Carbon Surface Research Articles

Simultaneously Enhanced Low Temperature Li+ Transport Kinetics and Crystal Stability of Nb1.94Mo0.06O5@C Anode Induced by Distorted NbO6 Octahedron

AbstractThe electrochemical performances of lithium‐ion batteries (LIBs) will be significantly degraded under low‐temperature conditions, which restricts their wide application in cold environments. Herein, the low‐temperature transport kinetics of a novel Nb1.94Mo0.06O5@C nanocomposite anode is accelerated greatly via engineering the microstructure and NbO6 octahedron. The detailed crystallographic features are characterized by using synchrotron radiation, spherical electron microscope, and density functional theory simulation methods. Both experimental and simulation analysis suggest that Mo6+ preferentially replaces Nb5+ in the regular octahedral location and distorts the NbO6 octahedron, resulting in a widened c‐axis spacing and a lowered ion diffusion barrier. Coupled with the enhanced electronic conductivity derived from surface carbon layer, Nb1.94Mo0.06O5@C anode exhibits an enhanced charge transfer process, improved Li+ diffusion kinetics, pronounced pseudo‐capacitance process, and excellent low temperature capacity. Furthermore, in situ X‐ray diffraction and ex situ electron microscope elucidate that the structural evolution of Nb1.94Mo0.06O5@C is highly reversible, unveiling its excellent cycling stability. The full cell assembled with LiNi0.6Co0.2Mn0.2O2 cathode demonstrates excellent practicality. This study reveals the critical role of distorting NbO6 octahedron and expanding crystal spacing in facilitating rapid Li+ diffusion and enhancing charge storage performance of Nb2O5 at low temperatures.

Carbon-centric dynamics of Earth’s marine phytoplankton

Marine phytoplankton are fundamental to Earth's ecology and biogeochemistry. Our understanding of the large-scale dynamics of phytoplankton biomass has greatly benefited from, and is largely based on, satellite ocean color observations from which chlorophyll-a (Chla), a commonly used proxy for carbon biomass, can be estimated. However, ocean color satellites only measure a small portion of the surface ocean, meaning that subsurface phytoplankton biomass is not directly monitored. Chla is also an imperfect proxy for carbon biomass because cellular physiology drives large variations in their ratio. The global network of Biogeochemical (BGC)-Argo floats now makes it possible to complement satellite observations by addressing both these issues at once. In our study, we use ~100,000 water-column profiles from BGC-Argo to describe Earth's phytoplankton carbon biomass and its spatiotemporal variability. We estimate the global stock of open ocean phytoplankton biomass at ~314 Tg C, half of which is present at depths not accessible through satellite detection. We also compare the seasonal cycles of carbon biomass stocks and surface Chla visible from space and find that surface Chla does not accurately identify the timing of the peak annual biomass in two-thirds of the ocean. Our study is a demonstration of global-scale, depth-resolved monitoring of Earth's phytoplankton, which will be crucial for understanding future climate-related changes and the effects of geoengineering interventions if implemented.

Satellite remote sensing reveals the footprint of biodiversity on multiple ecosystem functions across the NEON eddy covariance network

Abstract Biodiversity relates to ecosystem functioning by modulating biogeochemical cycles of carbon, water, energy, and nutrients within and between multiple biotic and abiotic components of the ecosystems. However, large-scale, systematic measurements of plant biodiversity are still lacking, and the effects of biodiversity on measured biogeochemical processes are understudied. Here, we combined alpha (α) and beta (β) taxonomic measurements, spectral diversity from satellite observations, structural properties of the vegetation, and climatic drivers to assess the effect of biodiversity on ecosystem functional properties. Ecosystem functional properties were computed from eddy-covariance fluxes at 44 sites of the National Ecological Observatory Network. Based on the spectral variation hypothesis, we used the near-infrared reflectance of vegetation (NIRv) derived from Sentinel-2 satellite imagery to compute Rao’s quadratic entropy (Rao Q), a distance metric related to spatial heterogeneity. Using an automatic model averaging technique, we found that biodiversity proxies hold substantial explanatory power when predicting several ecosystem functions related to carbon and water exchange. In particular, NIRv-based Rao Q (RaoQNIRv) reflected positive biodiversity effects on productivity, as expected from the literature. In contrast, traditional taxonomic α-diversity indices were generally not selected as relevant predictors of the ecosystem functional properties. Yet, β-diversity strongly contributed to the prediction of carbon use efficiency, surface conductance, and water use efficiency. We also found that the RaoQNIRv is less affected by issues of saturation and bare soil contribution compared to RaoQNDVI. We show that spectral heterogeneity based on remotely sensed NIRv holds the potential for globally characterizing the biodiversity-ecosystem functioning relationship (BEF). While systematic measurements of taxonomic diversity co-located at biogeochemical measurement stations could reduce the uncertainty surrounding the BEF relationship at whole-ecosystem scale, remotely- sensed metrics characterizing important functional and structural diversity aspects of the landscape will be crucial for continuous spatiotemporal monitoring of biodiversity with relevant implications for ecosystem services to humankind.

Preparation of high strength and rigidity carbon layer on SiO material surface by dynamic CVD method using gas carbon source C2H2

The main issue in the application of silicon-based negative electrode materials is the inevitable volume expansion, leading to negative electrode material fracture, which severely impacts the performance of batteries. This study employed Chemical Vapor Deposition (CVD) (C2H2@SiO), solid-phase coating method (Pitch@SiO), and liquid-phase coating method (RGFQ@SiO) to coat the surface of SiO materials with a dense amorphous carbon structure. Material property analysis revealed that C2H2@SiO has a relatively small specific surface area (1.8 m2 g−1) and surface carbon increment (2.4 %). It exhibited high reversible specific capacity (1563.4 mAh g−1), high initial Coulombic efficiency (81.45 %), and low volume expansion rate (9.3 %). Mechanical performance testing indicated that the surface carbon layer Young's modulus of C2H2@SiO was the highest (35 GPa), suggesting that using the CVD method to obtain a dense carbon layer can enhance the structural strength of the material. Based on the electrochemical-mechanical coupling theory simulation analysis of the stress during the charge-discharge process of electrode materials, the evolution of concentration and stress field during lithium insertion process was obtained, showing that the coating can further improve the electrochemical and mechanical performance of the negative electrode materials effectively. Additionally, the negative electrode sheets fabricated using sample C2H2@SiO were assembled into 18650 cylindrical batteries, exhibiting excellent cycling performance in 1000 cycles at 25 °C with a capacity retention rate of 85.7 %, along with good rate capability and high/low-temperature performance. The conclusions of this study provide certain guidance for the design and optimization of negative electrode materials for battery electrodes.

Preparation and Electrical Properties of Nanocomposite Based on Epoxy Resin and Core-Shell Polyaniline/Multi-Walled Carbon Nanotubes

Nanocomposites of epoxy resin containing various concentrations of carboxylated multiwalled carbon nanotubes (C-MWCNTs) and surface modified C-MWCNTs various concentration of both C-MWCNTs and core-shell nanoparticles were prepared. The physical, mechanical and electrical properties of prepared epoxy nanocomposites were investigated using experimental evaluations such as dynamic mechanical thermal analysis (DMTA), differential scanning calorimeter (DSC), and tensile strength measurements. The results of DSC tests revealed that the introduction of nanoparticles into the epoxy resin did not have much effect on the curing system, and by adding these nanoparticles to the epoxy resin, there is no need to change the curing system. However, the released energy during of epoxy curing show a 24% increase with the introduction of nanofiller into the epoxy matrix. The results of electrical conductivity measurements indicated a higher elastic dielectric constant for nanocomposites up to 200% incomparison with neat epoxy resin. The use of these epoxy nanocomposites in modern electrical and electro-optical industries is of great practical importance.

Ultrafast laser-induced simultaneous carbonization and texturization of titanium alloy surface and its tribological properties

Due to the poor tribological properties, the applications of titanium alloy are restricted. Both laser texturing and surface coating are effective methods to enhance the tribological properties of titanium alloy surfaces. Hence, this study proposed a new ultrafast laser-induced simultaneous carbonization and texturization of titanium alloy surfaces to improve its tribological properties by modifying titanium alloy’s surface composition and micro-nanostructures in one step. A polymer film (polyimide, PI) was selected as the carbon source preplaced on the titanium alloy (Ti-6Al-4 V, TC4) surface. On the one hand, under ultrafast laser (picosecond 355 nm laser) irradiation, the laser-induced photothermal effect led to the carbonization of the polymer film and the formation of the pyrolytic carbon coating on the titanium alloy surface. Pyrolytic carbon also reacted with titanium alloy to form titanium carbides. On the other hand, ultrafast lasers also led to the melting and ablation of the titanium alloy surface, creating micro-nanostructures with interlocking micro-holes and micro-bumps. The coefficient of friction (COF) and wear rate of the titanium alloy surfaces were significantly reduced due to the synergistic effects of carbon coating and micro-nanostructures. It showed great significance in improving the tribological properties and the surface treatment of metallic materials.

Defective carbon-bridged Cu sites to boost oxygen reduction reaction in neutral zinc-air batteries

Novel carbon nanomaterials containing N-coordinated metal centers present an advantage in promoting the oxygen reduction reaction (ORR). Despite considerable progress, substantial challenges persist with the advancement of neutral Zinc-air batteries (ZABs), particularly in optimizing the trade-off between the catalytic activity and stability. Herein, employing nanoporous carbon impregnated with Cu(II)-phenanthroline complexes to prepare Cu-ONCs catalysts rich in Cu-Nx sites. Controllable carbon defects to capture Cu2+ enable the enrichment of metal sites on the porous carbon surface, and simultaneously effectively suppress the aggregation of active centers. The metal moieties, specifically Cu-Nx, are incorporated into the porous N-doped carbon, thereby introducing accessible active sites within the partially graphitized carbon framework. Furthermore, the abundant mesopores inside the carbon nanofibers promote the exposure of accessible active sites to substantially augment the electrochemically active electrochemically active area area. Given the unique structure and composition, Cu-ONCs show outstanding ORR activity in neutral and alkaline media, alone with negligible decay observed after 3000 cycles. Moreover, Cu-ONCs based neutral ZABs demonstrate a peak power density of 48.28 mW cm−2 and impressive rate performance. This work provides defects/vacancies insight on transition metal (TM)-based carbon support to facilitate the advancement of cutting-edge neutral ZABs.

Conductance Channels in a Single-Entity Enzyme.

For a long time, the prevailing view in the scientific community was that proteins, being complex macromolecules composed of amino acid chains linked by peptide bonds, adopt folded structure with insulating or semiconducting properties, with high bandgaps. However, recent discoveries of unexpectedly high conductance levels, reaching values in the range of dozens of nanosiemens (nS) in proteins, have challenged this conventional understanding. In this study, we used scanning tunneling microscopy (STM) to explore the single-entity conductance properties of enzymatic channels, focusing on bilirubin oxidase (BOD) as a model metalloprotein. By immobilizing BOD on a conductive carbon surface, we discern its preferred orientation, facilitating the formation of electronic and ionic channels. These channels show efficient electron transport (ETp), with apparent conductance up to the 15 nS range. Notably, these conductance pathways are localized, minimizing electron transport barriers due to solvents and ions, underscoring BOD's redox versatility. Furthermore, electron transfer (ET) within the BOD occurs via preferential pathways. The alignment of the conductance channels with hydrophilicity maps, molecular vacancies, and regions accessible to electrolytes explains the observed conductance values. Additionally, BOD exhibits redox activity, with its active center playing a critical role in the ETp process. These findings significantly advance our understanding of the intricate mechanisms that govern ETp processes in proteins, offering new insights into the conductance of metalloproteins.

Experimental and Theoretical Study on Surface Reactivity and CO Generation Mechanism of Bituminous Coal during Room-Temperature Oxidation.

To investigate the evolution of the microscopic chemical structure during the oxidation of bituminous coal at room temperature (25 °C) and infer the formation mechanism of carbon monoxide (CO), a self-designed closed-system coal oxidation experimental setup was employed to measure the CO generation from three bituminous coal samples [Duanwang (DW), Linsheng (LS), and Kunning (KN)]. 13C nuclear magnetic resonance and X-ray photoelectron spectroscopy were used to determine the structures and contents of different carbon atoms and surface elemental compositions and chemical states of the coal samples. Molecular models were constructed on the basis of the experimental data, and reactive force field pyrolysis simulation was used to trace the carbon atoms in the generated CO molecules. In combination with the results of interactive Mantel correlation analysis on the Fourier transform infrared experimental data of coal samples oxidized at room temperature for 0, 12, 24, 36, 48, and 60 h, the main functional groups, structures, and evolution of coal involved in CO formation during normal temperature oxidation were determined. The constructed molecular formulas for the coal samples were C154H122O28N2S for DW, C145H114O16N2S2 for LS, and C155H92O16N2S for KN. The formation of CO was related to the transformation of carbonyl (C═O), phenolic hydroxyl (-OH), ether (C-O-C), aromatic, and aliphatic structures in the coal.

Confined mass transport in two-dimensional capillary

Abstract Over the past decade, nanofluidics has undergone significant expansion, propelled by advances in crafting artificial channels at nanometric and sub-nanometric scales with diverse geometries. Central to this domain, two-dimensional capillaries have risen as a pivotal research platform, marked by their angstrom-level precision, unparalleled wall surface smoothness, and clearly defined surface charge states. Their advent has profoundly deepened our understanding of mass transport dynamics, spanning gases, water molecules, and ions, shedding light on the complex interactions among various influencing factors and revealing a range of previously undiscovered physical phenomena. This review delves into the development of 2D capillaries, the principal fluid transport phenomena observed within, and the critical elements that affect these processes. We also touch on a fascinating discovery - the quantum liquid friction seen in water moving over carbon surfaces. In anticipation of future explorations in nanofluidics, we envision a trajectory aimed at emulating the efficiency levels of biological protein channels, setting the stage for a new era of scientific inquiry and technological innovation.

Unlocking the solution-phase molecular transformation of biochar during intensive rainfall events: Implications for the long-term carbon cycle under climate change

The unclear turnover of soluble and solid phases of biochar during increasingly severe climate change (e.g., intensive rainfall) raised questions about the carbon stability of biochar in soil. Here, we present an in-depth analysis of the molecular-level transformations occurring in both the soluble and solid phases of biochar subjected to prolonged wet-dry cycles with simulated rainwater. Biochar properties, including surface functionality and carbon texture, greatly affected the transformation route and led to a distinct stability variation. The rich alkyl −CH3 on the low-temperature biochar (450 °C) was oxidized to hydroxymethyl −CH2OH or formyl −CHO, and the ester −COOC− or peptide −CONHC− bonds were fragmented in the meantime, causing the release of protein- or lipid-like organic carbon and the declined carbon stability (Æ, tested by H2O2 oxidation, from 60.1% to 53.2%). After a high-temperature (750 °C) pyrolysis process, only oxidation of the surface −OH with limited bond breaking occurred after rainwater elution, presenting a marginal composition difference with constant stability. However, the fragile carbon nature of biochar, caused by CO2 activation, led to enhanced fragmentation, oxidation, and hydration, resulting in the release of tannin-like organic carbon, which compromised the carbon storage (Æ decreased from 81.2% to 73.0%). Our findings evaluated the critical transformation of biochar during intensive rainfall, offering crucial insights for designing sustainable biochar and achieving carbon neutrality.

Architectural Design of a Multichannel Porous Carbon Fiber for Efficient Electromagnetic Microwave Absorption.

An ingenious microstructure of electromagnetic microwave absorption materials is crucial to achieve strong absorption and a broad bandwidth. Herein, one-dimensional (1D) carbon fibers with implantation of zero-dimensional (0D) ZIF-8-derived carbon frameworks and construction of a three-dimensional (3D) microcosmic multichannel porous structure are fabricated by electro-blown spinning, solvent-thermal reaction, and high-temperature pyrolysis techniques. The 1D carbon fiber skeleton with a multichannel structure provides a direct axial conductive pathway for charge transport, which plays an important role in dielectric loss. The 0D surface carbon frameworks offer plenty of heterogeneous interfaces to trigger intensive interfacial polarization loss and act as dihedral angles for microwave scattering. The 3D microcosmic multichannel pores can not only generate multiple reflections as much as possible to dissipate electromagnetic microwave energy but also supply huge interior cavities to improve impedance matching. Thanks to the synergistic effect of a strong electrically conductive pathway for enhancing the conductive loss, a plenteous heterogeneous interface for triggering intensive interfacial polarization loss, microcosmic multichannel pores for generating multiple reflections and improving impedance matching, and N and O atom doping for inducing dipole polarization, the optimal sample with an ingenious microstructure delivers an excellent absorption performance of a minimum reflection loss of -35.5 dB at a thickness of 5.0 mm and an effective absorption bandwidth of 6.72 GHz (10.96-17.68 GHz) at a thickness of 2.0 mm. Such a well-designed multichannel porous carbon fiber may pave the way for the exploitation of high-performance microwave absorbing materials.

Cobalt-Doped Hydrochar Derived from Microalgae as an Efficient Peroxymonosulfate Activator for Paraben Degradation

Hydrochar, an attractive member of the carbonaceous materials, is derived from biomass and projects great potential in peroxymonosulfate (PMS) activation, but has not been studied much. Herein, by using the large-scale cultured Chlorella vulgaris and field-collected bloom algae, a series of porous hydrochar was synthesized via a facile hydrothermal carbonization reaction, while Co doping significantly increased their specific surface areas, carbonization degree, and surface functional groups. These Co-doped hydrochar (xCo-HC, x: amount of the Co precursor) could efficiently activate the PMS, resulting in nearly 100% removal of five common paraben pollutants within 40 min. A dosage of 0.2Co-HC of 0.15 g/L, a PMS concentration of 0.6 g/L, and an unadjusted pH of 6.4 were verified more appropriately for paraben degradation. The coexistence of Cl−, SO42−, and humic acid inhibited the degradation, while HCO3− showed an enhancing effect. No observable change was found at the presence of NO3−. Quenching results illustrated that the produced •SO4− during the conversion of doped Co3+/Co2+ acted as the dominant active species for paraben degradation, while •O2−, 1O2, and •OH contributed relatively less. The algae-based hydrochar potentially facilitated the electron transfer in the xCo-HC/PMS system. Overall, this study develops a new strategy for resource utilization of the abundant algae.

Functionalized construction of multiple active centers for durability controlling during catalytic combustion of chlorinated aromatic hydrocarbons

The catalytic combustion of chlorine-containing VOCs primarily encounters the bottleneck of catalyst poisoning by chlorine, thereby impeding the further industrial application of this technology. The development of multi-active catalytic materials for discerning chlorine fixation, chlorine transfer, deep oxidation during elimination of chlorine-containing VOCs can mitigate catalyst chlorination and enhance stability. Herein, we utilizing LDHs as catalyst precursors and successfully synthesized flower-like Co2FexCr1-xOy catalyst with different functionalized reaction centers. The addition of Cr improved the surface lattice oxygen, oxygen vacancies, and acid sites of catalyst. The removal efficiency of CB can be achieved >90 % at 247 °C (WHSV = 33000 mL · g−1·h−1). The fixation of dissociated chlorine contributed by Cr not only enhances oxidation performance and directional adsorption of chlorine, but also improves carbon deposition resistance and catalyst sintering resistance significantly. Compared with Co2Fe1Oy, Co2Fe0.67Cr0.33Oy catalyst achieves a remarkable threefold reduction in surface carbon deposition. The DFT calculation revealed that water dissociation energy over the Co site is −0.72 eV, which is significantly lower than Fe (−0.59 eV) and Cr (−0.17 eV), facilitating water dissociation and subsequently removes a substantial amount of accumulated chlorine on Cr to form HCl. With the help of In situ DRIFT and GC/MS analysis, we found the efficient removal of chlorine atoms enhances the exposure of active sites on the catalyst surface with hydrolyzed hydroxyl group, which facilitating the conversion of aromatic hydrocarbons into a greater quantity of maleate and carboxylate species. This phenomenon is beneficial for the subsequent mineralization process of chlorobenzene. This work provide valuable insights for multi-active site catalysis mechanism in practical applications aimed at eliminating chlorinated organic waste gases from industrial emissions.

Voltage-Driven Molecular Photoelectrocatalysis of Water Oxidation.

Molecular photocatalysis and photoelectrocatalysis have been widely used to conduct oxidation-reduction processes ranging from fuel generation to electroorganic synthesis. We recently showed that an electrostatic potential drop across the double layer contributes to the driving force for electron transfer (ET) between a dissolved reactant and a molecular catalyst immobilized directly on the electrode surface. In this article, we report voltage-driven molecular photoelectrocatalysis with a prevalent homogeneous water oxidation catalyst, (bpy)Cu (II), which was covalently attached to the carbon surface and exhibited photocatalytic activity. The strong potential dependence of the photooxidation current suggests that the electrostatic potential drop across the double layer contributes to the driving force for ET between a water molecule and the excited state of surface-bound (bpy)Cu (II). Scanning electrochemical microscopy (SECM) was used to analyze the products and determine the faradaic efficiencies for the generation of oxygen and hydrogen peroxide. Unlike electrocatalytic water oxidation by (bpy)Cu (II) in the dark, which produces only O2, the voltage-driven photooxidation includes an additional 2e- pathway generating H2O2. DFT calculations show that the applied voltage and the presence of light can alter the activation energy for the rate-determining water nucleophilic attack steps, thereby increasing the reaction rate of photo-oxidation of water and opening the 2e- pathway. These results suggest a new route for designing next-generation hybrid molecular photo(electro)catalysts for water oxidation and other processes.

Enhancement on Anaerobic Digestion of Food Waste using Spend Coffee Ground Derived Biochar for Biogas Production

In recent, one of the available energy sources is biogas where it is suitable for necessities of the future with the appropriate application of digestion technology. However, the technology used which is anaerobic digestion (AD) faces some challenges especially for food waste including low biogas productivity due to unstable operation efficiency. In order to overcome this shortcoming, spent coffee ground (SCG) derived biochar is introduced as an additive in AD process to enhance the production. To promote the efficiency of the AD, the optimum condition of biochar dosage, the amount of feedstock and pH value were studied. The experimental findings revealed that 13.528ml/g of biogas yield was achieved under optimum condition of 7g of biochar, 500g of feedstock at pH 7 for 14 days. The characterization analysis of biochar showed that, the carbon content and surface area as well as several functional groups of SCG biochar has led to the enhancement of the biogas production during AD process of food waste. The outcomes shows that the addition of SCG biochar can solve the instability issues of AD process yet increase the production of biogas.

Entangled S-doped LiFePO4 with carbon network for self-supporting cathode of flexible energy storage devices

This paper describes the development of a highly flexible self-supporting cathode incorporating a network of entangled carbon nanofibers (CNFs) and well-dispersed sulfur-doped lithium iron phosphate (SLFP) particles. Through a spin-on-dopant process, sulfur atoms were successfully incorporated into both the surface carbon layer and inner LFP particles. The resulting S-doped carbon@LFP (SLFP-CNF) flexible electrode featured a unique hybrid composite architecture in which the interconnecting CNF framework considerably enhanced both the physical and electrochemical properties. Notably, the SLFP-CNF electrode maintained its structural integrity even after 5000 flexibility cycles, demonstrating robust mechanical stability. The electrode exhibited a high ionic diffusion rate of 9.14 × 10–13 cm²/s, which is attributed to the expanded lattice constant of the S-doped LFP particles, which facilitates favorable Li-ion pathways. This contributes to a high specific capacity of 135.82 mAh/g and superior rate performance of 74.16 mAh/g after 1500 cycles (92.4 % retention rate) at a current density of 2000 mA/g. This enhanced performance is further supported by the conductive S-doped carbon layer, which enables rapid electron transport and ensures excellent cyclability. These results indicate that the SLFP-CNF flexible cathode is a promising candidate for next-generation flexible lithium-ion batteries.

Effects of carbon levels and surface area variations on mild steel strength: A comparative study

This study investigates the dynamic interplay between carbon levels and surface area variations on mild steel strength during the rolling process. Focused on understanding the nuanced relationship between these factors and steel durability, the research adopts a systematic approach. Controlled adjustments in carbon levels and surface area variations are employed to assess their impact on the structural integrity and tensile strength of mild steel. Through rigorous analysis and measurement, this study aims to unveil the intricate connections between carbon content, surface area alterations, and steel strength, offering critical insights for optimizing rolling processes in industrial settings. The experimental works have been conducted with carbon levels variations and surface area variations. The samples were tested in two different laboratories, however, the results of two laboratories are almost similar. The higher carbon content increases strength and yield strength varies with different carbon level and surface area. The surface area variations are affected the mechanical properties of mild steel. The maximum stress recorded was 700 MPa and the breaking point observed at 540 MPa. The findings aspire to contribute significantly to refining manufacturing techniques and developing more resilient steel products, thereby advancing our comprehension of material behavior in mechanical applications.

Mechanism of nanofiltration fouling in high hardness and dissolved organic carbon surface water based on chemical characterization of foulant

Nanofiltration (NF) membranes purifying high hardness and dissolved organic carbon (DOC) surface water are prone to much more severe fouling than those supplied by waters of better quality. We conducted analyses on an ultrafiltration/nanofiltration pilot plant supplied by high hardness and DOC water to investigate the NF foulant chemical composition and fouling mechanism. NF foulant was primarily organic (97 %). Analyses of the physically (PRF) and chemically (CRF) removable foulant components unveiled their different compositions. CRF, i.e., the fouling substances directly adsorbed on the nanofilter surface and pores, mainly comprised hydrophobic and low molecular weight & building blocks of humic substances. PRF, i.e., the gel-layer formed by the substances continuous deposition, contained more compounds with hydrophilic character and a wide range of molecular weights, from low molecular weight & building blocks (<1 kDa) to humic substances (1 – 20 kDa) and biopolymers (>20 kDa), showing a more uniform distribution of those features. Calcium and magnesium may have promoted the bridging of the organics with the NF membrane, and between the organics, strengthening the foulant structure. The presence of a humic- and EPS-conditioning film may have interfered with or contributed to bacterial adhesion, respectively, forming biofilm patches.

Effect of the carbon surface chemistry on the metal speciation in Ru/C catalysts. Impact on the transformation of levulinic acid to γ-valerolactone

A set of Ru/C catalysts prepared using a commercial active carbon and a series of carbon materials derived from it (treatment in N2 flow, at 300, 600 or 900 °C that selectively removes surface oxygen complexes), of similar textural properties and different surface chemistry, were used, without reduction treatment, in the aqueous phase transformation of levulinic acid (LA) to γ-valerolactone (GVL) at 70 °C. The prepared Ru/C catalysts were active, being activity and selectivity strongly dependent on the support surface chemistry. It was confirmed that the supported Ru species became reduced under reaction conditions, and this process was more efficient in catalysts prepared with the heat treated supports, due to the different interactions created between Ru species and the support surface. In a cleaner carbon surface, the anchorage of the Ru species on carbon oxygen groups was limited, and they were more prone to be reduced and to move, forming more defined metallic structures. The carbon surface chemistry determined the Ru speciation (reduced and oxidized species), and the proportion of reduced Ru drived the H spill over process, which was related to the creation of protonic acid sites, proposed to be key point to explain the trend in selectivity to GVL.