacity for Pb(2+) than ACF. Interestingly, the adsorption capacity of ammonia (NH(3)) functionalized ACFs for phenol was somewhat larger than that of the multiscale ACF/CNF web. Difference in the adsorption capacity of the adsorbents was attributed to differences in the size of the solutes and their reactivity towards ACF and ACF/CNF. The results indicated that ACF-based materials were efficient adsorbents for the removal of inorganic and organic solutes from wastewater.

Development of surface functionalized activated carbon fiber for control of NO and particulate matter

This study investigates the development and potential application of activated carbon fibers (ACF) functionalized with ammonia for control of NO and particulate matter (PM) in diesel engine exhaust. A tubular reactor packed with ACF was used to experimentally study the oxidation of NO at room temperature. Tests were conducted at ACF functionalized with three aqueous ammonia concentrations (3, 5, 10 M), three basic reagents (ammonia, pyridine, amine) and three NO concentrations (100, 300, 500 ppm). After offline investigation, the ACF-packed tubular reactor was installed downstream of the engines exhaust to ascertain the PM capturing efficiency of ACF. The experimental conditions for PM removal included three weights of ACF (2, 3.5, 4.5 g), three engine loads (0, 25, 50 Nm) and three temperatures (150, 300, 450 degrees C). The maximum 70% conversion for NO was obtained at NO concentration of 300 ppm for ACF functionalized with 5M ammonia, whereas maximum 90% reduction in PM was observed at engine load of 25 Nm and 450 degrees C. The study shows significant potential for the ACF based filters in capturing both homogeneous and heterogeneous pollutants emitted from automobiles. Our previously developed transport model incorporating the mechanism for the oxidation of NO was also used to explain the experimental data.

Preparation of surfactant-mediated silver and copper nanoparticles dispersed in hierarchical carbon micro-nanofibers for antibacterial applications

The antibacterial potential of copper (Cu) and silver (Ag) nanoparticles dispersed in a phenolic resin precursor-based multi-scale web of carbon microfibers (ACFs) and nanofibers (CNFs) was assessed in this study. The multi-scale web of ACF/CNF was prepared by growing the CNFs on the ACF substrate by chemical vapor deposition (CVD). The Ag or Cu nanoparticles were used as the catalyst, and acetylene (C2H2) gas was used as the carbon source. An anionic surfactant, sodium dodecyl sulfate (SDS), was used for the preparation of the Cu/Ag-ACF composites to prevent the agglomeration of Cu(II) and Ag(I) ions and achieve a uniform mono-dispersion during the impregnation step. The prepared composites with Cu and Ag dispersed in the ACF and ACF/CNF were characterized using several analytical techniques, including atomic absorption spectroscopy (AAS), Fourier transform infrared (FTIR), X-ray diffraction (XRD), and thermal programming reduction (TPR). The antibacterial properties of the prepared multi-scale or hierarchical structures were evaluated against the gram-negative bacteria Escherichia coli (E. coli) and the gram-positive bacteria Staphylococcus aureus (S. aureus). The results revealed that the prepared Ag-ACF/CNFs were highly effective against these bacteria, achieving a complete inhibition of bacterial growth for over 72 hours.

Copper/zinc bimetal nanoparticles-dispersed carbon nanofibers: A novel potential antibiotic material

Copper (Cu) and zinc (Zn) nanoparticles (NPs) were asymmetrically distributed in carbon nanofibers (CNFs) grown on an activated carbon fiber (ACF) substrate by chemical vapor deposition (CVD). The CVD conditions were chosen such that the Cu NPs moved along with the CNFs during tip-growth, while the Zn NPs remained adhered at the ACF. The bimetal-ACF/CNF composite material was characterized by the metal NP release profiles, in-vitro hemolytic and antibacterial activities, and bacterial cellular disruption and adhesion assay. The synergetic effects of the bimetal NPs distributed in the ACFs/CNFs resulted from the relatively slower release of the Cu NPs located at the tip of the CNFs and faster release of the Zn NPs dispersed in the ACF. The Cu/Zn-grown ACFs/CNFs inhibited the growth of the Gram negative Escherichia coli, Gram positive Staphylococcus aureus, and Methicillin resistance Staphylococcus aureus bacterial strains, with superior efficiency (instant and prolonged inhibition) than the Cu or Zn single metal-grown ACFs/CNFs. The prepared bimetal-carbon composite material in this study has potential to be used in different biomedical applications such as wound healing and antibiotic wound dressing.

Synthesis of phenolic precursor-based porous carbon beads in situ dispersed with copper–silver bimetal nanoparticles for antibacterial applications

Copper (Cu) and silver (Ag) bimetal-dispersed polymeric beads (~0.7 mm) were synthesized by suspension polymerization using phenol and formaldehyde monomers. The Cu:Ag bimetal nanoparticles (Nps) were incorporated into the polymeric matrix at the incipience of gel formation during polymerization using an anionic surfactant. The prepared bimetal-doped polymeric beads were carbonized, activated using steam, and reduced in a hydrogen atmosphere to produce metal Nps-doped porous carbon beads. The prepared bimetal (Cu and Ag) Nps-doped beads exhibited significantly larger anti-bacterial activities than single-(Cu or Ag) metal-doped beads for both gram-positive Staphylococcus aureus and gram-negative Escherichia coli bacteria. The prepared materials contained the total optimized amounts of Cu and Ag. These amounts were smaller (approximately half) than the amount of single metal (Cu or Ag) required for preparing single-metal-doped beads. Although Cu Nps exhibit lesser antibacterial activity than Ag Nps, it enhanced the porosity of the beads. The prepared bimetal beads remained effective for 120 h, completely inhibiting the bacterial growth, and therefore, they are potential antibacterial agents for water purification.

Multi-scale carbon micro/nanofibers-based adsorbents for protein immobilization

In the present study, different proteins, namely, bovine serum albumin (BSA), glucose oxidase (GOx) and the laboratory purified YqeH were immobilized in the phenolic resin precursor-based multi-scale web of activated carbon microfibers (ACFs) and carbon nanofibers (CNFs). These biomolecules are characteristically different from each other, having different structure, number of parent amino acid molecules and isoelectric point. CNF was grown on ACF substrate by chemical vapor deposition, using Ni nanoparticles (Nps) as the catalyst. The ultra-sonication of the CNFs was carried out in acidic medium to remove Ni Nps from the tip of the CNFs to provide additional active sites for adsorption. The prepared material was directly used as an adsorbent for proteins, without requiring any additional treatment. Several analytical techniques were used to characterize the prepared materials, including scanning electron microscopy, Fourier transform infrared spectroscopy, BET surface area, pore-size distribution, and UV-vis spectroscopy. The adsorption capacities of prepared ACFs/CNFs in this study were determined to be approximately 191, 39 and 70 mg/g for BSA, GOx and YqeH, respectively, revealing that the carbon micro-nanofibers forming synthesized multi-scale web are efficient materials for the immobilization of protein molecules.

Axisymmetric multiphase lattice Boltzmann method

A lattice Boltzmann method for axisymmetric multiphase flows is presented and validated. The method is capable of accurately modeling flows with variable density. We develop the classic Shan-Chen multiphase model [Phys. Rev. E 47, 1815 (1993)] for axisymmetric flows. The model can be used to efficiently simulate single and multiphase flows. The convergence to the axisymmetric Navier-Stokes equations is demonstrated analytically by means of a Chapmann-Enskog expansion and numerically through several test cases. In particular, the model is benchmarked for its accuracy in reproducing the dynamics of the oscillations of an axially symmetric droplet and on the capillary breakup of a viscous liquid thread. Very good quantitative agreement between the numerical solutions and the analytical results is observed.

Preparation of asymmetrically distributed bimetal ceria (CeO2) and copper (Cu) nanoparticles in nitrogen-doped activated carbon micro/nanofibers for the removal of nitric oxide (NO) by reduction

A novel multi-scale web of carbon micro/nanofibers (ACF/CNF) was prepared by the catalytic chemical vapor deposition (CCVD), in which CeO2 and Cu nanoparticles (NPs) were in-situ incorporated during a synthesis step. The CVD temperature was adjusted such that the prepared material had asymmetric distribution of the bimetals, with the Cu NPs located at the tips of the CNFs and the CeO2 particles adhered to the surface of the ACF substrate. The prepared bimetals-dispersed web of ACF/CNF was treated with pyridine and the surface functionalized material was applied for the removal of NO by reduction. The complete reduction of NO was achieved at 500°C and for 400ppm NO concentration. Whereas the Cu NPs acted as the catalyst for the reduction, CeO2 facilitated the incorporation of nitrogen from the pyridine source into the ACF/CNF surface. The produced nitrogen containing surface functional groups enhanced the reactivity of the material toward the NO. The bimetals CeO2 and Cu nanoparticles (NPs)-dispersed ACF/CNF produced in this study is a potential candidate for effectively removing NO by reduction, without requiring urea or ammonia used in conventional abatement methods.