Absorption-desorption Experiments Research Articles

A magnetic nanocatalyst based on Bronsted acid and Lewis acid centers for the efficient synthesis of polycyclic melting 1,5-benzodiazepines

In this study, 3-(Triethoxysilyl)propyl chloride (CPTES) was used to modify the surface of magnetic nanoparticles Fe3O4@SiO2, and aminomethylphosphonic acid (AMPA) was further anchored on the surface. Then, Ce (III) was used as the ligand to immobilize the surface of the modified material with N/O as the donor. Magnetic nanocatalysts (Fe3O4@SiO2@CPTES@AMPA@CeCl3) were successfully prepared. The prepared catalysts were characterized by infrared spectroscopy (FT-IR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen absorption-desorption experiment (BET), vibrating sample magnetometer (VSM), energy dispersive spectroscopy (EDS) and inductively coupled plasma atomic emission spectrometry (ICP-AES). A synergetic effect of Brønsted and Lewis acid (AMPA and CeCl3) of the magnetic nanocatalyst was examined to active carbonyl, imine or enamine bonds for the synthesis of polycyclic fused 1,5-benzodiazepine with quaternary carbon centers or quinoxaline ring in a one-pot method. It was found that this catalyst exhibited excellent catalytic activities (TON up to 111368, TOF up to 110232 h−1) and high selectivities in the synthesis of fused 1,5-benzodiazepine compounds (22 examples, 85–96 % yields). The mechanism for the synthesis of polycyclic fused 1,5-benzodiazepine catalyzed by Fe3O4@SiO2@CPTES@AMPA@CeCl3 was proposed. The nanocatalyst was readily recovered by simple magnetic decantation and can be recyclable without obviously reducing catalytic activity up to seven times.

Synergistic Catalysis of SO42-/TiO2-CNT for the CO2 Desorption Process with Low Energy Consumption.

To address the issue of high energy consumption associated with monoethanolamine (MEA) regeneration in the CO2 capture process, solid acid catalysts have been widely investigated due to their performance in accelerating carbamate decomposition. The recently discovered carbon nanotube (CNT) catalyst presents efficient catalytic activity for bicarbonate decomposition. In this paper, bifunctional catalysts SO42-/TiO2-CNT (STC) were prepared, which could simultaneously catalyze carbamate and bicarbonate decomposition, and outstanding catalytic performance has been exhibited. STC significantly increased the CO2 desorption amount by 82.3% and decreased the relative heat duty by 46% compared to the MEA-CO2 solution without catalysts. The excellent stability of STC was confirmed by 15 cyclic absorption-desorption experiments, showing good practical feasibility for decreasing energy consumption in an industrial CO2 capture process. Furthermore, associated with the results of experimental characterization and theoretical calculations, the synergistic catalysis of STC catalysts via proton and charge transfer was proposed. This work demonstrated the potential of STC catalysts in improving the efficiency of amine regeneration processes and reducing energy consumption, contributing to the design of more effective and economical catalysts for carbon capture.

Enhancing CO2 desorption rate in rich MEA solutions by metal-modified attapulgite catalyst

To overcome the high energy consumption of the CO2-rich monoethanolamine (MEA) solution regeneration process, this study proposes to catalytically promote CO2 desorption using transition metal-modified attapulgite (ATP) composite catalysts (M/ATP, M = Ni, Zr) in a 5 M CO2-loaded MEA solution at 90 °C. The catalysts were characterized by XRD, FT-IR, BET, and Py-IR. The influences of different metals and metal salts on the activity of CO2 desorption for the ATP-based composite catalyst were studied. The findings proved that the introduction of metal oxide enhanced the activity of catalytic CO2 desorption for the ATP catalyst and reduced the relative energy requirement. Ni/ATP presented the superior catalytic activity, with an increase of 195 % and 144 % in the rate of CO2 desorption and desorption amount, respectively, compared with the noncatalytic desorption process. The excellent catalytic performance of metal-modified ATP composite catalysts was mainly due to the enhanced Brønsted acid sites. After 8 cycles of CO2 absorption–desorption experiment, the Ni/ATP catalyst still showed excellent stability. The introduction of the Ni/ATP catalyst had no adverse impact on the CO2 absorption in the MEA solution. Moreover, a possible catalytic MEA solution regeneration pathway over Ni/ATP was suggested based on FT-IR and 13C NMR measurements.

Solid base LDH-catalyzed ultrafast and efficient CO2 absorption into a tertiary amine solution

Due to its high capacity, low energy consumption, and low corrosiveness, chemical absorption using aqueous tertiary amine solutions is a potential approach for CO2 capture. The fundamental limitation of this technology is its low CO2 absorption kinetics (rate), which impedes its large-scale use. Here, five typical solid-base catalysts, MgAl-layered double hydroxide (LDH) and its corresponding layered double oxide (LDO), BaCO3, MgCO3, and CaCO3, were adopted to improve the rate of CO2 absorption in an aqueous methyldiethanolamine solution (MDEA). The results indicated that LDH and LDO promoted CO2 absorption, with LDH exhibiting significantly superior catalytic activity. In particular, compared to the non-catalytic absorption, using LDH considerably improved the CO2 absorption rate by 92.7%. The catalytic effects of LDH on CO2 absorption were demonstrated by 13C NMR and FT-IR techniques, and theoretical calculation. A possible catalytic CO2 absorption mechanism over LDH was suggested. Additionally, the stability of LDH was certified with 10 cyclic CO2 absorption–desorption experiments. The excellent catalytic CO2 absorption performance of LDH may be primarily owing to the chemical absorption improvement mechanism of basic sites. Therefore, the LDH-catalyzed CO2 absorption process is a promising option for increasing the CO2 absorption rate in tertiary amine solution. This work may open up a new approach to developing plentiful and affordable solid-base catalysts for CO2 capture technologies with faster absorption kinetics and lower energy requirement.

Energy-efficient carbon dioxide capture using piperazine (PZ) activated EMEA+DEEA water lean solvent: Performance and mechanism

Water vapor contained in industrial waste gas will be accumulated in non-aqueous amine solvents when used for CO2 capture and subsequently affect capture efficiency. While Piperazine (PZ) could be considered as an activator of the solution. Hence the effect of different contents of water and PZ added into the non-aqueous amine solvents on the CO2 capture performance has been investigated. 13C NMR has been used to identify the compounds present in aqueous CO2-rich amine solvents to characterize the mechanism of reactions. The energy consumption using 2-(ethylamino)ethanol (EMEA) water-lean amine solvent and aqueous monoethanolamine (MEA) solution was tested and compared on lab-scale, and further a comprehensive evaluation in a bench-scale pilot plant has been performed; It was found that the regeneration efficiency of the solution was reduced by approximately 10% when the water content was 10 wt%. The addition of PZ can recover the regeneration efficiency of the solvent to 94.2%. And its energy consumption was reduced by about 45% compared to the aqueous MEA solution in a 72-hour continuous absorption-desorption experiment. The results demonstrated that the aqueous PZ solution could improve the regeneration efficiency by involving in the proton transfer process. This work has proven that the blend of water-lean amine solvent and PZ is a novel, energy-efficient absorbent for CO2 capture.

Experimental study of CO2 capture by nanoparticle-enhanced 2-amino-2-methyl-1-propanol aqueous solution.

2-Amino-2-methyl-1-propanol (AMP) is often used as a moderator to enhance the CO2 capture capacity of absorbents due to its unique spatial site resistance structure, and relatively few studies have been conducted on the enhancement of AMP aqueous solutions by nanoparticles for CO2 capture. In order to investigate the effect of nanoparticles on the CO2 capture performance of AMP aqueous solution, different nanofluids were formulated in this paper using a two-step method, and a bubbling reactor and an oil bath were used as the experimental setup for absorption/desorption, and through comparative experiments, it was found that the type of nanoparticles, the solid content, and the different parameters have great influences on the CO2 absorption load and desorption rate. The experimental results show that the addition of TiO2 nanoparticles to the AMP base solution can accelerate the absorption-desorption mass transfer rate of CO2, and there exists an optimal solid content of 1 g L-1 (±1.0%, ±2.5%); after multiple absorption-desorption experiments, good cycling performance can still be achieved. The experimental results of the nanofluid-promoted mass transfer mechanism are also illustrated and analyzed in this paper.

Investigating the concentration distribution characteristics of methane in large storage facility using desorption-concentration gradient method and CFD simulation

The continuous methane emission from the coal piles is associated with many environmental problems and safety risks, in large storage facility. The methane emission parameters of coal piles and the concentration distribution characteristics of methane, which are the basis of ventilation design, are rarely reported in large storage facilities. In this study, based on the mass-transfer diffusion theory, desorption-concentration gradient method for determining methane emission parameters of coal piles in large facilities is proposed. In this method, firstly, the coal pile methane diffusion coefficient was deduced by conducting the coal particles absorption-desorption experiments and the particle-size distribution. Then, combing the diffusion coefficient and methane concentration-gradient on the coal pile surface, the coal pile methane diffusion flux was calculated. Further, when methane diffusion flux was utilized as the source item for CFD calculations, the results were consistent with the onsite measured values, which demonstrated the accuracy of this method. The CFD simulation results show that methane has diffusion characteristics that adhere upward along the slope of the coal pile and converge on the coal ridge. The methane flow reaches the dome upwards, where a higher concentration is formed. Both the coal pile volume and the methane diffusion flux will affect the concentration distribution of methane in large storage facility. For a larger diffusion flux, the explosion limit will be exceeded, and measures need to be taken to eliminate the safety risk. These findings provide principal data and analysis guide for optimized design of ventilation performance in closed industrial building.

Synergistic promotion for CO2 absorption and solvent regeneration by fine waste red mud particles on in amine-based carbon capture: Performance and mechanism

Using waste red mud as catalysts for enhancing mass transfer and boosting amine-based solvent regeneration is a promising option for both resources recycling and efficient carbon capture. Here, the effect of fine red mud particles was firstly investigated on carbon dioxide (CO2) absorption and desorption. The Brownian motion and shuttle effect of submicron or micron red mud particles play a positive role in reducing the concentration boundary layer and updating the CO2-species concentration of liquid/gas film, which is beneficial for mass transfer enhancement. Additionally, the composite metal oxides of red mud support abundant acid/base active sites for water dissociation, which can promote the proton transfer and boost carbamate decomposition. Therefore, the average enhancement factor is ∼1.49 and the average absorption rate increases by 22.8 %; while the maximal desorption rate (2.14 mmol/min) increases by 289 % and relative heat duty decreases by 16.3 %, after adding 2.5–5 % red mud particles. The continuous CO2 absorption–desorption experiments verify red mud increases the capture efficiency from 51.6 % (blank test) to 62.4 %. The results offer a favorable technology for reuse of industrial solid waste in the field for low-energy carbon capture.

Chemical and Physical Ionic Liquids in CO2 Capture System Using Membrane Vacuum Regeneration.

Carbon Capture Utilization and Storage technologies are essential mitigation options to reach net-zero CO2 emissions. However, this challenge requires the development of sustainable and economic separation technologies. This work presents a novel CO2 capture technology strategy based on non-dispersive CO2 absorption and membrane vacuum regeneration (MVR) technology, and employs two imidazolium ionic liquids (ILs), [emim][Ac] and [emim][MS], with different behavior to absorb CO2. Continuous absorption–desorption experiments were carried out using polypropylene hollow fiber membrane contactors. The results show the highest desorption behavior in the case of [emim][Ac], with a MVR performance efficiency of 92% at 313 K and vacuum pressure of 0.04 bar. On the other hand, the IL [emim][MS] reached an efficiency of 83% under the same conditions. The MVR technology could increase the overall CO2 capture performance by up to 61% for [emim][Ac] and 21% for [emim][MS], which represents an increase of 26% and 9%, respectively. Moreover, adding 30%vol. demonstrates that the process was only favorable by using the physical IL. The results presented here indicate the interest in membrane vacuum regeneration technology based on chemical ILs, but further techno-economic evaluation is needed to ensure the competitiveness of this novel CO2 desorption approach for large-scale application.

Cerium-enriched magnetic/recyclable dual-acid nanocatalyst for one-pot three-component synthesis of functionalized 1,5-benzodiazepines

Cerium enriched magnetic dual-acid nanocatalyst (CoFe2O4@SiO2@APTES@ATA-CeCl3) as green and recoverable nanocatalyst was prepared. The novel nanocatalyst was characterized by Fourier transform infrared spectroscopy (FT-IR), powder X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), inductively coupled plasma atomic emission spectrometry (ICP-AES), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), nitrogen absorption-desorption experiment, and vibrating sample magnetometer (VSM). The dual-acid nanocatalyst was able to efficiently catalyze the synthesis of functionalized 1,5-benzodiazepines following through a three-component domino reaction of various substituted o-phenylenediamine, 1,3-dicarbonyl compounds, and phenylacetaldehyde. The dual-acid sites of Brønsted acid (2-aminoterephthalic acid (ATA)) and Lewis acid (CeCl3) of the catalysts were determinant features. Furthermore, a plausible catalytic mechanism has been proposed. The dual-acid nanocatalyst can be simply separated and reused without any remarkable decrease within the yield after six runs.

Novel biphasic solvent of AEP/1-propanol/H2O for CO2 capture with efficient regeneration performance and low energy consumption

Biphasic solvents have been attracting increasing attention in CO2 capture recently due to its energy-saving potential. However, most current biphasic solvents still face the problem of limited desorption performance. To solve the problem, a novel biphasic solvent of 1-(2-aminoethyl)piperazine (AEP)/1-propanol/H2O solution was proposed. The absorption capacity was 1.26 mol CO2·mol−1 amine, which was 2.3 times that of MEA. The regeneration efficiency was 74% and the cyclic capacity after 5 absorption-desorption experiments was 0.90 mol CO2·mol−1 amine, which was 2.7 times that of MEA. The absorption-desorption performance of AEP/1-propanol/H2O solution was much better compared with most current biphasic solvents. Meanwhile, AEP/1-propanol/H2O solution had a low regeneration heat of 2.74 GJ·t−1-CO2, which was 27.9% lower than that of MEA. Moreover, 13C NMR analysis was used to investigate the absorption-desorption mechanism and species distribution. The multiple amino groups in AEP could react with CO2 to produce carbamate and carbonate. The generated absorption products were mainly concentrated in the CO2-rich phase, while the CO2-lean phase contained much 1-propanol. Most of the absorption products were decomposed during regeneration, so the high desorption performance was achieved. Overall, AEP/1-propanol/H2O solution is a promising energy-saving candidate for industrial CO2 capture due to its competitive absorption-desorption performance and low regeneration energy.

A Novel Fe3O4/Graphene Oxide Composite Prepared by Click Chemistry for High-Efficiency Removal of Congo Red from Water

In this paper, a magnetic graphene oxide (MGO) composite was prepared by the click reaction between the alkyne-modified Fe3O4 nanoparticles and the azide-modified graphene oxide for the purpose of removing the Congo red (CR) dye from water. The deposition of the Fe3O4 nanoparticles on the graphene oxide to successfully prepare the MGO composite was evidenced by the Fourier-transform infrared spectrometer, wide-angle X-ray diffraction equipment, scanning electron microscope, thermal gravimetric analyzer, and Raman spectrometer. The value of saturation magnetization for the MGO composite was 34.9 emu/g. The CR absorption capacities of the MGO composite increased first and then decreased as the pH value increased. It was found that the maximum adsorption capacity of the MGO composite for the CR was as high as 769.2 mg/g. In the absorption-desorption experiment, the CR absorption capacities of the MGO composite from the second cycle to the fifth cycle remained stable to be about 130 mg/g. Moreover, both the Langmuir model for the adsorption isotherm and the pseudo-second-order kinetic model could be used to describe the CR absorption behaviors of the MGO composite.

CO2 Desorption Performance from Imidazolium Ionic Liquids by Membrane Vacuum Regeneration Technology.

In this work, the membrane vacuum regeneration (MVR) process was considered as a promising technology for solvent regeneration in post-combustion CO2 capture and utilization (CCU) since high purity CO2 is needed for a technical valorization approach. First, a desorption test by MVR using polypropylene hollow fiber membrane contactor (PP-HFMC) was carried out in order to evaluate the behavior of physical and physico-chemical absorbents in terms of CO2 solubility and regeneration efficiency. The ionic liquid 1-ethyl-3-methylimidazolium acetate, [emim][Ac], was presented as a suitable alternative to conventional amine-based absorbents. Then, a rigorous two-dimensional mathematical model of the MVR process in a HFMC was developed based on a pseudo-steady-state to understand the influence of the solvent regeneration process in the absorption–desorption process. CO2 absorption–desorption experiments in PP-HFMC at different operating conditions for desorption, varying vacuum pressure and temperature, were used for model validation. Results showed that MVR efficiency increased from 3% at room temperature and 500 mbar to 95% at 310 K and 40 mbar vacuum. Moreover, model deviation studies were carried out using sensitivity analysis of Henry’s constant and pre-exponential factor of chemical interaction, thus as to contribute to the knowledge in further works.

DBU-Glycerol Solution: A CO2 Absorbent with High Desorption Ratio and Low Regeneration Energy.

1,8-Diazabicyclo[5.4.0]-undec-7-ene (DBU)-glycerol solution is employed as a promising CO2 absorbent. The regeneration of the CO2-loaded solution is of vital importance for its commercialization. It was investigated and compared with 30 wt % monoethanolamine (MEA). Variables affecting the absorption and desorption processes were studied, including the solvent composition, reaction temperature, and agitation. It shows that the absorption capacity for DBU-glycerol is comparable with 30 wt % MEA, and the desorption ratio for CO2-loaded DBU-glycerol mixture can reach as high as 95% in 60 min, 363 K at the 3:1 molar ratio of DBU to glycerol, while it is only 68% even after 165 min for CO2-saturated 30 wt % MEA. DBU-glycerol solution has higher cycling CO2 loading than 30 wt % MEA. Its cyclic capacity could keep above 90% after 10 cycles of absorption-desorption experiments. The desorption reaction is irreversible at the initial stage, and the reaction rate is expected as a first-order reaction from 349 to 377 K, and the apparent activation energy is 68.94 kJ/mol. Moreover, the heat duty of the reboiler during regeneration is estimated to be reduced by about 27% when compared with 30 wt % MEA.

Performance and stability of a bio-inspired soybean-based solvent for CO2 capture from flue gas

A novel bio-inspired soybean-based solvent (SBB solvent) was formulated for the capture of CO2 with the partial pressure less than 15 kPa in the flue gas. The performance of the SBB solvent was thoroughly characterized in terms of equilibrium solubility of CO2, the heat of CO2 absorption, vapor pressure of the SBB solvent, and the CO2 absorption flux under different operating conditions including CO2 partial pressure in the flue gas, initial CO2 loading in the SBB solvent, SBB solvent concentration, and temperature. The results showed that the equilibrium solubility of CO2 in the SBB solvent was much lower than that in the conventional amine-based solvent at the regeneration condition. The heat of CO2 absorption is only at half of the monoethanolamine (MEA). The near-zero vapor pressure made the SBB solvent as a promising and environmentally friendly solvent for CO2 capture. The optimized concentration of the SBB solvent was 1.0 M for the effective absorption of CO2 from the flue gas. The CO2 absorption performance can be further improved by integrating the use of high concentration SBB solvent with reduced CO2-gas mass transfer resistance. Both thermal stability and oxidative stability of the SBB solvent were evaluated through a 120 h CO2 absorption-desorption experiment. The SBB solvent showed high thermal stability at the regeneration temperature up to 200 °C, and also excellent oxidative stability with the O2 concentration up to 17% in the flue gas.

Moisture absorption and cyclic absorption–desorption characters of fibre-reinforced epoxy composites

In this study, the temperature effects on moisture diffusion of epoxy resin and its glass/carbon fibre-reinforced epoxy composites in distilled water were tested. In 70 °C, their diffusion coefficients were found 20.9 times, 16.5 times and 29.5 times higher than those in room temperature (25 °C); meanwhile, their saturated moisture contents were measured increased by 1.68 times, 2.39 times and 2.55 times, respectively. Furthermore, a cyclic moisture absorption–desorption experiment of composite materials was designed and implemented. The results revealed that moisture weight gain is no longer well described by Fick’s law during the second and the third cycle of moisture absorption processes, e.g., moisture diffusion coefficients in these two periods are obviously higher and lower than the predictions by Fick’s law during the first half and second half of moisture absorption processes. A flux-dependent moisture diffusion model proposed represents this phenomenon. In this model, moisture diffusion coefficient is formulated exponentially depending upon water flux. Flexural strength degenerations of the bulk epoxy and composite materials were tested corresponding to saturated state and re-dried state of per cycle, after three moisture absorption–desorption cycles, the dry state strength retention rates of bulk epoxy, UD-GFRP and UD-CFRP are 93, 79 and 80%, and in wet state these rates decrease to 53, 48 and 78%, respectively.

Synthesis and characterization of activated carbon/conducting polymer composite electrode for supercapacitor applications

Activated carbon is prepared from coconut shell by heating it around 500 °C for 2 h in a muffle furnace. This method is one of the easiest and most economical methods for the synthesis of Activated carbon. The dried coconut shell is carbonized and it is treated with KOH in the ratio of 1:3 carbon-activating agent (KOH) and the resulting slurry is dried in an oven at 60 °C for overnight. The dried mass is further activated at 450 °C then it is washed with an acid solution to remove KOH. The surface area of the synthesized activated carbon can be obtained by using nitrogen absorption–desorption experiment. Conducting polymer such as polyaniline prepared by oxidative polymerization of the respective monomer in tetrafluoroboric acid solution using potassium persulphate as an oxidant. The structure and doping of polyaniline were studied by FTIR, UV and Cyclic voltammetry studies. The conducting polymer is mixed with AC and prepared composites were characterized by UV, FTIR, and CV. The specific capacitance of composites calculated from charge–discharge at 0.5 mA g− 1 was found to be 99.6 Fg− 1 and for cyclic voltammetry, at the scan rate of 2 mV s− 1, it is 77 Fg− 1.

Catalytic Pyrolysis of Tar Model Compound with Various Bio-Char Catalysts to Recycle Char from Biomass Pyrolysis

Tar and char can be regarded as unwanted byproducts during the gasification process. In this study, three types of catalyst, i.e., biomass char (bio-char), nickel supported on biomass (Ni+bio-char), and nickel supported on bio-char (bio-char+Ni), were studied to compare the catalytic effects of different preparation methods on tar model compound removal. The structural characteristics of the three catalysts were also investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and Brunauer-Emmett-Teller (BET) methods. The results revealed that Ni+bio-char catalyst showed much higher activity for the reformation of toluene (C7H8) as a tar model compound than the other two catalysts. Toluene could be completely converted to small gas molecules at a conversion rate of 99.92% at 800 °C, and the maximum yield of gas was 432 mL/(mL C7H8). In particular, the H2 and CH4 yields were 339 and 85 mL/(mL C7H8) at 850 °C, respectively. An N2 absorption-desorption experiment demonstrated that the specific surface area of Ni+bio-char was 32.87 times that of bio-char and 8.39 times that of bio-char+Ni. Moreover, metallic nickel (Ni0) particles could be generated in the carbon matrix of Ni+bio-char catalyst. SEM analysis confirmed that the Ni+bio-char catalyst had a more porous structure. Nickel supported on biomass might be a promising catalyst for tar reformation because of its excellent catalytic activities.

Solubility and Characterization of CO2 in 40 mass % N-Ethylmonoethanolamine Solutions: Explorations for an Efficient Nonaqueous Solution

The CO2 solubility in N-ethylmonoethanolamine (EMEA) solutions was investigated using the vapor–liquid equilibrium (VLE) and the absorption–desorption apparatus. A tertiary amine, N,N-diethylethanolamine (DEEA), was used as a novel solvent, and other nonaqueous solvents, diethylene glycol, triethylene glycol, benzyl alcohol, n-butyl alcohol and polyethylene glycol-200, were used for comparison. The EMEA + DEEA solution displayed a much higher CO2 solubility than other nonaqueous solutions though lower than the EMEA + H2O solution in the VLE experiment. However, the EMEA + DEEA solution exhibited a higher cyclic absorption capacity than EMEA + H2O solution in the cyclic absorption–desorption experiment. The reaction mechanism of EMEA + DEEA + CO2 was investigated by 13C NMR spectroscopy, which indicated that the nonaqueous solvent of DEEA participated in the chemical absorption of CO2, and thus improved the CO2 solubility. The tertiary amine DEEA used as a nonaqueous solvent shows more excellent performanc...

Synthesis and characterization of gadolinium-doped nanotubular titania for enhanced photocatalysis

Gadolinium-doped titanium dioxide nanotubes were fabricated with a facile two-step route. Precursors Gd-doped titania nanoparticles were synthesized by a traditional sol–gel method. Hydrothermal process and acid treatment were employed afterwards, and Gd-doped titania nanotubes were finally obtained after calcination. The nominal doping concentration was expressed by Gd/Ti atomic ratio, ranged from 0% to 5.0%. Both the precursors and nanotubes were characterized by X-ray photoelectron spectra, inductively coupled plasma-atomic emission spectrometry, transmission electron microscopy, scanning electron microscopy, X-ray diffraction, energy dispersive X-ray spectrometer, UV–vis diffusion reflection spectra and N2 absorption–desorption experiment. The photocatalytic activities were investigated using methyl orange as the model pollutant. The results indicated that Gd-doped titania nanotubes with nominal Gd/Ti of 0.5% possessed the optimal photocatalytic activity in our study.