Surface Phosphate Groups Research Articles

Lead stabilization in soil using P-modified biochars derived from kitchen waste

Kitchen waste is increasing rapidly worldwide. Utilization of biochar in pollution remediation is an economical approach to the sustainable management of kitchen waste. To date, information regarding the modification of kitchen waste biochar and their resulting ability to inhibit the bioavailability of toxic metals in soil is limited. Here, a novel type of kitchen waste-derived biochar was constructed through phosphate modification, and the sequestration, speciation, and migration of Pb(II) in the soil–plant system were explored through a combination of batch adsorption and pot experiment. The results indicated that the maximum adsorption capacities of P-modified biochar for Pb(II) reached 257.95 mg g −1 , which was approximately 50% higher than pristine biochar; further, P-modified biochar exhibited a greater potential to sequestrate Pb(II), compared to that commonly reported for biochar in previous investigations. In the pot experiments, as compared with the unamended soil, the application of P-modified biochar transformed 42% of acid extractable/exchangeable Pb mainly to easily reducible and residual fractions, significantly decreasing the Pb uptake of ryegrass by 37.9–62.6%. The stable speciation of Pb in soil was attributed primarily to the complexation and precipitation of P-modified biochar with Pb(II). Moreover, the binding of P-modified biochar with Pb(II) was dominated by the surface hydroxyl and phosphate groups, although phosphate modification promoted the formation of mesoporous structures and increased negative charge. The findings could lead to the development of novel methods for the reuse of waste and remediation of toxic metal-polluted soils. • A novel type of kitchen waste-derived biochar was developed using P modification. • Sequestration of Pb(II) on P-modified biochar exceeded most reported biochar. • P-modified biochar efficiently decreased Pb uptake of ryegrass by 37.9–62.6%. • Complexation and precipitation dominated the Pb(II) binding to P-modified biochar. • Pb(II) was transformed to the inert species in P-modified biochar treated soil.

Acidic Centers on the Surface of a Crystalline α-Sn(IV) Phosphate Characterized by the Solid-State 1H, 2H, 31P, and 119Sn MAS NMR Techniques.

A layered crystalline phosphate α-Sn(HPO4)2·H2O (1), prepared and characterized in the present study by the multinuclear solid-state nuclear magnetic resonance (NMR), powder X-ray diffraction, and thermogravimetric analysis techniques, was treated with D2O and HOD imitating the reaction conditions in a water medium. The 2H solid-echo magic angle spinning NMR spectra of the products have revealed on their surface low mobile water molecules and hydronium ions, forming a structure close to the Zundel cation, [D2O···D-OD2]+. All the deuterons in the hydronium ions are tangled by hydrogen bonds with the water and the surface phosphate groups and stabilized by ionic interactions.

Hydronium Ions on the Surface of a Partially Hydrolyzed α-Zirconium Phosphate: Solid-State 2H and 31P MAS NMR Evidence.

Characterization of the α-zirconium phosphates 1-D2Oh and 1-D2Oh/dr, partially hydrolyzed with D2O, by powder X-ray diffraction, scanning electron microscopy, and multinuclear solid-state NMR techniques led to an unprecedented observation of D3O+ ions located on the surface and stabilized by hydrogen bonds. These ions are formed after the surface phosphate groups have been lost.

Elucidating the Location of Cd2+ in Post-synthetically Treated InP Quantum Dots Using Dynamic Nuclear Polarization 31P and 113Cd Solid-State NMR Spectroscopy

Indium phosphide quantum dots (InP QD) are a promising alternative to traditional QD materials that contain toxic heavy elements such as lead and cadmium. However, InP QD obtained from colloidal synthesis are often plagued by poor photoluminescence quantum yields (PL-QYs). In order to improve the PL-QY of InP QD, a number of post-synthetic treatments have been devised. Recently, it has been shown that InP post-synthetically treated with Lewis acid metal divalent cations (M-InP) exhibit enhanced PL-QY; however, the molecular structure and mechanism behind the improved PL-QY are not fully understood. To determine the surface structure of M-InP QD, dynamic nuclear polarization surface-enhanced nuclear magnetic resonance spectroscopy (DNP SENS) experiments were employed on a series of InP magic size clusters treated with Cd ions, InP QD, cadmium phosphide (Cd₃P₂) QD, and Cd-treated InP QD (Cd–InP QD). With the use of DNP SENS, we were able to obtain the 1D ³¹P and ¹¹³Cd NMR spectra, ¹¹³Cd{³¹P} rotational-echo double-resonance (REDOR) NMR spectra, and ³¹P{¹¹³Cd} dipolar heteronuclear multiple quantum correlation (D-HMQC) sequence. Changes in the phosphide ³¹P chemical shifts after Cd treatment provide indirect evidence that some Cd alloys into the sub-surface regions of the particle. DNP-enhanced ¹¹³Cd solid-state NMR spectra suggest that most Cd ions are coordinated by oxygen atoms from either carboxylate ligands or surface phosphate groups. ¹¹³Cd{³¹P} REDOR and ³¹P{¹¹³Cd} D-HMQC experiments confirm that a subset of Cd ions are located on the surface of Cd–InP QD and coordinated with phosphate groups.

Reddish GaN:ZnO photoelectrode for improved photoelectrochemical solar water splitting.

Efficient light harvesting is one of the key prerequisites in improving the solar conversion efficiency for photoelectrochemical water splitting. As classic semiconductors for water splitting, the solid state solution GaN:ZnO based photoanodes exhibit poor water splitting efficiency mainly limited by its light absorption. To overcome this bottleneck, here we report that phosphorus modification shifts the absorption edge of GaN:ZnO from 480 nm to the red end of 650 nm and also leads to one order of magnitude increase of the carrier concentration. Further, taking the surface phosphate groups as anchors, cobalt can be adsorbed, leading to the in situ formation of cobalt phosphate as a cocatalyst for water oxidation, which results in drastically improved photocurrent density and stability. This work highlights the significance of phosphorization treatment in extending the light harvest and changing the surface reaction kinetics for an efficient solar conversion process.

Salt tolerance mechanism of a hydrocarbon-degrading strain: Salt tolerance mediated by accumulated betaine in cells

Rhodococcus sp. HX-2 could degrade diesel oil in the presence of 1%–10 % NaCl. The compatible solute betaine accumulated in cells with increasing NaCl concentration, and this was found to be the main mechanism of resistance of HX-2 to high salt concentration. Exogenously added betaine can be transported into cells, which improved cell growth and the percentage degradation of diesel oil in the presence of high [NaCl] in solution and in soil. Scanning electron microscopy data suggested that addition of exogenous betaine facilitated salt tolerance by stimulating exopolysaccharide production. Fourier-transform infrared analysis suggested that surface hydroxyl, amide and phosphate groups may be related to tolerance of high-salt environments. Four betaine transporter-encoding genes (H0, H1, H3, H5) and the betaine producer gene betB were induced in Rhodococcus sp. HX-2 by NaCl stress. The maximal induction of H0, H1, H3 and H5 transcription depended on high salinity plus the presence of betaine. These results demonstrate that salt tolerance is mediated by accumulated betaine in Rhodococcus sp. HX-2 cells, and the potential of this strain for application in bioremediation of hydrocarbon pollution in saline environments.

Ultrasonic treatment of Co7(PO4)2(HPO4)4 using NMP for supercapacitors and oxygen evolution reaction

In the alkaline system, the mechanism relationships of the transition metal phosphate materials between pseudocapacitors and OER are analyzed, more active sites, excellent conductivity and enhanced intrinsic activity are important factors in enhancing their OER and capacitance performances. In this study, the capacitance of synthesized Co7(PO4)2(HPO4)4 after ultrasonic treatment with N-methyl-pyrrolidinone (NMP) improved 20.1 % (345 F g−1 at 1 A g−1), the overpotential for OER reduced 20 mV (293 mV at 10 mA cm−2). Based on detailed characterization analysis, ultrasonic treatment with NMP does not destroy the phases and the surface phosphate groups of the materials, but reduce the overall particle size, improve the pore volume and create some new interfaces originally located inside the material. These changes bring increased active sites, reduced internal resistance, enhanced charge transfer capability and improved intrinsic activity to the synthesized Co7(PO4)2(HPO4)4, enhancing its OER and capacitance efficiency. Additionally, the ultrasonic treatment can achieve those changes, which is most likely achieved by sacrificing some mesopores with small diameters, it also provides a simple and convenient method for enhancing the performance of other three-dimensional mesoporous materials.

Efficient Elimination of Chlorinated Organics on a Phosphoric Acid Modified CeO2 Catalyst: A Hydrolytic Destruction Route.

The development of efficient technologies to prevent the emission of hazardous chlorinated organics from industrial sources without forming harmful byproducts, such as dioxins, is a major challenge in environmental chemistry. Herein, we report a new hydrolytic destruction route for efficient chlorinated organics elimination and demonstrate that phosphoric acid-modified CeO2 (HP-CeO2) can decompose chlorobenzene (CB) without forming polychlorinated congeners under the industry-relevant reaction conditions. The active site and reaction pathway were investigated, and it was found that surface phosphate groups initially react with CB and water to form phenol and HCl, followed by deep oxidation. The high on-stream stability of the catalyst was due to the efficient generation of HCl, which removes Cl from the catalyst surface and ensures O2 activation and therefore deep oxidation of the hydrocarbons. Subsequent density functional theory calculations revealed a distinctly decreased formation energy of an oxygen vacancy at nearest (VO-1) and next-nearest (VO-2) surface sites to the bonded phosphate groups, which likely contributes to the high rate of oxidation observed over the catalyst. Significantly, no dioxins, which are frequently formed in the conventional oxidation route, were observed. This work not only reports an efficient route and corresponding phosphate active site for chlorinated organics elimination but also illustrates that the rational design of the reaction route can solve some of the most important challenges in environmental catalysis.

Synthesis and Characterization of Hydroxyapatite/Fullerenol Nanocomposites.

Fullerenols are polyhydroxylated, water soluble derivatives of fullerene C60, with potential application in medicine as diagnostic agents, antioxidants or nano drug carriers. This paper describes synthesis and physical characterization of a new nanocomposite hydroxyapatite/fullerenol. Surface of the nanocomposite hydroxyapatite/fullerenol is inhomogeneous with the diameter of the particles in the range from 100 nm to 350 nm. The ζ potential of this nanocomposite is ten times lower when compared to hydroxyapatite. Surface phosphate groups of hydroxyapatite are prone to forming hydrogen bonds, when in close contact with hydroxyl groups, which could lead to formation of hydrogen bonds between hydroxyapatite and hydroxyl groups of fullerenol. The surface of hydroxyapatite particles (-2.5 mV) was modified by fullerenol particles, as confirmed by the obtained ζ potential value of the nanocomposite biomaterial hydroxyapatite/fullerenol (-25.0 mV). Keywords: Hydroxyapatite, Fullerenol, Nanocomposite, Surface Analysis.

Photochemistry: A Stable and Efficient Hematite Photoanode in a Neutral Electrolyte for Solar Water Splitting: Towards Stability Engineering (Adv. Energy Mater. 13/2014)

Surface phosphate groups facilitate solar water oxidation on the surface of iron oxide thin films, even in a neutral electrolyte. The method reported by Jae Sung Lee and co-workers in article number 1400476 provides an effective path to the stability engineering of photoelectrodes to employ any electrolyte of choice. Such stability engineering is a critical issue in solution-based energy devices based on hybrid materials with different stability characteristics.

Designable Architectures on Nanoparticle Surfaces: Zirconium Phosphate Nanoplatelets as a Platform for Tetravalent Metal and Phosphonic Acid Assemblies

Surface-functionalized zirconium phosphate (ZrP) nanoparticles were synthesized using a combination of ion exchange and self-assembly techniques. The surface of ZrP was used as a platform to deposit tetravalent metal ions by direct ion exchange with the protons of the surface phosphate groups. Subsequently, phosphonic acids were attached to the metal ion layer, effectively functionalizing the ZrP nanoparticles. Use of axially oriented bisphosphonic acids led to the ability to build layer-by-layer assemblies from the nanoparticle surface. Varying the metal ion and ligand used allowed designable architectures to be synthesized on the nanoparticle surface. X-ray powder diffraction, XPS, electron microprobe, solid-state NMR, FTIR, and TGA were used to characterize the synthesized materials.

Surface Functionalization of Zirconium Phosphate Nanoplatelets for the Design of Polymer Fillers

Inorganic-organic hybrid materials were synthesized by covalent attachment of epoxides to the surface of zirconium phosphate (ZrP) nanoplatelets. X-ray powder diffraction, FTIR, and TGA were utilized to confirm the presence of the modifiers and exclusive functionalization of the ZrP surface. NMR experiments were conducted to confirm the formation of P-O-C bonds between surface phosphate groups and epoxide rings. The applicability of the organically modified products was demonstrated by their use as fillers in a polymer matrix. Subsequently, a two step intercalation and surface modification procedure was utilized to prepare polymer nanocomposites that were imparted with functionality through the encapsulation of molecules within the interlayer of surface modified ZrP.

Energetics of Water Oxidation Catalyzed by Cobalt Oxide Nanoparticles: Assessing the Accuracy of DFT and DFT+U Approaches against Coupled Cluster Methods.

Some of the most promising catalysts for water oxidation rely on crystalline and amorphous cobalt oxide nanoparticles. Density functional theory (DFT) calculations are routinely used to study the electronic and atomic structures of these materials as well as the thermodynamics and mechanisms of the electrochemical oxygen evolution reaction. The accuracy of these theoretical predictions has never been compared to high-level quantum chemistry methods. We perform coupled cluster (CC) quantum chemistry calculations on model cobalt oxide surface sites and use them to benchmark the accuracy of the most popular exchange and correlation functionals. Hybrid B3LYP and PBE0 functionals lead to fair agreement with the CC energies, while standard gradient-corrected functionals show important discrepancies. The inclusion of on-site electronic repulsion (DFT+U) substantially improves the calculated electronic and structural properties, but no value of the U parameter reproduces the CC results. We discuss the implications of these findings for amorphous cobalt phosphate nanoparticles, showing that the reactivity of these catalysts is not altered by surface phosphate groups.

Adsorption and conversion of ethylene glycol on the surface of Ag-containing catalyst modified with phosphate

The interaction of ethylene glycol with the surface of Ag-containing catalysts modified with phosphates was studied by IR spectroscopy. It was found that ethylene glycol was adsorbed at the surface phosphate groups; the presence of water vapor increased the stability of adsorbed ethylene glycol to a temperature of 400°C. A study of the kinetics of oxidation of ethylene glycol showed that it was consecutively converted into glycolaldehyde and glyoxal at 400°C. At 500–550°C, glyoxal was formed upon both the consecutive and direct conversion of ethylene glycol. The presence of a stage of the consecutive conversion of ethylene glycol into glycolaldehyde and glyoxal was caused by the participation of surface phosphate groups in the adsorption of alcohol molecules to be oxidized.

Formulation of a killed whole cell pneumococcus vaccine - effect of aluminum adjuvants on the antibody and IL-17 response

BackgroundStreptococcus pneumoniae causes widespread morbidity and mortality. Current vaccines contain free polysaccharides or protein-polysaccharide conjugates, and do not induce protection against serotypes that are not included in the vaccines. An affordable and broadly protective vaccine is very desirable. The goal of this study was to determine the optimal formulation of a killed whole cell pneumococcal vaccine with aluminum-containing adjuvants for intramuscular injection.MethodsFour aluminium-containing adjuvants were prepared with different levels of surface phosphate groups resulting in different adsorptive capacities and affinities for the vaccine antigens. Mice were immunized three times and the antigen-specific antibody titers and IL-17 responses in blood were analyzed.ResultsAlthough all adjuvants induced significantly higher antibody titers than antigen without adjuvant, the vaccine containing aluminum phosphate adjuvant (AP) produced the highest antibody response when low doses of antigen were used. Aluminum hydroxide adjuvant (AH) induced an equal or better antibody response at high doses compared with AP. Vaccines formulated with AH, but not with AP, induced an IL-17 response. The vaccine formulated with AH was stable and retained full immunogenicity when stored at 4°C for 4 months.ConclusionsAntibodies are important for protection against systemic streptococcal disease and IL-17 is critical in the prevention of nasopharyngeal colonization by S. pneumoniae in the mouse model. The formulation of the whole killed bacterial cells with AH resulted in a stable vaccine that induced both antibodies and an IL-17 response. These experiments underscore the importance of formulation studies with aluminium containing adjuvants for the development of stable and effective vaccines.

Mechanism of Zn stabilization in hydroxyapatite and hydrated (0 0 1) surfaces ofhydroxyapatite

A basic understanding of Zn incorporation on bulk and hydrated (0 0 1) surfaces ofhydroxyapatite (HA) is attained through electronic structure calculations which use acombined first principles density functional (DFT) and extended Hückel tight binding(EHTB) methodology. A Zn substituted hydroxyapatite relaxed structure is obtainedthrough a periodic cell DFT geometry optimization method. Electronic structure propertiesare calculated by using both cluster DFT and periodic cell EHTB methods. Bond ordercalculations show that Zn preference for the Ca2 vacancy, near the OH channel and withgreater structural flexibility, is associated with the formation of a four-fold (bulk) andnearly four-fold (surface) coordination, as in ZnO. When occupying the octahedral Ca1vacancy, Zn remains six-fold in the bulk, but coordination decreases to five-fold in thesurface. In the bulk and surface, Zn2 is found to be more covalent than Zn1, due to adecrease in bond lengths at the four-fold site, which approach the 1.99 Å ZnO value. Znis however considerably less bound in the biomaterial than in the oxide, wherecalculated bond orders are twice as large as in HA. Surface phosphate groups(PO4) andhydroxide ions behave as compact individual units as in the bulk; no evidence is found for the presenceof HPO4. Ca–O bond orders decrease at the surface, with a consequent increase in ionicity.Comparison between DFT and EHTB results show that the latter method gives a goodqualitative account of charge and bonding in these systems.

Structure of Interfacial Water on Fluorapatite (100) Surface

The structure relaxation mechanism of the fluorapatite (100) surface under completely hydrated ambient conditions has been investigated with the grazing incidence X-ray diffraction (GIXRD) technique. Detailed information on lateral as well as perpendicular ordering corresponding to the water molecules and atomic relaxations of the (100) surface of fluorapatite (FAp) crystal was obtained from the experimental analysis of the CTR intensities. Two laterally ordered water layers are present at the water/mineral interface. The first layer consists of four water molecules located at 1.6(1) A above the relaxed fluorapatite (100) surface while the second shows the presence of only two water molecules at a distance of 3.18(10) A from the mineral surface. Thus, the first layer water molecules complete the truncated coordination sites of the topmost surface Ca atoms, while the second water layer molecules remain bonded by means of H-bonding to the first layer molecules and the surface phosphate groups. Molecular mechanics simulations using force field techniques are in good agreement with this general structural behavior determined from the experiment.

Initial stages of hydration and Zn substitution/occupation on hydroxyapatite (0 0 0 1) surfaces

The initial stages of the hydration process have been simulated on a single-Ca(I) terminated hydroxyapatite (0 0 0 1) surface in step-by-step fashion using periodic slab density functional theory (DFT). Adsorption configurations and energetic properties have been described at different H 2O coverage. At low H 2O coverage, oxygen prefers to form Ca O bonds with surface Ca cations, but as coverage increases, H 2O tends to loosely float on the already-formed water layer. The height of the first layer H 2O relative to the surface is found to be 1.6 Å. The hydration process does not cause the decomposition of surface phosphate groups and hydroxyl channel, but does affect the energetics of subsequent Zn substitution and occupation on Ca(I) and Ca(II) sites. The Ca(II) vacancy site is found to be energetically more favorable for occupation due to less spatial constraint. This suggested mechanism of preferential occupation is different from previous attempts to explain the cation substitution site preference in bulk by ionic radius and electronegativity differences.

Biomimetic Hydroxyapatite–Drug Nanocrystals as Potential Bone Substitutes with Antitumor Drug Delivery Properties

AbstractThis Full Paper investigates the adsorption and desorption of the anticancer drugs cis‐diamminedichloroplatinum(II) (CDDP, cisplatin) and the new platinum(II) complex di(ethylenediamineplatinum)medronate (DPM), as well as the clinically relevant bisphosphonate alendronate, towards two biomimetic synthetic HA nanocrystalline materials with either plate‐shaped (HAps) or needle‐shaped (HAns) morphologies and different chemico‐physical properties. The adsorption and desorption kinetics are dependent on the specific properties of the drugs and the morphology of the HA nanoparticles. Adsorption of the platinum complexes occurs with retention of the nitrogen ligands but the chloride ligands of cisplatin are displaced. Despite their opposite charges, the negatively charged alendronate bisphosphonate and the positively charged aquated cisplatin are strongly adsorbed, while the neutral DPM complex shows lower affinity towards the negatively charged apatitic surface. The data suggest that adsorption of the two platinum complexes is driven by electrostatic attractions, while interaction between the alendronate and the HA surface takes place by ligand exchange in which the two phosphonate groups of the drug molecule replace two surface phosphate groups. Significantly, adsorption of positively charged hydrolysis species of cisplatin is more favored on the phosphate‐rich HAns surface while adsorption of negatively charged alendronate is more favored on the calcium‐rich HAps surface. The latter type of short‐range electrostatic interactions also appear to dominate the desorption kinetics; consequently, drug release is greater for neutral DPM than for charged alendronate and aquated cisplatin. Moreover, while the release per unit area of charged species is the same for the two types of HAs, the release of DPM is faster from HAns, which is lower in surface calcium, than for HAps. Overall, this work demonstrates that the properties of HA nanocrystals can be modulated in such a way to produce HA/biomolecule conjugates tailored for specific therapeutic applications.

Aerobic oxidation of alcohols by organically modified ruthenium hydroxyapatite

The activity of ruthenium-hydroxyapatite (RuHAp) in the oxidation of benzyl alcohol with molecular oxygen was more than tripled by the incorporation of Ru into organically modified HAp and no detectable product beside benzaldehyde was formed. The effective modifiers prolinol, proline, benzoic acid, and hexanoic acid have functional groups that can form strong hydrogen bonds with the surface OH and phosphate groups of HAp. On the basis of catalytic, DRIFT, SEM, STEM-EDX, ICP-OES, and BET measurements, we assume that the major reason for the activity enhancement is the higher intrinsic activity of Ru species due to their different location and coordination in organically modified HAp. It is very probable that incorporation of Ru is not an ion-exchange process, but rather an adsorption process controlled by the polar organic compounds. Interestingly, during this process the modifiers leach out and thus do not disturb the catalytic oxidation of alcohols. The slope of the Hammett plot of p-substituted benzyl alcohols indicates that β-hydride elimination from the alcoholate intermediate is the rate-determining step under kinetically controlled reaction conditions. The catalysts are reusable with no sign of Ru leaching.