Surface Concentration Of Sites Research Articles

Micro-heater embedded ISFET pH sensor with high-k gate dielectrics for enhanced sensitivity

The measurement of pH is an important routine practice in many chemical and biomedical applications. This work reports the design of a pH sensor based on the Ion Sensitive Field Effect Transistor (ISFET). The COMSOL Multiphysics® platform has been used to model and simulate the pH sensor in three dimensions (3D) while combining heat transport, electrostatic, and semiconductor modules. The binding of ions in gate dielectrics results in induced charge carriers in the conducting channel of 3D ISFET, which is controlled by the applied gate voltage for determining ion concentration. Here, the pH of water as the bulk electrolyte is measured by attaining the required gate voltage to achieve a certain drain current in 3D ISFET. The pH sensitivity of 3D ISFET with different high-k gate dielectrics such as Ta2O5, Al2O3, HfO2, ZrO2, and SiO2 is measured and compared. The 3D ISFET with Ta2O5 exhibited excellent sensitivity of 59.0 mV pH−1 with a wide linear detection range of pH from 1 to 13 at room temperature compared to other high-k gate dielectrics. Furthermore, the sensitivity was further enhanced to 66.0 mV pH−1 at 60 °C due to the incorporation of a micro-heater into the ISFET. The excellent sensitivity and wide linear detection range can be attributed to the high concentration of surface sites in the Ta2O5 sensing film and improved disassociation constants in the presence of the gate dielectric in contact with the electrolyte. Finally, this sensor demonstrates its potential for real applications.

The Surface acidity of freshly synthesized microplastics particles in simple electrolyte

The surface chemistry of sub-micron microplastics (MP) particles, specifically, the pH-dependent surface charge (or surface acidity), plays a role on the transport, transformation, and effect of contaminants in the aquatic environment. Little is known on the origin of surface charge and the quantification of surface acidity of MP. In this study, the surface charge of submicron particles of six major polymers, including low-density polyethylene (LDPE), high-density polyethylene (HDPE), polypropylene (PP), polystyrene (PS), polyvinyl chloride (PVC), and polyethylene terephthalate (PET), was characterized in inert electrolytes, namely, NaClO4, NaCl, and NaNO3 for the elucidation of surface acidity. IR absorbance revealed that oxygen-rich functional groups were introduced during the resynthesis of MP particles, whose surface chemical structure consists of three main functional groups, i.e., carboxylic/ester, ether/alcohol, and aliphatic. Results show clearly that the zeta potential of MP particles was negatively charged in simple electrolytes at pH greater than ca. 2.0. Hydroxide ions adsorption on the non-polar aliphatic sites, and deprotonation of surface hydroxy group on the polar carboxylic/ester and ether/alcohol sites, contributed to the negative charges on MP surface. The surface acidity of selected MP particles was established in terms of acid strength (intrinsic acidity constants) and capacity (total surface site concentration) for the three distinct surface sites. Results also show the surface acid site density increases with hydration/hydrolysis time with rate constants of the polar surface sites, i.e., carboxylic/ester and ether/alcohol being 2.3 times greater than that of the non-polar aliphatic group.

Defect structures and (ferro)magnetism in Zn1-xFexO nanoparticles with the iron concentration level in the dilute regime (x = 0.001 – 0.01) prepared from acetate precursors

Zn1-xFexO nanoparticles with the iron concentrations level in the dilute regime (x = 0.001–––0.01) were produced by a sol–gel route from acetate precursors along with an un-doped and 3 at.% Fe-doped reference. The X-ray diffraction of the un-doped and 0.1–1 at.% Fe-doped samples reveal the reflections for only the ZnO wurtzite structure. Fe doping enhances the a-axis lattice constant, the unit cell volume and the microstrain. Iron doping reduces the average crystallite/particle size (confirmed by Scanning Electron Microscopy), improving the surface-to-volume ratio or the concentration of defective surface sites. XPS identifies the iron in both Fe3+ and Fe2+ states. XPS and 57Fe Mossbauer spectroscopy indicate a broad distribution (distortion) of Fe3+ sites on the surface of ZnO nanoparticles. The blue shift and broadening of the UV emission, and quenching of defect-related photoluminescence in the Fe-doped samples verify the presence of iron in the ZnO lattice and surface intrinsic defects. 0.1–1 at.% Fe-doped ZnO show room temperature ferromagnetism, RTFM, characteristic of dilute magnetic semiconductors, DMS. The magnetization measurements with temperature evidence an antiferromagnetic alignment and an increase of ferromagnetic contribution with Fe doping up to 1 at.%. Zn0.97Fe0.3O reference is a superparamagnetic ZnO/ZnFe2O4 nanocomposite with a blocking temperature of 20 K; HRTEM shows (ultra)fine ZnFe2O4 particles at the surface of ZnO nanoparticles. The analysis of experimental data of 0.1–1 at.% Fe-doped ZnO was done in terms of iron coupling with intrinsic defects, which can generate surface Fe3+ states with geometries similar to the Fe3+ in inverse spinel ZnFe2O4. The superexchange interaction (resembling that in the inverse spinel ZnFe2O4) between the Fe3+ sites with distorted configuration resulting in ferrimagnetism was hypothesised as a possible mechanism of RTFM. Experimental (structural, local chemical, magnetic, optical) and interpretation results can be used to optimize the processing conditions for Fe-doped ZnO to serve as an effective DMS, e.g. for spintronic applications.

Sulfate induced surface modification of Chlorella for enhanced mercury immobilization

In this study, living Chlorella sorokiniana FK with an elevated concentration of cell envelop sulfur sites, induced by adding excess sulfate to the medium, was used as biosorbents for the removal of Hg(II) from aqueous solution. The cellular surface sulfur-based sites density of the obtained biosorbents was determined through selective sulfhydryl site-blocking and potentiometric titration. The sorption was conducted as terms of pH and initial Hg(II) concentration, and characterized by SEM, AFM, HRTEM, FT-IR, XRD and XPS. The results showed that Chlorella possessed the highest sulfhydryl site concentration and showed the largest capacity for Hg(II) detoxification in the 40 mg/L sulfur culture (termed B-40) with 74.2% sulfate consumption for the growth of algae. The equilibrium data for the studied biosorbents was adequately represented by the Langmuir isotherm and B-40 exhibited the highest sorption capacity for Hg(II), 2 times greater than that of no sulfate culture Chlorella at the optimized pH 6. Mercury biomineral particles (HgS, HgSO4 and Hg2SO5) were formed on the cellular envelop which induced mainly by sulfur-based groups (-SH, -OSO3-) for enhanced Hg(II) immobilization. These results suggested that surface sites concentration of algae can be manipulated by the available nutrients, and therefore cells with induced high densities of sulfhydryl sites represented a promising and low cost biosorbent for the effective removal and immobilization of Hg and possibly other heavy metals.

Tellurite Adsorption onto Bacterial Surfaces.

Tellurium (Te) is an emerging contaminant and its chemical transformation in the environment is strongly influenced by microbial processes. In this study, we investigated the adsorption of tellurite [Te(IV), TeO32-] onto the common soil bacterium Bacillus subtilis. Thiol-blocking experiments were carried out to investigate the role of cell surface sulfhydryl sites in tellurite binding, and extended X-ray absorption fine structure (EXAFS) spectroscopy was performed to determine the chemical speciation of the adsorbed tellurite. The results indicate that tellurite reacts with sulfhydryl functional groups in the extracellular polymeric substances (EPS) produced by B. subtilis. Upon binding to sulfhydryl sites in the EPS, the Te changes from Te-O bonds to Te-S coordination. Further analysis of the surface-associated molecules shows that the EPS of B. subtilis contain proteins. Removal of the proteinaceous EPS dramatically decreases tellurite adsorption and the sulfhydryl surface site concentration. These findings indicate that sulfhydryl binding in EPS plays a key role in tellurite adsorption on bacterial surfaces.

Effect of moisture and molecular weight of polyaniline on H2S sensing characteristics

Chemical behavior of some gases, such as H2S, changes with presence of moisture. Sensing of H2S by polyaniline (PANI) has been studied; the sensing characteristics depend upon the specific surface area, concentration of active surface sites, pore size, and surface heterogeneity controlled by the chain configuration, which is further governed by the molecular weight. However, effects of moisture in the environment and molecular weight of PANI on H2S sensing characteristics have not been studied, and this is the motivation of the present work. Here we have studied the H2S sensing by PANI of different molecular weights in the same environment (N2) with different moisture (dry and humid) conditions, and in different environments (N2 and compressed air) at the same humidity level. It was observed that regardless of the environment, (i) with increasing concentration of H2S gas, the resistance of the sensors increased in dry atmosphere and decreased in presence of moisture, and (ii) the response time was lower in moist conditions. The sensitivity and response were non-monotonous with respect to the molecular weight. However, response time decreased monotonically with increase in band gap of PANI. New correlations were developed to get surface site kinetics from the response data.

Description of supported metal structure sensitivity by a geometric approach

A series of Pt/Al2O3 catalysts with uniform Pt particle sizes ranging from 0.95 to 2.62 nm was synthesized using the refilling method to control the growing of Pt nanoparticles and evaluated in propane dehydrogenation. An effect of particle size on the initial propane activity and TOF was demonstrated, the smallest particles being the most active. A geometric model was developed to quantify the surface site concentration for any fcc metal particle size. Comparing the evolution of initial activity for propane dehydrogenation with the different surface site concentrations, it was shown that the active sites of Pt/Al2O3 catalysts corresponded to the combination of corner and edge atoms. To get further, the model was confronted with numerous data extracted from literature demonstrating that it is an efficient tool to predict the structure–activity relationship of fcc metal catalysts and determine the exact nature of active sites for a wide range of reactions and metals.

PH-Dependent mechanisms and kinetics of the removal of acetaminophen by manganese dioxide

Acetaminophen is commonly found in aquatic environments because it is widely used as an analgesic. In this study, the extent of transformation and adsorption of acetaminophen by manganese dioxide (MnO2) at different pH conditions was systematically investigated. The adsorption of acetaminophen by MnO2 was significant under acidic conditions but negligible under neutral and alkaline conditions. This indicates that the rate-determining steps in the removal of acetaminophen are electron transfer under acidic conditions and precursor complex formation under neutral and alkaline conditions. The kinetic simulation result is consistent with the above results, and the kinetics can be described using a surface complexation and transformation kinetic model if the initial concentration of acetaminophen exceeds the total concentration of the reactive surface sites on MnO2. Otherwise, the Michaelis–Menten model and the pseudo-first-order kinetic model can be used to describe the removal kinetics under acidic conditions and under neutral and alkaline conditions, respectively. The main transformation products were p-benzoquinone and a dimer of 4-aminophenol and acetaminophen under acidic and alkaline conditions, respectively. This indicates that dehydration–oxidation is the main pathway only under acidic conditions. Under alkaline conditions, the main transformation mechanism is dimerization–hydrolysis.

The Structure of Molecular and Surface Platinum Sites Determined by DNP-SENS and Fast MAS 195Pt Solid-State NMR Spectroscopy.

The molecular level characterization of heterogeneous catalysts is challenging due to the low concentration of surface sites and the lack of techniques that can selectively probe the surface of a heterogeneous material. Here, we report the joint application of room temperature proton-detected NMR spectroscopy under fast magic angle spinning (MAS) and dynamic nuclear polarization surface enhanced NMR spectroscopy (DNP-SENS), to obtain the 195Pt solid-state NMR spectra of a prototypical example of highly dispersed Pt sites (single site or single atom), here prepared via surface organometallic chemistry, by grafting [(COD)Pt(OSi(OtBu)3)2] (1, COD = 1,5-cyclooctadiene) on partially dehydroxylated silica (1@SiO2). Compound 1@SiO2 has a Pt loading of 3.7 wt %, a surface area of 200 m2/g, and a surface Pt density of around 0.6 Pt site/nm2. Fast MAS 1H{195Pt} dipolar-HMQC and S-REDOR experiments were implemented on both the molecular precursor 1 and on the surface complex 1@SiO2, providing access to 195Pt isotropic shifts and Pt-H distances, respectively. For 1@SiO2, the measured isotropic shift and width of the shift distribution constrain fits of the static wide-line DNP-enhanced 195Pt spectrum, allowing the 195Pt chemical shift tensor parameters to be determined. Overall the NMR data provide evidence for a well-defined, single-site structure of the isolated Pt sites.

Cadmium adsorption to clay-microbe aggregates: Implications for marine heavy metals cycling

Interactions between microorganisms and clay minerals influence the transport and cycling of metal contaminants in both marine and terrestrial environments. The present study was conducted to quantify the adsorption of dissolved cadmium, Cd(II), under seawater-like conditions to the marine cyanobacterium Synechococcus sp. PCC 7002, three common clay minerals (kaolinite, montmorillonite and illite), as well as cell-clay aggregates. We show here that the Synechococcus-only experiments removed the most Cd above pH 5.5, followed in decreasing order by aggregates of 50% cells:50% individual clays, aggregates of cells and all 3 clays, and individual clays. Electron microscope imaging showed that clays associated in a tangential edge-on orientation to the cells in Synechococcus-clay mineral aggregates. A non-electrostatic surface complexation modeling approach was used to fit Cd adsorption onto Synechococcus cells and individual clay minerals. The resulting Cd binding constants were then used in consort with surface functional group pKa values and site concentrations to accurately predict the extent of Cd adsorption onto the Synechococcus-clay mineral aggregates using the component additivity (CA) approach. We observed that the addition of cyanobacterial cells to clay mineral suspensions led to significantly larger mean aggregate sizes of clay minerals, enhancing the clay sedimentation rate. Although specifically focused on Cd, our study indicates that the ratio of bacterial plankton to clay minerals is an important determinant in terms of understanding the rate with which metals are transferred from the water column to the seafloor.

Extracting meaningful standard enthalpies and entropies of activation for surface reactions from kinetic rates

While analyses based on the Arrhenius kinetic model have been successfully applied since its introduction, the Arrhenius model neglects to describe pre-exponential factor in a scientifically meaningful fashion. Since the 1930s, transition-state theory (TST), has met with success in interpreting the pre-exponential factor’s value, allowing a standard entropy of activation to be estimated. However, analyses based on TST’s assumptions have been applied inconsistently in the literature, particularly in corrosion science, leading to difficulty in comparison of standard entropy of activations from different studies. In this work, the foundational principles of TST and standard states are discussed and a standard method to apply TST in analyzing rates of surface reactions is recommended. When full details are not available, reacting species’ concentrations should be normalized to the concentration of active surface sites. For corrosion reactions, conversion relationships are given to convert from units of corrosion rate to surface reaction rate, consistent with TST. This method is dubbed a surface reactant equi-density approximation. Application of this standard to reported data results in adjustments of the standard entropy of activation between − 65 and +50 J/mol K and brings reported entropies into a narrower range of values.

Determination of surface protonation-deprotonation behavior, surface charge, and total surface site concentration for natural, pillared and porous nano bentonite heterostructure

In this paper, the physicochemical properties of natural, pillared and porous nano bentonite heterostructure in the points of view of surface protonation–deprotonation behaviors were studied. Moreover, the structural heterogeneity in each sample based on three-dimensional field-emission scanning electron microscopy (FESEM) plots were investigated to obtain its effect on the formation of surface active sites. To better understand the surface protonation properties and adsorptive capability of natural, pillared and porous clays, it is essential to investigate the surface charge, surface active sites, pH at point of zero charge (pHzpc), and surface acid-base equilibrium constants. Since the information about amphoteric acid-base groups especially in porous clays is still lacking, our main purpose is to obtain the best estimates to compare the surface properties of natural, pillared and porous clays by means of Gran method and surface complexation model from titration data. The 2 pK-diffusion layer model (DLM) was applied to evaluate the contribution and concentration of the various surface site species (such as SOH, SOH2+, and SO−) in the different pH and ionic strengths. This paper indicates considerable new information about surface acid-base reactions, total surface site concentrations, pHzpc measurement, which provides basic knowledge of the underlying adsorption mechanisms. The maximum value of total surface sites concentration (8.84 mmol/L) in ionic strengths of 0.05 M NaCl belonged to porous nano bentonite heterostructure (PBH) with the highest pHzpc at 9.73.

Acid-base buffering characteristics of non-calcareous soils: Correlation with physicochemical properties and surface complexation constants

The soil acid-base buffering capacity (BC) of twelve non-calcareous soil samples was determined by titration. The results of the correlation analysis show that the soil cation exchange capacity (CEC), organic matter (OM), and amorphous Al compounds (Ox-Al) were mainly responsible for the acid-base buffering reactions in the pH range from 3 to 8. A surface complexation model (SCM) was applied to further evaluate the acid-base buffering properties of the soils by assuming the buffering system to be a protonation-deprotonation process. The point of zero charge (pHpzc) calculated from the model matched the pHpzc values obtained from the continuous potentiometric titrations (CPTs), indicating that it is feasible to apply a SCM to non-calcareous soils. Compared with the pH, the pHpzc obtained from the SCM was better correlated with the acid-base properties of the soils, indicating that the pHpzc could be used to evaluate the main buffering processes. The surface site concentration (Hs) calculated from the SCM was significantly correlated with the soil CEC and OM (P < 0.01). Moreover, the Hs had a stronger correlation with the lime buffering capacity (LBC) than the multivariate relationships with the soil CEC and OM, suggesting that the SCM-calculated Hs can be used as an effective indicator of the lime requirement (LR). Our findings demonstrated that it is feasible to use the surface complexation constants to quantitatively evaluate the acid-base buffering process and predict the potential lime requirements for acidic soils.

Surface complexation model of Cd in paddy soil and its validation with bioavailability

In southern China, the paddy soils are mainly variable-charge soils, which have undergone high weathering processes and leaching processes. Due to deficiencies of carbonate and base cations, the variable-charge soil pH is normally less than 6.5, and decrease of soil pH can substantially enhance the mobility and bioavailability of heavy metals. Cadmium (Cd) is one of the most important pollutant influencing human health and environmental safety. Cd contamination is a serious problem in paddy soils, and the acidic condition could further aggravate the mobility and bioavailability of Cd. There is an urgent need to establish a model to investigate the adsorption characteristics of Cd and accurately assess the bioavailability of Cd in variable-charge paddy soils. In this study, the paddy soil was selected from agricultural regions in southern China. Batch experiments were conducted to investigate the Cd adsorption characteristics of the soils from pH 3 to 10. The results showed that Cd mainly existed in dissolved forms at pH 5.5, almost all Cd was adsorbed on the soil surface. Based on the potentiometric titration, the point of zero charge (pHpzc) was obtained when the surface charge density ( σ ) was equal to zero. The pHpzc of the paddy soil was 5.91. The 1-site/2-p K surface complexation model (SCM) was applied to further examine the acid-base properties of the soils by assuming the acid-base buffering system as a protonation-deprotonation process. The surface site concentration ( H s) and the surface site density ( D s) were obtained by Gran plot. The two acid equilibrium constants (p K a1 and p K a2) were determined by extrapolation and the calculated pHpzc were obtained by the average values of the p K a1 and p K a2. The value of pHpzc calculated from the model was 6.10, which was well matched with those from the potentiometric titration, indicating that it is feasible for the application of SCM to the variable-charge soils. The intrinsic equilibrium constants (lg K SOCd) was estimated from the Cd adsorption experimental data and acid-base parameters (p K a1, p K a2 and D s) using Visual MINTEQ software. The results showed that the adsorption of Cd on the paddy soil could be successfully modeled by the SCM. Based on the previous study, the pH was significantly negatively correlated with grain Cd content in paddy soil when pH was below 5.5 ( P 1 mol L−1 MgCl2 (exchangeable fraction) and 1 mol L−1 NaOAc/HOAc (bound to carbonate). Although the extracted Cd was positively correlated with Cd content in grain, the P value was much higher than 0.05, indicating the insignificant correlation. Compared with the extraction method, the dissolved Cd calculated from the SCM was significantly correlated with the grain Cd content (P

Green Synthesis of Magnetic Adsorbent Using Groundwater Treatment Sludge for Tetracycline Adsorption

Abstract Groundwater treatment sludge is an industrial waste that is massively produced from groundwater treatment plants. Conventional methods for treatment of this sludge, such as discharge into deep wells or the sea, or disposal at landfills, are not environmentally sustainable. Here, we demonstrate an alternative strategy to recycle the sludge by preparing a magnetic maghemite adsorbent via a one-step hydrothermal method with NaOH solution as the only solvent. With this method, the weakly magnetized sludge, which contained 33.2% iron (Fe) and other impurities (e.g., silicon (Si), aluminum (Al), and manganese (Mn)), was converted to magnetic adsorbent (MA) with the dissolution of Si/Al oxides (e.g., quartz and albite) into the liquid fraction. At a NaOH concentration of 2 mol·L−1, approximately 18.1% of the ferrihydrite in the Fe oxides of the sludge was converted into 11.2% maghemite and 6.9% hematite after the hydrothermal treatment. MA2 (i.e., MA produced by a 2 mol·L−1 NaOH concentration) exhibited a good magnetic response of 8.2 emu·g−1 (1 emu = 10−3 A·m2), and a desirable surface site concentration of 0.75 mmol·g−1. The synthesized MA2 was used to adsorb the cationic pollutant tetracycline (TC). The adsorption kinetics of TC onto MA2 fitted well with a pseudo-second-order model, and the adsorption isotherms complied well with the Langmuir model. The maximum adsorption capacity of MA2 for TC was 362.3 mg·g−1, and the main mechanism for TC adsorption was cationic exchange. This study is the first to demonstrate the preparation of an MA from recycled sludge without a reductant and/or exogenous Fe source. The prepared adsorbent can be used as a low-cost adsorbent with high capacity for TC sorption in the treatment of TC-containing wastewater.

Synthesis, characterization and acid-base properties of kaolinite and metal (Fe, Mn, Co) doped kaolinite

Pure kaolinite and metal ion doped kaolinite were synthesized successfully for the first time with different M/Al (M = Mn, Fe, Co) ratios (0, 0.042, 0.087, 0.19) at 220 °C by the hydrothermal method. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and BET techniques (N2/BET) were used for sample characterization. XRD patterns of the products showed that kaolinite was the only crystalline phase synthesized and the lattice parameters varied systematically with metal content. The surface acid-base properties of the pure kaolinite and doped kaolinite were studied by potentiometric titration. Surface site concentration (Hs) and surface site density (Ds) increased as metal ion content in the metal doped kaolinite increased. The relevant acid-base equilibrium constants of synthesized products were calculated by applying the constant capacitance model using computer software WinSGW. The surface pKa values of synthetic kaolinite were calculated as: logKa1 = 1.48; logKa2 = −7.03. The results showed that a small number of metal ions significantly affect the surface acid-base properties of kaolinite, which may explain the origin of variability of the reported surface pKa values of kaolinite.

Valorization of manganese-containing groundwater treatment sludge by preparing magnetic adsorbent for Cu(II) adsorption

Mn-containing sludge from groundwater treatment was converted to magnetic particles (MPs) via a one-step hydrothermal method using sodium ascorbate (SA) as the reductant. The MPs were characterized by X-ray diffraction spectroscopy, Mössbauer spectroscopy, X-ray fluorescence spectroscopy, magnetometry and Gran titration and the results showed that magnetic jacobsite was obtained as an intermediate product in transformation of Fe/Mn oxides to siderite and rhodochrosite. When the molar ratio of SA to Mn in the sludge was two, the produced MPs-2 contained a mixture of ferrihdyrite, hematite, jacobsite and Si/Al oxides, and could magnetize at 2.4 emu/g. Ferrihydrite content in MPs decreased with increase of the SA/Mn molar ratio, leading to decrease of the surface sites concentration (Hs). Thus, MPs-2 contained optimized Hs of 6.7 mmoL/g and a desirable adsorption capacity of Cu(II) (73.1 mg/g). The adsorption isotherms of MPs-2 on Cu(II) complied with the Langmuir model and the adsorption kinetics fitted well with the pseudo-second-order model. The major mechanism of adsorption was cationic exchange of the coordinated H and Na ions on MPs-2 surface sites with the Cu(II) ions. This study was the first time to report preparation of MPs by recycling Mn-containing sludge, which could be used as a high-capacity and low-cost adsorbent in treatment of heavy metal-containing wastewater.

Influence of Tetraalkylammonium Compounds on Photocatalytic and Physical Properties of TiO2

A wide range of experimental data are reported for the first time on the TiO2 prepared by hydrolysis of highly concentrated Ti(OiPr)4 in water solutions of quaternary ammonium compounds (QACs). These TiO2 materials have been shown to be photocatalytically active under visible light irradiation (LED, 450 nm) using acetone as a model substrate oxidized in the gas phase. Five-fold increase in activity in comparison with the commercial photocatalyst KRONOClean 7000 is achieved. Colloidal solutions of hydrolyzed Ti(OiPr)4 have been studied by SAXS method suggesting the way in which QACs solutions may influence the final composition of TiO2. Phase composition, morphology, texture and surface properties of the modified TiO2 have been studied using XRD, BET, SEM and low-temperature FTIR with CO probe. The surface elemental composition has been investigated by XPS method. Additional low-energy levels and high concentration of acid surface sites originated from N/C-doping, are likely to be the main reasons for exceptional photocatalytic performance of these samples.

Hydrothermal synthesis of a magnetic adsorbent from wasted iron mud for effective removal of heavy metals from smelting wastewater.

A magnetic adsorbent (MA) was synthesized from wasted iron mud of a groundwater treatment plant using a novel one-step hydrothermal method. The results showed that Fe content of MA was 41.8wt%, 2.5 times higher than that of iron mud, which was caused by hydrothermal dissolution of non-ferrous impurities under alkaline condition, such as quartz and albite, regardless of addition of ascorbic acid or not. Ferrihydrite was 92.7% in dry iron mud before adding ascorbic acid and gradually decreased to 58.1% by increasing the molar ratio of ascorbic acid to Fe following hydrothermal treatment. The strongest saturation magnetization of 16.29emu/g was observed in the prepared MA-4 when the ascorbic acid to Fe molar ratio was 1. The highest surface site concentration of 1.31mmol/g was observed in MA-2 when the ratio was 0.02. The mechanism of hydrothermal conversion of wasted iron mud to MA was reductive dissolution of ferrihydrite to form siderite, which was then reoxidized to maghemite. When 12.5g/L of MA-2 was applied to treat smelting wastewater, over 99% removal of Cu2+, Zn2+, Pb2+, and Cd2+ was achieved. The major mechanisms of Cu2+ and Zn2+ adsorption by the adsorbent were cationic exchange.

Conversion of hemicellulose-derived pentoses over noble metal supported on 1D multiwalled carbon nanotubes

Conversion of xylose was investigated over noble metals supported on multiwalled carbon nanotubes (MWCNT). Distinct metal nanoparticles were dispersed on functionalized MWCNT bearing acidic groups created by HNO3 oxidation and their catalytic performance and stability on aqueous-phase processing of pentoses were assessed. While oxidized MWCNT exhibited low activity to dehydration products, noble metal-based one-dimensional catalysts showed to be much more active. Ru decorated MWCNT was by far the most active catalyst with total xylose consumption within the first 1.5 h. Rh and Au supported samples could barely accomplish 40% conversion after 6 h. The activity order Ru > > Pd > Pt > Rh ∼ Au could be established among the studied samples. Xylitol derived from direct hydrogenation of pentoses was invariably the key product formed, accomplishing selectivities within 70–85%. It revealed that the metal centers were mostly acting independently. Furfuryl alcohol was the second major product and its formation was well correlated to the concentration of acidic surface sites created upon MWCNT oxidation, evidencing a cooperative role between metal and acidic sites. The oxygenated surface groups of fresh and spent catalysts assessed by TPD were shown to be stable under the aqueous-phase processing conditions used.