A NEW MODEL FOR PHYSICAL ADSORPTION ON SOLID SURFACES

The principal assumptions about equivalence and energy distribution of the asdorption sites on solidsurfaces used by Langmuir for deriving the equation of monomolecular adsorption are generalized and anew physical adsorption model is proposed and tested with experimental data published in literature.Themodels of Langmuir,Freundlich,Temkin etc.are only the special cases.Assuming uniform density distributionof adsorption energy,the isotherm equation is given asn=K.1n[1+（bop）1/Mor n=K.1n[1+（boC）1/M]where n is the amount of adsorption per unit weight or area of solid p or C is tbe pressure of gas or the concen-tration of solution respectively.K,bo,M are constants with physical meanings as described in this paper.This equation can be used over wide range to quantitatively represent the five types of physical adsorptionclassified by Brunauer.

Fabrication and characterization of Fe_3O_4@SiO_2@TiO_2@Ho nanostructures as a novel and highly efficient photocatalyst for degradation of organic pollution

In this work we synthesize a novel and highly efficient photocatalyst for degradation of methyl orange and rhodamine B. In addition, a new method for synthesis of FeO@SiO@TiO@Ho magnetic core-shell nanoparticles with spherical morphology is proposed. The crystal structures, morphology and chemical properties of the as-synthesized nanoparticles were characterized using Fourier transform infrared spectroscopy（FT-IR）, scanning electron microscopy（SEM）, transmission electron microscopy（TEM）, energy dispersive X-ray（EDS）, X-ray diffraction（XRD）, UV–vis diffuse reflectance spectroscopy（DRS） and vibrating sample magnetometer（VSM） techniques. The photocatalytic activity of FeO@SiO@TiO@Ho was investigated by degradation of methyl orange（MO） as cationic dye and rhodamine B（Rh B） as anionic dye in aqueous solution under UV/vis irradiation. The results indicate that about 92.1% of Rh B and78.4% of MO were degraded after 120 and 150 min, respectively. These degradation results show that FeO@SiO@TiO@Ho nanoparticles are better photocatalyst than Fe3O4@Si O2@TiO 2@Ho for degradation of MO and Rh B. As well as, the catalyst shows high recovery and stability even after several separation cycles.

Adsorbability of Mycobacterium phlei on hematite surface

The adsorption of microorganisms on the mineral surface is the base of microorganisms that are considered as mineral processing reagents. The principles of the use of a highly hydrophobic and negatively charged bacterium, Mycobacterium phlei, as a flocculating-flotating agent for finely divided hematite were investigated. The flocculating-floating recovery is strongly dependent on the pH and the dosage of the bacterium. Generally the pH should be controlled over the range of 5.5-7, and the dosage should be controlled about 16 mg/L. The infrared spectrometry analysis indicates that the six functional groups of M. phlei, substituted aromatic compound groups, -（CH2） n-groups, -CH2（-CH3） groups, carbonyl groups, aromatic hydrocarbon groups, and carboxyl groups, are on the hematite surface, among which the first five ones contribute physical adsorption and only the carboxyl groups provide chemisorption. Microscopic analysis reveals that the dimensions and tight aggregation degree of the flocs of hematite particles formed by M. phlei are also impacted by the pH and the content of M. phlei in flotation.

A Review of Hydrophobic Nanocellulose and Its Applications

Nanocellulose is of great interest in various areas nowadays as a natural nanostructured biomaterial.However,in many applications,the high hydrophilicity due to a large number of hydroxyl groups is not desired.The hydrophobic modification of nanocellulose can thus increase its application.This work reviewed recent developments of methods for nanocellulose hydrophobic modification,through physical adsorption and chemical grafting.The applications of hydrophobic nanocellulose were also reviewed.

DRIFT SPECTROSCOPIC STUDY OF THE MECHANISM OF SELECTIVE SHEAR-FLOCCULATION OF HEMATITE FROM KAOLINITE

The mechanism of separating hematite from kaolinite by shear-flocculation and the reason responsible for the selectivity of shear-flocculation was studied by using diffuse reflectance infrared Fourier transform (DRIFT) spec-troscopy, which was found to be effective for analysing adsorbed oleate species on the highly absorbing mineral hematite. The spectra suggest that chemisorption of oleate on hematite took place under shear-flocculation condition and that the chemisorbed species was bridged bidentate, corresponding to a peak at 1580 cm-1. Dimers of oleic acid, corresponding to a peak at 1710 cm-1, adsorbed via hydrocarbon chain association with the chemisorbed oleate. The coexistance of physically adsorbed oleic acid dimers and chemisorbed oleate ions made the surface of hematite hydrophobic, which would remain under the shear field. Under the same condition , the surface of kaolinite did not adsorb oleic acid or oleate and remained hydrophilic. The shear field of sufficient magnitude made the hydrophobic ultrafine particles of hematite to aggregate, whereas the hydrophilic ultrafine particles of kaolinite remained suspended in solution. This explains the mechanism of selective shear-flocculation of hematite from kaolinite.

Enzymatic Synthesis of Polycaprolactone:Effect of Immobilization Mechanism of CALB on Polycaprolactone Synthesis

Surface-modified rice husk ash was used as an inorganic support material for immobilization of Candida antarctica lipase B.(3-aminopropyl)trimethoxysilane was used for surface modification.Immobilization of CALB was performed via both physical adsorption and cross-linking.PCL synthesis was carried out by using these immobilized enzymes,free enzyme and Novozyme 435®.Molecular weight distribution of polymer samples was obtained by gel permeation chromatography(GPC)and chain structures of the polymer samples were observed by hydrogen nuclear magnetic resonance(1H-NMR).The highest monomer conversion is generally obtained by using cross-linked enzyme,around 90%.PDI values for all polymer samples were approximately 1.5 which can be considered as acceptable.In general cross-linked enzymes were better than physically adsorbed enzymes in terms of average molecular weights.It can be concluded that PCL can be synthesized with these immobilized enzymes with high molecular weight and low PDI values.

Efficient quasi-stationary charge transfer from quantum dots to acceptors physically-adsorbed in the ligand monolayer

Alkanoate-coated CdSe/CdS core/shell quantum dots(QDs)with near-unity photoluminescence(PL)quantum yield and monoexponential PL decay dynamics are applied for studying quasi-stationary charge transfer from photo-excited QDs to quinone derivatives physically-adsorbed within the ligand monolayer of a QD.Though PL quenching efficiency due to electron transfer can be up to>80%,transient PL and transient absorption spectra reveal that the charge transfer rate ranges from single-digit nanoseconds to sub-nanoseconds,which is~3 orders of magnitude slower than that of static charge transfer and〜2 orders of magnitude faster than that of collisional charge transfer.The physically-adsorbed acceptors can slowly(500-1,000 min dependent on the size of the quinone derivatives)desorb from the ligand monolayer after removal of the free acceptors.Contrary to collisional charge transfer,the efficiency of quasi-stationary charge transfer increases as the ligand length increases by providing additional adsorption compartments in the elongated hydrocarbon chain region.Because ligand monolayer commonly exists for a typical colloidal nanocrystal,the quasi-stationary charge transfer uncovered here would likely play an important role when colloidal nanocrystals are involved in photocatalysis,photovoltaic devices,and other applications related to photo-excitation.

Single-Molecular Imaging of Anticoagulation Factor I from Snake Venom by Atomic Force Microscopy

Anticoagulation factor I (ACF I) from the venom of Agki^strodon acutus is a binding protein to activated coagulation factor X (FXa) and possesses marked anticoagulant activity. Single ACF I molecule has been successfully imaged in air by tapping mode atomic force microscopy (AFM) with high resolution using glutaraldehyde as a coupling agent. The physical adsorption and covalent binding of ACF I onto the mica show very different surface topographies. The former exhibits the characteristic strand like structure with much less reproducibility, the latter displays a elliptic granular structure with better reproducibility, which suggests that the stability of ACF I molecules on the mica is enhanced by covalent bonding in the presence of glutaraldehyde. A small scale AFM amplitude mode image clearly shows that the covalently bonded ACF I molecule by glutaraldehyde has olive shape structure with an average size of 7 4 nm×3 6 nm×3 1 nm, which is very similar to the size determined from the crystal structure of ACF I.