Carbon Nanotube Catalyst Research Articles

The effect of different carbon-based CdTe alloys for efficient photocatalytic glucose electrooxidation

The activated carbon (AC), graphene (G), reduced graphene oxide (rGO), carbon nanotube (CNT) supported CdTe photocatalysts at (50–50) atomic molar are synthesized by the sodium borohydride (SBH) method and characterized by the XRD, Micro-Raman, TEM-EDS, XPS, and TPx (TPR, TPO, and TPD) analyses. The CV, CA, and EIS electrochemical analyses are performed to investigate the catalytic activities of catalysts for photocatalytic glucose electrooxidation. Characterization analyses reveal that their electronic structures and surface properties change when carbon materials are doped with metal. The photocatalytic glucose electrooxidation results indicate that the 0.1 % CdTe(50–50)/CNT catalyst exhibited better photocatalytic activity, stability, and resistance than other catalysts both at dark (1.9 mA/cm 2 ) and under UV illumination (2.57 mA/cm 2 ). Therefore, the CNT-supported CdTe catalyst can be said a promising catalyst for direct glucose fuel cells.

Alkaline aqueous redox flow batteries using 2,5‐dihydroxy‐1,4‐benzoquinone and ferrocyanide adopting bismuth and carboxylic acid functionalized carbon nanotube catalyst

Alkaline aqueous redox flow batteries using 2,5‐dihydroxy‐1,4‐benzoquinone and ferrocyanide adopting bismuth and carboxylic acid functionalized carbon nanotube catalyst

High productivity of tartronate from electrocatalytic oxidation of high concentration glycerol through facilitating the intermediate conversion

Selective electro-oxidation of glycerol to value-added chemicals has attracted much attention both for the upgrading of biodiesel industry and the coupled electrolytic hydrogen production. Here we report Pt nanoparticles decorated, Fe- and N co-doped carbon nanotube (Pt/FeNC) catalyst for the selective electro-oxidation of glycerol to tartronate, one of the valuable chemicals used in pharmaceuticals. In a high concentrated glycerol solution of 5.0 M, the Pt/FeNC catalyst reaches the glycerol conversion of 94% and tartronate yield over 47% at 0.9 V vs. RHE, equivalent to a tartronate production rate of 1182 mmol/h/gPt, about 20 times of the highest value ever reported in a batch electrocatalytic reactor. The valence band analysis and kinetic experiments reveal that the FeNC mediates the adsorption behavior of the glycerate intermediate on Pt surface, and promotes the glycerate-to-tartronate oxidation. Moreover, the anchoring effect of FeNC ensures the stable catalytic performance for ten cycles.

Intrinsic Catalytic Activity of Carbon Nanotubes for Electrochemical Nitrate Reduction

We study a variety of carbon nanotubes (CNTs) as cost-effective catalysts for the electrochemical nitrate (NO3–) reduction reaction, which holds promise for converting environmental NO3– pollutants into useful ammonia (NH3) products. We discover that pristine multi-walled carbon nanotubes (MWCNTs) exhibit notable electrocatalytic activity for NO3– reduction to NH3 in a near-neutral electrolyte. Single-walled carbon nanotubes have even higher activity and selectivity than MWCNTs for this reaction. Results from control experiments confirm that this activity originates from the native carbon surface rather than from metal impurities. Contrary to the prevalent notion that heteroatom doping into carbon materials increases their electrocatalytic performance, we find that introducing oxygen and nitrogen functional groups into MWCNTs reduces their electrocatalytic activity for NO3– reduction. After analyzing the potential-dependent electrocatalytic performance of the CNT catalysts, we further report an interesting positive correlation between total current density and Faradaic efficiency for NH3 formation irrespective of the type of CNT. This correlation suggests deeper NO3– reduction at higher reaction rates regardless of the catalyst identity. The findings presented in this work suggest a unique type of active site for electrocatalytic NO3– reduction, therefore broadening the role of carbon materials in electrocatalysis.

Application of multi-wall carbon nanotubes supported l-proline in continuous flow catalysis

l-proline on multi-wall carbon nanotubes (l-proline/MWCNTs) catalysts doped with suitable auxiliary support materials are successfully applied in the continuous flow catalytic syntheses, including Aldol reaction, Mannich reaction and Knoevenagel condensation reaction. With the advantages of easy operation, high efficiency and excellent stability, this method is promising in large-scale synthesis.

Promoting the reduction of CO2 to formate and formaldehyde via gas–liquid interface dielectric barrier discharge using a Zn0.5Cd0.5S/CoP/multiwalled carbon nanotubes catalyst

A Zn0.5Cd0.5S (ZCS) solid solution was prepared using a hydrothermal method, in which CoP nanowires were added as a co-catalyst and co-deposited with multiwalled carbon nanotubes (MWNTs) on sponge to prepare a series of ZCS/CoP/MWNTs/sponge electrodes. The microstructures of catalysts were analyzed to confirm ZCS and CoP were successfully loaded in MWNTs/sponge. The CO2 reduction products (formate and formaldehyde) produced via dielectric barrier discharge (DBD) using the different catalysts proved that the introduction of the CoP nanowires co-catalyst can enhance the catalytic activity of ZCS/MWNTs/sponge in the DBD system. Using 10% CoP and a ZCS/CoP concentration of 2.5 g·L−1, the resulting ZCS/CoP/MWNTs/sponge catalyst exhibited the best catalytic of CO2 reduction ability toward formate (7894.6 μmol·L−1) and formaldehyde (308.5 μmol·L−1) after 60 min of discharge, respectively. The proposed DBD catalytic mechanism for the reduction of CO2 was analyzed according to the Tafel slope, density functional theory calculations, photocurrent density and plasma reaction process. Furthermore, the application of the DBD catalytic technology for CO2 capture and reduction was shown to be efficient in a seawater system, and as such, it could be useful for marine CO2 storage and conversion.

Immobilization of Polyoxometalates on Carbon Nanotubes: Tuning Catalyst Activity, Selectivity and Stability in H2O2-Based Oxidations

In recent years, carbon nanotubes (CNTs), including N-doped ones (N-CNTs), have received significant attention as supports for the construction of heterogeneous catalysts. In this work, we summarize our progress in the application of (N)-CNTs for immobilization of anionic metal-oxygen clusters or polyoxometalates (POMs) and use of (N)-CNTs-supported POM as catalysts for liquid-phase selective oxidation of organic compounds with the green oxidant–aqueous hydrogen peroxide. We discuss here the main factors, which favor adsorption of POMs on (N)-CNTs and ensure a quasi-molecular dispersion of POM on the surface and their strong attachment to the support. The effects of the POM nature, N-doping of CNTs, acid additives, and other factors on the POM immobilization process and catalytic activity/selectivity of the (N)-CNTs-immobilized POMs are analyzed. Particular attention is drawn to the critical issue of the catalyst stability and reusability. The scope and limitations of the POM/(N)-CNTs catalysts in H2O2-based selective oxidations are discussed.

Nitrogen-doped carbon nanotubes derived from carbonized polyaniline as a robust peroxydisulfate activator for the oxidation removal of organic pollutants: Singlet oxygen dominated mechanism and structure-activity relationship

In this work, a novel nitrogen-doped carbon nanotube catalyst (CPNT-10) was developed using the low-cost polyaniline (PANI) nanotubes as the precursor, which exhibited excellent peroxydisulfate (PDS) catalytic activity to degrade 2,4-dichlorophenol (2,4-DCP). The CPNT-10/PDS system could achieve approximately 100% PDS utilization and was efficient over a wide pH range (3.00–9.00). Integrated with electron paramagnetic resonance (EPR), quenching tests and electrochemical analysis, singlet oxygen (1O2) dominated the degradation of 2,4-DCP and free radicals (O2•-, •OH and SO4•-) mainly played auxiliary roles, while direct electron transfer was negligible. Furthermore, the structure–activity relationship analysis validated that the vacancy, graphitic sp2 carbon, C = N, and pyridine-N-O jointly involved in PDS activation, and vacancy played the most important part. This study provides a cheap and efficient nitrogen-doped carbon nanotube for environmental remediation and deepens the insight into mechanisms of persulfate activation with carbon-based materials.

Why Carbon Nanotubes Grow.

Despite three decades of intense research efforts, the most fundamental question "why do carbon nanotubes grow?" remains unanswered. In fact, carbon nanotubes (CNTs) should not grow since the encapsulation of a catalyst with graphitic carbon is energetically more favorable than CNT growth in every aspect. Here, we answer this question using a theoretical model based on extensive first-principles and molecular dynamics calculations. We reveal a historically overlooked yet fundamental aspect of the CNT-catalyst interface, viz., that the interfacial energy of the CNT-catalyst edge is contact angle-dependent. The contact angle increases via graphitic cap lift-off, drastically decreasing the interfacial formation energy by up to 6-9 eV/nm, overcoming van der Waals cap-catalyst adhesion, and driving CNT growth. Mapping this remarkable and simple interplay allows us to understand, for the first time, why CNTs grow.

Oxidative desulfurization of a model fuel using MoO3 nanoparticles supported on carbon nanotubes catalyst: Examine most significance variables, optimization, kinetics and thermodynamics study

Molybdenum oxide nanoparticles MONP were dispersed on multiwall nanotubes MWNTs as an attempt to synthesize MONP/MWNTs catalyst, the synthesis method done by wet impregnation. The prepared catalyst was characterized by FTIR (Fourier –Transform Infrared Spectroscopy) and, XRD (X-ray diffraction), whilst the catalyst activity is done with catalytic oxidative desulfurization ODS reaction for oxidation dibenzothiophene DBT dissolved in heptane (model fuel) with hydrogen peroxide H2O2, in which catalyst activity investigation achieved via studying impact six from most affected variables on ODS reaction. The chosen variables are reaction temperature, contact time, sulfur initial sulfur concentration, stirring speed, oxidant/sulfur ratio and catalyst dosage, and then the studied variables were screened by application of Plackett-Burman design PBD to identify the more significant on response (DBT pollutant removal). DBT pollutant removal is referred to as sulfur removal efficiency. Analysis of variance ANOVA shows that the reaction temperature, oxidant/sulfur ratio, stirring speed, and sulfur initial concentration are the most significant from the chosen variables due to their F-values 37.60, 25.45, 11.62 and 6.71 respectively. Box –Behnken experimental design was used to complete the study the effect of the most significant more deeply on ODS reaction (sulfur removal efficiency),in which this part exhibited that sulfur removal efficiency at range between 51 and 93%, whilst the optimum sulfur removal efficiency was 96% at 70 °C,4.36, 957 rpm and 50 ppm for reaction temperature, oxidant/sulfur ration, stirring speed and initial sulfur concentration respectively. The study involves estimation of kinetics and thermodynamics parameters for ODS reaction; kinetics studying exhibited that ODS reaction followed pseudo-first-order reaction with activation energy (12.996 kJ/mol), while the thermodynamics study shows the low negative entropy change (-0.221 kJ /mol.K), positive enthalpy and free energy changes which confirm a high hydrate transition complex was formed.

Weakening O[sbnd]O binding on Au-Cu2O/carbon nanotube catalysts with local misfit dislocation by interfacial coupling interaction for oxygen reduction reaction

Au-incorporation into nonprecious metal oxides is a promising strategy to optimize the constitution and improve electron transfer at the interface. Regrettably, achieving the desired performances has remained a significant challenge in oxygen reduction reaction (ORR). Here, we report the synthesis of the xAu-Cu2O/carbon nanotube (CNTs) catalysts. In the case of 0.52Au-Cu2O/CNTs, the Au atoms are incorporated into the Cu2O lattice and an atomically dispersed Au is distributed on the outer shell regions of Cu2O microsphere, and it exhibits a superior ORR activity among the as-prepared catalysts due to strong interfacial coupling interaction. Density functional theory (DFT) calculations reveal that the adsorption of O2 on Au-Cu2O is the bridge mode between Cu and adjacent Au atoms, which can accelerate the kinetics of the OO bond split and increase the dissociation of OO bonds. The study evidences the significant role of interfacial coupling interaction in binary or multi-component electrocatalysts.

Electro‐Catalytic Oxidation of Methanol Catalyzed by Facet‐Controlled Pt‐WC Nanoparticles on In Situ Synthesized Carbon Nanotubes

AbstractThe facet‐controlled Pt‐WC nanoparticles on in situ synthesized carbon nanotubes (Pt‐WC/CNT) are prepared by the one‐step carburization in conjunction with simple displacement reaction. WC particles exhibit preferential (100) orientation due to the in situ growth of carbon nanotubes (CNTs), and the most predominant facet exhibited by the Pt immobilized on WC (100) is the (200) facet. Among the prepared catalysts, Pt‐WC/CNT‐2 shows the highest mass activity (2540.0 mA/mg Pt) for methanol oxidation reaction (MOR) with smaller onset overpotential (0.18 V) and lower activation free energy (32.87 kJ/mol) in acid media. Such enhanced catalytic activity originates from its larger ECSA (238.1 m2/g) and the synergistic effect of facet‐controlled Pt‐WC nanoparticles. And Pt‐WC/CNT catalyst has superior stability for MOR due to its structurally stable CNTs support, which provides a large area to contact with electrolyte, and facilitates the electron transfer.

Catalyst activation by cold plasma technology and its effect on isomerization of safflower seed oil

High voltage atmospheric cold plasma (HVACP) is a novel catalyst modification technology. In this study, a ruthenium/multi-walled carbon nanotubes (Ru/MWCNTs) catalyst was activated by HVACP instead of the thermal reduction method. The results showed that HVACP activation under the conditions of 180 s discharge time, 150 W discharge power, and 2.5 cm electrode spacing at 25 °C could effectively decrease the activation temperature and time. At this time, the Ru dispersion was 20.1% and the conjugated linoleic acid (CLA) yield was 43.0%. Catalyst characterization proved that the HVACP-treated catalyst did not aggregate and had a good activation effect. The catalyst was applied to the isomerization reaction of safflower seed oil to obtain CLA-rich safflower seed oil. The total CLA content was 43.02%, the trans-oleic acid content was 1.34%, the iodine value (IV) was 133.50 gI2/100 g, and after reusing five times, the relative activity of the catalyst remained at 77%, which provided the conditions for the preparation of functional oil.

Oxidized multiwalled nanotubes as efficient carbocatalyst for the general synthesis of azines

The carbocatalytic synthesis of azines (N-N linked diimines) by mild-oxidized multiwalled carbon nanotubes catalyst (oxMWNT) is presented. The material, just with a 5 %wt. loading, is able to carry out a smooth room-temperature metal-free condensation of aldehydes and hydrazine, without external additives, to obtain a wide library of symmetric and also asymmetric azines in excellent yields, even in gram scale, with an excellent selectivity for aromatic substrates. This methodology allows the synthesis of azines with application in nonlinear optics, and the organic materials and biological active compounds crafting. oxMWNT catalysed the reaction in just 3 h with full recyclability upon the recovery of the catalyst. In addition, due to the inherent oxMWNT oxidative capacity in the presence of nitric acid, we have also developed the one-pot synthesis of azines starting from alcohols.

New insight into the kinetic study on the different loadings of the CuO/CNT catalyst and its optimization for p-chloroaniline photodegradation.

The effect of the copper (Cu) content on Cu oxide loaded onto a carbon nanotube (CuO/CNT) catalyst on the mechanistic, kinetic, and photonic efficiency of the photodegradation of p-chloroaniline (PCA) under visible (Vis) and ultraviolet (UV) light irradiation has been explored. For low-loading (1–5 wt%) CuO/CNTs, photodegradation performed better under UV (>84%) rather than the Vis system; this may be due to the presence of abundant defect sites on both CuO and CNTs, which allowed the multielectron reduction of oxygen at their impurity levels to generate more hydrogen peroxide and subsequent ·OH radicals. The active species under UV were in the following order: h+ ≫ e− > ·OH, while it was vice versa for the Vis system with a well-balanced 50 wt% CuO/CNT catalyst that exhibited a similar performance. The kinetic study showed the transition of the kinetic order from the zeroth to the first order on increasing the PCA concentration under the Vis system and vice versa for the UV system. The Thiele modulus (ϕ) further confirmed that the effect of internal mass transfer was negligible under UV light. In contrast, the transition from mass transfer to kinetic control limitation was observed under the Vis system. The optimum PCA degradation predicted from the response surface analysis was 97.36% at the reaction pH of 7.3, catalyst dosage of 0.45 g L−1, and initial PCA concentration of 11.02 mg L−1. The condition obtained was fairly close to the forecasted value with an error of 0.26%.

Promotional effects of trace Ni on its dual-functional electrocatalysis of Co/N-doped carbon nanotube catalysts for ORR and OER

It is still a great challenge for developing efficient dual-functional electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). The electrocatalysts are critical to enhance the efficiency of metal-air cells and fuel cells. In this study, a one-pot vapor deposition method was used to realize the synchronously dope of N and Ni (trace) into Co/C to form Co–Ni (trace)/N-doped carbon nanotubes (Co–Ni (trace)/NCNTs). An interesting result is that injecting dicyandiamide (DCD) into Ni foam as a precursor led to the in situ formation of NCNTs, with synchronous doping of trace Ni into Co species. The cooperative effects of the Co–Ni (trace) and N-doped carbon nanotubes resulted in superior dual-functional electrocatalytic performance of Co–Ni (trace)/NCNTs for the ORR (half-wave potential E1/2 vs. RHE: 0.83 V, electron transfer number n: 3.97) and OER (overpotential vs. RHE: 337 mV at 10 mA cm−2, Tafel slope: 94.0 mV dec−1). Moreover, the Co–Ni (trace)/NCNTs catalyst showed excellent stability during 20,000 s of durability testing for both ORR and OER. This study provides a feasible strategy for designing efficient nonnoble metal-catalysts for renewable energy conversion devices.

Palladium nanoparticles supported on multı-walled carbon nanotube (MWCNT) for the catalytic hexavalent chromium reduction

Chromium (VI) is widely accepted as an acute toxic contaminant in living ecosystems, while the trivalent Chromium form (III) is thought to be an important element for living beings. This study showed that zero palladium (Pd0) metal nanoparticles supported onto a multi-walled carbon nanotube (MWCNT) catalyst (Pd@MWCNT) effectively catalyzed the reduction reaction of Chromium (VI) to Chromium (III) using HCOOH (formic acid) as a reducing agent. The catalyst (Pd@MWCNT) was prepared reproducibly in the aqueous mixture at room conditions through the impregnation-reduction technique and identified using some analytical characterization techniques (HRTEM, DR/UV–vis, TEM-EDX, TEM, XPS, ICP-OES, and P-XRD). The results of the characterization studies show that the palladium(0) nanoparticles (demean = 2.20 ± 0.25 nm) are very well dispersed onto the MWCNT support material surface. The stability and activity of catalytic performance of Pd(0) metal nanoparticles were investigated in the reactions of Chromium (VI) to Chromium (III) in HCOOH solution. The results show that the Pd@MWCNT catalyst exhibited excellent activity (TOF = 281 mol Cr2O72−/mol Pd min), even after 5 times of reuse (<86%) in the reduction reaction of Chromium (VI) to Chromium (III) at 298K. In addition, this study includes very rich kinetic data depending on [Pd@MWCNT], [HCOOH], [HCOONa], [Cr2O72−] concentrations and temperature parameters to determine the nature of the reduction rate and activation parameters of Cr(VI) catalyzed by Pd@MWCNT nanocatalyst in the formic acid medium as a reducing agent.

A mechanistic periodic DFT study on the dissociation of tetrachlorodibenzofuran (TCDF) by M-doped carbon nanotube catalysts (M = Al, Fe, Mn)

Previous literature data showed that pristine aromatic allotropes of carbon such as graphene and carbon nanotubes (CNT) don’t show good interaction with carbon-based pollutants. On the other hand, defects or metal/non-metal doping in these inexpensive available catalysts could increase their strength for the adsorption and dissociation of different pollutants. In this work, by using periodic DFT calculations, adsorption of Tetrachlorodibenzofuran (TCDF) on pristine, co-adsorbed, defected, and M-doped carbon nanotubes (M = Al, Fe, Mn) is studied, and possible pathways for its first step dissociation is investigated. Data show that all three models of dissociations of TCDF need very high barrier energies on the surface of pristine CNT. Its minimum barrier energy is 3.31 eV which belongs to CCl bond cleavage. On the other hand, co-adsorbed, defected, and M-doped CNTs need less barrier energies. Minimum barrier energy belongs to CH bond dissociation on oxygen co-adsorbed CNT with 0.92 eV which is almost equal to the temperature of 355 K. Co-adsorbed CNT catalyst can also activate CCl chemical bond by 0.93 eV. Some catalysts such as Al-doped CNT is selective for CO bond cleavage, but some other catalysts, such as co-adsorbed CNT for CH and CCl, have similar barrier energy for two models of dissociations. With considering kinetics point of view (by barrier energies) and thermodynamics point of view (by reaction energy), data show that co-adsorbed, defected, and Al-doped CNTs are good catalysts for the first step dissociation of TCDF.

Density functional theory study of CO2 reduction to CH3OH on the surfaces of metal (Cu, Ni, and Mn)-doped carbon nanotubes

The reduction reaction of carbon dioxide (RR-CO2) to CH3OH using metal catalysts can reduce the energy required by this process. In this study, we investigated the RR-CO2 mechanisms with Cu-, Ni-, and Mn-doped carbon nanotubes (CNTs). The substitutional (doping with carbon atom) positions in CNTs are suitable sites for adsorbing Cu, Ni, and Mn metals. The reaction paths to the RR-CO2 were investigated in the gas and solvent phases. The results demonstrated that the overpotential values with Cu-, Ni-, and Mn-doped CNT(8, 0) and CNT(6, 6) catalysts in the gas and solvent phases were lower than that obtained with metal catalysts in previous studies (−1.116 V). Thus, metal-doped CNT(8, 0) and CNT(6, 6) catalysts with low overpotentials could be applied in the RR-CO2.

Facile Synthesis of 1T-Phase MoS2 Nanosheets on N-Doped Carbon Nanotubes towards Highly Efficient Hydrogen Evolution.

1T-phase molybdenum disulfide is supposed to be one of the non-precious metal-based electrocatalysts for the hydrogen evolution reaction with the highest potential. Herein, 1T-MoS2 nanosheets were anchored on N-doped carbon nanotubes by a simple hydrothermal process with the assistance of urea promotion transition of the 1T phase. Based on the 1T-MoS2 nanosheets anchored on the N-doped carbon nanotubes structures, 1T-MoS2 nanosheets can be said to have highly exposed active sites from edges and the basal plane, and the dopant N in carbon nanotubes can promote electron transfer between N-doped carbon nanotubes and 1T-MoS2 nanosheets. With the synergistic effects of this structure, the excellent 1T-MoS2/ N-doped carbon nanotubes catalyst has a small overpotential of 150 mV at 10 mA cm−2, a relatively low Tafel slope of 63 mV dec−1, and superior stability. This work proposes a new strategy to design high-performance hydrogen evolution reaction catalysts.