A premixed flame aerosol reactor was used to produce titania particles by oxidation of titanium i... more A premixed flame aerosol reactor was used to produce titania particles by oxidation of titanium isopropoxide vapor. The growth, aggregation of particles, and the agglomerate structure were determined as a function of height in the flame using in situ light scattering and transmission electron microscopy (TEM) measurements. A methodology to determine the sintering characteristic time using light scattering data was established. The light scattering data provided the evolution of the fractal dimension which was then related to the normalized surface area change using a computer simulation. The sintering equation was redeveloped in terms of the normalized surface area, thus not having to account for coagulation effects. Experimental results indicate that isolated titania particles were observed at the high temperatures due to fast sintering. An agglomerate was obtained at downstream locations with an associated change in fractal dimension due to sintering.
Nano-structured sorbent injection is a promising technique for heavy metal capture in combustion ... more Nano-structured sorbent injection is a promising technique for heavy metal capture in combustion systems. The importance of sorbent injection strategies, including the form of the sorbent and its injection location for metal capture and removal is investigated in this study. A multi-component tri-modal aerosol dynamic model was employed to understand the evolution of heavy metals and sorbents, as well as their interactions in the incineration system. Experiments were conducted to assess the performance of in-situ generated SiO 2 , compared with bulk Ti-PICL sorbent, in capturing lead and cadmium from a demilitarization incineration system. Nano-structured SiO 2 generated in-situ was found to be more efficient than the bulk Ti-PICL sorbent because it offers a higher external surface area for condensation. The sorbent injection location is important as it affects the physical properties of the sorbent and the pathway for heavy metal capture. Extensive sintering and reduction in the surface area were observed when sorbent was injected into high temperature flue gas, i.e., directly into the combustor. However, when injected into much lower temperature flue gas, the pathway for heavy metal capture was altered from condensation to inter-particle coagulation due to the nucleation of heavy metal species. This study further revealed that new emission standards can be readily met with an optimal sorbent injection strategy.
Metallic Pd and/or reduced Pd oxide on Pd–TiO2 is found to be the intrinsic active site for O2 re... more Metallic Pd and/or reduced Pd oxide on Pd–TiO2 is found to be the intrinsic active site for O2 removal.
Most of the SnO 2-based perovskite cells(PSC) areeither fabricated in a controlled environment or... more Most of the SnO 2-based perovskite cells(PSC) areeither fabricated in a controlled environment or have low energy conversion efficiencies. In this research, we used a low-temperature processed SnO2as an electron transport layer (ETL) and fabricated planar PSC viaa spin coating technique under ambient condition.By adjusting the concentration of SnO2precursor solution, the efficiency of PSC was enhanced from 4% to 9%. Furthermore,different weight ratiosof 3Dstructured crumpled graphene oxide (CGO), which was synthesized usinga one-step furnace aerosol reactor, were introduced into the SnO2 ETL to improve the PSC performance. The 0.25% CGO ratio resulted in a cell with highestJscof 21 mA/cm 2 and the efficiencyof 11%. Photoluminescence measurements also showed the benefit of doping SnO2layer with CGO in charge transfer in the ETLand from the perovskite layer suppressing carrier recombination. The SnO2-based ETL with the presence of CGO can be a promising ETL for low-cost planar PSCs as well as tandem cells, fabricated under ambient condition.
Atmospheric pollution demands the development of solardriven photocatalytic technologies for the ... more Atmospheric pollution demands the development of solardriven photocatalytic technologies for the conversion of CO 2 into a fuel; state-of-the-art cocatalyst systems demonstrate conversion efficiencies currently unattainable by a single catalyst. Here, we upend the status quo demonstrating that the nanofibrillar conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) is a record-breaking single catalyst for the photoreduction of CO 2 to CO. This high catalytic efficiency stems from a highly conductive nanofibrillar structure that significantly enhances surface area, CO 2 adsorption and light absorption. Moreover, the polymer's band gap is optimized via chemical doping/dedoping treatments using hydrochloric acid, ammonia hydroxide, and hydrazine. The hydrazine-treated PEDOT catalyst exhibits 100% CO yield under a stable regime (>10 h) with a maximum rate of CO evolution (3000 μmol g cat -1 h -1 ) that is 2 orders of magnitude higher than the top performing single catalyst and surpassed only by three other cocatalyst systems. Nanofibrillar PEDOT provides a new direction for designing the next generation of high-efficiency photoreduction catalysts.
Current state-of-the-art synthetic strategies produce conducting polymers suffering from low proc... more Current state-of-the-art synthetic strategies produce conducting polymers suffering from low processability as well as unstable chemical and/or physical properties stifling research and development. Here, we introduce a platform for synthesizing scalable submicron-sized particles of the conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT). The synthesis is based on a hybrid approach utilizing an aerosol of aqueous oxidant droplets and monomer vapor to engineer a scalable synthetic scheme. This aerosol vapor polymerization (AVP) technology results in bulk quantities of discrete solid-state submicron particles (750 nm diameter) with so far the highest reported particle conductivity (330±70 S/cm). Moreover, particles are dispersible in organics and water, obviating the need for surfactants, and remain electrically conductive and doped over a period of months. This enhanced processability and environmental stability enables incorporation in thermoplastic and cementitious composites for engineering chemoresistive pH and temperature sensors.
A crumpled graphene oxide-SnO 2 nanocolumn (CGO-SnO 2 ) composite electrode was fabricated using ... more A crumpled graphene oxide-SnO 2 nanocolumn (CGO-SnO 2 ) composite electrode was fabricated using aerosol-based techniques. First, SnO 2 nanocolumn thin films were fabricated using an aerosol chemical vapor deposition (ACVD) technique. The surface of the nanocolumn was then decorated with CGO by electrospray deposition. The CGO-SnO 2 electrode was utilized for the electrochemical detection and determination of the free chlorine concentration in aqueous solutions using linear sweep voltammetry (LSV) and amperometric i-t curve techniques. The CGO-SnO 2 electrodes worked through the direct electrochemical reduction of hypochlorite ions (ClO -) on the surface of the electrode, which was used to determine the free chlorine concentration. The electrodes operate over a wide linear range of 0.1-10.08 ppm, with a sensitivity of 2.69 lA lM -1 cm -2 . Further, selectivity studies showed that these electrodes easily conquer the electrochemical signals of other common ions in drinking water distribution systems, and only shows the electrochemical reduction signals of free chlorine. Finally, the CGO-SnO 2 electrodes were successfully employed for the detection of free chlorine in tap water solutions (St. Louis, MO 63130, USA) with a sensitivity of 5.86 lA lM -1 cm -2 . Overall, the sensor fabricated using simple and scalable aerosol-based techniques showed a comparable performance to previous studies on amperometric chlorine sensing using carbonbased electrodes.
A series of TiO 2 /nitrogen (N) doped reduced graphene oxide (TiO 2 /NrGO) nanocomposites with va... more A series of TiO 2 /nitrogen (N) doped reduced graphene oxide (TiO 2 /NrGO) nanocomposites with varying concentration and bonding configurations of nitrogen were synthesized by a one-step urea-assisted hydrothermal method, and applied to photoreduction of CO 2 with H 2 O vapor in the gas-phase under the irradiation of a Xe lamp. The effect of the N dopant (doping quantity and bonding configuration) on the catalytic performance of TiO 2 /NrGO was examined. In particular, TiO 2 /NrGO-300, with a 300:1 mass ratio of urea/GO in precursor solution, had the highest CO production yield (356.5 μmole g -1 ), manifesting a significant 4.4 and 2.2-fold enhancements of CO yield over pure TiO 2 and TiO 2 /rGO, respectively. More significantly, TiO 2 /NrGO showed excellent catalytic stability during the prolonged reaction, while catalytic deactivation was observed for both pristine TiO 2 and TiO 2 /rGO after a few hours. The promoting effects of N dopants on the structure and activity of TiO 2 /NrGO were investigated. It was demonstrated that NrGO with an appropriate N quantity and N-bonding configuration acted as a dual-functional promoter, simultaneously enhancing CO 2 adsorption on the catalyst surface and facilitating electron-hole separation, while eventually boosted the photocatalytic performance. Experimental results in this work provide a better understanding of the critical roles of N dopants in the synthesized composites and also inspire the ongoing interest in better design of other N-doped graphene based materials for photoreduction of CO 2 .
Organometallic perovskite solar cells have gained immense attention due to their rapid increase i... more Organometallic perovskite solar cells have gained immense attention due to their rapid increase in efficiency and compatibility with low-cost fabrication methods. However, the material's instability in humid ambient conditions has remained a key challenge for the large-scale fabrication and application of such cells. In this work, we present devices fabricated under 50% humidity with significantly improved long-term stability through three parallel approaches. First, the small molecule hole transport material, Spiro-MeOTAD is replaced by a polymeric material P3HT. Second, the device stability is further enhanced by increasing the thickness of the mesoporous titania scaffold. Finally, tetraethyl orthosilicate (TEOS) is used as a processing additive in the perovskite precursor solution to form an in situ protective layer. On our optimized device, a remarkable long-term device stability of over 1200 hours is achieved. X-ray diffraction patterns suggest over 2500 hours of material stability.
Oriented one-dimensional nanostructures have been of substantial interest as electrodes for lithi... more Oriented one-dimensional nanostructures have been of substantial interest as electrodes for lithium-ion batteries due to the better performance both in terms of initial capacity and lower capacity fade compared to powder pressed electrodes. This paper focuses on a model driven approach to understanding the relationship between the morphology of these oriented nanostructures to the performance of the battery. The Newman-type P2D modeling technique is applied to a porous electrode made up with solid continuous cylinders that extends from the current collectors to separator. TiO 2 columnar nanostructures of varying heights were synthesized using the aerosol chemical vapor deposition (ACVD) and their performance as electrodes in a lithium-ion battery was measured. This electrochemical transport model was validated with the experimental data. This model was used to understand the role of transport parameters, including the diffusivity of lithium in the TiO 2 and the electronic conductivity of the TiO 2 columns, and structural parameters, including the height of the columns and the porosity of the electrode, on the areal capacity of a lithium ion battery at different rates of discharge. The model enables for the prediction of optimized structural parameters of one-dimensional electrodes tailored to the desired application of lithium and sodium-ion batteries.
An electrospray deposition technique to fabricate a perovskite (CH3NH3PbI3) layer for highly stab... more An electrospray deposition technique to fabricate a perovskite (CH3NH3PbI3) layer for highly stable and efficient perovskite solar cells at ambient humidity (30%–50% relative humidity) conditions is demonstrated. A detailed study is conducted to determine the effect of different electrospray parameters on the device performance and to provide a mechanistic explanation of the superior stability of the films. Due to the controlled reactivity that results in the formation of a smooth perovskite film, these cells exhibit stability exceeding 4000 h, in contrast to much lower stability of those fabricated by conventional spin coating methods. Furthermore, the perovskite film deposited by electrospray methods exhibits a self‐healing behavior when exposed to moisture. The authors hypothesize the formation of an intermediate metastable phase and smooth morphology of the film as the reason for this enhanced stability. Electrospray is a scalable technique that provides precise control over the...
Although there are many commercially available methods to capture Hg emission from coal combustio... more Although there are many commercially available methods to capture Hg emission from coal combustion, it is still difficult to use a single method that can control Hg emission both efficiently and economically from coal combustors due to the varying coal seams, operating conditions and downstream control devices. One methodology is the use of sorbent injection at elevated temperatures; and is examined in this study. V 2 O 5 was tested as the sorbent and was found to effectively oxidize elemental mercury (Hg 0 ). Ultrafine V 2 O 5 particles are formed during the combustion process resulting in a high surface area aerosol that can effectively catalyze the oxidation of Hg 0 . The effect of varying chlorine (Cl) concentration in coal on Hg 0 oxidation was also examined. The result shows that Cl can enhance Hg 0 oxidation on the V 2 O 5 surface.
The use of agrochemical-nutrient fertilizers has come under scrutiny in recent years due to conce... more The use of agrochemical-nutrient fertilizers has come under scrutiny in recent years due to concerns that they damage the ecosystem and endanger public health. Nanotechnology offers many possible interventions to mitigate these risks by use of nanofertilizers, nanopesticides, and nanosensors; and concurrently increases profitability, yields, and sustainability within the agricultural industry. Aerosol based foliar delivery of nanoparticles may help to enhance nanoparticle uptake and reduce environmental impacts of chemical fertilizers conventionally applied through a soil route. The purpose of this work was to study uptake, translocation, and accumulation of various gold nanostructures, 30-80 nm, delivered by aerosol application to a watermelon plant. Cellular uptake and accumulation of gold nanoparticles were quantified by Inductively Coupled Plasma-Mass Spectroscopy (ICP-MS). Observations suggested that nanoparticles could be taken up by the plant through direct penetration and transport through the stomatal opening. Observed translocation of nanoparticles from leaf to root shows evidence that nanoparticles travel by the phloem transport mechanism. Accumulation and transport of nanoparticles depend on nanoparticle shape, application method, and nature of plant tissues.
Graphene oxide (GO) materials have demonstrated considerable potential in next-generation water t... more Graphene oxide (GO) materials have demonstrated considerable potential in next-generation water treatment membrane-based technologies, which include antimicrobial applications. GO antimicrobial properties can be further enhanced by preloading or chemically generating surface associated nanoscale silver particles (nAg). However, for these systems, enhanced antimicrobial functionality decreases over time as a function of Ag mass loss via dissolution (as Ag(+)). In this work, we demonstrate facile photocatalytic in situ synthesis of nAg particles by crumpled GO-TiO2 (GOTI) nanocomposites as an approach to (re)generate, thus maintain, enhanced antimicrobial activity over extended operation times. The described photocatalytic formation process is highly efficient and relatively fast, producing nAg particles over a size range of 40 and 120 nm, and with active (111) planes. Additionally, we show in situ surface-based photocatalyzed synthesis of nAg particles at the surface of GOTI nanocomp...
: (SI-1) Experimental Method (SI-2) SEM image of 1-D columnar structure of TiO2 (SI-3) XRD data f... more : (SI-1) Experimental Method (SI-2) SEM image of 1-D columnar structure of TiO2 (SI-3) XRD data for TiO2 (SI-4) Calculation of surfactant concentration profile with time and distance travelled by PSI, PSII and cytochrome b6f (SI-5) Absorption spectra of the membrane in solution and after deposition (SI-6) Onset potential values (SI-7) Linear sweep voltammetry results for case 2 (SI-8) Photocurrent density values (SI-9) Photocurrent action spectra for case 1 and case 2 (SI-10) References (SI-1) Experimental Section: The thylakoid membrane was extracted from cyanobacteria Synechocystis 7803. Synechocystis sp. PCC 6803 strain was grown in BG11 medium at 30˚C under 30 μmol photons m -2 •s -1 with air bubbling in 15 l carboys autotrophically. Cells were harvested at exponential growth phase and resuspended in Resuspension Buffer (RB, 50 mM MES-NaOH, pH 6.5, 10 mM MgCl2, 5 mM CaCl2, 25% glycerol). DNase and protease inhibitor cocktail (Sigma, St. Louis, MO, USA) were added according to manufacturer's protocol. The cell suspension was broken with four cycles of French Press at 1000 psi. After removing unbroken cells by centrifugation at 1,500xg for 15 min, membranes were pelleted by centrifugation at 35,000xg for 30 min. The pelleted thylakoid membrane was washed twice using RB buffer and finally resuspended in RB at 1 mg/ml of chlorophyll a. Columnar TiO2 nanostructured films were deposited onto tin-doped indium oxide (ITO) coated aluminosilicate glass (Delta technologies, CO) using an aerosol chemical vapor deposition (ACVD) process described previously. 1 Briefly, titanium tetraisopropoxide (TTIP, 97% Sigma-Aldrich) was used as a precursor and loaded into a bubbler at 297 K. The N2 carrier gas was kept at a constant flow rate of 0.475 L min -1 through the bubbler. Additionally, a dilution flow rate (N2) of 0.475 L min -1 was
A facile development of highly efficient platinized titanium dioxide (Pt-TiO2) thin films with un... more A facile development of highly efficient platinized titanium dioxide (Pt-TiO2) thin films with unique one dimensional (1D) structure by using versatile gas phase deposition methods was established. The Pt-TiO2 thin films demonstrated excellent carbon dioxide (CO2) photoreduction efficiency with a maximum quantum efficiency of about 2.41%. Carbon dioxide was selectively converted into methane (CH4), with an optimal CH4 yield of over 1300 µmol/g-cat/hr, that is due to the synergistic effects of high surface area and minimized charge barriers by highly oriented single phase crystallinity of the TiO2 thin films, and efficient electron-hole separation by the ultra-small Pt NPs.
In this work, we describe multifunctional, crumpled graphene oxide (CGO) porous nanocomposites th... more In this work, we describe multifunctional, crumpled graphene oxide (CGO) porous nanocomposites that are assembled as advanced, reactive water treatment membranes. Crumpled 3D graphene oxide based materials fundamentally differ from 2D flat graphene oxide analogues in that they are highly aggregation and compression-resistant (i.e. π - π stacking resistant) and allow for the incorporation (wrapping) of other, multifunctional particles inside the 3D, composite structure. Here, assemblies of nanoscale, monomeric CGO with encapsulated (as a quasi core-shell structure) TiO2 (GOTI) and Ag (GOAg) nanoparticles, not only allow high water flux via vertically tortuous nanochannels (achieving water flux of 246 ± 11 L/(m(2)∙h∙bar) with 5.4 µm thick assembly, 7.4 g/m(2)), outperforming comparable commercial ultrafiltration membranes, but also demonstrate excellent separation efficiencies for model organic and biological foulants. Further, multifunctionality is demonstrated through the in situ ph...
Photocatalytic reduction of carbon dioxide (CO 2 ) to hydrocarbons by using nanostructured materi... more Photocatalytic reduction of carbon dioxide (CO 2 ) to hydrocarbons by using nanostructured materials activated by solar energy is a promising approach to recycling CO 2 as a fuel feedstock. CO 2 photoreduction, however, suffers from low efficiency mainly due to the inherent drawback of fast electron-hole recombination in photocatalysts. This work reports the synthesis of nanostructured composites of titania (TiO 2 ) nanoparticles (NPs) encapsulated by reduced graphene oxide (rGO) nanosheets via an aerosol approach. The role of synthesis temperature and TiO 2 /GO ratio in CO 2 photoreduction was investigated. As-prepared nanocomposites demonstrated enhanced CO 2 conversion performance as compared with that of pristine TiO 2 NPs due to the strong electron trapping capability of the rGO nanosheets.
Journal of the Air & Waste Management Association, 2004
A mechanistic model to predict the capture of gas-phase mercury (Hg) species using in situ-genera... more A mechanistic model to predict the capture of gas-phase mercury (Hg) species using in situ-generated titania nanosize particles activated by UV irradiation is developed. The model is an extension of a recently reported model for photochemical reactions by Almquist and Biswas that accounts for the rates of electron-hole pair generation, the adsorption of the compound to be oxidized, and the adsorption of water vapor. The role of water vapor in the removal efficiency of Hg was investigated to evaluate the rates of Hg oxidation at different water vapor concentrations. As the water vapor concentration is increased, more hydroxy radical species are generated on the surface of the titania particle, increasing the number of active sites for the photooxidation and capture of Hg. At very high water vapor concentrations, competitive adsorption is expected to be important and reduce the number of sites available for photooxidation of Hg. The predictions of the developed phenomenological model agreed well with the measured Hg oxidation rates in this study and with the data on oxidation of organic compounds reported in the literature. Hg is a toxic pollutant whose emissions will be regulated from coal-fired boilers. Low-cost, inorganic titanium dioxide-based sorbents are effective at trapping the Hg in combustion exhausts. Detailed phenomenological models that are developed to predict Hg capture rates will be useful at designing and scaling up processes for use in largerscale coal combustion systems.
A premixed flame aerosol reactor was used to produce titania particles by oxidation of titanium i... more A premixed flame aerosol reactor was used to produce titania particles by oxidation of titanium isopropoxide vapor. The growth, aggregation of particles, and the agglomerate structure were determined as a function of height in the flame using in situ light scattering and transmission electron microscopy (TEM) measurements. A methodology to determine the sintering characteristic time using light scattering data was established. The light scattering data provided the evolution of the fractal dimension which was then related to the normalized surface area change using a computer simulation. The sintering equation was redeveloped in terms of the normalized surface area, thus not having to account for coagulation effects. Experimental results indicate that isolated titania particles were observed at the high temperatures due to fast sintering. An agglomerate was obtained at downstream locations with an associated change in fractal dimension due to sintering.
Nano-structured sorbent injection is a promising technique for heavy metal capture in combustion ... more Nano-structured sorbent injection is a promising technique for heavy metal capture in combustion systems. The importance of sorbent injection strategies, including the form of the sorbent and its injection location for metal capture and removal is investigated in this study. A multi-component tri-modal aerosol dynamic model was employed to understand the evolution of heavy metals and sorbents, as well as their interactions in the incineration system. Experiments were conducted to assess the performance of in-situ generated SiO 2 , compared with bulk Ti-PICL sorbent, in capturing lead and cadmium from a demilitarization incineration system. Nano-structured SiO 2 generated in-situ was found to be more efficient than the bulk Ti-PICL sorbent because it offers a higher external surface area for condensation. The sorbent injection location is important as it affects the physical properties of the sorbent and the pathway for heavy metal capture. Extensive sintering and reduction in the surface area were observed when sorbent was injected into high temperature flue gas, i.e., directly into the combustor. However, when injected into much lower temperature flue gas, the pathway for heavy metal capture was altered from condensation to inter-particle coagulation due to the nucleation of heavy metal species. This study further revealed that new emission standards can be readily met with an optimal sorbent injection strategy.
Metallic Pd and/or reduced Pd oxide on Pd–TiO2 is found to be the intrinsic active site for O2 re... more Metallic Pd and/or reduced Pd oxide on Pd–TiO2 is found to be the intrinsic active site for O2 removal.
Most of the SnO 2-based perovskite cells(PSC) areeither fabricated in a controlled environment or... more Most of the SnO 2-based perovskite cells(PSC) areeither fabricated in a controlled environment or have low energy conversion efficiencies. In this research, we used a low-temperature processed SnO2as an electron transport layer (ETL) and fabricated planar PSC viaa spin coating technique under ambient condition.By adjusting the concentration of SnO2precursor solution, the efficiency of PSC was enhanced from 4% to 9%. Furthermore,different weight ratiosof 3Dstructured crumpled graphene oxide (CGO), which was synthesized usinga one-step furnace aerosol reactor, were introduced into the SnO2 ETL to improve the PSC performance. The 0.25% CGO ratio resulted in a cell with highestJscof 21 mA/cm 2 and the efficiencyof 11%. Photoluminescence measurements also showed the benefit of doping SnO2layer with CGO in charge transfer in the ETLand from the perovskite layer suppressing carrier recombination. The SnO2-based ETL with the presence of CGO can be a promising ETL for low-cost planar PSCs as well as tandem cells, fabricated under ambient condition.
Atmospheric pollution demands the development of solardriven photocatalytic technologies for the ... more Atmospheric pollution demands the development of solardriven photocatalytic technologies for the conversion of CO 2 into a fuel; state-of-the-art cocatalyst systems demonstrate conversion efficiencies currently unattainable by a single catalyst. Here, we upend the status quo demonstrating that the nanofibrillar conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) is a record-breaking single catalyst for the photoreduction of CO 2 to CO. This high catalytic efficiency stems from a highly conductive nanofibrillar structure that significantly enhances surface area, CO 2 adsorption and light absorption. Moreover, the polymer's band gap is optimized via chemical doping/dedoping treatments using hydrochloric acid, ammonia hydroxide, and hydrazine. The hydrazine-treated PEDOT catalyst exhibits 100% CO yield under a stable regime (>10 h) with a maximum rate of CO evolution (3000 μmol g cat -1 h -1 ) that is 2 orders of magnitude higher than the top performing single catalyst and surpassed only by three other cocatalyst systems. Nanofibrillar PEDOT provides a new direction for designing the next generation of high-efficiency photoreduction catalysts.
Current state-of-the-art synthetic strategies produce conducting polymers suffering from low proc... more Current state-of-the-art synthetic strategies produce conducting polymers suffering from low processability as well as unstable chemical and/or physical properties stifling research and development. Here, we introduce a platform for synthesizing scalable submicron-sized particles of the conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT). The synthesis is based on a hybrid approach utilizing an aerosol of aqueous oxidant droplets and monomer vapor to engineer a scalable synthetic scheme. This aerosol vapor polymerization (AVP) technology results in bulk quantities of discrete solid-state submicron particles (750 nm diameter) with so far the highest reported particle conductivity (330±70 S/cm). Moreover, particles are dispersible in organics and water, obviating the need for surfactants, and remain electrically conductive and doped over a period of months. This enhanced processability and environmental stability enables incorporation in thermoplastic and cementitious composites for engineering chemoresistive pH and temperature sensors.
A crumpled graphene oxide-SnO 2 nanocolumn (CGO-SnO 2 ) composite electrode was fabricated using ... more A crumpled graphene oxide-SnO 2 nanocolumn (CGO-SnO 2 ) composite electrode was fabricated using aerosol-based techniques. First, SnO 2 nanocolumn thin films were fabricated using an aerosol chemical vapor deposition (ACVD) technique. The surface of the nanocolumn was then decorated with CGO by electrospray deposition. The CGO-SnO 2 electrode was utilized for the electrochemical detection and determination of the free chlorine concentration in aqueous solutions using linear sweep voltammetry (LSV) and amperometric i-t curve techniques. The CGO-SnO 2 electrodes worked through the direct electrochemical reduction of hypochlorite ions (ClO -) on the surface of the electrode, which was used to determine the free chlorine concentration. The electrodes operate over a wide linear range of 0.1-10.08 ppm, with a sensitivity of 2.69 lA lM -1 cm -2 . Further, selectivity studies showed that these electrodes easily conquer the electrochemical signals of other common ions in drinking water distribution systems, and only shows the electrochemical reduction signals of free chlorine. Finally, the CGO-SnO 2 electrodes were successfully employed for the detection of free chlorine in tap water solutions (St. Louis, MO 63130, USA) with a sensitivity of 5.86 lA lM -1 cm -2 . Overall, the sensor fabricated using simple and scalable aerosol-based techniques showed a comparable performance to previous studies on amperometric chlorine sensing using carbonbased electrodes.
A series of TiO 2 /nitrogen (N) doped reduced graphene oxide (TiO 2 /NrGO) nanocomposites with va... more A series of TiO 2 /nitrogen (N) doped reduced graphene oxide (TiO 2 /NrGO) nanocomposites with varying concentration and bonding configurations of nitrogen were synthesized by a one-step urea-assisted hydrothermal method, and applied to photoreduction of CO 2 with H 2 O vapor in the gas-phase under the irradiation of a Xe lamp. The effect of the N dopant (doping quantity and bonding configuration) on the catalytic performance of TiO 2 /NrGO was examined. In particular, TiO 2 /NrGO-300, with a 300:1 mass ratio of urea/GO in precursor solution, had the highest CO production yield (356.5 μmole g -1 ), manifesting a significant 4.4 and 2.2-fold enhancements of CO yield over pure TiO 2 and TiO 2 /rGO, respectively. More significantly, TiO 2 /NrGO showed excellent catalytic stability during the prolonged reaction, while catalytic deactivation was observed for both pristine TiO 2 and TiO 2 /rGO after a few hours. The promoting effects of N dopants on the structure and activity of TiO 2 /NrGO were investigated. It was demonstrated that NrGO with an appropriate N quantity and N-bonding configuration acted as a dual-functional promoter, simultaneously enhancing CO 2 adsorption on the catalyst surface and facilitating electron-hole separation, while eventually boosted the photocatalytic performance. Experimental results in this work provide a better understanding of the critical roles of N dopants in the synthesized composites and also inspire the ongoing interest in better design of other N-doped graphene based materials for photoreduction of CO 2 .
Organometallic perovskite solar cells have gained immense attention due to their rapid increase i... more Organometallic perovskite solar cells have gained immense attention due to their rapid increase in efficiency and compatibility with low-cost fabrication methods. However, the material's instability in humid ambient conditions has remained a key challenge for the large-scale fabrication and application of such cells. In this work, we present devices fabricated under 50% humidity with significantly improved long-term stability through three parallel approaches. First, the small molecule hole transport material, Spiro-MeOTAD is replaced by a polymeric material P3HT. Second, the device stability is further enhanced by increasing the thickness of the mesoporous titania scaffold. Finally, tetraethyl orthosilicate (TEOS) is used as a processing additive in the perovskite precursor solution to form an in situ protective layer. On our optimized device, a remarkable long-term device stability of over 1200 hours is achieved. X-ray diffraction patterns suggest over 2500 hours of material stability.
Oriented one-dimensional nanostructures have been of substantial interest as electrodes for lithi... more Oriented one-dimensional nanostructures have been of substantial interest as electrodes for lithium-ion batteries due to the better performance both in terms of initial capacity and lower capacity fade compared to powder pressed electrodes. This paper focuses on a model driven approach to understanding the relationship between the morphology of these oriented nanostructures to the performance of the battery. The Newman-type P2D modeling technique is applied to a porous electrode made up with solid continuous cylinders that extends from the current collectors to separator. TiO 2 columnar nanostructures of varying heights were synthesized using the aerosol chemical vapor deposition (ACVD) and their performance as electrodes in a lithium-ion battery was measured. This electrochemical transport model was validated with the experimental data. This model was used to understand the role of transport parameters, including the diffusivity of lithium in the TiO 2 and the electronic conductivity of the TiO 2 columns, and structural parameters, including the height of the columns and the porosity of the electrode, on the areal capacity of a lithium ion battery at different rates of discharge. The model enables for the prediction of optimized structural parameters of one-dimensional electrodes tailored to the desired application of lithium and sodium-ion batteries.
An electrospray deposition technique to fabricate a perovskite (CH3NH3PbI3) layer for highly stab... more An electrospray deposition technique to fabricate a perovskite (CH3NH3PbI3) layer for highly stable and efficient perovskite solar cells at ambient humidity (30%–50% relative humidity) conditions is demonstrated. A detailed study is conducted to determine the effect of different electrospray parameters on the device performance and to provide a mechanistic explanation of the superior stability of the films. Due to the controlled reactivity that results in the formation of a smooth perovskite film, these cells exhibit stability exceeding 4000 h, in contrast to much lower stability of those fabricated by conventional spin coating methods. Furthermore, the perovskite film deposited by electrospray methods exhibits a self‐healing behavior when exposed to moisture. The authors hypothesize the formation of an intermediate metastable phase and smooth morphology of the film as the reason for this enhanced stability. Electrospray is a scalable technique that provides precise control over the...
Although there are many commercially available methods to capture Hg emission from coal combustio... more Although there are many commercially available methods to capture Hg emission from coal combustion, it is still difficult to use a single method that can control Hg emission both efficiently and economically from coal combustors due to the varying coal seams, operating conditions and downstream control devices. One methodology is the use of sorbent injection at elevated temperatures; and is examined in this study. V 2 O 5 was tested as the sorbent and was found to effectively oxidize elemental mercury (Hg 0 ). Ultrafine V 2 O 5 particles are formed during the combustion process resulting in a high surface area aerosol that can effectively catalyze the oxidation of Hg 0 . The effect of varying chlorine (Cl) concentration in coal on Hg 0 oxidation was also examined. The result shows that Cl can enhance Hg 0 oxidation on the V 2 O 5 surface.
The use of agrochemical-nutrient fertilizers has come under scrutiny in recent years due to conce... more The use of agrochemical-nutrient fertilizers has come under scrutiny in recent years due to concerns that they damage the ecosystem and endanger public health. Nanotechnology offers many possible interventions to mitigate these risks by use of nanofertilizers, nanopesticides, and nanosensors; and concurrently increases profitability, yields, and sustainability within the agricultural industry. Aerosol based foliar delivery of nanoparticles may help to enhance nanoparticle uptake and reduce environmental impacts of chemical fertilizers conventionally applied through a soil route. The purpose of this work was to study uptake, translocation, and accumulation of various gold nanostructures, 30-80 nm, delivered by aerosol application to a watermelon plant. Cellular uptake and accumulation of gold nanoparticles were quantified by Inductively Coupled Plasma-Mass Spectroscopy (ICP-MS). Observations suggested that nanoparticles could be taken up by the plant through direct penetration and transport through the stomatal opening. Observed translocation of nanoparticles from leaf to root shows evidence that nanoparticles travel by the phloem transport mechanism. Accumulation and transport of nanoparticles depend on nanoparticle shape, application method, and nature of plant tissues.
Graphene oxide (GO) materials have demonstrated considerable potential in next-generation water t... more Graphene oxide (GO) materials have demonstrated considerable potential in next-generation water treatment membrane-based technologies, which include antimicrobial applications. GO antimicrobial properties can be further enhanced by preloading or chemically generating surface associated nanoscale silver particles (nAg). However, for these systems, enhanced antimicrobial functionality decreases over time as a function of Ag mass loss via dissolution (as Ag(+)). In this work, we demonstrate facile photocatalytic in situ synthesis of nAg particles by crumpled GO-TiO2 (GOTI) nanocomposites as an approach to (re)generate, thus maintain, enhanced antimicrobial activity over extended operation times. The described photocatalytic formation process is highly efficient and relatively fast, producing nAg particles over a size range of 40 and 120 nm, and with active (111) planes. Additionally, we show in situ surface-based photocatalyzed synthesis of nAg particles at the surface of GOTI nanocomp...
: (SI-1) Experimental Method (SI-2) SEM image of 1-D columnar structure of TiO2 (SI-3) XRD data f... more : (SI-1) Experimental Method (SI-2) SEM image of 1-D columnar structure of TiO2 (SI-3) XRD data for TiO2 (SI-4) Calculation of surfactant concentration profile with time and distance travelled by PSI, PSII and cytochrome b6f (SI-5) Absorption spectra of the membrane in solution and after deposition (SI-6) Onset potential values (SI-7) Linear sweep voltammetry results for case 2 (SI-8) Photocurrent density values (SI-9) Photocurrent action spectra for case 1 and case 2 (SI-10) References (SI-1) Experimental Section: The thylakoid membrane was extracted from cyanobacteria Synechocystis 7803. Synechocystis sp. PCC 6803 strain was grown in BG11 medium at 30˚C under 30 μmol photons m -2 •s -1 with air bubbling in 15 l carboys autotrophically. Cells were harvested at exponential growth phase and resuspended in Resuspension Buffer (RB, 50 mM MES-NaOH, pH 6.5, 10 mM MgCl2, 5 mM CaCl2, 25% glycerol). DNase and protease inhibitor cocktail (Sigma, St. Louis, MO, USA) were added according to manufacturer's protocol. The cell suspension was broken with four cycles of French Press at 1000 psi. After removing unbroken cells by centrifugation at 1,500xg for 15 min, membranes were pelleted by centrifugation at 35,000xg for 30 min. The pelleted thylakoid membrane was washed twice using RB buffer and finally resuspended in RB at 1 mg/ml of chlorophyll a. Columnar TiO2 nanostructured films were deposited onto tin-doped indium oxide (ITO) coated aluminosilicate glass (Delta technologies, CO) using an aerosol chemical vapor deposition (ACVD) process described previously. 1 Briefly, titanium tetraisopropoxide (TTIP, 97% Sigma-Aldrich) was used as a precursor and loaded into a bubbler at 297 K. The N2 carrier gas was kept at a constant flow rate of 0.475 L min -1 through the bubbler. Additionally, a dilution flow rate (N2) of 0.475 L min -1 was
A facile development of highly efficient platinized titanium dioxide (Pt-TiO2) thin films with un... more A facile development of highly efficient platinized titanium dioxide (Pt-TiO2) thin films with unique one dimensional (1D) structure by using versatile gas phase deposition methods was established. The Pt-TiO2 thin films demonstrated excellent carbon dioxide (CO2) photoreduction efficiency with a maximum quantum efficiency of about 2.41%. Carbon dioxide was selectively converted into methane (CH4), with an optimal CH4 yield of over 1300 µmol/g-cat/hr, that is due to the synergistic effects of high surface area and minimized charge barriers by highly oriented single phase crystallinity of the TiO2 thin films, and efficient electron-hole separation by the ultra-small Pt NPs.
In this work, we describe multifunctional, crumpled graphene oxide (CGO) porous nanocomposites th... more In this work, we describe multifunctional, crumpled graphene oxide (CGO) porous nanocomposites that are assembled as advanced, reactive water treatment membranes. Crumpled 3D graphene oxide based materials fundamentally differ from 2D flat graphene oxide analogues in that they are highly aggregation and compression-resistant (i.e. π - π stacking resistant) and allow for the incorporation (wrapping) of other, multifunctional particles inside the 3D, composite structure. Here, assemblies of nanoscale, monomeric CGO with encapsulated (as a quasi core-shell structure) TiO2 (GOTI) and Ag (GOAg) nanoparticles, not only allow high water flux via vertically tortuous nanochannels (achieving water flux of 246 ± 11 L/(m(2)∙h∙bar) with 5.4 µm thick assembly, 7.4 g/m(2)), outperforming comparable commercial ultrafiltration membranes, but also demonstrate excellent separation efficiencies for model organic and biological foulants. Further, multifunctionality is demonstrated through the in situ ph...
Photocatalytic reduction of carbon dioxide (CO 2 ) to hydrocarbons by using nanostructured materi... more Photocatalytic reduction of carbon dioxide (CO 2 ) to hydrocarbons by using nanostructured materials activated by solar energy is a promising approach to recycling CO 2 as a fuel feedstock. CO 2 photoreduction, however, suffers from low efficiency mainly due to the inherent drawback of fast electron-hole recombination in photocatalysts. This work reports the synthesis of nanostructured composites of titania (TiO 2 ) nanoparticles (NPs) encapsulated by reduced graphene oxide (rGO) nanosheets via an aerosol approach. The role of synthesis temperature and TiO 2 /GO ratio in CO 2 photoreduction was investigated. As-prepared nanocomposites demonstrated enhanced CO 2 conversion performance as compared with that of pristine TiO 2 NPs due to the strong electron trapping capability of the rGO nanosheets.
Journal of the Air & Waste Management Association, 2004
A mechanistic model to predict the capture of gas-phase mercury (Hg) species using in situ-genera... more A mechanistic model to predict the capture of gas-phase mercury (Hg) species using in situ-generated titania nanosize particles activated by UV irradiation is developed. The model is an extension of a recently reported model for photochemical reactions by Almquist and Biswas that accounts for the rates of electron-hole pair generation, the adsorption of the compound to be oxidized, and the adsorption of water vapor. The role of water vapor in the removal efficiency of Hg was investigated to evaluate the rates of Hg oxidation at different water vapor concentrations. As the water vapor concentration is increased, more hydroxy radical species are generated on the surface of the titania particle, increasing the number of active sites for the photooxidation and capture of Hg. At very high water vapor concentrations, competitive adsorption is expected to be important and reduce the number of sites available for photooxidation of Hg. The predictions of the developed phenomenological model agreed well with the measured Hg oxidation rates in this study and with the data on oxidation of organic compounds reported in the literature. Hg is a toxic pollutant whose emissions will be regulated from coal-fired boilers. Low-cost, inorganic titanium dioxide-based sorbents are effective at trapping the Hg in combustion exhausts. Detailed phenomenological models that are developed to predict Hg capture rates will be useful at designing and scaling up processes for use in largerscale coal combustion systems.
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Papers by Pratim Biswas