Specific Surface Functional Groups Research Articles

Interfacial Interaction between Zn2+ and Surface Functional Groups Impacting Self-Assembly of ZnO on Cellulose Nanofibrils.

The mechanism underlying the interfacial interaction between ZnO and surface functional groups, which drives the self-assembly of ZnO nanoflowers on the cellulose nanofibril (CNF) surface, remains inadequately understood. Moreover, the ideal sites for the loading and growth of ZnO nanoflowers on the oxygen atoms (Os) of various surface functional groups on the CNF surface are not well-defined. This work addressed these gaps by systematically regulating the size and surface charge density of CNF templates through minor surface modifications and adjustments in processing cycles by using an ultrafine grinder. Physicochemical analyses demonstrated that the ZnO nanoflowers exhibited sizes (μm)/pieces/thickness (nm) of 0.86/16/20.1 for ZnO/TOCNFs, 0.88/17/20.4 for ZnO/ACNFs, and 0.89/16/20.5 for ZnO/ECNFs, respectively. Simulation calculations revealed that the interaction between Zn2+ ions and the Os of hydroxyl (-OH) groups exhibited the most favorable binding energy of -31.7 kcal/mol. These findings suggested that the surface charge density rather than specific surface functional groups primarily governs the loading and growth of ZnO nanoflowers on the CNF surface. The OS from -OH groups on the surface of CNF templates were optimal for both the loading and growth of ZnO nanoflowers. Overall, this study provides crucial theoretical insights into the design and optimization of the ZnO/CNF composites.

Adsorptive removal of heavy metals, dyes, and pharmaceuticals: Carbon-based nanomaterials in focus

The use of carbon-based nanomaterials, including carbon nanotubes, carbon dots, graphene/graphene oxide, fullerene, and their derivatives, in the removal of emerging pollutants from wastewater has become a promising method in water treatment. These nanomaterials exhibit exceptional adsorption capabilities and selectivity due to their extensive surface area, customizable surface chemistry, and unique structural features, which involve factors like π-π interactions, electrostatic interactions, and specific surface functional groups. A notable experiment demonstrated the effectiveness of carbon nanotubes as adsorbents for removing Ismate violet 2R dye from contaminated water. The results showed a remarkable maximum removal efficiency of 91.71 % at a concentration of 10 mg/L within a brief 120-min period. This article conducts a comprehensive evaluation of the adsorptive removal of emerging pollutants from wastewater using carbon-based nanomaterials, with a focus on developments between 2015 and 2023. An in-depth bibliometric analysis of 1285 research publications retrieved from the Web of Science (WOS) and Scopus databases reveals a substantial increase in the number of publications, rising from 50 in 2015 to 158 in 2023. This signifies a burgeoning emphasis on both practical application and technological advancement in this domain. Furthermore, this review explores the intricacies of adsorption mechanisms, factors influencing the adsorption performance of carbon-based nanomaterials, and the associated challenges and limitations when applied in wastewater treatment. By thoroughly investigating these constraints and potential advantages, this article provides valuable insights for the development of future carbon-based nanomaterials, aiming to enhance their efficiency and expand their applications in the field of wastewater treatment.

Physical separation of catalytic oxidation and reduction sites onto photocatalyst assisted by surface functional groups for enhanced hydrogen evolution

Physical separation of catalytic reduction and oxidation sites is a common approach in photocatalysis to optimize photogenerated charge separation and improve redox ability of catalysts. Herein, we report a novel site-directed photodeposition technology assisted by specific surface functional groups for the synthesis of Nix/NH2–Cd0.5Zn0.5S–S2- (Nix/N-CZS-S2-) catalyst. Two creative functions are exhibited. On the one hand, the surface functional groups –NH2 act as a bridge to anchor catalytic reduction center Ni, and this particular anchor form provides a new electron transfer channel for photocatalytic hydrogen evolution. On the other hand, the surface functional groups S2− provides sites for holes that can be eliminated by the sacrificial agent. As a result, these two advantages guarantee the hydrogen evolution of the Ni2/N-CZS-S2- to reach 32,025 μmol g−1·h−1 and the quantum yield to reach 25.68 % at 420 nm. This particular site-directed photodeposition technology can optimize charge transfer kinetics and improve redox reaction kinetics of catalyst. In addition, it can be extended to related systems as an effective strategy for enhanced photocatalysis performance.

COx‐Resistant Oxidative Dehydrogenation of Cyclohexane Catalyzed by sp3@sp2Nanodiamonds towards Highly Selective Cyclohexene Production

AbstractDeep oxidation/dehydrogenation are longstanding problems for decades in catalytic oxidative dehydrogenation (ODH) of cyclohexane and other alkanes. Here we show a metal‐free catalyst of nanodiamonds (NDs) with unique sp3@sp2hybrid structure that catalyzes COx‐resistant cyclohexane ODH with remarkable reactivity towards cyclohexene production. The selectivity of cyclohexene can reach as high as 67 % with significantly suppressed COxemission (<5 %), which is on top of the highest reported values among other metal(oxide)/metal‐free catalysts. Structural evolution of sp3@sp2NDs under annealing treatments and their specific surface functional groups are systematically studied using TEM, XPS, Raman and TPD. By comparing with carbon nanotubes (CNTs), we found that the carbonyl groups stabilized on strained sp3@sp2core‐shell NDs enhanced the cyclohexene selectivity via preferential cleavage of C−H over C−C bond. Kinetic studies further revealed the underlying reaction pathways that cyclohexane is rapidly dehydrogenated to cyclohexene which subsequently transforms into benzene (fast) and COx(slow). Deep oxidation of both cyclic hydrocarbons is largely suppressed due to the low density of electrophilic functional groups on strongly curved graphitic surface of sp3@sp2NDs.

A novel one-pot strategy for fabrication of PEGylated MoS2 composites for pH responsive controlled drug delivery

Abstract Molybdenum disulfide (MoS2) is one of the most promising two-dimensional (2D) materials after graphene oxide. Its excellent properties make it promising for various applications, especially in the field of biomedicine owing to its small size, unique 2D morphology and photothermal conversion capacity. However, the lack of specific surface functional groups has still largely impeded their surface modification and for drug loading and controlled release. In this paper, the surface of MoS2 sheets was modified by hydrazine groups, which could form dynamic hydrazone bonds with CHO-PEG and doxorubicin hydrochloride (DOX) to construct the PEGylated MoS2 based drug delivery systems. The structure, thermal stability, surface morphology and particle size of MoS2 related materials were characterized by different equipment. The characterization results confirm that these functionalized MoS2 (MS-CO-NH) composites have been successfully prepared through the formation of dynamic bonds. On the other hand, the release of MS-P-D composites loaded with CHO-PEG and DOX showed that pH responsive behavior, and had a good sustained-release effect. More importantly, cell viability and internalization results showed that MS-CO-NH material had excellent biocompatibility. MS-P-D composite has good cancer treatment effect, and can transport DOX into HepG2 cells and slowly release DOX into the nucleus to kill cancer cells. In view of the results, we believe that this new MoS2-based vector is expected to be a candidate for controlling intracellular drug delivery and cancer treatment.

Facile green synthesis of carbon dots from Pyrus pyrifolia fruit for assaying of Al3+ ion via chelation enhanced fluorescence mechanism

In this work, we synthesized fluorescent carbon dots (CDs) using Pyrus pyrifolia (pear) fruit via hydrothermal method at 180 °C for 6 h without using any further treatment or surface passivating agents. The synthesized CDs possess intense blue fluorescence under UV lamp at 365 nm and exhibit emission peak at 471 nm when excited at 390 nm. Because of specific surface functional groups, the synthesized CDs showed high selectivity to detect Al3+ ion through chelation enhanced fluorescence (CHEF) mechanism. The emission peak intensity of CDs at 471 nm was gradually enhanced with increasing concentration of Al3+ ion, thereby Al3+ ion was quantified by plotting calibration curve over the range of 0.005–50 μM with a detection limit of 0.0025 μM (2.5 nM). The nanoprobe was subsequently evaluated by assaying Al3+ ion from spiked water samples, signifying the utility of nanoprobe for assaying of Al3+ ion real samples. Furthermore, we also demonstrate that the bioimaging ability of CDs for imaging of Bacillus subtilis bacterial cell, suggesting that the nanoprobe can be used for cell imaging applications.

Ion Dynamics and Electrosorption in Carbon Electrodes with Bimodal Porosities and Heterogeneous Interfaces

Electrochemical capacitors offer high reliabilities and power densities and demonstrate exceptional promise in a broad range of energy storage and management applications. However, research efforts have not, to date, properly explored the influence of electrode interfaces’ heterogeneity and disorder on charge storage and dynamics of electrosorbed ions. Surface functional groups and structural carbon defects contribute quantum capacitance.[1] Specific surface functional groups, which must appropriately match the chemistries of electrosorbed ions, develop favorable interfaces that reduce impedance and improve cyclabilities.[2] Finally, ionophilic surfaces draw ions away from pore surfaces and improve electrosorption during charge and discharge processes.[3] However, these effects strongly depend on electrode pore dimensions and behaviors of ions in confinement. Furthermore, standard materials characterization and electrochemical testing techniques cannot properly assess interactions at electrode/electrolyte interfaces. Subsequently, in-depth studies must rely on combinations of well-tailored experimental model systems, in-depth X-ray and neutron scattering techniques, and computational modeling to assess the influences of disordered interfaces on capacitance. Our research investigated the effect of electrode surface heterogeneity and disorder in complex pore architectures and electrolytes with large, non-idealized electrolytes. The approach used carbide-derived carbons (CDCs) synthesized from a Mo2C precursor at 800 °C. This electrode material offered bimodal pore size distributions (0.8 nm and 2.6 nm diameter pores, shown in Figure 1a), and 1300 °C vacuum annealing or 400 °C air oxidation yielded, respectively, defunctionalized or oxidized pore surfaces. We filled these pores with 1-octyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([OMIm+][TFSI-]) room-temperature ionic liquid (RTIL). QENS measurements on these systems determined that the ions were significantly more mobile in oxidized pores than in defunctionalized pores (Figure 1b). A Cole-Cole model derived mobility information, and the RTIL diffusion coefficient in oxidized pores (2.71*10-10 m2 s-1) was more than twice as large as the one for the same RTIL in defunctionalized pores (1.05*10-10 m2 s-1) due to lower ion densities in oxidized pores. Electrochemical impedance analysis showed that electrochemically driven ionic mobility was higher in oxidized pores. On the other hand, defunctionalized pores demonstrated contained higher ion densities, and, subsequently, featured higher charge storage densities (Figure 3f). However, cyclic voltammograms suggested charge saturation and pore de-filling behaviors at low potentials; surface chemistry influenced the magnitude of this effect. Molecular dynamic (MD) simulations showed similar strong affinities of oxidized surfaces for RTIL ions, which lowered their charge storage densities in 2.6 nm diameter pores. X-ray Pair Distribution Function (PDF) analysis showed differences in ion-ion correlations between bulk and confined states and further underscored the influence of pore and ion diameter on electrode/electrolyte interactions at heterogeneous interfaces. [1] Dyatkin, B. & Gogotsi, Y. Effects of Structural Disorder and Surface Chemistry on Electric Conductivity and Capacitance of Porous Carbon Electrodes. Faraday Discussions172, 139-162, (2014). [2] Dyatkin, B., et al. Capacitance, Charge Dynamics, and Electrolyte-Surface Interactions in Functionalized Carbide-Derived Carbon Electrodes. Progress in Natural Science - Materials International25, 631–641, (2015). [3] Dyatkin, B., et al. Influence of Surface Oxidation on Ion Dynamics and Capacitance in Porous and Non-Porous Carbon Electrodes. The Journal of Physical Chemistry C, (2016). Figure 1

Nitrogen-Doped Activated Carbon-Based Ammonia Sensors: Effect of Specific Surface Functional Groups on Carbon Electronic Properties

Wood-based commercial activated carbon (BAX) and its oxidized counterpart (BAX-O) were treated with melamine and then heated at 450 °C in nitrogen. Further oxidation with nitric acid was also applied. The carbons were tested for ammonia sensing (45–500 ppm of NH3). Even though all samples exhibit p-type conduction, their exposure to NH3 led to different electrical outcomes. It was found that the electronic and transport properties of the carbons strongly depend on the type of nitrogen groups/surface defects, their concentration, and distribution in the carbon matrix. Pyridines and nitropyridines are the most important. A competition between the structural and chemical features of the carbons as those governing the sensing signals was observed. Exposure to ammonia altered the surface chemistry of the samples, and therefore their electrical properties. When sensitivity to H2S was tested to evaluate the selectivity of our sensors, the results showed that the chips are selective to NH3 in terms of the respons...

Effect of strong acid functional groups on electrode rise potential in capacitive mixing by double layer expansion.

The amount of salinity-gradient energy that can be obtained through capacitive mixing based on double layer expansion depends on the extent the electric double layer (EDL) is altered in a low salt concentration (LC) electrolyte (e.g., river water). We show that the electrode-rise potential, which is a measure of the EDL perturbation process, was significantly (P = 10(–5)) correlated to the concentration of strong acid surface functional groups using five types of activated carbon. Electrodes with the lowest concentration of strong acids (0.05 mmol g(–1)) had a positive rise potential of 59 ± 4 mV in the LC solution, whereas the carbon with the highest concentration (0.36 mmol g(–1)) had a negative rise potential (−31 ± 5 mV). Chemical oxidation of a carbon (YP50) using nitric acid decreased the electrode rise potential from 46 ± 2 mV (unaltered) to −6 ± 0.5 mV (oxidized), producing a whole cell potential (53 ± 1.7 mV) that was 4.4 times larger than that obtained with identical electrode materials (from 12 ± 1 mV). Changes in the EDL were linked to the behavior of specific ions in a LC solution using molecular dynamics and metadynamics simulations. The EDL expanded in the LC solution when a carbon surface (pristine graphene) lacked strong acid functional groups, producing a positive-rise potential at the electrode. In contrast, the EDL was compressed for an oxidized surface (graphene oxide), producing a negative-rise electrode potential. These results established the linkage between rise potentials and specific surface functional groups (strong acids) and demonstrated on a molecular scale changes in the EDL using oxidized or pristine carbons.

Synthesis of Latex Particles with Surface Functional Groups and Their Applications for the Fabrication of Porous Materials

In this study, monodisperse latex particles with specific surface functional groups were synthesized by emulsifier-free emulsion polymerization. Amidine or carboxylated polystyrene nanospheres with narrow size distribution were prepared by emulsion polymerization using AIBA (α,α′-zodiisobutyramidine dihydrochloride) as amine-containing initiator or acrylic acid as carboxyl-containing comonomer, respectively. Factors affecting the particle size and distribution were systemically studied by changing the amount of initiator or monomer, the polymerization temperature, and the stirring speed of emulsion polymerization reactor. Monodisperse polymethylmethacrylate beads were also synthesized by soapless emulsion polymerization using methacrylic acid or aminoethylmethacrylate hydrogen hydrochloride as comonomer for the surface functionalization of the particles. As applications of the latex beads, the polymeric particles were adopted as templating materials for the fabrication of macroporous titania film and meso-macroporous silica particles by colloidal templating method.

Studying the impact of RO membrane surface functional groups on alginate fouling in seawater desalination

Despite extensive studies on the relationship between membrane surface properties and fouling, the roles of specific surface functional groups in RO membrane fouling under different solution conditions are still poorly understood. This research aims to elucidate how specific surface functional groups affect RO membrane fouling by alginate in solution conditions relevant to seawater desalination. Common RO membrane surface functionalities are represented by self-assembled mono-layers with –COOH, –NH2, –CONH2 and –OH ending groups. Alginate adsorption and removal was studied under relevant solution conditions using quartz crystal microbalance with dissipation monitoring (QCM-D). The results show that ionic composition has great impacts on alginate–alginate interaction, which is more important than membrane surface chemistry in determining alginate adsorption equilibrium at the high ionic strength of seawater. The initial adsorption rate is highly sensitive to surface chemistry. The –NH2 group has strong affinity for alginate, yet the –COOH group exhibits the highest adsorption rate in simulated seawater. The reversibility of the adsorbed layer was influenced by both alginate–surface interaction and the structure of the layer. The large alginate aggregates formed in the presence of Ca2+ result in loosely packed and less viscous adsorbed layer on the surface, which is easier to remove by surfactant cleaning.

Influence of pH and surface oxygen-containing groups on multiwalled carbon nanotubes on the transformation and adsorption of 1-naphthol

The pH-dependent behavior, including the transformation of 1-naphthol by oxidative polymerization to form precipitates in solution and the adsorption of 1-naphthol onto carbon nanotubes (CNTs), was examined. Neglecting the precipitate loss of 1-naphthol and possibly of similar chemicals may result in the overestimation of their adsorption and inadequate interpretation of the underlying adsorption mechanisms. Surface oxygen-containing groups on CNTs and the dissociated species of these groups can interact with the dissociated and neutral species of 1-naphthol in a way similar to polymerization, thus promoting the adsorption of 1-naphthol onto CNTs. Adsorption onto CNTs may reduce the polymeric precipitates of 1-naphthol in solution by possibly decreasing aqueous 1-naphthol concentrations. These observations and the underlying mechanisms are important for predicting the fate and risks of naphthalene and carbaryl in the environment because 1-naphthol is a primary metabolite of naphthalene and carbaryl. In addition, it is possible to enhance the removal of 1-naphthol and similar chemicals by controlling the pH and designing specific surface functional groups for CNTs.

Single Particle Orientation and Rotation Tracking Discloses Distinctive Rotational Dynamics of Drug Delivery Vectors on Live Cell Membranes

Engineered nanoparticles have emerged as potentially revolutionary drug and gene delivery vectors. Using rod-shaped gold nanoparticles as a model, we studied for the first time the rotational dynamics of nanoparticle vectors on live cell membranes and its impact on the fate of these nanoparticle vectors. The rotational motions of gold nanorods with various surface modifiers were tracked continuously at 200 frames/s under a differential interference contrast microscope. We found that the rotational behaviors of gold nanorod vectors are strongly related to their surface charges. Specific surface functional groups and the availability of receptors on cell membranes also contribute to the rotational dynamics. The study of rotational brownian motion of nanoparticles on cell membranes will lead to a better understanding of the mechanisms of drug delivery and provide guidance in designing surface modification strategies for drug delivery vectors under various circumstances.

Understanding Nanoparticle Drug Delivery from Rotational Dynamics and Behaviors of Functionalized Gold Nanorods on Live Cell Membranes

Gold nanoparticles with distinctive surface properties share different interactions with the cell membranes, thus show different activities in drug delivery. We used gold nanoparticles themselves as non-blinking, non-photobleaching nanoprobes to study nanoparticle drug delivery. Unlike most single particle tracking experiments that studied the translational motions of particles, we tracked the real-time rotational behaviors of single gold nanorods on live A549 cell membranes. The rotations of differently functionalized gold nanorods are tracked constantly under a Differential Interference Contrast (DIC) Microscope at 200 frames per second. The time series of DIC intensities of the images reflect the rotational dynamics of the gold nanorods. The in-plane and out-of-plane rotations were characterized by calculating the correlation coefficients between bright part DIC intensities and dark part DIC intensities of the gold nanorod. The autocorrelations of the image contrast time-series were calculated, and the rotation characteristic times over time of observation were derived by a non-linear fitting. We found that on one hand, the rotational behaviors of gold nanorod probes are strongly related to the surface charges of the gold nanorods, such as positively charged gold nanorods (PEIs modified, TAT modified, and CTAB stabilized gold nanorods) show a stronger interaction with cell membranes than negative ones (tranferrin modified and carboxylic gold nanorods). On the other hand, specific surface functional groups and availabilities of receptors on cell membranes also contribute to the rotational dynamics of the gold nanorods (such as shown in the differences between transferring modified gold nanorods and carboxylic gold nanorods). This study of nanoparticle rotational diffusion on cell membranes will lead to better understanding of the mechanisms of drug delivery and provide guidance in designing the modification strategies for drug delivery agents under different circumstances.

Probing Functional Groups at the Gas–Aerosol Interface Using Heterogeneous Titration Reactions: A Tool for Predicting Aerosol Health Effects?

The complex chemical and physical nature of combustion and secondary organic aerosols (SOAs) in general precludes the complete characterization of both bulk and interfacial components. The bulk composition reveals the history of the growth process and therefore the source region, whereas the interface controls--to a large extent--the interaction with gases, biological membranes, and solid supports. We summarize the development of a soft interrogation technique, using heterogeneous chemistry, for the interfacial functional groups of selected probe gases [N(CH(3))(3), NH(2)OH, CF(3)COOH, HCl, O(3), NO(2)] of different reactivity. The technique reveals the identity and density of surface functional groups. Examples include acidic and basic sites, olefinic and polycyclic aromatic hydrocarbon (PAH) sites, and partially and completely oxidized surface sites. We report on the surface composition and oxidation states of laboratory-generated aerosols and of aerosols sampled in several bus depots. In the latter case, the biomarker 8-hydroxy-2'-deoxyguanosine, signaling oxidative stress caused by aerosol exposure, was isolated. The increase in biomarker levels over a working day is correlated with the surface density N(i)(O3) of olefinic and/or PAH sites obtained from O(3) uptakes as well as with the initial uptake coefficient, γ(0), of five probe gases used in the field. This correlation with γ(0) suggests the idea of competing pathways occurring at the interface of the aerosol particles between the generation of reactive oxygen species (ROS) responsible for oxidative stress and cellular antioxidants.

Surface Complexation of Neptunium(V) onto Whole Cells and Cell Components of Shewanella alga: Modeling and Experimental Study

We systematically quantified surface complexation of Np(V) onto whole cells, cell wall, and extracellular polymeric substances (EPS) of Shewanella alga strain BrY. We first performed acid and base titrations and used the mathematical model FITEQL to estimate the concentrations and deprotonation constants of specific surface functional groups. Deprotonation constants most likely corresponded to a carboxyl group not associated with amino acids (pK(a) approximately 5), a phosphoryl site (pK(a) approximately 7.2), and an amine site (pK(a) > 10). We then carried out batch sorption experiments with Np(V) and each of the S. alga components as a function of pH. Since significant Np(V) sorption was observed on S. alga whole cells and its components in the pH range 2-5, we assumed the existence of a fourth site: a low-pK(a) carboxyl site (pK(a) approximately 2.4) that is associated with amino acids. We used the SPECIATE submodel of the biogeochemical model CCBATCH to compute the stability constants for Np(V) complexation to each surface functional group. The stability constants were similar for each functional group on S. alga bacterial whole cells, cell walls, and EPS, and they explain the complicated sorption patterns when they are combined with the aqueous-phase speciation of Np(V). For pH < 8, the aquo NpO(2)(+) species was the dominant form of Np(V), and its log K values for the low-pK(a) carboxyl, mid-pK(a) carboxyl, and phosphoryl groups were 1.8, 1.8, and 2.5-3.1, respectively. For pH greater than 8, the key surface ligand was amine >XNH(3)(+), which complexed with NpO(2)(CO(3))(3)(5-). The log K for NpO(2)(CO(3))(3)(5-) complexed onto the amine groups was 3.1-3.9. All of the log K values are similar to those of Np(V) complexes with aqueous carboxyl and N-containing carboxyl ligands. These results help quantify the role of surface complexation in defining actinide-microbiological interactions in the subsurface.

Apatite-forming ability of polyglutamic acid hydrogels in a body-simulating environment

Artificial joints can replace damaged joints provided the surrounding bone is sufficiently dense. However, elderly patients generally have reduced osteoporosis-associated bone density. Therefore, restitution of bone density is essential to ensure implantation. Injectable and resorbable bioactive fillers with bone-bonding ability (osteoconductivity) are promising, as osteoporosis can be reversed with minimal invasion. Osteoconduction occurs through the surface formation of biologically active hydroxyapatite via reactions with body fluids. Heterogeneous nucleation of the hydroxyapatite is catalysed by specific surface functional groups. In addition, release of Ca2+ ions into the surrounding fluids enhances apatite nucleation by increasing its degree of supersaturation. We tested injectable bioactive filler made from cross-linked polyglutamic acid (PGA). This has many carboxyl groups that facilitate apatite nucleation. An insoluble hydrogel can be formed by cross-linkage. We exposed PGA gels to a simulated body fluid for 7 days. Trace amounts of calcium phosphate were formed, but were not identified as bone-like apatite by X-ray diffraction. However, formation of a bone-like apatite layer was detected using pre-treatment with CaCl2 solutions (>0.01 mol dm(-3)) dose dependently. Thus, this chemically cross-linked PGA gel could induce the heterogeneous nucleation of hydroxyapatite in a body environment, and this was enhanced by pre-treatment with CaCl2.

Surface modification of a microcellular porous solid: carbon foam

Microcellular solids such as carbon foams offer unique advantages over traditional solids in many applications. However, since these structures are 80–90% porous, they have a high interface/volume ratio, and surface driven properties such as atmospheric tolerance and bond formation with the matrix material are crucial for applicability. This calls for controlled surface modification techniques that can tailor surface-related properties without compromising the desirable bulk properties of the material (graphite in this case). Several types of modification, using liquid-phase and plasma-phase treatments, have been investigated by this group. One of the goals is to improve composite formation. If a composite is to be made with the foam, it needs to be infiltrated with a matrix phase (e.g. epoxy for structural composite or metal for thermal composite). Enhanced infiltration of the matrix material and optimum bond-strength is achieved by surface treatments that increase chemical affinity between the two phases. Hydrophilic coatings that increase oxygen-functional groups on the surface are seen to be very effective. The second modification goal is to enhance the foam’s durability as a stand-alone solid (such as in a lightweight sandwich structure or thermal dissipation foam). Coatings that incorporate moisture-repellent and chemically inert groups (such as fluorocarbons) achieve this. The following aspects of these coatings have been discussed: (a) chemistry of specific surface functional groups, (b) contact angle changes with water, and (c) infiltration of water (which is a predictor of infiltration of other polar compounds). The significance of these results to our understanding of composite interfaces and future fabrication issues has been discussed.

A comparison of the thermodynamics of metal adsorption onto two common bacteria

The cell walls of bacteria are known to adsorb a variety of metals, and thus they may control metal mobilities in many low-temperature aqueous systems. In order to quantify metal adsorption onto bacterial surfaces, recent studies have applied equilibrium thermodynamics to the specific chemical and electrostatic interactions occurring at the solution–cell wall interface. However, to date, few studies have used this approach to compare the surface properties and metal affinities of different species of bacteria. In this study, we use acid–base titrations to determine the concentrations and deprotonation constants of specific surface functional groups on Bacillus licheniformis. The cell wall displays carboxyl, phosphate and hydroxyl surface functional groups, with pK a values and 1 s errors of 5.2±0.3, 7.5±0.4 and 10.2±0.5, respectively. We perform metal– B. licheniformis adsorption experiments using Cd, Pb, Cu and Al. The average log K values for the Cd-, Pb-, Cu- and Al–carboxyl stability constants, with 1 s errors, are 3.9±0.5, 4.6±0.3, 4.9±0.4 and 5.8±0.3, respectively. Finally, we compare the surface characteristics and metal affinities of B. licheniformis to those of Bacillus subtilis, as determined by Fein et al. [Fein, J.B., Daughney, C.J., Yee, N., Davis, T., 1997. A chemical equilibrium model of metal adsorption onto bacterial surfaces. Geochim. Cosmochim. Acta 61, 3319–3328]. Our investigations indicate that these two species of bacteria have different relative and absolute concentrations of surface sites and slightly different deprotonation and metal adsorption stability constants. We relate these variations in surface properties to variations in metal affinity in order to predict metal mobilities in complex, natural systems.

Infrared analysis of carbon blacks

Results of computer-assisted analyses of the ir spectra of carbon blacks are presented. Absorption bands corresponding to specific surface functional groups have been identified and analysed by dispersing the blacks in KBr at different concentrations (0.03%–0.15% wt/wt). With few exceptions, Beer's law is obeyed. A relationship has been found between peak areas and acid-base characteristics (as reflected by the aqueous slurry pH). This is manifested by a sharp decrease in the intensities of the OH and COOH bands about pH 7. Bands attributed to C=O or aromatics and to CH groups pass through a maximum centered around pH = 6–7.