Carbonaceous Support Research Articles

Analyzing Platinum Catalyst Degradation in Fuel Cells Using Accelerated Stress Tests and X-Ray Absorption Spectroscopy

The exploration of sophisticated characterization techniques in the study of electrochemical processes is pivotal for progressing our understanding of energy conversion mechanisms. Among such , particularly the coupling with X-Ray Absorption Spectroscopy (XAS), have shown significant promise. To follow dynamic changes of the electrocatalysts during operation, such as activation, conditioning and degradation, advanced measurement routines are required to capture these changes, but in a much reduced analysis time. Accelerated stress test (AST) protocols are the method of choice here and have been published and agreed upon by various sources, e.g. the DOE. This work details our recent investigation using XAS to study the structural and oxidation state changes in supported platinum catalyst under accelerated stress (for oxygen reduction reaction).Our experiment was conducted at the P64 Beamline (DESY, Hamburg) with three distinct accelerated stress test (AST) protocols applied to carbon-supported platinum catalysts (Pt/C) to probe their durability and degradation patterns. These tests are crucial for understanding the longevity and efficiency of catalysts in practical applications. Pt/C material, commonly used in fuel cells, was spray-coated onto a gas diffusion layer with 1 mgPt cm-2 loading and tested in a 1 mol L-1 HClO4 electrolyte. After 5000 cycles, we collected the Pt L2,3-edges XAS spectra at open circuit potential. This was done ten times for each test protocol. All measurements were done in a nitrogen atmosphere using a special half-cell designed for fluorescence measurements. Three electrochemical protocols were being tested and compared for their applicability: Loading Cycling, Startup/Shut Down, and a Mixed Protocol [1-3]. Each of these protocols simulates different stress conditions that the catalyst might experience in real-world applications. Through these tests, we could observe and analyze the agglomeration and dissolution phenomena in the Pt nanoparticles.A key observation across all three protocols was that the degradation manifested itself through the dissolution of the PtO layer, evidenced by a reduction in the Pt-O coordination number. Additionally, we noted an increase in the Pt-Pt coordination number, indicative of nanoparticle agglomeration. These phenomena are critical as they directly impact the efficiency and lifespan of the catalyst. We hypothesize that the carbonaceous support material undergoes oxidation under extreme conditions set by the AST protocols. This oxidation potentially facilitates nanoparticle agglomeration. Concurrently, the oxide layer formed on the nanoparticle surface dissolves into the electrolyte, further contributing to the degradation process.Understanding these degradation mechanisms is vital for improving catalyst design and optimizing their performance in realistic conditions. This work demonstrates the efficacy of XAS coupled with electrochemical testing in providing insightful data on catalyst behavior under stress. These findings are instrumental in guiding the development of more durable and efficient electrochemical systems, particularly in the field of energy conversion.References Alinejad, S. et al 2020 Phys. Energy 2 024003.Ohma, A. et al 2011 ECS Trans. 41 775.Loukrakpam, R. et al 2023 Power Sources 569 232905.

Outstanding Activity and Durability of Supported NiCo2O4 Nanoparticles for Direct Ethanol Fuel Cells

ABSTRACTThe rational design of noble metal‐free electrocatalysts represents one of the basic stones for fuel cell development. With the exploration of eco‐friendly nanomaterials for the investigated alcohol oxidation process, nickel‐based electrodes have been recognized as the most auspicious anodes with promoted activity and stability. In this work, a series of NiCo2O4 nanoparticles were deposited onto graphite sheets (NiCo2O4/T) introducing varied proportions of cobalt oxide species. Co‐precipitation protocol of the respective metallic hydroxides onto the carbonaceous support was followed with consecutive annealing in an air atmosphere at 400°C. The fabricated mixed metallic oxide nanopowder was physically studied using X‐ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X‐ray analysis (EDX), X‐ray photoelectron spectroscopy (XPS), and selected area electron diffraction (SAED). Uniformly arranged nanoparticles were observed on graphite surface as evidenced by SEM and TEM. The cubic lattice structure of formed NiCo2O4 crystals was also confirmed by XRD through the defined peaks of binary metallic oxides clarifying their successful preparation scheme. The electrocatalytic properties of these NiCo2O4/T nanocatalysts were evaluated for oxidizing ethanol molecules in basic solution. Pronounced oxidation current densities were remarkably measured at NiCo2O4/T electrodes in relation to that at NiO/T. Differing the introduced cobalt oxide content into the synthesized nanocatalyst significantly controlled its catalytic performance. NiCo2O4/T‐20 exhibited the highest activity and stability among the prepared nanomaterials. Much decreased charge transfer resistances were also recorded at this electrode demonstrating its promoted electron transfer characteristics. This work could provide a reasonable route for the simple synthesis of comparable transition metallic oxides with promising attitudes for energy generation purposes.

Carbon Materials with Different Dimensions Supported Pt Catalysts for Selective Hydrogenation of 3,4-Dichloronitrobenzene to 3,4-Dichloroaniline

In this study, carbon materials with different dimensions, including the typical one-dimensional (1D) carbon nanotube (CNT), two-dimensional (2D) graphene (GF), and three-dimensional (3D) activated carbon (AC), were investigated as a support for Pt catalysts for the selective hydrogenation of 3,4-dichloronitrobenzene (3,4-DCNB) to 3,4-dichloroaniline (3,4-DCAN). Notably, the Pt/CNT catalyst with the lowest dimension exhibited the best conversion of 3,4-DCNB under mild reaction conditions, followed by Pt/GF. Comprehensive characterizations, including XRD, TEM, XPS, and in situ CO DRIFTS, reveal that the dimension of carbon supports plays an important role in the particle size and electronic properties of Pt species, consequently affecting the catalytic performances of Pt catalysts. According to the results, electron-deficient Pt particles with small sizes are more favorable for the hydrogenation of 3,4-DCNB to 3,4-DCAN. In addition, dynamic tests and in situ DRIFTS of 3,4-DCNB indicated that the carbonaceous supports will largely influence the adsorption and activation capacity of the Pt catalysts, so that Pt loaded on CNT and GF are superior to that on the AC. We believe this study will provide good guidance for designing efficient carbon-supported metal catalysts for selective hydrogenation.

Upcycling Waste Biomass–Production of Porous Carbonaceous Supports from Paper Mill Sludge and Application to CO2 Conversion (Adv. Sustainable Syst. 8/2024)

Upcycling Waste Biomass–Production of Porous Carbonaceous Supports from Paper Mill Sludge and Application to CO₂ Conversion (Adv. Sustainable Syst. 8/2024)

Carbon-supported hydroxyapatite hybrid catalysts for butan-1-ol conversion: Effect of the nature of carbon support on process selectivity

Hybrid systems of hydroxyapatite supported on carbonaceous materials of different nature (activated charcoals, acetylene black, carbon black, graphite flake, synthesized microporous and mesoporous carbons) are investigated as catalysts for vapor-phase Guerbet condensation of butan-1-ol. The structure, morphology, and acid–base characteristics of hydroxyapatite, carbon supports, and the hybrid systems have been characterized by XRD, SEM-EDX, low-temperature (77 K) nitrogen ad(de)sorption, NMR, XPS, EPR, Raman spectroscopy, and TPD-NH3/CO2 techniques. The butan-1-ol conversion and selectivity towards the reaction products are found to be highly dependent on carbonaceous supports of the hybrid catalysts. The important role of acid–base capacity ratio is highlighted to achieve high selectivity in vapor-phase Guerbet condensation of butan-1-ol to 2-ethylhexan-1-ol. In particular, the surface’s strong basic sites are preferable for elongating the carbon chain. The high selectivity towards 2-ethylhexan-1-ol of about 75% is achieved over HAP/graphite flake and up to 57% over HAP/activated coconut charcoal. Compared to the bulk hydroxyapatite, the enhanced performance of the hybrid catalysts (initial activity and target product yield) is associated with the redistribution of active sites over carbon supports by strength and location.

Nanoparticles of NiO and CoO simultaneously dispersed on a mesoporous carbonaceous support as bifunctional electrocatalysts for ORR and OER reactions and Zn-air battery performance

This work aims to study the effect of different atmospheres and temperatures in the synthesis of a bifunctional electrocatalyst for ORR and OER reactions in the cathode of a Zn-air battery, using a carbonaceous support for dispersing Ni and Co species. At 300 °C, NiCo2O4 with a size of 4.93 nm under O2 and 150.14 nm using air, were obtained. These materials exhibited low specific surface area and pore volume and failed to show bifunctional activity. Instead, the simultaneous dispersion of NiO and CoO nanoparticles, with a size of 2.55 nm was achieved at 300 °C under N2 (NiCo/MC-N300), leading to a surface enrichment in Co2+ and Ni2+ species, while Ni and Co nanoparticles, 12.81 nm, were obtained at 700 °C under N2 (NiCo/MC-N700). These catalysts exhibited high specific surface area and pore volume, and bifunctional electrochemical activity; as well as high specific-capacity in a home-made Zn-air battery.

Degradation of Bisphenol A by Nitrogen-Rich ZIF-8-Derived Carbon Materials-Activated Peroxymonosulfate.

Bisphenol A (BPA), representing a class of organic pollutants, finds extensive applications in the pharmaceutical industry. However, its widespread use poses a significant hazard to both ecosystem integrity and human health. Advanced oxidation processes (AOPs) based on peroxymonosulfate (PMS) via heterogeneous catalysts are frequently proposed for treating persistent pollutants. In this study, the degradation performance of BPA in an oxidation system of PMS activated by transition metal sites anchored nitrogen-doped carbonaceous substrate (M-N-C) materials was investigated. As heterogeneous catalysts targeting the activation of peroxymonosulfate (PMS), M-N-C materials emerge as promising contenders poised to overcome the limitations encountered with traditional carbon materials, which often exhibit insufficient activity in the PMS activation process. Nevertheless, the amalgamation of metal sites during the synthesis process presents a formidable challenge to the structural design of M-N-C. Herein, employing ZIF-8 as the precursor of carbonaceous support, metal ions can readily penetrate the cage structure of the substrate, and the N-rich linkers serve as effective ligands for anchoring metal cations, thereby overcoming the awkward limitation. The research results of this study indicate BPA in water matrix can be effectively removed in the M-N-C/PMS system, in which the obtained nitrogen-rich ZIF-8-derived Cu-N-C presented excellent activity and stability on the PMS activation, as well as the outstanding resistance towards the variation of environmental factors. Moreover, the biological toxicity of BPA and its degradation intermediates were investigated via the Toxicity Estimation Software Tool (T.E.S.T.) based on the ECOSAR system.

NiMn layered double hydroxides with promoted surface defects as bifunctional electrocatalysts for rechargeable zinc–air batteries

Layered double hydroxides (LDHs) are attractive bidimensional materials for electrochemical applications because of their high activity in the oxygen evolution reaction (OER). However, their limited bifunctionality due to the slow kinetics of the oxygen reduction reaction (ORR) is a bottleneck for their use in secondary Zn-air batteries (ZABs). In this work, cobalt-free NiMn LDHs were rationally designed by optimizing the Ni composition and incorporating surface defects onto the LDH (oxygen vacancies, Ov) while performing interface engineering using a carbonaceous support enriched with nitrogen heteroatoms. The LDHs without induced defects presented the optimal activity for the OER at a 3:1 Ni/Mn atomic ratio (onset potential 1.47 V vs. 1.45 V for IrO2/C), while the ORR was unfavorable. However, the further optimization by introducing Ov and N–heteroatoms (labeled as Ov-NiMn LDH/NCNTG) allowed bifunctionality by improving the onset potential to 0.90 V while decreasing the half-wave potential difference from 180 mV for the material without induced defects to 100 mV, and by improving the limiting current density by a factor of two. In this regard, density of states (DOS) calculations suggested that surface defects improved the electronic transfer while decreasing the oxygen adsorption energy. ZAB tests indicated that the interface-engineered material allowed a battery voltage of 1.47 V, and a power density of 64 mW cm−2. The battery also maintained stability over 180 charge/discharge cycles at 10 mA cm−2 (50 h), with ΔV below 150 mV between the initial and final cycles.

Upcycling Waste Biomass–Production of Porous Carbonaceous Supports from Paper Mill Sludge and Application to CO2 Conversion

AbstractThe urgent need for sustainable waste management strategies has led to the exploration of innovative approaches for the valorization of waste. In this study, a method is proposed for carbonizing waste biomass materials, particularly paper mill waste sludges (primary and biological) and knots, to produce porous carbonaceous supports. Through an initial hydrothermal carbonization followed by carbonization with nitrogen flow, porous carbon materials are successfully generated. The findings of this investigation validate the successful generation of effective carbonaceous supports utilizing waste biomass materials. These materials are then evaluated for their effectiveness as porous supports in the ionic liquid‐catalyzed cycloaddition reaction of CO2 to styrene oxide, achieving a remarkable conversion rate of up to 98% and an impressive selectivity exceeding 99%. Additionally, the results underscore the significant impact of the selected IL on the overall conversion process. Overall, this study presents a promising pathway for the valorization of paper mill waste sludge through the production of porous carbon materials with potential applications in catalysis and beyond.

Synthesis of nanoporous solid polymer electrolyte AuNiCe/NC hydrogenation membrane electrode

In this study, using graphite fiber cloth as the support, gold-based solid polymer electrolyte (SPE) membrane electrodes were synthesized by high-vacuum ion beam sputtering, nitrogen doping of the support, combined electrochemical dealloying, and hot-pressing technology. The application of the SPE membrane electrode to couple hydrogen evolution and liquid organic hydrogen storage is of significant importance for sustainable hydrogen energy and efficient carbon dioxide conversion. Using various characterization techniques, we systematically analyzed the phase structure, surface morphology, porous structure, and electrocatalytic performance of the membrane electrode for the hydrogenation of cyclohexene. The results indicated that doping the carbonaceous support with nitrogen (NC), doping with cerium as catalyst promoter, and combined electrochemical dealloying can all enhance the activity of the catalyst. Cerium doping provides the catalyst with oxygen vacancies for accelerated electron transfer. After combined electrochemical dealloying, AuNiCe/NC formed a three-dimensional bicontinuous porous structure. The electrochemically active surface area increased by 23.94 times, the energy consumption of catalytic cyclohexene hydrogenation decreased by 35.7%, and current efficiency and the formation rate of cyclohexane increased by 54.9% and 29.4%, respectively.

Efficient Alkyne Semihydrogenation Catalysis Enabled by Synergistic Chemical and Thermal Modifications of a PdIn MOF.

Recently, there has been a growing interest in using MOF templating to synthesize heterogeneous catalysts based on metal nanoparticles on carbonaceous supports. Unlike the common approach of direct pyrolysis of PdIn-MOFs at high temperatures, this work proposes a reductive chemical treatment under mild conditions before pyrolysis (resulting in PdIn-QT). The resulting material (PdIn-QT) underwent comprehensive characterization via state-of-the-art aberration-corrected electron microscopy, N2 physisorption, X-ray absorption spectroscopy, Raman, X-ray photoelectron spectroscopy, and X-ray diffraction. These analyses have proven the existence of PdIn bimetallic nanoparticles supported on N-doped carbon. In situ DRIFT spectroscopy reveals the advantageous role of indium (In) in regulating Pd activity in alkyne semihydrogenation. Notably, incorporating a soft nucleation step before pyrolysis enhances surface area, porosity, and nitrogen content compared to direct MOF pyrolysis. The optimized material exhibits outstanding catalytic performance with 96% phenylacetylene conversion and 96% selectivity to phenylethylene in the fifth cycle under mild conditions (5 mmol phenylacetylene, 7 mg cat, 5 mL EtOH, R.T., 1 H2 bar).

Catalytic pyrolysis of plastic waste using metal-incorporated activated carbons for monomer recovery and carbon nanotube synthesis

As the global plastic waste crisis intensifies, innovative and sustainable solutions are urgently needed. This study evaluated waste-derived metal-incorporated activated carbon (AC) catalysts for the pyrolysis of mixed plastic waste to generate value-added products, focusing on product yield distribution, composition, hydrogen, and carbon nanotube (CNT) formation. Pyrolysis-catalysis experiments were conducted using a two-stage fixed-bed reactor, wherein the temperature was maintained at 500 °C in first stage (pyrolysis) and varied (500, 600, and 700 °C) in the second stage (catalysis). The tested ACs were incorporated with nickel (Ni-AC), iron (Fe-AC), and zinc (Zn-AC) to assess the impact of metal particles distributed on the carbonaceous support in the second stage. The results from the ACs were compared to those obtained using zeolite (H-ZSM-5), Raw-AC, and non-catalytic runs. The Ni-AC and Fe-AC demonstrated superior catalytic activity, with Ni-AC being more efficient in producing hydrogen (4.24 wt%) and CNTs (34.5 wt%) with diameters of approximately 30 nm, and Fe-AC leading to higher gas yields (68.8 wt%) and CNTs (12.4 wt%) of around 60 nm. In contrast, Zn-AC and Raw-AC presented limited effectiveness, although Raw-AC moderately outperformed Zn-AC with enhanced gas yields and reduced oil/wax yields. The zeolite H-ZSM-5 exhibited the highest gas yields (78 wt%), converting heavy fractions into lighter molecules, notably the monomers ethylene and propylene. These findings provide valuable insights into catalyst selection and optimization for plastic waste pyrolysis processes, with H-ZSM-5 being the most effective catalyst for monomer recovery, and Ni-AC and Fe-AC demonstrating promising results.

Atomic Layer Deposition of Ru Nanoparticles on Low Surface Energy Carbon Supports for Alkaline Hydrogen Evolution Reaction

Platinum group metals such as Pt, Ru, Pd, Ir, etc., have superior performance for various catalytic applications.[1] Due to their scarcity, efforts were being made to reduce or replace these noble metals. Atomic Layer Deposition (ALD) is one among the best technique to facilitate lowering of loading mass on a support of interest.[2],[3] Furthermore, ALD is the most suitable technology that can decorate high aspect ratio and high surface area substrate architectures by noble metal nanoparticles.[4] Due to the governing surface energy variations between noble metals and support surfaces, the growth initiates as nanoparticles (NP) and with a further increase in ALD cycles the agglomeration among NP’s dominates over the individual NP size increase, thus developing thin films of relatively higher thickness. The surface energy variations are also known to increase the nucleation delay of noble metals especially for Ru considerably. In this regard our efforts were laid to improve the functionality with pretreatments on carbonaceous supports which were shown promising to reduce the nucleation delay of ALD deposited Ru.For electrocatalytic applications, it is important to choose the right substrates. Among available substrates, carbon papers (CP) and titania nanotube (TNT) layers are best choices considering their physio-chemical properties, availability, vast literature, and low costs incurred using these as support substrates in electrocatalysis and photocatalysis. Several surface modifications for CP’s and variations on morphological aspects of TNT layers had received a great attention form applied fields due to their improved surface area, conductivity and stability.[5]–[8] Uniformly decorating these CP’s and TNT layers by NPs or thin films of catalysts proved to be highly efficient with no boundaries on applications.[9] The presentation will introduce and describe the synthesis of different noble metal NPs by our ALD tool (Beneq TFS 200) on various aspect ratio TNT layers and CP substrates. It will also include the corresponding physical and electrochemical characterization and encouraging results obtained with alkaline hydrogen evolution reaction.

Improving Stability of CO2 Electroreduction by Incorporating Ag NPs in N-Doped Ordered Mesoporous Carbon Structures.

The electroreduction of carbon dioxide (eCO2RR) to CO using Ag nanoparticles as an electrocatalyst is promising as an industrial carbon capture and utilization (CCU) technique to mitigate CO2 emissions. Nevertheless, the long-term stability of these Ag nanoparticles has been insufficient despite initial high Faradaic efficiencies and/or partial current densities. To improve the stability, we evaluated an up-scalable and easily tunable synthesis route to deposit low-weight percentages of Ag nanoparticles (NPs) on and into the framework of a nitrogen-doped ordered mesoporous carbon (NOMC) structure. By exploiting this so-called nanoparticle confinement strategy, the nanoparticle mobility under operation is strongly reduced. As a result, particle detachment and agglomeration, two of the most pronounced electrocatalytic degradation mechanisms, are (partially) blocked and catalyst durability is improved. Several synthesis parameters, such as the anchoring agent, the weight percentage of Ag NPs, and the type of carbonaceous support material, were modified in a controlled manner to evaluate their respective impact on the overall electrochemical performance, with a strong emphasis on operational stability. The resulting powders were evaluated through electrochemical and physicochemical characterization methods, including X-ray diffraction (XRD), N2-physisorption, Inductively coupled plasma mass spectrometry (ICP-MS), scanning electron microscopy (SEM), SEM-energy-dispersive X-ray spectroscopy (SEM-EDS), high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM), STEM-EDS, electron tomography, and X-ray photoelectron spectroscopy (XPS). The optimized Ag/soft-NOMC catalysts showed both a promising selectivity (∼80%) and stability compared with commercial Ag NPs while decreasing the loading of the transition metal by more than 50%. The stability of both the 5 and 10 wt % Ag/soft-NOMC catalysts showed considerable improvements by anchoring the Ag NPs on and into a NOMC framework, resulting in a 267% improvement in CO selectivity after 72 h (despite initial losses) compared to commercial Ag NPs. These results demonstrate the promising strategy of anchoring Ag NPs to improve the CO selectivity during prolonged experiments due to the reduced mobility of the Ag NPs and thus enhanced stability.

Fabrication of CeO2/carbon molecular sieving membranes for enhanced O2/N2 gas separation

In this study, CeO2/carbon composite molecular sieving membranes (CMSMs) were prepared on carbonaceous plate supports using polyimide as precursor and cerium oxide (CeO2) as fillers via spin-coating method and pyrolysis. The microstructure and properties of CMSMs were analyzed by thermogravimetric analysis, infrared spectroscopy, X-ray diffraction, scanning electron microscope, particle size distribution and gas permeation test. The influence of the filler amount of CeO2 on the microstructure and performance of CMSMs was mainly investigated. The results showed that the incorporation of CeO2 significantly enhanced the graphitization degree and structural compactness of CMSMs. The optimal gas separation performance of CMSMs reaches to 16.3 for O2/N2 selectivity and 240.3 Barrer for O2 permeability, which is fabricated by the precursor containing CeO2 content of 0.2 % under the permeation condition of 30 °C and 0.02 MPa.

Enhancement of Mn-N-C single atom catalysts via sulfur and/or oxygen co-doping for oxygen reduction in acidic conditions: Unveiling the catalyst durability in fuel cells

Carbon-supported single Mn sites coordinated with nitrogen (Mn-N-C) catalysts are amongst the most favorable platinum group metal-free (PGM-free) catalysts for proton exchange membrane fuel cells (PEMFCs). However, the high overpotential of these catalysts, limits their application for oxygen reduction reaction (ORR). Experiments showed that O and S heteroatom co-doping increases the catalytic activity of Mn-N-C catalysts for electrochemical gas conversion. This prompted us to perform a systematic investigation of the formed co-doped configurations at the atomic scale and to study the corresponding reaction mechanisms for oxygen reduction in acidic environment. All probable configurations for Mn-NxOySz/C10 complexes are considered and the most stable and durable structures are selected as ORR active catalysts. Our results confirm the strong stabilization of the Mn sites over N4- and N3-doped carbonaceous support and consequently their stability against oxidation in contrast to other O and/or S co-doped heterostructures.

Magnetic Carbon Foam Adorned with Co/Fe Nanoneedles as an Efficient Activator of Oxone for Oxidative Environmental Remediation: Roles of Surficial and Chemical Enhancement

As heterogeneous catalysis is a practical method for activating Oxone, the immobilization of transition metals (e.g., Co, Fe) on carbonaceous supports is a promising platform. Thus, this study attempts to develop a carbon-supported metallic catalyst by growing Co/Fe on carbon foam (CF) via adopting melamine foam as a readily available template which could be transferred to nitrogen-doped CF with marcoporous structures. Specifically, a unique adornment of Co/Fe species on this CF is facilely fabricated through a complexation of Co/Fe with a plant extract, tannic acid, on melamine foam, followed by carbonization to produce nano-needle-like Co/Fe on N-doped CF, forming a magnetic CF (MCF). This resultant MCF exhibits a much higher surface area of 54.6 m2/g than CF (9.5 m2/g), and possesses a much larger specific capacitance of 9.7 F/g, than that of CF as 4.0 F/g. These superior features of MCF enable it to accelerate Oxone activation in order to degrade an emerging contaminant, bis(4-hydroxyphenyl)methanone (BHPM). Furthermore, MCF + Oxone exhibits a lower activation energy as 18.6 kJ/mol for BHPM elimination and retains its effectiveness in eliminating BHPM over multiple rounds. More importantly, the CF is also prepared and directly compared with the MCF to study the composition-structure-property relationship to provide valuable insights for further understanding of catalytic behaviors, surficial characteristics, and application of such a functional carbon material.

Ionothermal synthesis of magnetic N-doped porous carbon to immobilize Pd nanoparticles as an efficient nanocatalyst for the reduction of nitroaromatic compounds

Carbon materials play important roles as catalysts or catalyst supports for reduction reactions owing to their high porosity, large specific surface area, great electron conductivity, and excellent chemical stability. In this paper, a mesoporous N-doped carbon substrate (exhibited as N–C) has been synthesized by ionothermal carbonization of glucose in the presence of histidine. The N–C substrate was modified by Fe3O4 nanoparticles (N–C/Fe3O4), and then Pd nanoparticles were stabilized on the magnetic substrate to synthesize an eco-friendly Pd catalyst with high efficiency, magnetic, reusability, recoverability, and great stability. To characterize the Pd/Fe3O4–N–C nanocatalyst, different microscopic and spectroscopic methods such as FT-IR, XRD, SEM/EDX, and TEM were applied. Moreover, Pd/Fe3O4–N–C showed high catalytic activity in reducing nitroaromatic compounds in water at ambient temperatures when NaBH4 was used as a reducing agent. The provided nanocatalyst's great catalytic durability and power can be attributed to the synergetic interaction among well-dispersed Pd nanoparticles and N-doped carbonaceous support.

One-pot synthesis of a CdS–MoS2 / CNTs nano-composite for photocatalytic hydrogen production under visible light

The need to meet growing energy demands of global society in a sustainable fashion requires the development of techniques and processes to reduce dependence on fossil fuels and transit to renewable energy sources. Environmentally benign technologies for alternative fuel production in the form of hydrogen can be developed via heterogenous photocatalysis, a process based on utilization of solar energy. To this end, a cadmium sulfide (CdS) based photocatalyst was developed, doped with MoS2 in a one-pot solvothermal synthesis technique, and coupled with multi-walled carbon nanotubes (MWCNTs) as a carbonaceous support. The material exhibiting the highest rate of hydrogen evolution, CM5C3, involved a MWCNTs loading of 3% and MoS2 loading of 5%. Compared to pure CdS synthesized with the same adapted procedure, the 3% CNT loading improved the rate of hydrogen production by nearly 7-fold, and the optimal 5% MoS2 loading further improved the performance by 60%. CM5C3, achieved an apparent quantum efficiency of 7.34%, a 26-fold increase compared to pure CdS. FESEM and HRTEM imaging confirmed the nanorod-like growth of CdS–MoS2 on the CNT surface, with elemental mapping confirming homogenous dispersion of MoS2 and CNTs. In addition, lattice fringe spacings indicated the presence of cubic and hexagonal CdS growing predominantly along the (111) and (002) planes respectively, in addition to MoS2 distributed throughout the crystal lattice. XRD analysis confirmed the presence of hexagonal and cubic CdS, however, MoS2 phases were not registered perhaps due to the low concentration present in the bulk of the material. XPS survey scans showed the presence of C, Cd, Mo, and S only, with trace oxygen impurities. Peak deconvolution indicated the presence of characteristic peaks for CdS and MoS2, in addition to evidence of the presence of Cd–C bonds, indicating strong CdS heterojunctions to the CNT surface.

Sorption of Selenium(IV) and Selenium(VI) onto Iron Oxide/Hydroxide-Based Carbon Materials: Activated Carbon and Carbon Foam

Selenium pollution in water is a worldwide issue. Se(IV) and Se(VI) are mainly found in contaminated water due to their high solubility and mobility; their presence poses a serious risk as they can severely harm human health. Although iron oxide and hydroxide nanoparticles can be efficient candidates for the removal of selenium oxyanions due to their high adsorption capacity, the role of each iron species has not been fully elucidated. Furthermore, iron species are often found to be less effective for Se(VI) than Se(IV). The challenge and novelty of this study was to develop a carbon material impregnated with different iron phases, including oxides (magnetite/hematite) and hydroxides (goethite/lepidocrocite) capable of removing both Se(IV) and Se(VI). Since the phase and morphology of the iron nanoparticles play a significant role in Se adsorption, the study evaluated both characteristics by modifying the impregnation method, which is based on an oxidative hydrolysis with FeSO4 7H2O and CH3COONa, and the type of carbonaceous support (activated carbon or sucrose-based carbon foam). Impregnated activated carbons provide better removal efficiencies (70–80%) than carbon foams (<40%), due to their high surface areas and point zero charges. These results show that the adsorption of Se(VI) is more favorable on magnetic oxides (78%) and hydroxides (71%) than in hematite (<40%). In addition, the activated carbon decorated with magnetite showed a high adsorption capacity for both selenium species, even in alkaline conditions, when the sorbent surface is negatively charged. A mechanism based on the adsorption of inner-sphere complexes was suggested for Se(IV) immobilization, whereas Se(VI) removal occurred through the formation of outer-sphere complexes and redox processes.