Pt-Chitosan-TiO2 for Efficient Photocatalytic Hydrogen Evolution via Ligand-to-Metal Charge Transfer Mechanism under Visible Light

The Pt-chitosan-TiO₂ charge transfer (CT) complex was synthesized via the sol-gel and impregnation method. The synthesized photocatalysts were thoroughly characterized, and their photocatalytic activity were evaluated toward H₂ production through water reduction under visible-light irradiation. The effect of the preparation conditions of the photocatalysts (the degree of deacetylation of chitosan, addition amount of chitosan, and calcination temperature) on the photocatalytic activity was discussed. The optimal Pt-10%DD75-T200 showed a H₂ generation rate of 280.4 μmol within 3 h. The remarkable visible-light photocatalytic activity of Pt-chitosan-TiO₂ was due to the CT complex formation between chitosan and TiO₂, which extended the visible-light absorption and induced the ligand-to-metal charge transfer (LMCT). The photocatalytic mechanism of Pt-chitosan-TiO₂ was also investigated. This paper outlines a new and facile pathway for designing novel visible-light-driven photocatalysts that are based on TiO₂ modified by polysaccharide biomass wastes that are widely found in nature.     

Effect of the Folate Ligand Density on the Targeting Property of Folated‐Conjugated Polymeric Nanoparticles

Targeted drug delivery systems have attracted increasing attention due to their ability for delivering anticancer drugs selectively to tumor cells. Folic acid (FA)‐conjugated targeted block copolymers, FA‐Pluronic‐polycaprolactone (FA‐Pluronic‐PCL) are synthesized in this study. The anticancer drug paclitaxel (PTX) is loaded in FA‐Pluronic‐PCL nanoparticles by nanoprecipitation method. The in vitro release of PTX from FA‐Pluronic‐PCL nanoparticles shows slow and sustained release behaviors. The effect of FA ligand density of FA‐Pluronic‐PCL nanoparticles on their targeting properties is examined by both cytotoxicity and fluorescence methods. It is shown that FA‐Pluronic‐PCL nanoparticles indicated better targeting ability than non‐targeted PCL‐Pluronic‐PCL nanoparticles. Furthermore, FA‐F127‐PCL nanoparticle with 10% FA molar content has more effective antitumor activity and higher cellular uptake than those with 50% and 91% FA molar content. These results prove that FA‐F127‐PCL nanoparticle with 10% FA molar content can be a better candidate as the drug carrier in targeted drug delivery systems.     

单分散壳聚糖微囊的制备与表征

对水溶性壳聚糖和对苯二甲醛在水/油界面发生的交联反应进行了研究,考察了水相溶液的pH值和油相中对苯二甲醛的浓度对该界面交联反应的影响.采用微流控技术制备得到了单分散的壳聚糖微囊:首先通过毛细管同轴聚焦流微流控装置制备得到单分散的O/W/O乳液.乳液制备中,以Pluronic F-127作为水相乳化剂,羟乙基纤维素作为水相增稠剂,水溶性壳聚糖溶于中间水相;交联剂对苯二甲醛溶于内部油相;含乳化剂PGPR 90的大豆油作为外部油相.乳液制备完成后,以乳液为模板,对苯二甲醛通过油/水界面扩散进入水层,与壳聚糖的氨基发生交联反应,生成壳聚糖聚合物凝胶网络,从而构成微囊的囊壁.通过光学显微镜分析和扫描电镜观察发现:微囊具备良好的单分散性和球形度以及尺寸均一的内部空腔,微囊的囊壁致密无孔.所得单分散微囊在药物传递等领域具备潜在的应用价值.     

Mesoporous and mesostructured TiO2 coatings for photocatalytic applications

The correlation between the textural properties and the photocatalytic activity of nanocrystalline Titanium dioxide (TiO₂)-anatase films obtained by sol–gel has been investigated. Mesoporous and mesostructured TiO₂-anatase films were prepared using different titanium precursors and Pluronic (F127) and polyethylene glycol hexadecyl ether P5884 (Brij58) surfactants via acid catalysis. Ca(NO₃)₂ and WCl₆ were incorporated to TiO₂ sols to investigate the effect of the doping on the photocatalytic behaviour. The microstructure and textural properties were characterised by X-ray diffraction, spectral ellipsometry and transmission electronic microscopy. The photocatalytic properties were evaluated in aqueous solution (methyl orange) and in gas phase (trichloroethylene, sulphide acid and methyl-ethyl-ketone) using multilayer films deposited on glass-slides. TiO₂-B-Brij-58 films exhibited the most efficient photocatalytic activity either in aqueous or gas medium. The Ca doping strongly enhances the photocatalytic activity associated with the reduced recombination of electrons and holes in the catalyst.     

Energy and electron transfers in photosensitive chitosan

Novel photosensitive chitosan was synthesized. The modified chitosan contains photoactive anthracene chromophore moieties. Because of the presence of anthracene chromophores, the polymer absorbs light in the UV-vis spectral region. Electronically excited polymeric chromophores could participate in energy and electron transfer processes to the suitable acceptor molecules. The photosensitive chitosan developed herein could could act as an efficient photosensitizer and lead to the application of the environmentally friendly photocatalytic system for an efficient degradation of a wide range of pollutants.     

Photocatalytic activity of structured mesoporous TiO2 materials

Starting from colloidal TiO2 nanoparticles in combination with tetraethyl orthosilicate using neutral Pluronic or cationic cetyltrimethylammonium as templates, a series of structured mesoporous silicas has been obtained. The structure of the mesoporous titania was confirmed by isothermal gas adsorption, transmission electron microscopy, and X-ray diffraction. The pore diameter ranged between 3.8 and 10.9 nm, and the BET surface area varied from 99 to 584 m2 g(-1). The photocatalytic activity of these samples for the degradation of phenol in aqueous solution has been compared with that of standard P-25 TiO2. Even though the activity of these new mesostructured materials is lower that those found for P-25 TiO2, the turnover frequency of the photocatalytic activity (moles of phenol degraded per Ti atom present at initial reaction time) is much higher for the mesoporous titania, particularly with low titanium contents for those materials (mpTiO2-5 and TiO2SBA15-5).     

Soft-templating synthesis of mesoporous graphitic carbon nitride with enhanced photocatalytic H2 evolution under visible light

g-C(3)N(4) with worm-like pore and narrow pore size distribution was synthesized by using Pluronic P123 as soft-template. The worm-like porous g-C(3)N(4) not only possesses high BET surface area but also redshifts its absorbance edge up to 800 nm, and shows photocatalytic activity even when the irradiation light λ > 700 nm.     

Oxidation of catecholamines on chitosan-immobilized Co(II) salen complexes

L-Adrenaline and 3,4-dihydroxyphenylalanine (dopa) oxidation by molecular oxygen in the presence of the Co(II) complex of bis(salicylideneethylene diamine) (CoSalen) immobilized on unmodified chitosan and chitosan modified by 4-pyridinecarboxaldehyde is studied in aqueous solutions under mild conditions. The catalysts prepared are selective with respect to oxidation of the chosen substrates. Preparation of binary composite egg-shell systems, with a thin film of low-loaded CoSalen-chitosan supported on macroporous SiO₂ makes it possible to increase sufficiently the specific surface area and the efficiency of the catalyst.     

基于金属钴配合物的均相光催化还原二氧化碳研究进展

本文综述了自20世纪80年代以来基于钴配合物的均相光催化二氧化碳还原研究成果,以钴配合物催化剂的结构分类并结合时间顺序回顾了近四十年来该领域的发展轨迹,重点总结了用于光催化二氧化碳还原研究的金属钴配合物的结构、催化活性以及光催化体系的构成等特点,分析了该领域面临的挑战并展望了未来的发展方向。     

不同复合体系对含钛高炉渣光催化还原Cr(VI)的影响

采用煅烧的硫酸盐掺杂的含钛高炉渣(sulfate-modified titanium-bearing blast furnace slag, STBBFS)作为光催化剂, 研究了Cr(VI)-柠檬酸[Cr(VI)-CA]复合体系和Cr(VI)-柠檬酸-硝酸铁[Cr(VI)-CA-FN]复合体系对 STBBFS催化剂光催化活性的影响. 结果表明: 酸性条件下, 不同复合体系对STBBFS催化剂光催化活性的促进作用按Cr(VI)-CA-FN复合体系＞Cr(VI)-CA复合体系＞Cr(VI)单一体系增强. Cr(VI)-CA复合体系在pH＝2.5, 反应50 min后STBBFS催化剂光催化活性为0.426 mg•min―1•g―1时将溶液中的Cr(VI)全部还原; 而Cr(VI)-CA-FN复合体系在pH＝2.5, 反应16 min后STBBFS催化剂光催化活性为1.2425 mg•min―1•g―1时将溶液中的Cr(VI)全部还原. 两种复合体系中, Cr(VI)离子的光催化还原过程都遵循L-H动力学规律, 虽然加入CA和FN后, 降低了吸附对光催化还原Cr(VI)的影响, 但是Cr(VI)吸附至催化剂表面仍然是整个反应过程的关键.     

Nanocomposites based on modified chitosan and titanium oxide

The effect of primary amino groups and molecular mass of chitosan on the stability of suspensions based on nanoscale TiO₂ dispersions in acidic solutions of various concentrations at pH 2.5 was studied. In the case of chitosan prepared according to a commercialized process, the stability of TiO₂ suspensions was low and depended on the concentration of the polymer solution. Solutions of low-molecular-mass highly deacetylated chitosan prepared by solid-phase synthesis stabilized a dispersion of nanosized TiO₂ particles for a very long time. Nanocomposites based on a chitosan-PVA graft copolymer and TiO₂ were prepared, in which the initial filler dispersion is retained up to very high filling ratios. A potential use of these nanocomposites in photocatalytic processes is discussed. The results of this study can be used for refining engineering procedures and processes for the manufacture of new biocompatible, bioactive, and biodegradable functional composite materials based on chitosan and synthetic polymers.     

Polyrotaxane-based triblock copolymers synthesized via ATRP of N-isopropylacrylamide initiated from the terminals of polypseudorotaxane of Br end-capped pluronic 17R4 and β-cyclodextrins

Thermo-responsive polyrotaxane (PR)-based triblock copolymers were synthesized via the atom transfer radical polymerization (ATRP) of N-isopropylacrylamide initiated with self-assemblies made from a distal 2-bromoisobutyryl end-capped Pluronic 17R4 (PPO14-PEG24-PPO14) with a varying amount of β-cyclodextrins (β-CDs) in the presence of Cu(I)Cl/PMDETA at 25 °C in aqueous solution. The molecular structure was characterized by means of H NMR, FTIR, WXRD, GPC, TGA and 1 DSC analyses. About half of β-CDs are still entrapped on the Pluronic 17R4 chain while the number of incorporated NIPAAm monomers is nearly a double feed value in the resulting copolymers. The aggregate morphologies in aqueous solution were evidenced by TEM observations. A two-step thermo-responsive transition arising from a combination of a polypseudorotaxane middle block with poly(N-isopropylacrylamide) flanking blocks was also demonstrated by turbidity measurements. Given their thermo-responsive behavior in aqueous solution, these PR-based triblock copolymers show the potential to be used as smart materials for the controlled drug delivery systems, biosensors, and the like.     

Mesoporous TiO2 nanostructures: a route to minimize Pt loading on titania photocatalysts for hydrogen production

Mesostructured TiO(2) nanocrystals have been prepared using Pluronic F127 as the structure-directing agent. Platinum nanoparticles at different contents (0.1-1.0 wt%) have been photochemically deposited onto the mesoporous TiO(2). TEM investigation of 0.2 wt% Pt/TiO(2) calcined at 450 °C reveals that the TiO(2) particles are quite uniform in size and shape with the particle sizes of TiO(2) and Pt being 10 and 3 nm, respectively. The photocatalytic activities of the Pt loaded TiO(2) have been assessed and compared with those of nonporous commercial Pt/TiO(2)-P25 by determining the rates and the photonic efficiencies of molecular hydrogen production from aqueous methanol solutions. The results show that the amount of hydrogen evolved on Pt/TiO(2)-450 at low Pt loading (0.2 wt%) is three times higher than that evolved on Pt/TiO(2)-P25 and twelve times higher than that evolved on Pt/TiO(2)-350. Despite the BET surface area of the TiO(2)-450 photocatalyst being 3.5 times higher than that of TiO(2)-P25, a 60% smaller amount of the Pt co-catalyst is required to obtain the optimum photocatalytic hydrogen production activity. The reduced Pt loading on the mesoporous TiO(2) will be important both from a commercial and an ecological point of view.     

Preparation of chitosan nanoparticles by spray drying,and their antibacterial activity

Chitosan nanoparticles were prepared from chitosan of different molecular weight by spray drying. The morphology of the particles was characterized by SEM, and size distribution and zeta potential were determined. The effects of chitosan solution concentration, molecular weight of chitosan, and size of the spray dryer nozzles on average size, size distribution and zeta potential of chitosan nanoparticles were investigated. The effects of chitosan nanoparticles and chitosan nanoparticles–amoxicillin complex on Staphylococcus aureus were also tested. The results showed that the average size of chitosan nanoparticles were in the range 95.5–395 nm and zeta potentials were 39.3–45.7 mV, depending on the concentration and molecular weight of the chitosan. The lower the concentration and molecular weight of the chitosan, the smaller the chitosan nanoparticles and the higher the zeta potential. Testing for antibacterial activity against S. aureus indicated that chitosan nanoparticles strongly inhibited growth of the bacteria; the minimum inhibitory concentration, 20 μg/mL, was lower than those of chitosan solution or amoxicillin. The antibacterial capacity of chitosan nanoparticles also depended on the size, zeta potential, and molecular weight of the chitosan. Complexation of chitosan nanoparticles with amoxicillin improved the antibacterial activity of amoxicillin.     

Samarium-doped mesoporous TiO2 nanoparticles with improved photocatalytic performance for elimination of gaseous organic pollutants

Mesoporous TiO₂ doped with different amounts of Sm were prepared via a sol-gel route with Pluronic P123 as template. The materials were characterized by X-ray diffraction, transmission electron microscopy, and N₂ sorption experiments, etc. The photocatalytic activity of the mesoporous TiO₂ was tested in elimination of gaseous methanol and acetone. The Sm doped mesoporous TiO₂ have higher activity than those of the commercial photocatalyst (Degussa, P25) and Sm doped TiO₂ counterparts without mesopore structure under ultraviolet light irradiation. A possible mechanism was proposed to account for the high photocatalytic activity of the Sm doped mesoporous TiO₂. The superior activity of the Sm doped mesoporous TiO₂ may be attributed to the synergic effect of the high surface area, mesopore structure and doped Sm species.     

Parameterization of the chaotic surface relief based on atomic-force microscopic data

An approach to parameterization of the structure of chaotic surfaces was presented which employs the flicker-noise spectroscopic technique for analyzing the atomic-force microscopy data arrays. This approach implies calculation of the surface relief parameters with the use of the information parameters characterizing the components of the surface relief profiles for different spatial frequency ranges. The basic characteristics of the nanoscale surface structure include the nanorelief stepwiseness and spikiness describing the highest-frequency component of the nanorelief. The capabilities of the FNS methodology were demonstrated by the example of parameterization of AFM data arrays for binary and triple systems crystallized on mica from aqueous acidic solutions of chitosan, Pluronic, and porphyrin photosensitizer (dimegin). These systems attract much interest in the context of studies dedicated photoinduced oxidation of organic substrates in aqueous solutions.     

Probing molecular-level surface structures of polyethersulfone/pluronic F127 blends using sum-frequency generation vibrational spectroscopy

We blended Pluronic F127 into polyethersulfone (PES) to improve surface properties of PES, which has been extensively used in biomaterial and other applications. The molecular surface structures of PES/Pluronic F127 blends have been investigated by sum-frequency generation (SFG) vibrational spectroscopy. The molecular orientation of surface functional groups of PES changed significantly when blended with a small amount of Pluornic F127. Pluronic F127 on the blend surface also exhibited different features upon contacting with water. The entanglement of PES chains with Pluronic F127 molecules rendered the blends with long-term surface stability in water in contrast to the situation where a layer of Pluronic F127 adsorbed on the PES surface. Atomic force microscopy (AFM) and quartz crystal microbalance (QCM) measurements were included to determine the relative amount of protein that adsorbed to the blend surfaces. The results showed a decreased protein adsorption amount with increasing Pluronic F127 bulk concentration. The correlations between polymer surface properties and detailed molecular structures obtained by SFG would provide insight into the designing and developing of biomedical polymers and functional membranes with improved fouling-resistant properties.     

Preparation,Characterization and Photocatalytic Activity of Lanthanum Doped Mesoporous Titanium Dioxide

Lanthanum doped mesoporous titanium dioxide photocatalysts with different La content were synthesized by template method using tetrabutyltitanate (Ti(OC₄H₉)₄) as precursor and Pluronic P123 as template. The catalysts were characterized by thermogravimetric dif-ferential thermal analysis, N₂ adsorption-desorption measurements, X-ray diffraction, and UV-Vis adsorption spectroscopy. The effect of La³⁺ doping concentration from 0.1% to 1% on the photocatalytic activity of mesoporous TiO₂ was investigated. The characterizations indicated that the photocatalysts possessed a homogeneous pore diameter of about 10 nm with high surface area of 165 m²/g. X-ray photoelectron spectroscopy measurements in-dicated the presence of C in the doped samples in addition to La. Compared with pure mesoporous TiO₂, the La-doped samples extended the photoabsorption edge into the visible light region. The results of phenol photodecomposition showed that La-doped mesoporous TiO₂ exhibited higher photocatalytic activities than pure mesoporous TiO₂ under UV and visible light irradiation.     

Preparation of chitosan nanoparticles by TPP ionic gelation combined with spray drying,and the antibacterial activity of chitosan nanoparticles and a chitosan nanoparticle–amoxicillin complex

Chitosan nanoparticles were prepared from chitosan with various molecular weights by tripolyphosphate (TPP) ionic gelation combined with a spray drying method. The morphologies and characteristics of chitosan nanoparticles were determined by TEM, FE-SEM and from their mean sizes and zeta potentials. The effect of chitosan molecular weight (130, 276, 760 and 1200 cPs) and size of spray dryer nozzle (4.0, 5.5 and 7.0 µm) on mean size, size distribution and zeta potential values of chitosan nanoparticles was investigated. The results showed that the mean size of chitosan nanoparticles was in the range of 166–1230 nm and the zeta potential value ranged from 34.9 to 59 mV, depending on the molecular weight of chitosan and size of the spray dryer nozzles. The lower the molecular weight of chitosan, the smaller the size of the chitosan nanoparticles and the higher the zeta potential. A test for the antibacterial activity of chitosan nanoparticles (only) and a chitosan nanoparticle–amoxicillin complex against Streptococcus pneumoniae was also conducted. The results indicated that a smaller chitosan nanoparticle and higher zeta potential showed higher antibacterial activity. The chitosan nanoparticle–amoxicillin complex resulted in improved antibacterial activity as compared to amoxicillin and chitosan nanopaticles alone. Using a chitosan nanoparticle–amoxicillin complex could reduce by three times the dosage of amoxicillin while still completely inhibiting S. pneumoniae.