One-step CO2 Research Articles

Recurrence Rate after “One-Step” CO2 Fiber Laser Vaporization versus Cystectomy for Ovarian Endometrioma: A 3-Year Follow-up Study

Study ObjectiveTo assess postoperative recurrence rates in patients with endometriomas managed by either “one-step” CO2 fiber laser vaporization or cystectomy. DesignRetrospective study with prospective recording of data. SettingUniversity hospital. PatientsOne hundred twenty-five patients with symptomatic endometriomas. InterventionsPatients underwent a standardized laparoscopic stripping technique (group 1) or cyst vaporization with CO2 fiber laser (group 2). After surgery, patients were incorporated in a prolonged surveillance program with periodic clinical follow-up to check for recurrence of the cyst and/or recurrence of symptoms. Endometrioma recurrence was defined as an ovarian cyst (>10 mm) with a typical aspect arising on the operated ovary identified by transvaginal ultrasound. Measurements and Main ResultsThe primary endpoint was the comparison of recurrence rates between the 2 groups. The secondary endpoint was the evaluation of endometriosis-related pain recurrence in the 2 groups. Other endpoints selected for analysis included the identification of risk factors for the recurrence of endometrioma and of endometriosis-related symptoms. The mean follow-up was 29 ± 13 months (range, 13–49). Recurrence of ovarian endometriosis was recorded in 6.3% of patients (n = 4) treated with cystectomy and in 4.9% of patients (n = 3) managed with CO2 fiber laser (p = .74). Recurrence of endometriosis-related pain was observed in 5 patients (7.8%) in group 1 and in 6 patients (9.8%) in group 2 (p = .67). Mean endometrioma diameter > 5 cm at the time of surgery was identified as the only independent poor prognostic indicator for cyst recurrence (p = .008; odds ratio [OR], 2.21; 95% confidence interval [CI], 1.19–3.32). Moreover, the presence of deep endometriosis at surgery (p = .032; OR, 4.60; 95% CI, 1.14–18.57) and discontinuation of hormonal treatment (p = .015; OR, 3.18; 95% CI, 1.25–8.06) were independent poor prognostic indicators for pain recurrence. ConclusionThis study suggests that one-step CO2 fiber laser vaporization may be effective for endometrioma treatment because it is associated with recurrence rates comparable with those occurring after cystectomy, with the advantage of being an ovarian tissue-sparing technique.

Thermodynamic Analyses of a Moderate-Temperature Process of Carbon Dioxide Hydrogenation to Methanol via Reverse Water–Gas Shift with In Situ Water Removal

CO2 hydrogenation to methanol via the reverse water–gas shift (the CAMERE process) is an alternative method for methanol synthesis. High operating temperatures (600–800 °C) are required for the reverse water–gas shift (RWGS) process because of the thermodynamic limit. In this study, moderate temperatures (200–300 °C) were used for the RWGS part of the CAMERE process by the application of in situ water removal (ISWR). Thermodynamic analyses were conducted on this process using the Gibbs-free-energy-minimization method. The analyses show that by using ISWR with high water-removal fractions (e.g., 0.80–0.99), the CO2 conversion of the RWGS part can be significantly improved at moderate operating temperatures. One-step CO2 hydrogenation to methanol (CTM) with ISWR was also investigated, and it resulted in similar methanol yields. Both processes showed high potential and the ability to promote CO2 hydrogenation to methanol through the use of ISWR.

Highly active and selective Cu-ZnO based catalyst for methanol and dimethyl ether synthesis via CO2 hydrogenation

Highly active and selective Cu-ZnO based catalysts with high BET surface areas and Cu surface areas were prepared using the co-precipitation method. The Cu-ZnO based catalysts were systematically characterized and studied for methanol synthesis. Bifunctional catalysts, composed of Cu-ZnO based catalysts and HZSM-5 were studied for one-step dimethyl ether (DME) synthesis via CO2 hydrogenation. The effects of catalyst preparation conditions, reaction temperature, and pressure on methanol and DME synthesis were investigated and the optimum reaction conditions were determined. The optimized catalyst showed a BET surface area of 128 m2/g and a Cu surface area of over 59.3 m2/g, and demonstrated a high catalytic activity for CO2 hydrogenation. A bifunctional catalyst, prepared by a synthesized Cu-ZnO catalyst and HZSM-5, showed a high DME selectivity in one-step CO2 hydrogenation and methanol dehydration. The high activity and selectivity of the catalysts were attributed to the microstructure of the catalysts, which can be greatly affected by the catalyst preparation process. A long-term stability test showed a considerable decrease in activity within the first 20 h; however, the CO2 conversion (21.4%) and DME selectivity (55.5%) were still very high after 100 h.

Laser-Induced Graphene from Wood Impregnated with Metal Salts and Use in Electrocatalysis

The hybridization of graphene with other inorganic nanostructures has endowed graphene with enhanced and varied functionalities. Here we demonstrate a facile and improved approach to convert biodegradable cedar wood into graphene embedded with various metal nanocrystals (cedar-LIG-M, LIG is laser-induced graphene, M = Cu, Co, Ni, Fe, NiFe) by sonication-assisted soaking and one-step CO2 laser scribing. Organic biomass was transformed to hierarchical porous graphene via laser induction, whereas metal salts were reduced to elemental metals simultaneously by the carbothermal reaction and reducing atmosphere generated during the lignocellulose decomposition. The as-prepared cedar-LIG-M possesses an ordered porous structure, good conductivity, unique ferromagnetic behavior and excellent electrochemical catalytic performance. As a demonstration, the cedar-LIG-NiFe electrode has a low overpotential of 296 mV at a current density of 10 mA cm–2 for oxygen evolution reactions. The performance of the electrode conti...

One-Step Synthesis of Nb2 O5 /C/Nb2 C (MXene) Composites and Their Use as Photocatalysts for Hydrogen Evolution.

Hydrogen production through facile photocatalytic water splitting is regarded as a promising strategy to solve global energy problems. Transition-metal carbides (MXenes) have recently drawn attention as potential co-catalyst candidates for photocatalysts. Here, we report niobium pentoxide/carbon/niobium carbide (MXene) hybrid materials (Nb2 O5 /C/Nb2 C) as photocatalysts for hydrogen evolution from water splitting. The Nb2 O5 /C/Nb2 C composites were synthesized by one-step CO2 oxidation of Nb2 CTx . Nb2 O5 grew homogeneously on Nb2 C after mild oxidation, during which some amorphous carbon was also formed. With an optimized oxidation time of 1.0 h, Nb2 O5 /C/Nb2 C showed the highest hydrogen generation rate (7.81 μmol h-1 gcat-1 ), a value that was four times higher than that of pure Nb2 O5 . The enhanced performance of Nb2 O5 /C/Nb2 C was attributed to intimate contact between Nb2 O5 and conductive Nb2 C and the separation of photogenerated charge carriers at the Nb2 O5 /Nb2 C interface; the results presented herein show that transition-metal carbide are promising co-catalysts for photocatalytic hydrogen production.

CuFe and CuCo supported on pillared clay as catalysts for CO2 hydrogenation into value-added products in one-step

Value-added products synthesis by the one-step CO2 hydrogenation reaction has attracted much attention of researchers. In this paper, three catalysts: Cu/V-AlPILC,CuFe/V-AlPILC, and CuCo/V-Al PILC, prepared by impregnation method on Al-pillared clay support were studied. The effect of Fe and Co additives on the physicochemical properties of Cu-based catalysts was characterized by X-ray powder diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), scanning electron microscope (SEM), N2 adsorption/desorption isotherms, temperature programmed reduction (TPR), Transmission Electron Microscope (TEM), X-ray photoelectron spectroscopy (XPS), N2O decomposition, CO2 and NH3 temperature-programmed desorption (CO2-TPD and NH3-TPD), and Fourier Transform Infrared Spectroscopy after gaseous pyridine adsorption (Py-FTIR) techniques. These catalysts were evaluated for CO2 hydrogenation into value-added products at temperatures ranging from 250 to 300 °C for 3 h and 40 bar pressure. Stability test was performed at 250 °C for 24 h and 40 bar pressure. The catalytic behavior revealed that a linear relationship does exist between the CO2 conversion with the metallic area. The DME and methanol synthesis showed a correlation with the basic and acid sites. The CuFe/V-Al PILC catalyst showed the highest selectivity for methanol and DME at 250 °C.

Molybdenum oxide/carbon composites derived from the CO2 oxidation of Mo2CTx (MXene) for lithium ion battery anodes

Multilayer Mo2CTx MXene is used as a precursor to produce molybdenum oxide (MoO2)-disordered carbon hybrid materials using a one-step CO2 oxidation. The composites show clear, short plateaus in the charge/discharge curves as well as reversible phase transition peaks in cyclic voltammetry for the resulting MoO2. The electrochemical measurements support the generation of the metal oxide in the resulting composite materials. The generation of molybdenum oxide from Mo2CTx is verified from the plateau in Li+ charge-discharge profile as wells as various characterizations of XRD, XPS, etc. The resulting MoO2 active material coated on a copper foil shows a Li-ion capacity of 323 mAh/g at 50 mA/g (0.1 C) and 180 mAh/g at 1 A/g (4.0 C) with 85% retention for approximately 300 cycles.

Synthesis and Charge Storage Properties of Hierarchical Niobium Pentoxide/Carbon/Niobium Carbide (MXene) Hybrid Materials

Orthorhombic niobium pentoxide (T-Nb2O5) offers high capacitance and fast charging–discharging rate capabilities when used as an electrode material for Li-ion capacitors. A homogeneous distribution of T-Nb2O5 nanoparticles in a highly conductive matrix represents a promising approach to maximize its energy and power densities. Here we report a one-step CO2 oxidation of two-dimensional (2D) Nb2CTx, a member of the MXenes family of 2D transition metal carbides, which leads to a hierarchical hybrid material with T-Nb2O5 nanoparticles uniformly supported on the surface of Nb2CTx sheets with disordered carbon. The oxidation temperature, duration, and CO2 flow rate determine the T-Nb2O5 crystallite size as well as the structure, composition, and the charge storage properties of the hybrid material. Fifty micrometer thick electrodes of the hybrid material exhibit high capacitance (330 C g–1 and 660 mF cm–2 at a charge–discharge time of 4 min) and good cycling performance in a nonaqueous lithium electrolyte. The ...

Facile preparation of highly efficient CuO-ZnO-ZrO2/HZSM-5 bifunctional catalyst for one-step CO2 hydrogenation to dimethyl ether: Influence of calcination temperature

CuO-ZnO-ZrO2/HZSM-5 bifunctional catalysts were prepared by a facile route of solid-state reaction and tested for one-step synthesis of dimethyl ether (DME) from CO2 hydrogenation. The effects of calcination temperature (300–600°C) on the physicochemical and catalytic properties of the bifunctional catalysts were investigated by XRD, N2 adsorption, XPS, N2O chemisorption, SEM, H2-TPR, NH3-TPD, and CO2-TPD techniques. The results show that both the CO2 conversion and DME selectivity of the bifunctional catalysts decrease with the increase in calcination temperature, which can mainly be attributed to the decrease of metallic copper surface area (SCu), adsorption capacity of CO2, specific surface area, and reducibility of CuO.

Hydrogenation of CO2 into hydrocarbons over bifunctional system Cu–ZnO/Al2O3 + HZSM-5: Effect of proximity between the acidic and methanol synthesis sites

A one-step CO2 hydrogenation reaction into hydrocarbons (HC) using a bifunctional system constituted by a methanol synthesis catalyst [Cu–ZnO–Al2O3 (CZA)] and a zeolite (HZSM-5) has been studied. The influence of the catalyst bed configuration on activity, selectivity, and HC yield has been evaluated. The results obtained at TR = 623 K, PR = 3.0 MPa and WHSV = 6000 h−1 show that CO2 hydrogenation and hydrocarbon selectivity were strongly influenced by the proximity between oxide and zeolite, whatever the disposition of the two catalytic active sites. Indeed, the highest conversion and the best yield of hydrocarbons (mainly C2) were obtained with the M1 bifunctional catalysts in which the oxide–zeolite proximity is the lowest. This is ascribed to the hydrogen spillover phenomenon, which does not promote the carbon chain growth.

Expression, purification and activity assay of a patchoulol synthase cDNA variant fused to thioredoxin in Escherichia coli

Probing a cDNA library extracted from Pogostemon cablin (Indian Patchouli) with gene specific primers, a variant of patchoulol synthase PTS (GenBank acc. No.: AY508730) was amplified, cloned, and sequenced. The amino acid sequence deduced from the cloned cDNA exhibited a sequence variation of 3.4% compared to the annotated sequence. The enzyme variant tended to form inclusion bodies when expressed in Escherichia coli. The coding sequence was fused to the T7-tag, His-tag and to thioredoxin. Constructs were expressed in three different E. coli expression strains, with several strain/construct combinations yielding soluble enzyme. By fusion to thioredoxin and careful codon optimization of the eukaryotic sequence, soluble expression could be improved on average by 42% in comparison to an unoptimized, His-tagged construct. The thioredoxin-fused protein was successfully purified using a one-step Co2+-IMAC purification procedure. Bioactivity assays using prepared farnesyl diphosphate (FDP) in milliliter-scale batch reactions, showed activity of the fused enzyme even with thioredoxin attached. The product spectrum of the enzyme was compared to patchouli oil standards by GC–MS and the main products were identified. Interestingly, the variant showed a shift in product spectrum with germacrene A being the most abundant product instead of patchouli alcohol. In silico structural modeling shows a possible chemical and structural change in the active site of the enzyme, which might be responsible for the shift in product composition.

Catalytic behaviour of a bifunctional system for the one step synthesis of DME by CO2 hydrogenation

One-step CO2 hydrogenation reaction to dimethyl ether (DME) on a bifunctional system constituted by Cu–ZnO–ZrO2 (ZCZ) methanol synthesis catalyst and HZSM-5 zeolite was studied. The influence of the reactor configuration in terms of combination procedure of the admixed samples on activity, selectivity and DME yield has been evaluated. The results obtained at TR=513K, PR=3.0MPa and GHSV=9000NLgcat−1h−1 show a superior DME productivity (4.4mmolkgZCZ−1s−1) using the bifunctional catalyst prepared by physical mixing. A combined effect of active sites located at metal/oxide(s)–acid interface was claimed as the main factor affecting the CO2 conversion and DME productivity. The strong surface acidity of ZCZ catalyst is not suitable to drive DME synthesis through a consecutive mechanism, while DME formation effectively proceeds on weak and medium acid sites of HZSM-5.

Hybrid Cu–ZnO–ZrO2/H-ZSM5 system for the direct synthesis of DME by CO2 hydrogenation

One-step CO2 hydrogenation reaction to dimethyl ether (DME) was studied on a hybrid system characterized by different reactor bed configurations (physical mixing, dual-bed and mono-bed). Homemade Cu–ZnO–ZrO2 methanol catalytic system and a commercial H-ZSM5 zeolite were used to realize the hybrid system. The influence of preparation method on activity, selectivity and yield in the temperature range of 453–513K at 3.0MPa and CO2/H2/N2 feed concentration of 3/9/1 has been evaluated. The results obtained under kinetic conditions show a superior specific productivity of ca.430 gtotal MeOH kgcat−1 h−1 at 513K using the hybrid catalyst prepared by physical mixing. A combined effect of sites located at metal/oxide(s)-acid interface to drive DME synthesis through a consecutive mechanism was claimed as the main factor affecting the CO2 conversion and DME productivity.

Activated carbon prepared from oil palm stone by one-step CO2 activation for gaseous pollutant removal

Abstract The feasibility of preparing activated carbons from oil palm stones by one-step CO2 activation was studied. These oil palm stones are major solid wastes generated from palm-oil processing mills. Experimental results showed that the particle size of the starting material and heating rate appeared to have no significant effects on the BET surface areas of the activated carbons but CO2 flow-rate had a significant influence. Increasing the heating rate resulted in slight reductions in the micropore surface areas. The BET and micropore surface areas of the activated carbons were also found to be dependent on the activation temperature and the hold time. The optimum conditions for activation were for an activation temperature of 850°C and a hold time of 2 h, at which the BET and micropore surface areas were found to be maximum at 1410 and 942 m2 g−1 respectively. The pore size distributions of the activated carbon also confirmed these conditions. The development of microporosities in these activated carbons suggest their potential applications in gaseous pollutant adsorption. From chemical characterisation, the activation temperature was found to have an insignificant effect on the inorganic components of the activated carbons but possible effects on their surface functional groups. The amounts of NO2 adsorbed onto the oil-palm-stone activated carbons and a commercial one were measured during adsorption tests. The relationship between the amount of gas adsorbed and the BET surface area of the activated carbon indicated that the adsorptive capacity was linearly proportional to the surface area.

Non-invasive assessment of cardiac output and stroke volume in patients during exercise. Evaluation of a CO2-rebreathing method.

A one-step CO2 rebreathing method for the determination of cardiac output and stroke volume (SV) has been evaluated by comparison with the direct Fick technique during recumbent exercise (10-90 W) in 13 patients. In an initial analysis, the influence of different rebreathing times and of correction for haemoglobin concentration was studied. The best correlation with the direct Fick technique was obtained with the longest analysis time, i.e. 21 s, and correction for variations in haemoglobin concentration further improved the correlation. Consequently, an analysis time of 21 s and correction for haemoglobin have been used. At low cardiac outputs, the CO2-rebreathing method overestimated the flow compared to the Fick technique. The correlation between the methods, however, was so good that a valid estimate of cardiac output could be obtained from the CO2 rebreathing method with appropriate corrections (Cardiac output, CO2 method = 2.7 + 0.77. Cardiac output, Fick; r = 0.91; Residual Standard deviation (SD res) = 0.77 l X min-1). Stroke volumes measured with the CO2 rebreathing method did not differ significantly from those obtained with the direct Fick technique, although there was a tendency to overestimate stroke volume with the CO2 rebreathing method (SV, CO2 method = 12 + 0.89 X SV, Fick; r = 0.82; SD res = 11 ml).