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Upgrading CO2-rich natural gas or biogas through CO2 capture is essential to reduce greenhouse gas emissions and to increase its energy density. In this study, clathrate-based CO2 capture from CO2-rich natural gas or biogas was investigated with a primary focus on kinetic CO2 selectivity. The time-dependent CO2 selectivity during clathrate formation for pure water, tetrahydrofuran (THF, 5.6 mol%) solution, and tetra-n-butylammonium chloride (TBAC, 3.3 mol%) solution was examined through direct composition analysis and in situ Raman spectroscopy. In pure water, the CO2 composition in the clathrate phase was much higher at the early stage of clathrate formation than that at equilibrium, indicating that CO2 is kinetically and thermodynamically selective. For both the THF (5.6 mol%) and TBAC (3.3 mol%) solutions, the CO2 composition in the clathrate phase was almost constant during clathrate formation. However, the TBAC (3.3 mol%) solution showed significantly higher CO2 composition (∼74%) throughout the reaction, whereas the THF (5.6 mol%) solution exhibited enrichment of CH4 in the clathrate phase. The experimental results clearly demonstrate that CO2 selectivity is dependent on both kinetics and equilibrium of clathrate hydrates and that the addition of thermodynamic promoters, such as THF and TBAC, can affect kinetic CO2 selectivity as well as equilibrium CO2 selectivity in the clathrate phase.

Highlights • Thermodynamic and kinetic influences of NaCl on HFC-125a hydrate were investigated. • NaCl enrichment in the unconverted solution resulted in a lower conversion. • The presence of NaCl had little effect on the ΔH of HFC-125a hydrate. • The hydrate dissociation was retarded due to the formation of NaCl⋅2H2O. In this study, HFC-125a was selected as a hydrate-forming guest for gas hydrate-based desalination. The thermodynamic and kinetic effects of NaCl on HFC-125a hydrates were investigated with a primary focus on phase equilibria, gas uptake, dissociation enthalpy, and dissociation behavior. The equilibrium curve of HFC-125a hydrate shifted to higher pressure regions at any given temperature depending on the concentration of NaCl. The presence of NaCl also reduced the gas uptake and conversion to hydrates, because of the enrichment of NaCl in the solution during gas-hydrate formation. Even though NaCl did not affect the dissociation enthalpy of the HFC-125a hydrate, the thermograms obtained using a high-pressure micro-differential scanning calorimeter (HP μ-DSC) demonstrated that HFC-125a + NaCl hydrates started to dissociate at lower temperatures due to NaCl in unconverted solutions. Rietveld refinement of powder X-ray diffraction (PXRD) patterns indicated that the HFC-125a hydrate (sII) was transformed into Ih as it dissociated. The dissociation of HFC-125a + NaCl hydrates was retarded and completely ended at higher temperatures compared to the pure HFC-125a hydrate by the sodium chloride dihydrate (NaCl⋅2H2O). Overall, these results could facilitate a better understanding of HFC-125a hydrates in the presence of NaCl; further, they might also be useful in the design and operation of hydrate-based desalination plants using HFC-125a.

A practical-scale sandwich-type honeycomb catalyst reactor incorporating non-thermal plasma was developed for the high-throughput removal of isopropanol (IPA) from air. The Pd/γ-Al2O3/honeycomb catalyst was fabricated by coating a cordierite monolith with γ-alumina powder on which to support the palladium (Pd). The supported catalyst showed good activity and the combination of the honeycomb structure with plasma produced a uniform plasma inside the catalyst chamber. The influence of different parameters, including the energy density (SIE), humidity, initial concentration, and flow rate, on the plasma characteristics and IPA removal efficiency was investigated. The results showed that the SIE has the strongest effect on the IPA removal efficiency. The efficiency of IPA removal was 94.5% and the CO2 selectivity was 85% for an SIE of 180 J/L. Using optical emission spectroscopy, we found that the increased formation of atomic oxygen and reactive species plays an essential role in the oxidation of IPA by plasma catalysis. The main byproducts were identified by GC-MS, which indicated that acetone is the major liquid product. A plausible reaction mechanism for the plasma-catalytic oxidation of IPA is proposed based on the intermediates and byproducts.

In this study, the kinetics of guest exchange in sII (CH4 (90%) + C3H8 (10%)) hydrate – flue gas (CO2 (20%) + N2 (80%)) replacement was investigated to elucidate the replacement mechanism and guest exchange characteristics for hydrocarbon recovery and CO2 sequestration. The Rietveld refinement of Powder X-ray diffraction (PXRD) patterns of the replaced hydrates at two pressures (11.0 MPa and 17.0 MPa) demonstrated that sII hydrate – flue gas replacement occurred iso-structurally. The time-dependent guest compositions in the hydrate phase and the cage occupancy of guest molecules were examined to understand the effect of pressure on guest exchange behaviors. The increased CO2 inclusion in both the small (512) and large (51264) cages at a higher pressure resulted in the larger production of CH4 and C3H8 and a lower N2/CO2 ratio in the hydrate phase. The slower inclusion rate and lower N2 occupancy in the small (512) cages at a higher pressure during replacement were observed due to the competitive inclusion of CO2 and N2 in the small (512) cages. The molecular dynamics (MD) simulation demonstrated that the expansion or shrinkage of hydrate cages caused by guest exchange has a significant impact on the lattice parameter of the replaced hydrates and it was influenced by not only the average molecular size of guest molecules in each cage but also the dispersive movement of the guest molecules in each cage.

The aim of this study was to obtain indigenously the mesoporous silica (AMS) precursor to 3-aminopropyltriethoxysilane (APTES) and utilizing chitosan a templating natural biopolymer. The textural characteristics of AMS were obtained by the SEM (Scanning Electron Microscopy) and BET (Brunauer–Emmett–Teller) surface area measurements. AMS solid possessed specific surface area of 511.77 m2/g and having pore size and pore volume of 3.38 nm and 0.036 cm3/g, respectively. Further, the AMS was characterized by the XRD (X-ray Diffraction) and FT-IR (Fourier Transform- Infra Red) analyses. The mesoporous silica was employed for efficient removal of cadmium(II) and lead(II) from aqueous solutions. The influence of solution pH, initial cadmium(II)/or lead(II) concentrations, contact time, and background electrolyte concentrations were studied to deduce the mechanism involved at solid/solution interface. The equilibrium state adsorption data were utilized for the Langmuir and Freundlich adsorption isotherms and the Langmuir adsorption isotherm showed a good agreement with the experimental data. Uptake was found to be fairly fast and the kinetic modelling suggested that the adsorption of cadmium(II)/or lead(II) by AMS was occurred through fractal-like pseudo-second order kinetics. An increase in background electrolyte concentrations from 0.0001 to 0.01 mol/L NaNO3 did not affect the removal of lead(II), whereas the cadmium(II) removal was slightly suppressed. The XPS (X-ray Photoelectron Spectroscopy) analysis indicated that removal of cadmium(II) or lead(II) occurred through the formation of a chemical bond with the oxygen atoms present with AMS solid. Furthermore, fixed-bed column adsorption was conducted and the loading capacity of cadmium(II) and lead(II) was found to be 11.54 and 8.59 mg/g, respectively.

Removal of dilute N2O from gas streams by a cyclic adsorption–decomposition using Ca13X (Ca2+ exchanged 13X) in combination with N2 nonthermal plasma was studied in this work. Zeolite 13X was found to be the best for N2O uptake among tested commercial zeolites including 4A, H-β and 13X. By modifying 13X with Ca2+ cation using ion-exchange method, the N2O adsorption capacity was greatly enhanced from ca. 3.5 × 10−6 to 80 × 10−6 mol g zeolite - 1 due to the stronger interaction of N2O with Ca2+ cation than that with Na+ cation. Ca. 96% of N2O removal efficiency at a SIEeq (equivalent specific input energy) of 1116 J L−1 was obtained under the cyclic operation of 60-min N2O adsorption (initial concentration: 510 ppm, gas flow rate: 0.5 L min−1) over Ca13X followed by 20-min plasma decomposition of adsorbed N2O in stationary N2 atmosphere. In comparison, a similar performance was reached at a relatively high SIE of 1700 J L−1 as the reactor was operated under continuous plasma condition. The time period of plasma step and therefore the energy consumption could be reduced by properly circulating N2 gas in the reactor. Also, SIEeq was found to decrease with increasing the adsorption time, whereby ca. 95% of N2O removal efficiency could be achieved at a SIEeq of 298 J L−1 as the adsorption time was 180 min. The regeneration of N2O-adsorbed Ca13X by N2 plasma was initiated by plasma-induced desorption of adsorbed N2O followed by decomposing the desorbed N2O in plasma gas phase.

Combined removal of n-heptane and CO using a catalytic reactor coupled with dielectric barrier discharge plasma was investigated over several metal oxide catalysts including bare γ-Al 2 O 3 , Ag 2 O/γ-Al 2 O 3 , MnO/γ-Al 2 O 3 , RuO 2 /γ-Al 2 O 3 and PdO/γ-Al 2 O 3 . In order to effectively utilize the heat generated during plasma discharge for enhancing catalytic reactions, the plasma-catalytic reactor was thermally insulated by covering it with a glass wool jacket. Plasma propagated radially outward from the central high-voltage electrode with gradually increasing the applied voltage, and the temperature decreased with the radial distance due to the decreased plasma intensity, exhibiting a volcanic temperature distribution. The increased reactor temperature could improve the removal of CO and the selectivity toward CO 2 . The results obtained from separate experiments of n-heptane and CO removal showed that the PdO/γ-Al 2 O 3 was the best for the simultaneous removal purpose. The effects of specific input energy ( SIE ), oxygen content, reaction temperature and PdO loading on the simultaneous removal of n-heptane and CO and the formation of byproducts were examined. The removal efficiencies of n-heptane obtained with different catalysts were similar to one another, whereas the removal of CO strongly depended on the type of catalyst. The catalytic activity for the oxidation of CO followed the order: MnO/γ-Al 2 O 3 2 O/γ-Al 2 O 3 2 /γ-Al 2 O 3 2 O 3 . In the present plasma-catalytic hybrid reactor, the mixture of n-heptane and CO was mainly converted into CO 2 , and under an optimized condition, the selectivity toward CO 2 reached 100%.

Large-volume atmospheric-pressure plasma based on corona discharge was successfully generated in a sandwich-type plasma reactor by controlling the humidity of the feed gas. The reactor comprised a 5-cm-high and 9-cm-wide commercial honeycomb monolith and two perforated stainless-steel disk electrodes with 3-mm holes, which covered up both sides of the monolith. The high-voltage applied disk electrode was placed 2 ~ 6 mm away from the monolith, whereas the counter ground electrode typically touched it. The characteristics of air plasma such as power delivery, breakdown voltage, current, and impedance were found to strongly depend on the water vapor content in the feed gas as well as in the monolith, exhibiting an exponential increase of discharge power with increasing the humidity. The discharge characteristics also depended on the gas flow rate and the electrode-monolith distance. Better discharge performance was observed as the electrode was closer to the monolith, and as the air flow rate was higher. Discharge power above 30 W was achieved under the condition of gas flow rate 75 L/min, applied voltage 25 kV, and humidity 2.1%(v/v) when the high-voltage electrode was 2 mm away from the monolith, and the ground electrode kept up against it. The air plasma produced reactive species, being demonstrated by the formation of ozone at several tens of ppm, depending on specific energy input. The plasma source has potential applications in the abatements of odor, organic compounds, and NOx with high throughputs.

The aim of this study is to synthesize the three different hybrid materials precursor to natural biopolymer chitosan. The silanes viz., 3-mercaptopropyl trimethoxysilane, trimethoxy(octyl) silane and 3-aminopropyl triethoxysilane were grafted with the chitosan network and were named as CHMS, CHTS and CHAS, respectively. The materials were characterized by the FT-IR spectrometry, SEM–EDX and XPS analyses. These solids were then employed in the efficient removal of Cr(VI) from aqueous solutions using batch and column reactor operations. The functionalized biomaterials possessed extremely high percent removal of Cr(VI) compared to bare chitosan at wide pH range i.e., pH ∼3.0 to 8.0. A fast uptake of Cr(VI) was occurred and high percentage removal was obtained at wide range of Cr(VI) initial concentrations (7.7–100.58 mg/L). The equilibrium state sorption data were utilized for the Langmuir and Freundlich adsorption isotherm studies. Similarly, an increase in background electrolyte concentrations from 0.0001 to 0.05 mol/L NaNO 3 was assessed for the uptake of Cr(VI) by these hybrid materials. Relatively a fast uptake of Cr(VI) by these hybrid materials were obtained and further the time dependence data were fitted well to the pseudo-second-order and fractal-like pseudo-second-order kinetic models rather a pseudo-first-order kinetic model. Furthermore, a detailed sorption mechanism was included with the help of FT-IR, TOC and XPS analyses. In addition, CHMS and CHTS were used for dynamic studies under column reactor operations. The breakthrough curves were then used for the non-linear fitting of the Thomas equation and the loading capacity of the column for Cr(VI) were estimated.

The present communication addresses the development of a novel hybrid material precursor to natural sericite. The hybrid material is then successfully utilized for efficient removal of cadmium and phenol from aqueous solutions. Initially, sericite was annealed and activated with hydrochloric acid. The activation caused a significant increase in specific surface area of sericite, thereby provided a suitable surface structure for grafting of organosilanes. The activated sericite (AS) was functionalized with 3-aminopropyltriethoxysilane (APTES), and the resultant AS-APTES along with pristine sericite and AS were characterized using SEM–EDX, BET, XRD and FT-IR analyses. Batch reactor studies showed that increase in sorptive pH, contact time, initial concentration and temperature significantly favored the sorption of Cd(II), and a 100-fold increase in background electrolyte concentration did not significantly affect the uptake of Cd(II) or phenol from aqueous solutions. Cd(II) removal was found to be spontaneous and the uptake process was endothermic in nature. Further, the intra-particle diffusion was found to be the rate-limiting step in the sorption of Cd(II). Various physico-chemical parametric studies enabled to discuss the sorption mechanism of these contaminants at the solid/solution interface. In a single pollutant sorption studies, it was deduced that the Cd(II) was forming an inner-sphere complexes, whereas phenol was sorbed through the hydrogen bonding with the amino groups or partitioned within the interspace region. Simultaneous sorption studies suggested that these two pollutants were possibly removed simultaneously by the prevailing hydrophilic and hydrophobic groups. Furthermore, desorption and reusability studies as well as the applicability of the material for real wastewater treatment demonstrated that AS-APTES is a promising solid material for the efficient removal of two important water pollutants i.e., Cd(II) and phenol from aqueous waste.

This paper presents a facile method to fabricate the hole injection layer (HIL) for organic photovoltaic cells (OPVs) and organic light-emitting diodes (OLEDs) using a thermally annealed (NH 4 ) 2 WS 4 precursor under air ambient. The thermal gravimetric analysis curve shows that WS 3 , WS 2 , and WO x are formed by the thermal decomposition of (NH 4 ) 2 WS 4 above 160 °C. The disappearance of the S 2p peak in the photoemission spectra and of the W–S peak in the Raman spectra as well as the decrease in the water contact angle after annealing at 250 °C suggest that (NH 4 ) 2 WS 4 decomposed into WO x . The power conversion efficiency (PCE) of the OPV improved from 1.51% to 3.14% after the insertion of 250 °C-annealed (NH 4 ) 2 WS 4 as the HIL, which is comparable to the PCE of the OPV based on poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate) HIL (3.23%). Furthermore, the luminance efficiency of the OLED with 250 °C-annealed (NH 4 ) 2 WS 4 (15.76 cd/A) was higher than that of the device based on PEDOT:PSS (12.34 cd/A). The results of the in situ deposition experiments revealed that the improved device performance originates from the energy level alignment and electron–hole balance. These data demonstrate that 250 °C-annealed (NH 4 ) 2 WS 4 is a promising candidate for fabrication of the HIL in optoelectronic devices using a facile solution process under air ambient.

Nanopillars-TiO 2 was immobilized onto a borosilicate glass disk using sol–gel template method. The TiO 2 film was immobilized with and without polyethylene glycol as filler media and annealed at 500 °C. The prepared films were characterized by the IR, XRD, XRF and XPS analytical methods. The surface morphology was obtained using FE-SEM and AFM images of these thin films and the BET specific surface area was obtained. Further, the Nanopillars TiO 2 was employed in the photocatalytic degradation of micro-pollutants viz ., diclofenac sodium and tetracycline hydrochloride from aqueous solutions using UV-light under batch reactor operations. Various physico-chemical parametric studies viz ., effect of pH, pollutant concentration and interfering ions was studied to deduce the mechanism involved in photocatalytic degradation of these pollutants. The time dependence degradation of these pollutants provided kinetics of degradation of these pollutants from aqueous solutions. The studies were further extended with total organic carbon measurement using TOC analyser to demonstrate an apparent mineralization of these pollutants. The photocatalytic degradation was assessed in presence of scavengers and several co-existing ions to simulate the data for real wastewater matrix. The hydroxyl radical scavengers 2-propanol and sodium bicarbonate greatly suppressed the catalytic activity of the thin films. However, the singlet oxygen scavenger sodium azide could not affect significantly the catalytic activity of these thin films at least the degradation of diclofenac sodium and tetracycline from aqueous solutions.

Lithium nitrate has been highlighted as a high temperature phase change material with the melting temperature of ~256 °C for the applications of thermal energy storage. However, low thermal conductivity and corrosive property of lithium nitrate needs to be improved for wide applications. This report experimentally investigates thermal properties of a phase change composite consisting of lithium nitrate and porous copper oxide nanowires integrated on folded meshes. Specifically, porous copper oxide nanowires vertically aligned on the folded copper meshes with desired shapes are synthesized by carrying out chemical solution growth and subsequent heat treatment. Then, lithium nitrate is infiltrated in the network of the thermal conductive fillers under vacuum conditions. Our platform can provide a flexible geometrical configuration to enhance thermal performance by modifying the folded geometries to the target objects. As a result, the fabricated phase change composites with 7 vol% of filling materials exhibit the 6.7 times higher thermal conductivities than pure lithium nitrate, showing the excellent thermal transport by the fillers in the composite. Moreover, the porous copper oxide nanowires exhibit excellent anti-corrosive properties to lithium nitrate for stable operation under repeated phase change processes. Finally, the phase change composite heat storages exhibit the 1.3 times faster thermal charging and discharging characteristics than pure lithium nitrate ones.